CN117999327A

CN117999327A - Optical laminate, pressure-sensitive adhesive sheet, and image display device

Info

Publication number: CN117999327A
Application number: CN202280064867.6A
Authority: CN
Inventors: 久世雅大; 仲野武史
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-09-28
Filing date: 2022-08-24
Publication date: 2024-05-07
Also published as: WO2023053797A1; KR20240070613A; JP2023048829A; TW202313731A

Abstract

The present invention provides an optical laminate comprising an adhesive sheet having a sufficient gel fraction and improved durability. The optical laminate of the present invention comprises: an adhesive sheet having a gel fraction of 70% or more, and an optical film. The maximum value of the frequency number in the histogram prepared by the following test method is 1400 or more. The test method comprises the following steps: an elastic modulus was measured in a range of 500nm in the vertical direction and 500nm in the horizontal direction on the surface of the pressure-sensitive adhesive sheet using an atomic force microscope so that the number of measurement points was 65536, and a histogram of elastic modulus was prepared with a group spacing of 0.1 MPa.

Description

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

Technical Field

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

Background

In recent years, image display devices typified by liquid crystal display devices and Electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have been rapidly spreading. The various image display devices described above generally have a laminated structure of an image forming layer such as a liquid crystal layer or 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 films included in an optical laminate and bonding an image forming layer to the optical laminate. 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. An example of an optical laminate is disclosed in patent document 1.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2008-031214

Disclosure of Invention

Problems to be solved by the invention

Excessive changes in the size of the optical film accompanying temperature changes cause light leakage and color unevenness in the image display device. Light leakage and color unevenness are particularly likely to occur in an image display device having a large size using a polarizing plate with a retardation film. In addition, image display devices in which the frame (bezel) is designed to be narrow (narrowed frame) are becoming popular, and suppression of dimensional changes is becoming more important. In order to suppress the dimensional change, it is considered to increase the elastic modulus of the adhesive sheet contained in the optical laminate. As one of methods for increasing the elastic modulus of the adhesive sheet, increasing the gel fraction of the adhesive sheet can be considered. However, if the elastic modulus is merely increased, the durability of the adhesive sheet may be reduced, and the adhesive sheet may not follow the dimensional change.

To this end, the present invention aims to provide an optical laminate comprising an adhesive sheet having a sufficient gel fraction and improved durability.

Means for solving the problems

The present invention provides an optical laminate comprising:

Adhesive sheet having gel fraction of 70% or more, and

An optical film comprising an optical film and an optical film,

The maximum value of the frequency in the histogram of the optical laminate manufactured by the following test method is 1400 or more,

The test method comprises the following steps: an elastic modulus was measured in a range of 500nm in the vertical direction and 500nm in the horizontal direction on the surface of the pressure-sensitive adhesive sheet using an atomic force microscope so that the number of measurement points was 65536, and a histogram of the elastic modulus was prepared with a group spacing of 0.1 MPa.

The present invention also provides an adhesive sheet having a gel fraction of 70% or more,

The maximum value of the frequency number in the histogram of the adhesive sheet manufactured by the following test method is 1400 or more,

Further, the present invention provides an optical laminate comprising:

The adhesive sheet, and

An optical film.

The present invention further provides an image display device including the above optical laminate.

The adhesive sheet has a coefficient of variation of elastic modulus of less than 0.08 as measured by the following test method,

The test method comprises the following steps: the elastic modulus was measured in a range of 500nm in the longitudinal direction and 500nm in the transverse direction on the surface of the pressure-sensitive adhesive sheet using an atomic force microscope so that the number of measurement points was 65536.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an optical laminate comprising an adhesive sheet having a sufficient gel fraction and improved durability can be provided.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of an optical laminate of the present invention.

Fig. 2 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present invention.

Fig. 3A is a view showing an example of an atomic force microscope image of the surface of the pressure-sensitive adhesive sheet.

Fig. 3B is a diagram showing an example of a histogram of elastic modulus measured by an atomic force microscope.

Fig. 4 is a cross-sectional view schematically showing an example of the optical laminate of the present invention.

Fig. 5 is a cross-sectional view schematically showing an example of the optical laminate of the present invention.

Fig. 6 is a cross-sectional view schematically showing an example of the optical laminate of the present invention.

Fig. 7 is a cross-sectional view schematically showing an example of the image display device of the present invention.

Detailed Description

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be modified and implemented arbitrarily within the scope of the present invention.

(Embodiment of optical laminate)

An example of the optical laminate of the present embodiment is shown in fig. 1. The optical laminate 10A of fig. 1 includes an adhesive sheet 1 and an optical film 2, and the adhesive sheet 1 and the optical film 2 are laminated to each other. The optical laminate 10A may be used in the form of an optical film with an adhesive sheet.

(Adhesive sheet)

The gel fraction of the adhesive sheet 1 was 70% or more. The maximum value F _max of the frequency numbers in the histogram prepared by the test method described below is 1400 or more.

The test method comprises the following steps: an elastic modulus was measured in a range of 500nm in the vertical direction and 500nm in the horizontal direction on the surface of the adhesive sheet 1 using an Atomic Force Microscope (AFM) so that the number of measurement points was 2 ¹⁶ (65536), and a histogram of elastic modulus was prepared with a group spacing of 0.1 MPa.

The gel fraction of the adhesive sheet 1 can be determined by the following method. First, as a measurement sample, an adhesive sheet 1 (for example, fig. 2) having passed through 1 week or more from production was prepared. The pressure-sensitive adhesive sheet 1 is stored in an atmosphere of 55% RH at 23℃for 1 week or more after production, for example. When the adhesive sheet 1 is formed of an adhesive composition containing a crosslinking agent, the reaction by the crosslinking agent proceeds sufficiently by passing through 1 week or more after the production. In other words, the reaction based on the crosslinking agent ends. The end of the reaction by the crosslinking agent can be confirmed by, for example, fourier transform infrared spectroscopy (FT-IR). Next, a part of the adhesive sheet 1 was scraped to obtain a small sheet. Next, the obtained small pieces were wrapped with a stretched porous film of polytetrafluoroethylene and bound with kite strings, thereby obtaining test pieces. Next, the total weight (weight a) of the small pieces of the adhesive sheet 1, the stretched porous film, and the kite string was measured. The total of the stretched porous film and kite string used was defined as weight B. Next, the test piece was immersed in a container filled with ethyl acetate, and left to stand at 23 ℃ for 1 week. After standing, the test piece was taken out of the container, dried in a dryer set at 130℃for 2 hours, and then the weight C of the test piece was measured. The gel fraction of the adhesive sheet 1 can be calculated from the weight a, the weight B, and the weight C based on the following formula.

Gel fraction (wt%) = (C-B)/(a-B) ×100

The gel fraction of the pressure-sensitive 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, and may be 96% or more, 97% or more, 98% or more, or 100% or more, as the case may be. The pressure-sensitive adhesive sheet 1 having a gel fraction of 70% or more tends to be excellent in workability and process stability, and is easily inhibited from sagging during storage or the like. The adhesive sheet 1 is also suitable for suppressing dimensional changes of an optical film.

The maximum value F _max of the frequency number can be determined in detail by the following method. First, as a measurement sample, an adhesive sheet 1 (for example, fig. 2) having been manufactured for 1 week or more was prepared. Next, the adhesive sheet 1 was cut into a long strip shape as a test piece. At this time, the thickness of the test piece was adjusted to about 100 nm. The surface of the obtained test piece can be regarded as the surface of the adhesive sheet 1. Next, the test piece is disposed on a substrate such as a Si wafer. The elastic modulus was measured in a range of 500nm in the longitudinal direction and 500nm in the transverse direction on the surface of the test piece using AFM so that the number of measurement points was 65536. At this time, the interval between adjacent measurement points was adjusted to about 2nm. The elastic modulus is measured, for example, over the entire range of 500nm in the vertical direction and 500nm in the horizontal direction on the surface of the test piece. The elastic modulus of the test piece can be determined by vibrating a cantilever probe 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, OMCL-AC240TS (spring constant 3N/m) manufactured by Olympus corporation, for example, can be used. The measurement conditions of the elastic modulus are described in detail below.

Measurement conditions

Measurement mode: AM-FM viscoelastic imaging

Measurement range: 500nm in longitudinal direction and 500nm in transverse direction

Scanning speed: 3Hz

Setpoint (Set point): 0.8V

Target Amplitude (Target Amplitude): 2V of

Measuring temperature: 25 DEG C

By the above measurement, data of the elastic modulus can be obtained at a plurality of positions on the surface of the test piece. By imaging (mapping) this data, an AFM image as shown in fig. 3A can be obtained. In the AFM image, visual information of color tone is given to each pixel based on the value of elastic modulus. The size of 1 pixel in the AFM image corresponds to the size of the cantilever probe. The number of pixels constituting the AFM image coincides with the number of measurement points.

Next, a histogram of the elastic modulus at a group spacing of 0.1MPa was prepared (fig. 3B). In the histogram, the horizontal axis represents the elastic modulus, and the vertical axis represents the frequency (number of measurement points). As shown in fig. 3B, for example, there are 1 peak P in the histogram. Peak P is typically unimodal. The frequency corresponding to the peak of the peak P may be regarded as the maximum value F _max. In some cases, a plurality of peaks or a plurality of peaks exist in the histogram. In this case, however, the maximum F _max of the frequency tends to be lower than 1400.

