JP7346822B2 - Adhesive sheets, adhesive sheets with release sheets, and laminates - Google Patents

Description

The present invention relates to an adhesive sheet, an adhesive sheet with a release sheet, and a laminate.

2. Description of the Related Art In recent years, display devices such as liquid crystal displays (LCDs) and devices that combine display devices and input devices such as touch panels have been widely used in various fields. Among them, capacitive touch panels are rapidly becoming popular due to their functionality. In the manufacture of these display devices and input devices, adhesive sheets are used to bond optical members, and adhesive sheets are also used to bond display devices and input devices.

In a capacitive touch panel, when a finger approaches the surface, the capacitance between multiple electrodes changes simultaneously, and by measuring the ratio of current amounts, it is possible to detect the position with high precision. However, increasing the size of this method increases the number of touch panel malfunctions. In order to deal with such problems, the use of adhesive sheets with controlled dielectric constants is being considered. Among them, capacitive touch panels that have an image display device and a touch panel are susceptible to malfunction of the touch panel due to electrical noise from the image display device. The use of adhesive sheets with a low dielectric constant is being considered.

For example, Patent Document 1 discloses an adhesive composition that can form an adhesive layer with a low dielectric constant. Patent Document 1 states that the structural unit (A) derived from an alkyl methacrylate having a branched chain alkyl group having 5 to 9 carbon atoms is 40% by mass or more based on the total structural units, and the structural unit (A) is derived from a monomer having a hydroxyl group. A pressure-sensitive adhesive composition containing a (meth)acrylic polymer containing a structural unit (B) of 5% by mass or more and 15% by mass or less based on the total structural units, and a styrene polymer is disclosed. Further, Patent Document 2 discloses an adhesive composition containing a (meth)acrylic acid ester polymer (A) and a cyclodextrin (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 suppresses moist heat whitening resistance. This is being considered.

Japanese Patent Application Publication No. 2016-172865 International Publication No. 2015/151224

However, when the present inventors placed the adhesive layer in Patent Document 1 under high temperature and high humidity conditions, the adhesive layer sometimes whitened, and it was found that the moist heat whitening resistance was insufficient. Furthermore, it has been found that when a pressure-sensitive adhesive sheet is formed from the pressure-sensitive adhesive composition of Patent Document 2, the wet heat whitening resistance may be insufficient or the dielectric constant may not be sufficiently low.

Therefore, in order to solve the problems of the prior art, the present inventors have conducted studies with the aim of providing an adhesive sheet with a low dielectric constant and excellent wet heat whitening resistance. Ta.

As a result of intensive studies to solve the above problems, the present inventors have discovered that a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer having an alkylene glycol group. It has been found that by forming a pressure-sensitive adhesive sheet from a pressure-sensitive adhesive composition containing (C), it is possible to obtain a pressure-sensitive adhesive sheet with a low dielectric constant and excellent wet heat whitening resistance.
Specifically, the present invention has the following configuration.

[1] A pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer (C) having an alkylene glycol group. There it is,
A pressure-sensitive adhesive sheet in which the content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is 0.05 to 6 parts by mass based on 100 parts by mass of the crosslinkable acrylic polymer (A).
[2] The pressure-sensitive adhesive sheet according to [1], which has a dielectric constant of less than 3.0 at a frequency of 1 MHz.
[3] A glass plate and a PET film are laminated via an adhesive sheet to form a laminate, and the laminate is placed at 60°C and 95% relative humidity for 240 hours, and then in an environment of 23°C and 50% relative humidity. The adhesive sheet according to [1] or [2], which has a haze of 2% or less after being allowed to stand for 1 hour.
[4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group has a weight average molecular weight of 1,000 to less than 50,000.
[5] The crosslinkable acrylic polymer (A) includes a unit derived from a (meth)acrylic ester having a branched alkyl group having 5 to 9 carbon atoms, according to any one of [1] to [4]. adhesive sheet.
[6] The crosslinkable acrylic polymer (A) contains a unit derived from an acrylic ester and a unit derived from a methacrylic ester, and has an ester structure of units derived from an acrylic ester and units derived from a methacrylic ester. are the same, the pressure-sensitive adhesive sheet according to any one of [1] to [5].
[7] In the units constituting the crosslinkable acrylic polymer (A), the mass ratio of units derived from acrylic ester and units derived from methacrylic ester is 25:75 to 50:50, [6] Adhesive sheet as described.
[8] A pressure-sensitive adhesive sheet with a release sheet, comprising a pair of release sheets having different release forces on both surfaces of the pressure-sensitive adhesive sheet according to any one of [1] to [7].
[9] A laminate comprising the adhesive sheet according to any one of [1] to [7] and an adherend on at least one surface of the adhesive sheet.

According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that has a low dielectric constant and excellent wet heat whitening resistance.

FIG. 1 is a sectional view showing an example of the configuration of a pressure-sensitive adhesive sheet with a release sheet of the present invention.

In the following, the present invention will be explained in detail. Although the constituent elements described below may be explained based on typical embodiments and specific examples, the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after the "~" as lower and upper limits.

In this specification, "(meth)acrylic" represents both or either acrylic and methacrylic. Furthermore, in this specification, "monomer" and "monomer" have the same meaning, and "polymer" and "polymer" have the same meaning.

(adhesive sheet)
The present invention provides a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer (C) having an alkylene glycol group. Regarding. Here, the content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is 0.05 to 6 parts by weight based on 100 parts by weight of the crosslinkable acrylic polymer (A).

