JP2023151518A - adhesive - Google Patents

Abstract

To provide an adhesive capable of enduring large deformation while maintaining a high refractive index.SOLUTION: An adhesive has a refractive index of 1.55 or more, and produces deformation of 350% or more in a deformation test conducted under conditions that a temperature is -20°C and a speed is 300 mm/min.SELECTED DRAWING: None

Description

The present invention relates to adhesives.

In general, adhesives (also referred to as pressure-sensitive adhesives, hereinafter the same) exhibit a soft solid state (viscoelastic body) in a temperature range around room temperature, and have the property of easily adhering to an adherend under pressure. Taking advantage of these properties, adhesives are widely used for purposes such as bonding, fixing, and protection in various industrial fields such as home appliances, automobiles, various machines, electrical equipment, and electronic equipment. An example of the use of adhesives is to bond polarizing films, retardation films, cover window members, and various other light-transmissive members with other members in display devices such as liquid crystal displays and organic EL display devices. Examples of uses include: Technical documents regarding adhesives for optical members include Patent Documents 1 and 2.

Japanese Patent Application Publication No. 2014-169382 Japanese Patent Application Publication No. 2017-128732

Patent Documents 1 and 2 disclose a pressure-sensitive adhesive composition whose main component is a (meth)acrylic acid ester polymer containing a monomer having a plurality of aromatic rings as a monomer unit, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition. discloses the use of a monomer having multiple aromatic rings to increase the refractive index of the adhesive to 1.50 or more, particularly preferably 1.51 or more. For example, some materials to which adhesives are attached, such as optical components, have a high refractive index, and if a general acrylic adhesive is used to bond such high refractive index materials, the difference in refractive index between the two will be reduced. It is known that reflection occurs at the interface due to By using an adhesive with a high refractive index as the adhesive used for bonding the high refractive materials, the interface reflection can be prevented or suppressed. Note that the refractive index of the acrylic adhesive is usually about 1.47.

By the way, as an adhesive, one having good flexibility can be preferably used depending on the application site and usage mode. For example, in recent years, foldable displays and rollable displays have been put into practical use as displays such as organic EL display devices used in electronic devices such as smartphones. It is necessary to have the flexibility to follow the An adhesive having excellent flexibility easily follows and adheres to curved surfaces such as three-dimensional shapes, and is suitable for use in electronic devices having curved shapes. If the flexibility of an adhesive with a high refractive index can be increased, it can be expected to be applied to applications that are repeatedly folded, such as the above-mentioned foldable display. However, adhesive polymers with a high refractive index tend to have a high glass transition temperature, such as those having aromatic rings, and adhesives formed using high refractive index materials tend to have reduced flexibility. When designing adhesives, there is a trade-off between high refractive index and flexibility. It would be practically beneficial if an adhesive could be realized that has a high refractive index and is flexible enough to withstand use in applications that involve large deformations, such as the above-mentioned foldable display applications.

The present invention was created in view of the above circumstances, and an object of the present invention is to provide an adhesive that can withstand large deformations while maintaining a high refractive index.

According to this specification, there is provided an adhesive having a refractive index of 1.55 or more and a deformation amount of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm/min. . The above adhesive has a high refractive index and can deform by more than 350% in a low-temperature, high-speed deformation test, so it can deform sufficiently at high speed even in a low-temperature environment and can withstand large deformations. Can be done. A pressure-sensitive adhesive that satisfies the above characteristics preferably has a high refractive index, and can withstand use in applications involving large deformations, such as foldable display applications.

Adhesives according to some embodiments have a stress of 5.0 N/mm ² or less at a deformation amount of 350% in a deformation test conducted at a temperature of -20° C. and a speed of 300 mm/min. An adhesive that satisfies the above characteristics has a high refractive index and can be sufficiently deformed at high speed while maintaining a predetermined level of flexibility even in a low-temperature environment. Therefore, it is suitable for use in applications involving large deformations.

In some embodiments, adhesives with glass transition temperatures (Tg) in the range of -50°C to 0°C are used. Adhesives with Tg in the range of -50 to 0°C tend to have good flexibility. The effects of the technology disclosed herein can be preferably achieved using an adhesive having the above Tg.

The adhesives according to some embodiments have a stress S (-20°C) at a deformation amount of 350% in a deformation test conducted at a temperature of -20°C and a speed of 300mm/min, and a stress S (-20°C) at a temperature of 25°C and a speed of 300mm/min. The ratio (S(-20°C)/S(25°C)) to the stress S(25°C) at a deformation amount of 350% in a deformation test conducted under conditions of 50 or less. An adhesive that satisfies the above characteristics can exhibit stable performance over a wide temperature range including low temperatures.

Adhesives according to some embodiments have a bending portion after repeating a bending test 10 times at 25° C., in which each side of a sheet-like adhesive is bent into a U-shape with a radius of 2 mm. The total light transmittance is maintained at 85% or more of the total light transmittance before the bending test. An adhesive that satisfies the above properties has little change in optical properties (for example, whitening) even after repeated bending, and is therefore suitable for optical applications where bending is expected, such as foldable display applications.

Note that an appropriate combination of each element described in this specification may also be included within the scope of the invention for which protection by patent is sought by the present patent application.

FIG. 1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention are based on the teachings for carrying out the invention described in this specification and the common general knowledge at the time of filing. Can be understood by vendors. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.
In addition, in the following drawings, the same reference numerals may be attached and explained to members and parts that have the same function, and overlapping explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the products actually provided.

In this specification, the "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive. The above-mentioned rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. Furthermore, in this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight, unless otherwise specified.

In this specification, the term "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule, as monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer." Accordingly, an acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. Typical examples of acrylic polymers include acrylic polymers in which more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight) of the monomer components constituting the polymer are acrylic monomers.

Furthermore, in this specification, the term "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, the term "(meth)acryloyl group" is meant to comprehensively refer to acryloyl groups and methacryloyl groups. Therefore, the concept of acrylic monomer here may include both monomers having an acryloyl group (acrylic monomer) and monomers having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" comprehensively refers to acrylic acid and methacrylic acid, and "(meth)acrylate" comprehensively refers to acrylate and methacrylate, respectively. The same applies to other similar terms.

<Characteristics of adhesive>
(Refractive index)
The adhesive disclosed herein has a refractive index of 1.55 or more. The refractive index of the adhesive is suitably 1.560 or more, preferably more than 1.570. In some preferred embodiments, the refractive index of the adhesive may be 1.575 or more, 1.580 or more, 1.585 or more, 1.590 or more, 1.595 or more. But that's fine. According to the pressure-sensitive adhesive having such a refractive index, light reflection at the interface with the adherend can be suitably suppressed in a usage mode in which the pressure-sensitive adhesive is attached to a material having a high refractive index. The preferable upper limit of the refractive index of the adhesive is not limited to a specific range because it may vary depending on the refractive index of the adherend, etc., and may be, for example, 1.700 or less, 1.670 or less, and 1. It may be 650 or less, 1.620 or less, or 1.600 or less.

The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive. For example, by selecting an acrylic polymer with a high content of monomer (A1) in the monomer components, selecting the type of plasticizer, etc., it is possible to prepare an adhesive having a refractive index of a predetermined value or higher.

In this specification, the refractive index of an 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 commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, for example, model "DR-M4" manufactured by ATAGO or its equivalent is used. As the measurement sample, an adhesive layer made of the adhesive to be evaluated can be used. Specifically, the refractive index of the adhesive can be measured by the method described in Examples below.

(Deformation characteristics)
In addition to having a refractive index of 1.55 or more, the adhesive disclosed herein has a deformation amount of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm/min. characterized by something. Since the adhesive disclosed herein satisfies the above characteristics while having a high refractive index, it can be sufficiently deformed at high speed even in a low temperature environment and can withstand large deformations. A pressure-sensitive adhesive that satisfies the above characteristics preferably has a high refractive index, and can withstand use in applications involving large deformations, such as foldable display applications.

Further, the adhesive disclosed herein preferably has a stress of 5.0 N/mm ² or less at a deformation amount of 350% in a deformation test conducted at a temperature of -20°C and a speed of 300 mm/min. . An adhesive that satisfies the above characteristics has a high refractive index and can be sufficiently deformed at high speed while maintaining a predetermined level of flexibility even in a low-temperature environment. Therefore, it is suitable for use in applications involving large deformations. In some preferred embodiments, the stress at the deformation amount of 350% is 4.9 N/mm ² or less, 4.8 N/mm ² or less, 4.7 N/mm ² or less, or 4.6 N/mm ² or less. Good, 4.5N/mm ² or less, 4.4N/mm ² or less, 4.3N/mm ² or less, 4.2N/mm 2 or less, 4.1N/mm ^{2 or} less, 4.0N/mm ² or less , 3.9 N/mm ² or less, 3.8 N/mm ² or less, 3.7 N/mm ² or less, 3.6 N/mm ² or less, 3.5 N/mm ² or less, 3.4 N/mm ² or less, 3 .3N/ ^mm2 or less, 3.2N/ ^mm2 or less, 3.1N/ ^mm2 or less, 3.0N/mm2 ^or less, 2.9N/ ^mm2 or less, 2.8N/ ^mm2 or less, 2.7N / ^mm2 or less, 2.6N/ ^mm2 or less, 2.5N/ ^mm2 or less, 2.4N/ ^mm2 or less, 2.3N/mm2 ^or less, or 2.2N/ ^{mm2 or} less. The lower limit of stress at the above deformation amount of 350% is theoretically 0.0 N/mm ² or more, and in some preferred embodiments, 0.1 N/mm ² or more, 0.2 N/mm ² or more, 0. .3N/ ^mm2 or more, 0.4N/ ^mm2 or more, 0.5N/ ^mm2 or more, 0.6N/mm2 or more, 0.7N/ ^mm2 or more, 0.8N/ ^{mm2 or} more, 0.9N / ^mm2 or more, 1.0N/ ^mm2 or more, 1.1N/ ^mm2 or more, 1.2N/mm2 ^or more, 1.3N/mm2 ^or more, 1.4N/mm2 ^or more, 1.5N/mm ² or more, 1.6N/mm ² or more, 1.7N/mm ² or more, 1.8N/mm ² or more, 1.9N/mm ² or more, 2.0N/mm ² or more, 2.1N/mm ² or more Or it may be 2.2N/ ^mm2 or more, 2.3N/mm2 ^or more, 2.4N/mm2 ^or more, 2.5N/mm2 or more, 2.6N/ ^mm2 or more, 2.7N/ ^mm2 or more. ^mm2 or more, 2.8N/ ^mm2 or more, 2.9N/mm2 ^or more, 3.0N/mm2 ^or more, 3.1N/mm2 or more, 3.2N/ ^{mm2 or} more, 3.3N/ ^mm2 3.4 N/mm ² or more, 3.5 N/mm ² or more, 3.6 N/mm ² or more, 3.7 N/mm ² or more, 3.8 N/mm ² or more, 3.9 N/mm ² or more, 4.0 N/mm ² or more, 4.1 N/mm ² or more, 4.2 N/mm ² or more, 4.3 N/mm ² or more, 4.4 N/mm ² or more, 4.5 N/mm ² or more, or 4. It may be 6N/mm ² or more. An adhesive having stress at the deformation amount of 350% can have flexibility and appropriate cohesive force.

In some embodiments, the adhesive has a stress S (-20°C) at a deformation amount of 350% in a deformation test conducted at a temperature of -20°C and a speed of 300 mm/min, and a stress S (-20°C) at a temperature of 25°C and a speed of 300 mm/min. It is preferable that the ratio (S(-20°C)/S(25°C)) to the stress S(25°C) at a deformation amount of 350% in a deformation test conducted under conditions of 50 or less is 50 or less. An adhesive that satisfies the above characteristics can exhibit stable performance over a wide temperature range including low temperatures. In some preferred embodiments, the ratio (S(-20°C)/S(25°C)) is 49 or less, 48 or less, 47 or less, 46 or less, 45 or less, 44 or less, 43 or less, 42 or less, 41 40 or less, 39 or less, 38 or less, 37 or less, 36 or less, 35 or less, 34 or less, 33 or less, 32 or less, or 31 or less, 30 or less, 29 or less, 28 or less, 27 or less, 26 Below, it may be 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, or 15 or less. The lower limit of the ratio (S(-20°C)/S(25°C)) is usually 0 or more, and in some preferred embodiments, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, or 15 or more, 16 or more, 17 or more, 18 or more, 19 or more, 20 or more, 21 22 or more, 23 or more, 24 or more, 25 or more, 26 or more, 27 or more, 28 or more, 29 or more, 30 or more, or 31 or more.

More specifically, the deformation test carried out at a temperature of -20°C or 25°C and a speed of 300 mm/min is carried out by the method described in the Examples below. The temperature of the adhesive is -20°C, the deformability is 350% at a speed of 300 mm/min, the stress at 350% deformation, and the ratio (S (-20°C) / S (25°C)) of the base polymer selection of the composition of monomer components to be used, setting of the weight average molecular weight (Mw) of the base polymer, selection of the type and amount of plasticizer used, selection of whether to use a crosslinking agent, selection of the type and amount of use, selection of the use of additives, type and amount. It can be adjusted by selecting the amount used, etc.

(Storage modulus G')
Although not particularly limited, in some embodiments, the adhesive has a storage modulus G' (0°C) of 1.0 x 10 ⁴ Pa to 1.0 x 10 ⁶ Pa. be. According to the above-mentioned pressure-sensitive adhesive, the range of storage elastic modulus G' (0° C.) is suppressed to a low range while having a high refractive index, so that it can achieve both a high refractive index and flexibility. An adhesive having a storage modulus G' (0° C.) within the above range can have both a high refractive index and flexibility, and has flexibility that can withstand repeated bending operations. The storage elastic modulus G' (0° C.) is preferably 5.0×10 ⁵ Pa or less, may be 2.0×10 ⁵ Pa or less, or may be 1.0×10 ⁵ Pa or less, It may be 7.0×10 ⁴ Pa or less, 5.0×10 ⁴ Pa or less, or 3.0×10 ⁴ Pa or less. Further, the storage elastic modulus G' (0° C.) is preferably 2.0×10 ⁴ Pa or more, more preferably 4.0×10 ⁴ Pa or more, and may be 6.0×10 ⁴ Pa or more, It may be 1.0×10 ⁵ Pa or more.

The storage modulus G' (-20°C) of the adhesive disclosed herein is not particularly limited, and may be less than 1.0×10 ¹⁰ Pa, for example, 1.0×10 ⁹ It may be less than Pa, suitably less than 5.0×10 ⁸ Pa, may be less than 1.0×10 ⁸ Pa, may be less than 5.0×10 ⁷ Pa, and may be less than 1.0× It may be 10 ⁷ Pa or less, 5.0×10 ⁶ Pa or less, 1.0×10 ⁶ Pa or less, or 5.0×10 ⁵ Pa or less. An adhesive whose storage modulus G' (-20° C.) is limited as described above can have excellent flexibility. For example, it may have good flexibility in a lower temperature range, and may have flexibility that can withstand repeated bending operations in a wide temperature range including a low temperature range. The lower limit of the storage elastic modulus G' (-20°C) is not particularly limited, and is, for example, 1.0×10 ² Pa or more, suitably 1.0×10 ^{3 Pa or more, preferably 1.0×10 3} Pa or more. .0×10 ⁴ Pa or more, more preferably 1.0×10 ⁵ Pa or more, may be 5.0×10 ⁵ Pa or more, or 1.0×10 ⁶ Pa or more. An adhesive having the above storage modulus G' (-20° C.) can have flexibility and appropriate cohesive strength. Furthermore, the pressure-sensitive adhesive having the storage elastic modulus G' (-20° C.) tends to have both a high refractive index and flexibility even in a low temperature range.

The storage modulus G' (25°C) of the adhesive disclosed herein is not particularly limited, and is suitably less than 1.0×10 ⁶ Pa, preferably less than 5.0× It is less than 10 ⁵ Pa, more preferably less than 3.0×10 ⁵ Pa, may be less than 1.0×10 ⁵ Pa, and may be less than 5.0×10 ⁴ Pa. The adhesive whose storage modulus G' (25° C.) is limited as described above has good flexibility at normal usage temperatures such as room temperature environments. The lower limit of the storage modulus G' (25° C.) is not particularly limited, and is, for example, 1.0×10 ² Pa or more, suitably 5.0×10 ² Pa or more, preferably 1.0×10 2 Pa or more. It is 0×10 ³ Pa or more, more preferably 3.0×10 ³ Pa or more, and may be 5.0×10 ³ Pa or more. An adhesive having the above storage modulus G' (25° C.) is preferable because it has a suitable cohesive force even in a high temperature range and tends to have excellent heat resistance.

(Storage modulus ratio)
In some embodiments, the adhesive has a ratio of storage modulus G'(0°C) to storage modulus G'(25°C) at 25°C (G'(0°C)/G'(25°C)). )) is within the range of 1 to 1000. A pressure-sensitive adhesive that satisfies the above characteristics suppresses changes in elastic modulus in a wide temperature range from 0° C. to room temperature, and therefore tends to exhibit stable characteristics (flexibility, etc.) against temperature changes. The above ratio (G'(0°C)/G'(25°C)) is suitably 300 or less, preferably 100 or less, more preferably 50 or less, may be 25 or less, or even 10 or less. Often, it may be 5 or less. The lower limit of the ratio (G'(0°C)/G'(25°C)) may be, for example, 2 or more, or 3 or more.

In some embodiments, the adhesive has a ratio of storage modulus G'(-20°C) to storage modulus G'(25°C) at 25°C (G'(-20°C)/G' (25°C)) is within the range of 1 to 1000. According to adhesives that satisfy the above characteristics, changes in the elastic modulus are suppressed over a wide temperature range from lower temperatures to room temperature, so they exhibit stable characteristics (flexibility, etc.) against temperature changes. be able to. The above ratio (G'(-20°C)/G'(25°C)) may be 500 or less, 300 or less, 150 or less, 100 or less, 50 or less, 30 or less. But that's fine. The lower limit of the ratio (G'(-20°C)/G'(25°C)) may be, for example, 5 or more, 50 or more, 100 or more, or 200 or more.

(Glass-transition temperature)
The glass transition temperature (Tg) of the adhesive is not particularly limited, and can be set in consideration of flexibility in a low temperature range and cohesive strength (heat resistance, etc.) in a high temperature range. In some embodiments, the Tg of the adhesive is, for example, 30°C or less, may be 15°C or less, or may be 5°C or less. In some preferred embodiments, the Tg of the adhesive is 0°C or lower from the viewpoint of flexibility, more preferably -5°C or lower, even more preferably -10°C or lower, and -15°C or lower (for example, -20°C or lower). ℃ or less). The lower the Tg of the adhesive, the better the adhesive properties such as adhesion to adherends tend to be. Furthermore, by setting the Tg of the adhesive low, it is possible to suppress changes in the elastic modulus in a temperature range higher than Tg. The lower limit of the Tg of the adhesive is, for example, -50°C or higher, suitably -40°C or higher, may be -30°C or higher, or may be -25°C or higher. According to the pressure-sensitive adhesive having the above-mentioned Tg, there is a tendency that an appropriate cohesive force is easily obtained. In addition, there is a tendency to easily form a pressure-sensitive adhesive that has both a high refractive index and large deformability.

