Adhesive sheet, adhesive sheet with release sheet, laminate, and method for producing laminate

Abstract

To provide an adhesive sheet having a low dielectric constant and excellent wet heat whitening resistance.SOLUTION: The present invention relates to the adhesive sheet formed of an adhesive composition containing an acrylic syrup (A), a (meth)acrylate (B) having a C10-24 branched alkyl group, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, an adhesive sheet with a release sheet, a laminate, and a method for manufacturing the laminate.

Background Art

[0002] In recent years, in various fields, display devices such as liquid crystal displays (LCDs) and devices combining display devices and input devices such as touch panels have been widely used. Among them, capacitive touch panels have been rapidly spreading due to their functionality. In the manufacture of these display devices and input devices, adhesive sheets are used for applications such as bonding optical members, and adhesive sheets are also used for bonding display devices and input devices.

[0003] In a capacitive touch panel, when a finger approaches the surface, the capacitance between a plurality of electrodes changes simultaneously, enabling highly accurate position detection by measuring the ratio of the current amount. However, when this method is scaled up, the malfunction of the touch panel increases. In order to address such problems, the use of an adhesive sheet with a controlled relative permittivity has been studied. Among them, in a capacitive touch panel having an image display device and a touch panel, since malfunction of the touch panel is likely to occur due to electrical noise from the image display device, the use of an adhesive sheet with a low relative permittivity as the adhesive sheet used for bonding the image display device and the touch panel has been studied.

[0004] For example, Patent Document 1 discloses an adhesive composition capable of forming an adhesive layer with a low relative permittivity. Patent Document 1 discloses a (meth)acrylic polymer containing 40% by mass or more of a structural unit (A) derived from an alkyl methacrylate having a branched alkyl group with 5 to 9 carbon atoms with respect to all structural units, and 5% by mass or more and 15% by mass or less of a structural unit (B) derived from a monomer having a hydroxyl group with respect to all structural units, and a styrene-based polymer. Note that the adhesive composition of Patent Document 1 contains a solvent. Further, Patent Document 2 discloses a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester polymer (A) and cyclodextrins (B). Here, the (meth)acrylic acid ester polymer (A) has a monomer having a hydroxyl group and / or a monomer having a carboxyl group as a monomer unit constituting the polymer, and suppression of moisture and heat whitening has been studied.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the present inventors placed the adhesive layer in Patent Document 1 under high-temperature and high-humidity conditions, it was found that the adhesive layer sometimes whitened and the moisture and heat whitening resistance was insufficient. Further, when an adhesive sheet was formed from the pressure-sensitive adhesive composition of Patent Document 2, it was found that the moisture and heat whitening resistance was insufficient or the relative permittivity could not be sufficiently lowered.

[0007] Therefore, in order to solve such problems of the prior art, the present inventors have proceeded with studies for the purpose of providing an adhesive sheet having a low relative permittivity and excellent moisture and heat whitening resistance. [Means for Solving the Problems]

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that by forming an adhesive sheet from an adhesive composition containing acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D), an adhesive sheet having a low relative permittivity and excellent wet heat whitening resistance can be obtained. Specifically, the present invention has the following configurations.

[0009] [1] An adhesive sheet formed from an adhesive composition containing acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D), The acrylic syrup (A) contains a (meth)acrylic polymer having a weight average molecular weight of 50,000 to 500,000 and a (meth)acrylic monomer. The content of the (meth)acrylic polymer with respect to the total mass of the acrylic syrup (A) is 20% by mass or more, and the content of the (meth)acrylic monomer is 25% by mass or more. With respect to 100 parts by mass of the acrylic syrup (A), the content of the (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms is 10 to 40 parts by mass, and the content of the (meth)acrylate (C) having an alkylene glycol group is 0.05 to 6 parts by mass. The adhesive sheet. [2] The adhesive sheet according to [1], having a relative permittivity of less than 3.0 at a frequency of 1 MHz. [3] When a glass plate and a PET film are bonded through the adhesive sheet to form a laminate, and the laminate is placed under the conditions of 60 ° C. and 95% relative humidity for 240 hours, and then left standing in an environment of 23 ° C. and 50% relative humidity for 1 hour, the haze is 2% or less. The adhesive sheet according to [1] or [2]. [4] The (meth)acrylic monomer contained in the acrylic syrup (A) is a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms, The (meth)acrylic polymer contained in the acrylic syrup (A) contains units derived from a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms, and is the pressure-sensitive adhesive sheet according to any one of [1] to [3]. [5] The (meth)acrylic monomer contained in the acrylic syrup (A) includes an acrylic acid ester and a methacrylic acid ester, and the ester structures of the acrylic acid ester and the methacrylic acid ester are the same, The (meth)acrylic polymer contained in the acrylic syrup (A) contains units derived from an acrylic acid ester and units derived from a methacrylic acid ester, and the ester structures of the units derived from the acrylic acid ester and the units derived from the methacrylic acid ester are the same, and is the pressure-sensitive adhesive sheet according to any one of [1] to [4]. [6] The pressure-sensitive adhesive sheet according to [5], wherein the mass ratio of the acrylic acid ester and the methacrylic acid ester contained in the acrylic syrup (A) is 25:75 to 50:50. [7] A pressure-sensitive adhesive sheet with a release sheet, which is provided with a pair of release sheets having different peeling forces on both surfaces of the pressure-sensitive adhesive sheet according to any one of [1] to [6]. [8] A laminate including the pressure-sensitive adhesive sheet according to any one of [1] to [6] and an adherend on at least one surface side of the pressure-sensitive adhesive sheet.

Effect of the Invention

[0010] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet having a low relative permittivity and excellent wet heat whitening resistance.

Brief Description of the Drawings

[0011]

Figure 1

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0013] In this specification, "(meth)acrylic" represents both acrylic and methacrylic, or either one. Also, in this specification, "monomer" and "monomer" are synonymous, and "polymer" and "polymer" are synonymous.

[0014] (Adhesive sheet) The present invention relates to an adhesive sheet formed from an adhesive composition containing an acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D). Here, the acrylic syrup (A) contains a (meth)acrylic polymer having a weight average molecular weight of 50,000 to 500,000 and a (meth)acrylic monomer, and the content of the (meth)acrylic polymer with respect to the total mass of the acrylic syrup (A) is 20% by mass or more, and the content of the (meth)acrylic monomer is 25% by mass or more. Further, with respect to 100 parts by mass of the acrylic syrup (A), the content of the (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms is 10 to 40 parts by mass, and the content of the (meth)acrylate (C) having an alkylene glycol group is 0.05 to 6 parts by mass.