The adhesive sheet of the present invention is a sheet consisting of an adhesive layer that is a cured product of the above-mentioned adhesive composition. Since the pressure-sensitive adhesive sheet of the present invention is formed from the pressure-sensitive adhesive composition having the above-mentioned structure, it has a low relative dielectric constant and is also excellent in wet heat whitening resistance. 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.

The relative dielectric constant of the adhesive sheet at a frequency of 1 MHz is preferably less than 3.0, more preferably 2.9 or less. Note that the lower limit of the dielectric constant 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 dielectric constant. Note that the relative permittivity of the adhesive sheet is a relative permittivity at a frequency of 1 MHz, and a value calculated by a method specified in JIS C 2138 is used.

The humidity and heat whitening resistance of the adhesive sheet is determined by bonding a glass plate and a PET film together via an adhesive sheet to form a laminate, leaving the laminate under conditions of 60°C and 95% relative humidity for 240 hours, and testing at 23°C and relative humidity. It can be determined that the product is good if the haze value is low after leaving it for one hour in an environment with a humidity of 50%. Specifically, one side of the adhesive sheet was laminated to a 1.2 mm thick glass plate (manufactured by Matsunami Glass Industries Co., Ltd., S9112), and the other side was laminated to a PET film (manufactured by Toyobo Co., Ltd., Cosmoshine A4300). The laminate was left in an environment of 60°C and 95% relative humidity for 240 hours, and after being taken out, it was cooled for 1 hour at 23°C and 50% relative humidity, and then the haze was measured. do. Note that as a haze measuring device, for example, NDH 4000 manufactured by Nippon Denshoku Co., Ltd. can be used. The haze measured under the above conditions is preferably 2% or less, more preferably 1.8% or less, even more preferably 1.6% or less, and preferably 1.4% or less. Particularly preferred.

The adhesive sheet of the present invention is preferably a double-sided adhesive sheet, but may be a single-sided adhesive sheet with a base material etc. on one side of the adhesive sheet. The pressure-sensitive adhesive sheet of the present invention may further include another pressure-sensitive adhesive layer, or may have a support layered between the pressure-sensitive adhesive layers. In this case, it is preferable to use a transparent support as the support. Since such a double-sided adhesive sheet has excellent transparency as a whole, it can be suitably used for bonding optical members together. Among the above-mentioned pressure-sensitive adhesive sheets of the present invention, a base material-less type having no support is preferable, and a single-layer double-sided pressure-sensitive adhesive sheet consisting of an adhesive layer is preferable.

Preferably, the surface of the adhesive sheet is covered with a release sheet. That is, the present invention may relate to a pressure-sensitive adhesive sheet with a release sheet. FIG. 1 is a sectional view showing an example of the configuration of a pressure-sensitive 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 without a base material, and is a double-sided adhesive sheet.

The release sheet may be a release laminate sheet having a release sheet base material and a release agent layer provided on one side of the release sheet base material, or a polyolefin film such as polyethylene film or polypropylene film as a low polarity base material. can be mentioned.
Paper or polymer film is used as the base material for the release sheet in the release laminate sheet. As the release agent constituting the release agent layer, for example, a general-purpose addition type or condensation type silicone release agent or a long-chain alkyl group-containing compound is used. In particular, addition-type silicone release agents with high reactivity are preferably used.
Specific examples of silicone release agents include BY24-4527 and SD-7220 manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3600, KS-774, and X62-2600 manufactured by Shin-Etsu Chemical Co., Ltd. can be mentioned. Further, the silicone release agent may 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. preferable. Specific examples of silicone resins include BY24-843, SD-7292, SHR-1404, etc. manufactured by Dow Corning Toray Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.

The pressure-sensitive adhesive sheet with a release sheet preferably includes a pair of release sheets having different peeling forces on both surfaces of the pressure-sensitive adhesive sheet. That is, one surface of the adhesive sheet is provided with a first release sheet, the other surface of the adhesive sheet is provided with a second release sheet, and the peeling forces of the first release sheet and the second release sheet are different from each other. is preferred. In the example shown in FIG. 1, it is preferable that the release sheets 12a and 12b have different releasability in order to facilitate the release of the release sheets. That is, if the releasability from one side is different from the releasability from the other side, it becomes easy to peel only the release sheet 12 with higher releasability first. In that case, the releasability of the release sheet 12 between the release sheet 12a and the release sheet 12b may be adjusted depending on the method of lamination and the order of lamination.

The pressure-sensitive adhesive sheet of the present invention has a good balance between softness for embedding foreign matter and hardness in a high-temperature environment, and therefore has excellent foreign matter embedding properties. Here, the foreign matter embedding property is evaluated by the presence or absence of air bubbles around the glass beads, which are foreign matter, when the adhesive sheet is attached to an adherend on which glass beads have been sprinkled and placed under high temperature and high humidity conditions. be able to. Specifically, an adhesive sheet was attached to an adherend on which approximately 0.05 mg of glass beads with a center particle size of 30 μm were sprinkled on the surface of a polarizing plate, and the adhesive sheet was treated in an environment of 85° C. and 85% relative humidity for 24 hours. Later, if no air bubbles are generated around the glass beads, it can be determined that the foreign matter embedding property is good.

Usually, in adhesive sheets used for optical applications, in order to increase the cohesive force and durability of the adhesive sheet, for example, crosslinkable functional groups such as hydroxyl groups are contained in an amount of 1 to 20% by mass based on the total mass of the acrylic polymer. A blended adhesive sheet is used. However, when such a pressure-sensitive adhesive sheet is placed under high temperature and high humidity conditions, the pressure-sensitive adhesive sheet may whiten, which has been a problem. Further, when an acrylic polymer having 20% by mass or more of crosslinkable groups such as hydroxyl groups was used to suppress whitening of the pressure-sensitive adhesive sheet, a sufficient reduction in dielectricity was not achieved. However, after extensive study, the present inventors discovered that a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer (C) having a predetermined amount of alkylene glycol groups. By forming a pressure-sensitive adhesive sheet from the contained pressure-sensitive adhesive composition, we succeeded in increasing the cohesive force and durability of the pressure-sensitive adhesive sheet, lowering the dielectric constant of the pressure-sensitive adhesive sheet, and further increasing its wet heat whitening resistance.