The maximum value F _max is preferably 1600 or more, more preferably 1800 or more, and may be 2000 or more, 2200 or more, 2400 or more, or 2600 or more. 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 the variation in the elastic modulus of the adhesive sheet 1. It is considered that the larger the maximum value F _max is, the more variation in elastic modulus can be suppressed in the adhesive sheet 1. According to the studies by the present inventors, the pressure-sensitive adhesive sheet 1 having a sufficient gel fraction and a maximum value F _max of 1400 or more and suppressed variation in elastic modulus tends to have improved durability. The variation in elastic modulus is generally caused by fluctuation in concentration of a material (polymer or the like) constituting the pressure-sensitive adhesive sheet, and tends to occur significantly in the pressure-sensitive adhesive sheet having a high gel fraction.

In the histogram described above, 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, in the range of 10 to 100 MPa.

In the histogram, the ratio R of the total value T of the frequency numbers included in the range of ±2.0MPa from the elastic modulus G _max (MPa) corresponding to the maximum value F _max to the total frequency number is not particularly limited, and is, for example, 70% or more, preferably 75% or more, more preferably 80% or more, still more preferably 85% or more, and may be 90% or more, or 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 integral value of the entire peak P, and matches the number of all measurement points based on AFM. The total value T corresponds to the integrated value of the peak P in the range from G _max -2.0MPa to G _max +2.0 MPa. In the histogram, the integrated value of the peak P refers to the area of the peak P. Therefore, in this specification, the ratio R is sometimes referred to as an "area ratio".

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

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

In this embodiment, the coefficient of variation of the elastic modulus measured by the test method described below is preferably less than 0.08. The measurement of the elastic modulus can be performed in detail by the method described above with respect to the maximum value F _max of the frequency.

The test method comprises the following steps: the elastic modulus was measured in a range of 500nm in the longitudinal direction and 500nm in the transverse direction on the surface of the adhesive sheet 1 using an Atomic Force Microscope (AFM) so that the number of measurement points was 65536.

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

The storage modulus G' of the pressure-sensitive adhesive sheet 1 at 25 ℃ is not particularly limited, and may be, for example, 0.1MPa or more, preferably 0.15MPa or more, more preferably 0.2MPa or more, still more preferably 0.5MPa or more, particularly preferably 0.8MPa or more, or 1.0MPa or more. The upper limit of the storage modulus G' of the pressure-sensitive adhesive sheet 1 at 25 ℃ is not particularly limited, and is, for example, 5MPa. The pressure-sensitive adhesive sheet 1 having a storage modulus G' of 0.1MPa or more, particularly 0.15MPa or more is suitable for suppressing dimensional changes of an optical film. The pressure-sensitive adhesive sheet 1 having a storage modulus G' of 0.1MPa or more, particularly 1.0MPa or more tends to sufficiently suppress the change in appearance even when an optical laminate is bonded to an image forming layer or the like, for example.

The storage modulus G' of the adhesive sheet 1 at 25 ℃ can be determined by the following method. First, a sample for measurement formed of a material constituting the adhesive sheet 1 is prepared. The measurement sample was disk-shaped, and the bottom surface of the measurement sample had a diameter of 8mm and a thickness of 2mm. The measurement sample may be obtained by punching out a laminate in which a plurality of adhesive sheets 1 are laminated into a disc shape. Next, dynamic viscoelasticity measurement is performed on the measurement sample. As the dynamic viscoelasticity measurement, for example, "ARES-G2" manufactured by TA Instruments Co., ltd. From the result of the dynamic viscoelasticity measurement, the storage modulus G' of the adhesive sheet 1 at 25 ℃ can be determined. The conditions for dynamic viscoelasticity measurement are as follows.

Measurement conditions

Frequency: 1Hz

Deformation mode: torsion

Measuring temperature: -70-150 DEG C

Heating rate: 5 ℃/min

The adhesive sheet 1 preferably has high transparency. The haze of the pressure-sensitive 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 pressure-sensitive adhesive sheet 1 is not particularly limited, and is, for example, 0.1%. In the present specification, the haze of the pressure-sensitive adhesive sheet 1 is a value at a thickness of 25. Mu.m, and can be measured in accordance with Japanese Industrial Standard (old Japanese Industrial Standard; JIS) K7136:1981.

The adhesive force of the adhesive sheet 1 is, for example, 0.5N/25mm or more, preferably 2N/25mm or more, and more preferably 5N/25mm or more. From the viewpoint of reworkability, the upper limit value of the adhesive force of the adhesive sheet 1 is, for example, 10N/25mm. The adhesive force of the adhesive sheet 1 can be measured by the following method. First, the adhesive sheet 1 was cut out to have a width of 25mm×a length of 150mm, and used as a test piece. Next, a stainless steel test plate and an evaluation sheet were laminated via an adhesive sheet 1, and a 2kg roller was reciprocated 1 time, and these were pressed together. The evaluation sheet is not particularly limited as long as it has dimensions of 30mm wide by 150mm long and is not peeled off from the adhesive sheet 1 in the test. As the evaluation sheet, for example, an ITO film (125 TETOLIGHT OES (manufactured by Tail pool Co., ltd.) or the like can be used. Next, using a commercially available tensile tester, the adhesive sheet 1 was peeled from the stainless steel test plate at a peeling angle of 180 ° and a stretching speed of 300mm/min while holding the sheet for evaluation, and the average value of the peeling force at this time was determined as the adhesive force of the adhesive sheet 1. The above test was performed in an atmosphere at 23 ℃.

The press-in hardness of the adhesive sheet 1 at 25 ℃ is preferably adjusted to an appropriate range. The indentation hardness may be determined as follows: the displacement-load hysteresis (hysteresis) curve obtained by pressing a Berkovich type (triangular cone type) probe made of diamond perpendicularly to the surface of the adhesive sheet 1 was subjected to numerical processing by software (triboscan) attached to the measuring apparatus, and the determination was made. Specifically, the indentation hardness was measured by a single indentation method at 25℃using a nanoindenter (Triboindeter TI-950 manufactured by Hysicron Inc.), under conditions of an indentation speed of 500nm/sec and an indentation depth of 3000 nm.

The thickness of the pressure-sensitive adhesive sheet 1 is not particularly limited, and may be, for example, 1 to 200. Mu.m, 5 to 150. Mu.m, and further 10 to 100. Mu.m.

The composition of the pressure-sensitive adhesive sheet 1 is not particularly limited as long as the gel fraction and the maximum value F _max are within the above-mentioned ranges, and preferably two or more polymers are contained. As an example, the pressure-sensitive adhesive sheet 1 is formed of a pressure-sensitive adhesive composition containing a (meth) acrylic polymer (a) and a crosslinking agent (B). Examples of the crosslinking agent (B) include isocyanate-based crosslinking agents and polyfunctional (meth) acrylate-based crosslinking agents. The pressure-sensitive adhesive sheet 1 formed from the pressure-sensitive adhesive composition may contain a crosslinked product of the (meth) acrylic polymer (a) and the polymer (C) containing a structural unit derived from the crosslinking agent (B) as a main component. In the present specification, "main component" means a structural unit having the largest content in weight basis among all the structural units constituting the polymer. In the polymer (C), the content of the structural unit derived from the crosslinking agent (B) is, for example, 70% by weight or more, preferably 90% by weight or more. The polymer (C) is formed, for example, substantially only from structural units derived from the crosslinking 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. The IPN structure (or semi-IPN structure) is suitable for improving durability while increasing the elastic modulus of the adhesive sheet 1.

[ (Meth) acrylic Polymer (A) ]

The (meth) acrylic polymer (a) may function as a base polymer for an acrylic adhesive. The acrylic pressure-sensitive adhesive is excellent in optical transparency, has suitable adhesive properties such as wettability, cohesiveness and adhesiveness, and tends to be excellent in 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. In the present specification, "(meth) acrylate" means acrylate and/or methacrylate.

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

From the viewpoint of improving the adhesiveness of the adhesive sheet 1, the content of the structural unit derived from the alkyl (meth) acrylate in the (meth) acrylic polymer (a) is, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably 80% by weight or more.

The monomer constituting the (meth) acrylic polymer (a) may be at least one comonomer selected from the group consisting of an aromatic ring-containing monomer, an amide group-containing monomer, a carboxyl group-containing monomer, and a hydroxyl group-containing monomer, in addition to the alkyl (meth) acrylate. The comonomers may 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 having an aromatic ring structure in its structure and containing a polymerizable unsaturated double bond such as a (meth) acryloyl group or a vinyl group. Examples of the aromatic ring include: benzene ring, naphthalene ring, biphenyl ring, etc. The aromatic ring-containing monomer is preferably an aromatic ring-containing (meth) acrylate.

Examples of the aromatic ring-containing (meth) acrylate include: benzyl (meth) acrylate, phenyl (meth) acrylate, o-phenylphenol (meth) acrylate, phenoxymethyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypropyl (meth) 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, methoxybenzyl (meth) acrylate, chlorobenzyl (meth) acrylate, toluene (meth) acrylate, styrene (meth) acrylate and other (meth) acrylates having a benzene ring; (meth) acrylates having a naphthalene ring, such as hydroxyethylated β -naphthol acrylate, 2-naphthylethyl (meth) acrylate, 2-naphthyloxyethyl acrylate, 2- (4-methoxy-1-naphthyloxyethyl (meth) acrylate, and the like; aromatic ring-containing (meth) acrylates having a biphenyl ring, such as biphenyl (meth) acrylate. 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 an amide group-containing monomer. The amide group-containing monomer is a compound having an amide group in its structure and having a polymerizable unsaturated double bond such as a (meth) acryloyl group or a vinyl group. Examples of the amide group-containing monomer include: acrylamide monomers such as (meth) acrylamide, N-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, N-isopropyl acrylamide, N-methyl (meth) acrylamide, N-butyl (meth) acrylamide, N-hexyl (meth) acrylamide, N-hydroxymethyl-N-propyl (meth) acrylamide, aminomethyl (meth) acrylamide, aminoethyl (meth) acrylamide, mercaptomethyl (meth) acrylamide, mercaptoethyl (meth) acrylamide, and the like; n-acryl heterocyclic monomers such as N- (meth) acryl morpholine, N- (meth) acryl piperidine, and N- (meth) acryl pyrrolidine; and N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-. Epsilon. -caprolactam. Among these, from the viewpoint of improving the durability of the adhesive sheet 1, an N-vinyl group-containing lactam monomer is preferable.

