WO2024106389A1

WO2024106389A1 - Adhesive sheet

Info

Publication number: WO2024106389A1
Application number: PCT/JP2023/040797
Authority: WO
Inventors: 雅永井田; 哲士本田; 健太熊倉
Original assignee: 日東電工株式会社
Priority date: 2022-11-18
Filing date: 2023-11-13
Publication date: 2024-05-23

Abstract

The present invention provides an adhesive sheet that has a photocurable adhesive layer which is based on a polymer not obtained by solution polymerization and exhibits photocurability suitable for rendering peeling easy with light irradiation. Provided is an adhesive sheet comprising an adhesive layer which is cured by irradiation with light. In the adhesive layer, the total content of an azo-based polymerization initiator and a peroxide-based polymerization initiator is not more than 1.0 μg/g. The adhesive sheet has an initial storage modulus G' of less than 1.0×10⁶ Pa as measured using a measurement sample made of the adhesive layer, and post-curing-process storage modulus G' of not less than 1.0×10⁶ Pa, which is measured after a curing process has been performed by irradiating the measurement sample with ultraviolet rays.

Description

Adhesive sheet

The present invention relates to a pressure-sensitive adhesive sheet.
This application claims priority based on Japanese Patent Application No. 2022-185190, filed on November 18, 2022, the entire contents of which are incorporated herein by reference.

In general, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state at temperatures around room temperature, and have the property of easily adhering to an adherend when pressure is applied. Taking advantage of these properties, adhesives are widely used in a variety of fields, for example in the form of adhesive sheets having an adhesive layer. Some adhesive sheets have an adhesive layer that hardens when exposed to light (photocurable adhesive layer). Patent Document 1 is an example of a prior art document relating to this type of technology.

Japanese Patent Application Publication No. 2015-059179

Some adhesives are used by temporarily adhering to an adherend, and are peeled off from the adherend after their adhesive purpose has been fulfilled. Adhesives used in this manner in which they are peeled off from the adherend are required to have the performance to show good adhesion while they are attached to the adherend, and to be easily peeled off from the adherend after their adhesive purpose has been fulfilled. Adhesives with such performance can be used that adhere with a certain level of peel force when fixed, but can reduce the peel force when peeled off. For example, adhesive sheets equipped with an ultraviolet-curable adhesive layer that hardens when exposed to ultraviolet light and reduces the peel force are known.

In general, a liquid adhesive composition (solvent-based adhesive composition) containing a component having an ultraviolet-reactive functional group that reduces the peel strength due to ultraviolet irradiation and a photoinitiator that promotes the reaction of the ultraviolet-reactive functional group in an organic solvent is used to prepare an ultraviolet-curable adhesive layer. The solvent-based adhesive composition is applied to a suitable surface and then dried (to remove the organic solvent), whereby the solvent-based adhesive composition solidifies to form an ultraviolet-curable adhesive layer. A typical solvent-based adhesive composition contains a polymer obtained by solution polymerization using an azo-based or peroxide-based polymerization initiator or a modified product thereof as the base polymer that constitutes the adhesive layer. Therefore, in the ultraviolet-curable adhesive layer formed from the solvent-based adhesive composition, the azo-based or peroxide-based polymerization initiator used in the solution polymerization is usually present in the form of a decomposition product or residue of the polymerization initiator.

On the other hand, in recent years, there has been a growing demand to reduce the amount of organic solvents used, due to concerns about environmental hygiene, etc. Therefore, the object of the present invention is to provide an adhesive sheet that exhibits photocurability suitable for easy peeling by light irradiation and has a photocurable adhesive layer based on a polymer that is not solution polymerized.

According to this specification, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer (photocurable pressure-sensitive adhesive layer) that is cured by light irradiation is provided. The pressure-sensitive adhesive layer has a total content of an azo-based polymerization initiator and a peroxide-based polymerization initiator of 1.0 μg/g or less. By limiting the total content of the azo-based polymerization initiator and the peroxide-based polymerization initiator in this way, it is possible to prevent or suppress adverse effects caused by the polymerization initiator (for example, events that cause the polymerization initiator to be cleaved by heat, such as changes in the physical properties of the pressure-sensitive adhesive over time, deterioration or contamination of the adherend surface to which the pressure-sensitive adhesive sheet is attached, and generation of outgassing). For example, the pressure-sensitive adhesive layer may be a pressure-sensitive adhesive layer that does not contain either an azo-based or peroxide-based polymerization initiator. The pressure-sensitive adhesive sheet has an initial storage modulus G' at 25° C., measured using a measurement sample consisting of the pressure-sensitive adhesive layer, of less than 1.0×10 ⁶ Pa, and a post-curing storage modulus G' at 25° C., measured after a curing treatment of irradiating the measurement sample with ultraviolet light, of at least 1.0×10 ⁶ Pa. Hereinafter, the initial storage modulus G' may be abbreviated as "initial modulus G'" and the post-curing storage modulus G' may be abbreviated as "post-curing modulus G'".

The above-mentioned adhesive layer does not depend on solution polymerization using an azo- or peroxide-based polymerization initiator, so an adhesive sheet having this adhesive layer can reduce the amount of organic solvent used. In addition, an adhesive sheet in which the initial elastic modulus G' and post-curing elastic modulus G' of the adhesive layer are each within the above ranges tends to have a large decrease in peel strength when exposed to UV light, and therefore can become an adhesive sheet that can be easily peeled by irradiating light at a desired timing after application to an adherend. A low initial elastic modulus G' of the adhesive layer is also preferable from the viewpoint of improving the ability to conform to the surface shape of the adherend.

In some embodiments, the pressure-sensitive adhesive layer contains a polymer having a carbon-carbon double bond. The initial elastic modulus G' and the elastic modulus G' after curing treatment are each within the above ranges, and the pressure-sensitive adhesive layer containing a polymer having a carbon-carbon double bond is suitable for easy peeling by light irradiation.

In some embodiments, the polymer having the carbon-carbon double bond is preferably crosslinked with a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule. The fact that the polymer has a crosslinked structure with a polyfunctional monomer can be advantageous from the viewpoint of imparting appropriate cohesiveness to the photocurable adhesive layer containing the polymer.

In some embodiments, the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of carbon-carbon double bonds. When the amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer increases, the characteristics and physical properties tend to be easily changed by light irradiation. Therefore, a pressure-sensitive adhesive layer containing carbon-carbon double bonds in the above content can more effectively reduce the peel strength after curing treatment.

In some embodiments, the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of a photoinitiator. The pressure-sensitive adhesive layer containing the photoinitiator in the above content has good photocurability and is suitable for easy peeling by light irradiation.

In some embodiments, the pressure-sensitive adhesive layer preferably has a storage modulus increase rate calculated by the following formula of 300% or more.
Storage modulus increase rate [%] = (R / Q - 1) x 100
(Q in the formula is the initial storage modulus G′ [Pa], and R in the formula is the storage modulus G′ [Pa] after the curing treatment.)
A pressure-sensitive adhesive sheet having such a pressure-sensitive adhesive layer with a high storage modulus increase rate tends to have a large decrease in peel strength due to UV irradiation, and therefore can be a pressure-sensitive adhesive sheet with good peelability due to light irradiation.

In some embodiments, the pressure-sensitive adhesive layer preferably has a gel fraction of 70% or more measured after a curing treatment in which the pressure-sensitive adhesive layer is irradiated with ultraviolet light having an integrated light quantity of 300 mJ/cm ^{2. A} pressure-sensitive adhesive layer having a high gel fraction tends to favorably exhibit the effect of facilitating peeling by light irradiation.

The adhesive layer preferably has an organic solvent content of 1.0 μg/g or less. An adhesive layer with a low organic solvent content has a low odor and is desirable from the standpoint of environmental hygiene. A low organic solvent content in the adhesive layer can also be advantageous in terms of suppressing foaming caused by the evaporation of the organic solvent and in terms of low pollution.

In addition, any suitable combination of the elements described in this specification may be included within the scope of the invention for which patent protection is sought through this patent application.

1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment.

Preferred embodiments of the present invention will be described below. Note that matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field.
In the following drawings, the same reference numerals may be used to denote components or parts having the same function, and duplicated descriptions may be omitted or simplified. In addition, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the PSA sheet actually provided as a product.

In this specification, "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight) of an acrylic monomer. The above-mentioned acrylic monomer refers to a monomer derived from a monomer having at least one (meth)acryloyl group in one molecule. In addition, in this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

In this specification, "ethylenically unsaturated compound" refers to a compound having at least one ethylenically unsaturated group in the molecule. Examples of ethylenically unsaturated groups include (meth)acryloyl groups, vinyl groups, and allyl groups. Hereinafter, a compound having one ethylenically unsaturated group may be referred to as a "monofunctional monomer," and a compound having two or more ethylenically unsaturated groups may be referred to as a "polyfunctional monomer." Furthermore, among polyfunctional monomers, a compound having X ethylenically unsaturated groups may be referred to as an "X-functional monomer."

<Examples of adhesive sheet configurations>
The adhesive sheet disclosed herein comprises an adhesive layer. This adhesive layer typically constitutes at least one surface of the adhesive sheet. The adhesive sheet may be an adhesive sheet with a substrate in a form having an adhesive layer on one or both sides of a substrate (support), or may be an adhesive sheet without a substrate in a form in which the adhesive layer is held by a release liner (which may also be understood as a substrate having a release surface). In this case, the adhesive sheet may be composed of only an adhesive layer. The concept of an adhesive sheet as used herein may include those called adhesive tapes, adhesive labels, adhesive films, etc. In addition, the adhesive layer is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern. In addition, the adhesive sheet provided by the present specification may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet in the form of a further processed into various shapes.

One structural example of an adhesive sheet having an adhesive layer disclosed herein is shown in FIG. 1. This adhesive sheet 1 is a substrate-less double-sided adhesive sheet consisting of an adhesive layer 10. The adhesive sheet 1 before use (before application to an adherend) may be in the form of an adhesive sheet with release liner 50, in which each

surface

10A, 10B of the adhesive layer 10 is protected by

release liners

31, 32, at least the adhesive layer side of which is a releasable surface (release surface), as shown in FIG. 1. Alternatively, the back surface of the release liner 31 (the surface opposite to the adhesive side) may be the release surface, and the

adhesive surfaces

10A, 10B may be protected by being rolled or laminated so that the adhesive surface 10B abuts against the back surface of the release liner 31. The adhesive layer 10 may be a single layer, or may be a laminated structure of two or more layers.

The pressure-sensitive adhesive layer 10 is configured to be cured by light irradiation. In some preferred embodiments, the pressure-sensitive adhesive layer 10 contains a polymer having a carbon-carbon double bond and a photoinitiator. The amount of photoinitiator contained in the pressure-sensitive adhesive layer 10 is preferably 1.0×10 ⁻⁴ mol/100g or more. With such a content, good curing properties by light irradiation are likely to be obtained. For the same reason, in some embodiments, the amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer 10 is preferably 1.0×10 ⁻⁴ mol/100g or more.

The content of the organic solvent in the adhesive layer 10 is preferably 1.0 μg/g or less. An adhesive layer containing a polymer having a carbon-carbon double bond and a photoinitiator and having a limited content of the organic solvent can be preferably formed, for example, by irradiating an active energy ray (e.g., ultraviolet ray) curable adhesive composition with active energy rays to cure the composition to form a primary adhesive layer containing a primary polymer (typically a polymer not containing a carbon-carbon double bond obtained by active energy ray polymerization), and then adding a photoinitiator to the primary adhesive layer and introducing a carbon-carbon double bond into the primary polymer by a method in which no organic solvent is used or only a small amount of organic solvent is used (to the extent that the content of the organic solvent can be realized). In this formation method, a photoinitiator and a carbon-carbon double bond are newly contained in the pre-formed primary adhesive layer, so that an active energy ray curable adhesive composition can be preferably used as the adhesive composition for forming the primary adhesive layer. The active energy ray curable adhesive composition used is one that does not contain an organic solvent or contains only a small amount of organic solvent (to the extent that the content of the organic solvent can be realized).

The adhesive layer 10 preferably has a total content of azo-based polymerization initiator and peroxide-based polymerization initiator of 1.0 μg/g or less. Such an adhesive layer 10 can be preferably realized in a configuration that includes, as the polymer having a carbon-carbon double bond, a polymer obtained without performing solution polymerization using an azo-based or peroxide-based polymerization initiator (for example, a polymer obtained by obtaining a primary polymer that does not contain carbon-carbon double bonds by active energy ray polymerization and introducing a carbon-carbon double bond into the primary polymer).

Another example of the configuration of the adhesive sheet having the adhesive layer disclosed herein is shown in FIG. 2. This adhesive sheet 2 is configured as a one-sided adhesive sheet (single-sided adhesive sheet with substrate) including a photocurable adhesive layer 10, one surface 10A of which is the surface to be attached to an adherend (adhesive surface), and a substrate (support) 20 laminated on the other surface 10B of the adhesive layer 10. The adhesive layer 10 is bonded to one surface 20A of the substrate 20. As the substrate 20, for example, a resin film such as a polyester film can be used. The adhesive sheet 1 before use can be in the form of an adhesive sheet with release liner 50, in which the adhesive surface 10A is protected by a release liner 30, at least the adhesive layer side of which is a release surface (release surface), as shown in FIG. 2. Alternatively, the second surface 20B of the substrate 20 (the surface opposite to the first surface 20A, also called the back surface) may be the release surface, and the substrate 20 may be wound or laminated so that the adhesive surface 10A is in contact with the second surface 20B, thereby protecting the adhesive surface 10A.

The adhesive sheet disclosed herein may also be in the form of a double-sided adhesive sheet with a substrate, in which a first adhesive layer is laminated on one surface of a sheet-like substrate, and a second adhesive layer is laminated on the other surface of the substrate. In an adhesive sheet of this form, either or both of the first adhesive layer and the second adhesive layer may be composed of the photocurable adhesive layer disclosed herein.

<Characteristics of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein has a pressure-sensitive adhesive layer (photocurable pressure-sensitive adhesive layer) having an initial elastic modulus G' of less than 1.0 x 10 ⁶ Pa. The initial elastic modulus G' is a storage elastic modulus G' at 25 ° C. determined by dynamic viscoelasticity measurement using a measurement sample made of the pressure-sensitive adhesive layer. A low initial elastic modulus G' of the pressure-sensitive adhesive layer is advantageous from the viewpoint of making it easier to obtain a large elastic modulus change by light irradiation, and is also preferable from the viewpoint of improving the conformability to the surface shape of the adherend. In some embodiments, the initial elastic modulus G' is preferably less than 5.0 x 10 ⁵ Pa, more preferably less than 1.0 x 10 ⁵ Pa, may be less than 8.0 x 10 ⁴ Pa, may be less than 6.0 x 10 ⁴ Pa, or may be less than 5.0 x 10 ⁴ Pa. The lower limit of the initial elastic modulus G' is not particularly limited, and may be, for example, 1.0 x 10 ³ Pa or more. In some embodiments, from the viewpoints of appropriate cohesiveness in the pressure-sensitive adhesive layer before curing treatment and processability and handleability of a pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer, the initial elastic modulus G' of the pressure-sensitive adhesive layer is suitably 5.0×10 ³ Pa or more, advantageously 8.0×10 ³ Pa or more, preferably 1.0×10 ⁴ Pa or more, and may be 3.0×10 ⁴ Pa or more, or may be 5.0×10 ⁴ Pa or more. Specifically, the initial elastic modulus G' is measured by the method described in the Examples below.

The post-curing elastic modulus G' of the pressure-sensitive adhesive layer is 1.0 x 10 ⁶ Pa or more. The post-curing elastic modulus G' is a storage elastic modulus G' at 25 ° C., which is determined by performing a curing process of irradiating a measurement sample made of the pressure-sensitive adhesive layer with ultraviolet light, and then using the measurement sample after the curing process. A high post-curing elastic modulus G' is advantageous from the viewpoint of easy peeling by light irradiation. In some embodiments, the post-curing elastic modulus G' may be 1.1 x 10 ⁶ Pa or more, 1.3 x 10 ⁶ Pa or more, or 1.5 x 10 ⁶ Pa or more. The upper limit of the post-curing elastic modulus G' is not particularly limited, and may be, for example, 1.0 x 10 ⁸ Pa or less, 1.0 x 10 ⁷ Pa or less, 5.0 x 10 ⁶ Pa or less, or 3.0 x 10 ⁶ Pa or less. The elastic modulus G' after curing treatment is specifically measured by the method described in the Examples section below.

