JP7572176B2 - Polarizing plate with adhesive and image display device - Google Patents

Description

The present invention relates to a polarizing plate with pressure-sensitive adhesive used for forming an image display device , and to an image display device.

Liquid crystal display devices and organic electroluminescence (EL) display devices are widely used as various image display devices such as mobile phones, smartphones, car navigation devices, PC monitors, and televisions. Due to the display principle of the liquid crystal display device, a polarizing plate is placed on the viewing surface of the liquid crystal cell. In a self-luminous display device such as an organic EL display device, a circular polarizing plate (a laminate of a polarizing plate and a quarter-wave plate) is placed on the viewing surface of the cell to prevent external light from being reflected by the metal electrode (cathode) and being viewed as a mirror surface.

A front transparent plate (also called a "cover window") such as a transparent resin plate or glass plate is provided on the viewing side surface of the image display device to prevent damage to the image display panel due to impact from the outer surface. The cover window is attached to the polarizing plate placed on the viewing side surface of the image display panel via an adhesive sheet.

Polarizing plates generally have a laminated structure in which transparent protective films are bonded to both sides of a polarizer, but from the viewpoint of making image display devices thinner and more flexible, a structure has been proposed in which the transparent protective films on one or both sides of the polarizer are omitted. For example, Patent Document 1 discloses a structure in which a cover window is bonded to a polarizer via an adhesive sheet placed in contact with the polarizer.

International Publication No. 2017/216886

Image display devices in which a cover window is attached using an adhesive sheet provided in contact with the viewing side surface of a polarizer are used in a variety of environments, and are required to have high durability even under humid conditions. In view of this problem, the present invention aims to provide an adhesive sheet that is placed adjacent to a polarizer, and an adhesive composition used to form the adhesive sheet.

One embodiment of the present invention is a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive sheet that is used to bond a polarizer to a cover window of an image display device and is arranged in contact with the polarizer. When a sample in which the pressure-sensitive adhesive sheet is arranged in contact with the polarizer is subjected to a moist heat test in which the sample is left in an environment at a temperature of 85° C. and a relative humidity of 85% for 100 hours, it is preferable that ΔT ₁ , ΔT ₂ , ΔT ₃ and ΔT ₄ all satisfy 1.0 to 1.2, and it is preferable that δT ₁ , δT ₂ , δT ₃ and δT ₄ all satisfy 0.95 to 1.05.

ΔT _n = (T _n '-T ₀ ')/(T _n - T ₀ )
δT _n =(T _n '/ΣT _i ')/(T _n /ΣT _i )
In the above formula, n and i are integers from 1 to 4.

_T0 is the 100 μm equivalent transmittance at a wavelength of 380 nm before the moist heat test, _T1 is the 100 μm equivalent transmittance at a wavelength of 450 nm before the moist heat test, _T2 is the 100 μm equivalent transmittance at a wavelength of 520 nm before the moist heat test, _T3 is the 100 μm equivalent transmittance at a wavelength of 580 nm before the moist heat test, and _T4 is the 100 μm equivalent transmittance at a wavelength of 660 nm before the moist heat test. _T0 ' is the 100 μm equivalent transmittance at a wavelength of 380 nm after the moist heat test, _T1 ' is the 100 μm equivalent transmittance at a wavelength of 450 nm after the moist heat test, _T2 ' is the 100 μm equivalent transmittance at a wavelength of 520 nm after the moist heat test, _T3 ' is the 100 μm equivalent transmittance at a wavelength of 580 nm after the moist heat test, and _T4 ' is the 100 μm equivalent transmittance at a wavelength of 660 nm after the moist heat test.

The 100 μm converted transmittance T (%), the total thickness L (μm) of the pressure-sensitive adhesive sheet and the polarizer, and the measured transmittance t (%) are
log ₁₀ (T/100) = (100/L) x log ₁₀ (t/100)
Satisfy the relationship.

The adhesive composition preferably contains an ultraviolet absorber.

The adhesive composition is used to form an adhesive sheet. In one embodiment, the adhesive sheet is used to bond a polarizer to a cover window of an image display device, and is placed in contact with the polarizer.

One embodiment of the present invention is a polarizing plate with adhesive in which the above-mentioned adhesive sheet is disposed on the first principal surface of a polarizer having a first principal surface and a second principal surface. The polarizing plate with adhesive may further include an adhesive sheet on the second principal surface side of the polarizer. The adhesive sheet disposed on the second principal surface side of the polarizer may be in contact with the second principal surface of the polarizer, or may be laminated on the second principal surface of the polarizer via another layer.

One embodiment of the present invention is an image display device that includes, in this order, a second adhesive sheet, a polarizer made of a polyvinyl alcohol-based film containing iodine, a first adhesive sheet, and a cover window on the surface of an image display cell, and the first adhesive sheet is the above-mentioned adhesive sheet and is disposed in contact with the polarizer.

An image display device in which the pressure-sensitive adhesive sheet of the embodiment of the present invention is placed in contact with the viewing side surface of a polarizer has durability against external ultraviolet rays and can also exhibit high durability in a humid environment.

1 is a cross-sectional view illustrating an embodiment of an image display device. FIG. 1 is a cross-sectional view illustrating one embodiment of a polarizing plate with a pressure-sensitive adhesive. FIG. 1 is a cross-sectional view illustrating one embodiment of a polarizing plate with a pressure-sensitive adhesive.

One embodiment of the present invention is an adhesive sheet that is placed in contact with the viewing side surface of a polarizer in an image display device, and an adhesive composition for forming the adhesive sheet. The adhesive sheet is used to attach the polarizer to a cover window.

Figure 1 is a cross-sectional view showing one embodiment of an image display device with a cover window on the viewing side surface. The image display device 100 has a polarizing plate 10 attached to the surface of an image display cell 60 via an adhesive sheet 22, and a cover window 70 attached to the polarizing plate 10 via an adhesive sheet 21 of an embodiment of the present invention.

The polarizing plate 10 includes a polarizer 11 made of a polyvinyl alcohol-based film containing iodine. An appropriate optical layer 15 may be provided on the second main surface (the surface on the image display cell 60 side) of the polarizer 11. An adhesive sheet 21 according to an embodiment of the present invention is disposed on the first main surface (the surface on the viewing side) of the polarizer 11 in contact with the polarizer 11. By disposing the adhesive sheet 21 on the viewing side of the polarizer 11 without any other optical layer in between, it is possible to make the image display device thinner and more flexible.

[Heat and moisture resistance of adhesive sheet (change in transmittance)]
The pressure-sensitive adhesive sheet 21 according to the embodiment of the present invention is used to bond the polarizer 11 to a cover window 70 of an image display device, and is disposed in contact with the polarizer 21. The pressure-sensitive adhesive sheet 21 is formed using a pressure-sensitive adhesive composition described below.

The adhesive sheet 21 of the embodiment of the present invention is characterized by a small change in transmittance over a wide range of visible light when a sample in which the adhesive sheet is placed in contact with a polarizer is subjected to a moist heat test in which the sample is left in an environment at a temperature of 85°C and a relative humidity of 85% for 100 hours.