[0015] The adhesive sheet of the present invention is a sheet composed of an adhesive layer that is a cured product of the above-described adhesive composition. Since the adhesive sheet of the present invention is formed from an adhesive composition having the above configuration, it has a low relative dielectric constant and excellent resistance to wet heat whitening. Therefore, the adhesive sheet of the present invention is preferably used for adhering optical members and the like that constitute a display device equipped with a touch panel.

[0016] The relative permittivity of the pressure-sensitive adhesive sheet at a frequency of 1 MHz is preferably less than 3.0, more preferably 2.9 or less. The lower limit of the relative permittivity of the pressure-sensitive adhesive sheet at a frequency of 1 MHz is not particularly limited, but is preferably 2.0. Thus, the pressure-sensitive adhesive sheet of the present invention has a low relative permittivity. The relative permittivity of the pressure-sensitive adhesive sheet is the relative permittivity at a frequency of 1 MHz, and the value calculated by the method specified in JIS C 2138 is used.

[0017] The moisture and heat resistance whitening property of the pressure-sensitive adhesive sheet can be determined to be good when the haze value is low after laminating a glass plate and a PET film through the pressure-sensitive adhesive sheet to form a laminate, leaving the laminate under the conditions of 60 ° C and 95% relative humidity for 240 hours, and then leaving it still in an environment of 23 ° C and 50% relative humidity for 1 hour. Specifically, one surface of the pressure-sensitive adhesive sheet is bonded to a glass plate with a thickness of 1.2 mm (manufactured by Matsunami Glass Industry Co., Ltd., S9112), and the other surface is bonded to a PET film (manufactured by Toyobo Co., Ltd., Cosmo Shine A4300) to form a laminate. The laminate is left in an environment of 60 ° C and 95% relative humidity for 240 hours, taken out, and then cooled at 23 ° C and 50% relative humidity for 1 hour, and then the haze is measured. As the haze measuring device, for example, NDH 4000 manufactured by Nippon Denshoku Industries Co., Ltd. can be used. The haze measured under the above conditions is preferably 2% or less, more preferably 1.8% or less, still more preferably 1.6% or less, and particularly preferably 1.4% or less.

[0018] The pressure-sensitive adhesive sheet of the present invention is preferably a double-sided pressure-sensitive adhesive sheet, but may also be a single-sided pressure-sensitive adhesive sheet having a base material or the like on one side of the pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet of the present invention may further include another adhesive layer, or may be a laminate having a support laminated between the adhesive layers. In this case, it is preferable to use a transparent support as the support. Such a double-sided pressure-sensitive adhesive sheet is also excellent in transparency as a whole of the pressure-sensitive adhesive sheet, and thus can be suitably used for bonding optical members. Among the above, the pressure-sensitive adhesive sheet of the present invention preferably has a substrate-less type without a support, and is preferably a single-layer double-sided pressure-sensitive adhesive sheet composed of an adhesive layer.

[0019] The surface of the adhesive sheet is preferably covered with a release sheet. That is, the present invention may relate to an adhesive sheet with a release sheet. FIG. 1 is a cross-sectional view showing an example of the configuration of an adhesive sheet with a release sheet. The adhesive sheet 11 shown in FIG. 1 has release sheets (12a, 12b). Note that the adhesive sheet 11 in FIG. 1 is a single-layer adhesive sheet of the base material-less type and is a double-sided adhesive sheet.

[0020] Examples of the release sheet include a release laminate sheet having a base material for the release sheet and a release agent layer provided on one side of the base material for the release sheet, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity base material. For the base material for the release sheet in the release laminate sheet, papers and polymer films are used. As the release agent constituting the release agent layer, for example, general-purpose addition-type or condensation-type silicone-based release agents or long-chain alkyl group-containing compounds are used. In particular, addition-type silicone-based release agents with high reactivity are preferably used. Specific examples of the silicone-based release agents include BY24-4527, SD-7220, etc. manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3600, KS-774, X62-2600, etc. manufactured by Shin-Etsu Chemical Co., Ltd. Further, it is preferable to contain a silicone resin which is an organosilicon compound having SiO 2 units and (CH 3 ) 3 SiO 1 / 2 units or CH 2 =CH(CH 3 )SiO 1 / 2 units. Specific examples of the silicone resin include BY24-843, SD-7292, SHR-1404, etc. manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.

[0021] The pressure-sensitive adhesive sheet with a release sheet preferably includes a pair of release sheets having different release forces on both surfaces of the pressure-sensitive adhesive sheet. That is, it preferably includes a first release sheet on one surface of the pressure-sensitive adhesive sheet and a second release sheet on the other surface of the pressure-sensitive adhesive sheet, and the release forces of the first release sheet and the second release sheet are preferably different from each other. In the example of FIG. 1, in order to facilitate peeling of the release sheet, it is preferable that the peelabilities of the release sheet 12a and the release sheet 12b are different. That is, when the peelability from one side is different from the peelability from the other side, it becomes easy to first peel only the release sheet 12 with the higher peelability. In that case, the peelability of the release sheet 12 of the release sheet 12a and the release sheet 12b may be adjusted according to the bonding method and the bonding order.

[0022] In addition, the pressure-sensitive adhesive sheet of the present invention is also excellent in dipping resistance. Here, the dipping resistance can be evaluated by the presence or absence of the generation of peeling sound when peeling the release sheet from the pressure-sensitive adhesive sheet with a release sheet and the presence or absence of streaks on the peeling surface. When no peeling sound is generated and no streaks are formed on the peeling surface, it can be determined that the dipping resistance is excellent. Thereby, the release sheet can be peeled from the pressure-sensitive adhesive sheet more smoothly. Further, deterioration of the pressure-sensitive adhesive sheet due to peeling of the release sheet is also suppressed.

[0023] Generally, in an adhesive sheet used for optical applications, in order to enhance the cohesive force and durability of the adhesive sheet, for example, an adhesive sheet in which a crosslinkable functional group such as a hydroxyl group is blended in an amount of 1 to 20% by mass based on the total mass of the acrylic polymer is used. However, when such an adhesive sheet is placed under high-temperature and high-humidity conditions, the adhesive sheet may turn white, which has been a problem. Further, when an acrylic polymer having 20% by mass or more of a crosslinkable group such as a hydroxyl group is used to suppress the whitening of the adhesive sheet, low dielectric properties are not sufficiently achieved. Furthermore, since such an adhesive sheet has a high cohesive force, dipping (a phenomenon in which when the release sheet is peeled off, a peeling sound is generated or marks such as streaks appear on the peeling surface) may occur. However, as a result of intensive studies, the present inventors have formed an adhesive sheet from an adhesive composition containing a predetermined acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group having 10 to 24 carbon atoms, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D), thereby enhancing the cohesive force and durability of the adhesive sheet while reducing the relative permittivity of the adhesive sheet, and further succeeding in enhancing the moisture and heat resistance whitening property and the anti-dipping property.