The storage modulus G' of the adhesive and the glass transition temperature of the adhesive at each of the above temperatures can be measured by the dynamic viscoelasticity measurement method described in the Examples below, and from the results, each storage modulus ratio can be determined. It can be calculated. The storage modulus G', storage modulus ratio, and glass transition temperature of the adhesive are determined by, for example, the selection of the composition of the monomer components constituting the base polymer, the setting of the Mw of the base polymer, and the selection of the type and amount of plasticizer used. It can be adjusted by selecting whether or not to use a crosslinking agent, its type and amount used, and selecting whether or not to use an additive, its type and amount used, and the like.

(Change in elastic modulus after being held at 130°C for 1 hour)
Although not particularly limited, in some embodiments, the storage modulus G'1 at -20°C after holding the adhesive in a 130°C environment for 1 hour, and the storage modulus G'1 after holding the adhesive in a 130°C environment for 1 hour. It is preferable to use an adhesive whose ratio (G'1/G'0) to the storage elastic modulus G'0 at -20° C. before drying is 50 or less (specifically 1 to 50). A pressure-sensitive adhesive that satisfies this property has a change in elastic modulus that is limited within a predetermined range even when exposed to high temperatures, and can exhibit stable properties. The ratio (G'1/G'0) is preferably 30 or less, more preferably 10 or less, still more preferably 3 or less, may be 2 or less, and may be less than 1.5.

The change in elastic modulus after holding at 130°C for 1 hour is measured by the following method. That is, the adhesive composition is applied to the silicone-treated surface of PET film R1, one side of which has been silicone-treated, and heated at 130° C. for 3 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of PET film R2, one side of which has been silicone-treated, is bonded to the surface of the adhesive layer. One of the release liners is peeled off from the obtained adhesive layer with a release liner (release liner/adhesive layer/release liner), and the mixture is kept in an oven at 130° C. for 1 hour. Use an oven that has sufficient capacity for the sample to be measured and that can be heated while evacuating the sample. For example, an oven manufactured by espec can be used. The adhesive (layers) held at 130° C. for 1 hour are laminated to a thickness of approximately 1.5 mm, and then autoclaved (0.5 MPa, 50° C., 15 minutes) to adhere each layer. The storage modulus G' (G'1 ) Find [Pa]. Then, the ratio (G' 1/G'0).

(Haze value)
In some embodiments, the haze value of the adhesive (for example, the adhesive layer constituting the adhesive sheet) may be, for example, 5.0% or less, preferably 3.0% or less, and 2.0% or less. % or less, more preferably 1.0% or less, 0.9% or less, 0.8% or less, 0.5% or less, 0.3% or less But that's fine. Adhesives with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive. The lower limit of the haze value of the adhesive is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable it is. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more, or 0.10% or more, taking into consideration the refractive index and adhesive properties. These haze values regarding the adhesive also apply to the haze value of the adhesive sheet when the technology disclosed herein is implemented in the form of a base material-less adhesive sheet (typically, an adhesive sheet consisting of an adhesive layer). It can be preferably applied.

Here, the "haze value" refers to the ratio of diffusely transmitted light to the total transmitted light when visible light is irradiated onto the measurement target. Also called cloudiness value. The haze value can be expressed by the following formula.
Th(%)=Td/Tt×100
In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The haze value can be measured according to the method described in Examples below. The haze value of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

(Total light transmittance)
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 more than 90.0%). . Adhesives with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive. In practical terms, the upper limit of the total light transmittance may be, for example, about 98% or less, about 96% or less, or about 95% or less. In some embodiments, the total light transmittance of the adhesive may be about 94% or less, about 93% or less, or about 92% or less, taking into account the refractive index and adhesive properties. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used. The total light transmittance can be measured according to the method described in Examples below. The total light transmittance of the adhesive can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

In some embodiments, the adhesive is folded after a bending test is repeated 10 times at 25° C. in which each side of the sheet-like adhesive is bent into a U-shape with a radius of 2 mm. It is preferable that the total light transmittance of the part (total light transmittance after the bending test) is maintained at 85% or more of the total light transmittance before the bending test. An adhesive that satisfies the above characteristics has little change in optical properties (for example, whitening) even after repeated bending, and is therefore suitable for optical applications where bending is expected, such as foldable display applications. The total light transmittance after the bending test is more preferably 90% or more, still more preferably 95% or more, particularly preferably 98% or more (for example, 99% or more) of the total light transmittance before the bending test. More specifically, the total light transmittance before and after the bending test is measured by the method described in Examples below. The total light transmittance after the above bending test depends on the selection of the composition of the monomer components constituting the base polymer, the setting of the weight average molecular weight (Mw) of the base polymer, the selection of the type and amount of plasticizer used, and whether or not a crosslinking agent is used. It can be adjusted by selecting the type and amount used, whether or not additives are used, and selecting the type and amount used.

<Adhesive composition>
(base polymer)
In the technology disclosed herein, the type of adhesive (layer) is not particularly limited. The above-mentioned pressure-sensitive adhesives include acrylic polymers, rubber-based polymers (e.g. natural rubber, synthetic rubber, mixtures thereof, etc.), polyester-based polymers, urethane-based polymers, polyether-based polymers, and silicone-based polymers that can be used in the field of adhesives. , polyamide-based polymers, fluorine-based polymers, etc., as adhesive polymers (hereinafter also referred to as "base polymers" in the sense of structural polymers that form adhesives). obtain. From the viewpoint of adhesive performance, cost, etc., a pressure-sensitive adhesive containing an acrylic polymer or a rubber-based polymer as a base polymer can be preferably employed. Among these, adhesives having an acrylic polymer as a base polymer (acrylic adhesives) are preferred. The technique disclosed herein is preferably implemented in an embodiment using an acrylic pressure-sensitive adhesive.

Although acrylic pressure-sensitive adhesives will be mainly described below, it is not intended that the pressure-sensitive adhesives disclosed herein be limited to acrylic pressure-sensitive adhesives.

(acrylic polymer)
The technique disclosed herein can be preferably implemented in an embodiment using an acrylic pressure-sensitive adhesive. The acrylic polymer serving as the base polymer of the acrylic pressure-sensitive adhesive is preferably one containing an aromatic ring-containing monomer (A1) as a monomer component constituting the acrylic polymer. That is, an acrylic polymer containing the aromatic ring-containing monomer (A1) as a monomer unit is preferable. Here, in this specification, the term "monomer component constituting the acrylic polymer" refers to a monomer component that is contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or is a monomer component that is unpolymerized. It means a monomer that constitutes a repeating unit of an acrylic polymer in a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, regardless of whether it is contained in the pressure-sensitive adhesive composition in any form. That is, the monomer component constituting the acrylic polymer may be contained in the pressure-sensitive adhesive composition in any form of a polymerized product, an unpolymerized product, or a partially polymerized product. From the viewpoint of ease of preparation of the adhesive composition, in some embodiments, an adhesive composition containing substantially all of the monomer components (for example, 95% by weight or more, preferably 99% by weight or more) in the form of a polymer. Preferably.

(Monomer (A1))
As the monomer (A1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. As the monomer (A1), one kind of such compounds can be used alone or two or more kinds can be used in combination.

Examples of the ethylenically unsaturated group include (meth)acryloyl group, vinyl group, (meth)allyl group, and the like. A (meth)acryloyl group is preferred from the viewpoint of polymerization reactivity, and an acryloyl group is more preferred from the viewpoint of flexibility and adhesiveness. From the viewpoint of suppressing a decrease in flexibility of the adhesive, a compound having one ethylenically unsaturated group in one molecule (ie, a monofunctional monomer) is preferably used as the monomer (A1).

The number of aromatic rings contained in one molecule of the compound used as the monomer (A1) may be 1 or 2 or more. The upper limit of the number of aromatic rings is not particularly limited, and may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the acrylic polymer and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, and 6 or less. More preferably, it is 5 or less, 4 or less, 3 or less, or 2 or less.

The aromatic ring possessed by the compound used as the monomer (A1) is a benzene ring (it can be a benzene ring that constitutes a part of a biphenyl structure or a fluorene structure); a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, a phenanthrene ring. It may be a carbocyclic ring such as a condensed ring; , a thiophene ring; and the like may be used. The heteroatoms included as ring constituent atoms in the above-mentioned heterocycle may be, for example, one or more heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms making up the heterocycle can be one or both of nitrogen and sulfur. The monomer (A1) may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. When having a substituent, the substituent includes an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group. Examples include, but are not limited to. In a substituent containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the aromatic ring has no substituent on the ring constituent atoms, or one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (e.g., a bromine atom). It can be an aromatic ring having In addition, the phrase "the aromatic ring of the monomer (A1) has a substituent on its ring-constituting atoms" means that the aromatic ring has a substituent other than the substituent having an ethylenically unsaturated group.

The aromatic ring and the ethylenically unsaturated group may be bonded directly or may be bonded via a linking group. The above-mentioned linking group is, for example, an alkylene group, an oxyalkylene group, a poly(oxyalkylene) group, a phenyl group, an alkylphenyl group, an alkoxyphenyl group, or a structure in which one or more hydrogen atoms in these groups are substituted with a hydroxyl group. (for example, a hydroxyalkylene group), an oxy group (-O- group), a thiooxy group (-S- group), and the like. In some embodiments, the aromatic ring and the ethylenically unsaturated group are bonded directly or through a linking group selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. An aromatic ring-containing monomer having the following structure can be preferably employed. The number of carbon atoms in the alkylene group and the oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. The repeating number of oxyalkylene units in the poly(oxyalkylene) group may be, for example, 2 to 3.

Examples of compounds that can be preferably employed as the monomer (A1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylate and the aromatic ring-containing vinyl compound can each be used singly or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds may be used in combination.

In some preferred embodiments, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule is used as the monomer (A1) because it is easy to obtain a high refractive index effect. Examples of monomers having two or more aromatic rings in one molecule (monomers containing multiple aromatic rings) include monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group, and two or more non-fused aromatic rings. Monomers with a structure in which rings are chemically bonded directly (i.e., without intervening other atoms), monomers with a fused aromatic ring structure, monomers with a fluorene structure, monomers with a dinaphthothiophene structure, monomers with a dibenzothiophene structure , etc. Among these, monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group (for example, phenoxybenzyl (meth)acrylate described below) are preferably used. The monomer containing multiple aromatic rings can be used alone or in combination of two or more.

The above-mentioned linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (for example, a -O-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1). , thiooxyalkylene groups (e.g. -S-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1), linear alkylene groups (i.e. -(CH ₂ ) _n - group, where n is 1 to 6, preferably 1 to 3), the alkylene group in the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be partially halogenated or completely halogenated. From the viewpoint of the flexibility of the adhesive, preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a straight-chain alkylene group. Specific examples of monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (for example, m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth) Examples include acrylate, benzylbenzyl (meth)acrylate, and the like.

The monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded may be, for example, biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, vinyl group-containing biphenyl, and the like. Specific examples include o-phenylphenol (meth)acrylate, biphenylmethyl (meth)acrylate, and the like.

Examples of the monomer having the fused aromatic ring structure include naphthalene ring-containing (meth)acrylate, anthracene ring-containing (meth)acrylate, vinyl group-containing naphthalene, vinyl group-containing anthracene, and the like. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, -(4-methoxy-1-naphthoxy)ethyl (meth)acrylate and the like.

Specific examples of the monomer having the above fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene (meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (meth)acrylate etc. In addition, since the monomer having a fluorene structure includes a structural part in which two benzene rings are directly chemically bonded, it is included in the concept of a monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded.

Examples of the monomer having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, and the like. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (for example, a compound having a structure in which CH ₂ CH (R ¹ ) C (O) OCH ₂ - is bonded to the 5th or 6th position of the dinaphthothiophene ring. , R ¹ is a hydrogen atom or a methyl group), (meth)acryloyloxyethyldinaphthothiophene (for example, CH ₂ CH(R ¹ )C(O) at the 5th or 6th position of the dinaphthothiophene ring) A compound with a structure in which OCH(CH ₃ )- or CH ₂ CH(R ¹ )C(O)OCH ₂ CH ₂ - is bonded. Here, R ¹ is a hydrogen atom or a methyl group), vinyldinaphthothiophene (For example, a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of a naphthothiophene ring), (meth)allyloxydinaphthothiophene, and the like. In addition, monomers having a dinaphthothiophene structure are included in the above concept of monomers having a fused aromatic ring structure because they include a naphthalene structure or because they have a structure in which a thiophene ring and two naphthalene structures are condensed. Ru.

Examples of the monomer having the dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, and the like. A monomer having a dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are condensed, and therefore is included in the concept of a monomer having a condensed aromatic ring structure.
Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly chemically bonded.

In some preferred embodiments, a monomer having one aromatic ring (preferably a carbon ring) in one molecule is used as the monomer (A1). A monomer having one aromatic ring in one molecule (single aromatic ring-containing monomer) can be useful, for example, in improving the flexibility of the adhesive, adjusting the adhesive properties, and improving the transparency. The monomer containing a single aromatic ring can be used alone or in combination of two or more. In some embodiments, a monomer having one aromatic ring in one molecule may be used in combination with a monomer containing multiple aromatic rings from the viewpoint of improving the refractive index of the adhesive.

Examples of monomers having one aromatic ring in one molecule include benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, and phenoxypropyl (meth)acrylate. , phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, chlorobenzyl (meth)acrylate, and other carbon aromatic ring-containing (meth)acrylates; 2-(4, 6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6-(4,6-dibromo-2-s- Butylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl Bromine-substituted aromatic ring-containing (meth)acrylates such as phenyl acrylate; carbon aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, tert-butylstyrene; N-vinylpyridine, N-vinylpyrimidine, N-vinylpyridine, N-vinylpyrimidine, - Compounds having a vinyl substituent on a heteroaromatic ring, such as vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole; and the like.

As the monomer (A1), monomers having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in various aromatic ring-containing monomers as described above may be used. A monomer in which an oxyethylene chain is interposed between an ethylenically unsaturated group and an aromatic ring in this way can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CH ₂ CH ₂ O-) in the oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol. Examples include di(meth)acrylate.

The content of the monomer containing multiple aromatic rings in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the monomer containing multiple aromatic rings in the monomer (A1) may be, for example, 50% by weight or more, and is preferably 70% by weight or more from the viewpoint of making it easier to obtain a higher refractive index. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (A1) may be a monomer containing multiple aromatic rings. That is, only one or more aromatic ring-containing monomers may be used as the monomer (A1). In some other embodiments, the content of the monomer containing multiple aromatic rings in the monomer (A1) may be less than 100% by weight, for example, considering the balance between high refractive index and large deformability. , may be 98% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, 50% by weight or less, 25% by weight or less, It may be 10% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing multiple aromatic rings in the monomer (A1) is less than 5% by weight. A monomer containing multiple aromatic rings may not be used.

The content of the monomer containing multiple aromatic rings in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both a desired refractive index and large deformability. The content of the monomer containing multiple aromatic rings in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the monomer containing multiple aromatic rings in the monomer component may be, for example, more than 35% by weight, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, and may be more than 50% by weight. Advantageously, it is more than 70% by weight, preferably more than 75% by weight, more than 85% by weight, more than 90% by weight, more than 91% by weight, more than 92% by weight, It may be 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. Considering the balance between high refractive index and large deformability, the content of the monomer containing multiple aromatic rings in the above monomer component is advantageously approximately 99% by weight or less, and even if it is 98% by weight or less. Often, it may be 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some other embodiments, the content of the monomer containing multiple aromatic rings in the monomer component may be 70% by weight or less, from the viewpoint of easily achieving higher adhesive properties and/or optical properties (for example, transparency). , 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing multiple aromatic rings in the monomer component is less than 3% by weight.

The content of the monomer containing a single aromatic ring in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the monomer containing a single aromatic ring in the monomer (A1) may be, for example, 50% by weight or more, and is preferably 70% by weight or more from the viewpoint of making it easier to obtain a higher refractive index. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (A1) may be a monomer containing a single aromatic ring. That is, only one or more monomers containing a single aromatic ring may be used as the monomer (A1). Further, in some embodiments, for example, in consideration of the balance between high refractive index and large deformability, the content of the monomer containing a single aromatic ring in the monomer (A1) may be less than 100% by weight, and 98% by weight. It may be less than 90% by weight, it may be less than 80% by weight, it may be less than 70% by weight, it may be less than 65% by weight, it may be less than 50% by weight, it may be less than 25% by weight, and it may be less than 10% by weight. It may be less than %. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing a single aromatic ring in the monomer (A1) is less than 5% by weight. A monomer containing a single aromatic ring may not be used.

The content of the monomer containing a single aromatic ring in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both a desired refractive index and large deformability. The content of the monomer containing a single aromatic ring in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize a pressure-sensitive adhesive having a higher refractive index, the content of the monomer containing a single aromatic ring in the monomer component may be, for example, more than 35% by weight, and more than 50% by weight. Advantageously, it is 60% by weight or more, more preferably more than 70% by weight, it can be 75% by weight or more, it can be 85% by weight or more, it can be 90% by weight or more, it can be 95% by weight or more. It may be 98% by weight or more. The content of the monomer containing a single aromatic ring in the monomer component may be approximately 99% by weight or less, preferably 98% by weight or less, considering the balance between high refractive index and large deformability, It is more preferably 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some embodiments, the content of the monomer containing a single aromatic ring in the monomer component may be 70% by weight or less, from the viewpoint of easily realizing higher adhesive properties and/or optical properties (for example, transparency), and 60% by weight or less. It may be less than 50% by weight, less than 40% by weight, less than 25% by weight, less than 15% by weight, and less than 5% by weight. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing a single aromatic ring in the monomer component is less than 3% by weight.

In some preferred embodiments, a high refractive index monomer can be preferably employed as at least a portion of the monomer (A1). Here, the term "high refractive index monomer" refers to a monomer whose refractive index is, for example, about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoint of ease of preparation of the acrylic polymer and compatibility with flexibility suitable as an adhesive, it is, for example, 3.000 or less, and 2. It may be 500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomers can be used alone or in combination of two or more.
The refractive index of the monomer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, model "DR-M4" manufactured by ATAGO or its equivalent can be used. If a manufacturer or the like provides a nominal value of the refractive index at 25° C., that nominal value can be used.

The above-mentioned high refractive index monomer is one having a corresponding refractive index from among the compounds included in the concept of the aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and compound groups exemplified above). may be adopted as appropriate. Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), Ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (Refractive index (nD20): 1.517, homopolymer Tg: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Tg: -35°C), 6-acryloyloxymethyldinaphthothiophene ( 6MDNTA, refractive index: 1.75), 6-methacryloyloxymethyldinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyldinaphthothiophene (5EDNTA, refractive index: 1.786), 6 -Acryloyloxyethyldinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyldinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyldinaphthothiophene (abbreviation: 5VDNT, refractive index: 1) .793), but is not limited to these.