From the initial elastic modulus G′ and the elastic modulus after curing treatment G′, the increase rate of the storage elastic modulus of the pressure-sensitive adhesive layer is calculated by the following formula.
Storage modulus increase rate [%] = (R / Q - 1) x 100
Here, Q in the above formula is the initial elastic modulus G' [Pa], and R in the above formula is the elastic modulus G' [Pa] after curing treatment. The storage elastic modulus increase rate is typically more than 0% (e.g., more than 2.5 x ¹⁰² %), and is preferably 3.0 x ¹⁰² % or more. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a high storage elastic modulus increase rate tends to have a large decrease in peeling force due to UV irradiation. Therefore, it can be a pressure-sensitive adhesive sheet that shows good adhesion while it is used by adhering to an adherend (during the period of use), and can be easily peeled from the adherend after the adhesive purpose is completed. In some embodiments, the storage modulus increase rate is preferably 5.0×10 ² % or more, more preferably 7.0×10 ² % or more, may be 1.0×10 ³ % or more, 1.5×10 ³ % or more, 2.0×10 ³ % or more, 2.5×10 ³ % or more, or 3.0×10 ³ % or more. The upper limit of the storage modulus increase rate is not particularly limited. From the viewpoint of easily exhibiting a suitable cohesiveness before the curing treatment, in some embodiments, the storage modulus increase rate may be, for example, 1.0×10 ⁵ % or less, 1.0×10 ⁴ % or less, or 5.0×10 ³ % or less.

For the adhesive sheet disclosed herein, the initial peel strength (initial adhesive strength) measured based on JIS Z 0237:2000 under conditions of 23°C, 50% RH, a peel angle of 180 degrees, and a tensile speed of 300 mm/min using a silicon wafer as an adherend is not particularly limited and can be adjusted to an appropriate range depending on the purpose and application. The initial adhesive strength may be, for example, 0.5 N/20 mm or more, or 0.8 N/20 mm or more. An adhesive sheet that exhibits an initial adhesive strength equal to or greater than a predetermined value can adhere well to an adherend. From such a viewpoint, in some embodiments, the initial adhesive strength is preferably 1.0 N/20 mm or more (e.g., more than 1.0 N/20 mm), more preferably 1.5 N/20 mm or more, even more preferably 2.0 N/20 mm or more, and may be 2.5 N/20 mm or more, 3.0 N/20 mm or more, 3.5 N/20 mm or more, 4.0 N/20 mm or more, or 4.5 N/20 mm or more. The upper limit of the initial adhesive strength is not particularly limited, and may be, for example, less than 30 N/20 mm, and from the viewpoint of easily balancing with other properties, may be 25 N/20 mm or less, 20 N/20 mm or less, or 15 N/20 mm or less. The initial adhesive strength is a peel strength measured before the curing treatment. The initial adhesive strength is specifically measured by the method described in the Examples below.

The adhesive sheet disclosed herein preferably has a post-curing peel strength (post-curing adhesive strength) of 2.0 N/20 mm or less, more preferably 1.0 N/20 mm or less, measured after the adhesive layer is attached to a silicon wafer and cured by light irradiation. An adhesive sheet having such a limited post-curing peel strength can exhibit good peelability (easy peelability) in a use mode in which the adhesive sheet is peeled from an adherend after curing. From this viewpoint, in some embodiments, the post-curing adhesive strength is preferably less than 1.0 N/20 mm (e.g., less than 0.9 N/20 mm), more preferably less than 0.7 N/20 mm, even more preferably less than 0.5 N/20 mm, and may be 0.3 N/20 mm or less, 0.2 N/20 mm or less, 0.1 N/20 mm or less, or less than 0.1 N/20 mm (e.g., 0.08 N/20 mm or less or 0.05 N/20 mm or less). The lower limit of the adhesive strength after the curing process is not particularly limited, and may be, for example, 0 N/20 mm, or may be greater than 0 N/20 mm (for example, 0.005 N/20 mm or more). The adhesive strength after the curing process is specifically measured by the method described in the Examples below.

In the pressure-sensitive adhesive sheet disclosed herein, the peel strength reduction rate calculated by the following formula can be, for example, 10% or more, 20% or more, or 30% or more.
Peel strength reduction rate [%] = (1 - B/A) x 100
Here, A in the formula is the above-mentioned initial peel strength [N/20mm], and B in the formula is the above-mentioned peel strength after curing treatment [N/20mm]. In some embodiments, it is appropriate that the peel strength reduction rate is 50% or more. In this way, the adhesive sheet whose peel strength is greatly reduced by UV irradiation can be drastically reduced (easily peeled) from the adherend by applying light at a desired timing after being attached to the adherend. Therefore, it is useful as an adhesive sheet that shows good adhesion while being used by adhering to the adherend (during the period of use) and has the performance of being easily peeled from the adherend after the adhesive purpose is completed.

In some embodiments, the peel strength reduction rate is preferably 65% or more, more preferably 75% or more, and even more preferably 85% or more, and may be 90% or more, 94% or more, 96% or more, 97% or more, or 98% or more. A pressure-sensitive adhesive sheet with a higher peel strength reduction rate can achieve a higher level of both good adhesion during use and easy peelability after light irradiation. The peel strength reduction rate is typically 100% or less, and may be less than 100%, for example, 99.8% or less or 99.5% or less. A peel strength reduction rate of less than 100% can be advantageous, for example, from the viewpoint of preventing the pressure-sensitive adhesive sheet from unintentionally separating from the adherend after the curing treatment.

In the adhesive sheet disclosed herein, the difference between the initial peel strength [N/20mm] and the peel strength after the curing treatment [N/20mm] (peel strength difference) may be, for example, 0N/20mm or more, typically more than 0N/20mm, preferably 0.5N/20mm or more, more preferably 1.0N/20mm or more, even more preferably 1.5N/20mm or more or 2.0N/20mm or more, may be 3.0N/20mm or more, or may be 4.0N/20mm or more. An adhesive sheet whose peel strength is greatly reduced by UV irradiation in this way is useful as an adhesive sheet that can be easily peeled by irradiating light at a desired timing after application to an adherend. The peel strength difference may be, for example, less than 30N/20mm, and from the viewpoint of easily balancing with other properties, may be less than 25N/20mm, less than 20N/20mm, less than 15N/20mm, or less than 10N/20mm.

For the adhesive layer of the adhesive sheet disclosed herein, the loss modulus G" at 25°C measured by the method described in the Examples below is not particularly limited. In some embodiments, for example from the viewpoint of making it easier for the adhesive layer before curing treatment to exhibit appropriate adhesiveness, the loss modulus G" is suitably approximately 1.0 x ¹⁰⁶ Pa or less, advantageously less than 5.0 x ¹⁰⁵ Pa (e.g., less than 3.0 x ¹⁰⁵ Pa), preferably less than 1.5 x ¹⁰⁵ Pa (e.g., less than 1.0 x ¹⁰⁵ Pa), may be less than 5.0 x ¹⁰⁴ Pa, may be less than 1.0 x ¹⁰⁴ Pa, or may be less than 7.0 x ¹⁰³ Pa. The loss modulus G" of the pressure-sensitive adhesive layer may be, for example, 1.0×10 ² Pa or more, and from the viewpoint of better dissipating external forces that may be applied to the pressure-sensitive adhesive layer and making it easier to maintain adhesion to the adherend, it is advantageous to have a loss modulus G" of 5.0×10 ² Pa or more, and preferably 1.0×10 ³ Pa or more. A pressure-sensitive adhesive layer having such a loss modulus G" tends to be less likely to peel off from the adherend even when subjected to an external force (e.g., an external force in the shear direction). In some embodiments, the loss modulus G" may be 3.0×10 ³ Pa or more, 5.0×10 ³ Pa or more, 7.0×10 ³ Pa or more, or 1.0×10 ⁴ Pa or more.

The Young's modulus after the curing treatment by light irradiation (Young's modulus after curing treatment) of the adhesive layer of the adhesive sheet disclosed herein, measured by the method described in the Examples below, is not particularly limited and may be, for example, more than 0.05 MPa. In some embodiments, from the viewpoint of low contamination in a use mode in which, for example, a curing treatment is applied to an adhesive sheet attached to an adherend and then the adhesive sheet is peeled off from the adherend, the Young's modulus after the curing treatment is suitably more than 0.1 MPa, advantageously more than 0.5 MPa, and preferably 1.0 MPa or more. When the Young's modulus after the curing treatment of the adhesive layer is high, it tends to be easier to obtain good peelability from the adherend after light irradiation. For example, it is easier to prevent or suppress the occurrence of an event (glue residue) in which a part of the adhesive layer is torn off and remains on the adherend when peeled off from the adherend. From the viewpoint of making such effects easier to exhibit, in some embodiments, the Young's modulus after the curing treatment may be, for example, 1.2 MPa or more, 1.5 MPa or more, 2.0 MPa or more, 2.5 MPa or more, 3.5 MPa or more, 4.0 MPa or more, or 4.5 MPa or more. The Young's modulus after the curing treatment may be, for example, 10 MPa or less, and from the viewpoint of making it easier to achieve both good flexibility before the curing treatment, it is preferably 7.0 MPa or less, and more preferably 5.0 MPa or less.

The gel fraction of the adhesive layer of the adhesive sheet disclosed herein after the curing treatment by light irradiation, measured by the method described in the Examples below, is not particularly limited, and may be, for example, 50% or more, 60% or more, or 70% or more. From the viewpoint of easily exerting the effect of easy peeling by light irradiation, in some embodiments, the above gel fraction is preferably 80% or more, more preferably 82% or more, even more preferably 84% or more, may be 86% or more, may be 88% or more, or may be 90% or more. In addition, from the viewpoint of easily achieving both good flexibility and adhesiveness before the curing treatment, in some embodiments, the above gel fraction may be, for example, 99.5% or less, may be 99% or less, may be 97% or less, or may be 95% or less.

<Adhesive Layer>
The adhesive layer (photocurable adhesive layer) in the technology herein has an initial storage modulus G' of less than 1.0 x 10 ⁶ Pa and a storage modulus G' after curing treatment of 1.0 x 10 ⁶ Pa or more. The type of adhesive constituting the adhesive layer is not particularly limited, and may contain one or more of various rubber-like polymers such as acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers as base polymers. From the viewpoint of adhesive performance, cost, etc., an adhesive containing an acrylic polymer or a rubber polymer as a base polymer may be preferably adopted. As an example of an adhesive that can realize the above initial storage modulus G' and the above storage modulus G' after curing treatment, an acrylic adhesive containing an acrylic polymer as a base polymer will be mainly described below, but it is not intended to limit the adhesive disclosed herein to an acrylic adhesive.

In this specification, the "base polymer" of the adhesive layer refers to the main component of the polymer contained in the adhesive layer. The polymer is preferably a rubber-like polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the "main component" refers to a component that is contained in an amount of more than 50% by weight, unless otherwise specified.

(Polymers having carbon-carbon double bonds)
In some preferred embodiments, the adhesive constituting the adhesive layer includes a polymer having a carbon-carbon double bond. The adhesive layer including the polymer having a carbon-carbon double bond can be cured by a mechanism including reacting the carbon-carbon double bond in the polymer by light irradiation. By irradiating the adhesive layer attached to the adherend with light, the carbon-carbon double bond in the polymer reacts, causing the adhesive layer to cure and shrink, and the adhesive sheet having the adhesive layer can be effectively made easy to peel. Among these, an adhesive including a polymer having a carbon-carbon double bond as a base polymer is preferred.

The form in which the carbon-carbon double bond exists in the polymer is not particularly limited. The polymer may be a polymer having a carbon-carbon double bond in the side chain, or a polymer having a carbon-carbon double bond in the main chain. Here, having a carbon-carbon double bond in the main chain includes the presence of a carbon-carbon double bond in the main chain skeleton of the polymer and the presence of a carbon-carbon double bond at the end of the main chain. From the viewpoint of the reactivity of the carbon-carbon double bond and the improvement in the modulus of elasticity due to the reaction of the carbon-carbon double bond, a polymer having a carbon-carbon double bond in the side chain can be preferably used. Here, the main chain of the polymer refers to the chain structure that forms the skeleton of the polymer. In addition, the side chain of the polymer refers to a group (pendant group, side group) that is bonded to the main chain, or a molecular chain that can be considered as a pendant.

In some preferred embodiments, the polymer having a carbon-carbon double bond has the carbon-carbon double bond in the form of an ethylenically unsaturated group. The polymer having a carbon-carbon double bond is, for example, represented by the following formula (1):

(wherein R is a hydrogen atom or a methyl group);
The polymer may be a polymer having a carbon-carbon double bond in the form of a reactive group ((meth)acryloyl group) represented by the formula:

The polymer having a carbon-carbon double bond is not particularly limited, and an appropriate polymer can be selected and used taking into consideration the properties of the adhesive layer, etc. The polymer having a carbon-carbon double bond can be, for example, a secondary polymer in which a carbon-carbon double bond has been introduced into a primary polymer that does not contain a carbon-carbon double bond by a method such as chemical modification.

A specific example of a method for introducing a carbon-carbon double bond into a primary polymer is to prepare a primary polymer in which a monomer having a functional group (hereinafter also referred to as "functional group A") is copolymerized, and then the primary polymer is reacted with a compound having a carbon-carbon double bond and a functional group (hereinafter also referred to as "functional group B") that can react with the functional group A (for example, an ethylenically unsaturated compound having functional group B) in such a way that the carbon-carbon double bond is not lost, thereby obtaining a polymer (secondary polymer) in which a carbon-carbon double bond has been introduced. The reaction between functional group A and functional group B is preferably a reaction that does not involve the generation of radicals, such as a condensation reaction or an addition reaction. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among these, the combination of a hydroxyl group and an isocyanate group is preferable from the viewpoint of reaction traceability. In addition, as long as the combination of the functional groups A and B can produce a polymer having a carbon-carbon double bond, one of the functional groups in the combination may be functional group A and the other may be functional group B, or one of the functional groups may be functional group B and the other may be functional group A. For example, in the case of a combination of a hydroxyl group and an isocyanate group, the functional group A of the primary polymer may be a hydroxyl group (in which case, the functional group B is an isocyanate group) or an isocyanate group (in which case, the functional group B is a hydroxyl group). Among these, a combination in which the primary polymer has a hydroxyl group and the functional group B-containing compound having the carbon-carbon double bond (preferably an ethylenically unsaturated compound having the functional group B) has an isocyanate group is preferred. This combination is particularly preferred when the primary polymer is an acrylic polymer.

In reacting the functional group A of the primary polymer with the functional group B of the compound having a carbon-carbon double bond, the molar ratio (M _A /M _B ) of the moles of the functional group A (M _A ) to the moles of the functional group B (M _B ) is usually appropriate to be 0.2 or more from the viewpoint of the reactivity of both, and is preferably 0.5 or more (e.g., 0.7 or more, typically 1.0 or more), and may be more than 1.0 (e.g., 1.1 or more), or may be 1.2 or more. The molar ratio (M _A /M _B ) is usually appropriate to be 2000 or less (e.g., 1500 or less or 1000 or less), and is advantageously 500 or less, and may be 200 or less, 100 or less, or 50 or less. In some embodiments, the molar ratio (M _A /M _B ) is preferably 30 or less, may be 20 or less, may be 10 or less, may be 5.0 or less, may be 3.0 or less, may be 2.5 or less, may be 2.0 or less, may be 1.5 or less. In addition, from the viewpoint of increasing the contact opportunity between the functional group A and the functional group B, a larger amount of the functional group B-containing compound having a carbon-carbon double bond may be used, and in this case, the molar ratio (M _A /M _B ) is preferably less than 1 (e.g., less than 0.99, less than 0.95). In addition, for example, when the excess functional group A is also used for other purposes (e.g., improving the adhesion of the photocurable pressure-sensitive adhesive layer before curing treatment, etc.), the molar ratio (M _A /M _B ) is preferably greater than 1.