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 of the adhesive strength of the adhesive sheet to glass is not particularly limited, but is preferably set to 40 N/25 mm, for example. The pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition of the present invention can exhibit such high adhesive strength. Note that the adhesive strength of the adhesive sheet to glass is a value measured according to JIS Z 0237 "Adhesive tape/adhesive sheet testing method". Specifically, the adhesive sheet is bonded to a soda glass plate as an adherend in an environment of 23° C. and 50% relative humidity, and a 2 kg roll is moved back and forth once to press the adhesive sheet. Thereafter, the pressure-sensitive adhesive sheet is allowed to stand for 24 hours in an environment of 23° C. and 50% relative humidity, and the pressure-sensitive adhesive sheet is peeled from the soda glass plate in the 180° direction at a speed of 300 mm/min.

The gel fraction of the adhesive sheet is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more.
The gel fraction of the adhesive sheet can be calculated by the following method. First, about 0.1 g of the adhesive sheet is taken into a sample bottle, 30 ml of ethyl acetate is added thereto, and the mixture is shaken at 40° C. for 24 hours. Thereafter, the contents of this sample bottle are filtered through a 150-mesh stainless steel wire mesh, and the residue on the wire mesh is dried at 100° C. for 1 hour, and the dry weight W (g) is measured. The gel fraction is determined from the obtained dry weight using the following formula 1.
Gel fraction (%) = (dry weight/collected weight of adhesive sheet) x 100...Formula 1

The thickness of the adhesive sheet can be set appropriately depending on the application and is not particularly limited, but it is usually 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, and 30 μm or more and 450 μm or less. It is more preferably 40 μm or more and 400 μm or less, even 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, it is possible to sufficiently ensure foreign matter embedding properties and further improve durability. Furthermore, by setting the thickness of the adhesive sheet within the above range, the adhesive sheet can be easily manufactured.

(Adhesive composition)
The adhesive sheet of the present invention is formed from an adhesive composition containing a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer (C) having an alkylene glycol group. Ru. The crosslinking agent (B) is preferably a thermosetting crosslinking agent, and in this case, the adhesive composition can be said to be thermosetting. The pressure-sensitive adhesive composition of the present invention is cured by heating to form a pressure-sensitive adhesive sheet.

<Crosslinkable acrylic polymer (A)>
The adhesive composition contains a crosslinkable acrylic polymer (A). As the crosslinkable acrylic polymer (A), a known crosslinkable acrylic polymer can be used. The crosslinkable acrylic polymer (A) preferably has transparency to the extent that it does not reduce the visibility of the display device.

The adhesive composition contains a crosslinkable acrylic polymer (A) as a main component. The content of the crosslinkable acrylic polymer (A) in the pressure-sensitive adhesive composition includes the crosslinkable acrylic polymer (A) of the pressure-sensitive adhesive composition, the crosslinking agent (B), and (meth)acrylic having an alkylene glycol group. It 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 acid ester oligomer (C). The content of the crosslinkable acrylic polymer (A) in the adhesive composition is 99.9% by mass based on the total mass of components (A), (B), and (C) of the adhesive composition. It is preferable that it is below.

The crosslinkable acrylic polymer (A) contains a unit (a1) derived from a non-crosslinkable (meth)acrylic acid ester and a unit (a2) derived from a (meth)acrylic monomer having a crosslinkable functional group. It is preferable. In this case, the unit (a1) derived from a non-crosslinkable (meth)acrylic ester is preferably a unit derived from a (meth)acrylic ester having a branched alkyl group having 5 to 9 carbon atoms. When the crosslinkable acrylic polymer (A) contains a unit derived from a (meth)acrylic ester having a branched alkyl group having 5 to 9 carbon atoms, from the adhesive composition containing the crosslinkable acrylic polymer (A) It becomes easier to form a pressure-sensitive adhesive sheet with a sufficiently low dielectric constant. In addition, in this specification, a "unit" is a repeating unit (monomeric unit) which comprises a polymer.

A unit derived from a (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms has an alkyl group having 5 or more carbon atoms, and since such an alkyl group has a branched structure, the molar Large volume and low density. Therefore, when the crosslinkable acrylic polymer (A) contains a unit derived from a (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms, the molar volume of the crosslinkable acrylic polymer (A) can be increased and the density can be decreased. In addition, since the unit derived from the (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms has an alkyl group having 9 or less carbon atoms, the volume shrinkage rate when made into a polymer can be suppressed. It is considered that the molar volume of the crosslinkable acrylic polymer (A) can be maintained large. As a result, it becomes easier to form a pressure-sensitive adhesive sheet with a low dielectric constant.

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

The branched alkyl group possessed by the unit (a1) derived from the non-crosslinkable (meth)acrylic ester may have 5 to 9 carbon atoms, but preferably 7 to 9 carbon atoms. By setting the number of carbon atoms in the branched alkyl group within the above range, it becomes easier to form an adhesive layer with a sufficiently low dielectric constant. Furthermore, by controlling the number of carbon atoms in the branched alkyl group within the above range, it is possible to easily control the degree of polymerization of the crosslinkable acrylic polymer (A) and obtain a pressure-sensitive adhesive composition with excellent processability.

