Adhesive and adhesive sheet

Abstract

Provided is an adhesive having a low refractive index and high flexibility. The provided adhesive has a refractive index of 1.450 or less and a storage modulus (G '(-20 DEG C)) at-20 DEG C of 2.0 * 106 Pa or less.

Description

Technical Field

[0001] The present invention relates to an adhesive and an adhesive sheet having the adhesive. This application claims priority based on Japanese Patent Application No. 2022-157123 filed on September 29, 2022, the entire content of which is incorporated herein by reference. Background Art

[0002] Generally, an adhesive (also referred to as a pressure-sensitive adhesive; the same applies hereinafter) is in a state of a soft solid (viscoelastic body) within a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Utilizing such a property, adhesives are widely used for purposes such as joining, fixing, and protecting in various industrial fields from home appliances to automobiles, various machines, electrical equipment, and electronic equipment. As an example of the use of an adhesive, there can be mentioned the use of joining a polarizing film, a retardation film, a cover window member, and various other light-transmissive members to other members in a display device such as a liquid crystal display device and an organic EL display device. As technical documents related to adhesives, Patent Documents 1 to 4 can be cited.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-210343

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-111740

[0007] Patent Document 3: Japanese Patent No. 6014781

[0008] Patent Document 4: Japanese Patent Application Laid-Open No. 2018-193553 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] In Patent Documents 1 to 4, adhesives containing (meth)acrylate copolymers including structural units derived from fluorine-containing acrylic monomers are proposed. These are all adhesives focused on sebum resistance and / or chemical resistance and do not consider the refractive index. An adhesive with a low refractive index can, for example, contribute to controlling the behavior of light (reflection, waveguiding, diffraction) by utilizing the relationship between the refractive indices of adjacent materials.

[0011] Incidentally, adhesives can preferably be adhesives with good flexibility according to their application sites and usage forms. For example, in recent years, as displays such as organic EL display devices used in electronic devices such as smartphones, foldable displays and rollable displays have been put into practical use, and the adhesives used in the above applications also need to have the flexibility to follow the adherend that is repeatedly bent. An adhesive with excellent flexibility can easily follow and adhere to the surface of a curved shape such as a three-dimensional shape, and is also suitable for electronic device applications with a curved shape. For an adhesive with a low refractive index, if its flexibility can be improved, it can be applied to applications requiring the above flexibility and is useful.

[0012] Therefore, an object of the present invention is to provide an adhesive with a low refractive index and high flexibility. Another related object is to provide an adhesive sheet including an adhesive layer composed of the adhesive.

[0013] Means for Solving the Problem

[0014] According to this specification, there is provided an adhesive having a refractive index of 1.450 or less and a storage modulus (G’(-20°C)) at -20°C of 2.0×10 6 Pa or less. According to the above adhesive, since it has a low refractive index while the storage modulus (G’(-20°C)) is suppressed within a low range, it is possible to balance a low refractive index and flexibility. This adhesive is suitable for joining, fixing, protecting, etc. in applications such as foldable display applications that are expected to have a low refractive index and require flexibility to withstand repeated bending operations.

[0015] In some embodiments, the ratio (G’(-20°C) / E B ) [%] of the above storage modulus (G’(-20°C)) [Pa] of the above adhesive to the elongation at break (E B ) is preferably 20 or more and 2000 or less. According to the above adhesive, by having a low refractive index while the ratio (G’(-20°C) / E B ) is within the above range, good flexibility can be exhibited.

[0016] In some embodiments, the above adhesive is an adhesive formed from an active energy ray (such as ultraviolet ray) curable adhesive composition. This adhesive can easily achieve high surface smoothness on the bonding surface and can easily obtain good optical properties, so it is preferred.

[0017] The adhesive disclosed herein may contain an acrylic polymer (F). The monomer component constituting the above acrylic polymer (F) includes a fluorine-containing acrylic monomer (Mf). The acrylic polymer (F) containing a fluorine-containing acrylic monomer (Mf) as a monomer component can effectively contribute to reducing the refractive index of the adhesive.

[0018] In some embodiments, the monomer components constituting the above acrylic polymer (F) further include a non-acidic hydrophilic monomer (Mh). The above non-acidic hydrophilic monomer (Mh) can help to balance the softness of the adhesive and other properties (such as at least one of adhesive properties, optical properties, etc.).

[0019] As the above hydrophilic monomer (Mh), for example, a monomer having at least one group selected from the group consisting of a hydroxyl group, an amide group, and an (alkylene)oxy group can be preferably used. The technology disclosed herein can be preferably implemented in a manner of using such a hydrophilic monomer (Mh). 1-2 In some embodiments, the monomer components constituting the above acrylic polymer (F) further include a monomer (M1) represented by the following formula (1):

[0020] It should be noted that the technology disclosed in this specification may include an adhesive, an adhesive composition used in the formation thereof, an adhesive sheet including the adhesive (for example, an adhesive sheet having an adhesive layer including the above adhesive), a pressure-sensitive adhesive sheet with a release liner protecting the adhesive surface of the adhesive sheet, an optical member including the above adhesive layer, and the like.

[0021] In some embodiments, the content of the above hydrophilic monomer (Mh) in the above monomer components is preferably greater than 5.0% by weight. By using the non-acidic hydrophilic monomer (Mh) in the above content, it is possible to improve the moisture and heat resistance of the adhesive (the property of not easily turning white even when exposed to a humid and hot environment) while suppressing the decrease in softness.

[0022] In some embodiments, the above hydrophilic monomer (Mh) preferably includes a low-Tg hydrophilic monomer (Mh) having a glass transition temperature of the homopolymer of 40°C or lower. From the viewpoint of suppressing the increase in the storage modulus accompanying the use of the hydrophilic monomer (Mh), it is advantageous that at least a part of the above hydrophilic monomer (Mh) is the above low-Tg hydrophilic monomer (Mh). From the viewpoint of easily and appropriately exerting the use effect of the above low-Tg hydrophilic monomer (Mh), the content of the above low-Tg hydrophilic monomer (Mh) in the above monomer components is preferably greater than 2.0% by weight. L ). From the viewpoint of suppressing the increase in the storage modulus accompanying the use of the hydrophilic monomer (Mh), it is advantageous that at least a part of the above hydrophilic monomer (Mh) is the above low-Tg hydrophilic monomer (Mh). From the viewpoint of easily and appropriately exerting the use effect of the above low-Tg hydrophilic monomer (Mh), the content of the above low-Tg hydrophilic monomer (Mh) in the above monomer components is preferably greater than 2.0% by weight. L ). From the viewpoint of easily and appropriately exerting the use effect of the above low-Tg hydrophilic monomer (Mh), the content of the above low-Tg hydrophilic monomer (Mh) in the above monomer components is preferably greater than 2.0% by weight. L ). From the viewpoint of easily and appropriately exerting the use effect of the above low-Tg hydrophilic monomer (Mh), the content of the above low-Tg hydrophilic monomer (Mh) in the above monomer components is preferably greater than 2.0% by weight. L ). From the viewpoint of easily and appropriately exerting the use effect of the above low-Tg hydrophilic monomer (Mh), the content of the above low-Tg hydrophilic monomer (Mh) in the above monomer components is preferably greater than 2.0% by weight.

[0023] In some embodiments, the monomer components constituting the above acrylic polymer (F) further include a monomer (M1) represented by the following formula (1):

[0024] CH 2 =CR 1 COOR 2 (1)

[0025] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2is an alkyl group having 4 to 18 carbon atoms in a chain). The above (meth)acrylic acid alkyl ester can contribute to the adjustment of the properties of the adhesive.

[0026] In some embodiments, the content of the acidic functional group-containing monomer in the monomer components constituting the above acrylic polymer (F) is preferably less than 2.0% by weight. Limiting the amount of use of the acidic functional group-containing monomer can be advantageous from the viewpoint of improving the flexibility of the adhesive (especially the flexibility in the low-temperature region).

[0027] According to the present specification, there is provided an adhesive sheet comprising an adhesive layer containing any one of the adhesives disclosed herein (which may be an adhesive formed from any one of the adhesive compositions disclosed herein). The adhesives disclosed herein can be preferably used in applications such as optical applications that require moisture and heat resistance and whitening resistance at a low refractive index in the form of the above adhesive sheet.

[0028] In some embodiments, the haze of the above adhesive layer after a moisture and heat test of maintaining it in a moisture and heat environment of 85°C and 85% RH for 240 hours is less than 3.0%. The adhesive sheet exhibiting such moisture and heat resistance and whitening resistance can be preferably used in applications such as optical applications that require moisture and heat resistance and whitening resistance at a low refractive index.

[0029] In some embodiments, the peel strength of the above adhesive sheet from a glass plate (pulling speed: 300 mm / minute, peeling angle: 180 degrees) is 0.1 N / 25 mm or more. The adhesive sheet exhibiting such peel strength can be preferably used for bonding, fixing, protecting, etc. in applications such as optical applications that require moisture and heat resistance and whitening resistance at a low refractive index.

[0030] It should be noted that the solutions obtained by appropriately combining the various elements described in the present specification are also included in the scope of the invention claimed in this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a cross-sectional view schematically showing the structure of an adhesive sheet according to one embodiment.

[0032] Figure 2 is a cross-sectional view schematically showing the structure of an adhesive sheet according to another embodiment.

[0033] Figure 3 is a cross-sectional view schematically showing the structure of an adhesive sheet according to another embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Hereinafter, preferred embodiments of the present invention will be described. Matters required for implementing the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings regarding the implementation of the invention described in this specification and the common general knowledge in the art at the time of filing. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the art.

[0035] It should be noted that in the following drawings, components and parts that perform the same function may sometimes be denoted by the same reference numerals, and repeated descriptions may sometimes be omitted or simplified. In addition, in order to clearly illustrate the present invention, the embodiments described in the drawings are schematized and do not necessarily accurately represent the dimensions and scales of the actually provided products.

[0036] In this specification, the "monomer component constituting the polymer" refers to the monomer that forms the repeating unit of the polymer in the adhesive formed from the adhesive composition, regardless of whether it is contained in the adhesive composition in the form of a preformed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the above polymer can be contained in the above adhesive composition in any form of polymer, unpolymer, or partial polymer.

[0037] In this specification, the "base polymer" of the adhesive refers to the main component of the rubber-like polymer contained in the adhesive, and no other restrictive interpretation is made. The above rubber-like polymer refers to a polymer that exhibits rubber elasticity in the temperature range near room temperature. In addition, in this specification, the "main component" refers to a component having a content greater than 50% by weight unless otherwise specified.

[0038] In this specification, an "acrylic polymer" refers to a polymer that contains monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as the monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will be referred to as an "acrylic monomer". Therefore, the acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. As a typical example of the acrylic polymer, a polymer in which the proportion of acrylic monomers in all the monomers used in the synthesis of the acrylic polymer is greater than 50% by weight (preferably greater than 70% by weight, such as greater than 80% by weight or greater than 90% by weight) can be cited.

[0039] In this specification, the term “(meth)acryloyl” is used to generically denote acryloyl and methacryloyl. Similarly, “(meth)acrylate” is used to generically denote acrylate and methacrylate, and “(meth)acrylic acid” is used to generically denote acrylic acid and methacrylic acid. Accordingly, the concept of the acrylic monomer herein can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers).

[0040] <Properties of the Adhesive>

[0041] (Refractive Index)

[0042] The refractive index of the adhesive disclosed herein is 1.450 or less, for example, 1.300 or more and 1.450 or less. According to the technology disclosed herein, it is possible to provide an adhesive having such a refractive index, an adhesive composition capable of forming the adhesive, and an adhesive sheet including the above adhesive. In some embodiments, the refractive index of the adhesive is preferably 1.440 or less, more preferably 1.430 or less, and may be 1.425 or less or 1.424 or less. Further, in some embodiments, the refractive index of the above adhesive may be 1.420 or less, may be 1.410 or less, may be 1.400 or less, or may be less than 1.400 (for example, less than 1.390). Further, from the viewpoints of ease of obtaining the material and ease of achieving a balance with other properties (for example, resistance to moisture and heat whitening, flexibility), in some embodiments, the refractive index of the adhesive may be 1.320 or more, may be 1.350 or more, may be 1.360 or more, may be 1.370 or more, may be 1.380 or more, may be 1.400 or more, 1.410 or more, 1.420 or more, or 1.430 or more. The technology disclosed herein can be preferably implemented in such a manner that the refractive index of the adhesive is, for example, 1.350 or more and 1.450 or less, or 1.380 or more and 1.450 or less, or 1.400 or more and 1.440 or less. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (for example, the composition ratio of the monomer components of the base polymer constituting the adhesive).

[0043] It should be noted that in this specification, the refractive index of the adhesive refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a prism coupler under the conditions of a measurement temperature of 25° C. and a measurement wavelength of 594 nm. As the prism coupler, a commercially available measuring device can be used. For example, a model “2010M” manufactured by Metricon Corporation or an equivalent product can be used. As the measurement sample, an adhesive layer including the adhesive to be evaluated can be used. Specifically, the refractive index of the adhesive can be measured by the method described in the examples below.

[0044] (Storage modulus)

[0045] The storage modulus (G’(-20°C)) of the adhesive disclosed herein at -20°C is 2.0×10 6 Pa or less. An adhesive with such a limited G’(-20°C) can be, for example, a low refractive index adhesive having flexibility suitable for repeated bending operations in a wide temperature range including a low temperature region. From the viewpoint of obtaining higher flexibility, in some embodiments, the G’(-20°C) of the adhesive is preferably 1.5×10 6 Pa or less, more preferably 1.0×10 6 Pa or less, can be 8.0×10 5 Pa or less, can be 7.0×10 5 Pa or less, can be 6.0×10 5 Pa or less, can be 5.5×10 5 Pa or less, can be 5.0×10 5 Pa or less. There is no particular limitation on the lower limit of G’(-20°C) of the adhesive, and for example, it can be 5.0×10 3 Pa or more, can be 1.0×10 4 Pa or more, can be 5.0×10 4 Pa or more, can be 1.0×10 5 Pa or more, 3.0×10 5 Pa or more, or 5.0×10 5 Pa or more. An adhesive having the above G’(-20°C) can have appropriate cohesion while having flexibility. In addition, according to the adhesive having the above G’(-20°C), there is a tendency to easily balance low refractive index and flexibility.

[0046] There is no particular limitation on the storage modulus (G’(25°C)) of the adhesive disclosed herein at 25°C, and for example, it can be 1.0×10 6 Pa or less. In some preferred embodiments, the G’(25°C) of the adhesive can be, for example, 5.0×10 5 Pa or less, can be 1.0×10 5 Pa or less, can be 5.0×10 4 Pa or less, and can also be 4.5×10 4 Pa or less. From the viewpoint of balancing low refractive index and flexibility (for example, flexibility suitable for repeated bending operations), it is preferred that the G’(25°C) of the adhesive disclosed herein is low. There is no particular limitation on the lower limit of G’(25°C) of the adhesive, and for example, it can be 1.0×10 3 Pa or more, and can also be 5.0×10 3Pa or more. In some embodiments, from the perspective of easily achieving an adhesive that exhibits moderate cohesion and durability (e.g., durability suitable for repeated bending operations), the G’ (25 °C) of the adhesive is 1.0×10 4 Pa or more is suitable, and can be 2.0×10 4 Pa or more, can be 3.0×10 4 Pa or more, can also be 4.0×10 4 Pa or more.

[0047] The storage modulus (G’(60 °C)) of the adhesive disclosed herein is not particularly limited. For example, it can be 5.0×10 5 Pa or less, can be 2.0×10 5 Pa or less, can be 1.0×10 5 Pa or less, can be 8.0×10 4 Pa or less, can be 6.0×10 4 Pa or less, can be 4.0×10 4 Pa or less, can be 3.5×10 4 Pa or less or 3.0×10 4 Pa or less. For the adhesive with G’(60 °C) limited as described above, good flexibility is easily obtained in the room temperature region. The lower limit of the above G’(60 °C) is not particularly limited. For example, it can be 1.0×10 3 Pa or more, preferably 5.0×10 3 Pa or more, more preferably 1.0×10 4 Pa or more, can be 2.0×10 4 Pa or more, 2.5×10 4 Pa or more, 3.0×10 4 Pa or more or 3.5×10 4 Pa or more. The adhesive having the above G’(60 °C) also has moderate cohesion in the high temperature region and tends to have excellent heat resistance, which is preferred.

[0048] (Storage modulus ratio)

[0049] The ratio of G’(-20°C) to G’(25°C) of the adhesive, i.e., the storage modulus ratio (G’(-20°C) / G’(25°C)), can be, for example, 1500 or less, or can be 1200 or less, 1000 or less, or 900 or less. The above ratio (G’(-20°C) / G’(25°C)) is restricted to the specified value or less, and the adhesive suppresses the change in elastic modulus in the temperature range from the low-temperature region to the room-temperature region. Therefore, it is easy to exhibit stable characteristics (such as flexibility) against temperature changes and is preferred. In some embodiments, it is appropriate that the above (G’(-20°C) / G’(25°C)) is 800 or less, advantageous that it is 600 or less, preferably 500 or less, 400 or less, or 300 or less, can be 200 or less, can be 100 or less, can be 75 or less, 60 or less, 45 or less, 30 or less, 20 or less, or 15 or less. The lower limit of the above ratio (G’(-20°C) / G’(25°C)) is typically greater than 1.0, and can be, for example, 1.1 or more. Considering the balance with other characteristics, etc., in some embodiments, the above ratio (G’(-20°C) / G’(25°C)) can be 2.0 or more, can be 5.0 or more, can be 10 or more, 15 or more, or 20 or more.

