WO2023053797A1

WO2023053797A1 - Optical laminate, pressure-sensitive adhesive sheet, and image display device

Info

Publication number: WO2023053797A1
Application number: PCT/JP2022/031957
Authority: WO
Inventors: 雅大久世; 武史仲野
Original assignee: 日東電工株式会社
Priority date: 2021-09-28
Filing date: 2022-08-24
Publication date: 2023-04-06
Also published as: KR20240070613A; CN117999327A; JP2023048829A; TW202313731A

Abstract

The present invention provides an optical laminate including a pressure-sensitive adhesive sheet having a sufficient gel content and improved durability. This optical laminate comprises the pressure-sensitive adhesive sheet, which has a gel content of 70% or higher, and an optical film. A histogram drawn by the following test method has a maximum frequency of 1,400 or greater. Test method: An area of 500 nm (length) by 500 nm (width) in a surface of the pressure-sensitive adhesive sheet is examined for modulus with an atomic force microscope so that the number of measurement points is 65,536, and a histogram of modulus is drawn in which the class width is 0.1 MPa.

Description

Optical laminate, adhesive sheet and image display device

The present invention relates to an optical laminate, an adhesive sheet, and an image display device.

In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. These various image display devices usually have a laminated structure of an image forming layer such as a liquid crystal layer and an EL light emitting layer, and an optical laminate including an optical film and an adhesive sheet. The pressure-sensitive adhesive sheet is mainly used for bonding between films included in the optical layered body and bonding between the image forming layer and the optical layered body. Examples of the optical film are a polarizing plate, a retardation film, and a polarizing plate with a retardation film in which the polarizing plate and the retardation film are integrated. Patent Literature 1 discloses an example of an optical laminate.

JP 2008-031214 A

Excessive changes in the dimensions of the optical film due to temperature changes cause light leakage and color unevenness in image display devices. Light leakage and color unevenness are particularly likely to occur in a relatively large-sized image display device using a polarizing plate with a retardation film. In addition, image display devices designed with a narrow bezel (narrow bezel) are becoming popular, and suppression of dimensional change is becoming more and more important. In order to suppress the dimensional change, it is conceivable to increase the elastic modulus of the pressure-sensitive adhesive sheet included in the optical layered body. One possible method for increasing the elastic modulus of the adhesive sheet is to increase the gel fraction of the adhesive sheet. However, simply increasing the elastic modulus may reduce the durability of the pressure-sensitive adhesive sheet, making it impossible to follow changes in dimensions.

Accordingly, an object of the present invention is to provide an optical laminate containing a pressure-sensitive adhesive sheet having a sufficient gel fraction and improved durability.

The present invention
including an adhesive sheet having a gel fraction of 70% or more and an optical film,
Provided is an optical laminate having a maximum value of 1400 or more in a histogram prepared by the following test method.
Test method: Using an atomic force microscope, the elastic modulus was measured so that the number of measurement points was 65536 for a range of 500 nm in length × 500 nm in width on the surface of the pressure-sensitive adhesive sheet, and the class width was 0.1 MPa. Create a histogram of the modulus of elasticity.

Furthermore, the present invention
A pressure-sensitive adhesive sheet having a gel fraction of 70% or more,
Provided is a pressure-sensitive adhesive sheet having a maximum value of 1400 or more in a histogram prepared by the following test method.
Test method: Using an atomic force microscope, the elastic modulus was measured so that the number of measurement points was 65536 for a range of 500 nm in length × 500 nm in width on the surface of the pressure-sensitive adhesive sheet, and the class width was 0.1 MPa. Create a histogram of the modulus of elasticity.

Furthermore, the present invention
Provided is an optical laminate including the pressure-sensitive adhesive sheet described above and an optical film.

Furthermore, the present invention
Provided is an image display device comprising the above optical layered body.

Furthermore, the present invention
A pressure-sensitive adhesive sheet having a gel fraction of 70% or more,
Provided is a pressure-sensitive adhesive sheet having an elastic modulus coefficient of variation of less than 0.08 as measured by the following test method.
Test method: Using an atomic force microscope, the elastic modulus is measured so that the number of measurement points is 65,536 in a range of 500 nm long×500 nm wide on the surface of the pressure-sensitive adhesive sheet.

According to the present invention, it is possible to provide an optical laminate containing a pressure-sensitive adhesive sheet having a sufficient gel fraction and improved durability.

FIG. 1 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the invention. FIG. 3A is a diagram showing an example of an atomic force microscope image of the surface of the adhesive sheet. FIG. 3B is a diagram showing an example of a histogram of elastic moduli measured with an atomic force microscope. FIG. 4 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. FIG. 5 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. FIG. 6 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. FIG. 7 is a cross-sectional view schematically showing an example of the image display device of the present invention.

Although the present invention will be described in detail below, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

(Embodiment of Optical Laminate)
An example of the optical laminate of this embodiment is shown in FIG. An optical laminate 10A in FIG. 1 includes an adhesive sheet 1 and an optical film 2. As shown in FIG. The adhesive sheet 1 and the optical film 2 are laminated together. 10 A of optical laminated bodies can be used as an optical film with an adhesive sheet.

(adhesive sheet)
The adhesive sheet 1 has a gel fraction of 70% or more. Furthermore, the maximum value _Fmax of the frequency in the histogram created by the following test method is 1400 or more.
Test method: Using an atomic force microscope (AFM), the elastic modulus was measured so that the number of measurement points was 2 ¹⁶ (65536) for a range of 500 nm long × 500 nm wide on the surface of the pressure-sensitive adhesive sheet 1. Create a histogram of elastic moduli with a width of 0.1 MPa.

The gel fraction of the adhesive sheet 1 can be specified by the following method. First, as a measurement sample, a pressure-sensitive adhesive sheet 1 (for example, FIG. 2) that has been produced for one week or more is prepared. This pressure-sensitive adhesive sheet 1 has been stored in an environment of 23° C. and 55% RH for one week or more after being produced, for example. When the pressure-sensitive adhesive sheet 1 is formed from a pressure-sensitive adhesive composition containing a cross-linking agent, the reaction due to the cross-linking agent has sufficiently progressed after one week or more has passed since the preparation. In other words, the reaction with the cross-linking agent has finished. Completion of the reaction by the cross-linking agent can be confirmed by, for example, Fourier transform infrared spectroscopy (FT-IR). Next, a part of the adhesive sheet 1 is scraped off to obtain a small piece. The resulting strip is then wrapped with an expanded porous membrane of polytetrafluoroethylene and tied with kite string. A test piece is thus obtained. Next, the total weight (weight A) of the small piece of adhesive sheet 1, the stretched porous membrane and the kite string is measured. The sum of the stretched porous membrane and the kite string used is defined as weight B. Next, the test piece is immersed in a container filled with ethyl acetate and allowed to stand at 23° C. for one week. After standing still, the test piece is taken out from the container, dried for 2 hours in a dryer set at 130° C., and then the weight C of the test piece is measured. The gel fraction of the pressure-sensitive adhesive sheet 1 can be calculated from weight A, weight B, and weight C based on the following formula.
Gel fraction (% by weight) = (C - B) / (A - B) x 100

The gel fraction of the adhesive sheet 1 is 70% or more, preferably 80% or more, more preferably 90% or more, still more preferably 94% or more, particularly preferably 95% or more, Depending on the case, it may be 96% or more, 97% or more, 98% or more, or 100%. A pressure-sensitive adhesive sheet 1 having a gel fraction of 70% or more tends to be excellent in workability and process stability, and tends to suppress the occurrence of dents during storage, for example. This pressure-sensitive adhesive sheet 1 is also suitable for suppressing the dimensional change of the optical film.

More specifically, the maximum frequency value F _max can be specified by the following method. First, as a measurement sample, a pressure-sensitive adhesive sheet 1 (for example, FIG. 2) that has been produced for one week or longer is prepared. Next, the adhesive sheet 1 is cut into strips to obtain test pieces. At this time, the thickness of the test piece is adjusted to about 100 nm. The surface of the obtained test piece can be regarded as the surface of the adhesive sheet 1 . The specimen is then placed on a substrate such as a Si wafer. Using AFM, the elastic modulus is measured so that the number of measurement points is 65536 for the range of 500 nm long×500 nm wide on the surface of the test piece. At this time, the interval between adjacent measurement points is adjusted to about 2 nm. The elastic modulus is measured, for example, over the entire range of 500 nm long×500 nm wide on the surface of the test piece. The elastic modulus of the test piece can be determined by vibrating the cantilever tip of the AFM on the surface of the test piece and measuring the repulsive force generated between the test piece and the probe. As the AFM, for example, MFP-3D-SA manufactured by Oxford Instruments can be used. As the cantilever, for example, OMCL-AC240TS (spring constant of 3 N/m) manufactured by Olympus can be used. The details of the elastic modulus measurement conditions are as follows.
・Measurement conditions Measurement mode: AM-FM viscoelastic mapping Measurement range: vertical 500 nm × horizontal 500 nm
Scanning speed: 3Hz
Set point: 0.8V
Target Amplitude: 2V
Measurement temperature: 25°C

By the above measurements, it is possible to obtain elastic modulus data for each of multiple positions on the surface of the test piece. By mapping this data, an AFM image as shown in FIG. 3A can be obtained. In this AFM image, each pixel is provided with color tone visual information based on the numerical value of the elastic modulus. The size of one pixel in the AFM image corresponds to the size of the cantilever tip. The number of pixels that make up the AFM image matches the number of measurement points.

Next, a histogram of elastic moduli with a class width of 0.1 MPa is constructed (Fig. 3B). In this histogram, the horizontal axis indicates the elastic modulus, and the vertical axis indicates the frequency (the number of measurement points). As shown in FIG. 3B, the histogram has one peak P, for example. Peak P is typically unimodal. The frequency corresponding to the apex of this peak P can be regarded as the maximum value _Fmax . A histogram may have multiple peaks or multimodal peaks. However, in this case, the maximum frequency value _Fmax tends to fall below 1400.

The maximum value F _max is preferably 1600 or more, more preferably 1800 or more, may be 2000 or more, may be 2200 or more, may be 2400 or more, or may be 2600 or more. good too. The upper limit of the maximum value F _max is not particularly limited, and is 3500, for example.