The (meth) acrylic polymer (a) may contain a structural unit derived from a carboxyl group-containing monomer. The carboxyl group-containing monomer is a compound having a carboxyl group in its structure and having a polymerizable unsaturated double bond such as a (meth) acryloyl group or a vinyl group. Examples of the carboxyl group-containing monomer include: carboxylic ethyl (meth) acrylate, carboxylic pentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and the like. Among these, acrylic acid is preferable from the viewpoints of copolymerizability, price, and improvement of adhesive properties of the adhesive sheet 1. By providing the (meth) acrylic polymer (a) with a structural unit derived from a carboxyl group-containing monomer, particularly acrylic acid, for example, the self-polymerizability of the crosslinking agent (B), particularly an isocyanate-based crosslinking agent, can be improved. The improvement of the self-polymerizability of the crosslinking agent (B) can contribute particularly to the suppression of the peeling of the adhesive sheet 1 in a humidified environment and the stabilization of the physical properties of the adhesive sheet 1 in a system having a high content of the crosslinking agent (B).

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

Among the comonomers, aromatic ring-containing monomers and carboxyl group-containing monomers are preferably used, and aromatic ring-containing monomers are particularly preferably used, from the viewpoints of adhesion, durability, and the like. The (meth) acrylic polymer (a) containing a structural unit derived from a carboxyl group-containing monomer tends to promote the reaction of, for example, isocyanate-based crosslinking agents with each other by introducing water molecules in the surrounding atmosphere. Aromatic ring-containing monomers also tend to improve the compatibility of the (meth) acrylic polymer (a) with the polymer (C) and the durability of the optical laminate in a high-temperature and high-humidity environment.

The content of the structural unit derived from the comonomer in the (meth) acrylic polymer (a) is not particularly limited, and may be, for example, 0 to 40% by weight, 0.1 to 30% by weight, or 0.1 to 20% by weight.

In the (meth) acrylic polymer (a), the content of the structural unit derived from the aromatic ring-containing monomer is not particularly limited, and is, for example, 3 to 25% by weight, more preferably 22% by weight or less, and still more preferably 20% by weight or less. The content is more preferably 8% by weight or more, and still more preferably 12% by weight or more.

The content of the structural unit derived from the amide group-containing monomer in the (meth) acrylic polymer (a) is not particularly limited, but is, for example, 0.1 to 10% by weight, more preferably 0.2 to 8% by weight, and still more preferably 0.6 to 6% by weight.

In the (meth) acrylic polymer (a), the content of the structural unit derived from the 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 the reaction with the isocyanate-based crosslinking 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 the structural unit derived from a comonomer having active hydrogen, for example, a hydroxyl group-containing monomer, which has high reactivity with an isocyanate-based crosslinking agent, is preferably low. In the (meth) acrylic polymer (a), the content of the structural unit derived from the hydroxyl group-containing monomer is, for example, 1% by weight or less, more preferably 0.5% by weight or less, and still more preferably 0.2% by weight or less. The (meth) acrylic polymer (a) may be substantially free of structural units derived from hydroxyl group-containing monomers.

For the purpose of improving the adhesiveness and heat resistance of the pressure-sensitive adhesive sheet 1, other comonomers having a polymerizable functional group containing an unsaturated double bond such as a (meth) acryloyl group or vinyl group may be used as the monomer component in addition to the alkyl (meth) acrylate and the above-mentioned comonomers. Other comonomers may be used alone or in combination.

Examples of the other comonomer include: anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; sulfonic acid group-containing monomers such as allylsulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, (meth) acrylamidopropane sulfonic acid, and sulfopropyl (meth) acrylate; phosphate group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; alkylaminoalkyl (meth) acrylates such as aminoethyl (meth) acrylate, N-dimethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate and the like; alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; succinimide-based monomers such as N- (meth) acryloyloxymethylene succinimide, N- (meth) acryloyl-6-oxyhexamethylene succinimide, and N- (meth) acryloyl-8-oxyoctamethylene succinimide; maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-dodecylmaleimide and N-phenylmaleimide; itaconimide monomers such as N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide and N-dodecyl itaconimide; vinyl monomers such as vinyl acetate and vinyl propionate; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate; glycol (meth) acrylates such as polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, and methoxypolypropylene glycol (meth) acrylate; tetrahydrofurfuryl (meth) acrylate, fluorine-containing (meth) acrylate, polysiloxane (meth) acrylate, 2-methoxyethyl acrylate, and the like; silicon atom-containing silane monomers such as 3-acryloxypropyl triethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyl trimethoxysilane, 4-vinylbutyl triethoxysilane, 8-vinyloctyl trimethoxysilane, 8-vinyloctyl triethoxysilane, 10-methacryloxydecyl trimethoxysilane, 10-acryloxydecyl trimethoxysilane, 10-methacryloxydecyl triethoxysilane, and 10-acryloxydecyl triethoxysilane.

Examples of the other comonomer include: a multifunctional monomer having 2 or more unsaturated double bonds, such as 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 tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and caprolactone-modified dipentaerythritol hexa (meth) acrylate.

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

The weight average molecular weight of the (meth) acrylic polymer (A) is usually 30 to 400 tens of thousands. From the viewpoint of durability, the weight average molecular weight of the (meth) acrylic polymer (a) is preferably 30 to 300 tens of thousands, more preferably 40 to 220 tens of thousands. From the viewpoint of heat resistance, the weight average molecular weight is preferably 30 ten thousand or more. When the weight average molecular weight is 400 ten thousand or less, the pressure-sensitive adhesive sheet 1 tends to be hard and less likely to peel. The weight average molecular weight (Mw)/number average molecular weight (Mn) representing the molecular weight distribution is preferably 1.8 to 10, more preferably 1.8 to 7, still more preferably 1.8 to 5. From the viewpoint of durability, the molecular weight distribution (Mw/Mn) is preferably 10 or less. The weight average molecular weight and the molecular weight distribution (Mw/Mn) were determined from values measured by GPC (gel permeation chromatography) and calculated by polystyrene conversion.

The (meth) acrylic polymer (a) can be formed by polymerizing one or two or more monomers described above by a known method. The monomers may also be polymerized with a partial polymer of the monomers. The polymerization may be carried out by, for example, solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, active energy ray polymerization. Since an adhesive sheet excellent in optical transparency can be formed, solution polymerization and active energy ray polymerization are preferable. The polymerization is preferably carried out while avoiding contact between the monomer and/or a part of the polymer and oxygen, and for this purpose, polymerization in an inert gas atmosphere such as nitrogen or polymerization in a state of blocking oxygen by a resin film or the like may be used. The (meth) acrylic polymer (a) to be formed may be in any form of a random copolymer, a block copolymer, a graft copolymer, and the like.

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

The solvent used in the solution polymerization is, for example, 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 cyclohexane and methylcyclohexane; ketones such as methyl ethyl ketone and methyl isobutyl ketone, but the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

The polymerization initiator used in the solution polymerization is, for example, azo-based polymerization initiator, peroxide-based polymerization initiator, and redox-based polymerization initiator. The peroxide-based polymerization initiator is, for example, dibenzoyl peroxide or t-butyl peroxymaleate. Among them, the azo-based polymerization initiator disclosed in Japanese patent application laid-open No. 2002-69411 is preferable. The azo-based polymerization initiator is, for example, 2 '-Azobisisobutyronitrile (AIBN), 2' -azobis (2-methylbutyronitrile), dimethyl 2,2 '-azobis (2-methylpropionate), 4' -azobis (4-cyanovaleric acid), but the polymerization initiator is not limited to the above examples. The azo-based polymerization initiator may be used in an amount of, for example, 0.05 to 0.5 part by weight or 0.1 to 0.3 part by weight based on 100 parts by weight of the total amount of the monomers.

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

The photopolymerization initiator is, for example, benzoin ether type photopolymerization initiator, acetophenone type photopolymerization initiator, α -ketonic type photopolymerization initiator, aromatic sulfonyl chloride type photopolymerization initiator, photoactive oxime type photopolymerization initiator, benzoin type photopolymerization initiator, benzil type photopolymerization initiator, benzophenone type photopolymerization initiator, ketal type photopolymerization initiator, thioxanthone type photopolymerization initiator, but the photopolymerization initiator is not limited to the above examples.

