Adhesive sheet

Abstract

The present invention provides a novel adhesive sheet having good impact resistance and improved refractive index. According to the present invention, a double-coated adhesive sheet comprising an adhesive layer and not having a substrate is provided. The refractive index of the adhesive sheet is 1.50 or more, and the breaking strength of the adhesive sheet is 10 MPa or less.

Description

TECHNICAL FIELD

[0001] The present application relates to an adhesive sheet. This application claims priority based on Japanese Patent Application No. 2020-15791 filed on January 31, 2020, the entire contents of which are incorporated herein by reference. BACKGROUND

[0002] Generally, an adhesive (also referred to as a pressure-sensitive adhesive. The same applies hereinafter.) exhibits a state of a soft solid (a viscoelastic body) in a temperature range around room temperature, and has a property of easily adhering to an adherend by pressure. By utilizing such a property, the adhesive is widely used for the purpose of joining, fixing, protection, and the like of members in a portable electronic device such as a mobile phone. As a technical document relating to an adhesive sheet for a portable electronic device, Patent Document 1 can be cited. In addition, an adhesive sheet attached to a polarizing film of a liquid crystal display device or the like is disclosed in Patent Documents 2 and 3.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-57375

[0006] Patent Document 2: International Publication No. 2015 / 108159

[0007] Patent Document 3: Japanese Patent Application Publication No. 2019-196468 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] For example, a portable electronic device has a risk of falling from a high place due to its usage, and for an adhesive sheet for a portable electronic device, it is required to have impact resistance. For example, it is desirable that an adhesive disposed on the back of an image display portion of a portable electronic device has excellent impact resistance in the portable electronic device. In order to improve the impact resistance, it is effective to use an impact absorbing material such as a foam, and for the fixation of members in the above-described portable electronic device, due to the requirements of weight reduction and miniaturization, thickness reduction is being pursued, and it is sometimes difficult to use an impact absorbing material having a thickness such as a foam substrate.

[0010] In addition, in the above-described portable electronic device and the like, for the purpose of operation of the device, sensing of an approaching object, detection of the brightness of the surroundings (ambient light), data communication, and the like, a light sensor using light rays such as infrared rays, visible light, ultraviolet rays, and the like is used. The light rays used in the light sensor transmit through the material constituting the device to exert the intended function, but if the light rays are shielded by reflection or the like within the above-described device, the action accuracy of the sensor is affected, or the sensor becomes unresponsive. In the case of an adhesive sheet used in the above-described device, when the difference in refractive index from the member to which the adhesive sheet is attached is large, reflection of the light rays can occur at the interface thereof, and adversely affect the action accuracy of the light sensor. For example, the refractive index of the material to which the adhesive is attached, such as the back member disposed on the back of the above-described image display portion, is mostly higher than that of the adhesive, and due to the difference in refractive index between the adhesive sheet and the adherend, reflection of the light rays can occur at the interface thereof. In addition, in order to suppress reflection of light that has transmitted through the display portion and prevent a decrease in the visual recognition of the display image, an adhesive sheet having light shielding properties can be used for the adhesive sheet disposed on the back of the above-described image display portion. In the case of such a light shielding adhesive sheet, when light rays that should have been absorbed within the adhesive sheet are reflected at the interface between the adhesive sheet and the adherend, it can become a cause of erroneous operation or unresponsiveness.

[0011] However, in the case of an adhesive sheet used in a use requiring impact resistance as described above, there has been no study on suppressing reflection of light rays caused by the difference in refractive index from the adherend. If an adhesive sheet capable of suppressing reflection of light rays while having impact resistance is provided, in a use requiring impact resistance, such as within a portable electronic device, it is possible to prevent a decrease in the action accuracy of the above-described light sensor and the like, and the like, and a practical advantage is obtained.

[0012] The present application was achieved in view of the above-described circumstances, and aims to provide a novel adhesive sheet having good impact resistance and improved refractive index.

[0013] Means for solving the problem

[0014] According to the present specification, a double-coated adhesive sheet containing an adhesive layer and not having a substrate is provided. The refractive index of the adhesive sheet is 1.50 or greater, and the breaking strength is 10 MPa or less. According to the above-described adhesive sheet, good impact resistance is obtained, and reflection of light rays at the interface with the adherend can be suppressed when attached to an adherend having a higher refractive index than that of a conventional general-purpose adhesive. In addition, the double-coated adhesive sheet without a substrate can be thinned to the extent that it does not have a substrate, and can contribute to the miniaturization and space saving of a product in which the double-coated adhesive sheet is used. Furthermore, according to the adhesive sheet without a substrate, the function of the adhesive layer, such as adhesion and impact resistance, can be maximally exhibited.

[0015] The adhesive sheet disclosed herein may contain at least one particle selected from metal particles, metal compound particles, organic particles, and organic-inorganic complex particles. HRI Therefore, a refractive index of a specified value or higher can be preferably achieved. Preferably, the adhesive sheet contains particles comprising metal oxides as the aforementioned particle P. HRI .

[0016] In some preferred embodiments, the adhesive sheet contains the aforementioned particles P in a proportion of 25% to 75% by weight. HRI By using particle P HRI Setting the content of [amount] to 25% by weight or more can preferably increase the refractive index of the adhesive sheet. By using particles P... HRI The content is set below 75% by weight, which makes it easy to maintain good impact resistance.

[0017] In some preferred embodiments, the aforementioned particle P HRI The average particle size is in the range of 1 nm to 100 nm. This is achieved by using particles P with a particle size within the above range. HRI It can suppress the reduction of properties such as impact resistance and adhesion, and can preferably achieve a refractive index above a specified value.

[0018] In addition to the aforementioned particles P, some preferred methods of adhesive sheet bonding HRI In addition, it contains carbon black particles. Based on the above composition, it can improve the refractive index and have good light-blocking properties.

[0019] Some preferred adhesive sheets have a thickness of 20 μm or more but less than 50 μm. Setting the thickness of the adhesive sheet to 20 μm or more preferably achieves superior impact resistance. Setting the thickness of the adhesive sheet to less than 50 μm effectively addresses the requirements for thinner profiles and lighter weight.

[0020] The adhesive sheet disclosed herein may contain an acrylic polymer as the base polymer. In a configuration having an acrylic adhesive, the effect of increased refractive index resulting from the technology disclosed herein can preferably be achieved.

[0021] Some preferred adhesive sheets are formed from adhesive compositions containing isocyanate crosslinking agents and / or epoxy crosslinking agents. This configuration allows for good impact resistance and improved cohesion. In other words, it is easy to achieve a balance between cohesion and impact resistance.

[0022] Some preferred adhesive sheets exhibit a 180-degree peel strength of 2 N / 10 mm or higher against stainless steel sheets. In addition to improved impact resistance and refractive index, such adhesive sheets also possess excellent adhesive properties.

[0023] The adhesive sheet disclosed herein has impact resistance, and thus can be preferably used, for example, for joining (typically fixing) a member of a portable electronic device that has a risk of falling from a high place due to its usage. The portable electronic device can be built-in with a light sensor, and by using the adhesive sheet disclosed herein to suppress light reflection, the influence on the operation of the light sensor can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A cross-sectional view for schematically showing one configuration example of the adhesive sheet.

[0025] Figure 2 A cross-sectional view for schematically showing another configuration example of the adhesive sheet.

[0026] Figure 3 A schematic exploded perspective view for schematically showing one configuration example of a liquid crystal display device.

[0027] Figure 4 TEM observation-based number-based particles P of the adhesive of Example 1 HRI Histogram of particle size distribution.

[0028] Figure 5 TEM observation-based number-based particles P of the adhesive of Example 7 HRI Histogram of particle size distribution. DETAILED DESCRIPTION

[0029] Hereinafter, a preferred embodiment of the present application will be described. Note that matters other than those specifically mentioned in this specification, which are required for carrying out the present application, can be understood by those skilled in the art from the teachings with respect to the carrying out of the application described in this specification and the technical common sense at the time of filing. The present application can be carried out in accordance with the content disclosed in this specification and the technical common sense. In addition, in the following drawings, sometimes the same reference numerals will be assigned to members / positions that play the same role, and repeated description will sometimes be omitted or simplified. In addition, in order to clearly describe the present application, the embodiments described in the drawings are schematized, and do not necessarily accurately indicate the size, scale of the adhesive sheet of the present application actually provided as a product.

[0030] In this specification, an "adhesive" refers to a material that is in a state of a soft solid (a viscoelastic body) at a temperature range around room temperature, as described above, and has a property of easily adhering to an adherend by pressure. Here, the adhesive can be generally a material having a complex tensile elastic modulus E ＊(1 Hz) < 10 7 dyne / cm 2 The material having the above-mentioned properties at 25°C is typically a material having the above-mentioned properties at 25°C.

[0031] <Example of construction of adhesive sheet>

[0032] The adhesive sheet disclosed herein is a substrate-free adhesive sheet (i.e., an adhesive sheet not having a substrate that is not peeled) in the form of an adhesive layer described above being held on a release liner, and the like. The concept of an adhesive sheet as used herein can include articles referred to as adhesive tapes, adhesive labels, adhesive films, and the like. Note that the adhesive sheet disclosed herein can be in a roll shape or in a single sheet shape. Alternatively, it can be an adhesive sheet in a form further processed into various shapes.

[0033] An example of the construction of a double-sided adhesive type substrate-free adhesive sheet (substrate-free double-sided adhesive sheet) is shown in Figure 1 , 2 .The adhesive sheet 1 shown in FIG. 1 has a construction in which the double sides 21A, 21B of the substrate-free adhesive layer 21 are protected by the release liners 31, 32, at least the adhesive layer side of which becomes a release surface. Figure 1 The adhesive sheet 2 shown in FIG. 2 has a construction in which one surface (adhesive surface) 21A of the substrate-free adhesive layer 21 is protected by the release liner 31, the double sides of which become release surfaces. When this is wound, the other surface (adhesive surface) 21B of the adhesive layer 21 is in contact with the back surface of the release liner 31, and thus can have a construction in which the other surface 21B is also protected by the release liner 31. The technology disclosed herein can be preferably implemented in such a substrate-free form from the viewpoint of reducing the thickness of the adhesive sheet. A substrate-free adhesive sheet is easily thinned, and is also advantageous from the viewpoint of being able to maximize the adhesive properties such as adhesive strength, impact resistance, and the like. Figure 2

[0034] <Properties of adhesive sheet>

[0035] (Breaking strength)

[0036] The adhesive sheet disclosed herein is characterized by a breaking strength of 10 MPa or less. According to the adhesive sheet having a breaking strength of 10 MPa or less, good impact resistance can be exhibited. The breaking strength described above is, for example, less than 10 MPa, can be 8 MPa or less, more preferably 7 MPa or less, further preferably 6 MPa or less, particularly preferably 5 MPa or less, and can also be 3 MPa or less (for example, 1 MPa or less). The lower limit of the breaking strength described above is not particularly limited, and from the viewpoint of maintaining the adhesion properties such as holding power, 0.1 MPa or more is appropriate, preferably 0.5 MPa or more, more preferably 1 MPa or more, can be 2 MPa or more, can be 3 MPa or more, and can also be 4 MPa or more. The adhesive sheet having a strength of the prescribed value or more has a tendency to be excellent in handling properties. The breaking strength described above is measured by the method described in the Examples described later.

[0037] (refractive index)

[0038] The adhesive sheet disclosed herein is characterized by a refractive index of 1.50 or more. By having this characteristic, when adhered to a material having a higher refractive index than the adhesive, the reflection of light at the interface between the two can be suppressed. For example, for an adhesive sheet having light shielding properties, it is undesirable for light that should be absorbed within the adhesive sheet to be reflected at the interface with the adherend. In such a manner, it is particularly meaningful to suppress the reflection of light using a configuration having an increased refractive index. From such a viewpoint, the refractive index described above is preferably 1.52 or more, can be 1.54 or more, can be 1.56 or more, and can also be 1.58 or more. By using an adhesive sheet having the refractive index described above, in a manner in which it is adhered to a material having a higher refractive index, the reflection of light at the interface with the adherend can be appropriately suppressed. In some manners, the refractive index described above is 1.60 or more, and can also be 1.62 or more. By using an adhesive sheet having the refractive index described above, in a manner in which it is adhered to a material having an even higher refractive index, the reflection of light at the interface with the adherend can be appropriately suppressed. The upper limit of the refractive index described above can vary depending on the refractive index of the adherend and the like, and thus is not limited to a particular range, and for example, can be 1.70 or less, and can also be 1.66 or less. The refractive index of the adhesive sheet can be adjusted based on the type of adhesive by the adhesive containing components (for example, the monomer composition of the polymer, typically the type, amount, arrangement, and the like of the particles P HRI

[0039] In the case of a double-sided adhesive sheet having adhesive surfaces on both sides, the refractive index of each surface (each adhesive surface. The first adhesive surface and the second adhesive surface) can be the same or different. In a manner in which the refractive index of each surface (each adhesive surface) of the double-sided adhesive sheet is different, one surface (for example, the first adhesive surface) can have the refractive index described above, and the refractive index of the other surface (for example, the second adhesive surface) can be less than 1.50.

[0040] ​Note that the refractive index of the adhesive sheet in the present specification refers to the refractive index of the surface (adhesive surface) of the adhesive sheet. The refractive index of the adhesive sheet can be measured using a commercially available refractive index measuring device (a multi-wavelength Abbe refractometer or an ellipsometer) under the condition of 23°C. As the multi-wavelength Abbe refractometer, for example, a model "DR-M2" manufactured by ATAGO Co., Ltd. or the like can be used. As the ellipsometer, for example, a product name "EC-400" (manufactured by JA. Woolam Co., Ltd.) or the like can be used. The refractive index of the adhesive sheet can be specifically measured by the method described in the Examples described later. In the refractive index measuring method described later, light having a wavelength of 589 nm is used, but the range of the refractive index to which the technical idea grasped by the present specification is applied is not limited thereto. The concept of the refractive index in the technology disclosed in the present specification includes the refractive index of light having a specific wavelength region selected from the visible light region (380 nm to 780 nm), and can also include the refractive index of light having a specific wavelength region selected from the ultraviolet region (380 nm or less, for example, 100 nm to 380 nm), the infrared region (780 nm or more, for example, 780 nm to 2500 nm).

[0041] (total light transmittance)

[0042] The total light transmittance of the adhesive sheet disclosed herein can be set according to the purpose of use, the manner of use, and thus is not limited to a specific range. The total light transmittance described above can be, for example, 80% or less. By limiting the total light transmittance to a prescribed value or less, it is possible to adjust the appearance of the adherend through the adhesive sheet, for example, to suppress unevenness in the appearance of the adherend, or to impart designability. The total light transmittance described above is, for example, less than 80%, and from the viewpoint of improving light shielding properties, can be 75% or less, can be 70% or less, can be 65% or less, or can be 60% or less (for example, 55% or less). In addition, the lower limit of the total light transmittance described above is not particularly limited, and can be substantially 0%, that is, below the detection limit. From the viewpoint of maintaining the adhesive properties, including productivity and efficiency in industry, the total light transmittance described above can be greater than 0.01% (for example, greater than 0.05%), and further can be greater than 0.1%, can be 1% or more, for example, can be 3% or more, or can be about 5% or more.

[0043] In some embodiments, the total light transmittance of the adhesive sheet is greater than 10% and less than or equal to 80%. An adhesive sheet having such light transmittance can adjust the appearance of adherends across the adhesive sheet, for example, to suppress unevenness in the appearance of the adherends. In addition, a design property that moderately suppresses light transmittance can be imparted. Furthermore, a light-shielding property can be possessed and the visual recognition property of the adherends for inspection or the like can be possessed. In this embodiment, the total light transmittance described above is, for example, less than 80%, and from the viewpoint of improving the light-shielding property, is preferably 75% or less, more preferably 70% or less, further preferably 65% or less, and can be 60% or less (for example, 55% or less). In addition, from the viewpoint of the visual recognition property, design property, or the like across the adhesive sheet, the total light transmittance described above can be 20% or more, can be 30% or more, can be 50% or more (for example, greater than 50%), or can be greater than 60%.

[0044] In other embodiments, the total light transmittance of the adhesive sheet is 10% or less. Such an adhesive sheet can have a light-shielding property that is suitable for preventing light leakage and reducing reflection. In this embodiment, the total light transmittance of the adhesive sheet can be less than 10%. In some preferred embodiments, the total light transmittance of the adhesive sheet is less than 8.0%, can be less than 6.0%, can be less than 3.0%, more preferably less than 1.00%, further preferably less than 0.50%, and particularly preferably less than 0.30% (for example, less than 0.10%). With an adhesive sheet exhibiting the total light transmittance described above, an excellent light-shielding property can be achieved. The lower limit of the total light transmittance described above is not particularly limited and can be substantially 0%, that is, the detection limit or less.