The maximum value F _max can be used as an index of variations in elastic modulus in the adhesive sheet 1 . It can be said that the larger the maximum value F _max is, the more the variation in elastic modulus is suppressed in the pressure-sensitive adhesive sheet 1 . According to the studies of the present inventors, the adhesive sheet 1 having a sufficient gel fraction, a maximum value F _max of 1400 or more, and suppressed variation in elastic modulus tends to have improved durability. be. In general, variations in elastic modulus are caused by fluctuations in the concentration of materials (polymers, etc.) that constitute the adhesive sheet, and tend to occur remarkably in adhesive sheets with a high gel fraction.

In the above histogram, the elastic modulus G _max corresponding to the maximum value F _max corresponds to the mode. The elastic modulus G _max is not particularly limited and is, for example, within the range of 10 to 100 MPa.

Furthermore, in the above histogram, the ratio R of the total frequency T included in the range of ±2.0 MPa from the elastic modulus G _max (MPa) corresponding to the maximum value F _max to the total frequency is not particularly limited, For example, 70% or more, preferably 75% or more, more preferably 80% or more, still more preferably 85% or more, may be 90% or more, or may be 95% or more . The upper limit of the ratio R is not particularly limited, and is, for example, 99%.

In the ratio R, the total frequency corresponds to, for example, the integrated value of the entire peak P, which corresponds to the total number of measurement points by AFM. The total value T corresponds to the integrated value of the peak P in the range from G _max −2.0 MPa to G _max +2.0 MPa. In addition, in the histogram, the integrated value of the peak P means the area of the peak P. Therefore, in this specification, the ratio R may be referred to as "area ratio".

The half width of the peak P is not particularly limited, and may be, for example, 4.0 MPa or less, may be 3.5 MPa or less, or may be 3.0 MPa or less. The lower limit of the half-value width of the peak P is not particularly limited, and is, for example, 1.0 MPa.

In the peak P, the peak width at the position with a frequency of 5 is not particularly limited, and is, for example, 15 MPa or less, preferably 10 MPa or less, may be 9 MPa or less, or may be 8 MPa or less. The lower limit of the peak width is not particularly limited, and is, for example, 5 MPa.

In this embodiment, the coefficient of variation of elastic modulus measured by the following test method is preferably less than 0.08. In addition, the elastic modulus can be measured, in detail, by the method described above for the maximum frequency value F _max .
Test method: Using an atomic force microscope (AFM), the elastic modulus is measured so that the number of measurement points is 65,536 in the range of 500 nm long×500 nm wide on the surface of the pressure-sensitive adhesive sheet 1 .

It can be said that the smaller the coefficient of variation of the elastic modulus is, the more the variation in the elastic modulus is suppressed in the adhesive sheet 1 . The coefficient of variation of elastic modulus is more preferably 0.078 or less, more preferably 0.075 or less, may be 0.073 or less, or may be 0.07 or less. The lower limit of the coefficient of variation of elastic modulus is not particularly limited. The coefficient of variation of the elastic modulus may be 0.02 or more, 0.035 or more, 0.04 or more, 0.05 or more, or 0.06. or more, 0.065 or more, or 0.067 or more. The coefficient of variation of elastic modulus means the ratio of the standard deviation to the average elastic modulus.

The storage elastic modulus G′ of the adhesive sheet 1 at 25° C. is not particularly limited, and is, for example, 0.1 MPa or more, preferably 0.15 MPa or more, more preferably 0.2 MPa or more, further preferably 0. 0.5 MPa or more, particularly preferably 0.8 MPa or more, and may be 1.0 MPa or more. The upper limit of the storage elastic modulus G' of the pressure-sensitive adhesive sheet 1 at 25°C is not particularly limited, and is, for example, 5 MPa. The PSA sheet 1 having a storage elastic modulus G' of 0.1 MPa or more, particularly 0.15 MPa or more, is suitable for suppressing dimensional change of the optical film. According to the pressure-sensitive adhesive sheet 1 having a storage elastic modulus G' of 0.1 MPa or more, particularly 1.0 MPa or more, for example, when the optical laminate is attached to an image forming layer or the like, the change in appearance can be sufficiently suppressed. There is also a tendency

The storage elastic modulus G' of the adhesive sheet 1 at 25°C can be specified by the following method. First, a measurement sample made of the material constituting the adhesive sheet 1 is prepared. The shape of the measurement sample is disc-shaped. The measurement sample has a bottom diameter of 8 mm and a thickness of 2 mm. A sample for measurement may be obtained by punching a disc-shaped laminate from a laminate in which a plurality of pressure-sensitive adhesive sheets 1 are laminated. Next, a dynamic viscoelasticity measurement is performed on the measurement sample. For dynamic viscoelasticity measurement, for example, "ARES-G2" manufactured by TA Instruments can be used. From the results of the dynamic viscoelasticity measurement, the storage elastic modulus G' of the pressure-sensitive adhesive sheet 1 at 25°C can be specified. The conditions for the dynamic viscoelasticity measurement are as follows.
・Measurement conditions Frequency: 1Hz
Deformation mode: Torsion Measurement temperature: -70°C to 150°C
Heating rate: 5°C/min

The adhesive sheet 1 preferably has high transparency. The haze of the adhesive sheet 1 is, for example, 1.0% or less, preferably 0.8% or less, and more preferably 0.6% or less. The lower limit of the haze of the adhesive sheet 1 is not particularly limited, and is, for example, 0.1%. In this specification, the haze of the pressure-sensitive adhesive sheet 1 is the value when the thickness is 25 μm, and can be measured according to Japanese Industrial Standards (former Japanese Industrial Standards; JIS) K7136:1981.

The adhesive strength of the adhesive sheet 1 is, for example, 0.5 N/25 mm or more, preferably 2 N/25 mm or more, and more preferably 5 N/25 mm or more. The upper limit of the adhesive strength of the adhesive sheet 1 is, for example, 10 N/25 mm from the viewpoint of reworkability. The adhesive force of the adhesive sheet 1 can be measured by the following method. First, the pressure-sensitive adhesive sheet 1 is cut into a piece having a width of 25 mm and a length of 150 mm to obtain a test piece. Next, the stainless steel test plate and the evaluation sheet are overlaid with the adhesive sheet 1 interposed therebetween, and a 2 kg roller is reciprocated once to press them together. The sheet for evaluation has a size of 30 mm in width and 150 mm in length, and is not particularly limited as long as it does not separate from the pressure-sensitive adhesive sheet 1 during the test. As the evaluation sheet, for example, an ITO film (125 Tetraite OES (manufactured by Oike Kogyo Co., Ltd.), etc.) can be used. Next, using a commercially available tensile tester, the adhesive sheet 1 was peeled off from the stainless steel test plate at a peeling angle of 180 ° and a tensile speed of 300 mm / min while the evaluation sheet was held. A value is specified as the adhesive force of Adhesive Sheet 1. Note that the above test is performed in an atmosphere of 23°C.

The indentation hardness of the adhesive sheet 1 at 25°C is preferably adjusted within an appropriate range. For the indentation hardness, a displacement-load hysteresis curve obtained by pressing a diamond Berkovich (triangular pyramid) probe vertically against the surface of the adhesive sheet 1 is numerically measured using software (triboscan) attached to the measuring device. It can be identified by processing. Specifically, the indentation hardness is measured by a single indentation method at 25° C. using a nanoindenter (Triboindenter TI-950 manufactured by Hysitron Inc.) under conditions of an indentation speed of 500 nm/sec and an indentation depth of 3000 nm.

The thickness of the adhesive sheet 1 is not particularly limited, and may be, for example, 1-200 μm, 5-150 μm, or even 10-100 μm.

The composition of the pressure-sensitive adhesive sheet 1 is not particularly limited as long as the gel fraction and the maximum value _Fmax are within the ranges described above, but it preferably contains two or more types of polymers. As an example, the adhesive sheet 1 is formed from an adhesive composition containing a (meth)acrylic polymer (A) and a cross-linking agent (B). Examples of the cross-linking agent (B) include isocyanate-based cross-linking agents and polyfunctional (meth)acrylate-based cross-linking agents. The pressure-sensitive adhesive sheet 1 formed from this pressure-sensitive adhesive composition contains a crosslinked product of a (meth)acrylic polymer (A) and a polymer (C) containing, as a main component, a structural unit derived from a crosslinking agent (B). Sometimes. As used herein, the term “main component” means a structural unit that is the most contained on a weight basis among all the structural units that constitute the polymer. In the polymer (C), the content of structural units derived from the cross-linking agent (B) is, for example, 70% by weight or more, preferably 90% by weight or more. The polymer (C), for example, consists essentially of structural units derived from the cross-linking agent (B). In the adhesive sheet 1, the crosslinked product of the (meth)acrylic polymer (A) and the polymer (C) may constitute an interpenetrating network (IPN) structure or a semi-interpenetrating network (semi-IPN) structure. This IPN structure (or semi-IPN structure) is suitable for improving the durability while increasing the elastic modulus of the pressure-sensitive adhesive sheet 1 .

[(Meth) acrylic polymer (A)]
The (meth)acrylic polymer (A) can function as a base polymer for acrylic pressure-sensitive adhesives. Acrylic pressure-sensitive adhesives tend to have excellent optical transparency, appropriate wettability, cohesiveness, adhesiveness and other adhesive properties, and excellent weather resistance, heat resistance, and the like. The (meth)acrylic polymer (A) contains, for example, a structural unit derived from an alkyl (meth)acrylate as a main component. As used herein, "(meth)acrylate" means acrylate and/or methacrylate.

The number of carbon atoms in the alkyl group contained in the alkyl (meth)acrylate for forming the main skeleton of the (meth)acrylic polymer (A) is not particularly limited, and is, for example, 1-30. This alkyl group may be linear, branched, or cyclic. Examples of alkyl groups include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, amyl group, hexyl group, cyclohexyl group, heptyl group, 2-ethylhexyl group, isooctyl group, nonyl group and decyl group. , isodecyl group, dodecyl group, isomyristyl group, lauryl group, tridecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group and the like. Alkyl (meth)acrylates can be used alone or in combination. The average carbon number of the alkyl group is preferably 3-9. Alkyl (meth)acrylate is preferably butyl acrylate.