[0050] The ratio of G’(25°C) to G’(60°C) of the adhesive, i.e., the storage modulus ratio (G’(25°C) / G’(60°C)), can be, for example, 100 or less, or 70 or less, and it is advantageous that it is 50 or less, preferably 40 or less, or 30 or less, can be 20 or less, can be 10 or less, can be 8.0 or less, 6.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less, can be 1.8 or less, can be 1.6 or less, can be 1.5 or less, can be 1.4 or less. The above ratio (G’(25°C) / G’(60°C)) is restricted to the specified value or less, and the adhesive suppresses the change in elastic modulus in the temperature range from the room-temperature region to the high-temperature region. Therefore, it is easy to exhibit stable characteristics (such as flexibility) against temperature changes. The lower limit of the above ratio (G’(25°C) / G’(60°C)) is typically greater than 1.0, and can be, for example, 1.1 or more. Considering the balance with other characteristics, etc., in some embodiments, the above ratio (G’(25°C) / G’(60°C)) can be 1.2 or more, can be 1.3 or more, or can be 1.4 or more.

[0051] The storage modulus of the adhesive at each temperature can be measured by the method described in the following examples, and the above-mentioned storage modulus ratios can be calculated from the results. The storage modulus and storage modulus ratio of the adhesive can be adjusted, for example, by selecting the composition of the monomer components of the base polymer constituting the adhesive, selecting the type and amount of the crosslinking agent, etc.

[0052] (Glass transition temperature)

[0053] The glass transition temperature (Tg) of the adhesives disclosed herein is not particularly limited, and from the viewpoint of easily obtaining good flexibility in a low temperature region, it is preferably 5°C or lower (for example, -60°C or higher and 5°C or lower). In some embodiments, it is advantageous for the Tg of the adhesive to be 0°C or lower (for example, -5°C or lower), preferably -10°C or lower (for example, -15°C or lower), more preferably -20°C or lower, and it may be -22°C or lower, and it may be -24°C or lower. There is a tendency that the lower the Tg of the adhesive, the more excellent the adhesive properties such as adhesiveness to the adherend. The lower limit of the Tg of the adhesive can be, for example, -50°C or higher, -40°C or higher, or -30°C or higher. With the adhesive having the above Tg, there is a tendency to easily obtain appropriate cohesion. In addition, there is a tendency to easily form an adhesive having both a low refractive index and a low elastic modulus. The Tg of the adhesive can be measured by the method described in the examples below. The Tg of the adhesive can be adjusted, for example, by selecting the composition of the monomer components of the base polymer constituting the adhesive, and by selecting the type and amount of the crosslinking agent used.

[0054] (Elongation at break)

[0055] The elongation at break (E B ) of the adhesive is not particularly limited, and can be, for example, in the range of 200% or higher and 10,000% or lower. From the viewpoints of flexibility and elongation deformability, in some embodiments, the E B of the adhesive can be, for example, 300% or higher, and it is advantageous for it to be 400% or higher, preferably 500% or higher, more preferably 750% or higher, and it may be 800% or higher, 900% or higher, 1000% or higher, or 1200% or higher. In addition, from the viewpoints of easy balance with other properties, processability and handleability of the adhesive or the adhesive sheet having the adhesive, etc., in some embodiments, the E B of the adhesive is preferably 9000% or lower, advantageously 8000% or lower, preferably 7000% or lower, more preferably 6000% or lower, and it may be 5000% or lower, 4000% or lower, 3000% or lower, 2000% or lower, or 1500% or lower. The E B of the adhesive can be measured by the method described in the examples below. The E B of the adhesive can be adjusted, for example, by selecting the composition of the monomer components of the base polymer constituting the adhesive, and by selecting the type and amount of the crosslinking agent used.

[0056] (Ratio (G’(25°C) / E B ))

[0057] In some ways, the storage modulus at 25°C (G’(25°C)) relative to the above elongation at break (E B ), that is, the ratio (G’(25°C) / E B ) can be, for example, 1.0×10 5 or less, can be 5.0×10 4 or less, can be 1.0×10 4 or less, can be 5.0×10 3 or less, can be 1.0×10 3 or less, can be 500 or less, 300 or less, or 150 or less. The above ratio (G’(25°C) / E B ) is a dimensionless number calculated from the numerical part when G’(25°C) of the adhesive is expressed in the unit of "Pa" and the numerical part when E B of the adhesive is expressed in the unit of "%. A higher (harder) G’(25°C) and a smaller E B of the adhesive are the main reasons for making the value of the above ratio (G’(25°C) / E B ) larger. For example, brittle materials or weak (low cohesion) materials tend to be easily torn during elongation deformation, and the value of E B tends to become smaller. On the other hand, further reducing G’(25°C) and further increasing E B both have an impact on the above ratio (G’(25°C) / E B ) in the direction of further reducing the ratio. The above ratio (G’(25°C) / E B ) is limited to adhesives below a specified value, which exhibit good flexibility through moderate softness and moderate elongation deformability (resistance to tearing). Therefore, from the perspective of balancing low refractive index and softness, adhesives with a refractive index below a specified value and the above ratio (G’(25°C) / E B ) within the above range are preferred. The above flexible adhesives can also be suitable for applications envisaging repeated bending, for example. From the perspective of achieving better flexibility, in some preferred ways, the above ratio (G’(25°C) / E B ) being less than 100 (e.g., 95 or less) is appropriate, can be 80 or less, can be 70 or less, can be 60 or less, or can also be 50 or less. The lower limit of the above ratio (G’(25°C) / E B ) is not particularly limited. In some ways, considering the balance with other properties, the above ratio (G’(25°C) / E B ) can be, for example, 5.0 or more, can be 10 or more, can be 15 or more, can be 20 or more, 25 or more, or 30 or more, can be 40 or more, or can also be 45 or more.

[0058] (Ratio (G’(-20°C) / E B ))

[0059] In some embodiments, the storage modulus at -20°C (G’(-20°C)) relative to the elongation at break (E B ), i.e., the ratio (G’(-20°C) / E B ), can be, for example, 5.0×10 6 or less, can be 5.0×10 5 or less, can be 5.0×10 4 or less, can be 1.0×10 4 or less, can also be 5.0×10 3 or less. The ratio (G’(-20°C) / E B ) is a dimensionless number calculated from the numerical part of G’(-20°C) of the adhesive expressed in the unit of "Pa" and the numerical part of E B of the adhesive expressed in the unit of "%. From the viewpoint of achieving both a low refractive index and followability to rapid deformation, an adhesive having a refractive index of less than or equal to a specified value and the ratio (G’(-20°C) / E B ) within the above range is preferred. From the viewpoint of achieving better flexibility, in some preferred embodiments, it is appropriate for the ratio (G’(-20°C) / E B ) to be 2500 or less, advantageous to be 2000 or less, preferably 1500 or less (e.g., 1300 or less), more preferably 1200 or less (e.g., 1000 or less), can be 800 or less, can be 600 or less, 500 or less, 450 or less, or 400 or less. There is no particular limitation on the lower limit of the ratio (G’(-20°C) / E B ). In some embodiments, considering the balance with other properties, the ratio (G’(-20°C) / E B ) can be, for example, 20 or more, can be 50 or more, can be 100 or more, can be 150 or more, can be 200 or more, 250 or more, or 300 or more, can be 350 or more, or can also be 400 or more.

[0060] (Young's modulus)

[0061] The Young's modulus of the adhesive disclosed herein can be, for example, in the range of about 0.01 MPa to about 50 MPa. In some embodiments, from the perspective of initial adhesiveness and the like, it is appropriate for the Young's modulus of the adhesive to be 30 MPa or less (for example, 20 MPa or less or 10 MPa or less), and it is advantageous for it to be 8.0 MPa or less (for example, 6.0 MPa or less, 4.5 MPa or less, 3.0 MPa or less, or 2.0 MPa or less). It can be 1.0 MPa or less, or can be 0.80 MPa or less or less than 0.80 MPa. In some embodiments, from the perspective of improving flexibility, the Young's modulus of the adhesive can be, for example, less than 0.60 MPa, less than 0.50 MPa, less than 0.20 MPa, less than 0.10 MPa, or less than 0.08 MPa. Additionally, in some embodiments, from the perspective of the processability and handleability of the adhesive or the adhesive sheet having the adhesive, the Young's modulus of the adhesive can be 0.03 MPa or more, or can be 0.05 MPa or more. In some embodiments, considering the balance with other properties, the Young's modulus of the adhesive can be 0.06 MPa or more, or can be 0.07 MPa or more. The Young's modulus of the adhesive can be measured by the method described in the examples below. The Young's modulus of the adhesive can be adjusted, for example, by selecting the composition of the monomer components constituting the base polymer, the type and amount of the crosslinking agent used, and the like.

[0062] (Breaking stress)

[0063] The breaking stress of the adhesive disclosed herein can be, for example, in the range of about 0.10 MPa to about 30 MPa. In some embodiments, from the perspective of the processability and handleability of the adhesive or the adhesive sheet having the adhesive, it is appropriate for the breaking stress of the adhesive to be 0.2 MPa or more or 0.3 MPa or more, and it can be 0.4 MPa or more. Additionally, in some embodiments, from the perspective of easily improving the flexibility of the adhesive, it is appropriate for the breaking stress of the adhesive to be 15 MPa or less, preferably 12 MPa or less, and can be 10 MPa or less, 8.0 MPa or less, 4.0 MPa or less, 2.0 MPa or less, 1.0 MPa or less, 0.8 MPa or less, or 0.6 MPa or less. The breaking stress of the adhesive can be measured by the method described in the examples below. The breaking stress of the adhesive can be adjusted, for example, by selecting the composition of the monomer components constituting the base polymer, the type and amount of the crosslinking agent used, and the like.

[0064] (Composition of the adhesive)

[0065] (Base polymer)

[0066] In the technology disclosed herein, the type of the adhesive is not particularly limited. The above-mentioned adhesive may contain one or more of various rubbery polymers such as acrylic polymers, rubbery polymers (such as natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, polysiloxane polymers, polyamide polymers, fluorine-containing polymers, etc. that can be used in the field of adhesives as the adhesive polymer (the structural polymer forming the adhesive, hereinafter also referred to as the "base polymer"). From the viewpoints of adhesion performance, cost, etc., an adhesive containing an acrylic polymer or a rubbery polymer as the base polymer is preferably employed. Among them, an adhesive having an acrylic polymer as the base polymer (acrylic adhesive) is preferred. The technology disclosed herein is preferably implemented in a manner of using an acrylic adhesive.

[0067] Hereinafter, the acrylic adhesive will be mainly described, but it is not intended to limit the adhesives disclosed herein to acrylic adhesives.

[0068] (Acrylic polymer (F))

[0069] In some preferred embodiments, the adhesive disclosed herein contains an acrylic polymer (F). The monomer components constituting the above-mentioned acrylic polymer (F) include fluorine-containing acrylic monomers. In other words, the above-mentioned acrylic polymer (F) contains the above-mentioned fluorine-containing acrylic monomers as monomer units. The adhesive disclosed herein is preferably an acrylic adhesive containing the above-mentioned acrylic polymer (F) as the base polymer. Hereinafter, the above-mentioned acrylic polymer (F) may sometimes be abbreviated as "polymer (F)".

[0070] (Fluorine-containing acrylic monomer)

[0071] The above-mentioned polymer (F) may be a polymer of a monomer component containing at least a fluorine-containing acrylic monomer and may further contain other monomers copolymerizable with the monomer (copolymerizable monomers). The above-mentioned fluorine-containing acrylic monomer is not particularly limited as long as it is an acrylic monomer having at least one fluorine atom in the molecule. For example, fluorine-containing (meth)acrylate can be appropriately used. Preferred examples of the fluorine-containing (meth)acrylate include fluorine-containing (meth)acrylate having a fluorinated hydrocarbon group at the ester terminal. As the fluorinated hydrocarbon group, for example, fluorinated aliphatic hydrocarbon groups, fluorinated alicyclic hydrocarbon groups, fluorinated aromatic hydrocarbon groups, etc. can be cited. As the fluorinated hydrocarbon group, a fluorinated aliphatic hydrocarbon group is preferred. As the fluorinated aliphatic hydrocarbon group, fluorinated alkyl groups, etc. can be cited. In the fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon moiety may be linear or branched. In addition, in the fluorinated aliphatic hydrocarbon group, the fluorine atom may be bonded to any carbon atom in the aliphatic hydrocarbon group moiety. The number of fluorine atoms bonded to one carbon atom may be single or multiple. The number of carbon atoms to which the fluorine atom is bonded is not particularly limited.

[0072] In a fluoroaliphatic hydrocarbon group (wherein, a fluoroalkyl group), the number of carbon atoms in the hydrocarbon group moiety is not particularly limited. In some embodiments, in consideration of compatibility with other copolymerizable monomers, a fluoroaliphatic hydrocarbon group having about 1 to about 18 (preferably about 1 to about 12) carbon atoms is preferred. Specific examples of the fluoroaliphatic hydrocarbon group include: fluoromethyl groups such as trifluoromethyl, difluoromethyl, monofluoromethyl; fluoroethyl groups such as pentafluoroethyl, 1,1,2,2-tetrafluoroethyl, 1,2,2,2-tetrafluoroethyl, 1,1,2-trifluoroethyl, 1,2,2-trifluoroethyl, 2,2,2-trifluoroethyl, 1,1-difluoroethyl, 1,2-difluoroethyl, 2,2-difluoroethyl, 1-monofluoroethyl, 2-monofluoroethyl; etc. As fluoroalkyl groups having 3 or more carbon atoms, various fluoroalkyl groups in which one or more fluorine atoms are bonded to any one or more of the carbon atoms in the alkyl moiety can be exemplified in the same manner as the above-exemplified fluoromethyl or fluoroethyl groups.

[0073] As the fluoroalicyclic hydrocarbon group, fluoro cycloalkyl groups etc. can be enumerated. Similar to the above fluoroaliphatic hydrocarbon group, in the fluoroalicyclic hydrocarbon group, a fluorine atom can be bonded to any carbon atom in the alicyclic hydrocarbon group, and the number of fluorine atoms bonded to one carbon atom can be either single or multiple. In addition, the number of carbon atoms to which fluorine atoms are bonded is not particularly limited. The fluoroalicyclic hydrocarbon group includes, for example: cyclohexyl groups having one fluorine atom such as 2-fluorocyclohexyl, 3-fluorocyclohexyl, 4-fluorocyclohexyl; cyclohexyl groups having two fluorine atoms such as 2,4-difluorocyclohexyl, 2,6-difluorocyclohexyl; cyclohexyl groups having three fluorine atoms such as 2,4,6-trifluorocyclohexyl; etc.

[0074] The fluoroalkyl group may have no substituent or may have a substituent. As such a substituent, there is no particular limitation, and for example, hydrocarbon groups such as alkyl groups, alkoxy groups, hydroxyl groups, carboxyl groups, amino groups, nitro groups, cyano groups, halogen atoms, etc. can be enumerated. The substituents can be used alone or in combination of two or more.

[0075] Fluorine atom-containing (meth)acrylates [fluoro(meth)acrylates] include, for example: fluorine atom-containing (meth)acrylic acid alkyl esters [fluoro(meth)acrylic acid alkyl esters], fluorine atom-containing (meth)acrylic acid cycloalkyl esters [fluoro(meth)acrylic acid cycloalkyl esters], fluorine atom-containing (meth)acrylic acid aryl esters [fluoro(meth)acrylic acid aryl esters], etc.

[0076] As a fluorine atom-containing (meth)acrylate, (meth)acrylic acid fluoroalkyl ester (especially acrylic acid fluoroalkyl ester) is preferred. Examples of the (meth)acrylic acid fluoroalkyl ester include 2-(perfluorohexyl)ethyl acrylate (for example, trade name "C6SFA monomer" manufactured by Daikin Industries, Ltd.), 2,2,2-trifluoroethyl acrylate (for example, trade name "Viscoat3F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2,2,3,3-tetrafluoropropyl acrylate (for example, trade name "Viscoat4F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl acrylate (for example, trade name "Viscoat8F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl methacrylate (for example, trade name "Viscoat8FM" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2-(heptadecafluorononyl)ethyl acrylate (for example, trade name "FA-108" manufactured by Kyoeisha Chemical Co., Ltd.), and the like.

[0077] (Monomer (Mf))

[0078] In some embodiments, as the above-mentioned fluorine-containing acrylic monomer, (meth)acrylic acid fluoroalkyl ester (Mf) represented by the following formula (2) (hereinafter sometimes simply referred to as "monomer (Mf)") can be preferably used:

[0079] CH 2 =CR 1 COO(CH 2 ) n -Rf (2)

[0080] (In the formula, R 1 is a hydrogen atom or a methyl group, n is 1 or 2, and Rf is a linear fluoroalkyl group having 3 to 6 carbon atoms.). The monomer component constituting the polymer (F) can contain any one of the (meth)acrylic acid fluoroalkyl esters represented by the above formula (2) alone, or can contain two or more in combination. Among the fluorine-containing acrylic monomers contained in the monomer component constituting the polymer (F), the proportion of the monomer (Mf) can be, for example, 25% by weight or more, 50% by weight or more, 75% by weight or more, or 100% by weight.

[0081] From the viewpoints of the low refractive index effect, flexibility, etc., the number of carbon atoms of the chain-like fluoroalkyl group represented by Rf in the above formula (2) is preferably 4 or more, more preferably 5 or more (for example, 6). The chain-like fluoroalkyl group may be linear or may have a branched chain, and is preferably linear from the viewpoints of flexibility, etc. The chain-like fluoroalkyl group may be a perfluoroalkyl group or a partially fluorinated alkyl group (for example, a partially fluorinated alkyl group having a structure in which one or two of the fluorine atoms bonded to the terminal carbon atoms in the perfluoroalkyl group are replaced by hydrogen atoms). From the viewpoint of the low refractive index effect, the chain-like fluoroalkyl group is preferably a linear (preferably linear) perfluoroalkyl group. Further, from the viewpoints of the flexibility of the adhesive, etc., n in the above formula (2) is preferably 2. From the viewpoints of the flexibility of the adhesive, the polymerizability of the monomer (Mf), etc., R 1 is preferably a hydrogen atom.