[0045] The total light transmittance of the adhesive sheet can be measured by the method described in the Examples described later. The total light transmittance of the adhesive sheet can be adjusted by the components contained in the adhesive (preferably the kind and the amount of use of the particles such as pigments), the configuration of the colored layer, and the like.

[0046] (adhesive strength)

[0047] The 180-degree peeling strength (adhesive strength) of the adhesive sheet disclosed herein can differ depending on the purpose of use, the application site, and thus is not limited to a particular range. The adhesive strength of the adhesive sheet can be, for example, 0.3 N / 10 mm or more. From the viewpoint of obtaining good adhesiveness to the adherend, it is appropriate to set the 180-degree peeling strength described above to be about 1.0 N / 10 mm or more, is preferably about 2.0 N / 10 mm or more, and more preferably about 3.0 N / 10 mm or more. The adhesive sheet described above can balance the impact resistance and the adhesiveness. In some embodiments, for example, the particles P HRIIn order to achieve the refractive index of 1.50 or more, and at the same time achieve the adhesion, in some modes, for example, a colorant such as carbon black particles can be contained to achieve the total light transmittance of 80% or less, and at the same time achieve the adhesion. From the viewpoint of the adhesive stability to adherends, the adhesion can be about 4.0 N / 10 mm or more, or about 5.0 N / 10 mm or more (for example, about 6.0 N / 10 mm or more). The upper limit of the adhesion is not particularly limited, and for example, can be 12 N / 10 mm or less, or 8 N / 10 mm or less (for example, 5 N / 10 mm or less). The 180-degree peel strength can be measured by the method described in the Examples described later.

[0048] <Adhesive layer>

[0049] (Basic polymer)

[0050] In the technology disclosed herein, the type of the adhesive constituting the adhesive layer is not particularly limited. The adhesive can be an adhesive containing one or two or more of various rubber-like polymers such as an acrylic polymer, a rubber-based polymer (natural rubber, synthetic rubber, a mixture thereof, etc.), a polyester-based polymer, a urethane-based polymer, a polyether-based polymer, a polysiloxane-based polymer, a polyamide-based polymer, a fluorine-containing polymer, etc., as an adhesive polymer (refers to a structural polymer forming the adhesive, hereinafter also referred to as "basic polymer") that can be used in the field of adhesives. From the viewpoints of adhesion performance, cost, etc., an adhesive containing an acrylic polymer or a rubber-based polymer as a basic polymer can be preferably used. Among them, an adhesive in which an acrylic polymer is used as a basic polymer (acrylic adhesive) is preferable. By applying the technology disclosed herein, an acrylic adhesive having a refractive index of 1.50 or more can be appropriately obtained.

[0051] Hereinafter, an adhesive sheet having an adhesive layer composed of an acrylic adhesive, i.e., an acrylic adhesive layer will be mainly described, but the adhesive layer of the adhesive sheet disclosed herein is not intended to be limited to one composed of an acrylic adhesive.

[0052] Note that the "basic polymer" of the adhesive refers to the main component of the rubber-like polymer contained in the adhesive, and is not subject to any limiting explanation. The above-mentioned rubber-like polymer refers to a polymer that exhibits rubber elasticity in the temperature range around room temperature. In addition, in the present specification, "main component" means a component contained in an amount of more than 50% by weight, unless otherwise specified.

[0053] In addition, the "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as a monomer unit constituting the polymer. Hereinafter, the monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Thus, the acrylic polymer of the present specification is defined as a polymer containing monomer units derived from an acrylic monomer. As a typical example of the acrylic polymer, an acrylic polymer in which the proportion of the acrylic monomer among all monomer components used in the synthesis of the acrylic polymer is more than 50% by weight can be cited.

[0054] In addition, the "(meth)acryloyl group" collectively refers to an acryloyl group and a methacryloyl group. Similarly, the "(meth)acrylate" collectively refers to an acrylate and a methacrylate, and the "(meth)acrylic acid" collectively refers to an acrylic acid and a methacrylic acid.

[0055] (Acrylic Polymer)

[0056] As the acrylic polymer in the technology disclosed herein, a polymer obtained by polymerizing, for example, a monomer raw material containing an alkyl (meth)acrylate as a main monomer, which can further contain a sub monomer copolymerizable with the main monomer, is preferable. Herein, the main monomer refers to a component accounting for more than 50% by weight of the monomer composition of the above-mentioned monomer raw material.

[0057] As the alkyl (meth)acrylate, a compound represented by the following formula (1), for example, can be preferably used.

[0058] CH2=C(R 1 )COOR 2 (1)

[0059] wherein R 1 in the above formula (1) is a hydrogen atom or a methyl group. In addition, R 2 is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, such a range of the number of carbon atoms is sometimes expressed as "C 1-20 ". From the viewpoint of the storage modulus of the adhesive and the like, it is appropriate to use an alkyl (meth)acrylate in which R 2 is a chain alkyl group of C 1-14 (e.g., C 1-10 , typically C 4-8 ) as the main monomer. From the viewpoint of the adhesion properties, it is preferable to use an alkyl acrylate in which R 1 is a hydrogen atom and R 2 is a chain alkyl group of C 4-8 as the main monomer (hereinafter, also simply referred to as an alkyl acrylate of C 4-8 ).

[0060] As R 2 is C1-20 Specific examples of the (meth)acrylic acid alkyl ester having a chain-like alkyl group, which are not particularly limited, include, for example, (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid isopropyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid sec-butyl ester, (meth)acrylic acid t-butyl ester, (meth)acrylic acid amyl ester, (meth)acrylic acid isoamyl ester, (meth)acrylic acid hexyl ester, (meth)acrylic acid heptyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid octyl ester, (meth)acrylic acid iso-octyl ester, (meth)acrylic acid nonyl ester, (meth)acrylic acid iso-nonyl ester, (meth)acrylic acid decyl ester, (meth)acrylic acid iso-decyl ester, (meth)acrylic acid undecyl ester, (meth)acrylic acid dodecyl ester, (meth)acrylic acid tridecyl ester, (meth)acrylic acid tetradecyl ester, (meth)acrylic acid pentadecyl ester, (meth)acrylic acid hexadecyl ester, (meth)acrylic acid heptadecyl ester, (meth)acrylic acid octadecyl ester, (meth)acrylic acid nonadecyl ester, (meth)acrylic acid eicosyl ester, and the like. These (meth)acrylic acid alkyl esters can be used alone or in combination of two or more. As preferred examples of the (meth)acrylic acid alkyl ester, n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) can be cited.

[0061] The proportion of the (meth)acrylic acid alkyl ester in the monomer component constituting the acrylic polymer is typically greater than 50% by weight, and can be set to 70% by weight or more, for example, can be set to 85% by weight or more, or can be set to 90% by weight or more. The upper limit of the proportion of the (meth)acrylic acid alkyl ester is not particularly limited, and is preferably set to 99.5% by weight or less (for example, 99% by weight or less), or can be set to 98% by weight or less (for example, less than 97% by weight) from the viewpoint of preferably exerting the characteristics (for example, coagulation force) based on the side monomers such as the carboxyl group-containing monomer. Alternatively, the acrylic polymer can be a polymer obtained by polymerizing substantially only the (meth)acrylic acid alkyl ester.

[0062] In addition, in the case where acrylic acid C 4-8 In the case where the (meth)acrylic acid alkyl ester is used as the monomer component, the proportion of the acrylic acid C 4-8 The proportion of the (meth)acrylic acid alkyl ester in the monomer component constituting the acrylic polymer is typically greater than 50% by weight, and can be set to 70% by weight or more, for example, can be set to 85% by weight or more, or can be set to 90% by weight or more. The upper limit of the proportion of the (meth)acrylic acid alkyl ester is not particularly limited, and is preferably set to 99.5% by weight or less (for example, 99% by weight or less), or can be set to 98% by weight or less (for example, less than 97% by weight) from the viewpoint of preferably exerting the characteristics (for example, coagulation force) based on the side monomers such as the carboxyl group-containing monomer. Alternatively, the acrylic polymer can be a polymer obtained by polymerizing substantially only the (meth)acrylic acid alkyl ester.

[0063] The technology disclosed herein can be preferably implemented in a manner that the monomer component contains 50% by weight or more of a (meth)acrylic acid C 1-4 alkyl ester. The (meth)acrylic acid C 1-4 alkyl ester can be contained in the monomer component at a ratio of 70% by weight or more, or can be contained at a ratio of 85% by weight or more (for example, 90% by weight or more). On the other hand, from the viewpoint of obtaining good cohesive force, the (meth)acrylic acid C 1-4 alkyl ester can be contained in the monomer component at a ratio of 99.5% by weight or less, or can be contained at a ratio of 98% by weight or less (for example, less than 97% by weight).

[0064] The technology disclosed herein can be preferably implemented in a manner that the monomer component contains 50% by weight or more (for example, 70% by weight or more, or 85% by weight or more, or 90% by weight or more) of a (meth)acrylic acid C 2-4 alkyl ester. As the (meth)acrylic acid C 2-4 alkyl ester, specific examples can include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate (BA), isobutyl acrylate, sec-butyl acrylate, and t-butyl acrylate. The (meth)acrylic acid C 2-4 alkyl ester can be used alone or in combination with two or more. In this manner, an adhesive sheet having good adhesion to an adherend can be easily achieved. Among them, as a preferred manner, a manner in which the monomer component contains more than 50% by weight (for example, 70% by weight or more, or 85% by weight or more, or 90% by weight or more) of BA can be cited. By using the (meth)acrylic acid C 2-4 alkyl ester (for example, BA) in a prescribed amount or more, for example, in the case where a black colorant such as carbon black is incorporated in the adhesive, it is possible to cause the colorant to be well dispersed in the layer and to maintain good adhesive properties such as adhesive force. On the other hand, from the viewpoint of obtaining good cohesive force, the (meth)acrylic acid C 2-4 alkyl ester can be contained in the monomer component at a ratio of 99.5% by weight or less, or can be contained at a ratio of 98% by weight or less (for example, less than 97% by weight).

[0065] In some other manners, the monomer component can be implemented in a manner that contains 50% by weight or more (for example, 70% by weight or more, or 85% by weight or more, or 90% by weight or more) of a (meth)acrylic acid C 5-20 alkyl ester. As the (meth)acrylic acid C 5-20 alkyl ester, a (meth)acrylic acid C 6-14 alkyl ester is preferable. In some manners, a (meth)acrylic acid C 6-10 alkyl ester (for example, a (meth)acrylic acid C 8-10 alkyl ester) can be preferably used.

[0066] The acrylic polymer in the technology disclosed herein can be copolymerized with a comonomer. As a comonomer that can introduce a functional group capable of becoming a crosslinking point in the acrylic polymer, or that can contribute to an increase in adhesive strength, there can be cited a carboxyl group-containing monomer, a hydroxyl group (OH group)-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an epoxy group-containing monomer, a cyano group-containing monomer, a ketone group-containing monomer, a monomer having a ring containing a nitrogen atom, an alkoxysilyl group-containing monomer, an imide group-containing monomer, and the like. The above comonomer can be used alone or in combination with two or more.

[0067] As a preferred example of the acrylic polymer in the technology disclosed herein, there can be cited an acrylic polymer copolymerized with a carboxyl group-containing monomer as the above comonomer. As the carboxyl group-containing monomer, there can be cited acrylic acid (AA), methacrylic acid (MAA), (meth)acrylic acid carboxyethyl ester, (meth)acrylic acid carboxypentyl ester, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and the like. Of these, AA and MAA are preferred.

[0068] As another preferred example, there can be cited an acrylic polymer copolymerized with a hydroxyl group-containing monomer as the above comonomer. As examples of the hydroxyl group-containing monomer, there can be cited (meth)acrylic acid 2-hydroxyethyl ester, (meth)acrylic acid 2-hydroxypropyl ester, (meth)acrylic acid 3-hydroxypropyl ester, (meth)acrylic acid 2-hydroxybutyl ester, (meth)acrylic acid 4-hydroxybutyl ester, and the like (meth)acrylic acid hydroxyalkyl esters; polypropylene glycol mono(meth)acrylate; N-hydroxyethyl (meth)acrylamide; and the like. As a preferred hydroxyl group-containing monomer among these, there can be cited a linear (meth)acrylic acid hydroxyalkyl ester in which the alkyl group has 2 to 4 carbon atoms.

[0069] As the amide group-containing monomer, there can be cited, for example, (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N-butyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-hydroxymethylpropane (meth)acrylamide, N-methoxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide.

[0070] As the amino group-containing monomer, there can be cited, for example, (meth)acrylic acid aminoethyl ester, (meth)acrylic acid N,N-dimethylaminoethyl ester, and (meth)acrylic acid t-butylaminoethyl ester.

[0071] As the monomer having an epoxy group, there can be cited, for example, glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0072] As the cyano group-containing monomer, there can be cited, for example, acrylonitrile and methacrylonitrile.

[0073] As the monomer having a ketone group, for example, the following can be mentioned: diacetone (meth) acrylamide, diacetone (meth) acrylate, methyl ethyl ketone, ethyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.

[0074] As the monomer having a nitrogen atom-containing ring, for example, the following can be mentioned: N-vinyl-2-pyrrolidone, N-methyl vinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyl morpholine, N-vinylcaprolactam, N-(meth) acryloylmorpholine.

[0075] As the monomer having an alkoxysilyl group, for example, the following can be mentioned: 3- (meth) acryloyloxypropyltrimethoxysilane, 3- (meth) acryloyloxypropyltriethoxysilane, 3- (meth) acryloyloxypropylmethyldimethoxysilane, 3- (meth) acryloyloxypropylmethyldiethoxysilane.

[0076] In the case where the monomer component constituting the acrylic polymer contains the above-mentioned functional group-containing monomer, the content of the functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effects brought about by the use of the functional group-containing monomer, the content of the functional group-containing monomer in the monomer component can be set to 0.1% by weight or more, it is appropriate to set it to 0.5% by weight or more, and it can also be set to 1% by weight or more. In addition, from the viewpoint of easily obtaining a balance of adhesion properties in relation to the main monomer, it is appropriate to set the content of the functional group-containing monomer in the monomer component to 40% by weight or less, it is preferable to set it to 20% by weight or less, and it can also be set to 10% by weight or less (for example, 5% by weight or less).

[0077] In some preferred modes of the base polymer, the monomer component constituting the base polymer (for example, the acrylic polymer) can contain a carboxyl group-containing monomer. By causing the monomer component to contain a carboxyl group-containing monomer, an adhesive sheet that exhibits good adhesion properties (cohesion, etc.) is easily obtained. In addition, it is also advantageous in improving the adhesion of the adhesive layer to the adherend. Furthermore, by copolymerizing an appropriate amount of a carboxyl group-containing monomer, for example, in the case where a black colorant such as carbon black is incorporated in the adhesive, it is also easy to cause the colorant to be well dispersed within the layer, and the adhesion properties can be preferably maintained.

[0078] In the manner in which the carboxyl group-containing monomer is copolymerized in the base polymer, the content of the carboxyl group-containing monomer in the monomer component constituting the base polymer is not particularly limited, and for example, it can be set to 0.2% by weight or more (typically 0.5% by weight or more) of the monomer component, it is appropriate to set it to 1% by weight or more, it can be set to 2% by weight or more, and it can be set to 3% by weight or more. By setting the content of the carboxyl group-containing monomer to more than 3% by weight, a better effect can be exerted. In some manners, the content of the carboxyl group-containing monomer can be set to 3.2% by weight or more of the monomer component, it can be set to 3.5% by weight or more, it can be set to 4% by weight or more, and it can be set to 4.5% by weight or more. The upper limit of the content of the carboxyl group-containing monomer is not particularly limited, and for example, it can be set to 15% by weight or less, it can be set to 12% by weight or less, and it can be set to 10% by weight or less. The technology disclosed herein can be preferably implemented in a manner in which the content of the carboxyl group-containing monomer is 7% by weight or less (typically less than 7% by weight, for example, 6.8% by weight or less, or 6.0% by weight or less) of the monomer component.

[0079] For the purpose of improving cohesiveness and the like, the monomer component constituting the acrylic polymer can also contain other copolymerization components in addition to the above-described comonomer. As examples of the other copolymerization components, there can be cited: vinyl ester-based monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (a-methylstyrene and the like), and vinyltoluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; (meth)acrylates containing an aromatic ring such as (meth)acrylate phenyl ester, (meth)acrylate phenoxyalkyl ester (e.g., (meth)acrylate phenoxyethyl ester), and (meth)acrylate aralkyl ester (e.g., (meth)acrylate benzyl ester); olefin-based monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride and vinylidene chloride; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxyl group-containing monomers such as (meth)acrylate methoxyethyl ester and (meth)acrylate ethoxyethyl ester; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; and multifunctional monomers having two or more (e.g., three or more) polymerizable functional groups (e.g., (meth)acryloyl groups) in one molecule such as 1,6-hexanediol di(meth)acrylate and trimethylolpropane tri(meth)acrylate.