[0024] The adhesive force of the adhesive sheet to glass is preferably 15 N / 25 mm or more, more preferably 20 N / 25 mm or more, and even more preferably 25 N / 25 mm or more. Further, the upper limit value of the adhesive force of the adhesive sheet to glass is not particularly limited, but for example, it is preferably 40 N / 25 mm. The adhesive sheet formed from the adhesive composition of the present invention can exhibit such a high adhesive force. The adhesive force of the adhesive sheet to glass is a value measured in accordance with the "Test Method for Adhesive Tapes and Adhesive Sheets" of JIS Z 0237. Specifically, the adhesive sheet is bonded to a soda glass plate as an adherend in an environment of 23°C and a relative humidity of 50%, and a 2 kg roll is reciprocated once for pressure bonding. Then, it is allowed to stand in an environment of 23°C and a relative humidity of 50% for 24 hours, and in that environment, the adhesive sheet is peeled from the soda glass plate at a speed of 300 mm / min in the 180° direction for measurement.

[0025] The gel fraction of the pressure-sensitive adhesive sheet is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more. The gel fraction of the pressure-sensitive adhesive sheet can be calculated by the following method. First, collect about 0.1 g of the pressure-sensitive adhesive sheet into a sample bottle, add 30 ml of ethyl acetate, and shake it at 40°C for 24 hours. Then, filter the contents of this sample bottle through a 150-mesh stainless steel wire mesh, dry the residue on the wire mesh at 100°C for 1 hour, and measure the dry weight W (g). The gel fraction is determined from the obtained dry weight by the following formula 1. Gel fraction (%) = (dry weight / collected weight of the pressure-sensitive adhesive sheet) × 100 ··· Formula 1

[0026] The thickness of the pressure-sensitive adhesive sheet can be appropriately set according to the application and is not particularly limited. Usually, it is preferably in the range of 10 μm or more and 500 μm or less, more preferably 20 μm or more and 450 μm or less, even more preferably 30 μm or more and 450 μm or less, still more preferably 40 μm or more and 400 μm or less, even still more preferably 40 μm or more and 350 μm or less, and particularly preferably 40 μm or more and 300 μm or less. By setting the thickness of the pressure-sensitive adhesive sheet within the above range, sufficient step-following performance can be ensured, and further durability can be enhanced. Also, by setting the thickness of the pressure-sensitive adhesive sheet within the above range, the production of the pressure-sensitive adhesive sheet becomes easy.

[0027] (Pressure-sensitive adhesive composition) The pressure-sensitive adhesive sheet of the present invention is formed from a pressure-sensitive adhesive composition containing an acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms, a (meth)acrylate (C) having an alkylene glycol group, and a photopolymerization initiator (D). Since the pressure-sensitive adhesive composition contains the photopolymerization initiator (D), the pressure-sensitive adhesive composition is a photocurable type. The pressure-sensitive adhesive composition of the present invention is cured, for example, by irradiating ultraviolet rays to form a pressure-sensitive adhesive sheet.

[0028] Also, the pressure-sensitive adhesive composition of the present invention is preferably a solvent-free pressure-sensitive adhesive composition. In the present specification, the solvent-free pressure-sensitive adhesive composition refers to a composition in which the content of the solvent contained in the pressure-sensitive adhesive composition is 1% by mass or less, and in such a case, it can be said that substantially no solvent is contained.

[0029] <Acrylic syrup (A)> The pressure-sensitive adhesive composition contains acrylic syrup (A). Acrylic syrup (A) contains a (meth)acrylic polymer having a weight average molecular weight of 50,000 to 500,000 and a (meth)acrylic monomer. Thus, in the present specification, acrylic syrup refers to a liquid composition containing an acrylic polymer and an acrylic monomer.

[0030] The pressure-sensitive adhesive composition contains acrylic syrup (A) as a main component. The content of acrylic syrup (A) in the pressure-sensitive adhesive composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the pressure-sensitive adhesive composition. In addition, the content of acrylic syrup (A) in the pressure-sensitive adhesive composition is preferably 95% by mass or less, based on the total mass of the pressure-sensitive adhesive composition.

[0031] The content of the (meth)acrylic polymer with respect to the total mass of acrylic syrup (A) may be 20% by mass or more, and more preferably 25% by mass or more. Also, the content of the (meth)acrylic polymer with respect to the total mass of acrylic syrup (A) is preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 50% by mass or less.

[0032] On the one hand, the content of the (meth)acrylic monomer with respect to the total mass of the acrylic syrup (A) may be 25% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more. Also, the content of the (meth)acrylic monomer with respect to the total mass of the acrylic syrup (A) is preferably 80% by mass or less, and more preferably 75% by mass or less.

[0033] The (meth)acrylic monomer contained in the acrylic syrup (A) is preferably a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms. Similarly, the (meth)acrylic polymer contained in the acrylic syrup (A) preferably contains units derived from a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms. Here, in this specification, the "unit" is a repeating unit (monomer unit) constituting the polymer. Note that the carbon number of the branched alkyl group of the (meth)acrylic acid ester may be 5 to 9, but is preferably 7 to 9.

[0034] Since the alkyl group with 5 to 9 carbon atoms has a branched structure, it has a large molar volume and a small density. Therefore, when the acrylic syrup (A) contains a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms or units derived therefrom, the molar volume of the acrylic syrup (A) can be increased and the density can be decreased. Also, by the acrylic syrup (A) containing a (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms or units derived therefrom, the volume shrinkage rate when made into a polymer can be suppressed, and it is considered that the molar volume of the acrylic syrup (A) can be maintained large. As a result of these, it becomes easy to form a pressure-sensitive adhesive sheet with a low relative permittivity.

[0035] Examples of the (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms include isopentyl (meth)acrylate, isohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and the like. These may be used alone or in combination of two or more. Among them, the (meth)acrylic acid ester having a branched alkyl group with 5 to 9 carbon atoms is preferably 2-ethylhexyl (meth)acrylate.