The benzoin ether photopolymerization initiator is, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-dimethoxy-1, 2-diphenylethane-1-one, anisole methyl ether. Examples of the acetophenone photopolymerization initiator include 2, 2-diethoxyacetophenone, 2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4- (t-butyl) dichloroacetophenone. The α -ketonic photopolymerization initiator is, for example, 2-methyl-2-hydroxyphenylacetone, 1- [4- (2-hydroxyethyl) phenyl ] -2-methylpropan-1-one. The aromatic sulfonyl chloride-based photopolymerization initiator is, for example, 2-naphthalenesulfonyl chloride. The photo-active oxime photopolymerization initiator is, for example, 1-phenyl-1, 1-propanedione-2- (O-ethoxycarbonyl oxime). The benzoin photopolymerization initiator is, for example, benzoin. The benzil photopolymerization initiator is, for example, benzil. Examples of the benzophenone photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3' -dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α -hydroxycyclohexyl phenyl ketone. The ketal photopolymerization initiator is, for example, benzil dimethyl ketal. Examples of the thioxanthone photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2, 4-dimethylthioxanthone, isopropylthioxanthone, 2, 4-diisopropylthioxanthone and dodecylthioxanthone.

The photopolymerization initiator may be used in an amount of, for example, 0.01 to 1 part by weight or 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 adhesive composition may be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, and further 80% by weight or more, based on the solid content. The upper limit of the content is, for example, 99% by weight or less, 97% by weight or less, 95% by weight or less, 93% by weight or less, and further 90% by weight or less.

[ Cross-linking agent (B) ]

The crosslinking agent (B) is typically a multifunctional crosslinking agent having 2 or more crosslinking reactive groups per 1 molecule. The crosslinking agent (B) may be a crosslinking agent having 3 or more functions and having 3 or more crosslinking reactive groups per 1 molecule. The upper limit of the number of crosslinking reactive groups per 1 molecule is, for example, 5.

The crosslinking agent (B) is preferably excellent in compatibility with the (meth) acrylic polymer (A). By using the crosslinking agent (B) having good compatibility with the (meth) acrylic polymer (a), occurrence of clouding of the adhesive sheet 1 after the adhesive sheet 1 is produced can be easily suppressed. For example, when an isocyanate-based crosslinking agent is used as the crosslinking agent (B) as described later, the adhesive composition tends to exhibit a phase separation behavior of a low critical solution temperature type (Lower Critical Solution Temperature: LCST type). In this case, if the compatibility of the crosslinking agent (B) with the (meth) acrylic polymer (a) is good, the clouding of the adhesive sheet 1 can be suppressed even if the adhesive composition is dried at a relatively high temperature. That is, the range of the drying temperature applicable to the adhesive composition tends to be wide. In particular, when the (meth) acrylic polymer (a) contains a structural unit derived from an aromatic ring-containing monomer and 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 crosslinking agent (B) tends to be good.

The crosslinking agent (B) contains, for example, at least one selected from isocyanate-based crosslinking agents and polyfunctional (meth) acrylate-based crosslinking agents, and preferably contains isocyanate-based crosslinking agents. Isocyanate-based crosslinkers are suitable for solvent-based adhesive compositions. The multifunctional (meth) acrylate-based crosslinking agent is suitable for an active energy ray-curable adhesive composition.

As the isocyanate-based crosslinking agent, a compound having at least 2 isocyanate groups (isocyanate compound) can be used. 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, for example, 5. Examples of the isocyanate compound include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds. The isocyanate-based crosslinking agent is preferably capable of self-polymerization by reaction with water.

Examples of the aromatic isocyanate compound include: benzene diisocyanate, 2, 4-toluene diisocyanate, 2, 6-toluene diisocyanate, 2' -diphenylmethane diisocyanate, 4' -toluidine diisocyanate, 4' -diphenyl ether diisocyanate, 4' -biphenyl diisocyanate (4, 4' -diphenyl diisocyanate), 1, 5-naphthalene diisocyanate, xylylene diisocyanate, and the like.

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

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

Examples of the isocyanate-based crosslinking agent include polymers (dimers, trimers, pentamers, etc.) of the above isocyanate compounds, adducts obtained by adding a polyol such as trimethylolpropane, urea modified products, biuret modified products, allophanate modified products, isocyanurate modified products, carbodiimide modified products, urethane prepolymers obtained by adding a polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol, etc., and the like. From the viewpoint of compatibility with the (meth) acrylic polymer (a), the isocyanate-based crosslinking agent preferably contains a long-chain alkyl group.

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

The isocyanate-based crosslinking agent preferably contains an adduct of a polyol and toluene diisocyanate and an isocyanurate modified product of toluene diisocyanate as the TDI-based crosslinking agent. Specific examples of the adduct of a polyol and toluene diisocyanate include trimethylolpropane/toluene diisocyanate trimer adduct.

Examples of the commercial products of the isocyanate-based crosslinking agent include: trade names "Millionate MT"、"Millionate MTL"、"Millionate MR-200"、"Millionate MR-400"、"Coronate L"、"Coronate HL"、"Coronate HX" and others manufactured by "Takenate D-101E"、"Takenate D-262"、"Takenate D-110N"、"Takenate D-120N"、"Takenate D-140N"、"Takenate D-160N"、"Takenate D-165N"、"Takenate D-170HN"、"Takenate D-178N"、"Takenate 500"、"Takenate 600"、 Tosoh corporation, mitsui chemical Co., ltd., are preferably TAKENATE D-101E and TAKENATE D-262.

The isocyanate-based crosslinking agent may be used singly or in combination.

As the polyfunctional (meth) acrylate-based crosslinking agent, a compound having at least 2 (meth) acryloyl groups (polyfunctional (meth) acrylate compound) may be used. Examples of the polyfunctional (meth) acrylate compound include: polyalkylene glycol di (meth) acrylates such as polypropylene glycol di (meth) acrylate and polyethylene glycol di (meth) acrylate; alkylene glycol di (meth) acrylates such as 1, 6-hexanediol di (meth) acrylate and neopentyl glycol di (meth) acrylate; (meth) acrylic acid adducts of diglycidyl ether compounds such as bisphenol a diglycidyl ether di (meth) acrylate; compounds having 3 or more (meth) acryloyl groups such as trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and the like are preferable, and polypropylene glycol di (meth) acrylate is preferable.

As a commercially available product of the multifunctional (meth) acrylate crosslinking agent, for example, there may be mentioned the trade name "APG-400" manufactured by Xinzhou Chemicals Co., ltd.

The polyfunctional (meth) acrylate-based crosslinking agent may be used either alone or in combination of two or more.

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

The amount of the crosslinking agent (B) to be blended is, for example, 2 parts by weight or more, preferably 3 parts by weight or more, more preferably 5 parts by weight or more, still more preferably 8 parts by weight or more, particularly preferably 10 parts by weight or more, or 12 parts by weight or more, based on 100 parts by weight of the (meth) acrylic polymer (a). The amount of the crosslinking agent (B) to be blended may be, for example, 30 parts by weight or less, preferably 25 parts by weight or less, or may be less than 20 parts by weight based on 100 parts by weight of the (meth) acrylic polymer (a).

For example, when the crosslinking agent (B) is an adduct of trimethylolpropane containing a long-chain alkyl group and an isocyanate compound, the blending amount thereof is preferably about 10 parts by weight per 100 parts by weight of the (meth) acrylic polymer (a). When the crosslinking agent (B) is an isocyanurate modified product of an isocyanate compound containing a long-chain alkyl group, the blending amount thereof is preferably about 5 parts by weight relative to 100 parts by weight of the (meth) acrylic polymer (a). When the crosslinking agent (B) is a difunctional (meth) acrylate crosslinking agent, the blending amount thereof is preferably about 20 parts by weight per 100 parts by weight of the (meth) acrylic polymer (a). In the case where the crosslinking agent (B) is a 4-functional (meth) acrylate-based crosslinking agent, the blending amount thereof is preferably about 10 parts by weight per 100 parts by weight of the (meth) acrylic polymer (a). In the case where the crosslinking agent (B) is a 6-functional (meth) acrylate crosslinking agent, the blending amount thereof is preferably about 7 parts by weight per 100 parts by weight of the (meth) acrylic polymer (a). The amount of the crosslinking agent (B) to be blended is not limited to the above amount, and may be appropriately adjusted depending on the molecular weight and structure of the crosslinking agent (B).

In the pressure-sensitive adhesive composition, when the amount of the crosslinking agent (B) blended is about 2 parts by weight or more per 100 parts by weight of the (meth) acrylic polymer (a), the crosslinking agents (B) may react with each other to form the polymer (C) containing the structural unit derived from the crosslinking agent (B) as a main component in the production of the pressure-sensitive adhesive sheet 1. The polymer (C) is suitable for suppressing the dimensional change of the adhesive sheet 1 by imparting a sufficient cohesive force to the adhesive sheet 1. That is, the polymer (C) is suitable for suppressing display unevenness and light leakage in an image display device. The combination of the (meth) acrylic polymer (a) and the polymer (C) is suitable for improving the durability of the adhesive sheet 1 in a high-temperature and high-humidity environment or the like.

[ Other Components ]

The adhesive composition may further comprise a (meth) acrylic oligomer.

The (meth) acrylic oligomer may 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, or may be 2000 or more, 3000 or more, or 4000 or more. The upper limit of the weight average molecular weight (Mw) of the (meth) acrylic oligomer is, for example, 30000 or less, or 15000 or less, 10000 or less, and further 7000 or less.

The (meth) acrylic oligomer has, for example, one or two or more structural units derived from each of the following monomers: (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) 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, undecyl (meth) acrylate, and dodecyl (meth) acrylate; esters of (meth) acrylic acid and alicyclic alcohols such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and dicyclopentanyl (meth) acrylate; aromatic ring-containing (meth) acrylates such as phenyl (meth) acrylate and benzyl (meth) acrylate; and (meth) acrylic esters derived from terpene compound derivative alcohols.