[0080] The amount of the other copolymer component can be appropriately selected depending on the purpose and use, and is not particularly limited, but from the viewpoint of appropriately exerting the effects brought about by the use of the other copolymer component, it is appropriate to set to 0.05% by mass or more, and can be set to 0.5% by mass or more. In addition, from the viewpoint of easily obtaining a balance of adhesive properties, it is appropriate to set the content of the other copolymer component in the monomer component to 20% by mass or less, and can be set to 10% by mass or less (for example, 5% by mass or less). The technology disclosed herein can be preferably implemented in such a manner that the monomer component does not substantially contain the other copolymer component. Here, the monomer component does not substantially contain the other copolymer component means that the other copolymer component is not intentionally used, and it can be allowed to contain, for example, about 0.01% by mass or less of the other copolymer component unintentionally.

[0081] It is appropriate that the copolymerization composition of the acrylic polymer is designed in such a manner that the glass transition temperature (Tg) of the polymer is about -15°C or lower (for example, about -70°C or higher and -15°C or lower). Here, the Tg of the acrylic polymer refers to the Tg obtained based on the composition of the monomer component used in the synthesis of the polymer and by the Fox equation. The Fox equation is shown below, and the Fox equation is a relational expression of the Tg of a copolymer and the glass transition temperatures Tgi of homopolymers obtained by homopolymerizing the respective monomers constituting the copolymer.

[0082] 1 / Tg =∑(Wi / Tgi)

[0083] Note that in the above Fox equation, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of the monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature of the homopolymer of the monomer i (unit: K).

[0084] As the glass transition temperatures of the homopolymers used in the calculation of Tg, values described in publicly known documents can be used. For example, for the monomers listed below, the following values are used as the glass transition temperatures of the homopolymers of the monomers.

[0085]

[0086] For the glass transition temperatures of the homopolymers of monomers other than the above examples, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which a plurality of values are described in this document, the highest value is adopted. In the case where it is not described in the above Polymer Handbook, the value obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 is used.

[0087] Although not particularly limited, it is advantageous for the Tg of the acrylic polymer to be about -25°C or lower from the viewpoint of impact resistance and adhesion to the adherend, and it is preferably about -35°C or lower, and more preferably about -40°C or lower. In some modes, the Tg of the acrylic polymer can be, for example, about -65°C or higher, about -60°C or higher, or about -55°C or higher from the viewpoint of cohesiveness. The technology disclosed herein can be preferably implemented in a mode in which the Tg of the acrylic polymer is about -65°C or higher and -35°C or lower (for example, about -55°C or higher and -40°C or lower). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the kind, the ratio of use of the monomers used to synthesize the polymer).

[0088] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as the synthesis method of the acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, a photopolymerization method, and the like, can be appropriately used. For example, a solution polymerization method can be preferably used. The polymerization temperature when solution polymerization is performed can be appropriately selected depending on the kind of the monomer and the solvent used, the kind of the polymerization initiator, and the like, and can be set to, for example, about 20°C to about 170°C (typically, about 40°C to about 140°C).

[0089] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from the organic solvents known in the art. For example, any one solvent or a mixed solvent of two or more selected from the group consisting of aromatic compounds (typically, aromatic hydrocarbons) such as toluene; acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane, cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (for example, monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; and the like can be used.

[0090] The initiator used for polymerization can be appropriately selected from the polymerization initiators known in the art depending on the kind of the polymerization method. For example, one or two or more of azo-based polymerization initiators such as 2,2’-azobisisobutyronitrile (AIBN) can be preferably used. As other examples of the polymerization initiator, there can be mentioned: persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide, hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. As further other examples of the polymerization initiator, there can be mentioned redox-based initiators based on the combination of a peroxide and a reducing agent. Such polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used is a usual amount, and can be selected from the range of, for example, about 0.005 parts by weight to about 1 part by weight (typically, about 0.01 parts by weight to about 1 part by weight) with respect to 100 parts by weight of the monomer component.

[0091] By the above-mentioned solution polymerization, a polymerization reaction liquid in which an acrylic polymer is dissolved in an organic solvent can be obtained. The adhesive layer in the technology disclosed herein can be formed of an adhesive composition including the above-mentioned polymerization reaction liquid or an acrylic polymer solution obtained by subjecting the reaction liquid to an appropriate post-treatment. As the above-mentioned acrylic polymer solution, a reaction liquid obtained by adjusting the above-mentioned polymerization reaction liquid to an appropriate viscosity (concentration) as needed can be used. Alternatively, an acrylic polymer solution prepared by synthesizing an acrylic polymer by a polymerization method other than solution polymerization (for example, emulsion polymerization, photopolymerization, bulk polymerization, or the like) and dissolving the acrylic polymer in an organic solvent can be used.

[0092] The weight average molecular weight (Mw) of the base polymer (preferably, an acrylic polymer) in the technology disclosed herein is not particularly limited and can be, for example, in the range of about 10 x 10 4 to 500 x 10 4 . From the viewpoint of adhesive properties, the Mw of the base polymer is preferably in the range of about 30 x 10 4 to 200 x 10 4 , more preferably about 45 x 10 4 to 150 x 10 4 , and typically about 65 x 10 4 to 130 x 10 4 . By using a base polymer having a high Mw, there is a tendency that better impact resistance is easily obtained by the cohesive force of the polymer itself. Here, the Mw refers to a value converted to a standard polystyrene by GPC (gel permeation chromatography). As the GPC device, for example, a model name "HLC-8320GPC" (column: TSK gel GMH-H(S), manufactured by Tosoh Corporation) can be used.

[0093] (Particle P HRI )

[0094] The adhesive disclosed herein typically can contain a particle P HRI . The particle P HRI is a particle capable of increasing the refractive index of the adhesive (layer), and HRI refers to high refractive index. In this sense, the particle P HRI may be referred to as a high refractive index particle. By containing the particle P HRI in the adhesive layer, an adhesive sheet having a refractive index of 1.50 or more can be produced. In addition, for example, by adjusting the particle size, the content, the total light transmittance of the adhesive sheet can be reduced. The particle P HRI may be used alone or in combination with two or more.

[0095] As the particle P HRIVarious materials capable of increasing the refractive index of the adhesive layer to 1.50 or more can be used. The refractive index of a general adhesive known in the art is less than 1.50 (for example, about 1.47), and for such a basic adhesive, the refractive index of the adhesive sheet can be increased by containing an appropriate amount of, for example, particles containing a material having a refractive index of more than 1.50 in the adhesive layer. As the particles P HRI , for example, one or two or more of particles composed of a material having a refractive index of 1.60 or more, preferably 1.70 or more, more preferably 1.80 or more, further preferably 2.00 or more (for example, 2.20 or more) can be used. The upper limit of the refractive index of the material constituting the particles P HRI is not particularly limited, and for example, 3.00 or less, 2.80 or less, further 2.50 or less, or 2.20 or less can be used from the viewpoint of handling properties in consideration of compatibility with the adhesive. The refractive index of the material constituting the particles P HRI is the refractive index obtained by measuring a single layer film of the material (the film thickness is set to be able to measure the refractive index) using a commercially available ellipsometer at 23°C. The wavelength region of the measurement is the same as the refractive index of the adhesive sheet. As the ellipsometer, for example, a product name "EC-400" (manufactured by JA. Woolam) or an equivalent thereof can be used.

[0096] The kind of the particles P HRI is not particularly limited, and one or two or more of materials capable of increasing the refractive index of the adhesive sheet can be used selected from among metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. As the particles P HRI , inorganic oxides (for example, metal oxides) capable of increasing the refractive index of the adhesive sheet can be preferably used from among inorganic oxides. As a preferred example of the material constituting the particles P HRI , inorganic oxides (specifically, metal oxides) such as titanium oxide (titanium oxide, TiO2), zirconium oxide (zirconium oxide, ZrO2), cerium oxide, aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide (Nb2O5or the like) can be listed. The particles containing these inorganic oxides (for example, metal oxides) can be used alone or in combination with two or more. Among them, particles containing titanium dioxide and zirconium dioxide are preferred, and particles containing zirconium dioxide are particularly preferred. In addition, as metal particles, for example, iron-based materials, zinc-based materials, tungsten-based materials, platinum-based materials can have a high refractive index. As organic particles, the refractive index of particles containing resins such as styrene-based resins, phenolic resins, polyester-based resins, polycarbonate-based resins, and the like is relatively high. As organic-inorganic composite particles, a composite of the above-mentioned inorganic material and an organic material, a material obtained by coating an inorganic particle with an organic material such as a resin, and the like can be listed. Note that the particles P HRIThe particle P HRI does not include a light-absorbing black colorant.

[0097] In addition, as the particle P HRI from the viewpoint of compatibility with the binder component, it is preferable to use a particle obtained by surface-treating the aforementioned organic particle, inorganic particle, with a surface-treating agent. Such surface-treatment can bring about an effect of effectively improving compatibility for a nano-sized particle having an average particle diameter of less than 1 μm. The surface-treatment can be appropriately selected depending on the kind of core particle, the kind of dispersion medium, and the like, and is not limited to a particular treatment. The surface-treatment is typically a treatment in which a surface-treating agent modifies the core particle (for example, inorganic particle such as metal oxide). The surface-treating agent can be a compound having a functional group (carboxyl group, sulfonic acid group, phosphoric acid group, hydroxyl group, amino group, isocyanate group, vinyl group, alkoxysilyl group, and the like) that is reactive with the core particle (for example, inorganic particle such as metal oxide), and an alkyl group or alkenyl group, (meth)acryloyl group, phenyl group, or the like aliphatic; alicyclic; aromatic; and other organic group. The aforementioned organic group has a prescribed hydrophobicity (lipophilicity), and thus, by the aforementioned surface-treatment, the surface of the core particle (for example, inorganic particle such as metal oxide) is hydrophobized, and compatibility with the binder component including a polymer such as an acrylic, rubber, or the like is good. Such surface-treatment can be referred to as a hydrophobic surface-treatment (hydrophobization treatment). The aforementioned surface-treatment can preferably be a treatment in which a reactive group such as an alkenyl group or (meth)acryloyl group constitutes the surface of the particle P HRI . As the surface-treating agent, the following can be listed: organic acid such as aliphatic carboxylic acid, anionic surfactant (sulfonic acid type, phosphoric acid type, fatty acid type, and the like), and other surfactant (including reactive surfactant having a reactive functional group), functional group-containing (meth)acrylate, silane coupling agent or silane compound such as alkoxysilane, siloxane compound, silazane compound, titanium coupling agent, and the like. The surface-treating agent can be used alone or in combination with two or more. The surface-treating agent can be used for surface-treatment of the core particle under appropriate methods, conditions (amount of surface-treating agent used, presence or absence of use of a reaction aid, solvent, temperature, time, and the like) known to those skilled in the art.

[0098] In some preferable modes, a surface-treatment using a sulfonic acid compound (hydrophobization treatment) can be employed for the core particle (for example, inorganic particle such as metal oxide) of the particle P HRI . As the sulfonic acid compound, the following can be listed: alkylbenzenesulfonate such as nonylbenzenesulfonate, dodecylbenzenesulfonate; naphthalenesulfonate such as dodecyl naphthalenesulfonate; alkyl diphenyl ether disulfonate such as dodecyl diphenyl ether disulfonate; and the like sulfonic acid surfactant. The sulfonic acid compound can be used alone or in combination with two or more.

[0099] In some other ways, particle P can be... HRI For inorganic particles (such as metal oxides), surface treatment (hydrophobic treatment) is performed using saturated or unsaturated aliphatic carboxylic acids or carboxyl-containing compounds such as methacrylic acid as surface treatment agents. In other methods, surface treatment (hydrophobic treatment) can be performed using isocyanate-containing (meth)acrylates such as methacryloxyethyl isocyanate (MOI) and polyfunctional (meth)acrylates such as dipentaerythritol hexaacrylate (DPHA) as surface treatment agents. In still other methods, surface treatment (hydrophobic treatment) can be performed using vinyl-containing alkoxysilanes such as vinyltrimethoxysilane (VTMS) and alkoxysilanes containing (meth)acryloyl groups as surface treatment agents.

[0100] Particle P HRI For example, it can be added to the adhesive composition in the form of a surface-treated particle dispersion. There are no particular limitations on the dispersion medium used for the above dispersion, taking into account the particle P... HRI To ensure dispersion within the adhesive layer, a suitable dispersion medium can be used. From particle P... HRI From the viewpoint of dispersibility within the adhesive layer, organic solvents are preferred. Examples of dispersion media include: alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, methyl propyl ketone (MPK), cyclohexanone, and cyclopentanone; ethers such as diethyl ether, tetrahydrofuran, dioxane, anisole, propylene glycol monomethyl ether (PGME), and propylene glycol monomethyl ether acetate; esters such as ethyl acetate, butyl acetate, and methyl acetate; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-hexane and cyclohexane; amides such as dimethylformamide and dimethylacetamide (DMA); and cellosols such as methyl cellosol, ethyl cellosol, and butyl cellosol. These dispersion media can be used alone or in combination of two or more. Ketones and amides are preferred, methyl ethyl ketone, methyl isobutyl ketone, and dimethylacetamide are more preferred, and dimethylacetamide is even more preferred. From the viewpoint of compatibility with adhesive components (e.g., components of acrylic adhesives), it is preferable to avoid using alcohols and ethers. Containing particles P HRI Particles P in the dispersion HRI There is no particular limitation on the concentration of P; from the viewpoint of good dispersibility in the adhesive layer, the concentration of P particles is acceptable. HRI Particles P in the dispersion HRI The concentration is from about 1% to about 50% by weight (e.g., from about 15% to about 35% by weight).

[0101] Particle P HRIThere are no particular limitations on the average particle size; particles of an appropriate size can be used to achieve the desired increase in refractive index, depending on the thickness of the adhesive layer, the type of adhesive, etc. Particle P HRI The average particle size can be set to approximately 1 nm or more, with approximately 5 nm or more being appropriate. From the perspective of improving refractive index, compatibility, and operability, particle P... HRI The average particle size is preferably about 10 nm or more, and can be about 20 nm or more, or about 30 nm or more. Regarding the upper limit of the above average particle size, from the viewpoint of maintaining adhesion properties, for example, about 300 nm or less is appropriate, and from the viewpoint of improving the refractive index, it is preferably about 100 nm or less, more preferably about 70 nm or less, and even more preferably about 50 nm or less, and can also be about 35 nm or less (for example, about 25 nm or less).

[0102] It should be noted that the aforementioned particle P HRI The average particle size refers to the volume average particle size, specifically, the particle size distribution measured using a particle size distribution measuring device based on laser scattering / diffraction. HRI The particle size at which the cumulative value in the particle size distribution of the dispersion is 50% (50% volume average particle size; hereinafter sometimes simply referred to as D). 50 As a measuring device, for example, the product manufactured by Microtrac Bell under the name "Microtrac MT3000II" or its equivalent can be used.

[0103] Particles P in the adhesive layer HRI There are no particular restrictions on the content of the above-mentioned particles P. HRI The content of [amount] can vary depending on the refractive index of the target adhesive sheet. For example, for the aforementioned particle P... HRI The content of [specific component] can be appropriately set to achieve a refractive index exceeding the specified value, taking into account the required adhesive properties. Additionally, the aforementioned particle P... HRI The content can also be adjusted according to the type of adhesive and particle size. HRI The particle size varies depending on factors such as compatibility with the adhesive. The particles P in the adhesive layer... HRI The content of P can be more than about 1% by weight or more than about 10% by weight. From the viewpoint of effectively increasing the refractive index of the adhesive sheet, the above-mentioned P particles... HRI The content of P in the adhesive layer is preferably about 20% by weight or more (e.g., greater than 20% by weight), more preferably about 25% by weight or more, more preferably about 30% by weight or more, even more preferably about 35% by weight or more, particularly preferably about 40% by weight or more, and may also be about 45% by weight or more. From the viewpoint of maintaining compatibility with adhesive components, adhesion strength, impact resistance, and other adhesive properties, the content of P in the adhesive layer is... HRIThe content can be set to about 75% by weight or less, about 60% by weight or less is appropriate, preferably about 50% by weight or less, and can also be about 40% by weight or less.