The content of units derived from a (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms in the crosslinkable acrylic polymer (A) is based on the total mass of the crosslinkable acrylic polymer (A). , is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. By setting the content of units derived from a (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms within the above range, the dielectric constant of the pressure-sensitive adhesive sheet can be sufficiently lowered. The durability of the adhesive sheet can be increased.

The crosslinkable acrylic polymer (A) is preferably non-crosslinkable (meth), and the ester structures of the units derived from acrylic ester and the units derived from methacrylic ester are preferably the same. Here, the ester structures being the same means that the structures of the parts that make up the side chains containing ester bonds (in this case, the side chains refer to the parts that become side chains when made into a polymer) are the same. Say something.

Among acrylic esters and methacrylic esters that have the same ester structure, the glass transition temperature when 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. The temperature is preferably -15°C or higher. Examples of acrylic esters and methacrylic esters having the same ester structure include a combination of 2-ethylhexyl acrylate (2EHA) and 2-ethylhexyl methacrylate (2EHMA). In this way, by using two types of acrylic esters and making the ester structures the same in the two types of acrylic esters, the uniform mixability of the adhesive composition is improved, so whitening of the adhesive sheet is suppressed, and , it is possible to obtain a pressure-sensitive adhesive sheet with less variation in adhesive properties.

Furthermore, the mass ratio of units derived from acrylic ester and units derived from methacrylic ester in the (meth)acrylic polymer contained in the crosslinkable acrylic polymer (A) is 25:75 to 50:50. The ratio is preferably 25:75 to 40:60. By setting the mass ratio of units derived from acrylic esters to units derived from methacrylic esters within the above range, the moisture-heat whitening resistance of the pressure-sensitive adhesive sheet can be more effectively improved.

The crosslinkable acrylic polymer (A) contains a unit (a1) derived from a non-crosslinkable (meth)acrylic acid ester and a unit (a2) derived from a (meth)acrylic monomer having a crosslinkable functional group. It is preferable. (Meth)acrylic monomers having crosslinkable functional groups include carboxy group-containing (meth)monomers, hydroxy group-containing (meth)monomers, amino group-containing (meth)monomers, and glycidyl group-containing (meth)monomers. ) Monomers are preferred.

Examples of the carboxy 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; Examples include (meth)acrylic acid [(mono, di or poly)alkylene glycol] such as (meth)acrylic acid mono(diethylene glycol), and (meth)acrylic acid lactones 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.

Among these, 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. By further using such an acrylic monomer, the relative permittivity of the pressure-sensitive adhesive sheet can be lowered, and the wet heat whitening resistance can be further effectively increased. Note that the (meth)acrylic monomer having a crosslinkable functional group is preferably a methacrylic monomer rather than an acrylic monomer from the viewpoint of not increasing the dielectric constant of the adhesive composition, and methacrylic acid 2-hydroxy Particular preference is given to ethyl.

The content of units (a2) derived from a (meth)acrylic monomer having a crosslinkable functional group in the crosslinkable acrylic polymer (A) is 0 with respect to the total mass of the crosslinkable acrylic polymer (A). It is preferably 0.01% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. Further, the content of the unit (a2) is preferably 50% by mass or less, more preferably 20% by mass or less, particularly preferably 15% by mass or less. If the content of unit (a2) is at least the lower limit of the above range, it has sufficient crosslinking properties, and if it is below the upper limit of the above range, the necessary adhesive physical properties can be maintained and the dielectric constant is It is possible to form an adhesive layer with a sufficiently low pressure.

The weight average molecular weight of the crosslinkable acrylic polymer (A) is preferably 100,000 or more and 2,000,000 or less, more preferably 300,000 or more and 1,500,000 or less. By setting the weight average molecular weight within the above range, sufficient step followability can be ensured. Note that the weight average molecular weight of the crosslinkable acrylic polymer (A) is the value before crosslinking with a crosslinking agent. The weight average molecular weight is a value measured by gel permeation chromatography (GPC) based on polystyrene. As the crosslinkable acrylic polymer (A), a commercially available one may be used, or one synthesized by a known method may be used.

The measurement conditions for gel permeation chromatography (GPC) are as follows.
Solvent: Tetrahydrofuran
Column: Shodex KF801, KF803L, KF806L, (3 columns made by Showa Denko K.K. were connected and used)
Column temperature: 40℃
Sample concentration: 0.5% by mass
Detector: RI-2031plus (manufactured by JASCO)
Pump: RI-2080plus (manufactured by JASCO)
Flow rate (flow rate): 0.8ml/min
Injection volume: 10μl
Calibration curve: A calibration curve of 10 samples of standard polystyrene (Shodex standard polystyrene (manufactured by Showa Denko KK) Mw = 1320 to 2,500,000 was used.

The crosslinkable acrylic polymer (A) may optionally contain units other than the unit (a1) derived from a non-crosslinkable (meth)acrylic acid ester and the (meth)acrylic monomer unit (a2) having a crosslinkable functional group. It may also contain other monomer units. Other monomers may be those that can be copolymerized with non-crosslinkable (meth)acrylic acid esters and acrylic monomers having crosslinkable functional groups, such as (meth)acrylonitrile, vinyl acetate, styrene, Examples include vinyl chloride, vinylpyrrolidone, vinylpyridine, and the like. The content of other monomer units in the crosslinkable acrylic polymer (A) is preferably at most 20% by mass, more preferably at most 15% by mass, even more preferably at most 1% by mass. .