The change in transmittance is evaluated based on the 100 μm equivalent transmittance obtained by converting the measured transmittance t (%) of the laminate of the polarizer and the adhesive sheet into the transmittance at a thickness of 100 μm. When the total thickness of the adhesive sheet and the polarizer is L (μm) and the measured transmittance is t (%), according to Lambert's law, the 100 μm equivalent transmittance T (%), t (%), and L (μm) satisfy the following relationship.
log ₁₀ (T/100) = (100/L) x log ₁₀ (t/100)

The transmittance change is evaluated using the 100 μm equivalent transmittance _T0 at a wavelength of 380 nm, the 100 μm equivalent transmittance _T1 at a wavelength of 450 nm, the 100 μm equivalent transmittance _T2 at a wavelength of 520 nm, the 100 μm equivalent transmittance _T3 at a wavelength of 580 nm, and the 100 μm equivalent transmittance _T4 at a wavelength of 660 nm. The wavelength of 380 nm is in the ultraviolet region, the wavelength of 450 nm corresponds to blue light, the wavelength of 520 nm corresponds to green light, the wavelength of 580 nm corresponds to yellow light, and the wavelength of 660 nm corresponds to red light.

The 100 μm-equivalent transmittances of the sample at wavelengths of 380 nm, 450 nm, 520 nm, 580 nm, and 660 nm after subjecting the laminate of the polarizer and the adhesive sheet to a moist heat test in which the laminate is left in an environment at a temperature of 85° C. and a relative humidity of 85% for 100 hours are defined as T ₀ ', T ₁ , T ₂ ', T ₃ ', and T ₄ ', respectively.

The change in transmittance before and after the heat and humidity test is mainly due to the fading of the polarizer. In a polyvinyl alcohol-based polarizer containing iodine, the polymer chain of polyvinyl alcohol and polyiodine ions (I ₃ ^- and I ₅ ^- ) form a complex, and the polymer chain is oriented in a specific direction, so that the polyiodine ions are oriented and exhibit polarization performance. When the polarizer is exposed to a high-temperature and high-humidity environment, the polarizer fades due to structural changes in the polyiodine ions (e.g., change from I ₅ ^- to I ₃ ^- ), disturbance in the orientation of the polyiodine ions, release of iodine outside the system (e.g., sublimation of I ₂ ), etc. When the adhesive sheet arranged in contact with the polarizer has ultraviolet absorbing properties, the change in transmittance due to the fading of the polarizer is small in the ultraviolet region. Therefore, the 100 μm equivalent transmittance T ₀ at a wavelength of 380 nm of the sample before the moist heat test and the 100 μm equivalent transmittance T ₀ ' of the sample after the moist heat test can be used as standards for evaluating changes in visible light transmittance.

The change in visible light transmittance can be evaluated based on the index ΔT _n = (T _n '-T ₀ ')/(T _n -T ₀ ), where n is an integer from 1 to 4, and n=1 is an index of the change in transmittance at a wavelength of 450 nm, n=2 is an index of the change in transmittance at a wavelength of 520 nm, n=3 is an index of the change in transmittance at a wavelength of 580 nm, and n=4 is an index of the change in transmittance at a wavelength of 660 nm.

For example, the change in transmittance at a wavelength of 450 nm (when n=1) can be evaluated by the index ΔT ₁ = (T ₁ '-T ₀ ')/(T ₁ -T ₀ ). (T ₁ -T ₀ ) is the difference in the 100 μm-equivalent transmittance at wavelengths of 450 nm and 380 nm of the sample before the moist heat test, and (T ₁ '-T ₀ ') is the difference in the 100 μm-equivalent transmittance at wavelengths of 450 nm and 380 nm of the sample after the moist heat test. If the ratio ΔT ₁ between these is 1, it means that the difference in transmittance at wavelengths of 450 nm and 380 nm does not change before and after the moist heat test. When _ΔT1 is greater than 1, it means that the difference in transmittance between the wavelengths of 450 nm and 380 nm has increased after the moist heat test, and when _ΔT1 is smaller than 1, it means that the difference in transmittance between the wavelengths of 450 nm and 380 nm has decreased after the moist heat test.

As described above, when the pressure-sensitive adhesive sheet has ultraviolet absorption properties, the transmittance at a wavelength of 380 nm changes little before and after the moist heat test. When the polarizer fades, the transmittance of visible light increases, so the transmittance difference between the sample and the wavelength of 380 nm after the moist heat test tends to be large. Therefore, ΔT _n is generally 1.00 or more, and the smaller ΔT _n (closer to 1.00) means the smaller the fading of the polarizer.

It is important that ΔT _n is 1.0 to 1.2 (particularly, 1.00 to 1.20) for each of n=1 to 4 (i.e., each of wavelengths of 450 nm, 520 nm, 580 nm, and 660 nm). The upper limit of ΔT _n is more preferably 1.15 or less, further preferably 1.10 or less, particularly preferably 1.05 or less, and may be 1.04 or less.

When ΔT _n is 1.0 to 1.2, deterioration of the polarizer caused by external ultraviolet rays, heating, humidification, etc. is suppressed, and the polarizer has excellent durability. Therefore, the polarizer can be used under various conditions, and can exhibit high durability even under humid conditions in particular.

In order to make ΔT _n 1.20 or less, for example, the composition of the adhesive may be adjusted. For example, the composition of the base polymer in the adhesive composition may be adjusted, and in the case of an acrylic adhesive, it is preferable to reduce the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl-containing monomers in the base polymer. In addition, it is also useful to include an ultraviolet absorber in the adhesive composition in order to make ΔT _n 1.20 or less.

The change in transmittance before and after the moist heat test can be evaluated using ΔT _n as described above. On the other hand, even if ΔT _n is large, if the rate of change in transmittance at each wavelength of visible light is constant, there is no significant change in the transmitted light hue. Conversely, even if ΔT _n at each wavelength of visible light is small, if there is a large variation in ΔT _n depending on the wavelength, there is a large change in the transmitted light hue, which may cause deterioration in visibility, such as coloring of the image in the image display device.

The ratio of the transmittance of a specific wavelength to the transmittance of all visible light is expressed as T _n /ΣT _i , where i is an integer from 1 to 4, and ΣT _i = T ₁ + T ₂ + T ₃ + T _4. For example, T ₁ /ΣT _i is the 100 μm equivalent transmittance of a wavelength of 450 nm relative to the sum of the 100 μm equivalent transmittances of wavelengths of 450 nm, 520 nm, 580 nm, and 660 nm.

The ratio of the transmittance ratio of a specific wavelength after the moist heat test, T _{n '} /ΣT _i ', to the transmittance ratio of a specific wavelength before the moist heat test, T _n /ΣT _i , δT _n = (T _n '/ΣT _i ')/(T _n /ΣT _i ), is an index that represents how the ratio of the transmittance of a specific wavelength to all visible light has changed, and if δT _n is 1, it means that the ratio of the transmittance of a specific wavelength (for example, 450 nm when n = 1) to all visible light does not change before and after the moist heat test.

When _δT1 is greater than 1, it means that the ratio of the transmittance at a wavelength of 450 nm is increased after the wet heat test, and when _δT1 is smaller than 1, it means that the ratio of the transmittance at a wavelength of 450 nm is decreased after the wet heat test. The closer _δTn is to 1.00 for each wavelength, the smaller the color change of the transmitted light due to fading of the polarizer is.

For each of n=1 to 4 (that is, for each of wavelengths of 450 nm, 520 nm, 580 nm, and 660 nm), δT _n is preferably 0.95 to 1.05, more preferably 0.97 to 1.03, even more preferably 0.98 to 1.02, and particularly preferably 0.99 to 1.01.

When δT _n is 0.95 to 1.05, deterioration of the polarizer caused by external ultraviolet rays, heating, humidification, etc. can be further suppressed, and durability can be further improved. Therefore, the polarizer can be used under various conditions, and can exhibit high durability even under humid conditions in particular.