The content of the high refractive index monomer (that is, the aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) in the monomer (A1) is particularly The content is not limited, and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a higher refractive index, the content of the high refractive index monomer in the monomer (A1) may be, for example, 50% by weight or more, and preferably 70% by weight or more. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of monomer (A1) may be a high refractive index monomer. In some embodiments, the content of the high refractive index monomer in the monomer (A1) may be less than 100% by weight, for example from the viewpoint of achieving both high refractive index and large deformability in a well-balanced manner, and 98% by weight. It may be less than 90% by weight, less than 80% by weight, or less than 65% by weight. In some other embodiments, in consideration of adhesive properties and/or optical properties, the content of the high refractive index monomer in the monomer (A1) may be 50% by weight or less, 25% by weight or less, 15% by weight or less. % or less, or 10% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of the high refractive index monomer in the monomer (A1) is less than 5% by weight. High refractive index monomers may not be used.

The content of the high refractive index monomer in the monomer components constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both a desired refractive index and large deformability. In addition, if necessary, it may be set in consideration of compatibility with adhesive properties (for example, adhesive strength, etc.) and/or optical properties (for example, total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight, and from the viewpoint of making it easier to obtain a higher refractive index, it is more than 50% by weight. Advantageously, it is preferably greater than 70% by weight, may be greater than 75%, may be greater than 85%, may be greater than 90%, may be greater than 95% by weight. The content of the high refractive index monomer in the monomer component is advantageously 99% by weight or less, preferably 98% by weight or less, from the viewpoint of achieving both high refractive index and large deformability in a well-balanced manner. , more preferably 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some other embodiments, in consideration of adhesive properties and/or optical properties, the content of the high refractive index monomer in the monomer component may be 70% by weight or less, 50% by weight or less, or 25% by weight. It may be less than 15% by weight, or less than 5% by weight. The technology disclosed herein can also be practiced in an embodiment in which the content of the high refractive index monomer in the monomer components is less than 3% by weight.

In some preferred embodiments, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") whose homopolymer Tg is 10° C. or less is employed as at least a part of the monomer (A1). The content of the aromatic ring-containing monomer (A1) in the monomer component (in particular, the aromatic ring-containing monomer (A1) that corresponds to at least one of the above-mentioned monomer containing a plurality of aromatic rings, monomer containing a single aromatic ring, and high refractive index monomer) If the amount is increased, the flexibility of the adhesive generally tends to decrease, but by employing monomer L as part or all of the monomer (A1), the decrease in flexibility can be suppressed. This makes it possible to improve the refractive index while better maintaining large deformability. The Tg of the monomer L may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. The lower limit of Tg of the monomer L is not particularly limited. Considering the balance with the refractive index improvement effect, in some embodiments, the Tg of the monomer L may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. In some other embodiments, the Tg of the monomer L may be, for example, -30°C or higher, -10°C or higher, 0°C or higher, or 3°C or higher. Monomer L can be used alone or in combination of two or more.

As the monomer L, one having a corresponding Tg is appropriately adopted from among the compounds included in the concept of the aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and compound groups exemplified above). be able to. Suitable examples of aromatic ring-containing monomers that can be used as monomer L include m-phenoxybenzyl acrylate (homopolymer Tg: -35°C), benzyl acrylate (homopolymer Tg: 6°C), phenoxyethyl acrylate (homopolymer Tg: 6°C), Tg: 2°C), and phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

The content of monomer L in monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of monomer L in the monomer (A1) is, for example, 50% by weight or more, from the viewpoint of making it easier to obtain an adhesive that achieves both high refractive index and large deformability at a higher level. Generally, from the viewpoint of greatly improving deformability, the content is preferably 60% by weight or more, may be 70% by weight or more, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight. The above is fine. Substantially 100% by weight of monomer (A1) may be monomer L. In some other embodiments, the content of monomer L in the monomer (A1) may be less than 100% by weight, for example, from the viewpoint of achieving both high refractive index and large deformability in a well-balanced manner. It may be less than 90% by weight, less than 80% by weight, or less than 65% by weight.

The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of monomer L in the monomer component may be, for example, more than 35% by weight, from the viewpoint of making it easier to obtain an adhesive that combines high refractive index and large deformability at a higher level, From the viewpoint of improving the refractive index, it is advantageous to be more than 50% by weight, preferably more than 70% by weight, 75% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more. It may be more than % by weight. The content of monomer L in the monomer component is advantageously approximately 99% by weight or less, and preferably 98% by weight or less, from the viewpoint of achieving both high refractive index and large deformability in a well-balanced manner. It is more preferably 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

In some embodiments, the aromatic ring-containing monomer (A1) is a combination of monomer L (i.e., an aromatic ring-containing monomer whose homopolymer Tg is 10°C or less) and monomer H whose Tg is higher than 10°C. May be used. The Tg of the monomer H may be, for example, higher than 10°C, higher than 15°C, or higher than 20°C. By using monomer L and monomer H in combination, it is suitable for increasing the refractive index of the adhesive and adhering it to the adherend in an adhesive that has a high content of the aromatic ring-containing monomer (A1) in the monomer component. It is possible to achieve both a higher level of flexibility and flexibility. The usage ratio of monomer L and monomer H can be set so that this effect is suitably expressed, and is not particularly limited.

In some embodiments, the aromatic ring-containing monomer (A1) may be preferably selected from compounds that do not contain a structure in which two or more non-fused aromatic rings are directly chemically bonded (for example, a biphenyl structure). For example, the monomer component has a composition in which the content of a compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may be 0% by weight) An acrylic polymer constituted by is preferred. Limiting the amount of compounds that contain a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way is important from the perspective of creating an adhesive that has a better balance between high refractive index and large deformability. It can be advantageous.

The content of the monomer (A1) in the monomer components constituting the acrylic polymer is not particularly limited, and is based on the desired refractive index and large deformability, as well as adhesive properties (such as adhesive strength) and/or optical properties (such as total (light transmittance, haze value, etc.). In some embodiments, the content of the monomer (A1) in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and 70% by weight. It may be % or more. In some preferred embodiments, the content of the monomer (A1) in the monomer components constituting the acrylic polymer may be, for example, more than 70% by weight, suitably 75% by weight or more, and has a higher refractive index. From the viewpoint of making it easier to obtain the ratio, it is preferably 80% by weight or more, may be 85% by weight or more, may be 90% by weight or more, 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more. , 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. The content of the monomer (A1) in the above monomer component is typically less than 100% by weight, and from the viewpoint of achieving both high refractive index and large deformability in a well-balanced manner, it is advantageous that the content of the monomer (A1) is approximately 99% by weight or less. The content may be 98% by weight or less, 96% by weight or less, 93% by weight or less, or 90% by weight or less. In some embodiments, the content of the monomer (A1) in the monomer component may be less than 90% by weight, and may be less than 85% by weight, from the viewpoint of facilitating the realization of higher adhesive properties and/or optical properties (for example, transparency). % or less than 80% by weight.

(Monomer (A2))
In some preferred embodiments, the monomer component constituting the acrylic polymer may further contain a monomer (A2) in addition to the above monomer (A1). The monomer (A2) is a monomer that corresponds to at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxyl group (carboxy group-containing monomer). The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The above-mentioned carboxyl group-containing monomer is a compound containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer (A2) can be useful for introducing crosslinking points into the acrylic polymer and imparting appropriate cohesiveness to the adhesive. The monomers (A2) can be used alone or in combination of two or more. Monomer (A2) may contain an aromatic ring or may not contain an aromatic ring. As the monomer (A2), a monomer containing no aromatic ring is preferably used. Note that the monomer (A2) is defined as a monomer different from the above-mentioned monomer (A1), and for example, the above-mentioned monomer (A1) can be defined as a monomer having no hydroxyl group or carboxyl group.

Examples of the ethylenically unsaturated group contained in the monomer (A2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. A (meth)acryloyl group is preferred from the viewpoint of polymerization reactivity, and an acryloyl group is more preferred from the viewpoint of improved flexibility and adhesiveness. From the viewpoint of improving the flexibility of the adhesive, a compound having one ethylenically unsaturated group in one molecule (ie, a monofunctional monomer) is preferably used as the monomer (A2).

In some embodiments, a monomer in which the distance between an ethylenically unsaturated group (for example, a (meth)acryloyl group) and a hydroxyl group and/or a carboxy group is relatively long can be used as the monomer (A2). Thereby, in embodiments in which the hydroxyl group and/or carboxy group are used in the crosslinking reaction, a crosslinked structure with high flexibility can be easily obtained. For example, the number of atoms (typically carbon atoms or oxygen atoms) constituting the chain (linking chain) connecting the ethylenically unsaturated group and the hydroxyl group and/or carboxyl group is 3 or more (for example, 4 or more, 5 or more). or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more or 19 or more). It can be used as A2). The upper limit of the number of atoms constituting the connecting chain is, for example, 45 or less, 20 or less (for example, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less or 8 or less). In addition, the number of atoms forming a linking chain connecting the ethylenically unsaturated group and the hydroxyl group and/or carboxy group refers to the minimum number of atoms required to reach the hydroxyl group or carboxy group from the ethylenically unsaturated group. . For example, when the above-mentioned connecting chain is composed of a linear alkylene group (ie, -(CH ₂ ) _n - group), the number of n is the number of atoms constituting the above-mentioned connecting chain. For example, when the connecting chain is an oxyethylene group (that is, a -(C ₂ H ₄ O) _n - group), 3 and n, which is the sum of 2 carbon atoms and 1 oxygen atom, constituting the oxyethylene group. The product (3n) is the number of atoms constituting the connecting chain. Although not particularly limited, such monomers (A2) include, for example, alkylene represented by -(CH ₂ ) _n - between the ethylenically unsaturated group and the hydroxyl group and/or carboxyl group. units, oxyalkylene units represented by -(C _m H _2m O)- (for example, oxyethylene units in which m is 2 in the above formula, oxypropylene units in which m in the above formula is 3, A compound having at least one oxybutylene unit in which m is 4) can be used. The number of alkylene units and oxyalkylene units is not particularly limited, and may be 1 or more (for example, 1 to 15, 1 to 10, 2 to 6, or 2 to 4). Further, n in the formula representing the above alkylene unit is, for example, an integer from 1 to 10, and may be 2 or more, 3 or more, 4 or more, or 6 or less, or 5 or less. good. In the formula representing the oxyalkylene unit, m is an integer of 2 or more, for example, an integer of 2 to 4. In addition to the above-mentioned ethylenically unsaturated group, hydroxyl group and/or carboxy group, alkylene unit and/or oxyalkylene unit, the monomer (A2) also contains an ester bond, an ether bond, a thioether bond, an aromatic ring, an aliphatic ring, and a heterocyclic ring. (For example, a ring containing a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S)). Moreover, the above alkylene unit and oxyalkylene unit may have a substituent.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and ) Hydroxy (meth)acrylates such as 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Alkyl; polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polybutylene glycol mono(meth)acrylate; and the like, but are not limited to these. Examples of hydroxyl group-containing monomers that can be preferably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate, which has a lower Tg, is more preferred. In addition, in an embodiment in which hydroxyalkyl (meth)acrylate is used as the hydroxyl group-containing monomer and the hydroxyl group is utilized for the crosslinking reaction, from the viewpoint of obtaining a highly flexible crosslinked structure, the hydroxyalkyl (meth)acrylate is Monomers with a large number of carbon atoms in the hydroxyalkyl group, such as hydroxyalkyl (meth)acrylates (for example, 4-hydroxy acrylate) in which the hydroxyalkyl group has 3 or more carbon atoms (for example, 3 to 12, preferably 4 to 10). butyl) is preferred. In some preferred embodiments, more than 50% (eg, more than 50%, more than 70%, or more than 85%) by weight of monomer (A2) can be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

In some embodiments in which a hydroxyl group-containing monomer is used as the monomer (A2), the hydroxyl group-containing monomer may be one or more selected from compounds that do not have a methacryloyl group. Preferred examples of the hydroxyl group-containing monomer that does not have a methacryloyl group include the above-mentioned various hydroxyalkyl acrylates. For example, it is preferable that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl group-containing monomer used as the monomer (A2) is hydroxyalkyl acrylate. The use of hydroxyalkyl acrylates allows for the introduction of hydroxy groups into acrylic polymers that help provide cross-linking points and appropriate cohesive properties, and allows for the introduction of hydroxyl groups into acrylic polymers that help provide cross-linking points and provide adequate cohesive properties, and at room temperature compared to the corresponding hydroxyalkyl methacrylates alone. It is easy to obtain an adhesive with good flexibility and adhesiveness in this area.

Examples of carboxy group-containing monomers include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, Examples include, but are not limited to, isocrotonic acid and the like. Examples of carboxy group-containing monomers that can be preferably used include acrylic acid and methacrylic acid. Further, in some embodiments, from the viewpoint of improving the flexibility of the adhesive, it is preferable to use, for example, a compound represented by the following formula (1) as the carboxyl group-containing monomer.
CH ₂ =CR ¹ -COO-R ² -OCO-R ³ -COOH (1)
Here, R ¹ in the above formula (1) is hydrogen or a methyl group. R ² and R ³ are divalent linking groups (specifically, organic groups having 1 to 20 carbon atoms (for example, 2 to 10, preferably 2 to 5)), and may be the same as each other. May be different. R ² and R ³ in the above formula (1) may be, for example, a divalent aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alicyclic hydrocarbon group. For example, R ² and R ³ above can be alkylene having 2 to 5 carbon atoms. Specific examples of the carboxy group-containing monomer represented by the above formula (1) include 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-( meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropylhydrogen phthalate, 2-(meth)acryloyloxypropyltetrahydrohydrogen phthalate, and the like. Carboxy group-containing monomers can be used alone or in combination of two or more. A hydroxyl group-containing monomer and a carboxyl group-containing monomer may be used together.

The content of the monomer (A2) in the monomer components constituting the acrylic polymer is not particularly limited, and can be set depending on the purpose. In some embodiments, the content of the monomer (A2) is, for example, 0.01% by weight or more, suitably 0.1% by weight or more, preferably 0.5% by weight or more. In some embodiments, the content of the monomer (A2) may be 1% by weight or more, 2% by weight or more, or 4% by weight or more from the viewpoint of obtaining higher usage effects. The upper limit of the content of the monomer (A2) in the monomer component is set so that the total content of the monomer (A2) and the content of the monomer (A1) does not exceed 100% by weight. In some embodiments, it is appropriate for the content of the monomer (A2) to be, for example, 30% by weight or less or 25% by weight or less, and the content of the monomer (A1) is relatively increased to obtain a high refractive index. From the viewpoint of facilitating rate reduction, the content is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, and may be less than 7% by weight. . In some preferred embodiments, from the viewpoint of improving the large deformability of the adhesive, the content of the monomer (A2) is less than 5% by weight, more preferably less than 3% by weight, and 1.5% by weight. % or less.

(Monomer A3)
In some embodiments, the monomer component constituting the acrylic polymer may further contain an alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)") in addition to the monomer (A1). Monomer (A3) can help improve the flexibility of the adhesive. It can also help improve the compatibility of additives within the adhesive and adhesive properties such as adhesive strength. Monomers (A3) can be used alone or in combination of two or more.

As the monomer (A3), an alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms (ie, C _1-20 ) at the ester end can be preferably used. Specific examples of C _1-20 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, and n-(meth)acrylate. Butyl, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylate, ) heptyl 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, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, (meth)acrylate ) Heptadecyl acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like, but are not limited to these.

In some embodiments, as at least a portion of the monomer (A3), an alkyl (meth)acrylate whose homopolymer has a Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower) is preferably employed. It is possible. Such low Tg alkyl (meth)acrylates can help improve the flexibility of the adhesive. It can also help improve adhesive properties such as adhesive strength. The lower limit of Tg of the alkyl (meth)acrylate is not particularly limited, and may be, for example, -85°C or higher, -75°C or higher, -65°C or higher, or -60°C or higher. Specific examples of the low Tg alkyl (meth)acrylates include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptyl acrylate, octyl acrylate, isononyl acrylate (iNA), and the like. In some other embodiments, an alkyl (meth)acrylate whose homopolymer Tg is higher than -20°C (for example, higher than -10°C) can be employed as at least a part of the monomer (A3). The upper limit of Tg of the alkyl (meth)acrylate is, for example, 10°C or less, may be 5°C or less, or may be 0°C or less. Alkyl (meth)acrylates with Tg in this range can help adjust the flexibility of the adhesive. Although not particularly limited, the alkyl (meth)acrylate having the above-mentioned Tg is preferably used in combination with the above-mentioned low-Tg alkyl (meth)acrylate. A specific example of the alkyl (meth)acrylate having the above Tg is lauryl acrylate (LA).

In some embodiments using monomer (A3), it is preferred to use C _4-8 alkyl (meth)acrylate as monomer (A3). Among them, it is more preferable to use C _4-8 alkyl acrylate. The C _4-8 alkyl (meth)acrylates can be used alone or in combination of two or more. The use of C _4-8 alkyl (meth)acrylate tends to make it easier to improve the flexibility of the adhesive and to provide good adhesive properties (adhesive strength, etc.). In the embodiment in which C _4-8 alkyl (meth)acrylate is used as the monomer (A3), the proportion of C _4-8 alkyl (meth)acrylate among the alkyl (meth)acrylates contained in the monomer component is 30% by weight or more. The content is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 90% by weight or more, and may be substantially 100% by weight.

In some embodiments using monomer (A3), C _1-6 alkyl (meth)acrylate can be used as monomer (A3). By using C _1-6 alkyl (meth)acrylate, the storage modulus in each temperature range can be adjusted. For example, it is possible to set the storage modulus in the high temperature region relatively high, or to suppress the difference in storage modulus between the low temperature region and the high temperature region from increasing. Furthermore, C _1-6 alkyl (meth)acrylate tends to have excellent copolymerizability with monomer (A1). One type of C _1-6 alkyl (meth)acrylate can be used alone or two or more types can be used in combination. The C _1-6 alkyl (meth)acrylate is preferably C _1-6 alkyl acrylate, more preferably C _2-6 alkyl acrylate, and even more preferably C _4-6 alkyl acrylate. In some other embodiments, the C _1-6 alkyl (meth)acrylate is preferably a C _1-4 alkyl (meth)acrylate, more preferably a C _2-4 alkyl (meth)acrylate, even more preferably is C _2-4 alkyl acrylate. A preferred example of C _1-6 alkyl (meth)acrylate is BA.