[0082] Among the fluoroalkyl (meth)acrylates represented by the above formula (2), as an example of a preferable monomer (Mf), 2-(perfluorohexyl)ethyl acrylate can be mentioned from the viewpoint of achieving a balance between a low refractive index and flexibility. 2-(perfluorohexyl)ethyl acrylate can be used alone or in combination with other fluorinated acrylic monomers. The proportion of 2-(perfluorohexyl)ethyl acrylate in the fluorinated acrylic monomers contained in the monomer components constituting the polymer (F) can be, for example, 25% by weight or more, 50% by weight or more, 75% by weight or more, or 100% by weight.

[0083] The content of the fluorinated acrylic monomer in the monomer components constituting the polymer (F) (the content of monomer (Mf), or the content of 2-(perfluorohexyl)ethyl acrylate which can be used) can be, for example, 15% by weight or more. From the viewpoint of reducing the refractive index, 20% by weight or more is advantageous, preferably 25% by weight or more, more preferably 30% by weight or more, or 35% by weight or more. From the viewpoint of easily achieving an adhesive with a lower refractive index, in some embodiments, the above content can be, for example, 40% by weight or more, can be 43% by weight or more or greater than 43% by weight, can be 45% by weight or more or greater than 45% by weight, can be 47% by weight or more or greater than 47% by weight. In addition, the content of the fluorinated acrylic monomer in the monomer components constituting the polymer (F) (the content of monomer (Mf), or the content of 2-(perfluorohexyl)ethyl acrylate which can be used) is set such that the total with the content of other monomers does not exceed 100% by weight. For example, it can be less than 98% by weight, can be less than 95% by weight, or can also be 90% by weight or less. In some embodiments, from the viewpoints such as the flexibility of the adhesive, etc., the above content being 80% by weight or less is appropriate, 70% by weight or less is advantageous, can be 60% by weight or less, can be 55% by weight or less, or can also be 50% by weight or less. The content of the above fluorinated acrylic monomer can be applied to the content of monomer (Mf) in the monomer components constituting the polymer (F), and the content of 2-(perfluorohexyl)ethyl acrylate in the monomer components constituting the polymer (F).

[0084] (Non-acidic hydrophilic monomer (Mh))

[0085] The monomer components constituting the above polymer (F) can further contain a non-acidic hydrophilic monomer (Mh) (hereinafter sometimes simply referred to as "hydrophilic monomer (Mh)" or "monomer (Mh)"). The monomer (Mh) can, for example, contribute to imparting appropriate cohesion to the adhesive, increasing the peel strength, and suppressing the reduction in transparency caused by moisture (for example, suppressing the increase in haze value). As the above non-acidic hydrophilic monomer (Mh), a monomer having an ethylenically unsaturated group and a hydrophilic group in the molecule and not having an acidic functional group is used. The concept of the above acidic functional group includes a carboxyl group, a sulfo group, and a phosphoric acid group. Therefore, the above non-acidic hydrophilic monomer (Mh) is a monomer having an ethylenically unsaturated group and a hydrophilic group in the molecule and not having any of the acidic functional groups of a carboxyl group, a sulfo group, and a phosphoric acid group. From the viewpoint of suppressing the reduction in the flexibility of the adhesive (especially the increase in the storage modulus in the low-temperature region) accompanying the use of this monomer (Mh), it is advantageous that the monomer (Mh) is non-acidic. The non-acidic hydrophilic monomer (Mh) can be used alone or in combination of two or more.

[0086] Examples of the ethylenically unsaturated group possessed by the monomer (Mh) include: (meth)acryloyl, vinyl, (meth)allyl, etc. From the viewpoint of flexibility, preferred ethylenically unsaturated groups include acryloyl, vinyl, and allyl. From the viewpoint of polymerization reactivity, preferred ethylenically unsaturated groups include acryloyl and methacryloyl (more preferably acryloyl). From the viewpoint of suppressing a decrease in the flexibility of the adhesive, as the monomer (Mh), a compound having 1 ethylenically unsaturated group in one molecule (i.e., a monofunctional monomer) is preferably used.

[0087] The hydrophilic group possessed by the monomer (Mh) can be, for example, a hydroxyl group, an amide group, an amino group, a nitrogen atom-containing ring, (poly)oxyC 1-2 alkylene, etc. A monomer having at least 1 such hydrophilic group in the molecule and no acid can be used as the monomer (Mh). In some embodiments, as the monomer (Mh), a monomer selected from among hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, and (poly)oxyC 1-2 alkylene monomers can be used singly or in combination of two or more.

[0088] Examples of the above-mentioned hydroxyl group-containing monomers include: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, etc., (meth)acrylic acid hydroxyalkyl esters. The hydroxyl group-containing monomers can be used singly or in combination of two or more. As the monomer (Mh), one or more hydroxyl group-containing monomers and one or more other monomers (e.g., amide group-containing monomers) can be used in combination. The proportion of the hydroxyl group-containing monomer in the monomer (Mh) can be, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more, and can also be 100% by weight or less, 85% by weight or less, 70% by weight or less, 55% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less.

[0089] As preferred examples of the hydroxyl group-containing monomer, 4-hydroxybutyl acrylate (4HBA) (Tg of the homopolymer: -40°C) and 2-hydroxyethyl acrylate (HEA) (Tg of the homopolymer: -15°C) can be mentioned. From the viewpoint of improving the flexibility of the adhesive (especially improving the flexibility in the low-temperature region), 4HBA with a lower Tg of the homopolymer is more preferred. In some preferred embodiments, from the viewpoint of balancing the moisture and heat resistance and whitening resistance and flexibility of the adhesive, 50% by weight or more (for example, greater than 50% by weight, greater than 70% by weight, or greater than 85% by weight) and 100% by weight or less of the hydroxyl group-containing monomer used as the monomer (Mh) can be 4HBA.

[0090] As examples of the amide group-containing monomer, the following can be mentioned: (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; N-monoalkyl(meth)acrylamides such as N-ethyl(meth)acrylamide and N-isopropyl(meth)acrylamide; N-vinyl carboxamides such as N-vinylformamide and N-vinylacetamide; (meth)acrylamides having a hydroxyl group such as N-(2-hydroxyethyl)acrylamide and N-hydroxymethylacrylamide; N-vinyl cyclic amides such as N-vinylpyrrolidone (NVP), N-vinylpiperidone, N-vinylcaprolactam, and N-vinyl-3-morpholinone; cyclic amides having N-(meth)acryloyl group such as 1-(meth)acryloyl-2-pyrrolidone and 1-(meth)acryloylpiperidin-2-one; etc. The amide group-containing monomer can be used alone or in combination of two or more. As the monomer (Mh), one or two or more amide group-containing monomers and one or two or more other monomers (for example, hydroxyl group-containing monomer) can be used in combination. The proportion of the amide group-containing monomer in the monomer (Mh) can be, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more, and further, can be 100% by weight or less, 85% by weight or less, 70% by weight or less, 55% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less. As a preferred example of the amide group-containing monomer, N-vinyl cyclic amide can be mentioned. Among them, NVP is preferred.

[0091] It should be noted that among the amide group-containing monomers, there are monomers belonging to the hydroxyl group-containing monomer such as N-(2-hydroxyethyl)acrylamide, and monomers belonging to the monomer having a nitrogen atom-containing ring such as N-vinyl cyclic amide.

[0092] Examples of the above amino group-containing monomers include dimethylaminoethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, etc. The amino group-containing monomers can be used alone or in combination of two or more. As the monomer (Mh), one or more amino group-containing monomers and one or more other monomers can be used in combination. The proportion of the amino group-containing monomer in the monomer (Mh) can be, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more. Additionally, it can be 100% by weight or less, 85% by weight or less, 70% by weight or less, 55% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less.

[0093] Examples of the above monomers having a nitrogen atom-containing ring include vinylpyridine, vinylpyrimidine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinylis oxazole, (meth)acryloylmorpholine, (meth)acryloylpiperidine, (meth)acryloylpyrrolidine, etc. The monomers having a nitrogen atom-containing ring can be used alone or in combination of two or more. As the monomer (Mh), one or more monomers having a nitrogen atom-containing ring and one or more other monomers can be used in combination. The proportion of the monomer having a nitrogen atom-containing ring in the monomer (Mh) can be, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more. Additionally, it can be 100% by weight or less, 85% by weight or less, 70% by weight or less, 55% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less.

[0094] The above-mentioned (poly)oxyC 1-2 alkylene in the alkylene monomer 1-2 refers to an oxyalkylene having 1 to 2 carbon atoms, i.e., -O(CH 2 ) q - group (where q is 1 or 2). Additionally, the (poly)oxyC 1-2 alkylene refers to the meaning including oxyC 1-2 alkylene and polyoxyC 1-2 alkylene, and can be represented as -(O(CH 2 ) q ) r - group. Here, q in the above formula is 1 or 2, preferably q is 2, i.e., -(O(CH 2 ) q ) r-yl is preferably (poly) oxyethylene. In addition, r in the above formula can be, for example, 1 or more or 2 or more, and can also be, for example, 30 or less, 20 or less, 15 or less, 10 or less, 5 or less, or 3 or less. As an example of the monomer containing (poly) oxy C 1-2 alkylenes, examples include: methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, methoxypolyoxyethylene (meth) acrylate, ethoxypolyoxyethylene (meth) acrylate, etc. polyoxyethylene (meth) acrylates. As the above polyoxyethylene (meth) acrylate, a substance having a polyoxyethylene with a lower limit of r in the above formula of 3 or more, 4 or more, or 5 or more can be used, for example. The monomer containing (poly) oxy C 1-2 alkylenes can be used alone or in combination of two or more. As the monomer (Mh), one or two or more monomers containing (poly) oxy C 1-2 alkylenes and one or two or more other monomers can be used in combination. The proportion of the monomer containing (poly) oxy C 1-2 alkylenes in the monomer (Mh) can be, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more, and can also be 100% by weight or less, 85% by weight or less, 70% by weight or less, 55% by weight or less, 40% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less. As examples of the monomer containing (poly) oxy C 1-2 alkylenes that can be preferably used from the viewpoint of the flexibility of the adhesive, examples include: methoxyethyl acrylate (MEA, Tg of homopolymer: -50 °C), ethoxyethoxyethyl acrylate (alias: ethyl carbitol acrylate (CBA), Tg of homopolymer: -67 °C), etc.

[0095] The content of the non-acidic hydrophilic monomer (Mh) in the monomer components constituting the polymer (F) is set such that the total with the contents of other monomers is not more than 100% by weight. For example, it can be more than 0.5% by weight or more than 1.0% by weight. From the viewpoint of easily obtaining higher usage effects, it can be more than 2.0% by weight or more than 3.0% by weight. In some embodiments, from the viewpoint of suppressing the whitening phenomenon (humid heat whitening) of the adhesive due to exposure to high temperature and high humidity conditions, it is advantageous that the content of the monomer (Mh) in the above monomer components is more than 5.0% by weight. For example, it can be more than 5.5% by weight, can be more than 6.0% by weight, can be 8.0% by weight or more, can be 10% by weight or more, can be 15% by weight or more, can be 20% by weight or more, can be 25% by weight or more. In addition, the content of the monomer (Mh) in the above monomer components can be, for example, 50% by weight or less. From the viewpoint of reducing the refractive index of the adhesive, it is advantageous to be 40% by weight or less, preferably 35% by weight or less, can be 30% by weight or less, can be 25% by weight or less, can be 20% by weight or less, can be 15% by weight or less. In some embodiments, the content of the monomer (Mh) in the above monomer components can be 10% by weight or less, can also be 5.0% by weight or less, 1.0% by weight or less, or 0.5% by weight or less. It is also possible not to use the monomer (Mh).

[0096] The content of the hydroxyl group-containing monomer in the monomer components constituting the polymer (F) can be, for example, more than 0.5% by weight or more than 1.0% by weight, and can also be more than 2.0% by weight or more than 3.0% by weight. In some embodiments, from the viewpoint of appropriately considering flexibility and resistance to humid heat whitening in the case of a low refractive index, it is advantageous that the content of the above hydroxyl group-containing monomer is more than 4.0% by weight or more than 5.0% by weight. For example, it can be more than 5.5% by weight, can be more than 6.0% by weight, can be 8.0% by weight or more, can be 10% by weight or more, can be 15% by weight or more. The content of the hydroxyl group-containing monomer in the monomer components constituting the polymer (F) can be, for example, 50% by weight or less. From the viewpoint of reducing the refractive index of the adhesive, it is preferably 40% by weight or less or 35% by weight or less, can be 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less, can be 10% by weight or less, 5.0% by weight or less, 1.0% by weight or less, or 0.5% by weight or less. It is also possible not to use the hydroxyl group-containing monomer.

[0097] The above description regarding the content of the hydroxyl group-containing monomer in the monomer components constituting the polymer (F) can also be applied to the content of the monomer containing (poly)oxy C 1-2 alkylene in the monomer components constituting the polymer (F).

[0098] The content of the amide group-containing monomer in the monomer components constituting the polymer (F) can be, for example, greater than 0.5% by weight or greater than 1.0% by weight. From the perspective of easily obtaining higher usage effects, it can be greater than 2.0% by weight or greater than 3.0% by weight, and can be greater than 4.0% by weight, greater than 5.0% by weight, greater than 5.5% by weight, greater than 6.0% by weight, or 8.0% by weight or more. Additionally, from the perspective of lowering the refractive index of the adhesive, the content of the amide group-containing monomer in the monomer components constituting the polymer (F) is preferably 40% by weight or less or 30% by weight or less. From the perspective of the flexibility of the adhesive (especially the flexibility in the low-temperature region), 20% by weight or less is appropriate, preferably 15% by weight or less, more preferably 10% by weight or less, and can be 5.0% by weight or less, 1.0% by weight or less, or 0.5% by weight or less. It is also possible not to use the amide group-containing monomer.

[0099] The above description regarding the content of the amide group-containing monomer in the monomer components constituting the polymer (F) can also be applied to the content of the nitrogen atom-containing ring monomer and the amino group-containing monomer in the monomer components constituting the polymer (F).

[0100] In some aspects of the technology disclosed herein, a hydrophilic monomer (hereinafter also referred to as "low Tg hydrophilic monomer (Mh L )" or "monomer (Mh L )") whose homopolymer has a glass transition temperature (Tg) of 40 °C or lower (preferably 25 °C or lower, more preferably 0 °C or lower, still more preferably -10 °C or lower, such as -20 °C or lower, -25 °C or lower, or -30 °C or lower) is used as at least a part of the monomer (Mh). By using the low Tg hydrophilic monomer (Mh L ), it is possible to enjoy the effects brought by using the hydrophilic monomer (Mh) while suppressing the increase in the storage modulus G'. There is no particular limitation on the lower limit of the Tg of the homopolymer of the monomer (Mh L ). The Tg of the homopolymer of the monomer (Mh L ) can be, for example, -80 °C or higher, -70 °C or higher, -60 °C or higher, or -50 °C or higher. The monomer (Mh L ) can be used alone or in combination of two or more.

[0101] As the monomer (Mh L ), a monomer having a compatible Tg can be appropriately selected from the compounds included in the concept of the acid-free hydrophilic monomer (Mh) disclosed herein (such as the monomers (Mh) exemplified above). Examples of the acid-free hydrophilic monomer (Mh) that can be used as the monomer (Mh L ) include 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, and the like.

[0102] The proportion of the low-Tg hydrophilic monomer (Mh) in the monomer (Mh L ) is not particularly limited. From the viewpoint of improving the use effect of the monomer (Mh L ), in some embodiments, the proportion of the monomer (Mh) in the monomer (Mh L ) is suitably, for example, 5% by weight or more, advantageously 10% by weight or more, preferably 20% by weight or more, may be 25% by weight or more, may be 33% by weight or more, may be 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more. The above proportion may be 100% by weight. That is, one or two or more low-Tg hydrophilic monomers (Mh L ) may be used alone as the monomer (Mh). In addition, in some embodiments, the proportion of the monomer (Mh) in the monomer (Mh L ) may be, for example, 90% by weight or less, may be 75% by weight or less, may be 50% by weight or less, 30% by weight or less, 20% by weight or less, or 10% by weight or less.

[0103] The content of the low-Tg hydrophilic monomer (Mh L ) in the monomer components constituting the polymer (F) is not particularly limited. For example, it may be greater than 0.5% by weight, may be greater than 1.0% by weight, may be greater than 2.0% by weight, greater than 3.0% by weight, or greater than 4.0% by weight. From the viewpoint of improving the use effect of the monomer (Mh L ), in some embodiments, the content of the monomer (Mh L ) in the monomer components constituting the polymer (F) may be, for example, greater than 5.0% by weight, may be greater than 5.5% by weight, may be greater than 6.0% by weight, may be 8.0% by weight or more, may be 10% by weight or more, may be 15% by weight or more, may be 20% by weight or more, may be 25% by weight or more. In addition, the upper limit of the content of the monomer (Mh L ) in the above monomer components is set such that the total with the content of other monomers is not more than 100% by weight. For example, it may be 50% by weight or less, and from the viewpoint of lowering the refractive index of the adhesive, it is advantageously 40% by weight or less, preferably 35% by weight or less, may be 30% by weight or less, may be 25% by weight or less, may be 20% by weight or less, may be 15% by weight or less, may be 10% by weight or less, may be 5% by weight or less.