In order to set δT _n within the range of 0.95 to 1.05, for example, the composition of the adhesive may be adjusted. For example, the composition of the base polymer in the adhesive composition may be adjusted, and in the case of an acrylic adhesive, it is preferable to reduce the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl-containing monomers in the base polymer. In addition, the inclusion of an ultraviolet absorber in the adhesive composition is also useful for setting δT _n within the range of 0.95 to 1.05.

As described above, for each of n=1 to 4, the smaller ΔT _n (closer to 1.00) the smaller the change in transmittance before and after the moist heat test, and the closer δT _n is to 1.00 the smaller the change in color of the transmitted light. It is preferable that the sample in which a polarizer is attached to a pressure-sensitive adhesive sheet produced using the pressure-sensitive adhesive composition of the present invention has ΔT _n within the above range and δT _n within the above range for each of n=1 to 4.

[Adhesive composition]
The adhesive composition constituting the adhesive sheet 21 is not particularly limited in composition, so long as a sample in which a polarizer is attached to an adhesive sheet produced using the composition has the above-mentioned _ΔTn and/or _δTn . In order to set _ΔTn and/or _δTn within the above-mentioned range, it is preferable that the adhesive composition has ultraviolet shielding properties. For example, the adhesive composition contains an ultraviolet absorber, so that it can have ultraviolet absorbing properties and shield ultraviolet rays.

<Base polymer>
The pressure-sensitive adhesive composition generally contains a base polymer, such as an acrylic-based, silicone-based, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, or rubber-based polymer.

In particular, acrylic pressure-sensitive adhesives containing an acrylic polymer as a base polymer are preferred because of their excellent optical transparency and adhesiveness. In the acrylic pressure-sensitive adhesive, the aforementioned ΔT _{n can be set to 1.20 or less by reducing the ratio of polar monomers such as hydroxyl group-containing monomers and nitrogen-containing monomers in the base polymer. In addition, in the acrylic pressure-sensitive adhesive, the aforementioned δT n can} be set to the range of 0.95 to 1.05 by reducing the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl group-containing monomers in the base polymer.

When the amount of hydroxyl group-containing monomer used in the base polymer is large, the hydrophilicity and moisture permeability of the adhesive sheet increase with an increase in the polarity of the polymer, and the polarizer placed in contact with the adhesive sheet is likely to fade under high temperature and high humidity. When the adhesive sheet is highly hydrophilic and moisture permeable, moisture from the external environment easily reaches the polarizer, and the orientation of the polymer chains that make up the polarizer is disturbed by moisture, and polyiodine ions are detached from the polymer chains, which is thought to be one of the causes of the fading of the polarizer. In addition, as the amount of nitrogen-containing monomer used in the base polymer increases, the polarizer placed in contact with the adhesive sheet is likely to fade. Since nitrogen atoms are easily coordinated to iodine, when the amount of nitrogen atoms contained in the base polymer of the adhesive sheet increases, the iodine fixed to the polymer chain of the polarizer is coordinated with the nitrogen atoms of the adhesive and detached from the polymer chain, which is thought to be one of the causes of the fading of the polarizer.

Since the amount of the hydroxyl group-containing monomer, nitrogen-containing monomer, etc. in the base polymer is small, discoloration of the polarizer is suppressed, and ΔT _n and δT _n can be set within the above ranges.

The acrylic base polymer contains an alkyl (meth)acrylate ester as the main constituent monomer component. In this specification, "(meth)acrylic" means acrylic and/or methacrylic. As the alkyl (meth)acrylate ester, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group is preferably used. The alkyl group in the alkyl (meth)acrylate ester may be branched, or may have a cyclic alkyl group (alicyclic alkyl group).

Specific examples of (meth)acrylic acid alkyl esters having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples of such acrylates include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. (Meth)acrylic acid alkyl esters having an alicyclic alkyl group may have a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate.

The amount of (meth)acrylic acid alkyl ester relative to 100 parts by weight of the total amount of monomer components constituting the acrylic base polymer is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, even more preferably 80 parts by weight or more, and may be 85 parts by weight or more, 90 parts by weight or more, or 92 parts by weight or more.

The acrylic base polymer preferably contains an acrylic monomer having a crosslinkable functional group as a copolymerization monomer component. When the base polymer has a crosslinkable functional group, the base polymer can be reacted with a crosslinking agent to increase the cohesive strength of the adhesive and improve adhesion reliability.

Examples of acrylic monomers having crosslinkable functional groups include hydroxyl group-containing monomers and carboxyl group-containing monomers. For example, when an isocyanate-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between a hydroxyl group and an isocyanate group. When an epoxy-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between a carboxyl group and an epoxy group. As described below, from the viewpoint of making the adhesive acid-free, it is preferable to use a hydroxyl group-containing monomer as a copolymerization component of the base polymer and introduce a crosslinked structure by an isocyanate-based crosslinking agent. When the base polymer contains a hydroxyl group-containing monomer as a monomer component, the crosslinking property of the base polymer is enhanced and the opacity of the adhesive in a high-temperature and high-humidity environment tends to be suppressed, resulting in a highly transparent adhesive.

Examples of hydroxyl group-containing monomers include (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate. Among these, 2-hydroxyethyl acrylate (Tg of homopolymer: -15°C) and 4-hydroxybutyl acrylate (Tg of homopolymer: -32°C) are preferred because they contribute greatly to improving adhesive strength and can suppress clouding of the pressure-sensitive adhesive sheet in high humidity environments.

The amount of hydroxyl group-containing monomer relative to 100 parts by weight of the total amount of monomer components constituting the acrylic base polymer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 0.8 parts by weight or more, and may be 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more. By increasing the amount of hydroxyl group-containing monomer, the unreacted functional groups of the crosslinking agent are reduced, so that the degree of crosslinking can be increased with a small amount of crosslinking agent, improving adhesion reliability.

On the other hand, if the amount of the hydroxy group-containing monomer used in the base polymer is excessively large, the polarity of the adhesive increases, and discoloration of the polarizer 11 arranged in contact with the adhesive sheet 21 tends to occur easily, and accordingly, the deviation of ΔT _n and Δδ _n from 1.00 tends to become large. Therefore, the amount of the hydroxy group-containing monomer relative to 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer is preferably 8 parts by weight or less, more preferably 7 parts by weight or less, and may be 6 parts by weight or less, or 5 parts by weight or less.

The acrylic base polymer may contain monomer components other than those mentioned above. The acrylic base polymer may contain, as monomer components, for example, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, etc.

The acrylic base polymer may contain a nitrogen-containing monomer as a monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl carboxylic acid amides, N-vinylcaprolactam, acrylonitrile, and methacrylonitrile.

As the amount of the nitrogen-containing monomer used increases, discoloration of the polarizer 11 arranged in contact with the pressure-sensitive adhesive sheet 21 tends to occur, and accordingly, the deviation of ΔT _n and Δδ _n from 1.00 tends to increase. Therefore, the amount of the nitrogen-containing monomer relative to 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and may be 1 part by weight or less, 0.5 parts by weight or less, 0.1 parts by weight or less, or 0.05 parts by weight or less. The acrylic base polymer may not contain a nitrogen-containing monomer as a monomer component.