The content of C _1-6 alkyl (meth)acrylate in the monomer components constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, and 8% by weight. The above is fine. In some embodiments, the content of the C _1-6 alkyl (meth)acrylate may be 10% by weight or more, 15% by weight or more, 20% by weight or more, from the viewpoint of improving flexibility, adhesive strength, etc. It may be at least 25% by weight (for example, at least 30% by weight). The upper limit of the content of C _1-6 alkyl (meth)acrylate in the monomer component is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the content of the C _1-6 alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, and 17% by weight. It is more preferably less than 12% by weight, may be less than 7% by weight, may be less than 3% by weight, and may be less than 1% by weight. The technology disclosed herein can also be practiced in an embodiment in which C _1-6 alkyl (meth)acrylate is not substantially used.

In some other embodiments using monomer (A3), C _7-12 alkyl (meth)acrylate may be preferably used as monomer (A3). By using C _7-12 alkyl (meth)acrylates, the storage modulus can be advantageously reduced. One type of C _7-12 alkyl (meth)acrylate can be used alone or two or more types can be used in combination. As the C _7-12 alkyl (meth)acrylate, C _7-10 alkyl acrylate is preferred, C _7-9 alkyl acrylate is more preferred, and C ₈ alkyl acrylate is even more preferred. Examples of C _7-12 alkyl (meth)acrylates include 2EHA, iNA, and LA, and a preferred example includes 2EHA.

The content of C _7-12 alkyl (meth)acrylate in the monomer components constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, and 8% by weight. The above is fine. In some embodiments, the content of the C _7-12 alkyl (meth)acrylate may be 10% by weight or more, 15% by weight or more, 20% by weight or more, from the viewpoint of improving flexibility, adhesive strength, etc. It may be at least 25% by weight (for example, at least 30% by weight). The upper limit of the content of C _7-12 alkyl (meth)acrylate in the monomer component is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the content of the C _7-12 alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, and 17% by weight. It is more preferably less than 12% by weight, may be less than 7% by weight, may be less than 3% by weight, and may be less than 1% by weight. The technology disclosed herein can also be practiced in an embodiment that does not substantially use C _7-12 alkyl (meth)acrylate.

In some embodiments using monomer (A3), from the viewpoint of improving flexibility, it is preferable that at least a part of the monomer (A3) is an alkyl acrylate. The use of alkyl acrylates is also advantageous in terms of adhesive properties such as adhesive strength. For example, it is preferable that 50% by weight or more of the monomer (A3) is alkyl acrylate, and the proportion of alkyl acrylate in the monomer (A3) is more preferably 75% by weight or more, still more preferably 90% by weight or more, Substantially 100% by weight of monomer (A3) may be alkyl acrylate. An embodiment may be employed in which only one or more alkyl acrylates are used as the monomer (A3) and no alkyl methacrylate is used.

In the embodiment in which the monomer component contains an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so that the effect of its use is appropriately exhibited. In some embodiments, the content of the alkyl (meth)acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of monomer (A3) in the monomer component is set so that the total content of monomers (A1) and (A2) does not exceed 100% by weight, for example, less than 50% by weight, and 35% by weight. It may be less than %. In some embodiments, the content of the monomer (A3) may be, for example, 24% by weight or less. In general, the refractive index of alkyl (meth)acrylates is relatively low, so in order to increase the refractive index, the content of monomer (A3) in the monomer component should be limited, and the content of monomer (A1) should be relatively increased. It is advantageous to do so. From this point of view, the content of the monomer (A3) is suitably less than 23% by weight of the monomer components, preferably less than 20% by weight, more preferably less than 17% by weight, and 12% by weight. It may be less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be preferably implemented in an embodiment in which monomer (A3) is not substantially used.

(Other monomers)
The monomer components constituting the acrylic polymer may contain monomers other than the above monomers (A1), (A2), and (A3) (hereinafter referred to as "other monomers"), if necessary. The above-mentioned other monomers can be used, for example, for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. The above-mentioned other monomers can be used alone or in combination of two or more.

Examples of the above-mentioned other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive force and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, and the like. In addition, amide group-containing monomers ( For example, (meth)acrylamide, N-methylol (meth)acrylamide, etc.), amino group-containing monomers (such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), and nitrogen atom-containing rings. (for example, N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, etc. Can be mentioned. Note that among the monomers having a nitrogen atom-containing ring, some such as N-vinyl-2-pyrrolidone also fall under the category of amide group-containing monomers. The same applies to the relationship between the monomer having a nitrogen atom-containing ring and the amino group-containing monomer.

Other monomers that can be used other than the above functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; ethylene, Olefinic monomers such as butadiene and isobutylene; Chlorine-containing monomers such as vinyl chloride; Alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ethers such as methyl vinyl ether system monomer; etc. A suitable example of other monomers that can be used to improve the flexibility of the adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, homopolymer Tg: -67°C).

When using the above-mentioned other monomers, the amount used is not particularly limited, and can be appropriately set within a range where the total amount of the monomer components does not exceed 100% by weight. From the viewpoint of facilitating the effect of improving the refractive index by using the monomer (A1), the content of the above-mentioned other monomers in the monomer component can be, for example, about 35% by weight or less, and about 25% by weight or less (for example, 0% by weight or less). ~25% by weight), may be approximately 20% by weight or less (for example, 0 to 20% by weight), and advantageously approximately 10% by weight or less (for example, 0 to 10% by weight), Preferably it is about 5% by weight or less, for example about 1% by weight or less. The technique disclosed herein can be preferably carried out in an embodiment in which the monomer component does not substantially contain the other monomers mentioned above.

In some embodiments, the monomer components constituting the acrylic polymer may have a composition in which the amount of the methacryloyl group-containing monomer used is suppressed to a predetermined amount or less. The amount of the methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of the methacryloyl group-containing monomer used in this way can be advantageous from the viewpoint of realizing a pressure-sensitive adhesive that has a good balance of flexibility, adhesiveness, and high refractive index. The monomer component constituting the acrylic polymer may have a composition that does not contain a methacryloyl group-containing monomer (for example, a composition that consists only of an acryloyl group-containing monomer).

In some embodiments, the monomer component constituting the base polymer (e.g., acrylic polymer) of the adhesive has a limited amount of carboxy group-containing monomer from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the adhesive. has been done. The amount of the carboxy group-containing monomer used in the monomer component may be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, 0. It may be less than .05% by weight. This limitation on the amount of carboxy group-containing monomers is due to the fact that metal materials that may be placed in contact with or in close proximity to the adhesive disclosed herein (e.g., metal wiring that may be present on an adherend) This is also advantageous from the viewpoint of suppressing corrosion of metal films, etc.). The technique disclosed herein can be practiced in an embodiment in which the monomer component does not contain a carboxy group-containing monomer.
For the same reason, in some embodiments, the monomer component constituting the base polymer of the adhesive is a monomer having an acidic functional group (including a sulfonic acid group, a phosphoric acid group, etc. in addition to a carboxy group). The amount may be limited. As the amount of the acidic functional group-containing monomer used in the monomer component of this embodiment, the above-mentioned preferred amount of the carboxy group-containing monomer can be applied. The technology disclosed herein can be implemented in an embodiment in which the monomer component does not contain an acidic group-containing monomer (that is, an embodiment in which the base polymer of the adhesive is acid-free).

(Glass-transition temperature)
The monomer component constituting the base polymer (for example, acrylic polymer) of the adhesive preferably has a composition such that the glass transition temperature (Tg) based on the composition of the monomer component is approximately 15° C. or lower. In some embodiments, the Tg is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 1°C or lower, and may be 0°C or lower. In some other embodiments, the Tg may be -10°C or lower, -20°C or lower, -25°C or lower, -30°C or lower, or -35°C or lower. A low Tg can be advantageous from the viewpoint of improving the flexibility of the adhesive. Further, the above Tg may be, for example, -60°C or higher, and from the viewpoint of easily increasing the refractive index of the adhesive, it is preferably -50°C or higher, more preferably higher than -45°C, and -40°C. It may be super. In some embodiments, the Tg may be greater than -30°C, greater than -20°C, greater than -10°C, or greater than -5°C. An adhesive having both a high refractive index and large deformability can be preferably formed by using a base polymer having a composition having a Tg within the above range.

Here, the Tg based on the composition of the monomer components constituting the base polymer (for example, acrylic polymer) refers to the glass transition temperature determined by the Fox equation based on the composition of the monomer components, unless otherwise specified. The Fox equation, as shown below, is a relational equation between Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer.
1/Tg=Σ(Wi/Tgi)
In the above Fox equation, Tg is the glass transition temperature of the copolymer (unit: K), Wi is the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi is the homopolymer of monomer i. represents the glass transition temperature (unit: K) of
As the glass transition temperature of the homopolymer used to calculate Tg, the value described in publicly known materials such as "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) is used. For monomers for which multiple values are listed in the Polymer Handbook, the highest value is used. If the Tg of the homopolymer is not described in known materials, the value obtained by the measurement method described in JP-A No. 2007-51271 shall be used.

(Preparation method of base polymer)
In the technology disclosed herein, the method for obtaining the base polymer (for example, acrylic polymer) composed of such monomer components is not particularly limited, and may include solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. , photopolymerization, and other known polymerization methods can be appropriately employed. For example, a solution polymerization method can be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20°C to 170°C (typically 40°C to 140°C). ℃).

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds ; etc. Still another example of the polymerization initiator is a redox initiator using a combination of a peroxide and a reducing agent. One type of polymerization initiator can be used alone or two or more types can be used in combination. The amount of the polymerization initiator used may be any normal amount, for example, about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of the monomer component. ) can be selected from the range.

In the above polymerization, various conventionally known chain transfer agents can be used as necessary. For example, mercaptans such as n-dodecylmercaptan, t-dodecylmercaptan, thioglycolic acid, and α-thioglycerol can be used. Alternatively, a chain transfer agent that does not contain sulfur atoms (non-sulfur chain transfer agent) may be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; α-methylstyrene and α-methylstyrene dimer. styrenes; and the like. One type of chain transfer agent can be used alone or two or more types can be used in combination. When using a chain transfer agent, the amount used can be, for example, approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer component.

The weight average molecular weight (Mw) of the base polymer (for example, acrylic polymer) is not particularly limited, and is, for example, about 30 x 10 ⁴ or more, suitably about 50 x 10 ⁴ or more, and about 70 x 10 The number may be ⁴ or more, and may be approximately 80×10 ⁴ or more. By using a base polymer having Mw of a predetermined value or more, it is easy to obtain an appropriate cohesive force that can exhibit desired adhesive properties. Furthermore, it is possible to contain a larger amount of additives such as plasticizers, which tends to make it easier to achieve desired flexibility. Further, the upper limit of Mw of the base polymer is, for example, approximately 500×10 ⁴ or less, and from the viewpoint of adhesive performance, approximately 400×10 ⁴ or less (more preferably approximately 150×10 ⁴ or less, for example, approximately 130×10 ⁴ or less). ) is preferably within the range. In some embodiments, the Mw may be less than 100×10 ⁴ , 80×10 ⁴ or less, or 60×10 ⁴ or less. The effects of the technology disclosed herein can be preferably achieved in an embodiment using an acrylic polymer having Mw within the above range.

Here, the Mw of the polymer can be determined in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring device with the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation).
[GPC measurement conditions]
Sample concentration: 0.2% by weight (tetrahydrofuran solution)
Sample injection volume: 10μL
Eluent: Tetrahydrofuran (THF)
Flow rate (flow rate): 0.6 mL/min Column temperature (measurement temperature): 40°C
column:
Sample column: 1 product name “TSKguardcolumn SuperHZ-H” + 2 product name “TSKgel SuperHZM-H” (manufactured by Tosoh Corporation)
Reference column: 1 piece of product name “TSKgel SuperH-RC” (manufactured by Tosoh Corporation)
Detector: Differential refractometer (RI)
Standard sample: polystyrene

(Plasticizer)
In some embodiments, the adhesives described above (eg, acrylic adhesives) contain a plasticizer in addition to the base polymer. By using a plasticizer, the flexibility of the adhesive can be improved, and thus large deformability can be achieved. As the plasticizer, one or two or more plasticizers are selected from among the plasticizers described below, which can provide the adhesive with a refractive index of 1.55 or more and the above-mentioned 350% deformation property. used.

Preferred examples of the plasticizer disclosed herein include cyclic unsaturated organic compounds having two or more double bond-containing rings. In other words, the plasticizer as a preferred example is a compound having two or more double bond-containing rings in one molecule. Therefore, the plasticizer has at least a first double bond-containing ring and a second double bond-containing ring. By having two or more double bond-containing rings, it is possible to improve the flexibility of the adhesive and to achieve large deformability without impairing the refractive index of the adhesive or while maintaining the refractive index. The number of double bond-containing rings in the plasticizer is preferably 6 or less, may be 4 or less, or may be 3 or less, from the viewpoint of exhibiting a plasticizing effect.

Further, the plasticizer used in the technology disclosed herein is preferably a compound that is liquid at 30°C. Note that in this specification, "liquid" means exhibiting fluidity, and refers to a liquid state as a substance state. Such compounds include those having a melting point of 30°C or less. Since the above plasticizer is liquid at 30° C., the plasticizing effect is suitably exhibited, and the flexibility of the adhesive can be improved and, by extension, large deformability can be suitably realized. The plasticizer is preferably a compound that is liquid at 25°C, more preferably a compound that is liquid at 20°C. For example, by using a compound that is liquid at 30° C. and has two or more double bond-containing rings as a plasticizer, it is possible to preferably form an adhesive that has both a high refractive index and large deformability.

The molecular weight of the plasticizer is not particularly limited, but one having a molecular weight smaller than that of the base polymer (eg, acrylic polymer) is usually used. The molecular weight of the plasticizer is suitably 30,000 or less, advantageously 25,000 or less, and may be less than 10,000 (for example, less than 5,000), from the viewpoint of facilitating the expression of the plasticizing effect. It may be less than 3000. In some embodiments, the molecular weight of the plasticizer is preferably 2000 or less, more preferably 1200 or less, even more preferably 900 or less, may be 600 or less, may be 500 or less, may be 400 or less, and may be 300 or less. It may be less than or equal to 250 (for example, less than 220). It may be advantageous that the molecular weight of the plasticizer is not too large from the viewpoint of improving compatibility within the adhesive layer. In addition, the molecular weight of the plasticizer is suitably 100 or more, preferably 130 or more, more preferably 150 or more, and 170 or more, from the viewpoint of facilitating sufficient plasticizing effect. It may be 200 or more, 220 or more, or 250 or more. It is preferable that the molecular weight of the plasticizer is not too low from the viewpoint of the heat resistance performance of the adhesive and the suppression of contamination of the adherend. In some embodiments, the molecular weight of the plasticizer is, for example, 300 or more, suitably 315 or more, and may be 350 or more. Plasticizers with large molecular weights are difficult to vaporize, so by using plasticizers with large molecular weights in adhesives, it is easy to obtain adhesives that can exhibit stable characteristics. Furthermore, a plasticizer with a large molecular weight is difficult to move within the adhesive. Therefore, events that affect the adhesive properties, such as the movement of the plasticizer to the adhesive surface, are less likely to occur. The molecular weight of the plasticizer is more preferably 400 or more, still more preferably 450 or more, particularly preferably 500 or more, and may be 530 or more.
Note that, as the molecular weight of the plasticizer, the molecular weight calculated based on the chemical structure is used. If a nominal value of molecular weight is provided by a manufacturer, etc., that nominal value can be used.

Although not particularly limited, in some embodiments, as a plasticizer, the amount transferred to the gas phase at 130°C (130°C vaporized amount) is 10% or less (specifically 0 to 10% by weight) on a weight basis. ) may be used. By using a plasticizer that satisfies this property, the pressure-sensitive adhesive containing the plasticizer can suppress changes in properties caused by the plasticizer due to changes in temperature and humidity. For example, the adhesive can exhibit stable characteristics even when used in an environment exposed to high temperatures and high humidity or when used for a long period of time. The amount of plasticizer vaporized at 130°C may be less than 10% by weight, less than 5% by weight, less than 3% by weight, or less than 1% by weight.

The amount of plasticizer transferred to the gas phase at 130°C can be determined from the weight change before and after holding the plasticizer at 130°C for 1 hour. More specifically, it can be measured by the following method.
[Amount of plasticizer transferred to gas phase]
Approximately 1 g of plasticizer (measurement sample) is dropped into an aluminum cup and weighed to the nearest 0.01 mg using an electronic balance in an environment of 23° C. and 45% RH (W0g). Next, the cup containing the measurement sample is kept in an oven at 130° C. for 1 hour. Use an oven that has sufficient capacity for the sample to be measured and that can be heated while evacuating the sample. For example, an oven manufactured by espec can be used. After being held at 130° C. for 1 hour, the cup containing the measurement sample was taken out of the oven, returned to room temperature, and then weighed (W1 g). Substituting the weight W0 [g] of the measurement sample before heating in the oven and the weight W1 [g] of the measurement sample after heating in the oven into the formula: 1-W1/W0, the measurement sample at 130 ° C. Find the amount [%] transferred to the gas phase. The measurement is performed on three samples (n=3), and the average value is used.

Although not particularly limited, in some embodiments, the adhesive has a plasticizer weight loss of 5% or less (specifically (0 to 5% by weight). In a pressure-sensitive adhesive that satisfies this property, most of the plasticizer in the pressure-sensitive adhesive remains within the pressure-sensitive adhesive even when the pressure-sensitive adhesive is heated under predetermined conditions, and its effects (mainly the plasticizing effect) can be maintained. Therefore, the above-mentioned pressure-sensitive adhesive is suppressed from changing its properties due to the plasticizer, and can exhibit stable properties regardless of the environment in which it is used and even when used for a long period of time. The weight loss of the plasticizer in the adhesive after being held at 130°C for 1 hour is preferably less than 3% by weight, more preferably less than 1% by weight, even more preferably less than 0.5% by weight, and 0.3% by weight. It may be less than 0.1% by weight or less. The weight loss of the plasticizer in the adhesive after being held at 130°C for 1 hour can be determined from the change in weight of the plasticizer in the adhesive before and after being held in the 130°C environment for 1 hour.