The amount of the functional group B-containing compound having a carbon-carbon double bond (preferably, an ethylenically unsaturated compound having a functional group B) used relative to 100 parts by weight of the polymer having a functional group A (typically, a polymer before the carbon-carbon double bond is introduced) can be, for example, about 0.001 parts by weight or more, about 0.01 parts by weight or more, or about 0.1 parts by weight or more, and is appropriately about 0.5 parts by weight or more (for example, about 1.0 parts by weight or more), preferably about 3.0 parts by weight or more, more preferably about 5.0 parts by weight or more, may be about 7.0 parts by weight or more, may be about 9.0 parts by weight or more, may be about 10 parts by weight or more, or may be about 12 parts by weight or more. The amount of the compound containing functional group B having a carbon-carbon double bond used is suitably about 40 parts by weight or less, preferably about 35 parts by weight or less, more preferably about 30 parts by weight or less, and may be about 25 parts by weight or less, about 20 parts by weight or less, or about 17 parts by weight or less, relative to 100 parts by weight of the polymer having functional group A (typically, the polymer before the carbon-carbon double bond is introduced). The amount used is preferably set so as to satisfy the above-mentioned molar ratio (M _A /M _B ). For example, the above-mentioned molar ratio (M _A /M _B ) and the amount of the compound containing functional group B having a carbon-carbon double bond used can be preferably applied to a configuration in which an acrylic polymer described later is used as the polymer.

(Acrylic polymer having carbon-carbon double bond)
The photocurable pressure-sensitive adhesive layer disclosed herein can be preferably implemented in an embodiment containing an acrylic polymer (i.e., an acrylic polymer having a carbon-carbon double bond) as the polymer having a carbon-carbon double bond, from the viewpoint of ease of curing by light irradiation, etc. Acrylic polymers are advantageous in that there is a high degree of freedom in the selection of monomer raw materials and that physical properties are easily controlled. Acrylic polymers having carbon-carbon double bonds and pressure-sensitive adhesive layers containing the acrylic polymers are also preferable from the viewpoint of suitability for production by a method that does not rely on organic solvents, as described below.

An acrylic polymer having a carbon-carbon double bond may be one in which a carbon-carbon double bond has been introduced by chemically modifying an acrylic polymer (typically an acrylic polymer not containing a carbon-carbon double bond) as a primary polymer. The method of introducing a carbon-carbon double bond into an acrylic polymer is not particularly limited. For example, a method of reacting (typically condensation or addition reaction) a functional group (functional group A) introduced into an acrylic polymer by copolymerization with a functional group (functional group B) capable of reacting with the functional group A and a compound having a carbon-carbon double bond so that the carbon-carbon double bond does not disappear can be preferably adopted. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among them, a combination of a hydroxyl group and an isocyanate group is preferable from the viewpoint of reaction traceability. From the viewpoint of polymer design, etc., a combination in which the acrylic polymer has a hydroxyl group and the above compound has an isocyanate group is particularly preferable. In addition, from the viewpoint of the photocurability of the photocurable adhesive layer, it is preferable that the compound having the functional group B and the carbon-carbon double bond is an ethylenically unsaturated compound having the functional group B.

A suitable example of an ethylenically unsaturated compound having functional group B is an isocyanate group-containing monomer (isocyanate group-containing compound). Specific examples of isocyanate group-containing monomers include those described below as secondary monomers that can be used in the polymerization of acrylic polymers. Among these, 2-(meth)acryloyloxyethyl isocyanate is more preferred. An acrylic polymer having a carbon-carbon double bond is preferably realized by reacting the isocyanate group (functional group B) of the isocyanate group-containing monomer with the hydroxyl group (functional group A) of the acrylic polymer to form a bond (typically a urethane bond).

The amount of the isocyanate group-containing monomer used can be appropriately set within a range that satisfies the above-mentioned molar ratio (M _A /M _B ) from the viewpoint of reactivity with the hydroxyl group as the functional group A. For example, the amount of the isocyanate group-containing monomer used is appropriately about 1 part by weight or more (e.g., 3 parts by weight or more) relative to 100 parts by weight of an acrylic polymer (primary polymer) having a hydroxyl group, and from the viewpoint of making it easier to exhibit the effect of the curing treatment (e.g., the effect of reducing the peel strength), it is preferably 5 parts by weight or more (e.g., 7 parts by weight or more), may be 8.5 parts by weight or more, may be 10 parts by weight or more, or may be 12 parts by weight or more. The upper limit of the amount of the isocyanate group-containing monomer used is not particularly limited, and is appropriately about 40 parts by weight or less relative to 100 parts by weight of the acrylic polymer having a hydroxyl group, preferably about 35 parts by weight or less, more preferably about 30 parts by weight or less, and may be, for example, about 25 parts by weight or less.

Another suitable example of the ethylenically unsaturated compound having the functional group B is a hydroxyl group-containing monomer. Specific examples of the hydroxyl group-containing monomer include those described below as secondary monomers that can be used in the polymerization of acrylic polymers. For example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) are preferred, and 4HBA is particularly preferred. The hydroxyl group (functional group B) of the hydroxyl group-containing monomer reacts with the isocyanate group (functional group A) of the acrylic polymer to form a bond (typically a urethane bond), thereby suitably realizing an acrylic polymer having a carbon-carbon double bond. The amount of the hydroxyl group-containing monomer used as the ethylenically unsaturated compound having the functional group B can be appropriately set within a range that satisfies the above-mentioned molar ratio (M _A /M _B ) from the viewpoint of reactivity with the isocyanate group as the functional group A.

Other examples of ethylenically unsaturated compounds having functional group B include epoxy group-containing monomers. Specific examples of epoxy group-containing monomers include those described below as sub-monomers that can be used in the polymerization of acrylic polymers. For example, glycidyl acrylate and glycidyl methacrylate (GMA) are preferred. An acrylic polymer having a carbon-carbon double bond is suitably realized by reacting and bonding the epoxy group (functional group B) of the epoxy group-containing monomer with the carboxy group (functional group A) of the acrylic polymer. The amount of the epoxy group-containing monomer used as the ethylenically unsaturated compound having functional group B can be appropriately set within a range that satisfies the above-mentioned molar ratio (M _A /M _B ) from the viewpoint of reactivity with the carboxy group as the functional group A. In some embodiments, by making the molar ratio (M _A /M _B ) larger than 1, the effect of the excess carboxy group (for example, improvement in peel strength before the photocurable pressure-sensitive adhesive layer is cured, improvement in cohesiveness and heat resistance before and/or after the curing process, etc.) can be utilized. In such an embodiment, the molar ratio (M _A /M _B ) can be, for example, 1.1 or more, and may be 1.5 or more, or 2.0 or more.

The acrylic polymer as the primary polymer may be, for example, a polymer of a monomer raw material that contains an alkyl (meth)acrylate as the main monomer and may further contain a secondary monomer that is copolymerizable with the main monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

As the alkyl(meth)acrylate, for example, a compound represented by the following formula (2) can be suitably used.
_CH2 =C( ^R1 ) ^COOR2 (2)
Here, R ¹ in the above formula (2) is a hydrogen atom or a methyl group. R ² is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms may be referred to as "C _1-20 "). From the viewpoint of the storage elastic modulus of the pressure-sensitive adhesive layer, an alkyl (meth)acrylate in which R ² is a chain alkyl group having _1-14 (e.g., C _1-12 ) is preferred, and an alkyl acrylate in which R ¹ is a hydrogen atom and R ² is a chain alkyl group having _1-20 (e.g., C _1-14 , typically C _1-12 ) is more preferred.

Examples of alkyl(meth)acrylates in which R ² is a C _1-20 chain alkyl group include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, isopropyl(meth)acrylate, butyl ... Examples of the alkyl (meth)acrylate include octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more. Examples of preferred alkyl (meth)acrylates include ethyl acrylate (EA), n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and lauryl acrylate (LA).

In some preferred embodiments, the alkyl (meth)acrylate includes an alkyl (meth)acrylate A1 having an alkyl group with 9 or less carbon atoms (i.e., an alkyl (meth)acrylate in which R ² is a C _1-9 alkyl group). With such a configuration in which the length of the side chain alkyl group is limited, a photocurable pressure-sensitive adhesive layer suitable for increasing the storage modulus by light irradiation is easily obtained. For example, in a photocurable pressure-sensitive adhesive layer including an acrylic polymer having a carbon-carbon double bond in a side chain (typically a side chain terminal) as a polymer having a carbon-carbon double bond, the reaction of the carbon-carbon double bond can proceed smoothly during a curing treatment by light irradiation due to the limited length of the side chain alkyl group.

The proportion of alkyl (meth)acrylate A1 in all monomer components constituting the acrylic polymer is suitably approximately 10% by weight or more, and from the viewpoint of favorably expressing the action of alkyl (meth)acrylate A1, is preferably 20% by weight or more, more preferably 40% by weight or more, and even more preferably 55% by weight or more, may be 65% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or may be 95% by weight or more. There is no particular upper limit to the proportion of alkyl (meth)acrylate A1 in all monomer components. In some embodiments, taking into consideration the balance with the amount of secondary monomer (e.g., monomer having functional group A) used, it is appropriate that the blending ratio of alkyl (meth)acrylate A1 in the total monomer components is approximately 99.5% by weight or less (e.g., 99% by weight or less), preferably 95% by weight or less, may be 92% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, may be 75% by weight or less, or may be 70% by weight or less.

The content of alkyl (meth)acrylate A1 in the total alkyl (meth)acrylate as the main monomer is suitably approximately 50% by weight or more (e.g., more than 50% by weight), and from the viewpoint of favorably expressing the action of alkyl (meth)acrylate A1, it is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, and may be 95% by weight or more, or may be 99 to 100% by weight.

In some preferred embodiments, the alkyl (meth)acrylate A1 includes an alkyl (meth)acrylate A3 having an alkyl group with less than 8 carbon atoms. The alkyl (meth)acrylate A3 can be useful for improving adhesion to polar adherends such as metals. The number of carbon atoms in the alkyl group in the alkyl (meth)acrylate A3 is typically 7 or less, preferably 6 or less, more preferably 4 or less, and may be 2 or less. In some embodiments, from the viewpoint of flexibility of the photocurable adhesive layer before curing treatment, the number of carbon atoms in the alkyl group in the alkyl (meth)acrylate A3 is preferably 2 or more.

The proportion of alkyl (meth)acrylate A3 in all monomer components is suitably approximately 10% by weight or more, and from the viewpoint of favorably expressing the action of alkyl (meth)acrylate A3, it is preferably 20% by weight or more, more preferably 30% by weight or more, even more preferably 40% by weight or more, and particularly preferably 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more. There is no particular upper limit to the proportion of alkyl (meth)acrylate A3 in all monomer components. In some embodiments, taking into consideration the balance with the amount of the secondary monomer used, it is appropriate that the blending ratio of the alkyl (meth)acrylate A3 in the total monomer components is approximately 99.5% by weight or less (e.g., 99% by weight or less), preferably 95% by weight or less, and may be 90% by weight or less or 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, 30% by weight or less, 15% by weight or less, 10% by weight or less, or 5% by weight or less.

The content of the alkyl (meth)acrylate A3 in the entire alkyl (meth)acrylate as the main monomer is suitably about 5% by weight or more, and from the viewpoint of favorably expressing the action of the alkyl (meth)acrylate A3, it is preferably 20% by weight or more, more preferably 35% by weight or more, even more preferably 45% by weight or more, particularly preferably 55% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more (for example, 90% by weight or more). The upper limit of the content of the alkyl (meth)acrylate A3 in the entire alkyl (meth)acrylate is 100% by weight. In some embodiments, for example, when the alkyl (meth)acrylate A2 described later is included, from the viewpoint of favorably expressing its action, the content of the alkyl (meth)acrylate A3 in the entire alkyl (meth)acrylate may be, for example, 90% by weight or less, 75% by weight or less, 60% by weight or less, 45% by weight or less, 30% by weight or less, or 15% by weight or less.

In some embodiments, the alkyl (meth)acrylate includes an alkyl (meth)acrylate A2 having an alkyl group with 5 or more carbon atoms, either as the alkyl (meth)acrylate A1 or A3, or as a monomer different from the alkyl (meth)acrylate A1 or A3. By using the alkyl (meth)acrylate A2, for example, the adhesive strength after curing treatment is easily reduced, and better peelability and low contamination are easily obtained. The number of carbon atoms in the alkyl group in the alkyl (meth)acrylate A2 is preferably 7 or more (e.g., 8 or more), and may be 9 or more. From the viewpoint of adhesive properties such as adhesive strength, the number of carbon atoms in the alkyl group in the alkyl (meth)acrylate A2 is preferably 14 or less, more preferably 12 or less, and may be 10 or less or 9 or less.

The proportion of alkyl (meth)acrylate A2 in all monomer components constituting the acrylic polymer is suitably approximately 10% by weight or more, and from the viewpoint of favorably expressing the action of alkyl (meth)acrylate A2, is preferably approximately 20% by weight or more, more preferably approximately 40% by weight or more, even more preferably approximately 55% by weight or more, and particularly preferably approximately 65% by weight or more, for example, approximately 75% by weight or more, approximately 80% by weight or more, approximately 85% by weight or more, approximately 90% by weight or more, or approximately 95% by weight or more. The proportion of alkyl (meth)acrylate A2 in all monomer components is not particularly limited. In some embodiments, taking into consideration the balance with the amount of the secondary monomer used, the blending ratio of the alkyl (meth)acrylate A2 in the total monomer components is suitably about 99.5% by weight or less (e.g., 99% by weight or less), preferably 95% by weight or less, may be 90% by weight or less or 80% by weight or less, may be 70% by weight or less, may be 60% by weight or less, may be 50% by weight or less, may be 30% by weight or less, 15% by weight or less, 10% by weight or less, or may be 5% by weight or less.

The content of the alkyl (meth)acrylate A2 in the total alkyl (meth)acrylate as the main monomer may be, for example, approximately 1% by weight or more, and from the viewpoint of favorably expressing the action of the alkyl (meth)acrylate A2, it is preferably 5% by weight or more, more preferably 15% by weight or more, even more preferably 25% by weight or more, particularly preferably 35% by weight or more, and may be 45% by weight or more, 60% by weight or more, or 80% by weight or more (for example, 90% by weight or more). The upper limit of the content of the alkyl (meth)acrylate A2 in the total alkyl (meth)acrylate is 100% by weight. In some embodiments, for example, when the alkyl (meth)acrylate A3 is contained, from the viewpoint of favorably expressing its action, the content of the alkyl (meth)acrylate A2 in the total alkyl (meth)acrylate may be, for example, 90% by weight or less, 75% by weight or less, 60% by weight or less, 45% by weight or less, 30% by weight or less, or 15% by weight or less.

The blending ratio of the main monomer in all monomer components constituting the acrylic polymer is preferably 55% by weight or more, and more preferably 60% by weight or more (e.g., 65% by weight or more). There is no particular upper limit to the blending ratio of the main monomer. In some embodiments, taking into account the balance with the amount of the secondary monomer used, it is appropriate to make the blending ratio of the main monomer, for example, 99.5% by weight or less (e.g., 99% by weight or less), and it may be 95% by weight or less, 90% by weight or less, 85% by weight or less, or approximately 75% by weight or less.

A secondary monomer that is copolymerizable with the main monomer, alkyl (meth)acrylate, can be useful, for example, for increasing the cohesive strength of an acrylic polymer as a primary or secondary polymer, or for introducing crosslinking points into the polymer. It is preferable to employ, as at least a part of the secondary monomer, a monomer having a functional group (functional group A) that can react with a functional group (functional group B) of a compound having a carbon-carbon double bond, which will be described later. As the secondary monomer, for example, the following functional group-containing monomer components can be used alone or in combination of two or more. A monomer having functional group A may be used in combination with a monomer having another functional group.