If the acid component contained in the adhesive sheet migrates to the polarizer, it may promote hydrolysis of polyvinyl alcohol, which may cause the polarizer to deteriorate. Therefore, it is preferable that the adhesive sheet 21 has a low content of organic acid monomers (free organic acids) such as (meth)acrylic acid. In a thermosetting or photosetting polymer, the presence of unreacted residual monomers is inevitable. Therefore, in order to reduce the acid monomer content in the adhesive sheet, it is preferable to reduce the amount of organic acid monomer components such as (meth)acrylic acid in the monomer components constituting the base polymer. The content of the carboxyl group-containing monomer relative to the total amount of 100 parts by weight of the constituent monomer components of the acrylic base polymer is preferably 1 part by weight or less, more preferably 0.5 parts by weight or less, and even more preferably 0.1 parts by weight or less. It is preferable that the acrylic base polymer does not contain a carboxyl group-containing monomer as a monomer component.

In order to suppress fading of the polarizer 11 in a high-temperature and high-humidity environment and to bring ΔT _n and Δδ _n closer to 1.00, the base polymer constituting the pressure-sensitive adhesive sheet 21 arranged in contact with the polarizer 11 preferably has low polarity. In order to reduce the polarity of the base polymer, it is preferable that the content of polar monomers such as nitrogen-containing monomers, hydroxyl group-containing monomers, and carboxyl group-containing monomers as constituent monomer components is small. The content of the polar monomers relative to 100 parts by weight of the total amount of the constituent monomer components of the acrylic base polymer is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and may be 6 parts by weight or less, or 5 parts by weight or less.

The acrylic base polymer may not contain a polar monomer as a constituent monomer component. However, from the viewpoint of introducing a crosslinking structure into the base polymer by a thermal crosslinking agent such as an isocyanate-based crosslinking agent, it is preferable that the base polymer contains 0.1 parts by weight or more of a polar monomer such as a hydroxyl group-containing monomer. The content of the polar monomer relative to 100 parts by weight of the total amount of the constituent monomer components of the acrylic base polymer is more preferably 0.5 parts by weight or more, even more preferably 0.8 parts by weight or more, and may be 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more.

The above monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic base polymer. From the viewpoint of the balance of properties such as adhesive strength and retention strength of the adhesive, and from the viewpoint of cost, the solution polymerization method is preferable. Ethyl acetate, toluene, etc. are generally used as the solvent for solution polymerization. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator, azo initiators, peroxide initiators, redox initiators combining peroxides and reducing agents (for example, a combination of persulfate and sodium hydrogen sulfite, a combination of peroxide and sodium ascorbate), and other thermal polymerization initiators are preferably used. The amount of the polymerization initiator used is not particularly limited, but for example, it is preferably about 0.005 to 5 parts by weight, and more preferably about 0.02 to 3 parts by weight, based on 100 parts by weight of the total amount of the monomer components forming the base polymer.

A chain transfer agent may be used to adjust the molecular weight of the base polymer. The chain transfer agent receives radicals from the growing polymer chain to stop the polymer elongation, and the chain transfer agent that has received the radicals can attack the monomer to restart polymerization. Therefore, by using a chain transfer agent, it is possible to suppress an increase in the molecular weight of the base polymer without reducing the radical concentration in the reaction system. As the chain transfer agent, for example, thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol are preferably used.

The amount of chain transfer agent used is not particularly limited, but if the amount of chain transfer agent used is excessively large, the molecular weight of the base polymer may decrease, and the processability and processing dimensional stability of the adhesive sheet before photocuring may decrease. Therefore, the amount of chain transfer agent used is preferably 1 part by weight or less, more preferably 0.3 parts by weight or less, even more preferably 0.15 parts by weight or less, and particularly preferably 0.1 parts by weight or less, per 100 parts by weight of the total amount of the monomer components constituting the base polymer.

The weight average molecular weight of the acrylic base polymer is preferably 100,000 to 3,000,000, more preferably 250,000 to 2,000,000, and even more preferably 500,000 to 1,500,000. When a crosslinked structure is introduced into the acrylic base polymer, the molecular weight of the base polymer refers to the molecular weight before the crosslinked structure is introduced.

<Crosslinked structure of base polymer>
The acrylic base polymer preferably has a crosslinked structure. The method of introducing a crosslinked structure into the base polymer generally includes (1) a method of polymerizing a base polymer having a functional group capable of reacting with a crosslinking agent, adding a crosslinking agent, and reacting the base polymer with the crosslinking agent; and (2) a method of including a photopolymerizable multifunctional compound in the polymerization components of the base polymer to introduce a branched structure (crosslinked structure) into the polymer chain.

In the adhesive composition constituting the adhesive sheet 21 arranged in contact with the polarizer 11, the acrylic base polymer preferably has a crosslinked structure introduced by the above method (1). The adhesive composition constituting the adhesive sheet 21 may contain a photopolymerizable multifunctional compound and a photopolymerization initiator, and may be one in which the crosslinked structure of the above method (2) is introduced by performing photocuring after bonding the adhesive sheet 21 and the cover window 70. That is, the adhesive composition constituting the adhesive sheet 21 preferably has a base polymer with a crosslinked structure by a (thermal) crosslinking agent such as an isocyanate-based crosslinking agent, and may further be one in which a crosslinked structure by a photopolymerizable multifunctional compound (photocrosslinking agent) can be introduced by photocuring.

<Adhesive composition>
A pressure-sensitive adhesive composition is prepared by mixing an acrylic base polymer with a crosslinking agent, a photopolymerizable multifunctional compound, a photopolymerization initiator, and, if necessary, an oligomer or various additives. The pressure-sensitive adhesive composition preferably has a viscosity (e.g., about 0.5 to 20 Pa·s) suitable for application onto a substrate. The viscosity of the pressure-sensitive adhesive composition can be adjusted to an appropriate range by adjusting the molecular weight of the base polymer, the amount of the photopolymerizable multifunctional compound added, and the composition, molecular weight, and amount added of other components (e.g., oligomers). A thickening additive or the like may be used for the purpose of viscosity adjustment or the like.

(Ultraviolet absorber)
The adhesive sheet 21 preferably has ultraviolet absorbing properties. In a polarizing plate in which a transparent protective film is provided on the viewing side surface of the polarizer, the transparent protective film generally has ultraviolet absorbing properties, thereby suppressing deterioration of the polarizer due to ultraviolet rays incident from outside the display device. On the other hand, in a configuration in which the adhesive sheet 21 is disposed in contact with the viewing side surface of the polarizer 11, since a transparent protective film is not provided on the viewing side of the polarizer, it is preferable to impart ultraviolet absorbing properties to the adhesive sheet 21 to prevent photodeterioration of the polarizer 11 caused by ultraviolet rays (for example, color change of the polarizer associated with a structural change of polyiodine ions (change from I ₅ ^- to I ₃ ^- ), etc.).

In order to impart ultraviolet absorption to the adhesive sheet 21, it is preferable that the adhesive composition contains an ultraviolet absorber. Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. Triazine-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are preferred because they have high ultraviolet absorption and excellent compatibility with acrylic polymers, making it easy to obtain a highly transparent acrylic adhesive. Among these, triazine-based ultraviolet absorbers containing a hydroxyl group and benzotriazole-based ultraviolet absorbers having one benzotriazole skeleton per molecule are preferred.

Commercially available products may be used as the ultraviolet absorber. Commercially available triazine-based ultraviolet absorbers include the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl and [(alkyloxy)methyl]oxirane ("TINUVIN 400" manufactured by BASF), the reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine and (2-ethylhexyl)-glycidic acid ester ("TINUVIN 405" manufactured by BASF), and (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine ("TINUVIN 460"), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol ("TINUVIN 577" manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine ("TINUVIN 479" manufactured by BASF), 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-triazine-2,4-diyl]diphenol ("Tinosorb" manufactured by BASF) S"), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (ADEKA "ADK STAB LA-46"), etc.