The amount of plasticizer in the adhesive can be determined, for example, by liquid chromatography measurement. More specifically, it can be measured by the following method.
[Heating loss of plasticizer in adhesive]
The adhesive composition is applied to the silicone-treated surface of PET film R1, one side of which has been silicone-treated, and heated at 130° C. for 3 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of PET film R2, one side of which has been silicone-treated, is bonded to the surface of the adhesive layer. One of the release liners is peeled off from the obtained adhesive layer with a release liner (release liner/adhesive layer/release liner), and the mixture is kept in an oven at 130° C. for 1 hour. Use an oven that has sufficient capacity for the sample to be measured and that can be heated while evacuating the sample. For example, an oven manufactured by espec can be used. Liquid chromatography (LC) measurements are performed on the adhesive before and after heating in an oven under the following conditions. From the above LC results, the amount of plasticizer contained in the adhesive before and after heating was determined, and from the weight ratio, the weight loss [%] of the plasticizer in the adhesive after being kept in an environment of 130°C for 1 hour ] Find. The measurement is performed on three samples (n=3), and the average value is used. Note that, prior to the LC measurement of the adhesive, it is desirable to perform LC measurement of the plasticizer alone, create a calibration curve, and quantify the plasticizer in the adhesive based on this calibration curve.
[LC measurement conditions]
Approximately 0.01 g of the adhesive is collected, 2 mL of chloroform is added, and the mixture is shaken overnight. 8 mL of acetonitrile was added to this solution to reprecipitate the polymer component, and this supernatant was filtered with a 0.45 μm membrane filter. The obtained filtrate is diluted appropriately and injected into an analyzer (manufactured by Shimadzu Corporation, HPLC Prominence) for measurement.
Column: GL Sciences, Inertsil ODS-3 (4.6mmφ×250mm, 5μm)
Column temperature: 40℃
Column flow rate: 1.0mL/min
Eluent: Ultrapure water/acetonitrile gradient conditions Injection volume: 1 μL
Detector: DAD (190nm to 400nm, 272nm extraction)

In an embodiment in which a plasticizer having a double bond-containing ring is used, the double bond-containing ring of the plasticizer may be a conjugated double bond-containing ring (typically an aromatic ring), or a non-conjugated double bond-containing ring. It may be any ring containing a heavy bond. The plasticizer may have at least one type of ring selected from an aromatic ring and a heterocycle (heterocycle) as the double bond-containing ring. Note that the above-mentioned heterocycle may have a structure included in an aromatic ring, or may have a double bond-containing heterocyclic structure different from an aromatic ring. Examples of the double bond-containing ring (typically an aromatic ring) that the plasticizer may have include a benzene ring (which may be a benzene ring that forms part of a biphenyl structure or a fluorene structure); a naphthalene ring, and an indene ring. , an azulene ring, an anthracene ring, a fused ring of a phenanthrene ring; etc.; a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring; It may be a heterocyclic ring such as an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. The heteroatoms included as ring constituent atoms in the above-mentioned heterocycle may be, for example, one or more heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms making up the heterocycle can be one or both of nitrogen and sulfur. The plasticizer may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

The double bond-containing ring (typically an aromatic ring, preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. good. When having a substituent, the substituent includes an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group. Examples include, but are not limited to. In a substituent containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the double bond-containing ring has no substituents on the ring atoms, or has an alkyl group, an alkoxy group, an ethylenically unsaturated group (e.g. (meth)acryloxy group), a hydroxy group, and a hydroxy group. It may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups. As the substituent, an alkyl group, an alkoxy group, and a hydroxyalkyl group are preferably used.

In some embodiments, a compound having no ethylenically unsaturated group may be preferably employed as the plasticizer. Thereby, deterioration of the adhesive composition due to heat or light (decrease in leveling properties due to progress of gelation or increase in viscosity) can be suppressed, and storage stability can be improved. Adopting a plasticizer that does not have an ethylenically unsaturated group means that the pressure-sensitive adhesive containing the plasticizer may suffer from changes in elastic modulus, dimensional changes, or deformations (warping, waving, etc.) due to reactions of the ethylenically unsaturated group. , is also preferable from the viewpoint of suppressing the occurrence of optical distortion.

As the plasticizer, a high refractive index plasticizer having a refractive index of about 1.50 or more can be preferably used. By using a high refractive index plasticizer, it is easy to achieve both a high refractive index and large deformability. The refractive index of the plasticizer is preferably about 1.51 or more, more preferably about 1.53 or more, and still more preferably about 1.55, from the viewpoint of maintaining and improving the refractive index of the adhesive while obtaining flexibility. or more, and may be approximately 1.56 or more, approximately 1.58 or more, approximately 1.60 or more, or approximately 1.62 or more. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and compatibility within the adhesive, the refractive index of the plasticizer is suitably 2.50 or less, and 2.00 or less. Advantageously, it may be 1.90 or less, 1.80 or less, or 1.70 or less.
Note that, like the refractive index of the monomer, the refractive index of the plasticizer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. If a manufacturer or the like provides a nominal value of the refractive index at 25° C., that nominal value can be used.

In some embodiments, the plasticizer is a compound having a structure in which two or more non-fused double bond-containing rings (typically aromatic rings) are bonded via a linking group; Compounds with a structure in which rings (typically aromatic rings) are chemically bonded directly (i.e., without intervening other atoms), compounds with a fused double bond-containing ring structure (typically aromatic rings), fluorene One or more types selected from compounds having a structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, etc. may be used.

In some preferred embodiments, a compound A having a structure in which two or more non-fused double bond-containing rings are bonded via a linking group is used as the plasticizer. The above-mentioned linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (for example, a -O-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1). , thiooxyalkylene groups (e.g. -S-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1), linear alkylene groups (i.e. -(CH ₂ ) _n - group, where n is 1 to 6, preferably 1 to 3), the alkylene group in the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be partially halogenated or completely halogenated. The linking group may have an ester bond. In the plasticizer, the linking group that connects the first double bond-containing ring (non-fused ring) and the second double bond-containing ring (non-fused ring) may also be selected from the same types as mentioned above. From the viewpoint of large deformability of the adhesive, preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. The number of atoms in the linking group is not particularly limited, and in some embodiments is, for example, 1 to 30, may be 1 to 25, may be 1 to 20, and is suitably 1 to 18. The number is preferably 1 to 12, more preferably 1 to 10, even more preferably 1 to 8, particularly preferably 1 to 5, may be 1 to 3, or may be 1 or 2. In some other preferred embodiments, the number of atoms in the linking group is, for example, 10 or more, preferably 15 or more, more preferably 20 or more, and still more preferably 22 or more (for example, 25 or more, or 30 or more). ). Further, the upper limit of the number of atoms in the linking group is, for example, 50 or less, preferably 40 or less, and may be 35 or less. In the embodiment in which a plasticizer having an oxyalkylene group is used as the linking group, the number of atoms in the linking group is preferably applied. Note that the number of atoms in the linking group refers to the minimum number of atoms required to reach from one non-fused double bond-containing ring to the other non-fused double bond-containing ring. For example, when the linking group consists of a straight chain alkylene group (ie, -(CH ₂ ) _n - group), the number of n is the number of atoms in the linking group. For example, when the linking group is an oxyethylene group (that is, -(C ₂ H ₄ O) _n - group), 3 and n, which is the sum of 2 carbon atoms and 1 oxygen atom, which constitute the oxyethylene group. The product (3n) is the number of atoms in the linking group. Preferred examples of the above compounds include compounds having a phenoxybenzyl group. Examples of the above compounds include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), phenoxybenzyl alcohol, oxybis[(alkoxyalkyl)benzene] (e.g., 4,4'-oxybis[(methoxy) methyl)benzene]), polyethylene glycol benzoate, and the like.

In an embodiment in which Compound A having a structure in which two or more non-fused double bond-containing rings are bonded via a linking group is used as a plasticizer, the amount of Compound A used is not particularly limited, and the amount disclosed herein is not limited. The pressure sensitive adhesive is designed to achieve the desired adhesive properties and effectiveness. From the viewpoint of large deformability, in some preferred embodiments, the amount of the compound A used per 100 parts by weight of the base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, still more preferably 40 parts by weight or more. The amount is particularly preferably at least 45 parts by weight, and even more preferably at least 50 parts by weight, may be at least 55 parts by weight, and may be at least 60 parts by weight. In addition, from the viewpoint of achieving both a high refractive index and large deformability of the adhesive in a well-balanced manner, it is appropriate that the amount of the compound A used is approximately 200 parts by weight or less, and 150 parts by weight or less, based on 100 parts by weight of the base polymer. It is preferably at most 120 parts by weight, more preferably at most 120 parts by weight, may be at most 100 parts by weight, may be at most 80 parts by weight, and may be at most 70 parts by weight.

Further, in an embodiment in which Compound A having a structure in which two or more non-fused double bond-containing rings are bonded via a linking group is used as a plasticizer, the adhesive may be one of the plasticizers other than Compound A or Two or more types may be optionally included or may not be included. Plasticizers other than the above-mentioned compound A can be used in appropriate amounts as long as they do not impair the effects of the technology disclosed herein. In such embodiments, the amount of plasticizers other than Compound A used is suitably less than 50% by weight of the total plasticizers used in the adhesive, preferably less than 30% by weight, more preferably 10% by weight. less than 3% by weight, particularly preferably less than 1% by weight. The technique disclosed herein can be preferably carried out using an adhesive that does not substantially contain any plasticizer other than the compound A described above.

In some preferred embodiments, an ethylene glycol compound having two or more double bond-containing rings in one molecule can be used as the plasticizer. The number of oxyethylene units (i.e. -(C ₂ H ₄ O) - units) possessed by the above-mentioned ethylene glycol compound is, for example, 1 or more, suitably 2 or more, preferably 3 or more, more preferably 4 or more. (for example, 5 or more). Further, the upper limit of the number of oxyethylene units is, for example, 10 or less, may be 8 or less, or may be 6 or less. The ethylene glycol compound may be a compound having a structure in which two or more non-fused double bond-containing rings are bonded via the oxyethylene unit as a linking group. Such compounds may have one or more ester groups. Examples of the ethylene glycol compounds include compounds having a structure in which two or more benzoic acids are linked to triethylene glycol or polyethylene glycol via an ester bond.

In an embodiment in which an ethylene glycol compound having two or more double bond-containing rings in one molecule is used as a plasticizer, the amount of the ethylene glycol compound used is not particularly limited, and the adhesive disclosed herein Set to achieve properties and effects. From the viewpoint of large deformability, in some preferred embodiments, the amount of the ethylene glycol compound used per 100 parts by weight of the base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, still more preferably 40 parts by weight. Parts by weight or more, particularly preferably 45 parts by weight or more, even more preferably 50 parts by weight or more, may be 55 parts by weight or more, and may be 60 parts by weight or more. In addition, from the viewpoint of achieving both high refractive index and large deformability of the adhesive in a well-balanced manner, it is appropriate that the amount of the ethylene glycol compound used is approximately 200 parts by weight or less per 100 parts by weight of the base polymer. , is preferably 150 parts by weight or less, more preferably 120 parts by weight or less, may be 100 parts by weight or less, may be 80 parts by weight or less, and may be 70 parts by weight or less.

In addition, in an embodiment in which an ethylene glycol compound having two or more double bond-containing rings in one molecule is used as a plasticizer, the adhesive may contain one or more plasticizers other than the above-mentioned ethylene glycol compound. may or may not be included arbitrarily. Plasticizers other than the above-mentioned ethylene glycol compounds can be used in appropriate amounts as long as they do not impair the effects of the technology disclosed herein. In such an embodiment, the amount of plasticizers other than the ethylene glycol compound used is suitably less than 50% by weight, preferably less than 30% by weight, more preferably less than 10% by weight of the total plasticizers used in the adhesive. It is less than 1% by weight, more preferably less than 3% by weight, particularly preferably less than 1% by weight. The technology disclosed herein can be preferably carried out using an adhesive that does not substantially contain any plasticizer other than the ethylene glycol-based compound.

In some other embodiments, liquid rosins such as liquid rosin esters, liquid camphenphenol can be used as plasticizers. The liquid rosin (for example, liquid rosin ester) may correspond to the compound having the fused double bond-containing ring structure.

Furthermore, as a plasticizer, one or more of known plasticizers (for example, phthalate esters, terephthalate esters, adipic esters, adipic acid polyesters, benzoic acid glycol esters, etc.) may be used. Good too.

The amount of plasticizer used is not particularly limited and can be set depending on the purpose. From the viewpoint of large deformability, in some preferred embodiments, the amount of plasticizer used per 100 parts by weight of the base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, even more preferably 40 parts by weight or more, It is particularly preferably at least 45 parts by weight, and even more preferably at least 50 parts by weight, may be at least 55 parts by weight, and may be at least 60 parts by weight. In addition, from the viewpoint of achieving both a high refractive index and large deformability of the adhesive in a well-balanced manner, it is appropriate that the amount of plasticizer used per 100 parts by weight of the base polymer is approximately 200 parts by weight or less, and 150 parts by weight. It is preferably at most 120 parts by weight, more preferably at most 120 parts by weight, it may be at most 100 parts by weight, it may be at most 80 parts by weight, and it may be at most 70 parts by weight. In some embodiments where more emphasis is placed on adhesive properties, the amount of plasticizer used per 100 parts by weight of the base polymer may be 45 parts by weight or less, or 35 parts by weight or less.

(Additive ( _HRO ))
The adhesive disclosed herein may contain an organic material having a higher refractive index than the base polymer (eg, acrylic polymer) as an additive, if desired. Hereinafter, such organic materials may be referred to as "additives (H _RO )." Here, the above "H _RO " represents an organic material with a high refractive index. By using the additive (H _RO ), it is possible to realize a pressure-sensitive adhesive that has a better balance between refractive index and adhesive properties (peel strength, flexibility, etc.). The organic material used as the additive (H _RO ) may be polymeric or non-polymeric. Further, it may or may not have a polymerizable functional group. Note that in this specification, the additive (H _RO ) is defined as a compound different from the compound used as the plasticizer described above. For example, the additive (H _RO ) may be non-liquid at 30°C (eg 25°C or 20°C). The additive (H _RO ) can be used singly or in combination of two or more.

The refractive index of the additive (H _RO ) can be set within an appropriate range in relation to the refractive index of the base polymer (eg, acrylic polymer), and is therefore not limited to a specific range. The refractive index of the additive (H _RO ) can be selected, for example, from a range of greater than 1.55, greater than 1.56 or greater than 1.57 and higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, the refractive index of the additive (H _RO ) is advantageously 1.58 or more, preferably 1.60 or more, It is more preferably 1.63 or more, may be 1.65 or more, may be 1.70 or more, or may be 1.75 or more. With higher refractive index additives (H _RO ), the desired refractive index can also be achieved using smaller amounts of additive (H _RO ). This is preferable from the viewpoint of suppressing deterioration of adhesive properties and optical properties. The upper limit of the refractive index of the additive (H _RO ) is not particularly limited, but from the viewpoint of compatibility within the adhesive and the ease of achieving both a high refractive index and flexibility suitable for the adhesive, for example, 3. 000 or less, may be 2.500 or less, may be 2.000 or less, may be 1.950 or less, may be 1.900 or less, may be 1.850 or less.
Note that, like the refractive index of the monomer, the refractive index of the additive (H _RO ) is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. If a manufacturer or the like provides a nominal value of the refractive index at 25° C., that nominal value can be used.

The molecular weight of the organic material used as the additive (H _RO ) is not particularly limited and can be selected depending on the purpose. In some embodiments, the molecular weight of the additive (H _RO is suitably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (for example, less than 1,000), may be less than 800, may be less than 600, may be less than 500, It may be less than 400. It may be advantageous that the molecular weight of the additive (H _RO ) is not too large from the viewpoint of improving compatibility within the adhesive. Further, the molecular weight of the additive (H _RO ) may be, for example, 130 or more, or 150 or more. In some embodiments, the molecular weight of the additive (H _RO ) is preferably 170 or more, more preferably 200 or more, and 230 or more, from the viewpoint of increasing the refractive index of the additive (H _RO ). It may be more than 250, it may be more than 270, it may be more than 300, it may be more than 500, it may be more than 1000, it may be more than 2000. In some embodiments, a polymer having a molecular weight of about 1,000 to 10,000 (eg, 1,000 or more and less than 5,000) can be used as the additive (H _RO ).
As for the molecular weight of the additive (H _RO ), for non-polymers or polymers with a low degree of polymerization (e.g. dimer to pentamer), the molecular weight calculated based on the chemical structure, or matrix-assisted laser desorption ionization. Measured values using time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. When the additive (H _RO ) is a polymer with a higher degree of polymerization, the weight average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. If a nominal value of molecular weight is provided by a manufacturer, etc., that nominal value can be used.

Examples of organic materials that can be selected as additives (H _RO ) include organic compounds having an aromatic ring, organic compounds having a heterocycle (either an aromatic ring or a non-aromatic heterocycle), etc. Including, but not limited to:

The aromatic ring possessed by the above-mentioned organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the additive (H _RO ) is similar to the aromatic ring possessed by the compound used as the monomer (A1). can be selected from.

The aromatic ring may have one or more substituents on the ring-constituting atoms, or may have no substituents. When having a substituent, the substituent includes an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group. Examples include, but are not limited to. In a substituent containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3. and can be, for example, 1 or 2. In some embodiments, the aromatic ring has no substituent on the ring constituent atoms, or one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (e.g., a bromine atom). It can be an aromatic ring having

Examples of aromatic ring-containing compounds that can be used as additives (H _RO ) include: compounds that can be used as monomers (A1); oligomers containing compounds that can be used as monomers (A1) as monomer units; monomers (A1 ), excluding a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a portion of the group constituting an ethylenically unsaturated group, a hydrogen atom or Compounds with a structure in which an ethylenically unsaturated group is replaced with a group that does not have an ethylenically unsaturated group (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc.); Examples include, but are not limited to, those that do not fall under the plasticizers disclosed herein.

In some embodiments, the additive (H _RO ) is an organic compound having two or more aromatic rings in one molecule (hereinafter referred to as "compound containing multiple aromatic rings") because it is easy to obtain a high refractive index effect. ) can be preferably adopted. The compound containing multiple aromatic rings may or may not have a polymerizable functional group such as an ethylenically unsaturated group. Further, the compound containing multiple aromatic rings may be a polymer or a non-polymer. Further, the above polymer is an oligomer (preferably an oligomer with a molecular weight of about 5000 or less, more preferably about 1000 or less; for example, a low polymer of about 2 to 5 molecules) containing a monomer containing multiple aromatic rings as a monomer unit. obtain. The above oligomers are, for example: homopolymers of monomers containing a plurality of aromatic rings; copolymers of two or more monomers containing a plurality of aromatic rings; copolymers of one or more monomers containing a plurality of aromatic rings with other monomers. It can be a combination; etc. The above-mentioned other monomers may be aromatic ring-containing monomers that do not correspond to monomers containing multiple aromatic rings, may be monomers having no aromatic rings, or may be a combination thereof. In embodiments in which oligomers are used as additives (H _RO ), the oligomers can be obtained by polymerizing the corresponding monomer components by known methods.

Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-fused aromatic rings are bonded via a linking group, and compounds in which two or more non-fused aromatic rings are bonded directly (i.e., bonding to other atoms). Examples include a compound having a chemically bonded structure (without intervening), a compound having a fused aromatic ring structure, a compound having a fluorene structure, a compound having a dinaphthothiophene structure, a compound having a dibenzothiophene structure, and the like. The compound containing multiple aromatic rings can be used alone or in combination of two or more.

Examples of organic compounds having a heterocycle (hereinafter also referred to as heterocycle-containing organic compounds) that can be options for the additive (H _RO ) include thioepoxy compounds, compounds having a triazine ring, and the like. Examples of thioepoxy compounds include bis(2,3-epithiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent No. 3712653. Examples of compounds having a triazine ring include compounds having at least one (eg, 3 to 40, preferably 5 to 20) triazine rings in one molecule. In addition, since the triazine ring has aromaticity, compounds having a triazine ring are also included in the above concept of aromatic ring-containing compounds, and compounds having multiple triazine rings are also included in the above concept of compounds containing multiple aromatic rings. be done.