In the (meth)acrylic polymer (A), the content of structural units derived from alkyl (meth)acrylate is, for example, 50% by weight or more, preferably 60% by weight or more, from the viewpoint of improving the adhesiveness of the pressure-sensitive adhesive sheet 1. , more preferably 70% by weight or more, and still more preferably 80% by weight or more.

As monomers constituting the (meth)acrylic polymer (A), in addition to alkyl (meth)acrylates, aromatic ring-containing monomers, amide group-containing monomers, carboxyl group-containing monomers, hydroxyl group-containing monomers, At least one comonomer selected from the group consisting of monomers is included. Comonomers can be used alone or in combination.

The (meth)acrylic polymer (A) preferably contains structural units derived from aromatic ring-containing monomers. The aromatic ring-containing monomer is a compound containing an aromatic ring structure in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or vinyl group. Examples of aromatic rings include benzene ring, naphthalene ring, and biphenyl ring. The aromatic ring-containing monomer is preferably an aromatic ring-containing (meth)acrylate.

Examples of aromatic ring-containing (meth)acrylates include benzyl (meth)acrylate, phenyl (meth)acrylate, o-phenylphenol (meth)acrylate, phenoxy (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, ) acrylate, phenoxydiethylene glycol (meth) acrylate, ethylene oxide-modified nonylphenol (meth) acrylate, ethylene oxide-modified cresol (meth) acrylate, phenol ethylene oxide-modified (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, Those having a benzene ring such as methoxybenzyl (meth)acrylate, chlorobenzyl (meth)acrylate, cresyl (meth)acrylate, polystyryl (meth)acrylate; hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2 -naphthoxyethyl acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate and the like having a naphthalene ring; and biphenyl (meth)acrylate and the like having a biphenyl ring. Among these, benzyl (meth)acrylate and phenoxyethyl (meth)acrylate are preferable, and benzyl acrylate is more preferable, from the viewpoint of improving the adhesive properties and durability of the adhesive sheet 1 .

The (meth)acrylic polymer (A) may contain structural units derived from amide group-containing monomers. The amide group-containing monomer is a compound containing an amide group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or vinyl group. Examples of amide group-containing monomers include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N -butyl (meth)acrylamide, N-hexyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylol-N-propane (meth)acrylamide, aminomethyl (meth)acrylamide, aminoethyl (meth)acrylamide, mercapto acrylamide-based monomers such as methyl (meth)acrylamide and mercaptoethyl (meth)acrylamide; N-acryloyl heterocycles such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine Monomers: N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. Among these, N-vinyl group-containing lactam-based monomers are preferred from the viewpoint of improving the durability of the pressure-sensitive adhesive sheet 1 .

The (meth)acrylic polymer (A) may contain a structural unit derived from a carboxyl group-containing monomer. A carboxyl group-containing monomer is a compound containing a carboxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group and a vinyl group. Examples of carboxyl group-containing monomers include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Among these, acrylic acid is preferable from the viewpoint of improving copolymerizability, price, and adhesive properties of the adhesive sheet 1 . When the (meth)acrylic polymer (A) has a structural unit derived from a carboxyl group-containing monomer, particularly acrylic acid, for example, the self-polymerization of the cross-linking agent (B), particularly the isocyanate-based cross-linking agent, is improved. can be enhanced. Improvement of the self-polymerization property of the cross-linking agent (B) contributes to suppression of peeling of the pressure-sensitive adhesive sheet 1 in a humidified environment and stabilization of the physical properties of the pressure-sensitive adhesive sheet 1 in a system having a high content of the cross-linking agent (B). I can.

The (meth)acrylic polymer (A) may contain structural units derived from hydroxyl group-containing monomers. A hydroxyl group-containing monomer is a compound containing a hydroxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl. (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate and other hydroxyl group-containing alkyl (meth)acrylates; (4-hydroxymethylcyclohexyl)-methylacrylate and other hydroxyl group-containing cycloalkyl (meth)acrylates; ) acrylates. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.

Among comonomers, aromatic ring-containing monomers and carboxyl group-containing monomers are preferably used from the viewpoint of adhesiveness, durability, etc., and aromatic ring-containing monomers are particularly preferably used. The (meth)acrylic polymer (A) containing a structural unit derived from a carboxyl group-containing monomer tends to promote the reaction between, for example, isocyanate cross-linking agents by taking in water molecules in the surrounding atmosphere. be. The aromatic ring-containing monomer also tends to improve the compatibility between the (meth)acrylic polymer (A) and the polymer (C) and improve the durability of the optical laminate in a hot and humid environment.

In the (meth)acrylic polymer (A), the content of structural units derived from copolymer monomers is not particularly limited, and is, for example, 0 to 40% by weight, and 0.1 to 30% by weight. may be 0.1 to 20% by weight.

In the (meth)acrylic polymer (A), the content of structural units derived from aromatic ring-containing monomers is not particularly limited, and is, for example, 3 to 25% by weight, more preferably 22% by weight or less, and 20% by weight. Weight % or less is more preferable. This content is more preferably 8% by weight or more, and even more preferably 12% by weight or more.

In the (meth)acrylic polymer (A), the content of structural units derived from the amide group-containing monomer is not particularly limited, and is, for example, 0.1 to 10% by weight, and 0.2 to 8% by weight. is more preferred, and 0.6 to 6% by weight is even more preferred.

In the (meth)acrylic polymer (A), the content of structural units derived from a carboxyl group-containing monomer is not particularly limited, and is, for example, 0.1 to 25% by weight, more preferably 3% by weight or more. . From the viewpoint of suppressing reaction with the isocyanate-based cross-linking agent, the content is preferably 20% by weight or less, more preferably 10% by weight or less.

In the (meth)acrylic polymer (A), the content of structural units derived from a comonomer having an active hydrogen that is highly reactive with an isocyanate crosslinking agent, such as a hydroxyl group-containing monomer, is low. is preferred. In the (meth)acrylic polymer (A), the content of structural units derived from hydroxyl group-containing monomers is, for example, 1% by weight or less, more preferably 0.5% by weight or less, and 0.2% by weight or less. is more preferred. The (meth)acrylic polymer (A) may be substantially free of structural units derived from hydroxyl group-containing monomers.

As a monomer component, in addition to the alkyl (meth)acrylate and the above copolymerization monomer, an inert such as a (meth)acryloyl group or a vinyl group can be used for the purpose of improving the adhesiveness and heat resistance of the pressure-sensitive adhesive sheet 1. Other comonomers having polymerizable functional groups containing saturated double bonds can be used. Other comonomers can be used alone or in combination.

Other copolymerizable monomers include, for example, acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; allylsulfonic acid, 2-(meth)acrylamide-2- sulfonic acid group-containing monomers such as methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, and sulfopropyl (meth)acrylate; phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; aminoethyl (meth) Alkylaminoalkyl (meth)acrylates such as acrylates, N,N-dimethylaminoethyl (meth)acrylate and t-butylaminoethyl (meth)acrylate; Alkoxyalkyls such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate (meth)acrylates; succinimide-based monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; Maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide; N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide , N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide, N-lauryl itaconimide; vinyl monomers such as vinyl acetate and vinyl propionate; cyano such as acrylonitrile and methacrylonitrile Acrylate-based monomers; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate; polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate Glycol-based (meth)acrylates such as; tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, 2-methoxyethyl acrylate and other (meth)acrylate monomers; 3-acryloxypropyltri ethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyltrimethoxysilane, 4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane, 8-vinyloctyltriethoxysilane, 10-methacryloyloxydecyl Silicon atom-containing silane monomers such as trimethoxysilane, 10-acryloyloxydecyltrimethoxysilane, 10-methacryloyloxydecyltriethoxysilane, and 10-acryloyloxydecyltriethoxysilane are included.

Furthermore, other copolymer monomers include, for example, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol A diglycidyl ether di (Meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipenta Polyfunctional monomers having two or more unsaturated double bonds, such as erythritol hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate, can be mentioned.

When another copolymerization monomer is used as the monomer component, the content of structural units derived from the other copolymerization monomer in the (meth)acrylic polymer (A) is 10% by weight or less. is preferably 7% by weight or less, and even more preferably 5% by weight or less.

The (meth)acrylic polymer (A) usually has a weight average molecular weight of 300,000 to 4,000,000. From the viewpoint of durability, the (meth)acrylic polymer (A) preferably has a weight average molecular weight of 300,000 to 3,000,000, more preferably 400,000 to 2,200,000. A weight average molecular weight of 300,000 or more is preferable from the viewpoint of heat resistance. When the weight-average molecular weight is 4,000,000 or less, the pressure-sensitive adhesive sheet 1 tends to be hard to harden and to be hard to peel off. Weight average molecular weight (Mw)/number average molecular weight (Mn), which means molecular weight distribution, is preferably 1.8 to 10, more preferably 1.8 to 7, and 1.8 to 5. is more preferred. A molecular weight distribution (Mw/Mn) of 10 or less is preferable from the standpoint of durability. The weight average molecular weight and molecular weight distribution (Mw/Mn) are measured by GPC (gel permeation chromatography) and obtained from values calculated by polystyrene conversion.

The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above monomers by a known method. A monomer and a partial polymer of the monomer may be polymerized. Polymerization can be carried out, for example, by solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Solution polymerization and active energy ray polymerization are preferred because they can form a pressure-sensitive adhesive sheet with excellent optical transparency. Polymerization is preferably carried out while avoiding contact of the monomer and/or partial polymer with oxygen. Polymerization in shutdown can be employed. The (meth)acrylic polymer (A) to be formed may be in any form such as a random copolymer, a block copolymer, or a graft copolymer.

The polymerization system forming the (meth)acrylic polymer (A) may contain one or more polymerization initiators. The type of polymerization initiator can be selected depending on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

Solvents used for solution polymerization include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

Polymerization initiators used for solution polymerization are, for example, azo polymerization initiators, peroxide polymerization initiators, and redox polymerization initiators. Peroxide polymerization initiators are, for example, dibenzoyl peroxide and t-butyl permaleate. Among them, the azo polymerization initiator disclosed in JP-A-2002-69411 is preferable. The azo polymerization initiator, for example, 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis (2-methylpropion acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of the azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight, and may be 0.1 to 0.3 parts by weight, per 100 parts by weight of the total amount of the monomers.