The (meth) acrylic oligomer preferably has a structural unit derived from a (meth) acrylic monomer having a relatively large-volume structure. In this case, the adhesiveness of the adhesive sheet 1 can be further improved. Examples of the acrylic monomer are alkyl (meth) acrylates containing an alkyl group having a branched structure such as isobutyl (meth) acrylate and t-butyl (meth) acrylate; esters of (meth) acrylic acid and alicyclic alcohols such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and dicyclopentanyl (meth) acrylate; aromatic ring-containing (meth) acrylates such as phenyl (meth) acrylate and benzyl (meth) acrylate. Preferably, the monomer has a cyclic structure, and more preferably, has 2 or more cyclic structures. In addition, from the viewpoint that polymerization and/or formation of an adhesive sheet is not easily hindered when ultraviolet irradiation is performed in polymerizing a (meth) acrylic oligomer and/or in forming an adhesive sheet, it is preferable that the monomer does not have an unsaturated bond, and for example, an alkyl (meth) acrylate containing an alkyl group having a branched structure, an ester of (meth) acrylic acid and an alicyclic alcohol may be used.

Specific examples of the (meth) acrylic oligomer are butyl acrylate, a copolymer of methyl acrylate and acrylic acid, a copolymer of cyclohexyl methacrylate and isobutyl methacrylate, a copolymer of cyclohexyl methacrylate and isobornyl methacrylate, a copolymer of cyclohexyl methacrylate and acryloylmorpholine, a copolymer of cyclohexyl methacrylate and diethylacrylamide, a copolymer of 1-adamantyl acrylate and methyl methacrylate, a copolymer of dicyclopentanyl methacrylate and isobornyl methacrylate, a copolymer of at least one selected from dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate and cyclopentyl methacrylate and methyl methacrylate, a homopolymer of dicyclopentanyl acrylate, a homopolymer of 1-adamantyl methacrylate and a homopolymer of 1-adamantyl acrylate.

The polymerization of the (meth) acrylic oligomer may be carried out by the polymerization method of the (meth) acrylic polymer (a) described above.

When the pressure-sensitive adhesive composition contains a (meth) acrylic oligomer, the amount of the (meth) acrylic oligomer to be blended is, for example, 70 parts by weight or less, 50 parts by weight or less, and more preferably 40 parts by weight or less, based on 100 parts by weight of the (meth) acrylic polymer (a). The lower limit of the amount to be blended is, for example, 1 part by weight or more, may be 2 parts by weight or more, and further may be 3 parts by weight or more, based on 100 parts by weight of the (meth) acrylic polymer (a). The adhesive composition may also be free of (meth) acrylic oligomers.

The adhesive composition may further contain known additives. Examples of the additive include: silane coupling agents, polyfunctional alcohols, solvents, colorants, powders of pigments and the like, dyes, surfactants, plasticizers, tackifiers (tackifier), surface lubricants, leveling agents, re-working improvers, softeners, antioxidants, age inhibitors, light stabilizers, ultraviolet absorbers, polymerization inhibitors, antistatic agents (alkali metal salts as ionic compounds, ionic liquids, ionic solids and the like), inorganic or organic fillers, metal powders, particles, foils and the like. Further, within a controllable range, redox compounds to which a reducing agent is added may be used. These additives may be used, for example, in a range of 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 1 part by weight or less, relative to 100 parts by weight of the (meth) acrylic polymer (a).

Specific examples of the silane coupling agent include: epoxy-containing silane coupling agents such as 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, amino-containing silane coupling agents such as 3-aminopropyl trimethoxysilane, N-2- (aminoethyl) -3-aminopropyl methyldimethoxysilane, 3-triethoxysilyl-N- (1, 3-dimethylbutylidene) propylamine, N-phenyl-gamma-aminopropyl trimethoxysilane, 3-acryloxypropyl trimethoxysilane, 3-methacryloxypropyl triethoxysilane, and isocyanate-containing silane coupling agents such as 3-isocyanatopropyl triethoxysilane.

When the adhesive composition contains a silane coupling agent, the amount of the silane coupling agent to be blended is, for example, 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, and further 0.05 parts by weight or less based on 100 parts by weight of the (meth) acrylic polymer (a). The adhesive composition may also be free of silane coupling agents.

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

Examples of the polyfunctional alcohol are alkylene glycols such as ethylene glycol and propylene glycol and polymers thereof; ether diols such as diethylene glycol and polymers thereof; trimethylolethane; trimethylolpropane; glycerol; and sugar alcohols such as pentaerythritol and sorbitol. The polyfunctional alcohol is preferably trimethylolpropane, glycerol, diethylene glycol and polymers thereof, more preferably trimethylolpropane.

The polyfunctional alcohol may be 3 or more functions. Examples of 3-functional polyfunctional alcohols are trimethylol propane and glycerol.

The polyfunctional alcohol may have no reactive group other than the hydroxyl group, which is reactive with the crosslinking agent (B). The reactive group is, for example, at least one selected from the group consisting of an amino group, a carboxyl group and an epoxy group, and particularly an amino group.

The amount of the polyfunctional alcohol blended in the adhesive composition is, for example, 0.5 to 20 parts by weight based on 100 parts by weight of the (meth) acrylic polymer (a). The upper limit of the 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, and further 3 parts by weight or less.

The type of the adhesive composition is, for example, emulsion type, solvent type (solution type), active energy ray curing type (photo curing type), hot melt type (hot melt type). The pressure-sensitive adhesive composition may be of a solvent type or an active energy ray-curable type, or of a solvent type, from the viewpoint of being capable of forming a pressure-sensitive adhesive sheet excellent in durability. The solvent-based adhesive composition may contain no photo-curing agent such as an ultraviolet curing agent.

The adhesive sheet 1 can be produced from the adhesive composition by the following method. As for the solvent type, for example, an adhesive composition or a mixture of an 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 adhesive sheet 1. The adhesive composition thermally cures by heat upon drying. For example, a mixture of a monomer (group) that is polymerized to form the (meth) acrylic polymer (a), a crosslinking agent (B), and, if necessary, a partial polymer of the monomer (group), a polymerization initiator, an oligomer, an additive, a solvent, and the like is applied to a base film, and the resulting coating film is irradiated with an active energy ray to form the adhesive sheet 1. Before the irradiation with the active energy ray, the coating film may be dried to remove the solvent. The base film may be a film (release liner) having a coated surface subjected to a release treatment.

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

The substrate film may be coated by a known method. The coating may be performed by, for example, a roll coating method, a gravure coating method, a reverse coating method, a roll brushing method, a spray coating method, a dip roll coating method, a bar coating method, a blade coating method, an air knife coating method, a shower coating method, a die lip coating method, an extrusion coating method using a die coater, or the like.

Solvent-based adhesive compositions, particularly adhesive compositions containing isocyanate-based crosslinkers, have a tendency to exhibit phase separation behavior at low critical solution temperatures (Lower Critical Solution Temperature: LCST type). Therefore, in the case of using the solvent-based adhesive composition, the drying temperature of the coating film is preferably 200 ℃ or lower, and may be 160 ℃ or lower, 150 ℃ or lower, 130 ℃ or lower, 120 ℃ or lower, and further may be 100 ℃ or lower, for example. When the drying temperature is 130 ℃ or less, the reaction rate of the crosslinking agent (B), particularly the isocyanate crosslinking agent, can be appropriately adjusted, and the compatibility between the (meth) acrylic polymer (a) and the polymer (C) can be satisfactorily maintained, so that the variation in the elastic modulus of the adhesive sheet 1 tends to be reduced. The lower limit of the drying temperature of the coating film is not particularly limited, and may be, for example, 40℃or 60 ℃. The drying time of the coating film may be appropriately adjusted depending on the drying temperature, for example, 5 seconds to 20 minutes, or 5 seconds to 10 minutes, or further 10 seconds to 5 minutes. When the drying temperature is set to a high level, it is preferable to set the drying time to be short from the viewpoint of reducing the variation in the elastic modulus of the adhesive sheet 1. The drying of the coating film is preferably performed in an environment having a relatively high humidity. Thus, the crosslinking agent (B), particularly the isocyanate-based crosslinking agent, in the coating film tends to react quickly and uniformly. The relative humidity at the drying temperature of the coating film is, for example, 0% RH or more, may be 5% RH or more, 10% RH or more, 20% RH or more, and further may be 30% RH or more.

Active energy ray-curable adhesive compositions, particularly adhesive compositions containing multifunctional (meth) acrylate-based crosslinking agents, tend to exhibit phase separation behavior of the upper critical solution temperature type (Upper Critical Solution Temperature: UCST type). Therefore, in the case of using the active energy ray-curable adhesive composition, the coating film may be irradiated with active energy rays or may be further subjected to a drying treatment before and after the irradiation with active energy rays. The drying temperature of the coating film is preferably 60℃or higher, and may be 80℃or higher, 100℃or higher, 110℃or higher, and further 120℃or higher. By setting the drying temperature of the coating film to a high level, compatibility of the (meth) acrylic polymer (a) with the polymer (C), particularly the polymer (C) containing a structural unit derived from the polyfunctional (meth) acrylic crosslinking agent, tends to be well maintained, and variation in the elastic modulus of the adhesive sheet 1 tends to be reduced. The upper limit of the drying temperature of the coating film is not particularly limited, and is, for example, 200 ℃. The drying time of the coating film may be appropriately adjusted depending on the drying temperature, for example, 5 seconds to 20 minutes, 5 seconds to 10 minutes, and further 10 seconds to 5 minutes.