The glass transition temperature (Tg) of the crosslinkable acrylic polymer (A) is preferably -80°C or higher and -10°C or lower, more preferably -75°C or higher and -15°C or lower, and -70°C or higher. More preferably, the temperature is -18°C or lower. By setting the glass transition temperature (Tg) of the crosslinkable acrylic polymer (A) within the above range, the cohesive force when used as an adhesive layer can be further increased. As a result, an adhesive layer having excellent durability and adhesive strength can be obtained.

<Crosslinking agent>
The adhesive composition contains a crosslinking agent. The crosslinking agent is preferably a crosslinking agent that reacts with the crosslinkable acrylic polymer (A) by heat, and is preferably a thermosetting crosslinking agent.

Examples of the crosslinking agent include crosslinking functionalities possessed by the crosslinkable acrylic polymer (A) from among known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds. It can be selected as appropriate in consideration of the reactivity with the group. For example, when a hydroxy group is included as a crosslinkable functional group, an isocyanate compound can be used because of its reactivity with the hydroxy group. From the viewpoint of easily crosslinking the (meth)acrylic monomer unit (a2) having a crosslinkable functional group, it is preferable to use an isocyanate compound or an epoxy compound. In the present invention, the crosslinking agent is preferably one or more selected from difunctional or higher epoxy compounds and difunctional or higher isocyanate compounds, more preferably difunctional or higher isocyanate compounds. preferable.

Examples of the isocyanate compound include tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like. Diocyanate may be used as it is in a difunctional form, or may be used in the form of a trifunctional derivative such as an adduct, a nurate, or a buret.
Examples of the epoxy compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, neopentyl glycol diglycidyl ether, and 1,6-hexane diol diglycidyl ether. Glycidyl ether, tetraglycidyl xylene diamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, etc. Can be mentioned.
As the crosslinking agent, commercially available products can be used. Examples of commercially available products include xylylene diisocyanate compound (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.).

As the crosslinking agent, one type may be used alone or two or more types may be used in combination. The content of the crosslinking agent in the adhesive composition is appropriately selected depending on the desired adhesive properties, etc., and is not particularly limited, but is 0.01 parts by mass based on 100 parts by mass of the crosslinkable acrylic polymer (A). It is preferably 5 parts by mass or less, and more preferably 0.03 parts by mass or more and 3 parts by mass or less.

<(Meth)acrylic acid ester oligomer (C) having an alkylene glycol group>
The adhesive composition contains a (meth)acrylic acid ester oligomer (C) having an alkylene glycol group. In the present invention, the pressure-sensitive adhesive composition contains a predetermined amount of the (meth)acrylic acid ester oligomer (C) having a hydrophilic alkylene glycol group, so that it can take in excess moisture, resulting in moisture resistance. Heat whitening property is enhanced.

The (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is obtained by polymerizing two or more (meth)acrylic acid ester monomers having an alkylene glycol group. Here, the weight average molecular weight of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is preferably less than 50,000, and the upper limit of the degree of polymerization is determined so that the upper limit of the molecular weight is less than 50,000. be done. In addition, it is preferable that the weight average molecular weight of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is 1000 or more.

Examples of the alkylene glycol group contained in the (meth)acrylic acid ester having an alkylene glycol group include an ethylene glycol group, a propylene glycol group, a butylene glycol group, and the like. Among these, the alkylene glycol group that the (meth)acrylic acid ester has is preferably an ethylene glycol group.

The ethylene glycol group is a group represented by -CH ₂ CH ₂ O-. The (meth)acrylic acid ester having an ethylene glycol group may have one ethylene glycol group in one molecule, or may have two or more ethylene glycol groups. Among these, the number of ethylene glycol groups in one molecule of (meth)acrylic acid ester having an ethylene glycol group is preferably 1 to 50, more preferably 1 to 40, and even more preferably 1 to 30. The number is preferably 1 to 23, particularly preferably 1 to 23.

Examples of (meth)acrylic esters having an ethylene glycol group include alkoxyethylene glycol (meth)acrylate, alkoxypolyethylene glycol (meth)acrylate, phenol EO-modified acrylate, nonylphenol EO-modified acrylate, and 2-ethylhexyl EO-modified acrylate. can be mentioned. Among these, the (meth)acrylic ester having an ethylene glycol group is preferably at least one selected from alkoxyethylene glycol (meth)acrylate and alkoxypolyethylene glycol (meth)acrylate. That is, the (meth)acrylic acid ester having an alkylene glycol group is preferably a unit derived from at least one selected from alkoxyethylene glycol (meth)acrylate and alkoxypolyethylene glycol (meth)acrylate.

The number of carbon atoms in the alkoxy group of the alkoxyethylene glycol (meth)acrylate and the alkoxypolyethylene glycol (meth)acrylate is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less. . Among them, (meth)acrylic acid esters having an alkylene glycol group include 2-methoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and ethoxy (meth)acrylate. More preferably, the unit is derived from at least one selected from polyethylene glycol, and the unit is preferably derived from at least one selected from 2-methoxyethyl (meth)acrylate and methoxypolyethylene glycol (meth)acrylate. It is even more preferable that there be.

The (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is obtained by polymerizing a solvent, a (meth)acrylic acid ester monomer having an alkylene glycol group, and a polymerization initiator. Moreover, a commercially available product can also be used as the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group.