Hydroxyl group-containing monomers: for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc.; unsaturated alcohols such as vinyl alcohol, allyl alcohol, etc.; ether compounds such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, etc.
Isocyanate group-containing monomers: (meth)acryloyl isocyanate, 2-(meth)acryloyloxyethyl isocyanate, m-isopropenyl-α,α-dimethylbenzyl isocyanate.
Carboxy group-containing monomers: for example, ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), crotonic acid, etc.; ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, citraconic acid, etc., and their anhydrides (maleic anhydride, itaconic anhydride, etc.).
Amide group-containing monomers: for example, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide.
Amino group-containing monomers: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate.
Epoxy group-containing monomers: for example, glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, allyl glycidyl ether.
Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile.
Keto group-containing monomers: for example, diacetone (meth)acrylamide, diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine.
Alkoxysilyl group-containing monomers: for example, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane.

When using a secondary monomer having a functional group (functional group A) that can react with a functional group (functional group B) of a compound having a carbon-carbon double bond, the type of the secondary monomer can be selected according to the type of functional group B. Preferred secondary monomers having functional group A include, for example, hydroxyl group-containing monomers, isocyanate group-containing monomers, carboxy group-containing monomers, and epoxy group-containing monomers.

In some embodiments, a hydroxyl-containing monomer may be preferably used as the secondary monomer having functional group A from the viewpoint of reactivity with a compound having functional group B. By using a hydroxyl-containing monomer as the secondary monomer, the resulting acrylic polymer (primary polymer) has a hydroxyl group. In contrast, by using a compound having an isocyanate group as the compound having a carbon-carbon double bond, the hydroxyl group of the acrylic polymer reacts with the isocyanate group of the compound, and the carbon-carbon double bond derived from the compound is introduced into the acrylic polymer, thereby obtaining an acrylic polymer (secondary polymer) having a carbon-carbon double bond. Suitable examples of hydroxyl-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA). Among these, 4HBA is preferred.

The amount of the sub-monomer is not particularly limited and may be appropriately selected so as to achieve the desired purpose of use (introduction of a reactive site with functional group B, adjustment of the cohesiveness and adhesive properties of the photocurable adhesive layer, etc.). In general, from the viewpoint of favorably exerting the effect of performing light irradiation (curing treatment) on the photocurable adhesive layer (for example, the effect of reducing the peeling force), the amount of the sub-monomer is appropriate to be 0.1% by weight or more of the total monomer components of the acrylic polymer, and preferably 0.3% by weight or more (for example, 1% by weight or more). In addition, the amount of the sub-monomer is appropriate to be 70% by weight or less (for example, 60% by weight or less) of the total monomer components, and in some embodiments, from the viewpoint of the flexibility of the photocurable adhesive layer, it is preferable to set it to 50% by weight or less, more preferably 45% by weight or less, and may be 40% by weight or less, 30% by weight or less, 20% by weight or less, 10% by weight or less, or 5% by weight or less.

When a sub-monomer having a functional group A is used for the purpose of reacting with a compound having a carbon-carbon double bond (preferably an ethylenically unsaturated compound having a functional group B), the amount of the sub-monomer having the functional group A (e.g., a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an isocyanate group-containing monomer, an epoxy group-containing monomer, etc., depending on the type of functional group B) is appropriate to be 1% by weight or more of the total monomer components of the acrylic polymer from the viewpoint of the increase in storage modulus due to the curing treatment (typically a light irradiation treatment), and is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 12% by weight or more (e.g., 14% by weight or more). In addition, from the viewpoint of maintaining good adhesive properties such as adhesion in the adhesive layer (photocurable adhesive layer) before the curing treatment, the amount of the sub-monomer having the functional group A is appropriate to be 50% by weight or less (e.g., 40% by weight or less) of the total monomer components, and is preferably 30% by weight or less, more preferably 25% by weight or less, and may be 20% by weight or less, or may be 15% by weight or less.

In some embodiments, a monomer having a nitrogen atom-containing ring may be preferably used as the secondary monomer. The monomer having a nitrogen atom-containing ring may be useful for improving the peel strength of the photocurable adhesive layer in its initial state (before the curing process). It may also be advantageous from the viewpoint of increasing the extent of the decrease in peel strength (peel strength difference) caused by the light irradiation (curing process) of the photocurable adhesive layer. Specific examples of the monomer having a nitrogen atom-containing ring are as described above, and suitable examples include N-vinyl-2-pyrrolidone (NVP) and N-acryloylmorpholine (ACMO). The amount of the monomer having a nitrogen atom-containing ring used may be, for example, 0.5% by weight or more or 1% by weight or more of the total monomer components used as the raw material for the acrylic polymer (primary polymer), and from the viewpoint of obtaining a higher usage effect, it is appropriate to set it to 3% by weight or more, and it is advantageous to set it to 5% by weight or more, and it may be 10% by weight or more, 12% by weight or more, 17% by weight or more, or 20% by weight or more. In addition, the amount of the monomer having a nitrogen atom-containing ring used can be, for example, 40% by weight or less of all monomer components used as raw materials for the acrylic polymer (primary polymer). From the viewpoint of flexibility of the photocurable adhesive layer, it is appropriate to set it to 35% by weight or less in some embodiments, and it is preferable to set it to 30% by weight or less (for example, 28% by weight or less).

In addition, for purposes such as increasing the cohesive strength of the acrylic polymer, other copolymerization components other than the above-mentioned secondary monomers can be used as necessary. Examples of such copolymerization components include vinyl ester monomers such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene, substituted styrenes (α-methylstyrene, etc.), and vinyl toluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl di(meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. Copolymerization components other than these secondary monomers may be used alone or in combination of two or more. The amount of the other copolymerization components is not particularly limited and may be appropriately selected depending on the purpose and application, but it is preferable that the amount is, for example, 20% by weight or less (e.g., 2 to 20% by weight, typically 3 to 10% by weight) of the total monomer components constituting the acrylic polymer.

A polyfunctional monomer may be used as the other copolymerization component. Examples of polyfunctional monomers include various polyfunctional (meth)acrylates having two or more (meth)acryloyl groups in one molecule, polyfunctional vinyl monomers such as divinylbenzene, and polyfunctional monomers having a combination of a (meth)acryloyl group and another ethylenically unsaturated group such as allyl (meth)acrylate and vinyl (meth)acrylate. The polyfunctional monomers may be used alone or in combination of two or more. Among them, polyfunctional (meth)acrylates may be preferably used. Examples of the polyfunctional (meth)acrylate include 1,6-hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, and vinyl (meth)acrylate. As the polyfunctional (meth)acrylate for the acrylic polymer, one type of polyfunctional (meth)acrylate may be used alone, or two or more types of polyfunctional (meth)acrylates may be used in combination. In some embodiments, as the polyfunctional (meth)acrylate for the acrylic polymer, preferably, at least one selected from the group consisting of 1,6-hexanediol diacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate is used.

By polymerizing a monomer component containing a polyfunctional monomer, typically, an acrylic polymer (primary polymer) having a structure crosslinked by the polyfunctional monomer is obtained. That is, the polyfunctional monomer can function as a copolymerizable crosslinking agent. By introducing a carbon-carbon double bond into an acrylic polymer having such a structure, an acrylic polymer (secondary polymer) having a carbon-carbon double bond and having a structure crosslinked by the polyfunctional monomer is obtained. The fact that the acrylic polymer having a carbon-carbon double bond has a crosslinked structure can be advantageous from the viewpoint of imparting appropriate cohesiveness to the photocurable adhesive layer containing the polymer. In a photocurable adhesive layer containing an acrylic polymer having a carbon-carbon double bond as a base polymer, it is particularly significant that the acrylic polymer is crosslinked.

The amount of the polyfunctional monomer (copolymerizable crosslinking agent) used as the other copolymerization component may be appropriately selected according to the purpose and application, and is not particularly limited. For example, the amount of the polyfunctional monomer may be 0.001% by weight or more of the total monomer components constituting the acrylic polymer (primary polymer). From the viewpoint of easily obtaining a higher usage effect, it is preferable to make it 0.005% by weight or more, more preferably 0.007% by weight or more, and it may be 0.01% by weight or more, or it may be 0.03% by weight or more. In addition, from the viewpoint of easily exhibiting the effect of curing the photocurable adhesive layer (for example, the effect of increasing the storage modulus and decreasing the peel strength) and from the viewpoint of the flexibility of the photocurable adhesive layer, the amount of the polyfunctional monomer used may be, for example, 10% by weight or less of the total monomer components constituting the acrylic polymer, advantageously 5% by weight or less, preferably less than 5% by weight, may be 3% by weight or less, or may be 1% by weight or less. In some embodiments, the amount of the polyfunctional monomer used is preferably less than 1 wt% (e.g., 0.9 wt% or less) of the total monomer components constituting the acrylic polymer (typically, the acrylic polymer as the primary polymer), more preferably 0.5 wt% or less, and may be 0.3 wt% or less, 0.2 wt% or less, 0.1 wt% or less (e.g., less than 0.1 wt%), 0.09 wt% or less, 0.08 wt% or less, or 0.07 wt% or less. Not using too much polyfunctional monomer as a copolymerization component of the primary polymer can be advantageous in terms of making it easier to favorably exert the effects (e.g., easy peeling effect) of curing the photocurable adhesive layer (e.g., ultraviolet irradiation treatment).

The method for obtaining an acrylic polymer (primary polymer) from the monomer components as described above can be selected from various polymerization methods known as a synthesis method for acrylic polymers. From the viewpoint of avoiding the use of organic solvents, it is preferable to adopt a polymerization method other than solution polymerization (e.g., solution polymerization performed using an azo-based polymerization initiator or a peroxide-based polymerization initiator). In some embodiments, the acrylic polymer (primary polymer) can be obtained by curing an active energy ray-curable adhesive composition containing a part of the monomer components constituting the polymer in the form of a polymer and the remaining part in the form of an unpolymerized product (unreacted monomer). For example, the active energy ray-curable adhesive composition is applied to an appropriate surface, and cured by irradiation with active energy rays (e.g., ultraviolet rays), to obtain an adhesive layer (primary adhesive layer) containing an acrylic polymer formed from the monomer components. The acrylic polymer is an active energy ray polymer of the monomer components. In general, the carbon-carbon double bonds (e.g., ethylenically unsaturated bonds) contained in the active energy ray-curable adhesive composition react and disappear when the adhesive composition is cured to form an adhesive layer by irradiation with active energy rays. Therefore, the above method typically results in the formation of an adhesive layer (primary adhesive layer) that does not contain carbon-carbon double bonds.

In some embodiments, a carbon-carbon double bond is introduced into the acrylic polymer (acrylic polymer not containing a carbon-carbon double bond) in the primary adhesive layer, and an appropriate amount of photoinitiator is added as necessary. This imparts photocurability to the primary adhesive layer, and a photocurable adhesive layer (secondary adhesive layer) containing an acrylic polymer having a carbon-carbon double bond and a predetermined amount or more of a photoinitiator can be obtained. The acrylic polymer having a carbon-carbon double bond is an acrylic polymer obtained by introducing a carbon-carbon double bond into the active energy ray polymer of the monomer component by chemical modification, and corresponds to a modified product of the active energy ray polymer. Some suitable examples of methods for obtaining a secondary adhesive layer from a primary adhesive layer will be described later.

In some preferred embodiments, the active energy ray-curable adhesive composition used to form the primary adhesive layer contains a partial polymer of a monomer mixture that contains at least a portion of the monomer components (raw material monomers) that constitute the acrylic polymer. Such a partial polymer is a mixture of a polymer derived from the monomer mixture and an unreacted monomer, and typically has a syrup-like appearance (a viscous liquid). Hereinafter, a partial polymer with such properties may be referred to as "monomer syrup" or simply as "syrup."

The polymerization method for obtaining the above-mentioned polymerization reaction product is not particularly limited, and various known polymerization methods can be appropriately selected and used. From the viewpoint of avoiding the use of organic solvents, it is preferable to adopt a method other than solution polymerization (for example, solution polymerization carried out using an azo-based polymerization initiator or a peroxide-based polymerization initiator). Among them, from the viewpoints of efficiency and simplicity, a photopolymerization method can be preferably adopted. With photopolymerization, the polymerization conversion rate of the above-mentioned monomer mixture can be easily controlled by the polymerization conditions such as the amount of light irradiation (light amount).

The polymerization conversion rate (monomer conversion) of the monomer mixture in the partial polymer is not particularly limited. The polymerization conversion rate can be, for example, about 70% by weight or less, and is preferably about 60% by weight or less. From the viewpoint of ease of preparation and coatability of the adhesive composition containing the partial polymer, the polymerization conversion rate is usually appropriately about 50% by weight or less, and preferably about 40% by weight or less (for example, about 35% by weight or less). The lower limit of the polymerization conversion rate is not particularly limited, but is typically about 1% by weight or more, and usually about 5% by weight or more is appropriate.

The adhesive composition containing the partial polymer of the monomer mixture can be obtained, for example, by partially polymerizing a monomer mixture containing some or all of the monofunctional monomers among the raw material monomers by an appropriate polymerization method (for example, photopolymerization method). The adhesive composition containing the partial polymer may contain other components (for example, a photoinitiator, a polyfunctional monomer as a copolymerizable crosslinking agent, etc.) that are used as needed. There are no particular limitations on the method of blending such other components, and for example, they may be contained in the monomer mixture in advance, or may be added to the partial polymer.

The adhesive composition disclosed herein may be in a form in which a partial polymer or a complete polymer of a monomer mixture containing some types of monomers among the monomer components (raw material monomers) is dissolved in the remaining types of monomers or their partial polymers. Adhesive compositions in such a form are also included in examples of adhesive compositions containing polymerized and unpolymerized monomer components. In this specification, the term "completely polymerized" refers to a polymerization conversion rate of more than 95% by weight.

First Photoinitiator
The active energy ray curable adhesive composition used to form the primary adhesive layer may contain a photoinitiator for the purpose of curing promotion and the like. When light such as ultraviolet light is used as the active energy ray, it is particularly preferable to blend a photoinitiator into the adhesive composition. As the photoinitiator to be contained in the adhesive composition, one or more types selected from the examples of materials that can be used as photoinitiators contained in the adhesive layer (photocurable adhesive layer) of the adhesive sheet disclosed herein can be used. The photoinitiator blended in the adhesive composition functions as a catalyst for advancing the polymerization and crosslinking reaction of the above-mentioned monomer components and crosslinking agents to form an acrylic polymer. Therefore, the photoinitiator is inactivated and decomposed by the active energy ray irradiation (typically ultraviolet irradiation) when forming the adhesive layer (primary adhesive layer) from the adhesive composition, and is not left in the adhesive layer of the adhesive sheet disclosed herein, or if it remains, it is considered to be only a trace amount. On the other hand, the photoinitiator contained in the adhesive layer (photocurable adhesive layer) of the adhesive sheet disclosed herein is contained in the adhesive together with a polymer having a carbon-carbon double bond, and promotes the crosslinking reaction by the carbon-carbon double bond. Hereinafter, a photoinitiator contained in a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer from the pressure-sensitive adhesive composition may be referred to as a "first photoinitiator." Also, a photoinitiator contained in a pressure-sensitive adhesive layer (photocurable pressure-sensitive adhesive layer) of the pressure-sensitive adhesive sheet disclosed herein and used for photocuring the pressure-sensitive adhesive layer may be referred to as a "second photoinitiator." The first photoinitiator and the second photoinitiator may be the same type of material or different materials.

(catalyst)
In some embodiments, the primary adhesive layer may contain a catalyst that promotes the reaction between functional group A and functional group B. For example, examples of catalysts that can be used to promote the addition reaction between an isocyanate group and a hydroxyl group include metal catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric nursem, butyltin oxide, and dioctyltin dilaurate. Examples of catalysts that can be used to promote the addition reaction between a carboxyl group and an epoxy group include quaternary ammonium compounds and derivatives thereof such as tetrabutylammonium bromide (TBAB) and tetrabenzylammonium bromide; phosphorus compounds and derivatives thereof such as triphenylphosphine (TPP); amine compounds and derivatives thereof such as benzyldimethylamine; imidazole compounds and derivatives thereof such as 2-ethyl-4-methyl-imidazole; and the like. The amount of the catalyst used is not particularly limited, and can be set so as to appropriately promote the reaction between functional group A and functional group B. In some embodiments, the amount of the catalyst used may be, for example, about 0.05 to 15 g, alternatively about 0.1 to 10 g, or alternatively about 0.5 to 5 g per 100 g of the primary pressure-sensitive adhesive layer.