The active energy rays used for active energy ray polymerization are, for example, ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams and electron beams, and ultraviolet rays. The active energy rays are preferably ultraviolet rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. A polymerization system for active energy ray polymerization typically contains a photopolymerization initiator. Polymerization conditions for active energy ray polymerization are not limited as long as the (meth)acrylic polymer (A) is formed.

Photopolymerization initiators include, for example, benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, and photoactive oxime-based photopolymerization initiators. , a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, a ketal-based photopolymerization initiator, and a thioxanthone-based photopolymerization initiator. However, the photopolymerization initiator is not limited to the above examples.

Benzoin ether-based photopolymerization initiators include, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, anisolemethyl is ether. Acetophenone-based photopolymerization initiators include, for example, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenylketone, 4-phenoxydichloroacetophenone, 4-(t-butyl)dichloro Acetophenone. Examples of α-ketol photopolymerization initiators are 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. The aromatic sulfonyl chloride photopolymerization initiator is, for example, 2-naphthalenesulfonyl chloride. A photoactive oxime-based photopolymerization initiator is, for example, 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. A benzoin-based photopolymerization initiator is, for example, benzoin. A benzylic photopolymerization initiator is, for example, benzyl. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. A ketal photopolymerization initiator is, for example, benzyl dimethyl ketal. Thioxanthone-based photopolymerization initiators are, for example, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

The amount of the photopolymerization initiator used is, for example, 0.01 to 1 part by weight, and may be 0.05 to 0.5 part by weight, based on 100 parts by weight of the total amount of the monomers.

The content of the (meth)acrylic polymer (A) in the pressure-sensitive adhesive composition is, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, and further 80% by weight or more in terms of solid content. may The upper limit of the content is, for example, 99% by weight or less, and may be 97% by weight or less, 95% by weight or less, 93% by weight or less, or even 90% by weight or less.

[Crosslinking agent (B)]
Cross-linking agent (B) is typically a polyfunctional cross-linking agent having two or more cross-linking reactive groups per molecule. The cross-linking agent (B) may be a tri- or higher functional cross-linking agent having 3 or more cross-linking reactive groups per molecule. The upper limit of the number of cross-linking reactive groups per molecule is 5, for example.

The cross-linking agent (B) preferably has good compatibility with the (meth)acrylic polymer (A). By using the cross-linking agent (B) having good compatibility with the (meth)acrylic polymer (A), it is possible to easily suppress the white turbidity of the adhesive sheet 1 after the adhesive sheet 1 is produced. For example, as described later, when an isocyanate-based cross-linking agent is used as the cross-linking agent (B), the pressure-sensitive adhesive composition tends to exhibit lower critical solution temperature (LCST) phase separation behavior. . In this case, if the compatibility between the cross-linking agent (B) and the (meth)acrylic polymer (A) is good, clouding of the adhesive sheet 1 is suppressed even if the adhesive composition is dried at a relatively high temperature. be able to. In other words, there is a tendency for the range of drying temperatures applicable to pressure-sensitive adhesive compositions to be wide. In particular, when the (meth)acrylic polymer (A) contains a structural unit derived from an aromatic ring-containing monomer or a structural unit derived from a monomer having a relatively small molecular weight such as methyl acrylate or ethyl acrylate, , the compatibility between the (meth)acrylic polymer (A) and the cross-linking agent (B) tends to be good.

The cross-linking agent (B) includes, for example, at least one selected from the group consisting of an isocyanate-based cross-linking agent and a polyfunctional (meth)acrylate-based cross-linking agent, preferably an isocyanate-based cross-linking agent. Isocyanate-based cross-linking agents are suitable for solvent-based pressure-sensitive adhesive compositions. Polyfunctional (meth)acrylate cross-linking agents are suitable for active energy ray-curable pressure-sensitive adhesive compositions.

A compound having at least two isocyanate groups (isocyanate compound) can be used as the isocyanate-based cross-linking agent. The number of isocyanate groups contained in the isocyanate compound is preferably 3 or more. The upper limit of the number of isocyanate groups is not particularly limited, and is 5, for example. Examples of isocyanate compounds include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds. The isocyanate-based cross-linking agent is preferably capable of self-polymerization by reacting with water.

Examples of aromatic isocyanate compounds include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, and 4,4′-toluidine. diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, xylylene diisocyanate and the like.

Examples of alicyclic isocyanate compounds include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated tolylene diisocyanate. , hydrogenated tetramethylxylylene diisocyanate, and the like.

Examples of aliphatic isocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene. and diisocyanate.

Examples of isocyanate-based cross-linking agents include polymers of the above isocyanate compounds (dimers, trimers, pentamers, etc.), adducts obtained by addition to polyhydric alcohols such as trimethylolpropane, urea modified products, Urethane prepolymers obtained by addition to biuret-modified, allophanate-modified, isocyanurate-modified, carbodiimide-modified, polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol and the like are also included. From the viewpoint of compatibility with the (meth)acrylic polymer (A), the isocyanate cross-linking agent preferably contains a long-chain alkyl group.

Preferred examples of isocyanate-based cross-linking agents are aromatic isocyanate compounds and derivatives thereof. Specifically, tolylene diisocyanate-based (TDI-based) cross-linking agents (tolylene diisocyanate and derivatives thereof) and diphenylmethane diisocyanate-based (MDI-based) cross-linking agents agent (diphenylmethane diisocyanate and its derivatives). However, the isocyanate-based cross-linking agent may be a hexamethylene diisocyanate-based (HDI-based) cross-linking agent (hexamethylene diisocyanate and its derivatives). The isocyanate-based cross-linking agent is particularly preferably a TDI-based cross-linking agent. The TDI-based cross-linking agent and the MDI-based cross-linking agent are more likely to react with each other than the HDI-based cross-linking agent, and are suitable for producing the pressure-sensitive adhesive sheet 1 having an IPN structure.

The isocyanate-based cross-linking agent preferably contains, as a TDI-based cross-linking agent, an adduct of a polyhydric alcohol and tolylene diisocyanate, or an isocyanurate-modified tolylene diisocyanate. A specific example of the adduct of a polyhydric alcohol and tolylene diisocyanate is a trimethylolpropane/tolylene diisocyanate trimer adduct.

Examples of commercially available isocyanate-based cross-linking agents include, for example, Mitsui Chemicals' trade names "Takenate D-101E", "Takenate D-262", "Takenate D-110N", "Takenate D-120N", and "Takenate D". -140N”, “Takenate D-160N”, “Takenate D-165N”, “Takenate D-170HN”, “Takenate D-178N”, “Takenate 500”, “Takenate 600”, trade name “Millionate” manufactured by Tosoh Corporation MT", "Millionate MTL", "Millionate MR-200", "Millionate MR-400", "Coronate L", "Coronate HL", "Coronate HX" and the like, preferably Takenate D-101E and Takenate D -262.

As for the isocyanate-based cross-linking agents, the above-mentioned ones may be used singly or in combination of two or more.

A compound having at least two (meth)acryloyl groups (polyfunctional (meth)acrylate compound) can be used as the polyfunctional (meth)acrylate cross-linking agent. Examples of polyfunctional (meth)acrylate compounds include polyalkylene glycol di(meth)acrylates such as polypropylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; 1,6-hexanediol di(meth)acrylate, neopentyl alkyldiol di(meth)acrylates such as glycol di(meth)acrylate; (meth)acrylic acid adducts of diglycidyl ether compounds such as bisphenol A diglycidyl ether di(meth)acrylate; trimethylolpropane tri(meth)acrylate; compounds having three or more (meth)acryloyl groups such as pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc.; and polypropylene glycol di(meth)acrylate is preferred.

Commercially available polyfunctional (meth)acrylate cross-linking agents include, for example, the product name "APG-400" manufactured by Shin-Nakamura Chemical Co., Ltd.

As for the polyfunctional (meth)acrylate-based cross-linking agents, the above-mentioned ones may be used singly or in combination of two or more.

The cross-linking agent (B) is not limited to isocyanate-based cross-linking agents and polyfunctional (meth)acrylate-based cross-linking agents. Other examples of the cross-linking agent (B) include peroxide-based cross-linking agents, epoxy-based cross-linking agents, imine-based cross-linking agents, polyfunctional metal chelates, and the like. Two or more of these cross-linking agents may be mixed and used. For example, a polyfunctional (meth)acrylate cross-linking agent and an epoxy cross-linking agent may be mixed and used.

The amount of the cross-linking agent (B) is, for example, 2 parts by weight or more, preferably 3 parts by weight or more, and more preferably 5 parts by weight or more with respect to 100 parts by weight of the (meth)acrylic polymer (A). , more preferably 8 parts by weight or more, particularly preferably 10 parts by weight or more, and may be 12 parts by weight or more. The amount of the cross-linking agent (B) is, for example, 30 parts by weight or less, preferably 25 parts by weight or less, and less than 20 parts by weight with respect to 100 parts by weight of the (meth)acrylic polymer (A). good too.

As an example, when the cross-linking agent (B) is an adduct of trimethylolpropane and an isocyanate compound containing a long-chain alkyl group, the amount is (meth)acrylic polymer (A) 100 parts by weight preferably about 10 parts by weight. When the cross-linking agent (B) is an isocyanurate-modified isocyanate compound containing a long-chain alkyl group, the amount thereof is about 5 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). Preferably. When the cross-linking agent (B) is a bifunctional (meth)acrylate cross-linking agent, it is preferably added in an amount of about 20 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). When the cross-linking agent (B) is a tetrafunctional (meth)acrylate-based cross-linking agent, it is preferably added in an amount of about 10 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). When the cross-linking agent (B) is a hexafunctional (meth)acrylate-based cross-linking agent, its blending amount is preferably about 7 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). However, the blending amount of the cross-linking agent (B) is not limited to those described above, and can be appropriately adjusted according to the molecular weight and structure of the cross-linking agent (B).