[0104] In addition, the particles P in the adhesive HRI The content can also be determined based on its relative relationship with the base polymer of the adhesive (e.g., acrylic polymers). Particle P HRI The content of P can be set to about 1 part by weight or more relative to 100 parts by weight of the base polymer, about 10 parts by weight or more is appropriate, and it can also be about 30 parts by weight or more (e.g., more than 30 parts by weight). From the viewpoint of increasing the refractive index of the adhesive sheet, relative to 100 parts by weight of the base polymer, the content of P particles... HRI The content of P is preferably about 50 parts by weight or more, more preferably about 70 parts by weight or more, and even more preferably about 90 parts by weight or more. From the viewpoint of maintaining compatibility with the adhesive components, adhesion strength, impact resistance, and other adhesive properties, the content of P particles in the adhesive layer is [percentage missing] relative to 100 parts by weight of the base polymer. HRI It is appropriate to set the content of the substance to be about 200 parts by weight or less, preferably about 170 parts by weight or less, more preferably about 140 parts by weight or less, and even more preferably about 120 parts by weight or less.

[0105] (particles P in the adhesive layer) HRI (particle size characteristics)

[0106] Although there are no specific restrictions, the adhesive layer contains particles P HRI In this method, particles P exist within the adhesive layer HRI The average particle size can be, for example, less than 300 nm. The particles P that exist within the binder layer are referred to here. HRI The average particle size refers to the average particle size derived from a particle size distribution based on TEM observations, specifically measured using frozen ultrathin sections of the adhesive. Particles P in the adhesive layer HRI An average particle size of less than 300 nm can mean a certain amount of particles P HRI It exists in a well-compatible state within the adhesive layer. Therefore, the use of particle P can be effectively utilized. HRI This results in an increase in the refractive index of the adhesive layer. An average particle size of less than 100 nm is suitable, preferably less than 80 nm, more preferably less than 60 nm, even more preferably less than 40 nm, and can also be less than 30 nm. Furthermore, there is no particular limitation on the lower limit of the average particle size; approximately 1 nm or more is suitable. From the viewpoint of appropriately achieving the effect of increasing the refractive index, approximately 5 nm or more is preferred, more preferably approximately 10 nm or more, and even more preferably approximately 20 nm or more. Particles P with an average particle size within the adhesive layer in the above-mentioned range... HRITypically, the particles P are present in the adhesive layer in a dispersed state. In other words, the above-mentioned adhesive layer contains an adhesive ingredient such as a base polymer, and the particles P HRI may be particles dispersed in such an adhesive layer.

[0107] In addition, the particles P present in the adhesive layer disclosed herein HRI have a standard deviation of the particle size distribution on a number basis based on the above-mentioned TEM observation of less than 35 nm, and preferably 20 nm or less (for example, less than 20 nm). Thereby, the effect of increasing the refractive index brought about by the use of the particles P HRI can be effectively exerted. The above-mentioned standard deviation is more preferably less than 15 nm, further preferably less than 10 nm, and particularly preferably less than 8 nm. The lower limit of the above-mentioned standard deviation is not particularly limited, and can be about 1 nm or more, for example, can be about 2 nm or more (typically, about 3 nm or more).

[0108] The particles P present in the adhesive layer disclosed herein HRI have a proportion of particles having a particle size of 50 nm or more in the particle size distribution on a number basis based on the above-mentioned TEM observation of about 5% or less. A small proportion of large-diameter particles having a particle size of 50 nm or more can mean that the amount of agglomerated particles is limited. In such a configuration, the effect of the particles P HRI being well compatible with the adhesive ingredient can be more appropriately exerted. In the above-mentioned particle size distribution, the proportion of particles having a particle size of 50 nm or more is preferably about 3% or less.

[0109] Although not particularly limited, the particles P present in the adhesive layer HRI preferably have a proportion of particles having a particle size of less than 15 nm in the particle size distribution on a number basis based on the above-mentioned TEM observation limited. This is because the particles having a particle size of less than 15 nm contain small-diameter particles that are considered to have a small contribution to the increase in the refractive index. From such a viewpoint, in the above-mentioned particle size distribution, the proportion of particles having a particle size of less than 15 nm is preferably about 30% or less, more preferably about 20% or less, and further preferably about 15% or less. Taking into account the difficulty of completely controlling the particle size distribution and the like, in the above-mentioned particle size distribution, the proportion of particles having a particle size of less than 15 nm can be about 1% or more, for example, can be 2% or more (further, about 3% or more).

[0110] The average particle size, the standard deviation, and other particle size distribution characteristics calculated from the particle size distribution on a number basis based on the above-mentioned TEM observation can be controlled by the selection of the kind of the particles P HRI , the composition of the adhesive (mainly the monomer composition of the base polymer, the kind and amount of the crosslinking agent, and the like), the surface treatment of the above-mentioned particles P HRI suitable for the adhesive, the selection of the kind and the amount of the dispersant, and the particles PHRI The addition form (dispersion liquid, dispersion medium, etc.), the addition conditions, etc. in the adhesive composition are implemented. For example, by combining different particles P HRI , surface treatment methods, adhesive components, thereby making various adhesives, and using the above-mentioned TEM observation to screen (if necessary, repeating the operation), an adhesive containing particles P HRI having the desired particle size distribution characteristics can be obtained. The kind and surface treatment method of the particles P HRI can be selected based on the properties of the adhesive containing the particles P HRI based on the content of the description and technical knowledge of the present specification. The average particle size, standard deviation, and other particle size characteristics calculated from the number-based particle size distribution based on the above-mentioned TEM observation are specifically determined by the method described in the examples described later.

[0111] (Coloring agent)

[0112] A coloring agent can be contained in the adhesive layer. Thereby, the light transmittance (light shielding property) of the adhesive sheet can be adjusted. As the coloring agent, various materials capable of attenuating light traveling in the adhesive layer by absorption can be used. The coloring agent can be, for example, a black, gray, red, blue, yellow, green, yellow-green, orange, purple, etc. coloring agent. The above-mentioned coloring agent can typically be contained in the adhesive layer in a state of being dispersed in the constituent material of the adhesive layer (may be a state of being dissolved). As the coloring agent, one or two or more materials capable of reducing the total light transmittance among the pigments and dyes known in the past can be used. As the pigments, inorganic pigments, organic pigments can be listed. As the dyes, for example, azo dyes, anthraquinone, quinophthalone, styryl, diphenylmethane, triphenylmethane, oxazine, triazine, xanthan gum, methane, azomethine, acridine, diazine can be listed. The coloring agent can be used alone or in combination with two or more as appropriate.

[0113] (Black coloring agent)

[0114] Since the light shielding property can be efficiently adjusted with a small amount of coloring agent, a black coloring agent can be preferably used. As specific examples of the black coloring agent, carbon black, graphite, aniline black, perylene black, cyanine black, activated carbon, molybdenum disulfide, chromium complex, anthraquinone coloring agent, etc. can be listed. The black coloring agent can be used alone or in combination with two or more as appropriate.

[0115] (Carbon black particles)

[0116] In some preferred embodiments, the adhesive layer contains carbon black particles. The carbon black particles used can be of any type commonly known as carbon black (furnace black, channel black, acetylene black, thermal cracking black, lampblack, pine soot, etc.) without particular limitation. Alternatively, surface-modified carbon black particles having functional groups such as carboxyl, amino, sulfonic acid, or silicon-containing groups (e.g., alkoxysilyl, alkylsilyl) can also be used. Such surface-modified carbon black particles are also called self-dispersing carbon black, eliminating the need for dispersants or reducing their dosage. The aforementioned carbon black particles can be used alone or in combination of two or more.

[0117] In the case where the adhesive layer contains carbon black particles, the content of colorant other than carbon black particles in the adhesive layer is not particularly limited. For example, it can be set to less than 13% by weight, preferably less than 10% by weight, for example, less than 5% by weight, and can be set to less than 3.0% by weight (e.g., less than 2.0% by weight, further less than 1% by weight). The technology disclosed herein is preferably implemented in a manner having an adhesive layer that substantially does not contain colorant other than carbon black particles. It should be noted that, in this specification, "substantially does not contain" means not intentionally added, for example, the content in the adhesive layer can be less than 0.3% by weight (e.g., less than 0.1% by weight, typically less than 0.01% by weight).

[0118] Since the opacity of the adhesive layer can be efficiently adjusted using a small amount of colorant, particulate colorants (pigments) are preferred. In some preferred embodiments, colorants with an average particle size of about 10 nm or more (e.g., about 30 nm or more) (e.g., particulate black colorants such as carbon black) can be used. The aforementioned average particle size is, for example, about 50 nm or more, about 100 nm or more, or about 150 nm or more. There is no particular upper limit to the average particle size of the aforementioned colorant; for example, it is about 3000 nm or less, or about 1000 nm or less. From the viewpoint of improving opacity, it is appropriate for the average particle size of the aforementioned colorant to be about 500 nm or less, preferably about 300 nm or less, more preferably about 250 nm or less, and even more preferably about 200 nm or less (e.g., about 120 nm or less, and even more preferably about 100 nm or less).

[0119] It should be noted that the average particle size of the colorant in this specification refers to the volume average particle size. Specifically, it refers to the particle size at which the cumulative value of the particle size distribution reaches 50% (50% volume average particle size; sometimes abbreviated as D below) as measured by a particle size distribution measuring device based on laser scattering / diffraction. 50 As the measuring device, products such as "Microtrac MT3000II" or equivalents manufactured by MicrotracBell can be used.

[0120] In the technology disclosed herein, the form of addition of the colorant (preferably black colorant such as carbon black particles) in the adhesive composition is not particularly limited. The colorant such as carbon black particles can be added to the adhesive composition in the form of a dispersion liquid in which the particles are dispersed in a dispersion medium. The dispersion medium constituting the dispersion liquid is not particularly limited, and examples include water (ion exchange water, reverse osmosis water, distilled water, etc.), various organic solvents (alcohols such as ethanol; ketones such as acetone; ethers such as butyl cellosolve, propylene glycol monomethyl ether acetate; esters such as ethyl acetate; aromatic hydrocarbons such as toluene; mixed solvents thereof), and aqueous mixed solvents of water and the above-mentioned organic solvents. The above-mentioned dispersion liquid can contain the above-mentioned dispersant. By mixing the above-mentioned dispersion liquid into the adhesive composition, the above-mentioned adhesive composition contains the colorant (preferably black colorant such as carbon black particles), and can also contain the dispersant.

[0121] The content of the colorant (preferably black colorant such as carbon black particles) is not particularly limited, and can be appropriately set in consideration of the adhesive layer thickness, the light shielding property to be achieved, the required adhesive properties, etc. The content of the colorant in the adhesive layer is preferably about 0.1% by weight or more, and from the viewpoint of light shielding property, it is preferably about 0.5% by weight or more, more preferably about 1% by weight or more, further preferably about 2% by weight or more, particularly preferably about 2.5% by weight or more, and for example, it can be about 3% by weight or more. In addition, the content of the above-mentioned colorant (preferably black colorant such as carbon black particles) can be set to about 50% by weight or less, and about 30% by weight or less is appropriate, and from the viewpoint of adhesive properties, etc., it is preferably about 10% by weight or less. In the case of preferentially increasing the refractive index, or in the case of emphasizing the adhesive properties such as adhesion, the content of the above-mentioned colorant (preferably black colorant such as carbon black particles) is preferably about 7% by weight or less, more preferably about 5% by weight or less, and can be about 3% by weight or less.

[0122] The technology disclosed herein is implemented in a manner in which the adhesive layer contains the above-mentioned particles P HRI and a colorant (for example, black colorant, preferably carbon black particles). HRI The content ratio of the particles P HRI and the colorant is set in a manner to achieve the target refractive index and light shielding property, and thus is not limited to a particular range. The content ratio of the particles P HRI and the colorant is preferably set in a range that does not impair the dispersibility, compatibility, etc. of both in the adhesive layer. For example, the content C HRI of the particles P CB relative to the content C HRI of the carbon black particles as the colorant can be set in a range of 1 to 100 in terms of the weight ratio (C CB / C HRIfrom the viewpoint of appropriately exhibiting the coloring effect (blackening) due to the carbon black particles in the configuration containing the particles P HRI from the viewpoint of appropriately exhibiting the coloring effect (blackening) due to the carbon black particles in the configuration containing the particles P CB ) of 70 or less is appropriate, 50 or less is preferable, 40 or less is more preferable, and for example, 35 or less can be used. HRI from the viewpoint of appropriately exhibiting the coloring effect (blackening) due to the carbon black particles in the configuration containing the particles P HRI from the viewpoint of appropriately exhibiting the coloring effect (blackening) due to the carbon black particles in the configuration containing the particles P CB

[0123] The adhesive composition disclosed herein can contain a component that contributes to improving the dispersibility of the coloring agent described above. The dispersibility-improving component can be, for example, a polymer, an oligomer, a liquid resin, a surfactant (anionic surfactant, cationic surfactant, nonionic surfactant, amphoteric surfactant), or the like. The dispersibility-improving component can be used alone or in combination with two or more. The dispersibility-improving component described above is preferably dissolved in the adhesive composition. The oligomer described above can be, for example, a low-molecular-weight polymer (for example, an acrylic oligomer having a Mw of less than about 10 x 10 4 , preferably less than 5 x 10 4 ) containing one or two or more of the monomer components exemplified above. The liquid resin described above can be, for example, a tackifying resin having a softening point of about 50°C or less, more preferably about 40°C or less (typically, a tackifying resin such as a rosin-based, terpene-based, or hydrocarbon-based tackifying resin, for example, hydrogenated methyl rosin, or the like). With such a dispersibility-improving component, it is possible to suppress uneven dispersion of the coloring agent (for example, a particulate black coloring agent such as carbon black), and further, it is possible to suppress uneven color of the adhesive layer. Thus, it is possible to form an adhesive sheet having better appearance quality.

[0124] The method of adding the dispersibility-improving component is not particularly limited, and it can be contained in a liquid containing the coloring agent (preferably, a black coloring agent such as carbon black particles) before being compounded into the adhesive composition, or it can be supplied to the adhesive composition at the same time as the coloring agent or before or after the coloring agent is added.

[0125] ​The content of the dispersibility-improving component is not particularly limited, and is desirably set to be 20% by mass or less (preferably 10% by mass or less, more preferably 7% by mass or less, for example, 5% by mass or less) of the adhesive layer as a whole from the viewpoint of suppressing the influence on the adhesion properties (for example, reduction in cohesiveness). In some modes, the content of the dispersibility-improving component can be set to be 10 times or less (preferably 5 times or less, for example, 3 times or less) of the weight of the colorant. On the other hand, the content is desirably set to be 0.2% by mass or more (typically 0.5% by mass or more, preferably 1% by mass or more) of the adhesive layer as a whole from the viewpoint of appropriately exerting the effect of the dispersibility-improving component. In some modes, the content of the dispersibility-improving component can be set to be 0.2 times or more (preferably 0.5 times or more, for example, 1 times or more) of the weight of the colorant.

[0126] (tackifying resin)

[0127] The adhesive layer in the technology disclosed herein can contain a tackifying resin. Thereby, the peel strength of the adhesive sheet can be increased. As the tackifying resin, one or two or more selected from among various tackifying resins known in the art such as phenol-based tackifying resins, terpene-based tackifying resins, modified terpene-based tackifying resins, rosin-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, ketone-based tackifying resins, and the like can be used.

[0128] Examples of the phenol-based tackifying resin include terpene phenol resins, hydrogenated terpene phenol resins, alkyl phenol resins, and rosin phenol resins.

[0129] The terpene phenol resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept including both a copolymer of a terpene compound and a phenol compound (terpene-phenol copolymer resin) and a resin obtained by phenol-modification of a homopolymer or a copolymer of a terpene compound (phenol-modified terpene resin). As a preferable example of the terpene compound constituting such a terpene phenol resin, monoterpenes such as α-pinene, β-pinene, limonene (containing d-body, l-body, and d / l-body (terpene hydrate)), and the like can be listed. The hydrogenated terpene phenol resin refers to a hydrogenated terpene phenol resin having a structure obtained by hydrogenation of such a terpene phenol resin. It is also sometimes referred to as a hydrogenated terpene phenol resin.

[0130] The alkyl phenol resin is a resin (oily phenol resin) obtained from an alkyl phenol and formaldehyde. As examples of the alkyl phenol resin, novolak type and resol type can be listed.

[0131] Rosin phenol resins are typically phenol-modified products of rosins or various derivatives of rosins described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenol resins include rosin phenol resins obtained by a method of adding phenol to rosins or various derivatives of rosins described above with an acid catalyst and performing thermal polymerization, and the like.

[0132] Examples of terpene-based tackifying resins include polymers of terpene-based compounds (typically monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene, terpinenes, and the like. The polymers can be homopolymers of one terpene-based compound, or copolymers of two or more terpene-based compounds. As homopolymers of one terpene-based compound, α-pinene polymers, β-pinene polymers, terpinene polymers, and the like can be given. As examples of modified terpene resins, resins obtained by modifying the above-described terpene resins can be given. Specifically, styrene-modified terpene resins, hydrogenated terpene resins, and the like can be given as examples.