The catalyst can be easily included in the adhesive composition (e.g., active energy ray curable adhesive composition) for forming the primary adhesive layer. For example, an ethylenically unsaturated compound having functional group B is impregnated into a primary adhesive layer containing a primary polymer (preferably an acrylic polymer) having functional group A and the catalyst, and then the functional group A and the functional group B are reacted in the presence of the catalyst to efficiently obtain a polymer having a carbon-carbon double bond (a modified product obtained by chemical modification of the primary polymer). As another method for carrying out the reaction between the functional group A and the functional group B in the presence of the catalyst, for example, the catalyst can be included in the post-coating liquid described below. The method of including the catalyst in the adhesive composition used for forming the primary adhesive layer is preferable from the viewpoint of controllability of the reaction between the functional group A and the functional group B.

Second Photoinitiator
The adhesive layer (photocurable adhesive layer) constituting the adhesive sheet disclosed herein preferably contains a photoinitiator. By including a photoinitiator, radicals are generated from the photoinitiator during the curing process, and the photocuring of the adhesive layer proceeds quickly. Examples of photoinitiators include ketal-based photoinitiators, acetophenone-based photoinitiators, benzoin ether-based photoinitiators, acylphosphine oxide-based photoinitiators, α-ketol-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzoin-based photoinitiators, benzyl-based photoinitiators, benzophenone-based photoinitiators, and thioxanthone-based photoinitiators. The photoinitiators can be used alone or in appropriate combination of two or more.

Specific examples of ketal-based photoinitiators include 2,2-dimethoxy-1,2-diphenylethan-1-one (for example, trade name "Omnirad 651", manufactured by IGM Resins BV).
Specific examples of acetophenone-based photoinitiators include 1-hydroxycyclohexyl-phenyl-ketone (e.g., trade name "Omnirad 184", manufactured by IGM Resins B.V.), 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, methoxyacetophenone, etc. Specific examples of benzoin ether-based photoinitiators include benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, and benzoin isobutyl ether, and substituted benzoin ethers such as anisole methyl ether. Specific examples of acylphosphine oxide photoinitiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like. Specific examples of α-ketol photoinitiators include 2-methyl-2-hydroxypropiophenone, 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one, and the like. Specific examples of aromatic sulfonyl chloride photoinitiators include 2-naphthalenesulfonyl chloride, and the like. Specific examples of photoactive oxime photoinitiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime, and the like. Specific examples of benzoin photoinitiators include benzoin, and the like. Specific examples of benzyl photoinitiators include benzyl, etc. Specific examples of benzophenone photoinitiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexyl phenyl ketone, etc. Specific examples of thioxanthone photoinitiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, etc.

The content of the photoinitiator in the photocurable adhesive layer disclosed herein is suitably 1.0×10 ⁻⁴ mol/100g or more (i.e., 1.0×10 ⁻⁴ mol or more per 100g of adhesive layer), and from the viewpoint of accurately progressing the curing reaction, it is advantageous to have it be 3.0×10 ⁻⁴ mol/100g or more, preferably 5.0×10 ⁻⁴ mol/100g or more, and may be 7.0×10 ⁻⁴ mol/100g or more, 1.0×10 ⁻³ mol/100g or more, 2.0×10 ⁻³ mol/100g or more, or 3.0×10 ⁻³ mol/100g or more. There is no particular upper limit to the content of the photoinitiator. In some embodiments, from the viewpoint of the storage stability of the pressure-sensitive adhesive sheet, it may be, for example, 1.0×10 ⁻¹ mol/100 g or less, 5.0×10 ⁻² mol/100 g or less, 1.0×10 ⁻² mol/100 g or less, or 5.0×10 ⁻³ mol/100 g or less.

The content of the photoinitiator in the photocurable adhesive layer can be calculated based on the total parts by weight of the materials used as the raw materials for producing the adhesive layer, the parts by weight of the photoinitiator used so as to remain in the obtained adhesive layer, and the molecular weight of the photoinitiator. For example, in a photocurable adhesive layer obtained by post-coating and penetrating an additional photoinitiator into a primary adhesive layer formed using an adhesive composition containing a photoinitiator, at least the photoinitiator supplied by post-coating can be said to be a photoinitiator used so as to remain in the obtained photocurable adhesive layer, unless a treatment (such as ultraviolet irradiation treatment) is subsequently performed to actively promote the decomposition of the photoinitiator. Therefore, the content of the photoinitiator in the photocurable adhesive layer can be considered to be equal to or greater than the content calculated based on the photoinitiator supplied by post-coating. In a photocurable adhesive layer obtained by post-coating and penetrating a photoinitiator into a primary adhesive layer obtained by irradiating a photoinitiator-containing adhesive composition with light to cure (primary curing), the content of the photoinitiator in the photocurable adhesive layer can be considered to be roughly the same as the content calculated based on the photoinitiator supplied by post-coating.

If this information is unknown, the value obtained from analysis based on HPLC (high performance liquid chromatography) can be used as the content of the photoinitiator in the photocurable adhesive layer. The photoinitiator is identified by component analysis of the eluate corresponding to the photoinitiator peak among the peaks appearing in the chromatogram, and the content of the photoinitiator in the measurement sample can be determined by creating a calibration curve using the identified substance or a compound with a similar molecular structure as a standard. The content of the photoinitiator in the adhesive layer [mol/100 g] can be calculated based on the content and the molecular weight of the photoinitiator.

The measurement sample for HPLC can be prepared as follows. That is, an appropriate amount (for example, about 0.1 g) of adhesive is collected from the adhesive layer, put into a screw tube, and weighed. 3 mL of chloroform is added to the screw tube, and the sample is shaken overnight (about 16 hours) in a cool, dark place to dissolve the photoinitiator in the chloroform. Then, 10 mL of acetonitrile is added to reprecipitate the adhesive component, and the supernatant in which the photoinitiator is dissolved is filtered through a membrane filter (pore size 0.20 μm). This is used as the measurement sample for HPLC. As an analytical device, Thermo Fisher Scientific's "UltiMate 3000" or an equivalent product may be used. As the measurement conditions, the following conditions may be adopted.
[Measurement condition]
Column: ZORBAX Eclipse Plus C18 (3.0 mmφ×100 mm, average particle size of carrier: 1.8 μm)
Column temperature: 40°C
Column flow rate: 0.5 mL/min
Eluent composition: pure water/acetonitrile gradient condition Injection volume: 10 μL
Detector: DAD (190 nm to 800 nm, 210 nm and 245 nm extraction)

(Other polymers)
When the photocurable pressure-sensitive adhesive layer disclosed herein contains an acrylic polymer having a carbon-carbon double bond, the photocurable pressure-sensitive adhesive layer may contain other polymers in addition to the acrylic polymer having a carbon-carbon double bond. The other polymer may be an acrylic polymer having no carbon-carbon double bond, or may be a polymer other than an acrylic polymer. As the polymer other than the acrylic polymer, a polymer other than an acrylic polymer among the various polymers exemplified as the polymer that may be contained in the pressure-sensitive adhesive layer is preferably one other than an acrylic polymer. Such a polymer may be a polymer having a carbon-carbon double bond. As the acrylic polymer having no carbon-carbon double bond, a preferred example is an acrylic polymer as the primary polymer described above (i.e., an acrylic polymer that has not been chemically modified to introduce a carbon-carbon double bond). When the pressure-sensitive adhesive layer disclosed herein contains the other polymer in addition to the acrylic polymer having a carbon-carbon double bond, the content of the other polymer is suitably 100 parts by weight or less, preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 10 parts by weight or less, relative to 100 parts by weight of the acrylic polymer having a carbon-carbon double bond. The content of the other polymer may be 5 parts by weight or less, or may be 1 part by weight or less, relative to 100 parts by weight of the acrylic polymer having a carbon-carbon double bond. The technology disclosed herein can be preferably carried out in an embodiment in which, for example, 99.5 to 100% by weight of the polymer contained in the pressure-sensitive adhesive layer is an acrylic polymer having a carbon-carbon double bond.

(Compounds containing carbon-carbon double bonds other than polymers)
The photocurable pressure-sensitive adhesive layer disclosed herein may contain a carbon-carbon double bond-containing compound other than the carbon-carbon double bond-containing polymer. Examples of such a carbon-carbon double bond-containing compound include a polyfunctional monomer, a monofunctional monomer, a polyfunctional or polyfunctional oligomer having a carbon-carbon double bond, and the like. The photocurable pressure-sensitive adhesive layer containing the carbon-carbon double bond-containing compound means that the carbon-carbon double bond of the carbon-carbon double bond-containing compound is contained in an unreacted form.

In some embodiments, the photocurable adhesive layer may contain a polyfunctional monomer as the carbon-carbon double bond-containing compound. The polyfunctional monomer contained in the photocurable adhesive layer may be one or more selected from the same polyfunctional monomers (copolymerizable crosslinking agents) that can be used as copolymerization components of the primary polymer. When the photocurable adhesive layer contains a polyfunctional monomer, the photocurable adhesive layer preferably contains a polymer having a carbon-carbon bond (preferably an acrylic polymer having a carbon-carbon bond) in combination with the polyfunctional monomer. The polyfunctional monomer contained in the photocurable adhesive layer may be useful for improving the flexibility of the photocurable adhesive layer and improving the elastic modulus after curing treatment. For example, a method of containing a polyfunctional monomer in the photocurable adhesive layer may be a method of coating a polyfunctional monomer on a primary adhesive layer (which may be a primary adhesive layer formed by irradiating an active energy ray-curable adhesive composition with active energy rays) and allowing it to penetrate.

In the photocurable adhesive layer disclosed herein, the content of the carbon-carbon double bond-containing compound (e.g., polyfunctional monomer) other than the carbon-carbon double bond-containing polymer can be set so as to appropriately exhibit the desired effect of use. For example, it can be 0.01 parts by weight or more, or 0.1 parts by weight or more, or 0.5 parts by weight or more, per 100 parts by weight of the base polymer (e.g., an acrylic polymer having a carbon-carbon bond) of the photocurable adhesive layer. In addition, from the viewpoint of the cohesiveness of the photocurable adhesive layer and the peelability from the release liner, in some embodiments, the content of the carbon-carbon double bond-containing compound is appropriately 10 parts by weight or less, preferably 5 parts by weight or less, or may be 1 part by weight or less, or may be less than 1 part by weight, per 100 parts by weight of the base polymer of the photocurable adhesive layer. The technology disclosed herein can be preferably implemented in an embodiment in which the photocurable adhesive layer does not contain any carbon-carbon double bond-containing compound other than the carbon-carbon double bond-containing polymer.

(Other optional ingredients)
The adhesive layer disclosed herein may contain, as necessary, various additives commonly used in the field of adhesives as other optional components, such as leveling agents, crosslinking assistants, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, UV absorbers, light stabilizers, etc. As for these various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed explanations are omitted.

In some preferred embodiments, the adhesive layer disclosed herein may have a composition in which the content of the polymer (typically the base polymer) is about 90% by weight or more of the total weight of the adhesive (solid content of the adhesive composition) (i.e., the weight of the adhesive layer composed of this adhesive). This can preferably achieve easy peeling of the adhesive layer by the curing treatment. From this viewpoint, the content of the polymer is preferably about 95% by weight or more of the total weight of the adhesive layer, more preferably about 97% by weight or more, even more preferably about 98% by weight or more, and may be about 99% by weight or more (e.g., 99 to 100% by weight). In other words, the content of components other than the polymer (additives, etc.) in the solid content (adhesive layer) of the adhesive composition is suitably about 10% by weight or less, preferably about 5% by weight or less, more preferably about 3% by weight or less, even more preferably about 2% by weight or less, and may be about 1% by weight or less.

The amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer disclosed herein may be, for example, 1.0×10 ⁻⁶ mol/100 g or more, or may be 1.0×10 ⁻⁵ mol/100 g or more. In some embodiments, from the viewpoint of facilitating changes in characteristics and physical properties due to light irradiation, the amount of the carbon-carbon double bonds is suitably 5.0×10 ⁻⁵ mol/100g or more, advantageously 1.0×10 ⁻⁴ mol/100g or more, preferably 5.0×10 ⁻⁴ mol/100g or more or 1.0×10 ⁻³ mol/100g or more, may be 5.0×10 ⁻³ mol/100g or more, may be 1.0×10 ⁻² mol/100g or more, may be 3.0×10 ⁻² mol/100g or more, may be 4.0×10 ⁻² mol/100g or more, or may be 5.0×10 ⁻² mol/100g or more. The amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer may be, for example, 1.0 mol/100g or less, 5.0×10 ⁻¹ mol/100g or less, 1.0×10 ⁻¹ mol/100g or less, 8.0×10 ⁻² mol/100g or less, or 7.0×10 ⁻² mol/100g or less. Not having too much carbon-carbon double bond content can be advantageous from the viewpoint of storage stability of the pressure-sensitive adhesive layer or the pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer, and from the viewpoint of ease of balancing with other properties. In this specification, the unit "mol/100g" of the amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer means the molar amount of carbon-carbon double bonds per 100g of the pressure-sensitive adhesive layer.

The carbon-carbon double bond contained in the pressure-sensitive adhesive layer disclosed herein may be in the form of a polymer having a carbon-carbon double bond, or may be in the form of a polymer other than a carbon-carbon double bond (e.g., a polyfunctional monomer, a monofunctional monomer, an oligomer, etc. having a carbon-carbon double bond). At least a part of the carbon-carbon double bonds contained in the pressure-sensitive adhesive layer is preferably in the form of a polymer having a carbon-carbon double bond. In some embodiments, the amount of carbon-carbon double bonds contained in the pressure-sensitive adhesive layer in the form of a polymer having carbon-carbon double bonds may be, for example, 1.0×10 ⁻⁶ mol/100g or 1.0×10 ⁻⁵ mol/100g or more, and from the viewpoint of easily obtaining changes in characteristics and physical properties due to light irradiation, it is appropriate that it is 5.0×10 ⁻⁵ mol/100g or more, advantageously 1.0×10 ⁻⁴ mol/100g or more, preferably 5.0×10 ⁻⁴ mol/100g or more or 1.0×10 ⁻³ mol/100g or more, may be 5.0×10 ⁻³ mol/100g or more, may be 1.0×10 ⁻² mol/100g or more, may be 3.0×10 ⁻² mol/100g or more, may be 4.0×10 ⁻² mol/100g or more, and may be 5.0×10 ^-2 mol/100g or more, and may be, for example, 1.0 mol/100g or less, 5.0×10 ^-1 mol/100g or less, 1.0×10 ^-1 mol/100g or less, 8.0×10 ^-2 mol/100g or less, or 7.0×10 ^-2 mol/100g or less.

The amount of carbon-carbon double bonds (typically, ethylenically unsaturated groups) contained in the pressure-sensitive adhesive layer can be determined by calculation based on the total parts by weight of materials used as raw materials for producing the pressure-sensitive adhesive layer, and the parts by weight and molecular weight of materials used so that carbon-carbon double bonds remain in the pressure-sensitive adhesive layer.
When these pieces of information are unknown, a measured value based on the NMR method can be used as the content of carbon-carbon double bonds in the adhesive layer. Specifically, an appropriate amount of sample is taken from the adhesive layer, and the sample is dissolved in a measurement solvent to which a predetermined amount of an internal standard substance has been added, and then the amount of carbon-carbon double bonds present can be determined. As an analytical device, a Fourier transform NMR device ("AVANCE III-600" manufactured by Bruker Biospin) or an equivalent device can be used. As the measurement conditions, the following conditions can be adopted.
[Measurement condition]
Observation frequency: ^1H 600MHz
Measurement solvent: _CDCl3
Measurement temperature: 300K
Chemical shift reference: measurement solvent ¹ H; 7.25 ppm

In some embodiments of the adhesive layer disclosed herein, the adhesive layer preferably has an organic solvent content of 1.0 μg/g or less (i.e., the organic solvent content per gram of the adhesive layer is 1.0 μg or less), for example, preferably less than 1.0 μg/g, more preferably less than 0.5 μg/g, may be less than 0.2 μg/g, or may be 0 μg/g. Specific examples of the organic solvent include ethyl acetate and toluene. An adhesive layer with a low organic solvent content has a low odor and is desirable from the viewpoint of environmental hygiene. The organic solvent content of the adhesive layer is measured by the method described in the Examples below.