[0036] The (meth)acrylic monomers contained in the acrylic syrup (A) include acrylic acid esters and methacrylic acid esters, and it is preferable that the ester structures of the acrylic acid esters and methacrylic acid esters are the same. Similarly, the (meth)acrylic polymers contained in the acrylic syrup (A) include units derived from acrylic acid esters and units derived from methacrylic acid esters, and it is preferable that the ester structures of the units derived from acrylic acid esters and the units derived from methacrylic acid esters are the same. Here, the same ester structure means that the structures of the portions constituting the side chain containing the ester bond (the side chain in this case refers to the portion that becomes the side chain when formed into a polymer) are the same.

[0037] Among the acrylic acid ester and methacrylic acid ester having the same ester structure, the glass transition temperature when either one is made into a homopolymer is preferably -60°C or lower, and the glass transition temperature when the other is made into a homopolymer is preferably -15°C or higher. Examples of the acrylic acid ester and methacrylic acid ester having the same ester structure include a combination of 2-ethylhexyl acrylate (2EHA) and 2-ethylhexyl methacrylate (2EHMA). By using two kinds of acrylic acid esters in this way and making the ester structures the same in the two kinds of acrylic acid esters, the uniform mixing property of the pressure-sensitive adhesive composition is enhanced, so that whitening of the pressure-sensitive adhesive sheet is suppressed, and a pressure-sensitive adhesive sheet with little variation in pressure-sensitive adhesive properties can be obtained.

[0038] Furthermore, the mass ratio of the acrylate ester to the methacrylate ester contained in the acrylic syrup (A) is preferably from 25:75 to 50:50, more preferably from 25:75 to 40:60. Similarly, the compositional mass ratio of the unit derived from the acrylate ester to the unit derived from the methacrylate ester in the (meth)acrylic polymer contained in the acrylic syrup (A) is also preferably from 25:75 to 50:50, more preferably from 25:75 to 40:60. By setting the mass ratio of the acrylate ester to the methacrylate ester within the above range, the wet heat whitening resistance of the adhesive sheet can be more effectively enhanced.

[0039] The weight average molecular weight of the (meth)acrylic polymer contained in the acrylic syrup (A) may be 50,000 or more, preferably 100,000 or more. Also, the weight average molecular weight of the (meth)acrylic polymer contained in the acrylic syrup (A) may be 500,000 or less, more preferably 400,000 or less. By setting the weight average molecular weight of the (meth)acrylic polymer within the above range, sufficient adhesive strength and wet heat whitening resistance can be ensured. The weight average molecular weight is a value measured by gel permeation chromatography (GPC) and determined based on polystyrene standards.

[0040] The measurement conditions of gel permeation chromatography (GPC) are as follows. Solvent: Tetrahydrofuran Column: Shodex KF801, KF803L, KF806L (three columns manufactured by Showa Denko K.K. were connected and used) Column temperature: 40 °C Sample concentration: 0.5 mass% Detector: RI-2031plus (manufactured by JASCO) Pump: RI-2080plus (manufactured by JASCO) Flow rate: 0.8 ml / min Injection volume: 10 μl Calibration curve: A calibration curve using 10 samples of Shodex standard polystyrene (manufactured by Showa Denko K.K.) with Mw ranging from 1320 to 2,500,000 was used.

[0041] Acrylic syrup (A) is preferably obtained by polymerizing the above-mentioned (meth)acrylic acid ester by photopolymerization. That is, acrylic syrup (A) preferably contains a (meth)acrylic photopolymer. Further, acrylic syrup (A) preferably contains the monomer used for the polymerization of the (meth)acrylic photopolymer as a (meth)acrylic monomer. Thus, acrylic syrup (A) is preferably a mixed solution containing a (meth)acrylic monomer having the same composition as the (meth)acrylic polymer.

[0042] When synthesizing acrylic syrup (A), in addition to the above-mentioned acrylic monomer, other acrylic monomers may be further used. Examples of such acrylic monomers include (meth)acrylic monomers having a crosslinkable functional group. The (meth)acrylic monomer having a crosslinkable functional group is preferably a carboxyl group-containing (meth)monomer, a hydroxy group-containing (meth)monomer, an amino group-containing (meth)monomer, or a glycidyl group-containing (meth)monomer.

[0043] Examples of the carboxyl group-containing monomer include acrylic acid and methacrylic acid. Examples of the hydroxy group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate, (meth)acrylic acid [(mono, di, or poly)alkylene glycol] such as (meth)acrylic acid mono(diethylene glycol), and lactones of (meth)acrylic acid such as (meth)acrylic acid monocaprolactone. Examples of the amino group-containing monomer include (meth)acrylamide and allylamine. Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and the like.

[0044] Among them, the (meth)acrylic monomer having a crosslinkable functional group is preferably a hydroxy group-containing (meth)acrylic monomer, and more preferably 2-hydroxyethyl (meth)acrylate.

[0045] The content of the (meth)acrylic monomer having a crosslinkable functional group is preferably 0.01% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more with respect to the total mass of the (meth)acrylic monomers in the acrylic syrup (A). Also, the content of the (meth)acrylic monomer having a crosslinkable functional group is preferably 40% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less with respect to the total mass of the (meth)acrylic monomers in the acrylic syrup (A). Note that the content of the unit derived from the (meth)acrylic monomer having a crosslinkable functional group is preferably 0.01% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more with respect to the total mass of the (meth)acrylic polymer in the acrylic syrup (A). Also, the content of the unit derived from the (meth)acrylic monomer having a crosslinkable functional group is preferably 40% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less with respect to the total mass of the (meth)acrylic polymer in the acrylic syrup (A).

[0046] The viscosity of the acrylic syrup (A) is preferably 1000 mPa·s or more, more preferably 1500 mPa·s or more, and even more preferably 2000 mPa·s or more. Also, the viscosity of the acrylic syrup (A) is preferably 10000 mPa·s or less, more preferably 8000 mPa·s or less, and even more preferably 6000 mPa·s or less. Note that the viscosity of the acrylic syrup (A) is a value measured at 23°C and a relative humidity of 50% using a B-type viscometer at 60 revolutions per minute.

[0047] <(Meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms> The pressure-sensitive adhesive composition contains a (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms. The number of carbon atoms of the branched alkyl group possessed by the (meth)acrylic acid ester (B) may be 10 or more, preferably 12 or more, and more preferably 15 or more. Further, the number of carbon atoms of the branched alkyl group possessed by the acrylic acid ester (B) may be 24 or less, preferably 22 or less, and more preferably 20 or less.