[0104] In some embodiments, the glass transition temperature Tg of the non-acid hydrophilic monomer (Mh) contained in the monomer components constituting the polymer (F) based on the composition of the monomer (Mh h ) is advantageously 100 °C or lower, preferably 80 °C or lower, more preferably 60 °C or lower. By making Tgh When using the monomer (Mh) at a temperature below the above temperature, it is possible to enjoy the effects brought by using the hydrophilic monomer (Mh) while suppressing the increase in the storage modulus G'. In some modes that pay more attention to flexibility, the Tg h being 50 °C or lower is appropriate, being 40 °C or lower is advantageous, preferably 30 °C or lower or 15 °C or lower, and can be 0 °C or lower, can be -10 °C or lower, can be -20 °C or lower, can be -25 °C or lower, can be -30 °C or lower. The Tg h has no particular limitation on the lower limit, and can be, for example, -80 °C or higher, -70 °C or higher, -60 °C or higher, or -50 °C or higher.

[0105] Here, the glass transition temperature Tg h based on the composition of the monomer (Mh) refers to the glass transition temperature calculated using the Fox equation based only on the composition of the non-acidic hydrophilic monomer (Mh) among the monomer components constituting the polymer (F). The Fox equation is as follows and is a relationship between the Tg of the copolymer and the glass transition temperatures Tgi of the homopolymers obtained by polymerizing the monomers constituting the copolymer separately.

[0106] 1 / Tg = Σ(Wi / Tgi)

[0107] In the above Fox equation, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (the copolymerization ratio based on weight), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K). As the glass transition temperature of the homopolymer used in the calculation of Tg, the values described in publicly known materials such as "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989), the manufacturer's catalog, etc. are used. For monomers with multiple values described in the above Polymer Handbook, the highest value is adopted. In the case where the Tg of the homopolymer is not described in publicly known materials, the value obtained by the measurement method described in Japanese Patent Application Laid-Open No. 2007-51271 is used.

[0108] The above glass transition temperature Tg h is calculated by applying the above Fox equation only to the monomer (Mh) among the monomer components constituting the polymer (F), and can be calculated from the glass transition temperature of the homopolymer of each non-acidic hydrophilic monomer used as the monomer (Mh) and the weight fraction of each non-acidic hydrophilic monomer in the total amount of the monomer (Mh). In the mode where only one non-acidic hydrophilic monomer is used as the monomer (Mh), the Tg of the homopolymer of this monomer is consistent with the glass transition temperature Tg h and is the same.

[0109] ((Meth)acrylic acid C 4-18(Chain alkyl ester)

[0110] In addition to the fluorine-containing acrylic monomer and the acidless hydrophilic monomer (Mh), the monomer component constituting the polymer (F) may further contain a monomer (M1) represented by the following formula (1):

[0111] CH 2 =CR 1 COOR 2 (1)

[0112] In the above formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a chain alkyl group having 4 to 18 carbon atoms (hereinafter, such a carbon atom number range may be expressed as "C 4-18 "). The monomer (M1) represented by the above formula (1) can also be referred to as (meth)acrylic acid C 4-18 chain alkyl ester. The monomer (M1) can contribute to the regulation of the storage modulus G' of the adhesive and the improvement of stretchability. The monomer (M1) can be used alone or in combination of two or more.

[0113] As specific examples of the (meth)acrylic acid C 4-18 chain alkyl ester, there can be mentioned: n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, etc., but are not limited to these substances.

[0114] In some embodiments, from the viewpoint of the storage modulus of the adhesive, etc., as the above monomer (M1), the monomer component constituting the polymer (F) contains a (meth)acrylic acid alkyl ester in which R 2 in the above formula (1) is a chain alkyl group of C 4-12 , that is, a (meth)acrylic acid C 4-12 chain alkyl ester is advantageous. From the viewpoint of the low-temperature properties of the adhesive, etc., it is preferable to contain a (meth)acrylic acid C 4-10 chain alkyl ester, and more preferably to contain an acrylic acid C 4-10 chain alkyl ester (for example, acrylic acid C 5-9(Chain alkyl esters). As (meth)acrylic acid C 4-12 Specific examples of the chain alkyl esters include: n-butyl acrylate, 2-ethylhexyl acrylate, n-heptyl acrylate, n-octyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, lauryl methacrylate, etc. These substances can be used alone or in combination of two or more.

[0115] In the mode where the monomer component constituting the polymer (F) contains the monomer (M1), the content of the monomer (M1) in the monomer component can be set in a manner that appropriately exhibits its usage effect. In some modes, the content of the monomer (M1) can be, for example, 1% by weight or more, 5% by weight or more, 8% by weight or more. In some modes, the content of the above monomer (M1) can be 10% by weight or more, 15% by weight or more, 20% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more. The upper limit of the content of the monomer (M1) in the monomer component is set in a manner that the total with the content of other monomers is not more than 100% by weight, and can be, for example, less than 80% by weight. From the viewpoint of easily achieving the balance between low refractive index and other properties, in some modes, it is appropriate that the content of the monomer (M1) in the monomer component constituting the polymer (F) is 75% by weight or less, can be 65% by weight or less, can be 55% by weight or less, can be 50% by weight or less. The technology disclosed herein can be implemented in a manner where the content of the above monomer (M1) is 45% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 10% by weight or less, 5% by weight or less, or 0% by weight.

[0116] In some modes, it is preferable to use a chain (meth)acrylic acid C with a Tg of 0 °C or lower (more preferably -10 °C or lower, further preferably -25 °C or lower, such as -35 °C or lower, -45 °C or lower, -50 °C or lower, -55 °C or lower, or -60 °C or lower) of the homopolymer 4-18A chain alkyl ester (a low-Tg (meth)acrylic acid alkyl ester) is at least part of the monomer (M1). Such a low-Tg (meth)acrylic acid alkyl ester can help improve the flexibility of the adhesive. The lower limit of the Tg of the above (meth)acrylic acid alkyl ester is not particularly limited. For example, it can be -85°C or higher, -80°C or higher, -75°C or higher. Specific examples of the above low-Tg (meth)acrylic acid alkyl ester include: n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), hexyl acrylate (HxA), n-octyl acrylate (NOAA), isononyl acrylate, isodecyl acrylate, lauryl acrylate, lauryl methacrylate, isostearyl acrylate, etc. From the viewpoint of flexibility in the low-temperature region, a (meth)acrylic acid C 4-10 chain alkyl ester is preferred, and a (meth)acrylic acid C 4-10 chain alkyl ester (for example, a (meth)acrylic acid C 5-9 chain alkyl ester) is more preferred.

[0117] The proportion of the above low-Tg (meth)acrylic acid alkyl ester in the monomer (M1) is not particularly limited. From the viewpoint of improving the use effect of the above low-Tg (meth)acrylic acid alkyl ester, in some embodiments, the proportion of the above low-Tg (meth)acrylic acid alkyl ester in the monomer (M1) is, for example, suitably 5% by weight or more, advantageously 10% by weight or more, preferably 20% by weight or more, and can be 25% by weight or more, 33% by weight or more, 50% by weight or more, 65% by weight or more, 80% by weight or more, or 90% by weight or more. The above proportion can be 100% by weight. That is, as the monomer (M1), one or two or more low-Tg (meth)acrylic acid alkyl esters can be used alone. In addition, in some embodiments, the proportion of the above low-Tg (meth)acrylic acid alkyl ester in the monomer (M1) can be, for example, 90% by weight or less, 75% by weight or less, 50% by weight or less, 30% by weight or less, 20% by weight or less, or 10% by weight or less.

[0118] The content of the above low-Tg (meth)acrylic acid alkyl ester in the monomer components constituting the polymer (F) can be, for example, 1% by weight or more, 5% by weight or more, 8% by weight or more. In some embodiments, the content of the above low-Tg (meth)acrylic acid alkyl ester can be 10% by weight or more, 15% by weight or more, 20% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more. The upper limit of the content of the above low-Tg (meth)acrylic acid alkyl ester in the monomer components is set such that the total with the content of other monomers is not more than 100% by weight, and can be, for example, less than 80% by weight. From the viewpoint of easily achieving the balance between low refractive index and other properties, in some embodiments, the content of the above low-Tg (meth)acrylic acid alkyl ester being 75% by weight or less is appropriate, and can be 65% by weight or less, 55% by weight or less, 50% by weight or less. The technology disclosed herein can also be implemented in such a manner that the content of the above low-Tg (meth)acrylic acid alkyl ester in the monomer components constituting the polymer (F) is 45% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 10% by weight or less, 5% by weight or less, or 0% by weight.

[0119] (Other monomers)

[0120] The monomer components constituting the polymer (F) may optionally contain monomers other than the above fluorine-containing acrylic monomers, monomer (Mh), and monomer (M1) (hereinafter also referred to as "other monomers").

[0121] Examples of the above other monomers include: (meth)acrylic acid C 1-3 alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate; (meth)acrylic acid chain alkyl esters having 19 or more carbon atoms in the chain alkyl group (for example, about 19 to about 24) such as nonadecyl (meth)acrylate and eicosyl (meth)acrylate; non-aromatic ring-containing monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic ring-containing monomers such as styrene, α-methylstyrene, and vinyltoluene; vinyl ester monomers such as vinyl acetate; olefin monomers such as ethylene, butadiene, and isobutene; chlorine-containing monomers such as vinyl chloride; vinyl ether monomers such as methyl vinyl ether; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; monomers containing acidic functional groups; and the like.

[0122] When using the above-mentioned other monomers, their usage amounts are not particularly limited and can be appropriately set within the range where the total amount of monomer components does not exceed 100% by weight. In some embodiments, the content of the above-mentioned other monomers in the monomer components constituting the polymer (F) can be, for example, about 35% by weight or less, about 25% by weight or less (e.g., 0% by weight to 25% by weight) is appropriate, can be about 20% by weight or less (e.g., 0% by weight to 20% by weight), can be about 10% by weight or less, can be about 5% by weight or less, for example, can be about 1% by weight or less, can be 0.5% by weight or less, 0.3% by weight or less, 0.1% by weight or less, or 0.05% by weight or less. It is also possible not to use the above-mentioned other monomers.

[0123] When using an acidic functional group-containing monomer as the above-mentioned other monomer, the acidic functional group-containing monomer can be, for example, one or more selected from carboxyl group-containing monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid; sulfonic acid group-containing monomers; phosphoric acid group-containing monomers. When using an acidic functional group-containing monomer, the content of the acidic functional group-containing monomer in the monomer components constituting the polymer (F) can be, for example, 0.01% by weight or more. The upper limit of the content of the carboxyl group-containing monomer in the monomer components is set in such a way that the total with the usage amount of other monomers does not exceed 100% by weight. In some embodiments, it is appropriate that the content of the acidic functional group-containing monomer in the monomer components constituting the polymer (F) is less than 7.0% by weight, preferably less than 5.0% by weight, more preferably less than 3.0% by weight, can be less than 2.0% by weight, can be less than 1.0% by weight, can be less than 0.5% by weight, can be less than 0.3% by weight, or less than 0.1% by weight, or less than 0.05% by weight. Limiting the content of the acidic functional group-containing monomer (e.g., carboxyl group-containing monomer) in this way is preferable from the viewpoint of suppressing the coloring or discoloration (e.g., yellowing) of the adhesive, and is also advantageous from the viewpoint of improving the flexibility of the adhesive (especially the flexibility in the low-temperature region). In addition, from the viewpoint of suppressing the corrosion of metal materials that can be in contact with or close to the adhesive disclosed herein (e.g., metal wirings, metal films, etc. that may be present on the adherend), it is also preferable to limit the content of the acidic functional group-containing monomer. The technology disclosed herein can be preferably implemented in such a way that the monomer components constituting the polymer (F) do not contain acidic functional group-containing monomers (i.e., the polymer (F) is acid-free).

[0124] <Adhesive composition>

[0125] The adhesives disclosed herein can be formed using an adhesive composition containing monomer components having the above-described composition in the form of a polymer, an unpolymerized form (i.e., a form in which polymerizable functional groups are unreacted), or a mixture thereof. The above adhesive composition can be in various forms such as a composition containing an adhesive (adhesive component) in an organic solvent (solvent-based adhesive composition), a composition in which the adhesive is dispersed in an aqueous solvent (aqueous dispersion adhesive composition), a composition prepared by curing with active energy rays such as ultraviolet rays and radiation rays to form an adhesive (active energy ray-curable adhesive composition), a hot-melt adhesive composition in which the composition is coated in a heat-melt state and forms an adhesive when cooled to near room temperature, and the like.

[0126] Here, in the present specification, "active energy rays" refer to energy rays having energy capable of causing chemical reactions such as polymerization reactions, crosslinking reactions, and decomposition of initiators. Examples of the active energy rays mentioned here include light such as ultraviolet rays, visible light, and infrared rays, and radiation rays such as α rays, β rays, γ rays, electron rays, neutron rays, and X rays.

[0127] In some preferred embodiments, the above adhesive composition contains at least a part (which can be a part of the type of monomers or a part of the amount) of the monomer components constituting the polymer (F) in the form of a polymer. There is no particular limitation on the polymerization method for forming the above polymer, and various conventionally known polymerization methods can be appropriately employed. For example, solution polymerization, emulsion polymerization, bulk polymerization, etc. (typically carried out in the presence of a thermal polymerization initiator); photopolymerization by irradiating ultraviolet rays or the like (typically carried out in the presence of a photopolymerization initiator); radiation polymerization by irradiating radiation rays such as β rays and γ rays; and the like can be appropriately used. Among them, photopolymerization is preferred. In these polymerization methods, there is no particular limitation on the polymerization mode, and conventionally known monomer supply methods, polymerization conditions (temperature, time, pressure, light irradiation amount, radiation ray irradiation amount, etc.), materials used other than monomers (polymerization initiators, surfactants, etc.) can be appropriately selected for carrying out.

[0128] During polymerization, known or conventional photopolymerization initiators and thermal polymerization initiators can be used according to the polymerization method, polymerization mode, etc. Such polymerization initiators can be used alone or in appropriate combination of two or more.

[0129] As the photopolymerization initiator, there is no particular limitation. For example, ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzil-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, etc. can be used.

[0130] Specific examples of ketal-based photopolymerization initiators include 2,2-dimethoxy-1,2-diphenylethane-1-one (e.g., trade name “Omnirad 651” manufactured by IGM Resins), etc.

[0131] Specific examples of acetophenone-based photopolymerization initiators include: 1-hydroxycyclohexyl phenyl ketone (e.g., trade name “Omnirad184” manufactured by IGM Resins), 4-phenoxydichloroacetophenone, 4-tert-butyl-dichloroacetophenone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, methoxyacetophenone, etc.

[0132] Specific examples of benzoin ether-based photopolymerization initiators include: benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether and other benzoin ethers and substituted benzoin ethers such as anisoin methyl ether.

[0133] Specific examples of acylphosphine oxide-based photopolymerization initiators include: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc.

[0134] Specific examples of α-ketol-based photopolymerization initiators include: 2-methyl-2-hydroxypropiophenone, 1-[4-(2-hydroxyethyl)phenyl]-2-methyl-1-propanone, etc. Specific examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride, etc. Specific examples of photoactive oxime-based photopolymerization initiators include 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)-oxime, etc. Specific examples of benzoin-based photopolymerization initiators include benzoin, etc. Specific examples of benzil-based photopolymerization initiators include benzil, etc.

[0135] Specific examples of benzophenone-based photopolymerization initiators include: benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, poly(vinylbenzophenone), 1-hydroxycyclohexyl phenyl ketone, etc.

[0136] Specific examples of thioxanthone-based photoinitiators include: thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, etc.

[0137] As the thermal polymerization initiator, there is no particular limitation. For example, azo-based polymerization initiators, peroxide-based initiators, redox initiators formed by the combination of peroxide and reducing agent, substituted ethane-based initiators, etc. can be used. More specifically, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(N,N'-dimethylisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate and other azo-based initiators can be exemplified; for example, persulfates such as potassium persulfate and ammonium persulfate; peroxide-based initiators such as benzoyl peroxide, tert-butyl hydroperoxide, and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; redox initiators such as the combination of persulfate and sodium bisulfite, and the combination of peroxide and sodium ascorbate; etc., but are not limited to these substances. Thermal polymerization can be preferably carried out at a temperature of about 20°C to about 100°C (typically about 40°C to about 80°C).

[0138] The usage amount of such a thermal polymerization initiator or photoinitiator can be set to a usual usage amount according to the polymerization method, polymerization mode, etc., and there is no particular limitation. For example, relative to 100 parts by weight of the monomer to be polymerized, about 0.001 part by weight to about 5 parts by weight (typically about 0.01 part by weight to about 2 parts by weight, for example about 0.01 part by weight to about 1 part by weight) of the polymerization initiator can be used.

[0139] (Polymer and unpolymerized binder composition containing monomer components)

[0140] Some types of binder compositions contain the polymerization reaction product of a monomer mixture containing at least a part of the monomer components (raw materials monomers). Typically, a part of the above monomer components is contained in the form of a polymer, and the remaining part is contained in the form of unpolymerized (unreacted monomers). The binder composition containing the polymer and unpolymerized monomer components can be preferably used as an active energy ray-curable binder composition, for example. The polymerization reaction product of the above monomer mixture can be prepared by polymerizing at least part of the monomer mixture.

[0141] The above polymerization reaction product is preferably a partial polymer of the above monomer mixture. Such a partial polymer is a mixture of a polymer derived from the above monomer mixture and unreacted monomers, typically in the form of a slurry (viscous liquid). Hereinafter, the partial polymer having such a property may sometimes be referred to as "monomer slurry" or simply "slurry".