In some embodiments, a compound having no ethylenically unsaturated group can be preferably employed as the additive (H _RO ). Thereby, deterioration of the adhesive composition due to heat or light (decrease in leveling properties due to progress of gelation or increase in viscosity) can be suppressed, and storage stability can be improved. Adopting an additive (H _RO ) that does not have an ethylenically unsaturated group means that the adhesive containing the additive (H _RO ) is free from dimensional changes and deformations (warping, warping, etc.) caused by reactions of the ethylenically unsaturated group. It is also preferable from the viewpoint of suppressing the occurrence of optical distortion (waving, etc.) and optical distortion.

The additive (H _RO ) may be used in an appropriate amount as long as the effects of the technology disclosed herein are not significantly impaired. In some embodiments, the amount of the additive (H _RO ) used (if multiple types of compounds are used, the total amount thereof) based on 100 parts by weight of the base polymer (e.g., acrylic polymer) may be greater than 0 parts by weight. It is not particularly limited, and can be set depending on the purpose. In some embodiments, the amount of the additive (H _RO ) used per 100 parts by weight of the base polymer can be, for example, 80 parts by weight or less, increasing the refractive index of the adhesive and suppressing deterioration of adhesive properties and optical properties. From the viewpoint of achieving both in a well-balanced manner, it is advantageous to set the amount to 60 parts by weight or less, and preferably to set it to 45 parts by weight or less. In some embodiments where more emphasis is placed on adhesive properties and optical properties, the amount of the additive (H _RO ) used relative to 100 parts by weight of the base polymer may be, for example, 30 parts by weight or less, 10 parts by weight or less, 3 The amount may be less than 1 part by weight, or less than 1 part by weight. The technology disclosed herein can be preferably implemented in an embodiment using an adhesive that does not contain an additive (H _RO ). In addition, from the viewpoint of increasing the refractive index of the adhesive, the amount of the additive (H _RO ) to be used with respect to 100 parts by weight of the base polymer can be, for example, 1 part by weight or more, and preferably 3 parts by weight or more. The amount is preferably 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, and 20 parts by weight or more.

(Crosslinking agent)
In the technology disclosed herein, the adhesive composition used to form the adhesive may contain a crosslinking agent, if necessary, for the purpose of adjusting the cohesive force of the adhesive. As the crosslinking agent, use a crosslinking agent known in the adhesive field, such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, an oxazoline crosslinking agent, a melamine resin, a metal chelate crosslinking agent, etc. I can do it. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents can be preferably employed. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, ie, polyfunctional monomers. One type of crosslinking agent can be used alone or two or more types can be used in combination.

As the isocyanate crosslinking agent, a bifunctional or higher-functional isocyanate compound can be used, such as aliphatic polystyrene such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), dimer acid diisocyanate, etc. Isocyanates; Alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cyclohexane; 2,4-tolylene diisocyanate, 4,4'- Aromatic isocyanates such as diphenylmethane diisocyanate and xylylene diisocyanate (XDI); the above isocyanate compounds are modified with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc. Examples include modified polyisocyanates (eg, isocyanurate of HDI, allophanate of HDI, etc.). Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N, Takenate D178NL (all manufactured by Mitsui Chemicals), Sumidur T80, Sumidur L, Desmodur N3400 (all manufactured by Mitsui Chemicals). (manufactured by Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (manufactured by Tosoh Corporation), and Duranate A201H (trade name, manufactured by Asahi Kasei Corporation). The isocyanate compounds can be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or more functional isocyanate compound may be used together.

Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, and trimethylol. Propane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. can be mentioned. These can be used alone or in combination of two or more.

Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecane Diol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate , polyester acrylate, urethane acrylate, butyldiol (meth)acrylate, hexyldiol di(meth)acrylate, and the like. One type of polyfunctional monomer can be used alone or two or more types can be used in combination.

In some embodiments, at least a portion of the crosslinking agent is a bifunctional crosslinking agent having two crosslinking reactive groups (eg, isocyanate groups) per molecule. By using a bifunctional crosslinking agent, a flexible crosslinked structure can be easily formed. One type of bifunctional crosslinking agent can be used alone or two or more types can be used in combination. Moreover, a bifunctional crosslinking agent may be used in combination with a trifunctional or more functional crosslinking agent.

In some embodiments, as the crosslinking agent, 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. For example, among the above-mentioned isocyanate-based crosslinking agents, it is preferable to use isocyanate-based compounds that do not have a ring structure such as an aromatic ring or an isocyanurate ring. By using an acyclic isocyanate compound as a crosslinking agent, a highly flexible crosslinking agent can be easily formed. Specific examples of the acyclic isocyanates include aliphatic isocyanate compounds (e.g., PDI and HDI) and modified aliphatic isocyanate compounds (e.g., allophanate bonds, biuret bonds, urea bonds, and carbodiimide bonds of PDI and HDI). modified polyisocyanates). One type of acyclic crosslinking agent can be used alone or two or more types can be used in combination. In some preferred embodiments, an acyclic bifunctional crosslinking agent may be used as the crosslinking agent.

In some embodiments, a crosslinking agent may be used in which the distance between one crosslinking reactive group (eg, an isocyanate group) and another crosslinking reactive group in one molecule is relatively long. As a result, a flexible crosslinked structure having a length longer than a predetermined length is formed. For example, a compound in which the number of atoms constituting a linking chain connecting one crosslinking reactive group and another crosslinking reactive group in one molecule of the crosslinking agent is 10 or more (for example, 12 or more or 14 or more) is used as a crosslinking agent. It can be used as The upper limit of the number of atoms constituting the connecting chain is not particularly limited as it can be prepared by polymerization etc. depending on the purpose, and is, for example, 2000 or less, may be 1000 or less, may be 500 or less, may be 100 or less, It may be 50 or less, 30 or less, or 20 or less. In addition, the number of atoms constituting a linking chain connecting the above-mentioned crosslinking-reactive groups refers to the number of atoms constituting a linking chain that connects the above-mentioned crosslinking-reactive groups, from one cross-linking-reactive group to another cross-linking-reactive group (if it has three or more cross-linking-reactive groups, the number of The minimum number of atoms required to reach the crosslinking-reactive group (the closest cross-linking-reactive group). The above-mentioned crosslinking agents having a connecting chain can be used alone or in combination of two or more. In some preferred embodiments, an acyclic bifunctional crosslinking agent may be used as the crosslinking agent. Examples of commercially available crosslinking agents include Coronate 2770 (manufactured by Tosoh Corporation), Takenate D178NL (manufactured by Mitsui Chemicals), Duranate A201H (manufactured by Asahi Kasei Corporation), and the like.

When using a crosslinking agent, the amount used is not particularly limited, and may range, for example, from about 0.001 parts by weight to 5.0 parts by weight based on 100 parts by weight of the base polymer. From the viewpoint of improving the flexibility of the adhesive and the adhesion to the adherend, in some embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less. The amount may be 0 parts by weight or less, 1.0 parts by weight or less, or 0.5 parts by weight or less. In some preferred embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer is less than 0.5 parts by weight, may be less than 0.4 parts by weight, may be less than 0.3 parts by weight, It may be 0.2 part by weight or less. Further, from the viewpoint of appropriately exhibiting the effect of using the crosslinking agent, in some embodiments, the amount of the crosslinking agent used relative to 100 parts by weight of the base polymer may be, for example, 0.005 parts by weight or more, and 0.01 parts by weight. part or more, 0.05 part by weight or more, 0.08 part by weight or more, or 0.1 part by weight or more. In some preferred embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer is greater than 0.1 parts by weight, may be greater than or equal to 0.2 parts by weight, may be greater than or equal to 0.3 parts by weight, and may be greater than or equal to 0.4 parts by weight. It may be more than part by weight. According to the technology disclosed herein, by using an appropriate amount of the crosslinking agent within the above range, it is possible to preferably form an adhesive that can withstand large deformations.

A crosslinking catalyst may be used to advance the crosslinking reaction more effectively. Examples of the crosslinking catalyst include metal crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, zirconium tetraacetylacetonate, ferric nathem, butyltin oxide, dioctyltin dilaurate, and the like. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of crosslinking catalyst used is not particularly limited. The amount of crosslinking catalyst to be used with respect to 100 parts by weight of the base polymer is, for example, in the range of approximately 0.0001 part by weight or more and 1 part by weight or less, taking into consideration the balance between the speed of the crosslinking reaction and the length of the pot life of the adhesive composition. It is preferably in the range of 0.001 part by weight or more and 0.5 part by weight or less.

The adhesive composition may contain a compound that causes keto-enol tautomerism as a crosslinking retarder. Thereby, the effect of extending the pot life of the adhesive composition can be realized. For example, in a pressure-sensitive adhesive composition containing an isocyanate-based crosslinking agent, a compound that causes keto-enol tautomerism can be preferably used. Various β-dicarbonyl compounds can be used as the compound that causes keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably employed. Compounds that cause keto-enol tautomerism can be used singly or in combination of two or more. The amount of the compound that causes keto-enol tautomerism can be, for example, 0.1 parts by weight or more and 20 parts by weight or less, and 0.5 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the base polymer. Alternatively, the content may be 1 part by weight or more and 5 parts by weight or less.

(Tackifier)
The adhesive disclosed herein may contain a tackifier. Examples of tackifiers include rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomers. Known tackifier resins such as tackifier resins can be used. These 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 so that appropriate adhesive performance is exhibited depending on the purpose and use. In some embodiments, from the viewpoint of refractive index and transparency, the amount of tackifier used per 100 parts by weight of the base polymer is appropriately 30 parts by weight or less, preferably 10 parts by weight or less. , more preferably 5 parts by weight or less. The technology disclosed herein can be preferably practiced without using a tackifier.

(High refractive index particles)
The adhesive disclosed herein can contain high refractive index particles as an optional component. Here, high refractive index particles mean particles that can increase the refractive index of the adhesive by being included in the adhesive. Hereinafter, high refractive index particles may be referred to as "particles P _HRI ." HRI means high refractive index. The type of particle P _HRI is not particularly limited, and one or more materials that can improve the refractive index of the adhesive are selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. can be selected and used. As the particles P _HRI , those that can improve the refractive index of the adhesive from among inorganic oxides (for example, metal oxides) can be preferably used. Suitable examples of materials constituting the particles P _HRI include titania (titanium oxide, TiO ₂ ), zirconia (zirconium oxide, ZrO ₂ ), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide ( Examples include inorganic oxides (specifically metal oxides) such as Nb ₂ O ₅ etc.). Particles made of these inorganic oxides (for example, metal oxides) can be used singly or in combination of two or more. The average particle size (meaning the 50% volume average particle size based on laser scattering/diffraction method) of the particles P _HRI is not particularly limited, and can be selected, for example, from the range of approximately 1 nm or more and 1000 nm or less.

The content of particle P _HRI in the adhesive may be adjusted to an appropriate amount within a range that does not impair the effects of the technology disclosed herein. Further, the content of the particles P _HRI may vary depending on the desired refractive index. For example, the content of the particles P _HRI can be appropriately set in consideration of required adhesive properties and the like so as to provide a refractive index of a predetermined value or higher. In some embodiments, the content of particulate P _HRI in the adhesive is, for example, less than 10%, may be less than 1%, and may be less than 0.1% by weight in the adhesive. The techniques disclosed herein can be practiced in such a manner that the adhesive is substantially free of particle P _HRI .

(Leveling agent)
In some embodiments, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer includes improvements in the appearance of the pressure-sensitive adhesive layer formed from the composition (e.g., improved thickness uniformity), and A leveling agent can be included as necessary for the purpose of improving coating properties. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, silicone leveling agents, and the like. For example, an appropriate leveling agent can be selected from commercially available leveling agents and used in a conventional manner.

(Other additives)
In the technology disclosed herein, the adhesive composition used to form the adhesive contains softeners, colorants (dyes, pigments, etc.), fillers, and antistatic agents to the extent that the effects of the present invention are not significantly impaired. If necessary, the adhesive composition may contain known additives that can be used in pressure-sensitive adhesive compositions, such as additives, antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives. Regarding such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed explanations will be omitted.

Although not particularly limited, the effects of the technology disclosed herein can be preferably achieved by using an adhesive containing the above-mentioned base polymer (typically an acrylic polymer) and a plasticizer. The technique disclosed herein can be preferably implemented in an embodiment using an adhesive mainly composed of the above base polymer and the above plasticizer. Therefore, in some preferred embodiments, a composition may be employed in which the content of components (other components) other than the base polymer and the plasticizer is limited. For example, the total amount of the base polymer and the plasticizer in the adhesive can be 75% by weight or more (for example, 75% by weight or more and 100% by weight or less, or less than 100% by weight), and 85% by weight or more. The content may be 90% by weight or more, 95% by weight or more, 98% by weight or more, or 99% by weight or more (for example, more than 99% by weight). Limiting the use of components other than the base polymer and the plasticizer can be advantageous in achieving large deformability of the adhesive.

(Formation of adhesive (layer))
The adhesive disclosed herein can be formed using an adhesive composition. The form of the pressure-sensitive adhesive composition to be used is not particularly limited, and examples thereof include a solvent-based pressure-sensitive adhesive composition containing a pressure-sensitive adhesive forming component in an organic solvent, and a pressure-sensitive adhesive composition that is cured by active energy rays such as ultraviolet rays and radiation. An active energy ray-curable adhesive composition prepared to form an active energy ray-curable adhesive composition, a water-dispersed adhesive composition in which an adhesive-forming component is dispersed in water, and a water-dispersed adhesive composition that is applied in a heated molten state and becomes sticky when cooled to around room temperature. It can be in various forms, such as a hot-melt adhesive composition forming an adhesive. The adhesive is an adhesive obtained by curing a solvent-based, active energy ray-curable, water-dispersed, hot-melt, or other adhesive composition by drying, crosslinking, polymerization, cooling, etc., that is, the above-mentioned adhesive. It may be a cured product of the composition. Only one type of curing means (for example, drying, crosslinking, polymerization, cooling, etc.) for the adhesive composition may be applied, or two or more types may be applied simultaneously or in multiple stages. For solvent-based adhesive compositions, the composition can typically be dried (and preferably further crosslinked) to form the adhesive. In active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating active energy rays to advance a polymerization reaction and/or a crosslinking reaction. When it is necessary to dry the active energy ray-curable pressure-sensitive adhesive composition, it is preferable to irradiate it with active energy rays after drying. Although not particularly limited, the adhesive disclosed herein can be preferably formed using a solvent-based adhesive composition. In embodiments including a solvent-based adhesive layer formed from a solvent-based adhesive composition, both high refractive index and large deformability can be preferably achieved.

The adhesive layer can be formed by applying (for example, coating) an adhesive composition to a suitable surface and then curing the composition. The adhesive composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, and a spray coater.

The thickness of the adhesive (specifically, the thickness of the adhesive film (adhesive film), for example, the thickness of the adhesive layer constituting the adhesive sheet) is not particularly limited, and should be, for example, 3 μm or more. Can be done. In some embodiments, the thickness of the adhesive (layer) is, for example, suitably 5 μm or more, may be 10 μm or more, may be 15 μm or more, may be 20 μm or more, may be 30 μm or more, It may be 50 μm or more, 70 μm or more, or 85 μm or more. Adhesive strength tends to increase as the thickness of the adhesive (layer) increases. Further, in some embodiments, the thickness of the adhesive (layer) may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 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, even more preferably 70 μm or less, may be 50 μm or less, or may be 30 μm or less. It can be advantageous that the thickness of the adhesive (layer) is not too large from the viewpoint of making the adhesive sheet thinner. Moreover, a thin adhesive (layer) tends to have excellent followability to an adherend. The technology disclosed herein can be preferably carried out, for example, in an embodiment in which the thickness of the adhesive (layer) is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm, even more preferably 5 μm to 75 μm). In addition, in the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first and second surfaces of the base material, the thickness of the pressure-sensitive adhesive (layer) described above is at least the thickness of the first pressure-sensitive adhesive layer. Can be applied to thickness. The thickness of the second adhesive layer may also be selected from a similar range. Further, in the case of a base material-less adhesive sheet, the thickness of the adhesive sheet matches the thickness of the adhesive layer.

<Adhesive sheet>
This specification provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer. The adhesive constituting the adhesive layer is as described above, and may be an adhesive formed from the above-mentioned adhesive composition (for example, a cured product of the adhesive composition).
The adhesive sheet may be a base-attached adhesive sheet having the adhesive layer on one or both sides of a non-peelable base material (supporting base material), and the adhesive layer is held by a release liner. A pressure-sensitive adhesive sheet without a base material (that is, a pressure-sensitive adhesive sheet without a non-peelable base material; typically a pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer) may be used. The concept of adhesive sheet here may include what is called an adhesive tape, an adhesive label, an adhesive film, and the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be further processed into various shapes.

A configuration example of a double-sided adhesive type base material-less adhesive sheet (substrate-less double-sided adhesive sheet) is shown in FIGS. 1 and 2. The adhesive sheet 1 shown in FIG. 1 has a structure in which both surfaces 21A and 21B of the adhesive layer 21 without a base material are protected by release liners 31 and 32, respectively, with at least the adhesive layer side serving as a release surface. The adhesive sheet 2 shown in FIG. 2 has a structure in which one surface (adhesive surface) 21A of the adhesive layer 21 without a base material is protected by a release liner 31 whose both surfaces are release surfaces. When wound, the other surface (adhesive surface) 21B of the adhesive layer 21 comes into contact with the back surface of the release liner 31, so that the other surface 21B can also be protected by the release liner 31. The technique disclosed herein is preferably implemented in the form of a base material-less adhesive sheet consisting of an adhesive layer from the viewpoint of flexibility that follows an adherend that is repeatedly folded. The above-mentioned base material-less pressure-sensitive adhesive sheet is preferable also from the viewpoint of reducing the thickness of the pressure-sensitive adhesive sheet and increasing the transparency of the pressure-sensitive adhesive sheet.

The adhesive sheet disclosed herein may have a cross-sectional structure schematically shown in FIG. 3, for example. The adhesive sheet 3 shown in FIG. 3 includes a support base material 10 and a first adhesive layer 21 and a second adhesive layer 22 supported on the first surface 10A and second surface 10B of the support base material 10, respectively. Be prepared. The first surface 10A and the second surface 10B are both non-peeling surfaces (non-peeling surfaces). The adhesive sheet 3 is used by attaching the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 to an adherend, respectively. That is, the adhesive sheet 3 is configured as a double-sided adhesive sheet (adhesive sheet with adhesive properties on both sides). In the adhesive sheet 3 before use, the first adhesive surface 21A and the second adhesive surface 22A are each protected by release liners 31 and 32, in which at least the adhesive surface side is a surface having releasability (release surface). It has a structure. Alternatively, the release liner 32 may be omitted and a release liner 31 having release surfaces on both sides may be used, and the adhesive sheet 3 may be wound to bring the second adhesive surface 22A into contact with the back surface of the release liner 31. Accordingly, the second adhesive surface 22A may also be protected by the release liner 31.