In the pressure-sensitive adhesive composition, when the amount of the cross-linking agent (B) added to 100 parts by weight of the (meth)acrylic polymer (A) is as large as about 2 parts by weight or more, when the pressure-sensitive adhesive sheet 1 is produced, the cross-linking agent (B ) react with each other to form a polymer (C) containing structural units derived from the cross-linking agent (B) as a main component. The polymer (C) is suitable for suppressing dimensional change of the adhesive sheet 1 by imparting sufficient cohesion to the adhesive sheet 1 . That is, the polymer (C) is suitable for suppressing display unevenness and light leakage in an image display device. Furthermore, the combination of the (meth)acrylic polymer (A) and the polymer (C) is suitable for improving the durability of the pressure-sensitive adhesive sheet 1 under hot and humid environments.

[Other ingredients]
The pressure-sensitive adhesive composition may further contain a (meth)acrylic oligomer.

The (meth)acrylic oligomer can have the same composition as the (meth)acrylic polymer (A) described above, except that the weight average molecular weight (Mw) is different. The weight average molecular weight (Mw) of the (meth)acrylic oligomer is, for example, 1000 or more, and may be 2000 or more, 3000 or more, or even 4000 or more. The upper limit of the weight average molecular weight (Mw) of the (meth)acrylic oligomer is, for example, 30,000 or less, and may be 15,000 or less, 10,000 or less, or even 7,000 or less.

The (meth)acrylic oligomer has, for example, one or more structural units derived from the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate. , isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate ) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate ) acrylates, alkyl (meth)acrylates such as undecyl (meth)acrylate and dodecyl (meth)acrylate; esters with alicyclic alcohols; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

The (meth)acrylic oligomer preferably has structural units derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesiveness of the adhesive sheet 1 can be further enhanced. Examples of the acrylic monomer include alkyl (meth)acrylates having a branched alkyl group such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; cyclohexyl (meth)acrylate and isobornyl (meth)acrylate. and esters of (meth)acrylic acid and alicyclic alcohols such as dicyclopentanyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, more preferably two or more cyclic structures. In addition, when the (meth)acrylic oligomer is polymerized and/or the adhesive sheet is irradiated with ultraviolet rays during the formation of the pressure-sensitive adhesive sheet, the progress of polymerization and/or formation is less likely to be inhibited. For example, an alkyl (meth)acrylate having an alkyl group having a branched structure, or an ester of (meth)acrylic acid and an alicyclic alcohol can be used.

Specific examples of (meth)acrylic oligomers include copolymers of butyl acrylate, methyl acrylate and acrylic acid, copolymers of cyclohexyl methacrylate and isobutyl methacrylate, copolymers of cyclohexyl methacrylate and isobornyl methacrylate, cyclohexyl Copolymers of methacrylate and acryloylmorpholine, copolymers of cyclohexyl methacrylate and diethylacrylamide, copolymers of 1-adamantyl acrylate and methyl methacrylate, copolymers of dicyclopentanyl methacrylate and isobornyl methacrylate, Copolymers of methyl methacrylate and at least one selected from dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate and cyclopentanyl methacrylate, homopolymers of dicyclopentanyl acrylate, 1- They are homopolymers of adamantyl methacrylate and homopolymers of 1-adamantyl acrylate.

The polymerization method for the (meth)acrylic polymer (A) described above can be employed for the polymerization of the (meth)acrylic oligomer.

When the pressure-sensitive adhesive composition contains a (meth)acrylic oligomer, the amount thereof is, for example, 70 parts by weight or less, 50 parts by weight or less, and further 100 parts by weight of the (meth)acrylic polymer (A). may be 40 parts by weight or less. The lower limit of the amount to be blended is, for example, 1 part by weight or more, 2 parts by weight or more, and may be 3 parts by weight or more with respect to 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition may not contain a (meth)acrylic oligomer.

The adhesive composition may further contain known additives. Additives include, for example, silane coupling agents, polyfunctional alcohols, solvents, colorants, powders such as pigments, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework improvers, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, antistatic agents (ionic compounds such as alkali metal salts, ionic liquids, ionic solids, etc.), Examples include inorganic or organic fillers, metal powders, particles, and foil-like materials. Furthermore, a redox system with a reducing agent may be employed within a controllable range. These additives can be used in an amount of, for example, 10 parts by weight or less, preferably 5 parts by weight or less, and more preferably 1 part by weight or less per 100 parts by weight of the (meth)acrylic polymer (A).

Specific examples of silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4- Epoxy group-containing silane coupling agents such as epoxycyclohexyl)ethyltrimethoxysilane; 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N- Amino group-containing silane coupling agents such as (1,3-dimethylbutylidene)propylamine and N-phenyl-γ-aminopropyltrimethoxysilane; 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane; (Meth)acrylic group-containing silane coupling agents such as; isocyanate group-containing silane coupling agents such as 3-isocyanatopropyltriethoxysilane;

When the pressure-sensitive adhesive composition contains a silane coupling agent, the amount is, for example, 5 parts by weight or less, 3 parts by weight or less, and 1 part by weight with respect to 100 parts by weight of the (meth)acrylic polymer (A). It may be 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, or even 0.05 parts by weight or less. The adhesive composition may not contain a silane coupling agent.

The adhesive composition may contain a polyfunctional alcohol. The molecular weight of the polyfunctional alcohol is, for example, 240 or less, and may be 230 or less, 220 or less, 210 or less, 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, or even 150 or less. The lower limit of the molecular weight is, for example, 60 or more, and may be 80 or more, 90 or more, or even 100 or more.

Examples of polyfunctional alcohols are alkylene glycols such as ethylene glycol and propylene glycol and their polymers; ether glycols such as diethylene glycol and their polymers; trimethylolethane; trimethylolpropane; is. Polyfunctional alcohols are preferably trimethylolpropane, glycerin, and diethylene glycol and polymers thereof, more preferably trimethylolpropane.

The polyfunctional alcohol may be trifunctional or higher. Examples of trifunctional polyfunctional alcohols are trimethylolpropane and glycerin.

The polyfunctional alcohol does not have to have a reactive group with reactivity with the cross-linking agent (B) other than the hydroxyl group. The reactive group is, for example, at least one selected from an amino group, a carboxyl group and an epoxy group, particularly an amino group.

The blending amount of the polyfunctional alcohol in the adhesive composition is, for example, 0.5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the (meth)acrylic polymer (A). The upper limit of the blending amount may be 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, or even 3 parts by weight or less.

Types of pressure-sensitive adhesive compositions are, for example, emulsion type, solvent type (solution type), active energy ray-curable type (light-curing type), and heat-melting type (hot-melt type). From the viewpoint of being able to form the adhesive sheet 1 having excellent durability, the adhesive composition may be solvent-based, active energy ray-curable, or solvent-based. The solvent-based pressure-sensitive adhesive composition may not contain a photocuring agent such as an ultraviolet curing agent.

The adhesive sheet 1 can be produced from the adhesive composition by the following method. For the solvent type, for example, the pressure-sensitive adhesive composition or a mixture of the pressure-sensitive adhesive composition and a solvent is applied to a base film to form a coating film, and the formed coating film is dried to form the pressure-sensitive adhesive sheet 1. . The pressure-sensitive adhesive composition is thermally cured by heat during drying. For the active energy ray-curable type (photocurable type), for example, a monomer (group) that becomes a (meth)acrylic polymer (A) by polymerization, a cross-linking agent (B), and, if necessary, a monomer A mixture of (group) partial polymer, polymerization initiator, oligomer, additive, solvent, etc. is applied to a substrate film, and the formed coating film is irradiated with active energy rays to form a pressure-sensitive adhesive sheet 1. The solvent may be removed by drying the coating film before irradiation with the active energy ray. The base film may be a film (release liner) whose coating surface has undergone a release treatment.

The adhesive sheet 1 formed on the base film can be transferred to any layer. Moreover, the base film may be an optical film, and in this case, an optical laminate including the adhesive sheet 1 and the optical film is obtained.

A known method can be adopted for application to the base film. Coating is, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, extrusion coating using a die coater, or the like. can be implemented by

Solvent-based PSA compositions, particularly PSA compositions containing an isocyanate cross-linking agent, tend to exhibit Lower Critical Solution Temperature (LCST) phase separation behavior. Therefore, when using a solvent-based pressure-sensitive adhesive composition, the drying temperature of the coating film is preferably 200° C. or less, for example, 160° C. or less, 150° C. or less, 130° C. or less, 120° C. or less, and further 100° C. or less. There may be. When the drying temperature is 130° C. or less, the reaction rate of the cross-linking agent (B), particularly the isocyanate-based cross-linking agent, can be appropriately adjusted, and the compatibility between the (meth)acrylic polymer (A) and the polymer (C) can be improved. There is a tendency that the elastic modulus variation in the pressure-sensitive adhesive sheet 1 can be reduced by maintaining it well. The lower limit of the drying temperature of the coating film is not particularly limited, and is, for example, 40°C, and may be 60°C. The drying time of the coating film can be appropriately adjusted depending on the drying temperature and the like, and is, for example, 5 seconds to 20 minutes, 5 seconds to 10 minutes, or even 10 seconds to 5 minutes. When the drying temperature is set high, it is preferable to set the drying time short from the viewpoint of reducing variations in elastic modulus in the pressure-sensitive adhesive sheet 1 . It is preferable to dry the coating film in an environment with relatively high humidity. As a result, the reaction of the cross-linking agent (B), especially the isocyanate-based cross-linking agent, in the coating film tends to proceed quickly and uniformly. The relative humidity at the drying temperature of the coating film is, for example, 0% RH or higher, and may be 5% RH or higher, 10% RH or higher, 20% RH or higher, or even 30% RH or higher.