[0048] Examples of the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms include isostearyl (meth)acrylate, isoeicosyl (meth)acrylate, stearyl acrylate (meth)acrylate, lauryl (meth)acrylate, and the like. Among them, the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms is preferably isostearyl (meth)acrylate.

[0049] As the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms, commercially available products can also be used. Examples of the commercially available products include ISTA, STA, LA, etc. manufactured by Osaka Organic Chemical Industry Co., Ltd.

[0050] The content of the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the acrylic syrup (A). Further, the content of the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms is preferably 40 parts by mass or less with respect to 100 parts by mass of the acrylic syrup (A). By setting the content of the (meth)acrylic acid ester (B) having a branched alkyl group with 10 to 24 carbon atoms within the above range, it becomes easy to lower the relative permittivity of the pressure-sensitive adhesive sheet.

[0051] <(Meth)acrylate (C) having an alkylene glycol group> The pressure-sensitive adhesive composition contains a (meth)acrylate (C) having an alkylene glycol group. In the present invention, by containing a predetermined amount of a (meth)acrylate (C) having a hydrophilic alkylene glycol group, the pressure-sensitive adhesive composition can take in excess moisture, and as a result, the wet heat whitening resistance is enhanced.

[0052] Examples of the alkylene glycol group of the (meth)acrylate (C) include an ethylene glycol group, a propylene glycol group, and a butylene glycol group. Among them, the alkylene glycol group of the (meth)acrylate (C) is preferably a propylene glycol group.

[0053] The propylene glycol group is a group represented by -CH 2 CH 2 CH 2 O-. The (meth)acrylate (C) having a propylene glycol group may have one propylene glycol group or two or more propylene glycol groups in one molecule. Among them, the number of propylene glycol groups in one molecule of the (meth)acrylate (C) having a propylene glycol group is preferably 1 to 50, more preferably 1 to 40, still more preferably 1 to 30, and particularly preferably 1 to 23.

[0054] Examples of the (meth)acrylic acid ester (C) having a propylene glycol group include alkoxypropylene glycol (meth)acrylate and alkoxypolypropylene glycol (meth)acrylate. Among them, the (meth)acrylic acid ester (C) having a propylene glycol group is preferably at least one selected from alkoxyepropylene glycol (meth)acrylate and alkoxypolypropylene glycol (meth)acrylate. That is, the (meth)acrylic acid ester (C) having an alkylene glycol group is preferably a unit derived from at least one selected from alkoxypropylene glycol (meth)acrylate and alkoxypolypropylene glycol (meth)acrylate.

[0055] The number of carbon atoms of the alkoxy group in alkoxypropylene glycol (meth)acrylate and alkoxypolypropylene glycol (meth)acrylate is preferably 20 or less, more preferably 15 or less, and even more preferably 5 or less. Among them, the (meth)acrylic acid ester having an alkylene glycol group is more preferably a unit derived from at least one selected from 2-methoxyethyl (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate, and even more preferably a unit derived from at least one selected from 2-methoxyethyl (meth)acrylate and methoxypolypropylene glycol (meth)acrylate.

[0056] As the (meth)acrylic acid ester (C) having an alkylene glycol group, commercially available products can also be used. Examples of commercially available products include Aronix M-220, M-225, M-270, M-240 manufactured by Toagosei Co., Ltd., 2-MTA manufactured by Osaka Organic Chemical Industry Co., Ltd., NK Ester AM-130G, NK Ester AM-230G, and Light Acrylate EC-A manufactured by Kyoeisha Chemical Co., Ltd.

[0057] The content of the (meth)acrylic acid ester (C) having an alkylene glycol group is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more with respect to 100 parts by mass of the acrylic syrup (A). Also, the content of the (meth)acrylic acid ester (C) having an alkylene glycol group is preferably 6 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less with respect to 100 parts by mass of the acrylic syrup (A). By setting the content of the (meth)acrylic acid ester (C) having an alkylene glycol group within the above range, it is possible to more effectively suppress the wet heat whitening of the pressure-sensitive adhesive sheet while keeping the relative permittivity of the pressure-sensitive adhesive sheet low.

[0058] <Photoinitiator (D)> The pressure-sensitive adhesive composition contains a photoinitiator (D). The photoinitiator is preferably a polymerization initiator that reacts with the acrylic syrup (A) by ultraviolet rays, for example. Also, as the photoinitiator (D) of the pressure-sensitive adhesive composition, a hydrogen abstraction type photoinitiator may be used. By using a hydrogen abstraction type photoinitiator, after-curing properties can also be imparted to the obtained pressure-sensitive adhesive sheet.

[0059] Examples of the photoinitiator include acetophenone-based initiators, benzoin ether-based initiators, benzophenone-based initiators, hydroxyalkylphenone-based initiators, thioxanthone-based initiators, amine-based initiators, and the like. Specific examples of the acetophenone-based initiator include diethoxyacetophenone, benzyldimethylketal, and the like. Specific examples of the benzoin ether-based initiator include benzoin, benzoin methyl ether, and the like. Specific examples of the benzophenone-based initiator include benzophenone, methyl o-benzoylbenzoate, and the like. Specific examples of the hydroxyalkylphenone-based initiator include 1-hydroxy-cyclohexyl-phenyl-ketone, and the like. Specific examples of the thioxanthone-based initiator include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, and the like. Specific examples of the amine-based initiator include triethanolamine, ethyl 4-dimethylbenzoate, and the like. Note that as the photopolymerization initiator, one kind may be used alone or two or more kinds may be used in combination.

[0060] Commercially available products can be used as the photopolymerization initiator. Examples of commercially available products include Irgacure 1173, Irgacure 184, etc. manufactured by BASF.

[0061] The content of the photopolymerization initiator in the pressure-sensitive adhesive composition is appropriately selected according to the desired adhesive properties and the like, and is not particularly limited. However, it is preferably 0.01 part by mass or more and 5 parts by mass or less, more preferably 0.03 part by mass or more and 3 parts by mass or less, based on 100 parts by mass of the acrylic syrup (A).

[0062] <Optional Component> The pressure-sensitive adhesive composition may contain optional components other than the above-described components. Examples of the optional components include plasticizers. When the pressure-sensitive adhesive composition contains a plasticizer, the content of the plasticizer is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, based on 100 parts by mass of the acrylic syrup (A).

[0063] As the plasticizer, for example, a non-functional acrylic polymer can be used. The non-functional acrylic polymer means a polymer composed only of acrylic monomer units having no functional groups other than acrylate groups, or a polymer composed of acrylic monomer units having no functional groups other than acrylate groups and non-acrylic monomer units having no functional groups. Examples of the non-acrylic monomer units having no functional groups include vinyl carboxylates such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl benzoate, and styrene.