[0142] The polymerization method for obtaining the above polymerization reaction product is not particularly limited, and the above various polymerization methods can be appropriately selected and used. From the viewpoints of efficiency and simplicity, the photopolymerization method can be preferably adopted. According to photopolymerization, the polymerization conversion rate of the above monomer mixture can be easily controlled by polymerization conditions such as the irradiation amount (light amount) of light.

[0143] The polymerization conversion rate (monomer conversion rate) of the monomer mixture in the above partial polymer is not particularly limited. The above polymerization conversion rate can be, for example, about 70% by weight or less, preferably about 60% by weight or less. From the viewpoints of the ease of preparation and coatability of the adhesive composition containing the above partial polymer, etc., usually the above polymerization conversion rate is appropriately about 50% by weight or less, preferably about 40% by weight or less (for example, about 35% by weight or less). The lower limit of the polymerization conversion rate is not particularly limited, typically about 1% by weight or more, and usually about 5% by weight or more is appropriate.

[0144] The adhesive composition containing the partial polymer of the above monomer mixture can be obtained, for example, by partially polymerizing the monomer mixture containing all the raw material monomers by using an appropriate polymerization method (for example, the photopolymerization method). Other components (for example, a photopolymerization initiator, a crosslinking agent (which may be a polyfunctional monomer), etc.) that are used as needed can be incorporated into the adhesive composition containing the above partial polymer. The method of incorporating such other components is not particularly limited. For example, they can be pre-incorporated into the above monomer mixture or added to the above partial polymer.

[0145] The adhesive composition disclosed herein can be in a form in which a partial polymer or a complete polymer of a monomer mixture containing some types of monomers (raw material monomers) is dissolved in the remaining types of monomers or their partial polymers. The adhesive composition in such a form is also included in the examples of the adhesive composition containing a polymer and an unpolymerized monomer component. It should be noted that in this specification, "complete polymer" means that the polymerization conversion rate is greater than 95% by weight.

[0146] As a curing method (polymerization method) when forming an adhesive from an adhesive composition comprising a polymer containing monomer components and unpolymerized components, a photopolymerization method can be preferably employed. For an adhesive composition comprising a polymerization reaction product prepared by a photopolymerization method, as its curing method, a photopolymerization method is particularly preferably employed. Since the polymerization reaction product obtained by the photopolymerization method already contains a photoinitiator, when forming an adhesive by further curing the adhesive composition containing the polymerization reaction product, it can be photocured even without adding a new photoinitiator. Alternatively, it can also be an adhesive composition having a composition in which a photoinitiator is added as needed to the polymerization reaction product prepared by the photopolymerization method. The added photoinitiator can be the same as or different from the photoinitiator used in the preparation of the polymerization reaction product. An adhesive composition prepared by a method other than photopolymerization can be adjusted to be photocurable by adding a photoinitiator. The photocurable adhesive composition has the advantage that even a thick adhesive layer can be easily formed. In a preferred embodiment, the photopolymerization when forming an adhesive from the adhesive composition can be carried out by ultraviolet irradiation. Ultraviolet irradiation can be performed using a known high-pressure mercury lamp, low-pressure mercury lamp, metal halide lamp, etc.

[0147] (An adhesive composition containing monomer components in the form of a fully polymerized polymer)

[0148] Some other types of adhesive compositions contain monomer components in the form of a fully polymerized polymer. Such an adhesive composition can be, for example, a solvent-based adhesive composition of a polymer (F) containing a fully polymerized polymer (e.g., a fully polymer obtained by solution polymerization or emulsion polymerization) as a monomer component in an organic solvent, a water-dispersion type adhesive composition in which the above polymer (F) is dispersed in an aqueous solvent, etc. The solvent (polymerization solvent) used in the solution polymerization of the monomer components can be appropriately selected from conventionally known organic solvents. For example, it can be any one solvent selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc., or a mixed solvent of two or more of them.

[0149] (Crosslinking agent)

[0150] In the adhesive composition, a crosslinking agent can be contained as needed to adjust the cohesion of the adhesive, etc. As the crosslinking agent, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, Crosslinking agents well-known in the adhesive field, such as oxazoline-based crosslinking agents, melamine-based resins, metal chelate-based crosslinking agents, etc. Among them, as preferred examples, isocyanate-based crosslinking agents and epoxy-based crosslinking agents can be cited. As other examples of crosslinking agents, monomers having two or more ethylenically unsaturated groups in one molecule, that is, polyfunctional monomers having two or more functional groups, can be cited. The crosslinking agent can be used alone or in combination of two or more kinds.

[0151] As polyfunctional monomers, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentadienyl di(meth)acrylate, di(meth)acryloyl isocyanurate, bisphenol A di(meth)acrylate, alkylene oxide-modified bisphenol di(meth)acrylate and other difunctional (meth)acrylates;

[0152] For example, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, isocyanuric acid tris(acryloyloxyethyl) ester and other trifunctional (meth)acrylates;

[0153] For example, bis(trimethylolpropane) tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, dipentaerythritol penta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate having four or more (meth)acryloyl groups, polyester acrylate having four or more (meth)acryloyl groups, urethane acrylate having four or more (meth)acryloyl groups and other polyfunctional (meth)acrylates having four or more functional groups;

[0154] Polyfunctional monomers having at least one ethylenically unsaturated group other than (meth)acryloyl group (for example, difunctional monomers) such as allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, etc.; etc. The polyfunctional monomers can be used alone or in combination of two or more kinds.

[0155] As the isocyanate crosslinking agent, polyfunctional isocyanate compounds having two or more functional groups can be used. For example, they include aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate (XDI); polyisocyanate modified products obtained by modifying the above isocyanate compounds through urethane bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, polyisocyanate modified products obtained by modifying the above isocyanate compounds through diazinetrione bonds (for example, isocyanurate body of HDI, urethane body of HDI, etc.); polyol adducts of the above isocyanate compounds (for example, trimethylolpropane adduct of XDI, etc.); etc. As examples of commercially available products, there can be mentioned trade names Takenate 300S, Takenate 500, Takenate 600, Takenate D110N, Takenate D120N, Takenate D140N, Takenate D160N, Takenate D165N, Takenate D178N, Takenate D178 NL (all of the above are manufactured by Mitsui Chemicals, Inc.), Sumidur T80, Sumidur L, Desmodur N3400 (all of the above are manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (all of the above are manufactured by Tosoh Corporation), trade names Duranate A201H, Duranate TPA-100 (all of the above are manufactured by Asahi Kasei Corporation), etc. The isocyanate compounds can be used alone or in combination of two or more. A bifunctional isocyanate compound and a polyfunctional isocyanate compound having three or more functional groups can also be used in combination.

[0156] As epoxy crosslinking agents, examples include: bisphenol A, epoxy resins of bisphenol A and epichlorohydrin type, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diaminodiglycidylamine, N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. These substances can be used alone or in combination of two or more.

[0157] In some embodiments, as at least a part of the crosslinking agent, a bifunctional crosslinking agent having two crosslinking reactive groups (e.g., ethylenically unsaturated group, isocyanate group, etc.) per molecule is used. By using a bifunctional crosslinking agent, a soft crosslinked structure is easily formed. The bifunctional crosslinking agent can be used alone or in combination of two or more. Examples of the bifunctional crosslinking agent include bifunctional monomers such as bifunctional (meth)acrylate, bifunctional isocyanate compounds, etc. The bifunctional crosslinking agent can be used in combination with a crosslinking agent having three or more functional groups.

[0158] In some embodiments, an acyclic crosslinking agent (also referred to as a chain crosslinking agent) that does not have a ring structure such as an aromatic ring or an aliphatic ring is preferably used as the crosslinking agent. By using a chain crosslinking agent as the crosslinking agent, a crosslinked structure with high flexibility is easily formed, and further, an adhesive with high flexibility is easily formed.

[0159] As the acyclic crosslinking agent, for example, among the above polyfunctional monomers, polyfunctional monomers without a ring structure such as chain alkylene glycol di(meth)acrylate and alkylene glycol di(meth)acrylate are preferably used. In addition, for example, among the above isocyanate crosslinking agents, isocyanate compounds without a ring structure such as an aromatic ring and an isocyanurate ring are preferably used. Specific examples of the above acyclic isocyanate include: aliphatic isocyanate compounds (e.g., PDI, HDI), modified products of aliphatic isocyanate compounds (e.g., polyisocyanate modified products obtained by modifying PDI and HDI with urethane bond, biuret bond, urea bond, carbodiimide bond). The acyclic crosslinking agent can be used alone or in combination of two or more. In some preferred embodiments, an acyclic bifunctional crosslinking agent can be used as the crosslinking agent.

[0160] When a crosslinking agent (which may be a polyfunctional monomer) is used, its amount of use is not particularly limited and can be set in a manner that can obtain the desired properties. With respect to 100 parts by weight of the monomer components constituting the polymer (F), the amount of the crosslinking agent used can be, for example, in the range of about 0.001 part by weight to about 5.0 parts by weight. From the viewpoint of improving the flexibility and elongation of the adhesive, in some embodiments, with respect to 100 parts by weight of the above monomer components, the amount of the crosslinking agent used is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and can be, for example, 1.5 parts by weight or less, 1.0 part by weight or less, 0.50 part by weight or less, 0.30 part by weight or less, 0.25 part by weight or less, 0.20 part by weight or less, 0.15 part by weight or less, 0.12 part by weight or less, 0.10 part by weight or less, or 0.09 part by weight or less. On the other hand, from the viewpoint of appropriately exerting the effect of using the crosslinking agent, in some embodiments, with respect to 100 parts by weight of the above monomer components, the amount of the crosslinking agent used can be, for example, 0.005 part by weight or more, 0.010 part by weight or more, 0.015 part by weight or more, 0.02 part by weight or more, 0.04 part by weight or more, 0.06 part by weight or more, or 0.08 part by weight or more, 0.10 part by weight or more, or 0.15 part by weight or more.

[0161] In order to carry out the crosslinking reaction more effectively, a crosslinking catalyst can be used. Examples of the crosslinking catalyst include: metal crosslinking catalysts such as tetra-n-butyl titanate, tetra-isopropyl titanate, iron(III) acetylacetonate, butyltin oxide, and dioctyltin dilaurate. Among them, tin-containing crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of use of the crosslinking catalyst is not particularly limited. Considering the balance between the speed of the crosslinking reaction and the service life of the adhesive composition, with respect to 100 parts by weight of the monomer components constituting the polymer (F), the amount of the crosslinking catalyst used can be, for example, in the range of about 0.0001 part by weight or more and 1 part by weight or less, preferably in the range of 0.001 part by weight or more and 0.5 part by weight or less.

[0162] In the adhesive composition, a compound capable of keto-enol tautomerism can be contained as a crosslinking retarder. Thereby, the effect of extending the service life of the adhesive composition can be achieved. For example, in an adhesive composition containing an isocyanate crosslinking agent, a compound capable of keto-enol tautomerism can be preferably used. As the compound capable of keto-enol tautomerism, various β-dicarbonyl compounds can be used. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.), acetoacetates (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably employed. The compound capable of keto-enol tautomerism can be used alone or in combination of two or more. With respect to 100 parts by weight of the monomer components constituting the polymer (F), the amount of the compound capable of keto-enol tautomerism used can be, for example, 0.1 part by weight or more and 20 parts by weight or less, can be 0.5 part by weight or more and 10 parts by weight or less, or can be 1 part by weight or more and 5 parts by weight or less.

[0163] (Silane coupling agent)

[0164] In some embodiments, the adhesive can contain a silane coupling agent. The silane coupling agent can help improve the adhesive strength to the adherend, etc. The silane coupling agent can be used alone or in combination of two or more.

[0165] Examples of the silane coupling agent include: epoxy group-containing silicon compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; acetylacetonyl group-containing trimethoxysilane, (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatopropyltriethoxysilane, etc. Among them, as preferred examples, 3-glycidoxypropyltrimethoxysilane, acetylacetonyl group-containing trimethoxysilane can be cited.

[0166] The amount of the silane coupling agent used can be set in a manner that can achieve the desired usage effect, and there is no particular limitation. In some embodiments, based on 100 parts by weight of the monomer components constituting the polymer (F), the amount of the silane coupling agent used can be, for example, 0.001 part by weight or more. From the perspective of obtaining higher effects, it can be 0.005 part by weight or more, 0.01 part by weight or more, 0.05 part by weight or more, 0.1 part by weight or more, 0.2 part by weight or more. Additionally, from the perspective of the storage stability of the adhesive, etc., in some embodiments, based on 100 parts by weight of the monomer components constituting the polymer (F), the amount of the silane coupling agent used can be, for example, less than 3.0 parts by weight, less than 2.0 parts by weight, less than 1.5 parts by weight, less than 1.0 parts by weight, or 0.5 part by weight or less. It is also possible not to use the silane coupling agent.

[0167] (Tackifier)

[0168] The adhesive layer in the technology disclosed herein may contain a tackifier. As the tackifier, known tackifying resins such as rosin-based tackifying resins, terpene-based tackifying resins, phenolic tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins can be used. These resins can be used alone or in combination of two or more. The amount of the tackifying resin used is not particularly limited and can be set according to the purpose and use to exhibit appropriate adhesive properties. In some embodiments, from the perspective of refractive index and transparency, based on 100 parts by weight of the monomer components constituting the polymer (F), it is appropriate that the amount of the tackifier used is 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technology disclosed herein can preferably be implemented in a manner without using a tackifier.

[0169] (Other Additives)

[0170] In the technology disclosed herein, the adhesive composition used in the formation of the adhesive may contain, as needed, known additives that can be used in the adhesive composition, such as plasticizers, softeners, colorants, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, within a range that does not significantly interfere with the effects of the present invention. Regarding such various additives, conventionally known substances can be used by conventional methods, and no particular features are imparted to the present invention, so detailed descriptions are omitted.

[0171] (Gel Fraction)

[0172] The gel fraction of the adhesives disclosed herein is appropriately set according to the purpose of use, the mode of use, etc., and is not limited to a specific range. From the viewpoint of imparting appropriate cohesiveness to the adhesive and properly exhibiting adhesive properties, the above gel fraction is, for example, about 10% or more, appropriately about 30% or more, preferably about 40% or more, more preferably about 50% or more, can be 75% or more, can be 85% or more, can be 90% or more, can be 92% or more, 94% or more, 94% or more, or 98% or more. In addition, from the viewpoint of easily achieving a good balance between low refractive index and adhesive properties, the gel fraction of the adhesive is appropriately 99.9% or less, and can be, for example, 99.7% or less, 99.5% or less, 99% or less, 97% or less, 95% or less, 93% or less. From the viewpoint of appropriately following the unevenness that may exist on the surface of the adherend and adhering well, it is advantageous that the gel ratio is not too high. The gel fraction is measured by the following method.

[0173] [Measurement of Gel Fraction]

[0174] Wrap a specified amount of the adhesive sample (weight Wg 1 ) in a porous polytetrafluoroethylene membrane with an average pore size of 0.2 μm (weight Wg 2 ) into a purse shape (pouch shape), and tie the mouth of the bag with kite string (weight Wg 3 ). As the above porous polytetrafluoroethylene (PTFE) membrane, use the product name “NITOFLON (registered trademark) NTF1122” (average pore size 0.2 μm, porosity 78%, thickness 85 μm) or its equivalent product available from Nitto Denko Corporation.

[0175] Immerse the wrapped product in a sufficient amount of ethyl acetate, keep it at room temperature (typically 23 °C) for 7 days to dissolve only the sol part in the adhesive outside the membrane, then take out the wrapped product, wipe off the ethyl acetate adhering to the outer surface, dry the wrapped product at 130 °C for 2 hours, and measure the weight of the wrapped product (Wg 4 ). The gel fraction of the adhesive layer is obtained by substituting each value into the following formula.

[0176] Gel fraction (%) = [(Wg 4 - Wg 2 - Wg 3 ) / Wg 1 × 100

[0177] (Reactive Energy Ray Curable Adhesive)

[0178] In some preferred embodiments, the adhesives disclosed herein can be adhesives formed from an active energy ray (e.g., ultraviolet ray) curable adhesive composition, i.e., adhesives that are the cured products of active energy ray curable adhesive compositions. The adhesive can be formed by curing the adhesive composition in a state where the surface of the adhesive composition is in contact with a smooth release surface (e.g., a release liner having such a release surface), so that it is easy to achieve high surface smoothness at the adhesive surface (the interface with the above-mentioned release surface), and it is easy to obtain good optical properties, so it is preferred. In addition, the active energy ray curable adhesive composition does not contain a solvent that should be removed during the formation of the adhesive from the adhesive composition, or even if it contains, it is in a small amount (typically less than 10% by weight of the adhesive composition, less than 5% by weight of the adhesive composition, or less than 1% by weight of the adhesive composition), so it is easy to obtain an adhesive (adhesive layer) with high homogeneity in the thickness direction. This is advantageous from the viewpoint of optical isotropy. In addition, by using an adhesive composition that does not contain a solvent or contains a small amount of solvent to form the adhesive, it is easy to suppress the deviation of hydrophilicity in the adhesive and easy to improve the resistance to moisture and heat-induced whitening.

[0179] (Polymerization rate)

[0180] It is appropriate that the polymerization rate (polymerization conversion rate) of the adhesives disclosed herein is 95.0% by weight or more, preferably 97% by weight or more (e.g., 97.5% by weight or more), and more preferably 98.5% by weight or more (e.g., 99.0% by weight or more). A higher polymerization rate of the adhesive means that there are fewer unreacted monomers contained in the adhesive. From the viewpoint of preventing the uneven distribution (bias) of low molecular weight substances that may be contained in the adhesive from adversely affecting the adhesive properties and optical properties, it is preferred that the polymerization rate of the adhesive is above a specified value. The polymerization rate of the adhesive can be measured by the method described in the examples below.