Commercially available benzotriazole-based UV absorbers include 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF's "TINUVIN 928"), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (BASF's "TINUVIN PS"), 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (BASF's "TINUVIN 900"), 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (BASF's "TINUVIN 928"), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol ("TINUVIN 571" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-p-cresol ("TINUVIN P" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol ("TINUVIN 234" manufactured by BASF), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol ("TINUVIN 326," manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol ("TINUVIN" manufactured by BASF) 328"), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 329" manufactured by BASF), ester compound of benzenepropanoic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7-9 side chain and linear alkyl) ("TINUVIN 384-2" manufactured by BASF), reaction product of methyl-3-(3-(2H-benzotriazol-2-yl)-5-t-butyl-4-hydroxyphenyl)propionate with polyethylene glycol ("TINUVIN 1 130" manufactured by BASF), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate with polyethylene glycol 300 ("TINUVIN 1 130" manufactured by BASF), 213"), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole (Sumitomo Chemical's "Sumisorb 250"), etc.

The content of the UV absorber in the adhesive composition is about 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 0.3 to 3 parts by weight, per 100 parts by weight of the base polymer. By setting the content of the UV absorber within the above range, it is possible to suppress a decrease in transparency due to bleeding out of the UV absorber, while imparting UV shielding properties to the adhesive sheet 21, thereby improving weather resistance and suppressing photodegradation of the polarizer caused by external UV rays.

(Crosslinking Agent)
As described above, the acrylic base polymer preferably has a crosslinked structure. The crosslinked structure is introduced into the base polymer by adding a crosslinking agent to the adhesive composition and heating it as necessary. In order to distinguish it from the crosslinked structure introduced by the photopolymerizable multifunctional compound, the crosslinking by the isocyanate crosslinking agent or the like may be described as "thermal crosslinking", but the introduction of the crosslinked structure by the crosslinking agent may not be accompanied by heating. By introducing a thermal crosslinked structure into the acrylic base polymer, the cohesiveness of the adhesive sheet is increased, and the adhesiveness tends to be improved.

Examples of crosslinking agents include compounds that react with functional groups such as hydroxyl groups contained in the base polymer. Specific examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred because they are highly reactive with the hydroxyl groups of the base polymer and allow easy introduction of a crosslinked structure.

As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane/ Examples of isocyanate adducts include tolylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate L"), trimethylolpropane/hexamethylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate HL"), xylylene diisocyanate trimethylolpropane adducts (e.g., Mitsui Chemicals' "Takenate D110N"), and hexamethylene diisocyanate isocyanurate (e.g., Tosoh's "Coronate HX"), etc.

By adjusting the amount of crosslinking agent added, the cohesive strength and adhesive strength of the adhesive can be adjusted. The amount of crosslinking agent added is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.7 parts by weight, and even more preferably 0.1 to 0.5 parts by weight, per 100 parts by weight of the base polymer.

(Photopolymerizable polyfunctional compound)
In order to impart photocurability to the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition preferably contains a photopolymerizable multifunctional compound. The photopolymerizable multifunctional compound has two or more photopolymerizable functional groups in one molecule. The photopolymerizable functional group may be any of radical polymerizable, cationic polymerizable, and anionic polymerizable, but a radical having an unsaturated double bond (ethylenically unsaturated group) is preferred because of its excellent reactivity. The photopolymerizable polyfunctional compound is preferably a polyfunctional (meth)acrylate because of its high compatibility with the acrylic base polymer, and more preferably a polyfunctional acrylate because of its high photoradical reactivity. is particularly preferred.

Examples of polyfunctional (meth)acrylates include hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin di(meth)acrylate. difunctional (meth)acrylic acid esters such as pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethoxylated isocyanuric acid tri(meth)acrylate; tetrafunctional (meth)acrylic acid esters such as ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and pentafunctional or higher (meth)acrylic acid esters such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

From the viewpoint of improving the adhesive reliability of the adhesive sheet after photocuring, the molecular weight of the photopolymerizable multifunctional compound is preferably 1500 or less, more preferably 1000 or less. The functional group equivalent (g/eq) of the multifunctional compound is preferably 50 to 500, more preferably 70 to 300, and even more preferably 80 to 200. Since it shows moderate compatibility with the base polymer, it is preferable that the photopolymerizable multifunctional compound is liquid at room temperature.

The content of the photopolymerizable multifunctional compound in the adhesive composition is preferably 0.3 to 15 parts by weight, more preferably 0.5 to 10 parts by weight, and even more preferably 1 to 5 parts by weight, per 100 parts by weight of the acrylic base polymer. If the content of the photopolymerizable multifunctional compound is low, the adhesive reliability of the adhesive sheet after photocuring tends to be insufficient. On the other hand, if the content of the photocurable multifunctional compound is excessively large, the ratio of the base polymer in the adhesive sheet (adhesive composition) before photocuring becomes small, and the processability and processing dimensional stability of the adhesive sheet may decrease. In addition, if the content of the photocurable multifunctional compound is excessively large, the adhesive sheet after photocuring becomes hard, and the adhesive strength and impact resistance of the adhesive sheet 21 at low temperatures may become insufficient.

(Photopolymerization initiator)
The photocurable adhesive composition containing a photopolymerizable polyfunctional compound preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, a photoactive oxime-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, a ketal-based photopolymerization initiator, a thioxanthone-based photopolymerization initiator, and an acylphosphine oxide-based photopolymerization initiator. The content of the photopolymerization initiator in the adhesive composition is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, based on 100 parts by weight of the base polymer.

(Oligomer)
The pressure-sensitive adhesive composition may contain various oligomers for the purpose of adjusting the adhesive strength and viscosity of the pressure-sensitive adhesive sheet, etc. As the oligomer, for example, one having a weight average molecular weight of about 1000 to 30000 is used. As the oligomer, an acrylic oligomer is preferable because it has excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains an alkyl (meth)acrylate ester as the main constituent monomer component. Among them, those containing an alkyl (meth)acrylate ester having a chain alkyl group (chain alkyl (meth)acrylate) and an alkyl (meth)acrylate ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate) as the constituent monomer component are preferred. Specific examples of the chain alkyl (meth)acrylate and the alicyclic alkyl (meth)acrylate are as exemplified above as the constituent monomers of the acrylic base polymer.

The glass transition temperature of the acrylic oligomer is preferably 20°C or higher, more preferably 50°C or higher, even more preferably 80°C or higher, and particularly preferably 100°C or higher. The adhesive strength of the pressure-sensitive adhesive sheet tends to be improved by using a low Tg base polymer into which a crosslinked structure has been introduced and a high Tg acrylic oligomer in combination. There is no particular upper limit to the glass transition temperature of the acrylic oligomer, but it is generally 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

Among the exemplified alkyl (meth)acrylates, methyl methacrylate is preferred as the chain alkyl (meth)acrylate because it has a high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. In other words, the acrylic oligomer preferably contains, as the constituent monomer components, one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

The amount of alicyclic alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight. The amount of chain alkyl (meth)acrylate relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight.

The weight average molecular weight of the acrylic oligomer is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, and even more preferably 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, the adhesive strength and adhesive retention of the pressure-sensitive adhesive sheet tend to be improved.

Acrylic oligomers can be obtained by polymerizing the above monomer components using various polymerization methods. Various polymerization initiators may be used when polymerizing the acrylic oligomers. Chain transfer agents may also be used to adjust the molecular weight.