[0064] In addition, as optional components, components known as additives for adhesives can be mentioned, such as antioxidants, metal corrosion inhibitors, tackifiers, silane coupling agents, ultraviolet absorbers, and light stabilizers such as hindered amine compounds. Examples of the antioxidant include phenolic antioxidants, amine antioxidants, lactone antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. These antioxidants may be used alone or in combination of two or more. Examples of the metal corrosion inhibitor include benzotriazole-based resins. Examples of the tackifier include rosin-based resins, terpene-based resins, terpene phenol-based resins, coumarone indene-based resins, styrene-based resins, xylene-based resins, phenol-based resins, petroleum resins, etc. Examples of the silane coupling agent include mercaptoalkoxysilane compounds (for example, mercapto group-substituted alkoxy oligomers, etc.). Examples of the ultraviolet absorber include benzotriazole-based compounds, benzophenone-based compounds, etc.

[0065] The content of the thermosetting crosslinking agent in the adhesive composition is preferably less than 0.1% by mass based on the total mass of the adhesive composition. This means that the adhesive composition substantially does not contain a thermosetting crosslinking agent. Examples of the thermosetting crosslinking agent include known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds.

[0066] (Method for manufacturing an adhesive sheet) The manufacturing process of the adhesive sheet preferably includes a step of applying an adhesive composition onto a release sheet to form a coating film, and a step of curing the coating film by irradiating light on a laminate obtained by laminating another release sheet on the coating film.

[0067] The application of the adhesive composition for forming the adhesive sheet can be carried out using a known coating device. Examples of the coating device include a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a microgravure coater, a rod blade coater, a lip coater, a die coater, a curtain coater, etc.

[0068] Examples of the light used during light irradiation include ultraviolet rays and visible light. Among them, it is preferable to use ultraviolet rays with a wavelength of 250 to 400 nm. The ultraviolet irradiation conditions are such that the irradiance measured with an ultraviolet illuminometer having a spectral sensitivity centered at a wavelength of 365 nm is 0.1 mW / cm 2 and the light quantity is 500 mJ / cm 2 or more, which is desirable. By adopting such ultraviolet irradiation conditions, an adhesive sheet with a high gel fraction and excellent durability can be obtained. Examples of the light source include ultraviolet fluorescent lamps such as chemical lamps and black lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, mercury xenon lamps, metal halide lamps, LED lamps, carbon arcs, xenon arcs, etc.

[0069] (Laminate) The present invention may relate to a laminate including the above-described adhesive sheet and an adherend on at least one surface side of the adhesive sheet. Here, the adherend is preferably an optical member. Further, the adherend may have a stepped portion or irregularities derived from a step. Among them, the adherend is preferably an optical member constituting an image display device having a liquid crystal module or an optical member constituting a touch panel. The laminate is preferably obtained through a step of bringing the adhesive sheet into contact with the surface of the adherend.

[0070] Examples of the optical member include each constituent member in optical products such as touch panels and image display devices. Examples of the constituent members of the touch panel include, for example, an ITO film in which an ITO film is provided on a transparent resin film, ITO glass in which an ITO film is provided on the surface of a glass plate, a transparent conductive film in which a conductive polymer is coated on a transparent resin film, a hard coat film, and a fingerprint-resistant film. The adhesive sheet of the present invention is preferably for laminating a touch panel and an image display device, and more preferably for laminating a touch panel using a touch pen and an image display device. From this viewpoint, as the adherend of the adhesive sheet of the present invention, an ITO film in which an ITO film is provided on a transparent resin film, ITO glass in which an ITO film is provided on the surface of a glass plate, and a transparent conductive film in which a conductive polymer is coated on a transparent resin film are preferable, and it is preferable to stick the adhesive sheet on the back surface (the surface without the conductive layer) of these glasses or films. Examples of the constituent members of the image display device include, for example, an antireflection film, an alignment film, a polarizing film, a retardation film, and a brightness enhancement film used in a liquid crystal display device. Examples of the materials used for these members include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, and cellulose acylate. Note that a functional layer such as a hard coat layer may be provided on the side of these films in contact with the adhesive sheet.

[0071] When the pressure-sensitive adhesive sheet of the present invention is a double-sided pressure-sensitive adhesive sheet, it can be used for bonding two adherends. In this case, the pressure-sensitive adhesive sheet of the present invention is used for bonding ITO films inside a touch panel, bonding an ITO film and ITO glass, bonding an ITO film of a touch panel and a liquid crystal panel, bonding a cover glass and an ITO film, bonding a cover glass and a decorative film, and the like.

[0072] (Method for manufacturing a laminate) When manufacturing a laminate, it includes a step of bonding the above-described pressure-sensitive adhesive sheet and an adherend. When manufacturing a laminate, after bonding the above-described pressure-sensitive adhesive sheet to an adherend, active energy rays may be irradiated to cure the pressure-sensitive adhesive sheet. In this case, before irradiating the active energy rays, the pressure-sensitive adhesive sheet may be in a semi-cured state. When the pressure-sensitive adhesive sheet is in a semi-cured state, the initial adhesion to the substrate becomes better.

[0073] Examples of the active energy rays include ultraviolet rays, electron beams, visible light rays, X-rays, ion beams, etc., and can be appropriately selected according to the polymerization initiator contained in the pressure-sensitive adhesive sheet. Among them, from the viewpoint of versatility, ultraviolet rays or electron beams are preferable, and ultraviolet rays are particularly preferable. As a light source for ultraviolet rays, for example, a high-pressure mercury lamp, a low-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a carbon arc, a xenon arc, a electrodeless ultraviolet lamp, etc. can be used. As an electron beam, for example, electron beams emitted from various types of electron beam accelerators such as a Cockcroft-Walton type, a Van de Graaff type, a resonance transformer type, an insulated core transformer type, a linear type, a dynamitron type, and a high-frequency type can be used. The irradiation output of ultraviolet rays is preferably such that the integrated light quantity becomes 100 to 10000 mJ / cm 2 and more preferably such that it becomes 500 to 5000 mJ / cm 2

Examples

[0074] ​Examples and comparative examples are given below to more specifically explain the features of the present invention. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0075] (Synthesis of Acrylic Syrup A-1) 2-Ethylhexyl acrylate (2-EHA), 2-ethylhexyl methacrylate (2-EHMA), and 2-hydroxyethyl acrylate (2-HEA) were blended so that the mass ratio was 25:65:10, and 3 parts by mass of a photopolymerization initiator (Irg.1173, manufactured by BASF) was dissolved in the solution. After replacing the air in the container with nitrogen gas, ultraviolet rays having an output peak at a wavelength of 365 nm were irradiated while stirring to obtain a (meth)acrylic polymer. The weight average molecular weight of the (meth)acrylic polymer was 400,000. Next, a monomer composition liquid having the same composition ratio as the (meth)acrylic polymer was added to the (meth)acrylic polymer obtained above so that the solid content was 30% by mass, to obtain Acrylic Syrup A-1.