[0181] <Adhesive sheet>

[0182] According to this specification, an adhesive sheet having an adhesive layer is provided. The adhesive constituting the above-mentioned adhesive layer can be an adhesive formed from any of the adhesive compositions disclosed herein (e.g., the cured product of the adhesive composition).

[0183] The above-mentioned adhesive sheet may be a substrate-bearing adhesive sheet in the form of having the above-mentioned adhesive layer on one or both sides of a non-peelable substrate (support substrate), or may be a substrate-free adhesive sheet in the form of the above-mentioned adhesive layer being held by a release liner (i.e., an adhesive sheet without a non-peelable substrate, typically an adhesive sheet composed of an adhesive layer). The concept of the adhesive sheet mentioned here may include objects such as adhesive tapes, adhesive labels, and adhesive films. The adhesive sheet disclosed here may be in the form of a roll or a single sheet. Alternatively, it may also be an adhesive sheet in a form further processed into various shapes.

[0184] A structural example of a double-sided adhesive type substrate-free adhesive sheet (substrate-free double-sided adhesive sheet) is illustrated in Figure 1 , 2 . Figure 1 The adhesive sheet 1 shown has a structure in which both surfaces 21A and 21B of the substrate-free adhesive layer 21 are protected by release liners 31 and 32 that are at least on the adhesive layer side and form release surfaces. Figure 2 The adhesive sheet 2 shown has a structure in which one surface (adhesive surface) 21A of the substrate-free adhesive layer 21 is protected by a release liner 31 that has release surfaces on both sides. When it is wound, it can be formed into a structure in which the other surface (adhesive surface) 21B of the adhesive layer 21 contacts the back surface of the release liner 31 and thus the other surface 21B is also protected by the release liner 31. The technology disclosed here is preferably implemented in the form of a substrate-free adhesive sheet formed by an adhesive layer, for example, from the viewpoints of reducing the thickness of the adhesive sheet and improving the transparency of the adhesive sheet. The above-mentioned substrate-free adhesive sheet is also preferred from the viewpoint of flexibility (for example, the flexibility to follow a adherend that is repeatedly bent).

[0185] The adhesive sheet disclosed here may, for example, have a cross-sectional structure schematically shown in Figure 3 . Figure 3The adhesive sheet 3 shown has a support substrate 10 and a first adhesive layer 21 and a second adhesive layer 22 supported by the first surface 10A and the second surface 10B of the support substrate 10, respectively. Both the first surface 10A and the second surface 10B are non-peeling surfaces (non-peeling faces). The adhesive sheet 3 is used by pasting the surface (first adhesive face) 21A of the first adhesive layer 21 and the surface (second adhesive face) 22A of the second adhesive layer 22 to an adherend, respectively. That is, the adhesive sheet 3 is configured in the form of a double-sided adhesive sheet (a double-sided adhesive adhesive sheet). Before use, the adhesive sheet 3 has a configuration in which the first adhesive face 21A and the second adhesive face 22A are protected by release liners 31, 32, respectively, which are surfaces having peelability (peel faces) at least on the adhesive face side. Alternatively, it may be configured as follows: The release liner 32 is omitted, and a release liner having both sides as peel faces is used as the release liner 31, and the second adhesive face 22A is brought into contact with the back face of the release liner 31 by winding the adhesive sheet 3, so that the second adhesive face 22A is also protected by the release liner 31.

[0186] The technology disclosed herein is preferably implemented in the form of the above-described substrate-free or substrate-bearing double-sided adhesive sheet. Alternatively, the adhesive sheet disclosed herein may be in the form of a substrate-bearing single-sided adhesive sheet having an adhesive layer only on one side of a non-peeling substrate (support substrate), but is not particularly illustrated. As an example of the form of the single-sided adhesive sheet, a form in which neither the first adhesive layer 21 nor the second adhesive layer 22 is present in the configuration shown can be cited. Figure 3 a form in which neither the first adhesive layer 21 nor the second adhesive layer 22 is present in the configuration shown.

[0187] (Adhesive layer)

[0188] The adhesive constituting the adhesive layer may be an adhesive obtained by curing an adhesive composition in a form such as a solvent type, an active energy ray curable type, a water dispersion type, a hot melt type, etc. by drying, crosslinking, polymerization, cooling, etc., that is, a cured product of the above-described adhesive composition. The curing method (for example, drying, crosslinking, polymerization, cooling, etc.) of the adhesive composition may apply only one kind, or may apply two or more kinds simultaneously or in multiple stages. For a solvent type adhesive composition, typically, the composition is dried (preferably further crosslinked) to form an adhesive. For an active energy ray curable type adhesive composition, typically, an adhesive is formed by irradiating active energy rays to perform a polymerization reaction and / or a crosslinking reaction. In the case where it is necessary to dry the active energy ray curable type adhesive composition, active energy rays may be irradiated after drying.

[0189] The above-mentioned adhesive layer can be formed by curing the adhesive composition after applying (e.g., coating) it on a suitable surface. Coating of the adhesive composition can be carried out, for example, using conventional coating machines such as a gravure roll coater, an inversion roll coater, a contact roll coater, an immersion roll coater, a bar coater, a knife coater, a spray coater, etc.

[0190] The thickness of the adhesive layer is not particularly limited. For example, it can be 3 μm or more, suitably 5 μm or more, can be 10 μm or more, can be 15 μm or more, can be 20 μm or more, can be 30 μm or more, can be 45 μm or more. By increasing the thickness of the adhesive layer, there is a tendency for the adhesive strength to increase. In some embodiments, the thickness of the adhesive layer can be 50 μm or more, can also be 70 μm or more or 85 μm or more. Additionally, the thickness of the adhesive layer can be, for example, 300 μm or less, can be 250 μm or less, can be 200 μm or less, can be 150 μm or less, can also be 120 μm or less. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 75 μm or less, further preferably 70 μm or less, can be 60 μm or less. Considering viewpoints such as thinning of the adhesive sheet, it can be advantageous that the thickness of the adhesive layer is not too large. In addition, an adhesive layer with a small thickness has a tendency to have excellent followability to the adherend. In some embodiments, the thickness of the adhesive layer can be 40 μm or less, can also be 30 μm or less. The technology disclosed herein can be preferably implemented, for example, in such a manner that the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm, further preferably 5 μm to 75 μm). It should be noted that in the case of an adhesive sheet having a first adhesive layer and a second adhesive layer on the first surface and the second surface of the substrate, the above-mentioned thickness of the adhesive layer can be applied at least to the thickness of the first adhesive layer. The thickness of the second adhesive layer can be selected from the same range. Additionally, in the case of a substrate-free adhesive sheet, the thickness of the adhesive sheet is the same as the thickness of the adhesive layer.

[0191] (Total light transmittance)

[0192] In some embodiments, the total light transmittance of the adhesive layer is preferably 85.0% or more (e.g., 88.0% or more, 90.0% or more, or greater than 90.0%). The adhesive sheet having an adhesive layer with such high transparency can be preferably applied to applications that require high light transmittance (e.g., optical applications) and applications that require the ability to visually recognize the adherend well through the adhesive sheet. The upper limit of the total light transmittance can be, for example, about 98% or less, about 96% or less, or about 95% or less in practical use. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the adhesive layer can be about 94% or less, about 93% or less, or about 92% or less. The total light transmittance is measured according to JIS K7136:2000 using a commercially available transmittance meter. As the transmittance meter, a product named "HAZEMETERH M-150" manufactured by Murakami Color Research Institute or its equivalent product is used. The total light transmittance can be measured by the method described in the examples below. The total light transmittance of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

[0193] In some embodiments, the total light transmittance of the adhesive sheet is preferably 85.0% or more (e.g., 88.0% or more, 90.0% or more, or greater than 90.0%). The adhesive sheet with such high transparency can be preferably applied to applications that require high light transmittance (e.g., optical applications) and applications that require the ability to visually recognize the adherend well through the adhesive sheet. The upper limit of the total light transmittance can be, for example, about 98% or less, about 96% or less, or about 95% or less in practical use. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the adhesive sheet can be about 94% or less, about 93% or less, or about 92% or less. The total light transmittance of the adhesive sheet can be measured by the same method as the measurement of the total light transmittance of the above adhesive layer. The total light transmittance of the adhesive sheet can be obtained by selecting the composition of the above adhesive layer, etc., the type of the substrate, and the thickness of the substrate in the configuration with a substrate.

[0194] (Haze value)

[0195] In some embodiments, the haze value (sometimes simply referred to as "haze") of the adhesive layer constituting the adhesive sheet can be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, can be 0.9% or less, can be 0.8% or less, can be 0.5% or less, or can also be 0.3% or less. An adhesive sheet having an adhesive layer with such high transparency can be preferably applied to applications that require high light transmittance (such as optical applications) in configurations with or without a substrate, and applications that require the ability to visually recognize the adherend well through the adhesive sheet. The lower limit of the haze value of the adhesive layer is not particularly limited, and from the perspective of improving transparency, the smaller the haze value, the more preferred. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value can be, for example, 0.05% or more, or can be 0.10% or more. These haze values related to the adhesive layer can be preferably applied to the haze value of the adhesive sheet in the case where the technology disclosed herein is implemented in the form of a substrate-free adhesive sheet (typically an adhesive sheet formed by an adhesive layer).

[0196] Here, the "haze value" refers to the ratio of diffused transmitted light to total transmitted light when visible light is irradiated on the measurement object. It is also called turbidity. The haze value can be expressed by the following formula.

[0197] Th(%) = Td / Tt × 100

[0198] In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The measurement of the haze value can be carried out according to the method described in the examples below. The haze value of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

[0199] In some embodiments, the haze value of the adhesive sheet can be, for example, 10.0% or less, preferably 5.0% or less, more preferably 3.0% or less, still more preferably 2.0% or less, can be 1.7% or less, can be 1.5% or less, can be 1.2% or less, can be 1.0% or less, or can be 0.8% or less. An adhesive sheet with such high transparency can be preferably applied to applications that require high light transmittance (such as optical applications) and applications that require the ability to visually recognize the adherend well through the adhesive sheet. The lower limit of the haze value of the adhesive sheet is not particularly limited, and from the perspective of improving transparency, the smaller the haze value, the more preferred. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value can be, for example, 0.05% or more, can be 0.1% or more, can be 0.2% or more, or can also be 0.3% or more. The haze value of the adhesive sheet can be measured by the same method as the measurement of the haze value of the above-mentioned adhesive layer. The above-mentioned haze value of the adhesive sheet can be obtained by selecting the composition of the above-mentioned adhesive layer, etc., the type of substrate and the thickness of the substrate in the configuration with a substrate.

[0200] (Peeling strength)

[0201] There is no particular limitation on the peeling strength of the adhesive sheet from the glass plate. In some embodiments, the peeling strength of the adhesive sheet from the glass plate (peeling strength from the glass plate) is, for example, 0.1 N / 25 mm or more, and may be 0.5 N / 25 mm or more. In some preferred embodiments, the peeling strength from the glass plate is 1.0 N / 25 mm or more, more preferably 1.5 N / 25 mm or more, further preferably 2.0 N / 25 mm or more, may be 3.0 N / 25 mm or more, may be 5.0 N / 25 mm or more, may be 6.0 N / 25 mm or more, 7.0 N / 25 mm or more, 8.0 N / 25 mm or more, 9.0 N / 25 mm or more, or 10 N / 25 mm or more. An adhesive sheet having a peeling strength from the glass plate of a specified value or more is suitable for joining and fixing glass components, etc. There is no particular limitation on the upper limit of the peeling strength, and it may be, for example, 30 N / 25 mm or less, 25 N / 25 mm or less, or 20 N / 25 mm or less.

[0202] Here, the peeling strength can be determined by the following operation: The adhesive sheet is pressed onto an alkali glass plate as the adherend and left in an environment of 23°C and 50% RH for 30 minutes, and then the peeling strength is measured under the conditions of a peeling angle of 180 degrees and a pulling speed of 300 mm / minute. When measuring, if necessary, an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to about 50 μm) can be pasted on the adhesive sheet to be measured for reinforcement. The peeling strength can be more specifically measured according to the method described in the examples below.

[0203] (Moisture and heat resistance of whitening)

[0204] In some embodiments of the adhesives disclosed herein, the adhesive layer formed from the adhesive can exhibit, for example, moisture and heat resistance of whitening with a haze (haze after moisture and heat) of less than about 3.0% after a moisture and heat test of maintaining for 240 hours in a moist and hot environment of 85°C and 85% RH. In some embodiments, the haze after moisture and heat is preferably 2.0% or less, more preferably 1.0% or less, may be 0.8% or less, may be 0.6% or less, may be 0.5% or less, may be 0.4% or less, may be 0.3% or less, or 0.2% or less. The haze after moisture and heat of the adhesive layer is measured by the method described in the examples below.

[0205] The increase in haze after the above-mentioned heat and humidity treatment relative to the initial haze (before the heat and humidity test), that is, haze after heat and humidity [%] - initial haze [%], can be, for example, less than 3.0%, preferably 2.0% or less or less than 2.0%, more preferably 1.0% or less or less than 1.0%, can be 0.8% or less, can be 0.6% or less, can be 0.5% or less, can be 0.4% or less, can be 0.3% or less, can be 0.2% or less, can be 0.1% or less, can be less than 0.1%, and can be 0.0%.

[0206] (Surface smoothness of the adhesive surface)

[0207] In some embodiments, the surface of the adhesive layer (adhesive surface) preferably has high surface smoothness.

[0208] For example, the above-mentioned adhesive surface preferably has its arithmetic mean roughness Ra limited to a specified value or less. A configuration having an adhesive surface with a low arithmetic mean roughness Ra is preferable from the viewpoint of optical homogeneity. By limiting the arithmetic mean roughness Ra, for example, in a usage mode in which light is extracted through the above-mentioned adhesive surface (such as an adhesive sheet disposed at a position closer to the viewing point side than the self-luminous element in a light-emitting device), an effect of suppressing the occurrence of brightness unevenness caused by the surface state of the adhesive layer can be exerted. A low arithmetic mean roughness Ra of the adhesive surface is also advantageous for suppressing optical distortion, and the suppression of optical distortion contributes to the improvement of optical homogeneity. When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferable that at least the arithmetic mean roughness Ra of the first adhesive surface is limited to a specified value or less, and more preferably the arithmetic mean roughness Ra of both adhesive surfaces is limited to a specified value or less. By each adhesive surface of the double-sided adhesive sheet having high surface smoothness, satisfactory adhesion with excellent optical homogeneity can be achieved.

[0209] In some embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably about 70 nm or less, more preferably about 65 nm or less, further preferably about 55 nm or less, can be less than 50 nm, can be less than 45 nm, can be less than 40 nm. From the viewpoint of production efficiency and the like, in some embodiments, the arithmetic mean roughness Ra of the adhesive surface can be, for example, about 10 nm or more, can be about 20 nm or more, and can also be about 30 nm or more (for example, about 40 nm or more). In a form in which the adhesive sheet has a first adhesive surface and a second adhesive surface, the arithmetic mean roughness Ra of the first adhesive surface and the arithmetic mean roughness Ra of the second adhesive surface can be of the same degree or different degrees.

[0210] In addition, for example, it is preferable that the maximum height Rz of the adhesive surface is limited to a value below a specified value. A configuration having an adhesive surface with a low maximum height Rz is preferable from the viewpoint of optical homogeneity. By limiting the maximum height Rz, for example, in the usage mode of extracting light through the adhesive surface as described above, an effect of suppressing the occurrence of brightness unevenness caused by the surface state of the adhesive layer can be exerted. A low maximum height Rz of the adhesive surface is also beneficial for suppressing optical distortion. In the case where the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferable that at least the maximum height Rz of the first adhesive surface is limited to a value below a specified value, and more preferably, the maximum height Rz of both adhesive surfaces is limited to a value below a specified value. By each adhesive surface of the double-sided adhesive sheet having high surface smoothness, satisfactory adhesion with excellent optical homogeneity can be achieved.

[0211] In some embodiments, the maximum height Rz of the adhesive surface is preferably about 600 nm or less, more preferably about 500 nm or less, further preferably about 450 nm or less, particularly preferably about 400 nm or less, may be less than 350 nm, may be less than 300 nm, or may be less than 250 nm. From the viewpoints of production efficiency and the like, in some embodiments, the maximum height Rz of the adhesive surface can be, for example, about 10 nm or more, can be about 50 nm or more, can be about 100 nm or more, or can be about 200 nm or more. In the form having a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface can be of the same degree or of different degrees.

[0212] The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. As the non-contact surface roughness measuring device, a surface roughness measuring device using an optical interference method can be used. For example, a three-dimensional optical profiler (trade name “NewView7300”, manufactured by ZYGO Corporation) or an equivalent product thereof can be used. Specifically, for example, the arithmetic mean roughness Ra and the maximum height Rz can be measured by the following measurement method or by setting the measurement operation and measurement conditions in such a way as to obtain results equivalent to or corresponding to those of this measurement method.

[0213] That is, in an environment of 23°C and 50% RH, using a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation), the surface shape of the measurement sample was measured under the following conditions. From the measured data, the arithmetic surface roughness Ra was calculated according to JIS B0601-2001. Regarding the data (roughness curve) obtained through the above measurement, the maximum height Rz was obtained as the sum of the height Rp of the highest peak above the average line of the roughness curve and the depth Rv of the deepest valley below the above average line. The measurement was carried out 5 times (i.e., N = 5), and their average value was used.