An active energy ray-curable pressure-sensitive adhesive composition, particularly a pressure-sensitive adhesive composition containing a polyfunctional (meth)acrylate cross-linking agent, exhibits upper critical solution temperature (UCST type) phase separation behavior. Tend. Therefore, when an active energy ray-curable pressure-sensitive adhesive composition is used, the coating film may be subjected to drying treatment while being irradiated with the active energy ray, or before and after the application of the active energy ray. The drying temperature of the coating film is preferably, for example, 60° C. or higher, and may be 80° C. or higher, 100° C. or higher, 110° C. or higher, or even 120° C. or higher. By setting the drying temperature of the coating film high, the (meth)acrylic polymer (A) and the polymer (C), particularly the polymer (C) containing structural units derived from a polyfunctional (meth)acrylate cross-linking agent, There is a tendency that the variation in elastic modulus in the pressure-sensitive adhesive sheet 1 can be reduced by maintaining good compatibility with. The upper limit of the drying temperature of the coating film is not particularly limited, and is 200° C., for example. The drying time of the coating film can be appropriately adjusted depending on the drying temperature and the like, and is, for example, 5 seconds to 20 minutes, 5 seconds to 10 minutes, or even 10 seconds to 5 minutes.

(optical film)
Examples of the optical film 2 are polarizing plates, retardation films, and laminated films containing polarizing plates and/or retardation films. However, the optical film 2 is not limited to the above examples. The optical film 2 may contain a film made of glass.

A polarizing plate is, for example, a laminate containing a polarizer and a transparent protective film. The transparent protective film is arranged, for example, in contact with the main surface (the surface having the widest area) of the layered polarizer. A polarizer may be placed between two transparent protective films.

The polarizer is not particularly limited, and various types can be used. As a polarizer, for example, hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films are added with dichroic properties such as iodine and dichroic dyes. Monoaxially stretched after adsorbing a substance; oriented polyene films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferable, and an iodine-based polarizer containing iodine and/or iodine ions is more preferable. Although the thickness of the polarizer is not particularly limited, it is generally about 5 to 80 μm.

A polarizer made by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine and stretching it to 3 to 7 times its original length. If necessary, the polyvinyl alcohol can be immersed in an aqueous solution of potassium iodide containing boric acid, zinc sulfate, zinc chloride and the like. Furthermore, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol film with water, dirt and anti-blocking agents on the surface of the polyvinyl alcohol film can be washed away, and by swelling the polyvinyl alcohol film, uneven dyeing can be suppressed. There is also The stretching of the polyvinyl alcohol-based film may be performed after dyeing with iodine, may be performed while dyeing, or may be performed before dyeing with iodine. Stretching may be performed in an aqueous solution of boric acid, potassium iodide, or the like, or in a water bath.

A thin polarizer with a thickness of 10 μm or less can also be used as the polarizer. From the viewpoint of thickness reduction, the thickness of the polarizer is preferably 1 to 7 μm. Such a thin polarizer is preferable because it has little unevenness in thickness, is excellent in visibility, is excellent in durability due to little dimensional change, and is capable of achieving a thin polarizing plate.

Typical thin polarizers include JP-A-51-069644, JP-A-2000-338329, WO2010/100917, JP-A-4751481, JP-A-2012-073563. can be mentioned thin polarizers described in. These thin polarizers can be obtained by a manufacturing method including a step of stretching a polyvinyl alcohol-based resin (hereinafter also referred to as a PVA-based resin) layer and a stretching resin substrate in the state of a laminate, and a step of dyeing. With this manufacturing method, the PVA-based resin layer is supported by the stretching resin base material, so even if the PVA-based resin layer is thin, problems such as breakage due to stretching can be suppressed.

Among the manufacturing methods including the step of stretching and the step of dyeing in the state of a laminate, it can be stretched at a high magnification and can improve the polarization performance. 073563, a method including a step of stretching in an aqueous boric acid solution is preferable, and in particular, auxiliary before stretching in an aqueous boric acid solution described in Japanese Patent No. 4751481 and Japanese Patent Application Laid-Open No. 2012-073563. A manufacturing method including a step of stretching in the air is preferred.

As a material for forming the transparent protective film provided on one side or both sides of the polarizer, for example, a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, moisture blocking property, isotropy, etc. is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic Polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof can be used. The material of the transparent protective film may be a thermosetting resin such as (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone, or an ultraviolet curable resin. When the polarizing plate has two transparent protective films, the materials of the two transparent protective films may be the same or different. For example, a transparent protective film made of a thermoplastic resin is attached to one main surface of the polarizer via an adhesive, and a thermosetting resin or ultraviolet light is applied to the other main surface of the polarizer. A transparent protective film made of a curable resin may be attached. The transparent protective film may contain one or more optional additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, and colorants. The thermoplastic resin content in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, particularly preferably 70 to 97% by weight. When the content of the thermoplastic resin in the transparent protective film is 50% by weight or more, there is a tendency that the high transparency inherent in the thermoplastic resin can be sufficiently exhibited.

Although the thickness of the transparent protective film can be determined as appropriate, it is generally about 10 to 200 μm in terms of strength, workability such as handleability, and thinness.

The polarizer and transparent protective film are usually in close contact with each other via a water-based adhesive or the like. Examples of water-based adhesives include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl-based latexes, water-based polyurethanes, and water-based polyesters. Examples of adhesives other than the adhesives described above include ultraviolet curing adhesives, electron beam curing adhesives, and the like. The electron beam curable polarizing plate adhesive exhibits suitable adhesion to various transparent protective films. The adhesive may contain a metallic compound filler.

In the polarizing plate, a retardation film or the like can be formed on the polarizer instead of the transparent protective film. On the transparent protective film, it is also possible to provide another transparent protective film, or to provide a retardation film or the like.

Regarding the transparent protective film, a hard coat layer may be provided on the surface facing the surface adhered to the polarizer, and it is also possible to apply treatments for the purpose of antireflection, antisticking, diffusion, antiglare, etc. can.

As the retardation film, one obtained by stretching a polymer film or one obtained by aligning and fixing a liquid crystal material can be used. A retardation film has, for example, birefringence in the plane and/or in the thickness direction.

As the retardation film, antireflection retardation film (see JP 2012-133303 [0221], [0222], [0228]), viewing angle compensation retardation film (JP 2012-133303 [0225 ], see [0226]), oblique orientation retardation film for viewing angle compensation (see JP-A-2012-133303 [0227]), and the like.

As the retardation film, as long as it substantially has the above functions, for example, retardation value, arrangement angle, three-dimensional birefringence, monolayer or multilayer is not particularly limited, and known retardation film Film can be used.

The thickness of the retardation film is preferably 20 μm or less, more preferably 10 μm or less, still more preferably 1 to 9 μm, and particularly preferably 3 to 8 μm.

A retardation film is composed of two layers, for example, a quarter-wave plate and a half-wave plate in which a liquid crystal material is oriented and fixed.

Another example of the optical laminate of this embodiment is shown in FIG. The optical layered body 10B of FIG. 4 has a layered structure in which a release liner 3, an adhesive sheet 1 and an optical film 2 are layered in this order. By peeling off the release liner 3, the optical laminate 10B can be used as an optical film with an adhesive sheet.

Materials constituting the release liner 3 include, for example, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films; porous materials such as paper, cloth, and nonwoven fabric; nets, foam sheets, metal foils, and laminates thereof. However, a plastic film is preferably used because of its excellent surface smoothness.

The plastic film is not particularly limited as long as it is a film capable of protecting the adhesive sheet 1. Examples include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, and vinyl chloride copolymer. film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, ethylene-vinyl acetate copolymer film and the like.

The thickness of the release liner 3 is usually 5-200 μm, preferably about 5-100 μm. The release liner 3 may be subjected, if necessary, to silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based release agents, release and antifouling treatment using silica powder, etc., coating type, kneading type, vapor deposition. The mold may be subjected to antistatic treatment. In particular, by subjecting the surface of the release liner 3 to a release treatment such as silicone treatment, long-chain alkyl treatment, fluorine treatment, etc., the releasability from the pressure-sensitive adhesive sheet 1 can be further enhanced.

Note that, as described above, the release film used when producing the pressure-sensitive adhesive sheet 1 may be used as the release liner 3.

Another example of the optical laminate of this embodiment is shown in FIG. The optical laminate 10C of FIG. 5 has a laminate structure in which a release liner 3, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4 and a polarizing plate 2B are laminated in this order. After peeling off the release liner 3, the optical layered body 10C can be used by attaching it to, for example, an image forming layer.

A known adhesive can be used for the interlayer adhesive 4 . The adhesive sheet 1 may be used as the interlayer adhesive 4 .

Another example of the optical laminate of this embodiment is shown in FIG. The optical laminate 10D of FIG. 6 has a laminate structure in which a release liner 3, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B and a protective film 5 are laminated in this order. After peeling off the release liner 3, the optical layered body 10D can be used by attaching it to, for example, an image forming layer.

The protective film 5 has a function of protecting the outermost optical film 2 (polarizing plate 2B) during distribution and storage of the optical layered body 10D and when the optical layered body 10D is incorporated in an image display device. Moreover, it may be the protective film 5 that functions as a window to an external space when incorporated in the image display device. Protective film 5 is typically a resin film. The resin constituting the protective film 5 is, for example, polyester such as PET, polyolefin such as polyethylene and polypropylene, acrylic, cycloolefin, polyimide, and polyamide, preferably polyester. However, the protective film 5 is not limited to the above examples. The protective film 5 may be a glass film or a laminated film containing a glass film. The protective film 5 may be subjected to surface treatments such as antiglare, antireflection, and antistatic.

The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding with the adhesive sheet 1 is also possible.

The optical layered body of the present embodiment can be distributed and stored, for example, as a wound body in which a strip-shaped optical layered body is wound, or as a sheet-shaped optical layered body.

The optical laminate of this embodiment is typically used in an image display device. The image display device is, for example, an EL display such as a liquid crystal display, an organic EL display and an inorganic EL display.

(Embodiment of image display device)
An example of the image display device of this embodiment is shown in FIG. The image display device 11 in FIG. 7 includes a substrate 7, an image forming layer (for example, an organic EL layer or a liquid crystal layer) 6, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B and a protective film 5 in this order. It has a laminated structure. The image display device 11 has the

optical laminate

10B, 10C or 10D of FIGS. 4-6 (excluding the release liner 3). The substrate 7 and the image forming layer 6 may have the same configurations as those of the substrate and the image forming layer provided in a known image display device.

The image display device 11 in FIG. 7 may be an organic EL display or a liquid crystal display. However, the image display device 11 is not limited to this example. The image display device 11 may be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED: Field Emission Display), or the like. The image display device 11 can be used for home appliance applications, vehicle applications, public information display (PID) applications, and the like.