(Optical film)

Examples of the optical film 2 are laminated films including a polarizing plate, a phase difference film, and a polarizing plate and/or a phase difference film. The optical film 2 is not limited to the above examples, and the optical film 2 may include a glass film.

The polarizing plate is, for example, a laminate including a polarizer and a transparent protective film. The transparent protective film is disposed in contact with, for example, a principal surface (surface having the largest area) of the layered polarizer. The polarizer may be disposed between two transparent protective films.

The polarizer is not particularly limited, and various polarizers can be used. Examples of the polarizer include a film obtained by unidirectionally stretching a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film, which is adsorbed with a dichroic substance such as iodine or a dichroic dye; and a polyene oriented film such as a dehydrated polyvinyl alcohol product or a desalted polyvinyl chloride product. Among these, a polarizer formed of a polyvinyl alcohol film and a dichroic substance such as iodine is preferable, and an iodine-based polarizer containing iodine and/or iodide ions is more preferable. The thickness of the polarizer is not particularly limited, and is usually about 5 to 80. Mu.m.

A polarizer produced by dyeing a polyvinyl alcohol film with iodine and stretching the film in one direction can be produced, for example, by immersing polyvinyl alcohol in an aqueous solution of iodine to dye and stretching the film to 3 to 7 times the original length. If necessary, the polyvinyl alcohol may be immersed in an aqueous solution containing boric acid, zinc sulfate, zinc chloride, etc. such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water before dyeing and washed with water. By washing the polyvinyl alcohol film with water, dirt and an anti-blocking agent on the surface of the polyvinyl alcohol film can be removed, and the polyvinyl alcohol film can be swelled to suppress occurrence of uneven dyeing. Stretching of the polyvinyl alcohol film may be performed after dyeing with iodine, while dyeing, or 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.

As the polarizer, a thin polarizer having a thickness of 10 μm or less may be used. From the viewpoint of thickness reduction, the thickness of the polarizer is preferably 1 to 7 μm. Such a thin polarizer is preferable in that it has little thickness unevenness, excellent visibility, and little dimensional change, and therefore, it has excellent durability, and further, it can be thinned.

Typical thin polarizers include those described in Japanese patent application laid-open No. 51-069644, japanese patent application laid-open No. 2000-338329, international publication No. 2010/100917, japanese patent No. 4751481, and Japanese patent application laid-open No. 2012-073563. These thin polarizers can be obtained by a method including a step of stretching a polyvinyl alcohol resin (hereinafter also referred to as PVA) layer and a stretching resin base material in a laminate state, and a step of dyeing. In this method, since the PVA-based resin layer is supported by the resin base material for stretching, even if the PVA-based resin layer is thin, it is possible to suppress defects such as breakage due to stretching.

Among the production methods including the step of stretching in a laminate and the step of dyeing, those described in international publication No. 2010/100917, japanese patent No. 4751481, and japanese patent application laid-open No. 2012-073563, which include the step of stretching in an aqueous boric acid solution, are preferred, and those described in japanese patent application laid-open No. 4751481 and japanese patent application laid-open No. 2012-073563, which include the step of stretching in an atmosphere of an auxiliary gas prior to stretching in an aqueous boric acid solution, are particularly preferred, in view of improving polarization performance by stretching at a high magnification.

As a material for forming the transparent protective film provided on one or both surfaces of the polarizer, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like can be used. Specific examples of such thermoplastic resins include cellulose resins such as cellulose triacetate, polyester resins, polyether sulfone 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. 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. In the case where 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 may be bonded to one principal surface of the polarizer by an adhesive, and a transparent protective film made of a thermosetting resin or an ultraviolet-curable resin may be bonded to the other principal surface of the polarizer. The transparent protective film may contain one or more arbitrary additives. Examples of the additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, coloring resists, flame retardants, nucleating agents, antistatic agents, pigments, colorants, and the like. The content of the thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, still more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. When the content of the thermoplastic resin in the transparent protective film is 50 wt% or more, the thermoplastic resin tends to exhibit sufficiently high transparency and the like inherent in the thermoplastic resin.

The thickness of the transparent protective film can be appropriately determined, and is generally about 10 to 200 μm in view of handling properties such as strength and handling properties, film properties, and the like.

The polarizer and the transparent protective film are usually bonded together by an aqueous adhesive or the like. Examples of the aqueous adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex, aqueous polyurethane, aqueous polyester, and the like. Examples of the adhesive other than the above-mentioned adhesive include an ultraviolet-curable adhesive and an electron beam-curable adhesive. The adhesive for an electron beam curable polarizing plate exhibits suitable adhesion to various transparent protective films. The adhesive may also contain a metal compound filler.

In the polarizing plate, a retardation film or the like may be formed on the polarizer instead of the transparent protective film, and another transparent protective film, a retardation film, or the like may be further provided on the transparent protective film.

The transparent protective film may be provided with a hard coat layer on a surface of the transparent protective film opposite to the surface to which the polarizer is bonded, or may be subjected to a treatment for the purpose of antireflection, adhesion prevention, diffusion prevention, antiglare, and the like.

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

Examples of the retardation film include an antireflection retardation film (see japanese patent application laid-open nos. 2012-133303 [0221], [0222], [0228 ]), a viewing angle compensation retardation film (see japanese patent application laid-open nos. 2012-133303 [0225], [0226 ]), and a viewing angle compensation tilt orientation retardation film (see japanese patent application laid-open No. 2012-133303 [0227 ]).

The retardation film is not particularly limited as long as it has substantially the above-described function, and for example, a retardation value, an arrangement angle, a three-dimensional birefringence, a single layer or a plurality of layers, and the like, and a known retardation film may be used.

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

The retardation film is composed of two layers, i.e., a 1/4 wave plate and a 1/2 wave plate, which are obtained by aligning and fixing a liquid crystal material.

Fig. 4 shows another example of the optical laminate of the present embodiment. The optical laminate 10B of fig. 4 has a laminated structure in which the release liner 3, the adhesive sheet 1, and the optical film 2 are laminated in this order. The optical laminate 10B may be used in the form of an optical film formed as a pressure-sensitive adhesive sheet by peeling the release liner 3.

Examples of the constituent material of the release liner 3 include: plastic films such as polyethylene, polypropylene, polyethylene terephthalate and polyester films, porous materials such as paper, cloth and nonwoven fabric, and suitable sheet materials such as nets, foam sheets, metal foils and laminates thereof are preferably used from the viewpoint of excellent surface smoothness.

The plastic film is not particularly limited as long as it can protect the adhesive sheet 1, and examples thereof include: polyethylene film, polypropylene film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, 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 about 5 to 200. Mu.m, preferably about 5 to 100. Mu.m. The release liner 3 may be subjected to an antistatic treatment such as a release treatment using a release agent such as silicone, fluorine, long-chain alkyl, or fatty acid amide, a silica powder, or the like, an antifouling treatment, a coating treatment, a mixing treatment, or a vapor deposition treatment, as necessary. In particular, by appropriately subjecting the surface of the release liner 3 to release treatment such as silicone treatment, long-chain alkyl treatment, fluorine treatment, etc., the releasability from the adhesive sheet 1 can be further improved.

As described above, a release film used in manufacturing the adhesive sheet 1 may be used as the release liner 3.

Fig. 5 shows another example of the optical laminate of the present embodiment. The optical laminate 10C of fig. 5 has a laminated 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. The optical laminate 10C may be used by, for example, attaching the release liner 3 to an image forming layer after peeling.

The interlayer adhesive 4 may be any known adhesive, or the adhesive sheet 1 may be used for the interlayer adhesive 4.

Another example of the optical laminate of the present embodiment is shown in fig. 6, and an optical laminate 10D of fig. 6 has a laminated 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. The optical laminate 10D may be used by, for example, attaching the release liner 3 to an image forming layer after peeling.

The protective film 5 has a function of protecting the optical film 2 (polarizing plate 2B) as the outermost layer in the case of distribution and storage of the optical laminate 10D and in the case of introducing the optical laminate 10D into an image display device. In addition, the protective film 5 may function as a window to the outside space in a state of being introduced into the image display apparatus. The 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, and polyester is preferable. The protective film 5 is not limited to the above example, and the protective film 5 may be a glass film or a laminated film including a glass film. The protective film 5 may be subjected to surface treatments such as antiglare, antireflection, antistatic, and the like.

The protective film 5 may be bonded to the optical film 2 via an arbitrary adhesive, or may be bonded by the pressure-sensitive adhesive sheet 1.

The optical laminate of the present embodiment can be distributed and stored in the form of a wound body obtained by winding a band-shaped optical laminate, or in the form of a sheet-shaped optical laminate, for example.

The optical layered body of the present embodiment is typically used for 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)

Fig. 7 shows an example of the image display device according to the present embodiment. The image display device 11 of fig. 7 has a laminated structure in which 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 are laminated in this order. The image display device 11 has the optical layered body 10B, 10C, or 10D of fig. 4 to 6 (except for the release liner 3). The substrate 7 and the image forming layer 6 may have the same configuration as those of a substrate and an image forming layer provided in a known image display device.

The image display device 11 of 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, and 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-mounted applications, public Information Display (PID) applications, and the like.

The image display device of the present embodiment may have any configuration as long as the image display device includes the optical layered body of the present embodiment.

Examples

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples shown below.