When an oligomer component such as an acrylic oligomer is included in the pressure-sensitive adhesive composition, the content is preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the above-mentioned base polymer. When the content of the oligomer in the pressure-sensitive adhesive composition is within the above range, improved adhesion can be expected.

(Silane coupling agent)
A silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting adhesive strength, etc. When a silane coupling agent is added to the pressure-sensitive adhesive composition, the amount added is usually about 0.01 to 5.0 parts by weight, and preferably about 0.03 to 2.0 parts by weight, per 100 parts by weight of the base polymer.

(Antioxidants)
The pressure-sensitive adhesive composition may contain an antioxidant. By containing an antioxidant, it is possible to suppress the reaction or deterioration of the curable component caused by heat or light in the storage environment or use environment of the pressure-sensitive adhesive composition or the pressure-sensitive adhesive sheet. Examples of the antioxidant include amine-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and phenol-based antioxidants. Among them, those that act as radical chain inhibitors such as amine-based antioxidants and phenol-based antioxidants are preferred, and phenol-based antioxidants having a hindered phenol structure are particularly preferred.

An antioxidant with a hindered phenol structure has a group with large steric hindrance, such as a tert-butyl group, bonded to at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring to which the OH group of phenol is bonded. Examples of antioxidants with a hindered phenol structure include dibutylhydroxytoluene (BHT), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (BASF's "Irganox 1010"), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (BASF's "Irganox 1076"), 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol (BASF's "Irganox 1330"), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (BASF "Irganox 3114"), tris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate (BASF "Irganox 3125"), pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (ADEKA "ADEKA STAB" AO-60"), 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane (ADEKA "ADEKA STAB AO-80"), 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate (Sumitomo Chemical "Sumilizer GS"), 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate (Sumitomo Chemical "Sumilizer GM"), 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diyl=bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoate] (Sumitomo Chemical's "Sumilizer GA-80"), 1,3,5-tris(3-hydroxy-4-tert-butyl-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (Cyanox 1790 manufactured by Cytec), etc.

When the adhesive composition contains an antioxidant, the content of the antioxidant is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, even more preferably 0.1 parts by weight or more, and may be 0.3 parts by weight or more or 0.5 parts by weight or more, relative to 100 parts by weight of the acrylic base polymer, from the viewpoint of suppressing undesired curing reactions and deterioration. On the other hand, if the content of the antioxidant is excessively high, it may cause curing inhibition when the adhesive sheet is photocured. Therefore, the content of the antioxidant is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably 3 parts by weight or less, relative to 100 parts by weight of the acrylic base polymer.

(Other Additives)
In addition to the above-exemplified components, the pressure-sensitive adhesive composition may contain additives such as a chain transfer agent, a tackifier, a plasticizer, a softener, an antidegradant, a filler, a colorant, a surfactant, and an antistatic agent.

[Formation of Adhesive Sheet]
The adhesive composition is applied onto a substrate, and the solvent is dried and removed as necessary to form an adhesive sheet on the substrate. Any suitable substrate is used for forming the adhesive sheet. The substrate may be a release film having a release layer on the surface of a resin film.

Examples of resin materials for the release film include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the release film is preferably 10 to 200 μm, and more preferably 25 to 150 μm. Examples of materials for the release layer include silicone-based release agents, fluorine-based release agents, long-chain alkyl release agents, and fatty acid amide-based release agents. The thickness of the release layer is generally about 10 to 2000 nm.

Methods for applying the adhesive composition onto a substrate include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

When the adhesive composition contains a solvent, it is preferable to dry the solvent after applying the adhesive composition to the substrate. As the drying method, an appropriate method can be adopted depending on the purpose. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. As the drying time, an appropriate time can be adopted. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

After the solvent has dried, it is preferable to attach a cover sheet to protect the surface of the adhesive sheet. As the cover sheet, it is preferable to use a release film that has a release layer on the surface that comes into contact with the adhesive sheet, similar to the base film.

After the adhesive composition is applied onto the substrate, it is heated as necessary to introduce a crosslinked structure into the base polymer. The heating temperature and heating time can be set appropriately depending on the type of crosslinking agent used, and are usually in the range of 20°C to 160°C and about 1 minute to 7 days. The heating for drying the solvent may also serve as the heating for crosslinking. As mentioned above, the introduction of a crosslinked structure does not necessarily have to be accompanied by heating.

A crosslinking catalyst may be used to promote the formation of a crosslinked structure. For example, crosslinking catalysts for isocyanate-based crosslinking agents include metal-based crosslinking catalysts (especially tin-based crosslinking catalysts) such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, dioctyltin dilaurate, and dibutyltin dilaurate.

By laminating a release film onto the surface of the adhesive sheet, an adhesive sheet with release films temporarily attached to both sides is obtained. The substrate or cover sheet used when forming the adhesive sheet may also be used as the release film.

When release films are provided on both sides of the adhesive sheet, the thickness of one release film and the thickness of the other release film may be the same or different. The peeling force when peeling the release film temporarily attached to one side from the adhesive sheet and the peeling force when peeling the release film temporarily attached to the other side from the adhesive sheet may be the same or different.

The thickness of the adhesive sheet 21 used to bond the polarizer 11 and the cover window 70 is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more. Increasing the thickness of the adhesive sheet 21 tends to increase impact resistance. In addition, if the cover window 70 has a printing step due to decorative printing, the adhesive sheet 21 can be made to have step absorption properties. There is no particular upper limit on the thickness of the adhesive sheet 21, but from the viewpoint of the productivity of the adhesive sheet, etc., it is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 250 μm or less.

The total light transmittance of the adhesive sheet 21 is preferably 85% or more, and more preferably 90% or more. The haze of the adhesive sheet is preferably 1.5% or less, and more preferably 1% or less.

The optical transmittance of the adhesive sheet 21 at a wavelength of 380 nm is preferably 5% or less, more preferably 4% or less, and may be 3% or less. By increasing the ultraviolet shielding property of the adhesive sheet 21, the weather resistance is improved and photodegradation such as yellowing of the polarizer 11 caused by ultraviolet light incident from the outside can be suppressed. As described above, by including an ultraviolet absorber in the adhesive composition, it is possible to impart ultraviolet absorption properties to the adhesive sheet 21 while maintaining the transparency of visible light.

[Polarizing plate]
<Polarizer>
The polarizing plate 10 includes a polarizer 11. The polarizer 11 is, for example, a polyvinyl alcohol-based film containing iodine. As a material for the polyvinyl alcohol-based film applied to the polarizer, polyvinyl alcohol or a derivative thereof is used. Examples of polyvinyl alcohol derivatives include polyvinyl formal, polyvinyl acetal, etc., as well as derivatives modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, their alkyl esters, acrylamide, etc. Polyvinyl alcohols having a degree of polymerization of about 1000 to 10000 and a degree of saponification of about 80 to 100 mol % are generally used.

A polarizer is obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching treatment. The thickness of the polarizer is preferably about 1 to 50 μm. A thin polarizer having a thickness of 10 μm or less can also be used as the polarizer. Examples of thin polarizers include polarizers described in JP-A-51-069644, JP-A-2000-338329, WO2010/100917, Japanese Patent No. 4691205, Japanese Patent No. 4751481, etc. Such a thin polarizer can be obtained, for example, by a manufacturing method including a step of stretching a polyvinyl alcohol-based resin layer and a resin substrate for stretching in a laminated state, and a step of dyeing with iodine.