The technology disclosed herein is preferably implemented in the form of the above-mentioned double-sided pressure-sensitive adhesive sheet without a base material or with a base material for fixing and bonding members (for example, optical members). Alternatively, although not particularly shown, the adhesive sheet disclosed herein may be in the form of a single-sided adhesive sheet with a base material having an adhesive layer on only one side of a non-peelable base material (supporting base material). An example of the form of a single-sided adhesive sheet is a form in which the structure shown in FIG. 3 does not include either the first adhesive layer 21 or the second adhesive layer 22.

In some embodiments, the haze value of the adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, and 1.0% or less. % or less, and may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Adhesive sheets with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive sheet is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable it is. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more, or 0.10% or more, taking into consideration the refractive index and adhesive properties. The haze value of the pressure-sensitive adhesive sheet can be measured in the same manner as the measurement of the haze value of the pressure-sensitive adhesive layer. The haze value of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, and the type and thickness of the base material in the case of a structure including a base material.

In some embodiments, the total light transmittance of the adhesive sheet is preferably 85.0% or more (for example, 88.0% or more, 90.0% or more, or more than 90.0%). Adhesive sheets with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive sheet. In practical terms, the upper limit of the total light transmittance may be, for example, about 98% or less, about 96% or less, or about 95% or less. In some embodiments, the total light transmittance of the adhesive sheet may be about 94% or less, about 93% or less, or about 92% or less, taking into account the refractive index and adhesive properties. The total light transmittance of the pressure-sensitive adhesive sheet can be measured in the same manner as the measurement of the total light transmittance of the pressure-sensitive adhesive layer. The total light transmittance of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, and the type and thickness of the base material in the case of a structure including a base material.

(Peel strength)
The peel strength of the adhesive sheet to the glass plate is not particularly limited. In some embodiments, the adhesive sheet has a peel strength against a glass plate of, for example, 0.1 N/25 mm or more, and may be 0.5 N/25 mm or more. In some preferred embodiments, the peel strength against the glass plate is 1.0 N/25 mm or more, more preferably 1.5 N/25 mm or more, even more preferably 2.0 N/25 mm or more, and 3.0 N/25 mm or more. It may be 25 mm or more, 5.0 N/25 mm or more, or 10 N/25 mm or more. A pressure-sensitive adhesive sheet having a peel strength against a glass plate of a predetermined value or more is suitable for joining or fixing glass members, for example. The upper limit of the peel strength is not particularly limited, and may be, for example, 30 N/25 mm or less, 25 N/25 mm or less, or 20 N/25 mm or less. In addition, in the case where the adhesive sheet is a base material-less adhesive sheet consisting only of an adhesive layer, the above-mentioned peel strength against a glass plate can be referred to as the peel strength of the adhesive against a glass plate.

Here, the above peel strength is measured after being pressure-bonded to an alkali glass plate as an adherend and left for 30 minutes in an environment of 23°C and 50% RH, and then at a peel angle of 180 degrees and a tensile speed of 300 mm/min. It can be understood by measuring. In the measurement, if necessary, the adhesive sheet to be measured can be reinforced with a suitable backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to about 50 μm). More specifically, the peel strength can be measured by the following method.
[Peel strength against glass plate]
Under a measurement environment of 23°C and 50% RH, the release liner was peeled off from one side of the adhesive sheet, and a 50 μm thick PET film was pasted and lined, and then cut into a size of 25 mm in width and 100 mm in length. is the test piece. The release liner on the other side of the test piece was peeled off, and a 2 kg roller was moved back and forth on the surface of an alkali glass plate (manufactured by Matsunami Glass Industries Co., Ltd., thickness 1.35 mm, blue plate edge polished) as an adherend. and crimp. After leaving this in the same environment for 30 minutes, the peel strength (adhesive strength ) [N/25mm] is measured. As a universal tensile compression tester, for example, "Tensile Compression Tester, TG-1kN" manufactured by Minebea Corporation can be used. In addition, in the case of a single-sided adhesive sheet with a base material, backing with PET film is not essential.

(thickness of adhesive sheet)
The thickness of the adhesive sheet disclosed herein (substrate-less adhesive sheet or adhesive sheet with base material) may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, or 75 μm or less. The thickness may be 50 μm or less. In addition, the thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more, from the viewpoint of handleability.
Note that the thickness of the adhesive sheet refers to the thickness of the portion to be attached to the adherend. For example, in the adhesive sheet 3 having the configuration shown in FIG. 3, the thickness refers to the thickness from the first adhesive surface 21A to the second adhesive surface 22A, and does not include the thickness of the release liners 31 and 32.

<Support base material>
The pressure-sensitive adhesive sheet according to some embodiments may be in the form of a pressure-sensitive adhesive sheet with a base material, which includes a pressure-sensitive adhesive layer on one or both sides of a supporting base material. The material of the support base material is not particularly limited, and can be appropriately selected depending on the purpose and manner of use of the pressure-sensitive adhesive sheet. Non-limiting examples of substrates that can be used include polyolefin films based on polyolefins such as polypropylene (PP) and ethylene-propylene copolymers, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). Plastic films such as polyester films whose main component is polyester such as phthalate (PEN), and polyvinyl chloride films whose main component is polyvinyl chloride; consisting of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam. Foam sheets; Woven and non-woven fabrics made of various fibrous materials (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 combination; Examples include papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and the like. A base material having a composite structure of these materials may also be used. Examples of such composite base materials include base materials having a structure in which metal foil and the above-mentioned plastic film are laminated, and plastic base materials reinforced with inorganic fibers such as glass cloth.

In some embodiments, various film substrates can be preferably used. The film base material may be a porous base material such as a foam film or a non-woven fabric sheet, or a non-porous base material, and may have a porous layer and a non-porous layer. The base material may have a laminated structure. In some embodiments, as the above-mentioned film base material, a base film that includes a (self-supporting or independent) resin film that can maintain its shape independently can be preferably used. Here, the term "resin film" refers to a resin film that has a non-porous structure and typically is substantially void-free. Therefore, the resin film is a concept that is distinguished from foam films and nonwoven fabrics. As the resin film, one that can maintain its shape independently (self-supporting or independent) can be preferably used. The resin film may have a single layer structure or a multilayer structure of two or more layers (for example, a three layer structure).

Examples of the resin material constituting the resin film include polyester; polyolefin; polycycloolefin derived from a monomer having an aliphatic ring structure such as norbornene structure; polyamide (PA) such as nylon 6, nylon 66, and partially aromatic polyamide. Polyimide (PI) such as transparent polyimide (CPI); Polyamideimide (PAI); Polyetheretherketone (PEEK); Polyethersulfone (PES); Polyphenylene sulfide (PPS); Polycarbonate (PC); Polyurethane (PU); Ethylene-vinyl acetate copolymer (EVA); Fluororesin such as polytetrafluoroethylene (PTFE); Acrylic resin; Cellulose polymer such as triacetyl cellulose (TAC); Polyarylate; Polystyrene; Polyvinyl chloride; Polyvinylidene chloride Resins such as can be used.

The resin film may be formed using a resin material containing only one type of such resin, or may be formed using a resin material that is a blend of two or more types of resin. Good too. The resin film may be unstretched or may be stretched (for example, uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low density polyethylene (LDPE) film, linear low density polyethylene (LLDPE) film, PP/PE Blend films, cycloolefin polymer (COP) films, CPI films, TAC films, etc. can be preferably used. Examples of resin films preferable from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of availability, and PET film is particularly preferred.

The resin film may contain known substances such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, anti-blocking agents, etc., to the extent that the effects of the present invention are not significantly impaired. Additives may be added as necessary. The blending amount of the additive is not particularly limited, and can be appropriately set depending on the use of the pressure-sensitive adhesive sheet.

The method for producing the resin film is not particularly limited. For example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calender roll molding can be appropriately employed.

The substrate may consist essentially of such a base film. Alternatively, the base material may include an auxiliary layer in addition to the base film. Examples of the above-mentioned auxiliary layers include optical property adjustment layers (e.g., colored layers, antireflection layers), printing layers and laminate layers for imparting a desired appearance to the substrate, antistatic layers, undercoat layers, and release layers. Examples include surface treatment layers such as.

In some embodiments, a light-transmitting base material (hereinafter also referred to as a light-transmitting base material) can be preferably employed as the supporting base material. Thereby, it becomes possible to construct a pressure-sensitive adhesive sheet with a base material having light transmittance. The total light transmittance of the light-transmissive base material may be, for example, more than 50%, and may 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 may be 95% or more (eg, 95-100%). The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used. A preferred example of the above-mentioned light-transmitting base material is a light-transmitting resin film. The light-transmitting substrate may be an optical film.

The thickness of the base material is not particularly limited, and can be selected depending on the purpose and manner of use of the adhesive sheet. The thickness of the base material may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of handling and processability of the adhesive sheet, 150 μm or less, 100 μm or less, 50 μm or less, and 25 μm or less. The thickness may be less than or equal to 10 μm. As the thickness of the base material decreases, the ability to follow the surface shape of the adherend tends to improve. Further, from the viewpoint of handleability, processability, etc., the thickness of the base material may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

The surface of the base material on which the adhesive layer will be laminated may be treated with corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of an undercoat (primer) to form an undercoat layer, as necessary. Conventionally known surface treatments such as forming may be applied. Such surface treatment may be a treatment for improving the anchoring ability of the adhesive layer to the base material. The composition of the primer used to form the undercoat layer is not particularly limited, and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but it is usually approximately 0.01 μm to 1 μm, preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the base material as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, and the like. These treatments can be applied alone or in combination.

<Adhesive sheet with release liner>
The adhesive sheet disclosed herein can take the form of an adhesive product in which the surface (adhesive surface) of an adhesive layer is brought into contact with the release surface of a release liner. Therefore, this specification provides a pressure-sensitive adhesive sheet with a release liner (adhesive product) that includes any pressure-sensitive adhesive sheet disclosed herein and a release liner having a release surface that comes into contact with the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet. Ru.

The release liner is not particularly limited, and includes, for example, a release liner having a release layer on the surface of a liner base material such as a resin film or paper (paper laminated with a resin such as polyethylene), or a fluorine-based polymer. A release liner made of a resin film made of a low adhesive material such as (polytetrafluoroethylene, etc.) or polyolefin resin (polyethylene, polypropylene, etc.) can be used. Since they have excellent surface smoothness, a release liner having a release layer on the surface of a resin film as a liner base material or a release liner made of a resin film made of a low adhesive material can be preferably employed. The resin film is not particularly limited as long as it can protect the adhesive layer, and examples thereof include polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, and polyvinyl chloride film. , vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, and the like. For forming the above-mentioned release layer, for example, a silicone-based release agent, a long-chain alkyl-based release agent, an olefin-based release agent, a fluorine-based release agent, a fatty acid amide-based release agent, molybdenum sulfide, silica powder, etc. , a known release agent can be used.

<Application>
The uses of the adhesive and adhesive sheet disclosed herein are not limited, and can be used for various purposes. The adhesives and adhesive sheets disclosed herein can withstand large deformations while maintaining a high refractive index, so they can be used in various applications that require a high refractive index and flexibility, especially large-sized ones. It can be used for applications that involve deformation. For example, in electronic devices such as portable electronic devices, display devices (image display devices) such as liquid crystal display devices, organic EL (electroluminescent) display devices, PDP (plasma display panels), electronic paper, input devices such as touch panels, etc. It is suitable as an adhesive or adhesive sheet for equipment (optical equipment), especially foldable displays and rollable displays. For example, in foldable displays and rollable displays, it is preferably used as a means for joining, fixing, and protecting members having a high refractive index. The adhesive or adhesive sheet disclosed herein has a high refractive index and has flexibility that can withstand repeated bending operations, so it can be used in a state where it is attached to a foldable display or a rollable display. , it can well follow adherends that are repeatedly folded (foldable displays, etc.). Examples of objects to be pasted in such usage patterns include glass members such as window glasses and cover glasses used in foldable displays and rollable displays. Furthermore, the adhesive and adhesive sheet disclosed herein can easily follow and adhere to curved surfaces such as the three-dimensional shapes of portable electronic devices, so they are suitable for use in electronic devices having such curved shapes. be. Furthermore, in some preferred embodiments, the adhesive may have improved stability in properties such as elastic modulus in addition to having a high refractive index and flexibility. The above-mentioned portable electronic devices are sometimes used in high-temperature environments, and their internal spaces can become heated due to the heat generated by electronic components, so there is a great advantage of using an adhesive with the above-mentioned characteristics and good stability. .

Examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, and various wearable devices (e.g., wrist-wear devices that are worn on the wrist like watches, and devices that are attached to the body using clips, straps, etc.). Eyewear types include modular types that are attached to the body, eyewear types (monocular and binocular types, including head-mounted types), clothing types that are attached to shirts, socks, hats, etc. in the form of accessories, and earphones. digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, electronic books, in-vehicle information. This includes devices such as portable radios, portable televisions, portable printers, portable scanners, and portable modems. Note that in this specification, "portable" does not mean that it is simply portable; it also means that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. shall mean.

The material (adherend material) to which the adhesive or adhesive sheet disclosed herein is attached is not particularly limited, but includes, for example, copper, silver, gold, iron, tin, palladium, aluminum, and nickel. , titanium, chromium, zinc, etc., or alloys containing two or more of these; for example, polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resin, polyethylene naphthalate resin, etc.), polyvinyl chloride resin, polyphenylene sulfide resin, polyether ether ketone resin, polyamide resin (so-called aramid resin, etc.), polyarylate resin, polycarbonate resin, diacetyl cellulose, etc. Cellulose polymers such as triacetyl cellulose, vinyl butyral polymers, various resin materials (typically plastic materials) such as liquid crystal polymers, inorganic materials such as alumina, zirconia, alkali glass, alkali-free glass, quartz glass, carbon, etc. can be mentioned. The adhesive or adhesive sheet disclosed herein can be used by being attached to a member (for example, an optical member) made of the above-mentioned material.

The member or material to which the adhesive or adhesive sheet disclosed herein is attached (at least one adherend in a double-sided adhesive sheet) has a higher refractive index than general adhesives (for example, acrylic adhesives). It may be made of a material with a high The refractive index of the adherend material is, for example, 1.50 or more, and some adherend materials have a refractive index of 1.55 or more or 1.58 or more, and even have a refractive index of 1.62 or more (for example, 1.50 or more). .66) exists. Such high refractive index adherend materials are typically resin materials. More specifically, it may be a polyester resin such as PET, a polyimide resin, an aramid resin, a polyphenylene sulfide resin, a polycarbonate resin, or the like. For such materials, the effect of using the adhesive or adhesive sheet disclosed herein (suppression of light ray reflection caused by a difference in refractive index) can be preferably exhibited. The upper limit of the refractive index of the adherend material is, for example, 1.80 or less, and may be 1.70 or less. The adhesive or adhesive sheet disclosed herein can be preferably used in an embodiment in which it is attached to an adherend (for example, a member) having a high refractive index as described above. A suitable example of such an adherend is a resin film having a refractive index of 1.50 to 1.80 (preferably 1.55 to 1.75, for example 1.60 to 1.70). The refractive index can be measured in the same manner as the refractive index of the adhesive.

The member or material to which the adhesive or adhesive sheet is attached (at least one adherend in a double-sided adhesive sheet) may have light transmittance. With such an adherend, the advantage of the technique disclosed herein (suppression of light reflection at the interface between the adherend and the adhesive) can easily be obtained. The total light transmittance of the adherend may be, for example, greater than 50%, preferably 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95 to 100%). The adhesive or adhesive sheet disclosed herein can be preferably used in a mode where it is attached to an adherend (for example, an optical member) having a total light transmittance of a predetermined value or more. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used.

In some preferred embodiments, the adherend (eg, member) to which the adhesive or adhesive sheet is attached may have the above-mentioned refractive index and the above-mentioned total light transmittance. Specifically, the refractive index is 1.50 or more (for example, 1.55 or more, 1.58 or more, 1.62 or more, about 1.66, etc.), and the total light transmittance is greater than 50% ( For example, the pressure-sensitive adhesive or pressure-sensitive adhesive sheet disclosed herein can be applied to an adherend, such as a member (for example, 70% or more, preferably 80% or more, more preferably 90% or more, and even 95% or more). It can be preferably used. The effects of the technique disclosed herein are particularly preferably exhibited in the embodiment in which the adhesive is attached to such a member.

An example of a preferred application is an optical application. More specifically, for example, optical adhesives and optical adhesive sheets used for bonding optical members (for bonding optical members) and manufacturing products (optical products) using the above-mentioned optical members. As such, the adhesives and adhesive sheets disclosed herein can be preferably used.

The above-mentioned optical member refers to a member having optical properties (for example, polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.). say. The above-mentioned optical member is not particularly limited as long as it has optical properties, but for example, it may be a member constituting a device (optical device) such as a display device (image display device) or an input device, or a member used in these devices. Members include, for example, polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, antireflection films, hard coat (HC) films, shock absorption films, antifouling films, Photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and members on which these are laminated (collectively referred to as (sometimes referred to as "functional film"). In addition, the above-mentioned "plate" and "film" each include shapes such as plate, film, and sheet. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet", etc. The "light guide plate" includes "light guide film", "light guide sheet", etc. Furthermore, the above-mentioned "polarizing plate" includes a circularly polarizing plate.

Examples of the display device include a liquid crystal display device, an organic EL display device, a micro LED (μLED), a mini LED (miniLED), a PDP, and an electronic paper. Moreover, a touch panel etc. are mentioned as said input device.

The above-mentioned optical member is not particularly limited, but includes, for example, a member (for example, a sheet-like, film-like, or plate-like member) made of glass, acrylic resin, polycarbonate, PET, metal thin film, or the like. Note that the term "optical member" in this specification includes members (design films, decorative films, surface protection films, etc.) that play a role of decoration and protection while maintaining the visibility of display devices and input devices.

The technology disclosed herein uses, for example, an optical film such as a film having one or more functions such as light transmission, reflection, diffusion, waveguide, condensing, and diffraction, or a fluorescent film, and other optical members ( It can be preferably used for bonding to other optical films. In particular, in bonding optical films that have at least one of the functions of light waveguide, condensation, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and the technology disclosed herein is preferably applied. Can be targeted.

The adhesive disclosed herein can be preferably used for bonding optical films such as light guiding films, diffusion films, fluorescent films, toning films, prism sheets, lenticular films, and microlens array films. In these applications, from the viewpoint of the trend toward miniaturization of optical members and higher performance, there is a demand for thinner optical members and improved light extraction efficiency. The adhesive disclosed herein can be preferably used as an adhesive that can meet such demands. More specifically, for example, in bonding a light guide film or a diffusion film, adjusting the refractive index (for example, increasing the refractive index) of the adhesive (layer) as a bonding layer can contribute to thinning. In bonding fluorescent films, light extraction efficiency (which can also be understood as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. When bonding color toning films, by appropriately adjusting the refractive index of the adhesive so that the difference in refractive index with the color toning pigment is reduced, scattering components can be reduced, contributing to improved light transmittance. When bonding prism sheets, lenticular films, microlens array films, etc., appropriately adjusting the refractive index of the adhesive can control light diffraction and contribute to improving brightness and/or viewing angle.