The content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is preferably 0.05 parts by mass or more, and 0.1 parts by mass or more, based on 100 parts by mass of the crosslinkable acrylic polymer (A). It is more preferably at least 0.2 parts by mass, and even more preferably at least 0.2 parts by mass. Further, the content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is preferably 6 parts by mass or less, and 5 parts by mass based on 100 parts by mass of the crosslinkable acrylic polymer (A). It is more preferable that it is below. By setting the content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group within the above range, it is possible to more effectively prevent the pressure-sensitive adhesive sheet from moist heat whitening while keeping the relative dielectric constant of the pressure-sensitive adhesive sheet low. can be suppressed to

<Solvent>
The adhesive composition may contain a solvent. In this case, the solvent is used to improve the coating suitability of the pressure-sensitive adhesive composition. Examples of solvents include hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane; methanol, ethanol, Alcohols such as propanol, isopropyl alcohol, butanol, isobutyl alcohol, and diacetone alcohol; Ethers such as diethyl ether, diisopropyl ether, dioxane, and tetrahydrofuran; Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, and cyclohexanone; Methyl acetate , ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, ethyl butyrate and other esters; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene Examples include polyols such as glycol monomethyl ether acetate and derivatives thereof.

The content of the solvent in the adhesive composition is not particularly limited, but is preferably 25 to 500 parts by weight, more preferably 30 to 400 parts by weight, based on 100 parts by weight of the crosslinkable acrylic polymer (A).

<Optional ingredients>
The adhesive composition may contain arbitrary components other than the above-mentioned components, and examples of the arbitrary components include a plasticizer. When the adhesive composition contains a plasticizer, the content of the plasticizer is preferably 50 parts by mass or less, and 30 parts by mass or less, based on 100 parts by mass of the crosslinkable acrylic polymer (A). More preferably, the amount is 10 parts by mass or less.

As the plasticizer, for example, a non-functional acrylic polymer can be used. A non-functional acrylic polymer is a polymer consisting only of acrylic monomer units that have no functional groups other than acrylate groups, or acrylic monomer units that have no functional groups other than acrylate groups and no functional groups. It means a polymer consisting of non-acrylic monomer units. Examples of non-acrylic monomer units having no functional group include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, and stearin. Examples include carboxylic acid vinyl esters such as vinyl acid, vinyl cyclohexanecarboxylate, and vinyl benzoate, and styrene.

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

(Method for manufacturing adhesive sheet)
Preferably, the process for producing the pressure-sensitive adhesive sheet includes a step of coating the pressure-sensitive adhesive composition on a release sheet to form a coating film, and a step of heating the coating film to form a cured product.

In the above-mentioned process, the reaction between the crosslinkable acrylic polymer and the crosslinking agent progresses by heating the coating film, and a cured product (adhesive sheet) is formed. In order to bring the adhesive composition into a cured state, after the solvent is removed after coating, an aging treatment may be performed in which the adhesive sheet is left at a constant temperature for a certain period of time. The aging treatment can be performed, for example, by leaving it at 23° C. for 7 days.

Coating of the pressure-sensitive adhesive composition for forming the pressure-sensitive 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, and a curtain coater.
Further, the coating film can be heated using a known heating device such as a heating furnace or an infrared lamp.

(laminate)
The present invention may also relate to a laminate including the above-described adhesive sheet and an adherend on at least one surface of the adhesive sheet. Here, the adherend may have a stepped portion or unevenness derived from the step. 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. It is preferable that the laminate is obtained through a step of bringing the pressure-sensitive adhesive sheet into contact with the surface of the adherend.

Examples of the optical member include various constituent members of optical products such as touch panels and image display devices.
Components of the touch panel include, for example, an ITO film in which an ITO film is provided on a transparent resin film, an ITO glass in which an ITO film is provided on the surface of a glass plate, a transparent conductive film in which a transparent resin film is coated with a conductive polymer, Examples include hard coat film and anti-fingerprint film. The adhesive sheet of the present invention is preferably used 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 point of view, the adherends of the adhesive sheet of the present invention include an ITO film in which an ITO film is provided on a transparent resin film, an ITO glass in which an ITO film is provided on the surface of a glass plate, and a conductive polymer in a transparent resin film. A transparent conductive film coated with is preferable, and it is preferable to attach an adhesive sheet to the back side (the side without the conductive layer) of these glasses or films.
Examples of the constituent members of the image display device include antireflection films, alignment films, polarizing films, retardation films, and brightness enhancement films used in liquid crystal display devices.
Examples of materials used for these members include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetylcellulose, 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.

When the adhesive sheet of the present invention is a double-sided adhesive sheet, it can be used for bonding two adherends together. In this case, the adhesive sheet of the present invention can be used for bonding ITO films together inside a touch panel, bonding an ITO film and ITO glass, bonding an ITO film of a touch panel and a liquid crystal panel, and bonding a cover glass and an ITO film. Used for lamination, lamination of cover glass and decorative film, etc.

EXAMPLES The features of the present invention will be explained in more detail below with reference to Examples and Comparative Examples. The materials, usage amounts, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

(Synthesis of crosslinkable acrylic polymer (A-1))
2-ethylhexyl acrylate (2-EHA), 2-ethylhexyl methacrylate (2-EHMA), and 2-hydroxyethyl methacrylate (2-HEMA) were blended at a mass ratio of 25:65:10, and radical polymerization was initiated. As an agent, 2,2'-azobis(2,4-dimethylvaleronitrile) was dissolved in the solution. The solution was heated to 60° C. for random copolymerization to obtain a crosslinkable acrylic polymer (A-1). The weight average molecular weight of the crosslinkable acrylic polymer (A-1) was 500,000.

(Synthesis of crosslinkable acrylic polymer (A-2))
(A A crosslinkable acrylic polymer (A-2) was obtained in the same manner as in -1). The weight average molecular weight of the crosslinkable acrylic polymer (A-2) was 500,000.

(Synthesis of crosslinkable acrylic polymer (A-3))
(A A crosslinkable acrylic polymer (A-3) was obtained in the same manner as in -1). The weight average molecular weight of the crosslinkable acrylic polymer (A-3) was 500,000.