[0133] The concept of rosin-based tackifying resins described here includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (crude rosin) such as gum rosin, wood rosin, tall oil rosin, and the like; and modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins) obtained by modifying these unmodified rosins by hydrogenation, disproportionation, polymerization, and the like.

[0134] Rosin derivative resins are typically derivatives of rosins as described above. The concept of rosin resins described here includes derivatives of unmodified rosins and derivatives of modified rosins (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). Rosin esters such as unmodified rosin esters as esters of unmodified rosins with alcohols, modified rosin esters as esters of modified rosins with alcohols, and the like can be given. Unsaturated fatty acid-modified rosins obtained by modifying rosins with unsaturated fatty acids can be given. Unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids can be given. Rosin alcohols obtained by reducing the carboxyl groups of rosins or various derivatives of rosins described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters) can be given. Metal salts of rosins or various derivatives of rosins described above can be given. As specific examples of rosin esters, methyl esters, triethylene glycol esters, glycerol esters, pentaerythritol esters, and the like of unmodified rosins or modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, and the like) can be given.

[0135] As examples of hydrocarbon-based tackifying resins, various resins of hydrocarbons such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers and the like), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, coumarone-indene-based resins, and the like can be given.

[0136] The softening point of the tackifying resin is not particularly limited. From the viewpoint of improving cohesiveness, in some embodiments, it can be preferable to use a tackifying resin having a softening point (softening temperature) of about 80°C or higher (preferably about 100°C or higher). The technology disclosed herein can be preferably implemented in such a manner that the total amount of the tackifying resin contained in the adhesive layer is set to 100% by weight, of which more than 50% by weight (more preferably more than 70% by weight, for example, more than 90% by weight) is a tackifying resin having the above-mentioned softening point. For example, it can be preferable to use a phenolic tackifying resin (terpene phenol resin or the like) having such a softening point. The tackifying resin can contain, for example, a terpene phenol resin having a softening point of about 135°C or higher (furthermore, about 140°C or higher). The upper limit of the softening point of the tackifying resin is not particularly limited. From the viewpoint of improving adhesion to the adherend, in some embodiments, it can be preferable to use a tackifying resin having a softening point of about 200°C or lower (more preferably about 180°C or lower). Note that the softening point of the tackifying resin can be measured based on the softening point test method (ring and ball method) prescribed in JIS K2207.

[0137] In some preferred embodiments, the tackifying resin described above can contain one or two or more phenolic tackifying resins (typically, terpene phenol resins). The technology disclosed herein can be preferably implemented, for example, in such a manner that the total amount of the tackifying resin is set to 100% by weight, of which about 25% by weight or more (more preferably about 30% by weight or more) is a terpene phenol resin. It can be that about 50% by weight or more of the total amount of the tackifying resin is a terpene phenol resin, or it can be that about 80% by weight or more (for example, about 90% by weight or more) is a terpene phenol resin. It can also be that substantially all (for example, about 95% by weight to 100% by weight, further about 99% by weight to 100% by weight) of the tackifying resin is a terpene phenol resin.

[0138] Although not particularly limited, in some embodiments, the tackifying resin described above can contain a tackifying resin having a hydroxyl value higher than 20 mgKOH / g. Of these, a tackifying resin having a hydroxyl value of 30 mgKOH / g or more is preferable. Hereinafter, a tackifying resin having a hydroxyl value of 30 mgKOH / g or more will sometimes be referred to as a “high hydroxyl value resin”. By using a tackifying resin containing such a high hydroxyl value resin, it is possible to achieve an adhesive layer that has excellent adhesion to the adherend and high cohesiveness. In some embodiments, the tackifying resin described above can contain a high hydroxyl value resin having a hydroxyl value of 50 mgKOH / g or more (more preferably 70 mgKOH / g or more).

[0139] Note that, as the value of the hydroxyl value described above, a value measured according to the potentiometric titration method prescribed in JIS K0070:1992 can be used.

[0140] As the high-hydroxyl group resin, a resin having a hydroxyl group value of a prescribed value or more among the various tackifying resins described above can be used. The high-hydroxyl group resin can be used alone or in combination with two or more. For example, as the high-hydroxyl group resin, a phenolic tackifying resin having a hydroxyl group value of 30 mgKOH / g or more can be preferably used. In some preferred modes, as the tackifying resin, at least a terpene phenol resin having a hydroxyl group value of 30 mgKOH / g or more is used. The terpene phenol resin is suitable because the hydroxyl group value can be arbitrarily controlled by the copolymerization ratio of the phenol.

[0141] The upper limit of the hydroxyl group value of the high-hydroxyl group resin is not particularly limited. From the viewpoint of compatibility with the base polymer and the like, it is appropriate that the hydroxyl group value of the high-hydroxyl group resin be about 200 mgKOH / g or less, preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less, and further preferably about 140 mgKOH / g or less. The technology disclosed herein can be preferably implemented in a mode in which the tackifying resin contains a high-hydroxyl group resin (for example, a phenolic tackifying resin, preferably a terpene phenol resin) having a hydroxyl group value of 30 mgKOH / g to 160 mgKOH / g. In some modes, it can be preferable to use a high-hydroxyl group resin having a hydroxyl group value of 30 mgKOH / g to 80 mgKOH / g (for example, 30 mgKOH / g to 65 mgKOH / g). In other modes, it can be preferable to use a high-hydroxyl group resin having a hydroxyl group value of 70 mgKOH / g to 140 mgKOH / g.

[0142] Although not particularly limited, in the case of using a high-hydroxyl group resin, the proportion of the high-hydroxyl group resin (for example, a terpene phenol resin) in the entire tackifying resin contained in the adhesive layer can be set to about 25% by mass or more, preferably about 30% by mass or more, and more preferably about 50% by mass or more (for example, about 80% by mass or more, typically about 90% by mass or more), for example. It can also be that substantially all (for example, about 95% by mass to 100% by mass, further about 99% by mass to 100% by mass) of the tackifying resin is a high-hydroxyl group resin.

[0143] In the case where the adhesive layer contains a tackifying resin, the amount of use of the tackifying resin is not particularly limited, and can be appropriately set in the range of about 1 part by mass to about 100 parts by mass with respect to 100 parts by mass of the base polymer, for example. From the viewpoint of appropriately exerting the effect of improving the peeling strength, it is appropriate that the amount of use of the tackifying resin be set to 5 parts by mass or more, and preferably 10 parts by mass or more, with respect to 100 parts by mass of the base polymer (for example, an acrylic polymer). In addition, from the viewpoint of impact resistance and cohesiveness, it is appropriate that the amount of use of the tackifying resin be set to 50 parts by mass or less, and can be set to 40 parts by mass or less, or 30 parts by mass or less, with respect to 100 parts by mass of the base polymer (for example, an acrylic polymer).

[0144] (Cross-linking agent)

[0145] In the disclosed technology, the adhesive composition used in the formation of the adhesive layer may include a crosslinking agent as needed. There are no particular limitations on the type of crosslinking agent, and it can be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include, for instance, isocyanate crosslinking agents, epoxy crosslinking agents, etc. Crosslinking agents include zopyridine, melamine, peroxide, urea, metal alkoxide, metal chelate, metal salt, carbodiimide, hydrazine, amine, and silane coupling agents. Among these, isocyanate and epoxy crosslinking agents are preferred. Zoltidine crosslinking agents, aziridine crosslinking agents, and melamine crosslinking agents are preferred, with isocyanate crosslinking agents and epoxy crosslinking agents being particularly preferred. By using isocyanate crosslinking agents, it is desirable to obtain adhesive layer cohesion and superior impact resistance compared to other crosslinking systems. Furthermore, the use of isocyanate crosslinking agents is advantageous, for example, from the viewpoint of improving adhesive strength to adhered materials made of polyester resins such as PET. One crosslinking agent can be used alone, or two or more can be used in combination.

[0146] As isocyanate crosslinking agents, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including substances with isocyanurate structures) are preferred. Isocyanate crosslinking agents can be used alone or in combination of two or more.

[0147] Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

[0148] Specific examples of aliphatic polyisocyanates include: 1,2-ethylidene diisocyanate; 1,2-butylidene diisocyanate, 1,3-butylidene diisocyanate, 1,4-tetramethylene diisocyanate, and other butylidene diisocyanates; 1,2-hexylidene diisocyanate, 1,3-hexylidene diisocyanate, 1,4-hexylidene diisocyanate, 1,5-hexylidene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexylidene diisocyanate, and other hexylidene diisocyanates; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, etc.

[0149] As specific examples of the alicyclic polyisocyanates, there can be mentioned isophorone diisocyanate; 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate, and the like; 1,2-cyclopentyl diisocyanate, 1,3-cyclopentyl diisocyanate, and the like; hydrogenated xylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethyl xylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and the like.

[0150] As specific examples of the aromatic polyisocyanates, there can be mentioned 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthalene 1,4-diisocyanate, naphthalene 1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene 1,4-diisocyanate, xylylene 1,3-diisocyanate, and the like.

[0151] As the preferred polyfunctional isocyanate, there can be exemplified a polyfunctional isocyanate having three or more isocyanate groups per molecule on average. The tri- or higher functional isocyanate can be a polymer (typically, a dimer or a trimer) of di- or tri- or higher functional isocyanate, a derivative (for example, an addition reaction product of a polyhydric alcohol with two or more molecules of a polyfunctional isocyanate), a polymer, or the like. For example, there can be mentioned a dimer of diphenylmethane diisocyanate or a trimer of diphenylmethane diisocyanate, an isocyanurate of hexamethylene diisocyanate (a trimer addition product of an isocyanurate structure), a reaction product of trimethylolpropane with toluene diisocyanate, a reaction product of trimethylolpropane with hexamethylene diisocyanate, a polymeric methylene polyphenyl isocyanate, a polyether polyisocyanate, a polyester polyisocyanate, and the like. As commercially available products of the polyfunctional isocyanate, there can be mentioned "DURANATE TPA-100" manufactured by Asahi Kasei Chemicals Corporation, "CORONATE L" manufactured by DKS Co., Ltd., "CORONATE HL" of DKS Co., Ltd., "CORONATE HK" of DKS Co., Ltd., "CORONATE HX" of DKS Co., Ltd., "CORONATE 2096" of DKS Co., Ltd., and the like.

[0152] The amount of use of the isocyanate-based crosslinking agent is not particularly limited. For example, it can be set to 0.5 parts by weight or more with respect to 100 parts by weight of the base polymer. From the viewpoint of balancing cohesiveness and adhesion, impact resistance, and the like, the amount of use of the isocyanate-based crosslinking agent can be set to 1.0 parts by weight or more, and can also be set to 1.5 parts by weight or more (typically 2.0 parts by weight or more, for example, 2.5 parts by weight or more) with respect to 100 parts by weight of the base polymer. On the other hand, from the viewpoint of improving adhesion to adherends, it is appropriate that the amount of use of the isocyanate-based crosslinking agent is set to 10 parts by weight or less with respect to 100 parts by weight of the base polymer, and can be set to 8 parts by weight or less, and can also be set to 5 parts by weight or less (for example, 3 parts by weight or less).

[0153] In some preferred modes, as the crosslinking agent, an isocyanate-based crosslinking agent and at least one crosslinking agent different in kind of crosslinkable functional group from the isocyanate-based crosslinking agent can be used in combination. According to the technology disclosed herein, by using in combination a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent different in kind of crosslinkable reactive group from the isocyanate-based crosslinking agent. Hereinafter also referred to as "non-isocyanate-based crosslinking agent".) and an isocyanate-based crosslinking agent, excellent cohesiveness can be exerted. For example, in a configuration including a rust preventive such as an azole-based rust preventive, high heat-resistant cohesiveness and excellent metal corrosion prevention can be appropriately balanced. Note that the adhesive layer in the technology disclosed herein can contain the above crosslinking agent in a state after crosslinking reaction, a state before crosslinking reaction, a state in which a part of the crosslinking reaction is performed, an intermediate or a complex of these states, or the like. The above crosslinking agent is typically contained in the adhesive layer mainly in a state after crosslinking reaction.

[0154] The kind of non-isocyanate-based crosslinking agent that can be used in combination with the isocyanate-based crosslinking agent is not particularly limited, and can be appropriately selected from the above crosslinking agents. The non-isocyanate-based crosslinking agent can be used alone or in combination with two or more kinds.

[0155] In some preferred modes, an epoxy-based crosslinking agent can be used as the non-isocyanate-based crosslinking agent. For example, by using an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent in combination, cohesiveness and impact resistance can be easily balanced. As the epoxy-based crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based crosslinking agent having three to five epoxy groups in one molecule is preferred. The epoxy-based crosslinking agent can be used alone or in combination with two or more kinds.

[0156] Although not particularly limited, as specific examples of the epoxy-based crosslinking agent, for example, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, and the like can be exemplified. As commercially available products of the epoxy-based crosslinking agent, for example, "TETRAD-C" and "TETRAD-X" manufactured by Mitsubishi Gas Chemical Company, Inc., "EPICLON CR-5L" manufactured by DIC Corporation, "Denacol EX-512" manufactured by Nagase Chemtex Corporation, "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd., and the like can be exemplified.

[0157] The use amount of the epoxy-based crosslinking agent is not particularly limited. The use amount of the epoxy-based crosslinking agent can be set to be greater than 0 parts by weight and about 1 part by weight or less (typically, about 0.001 parts by weight to 0.5 parts by weight) with respect to 100 parts by weight of the base polymer, for example. From the viewpoint of appropriately exerting the effect of improving the cohesiveness, it is appropriate for the use amount of the epoxy-based crosslinking agent to be set to be about 0.002 parts by weight or more, preferably about 0.005 parts by weight or more, and more preferably about 0.008 parts by weight or more with respect to 100 parts by weight of the base polymer. In addition, from the viewpoint of improving the adhesion to the adherend, it is appropriate for the use amount of the epoxy-based crosslinking agent to be set to be about 0.2 parts by weight or less, preferably about 0.1 parts by weight or less, and more preferably less than about 0.05 parts by weight, and further preferably less than about 0.03 parts by weight (for example, about 0.025 parts by weight or less) with respect to 100 parts by weight of the base polymer. By reducing the use amount of the epoxy-based crosslinking agent, there is a tendency that the impact resistance is improved.

[0158] In the technology disclosed herein, the relationship between the content of the isocyanate-based crosslinking agent and the content of the non-isocyanate-based crosslinking agent (e.g., the epoxy-based crosslinking agent) is not particularly limited. The content of the non-isocyanate-based crosslinking agent can be set to be about 1 / 50 or less of the content of the isocyanate-based crosslinking agent, for example. From the viewpoint of more appropriately balancing the adhesion to the adherend and the cohesiveness, it is appropriate for the content of the non-isocyanate-based crosslinking agent to be set to be about 1 / 75 or less, and preferably about 1 / 100 or less (e.g., 1 / 150 or less) of the content of the isocyanate-based crosslinking agent on a weight basis. In addition, from the viewpoint of appropriately exerting the effect brought about by the combination use of the isocyanate-based crosslinking agent and the non-isocyanate-based crosslinking agent (e.g., the epoxy-based crosslinking agent), it is appropriate for the content of the non-isocyanate-based crosslinking agent to be set to be about 1 / 1000 or more, for example, about 1 / 500 or more of the content of the isocyanate-based crosslinking agent.

[0159] There is no particular limitation on the total amount (total amount) of crosslinking agent used. For example, it can be set to about 10 parts by weight or less relative to 100 parts by weight of the base polymer (preferably an acrylic polymer), and can be selected from a range of about 0.005 parts by weight to 10 parts by weight, more preferably from about 0.01 parts by weight to 5 parts by weight.

[0160] (Rust inhibitor)

[0161] In some preferred embodiments, the adhesive layer may contain a rust inhibitor. Zolidine-based rust inhibitors are preferably used as rust inhibitors. Adhesive layers containing the aforementioned rust inhibitors are preferred when adhesion to metals or other applications requiring protection against metal corrosion. As azole-based rust inhibitors, azole compounds containing a five-membered ring aromatic compound with two or more heteroatoms, at least one of which is a nitrogen atom, are preferably used as the active ingredient. As the aforementioned azole compound, azole compounds not conventionally used as rust inhibitors for metals such as copper can be appropriately employed.