The image display device of this embodiment can have any configuration as long as it includes the optical layered body of this embodiment.

The present invention will be described in more detail below with reference to examples. The invention is not limited to the examples shown below.

[(Meth) acrylic polymer A1]
81.9 parts by weight of butyl acrylate, 4.8 parts by weight of acrylic acid, 0.1 parts by weight of 4-hydroxybutyl acrylate and benzyl A monomer mixture containing 13.2 parts by weight of acrylate was charged. Further, 0.1 part by weight of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was added to 100 parts by weight of the monomer mixture together with ethyl acetate, and nitrogen gas was introduced while gently stirring. After introducing and purging with nitrogen, the temperature of the liquid in the flask was kept around 55° C., and the polymerization reaction was carried out for 7 hours. Thereafter, ethyl acetate was added to the resulting reaction solution to adjust the solid content concentration to 30% by weight to obtain a solution of (meth)acrylic polymer A1.

[(Meth) acrylic polymer A2]
94.9 parts by weight of butyl acrylate, 5.0 parts by weight of acrylic acid, and 0.1 part by weight of 4-hydroxybutyl acrylate were placed in a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser. The containing monomer mixture was charged. Next, 0.1 part by weight of AIBN as a polymerization initiator is added to 100 parts by weight of the monomer mixture, and nitrogen gas is introduced while gently stirring to replace the inside of the flask with nitrogen. was maintained at around 55° C., and the polymerization reaction was allowed to proceed for 7 hours. Next, ethyl acetate was added to the obtained reaction solution to adjust the solid content concentration to 12% by weight to obtain a solution of (meth)acrylic polymer A2.

Abbreviations in Table 1 are as follows.
BA: n-butyl acrylate AA: acrylic acid HBA: 4-hydroxybutyl acrylate BzA: benzyl acrylate AIBN: azo polymerization initiator, 2,2'-azobisisobutyronitrile (manufactured by Kishida Chemical Co., Ltd.)

[Production of adhesive sheet]
(Examples 1-3 and Comparative Examples 1-2)
A (meth)acrylic polymer and a cross-linking agent were mixed so as to have the composition shown in Table 2 below to obtain a solvent-based pressure-sensitive adhesive composition. Next, the pressure-sensitive adhesive composition was applied to the surface of the PET film as the base film (release liner) so that the thickness of the pressure-sensitive adhesive sheet after drying was 25 μm. A fountain coater was used to apply the adhesive composition. The resulting coating film was dried for 1 minute in an air circulating constant temperature oven set at the drying temperature shown in Table 2 to form pressure-sensitive adhesive sheets of Examples 1-3 and Comparative Examples 1-2.

(Example 4)
A (meth)acrylic polymer, a cross-linking agent and an additive were mixed so as to have the composition shown in Table 2 below to obtain an active energy ray-curable pressure-sensitive adhesive composition. Next, the pressure-sensitive adhesive composition was applied to the surface of the PET film as the base film (release liner) so that the thickness of the pressure-sensitive adhesive sheet was 25 μm. A fountain coater was used to apply the adhesive composition. A release liner was further attached to the surface of the obtained coating film. The coating film was dried at 130° C. and then irradiated with ultraviolet rays under the conditions of an illuminance of 4 mW/cm ² and a light amount of 1200 mJ/cm ² . As a result, curing of the coating film progressed, and a pressure-sensitive adhesive sheet of Example 4 was obtained.

Abbreviations in Table 2 are as follows.
D262: isocyanurate modified form of tolylene diisocyanate (manufactured by Mitsui Chemicals, trade name: Takenate D-262)
D101E: Trimethylolpropane/tolylene diisocyanate adduct (manufactured by Mitsui Chemicals, trade name: Takenate D-101E)
APG400: polypropylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: APG-400)
Tetrad C: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (polyfunctional epoxy-based cross-linking agent; manufactured by Mitsubishi Gas Chemical Co., Ltd., Tetrad C)
Omnirad 651: photoinitiator, 2,2-dimethoxy-1,2-diphenylethan-1-one (manufactured by IGM Resins BV)

[evaluation]
<Weight average molecular weight (Mw) of (meth)acrylic polymer>
The weight average molecular weight (Mw) of the obtained (meth)acrylic polymer was measured by GPC (gel permeation chromatography).
・ Analyzer: HLC-8120GPC manufactured by Tosoh Corporation
・ Column: G7000H _XL + GMH _XL + GMH _XL manufactured by Tosoh Corporation
・Column size: 7.8 mmφ×30 cm each, 90 cm in total
・Column temperature: 40°C
・Flow rate: 0.8 ml/min
・Injection volume: 100 μl
・ Eluent: Tetrahydrofuran ・ Detector: Differential refractometer (RI)
・Standard sample: Polystyrene

<Thickness>
The thickness of the adhesive sheet and the like was measured using a dial gauge (manufactured by Mitutoyo).

<Gel fraction>
Evaluation of the gel fraction for the produced pressure-sensitive adhesive sheet was carried out by the method described above. The weight of the small piece obtained by scraping off part of the adhesive sheet was about 0.2 g. Nitto Denko's NTF1122 (average pore diameter: 0.2 μm) was used as the stretched porous membrane of polytetrafluoroethylene.

<Adhesive strength>
Evaluation of the adhesive strength of the produced adhesive sheet was implemented by the above-mentioned method. Autograph AG-IS manufactured by Shimadzu Corporation was used as a tensile tester.

<Haze>
The haze of the produced pressure-sensitive adhesive sheet was measured in an atmosphere of 25° C. using a haze meter HZ-V3 manufactured by Suga Test Instruments in accordance with JIS K7136:1981. The measurement was carried out in a state in which the pressure-sensitive adhesive sheet to be evaluated was laminated on a slide glass S012140 (thickness: 1.3 mm) manufactured by Matsunami Glass Industry.

<Storage elastic modulus G'>
The storage modulus G' of the PSA sheet at 25°C was evaluated by the method described above. Dynamic viscoelasticity measurement was performed using "ARES-G2" manufactured by TA Instruments.

<Atomic force microscope measurement>
The elastic modulus was measured using AFM by the method described above so that the number of measurement points was 65,536 in the range of 500 nm long×500 nm wide on the surface of the pressure-sensitive adhesive sheet. As AFM, MFP-3D-SA manufactured by Oxford Instruments was used. As the cantilever, OMCL-AC240TS (spring constant: 3 N/m) manufactured by Olympus was used. A histogram of elastic modulus with a class width of 0.1 MPa was created, and the maximum frequency F _max and the like were specified. In addition, the average value and standard deviation of elastic modulus were calculated to identify the coefficient of variation.

<Humidification durability>
Humidification durability (corresponding to an accelerated durability test) of the PSA sheet was evaluated by the following method. First, a pressure-sensitive adhesive sheet-attached circularly polarizing plate having the pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples on one exposed surface was formed. A sample with a size of 100 mm long×40 mm wide was prepared as the circularly polarizing plate with an adhesive sheet. Next, a circularly polarizing plate was fixed to the surface of a glass plate (Eagle XG manufactured by Corning) via the adhesive sheet. Fixing of the circularly polarizing plate was performed in an atmosphere of 23° C. and 50% RH. Next, after treatment in an autoclave at 50 ° C. and 5 atmospheres (absolute pressure) for 15 minutes, it was left to stand until it cooled to 23 ° C., and after stabilizing the bonding of the circularly polarizing plate to the glass plate, it was heated at 60 ° C. and 95 ° C. It was left for 500 hours in a heated and humidified atmosphere of % RH. After standing, the atmosphere was returned to 23° C. and 50% RH, and the circularly polarizing plate was visually checked for peeling from the glass plate and bubbles between the glass plate and the circularly polarizing plate. Humidification durability was evaluated as follows.
A: No change in appearance such as foaming or peeling is observed.
C: Significant peeling or foaming is observed at the edge, which poses a problem in practical use.

Below, the method of forming the circularly polarizing plate with the adhesive sheet used to evaluate the humidification durability is shown.

<Preparation of polarizing plate P1>
(Production of polarizer)
A long polyvinyl alcohol (PVA) resin film (manufactured by Kuraray, product name “PE3000”, thickness 30 μm) is uniaxially stretched in the longitudinal direction using a roll stretching machine (total stretching ratio 5.9 times) at the same time. , swelling, dyeing, cross-linking, washing and drying were sequentially performed on the resin film to prepare a polarizer having a thickness of 12 μm. In the swelling treatment, the resin film was stretched 2.2 times while being treated with pure water at 20°C. In the dyeing treatment, the resin film was stretched 1.4 times while being treated with an aqueous solution containing iodine and potassium iodide at a weight ratio of 1:7 at 30°C. The iodine concentration in the aqueous solution was adjusted so that the single transmittance of the polarizer to be produced was 45.0%. A two-step process was employed for the cross-linking treatment. In the first-stage cross-linking treatment, the resin film was stretched 1.2 times while being treated with an aqueous solution of boric acid and potassium iodide at 40°C. The content of boric acid in the aqueous solution used for the first-stage cross-linking treatment was 5.0% by weight, and the content of potassium iodide was 3.0% by weight. In the second-stage cross-linking treatment, the resin film was stretched 1.6 times while being treated with an aqueous solution of boric acid and potassium iodide at 65°C. The content of boric acid in the aqueous solution used in the second-stage cross-linking treatment was 4.3% by weight, and the content of potassium iodide was 5.0% by weight. A potassium iodide aqueous solution at 20° C. was used for the cleaning treatment. The content of potassium iodide in the aqueous solution used for the cleaning treatment was 2.6% by weight. The drying treatment was performed under drying conditions of 70° C. and 5 minutes.

(Preparation of polarizing plate P1)
A triacetyl cellulose (TAC) film (manufactured by Konica Minolta, product name “KC2UA”, thickness 25 μm) was attached to each main surface of the polarizer prepared above with a polyvinyl alcohol-based adhesive. However, in the TAC film attached to one main surface, a hard coat (7 μm thick) was formed on the main surface opposite to the polarizer side. Thus, a polarizing plate P1 having a structure of protective layer with hard coat/polarizer/protective layer (no hard coat) was obtained.