[ (Meth) acrylic Polymer A1]

A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a condenser was charged with a monomer mixture containing 81.9 parts by weight of butyl acrylate, 4.8 parts by weight of acrylic acid, 0.1 part by weight of 4-hydroxybutyl acrylate, and 13.2 parts by weight of benzyl acrylate. Further, 0.1 part by weight of 2,2' -Azobisisobutyronitrile (AIBN) as a polymerization initiator was added together with ethyl acetate to 100 parts by weight of the monomer mixture, and after nitrogen substitution was performed by introducing nitrogen gas while stirring slowly, the liquid temperature in the flask was kept around 55 ℃ and polymerization was performed for 7 hours. Then, ethyl acetate was added to the obtained reaction solution, and the solid content concentration was adjusted to 30% by weight, thereby obtaining a solution of the (meth) acrylic polymer A1.

[ (Meth) acrylic Polymer A2]

A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube and a condenser was charged with a monomer mixture containing 94.9 parts by weight of butyl acrylate, 5.0 parts by weight of acrylic acid and 0.1 parts by weight of 4-hydroxybutyl acrylate. Next, 0.1 part by weight of AIBN as a polymerization initiator was added to 100 parts by weight of the monomer mixture, nitrogen was introduced while stirring slowly to replace the inside of the flask with nitrogen, and then the liquid temperature in the flask was kept at around 55℃to carry out the polymerization reaction for 7 hours. Next, ethyl acetate was added to the obtained reaction solution, and the solid content concentration was adjusted to 12% by weight, thereby obtaining a solution of the (meth) acrylic polymer A2.

TABLE 1

The abbreviations in table 1 are as follows.

BA: acrylic acid n-butyl ester

AA: acrylic acid

HBA: acrylic acid 4-hydroxybutyl ester

BzA: benzyl acrylate

AIBN: azo polymerization initiator, 2' -azobisisobutyronitrile (KISHIDA CHEMICAL Co., ltd.)

[ Production of adhesive sheet ]

(Examples 1 to 3 and comparative examples 1 to 2)

The (meth) acrylic polymer and the crosslinking agent were mixed so as to have the compositions shown in table 2 below, to obtain solvent-based adhesive compositions. Next, the adhesive composition was applied to the surface of a PET film as a base film (release liner), and the thickness of the dried adhesive sheet was set to 25 μm. The adhesive composition was applied using a spray coater (fountain coater). The obtained coating films were dried in an air circulation type constant temperature oven set to the drying temperature shown in table 2 for 1 minute, and adhesive sheets of examples 1 to 3 and comparative examples 1 to 2 were formed.

Example 4

The (meth) acrylic polymer, the crosslinking agent and the additive were mixed so as to have the compositions shown in table 2 below, to obtain an active energy ray-curable adhesive composition. Next, the adhesive composition was applied to the surface of a PET film as a base film (release liner) and the thickness of the adhesive sheet was made to 25 μm. The adhesive composition was applied using a spray coater (fountain coater). The release liner was further attached to the surface of the obtained coating film. After the coating film was dried at 130 ℃, ultraviolet irradiation was performed under conditions of illuminance of 4mW/cm ² and light quantity of 1200mJ/cm ². Thus, the curing of the coating film was performed, and the adhesive sheet of example 4 was obtained.

TABLE 2

The abbreviations in table 2 are as follows.

D262: isocyanurate modification of toluene diisocyanate (trade name: TAKENATE D-262 made by Mitsui chemical Co., ltd.)

D101E: trimethylolpropane/toluene diisocyanate adduct (trade name: TAKENATE D-101E, manufactured by Sanjing chemical Co., ltd.)

APG400: polypropylene glycol diacrylate (trade name: APG-400, new Zhongcun chemical Co., ltd.)

Tetrad C:1, 3-bis (N, N-diglycidyl aminomethyl) cyclohexane (multifunctional epoxy-based cross-linking agent; mitsubishi gas chemical systems, TETRAD C)

Omnirad 651: photopolymerization initiator, 2-dimethoxy-1, 2-diphenylethan-1-one (IGM RESINS B.V. Co., ltd.)

[ 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).

Analysis device: HLC-8120GPC manufactured by Tosoh Co., ltd

Chromatographic column: manufactured by Tosoh corporation, G7000H _XL+GMH_XL+GMH_XL

Column size: each of which is provided with90Cm in total

Column temperature: 40DEG C

Flow rate: 0.8ml/min

Injection amount: 100 μl of

Eluent: tetrahydrofuran (THF)

Detector: differential Refractometer (RI)

Standard sample: polystyrene

< Thickness >

The thickness of the adhesive sheet or the like was measured using a micrometer (manufactured by MITUTOYO).

< Gel fraction >)

The gel fraction of the produced adhesive sheet was evaluated by the method described above. The weight of the resulting pellet obtained by scraping a part of the pressure-sensitive adhesive sheet was about 0.2g, and as a stretched porous polytetrafluoroethylene film, NTF1122 (average pore size: 0.2 μm) manufactured by Nitto electric Co., ltd was used.

< Adhesion >

The adhesive force of the produced adhesive sheet was evaluated by the method described above. The tensile tester used was Autograph AG-IS manufactured by Shimadzu corporation.

< Haze >)

Haze of the adhesive sheet thus produced was measured in an atmosphere at 25℃using a SUGA tester haze meter HZ-V3 according to JIS K7136:1981. The measurement was performed with an adhesive sheet to be evaluated attached to a glass slide S01140 (thickness 1.3 mm) manufactured by Song Nitro industries.

< Storage modulus G' >

The storage modulus G' of the adhesive sheet at 25℃was evaluated by the method described above, and the dynamic viscoelasticity was measured using the "ARES-G2" manufactured by TA Instruments.

Atomic force microscope determination

By the above method, the elastic modulus was measured in the range of 500nm in the longitudinal direction and 500nm in the transverse direction on the surface of the pressure-sensitive adhesive sheet using AFM so that the number of measurement points was 65536. As the AFM, MFP-3D-SA manufactured by Oxford Instruments was used. As the cantilever, OMCL-AC240TS (spring constant 3N/m) manufactured by Olympus corporation was used. A histogram of elastic modulus with a group spacing of 0.1MPa was prepared, and the maximum value F _max of the frequency was determined. Further, the mean value and standard deviation of the elastic modulus were calculated, and the coefficient of variation was determined.

< Humidification durability >)

The wet durability (corresponding to an accelerated test of durability) of the adhesive sheet was evaluated by the following method. First, a circularly polarizing plate with an adhesive sheet having the adhesive sheets produced in examples and comparative examples on one exposed surface was formed. As a circularly polarizing plate with an adhesive sheet, a sample having dimensions of 100mm in the longitudinal direction and 40mm in the transverse direction was prepared. Next, the circularly polarizing plate was fixed to the surface of a glass plate (Eagle XG, corning) via the adhesive sheet, and the fixation of the circularly polarizing plate was performed in an atmosphere of 23 ℃ and 50% rh. Then, after 15 minutes of treatment in an autoclave at 50℃and 5 atmospheres (absolute pressure), the sheet was allowed to stand until cooled to 23℃to stabilize the bonding between the circularly polarizing plate and the glass plate, and then the sheet was allowed to stand in a heated and humidified atmosphere at 60℃and 95% RH for 500 hours. After leaving the glass plate, the glass plate was returned to an atmosphere of 23℃and 50% RH, and whether or not peeling of the circularly polarizing plate from the glass plate and foaming between the glass plate and the circularly polarizing plate were observed by naked eyes were confirmed, and the humidification durability was evaluated as described below.

A: no change in appearance such as foaming and peeling was observed.

C: significant peeling or foaming was observed at the end, and there was a practical problem.

The method for forming the circularly polarizing plate with an adhesive sheet used for evaluating the wet durability is shown below.

< Production of polarizer P1 >)

(Production of polarizer)

A long polyvinyl alcohol (PVA) -based resin film (product name "PE3000", 30 μm thick, made by kohly) was uniaxially stretched (total stretching ratio 5.9 times) in the longitudinal direction using a roll stretcher, and each treatment of swelling, dyeing, crosslinking, washing and drying was 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 in pure water at 20 ℃. In the dyeing treatment, the resin film was stretched 1.4 times while being treated in an aqueous solution of 30℃containing iodine and potassium iodide in a weight ratio of 1:7. The iodine concentration in the aqueous solution was adjusted so that the transmittance of the monomer of the polarizer produced reached 45.0%. The crosslinking treatment used 2 stages. In the crosslinking treatment in the 1 st stage, the resin film was stretched 1.2 times while being treated in an aqueous solution of 40 ℃ in which boric acid and potassium iodide were dissolved. The content of boric acid in the aqueous solution used in the crosslinking treatment in the stage 1 was 5.0 wt% and the content of potassium iodide was 3.0 wt%. In the crosslinking treatment in the 2 nd stage, the resin film was stretched 1.6 times while being treated in an aqueous solution of 65 ℃ in which boric acid and potassium iodide were dissolved. The content of boric acid in the aqueous solution used in the crosslinking treatment in the 2 nd stage was 4.3 wt% and the content of potassium iodide was 5.0 wt%. An aqueous potassium iodide solution at 20℃was used for the washing treatment. The content of potassium iodide in the aqueous solution used in the washing treatment was set to 2.6 wt%. The drying treatment was carried out at 70℃for 5 minutes.

(Production of polarizing plate P1)

Cellulose Triacetate (TAC) films (product name "KC2UA", product name 25 μm, manufactured by konicarb) were respectively bonded to the main surfaces of the polarizer manufactured as described above using a polyvinyl alcohol-based adhesive. Wherein a hard coat layer (thickness 7 μm) is formed on the main surface of the TAC film bonded to one main surface on the side opposite to the polarizer side. Thus, a polarizer P1 having a structure of a protective layer with a hard coat layer/a polarizer/a protective layer (without a hard coat layer) was obtained.