<Optical Layer>
No optical layer is provided on the first main surface (the surface on the viewing side) of the polarizer 11, and as described above, the adhesive sheet 21 is provided in contact with the polarizer 11. The polarizing plate 10 may be composed of only the polarizer 11, or an appropriate optical layer 15 may be disposed on the second main surface (the surface on the image display cell 60 side) of the polarizer 11.

The optical layer 15 may be a transparent protective film for protecting the polarizer 11, or may have the functions of an optical compensation layer for the purpose of widening the viewing angle, or a quarter-wave plate for forming a circular polarizing plate together with the polarizer 11. The optical layer 15 may have both the function of a transparent protective film and the function of a retardation plate.

Examples of materials constituting the optical layer 15 include resin materials that are excellent in transparency, mechanical strength, and thermal stability. Specific examples of such resin materials include cellulose-based resins such as triacetyl cellulose, polyester-based resins, polyethersulfone-based resins, polysulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, cyclic polyolefin-based resins (norbornene-based resins), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof. The optical layer 15 may be a liquid crystal material. For example, a liquid crystal layer in which liquid crystal molecules are oriented in a predetermined direction may be used as the optical layer 15.

The optical layer 15 may be in direct contact with the second main surface of the polarizer 11, or may be attached via an appropriate adhesive layer. The optical layer 15 may be a laminate of two or more layers. For example, the optical layer 15 may be a laminate of two or more films, a laminate in which a liquid crystal layer is provided on a film substrate, or a laminate in which two or more liquid crystal layers are laminated. The optical layer 15 may include an alignment film for aligning liquid crystal molecules in a predetermined direction.

[Polarizing plate with adhesive]
The adhesive sheet 21 may be provided as an adhesive-attached polarizing plate 81 integrally laminated with the polarizing plate 10, as shown in Fig. 2. In the adhesive-attached polarizing plate, the adhesive sheet 21 is disposed in contact with a first main surface of the polarizer 11. In Fig. 2, an optical layer 15 is provided on the second main surface of the polarizer 11, but as described above, the polarizing plate 10 does not need to have an optical layer on the second main surface of the polarizer.

There is no particular limitation on the method for attaching the adhesive sheet 21 to the first main surface of the polarizer 11. The adhesive sheet 21 may be prepared in advance on a substrate and attached to the polarizer 11, or the adhesive sheet 21 may be formed using the polarizer 11 as a substrate.

In the polarizing plate 81 with adhesive, it is preferable that a release film 41 is removably attached onto the adhesive sheet 21. The release film has the function of protecting the exposed surface of the adhesive sheet 21 until the adhesive sheet 21 is bonded to the cover window 70. The base material used when forming (applying) the adhesive sheet may be used as it is as the release film 41 on the adhesive sheet 21.

As shown in FIG. 3, the polarizing plate with adhesive may be a double-sided polarizing plate with adhesive, which has an adhesive sheet 21 in contact with the polarizer 11 on the viewing side surface of the polarizing plate 10, and another adhesive sheet 22 on the other side of the polarizing plate. It is preferable that a release film 42 is removably attached to the adhesive sheet 22.

In the adhesive polarizing plate 81 shown in FIG. 3, the polarizing plate 10 has an optical layer 15 on the second main surface of the polarizer 11, and an adhesive sheet 22 is disposed on the optical layer 15. The adhesive sheet 22 may be laminated on the second main surface of the polarizer 11 in contact with the polarizer 11 without any other layer interposed therebetween.

In this way, by using a double-sided adhesive polarizing plate in which an adhesive layer has already been applied to both sides of the polarizing plate 10, the process of attaching a separate adhesive sheet to the polarizing plate after bonding the polarizing plate to the surface of the image display cell can be omitted, simplifying the manufacturing process of the image display device.

The adhesive sheet 22 is used to bond the polarizing plate 10 and the image display cell 60. The thickness of the adhesive sheet 22 is preferably 3 μm to 30 μm, more preferably 5 μm to 27 μm, and even more preferably 10 μm to 25 μm. As the adhesive sheet 22, various adhesives used to bond the polarizing plate and the image display cell can be used. As the adhesive constituting the adhesive sheet 22, an acrylic adhesive is preferably used.

When the adhesive-attached polarizing plate in which the adhesive sheet 21 is disposed in contact with one side of the polarizer 11 is subjected to a _moist heat test in which the plate is left for 100 hours in an environment at a temperature of 85° C. and a relative humidity of 85%, it is preferable that all of ΔT ₁ , ΔT ₂ , ΔT 3 and ΔT ₄ satisfy 1.00 to 1.20. ΔT ₁ , ΔT ₂ , ΔT ₃ and ΔT ₄ are as defined above. ΔT _n of the adhesive-attached polarizing plate is preferably 1.15 or less, more preferably 1.10 or less, particularly preferably 1.05 or less, and may be 1.04 or less, for each of n=1 to 4. The closer ΔT _n is to 1.00, the less the polarizer fades and the more excellent the moist heat resistance is.

When the adhesive-attached polarizing plate in which the adhesive sheet 21 is disposed in contact with one side of the polarizer 11 is subjected to a _moist heat test in which the plate is left for 100 hours in an environment at a temperature of 85° C. and a relative humidity of 85%, it is preferable that all of δT ₁ , δT ₂ , δT 3 and δT ₄ satisfy 0.95 to 1.05. δT ₁ , δT ₂ , δT ₃ and δT ₄ are as defined above. δT _n of the adhesive-attached polarizing plate is more preferably 0.97 to 1.03, further preferably 0.98 to 1.02, and particularly preferably 0.99 to 1.01 for each of n=1 to 4. The closer δT _n is to 1.00, the smaller the color change of the transmitted light is.

It is preferable that the adhesive-attached polarizing plate in which the adhesive sheet 21 is arranged in contact with one surface of the polarizer 11 has ΔT _n within the above range and δT _n within the above range.

[Image display device]
1, the image display device 100 includes a cover window 70 attached to the viewing side of a polarizing plate 10 via an adhesive sheet 21. An image display cell 60 such as a liquid crystal cell or an organic EL cell is attached to the other surface of the polarizing plate 10 via an adhesive sheet 22. The image display cell 60 may be foldable.

A transparent plate having appropriate mechanical strength and thickness is used as the cover window 70. Such a transparent plate may be, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate. If the image display cell 60 is foldable, the cover window 70 may also be foldable. The cover window may be made of multiple transparent films laminated together with an adhesive or bonding agent, and may include a touch panel sensor. As the touch panel sensor, any type of touch panel may be used, such as a resistive film type, a capacitive type, an optical type, or an ultrasonic type.

The order of bonding the polarizing plate 10 and the cover window 70 with the adhesive sheet 21 and bonding the adhesive sheet 22 and the image display cell 60 is not particularly limited. As described above, an adhesive-backed polarizing plate in which an adhesive sheet is previously attached to the surface of the polarizing plate may be used.

After bonding the polarizing plate 10 and the cover window 70 with the adhesive sheet 21 interposed therebetween, degassing may be performed to remove air bubbles at the bonding interface and near the printing step. As a degassing method, any suitable method such as heating, pressurization, or decompression may be used. For example, bonding may be performed under reduced pressure and heating while suppressing the inclusion of air bubbles, and then heating and pressurization may be performed simultaneously by autoclaving or the like in order to suppress delay bubbles, etc.

When the adhesive sheet 21 is made of a photocurable adhesive composition, the adhesive composition is photocured after the polarizing plate 10 and the cover window 70 are attached to each other. The polymerization reaction of the photopolymerizable multifunctional compound proceeds by the light irradiation, and the adhesive reliability of the adhesive sheet is improved accordingly.