[0076] The weight average molecular weight of the (meth)acrylic polymer was measured by gel permeation chromatography (GPC) and determined based on polystyrene standards. The measurement conditions for gel permeation chromatography (GPC) were as follows. Solvent: Tetrahydrofuran Column: Shodex KF801, KF803L, KF806L (three manufactured by Showa Denko K.K. were connected and used) Column temperature: 40 °C Sample concentration: 0.5% by mass Detector: RI-2031plus (manufactured by JASCO) Pump: RI-2080plus (manufactured by JASCO) Flow rate: 0.8 ml / min Injection volume: 10 μl Calibration curve: A calibration curve using 10 samples of Shodex standard polystyrene (manufactured by Showa Denko K.K.) with Mw ranging from 1320 to 2,500,000 was used.

[0077] (Synthesis of Acrylic Syrup A-2) Acrylic syrup A-2 was prepared in the same manner as in Example 1, except that 2-ethylhexyl acrylate (2-EHA), 2-ethylhexyl methacrylate (2-EHMA), and 2-hydroxyethyl acrylate (2-HEA) were blended at a mass ratio of 30:60:10. The weight average molecular weight of the (meth)acrylic polymer was 400,000.

[0078] (Example 1) <Preparation of Adhesive Composition> To 100 parts by mass of the obtained acrylic syrup A-1, 30 parts by mass of isostearyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., ISTA), 0.3 parts by mass of a polyfunctional monomer (manufactured by Toagosei Co., Ltd., M-240), and 1.0 part by mass of a photopolymerization initiator (manufactured by BASF, Irg.819) were added to obtain an adhesive composition.

[0079] (Example 2) <Preparation of Adhesive Composition> An adhesive composition was obtained in the same manner as in Example 1, except that the polyfunctional monomer was changed to M-270.

[0080] (Example 3) <Preparation of Adhesive Composition> An adhesive composition was obtained in the same manner as in Example 1, except that the polyfunctional monomer was changed to M-220 and the addition amount was changed to 1.0 part by mass.

[0081] (Example 4) <Preparation of Adhesive Composition> An adhesive composition was obtained in the same manner as in Example 1, except that the polyfunctional monomer was changed to 2-MTA and the addition amount was changed to 1.5 parts by mass.

[0082] (Example 5) <Preparation of Adhesive Composition> An adhesive composition was obtained in the same manner as in Example 1, except that the polyfunctional monomer was changed to AM-130G and the addition amount was changed to 1.5 parts by mass.

[0083] (Example 6) (Preparation of Adhesive Composition) To 100 parts by mass of the obtained acrylic syrup A-2, 30 parts by mass of isostearyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., ISTA), 1.0 part by mass of a polyfunctional monomer (manufactured by Toagosei Co., Ltd., M-220), and 1.0 part by mass of a photopolymerization initiator (manufactured by BASF, Irg.819) were added to obtain an adhesive composition.

[0084] (Example 7) (Preparation of Adhesive Composition) An adhesive composition was obtained in the same manner as in Example 6, except that the polyfunctional monomer was changed to 2-MTA and the addition amount was changed to 1.5 parts by mass.

[0085] (Comparative Example 1) (Preparation of Adhesive Composition) An adhesive composition was obtained in the same manner as in Example 1, except that the polyfunctional monomer was changed to M-211B.

[0086] (Comparative Example 2) (Preparation of Adhesive Composition) An adhesive composition was obtained in the same manner as in Example 1, except that no polyfunctional monomer was added.

[0087] (Comparative Example 3) (Preparation of Adhesive Composition) 2-Ethylhexyl acrylate (2-EHA), 2-ethylhexyl methacrylate (2-EHMA), and 2-hydroxyethyl methacrylate (2-HEMA) were blended so that the mass ratio was 25:65:10, and 2,2'-azobis(2,4-dimethylvaleronitrile) was dissolved in the solution as a radical polymerization initiator. The solution was heated to 60 °C and randomly copolymerized to obtain a (meth)acrylic polymer (A-3). The weight average molecular weight of the (meth)acrylic polymer (A-3) was 500,000. To 100 parts by mass of the (meth)acrylic polymer (A-3), isostearyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., ISTA), photoinitiator Irgacure 819, and thermal crosslinking agent Coronate L-55E were blended so that the ratio was 100:15:1.0:0.5 to obtain an adhesive composition.

[0088] <Production of Adhesive Sheet (Examples and Comparative Examples 1 and 2)> The adhesive compositions prepared in the examples and comparative examples 1 and 2 were uniformly applied with an applicator on the surface of a 100-μm-thick polyethylene terephthalate film (first release sheet) (manufactured by Oji Eftex Co., Ltd.: 100RL-07(2)) having a release agent layer treated with a silicone-based release agent so that the coating thickness after drying was 150 μm, and an adhesive layer was formed on the surface of the first release sheet. Next, a 75-μm-thick second release sheet (manufactured by Oji Eftex Co., Ltd.: 75RL-07(L)) was laminated on the surface of this adhesive layer, and ultraviolet light with a wavelength of 365 nm was irradiated so that the integrated light quantity was 500 mJ / cm 2 to obtain an adhesive sheet with a release sheet having a structure of a first release sheet / adhesive sheet / second release sheet in which the adhesive layer was sandwiched between a pair of release sheets having a difference in peel strength.

[0089] <Production of Adhesive Sheet (Comparative Example 3)> The adhesive composition prepared in Comparative Example 3 was uniformly applied with an applicator on the surface of a 100-μm-thick polyethylene terephthalate film (first release sheet) (manufactured by Oji Eftex Co., Ltd.: 100RL-07(2)) having a release agent layer treated with a silicone-based release agent so that the coating thickness after drying was 150 μm, and an adhesive layer was formed on the surface of the first release sheet. Next, this adhesive layer was dried at 100°C for 3 minutes, and a 75-μm-thick second release sheet (manufactured by Oji Eftex Co., Ltd.: 75RL-07(L)) was laminated on the surface of the dried adhesive sheet, and it was left standing for 7 days in an environment of 23°C and 50% relative humidity to obtain an adhesive sheet with a release sheet having a structure of a first release sheet / adhesive sheet / second release sheet in which the adhesive layer was sandwiched between a pair of release sheets having a difference in peel strength.