< Preparation of phase-difference film R1 >

(Production of the 1 st phase-difference film)

26.2 Parts by weight of Isosorbide (ISB), 100.5 parts by weight of 9,9- [4- (2-hydroxyethoxy) phenyl ] fluorene (BHEPF), 10.7 parts by weight of 1, 4-cyclohexanedimethanol (1, 4-CHDM), 105.1 parts by weight of diphenyl carbonate (DPC) and 0.591 part by weight of cesium carbonate (0.2% by weight aqueous solution) as a catalyst were charged into a reaction vessel, and dissolved in a nitrogen atmosphere (about 15 minutes). At this time, the temperature of the heat medium in the reaction vessel was 150℃and, if necessary, stirred. Next, the pressure in the reaction vessel was reduced to 13.3kPa, while taking 1 hour to raise the temperature of the heat medium to 190 ℃. Phenol generated with the increase in the temperature of the heat medium is discharged to the outside of the reaction vessel (the same applies hereinafter). Next, after the temperature in the reaction vessel was kept at 190 ℃ for 15 minutes, the pressure in the reaction vessel was changed to 6.67kPa, and it took 15 minutes to raise the temperature of the heat medium to 230 ℃. At the time of the increase in the stirring torque of the stirrer provided in the reaction vessel, it took 8 minutes to raise the temperature of the heat medium to 250℃and further the pressure in the reaction vessel was set to 0.200kPa or less. After a predetermined stirring torque was reached, the reaction was terminated, and the resultant reactant was extruded into water to be 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 glass transition temperature of the obtained polycarbonate resin was 136.6 ℃and the reduced viscosity was 0.395dL/g.

After the pellets of the produced polycarbonate resin were dried under vacuum at 80℃for 5 hours, a long resin film having a thickness of 120 μm was obtained by using a film-forming apparatus equipped with a single screw extruder (Isuzu Chemical Industries, screw diameter 25mm, cylinder set temperature 220 ℃), T-die (width 200mm, set temperature 220 ℃), chilled rolls (set temperature 120 to 130 ℃) and a winder. Next, the obtained resin film was stretched in the width direction by a tenter at a stretching temperature of 137 to 139 ℃ and a stretching ratio of 2.5 times, to obtain a1 st retardation film.

(Production of No. 2 retardation film)

A liquid crystal coating liquid was prepared by dissolving 20 parts by weight of a side chain type liquid crystal polymer (weight average molecular weight: 5000) represented by the following chemical formula (I) (in the formula, 65 and 35 are mol% of each structural unit), 80 parts by weight of a polymerizable liquid crystal (manufactured by BASF under the trade name of "Paliocor LC 242") exhibiting a nematic liquid crystal phase, and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba SPECIALTY CHEMICALS under the trade name of "IRGACURE 907") in 200 parts by weight of cyclopentanone. Next, the prepared liquid crystal coating liquid was applied on the surface of a norbornene-based resin film (trade name "ZEONEX" manufactured by japan rayleigh) as a base film by a bar coater, and then heated and dried at 80 ℃ for 4 minutes, so that the liquid crystal contained in the coating film was aligned. Then, the coating film was cured by irradiation of ultraviolet rays, and a liquid crystal fixed layer (thickness 0.58 μm) was formed as a 2 nd retardation film on the base film. The liquid crystal fixing layer has an in-plane retardation Re of 0nm for light having a wavelength of 550nm and a retardation Rth in the thickness direction of-71 nm (nx= 1.5326, ny= 1.5326, nz= 1.6550), and the liquid crystal fixing layer exhibits refractive index characteristics of nz > nx=ny.

[ Chemical formula 1]

(Production of retardation film R1)

One surface of the 1 st retardation film produced as described above was bonded to the liquid crystal fixing layer of the 2 nd retardation film with an adhesive, to produce a retardation film R1.

< Production of circular polarizer with adhesive sheet >

(Preparation of interlayer adhesive)

A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a condenser was charged with a monomer mixture containing 79.9 parts by weight of butyl acrylate, 15 parts by weight of benzyl acrylate, 5 parts by weight of acrylic acid, and 0.1 part by weight of 4-hydroxybutyl acrylate. Then, 0.1 part by weight of 2,2' -azobisisobutyronitrile as a polymerization initiator was added together with ethyl acetate to 100 parts by weight of the monomer mixture, and after nitrogen substitution was performed in the flask by introducing nitrogen gas while stirring slowly, the liquid temperature in the flask was kept at about 55℃for 7 hours, and polymerization was performed. Next, ethyl acetate was added to the obtained reaction solution, and the solid content concentration was adjusted to 30% by weight, to obtain a solution of a (meth) acrylic polymer for an interlayer adhesive. The weight average molecular weight of the obtained polymer was 220 ten thousand.

Next, 0.5 part by weight of a trimethylolpropane/toluene diisocyanate trimer adduct (trade name "Coronate L" manufactured by eason corporation), 0.1 part by weight of benzoyl peroxide as a peroxide-based crosslinking agent, 0.2 part by weight of an epoxy-containing silane coupling agent (trade name "KBM-403" manufactured by singe chemical industry co., ltd.) and 0.5 part by weight of a polyether compound having a reactive silyl group (Kaneka manufactured by Silyl SAT, silyl SAT) were mixed with 100 parts by weight of the solid content of the obtained (meth) acrylic polymer solution, to obtain an adhesive composition PSA1 used for an interlayer adhesive for joining a polarizing plate P1 and a retardation film R1.

(Production of polarizing plate with adhesive layer between layers)

The adhesive composition PSA1 prepared above was applied to a release surface of a polyethylene terephthalate (PET) film (manufactured by mitsubishi chemical polyester film, MRF 38) whose release surface was treated with silicone, the release surface of which was coated with the adhesive composition PSA1 so that the thickness of the dried layer became 12 μm, and the adhesive composition was dried at 155 ℃ for 1 minute, thereby forming an interlayer adhesive layer. Next, the formed interlayer adhesive layer was transferred to the protective layer (no hard coat layer) side of the polarizing plate P1, to obtain a polarizing plate with an interlayer adhesive layer.

(Production of circular polarizing plate with adhesive sheet)

Each of the adhesive sheets produced in examples and comparative examples was transferred from the release liner to the 2 nd retardation film side of the retardation film R1 (the norbornene-based resin film used as the base film at the time of producing the 2 nd retardation film was peeled off) and attached. Next, the produced polarizing plate with the interlayer adhesive layer was attached to the 1 st retardation film side of the retardation film R1 via the interlayer adhesive layer, to obtain a circular polarizing plate with an adhesive sheet. The retardation film R1 and the polarizing plate having the interlayer adhesive layer are attached such that the angle between the slow axis of the 1 st retardation film and the absorption axis of the polarizer is 45 degrees in the counterclockwise direction when viewed from the 1 st retardation film side.

As is clear from table 3, the adhesive sheets of examples, in which the gel fraction was 70% or more and the maximum value F _max of the frequency number in the histogram of the elastic modulus was 1400 or more, were improved in durability as compared with the adhesive sheets of comparative examples.

Industrial applicability

The adhesive composition of the present invention can be suitably used for producing an adhesive sheet provided in an image display device such as an EL display or a liquid crystal display.

Claims

1. An optical laminate comprising:

Adhesive sheet having gel fraction of 70% or more, and

An optical film comprising an optical film and an optical film,

2. An adhesive sheet having a gel fraction of 70% or more,

3. The adhesive sheet according to claim 2, wherein,

In the histogram, the elastic modulus G _max corresponding to the maximum value is in the range of 10 to 100 MPa.

4. The adhesive sheet according to claim 2 or 3, wherein,

The modulus of elasticity has a coefficient of variation of less than 0.08 as measured by the test method.

5. The adhesive sheet according to any one of claims 2 to 4, wherein,

The modulus of elasticity measured by the test method has a coefficient of variation of 0.035 or more.

6. The adhesive sheet according to any one of claims 2 to 5, wherein,

In the histogram, a ratio of a total value of frequency numbers included in a range of ±2.0MPa from an elastic modulus G _max (MPa) corresponding to the maximum value to a total frequency number is 70% or more.

7. The adhesive sheet according to any one of claims 2 to 6, which has a storage modulus G' at 25 ℃ of 0.1MPa or more.

8. The adhesive sheet according to any one of claims 2 to 7, which has a haze of 1.0% or less.

9. The adhesive sheet according to any one of claims 2 to 8, which is formed from an adhesive composition comprising a (meth) acrylic polymer (a) and a crosslinking agent (B).

10. The adhesive sheet according to claim 9, wherein,

The crosslinking agent (B) contains at least one selected from isocyanate-based crosslinking agents and polyfunctional (meth) acrylate-based crosslinking agents.

11. The adhesive sheet according to claim 9 or 10, wherein,

The amount of the crosslinking agent (B) blended in the adhesive composition is 2 parts by weight or more based on 100 parts by weight of the (meth) acrylic polymer (a).

12. The adhesive sheet according to any one of claims 9 to 11, wherein,

The adhesive composition is a solvent-type or active energy ray-curable adhesive composition.

13. An optical laminate comprising:

the adhesive sheet according to any one of claims 2 to 12, and

An optical film.

14. An image display device comprising the optical laminate according to claim 13.

15. An adhesive sheet having a gel fraction of 70% or more,