The adhesive layer disclosed herein is preferably limited to a total content of azo-based polymerization initiators and peroxide-based polymerization initiators (which may be polymerization initiators contained in the form of decomposition products or residues) of 1.0 μg/g or less. That is, the total content of azo-based polymerization initiators and peroxide-based polymerization initiators per gram of the adhesive layer is 1.0 μg or less. This makes it possible to prevent or suppress adverse effects caused by the polymerization initiators. Examples of the adverse effects include unintentional changes in the physical properties of the adhesive (e.g., hardening) caused by the azo-based polymerization initiator or peroxide-based polymerization initiator, which are thermal polymerization initiators, being cleaved by heat or over time to generate radicals, causing alteration (e.g., oxidation accompanying the cleavage of the peroxide-based polymerization initiator) or contamination (e.g., contamination by low molecular weight decomposition products or reactants) on the surface of the adherend to which the adhesive sheet is attached, and generation of outgas (e.g., _N2 gas due to decomposition of the azo-based polymerization initiator). From the viewpoint of better suppressing such adverse effects, in some embodiments, the pressure-sensitive adhesive layer preferably has a total content of azo-based polymerization initiator and peroxide-based polymerization initiator of less than 1.0 μg/g, more preferably less than 0.5 μg/g, and may be less than 0.2 μg/g or may be 0 μg/g (i.e., none). The total content of azo-based and peroxide-based polymerization initiators in the pressure-sensitive adhesive layer is measured by the method in the Examples described below.

(Thickness of adhesive layer)
The thickness of the adhesive layer (photocurable adhesive layer) of the adhesive sheet disclosed herein is not particularly limited and can be appropriately selected according to the purpose. The thickness of the adhesive layer can be selected, for example, from a range of 2 μm or more to about 2000 μm. In some embodiments, from the viewpoint of thinning the adhesive sheet, the thickness of the adhesive layer may be, for example, 1000 μm or less, 500 μm or less, 200 μm or less, 150 μm or less, or 100 μm or less. From the viewpoint of reducing the peel strength after light irradiation, in some embodiments, the thickness of the adhesive layer may be, for example, less than 100 μm, 80 μm or less, 60 μm or less, 40 μm or less, or 30 μm or less. When the thickness of the photocurable adhesive layer is not too large, the effect of easy peeling by light irradiation of the adhesive layer tends to be easily obtained. For example, when forming a photocurable adhesive layer by a method including forming a primary adhesive layer having a functional group A, applying a post-coating liquid containing an ethylenically unsaturated compound having a functional group B to the primary adhesive layer and allowing it to penetrate, and then reacting the functional group A in the primary adhesive layer with the ethylenically unsaturated compound having the functional group B, the thickness of the photocurable adhesive layer is advantageous from the viewpoint of uniformly proceeding the reaction between the functional group A and the functional group B throughout the entire thickness of the adhesive layer. In addition, the thickness of the adhesive layer is preferably 10 μm or more, more preferably 15 μm or more, and may be 20 μm or more, from the viewpoint of adhesion to the adherend before the curing treatment, etc. When the adhesive sheet disclosed herein is a double-sided adhesive sheet having adhesive layers on both sides of a substrate, the thicknesses of the adhesive layers may be the same or different.

<Preparation of Adhesive Layer>
The pressure-sensitive adhesive layer disclosed herein can be suitably produced, for example, by a method including the following steps.
(a) forming a primary pressure-sensitive adhesive layer containing a primary polymer having a functional group A (primary pressure-sensitive adhesive layer forming step);
(b) preparing a post-coating liquid containing a functional group B-containing compound having a carbon-carbon double bond (e.g., an ethylenically unsaturated compound having a functional group B) and a photoinitiator, and then applying the coating liquid to at least one surface of the primary pressure-sensitive adhesive layer (post-coating liquid application step);
(c) allowing the compound containing functional group B having a carbon-carbon double bond and the photoinitiator contained in the post-coating liquid to penetrate into the primary pressure-sensitive adhesive layer (post-coating liquid penetration step);
(d) The primary pressure-sensitive adhesive layer permeated with the post-coating liquid is heated to promote the reaction between the functional group A and the functional group B (reaction step).

The primary adhesive layer forming step may include applying an adhesive composition for forming the primary adhesive layer onto a support, and curing the applied adhesive composition to form a primary adhesive layer containing a primary polymer having a functional group A. As the support, a plastic film that can be used as a base layer described below, or a release liner described below may be used. A known coating method may be used to apply (coat) the adhesive composition, and for example, a coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater may be used.

In the primary adhesive layer forming step, the method of curing the applied adhesive composition is not particularly limited, but examples thereof include heating the applied adhesive composition and curing the adhesive composition by irradiating it with active energy rays. If necessary, the adhesive composition may be further dried by heating. In some embodiments, a method of using an active energy ray curable adhesive composition (preferably an organic solvent-free active energy ray curable adhesive composition) as the adhesive composition and curing the composition by irradiating it with active energy rays can be preferably adopted. Examples of active energy rays include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, and ultraviolet rays, and ultraviolet rays are particularly preferred.

The applied adhesive composition may be irradiated directly with ultraviolet light, but it is preferable to irradiate it through a support (which may be a release film) in order to block oxygen, which inhibits curing by ultraviolet light irradiation. For example, the surface of the adhesive composition applied to the support is covered with another support, and ultraviolet light is irradiated through the other support. The illuminance and time of ultraviolet light irradiation are appropriately set depending on the composition of the primary adhesive layer, the thickness of the adhesive layer, etc. High-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, etc. can be used for ultraviolet light irradiation.

Next, the support is peeled off from one side of the primary adhesive layer, a post-coating liquid containing a functional group B-containing compound having a carbon-carbon double bond and a photoinitiator (second photopolymerization initiator) is prepared, and the post-coating liquid is applied to one side of the primary adhesive layer (post-coating liquid application process). The post-coating liquid is not particularly limited as long as it is liquid and can be applied to and penetrates the adhesive layer. For example, when the functional group B-containing compound having a carbon-carbon double bond and/or the photoinitiator are liquid, they may be applied individually in any order, or a mixture of the functional group B-containing compound having a carbon-carbon double bond and the photoinitiator may be used. The post-coating liquid may also be a liquid in which the photoinitiator is dissolved in the functional group B-containing compound having a carbon-carbon double bond, or vice versa.

When the post-coating liquid is applied to the surface of the primary adhesive layer, the components contained in the post-coating liquid permeate into the adhesive layer. After the post-coating liquid is applied to the primary adhesive layer, a time for leaving the liquid to stand may be provided before proceeding to the next reaction step, as necessary, to allow the above-mentioned permeation to proceed sufficiently. The time for leaving the liquid to stand is not particularly limited, and can be appropriately selected, for example, from within 15 minutes, and in some embodiments, can be selected from the range of 1 second to 10 minutes (e.g., 10 seconds to 10 minutes), preferably 5 seconds to 5 minutes (e.g., 10 seconds to 5 minutes). The temperature for leaving the liquid to stand can be approximately at room temperature (e.g., about 10 to 30°C). By leaving the liquid to stand under the above conditions, the post-coating liquid can be allowed to fully permeate into the primary adhesive layer.

Then, the primary adhesive layer permeated with the post-coating liquid is heated to allow the reaction between the functional group A and the functional group B to proceed (reaction step). The heating temperature in the reaction step is preferably 40 to 200°C, more preferably 50 to 180°C, and even more preferably 60 to 170°C (e.g., 100 to 150°C). The heating time can be appropriately set to an appropriate time, for example, 5 seconds to 20 minutes, preferably 5 seconds to 10 minutes, and more preferably 10 seconds to 5 minutes.

<Base layer>
In a single-sided or double-sided adhesive substrate-attached adhesive sheet, various sheet-like substrates can be used as the substrate (layer) that supports (backs) the adhesive layer. The substrate can be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or a composite of these. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyamide resin films; fluororesin films; cellophane; and the like. Other examples of resin films include resin films formed from one or more engineering plastics (which may be super engineering plastics) such as polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, and polyimide resins. The use of engineering plastics is preferred from the viewpoint of heat resistance. Examples of paper include Japanese paper, craft paper, glassine paper, fine paper, synthetic paper, topcoated paper, etc. Examples of cloth include woven fabrics and nonwoven fabrics made of various fibrous materials, either alone or in combination. Examples of the fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, etc. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

In a preferred embodiment, a resin film having a predetermined rigidity (strength) and excellent processability and handling properties is used as the substrate (layer). By using a resin film substrate with high rigidity, when the adherend is thin, it is possible to suitably prevent the adherend from being bent or damaged during transportation. From the same viewpoint, it is preferable to use a polyester film as the resin film substrate. In this specification, the term "resin film" refers to a typically non-porous film, and is a concept that is distinguished from so-called nonwoven fabrics and woven fabrics. The density of the resin film that can be used as the substrate can be about 0.85 to 1.50 g/cm ³ (for example, 0.90 g/cm ³ to 1.20 g/cm ³ , typically 0.92 g/cm ³ to 1.05 g/cm ³ ).

In addition, the above-mentioned substrate (e.g., resin film substrate) may contain various additives such as fillers (inorganic fillers, organic fillers, etc.), anti-aging agents, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, colorants (pigments, dyes, etc.), etc., as necessary.

The surface of the above-mentioned substrate layer (e.g., a resin film substrate, a rubber sheet substrate, a foam sheet substrate, etc.) on which the adhesive layer is disposed (the surface on the side of the adhesive layer) may be subjected to a known or conventional surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, or application of a primer. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the substrate.

In some preferred embodiments, an undercoat layer is provided on the adhesive layer side surface of the substrate layer. In other words, an undercoat layer may be disposed between the substrate layer and the adhesive layer. The undercoat layer forming material is not particularly limited, and one or more of urethane (polyisocyanate) resins, polyester resins, acrylic resins, polyamide resins, melamine resins, olefin resins, polystyrene resins, epoxy resins, phenol resins, isocyanurate resins, polyvinyl acetate resins, etc. may be used. When an acrylic adhesive layer is provided on a resin film substrate, a polyester, urethane, or acrylic undercoat layer is preferred, and when an acrylic adhesive layer is provided on a polyester substrate layer such as a PET film, a polyester undercoat layer is particularly preferred. The thickness of the undercoat layer is not particularly limited, and may usually be in the range of about 0.1 μm to 10 μm (for example, 0.1 μm to 3 μm, typically 0.1 μm to 1 μm). The undercoat layer can be formed using a known or conventional coater such as a gravure roll coater or a reverse roll coater.

In addition, when the adhesive sheet disclosed herein is a one-sided adhesive sheet in which an adhesive layer is provided on one side of a base layer, the surface of the base layer on which the adhesive layer is not formed (back surface) may be subjected to a release treatment using a release treatment agent (back surface treatment agent). There are no particular limitations on the back surface treatment agent that can be used to form the back surface treatment layer, and silicone-based back surface treatment agents, fluorine-based back surface treatment agents, long-chain alkyl-based back surface treatment agents, and other known or commonly used treatment agents can be used depending on the purpose and application.

The thickness of the base layer is not particularly limited and can be selected appropriately depending on the purpose, but can generally be 1 to 800 μm. From the viewpoints of processability, handling, workability, etc., the thickness of the base layer is suitably 2 μm or more (e.g. 3 μm or more, typically 5 μm or more), preferably approximately 10 μm or more, more preferably approximately 25 μm or more (e.g. 30 μm or more), and is suitably approximately 700 μm or less (e.g. 500 μm or less, typically 200 μm or less), preferably approximately 100 μm or less, more preferably approximately 80 μm or less (e.g. approximately 70 μm or less).

<Release Liner>
The release liner can be any conventional release paper, and is not particularly limited. For example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.) can be used. The release treatment layer can be formed by surface-treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

The total thickness of the adhesive sheet disclosed herein (which may include an adhesive layer and a base layer, but does not include a release liner) is not particularly limited, and is suitably in the range of approximately 5 to 1000 μm. Taking into consideration the adhesive properties, etc., it is preferable that the total thickness of the adhesive sheet is approximately 10 to 500 μm (e.g., 15 to 300 μm, typically 20 to 200 μm). Furthermore, from the standpoint of handleability, etc., it is more preferable that the total thickness of the adhesive sheet is 30 μm or more (e.g., 50 μm or more, typically 70 μm or more).

<Applications>
The use of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and it can be preferably used in applications in which it is attached to an adherend and then peeled off, taking advantage of its ability to highly prevent adhesive residue when separated from the adherend after curing treatment. Such applications include temporary fixing sheets and protective sheets. In addition, it can be preferably used as a process material that is fixed to an adherend and peeled off in the manufacturing process of electronic devices and electronic parts.

A suitable application of the adhesive sheet disclosed herein is the manufacturing of semiconductor elements. For example, it can be preferably used as a wafer fixing sheet (typically a sheet for laser dicing) for fixing the wafer to a fixing plate (e.g. a hard substrate such as a glass plate or an acrylic plate) in semiconductor wafer processing (typically silicon wafer processing). The adhesive sheet disclosed herein can also be preferably used as a protective sheet for protecting the wafer (e.g. the circuit formation surface) in the above wafer processing. The above sheet is required to have a moderate adhesion so that it does not peel off from the adherend (typically a semiconductor element or a hard substrate) during processing or transportation in the above manufacturing, and to have the property of being easily peeled off from the adherend after the purpose is achieved. The adhesive sheet disclosed herein can be preferably used as one that satisfies the performance required for the above applications.

Furthermore, for example, a suitable application of the adhesive sheet disclosed herein may be to fix multiple miniaturized semiconductor chips (such as LED chips) on the adhesive surface of a single adhesive sheet, process the semiconductor chips on the adhesive sheet by sealing them with resin, and separate the semiconductor chips from the adhesive sheet after processing is completed. The adhesive sheet disclosed herein satisfactorily fixes the semiconductor chips during the above processing, and can be easily peeled off by light irradiation when peeling off from the adherend (semiconductor chip). Such an adhesive sheet can prevent damage to the adherend surface during peeling. The adhesive sheet is suitable as an adhesive sheet for use in FOWLP (Fan Out Wafer Level Package) and CSP (Chip Scale Package), and by using it for the above applications, it can contribute to increasing the capacity and performance of various semiconductor products.

As described above, the adhesive sheet disclosed herein is preferably applied to the manufacturing of semiconductor elements. Therefore, according to this specification, a method for manufacturing a semiconductor element using the adhesive sheet disclosed herein is provided. In a preferred embodiment, this manufacturing method includes a step of fixing a semiconductor to the adhesive sheet (fixing step); and a step of processing the semiconductor (processing step). The processing step can be, for example, a backgrinding step, a dicing step, a resin sealing step for semiconductor chips, etc.

The above manufacturing method may also include a step (removal step, typically a peeling step) of separating the adhesive sheet from the semiconductor (typically a semiconductor chip) after the processing step. The separation may be performed by attaching a transfer tape to the surface of the semiconductor (the surface opposite to the adhesive sheet adhesive surface). In the above manufacturing method, typically, after the processing step and before the separation step, a curing treatment is performed on the adhesive sheet. The curing treatment may preferably be an active energy ray (e.g., UV) irradiation step. Note that other technical matters necessary for the manufacture of semiconductor elements will not be described here in particular, as they can be performed by a person skilled in the art based on technical common sense in the field.

The adhesive sheet disclosed herein is also suitable as a temporary fixing sheet used in the manufacture of thin substrates such as circuit boards (e.g., printed circuit boards (PCBs) and flexible circuit boards (FPCs)), organic EL panels, color filters, electronic paper, and flexible displays. For example, in fixing chips on a PCB, the adhesive sheet disclosed herein can be used to firmly adhere and fix the adherend, and a curing treatment can be performed at the desired timing, thereby allowing the adhesive sheet to be satisfactorily separated from the adherend while preventing adhesive residue to a high degree. Furthermore, the adhesive sheet disclosed herein can be preferably used as a support tape for a thin wafer. In this application, for example, in printing solder paste on a thin wafer, the adhesive sheet disclosed herein can be attached to the thin wafer as an adherend and used as a support tape, and then a curing treatment can be performed at an appropriate timing, allowing the adhesive sheet to be satisfactorily separated from the adherend while preventing adhesive residue to a high degree when separated from the adherend.