[0162] Examples of azole compounds include: imidazole, pyrazole, etc. azole, isotonic azole, thiazole, isothiazole, selenazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,5- diazole, 1,3,4- Azides such as diazoles, 1,2,3-thiadiazoles, 1,2,4-thiadiazoles, 1,3,4-thiadiazoles, tetraazoles, and 1,2,3,4-thiatriazoles; their derivatives; their amine salts; their metal salts; etc. Examples of derivatives of azoles include compounds with fused ring structures containing an azole ring and other rings, such as a benzene ring. Specific examples include: indazoles, benzimidazoles, benzotriazoles (i.e., 1,2,3-benzotriazoles with a structure obtained by fusion of the azole ring of a 1,2,3-triazole with a benzene ring), benzothiazoles, and further, alkylbenzotriazoles (e.g., 5-methylbenzotriazole, 5-ethylbenzotriazole, 5-n-propylbenzotriazole, 5-isobutylbenzotriazole, 4-methylbenzotriazole), alkoxybenzotriazoles (e.g., 5-methoxybenzotriazole), and alkylamines. Benzotriazoles, alkylaminosulfonylbenzotriazoles, mercaptobenzotriazoles, hydroxybenzotriazoles, nitrobenzazoles (e.g., 4-nitrobenzazole), halobenzotriazoles (e.g., 5-chlorobenzotriazole), hydroxyalkylbenzotriazoles, hydroxybenzotriazoles, aminobenzotriazoles, (substituted aminomethyl)-tolyltriazoles, carboxybenzotriazoles, N-alkylbenzotriazoles, bisbenzotriazoles, naphthiazoles, mercaptobenzothiazoles, aminobenzothiazoles, etc., their amine salts, their metal salts, etc. Other examples of azole derivatives include: non-fused-ring azole derivatives, such as compounds with substituents on a non-fused azole ring like 3-amino-1,2,4-triazoles and 5-phenyl-1H-tetrazoles. Azole compounds can be used alone or in combination of two or more.

[0163] Preferred examples of compounds that can be used as azole-based rust inhibitors include benzotriazole-based rust inhibitors with benzotriazole compounds as active ingredients. The techniques disclosed herein are preferably implemented, for example, in a manner where the base polymer is an acrylic polymer and the rust inhibitor is a benzotriazole-based rust inhibitor. In such a manner, adhesive sheets with good resistance to metal corrosion and excellent adhesive reliability can be suitably achieved. Preferred examples of benzotriazole compounds include: 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, carboxybenzotriazole, etc.

[0164] Examples of rust inhibitors other than azole-based rust inhibitors that can be included in the adhesive layer disclosed herein are not particularly limited, and examples include: amine compounds, nitrites, ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, hexamethylenetetramine, thiourea, phenyl carbamate, N-cyclohexylcarbamate cyclohexylammonium (CHC), etc. These rust inhibitors other than azole-based rust inhibitors (non-azole-based rust inhibitors) can be used alone or in combination of two or more. The technology disclosed herein is preferably implemented in a manner that substantially avoids the use of non-azole-based rust inhibitors.

[0165] The content of the rust preventive agent (preferably an azole-based rust preventive agent such as a benzotriazole-based rust preventive agent) is not particularly limited, and for example, it can be set to 0.01 parts by weight or more (typically 0.05 parts by weight or more) with respect to 100 parts by weight of the base polymer. From the viewpoint of obtaining a more excellent effect of preventing metal corrosion, the above content can be 0.1 parts by weight or more, can be 0.3 parts by weight or more, or can be 0.5 parts by weight or more. On the other hand, from the viewpoint of improving the cohesiveness of the adhesive, it is appropriate that the content of the rust preventive agent is set to less than 8 parts by weight with respect to 100 parts by weight of the base polymer, can be set to 6 parts by weight or less, or can be set to 5 parts by weight or less.

[0166] (Other additives)

[0167] The adhesive composition can contain various additives commonly used in the field of adhesives, such as a leveling agent, a crosslinking aid, a plasticizer, a softening agent, an antistatic agent, an anti-aging agent, an ultraviolet absorber, an antioxidant, a light stabilizer, and the like, as needed. For such various additives, conventionally known substances can be used by a conventional method, and are not the features of the present application, and thus detailed description is omitted.

[0168] (Adhesive composition)

[0169] The adhesive layer (layer composed of an adhesive) disclosed herein can be an adhesive layer formed of an aqueous adhesive composition, a solvent-type adhesive composition, a hot-melt-type adhesive composition, or a living energy ray-curable adhesive composition that is cured by irradiation of a living energy ray such as ultraviolet rays or electron rays. The aqueous adhesive composition refers to an adhesive composition in a form in which an adhesive (adhesive layer-forming component) is contained in a solvent (aqueous solvent) in which water is the main component, and is typically a so-called water-dispersible adhesive composition (composition in a form in which at least a part of the adhesive is dispersed in water) or the like. In addition, the solvent-type adhesive composition refers to an adhesive composition in a form in which an adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-type adhesive composition, one or two or more of the organic solvents exemplified as the organic solvents that can be used in the above-described solution polymerization (toluene, ethyl acetate, and the like) can be used without particular limitation. The technology disclosed herein can be preferably implemented in a manner in which an adhesive layer formed of a solvent-type adhesive composition is provided from the viewpoint of adhesive properties and the like. In the manner in which a solvent-type adhesive layer formed of a solvent-type adhesive composition is provided, the effect of increasing the refractive index brought about by the technology disclosed herein can be preferably achieved.

[0170] As described above, according to the present specification, an adhesive composition is provided, which contains one or two or more of the components that can be contained in the adhesive layer disclosed herein. By using the adhesive composition, an adhesive sheet having an increased refractive index and good impact resistance can be obtained. The above-mentioned adhesive composition contains a base polymer, and preferably can contain the particles P HRI In addition, a colorant (preferably a black colorant, more preferably carbon black particles) can be contained. Furthermore, the above-mentioned components that can be contained in the adhesive layer can be contained. The content (wt%) of each component that can be contained in the adhesive layer can be referred to as the content (wt%) of the solid component basis (also referred to as the non-volatile component basis) in the adhesive composition. For details of the other adhesive composition, as described in the adhesive layer, the repeated description is omitted.

[0171] (Formation of the adhesive layer)

[0172] The adhesive layer disclosed herein can be formed by a method known in the art. For example, a method of forming an adhesive layer by applying an adhesive composition on a surface having a peeling property (peeling surface) and drying it can be employed. As the above-mentioned peeling surface, for example, the surface of a peeling liner described later can be preferably used.

[0173] The coating of the adhesive composition can be performed using a coating machine known in the art such as a gravure roll coater, a die coater, a bar coater, and the like. Alternatively, the adhesive composition can be coated by dipping, curtain coating, and the like.

[0174] From the viewpoint of promoting the crosslinking reaction, improving the manufacturing efficiency, and the like, the drying of the adhesive composition is preferably performed under heating. The drying temperature can be set to, for example, about 40°C to about 150°C, and is preferably set to about 60°C to about 130°C. After the adhesive composition is dried, further aging can be performed for the purpose of adjustment of the transfer of the components within the adhesive layer, progress of the crosslinking reaction, relaxation of the strain that can exist within the adhesive layer, and the like.

[0175] The adhesive layer disclosed herein can be a single layer structure, or can be a multilayer structure having two or more layers. From the viewpoint of productivity and the like, the adhesive layer is preferably a single layer structure. Alternatively, in the adhesive layer, the above-mentioned particles P HRI and the like can be contained in a prescribed thickness region on the surface side of the adhesive layer, and the colorant and the like can be contained in a prescribed region of the adhesive layer. By such a configuration, an adhesive sheet having a breaking strength of a prescribed value or less and a refractive index of a prescribed value or more can be obtained. The adhesive layer having the above-mentioned multilayer structure, and the adhesive layer in which a specific component is biased can be obtained by laminating adhesive layers, adhesive compositions having different compositions under appropriate conditions (temperature, lamination speed, and the like), and the like.

[0176] The thickness of the adhesive layer is not particularly limited. From the viewpoint of avoiding the adhesive sheet from becoming too thick, the thickness of the adhesive layer is preferably about 100 μm or less, more preferably about 70 μm or less, and even more preferably about 50 μm or less (for example, about 30 μm or less). The thickness of the adhesive layer can be set to about 35 μm or less, for example, about 25 μm or less, and even more, for example, about 15 μm or less. The adhesive layer with the thickness limited can well cope with the requirements of thickness reduction and light weight. The lower limit of the thickness of the adhesive layer is not particularly limited, and from the viewpoint of adhesion to the adherend and impact resistance, it is advantageous to set it to about 1 μm or more, and it is appropriate to set it to about 3 μm or more, preferably about 5 μm or more, and more preferably about 8 μm or more, and from the viewpoints of adhesiveness, impact resistance, and the like, it is even more preferably about 12 μm or more (for example, about 15 μm or more), and particularly preferably about 20 μm or more, and can be about 30 μm or more, about 35 μm or more, or about 40 μm or more. By setting the thickness to the prescribed value or more, the limited light transmittance (for example, light shielding property) and the desired adhesive properties can be preferably achieved. In addition, according to the adhesive layer having the thickness of the prescribed value or more, a more excellent impact resistance is easily obtained. Note that the adhesive sheet disclosed herein is a base material-free adhesive sheet, and thus the thickness of the adhesive layer is the total thickness of the adhesive sheet (excluding the release liner).

[0177] <Release Liner>

[0178] In the technology disclosed herein, a release liner can be used at the time of formation of the adhesive layer, production of the adhesive sheet, storage of the adhesive sheet before use, circulation, shape processing, and the like. The release liner is not particularly limited, and for example, a release liner having a release-treated layer on the surface of a liner substrate of a resin film, paper, or the like; a release liner including a low-adhesive material containing a fluorine-containing polymer (polytetrafluoroethylene or the like), a polyolefin-based resin (polyethylene, polypropylene, or the like), or the like can be used. The release-treated layer described above can be formed, for example, by surface treatment of the liner substrate described above with a silicone-based, long-chain alkyl-based, fluorine-based, molybdenum sulfide, or the like.

[0179] <Use>

[0180] The adhesive sheet disclosed herein preferably has impact resistance, and is suitable for use in which it is attached to a material having a higher refractive index than a general adhesive. For example, portable electronic devices have a risk of falling from a high place due to their usage, and for an adhesive sheet for a portable electronic device, it is required to have impact resistance. For such a portable electronic device, the adhesive sheet disclosed herein is suitable. The adhesive sheet disclosed herein has excellent impact resistance, and thus can be preferably used for fixing of members in a portable electronic device having an organic EL display, which often requires higher impact resistance.

[0181] Non-limiting examples of the above portable electronic device include: a cellular phone, a smartphone, a tablet personal computer, a notebook personal computer, various wearable devices (for example, a wrist-worn type worn on a wrist like a watch, a modular type worn on a part of a body with a clip, a band, or the like, an eyewear type including a glasses type (a monocular type, a binocular type. A helmet type is also included.), a clothing type worn on a shirt, a sock, a hat, or the like in the form of, for example, an ornament, an ear-worn type worn on an ear like an earphone, and the like), a digital still camera, a digital video camera, a sound equipment (a portable music player, a voice recorder, and the like), a calculator (a desk calculator, and the like), a portable game device, an electronic dictionary, an electronic organizer, an electronic book, an in-vehicle information device, a portable radio, a portable television, a portable printer, a portable scanner, a portable modem, and the like. Note that "portable" in the present specification is not sufficient to mean only that it can be carried, and actually has portability of a level that a person (a standard adult) can move relatively easily.

[0182] The adhesive sheet disclosed herein can be preferably used, for example, for the purpose of fixing a pressure-sensitive sensor and other members in a portable electronic device having the pressure-sensitive sensor in such a portable electronic device. In some preferred modes, the adhesive sheet can be used for fixing a pressure-sensitive sensor and other members in an electronic device (typically, a portable electronic device) having a function of being able to designate an absolute position on a plate (typically, a touch panel) corresponding to a screen by means of a device (typically, a pen type, a mouse type device) for indicating a position on the screen and a device for detecting a position.

[0183] In addition, the adhesive sheet disclosed herein is also suitable for the use of being disposed on the back of a display screen (display portion) of a touch panel display or the like in a portable electronic device, thereby preventing reflection of light transmitted through the display screen. By disposing the adhesive sheet disclosed herein on the back of the above display screen (display portion), it is possible to prevent a decrease in visual recognition of the display screen regardless of the use mode of the portable electronic device. In addition, the above reflection can occur due to a metal-made member disposed on the back side of the display screen, and by using the adhesive sheet disclosed herein for, for example, joining of the above metal-made member and the display portion, it is possible to simultaneously achieve joining of the members and imparting of light shielding properties.

[0184] In addition, the adhesive sheet disclosed herein is suitable for a portable electronic device in which a light sensor is built in. The above-described portable electronic device and the like can have a light sensor that utilizes light rays such as infrared rays, visible light, and ultraviolet rays for the purpose of operation of the device, sensing of an approach, detection of the brightness of the surroundings (ambient light), data communication, and the like. Although not particularly limited, as the light sensor, an acceleration sensor, a proximity sensor, a brightness sensor (ambient light sensor), and the like can be cited. Such a light sensor has a light-receiving element of light rays such as ultraviolet rays, visible light, and infrared rays, and can also have a light-emitting element of specific light rays such as infrared rays. In other words, the light sensor can contain a light-emitting element and / or a light-receiving element of light rays in a specific wavelength region within a wavelength region of ultraviolet rays, visible light, and infrared rays. For such a device, the technology disclosed herein is applied to suppress reflection of light rays utilized in the light sensor, whereby it is possible to prevent a decrease in the action precision of the sensor.

[0185] As a material (object-to-be-adhered material) to which the adhesive sheet disclosed herein is attached, there is no particular limitation, and, for example, a metal material such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, or an alloy containing two or more of these, a resin material such as various resin materials (typically, plastic materials) such as a polyimide-based resin, an acrylic-based resin, a polyether nitrile-based resin, a polyether sulfone-based resin, a polyester-based resin (a PET-based resin, a polyethylene naphthalate-based resin, or the like), a polyvinyl chloride-based resin, a polyphenylene sulfide-based resin, a polyether ether ketone-based resin, a polyamide-based resin (so-called aramid resin, or the like), a polyarylate-based resin, a polycarbonate-based resin, a liquid crystal polymer, or the like, an inorganic material such as alumina, zirconia, soda lime glass, quartz glass, carbon, or the like can be cited. Among these, a metal material such as copper, aluminum, stainless steel, or the like, a polyester-based resin such as PET, a polyimide-based resin, an aramid resin, a polyphenylene sulfide-based resin, or the like (typically, a plastic material) is widely used. The above-described material can be a material of a member constituting a product such as an electronic device. The adhesive sheet disclosed herein can be used by being attached to a member constituted of the above-described material. In addition, the above-described material can be a material of a fixed object (for example, a back member such as an electromagnetic wave shield, a reinforcing plate, or the like) constituting the above-described pressure-sensitive sensor, a display portion, or the like. Note that the fixed object refers to an object to which the adhesive sheet is attached, that is, an object-to-be-adhered. In addition, the back member refers to a member disposed on the opposite side of the surface (the visually recognized side) of the above-described pressure-sensitive sensor, a display portion, or the like in a portable electronic device, for example. In addition, the above-described fixed object can be in any one of a single-layer structure, a multi-layer structure, and the like, and various surface treatments can be applied to the surface (the attachment surface) to which the adhesive sheet is attached. Although not particularly limited, as an example of the fixed object, a back member having a thickness of about 1 pm or more (typically, about 5 pm or more, for example, about 60 pm or more, further, about 120 pm or more) and about 1500 pm or less (for example, about 800 pm or less) can be cited.

[0186] The member, material (at least one adherend in the case of a double-coated adhesive sheet) to which the adhesive sheet disclosed herein is attached can be a member, material containing a material having a higher refractive index than that of a general adhesive. The refractive index of the adherend material is, for example, 1.50 or higher, and there are adherend materials having a refractive index of 1.58 or higher, and adherend materials having a refractive index of 1.62 or higher (for example, about 1.66). Such a high-refractive adherend material is typically a resin material. More specifically, it can be a polyester-based resin such as PET, a polyimide-based resin, an aromatic polyamide resin, a polyphenylene sulfide-based resin, a polycarbonate-based resin, or the like. For such a material, the effect of using the adhesive sheet disclosed herein (suppression of reflection of light caused by a difference in refractive index) can be preferably exerted. The upper limit of the refractive index of the above-mentioned adherend material is, for example, 1.80 or lower, and can be 1.70 or lower. The adhesive sheet disclosed herein can be preferably used in a manner attached to a high-refractive adherend (for example, a member) as described above. As a preferable example of such an adherend, a resin film having a refractive index of 1.50 to 1.80 (preferably, 1.60 to 1.70) can be cited. The above-mentioned refractive index can be measured by the same method as the refractive index of the adhesive sheet.

[0187] In addition, it is appropriate that the difference (refractive index difference) between the refractive index of the member, material (at least one adherend in the case of a double-coated adhesive sheet) to which the adhesive sheet is attached and the refractive index of the adhesive sheet be less than about 0.18. Thereby, reflection of light at the interface of the adherend and the adhesive sheet is preferably suppressed. The above-mentioned refractive index difference is preferably less than 0.12, more preferably less than 0.10, further preferably less than 0.08, and particularly preferably less than 0.05. Note that the above-mentioned refractive index difference is theoretically zero (±0.00), but a difference of about 0.01 or higher (for example, about 0.03 or higher) is practically allowable.