(Synthesis of (meth)acrylic acid ester oligomer (C-1) having an alkylene glycol group)
50 parts by mass of ethyl acetate was added to a reaction apparatus equipped with a stirrer, a reflux condenser, a sequential dropping device, and a thermometer, heated, and maintained at reflux temperature for 10 minutes. Next, 100 parts by mass of 2-ethylhexyl EO modified acrylate (manufactured by Toagosei Co., Ltd., M-120), 20 parts by mass of ethyl acetate, and dimethyl 2,2-azobis(2-methylpropionate) ( V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) 6 parts by mass of a monomer mixture was sequentially added dropwise over a period of 200 minutes, and after the completion of the dropwise addition, the polymerization reaction was further carried out for 180 minutes to obtain a polymer having an ethylene glycol group (meth). Acrylic ester oligomer (C-1) was obtained. The weight average molecular weight of the (meth)acrylic acid ester oligomer (C-1) having an ethylene glycol group was 8,000.

(Synthesis of (meth)acrylic acid ester oligomer (C-2) having an alkylene glycol group)
Ethylene was prepared in the same manner as in (C-1) except that 2-ethylhexyl EO modified acrylate (M-120, manufactured by Toagosei Co., Ltd.) was replaced with ethoxy-diethylene glycol acrylate (Light Acrylate EC-A, manufactured by Kyoeisha Chemical Co., Ltd.). A (meth)acrylic acid ester oligomer (C-2) having a glycol group was obtained. The weight average molecular weight of the (meth)acrylic acid ester oligomer (C-2) having an ethylene glycol group was 7,500.

(Example 1)
<Preparation of adhesive composition>
The pressure-sensitive adhesive composition is prepared by blending each component so that the proportion of each component with respect to the total mass of components (A), (B), and (C) in the pressure-sensitive adhesive composition is as shown in Table 1. Obtained. That is, thermal crosslinking agent Coronate L-55E and oligomer (C-1) were blended in a ratio of 100:0.1:0.7 to 100 parts by mass of crosslinkable acrylic polymer (A-1). , an adhesive composition was obtained.

(Example 2)
<Preparation of adhesive composition>
To 100 parts by mass of crosslinkable acrylic polymer (A-1), thermal crosslinking agent Coronate L-55E and oligomer (C-1) were blended in a ratio of 100:0.1:1.5 to form an adhesive. A drug composition was obtained.

(Example 3)
<Preparation of adhesive composition>
To 100 parts by mass of crosslinkable acrylic polymer (A-1), thermal crosslinking agent Coronate L-55E and oligomer (C-1) were blended in a ratio of 100:0.1:5.0 to create an adhesive. A drug composition was obtained.

(Example 4)
<Preparation of adhesive composition>
Thermal crosslinking agent Coronate L-55E and oligomer (C-2) were blended in a ratio of 100:0.1:0.7 to 100 parts by mass of the crosslinkable acrylic polymer (A-1) to form an adhesive. A drug composition was obtained.

(Example 5)
<Preparation of adhesive composition>
Thermal crosslinking agent Coronate L-55E and oligomer (C-2) were blended in a ratio of 100:0.1:1.5 to 100 parts by mass of the crosslinkable acrylic polymer (A-1) to form an adhesive. A drug composition was obtained.

(Example 6)
<Preparation of adhesive composition>
To 100 parts by mass of the crosslinkable acrylic polymer (A-1), the thermal crosslinking agent Coronate L-55E and the oligomer (C-2) were blended in a ratio of 100:0.1:5.0 to form an adhesive. A drug composition was obtained.

(Example 7)
<Preparation of adhesive composition>
An adhesive composition was obtained in the same manner as in Example 1, except that the crosslinkable acrylic polymer (A-1) was changed to (A-2).

(Example 8)
<Preparation of adhesive composition>
An adhesive composition was obtained in the same manner as in Example 1, except that the crosslinkable acrylic polymer (A-1) was changed to (A-3).

(Comparative example 1)
<Preparation of adhesive composition>
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that the oligomer (C) was not blended.

(Comparative example 2)
<Preparation of adhesive composition>
Thermal crosslinking agent Coronate L-55E and oligomer (C-1) were blended in a ratio of 100:0.1:7.5 to 100 parts by mass of the crosslinkable acrylic polymer (A-1) to form an adhesive. A drug composition was obtained.

<Preparation of adhesive sheet>
The pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples were applied to a 100 μm thick polyethylene terephthalate film (first release sheet) (manufactured by Oji F-Tex Co., Ltd.: 100RL) equipped with a release agent layer treated with a silicone release agent. -07(2)) was uniformly coated with an applicator so that the coating thickness after drying was 150 μm. Thereafter, it was dried for 3 minutes in an air circulating constant temperature oven at 100° C. to form an adhesive layer on the surface of the first release sheet. Next, a second release sheet (manufactured by Oji F-Tex Co., Ltd.: 75RL-07(L)) with a thickness of 75 μm is laminated on the surface of this adhesive layer, and the adhesive sheet forms a pair of release sheets with a difference in peel strength. A pressure-sensitive adhesive sheet with a release sheet having a configuration of a first release sheet/adhesive sheet/second release sheet sandwiched between the sheets was obtained. This pressure-sensitive adhesive sheet was subjected to an aging treatment in which it was allowed to stand for 7 days at a temperature of 23° C. and a relative humidity of 50%.

(Example 9)
A pressure-sensitive adhesive sheet with a release sheet was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer in <Preparation of pressure-sensitive adhesive sheet> was changed to 100 μm.

(Example 10)
A pressure-sensitive adhesive sheet with a release sheet was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer in <Preparation of pressure-sensitive adhesive sheet> was changed to 200 μm.