The pressure-sensitive adhesive or pressure-sensitive adhesive sheet disclosed herein is preferably used in an embodiment in which it is attached to a high refractive index adherend (which may be a high refractive index layer or member, etc.), and is used in a manner that it is attached to a high refractive index adherend (which may be a high refractive index layer or member, etc.), and is bonded to the adherend. Interfacial reflection can be suppressed. The adhesive or adhesive sheet used in such an embodiment preferably has a small refractive index difference with the adherend and high adhesion at the interface with the adherend, as described above. Further, from the viewpoint of improving the homogeneity of the appearance, it is preferable that the thickness of the adhesive (layer) is highly uniform, for example, it is preferable that the surface smoothness of the adhesive surface is high. When the thickness of the adherend with a high refractive index is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), it is necessary to It is particularly useful to suppress reflexes. As an example of such a usage mode, in a polarizing plate with a retardation layer that includes a polarizer, a first retardation layer, and a second retardation layer in this order, bonding of the polarizer and the first retardation layer and/or Another example is an embodiment used for bonding the first retardation layer and the second retardation layer.

In addition, since the adhesives and adhesive sheets disclosed herein are suitable for increasing the refractive index, they can be applied to light-emitting layers such as optical semiconductors (e.g., high-refractive light-emitting layers mainly composed of inorganic materials). It can be preferably used in embodiments. By reducing the difference in refractive index between the light emitting layer and the adhesive (layer), reflection at the interface between them can be suppressed and light extraction efficiency can be improved. The pressure-sensitive adhesive or pressure-sensitive adhesive sheet used in such an embodiment preferably includes a pressure-sensitive adhesive (layer) with a high refractive index. Further, from the viewpoint of improving brightness, it is preferable that the adhesive or adhesive sheet has low coloring. This can also be advantageous from the viewpoint of suppressing unintentional coloring caused by the adhesive or adhesive sheet.

Note that in this specification, a self-luminous element means a light-emitting element whose luminance can be controlled by the value of a flowing current. The self-luminous element may be composed of a single unit or an aggregate. Specific examples of self-luminous elements include, but are not limited to, light emitting diodes (LEDs) and organic EL. Furthermore, in this specification, a light-emitting device means a device including such a self-luminous element as a component. Examples of the light emitting device include, but are not limited to, a light source module device used for illumination (for example, a planar light emitting module) and a display device in which pixels are formed.

The adhesive disclosed herein can be used in microlenses and other lens members used as constituent members of cameras, light emitting devices, etc. (for example, microlenses constituting microlens array films, lens members such as microlenses for cameras). , a coating layer covering the lens surface, a bonding layer with a member facing the lens surface (for example, a member having a surface shape corresponding to the lens surface), a filling layer filled between the lens surface and the member, It can be preferably used as such. Since the adhesive disclosed herein is suitable for increasing the refractive index, it can be used with high refractive index lenses (for example, lenses made of high refractive index resin or lenses having a surface layer made of high refractive index resin). Even if there is, the difference in refractive index with the lens can be reduced. This is advantageous from the standpoint of making the lens and products equipped with the lens thinner, and can also contribute to suppressing aberrations and improving the Abbe number. The adhesive disclosed herein can also be used as a lens resin by itself, for example in the form of being filled in the recesses or voids of a suitable transparent member.

The mode of bonding optical members together using the adhesive or adhesive sheet disclosed herein is not particularly limited, but includes, for example, (1) bonding optical members together via the adhesive or adhesive sheet disclosed herein; (2) the optical member may be bonded to a member other than the optical member via the adhesive or adhesive sheet disclosed herein, or (3) the adhesive sheet disclosed herein may be attached to a member other than the optical member. The adhesive sheet may include an optical member and may be bonded to an optical member or a member other than the optical member. In the above embodiment (3), the pressure-sensitive adhesive sheet containing an optical member may be, for example, a pressure-sensitive adhesive sheet whose support is an optical member (for example, an optical film). A pressure-sensitive adhesive sheet that includes an optical member as a support in this manner can also be understood as a pressure-sensitive adhesive optical member (for example, a pressure-sensitive adhesive optical film). Further, when the adhesive sheet disclosed herein is a type of adhesive sheet having a support and the functional film is used as the support, the adhesive sheet disclosed herein is a type of adhesive sheet having a support, and when the functional film is used as the support, the adhesive sheet disclosed herein is a type of adhesive sheet having a support. It can also be understood as an "adhesive functional film" having the adhesive layer disclosed herein on at least one side.

As described above, according to the technology disclosed herein, a laminate including the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached is provided. The member to which the adhesive sheet is attached may have the refractive index of the adherend material described above. Further, the difference between the refractive index of the adhesive sheet and the refractive index of the member (refractive index difference) may be the refractive index difference between the adherend and the adhesive sheet described above. The members constituting the laminate are the same as those described above for the members, materials, and adherends, so duplicate explanations will not be repeated.

Hereinafter, some examples related to the present invention will be described, but the present invention is not intended to be limited to what is shown in these specific examples. In the following description, "parts" and "%" expressing usage amounts and contents are based on weight unless otherwise specified.

<Example 1>
(Preparation of acrylic polymer solution)
In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser, m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A", refractive index: 1) was added as a monomer component. .566, hereinafter referred to as "POB-A") 95 parts, 3 parts of 4-hydroxybutyl acrylate (4HBA) and 2-acryloyloxyethyl-succinic acid (manufactured by Kyoeisha Chemical Co., Ltd., trade name "HOA-MS") (N)", hereinafter referred to as "HOA-MS"), 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as a polymerization solvent, and slowly Nitrogen gas was introduced while stirring, the temperature of the liquid in the flask was maintained at around 60° C., and a polymerization reaction was carried out for 6 hours to prepare a solution (40%) of acrylic polymer P1. The Mw of the acrylic polymer P1 was 500,000.

(Preparation of adhesive composition)
The solution of the above acrylic polymer P1 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (non-volatile content: 100 parts) was added as a plasticizer A1 to polyethylene glycol benzoate (manufactured by Sanyo Chemical Industries, Ltd., trade name: "Sunflex EB-300", molecular weight: 538, refractive index: 1.515, liquid at 20°C, hereinafter referred to as "EB-300") 60 parts, acyclic bifunctional isocyanate crosslinking agent as a crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate 2770", hexamethylene diisocyanate (HDI) allophanate) 0.3 parts, acetylacetone 2 parts as a crosslinking retarder, 1 part Naseem ferric 1% ethyl acetate solution as a crosslinking catalyst ( 0.01 part of non-volatile matter) was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The acrylic pressure-sensitive adhesive composition prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness: 50 μm), which had been silicone-treated on one side, and heated at 130°C for 2 minutes. An adhesive layer having a thickness of 20 μm was formed. Next, the silicone-treated side of PET film R2 (thickness: 25 μm), which had been silicone-treated on one side, was bonded to the surface of the pressure-sensitive adhesive layer. In this way, a base material-less double-sided adhesive sheet consisting of the above-mentioned adhesive layer was obtained. Both sides of this adhesive sheet are protected by PET films (release liners) R1 and R2.

<Example 2>
A solution of acrylic polymer P2 was prepared in the same manner as in the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 99 parts of POB-A and 1 part of HOA-MS. The Mw of the acrylic polymer P2 was 500,000. The solution of the above acrylic polymer P2 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of nonvolatile content) was added with 60 parts of the above plasticizer A1 (EB-300) and an epoxy crosslinking agent as a crosslinking agent. (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was added, stirred and mixed, and the acrylic resin according to this example was added. An adhesive composition was prepared. A pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet consisting of an adhesive layer) according to this example was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 3>
The acrylic polymer solution was prepared in the same manner as in Example 1, except that the composition of the monomer components was changed to 95 parts of POB-A, 2 parts of lauryl acrylate (LA), 2 parts of 2-ethylhexyl acrylate (2EHA), and 1 part of 4HBA. A solution of polymer P3 was prepared. The Mw of acrylic polymer P3 was 500,000. The above solution of acrylic polymer P3 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (non-volatile content: 100 parts) was added with 3-phenoxybenzyl alcohol (manufactured by Tokyo Kasei Kogyo Co., Ltd., refractive index: 1.591, liquid at 20°C, hereinafter referred to as "POB-AL") 60 parts, 0.3 parts of the above isocyanate crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, Naseem ferric as a crosslinking catalyst. One part of a 1% ethyl acetate solution (nonvolatile content: 0.01 part) was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example. A pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet consisting of an adhesive layer) according to this example was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 4>
A solution of acrylic polymer P4 was prepared in the same manner as in the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 90 parts of POB-A, 9 parts of 2EHA, and 1 part of 4HBA. The Mw of acrylic polymer P4 was 500,000. A solution of the above acrylic polymer P4 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of non-volatile content) was added with 60 parts of the above plasticizer A2 (POB-AL) and 0.0 parts of the above isocyanate crosslinking agent. 5 parts of acetylacetone as a crosslinking retarder, 1 part of a 1% ethyl acetate solution of Naseem ferric iron as a crosslinking catalyst (non-volatile content 0.01 part) were added and mixed with stirring to obtain the acrylic pressure-sensitive adhesive composition according to this example. I prepared something. A pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet consisting of an adhesive layer) according to this example was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 5>
A solution of acrylic polymer P5 was prepared in the same manner as in the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 98 parts of POB-A, 1 part of 4HBA, and 1 part of HOA-MS. The Mw of acrylic polymer P5 was 500,000. The solution of the above acrylic polymer P5 was diluted with ethyl acetate to a polymer concentration of 30%, and to 334 parts of this solution (100 parts of non-volatile content), 20 parts of the above plasticizer A1 (EB-300) and the above isocyanate crosslinking agent were added. 0.1 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric Naseem (nonvolatile content 0.01 part) as a crosslinking catalyst were added and mixed with stirring to obtain the acrylic adhesive according to this example. A drug composition was prepared. A pressure-sensitive adhesive sheet according to this example (substrate-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer) was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Evaluation method>
(Deformation test)
The adhesive layer (substrate-less double-sided adhesive sheet) according to each example was cut into a width of 300 mm in length and a cross-sectional area of 1 ^mm2 , and the adhesive layer was rolled into a cylindrical shape in an environment of 23°C and 50% RH. , a test piece was obtained. Using a tensile testing machine (manufactured by Shimadzu Corporation, device name: "Precision Universal Testing Machine Autograph AG-X plus 5kN"), the above test piece was deformed under the conditions of -20°C, chuck distance 100mm, and tensile speed 300mm/min. A test (tensile test) was conducted to determine the SS curve, and it was evaluated whether the test piece deformed (elongated) by 350% or more. When the test piece was deformed by 350% or more, the stress [N/mm ² ] at the time of 350% deformation was measured. In the above deformation test, an adhesive that can deform by 350% or more at -20°C is determined to be an adhesive that can withstand large deformations.

Further, a deformation test was conducted in the same manner as above except that the temperature of the deformation test was changed to 25° C., and the stress [N/mm ² ] at 350% deformation was measured. From the obtained results, the stress S (-20°C) at a deformation amount of 350% in the deformation test conducted at a temperature of -20°C and a speed of 300 mm/min, and the stress S (at -20°C) at a temperature of 25°C and a speed of 300 mm/min. The ratio (S(-20°C)/S(25°C)) to the stress S(25°C) at a deformation amount of 350% in the deformation test conducted was determined.

In addition, when the thickness of the adhesive layer is relatively small, for the purpose of improving operability, etc., the above deformation test is conducted using a test piece prepared so that the thickness is 5 μm or more (for example, about 5 μm to 200 μm). You can. The thickness of the test piece can be adjusted, for example, by appropriately overlapping adhesive layers. In addition, using the same adhesive composition as that used to form the adhesive layer to be measured, a test piece with a thickness that facilitates the deformation test was prepared, and the above deformation test was performed on the test piece. Good too. The above deformation test can be carried out using, for example, a test piece with a thickness of about 10 μm to 50 μm. Further, during the test, it is preferable to apply powder to the adhesive surface of the area to be chucked to remove the influence of stickiness of the adhesive.

(Refractive index)
The adhesive layer (substrate-less double-sided adhesive sheet) according to each example was measured using an Abbe refractometer (manufactured by ATAGO, model "DR-M4") under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. The rate was measured.

(Glass-transition temperature)
The pressure-sensitive adhesive layers according to each example were laminated to a thickness of about 1.5 mm, which was punched out into a disc shape with a diameter of 7.9 mm, and this was used as a sample for measurement. Dynamic viscoelasticity measurements were performed using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific under the following conditions. The temperature corresponding to the peak top temperature of the loss tangent tan δ (loss modulus G"/storage modulus G') in the dynamic viscoelasticity measurement was determined as the glass transition temperature (Tg) [° C.] of the adhesive.
[Measurement condition]
Deformation mode: Torsion Measurement frequency: 1Hz
Temperature range: -50℃~150℃
Heating rate: 5℃/min Shape: Parallel plate 7.9mmφ

(Total light transmittance and haze)
Using a test piece in which the adhesive layer according to each example was attached to alkali-free glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%), under a measurement environment of 23 ° C. The total light transmittance and haze of the test piece were measured using a haze meter ("HM-150" manufactured by Murakami Color Research Institute). The values obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values were defined as the total light transmittance [%] and haze [%] of the adhesive (layer). Regarding the base material-less pressure-sensitive adhesive sheet consisting of the pressure-sensitive adhesive layer, the total light transmittance [%] and haze [%] of the pressure-sensitive adhesive layer are the total light transmittance [%] and haze [%] of the pressure-sensitive adhesive sheet. Note that the above-mentioned total light transmittance is sometimes referred to as initial total light transmittance for the purpose of distinguishing from the total light transmittance after a bending test described later.

(Total light transmittance after bending test)
The adhesive layer according to each example was cut into a rectangle of 2 cm x 10 cm to obtain a test piece for measurement. A 4 mm cylindrical rod was fixed horizontally at a height sufficient for measurement, the test piece obtained above was hung on the rod, one side was bent into a U shape with a radius of 2 mm, and held for 1 minute. Specifically, the longitudinal center portion of the test piece was hung on a rod to form an inverted U-shape. Then, the lower ends of the test piece were fixed with clips (13 g), and a 60 g weight was suspended and fixed from the clip via a 1 cm long thread, and a load was applied to the bent part of the test piece. . In this state, the test piece was held in a predetermined temperature environment (25°C) for 1 minute, and after 1 minute had passed, the test piece was removed from the rod. Next, under the same temperature environment, the other side of the test piece (the opposite side to the above one side) was also heated at a radius of 2 mm on the opposite side of the bent part of the above one side, in the same way as the above one side. It was bent into a U shape and held for 1 minute. After repeating this bending test 10 times on the above-mentioned bending part of the same test piece, the bending test was performed on the above-mentioned bending part by the same method as the above-mentioned method for measuring the initial total light transmittance. The total light transmittance [%] was measured.

Table 1 shows the outline and evaluation results of the adhesives according to each example.

As shown in Table 1, the adhesives according to Examples 1 to 4 have a refractive index of 1.55 or more and a deformation test of 350% in the deformation test conducted at a temperature of -20°C and a speed of 300 mm/min. Larger deformations were possible. Further, the pressure-sensitive adhesives according to Examples 1 to 4 have a ratio (S(-20°C)/S(25°C)) of 50 or less, indicating that they can exhibit stable performance over a wide temperature range. Furthermore, it can be seen that the above adhesive shows little change in total light transmittance after the bending test, and can be used for foldable optical applications such as foldable display applications. On the other hand, although the adhesive according to Example 5 had a refractive index of 1.55 or more, it broke at an early stage of deformation in a deformation test at a temperature of -20°C and a speed of 300 mm, and could not withstand large deformations. could not.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above.

1, 2, 3 Adhesive sheet 10 Support base material 10A First surface 10B Second surface 21 Adhesive layer, first adhesive layer 21A Adhesive surface, first adhesive surface 21B Adhesive surface 22 Second adhesive layer 22A Second adhesive Surface 31, 32 Release liner

Claims (13)

An adhesive having a refractive index of 1.55 or more and a deformation amount of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm/min. The adhesive according to claim 1, which has a stress of 5.0 N/mm ² or less at a deformation amount of 350% in a deformation test conducted at a temperature of -20° C. and a speed of 300 mm/min. The pressure-sensitive adhesive according to claim 1 or 2, having a glass transition temperature within the range of -50°C to 0°C. Stress S at 350% deformation (-20°C) in a deformation test conducted at a temperature of -20°C and a speed of 300mm/min, and stress S (at -20°C) in a deformation test conducted at a temperature of 25°C and a speed of 300mm/min. The adhesive according to any one of claims 1 to 3, wherein the ratio (S(-20°C)/S(25°C)) to stress S(25°C) at a deformation amount of 350% is 50 or less. . At 25°C, the total light transmittance of the bent part after repeating the bending test 10 times, which consists of one set of bending each side of the sheet-like adhesive into a U-shape with a radius of 2 mm, is the total light transmittance of the bent part before the bending test. The adhesive according to any one of claims 1 to 4, which maintains a total light transmittance of 85% or more. The pressure-sensitive adhesive according to any one of claims 1 to 5, comprising an acrylic polymer having a weight average molecular weight of less than 100×10 ⁴ . Contains a base polymer and a crosslinker,
The adhesive according to any one of claims 1 to 6, wherein the content of the crosslinking agent is more than 0.1 part by weight and less than 0.5 part by weight based on 100 parts by weight of the base polymer. As a plasticizer, it contains an ethylene glycol compound having two or more double bond-containing rings in one molecule,
The adhesive according to any one of claims 1 to 7, wherein the ethylene glycol compound has 3 or more oxyethylene units. The adhesive according to any one of claims 1 to 8, comprising a plasticizer having a molecular weight of 315 or more. Contains acrylic polymer,
The monomer component constituting the acrylic polymer includes a monomer (A2) corresponding to at least one of a hydroxyl group-containing monomer and a carboxyl group-containing monomer,
The monomer (A2) has a (meth)acryloyl group, and the number of atoms constituting a chain connecting the (meth)acryloyl group and a hydroxyl group and/or a carboxyl group is 6 or more, The adhesive according to any one of the items. The pressure-sensitive adhesive according to any one of claims 1 to 10, comprising a bifunctional crosslinking agent having two crosslinking-reactive groups per molecule. The adhesive according to any one of claims 1 to 11, comprising an acyclic crosslinking agent having no ring structure. Any one of claims 1 to 12, wherein the crosslinking agent contains a compound in which the number of atoms constituting a linking chain connecting one crosslinking reactive group and another crosslinking reactive group is 10 or more in one molecule. The adhesive described in item 1.

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