[0188] In addition, the member, material (at least one adherend in the case of a double-coated adhesive sheet) to which the adhesive sheet is attached as an adherend can be a member, material having light transmittance. Such an adherend easily obtains the advantages of the effects brought by the technology disclosed herein (reduction of light reflection at the interface between the adherend and the adhesive sheet) because light from, for example, a sensor reaches the adhesive sheet through the adherend. The total light transmittance of the above-mentioned adherend is, for example, greater than 50%, and can be 70% or more. In some preferred embodiments, the total light transmittance of the above-mentioned adherend is 80% or more, more preferably 90% or more, and can be 95% or more (for example, 95 to 100%). Such a material can be a resin film disposed on the back of an image display portion of various devices such as a portable electronic device. The adhesive sheet disclosed herein can be preferably used in a manner attached to an adherend (for example, a member) having a total light transmittance of 50% or more as described above. The above-mentioned total light transmittance can be measured by the same method as the total light transmittance of the adhesive sheet.

[0189] In some preferred embodiments, the adherend (for example, a member) to which the adhesive sheet is attached can be an adherend having the above-mentioned refractive index and having the above-mentioned total light transmittance. Specifically, the adhesive sheet can be preferably used in a manner attached to an adherend (for example, a member) having a refractive index of 1.50 or more (for example, about 1.58 or more, further about 1.62 or more, typically about 1.66) and a total light transmittance of greater than 50% (for example, can be 70% or more, preferably 80% or more, more preferably 90% or more, further 95% or more). In such a manner of attachment to an adherend material, the effects brought by the technology disclosed herein can be particularly preferably exerted.

[0190] As described above, according to the technology disclosed herein, a laminate having the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached is provided. The member to which the adhesive sheet is attached can be a member having a refractive index of the above-mentioned adherend material. In addition, the difference between the refractive index of the adhesive sheet and the refractive index of the member (refractive index difference) can be the refractive index difference between the above-mentioned adherend and the adhesive sheet. As for the member constituting the laminate, the description is not repeated as described as the above-mentioned member, material, adherend.

[0191] The adhesive sheet disclosed herein is, for example, a light transmittance-limited adhesive sheet, and in preferred embodiments, can be an adhesive sheet having excellent light blocking properties, and is thus preferably used for electronic devices containing various light sources such as LEDs (light-emitting diodes), light-emitting elements such as self-luminous organic ELs (electroluminescence). For example, it can be preferably used for electronic devices (typically, portable electronic devices) having liquid crystal display devices that require prescribed optical properties. More specifically, it can be preferably used for the junction of a liquid crystal display module unit (LCD unit) and a backlight module unit (BL unit) in a liquid crystal display device having the LCD unit and the BL unit.

[0192] Figure 3 Fig. 1 is a schematic exploded perspective view showing a configuration example of a liquid crystal display device. As shown in Fig. 1, a portable electronic device 100 has a liquid crystal display device 200. The liquid crystal display device 200 has an LCD unit (member) 210 and a BL unit (member) 220. The liquid crystal display device 200 further includes an adhesive sheet 230 and is configured. In this configuration example, the adhesive sheet 230 is in the form of a double-sided adhesive sheet processed into a frame shape (a frame shape) and is disposed between the BL unit 220 and the LCD unit 210 to join the two. Note that the BL unit 220 is typically configured to include a reflective sheet, a light guide plate, a diffusion sheet, a prism sheet, and the like in addition to a light source. Figure 3

[0193] The adhesive sheet disclosed herein can be used as a joining member processed into various shapes in the joining of, for example, the LCD unit and the BL unit and other joining applications. As a preferable form of such a joining member, a form having a narrow portion with a width of less than 2.0 mm (for example, less than 1.0 mm) can be cited. The adhesive sheet of some of the preferable forms can exhibit good light shielding properties and thus can exhibit good performance even when used as a joining member including a shape (for example, a frame shape) having a narrow portion as described above. In some forms, the width of the narrow portion described above can be 0.7 mm or less, can be 0.5 mm or less, or can be about 0.3 mm or less. The lower limit of the width of the narrow portion is not particularly limited, and 0.1 mm or more (typically, 0.2 mm or more) is appropriate from the viewpoint of the handleability of the adhesive sheet.

[0194] The narrow portion described above is typically linear. Here, linear means the concept of including a frame shape, a circular shape, and the like, in addition to a straight line shape, a curved line shape, a broken line shape (for example, an L shape), and the like, a composite shape thereof, or an intermediate shape. The circular shape described above is not limited to a circular shape composed of a curved line and is the concept of including a circular shape in which a part or the whole is formed into a straight line shape, such as a shape along the outer periphery of a quadrangle (a frame shape), a shape along the outer periphery of a fan shape. The length of the narrow portion described above is not particularly limited. For example, in a form in which the length of the narrow portion described above is 10 mm or more (typically, 20 mm or more, for example, 30 mm or more), the effects of applying the technology disclosed herein can be appropriately exhibited.

[0195] The matters disclosed in this specification include the following matters.

[0196] [1] A liquid crystal display device having a liquid crystal display module unit, a backlight module unit, and a double-sided adhesive adhesive sheet joining the liquid crystal display module unit and the backlight module unit, wherein

[0197] the adhesive sheet is a double-sided adhesive adhesive sheet including an adhesive layer and not having a substrate,​

[0198] The adhesive sheet has a refractive index of 1.50 or more, and a breaking strength of 10 MPa or less.

[0199] [2] The liquid crystal display device according to the above [1], wherein the liquid crystal display device incorporates a light sensor, the light sensor containing a light-emitting element and / or a light-receiving element that contain light rays in a specific wavelength region among wavelength regions of ultraviolet rays, visible light, and infrared rays.

[0200] [3] The liquid crystal display device according to the above [1] or [2], wherein the adhesive sheet contains at least one particle P selected from the group consisting of metal particles, metal compound particles, organic particles, and organic / inorganic composite particles. HRI .

[0201] [4] The liquid crystal display device according to the above [3], wherein the particle P is contained in the adhesive sheet at a proportion of 25% by mass to 75% by mass. HRI .

[0202] [5] The liquid crystal display device according to the above [3] or [4], wherein the particle P has an average particle diameter in the range of 1 nm to 100 nm. HRI

[0203] [6] The liquid crystal display device according to any one of the above [3] to [5], wherein the adhesive sheet contains carbon black particles in addition to the particle P. HRI

[0204] [7] The liquid crystal display device according to any one of the above [1] to [6], wherein the adhesive sheet has a thickness of 20 μm or more and 50 μm or less.

[0205] [8] The liquid crystal display device according to any one of the above [1] to [7], wherein the adhesive sheet contains an acrylic polymer as a base polymer.

[0206] [9] The liquid crystal display device according to any one of the above [1] to [8], wherein the adhesive sheet is formed of an adhesive composition containing an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent.

[0207]

[10] The liquid crystal display device according to any one of the above [1] to [9], wherein the adhesive sheet has a 180-degree peeling strength with respect to a stainless steel plate of 2 N / 10 mm or more.

[0208]

[11] An adhesive sheet which is a double-coated adhesive sheet containing an adhesive layer and not having a substrate, wherein,

[0209] ​​The adhesive sheet has a refractive index of 1.50 or more and a breaking strength of 10 MPa or less.

[0210]

[12] The adhesive sheet according to the above

[11] , wherein the adhesive sheet contains at least one particle P selected from the group consisting of metal particles, metal compound particles, organic particles, and organic-inorganic composite particles HRI .

[0211]

[13] The adhesive sheet according to the above

[12] , wherein the particle P is contained in a proportion of 25% by weight to 75% by weight HRI .

[0212]

[14] The adhesive sheet according to the above

[12] or

[13] , wherein the particle P has an average particle diameter in the range of 1 nm to 100 nm HRI .

[0213]

[15] The adhesive sheet according to any one of the above

[12] to

[14] , wherein the adhesive sheet contains carbon black particles in addition to the particle P HRI .

[0214]

[16] The adhesive sheet according to any one of the above

[11] to

[15] , wherein the adhesive sheet has a thickness of 20 μm or more and 50 μm or less

[0215]

[17] The adhesive sheet according to any one of the above

[11] to

[16] , wherein the adhesive sheet contains an acrylic polymer as a base polymer

[0216]

[18] The adhesive sheet according to any one of the above

[11] to

[17] , wherein the adhesive sheet is formed of an adhesive composition containing an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent

[0217]

[19] The adhesive sheet according to any one of the above

[11] to

[18] , wherein the adhesive sheet has a 180-degree peeling strength with respect to a stainless steel plate of 2 N / 10 mm or more

[0218]

[20] The adhesive sheet according to any one of the above

[11] to

[19] , wherein the adhesive layer contains a black colorant

[0219]

[21] The adhesive sheet according to any one of the above

[11] to

[20] , wherein the adhesive sheet has a total light transmittance of 80% or less and a refractive index of 1.50 or more

[0220]

[22] The adhesive sheet according to the above

[21] , wherein the total light transmittance is greater than 10% and 80% or less

[0221]

[23] The adhesive sheet described in any one of the above

[21] , wherein the total light transmittance is 10% or less.

[0222]

[24] The adhesive sheet described in any one of the above

[21] to

[23] , wherein the adhesive layer contains at least one particle P selected from the group consisting of metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI .

[0223]

[25] The adhesive sheet described in the above

[24] , wherein the adhesive layer contains a particle containing a metal oxide as the particle P HRI .

[0224]

[26] The adhesive sheet described in the above

[24] or

[25] , wherein the particle P HRI has an average particle diameter in the range of 1 nm to 100 nm.

[0225]

[27] The adhesive sheet described in any one of the above

[24] to

[26] , wherein the particle P HRI is contained in the adhesive layer at a proportion of 25% by mass or more.

[0226]

[28] The adhesive sheet described in any one of the above

[21] to

[27] , wherein the adhesive layer is an acrylic adhesive layer containing an acrylic polymer as a base polymer.

[0227]

[29] The adhesive sheet described in any one of the above

[21] to

[28] , wherein the thickness of the adhesive sheet is in the range of 10 μm to 50 μm.

[0228]

[30] The adhesive sheet described in any one of the above

[21] to

[29] , wherein the adhesive layer contains a black colorant.

[0229]

[31] The adhesive sheet described in any one of the above

[11] to

[30] , wherein,

[0230] the adhesive layer contains a high refractive index particle P HRI ,

[0231] the particle P HRI existing in the adhesive layer has an average particle diameter of less than 100 nm, and the particle P HRI existing in the adhesive layer has a standard deviation of 20 nm or less, where the average particle diameter and the standard deviation are respectively an average particle diameter and a standard deviation calculated from a number-based particle size distribution based on TEM observation.

[0232]

[32] The adhesive sheet according to any one of

[11] to

[30] above, wherein the adhesive layer contains the particles P comprising a metal oxide HRI ,

[0233] The average particle diameter of the particles P present in the adhesive layer HRI is less than 100 nm, and the standard deviation of the particles P present in the adhesive layer HRI is 20 nm or less, where the average particle diameter and the standard deviation are respectively an average particle diameter and a standard deviation calculated from a number-based particle diameter distribution based on TEM observation.

[0234]

[33] The adhesive sheet according to

[31] or

[32] above, wherein the average particle diameter of the particles P present in the adhesive layer HRI is less than 80 nm.

[0235]

[34] The adhesive sheet according to any one of

[31] to

[33] above, wherein the particles P HRI are contained in the adhesive layer at a proportion of more than 20% by mass.

[0236]

[35] The adhesive sheet according to any one of

[31] to

[34] above, wherein the particles P HRI comprise at least one particle selected from the group consisting of metal particles, metal compound particles, organic particles, and organic-inorganic composite particles.

[0237]

[36] The adhesive sheet according to

[35] above, wherein the particles P HRI comprise a metal oxide.

[0238]

[37] The adhesive sheet according to any one of

[31] to

[36] above, wherein the adhesive layer is a solvent-type adhesive layer formed from a solvent-type adhesive composition.

[0239]

[38] The adhesive sheet according to any one of

[31] to

[37] above, wherein the adhesive layer is an acrylic adhesive layer containing an acrylic polymer as a base polymer.

[0240]

[39] The adhesive sheet according to any one of

[31] to

[38] above, wherein the particles P HRI are subjected to surface treatment for hydrophobicity.

[0241]

[40] The adhesive sheet according to any one of

[31] to

[39] above, wherein the thickness of the adhesive sheet is in the range of 10 μm to 50 μm.

[0242]

[41] An adhesive sheet as described in any one of

[11] to

[40] above, wherein the adhesive layer contains carbon black particles.

[0243]

[42] The adhesive sheet as described in

[41] above, wherein the volume average particle size of the carbon black particles is less than 500 nm.

[0244]

[43] The adhesive sheet as described in

[41] or

[42] above, wherein the content of the carbon black particles in the adhesive layer is 1% by weight or more.

[0245]

[44] The adhesive sheet as described in any one of

[41] to

[43] above, wherein the adhesive layer contains, in addition to the carbon black particles, at least one particle P selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI .

[0246]

[45] As described in

[44] above, the adhesive sheet wherein the adhesive layer contains particles comprising metal oxides as the particles P HRI .

[0247]

[46] The adhesive sheet as described in

[44] or

[45] above, wherein the particle P HRI The average particle size is in the range of 1 nm to 100 nm.

[0248]

[47] An adhesive sheet as described in any one of

[44] to

[46] above, wherein the particle P HRI Content C HRI Relative to the content C of the carbon black particles CB weight ratio (C) HRI / C CB (In the range of 1 to 100)

[0249]

[48] ​​The adhesive sheet as described in any one of

[41] to

[47] above, wherein the adhesive layer is an acrylic adhesive layer having an acrylic polymer as the base polymer.

[0250]

[49] An adhesive composition comprising carbon black particles and particles P that are different from carbon black. HRI ,

[0251] The particle P HRI It contains at least one particle selected from metal particles, metal compound particles, organic particles, and organic-inorganic complex particles.

[0252]

[50] An adhesive sheet as described in any one of

[11] to

[48] above, wherein the adhesive sheet is used for fixing components in a portable electronic device.

[0253]

[51] The adhesive sheet according to any one of

[11] to

[48] above, wherein the adhesive sheet is disposed on the back of a display portion of a portable electronic device.

[0254]

[52] The adhesive sheet according to any one of

[11] to

[48] above, wherein the adhesive sheet is used for a portable electronic device in which a light sensor is built in.

[0255]

[53] The adhesive sheet according to any one of

[11] to

[48] ,

[50] to

[52] above, wherein the adhesive sheet is attached to a material having a refractive index of 1.50 or more.

[0256]

[54] The adhesive sheet according to

[53] above, wherein the material has a total light transmittance of 80% or more.

[0257]

[55] A laminate having the adhesive sheet according to any one of

[11] to

[48] ,

[50] to

[52] above and a member to which the adhesive sheet is attached, and

[0258] the member has a refractive index of 1.50 or more.

[0259]

[56] The laminate according to

[55] above, wherein the member has a total light transmittance of 80% or more.

[0260] Examples

[0261] Hereinafter, some examples of the present application will be described, but the present application is not intended to be limited to what is shown in these examples. Note that, unless otherwise specified, "parts" in the following description are on a weight basis.

[0262] < Evaluation Method >

[0263] [Total Light Transmittance]

[0264] The total light transmittance of the adhesive sheet [%] is the total light transmittance in the thickness direction of the adhesive sheet peeled from the release liner, and is measured according to JIS K 7136:2000 using a commercially available transmittance meter. As the transmittance meter, a product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent thereof is used.

[0265] [Refractive Index]

[0266] As for the refractive index of the adhesive sheet, in the case where the total light transmittance of the adhesive sheet is 50% or more, the measurement is performed under Condition (1). In the case where the above total light transmittance is less than 50%, the measurement is performed under Condition (2).

[0267] (Condition (1))

[0268] The measurement was performed at a wavelength of 589 nm and at 23°C using a multi-wavelength Abbe refractometer. As the multi-wavelength Abbe refractometer, a model "DR-M2" manufactured by ATAGO Co., Ltd. or an equivalent thereof was used.

[0269] (Condition (2))

[0270] The refractive index of the sodium D line (589 nm) was measured at 23°C using an ellipsometer. Specifically, the average surface refractive index from the surface of the adhesive sheet from which the release liner was peeled (adhesive surface) was measured. The measurement was performed on the basis that a black plate was attached to the side opposite to the measurement surface (non-measurement surface). As the ellipsometer, a product name "EC-400" manufactured by JA. Woolam Co., Ltd. or an equivalent thereof was used.