[0214] The above measurement sample can be prepared, for example, by cutting the adhesive layer to be measured or the adhesive sheet containing the adhesive layer into a size of about 150 mm in length and about 50 mm in width. When the adhesive surface is protected by a release liner, the release liner is gently peeled off (for example, under the conditions of a pulling speed of 300 mm / minute and a peeling angle of 180°) to expose the adhesive surface. It is preferable to perform the measurement after leaving it to stand for about 30 minutes after exposing the adhesive surface.

[0215] [Measurement Conditions]

[0216] Measurement area: 5.62 mm × 4.22 mm

[0217] (Objective lens: 2.5 times, internal lens: 0.5 times)

[0218] Analysis mode:

[0219] Removal: Cylinder

[0220] Data Fill: ON (Max: 25)

[0221] Remove Spikes: ON (xRMS: 1)

[0222] Filter: OFF

[0223] The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface can be adjusted by the composition, properties (viscosity, leveling property, etc.) of the adhesive composition used in the formation of the adhesive layer, the method of forming the adhesive layer, and the properties of the surface (peeling surface) of the release liner protecting the adhesive surface.

[0224] <Support Substrate>

[0225] The adhesive sheet in some embodiments may be in the form of an adhesive sheet with a carrier substrate having an adhesive layer on one or both sides of the support substrate. The material of the support substrate is not particularly limited and can be appropriately selected according to the purpose of use, usage mode, etc. of the adhesive sheet. Non-limiting examples of the substrates that can be used include: polyolefin films mainly composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymers; polyester films mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); plastic films such as polyvinyl chloride films mainly composed of polyvinyl chloride; foamed sheets formed from foams such as polyurethane foams, polyethylene (PE) foams, and polychloroprene foams; woven fabrics and non-woven fabrics obtained by using various fibrous materials (which can be natural fibers such as hemp and cotton; synthetic fibers such as polyester and vinylon; semi-synthetic fibers such as acetate, etc.) alone or in blend; papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; etc. It can be a substrate formed by laminating them. As an example of such a composite substrate, for example, a substrate having a structure obtained by laminating a metal foil and the above-mentioned plastic film, a plastic substrate reinforced with inorganic fibers such as glass cloth, etc. can be cited.

[0226] In some embodiments, various film substrates can be preferably used. The above-mentioned film substrates can be porous substrates such as foamed films and non-woven fabric sheets, non-porous substrates, or substrates having a structure obtained by laminating a porous layer and a non-porous layer. In some embodiments, as the above-mentioned film substrate, a film substrate including a resin film capable of independently maintaining its shape (self-supporting or non-dependent) as the base film can be preferably used. Here, the "resin film" refers to a non-porous structure, typically a resin film substantially free of air bubbles (void-free). Therefore, the above-mentioned resin film is a concept different from foamed films and non-woven fabrics. As the above-mentioned resin film, a film capable of independently maintaining its shape (self-supporting or non-dependent) can be preferably used. The above-mentioned resin film can be a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0227] As the resin material constituting the resin film, for example, the following can be used: polyesters; polyolefins; polycycloolefins derived from monomers having an alicyclic structure such as a norbornene structure; polyamides (PA) such as nylon 6, nylon 66, and partially aromatic polyamides; polyimides (PI) such as clear polyimide (CPI); polyamide-imide (PAI); polyetheretherketone (PEEK); polyethersulfone (PES); polyphenylene sulfide (PPS); polycarbonate (PC); polyurethane (PU); fluorine-containing resins such as ethylene-vinyl acetate copolymer (EVA) and polytetrafluoroethylene (PTFE); acrylic resins; cellulose polymers such as triacetyl cellulose (TAC); polyarylate; polystyrene; polyvinyl chloride; polyvinylidene chloride; etc. resins.

[0228] The above resin film can be a film formed from a resin material containing only one such resin, or can be a film formed from a resin material obtained by blending two or more resins. The above resin film can be unstretched or can be stretched (e.g., uniaxially stretched or biaxially stretched). For example, it is preferable to use a PET film, a PBT film, a PEN film, an unstretched polypropylene (CPP) film, a biaxially stretched polypropylene (OPP) film, a low-density polyethylene (LDPE) film, a linear low-density polyethylene (LLDPE) film, a PP / PE blend film, a cyclic olefin polymer (COP) film, a CPI film, a TAC film, etc. As examples of resin films preferably used from the viewpoints of strength and dimensional stability, PET films, PEN films, PPS films, and PEEK films can be cited. From the viewpoints of ease of acquisition, etc., PET films and PPS films are particularly preferred, and among them, PET films are preferred.

[0229] In the resin film, within a range that does not significantly impede the effects of the present invention, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), filler materials, slip agents, antiblocking agents, etc. can be blended as needed. The blending amount of the additives is not particularly limited and can be appropriately set according to the use of the adhesive sheet, etc.

[0230] The manufacturing method of the resin film is not particularly limited. For example, conventionally known general resin film forming methods such as extrusion molding, blow molding, T-die casting molding, calender roll molding, etc. can be appropriately adopted.

[0231] The above substrate can be substantially composed of such a base film. Alternatively, in addition to including the above base film, the above substrate can also include an auxiliary layer. As examples of the above auxiliary layer, surface treatment layers such as an optical property adjusting layer (e.g., a coloring layer, an antireflection layer), a printing layer for imparting a desired appearance to the substrate, a laminated layer, an antistatic layer, a primer layer, a release layer, etc. can be cited.

[0232] In some embodiments, as the support substrate, it is preferable to use a substrate having light transmittance (hereinafter, also referred to as a light-transmissive substrate). Thereby, an adhesive sheet with a light-transmissive substrate can be formed. The total light transmittance of the light-transmissive substrate can be, for example, greater than 50%, or can be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and can also be 95% or more (e.g., 95% - 100%). The above total light transmittance is measured according to JIS K7136:2000 using a commercially available transmittance meter. As the transmittance meter, a product named "HAZEMETERH M-150" manufactured by Murakami Color Research Institute or its equivalent product is used. As a preferred example of the above light-transmissive substrate, a resin film having light transmittance can be cited. The above light-transmissive substrate can be an optical film.

[0233] The thickness of the base material is not particularly limited and can be selected according to the purpose of use, usage mode, etc. of the adhesive sheet. The thickness of the base material can be, for example, 500 μm or less, and from the viewpoints of the processability and workability of the adhesive sheet, it is preferably 300 μm or less, can be 150 μm or less, can be 100 μm or less, can be 50 μm or less, can be 25 μm or less, and can also be 10 μm or less. When the thickness of the base material becomes smaller, there is a tendency for the followability to the surface shape of the adherend to improve. In addition, from the viewpoints of processability, workability, etc., the thickness of the base material can be, for example, 2 μm or more, can be 10 μm or more, and can also be 25 μm or more.

[0234] For the surface of the base material on the side where the adhesive layer is to be laminated, surface treatments known in the art such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and formation of a primer layer by coating with a primer can be performed as needed. Such surface treatment can be a treatment for improving the anchoring property of the adhesive layer to the base material. The composition of the primer used for the formation of the primer layer is not particularly limited and can be appropriately selected from known compositions. The thickness of the primer layer is not particularly limited and is usually appropriately about 0.01 μm to about 1 μm, and preferably about 0.1 μm to about 1 μm. As other treatments that can be performed on the base material as needed, antistatic layer formation treatment, coloring layer formation treatment, printing treatment, etc. can be cited. These treatments can be used alone or in combination.

[0235] <Adhesive sheet with release liner>

[0236] The adhesive sheet disclosed herein can be in the form of an adhesive article in which the surface (adhesive surface) of the adhesive layer is in contact with the release surface of the release liner. Therefore, according to this specification, there is provided an adhesive sheet (adhesive article) with a release liner, which includes any of the adhesive sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the adhesive sheet.

[0237] As the release liner, there is no particular limitation. For example, the following can be used: a release liner having a release layer on the surface of a liner substrate such as a resin film, paper (which may be paper laminated with a resin such as polyethylene), etc.; a release liner including a resin film formed of a low tack material such as a fluorine-containing polymer (polytetrafluoroethylene, etc.), a polyolefin resin (polyethylene, polypropylene, etc.). From the viewpoint of excellent surface smoothness, a release liner having a release layer on the surface of a resin film as the liner substrate or a release liner including a resin film formed of a low tack material is preferably used. As the resin film, as long as it is a film capable of protecting the adhesive layer, there is no particular limitation. For example, polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, etc. can be cited. In the formation of the above release layer, for example, known release treating agents such as polysiloxane-based release treating agents, long-chain alkyl-based release treating agents, olefin-based release treating agents, fluorine-containing release treating agents, fatty acid amide-based release treating agents, molybdenum disulfide, silica powder, etc. can be used.

[0238] <Usage>

[0239] The adhesives disclosed herein can be used by adhering to various adherends. As the constituent materials (adherend materials) of the above adherends, there is no particular limitation. For example, the following can be cited: metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, etc., or alloys containing two or more of them; various resin materials (typically plastic materials) such as polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called aromatic polyamide resins, etc.), polyarylate resins, fluorine-containing resins, polycarbonate resins, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polyvinyl butyral polymers, liquid crystal polymers, carbon materials such as graphene; inorganic materials such as alumina, zirconia, titanium dioxide, SiO 2 , metal oxides and their mixtures such as ITO (indium tin oxide) and ATO (antimony-doped tin oxide), nitrides and their composites such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, indium nitride, and inorganic materials such as soda glass, alkali-free glass, quartz glass, borosilicate glass, sapphire glass carbon. The adhesives disclosed herein can be used by adhering to a member (such as an optical member) at least the surface of which is made of the above materials.

[0240] The adhesives disclosed herein can be used in a pasting manner that does not require heating to a temperature higher than the temperature range around room temperature (e.g., 20°C to 35°C) after being applied to the adherend. Additionally, when permitted according to the type of the adherend, etc., heat treatment can be performed at least at any one of the moments after, during, and before applying to the adherend. The heat treatment can be carried out to improve the adhesion of the adhesive to the adherend, promote adhesion, etc. The heat treatment temperature can be appropriately set within the range permitted according to the constituent materials of the adhesive sheet and the type of the adherend, in a manner that takes into account the surface state of the adherend, etc., to obtain the desired effect. For example, it can be about 100°C or below 100°C, can be below 80°C, can be below 60°C, can be below 50°C.

[0241] The members and materials to which the adhesive is applied can have light transmissivity. In such adherends, it is easy to obtain the advantage that the adhesives disclosed herein can be highly transparent. The total light transmissivity of the above-mentioned adherend can be, for example, greater than 50%, or can be 70% or more. In some preferred embodiments, the total light transmissivity of the above-mentioned adherend is 80% or more, more preferably 90% or more, and further preferably 95% or more (e.g., 95% to 100%). The adhesives disclosed herein can preferably be used in a manner of being applied to an adherend (e.g., an optical member) with a total light transmissivity of a specified value or more. The above-mentioned total light transmissivity is measured according to JIS K7136:2000 using a commercially available transmittance meter. As the transmittance meter, a product named "HAZEMETERH M-150" manufactured by Murakami Color Technology Research Institute or its equivalent product is used.

[0242] The refractive index of the adherend and the refractive index of the adhesive layer disposed in contact with the adherend can be of the same degree or can be different. For example, by relatively reducing the refractive index of the adhesive layer with respect to the refractive index of the adherend, the light incident on the adherend from the adhesive layer side can be refracted toward the front side, thereby improving the front brightness. On the other hand, by reducing the refractive index difference between the adhesive layer and the adherend, light reflection at the interface can be suppressed. The refractive index of the adherend can be measured by the same method as the refractive index of the adhesive.

[0243] In some preferred embodiments, the above-mentioned adherend can have any of the above total light transmissivities. In an optical article (e.g., a light-emitting device) in the form of an adhesive being pasted or laminated on such an adherend, it is particularly preferable to exhibit the effects brought by the technology disclosed herein.

[0244] As an example of a preferred use, an optical use can be cited. More specifically, for example, as a use for bonding optical members (for bonding optical members), an optical adhesive sheet can be preferably used in the manufacture of articles (optical articles) using the above optical members. The above optical article can also be a so-called configuration without a polarizing plate. For example, it can be an optical article in which only the visually recognizable side of a light source (such as an organic EL panel) in an optical article having a light source is composed of a layer with a polarization degree of 80% or less.

[0245] The above optical member refers to a member having optical properties (for example, polarization property, light refraction property, light scattering property, light reflection property, light transmittance, light absorption property, light diffraction property, optical rotation property, visual recognition property, etc.). As the above optical member, there is no particular limitation as long as it is a member having optical properties. For example, members constituting devices (optical devices) such as display devices (image display devices) and input devices or members used in these devices can be cited. For example, it can be cited: polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflection films, antireflection films, hard coat (HC) films, impact absorption films, antifouling films, photochromic films, dimming films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates; members further laminated with these films (sometimes collectively referred to as "functional films"), etc. It should be noted that the above "plates" and "films" each include plate-like, film-like, sheet-like and other forms. For example, "polarization films" include "polarizing plates", "polarization sheets", etc., and "light guide plates" include "light guide films", "light guide sheets", etc. In addition, the above "polarizing plate" includes a circular polarizing plate.

[0246] As the above display device, for example, it can be cited: liquid crystal display devices, organic EL (electroluminescence) display devices, micro LEDs (μLEDs), mini LEDs (miniLEDs), PDPs (plasma display panels), electronic papers, etc. In addition, as the above input device, a touch panel, etc. can be cited.

[0247] As the above optical member, there is no particular limitation. For example, it can be cited: members containing glass, acrylic resins, polycarbonate, polyethylene terephthalate, metal thin films, etc. (for example, sheet-like, film-like, plate-like members), etc. It should be noted that the "optical member" in this specification includes members (design films, decorative films, surface protection films, etc.) that play a role in decoration and protection while maintaining the visual recognition of display devices and input devices.

[0248] The adhesives disclosed herein (which may be in the form of adhesive sheets containing the adhesives) can be used, for example, in a manner disposed between an optical film such as a film having one or more functions of light transmission, reflection, diffusion, waveguide, light collection, diffraction, etc., or a fluorescent film and other optical members (which may be other optical films), and are preferably used for joining the above optical film and the above other optical members. Among them, in the joining of an optical film having at least one function of light waveguide, light collection, or diffraction, it is desired that the entire joining layer has a low refractive index.

[0249] The adhesive layers disclosed herein can be preferably used, for example, for joining optical films such as light guide films, diffusion films, fluorescent films, color adjustment films, prism sheets, lenticular films, and microlens array films. In these applications, from the perspectives of the trend towards miniaturization and high performance of optical members, improvement in thinning and light extraction efficiency is required. As an adhesive layer that can meet this demand, the adhesive layer disclosed herein can be preferably utilized. More specifically, for example, in the joining of a light guide film and a diffusion film, by adjusting the refractive index (for example, reducing the refractive index) of the adhesive layer as the joining layer, it is possible to contribute to thinning. In the joining of a fluorescent film, by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive, the light extraction efficiency (which can also be understood as the luminescence efficiency) can be improved. In the joining of a color adjustment film, by appropriately adjusting the refractive index of the adhesive in a manner that reduces the refractive index difference from the color adjustment pigment, it is possible to contribute to reducing the scattering component and improving the light transmittance. In the joining of prism sheets, lenticular films, microlens array films, etc., by appropriately adjusting the refractive index of the adhesive, it is possible to contribute to controlling the diffraction of light and improving the brightness and / or viewing angle.

[0250] The method of laminating optical members using the adhesive layers disclosed herein is not particularly limited. For example, it can be (1) a method of laminating optical members to each other through the adhesive layers disclosed herein, (2) a method of laminating an optical member to a member other than an optical member through the adhesive layers disclosed herein, or (3) a method in which the adhesive layers disclosed herein are in the form of an adhesive sheet containing an optical member and laminating the adhesive sheet to an optical member or a member other than an optical member. It should be noted that in the method (3) above, the adhesive sheet in the form containing an optical member can be, for example, an adhesive sheet whose support is an optical member (such as an optical film). An adhesive sheet in a form containing an optical member as a support can be understood as an adhesive type optical member (such as an adhesive type optical film). In addition, when the adhesive layers disclosed herein constitute an adhesive sheet of a type having a support and the above functional film is used as the support, the adhesive sheet can be understood as an "adhesive type functional film" having the adhesive layers disclosed herein on at least one side of the functional film.

[0251] As described above, according to the technology disclosed herein, an optical laminate having the adhesive layer disclosed herein and a member (such as a resin film like an optical film) to which the adhesive sheet is adhered is provided. The member to which the adhesive layer is adhered may have the refractive index of the adherend material described above. In addition, the difference in refractive index (refractive index difference) between the adhesive layer and the member may be the refractive index difference between the adherend and the adhesive layer. For the members constituting the laminate, as described for the above members, materials, and adherends, no repeated description will be made.

[0252] As understood from the above description and the following examples, the matters disclosed in this specification include the following.

[0253] [1] An adhesive, wherein the refractive index of the adhesive is 1.450 or less, and the storage modulus (G’(-20°C)) at -20°C is 2.0×10 6 Pa or less.

[0254] [2] The adhesive according to the above [1], wherein the ratio of the storage modulus (G’(-20°C)) [Pa] to the elongation at break (E B ) [%] (G’(-20°C) / E B ) is 20 or more and 2000 or less.

[0255] [3] The adhesive according to the above [1] or [2], wherein the adhesive is an adhesive formed from a radiation-curable adhesive composition.

[0256] [4] The adhesive according to any one of the above [1] to [3], wherein the adhesive contains an acrylic polymer (F), and the monomer components constituting the acrylic polymer (F) include: a fluorine-containing acrylic monomer (Mf) and a non-acidic hydrophilic monomer (Mh), and the hydrophilic monomer (Mh) includes a low-Tg hydrophilic monomer (Mh L ) having a glass transition temperature of 40°C or less for the homopolymer, and the content of the low-Tg hydrophilic monomer (Mh L ) in the monomer components constituting the acrylic polymer (F) is greater than 2.0% by weight.