[0090] [Evaluation] <Relative permittivity> The relative permittivity of the pressure-sensitive adhesive sheet was evaluated according to the following procedure. Two pressure-sensitive adhesive sheets (after peeling the first release sheet and the second release sheet from the pressure-sensitive adhesive sheet) were sandwiched between two copper foils, and autoclave treatment (40 °C, 0.5 MPa, 30 minutes) was performed. Then, the relative permittivity was measured based on JIS C 2138 using a dielectric measurement system (manufactured by Toyo Technica Co., Ltd., Model 1260). The frequency and measurement environment were measured under the following conditions. Frequency: 1 MHz Measurement environment: 23 °C, relative humidity 50%

[0091] <Moisture and heat resistance whitening property> From the pressure-sensitive adhesive sheet cut into a size of 50 mm in width × 50 mm in length, the first release sheet (light release film) was peeled off and bonded to a glass plate with a thickness of 1.2 mm (manufactured by Matsunami Glass Industry Co., Ltd., S9112). Then, the second release sheet (heavy release film) was peeled off, and a PET film (manufactured by Toyobo Co., Ltd., Cosmo Shine A4300) was bonded to the pressure-sensitive adhesive sheet to prepare a test sample. The test sample was left in an environment of 60 °C and relative humidity 95% for 240 hours, taken out, cooled at 23 °C and relative humidity 50% for 1 hour, and then the haze was measured. The haze was measured using an NDH 4000 manufactured by Nippon Denshoku Industries Co., Ltd. Then, the moisture and heat resistance whitening property was evaluated according to the following criteria. ○: Haze ≤ 2.0% ×: Haze > 2.0%

[0092] <Dipping resistance> The presence or absence of peeling sound when manually peeling the first or second release sheet from the pressure-sensitive adhesive sheet was examined. Also, the presence or absence of marks such as streaks on the peeling surface of the pressure-sensitive adhesive sheet was visually observed. Then, the dipping resistance was evaluated according to the following criteria. ○: No peeling sound occurred and no streaks were observed on the peeling surface of the release sheet. ×: Peeling sound occurred or streaks were observed on the peeling surface of the release sheet.

[0093]

Table 1

[0094] 2EHA: 2-Ethylhexyl acrylate 2EHMA: 2-Ethylhexyl methacrylate 2HEA: 2-Hydroxyethyl acrylate 2HEMA: 2-Hydroxyethyl methacrylate ISTA: Isostearyl (meth)acrylate M-240: Tetrapolyethylene glycol diacrylate M-270: Polypropylene glycol diacrylate M-220: Tripolypropylene glycol diacrylate 2-MTA: 2-Methoxyethyl acrylate AM-130G: Methoxypolyethylene glycol #550 acrylate M-211B: Bisphenol A EO modified (n≈2) diacrylate

[0095] The pressure-sensitive adhesive composition obtained in the examples was a pressure-sensitive adhesive sheet having a low relative permittivity and formed a pressure-sensitive adhesive sheet excellent in moisture and heat resistance whitening property. Further, the pressure-sensitive adhesive composition obtained in the examples was a photocurable pressure-sensitive adhesive, and since it could construct a more uniform network structure than a thermosetting pressure-sensitive adhesive, it formed a pressure-sensitive adhesive sheet excellent in dipping resistance despite having high cohesive force.

Explanation of symbols

[0096] 1 Pressure-sensitive adhesive sheet with release sheet 11 Pressure-sensitive adhesive sheet (adhesive layer) 12a, 12b Release sheet

Claims

1. An adhesive sheet formed from an adhesive composition containing acrylic syrup (A), a (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms, an acrylate (C), and a photopolymerization initiator (D), wherein the (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms is isostearyl (meth)acrylate or isoeicosyl (meth)acrylate, the acrylate (C) is tetra polyethylene glycol diacrylate (M-240), polypropylene glycol diacrylate (M-270), tripropylene glycol diacrylate (M-220), 2-methoxyethyl acrylate (2-MTA), or methoxypolyethylene glycol #550 acrylate (AM-130G), the acrylic syrup (A) contains a (meth)acrylic polymer having a weight average molecular weight of 50,000 to 500,000 and a (meth)acrylic monomer, and the content of the (meth)acrylic polymer relative to the total mass of the acrylic syrup (A) is 20% by mass or more and 75% by mass or less, and the content of the (meth)acrylic monomer is 25% by mass or more and 80% by mass or less, the (meth)acrylic monomer contained in the acrylic syrup (A) is an acrylate having a branched alkyl group with 5 to 9 carbon atoms, a methacrylate having a branched alkyl group with 5 to 9 carbon atoms, 2-hydroxyethyl (meth)acrylate, and consists of the ester structures of the acrylate and the methacrylate are the same, the (meth)acrylic polymer contained in the acrylic syrup (A) contains units derived from an acrylate having a branched alkyl group with 5 to 9 carbon atoms and units derived from a methacrylate having a branched alkyl group with 5 to 9 carbon atoms, and the ester structures of the units derived from the acrylate and the units derived from the methacrylate are the same, the content of the (meth)acrylate (B) having a branched alkyl group with 10 to 24 carbon atoms is 10 to 40 parts by mass, and the content of the acrylate (C) is 0.05 to 6 parts by mass with respect to 100 parts by mass of the acrylic syrup (A). An adhesive sheet.

2. The adhesive sheet according to claim 1, having a relative permittivity of less than 3.0 at a frequency of 1 MHz.

3. When the glass plate and the PET film are laminated through the adhesive sheet to form a laminate, the haze after leaving the laminate at 60°C and a relative humidity of 95% for 240 hours and then leaving it standing in an environment of 23°C and a relative humidity of 50% for 1 hour is 2% or less. The adhesive sheet according to claim 1 or 2.

4. The mass ratio of the acrylate ester and the methacrylate ester contained in the acrylic syrup (A) is 25:75 to 50:

50. The adhesive sheet according to any one of claims 1 to 3.

5. An adhesive sheet with a release sheet, comprising a pair of release sheets with different release forces on both surfaces of the adhesive sheet according to any one of claims 1 to 4.

6. A laminate comprising the adhesive sheet according to any one of claims 1 to 4 and an adherend on at least one surface side of the adhesive sheet.

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