[0271] [180-degree peeling strength (adhesive strength)]

[0272] A measurement sample was produced by attaching a PET film having a thickness of 50 μm to one adhesive surface of the double-coated adhesive sheet as a backing, cutting it into a size of 10 mm in width and 100 mm in length, under a measurement environment of 23°C and 50% RH. For the produced measurement sample, the adhesive surface of the measurement sample was pressure-bonded to the surface of a stainless steel plate (SUS304BA plate) by reciprocating a 2-kg roller once under an environment of 23°C and 50% RH. After leaving it under the same environment for 30 minutes, the peeling strength (adhesive strength) [N / 10 mm] was measured using a universal tensile compression tester according to JIS Z 0237:2000 under conditions of a tensile speed of 300 mm / minute and a peeling angle of 180 degrees. As the universal tensile compression tester, for example, a "Tensile Compression Tester, TG-1 kN" manufactured by Minebea Co., Ltd. or an equivalent thereof can be used. Note that, in the case of a single-coated adhesive sheet, the backing with the PET film is not necessary.

[0273] [Breaking strength]

[0274] As for the breaking strength of the adhesive sheet, for the adhesive sheet without a support substrate (substrate-free adhesive sheet), the measurement was performed under Condition (1). For the adhesive sheet with a support substrate (substrate-equipped adhesive sheet), the measurement was performed under Condition (2).

[0275] (Condition (1))

[0276] A release film-equipped adhesive sheet was prepared by cutting it into a size of 150 mm in length and 1 mm 2A test piece having a width of 10 mm was prepared from the adhesive sheet with the release film, and the two release films were peeled off in an environment of 23°C and 50% RH to expose the adhesive layer. The tensile test of the test piece was performed using a tensile testing machine (Minebea Co., Ltd., universal tensile compression testing machine, device name "Tensile Compression Tester, TCM-1kNB") under conditions of a distance between the clamps of 120 mm and a tensile speed of 50 mm / min, and the S-S curve was obtained. The strength at the time of breakage of the test piece (breakage strength) [MPa] was measured.

[0277] (Condition (2))

[0278] A test piece having a width of 10 mm was prepared from the adhesive sheet with the release film, and the two release films were peeled off in an environment of 23°C and 50% RH to expose the adhesive layer. The tensile test of the test piece was performed using a tensile testing machine (Minebea Co., Ltd., universal tensile compression testing machine, device name "Tensile Compression Tester, TCM-1kNB") under conditions of a distance between the clamps of 120 mm and a tensile speed of 50 mm / min, and the S-S curve was obtained. The strength at the time of breakage of the test piece (breakage strength) [MPa] was measured.

[0279] Note that, as described above, the thickness of the test piece used in the tensile test can be the same as the thickness of the adhesive sheet, or can be different. For example, in the case where the thickness of the adhesive sheet is small, the result obtained by performing the tensile test using a test piece prepared so as to have a thickness of 5 μm or more (for example, about 5 μm to about 200 μm) can be adopted as the breakage strength of the adhesive sheet. The thickness of the test piece can be adjusted by, for example, appropriately overlapping the adhesive sheet. Alternatively, a test piece having a thickness that is easy to perform the tensile test can be prepared using the same adhesive composition as the adhesive composition used in the formation of the adhesive sheet to be measured, the tensile test can be performed on the test piece, and the result obtained thereby can be adopted as the breakage strength of the adhesive sheet. The tensile test can be performed using, for example, a test piece having a thickness of about 10 μm to about 50 μm. In addition, it is preferable to apply powder to the adhesive surface at the portion to be clamped at the time of the test, so as to eliminate the influence of tackiness of the adhesive.

[0280] [Impact resistance]

[0281] An adhesive sheet (double-coated adhesive sheet) having an adhesive surface protected with a release liner was punched into a frame shape of 24.5 mm square in outer diameter with a width of 2 mm, thereby obtaining a window frame-shaped adhesive sheet. In addition, a stainless steel plate having a hole in the central portion of a square of 50 mm x 50 mm in outer shape and 2 mm in thickness and a square PET plate (25 mm square in outer shape and 2 mm in thickness) were prepared, the window frame-shaped adhesive sheet from which the release liner had been removed was disposed between the two, and pressure bonding was performed under conditions of 62 N, 10 seconds in a manner such that pressure was uniformly applied, thereby fixing the stainless steel plate and the PET plate with the window frame-shaped adhesive sheet. This was left to stand in an environment of 50°C for 2 hours, and after being taken out, it was returned to 23°C. This was used as an evaluation sample. A cylindrical measuring stage of 50 mm in length, 49 mm in outer diameter, and 43 mm in inner diameter was set on the base of a DuPont-type impact testing machine (manufactured by Toyo Seiki Jidai Mfg. Co., Ltd.). The evaluation sample was placed on the measuring stage with the square PET plate as the lower side. With respect to the evaluation sample, the upper side stainless steel plate was supported by the measuring stage, and the lower side PET plate was disposed so as to enter the hollow portion of the measuring stage in a state of being adhered to the stainless steel plate by the window frame-shaped adhesive sheet. A steel impact core (impact die) having a tip radius of 3.1 mm was placed on the PET plate on the lower side of the evaluation sample, and a weight was dropped onto the impact core under the following conditions (weight of the weight and height of drop) at 23°C, 50% RH. The weight of the weight and the height of drop were changed so that the energy increased from the condition of the smallest energy. The height of drop was increased at intervals of 50 mm. When the weight was changed, the energy (energy calculated from the weight of the weight and the height of drop) that had been measured was not measured, and a condition (weight of the weight x height of drop) in which the energy was not repeated was set, and the weight drop test was performed.

[0282]

[0283] The energy (J) of the previous condition in which the stainless steel plate and the PET plate were peeled apart was calculated from the weight of the weight (load) and the height of drop, and this was recorded as a measured value of impact resistance, and was judged according to the following criteria.

[0284] (Evaluation Criteria)

[0285] O: 0.15 J or more

[0286] X: Less than 0.15 J

[0287] [Particles P in the Adhesive Layer HRI Particle Diameter Measurement]

[0288] The adhesive sample was rapidly frozen under a liquid nitrogen atmosphere, and the sample was cut into a thickness of about 100 nm using an ultramicrotome (Model "UC7" manufactured by Leica) under a frozen atmosphere at -30°C, thereby obtaining an ultrathin section. For the obtained ultrathin section, TEM observation was performed using a transmission electron microscope (TEM; manufactured by Hitachi High-Technologies Corporation, acceleration voltage 100 kV). Image processing (binarization) was performed on one field of view (10 μm x 10 μm square) of a TEM image enlarged to about 40,000 times, particles were identified, and the area fraction of each particle was calculated for all of the identified particles. Then, the equivalent circle diameter was calculated from the area of each particle. The equivalent circle diameter refers to the diameter of a circle (a true circle) having the same area as that of one particle as a measurement object. The above operation was performed on four different fields of view in the TEM image (N = 4), and the particles classified by the equivalent circle diameter were histogramed on a number basis, thereby obtaining a particle size distribution (number basis). The number as a calculation basis for the particle size distribution was obtained by counting the number of particles present in the above one field of view. The average particle size [nm] and the standard deviation [nm] were calculated from the obtained particle size distribution. Note that, in identifying the particles, particles located at the end of the image were omitted from the analysis. As the image analysis software, for example, imageJ can be used.

[0289] Example 1

[0290] (Preparation of acrylic polymer)

[0291] Into a reaction vessel having a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser, and a dropping funnel, 95 parts of BA and 5 parts of AA as monomer components and 233 parts of ethyl acetate as a polymerization solvent were charged, and while nitrogen gas was introduced, the mixture was stirred for 2 hours. Thereby, oxygen in the polymerization system was removed, and then 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator was added, and solution polymerization was performed at 60°C for 8 hours, thereby obtaining an acrylic polymer solution. The Mw of the acrylic polymer was about 70 x 10 4 .

[0292] (Preparation of adhesive composition)

[0293] Into the above acrylic polymer solution, 100 parts of the particle P HRIA dispersion liquid of surface-treated zirconium dioxide particles A (ZrO2-A), 20 parts of a terpene phenol resin as a tackifying resin, 0.8 parts of 1,2,3-benzotriazole (trade name "BT-120", manufactured by J-CHEM, Co., Ltd.) as a rust preventive, 3 parts of an isocyanate crosslinking agent as a crosslinking agent, and 0.01 parts of an epoxy crosslinking agent were mixed by stirring to thereby prepare an adhesive composition.

[0294] As ZrO2-A, a dispersion liquid of surface-treated zirconium dioxide particles obtained by dispersing surface-treated zirconium dioxide particles (average particle diameter: 40 nm, surface treatment: sulfonic acid-based hydrophobic treatment, manufactured by CIK NanoTech Co., Ltd.) in dimethylacetamide (DMA) was used. As the terpene phenol resin (tackifying resin), a product with the trade name "YS Polystar T-115" (manufactured by Yasuhara Chemical Co., Ltd., softening point: about 115°C, hydroxyl value: 30 mgKOH / g to 60 mgKOH / g) was used. As the isocyanate crosslinking agent, a product with the trade name "CORONATE L" (manufactured by Nippon Polyurethane Industry Co., Ltd., 75% ethyl acetate solution of trimethylolpropane / toluene diisocyanate trimer adduct) was used. As the epoxy crosslinking agent, a product with the trade name "TETRAD-C" (manufactured by Mitsubishi Gas Chemical Co., Inc., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was used.

[0295] (Production of Adhesive Sheet)

[0296] The above-described adhesive composition was applied to the release surface of a polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Film, Inc.) having a thickness of 38 μm, and dried at 100°C for 2 minutes to form an adhesive layer having a thickness of 20 μm. The release surface of a polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Film, Inc.) having a thickness of 25 μm was attached to the adhesive layer. Thus, a double-coated adhesive sheet having a thickness of 20 μm and no substrate, which was protected by the above-described two polyester release liners, was obtained.

[0297] Examples 2 to 10

[0298] The thickness of the adhesive sheet (thickness of the adhesive layer), the kind and the use amount of the particles P HRI were set as shown in Table 1. Otherwise, the same as in Example 1 was performed, and the adhesive composition of each example was prepared, and a double-coated adhesive sheet was produced using the adhesive composition. In Example 10, the particles P HRI were not used.

[0299] Note that Zr02-B in Table 1 is a surface-treated zirconia particle dispersion liquid B obtained by dispersing surface-treated zirconia particles (average particle diameter: 20 nm, surface treatment: methacrylic reactive group, manufactured by CIK NanoTech) in methyl ethyl ketone (MEK). Ti02-A is a surface-treated titanium dioxide particle dispersion liquid A obtained by dispersing surface-treated titanium dioxide particles (average particle diameter: 15 nm, surface treatment: methacrylic reactive group, manufactured by CIK NanoTech) in MEK. Ti02-B is a surface-treated titanium dioxide particle dispersion liquid B obtained by dispersing surface-treated titanium dioxide particles (average particle diameter: 15 nm, surface treatment: sulfonic acid-based hydrophobic treatment, manufactured by CIK NanoTech) in methyl propyl ketone (MPK). Ti02-C is a surface-treated titanium dioxide particle dispersion liquid C obtained by dispersing surface-treated titanium dioxide particles (average particle diameter: 10 nm, surface treatment: methacrylic reactive group, manufactured by CIK NanoTech) in propylene glycol monomethyl ether (PGME).

[0300] Example 11

[0301] In the preparation of the adhesive composition of Example 1, carbon black particles A (manufactured by Oji-Colorants Co., Ltd., trade name "ATDN101 BLACK", average particle diameter: 350 nm, described as "CB-A" in the table) were further added in such a manner as to achieve 1.0% by weight in the adhesive layer. Otherwise, the same as in Example 1 was performed, and the adhesive composition of the present example was prepared, and a substrate-free double-coated adhesive sheet having a thickness of 25 μm was produced using the adhesive composition.

[0302] Examples 12 to 17

[0303] The thickness of the adhesive sheet (the thickness of the adhesive layer) and the kind and the amount of use of the carbon black particles were set as shown in Table 2. Otherwise, the same as in Example 11 was performed, and the adhesive composition of each example was prepared, and a substrate-free double-coated adhesive sheet was produced using the adhesive composition.

[0304] Note that CB-B in Table 2 is carbon black particles B (manufactured by Oji-Colorants Co., Ltd., product number "No. 3057") having an average particle diameter of 90 nm.

[0305] Example 18

[0306] A polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Film Corp.) having a thickness of 38 μm and a polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Film Corp.) having a thickness of 25 μm were prepared. The same adhesive composition as used in Example 12 was applied to the release surfaces of these release liners and dried to a thickness of 12.5 μm, and dried at 100°C for 2 minutes. Thus, adhesive layers were formed on the release surfaces of the two release liners.

[0307] As the support substrate, a transparent PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) having a thickness of 5 μm was used. The adhesive layers formed on the two release liners were attached to the first and second surfaces of the support substrate, respectively, to produce a double-coated adhesive sheet with a support substrate (total thickness: 30 μm) of this example (transfer method). The release liners remained on the adhesive layers to protect the surfaces (adhesive surfaces) of the adhesive layers.

[0308] Example 19

[0309] The thickness of each adhesive layer was changed to 19 μm, and the thickness of the support substrate (PET film) was changed to 12 μm, and otherwise the same as in Example 18, to produce a double-coated adhesive sheet with a support substrate (total thickness: 50 μm) of this example.

[0310] Example 20

[0311] No particles P were used HRI The thickness of the adhesive sheet (thickness of the adhesive layer) was changed to 35 μm, and otherwise the same as in Example 13, to produce a double-coated adhesive sheet without a support substrate of this example.

[0312] The results of the evaluation of the outline, total light transmittance, refractive index, adhesive strength, breaking strength, and impact resistance of the adhesive sheets of each example are shown in Tables 1 and 2. In addition, for the adhesives of Examples 1 and 7, the particle size distribution of particles P HRI based on the TEM observation was obtained, and the average particle size [nm] and standard deviation [nm] of particles P HRI were calculated. The particle size distribution, average particle size [nm], and standard deviation [nm] are shown in Table 3. Note that, for the range of particle sizes in Table 3, for example, "10 nm to 15 nm" means 10 nm or more and less than 15 nm, and the same applies to other ranges of particle sizes in the table. Figures 4-5 Figures 4-5

[0313]

[0314] ​​

[0315] As shown in Tables 1 and 2, the adhesive sheets of Examples 1 to 9 and Examples 11 to 17 had a breaking strength of 10 MPa or less and the evaluation results of the impact resistance test were good. In addition, in these examples, the adhesive sheets had a refractive index of 1.50 or more. On the other hand, in Examples 18 and 19 in which the adhesive sheets had a breaking strength of more than 10 MPa, good impact resistance was not obtained. In addition, in Examples 10 and 20, the adhesive sheets had a refractive index of less than 1.50.

[0316] The above detailed description of the specific examples of the present application is merely illustrative and does not limit the scope of the claims. The technology recited in the claims includes various modifications and changes of the above-described specific examples.

[0317] Explanation of Reference Numerals

[0318] 1, 2 Adhesive sheet

[0319] 21 Adhesive layer

[0320] 21A, 21B Adhesive surface

[0321] 31, 32 Release liner

Claims

1. An adhesive sheet which is a double-coated adhesive sheet comprising an adhesive layer and not having a substrate, wherein, the adhesive sheet contains an acrylic polymer as a base polymer, at least one particle P selected from the group consisting of metal particles, metal compound particles, organic particles, and organic / inorganic composite particles HRI , and carbon black particles, the average particle diameter of the carbon black particles is 10 nm or more and 200 nm or less, The content C of the particles P in the adhesive sheet HRI HRI The content C of the particles P in the adhesive sheet CB The weight ratio (C HRI / C CB ) of the content C of the particles P to the content C of the carbon black particles is in the range of 10 to 100.​ the refractive index of the adhesive sheet is 1.50 or more, and the breaking strength of the adhesive sheet is 10 MPa or less.

2. The adhesive sheet according to claim 1, wherein contain the particles P in a proportion of 25% to 75% by weight HRI .

3. The adhesive sheet according to claim 1 or 2, wherein The particles P HRI have an average particle size in the range of 1 nm to 100 nm.

4. The adhesive sheet according to claim 1 or 2, wherein the adhesive sheet has a thickness of 20 μm or more and 50 μm or less.

5. The adhesive sheet according to claim 1 or 2, wherein the adhesive sheet is formed from an adhesive composition containing an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent.

6. The adhesive sheet according to claim 1 or 2, wherein the 180-degree peeling strength of the adhesive sheet with respect to a stainless steel plate is 2 N / 10 mm or more.

7. The adhesive sheet according to claim 1 or 2, wherein the adhesive sheet is used for fixing members in a portable electronic device.

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