As described above, the adhesive sheet disclosed herein is preferably applied to the manufacture of thin substrates such as circuit boards (typically PCBs). Thus, this specification provides a method for manufacturing a thin substrate (e.g., a circuit board, an organic EL panel, a color filter, electronic paper, a flexible display) using the adhesive sheet. In a preferred embodiment, this manufacturing method includes a step of fixing a thin substrate (typically the back surface of the substrate) to the adhesive sheet (fixing step); and a step of processing the thin substrate.

The processing steps according to some embodiments include a die bonding step and a wire bonding step, and may further include a molding step and a package dicing step. The die bonding step is typically a step of arranging multiple chips on a thin substrate such as a PCB, the wire bonding step is a step of joining wires to the chips, and the molding step may be, for example, a step of sealing the chips on the PCB with a resin such as an epoxy resin. The manufacturing method may also include a step of separating the adhesive sheet from the thin substrate after the processing step (a removal step, typically a peeling step). The manufacturing method typically includes a curing process for the adhesive sheet after the processing step and before the separation step. The curing process may preferably be an active energy ray (e.g., UV) irradiation step. Note that other technical matters necessary for manufacturing a thin substrate such as a PCB will not be described here, since they can be implemented by a person skilled in the art based on the technical common sense of the field.

A method for manufacturing a circuit board (typically a flexible printed circuit (FPC)) according to some other embodiments includes the steps of: laminating the adhesive sheet disclosed herein as a support tape to the rear surface of a fixing tape to which a thin wafer is fixed; and processing the thin wafer. The manufacturing method may include a step of separating the adhesive sheet and the fixing tape after the processing step (a removal step, typically a peeling step). In the manufacturing method, typically, a curing process is performed on the adhesive sheet after the processing step and before the separation step. The curing process may preferably be an active energy ray (e.g., UV) irradiation step. Note that other technical matters necessary for manufacturing a thin substrate such as an FPC will not be described here in detail, as they can be implemented by a person skilled in the art based on the technical common sense in the field.

The matters disclosed in this specification include the following.
[1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is cured by light irradiation,
the pressure-sensitive adhesive layer has a total content of an azo-based polymerization initiator and a peroxide-based polymerization initiator of 1.0 μg/g or less;
The initial storage modulus G' measured using a measurement sample made of the pressure-sensitive adhesive layer is less than 1.0 x 10 ⁶ Pa, and
The pressure-sensitive adhesive sheet has a post-curing storage modulus G' of 1.0 x ¹⁰⁶ Pa or more, measured after the measurement sample is subjected to a curing treatment of irradiating it with ultraviolet light.
[2] The pressure-sensitive adhesive sheet according to [1] above, wherein the pressure-sensitive adhesive layer contains a polymer having a carbon-carbon double bond.
[3] The pressure-sensitive adhesive sheet according to the above-mentioned [2], wherein the polymer having a carbon-carbon double bond is crosslinked with a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule.
[4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of carbon-carbon double bonds.
[5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of a photoinitiator.
[6] The pressure-sensitive adhesive sheet according to any one of the above [1] to [5], wherein an increase in storage modulus calculated by the following formula is 300% or more.
Storage modulus increase rate [%] = (R / Q - 1) x 100
(Q in the formula is the initial storage modulus G′ [Pa], and R in the formula is the storage modulus G′ [Pa] after the curing treatment.)
[7] The pressure-sensitive adhesive layer has a gel fraction of 70% or more measured after a curing treatment in which the pressure-sensitive adhesive layer is irradiated with ultraviolet light having an integrated light quantity of 300 mJ/ ^cm2 . The pressure-sensitive adhesive sheet according to any one of [1] to [6].
[8] The pressure-sensitive adhesive sheet according to any one of [1] to [7] above, wherein the pressure-sensitive adhesive layer has an organic solvent content of 1.0 μg/g or less.

Furthermore, the pressure-sensitive adhesive sheet disclosed in this specification includes an embodiment in which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet has no limit on the total content of the azo-based polymerization initiator and the peroxide-based polymerization initiator, and in such an embodiment, the total content is not important. For example, the following matters are also included in the matters disclosed in this specification.
[9] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is cured by light irradiation,
The pressure-sensitive adhesive layer is formed under the following conditions:
(A) the total content of the azo polymerization initiator and the peroxide polymerization initiator is 1.0 μg/g or less;
(B) the content of organic solvent is 1.0 μg/g or less;
(C) a photocured product of a photocurable pressure-sensitive adhesive composition or a modified product thereof; and
(D) containing a polymer that is a photopolymer or a modified product thereof as a base polymer;
At least one of the following conditions is satisfied:
The initial storage modulus G' measured using a measurement sample made of the pressure-sensitive adhesive layer is less than 1.0 x 10 ⁶ Pa, and
The pressure-sensitive adhesive sheet has a post-curing storage modulus G' of 1.0 x ¹⁰⁶ Pa or more, as measured after the measurement sample is subjected to a curing treatment of irradiating it with ultraviolet light.
[10] The pressure-sensitive adhesive sheet according to [9] above, wherein the pressure-sensitive adhesive layer contains a polymer having a carbon-carbon double bond.
[11] The pressure-sensitive adhesive sheet according to the above-mentioned [10], wherein the polymer having a carbon-carbon double bond is crosslinked with a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule.
[12] The pressure-sensitive adhesive sheet according to any one of [9] to [11] above, wherein the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of carbon-carbon double bonds.
[13] The pressure-sensitive adhesive sheet according to any one of [9] to [12] above, wherein the pressure-sensitive adhesive layer contains 1.0×10 ⁻⁴ mol/100 g or more of a photoinitiator.
[14] The pressure-sensitive adhesive sheet according to any one of the above [9] to [13], wherein an increase in storage modulus calculated by the following formula is 300% or more.
Storage modulus increase rate [%] = (R / Q - 1) x 100
(Q in the formula is the initial storage modulus G′ [Pa], and R in the formula is the storage modulus G′ [Pa] after the curing treatment.)
[15] The pressure-sensitive adhesive layer has a gel fraction of 70% or more measured after a curing treatment in which the pressure-sensitive adhesive layer is irradiated with ultraviolet light having an integrated light quantity of 300 mJ/ ^cm2 . The pressure-sensitive adhesive sheet according to any one of [9] to [14].
[16] The pressure-sensitive adhesive sheet according to any one of [9] to [15] above, wherein the pressure-sensitive adhesive layer at least satisfies the condition (B).

[17] The initial elastic modulus G' is less than 1.0 x 10 ⁶ Pa, and
The pressure-sensitive adhesive sheet according to any one of the above [1] to [16], wherein the elastic modulus G' after curing treatment is 1.0 x 10 ⁶ Pa or more.
[18] The pressure-sensitive adhesive sheet according to any one of the above-mentioned [1] to [17], which has an initial peel strength of 1.0 N/20 mm or more (e.g., 2.0 N/20 mm or more) measured under conditions of a tensile speed of 300 mm/min and a peel angle of 180 degrees after attachment to a silicon wafer.
[19] The pressure-sensitive adhesive sheet according to any one of the above [1] ^to [18], which, after being attached to a silicon wafer and subjected to a curing treatment in which it is irradiated with ultraviolet light at an integrated light quantity of 300 mJ/cm2, has a post-curing peel strength of less than 1.0 N/20 mm, measured under conditions of a tensile speed of 300 mm/min and a peel angle of 180 degrees.
[20] The pressure-sensitive adhesive sheet according to any one of [1] to [19] above, wherein the peel strength reduction rate calculated by the following formula is 50% or more.
Peel strength reduction rate [%] = (1 - B/A) x 100
(A in the formula is the initial peel strength (unit: [N/20 mm]) measured under conditions of a tensile speed of 300 mm/ ^min and a peel angle of 180 degrees after being attached to a silicon wafer, and B in the formula is the post-curing treatment peel strength (unit: [N/20 mm]) measured under conditions of a tensile speed of 300 mm/min and a peel angle of 180 degrees after being attached to a silicon wafer and subjected to a curing treatment of irradiating ultraviolet light with an integrated light quantity of 300 mJ/cm2.)
[21] The pressure-sensitive adhesive sheet according to any one of [1] to [20] above, wherein the pressure- ^sensitive adhesive layer has a Young's modulus of 1.0 MPa or more as measured by a tensile test after being subjected to an ultraviolet irradiation treatment with an integrated light quantity of 300 mJ/cm2.
[22] The pressure-sensitive adhesive sheet according to any one of the above [1] to [21], wherein the pressure-sensitive adhesive layer has a loss modulus at 25° C. of 1.0×10 ³ Pa or more and 1.0×10 ⁶ Pa or less.
[23] The pressure-sensitive adhesive sheet according to any one of [1] to [22] above, wherein the pressure-sensitive adhesive layer has a thickness of 10 μm or more and less than 100 μm.

[24] The pressure-sensitive adhesive sheet according to any one of [1] to [23] above, wherein the pressure-sensitive adhesive layer contains an acrylic polymer having a carbon-carbon double bond.
[25] The pressure-sensitive adhesive sheet according to the above-mentioned [24], wherein the acrylic polymer is crosslinked with a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule.
[26] The pressure-sensitive adhesive sheet according to [24] or [25] above, wherein the acrylic polymer is a photopolymer or a modified product thereof.
[27] The pressure-sensitive adhesive sheet according to any one of [24] to [26] above, wherein 50% by weight or more of all monomer components constituting the acrylic polymer are linear alkyl (meth)acrylates having an alkyl group with 5 or more carbon atoms.
[28] The pressure-sensitive adhesive sheet according to any one of [24] to [27], wherein the pressure-sensitive adhesive layer contains the acrylic polymer as a base polymer.

[29] A method for producing a pressure-sensitive adhesive layer that is cured by light irradiation (photocurable pressure-sensitive adhesive layer), comprising the steps of:
forming a first adhesive layer comprising a first polymer having a functional group A;
preparing a post-coating liquid containing a functional group B-containing compound having a carbon-carbon double bond and a photoinitiator, and applying the post-coating liquid to at least one surface of the primary pressure-sensitive adhesive layer;
allowing a compound containing a functional group B having a carbon-carbon double bond and a photoinitiator contained in the post-coating liquid to penetrate into the primary pressure-sensitive adhesive layer; and
heating the primary pressure-sensitive adhesive layer permeated with the post-coating liquid to promote the reaction between the functional group A and the functional group B;
A method for producing a pressure-sensitive adhesive layer, comprising the steps of:
[30] The method for producing a pressure-sensitive adhesive layer according to the above-mentioned [29], which is applied to the production of a pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet according to any one of the above-mentioned [1] to [28].
[31] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained by the method for producing a pressure-sensitive adhesive layer according to [29] or [30] above.

Below, several examples of the present invention are described, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Example 1>
(Preparation of Prepolymer Composition)
A mixture of 100 parts of 2-ethylhexyl acrylate (2EHA) and 13 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components was mixed with 0.05 parts of a photoinitiator (product name "Omnirad 184", manufactured by IGM Resins B.V.; hereinafter referred to as "Omni.184"), and the mixture was irradiated with ultraviolet light under a nitrogen atmosphere until the viscosity (BH viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) reached about 20 Pa s, thereby obtaining a prepolymer composition in which a portion of the monomer components was polymerized.

(Preparation of UV-curable adhesive composition)
To the prepolymer composition, 0.05 parts of a multifunctional acrylate (hexanediol diacrylate (HDDA)) as a crosslinking agent, 0.05 parts of a photoinitiator (Omni.184), and 1 part of dioctyltin dilaurate (product name "Envirizer OL-1", manufactured by Tokyo Fine Chemical Co., Ltd.; hereinafter referred to as "OL-1") were added and mixed to obtain an ultraviolet-curable pressure-sensitive adhesive composition C1.

(Formation of the primary adhesive layer)
The pressure-sensitive adhesive composition C1 was applied onto the release-treated surface of a release film (trade name "MRF#38", manufactured by Mitsubishi Chemical Corporation) to form a pressure-sensitive adhesive composition layer. The surface of the pressure-sensitive adhesive composition layer was covered with a release film (trade name "MRE#38", manufactured by Mitsubishi Chemical Corporation) to block air, and ultraviolet light was irradiated under conditions of illuminance: 5 mW/cm ² and accumulated light amount: 2400 mJ/cm ² to photocure the pressure-sensitive adhesive composition layer to form a primary pressure-sensitive adhesive layer (unmodified pressure-sensitive adhesive layer) D1. This primary pressure-sensitive adhesive layer D1 contains an acrylic polymer, which is a polymer of the monomer components and crosslinked with the polyfunctional acrylate, as a base polymer (primary polymer).

(Preparation and application of post-coating liquid)
A post-coating liquid E1 was prepared by mixing 11 parts of methacryloyloxyethyl isocyanate (MOI) and 1 part of a photoinitiator (trade name "Omnirad 651", manufactured by IGM Resins B.V.; hereinafter referred to as "Omni. 651"). The release film was peeled off from one surface of the primary pressure-sensitive adhesive layer D1, and the post-coating liquid E1 was applied to the exposed surface using a Wire Wound Rod type bar coater manufactured by RD Specialties. After application, the mixture was left to stand for about 10 seconds to 10 minutes to allow the post-coating liquid E1 to penetrate into the primary pressure-sensitive adhesive layer D1.

(Introduction of Carbon-Carbon Double Bond)
Next, the primary adhesive layer D1 permeated with the post-coating liquid E1 was heated in an oven at 130° C. for 3 minutes to add react the MOI, thereby introducing a carbon-carbon double bond into the side chain of the base polymer. In this way, a photocurable adhesive layer (substrate-less adhesive sheet) S1 containing a base polymer having a carbon-carbon double bond and a photoinitiator was obtained. The release-treated surface of a release film was attached to one surface of the obtained adhesive layer S1 for protection. The coating amount of the adhesive composition C1 and the coating amount of the post-coating liquid E1 were adjusted so that the content of each component in the adhesive layer S1 was as shown in the table below, and the thickness of the adhesive layer S1 was 25 μm.

<Example 2>
100 parts of 2EHA as a monomer component was mixed with 0.05 parts of a photoinitiator (Omni.184), and the mixture was irradiated with ultraviolet light in the same manner as in Example 1 to obtain a prepolymer composition in which a portion of the monomer component was polymerized.
To the above prepolymer composition, 13 parts of 4HBA as a monomer component, 0.05 parts of HDDA as a crosslinking agent, 0.05 parts of a photoinitiator (Omni.184), and 1 part of OL-1 were added and mixed to obtain an ultraviolet-curable pressure-sensitive adhesive composition C2.
A pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S2 according to this example was produced in the same manner as in Example 1, except that pressure-sensitive adhesive composition C2 was used instead of pressure-sensitive adhesive composition C1.

<Example 3>
100 parts of 2EHA as a monomer component was mixed with 0.05 parts of a photoinitiator (Omni.184), and the mixture was irradiated with ultraviolet light in the same manner as in Example 1 to obtain a prepolymer composition in which a portion of the monomer component was polymerized.
To the above prepolymer composition, 12 parts of MOI as a monomer component, 0.05 parts of HDDA as a crosslinking agent, 0.05 parts of a photoinitiator (Omni.184), and 1 part of OL-1 were added and mixed to obtain an ultraviolet-curable pressure-sensitive adhesive composition C3.
11 parts of 4HBA and 1 part of a photoinitiator (Omni.651) were mixed to prepare post-coating liquid E3. A pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S3 according to this example was produced in the same manner as in Example 1, except that pressure-sensitive adhesive composition C3 was used instead of pressure-sensitive adhesive composition C1, and post-coating liquid E3 was used instead of post-coating liquid E1.