[evaluation]
<Relative dielectric constant>
Evaluation of the dielectric constant of the pressure-sensitive adhesive sheet was performed using the following procedure. The adhesive sheet (the first release sheet and the second release sheet were peeled off from the adhesive sheet) was sandwiched between two pieces of copper foil, and autoclaved (40° C., 0.5 MPa, 30 minutes). Thereafter, the dielectric constant was measured based on JIS C 2138 using a dielectric measurement system (Model 1260, manufactured by Toyo Technica Co., Ltd.). The frequency and measurement environment were measured under the following conditions.
Frequency: 1MHz
Measurement environment: 23℃, relative humidity 50%

<Moist heat whitening resistance>
The first release sheet (light release film) was peeled off from the adhesive sheet cut into a size of 50 mm width x 50 mm length, and it was bonded to a 1.2 mm thick glass plate (manufactured by Matsunami Glass Industry Co., Ltd., S9112). . Thereafter, the second release sheet (heavy release film) was peeled off, and a PET film (manufactured by Toyobo Co., Ltd., Cosmoshine A4300) was laminated to the adhesive sheet to prepare a test sample. The test sample was left in an environment of 60° C. and 95% relative humidity for 240 hours, taken out, and cooled for 1 hour at 23° C. and 50% relative humidity, and then the haze was measured. The haze was measured using NDH 4000 manufactured by Nippon Denshoku Co., Ltd. The moisture and heat whitening resistance was evaluated based on the following criteria.
○: Haze ≦2.0%
×: Haze>2.0%

<Foreign matter embedding property>
The pressure-sensitive adhesive sheet was cut into a shape of 50 mm long x 25 mm wide, the first release sheet was peeled off, and the cut sheet was laminated onto a 100 μm thick transparent PET film (product name: Cosmoshine A4300, manufactured by Toyobo Co., Ltd.). As an adherend, a polarizing plate (manufactured by Polatechno Co., Ltd., SKN-18243T) was cut out in advance to the same dimensions as one side of a glass plate (90 mm long x 50 mm wide x 0.5 mm thick), and a center grain was placed on the surface of the polarizing plate. Approximately 0.05 mg of glass beads having a diameter of 30 μm were dispersed to prepare a sample. Next, the second release sheet of the adhesive sheet integrated with the transparent PET film was peeled off, and using a laminator, it was bonded to the surface of the polarizing plate of the adherend on which the glass beads had been scattered. Thereafter, autoclave treatment (40° C., 0.5 MPa, 30 minutes) was performed to obtain a laminate.
The laminate was treated in an environment of 85°C and 85% relative humidity for 24 hours, and the area where the glass beads were scattered after the treatment was observed with a microscope (magnification: 25x), and the foreign matter embedding ability of the adhesive sheet was evaluated based on the following criteria. evaluated.
○: No bubbles were generated around the glass beads.
×: Bubbles are generated from around the glass beads.

2EHA: 2-ethylhexyl acrylate 2EHMA: 2-ethylhexyl methacrylate 2HEMA: 2-hydroxyethyl methacrylate

The pressure-sensitive adhesive compositions obtained in the examples formed pressure-sensitive adhesive sheets with a low dielectric constant and excellent wet heat whitening resistance. Furthermore, the adhesive compositions obtained in the examples formed adhesive sheets with excellent foreign matter embedding properties.

1 Adhesive sheet with release sheet 11 Adhesive sheet (adhesive layer)
12a, 12b release sheet

Claims (9)

A pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing a crosslinkable acrylic polymer (A), a crosslinking agent (B), and a (meth)acrylic acid ester oligomer (C) having an alkylene glycol group,
The (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is alkoxyethylene glycol (meth)acrylate, alkoxypolyethylene glycol (meth)acrylate, phenol EO-modified acrylate, nonylphenol EO-modified acrylate, or 2-ethylhexyl EO. It is made by polymerizing modified acrylate alone ,
A pressure-sensitive adhesive sheet, wherein the content of the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group is 0.05 to 6 parts by mass based on 100 parts by mass of the crosslinkable acrylic polymer (A). The adhesive sheet according to claim 1, having a dielectric constant of less than 3.0 at a frequency of 1 MHz. A glass plate and a PET film are pasted together via the adhesive sheet to form a laminate, and the laminate is placed under conditions of 60°C and 95% relative humidity for 240 hours, and then placed in an environment of 23°C and 50% relative humidity. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a haze of 2% or less after being left to stand for 1 hour. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the (meth)acrylic acid ester oligomer (C) having an alkylene glycol group has a weight average molecular weight of 1,000 to less than 50,000. The adhesive according to any one of claims 1 to 4, wherein the crosslinkable acrylic polymer (A) contains a unit derived from a (meth)acrylic acid ester having a branched alkyl group having 5 to 9 carbon atoms. sheet. The crosslinkable acrylic polymer (A) includes a unit derived from an acrylic ester and a unit derived from a methacrylic ester, and has an ester structure of the unit derived from the acrylic ester and the unit derived from the methacrylic ester. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein are the same. According to claim 6, in the units constituting the crosslinkable acrylic polymer (A), the mass ratio of the units derived from the acrylic ester and the units derived from the methacrylic ester is 25:75 to 50:50. Adhesive sheet as described. A pressure-sensitive adhesive sheet with a release sheet, comprising a pair of release sheets having different peeling forces on both surfaces of the pressure-sensitive adhesive sheet according to any one of claims 1 to 7. A laminate comprising the adhesive sheet according to any one of claims 1 to 7 and an adherend on at least one surface of the adhesive sheet.

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