<Preparation of retardation film R1>
(Preparation of first retardation film)
Isosorbide (ISB) 26.2 parts by weight, 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF) 100.5 parts by weight, 1,4-cyclohexanedimethanol (1,4-CHDM) 10 .7 parts by weight, 105.1 parts by weight of diphenyl carbonate (DPC), and 0.591 parts by weight of cesium carbonate (0.2% by weight aqueous solution) as a catalyst were charged into a reaction vessel and dissolved under a nitrogen atmosphere ( about 15 minutes). At this time, the temperature of the heat medium in the reaction vessel was set at 150° C., and stirring was carried out as necessary. Next, the pressure inside the reaction vessel was reduced to 13.3 kPa, and the temperature of the heat medium was raised to 190° C. in 1 hour. Phenol generated as the temperature of the heat medium increased was discharged out of the reaction vessel (the same applies hereinafter). Next, after maintaining the temperature in the reaction vessel at 190° C. for 15 minutes, the pressure in the reaction vessel was changed to 6.67 kPa, and the temperature of the heat medium was raised to 230° C. in 15 minutes. When the stirring torque of the stirrer provided in the reaction vessel increased, the temperature of the heat medium was raised to 250° C. in 8 minutes, and the pressure in the reaction vessel was reduced to 0.200 kPa or less. After reaching a predetermined stirring torque, the reaction was terminated, and the produced reaction product was extruded into water and pelletized. Thus, a polycarbonate resin having a composition of BHEPF/ISB/1,4-CHDM=47.4 mol %/37.1 mol %/15.5 mol % was obtained. The obtained polycarbonate resin had a glass transition temperature of 136.6° C. and a reduced viscosity of 0.395 dL/g.

After vacuum drying the prepared polycarbonate resin pellets at 80 ° C. for 5 hours, a single screw extruder (manufactured by Isuzu Kakoki, screw diameter 25 mm, cylinder set temperature 220 ° C.), T die (width 200 mm, set temperature 220 ° C.), chill roll A long resin film having a thickness of 120 μm was obtained using a film forming apparatus equipped with a set temperature of 120 to 130° C. and a winder. Next, the obtained resin film was stretched in the width direction with a tenter stretching machine at a stretching temperature of 137 to 139° C. and a stretching ratio of 2.5 to obtain a first retardation film.

(Production of second retardation film)
20 parts by weight of a side chain type liquid crystal polymer (weight average molecular weight 5000) represented by the following chemical formula (I) (where 65 and 35 are mol% of each structural unit), a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF) , trade name “Paliocolor LC242”) 80 parts by weight, and a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name “Irgacure 907”) 5 parts by weight are dissolved in 200 parts by weight of cyclopentanone to form a liquid crystal coating liquid. prepared. Next, the surface of a norbornene-based resin film (manufactured by Nippon Zeon, trade name “Zeonex”), which is a base film, is coated with the prepared liquid crystal coating liquid using a bar coater, and then heated at 80 ° C. for 4 minutes. By drying, the liquid crystal contained in the coating film was oriented. Next, the coating film was cured by irradiation with ultraviolet rays to form a liquid crystal solidified layer (thickness: 0.58 μm) as a second retardation film on the substrate film. The in-plane retardation Re of the liquid crystal solidified layer for light with a wavelength of 550 nm is 0 nm, and the thickness direction retardation Rth is -71 nm (nx = 1.5326, ny = 1.5326, nz = 1.6550). The solidified layer exhibited refractive index properties of nz>nx=ny.

(Preparation of retardation film R1)
One surface of the first retardation film prepared above and the liquid crystal solidified layer of the second retardation film were pasted together via an adhesive to prepare a retardation film R1.

<Preparation of circularly polarizing plate with adhesive sheet>
(Production of interlayer adhesive)
79.9 parts by weight of butyl acrylate, 15 parts by weight of benzyl acrylate, 5 parts by weight of acrylic acid and 0.5 parts by weight of 4-hydroxybutyl acrylate were placed in a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser. A monomer mixture containing 1 part by weight was charged. Next, 0.1 part by weight of 2,2'-azoisobutyronitrile as a polymerization initiator was added to 100 parts by weight of the monomer mixture together with ethyl acetate, and nitrogen gas was introduced while gently stirring. After the inside of the flask was replaced with nitrogen, the polymerization reaction was allowed to proceed for 7 hours while maintaining the liquid temperature in the flask around 55°C. Next, ethyl acetate was added to the resulting reaction solution to adjust the solid content concentration to 30% by weight to obtain a solution of a (meth)acrylic polymer used as an interlaminar pressure-sensitive adhesive. The weight average molecular weight of the obtained polymer was 2,200,000.

Next, a trimethylolpropane/tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L ”) 0.5 parts by weight, 0.1 parts by weight of benzoyl peroxide which is a peroxide-based cross-linking agent, and 0.2 parts by weight of an epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBM-403”). parts by weight and 0.5 parts by weight of a polyether compound having a reactive silyl group (manufactured by Kaneka, Silyl SAT10) are mixed, and used as an interlayer adhesive for bonding the polarizing plate P1 and the retardation film R1. An adhesive composition PSA1 was obtained.

(Preparation of polarizing plate with interlayer pressure-sensitive adhesive layer)
The pressure-sensitive adhesive composition PSA1 prepared above was applied to the release surface of a polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., MRF38) having a thickness of 38 μm, which is a release liner having a silicone-treated release surface. It was coated so that the thickness of the layer after drying was 12 μm, and dried at 155° C. for 1 minute to form an interlayer pressure-sensitive adhesive layer. Next, the formed interlayer pressure-sensitive adhesive layer was transferred to the protective layer (no hard coat) side of the polarizing plate P1 to obtain a polarizing plate with an interlayer pressure-sensitive adhesive layer.

(Preparation of circularly polarizing plate with adhesive sheet)
On the second retardation film side of the retardation film R1 (the norbornene-based resin film used as the base film when producing the second retardation film is peeled off), each pressure-sensitive adhesive sheet prepared in Examples and Comparative Examples was transferred from the release liner and pasted. Next, the polarizing plate with an interlayer pressure-sensitive adhesive layer prepared above was attached to the first retardation film side of the retardation film R1 via the interlayer pressure-sensitive adhesive layer to obtain a circularly polarizing plate with an pressure-sensitive adhesive sheet. The attachment of the retardation film R1 and the polarizing plate with an interlayer pressure-sensitive adhesive layer is performed by adjusting the angle formed by the slow axis of the first retardation film and the absorption axis of the polarizer when viewed from the side of the first retardation film. was 45 degrees counterclockwise.

As can be seen from Table 3, the pressure-sensitive adhesive sheets of Examples having a gel fraction of 70% or more and a maximum frequency value F _max in the histogram of elastic modulus of 1400 or more are compared with the pressure-sensitive adhesive sheets of Comparative Examples. Durability was improved.

The adhesive composition of the present invention can be suitably used for producing adhesive sheets provided in image display devices such as EL displays and liquid crystal displays.

Claims

including an adhesive sheet having a gel fraction of 70% or more and an optical film,
An optical laminate having a maximum frequency value of 1400 or more in a histogram prepared by the following test method.
Test method: Using an atomic force microscope, the elastic modulus was measured so that the number of measurement points was 65536 for a range of 500 nm in length × 500 nm in width on the surface of the pressure-sensitive adhesive sheet, and the class width was 0.1 MPa. Create a histogram of the modulus of elasticity.
A pressure-sensitive adhesive sheet having a gel fraction of 70% or more,
A pressure-sensitive adhesive sheet having a maximum value of 1400 or more in a histogram prepared by the following test method.
Test method: Using an atomic force microscope, the elastic modulus was measured so that the number of measurement points was 65536 for a range of 500 nm in length × 500 nm in width on the surface of the pressure-sensitive adhesive sheet, and the class width was 0.1 MPa. Create a histogram of the modulus of elasticity.
3. The pressure-sensitive adhesive sheet according to claim 2, wherein the elastic modulus G max corresponding to the maximum value in the histogram is in the range of 10 to 100 MPa.
The pressure-sensitive adhesive sheet according to claim 2 or 3, wherein the coefficient of variation of the elastic modulus measured by the test method is less than 0.08.
The pressure-sensitive adhesive sheet according to any one of claims 2 to 4, wherein the coefficient of variation of the elastic modulus measured by the test method is 0.035 or more.
Claims 2 to 5, wherein in the histogram, the ratio of the total value of frequencies included in the range of ±2.0 MPa from the elastic modulus G max (MPa) corresponding to the maximum value to the total frequency is 70% or more. The pressure-sensitive adhesive sheet according to any one of items 1 and 2.
The pressure-sensitive adhesive sheet according to any one of claims 2 to 6, which has a storage elastic modulus G' at 25°C of 0.1 MPa or more.
The pressure-sensitive adhesive sheet according to any one of claims 2 to 7, which has a haze of 1.0% or less.
The pressure-sensitive adhesive sheet according to any one of claims 2 to 8, which is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A) and a cross-linking agent (B).
The adhesive sheet according to claim 9, wherein the cross-linking agent (B) contains at least one selected from the group consisting of an isocyanate-based cross-linking agent and a polyfunctional (meth)acrylate-based cross-linking agent.
The pressure-sensitive adhesive sheet according to claim 9 or 10, wherein the amount of the cross-linking agent (B) in the pressure-sensitive adhesive composition is 2 parts by weight or more with respect to 100 parts by weight of the (meth)acrylic polymer (A). .
The pressure-sensitive adhesive sheet according to any one of claims 9 to 11, wherein the pressure-sensitive adhesive composition is solvent-based or active energy ray-curable.
An optical laminate comprising the adhesive sheet according to any one of claims 2 to 12 and an optical film.
An image display device comprising the optical laminate according to claim 13.
A pressure-sensitive adhesive sheet having a gel fraction of 70% or more,
A pressure-sensitive adhesive sheet having an elastic modulus coefficient of variation of less than 0.08 as measured by the following test method.
Test method: Using an atomic force microscope, the elastic modulus is measured so that the number of measurement points is 65,536 in a range of 500 nm long×500 nm wide on the surface of the pressure-sensitive adhesive sheet.