<Example 4>
A mixture of 100 parts of 2EHA and 13 parts of acrylic acid (AA) as monomer components was mixed with 0.05 parts of a photoinitiator (Omni.184) and irradiated with ultraviolet light in the same manner as in Example 1 to obtain a prepolymer composition in which a portion of the monomer components was polymerized.
To the prepolymer composition, 0.05 parts of HDDA as a crosslinking agent, 0.05 parts of a photoinitiator (Omni.184), and 4 parts of tetrabutylammonium bromide (TBAB) were added and mixed to obtain an ultraviolet-curable pressure-sensitive adhesive composition C4.
11 parts of glycidyl methacrylate (GMA) and 1 part of a photoinitiator (Omni.651) were mixed to prepare post-coating liquid E4. A pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S4 according to this example was produced in the same manner as in Example 1, except that the pressure-sensitive adhesive composition C4 was used instead of the pressure-sensitive adhesive composition C1, and the post-coating liquid E4 was used instead of the post-coating liquid E1.

<Examples 5 to 7>
Except for changing the composition of the post-coating liquid as shown in Table 1, pressure-sensitive adhesive layers (substrate-less pressure-sensitive adhesive sheets) S5 to S7 according to each example were prepared in the same manner as in Example 2.

<Example 8>
A monomer mixture was prepared in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, etc., with a mixing ratio of 85 parts of 2EHA and 15 parts of hydroxyethyl acrylate (HEA). 0.2 parts of N,N'-azobisisobutyronitrile (AIBN) as an azo polymerization initiator and ethyl acetate as a polymerization solvent were added to 100 parts of this monomer mixture, and solution polymerization was carried out at about 60°C under a nitrogen gas stream to obtain an ethyl acetate solution of an acrylic polymer. 0.02 parts of OL-1 and 12 parts of MOI were added to this solution and subjected to an addition reaction to prepare an acrylic polymer having a carbon-carbon double bond. The ethyl acetate solution of the acrylic polymer having a carbon-carbon double bond was added in a ratio of 1 part of an isocyanate crosslinking agent (trade name "Takenate D-101E" manufactured by Mitsui Chemicals, Inc.) and 1 part of a photoinitiator (Omni.651) to 100 parts of the solid content of the acrylic polymer. In this manner, a solvent-based pressure-sensitive adhesive composition C8 (solid content: 50%) was prepared.
The above-mentioned adhesive composition C8 was applied to the release-treated surface of the release-treated polyester film, dried at 120°C for 3 minutes, and further aged at 50°C for 24 hours to produce the adhesive layer (substrate-less adhesive sheet) S8 of this example.

<Example 9>
In the above solution polymerization, 0.2 parts of benzoyl peroxide (trade name "Niper BMT-40SV" manufactured by NOF Corporation), which is a peroxide-based polymerization initiator, was used instead of 0.2 parts of AIBN. In all other respects, the same procedure was followed as in Example 8 to produce a pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S9 according to this example.

<Examples 10 and 11>
PSA layers (substrate-less PSA sheets) S10 and S11 according to each example were prepared in the same manner as in Example 1, except that the types and amounts of monomers shown in Table 2 were further added to the prepolymer composition. In Table 2, "ACMO" stands for N-acryloylmorpholine, and "NVP" stands for N-vinyl-2-pyrrolidone.

<Example 12>
A mixture of 100 parts of n-butyl acrylate (BA) and 22 parts of 4HBA as monomer components was mixed with 0.05 parts of a photoinitiator (Omni.184), and irradiated with ultraviolet light in the same manner as in Example 1 to obtain a prepolymer composition in which a portion of the monomer components was polymerized.
To the prepolymer composition, 0.05 parts of HDDA as a crosslinking agent, 0.05 parts of a photoinitiator (Omni.184), and 1 part of OL-1 were added and mixed to obtain an ultraviolet-curable pressure-sensitive adhesive composition C12.
18 parts of MOI and 1 part of photoinitiator (Omni.651) were mixed to prepare post-coating liquid E12. A pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S12 according to this example was produced in the same manner as in Example 1, except that pressure-sensitive adhesive composition C12 was used instead of pressure-sensitive adhesive composition C1, and post-coating liquid E12 was used instead of post-coating liquid E1.

<Example 13>
A pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) S13 according to this example was produced in the same manner as in Example 12, except that the type and amount of monomer shown in Table 2 was further added to the prepolymer composition.

<Measurement and Evaluation>
[Amount of carbon-carbon double bonds]
The amount of carbon-carbon double bonds (amount of unreacted double bonds) contained in the pressure-sensitive adhesive layers obtained in each example (pressure-sensitive adhesive layers S1 to S13) was calculated according to the following formula.
Carbon-carbon double bond content [mol/100 g]=((number of parts [parts] of carbon-carbon double bond-containing compound contained in post-coating liquid × number of carbon-carbon double bonds contained in one molecule of the carbon-carbon double bond-containing compound)/total number of parts of adhesive blended [parts])×100 [g]/molecular weight of the carbon-carbon double bond-containing compound [g/mol]

[Amount of photoinitiator]
The amount of photoinitiator (amount of unreacted photoinitiator) contained in the pressure-sensitive adhesive layer obtained in each example was calculated according to the following formula.
Amount of photoinitiator [mol/100 g]=(number of parts of photoinitiator contained in post-coating liquid [parts]/total number of parts of adhesive blended [parts])×100 [g]/molecular weight of the photoinitiator [g/mol]

[Amount of azo-based and peroxide-based polymerization initiators]
Approximately 3 mg of a sample was taken from the pressure-sensitive adhesive layer obtained in each example, and outgassing was measured by gas chromatography mass spectrometry (GC/MS) at 180° C. for 1 hour. Specific measurement conditions are as follows. Based on the measurement results, the total content of the azo polymerization initiator and the peroxide polymerization initiator in the pressure-sensitive adhesive layer (including the amount contained in the form of decomposition products and residues) was calculated.
(Analysis equipment)
Heating device: GERSTEL, TDU2
GC/MS: Agilent Technologies, 8890/5977B
(Measurement condition)
TDU conditions (sample): 30°C (1 min) → 720°C/min → 180°C (60 min)
TDU conditions (standard): 30°C (1 min) → 720°C/min → 300°C (5 min)
CIS conditions: -150°C (2.5 min) → 12°C/sec → 300°C (10 min)
GC/MS conditions Column: HP-Ultra1 (0.20 mmφ×25 m, df=0.33 μm)
Column temperature: 40°C (5 min) → 10°C/min → 100°C → 20°C/min → 300°C (9 min)
Column pressure: constant flow mode (113 kPa, Vac)
Column flow rate: 1 mL/min (He)
Injection method: CIS, Split (20:1)
Detector: MS
Ion source temperature: 230° C.
Ionization method: EI (70 eV)
Scan range: m/z 10-800

[Organic solvent content]
About 3 mg of a sample was taken from the pressure-sensitive adhesive layer obtained in each example, and outgassing analysis was performed by gas chromatography mass spectrometry (GC/MS) at 180° C. for 1 hour to measure the organic solvent content in the pressure-sensitive adhesive layer. The specific measurement conditions are as described above.

[Dynamic viscoelasticity measurement]
The pressure-sensitive adhesive layers (substrate-less pressure-sensitive adhesive sheets) obtained in each example were laminated to a thickness of approximately 2 mm, and then punched out into disks with a diameter of 7.9 mm to prepare measurement samples. Using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, dynamic viscoelasticity measurements were performed under the following conditions to determine the initial elastic modulus G' and loss elastic modulus G" at 25°C.
(Measurement condition)
Deformation mode: torsion Measurement frequency: 1 Hz
Heating rate: 5°C/min. Shape: Parallel plate 7.9mmφ

Next, the measurement sample was subjected to a curing treatment by irradiating it with ultraviolet light at an illuminance of 300 mW/cm and an integrated light quantity of 3000 mJ/cm ^2. The processed sample was subjected to dynamic viscoelasticity measurement by the above-mentioned method to determine the elastic modulus G' after the curing treatment at 25°C.

From the obtained values of the initial elastic modulus G' [Pa] and the elastic modulus after curing treatment G' [Pa], the increase rate of the storage elastic modulus G' was calculated according to the following formula.
Increase rate of storage elastic modulus G′ [%]=(R/Q−1)×100
(In the formula, Q is the initial elastic modulus G', and R is the elastic modulus G' after curing treatment.)

[Young's modulus (Young's modulus after curing treatment)]
The adhesive layer (substrate-less adhesive sheet) obtained in each example was subjected to a curing treatment of irradiating ultraviolet light under the following conditions in a form in which the adhesive layer was sandwiched between two release films. Next, the adhesive layer was cut together with the release film to a size of 80 mm in width and 30 mm in length. This width of 80 mm was set according to the thickness of the adhesive layer so that the cross-sectional area of the adhesive layer in the cross section along the width direction was about ² mm2. Next, one release film was removed from the adhesive layer, and the adhesive layer was wound on the other release film with its length direction as an axis so as not to introduce air bubbles, to prepare a rod-shaped sample with a length of 30 mm.
The rod-shaped sample was set in a tensile tester (manufactured by ORIENTEC, product name "RTC-1150A"), and the SS curve was measured under conditions of a measurement temperature of 23°C, a chuck distance of 10 mm, and a tensile speed of 300 mm/min. The initial elastic modulus was determined from the rise of the SS curve, and this was defined as the tensile elastic modulus of the pressure-sensitive adhesive layer after curing treatment (Young's modulus after curing treatment).
(UV irradiation conditions)
UV irradiator: Nitto Seiki Co., Ltd., product name "NEL SYSTEM UM810", high pressure mercury lamp light source (characteristic wavelength 365 nm)
Irradiation amount: illuminance 60 mW/cm ² , cumulative light amount 300 mJ/cm ²

[Gel fraction]
The adhesive layer (substrate-less adhesive sheet) obtained in each example was sandwiched between two release films and cured by irradiating ultraviolet light under the following conditions. Next, a measurement sample of about 0.5 g was taken from the adhesive layer and weighed precisely (weight W1). This measurement sample was wrapped in a porous PTFE (polytetrafluoroethylene) sheet and immersed in ethyl acetate at room temperature for one week, then dried, and the weight of the ethyl acetate insoluble matter (weight W2) was measured. The weights W1 and W2 were calculated using the following formula:
Gel fraction [%] = W2/W1 × 100;
The gel fraction of the pressure-sensitive adhesive layer after the curing treatment was calculated by substituting the above. As the porous PTFE sheet, a product name "Nitoflon NTF1122" manufactured by Nitto Denko Corporation was used.
(UV irradiation conditions)
UV irradiator: Nitto Seiki Co., Ltd., product name "NEL SYSTEM UM810", high pressure mercury lamp light source (characteristic wavelength 365 nm)
Irradiation amount: illuminance 60 mW/cm ² , cumulative light amount 300 mJ/cm ²

[180 degree peel strength]
One release liner was peeled off from the adhesive layer (substrate-less adhesive sheet) obtained in each example, and a transparent PET film having a thickness of 50 μm was attached to the backing, and then cut into a strip having a width of 20 mm and a length of 80 mm to prepare a test piece. In an environment of 23 ° C. and 50% RH, the other release liner was peeled off from the test piece, and the test piece was attached to the mirror surface of a silicon wafer (manufactured by Shin-Etsu Chemical Co., Ltd., 6 inch N<100>-100) as an adherend with a hand roller. After autoclaving (50 ° C., 5 atm, 15 minutes), the test piece was peeled off from the silicon wafer under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees using a tensile tester (manufactured by Minebea Co., Ltd., universal tensile compression tester, device name "tensile compression tester, TCM-1kNB") in an environment of 23 ° C. and 50% RH, and the peel strength at this time was measured. The measurement was carried out three times, and the arithmetic mean value was taken as the value of the initial peel strength.

In addition, after the autoclave treatment, a curing treatment was performed in which ultraviolet (UV) rays were irradiated from the PET film side under the following conditions, and then the test piece was peeled off from the silicon wafer. The peel strength after the curing treatment was measured in the same manner as in the measurement of the initial peel strength.
(UV irradiation conditions)
UV irradiator: Nitto Seiki Co., Ltd., product name "NEL SYSTEM UM810", high pressure mercury lamp light source (characteristic wavelength 365 nm)
Irradiation amount: illuminance 60 mW/cm ² , cumulative light amount 300 mJ/cm ²

From the obtained values of the initial peel strength [N/20 mm] and the peel strength after curing treatment [N/20 mm], the peel force reduction rate (peel strength reduction rate) was calculated according to the following formula.
Peel strength reduction rate [%] = (1 - B/A) x 100
(In the formula, A is the initial peel strength, and B is the peel strength after curing treatment.)

The results obtained are shown in Tables 1 and 2, along with an overview of the adhesive layer for each example. Example 1 in Table 2 is a repeat of Example 1 in Table 1.

As shown in Tables 1 and 2, the pressure-sensitive adhesive layers of Examples 1 to 6 and 10 to 13 had an initial elastic modulus G of less than 1.0×10 ⁶ Pa and an elastic modulus G' after curing treatment of 1.0×10 ⁶ Pa or more, the peel strength was significantly reduced by the curing treatment, and the pressure-sensitive adhesive layers were excellent in ease of peeling by light irradiation. The pressure-sensitive adhesive layers of Examples 1 to 6 and 10 to 13 are photocurable pressure-sensitive adhesive layers capable of achieving such effects, but they can be produced by a method that does not use organic solvents even in the process of obtaining the pressure-sensitive adhesive layer of each example from the pressure-sensitive adhesive composition, which is desirable from the viewpoint of environmental hygiene.

On the other hand, the adhesive layer according to Example 7 had an initial elastic modulus G of less than 1.0×10 ⁶ Pa, but an elastic modulus G' after curing treatment was below 1.0×10 ⁶ Pa, and no effect of easy peeling by light irradiation was observed. The adhesive layers according to Examples 8 and 9 shown in Table 1 were obtained by coating and drying a solvent-based adhesive composition containing an acrylic polymer (an acrylic polymer having a carbon-carbon double bond) obtained by introducing a carbon-carbon double bond by a reaction in a solution into an acrylic polymer obtained by solution polymerization using an azo polymerization initiator in Example 8 and a peroxide polymerization initiator in Example 9. It can be seen that the adhesive layers of Examples 8 and 9 have a high amount of azo and peroxide polymerization initiators of 13 to 96 μg/100 g, reflecting such a manufacturing process, and the amount of remaining solvent (organic solvent content) is also clearly large.

　Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

1, 2 Adhesive sheet 10 Adhesive layer 10A One surface (adhesive surface)
10B: other surface 20: substrate 20A: first surface 20B: second surface (rear surface)
30, 31, 32 Release liner 50 Adhesive sheet with release liner

Claims

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is cured by light irradiation,
the pressure-sensitive adhesive layer has a total content of an azo-based polymerization initiator and a peroxide-based polymerization initiator of 1.0 μg/g or less;
The initial storage modulus G′ measured using a measurement sample made of the pressure-sensitive adhesive layer is less than 1.0×10 6 Pa, and
The pressure-sensitive adhesive sheet has a post-curing storage modulus G' of 1.0 x 106 Pa or more, measured after the measurement sample is subjected to a curing treatment of irradiating it with ultraviolet light.
The adhesive sheet of claim 1, wherein the adhesive layer contains a polymer having a carbon-carbon double bond.
The adhesive sheet according to claim 2, wherein the polymer having a carbon-carbon double bond is crosslinked with a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule.
The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer contains carbon-carbon double bonds of 1.0 x 10 -4 mol/100 g or more.
The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer contains 1.0 x 10 -4 mol/100 g or more of a photoinitiator.
The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein an increase in storage modulus calculated by the following formula is 300% or more.
Storage modulus increase rate [%] = (R / Q - 1) x 100
(Q in the formula is the initial storage modulus G′ [Pa], and R in the formula is the storage modulus G′ [Pa] after the curing treatment.)
The pressure-sensitive adhesive layer has a gel fraction of 70% or more measured after a curing treatment in which the pressure-sensitive adhesive layer is irradiated with ultraviolet light having an integrated light quantity of 300 mJ/ cm2 .
The adhesive sheet according to any one of claims 1 to 3, wherein the adhesive layer has an organic solvent content of 1.0 μg/g or less.