[0257] [5] The adhesive according to the above [4], wherein the content of the hydrophilic monomer (Mh) in the monomer components constituting the acrylic polymer (F) is greater than 5.0% by weight.

[0258] [6] The adhesive according to the above [4] or [5], wherein the monomer components constituting the acrylic polymer (F) further include a monomer (M1), and the monomer (M1) is represented by the following formula (1):

[0259] CH2 =CR 1 COOR 2 (1),

[0260] (wherein, R 1 is a hydrogen atom or a methyl group, and R 2 is a linear alkyl group having 4 to 18 carbon atoms).

[0261] [7] The adhesive according to any one of claims [4] to [6] above, wherein the content of the acidic functional group-containing monomer in the monomer components of the acrylic polymer (F) constituting the adhesive is less than 2.0% by weight.

[0262] [8] An adhesive sheet, wherein the adhesive sheet includes an adhesive layer, and the adhesive layer includes the adhesive according to any one of [1] to [7] above.

[0263] [9] The adhesive sheet according to [8] above, wherein after a damp heat test of maintaining for 240 hours in a damp heat environment of 85°C and 85% RH, the haze of the adhesive layer is less than 3.0%.

[0264]

[10] The adhesive sheet according to [8] or [9] above, wherein the peel strength of the adhesive sheet from a glass plate (pulling speed 300 mm / minute, peeling angle 180 degrees) is 1.0 N / 25 mm or more.

[0265] Examples

[0266] Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to the content shown in these specific examples. It should be noted that in the following description, unless otherwise specified, "parts" and "%" indicating amounts used and contents are based on weight.

[0267] <Example 1>

[0268] (Preparation of Adhesive Composition)

[0269] 100 parts of a fluorine-containing acrylic monomer and 0.1 part of a photoinitiator were put into a four-necked flask, and ultraviolet rays were irradiated under a nitrogen atmosphere for photopolymerization until the viscosity (BH viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) reached about 15 Pa·s, thereby preparing a monomer slurry containing a partial polymer of the above-mentioned fluorine-containing acrylic monomer. 0.10 part of 1,9-nonanediol diacrylate (NDDA) as a crosslinking agent and 0.3 part of a silane coupling agent were added to 100 parts of the above monomer slurry and uniformly mixed, thereby preparing an ultraviolet curable adhesive composition U1.

[0270] Here, as the above-mentioned fluorinated acrylic monomer, 2-(perfluorohexyl)ethyl acrylate was used (the same applies to the following examples unless otherwise specified). As the above-mentioned photoinitiator, the product names "Omnirad651" and "Omnirad184" manufactured by IGM Resins were used at a weight ratio of 1:1 (the same applies to the following examples unless otherwise specified). As the above-mentioned silane coupling agent, 3-glycidoxypropyltrimethoxysilane was used (the same applies to the following examples unless otherwise specified).

[0271] (Fabrication of Adhesive Sheet)

[0272] The above-obtained adhesive composition U1 was coated on a release liner R1 with a thickness of 38 μm whose one side on the polyester film was the release surface (manufactured by Mitsubishi Materials Corporation, MRF#38), covered with a release liner R2 with a thickness of 38 μm whose one side on the polyester film was the release surface (manufactured by Mitsubishi Materials Corporation, MRE#38) to block air, and irradiated with ultraviolet rays to cure it, thereby fabricating an adhesive layer (substrate-free double-sided adhesive sheet) with a thickness of 50 μm. The above ultraviolet irradiation was carried out using a black light under the conditions of an illuminance of 2.5 mW / cm 2 and an accumulated light quantity of 2400 mJ / cm 2 .

[0273] <Examples 2 to 4>

[0274] 100 parts of a monomer mixture containing a fluorinated acrylic monomer and 2-ethylhexyl acrylate (2EHA) in the weight ratio shown in Table 1 and 0.1 part of a photoinitiator were put into a four-necked flask, and photopolymerization was carried out in the same manner as in Example 1 to prepare a monomer slurry containing a partial polymer of the above monomer mixture. 0.10 part of 1,9-nonanediol diacrylate (NDDA) as a crosslinking agent and 0.3 part of a silane coupling agent were added to 100 parts of the above monomer slurry and mixed uniformly, thereby preparing ultraviolet-curable adhesive compositions U2 to U4 for each example. Except for using the above adhesive compositions U2 to U4 instead of the adhesive composition U1, the same operations as in Example 1 were carried out to fabricate an adhesive layer (substrate-free double-sided adhesive sheet) with a thickness of 50 μm.

[0275] <Examples 5 to 13>

[0276] 100 parts of a monomer mixture containing a fluorinated acrylic monomer, 2-ethylhexyl acrylate (2EHA), and 4-hydroxybutyl acrylate (4HBA) in the weight ratios shown in Tables 1 and 2 and 0.1 part of a photopolymerization initiator were put into a four-necked flask, and photopolymerization was carried out in the same manner as in Example 1 to prepare a monomer slurry containing a partial polymer of the above monomer mixture. 0.3 part of NDDA and a silane coupling agent in the amounts shown in Tables 1 and 2 were added to 100 parts of the above monomer slurry and mixed uniformly to prepare the ultraviolet curable adhesive compositions U5 to U13 of each example. Except for using the above adhesive compositions U5 to U13 instead of the adhesive composition U1, the operation was carried out in the same manner as in Example 1 to produce an adhesive layer (substrate-free double-sided adhesive sheet) with a thickness of 50 μm.

[0277] <Examples 14 to 17>

[0278] In Example 14, n-hexyl acrylate (HxA) was used instead of 2EHA in Example 8, in Example 15, n-octyl acrylate (NOAA) was used instead of 2EHA in Example 8, in Example 16, n-butyl acrylate (BA) was used instead of 2EHA in Example 8, and in Example 17, lauryl acrylate (LA) was used instead of 2EHA in Example 8. Regarding other aspects, the operation was carried out in the same manner as in Example 8 to prepare the ultraviolet curable adhesive compositions U14 to U17 of each example. Except for using the above adhesive compositions U14 to U17 instead of the adhesive composition U1, the operation was carried out in the same manner as in Example 1 to produce an adhesive layer (substrate-free double-sided adhesive sheet) with a thickness of 50 μm.

[0279] <Evaluation method>

[0280] (Gel fraction)

[0281] Approximately 0.1 g of an adhesive sample (weight Wg 1 ) was collected from the adhesive layer (substrate-free adhesive sheet) of each example and wrapped into a purse shape with a porous polytetrafluoroethylene membrane having an average pore size of 0.2 μm (weight Wg 2 ), and the mouth of the bag was tied with a kite string (weight Wg 3 ). As the above porous polytetrafluoroethylene (PTFE) membrane, the product named "NITOFLON (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 78%, thickness 85 μm) manufactured by Nitto Denko Corporation was used.

[0282] The wrapped object was immersed in a sufficient amount of ethyl acetate and kept at 23 °C for 7 days to dissolve only the sol part in the adhesive out of the above membrane, and then the wrapped object was taken out, the ethyl acetate attached to the outer surface was wiped off, and the wrapped object was dried at 130 °C for 2 hours, and the weight (Wg 4 ) of the wrapped object was measured. The gel fraction of the adhesive layer was calculated from the obtained results by the following formula.

[0283] Gel fraction (%) = [(Wg 4 - Wg 2 - Wg 3 ) / Wg 1 × 100

[0284] (Polymerization rate)

[0285] Collect about 0.3 g of the adhesive sample from the adhesive layer (substrate-free double-sided adhesive sheet) of each example and heat it at 130 °C for 2 hours. Based on the weights of the samples before and after heating, the polymerization rate is calculated by the following formula.

[0286] Polymerization rate [%] = (Weight of the sample after heating / Weight of the sample before heating) × 100

[0287] (Refractive index)

[0288] For the adhesive layer (substrate-free double-sided adhesive sheet) of each example, measure the refractive index using a prism coupler (manufactured by Metricon, model "2010M") under the conditions of a measurement temperature of 25 °C and a measurement wavelength of 594 nm.

[0289] (Total light transmittance and haze)

[0290] A laminate having a structure in which the adhesive layer (substrate-free adhesive sheet) of each example is sandwiched between two alkali-free glass plates (thickness 0.8 mm to 1.0 mm, total light transmittance 92%, haze 0.4%) (i.e., a three-layer structure of glass plate / adhesive layer / glass plate), and having a rectangular shape with a size of 4.5 cm × 5 cm when viewed from above was fabricated. Under a measurement environment of 23 °C and 50% RH, measure the total light transmittance and haze of the above laminate using a haze meter ("HM-150" manufactured by Murakami Color Technology Research Institute). The measurement position is near the intersection of the diagonals in the above rectangular laminate. The value obtained by subtracting the total light transmittance and haze of the above two alkali-free glass plates from the measured value is taken as the total light transmittance (initial transmittance) [%] and haze (initial haze) [%] of the initial adhesive layer. For the substrate-free adhesive sheet formed from the above adhesive layer, the total light transmittance [%] and haze [%] of the adhesive layer are the total light transmittance [%] and haze [%] of the adhesive sheet.

[0291] Keep the above laminate in a damp heat environment of 85 °C and 85% RH for 240 hours, then leave it to stand in an environment of 23 °C and 50% RH for 30 minutes, and then measure the haze of the above laminate in the same manner as above. The value obtained by subtracting the total light transmittance of the above two alkali-free glass plates from the measured value is taken as the haze (haze after damp heat) [%] of the adhesive layer after damp heat.

[0292] (Storage modulus G' and glass transition temperature Tg)

[0293] The adhesives of each example were laminated layer by layer to form a disk with a thickness of about 1.5 mm and a diameter of 7.9 mm, which was used as a sample for measurement. Using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, dynamic viscoelasticity measurement was carried out under the following conditions. The storage modulus G' [Pa] of the adhesive at each temperature (-20 °C, 25 °C, and 60 °C) was obtained from the measurement results. In addition, the temperature corresponding to the peak temperature of the loss tangent tanδ (loss elastic modulus G'' / storage modulus G') in the above dynamic viscoelasticity measurement was obtained as the glass transition temperature (Tg) [°C] of the adhesive.

[0294] [Measurement conditions]

[0295] Deformation mode: Torsion

[0296] Measurement frequency: 1 Hz

[0297] Temperature range: -50 °C to 150 °C

[0298] Heating rate: 5 °C / min

[0299] Shape: Parallel plates, 7.9 mm φ

[0300] (Young's modulus, fracture stress, and fracture elongation E B )

[0301] The adhesive layer (double-sided adhesive tape without substrate) of each example was cut into a size of 30 mm in length and 40 mm in width with a form sandwiched between two release liners. The above width of 40 mm was set according to the thickness of the adhesive layer so that the cross-sectional area of the adhesive layer in the cross-section along this width direction was about 2 mm 2 . Then, one release liner was removed to expose one surface of the adhesive layer, and the adhesive layer was wound around the other release liner with its length direction as the axis, thereby making a cylindrical sample with a length of 30 mm.

[0302] In a measurement environment of 23 °C and 50% RH, the above cylindrical sample was set on a tensile-compression testing machine (device name "AGS-50NX", manufactured by Shimadzu Corporation), and was stretched axially along the cylinder until the sample broke under the conditions of a distance between chucks of 10 mm and a pulling speed of 300 mm / min. In the obtained S-S (strain-strength) curve, the tensile stresses corresponding to the two tensile strains (ε 1 = 5% and ε 2 = 10%) were respectively set as σ 1 and σ2 , the tensile modulus (Young's modulus) of the adhesive layer is calculated by the tensile modulus E 0 = (σ 2 - σ 1 ) / (ε 2 - ε 1 ).

[0303] Here, the tensile strain ε is calculated based on the distance between the chucks.

[0304] ε = (L 1 - L 0 ) / L 0 or

[0305] ε(%) = 100×(L 1 - L 0 ) / L 0

[0306] ε: tensile strain (dimensionless ratio or %)

[0307] L 0 : initial distance between the chucks (mm)

[0308] L 1 : distance between the chucks after stretching (mm)

[0309] The tensile stress σ is calculated based on the cross-sectional area of the measurement sample before stretching.

[0310] σ = F / A

[0311] σ: tensile stress (MPa)

[0312] F: measurement load (N)

[0313] A: cross-sectional area of the measurement sample before stretching (mm 2 )

[0314] In addition, by the above stretching, the fracture stress [MPa] and fracture elongation E B [%] of the above sample are measured. From the obtained value of the fracture elongation E B [%] and the value of the storage modulus G’ [Pa] at each of the above temperatures, the ratios (G’(-20°C) / E B ) and (G’(25°C) / E B ) are calculated.

[0315] (Peel strength)

[0316] Under the measurement environment of 23°C and 50% RH, the release liner was peeled off from one side of the adhesive layer (substrate-free double-sided adhesive sheet) of each example, a PET film with a thickness of 50 μm was pasted for backing, and then it was cut into a size of 25 mm in width and 100 mm in length, which was used as a test piece. The release liner on the other side was peeled off from the test piece, and a 2 kg roller was reciprocated once and pressed against the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35 mm, green plate with ground edges) as the adherend. After leaving it in the same environment for 30 minutes, a tensile-compression testing machine (device name "AGS-50NX", manufactured by Shimadzu Corporation) was used to measure the peel strength (adhesive force) [N / 25 mm] under the conditions of a pulling speed of 300 mm / minute and a peel angle of 180 degrees according to JIS Z0237:2000. It should be noted that in the case of a single-sided adhesive sheet with a substrate, backing with a PET film is not necessary.

[0317] The results obtained were shown together with the approximate composition of the adhesives of each example in Tables 1 and 2. In the table, "~" in the monomer component column indicates that the monomer is not used. In addition, "n.e." in Table 1 indicates that the item was not evaluated.

[0318]

[0319]

[0320] As shown in the above table, the refractive indices of the adhesives of Examples 3 to 15 were all 1.450 or less, and the storage moduli (G'(-20°C)) were all 2.0×10 6 Pa or less, and good flexibility was exhibited in the low refractive index at low temperature regions. In Examples 3 to 6 and Examples 8 to 15, better low-temperature flexibility was obtained. In contrast, the refractive indices of the adhesives of Examples 1, 2, 16, and 17 were 1.450 or less, but the storage moduli (G'(-20°C)) were high and the flexibility at low temperature was low. It should be noted that except for using 2EHA alone as the monomer component, a UV-curable adhesive composition was prepared in the same manner as in Example 1. Except for using this adhesive composition, the refractive index of the adhesive prepared in the same manner as in Example 1 measured by the above method was 1.464, which did not meet the condition of a refractive index of 1.450 or less.

[0321] The specific examples of the present invention have been described in detail above, but they are merely illustrative and do not limit the claims. The technology described in the claims includes the content obtained by various deformations and changes of the above-described specific examples.

[0322] Reference Signs Explanation

[0323] 1, 2, 3 Adhesive Sheets

[0324] 10 Support Substrate

[0325] 10A First Side

[0326] 10B Second Side

[0327] 21 Adhesive Layer, First Adhesive Layer

[0328] 21A Adhesive Surface, First Adhesive Surface

[0329] 21B Adhesive Surface

[0330] 22 Second Adhesive Layer

[0331] 22A Second Adhesive Surface

[0332] 31, 32 Release Liners

Claims

1. An adhesive, wherein, The refractive index of the adhesive is 1.450 or less, and the storage modulus (G'(-20°C)) at -20°C is 2.0×10 6 Pa or less.

2. The adhesive according to claim 1, wherein, The ratio of the storage modulus (G’(-20°C)) [Pa] to the elongation at break (E B ) [%] (G’(-20°C) / E B ) is 20 or more and 2000 or less.

3. The adhesive according to claim 1, wherein, the adhesive is an adhesive formed from an active energy ray-curable adhesive composition.

4. The adhesive according to claim 1, wherein, the adhesive contains an acrylic polymer (F), the monomer components constituting the acrylic polymer (F) include: a fluorine-containing acrylic monomer (Mf) and a non-acidic hydrophilic monomer (Mh), The hydrophilic monomer (Mh) includes a low-Tg hydrophilic monomer (Mh L ) having a glass transition temperature of the homopolymer of 40 °C or lower. The content of the low-Tg hydrophilic monomer (Mh L ) in the monomer components constituting the acrylic polymer (F) is greater than 2.0% by weight.

5. The adhesive according to claim 4, wherein, the content of the hydrophilic monomer (Mh) in the monomer components constituting the acrylic polymer (F) is greater than 5.0% by weight.

6. The adhesive according to claim 4, wherein, the monomer components constituting the acrylic polymer (F) further include a monomer (M1), and the monomer (M1) is represented by the following formula (1): CH 2 =CR 1 COOR 2 (1) (In the formula, R 1 is a hydrogen atom or a methyl group, and R 2 is a linear alkyl group having 4 to 18 carbon atoms).

7. The adhesive according to claim 4, wherein, the content of the acidic functional group-containing monomer in the monomer components constituting the acrylic polymer (F) is less than 2.0% by weight.

8. An adhesive sheet, wherein, the adhesive sheet includes an adhesive layer, and the adhesive layer includes the adhesive according to any one of claims 1 to 7.

9. The adhesive sheet according to claim 8, wherein, after a damp heat test of maintaining for 240 hours in a damp heat environment of 85°C and 85% RH, the haze of the adhesive layer is less than 3.0%.

10. The adhesive sheet according to claim 8, wherein, the peel strength of the adhesive sheet from a glass plate (pulling speed 300 mm / minute, peeling angle 180 degrees) is 1.0 N / 25 mm or more.

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