The amount of light irradiated during photocuring is not particularly limited as long as it is within a range that allows the adhesive sheet to be photocured, and is, for example, about 50 to 10,000 mJ/ ^cm2 in accumulated light. The adhesive sheet 21 may be irradiated with light from either the polarizing plate 10 side or the cover window 60 side, but from the viewpoint of preventing deterioration of the polarizer 11 due to ultraviolet light, it is preferable to irradiate the ultraviolet light from the cover window 10 side. If the adhesive sheet 21 has ultraviolet shielding properties, even when ultraviolet light is irradiated to photocur the adhesive sheet 21, most of the ultraviolet light is absorbed by the adhesive sheet 21, and the amount of ultraviolet light irradiated to the polarizer can be reduced.

In the image display device 100, the adhesive composition used to form the adhesive sheet 21 arranged in contact with the viewing side of the polarizer 11 has the properties described above. Therefore, an image display device equipped with the adhesive sheet 21 has excellent durability with little deterioration such as fading or yellowing of the polarizer even when exposed to a high-temperature and high-humidity environment or to external light for a long period of time.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Examples 1 to 3 and Comparative Examples 1 and 2]
<Polymerization of Base Polymer>
In a reaction vessel equipped with a thermometer, a stirrer, a cooler, and a nitrogen gas inlet tube, monomer components (total 100 parts by weight) in the ratio shown in Table 1 and azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were charged together with 233 parts by weight of ethyl acetate, and the mixture was stirred for 1 hour in a nitrogen atmosphere at 23° C., followed by nitrogen substitution. Thereafter, the mixture was reacted at 56° C. for 5 hours, and then at 70° C. for 3 hours to prepare an acrylic base polymer solution.

In Table 1, the monomers are described by the following abbreviations.
BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate 4HBA: 4-hydroxybutyl acrylate

<Preparation of Pressure-Sensitive Adhesive Composition>
The following components were added to the acrylic base polymer solution obtained above in the amounts shown in Table 1 per 100 parts by weight of the base polymer, and then mixed uniformly to prepare a pressure-sensitive adhesive composition.
Isocyanate-based crosslinking agent: xylylene diisocyanate trimethylolpropane adduct ("Takenate D110N" manufactured by Mitsui Chemicals)
Ultraviolet absorber: 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-triazine-2,4-diyl]diphenol ("Tinosorb S" manufactured by BASF)

<Preparation of adhesive sheet>
The above photocurable adhesive composition was applied onto a release film (a polyethylene terephthalate film with a silicone-based release layer on one side), heated at 100° C. for 3 minutes to remove the solvent, and then another release film was attached to the surface. This laminate was aged in an atmosphere of 25° C. for 3 days to promote crosslinking, and an adhesive sheet with release films temporarily attached to both sides was obtained.

[Preparation of Adhesive Sheet A]
In a reaction vessel equipped with a thermometer, a stirrer, a cooler and a nitrogen gas inlet tube, 97 parts by weight of butyl acrylate and 3 parts by weight of acrylic acid as monomer components, and 0.2 parts by weight of AIBN as a thermal polymerization initiator were added together with 233 parts by weight of ethyl acetate, and the mixture was stirred for 1 hour under a nitrogen atmosphere at 23°C, and nitrogen substitution was performed. Then, the mixture was reacted at 60°C for 5 hours to obtain a solution of an acrylic base polymer having a weight average molecular weight (Mw) of 1.1 million. To this base polymer solution, 0.8 parts by weight of trimethylolpropane tolylene diisocyanate ("Coronate L" manufactured by Nippon Polyurethane Industry Co., Ltd.) as an isocyanate crosslinking agent and 0.1 parts by weight of a silane coupling agent ("KBM403" manufactured by Shin-Etsu Chemical Co., Ltd.) were added, and then the mixture was mixed uniformly to prepare a pressure-sensitive adhesive composition solution.

The above adhesive composition was applied onto a release film so that the thickness after drying would be 20 μm, and after drying at 100°C for 3 minutes to remove the solvent, another release film was attached to the surface. This laminate was aged in an atmosphere at 50°C for 2 days to promote crosslinking, and adhesive sheet A with release films temporarily attached to both sides was obtained.

[evaluation]
A polarizer made of a 25 μm-thick stretched polyvinyl alcohol film impregnated with iodine was attached to a first non-alkali glass plate via an adhesive sheet A. A second non-alkali glass plate was attached thereon via the adhesive sheets of the examples and comparative examples to prepare evaluation samples.

(Weather resistance test)
A weather fade test was carried out by irradiating the ^second non-alkali glass plate with light from a carbon arc lamp for 100 hours under conditions of a temperature of 40°C, a relative humidity of 20%, and a radiation intensity (300-700 nm integrated illuminance) of 500±50 W/m2 using an ultraviolet fade meter (U48AU manufactured by Suga Test Instruments). The difference Δb ^* = b ^* ₁ - b ^* between the b ^* ₀ of the transmitted light of the sample before the test and the b ^* ₁ of the transmitted light of the sample after the test was calculated. Note that b ^* is the chromaticness index b ^* of the CIE 1976 color space, and was measured by placing the sample on a backlight.

(Damp heat test)
The transmittance spectrum of the evaluation sample was measured by a visible-ultraviolet spectrophotometer, and the initial transmittances t ₀ , t ₁ , t ₂ , t ₃ and t ₄ at wavelengths of 380 nm, 450 nm, 520 nm, 580 nm and 660 nm were read. The evaluation sample was held in a thermohygrostat at a temperature of 85° C. and a relative humidity of 85% for 100 hours to perform a moist heat test. The transmittance spectrum of the sample before and after the moist heat test was measured, and the transmittances t ₀ ', t ₁ ', t ₂ ', t ₃ ' and t ₄ ' at wavelengths of 380 nm, 450 nm, 520 nm, 580 nm and 660 nm were read.

From the measured transmittance value t, the 100 μm equivalent transmittance T was calculated based on the following formula in accordance with Lambert's law, converting the total thickness L = 125 μm of the polarizer (25 μm) and the adhesive sheet (100 μm) into the transmittance at a thickness of 100 μm.
log ₁₀ (T/100) = (100/L) x log ₁₀ (t/100)

_T0 : 100 μm-equivalent transmittance at a wavelength of 380 nm before moist heat test _T1 : 100 μm-equivalent transmittance at a wavelength of 450 nm before moist heat test _T2 : 100 μm-equivalent transmittance at a wavelength of 520 nm before moist heat test _T3 : 100 μm-equivalent transmittance at a wavelength of 580 nm before moist heat test _T4 : 100 μm-equivalent transmittance at a wavelength of 660 nm before moist heat test _T0 ': 100 μm-equivalent transmittance at a wavelength of 380 nm after moist heat test _T1 ': 100 μm-equivalent transmittance at a wavelength of 450 nm after moist heat test _T2 ': 100 μm-equivalent transmittance at a wavelength of 520 nm after moist heat test _T3 ': 100 μm-equivalent transmittance at a wavelength of 580 nm after moist heat test _T4 ' : 100 μm-equivalent transmittance at a wavelength of 660 nm after wet heat test

The following ΔT _n and δT _n (n=1 to 4) were calculated from the 100 μm equivalent transmittances T ₀ to T ₄ before the moist heat test and the 100 μm equivalent transmittances T ₀ ' to T ₄ ' after the moist heat test.
ΔTn=( _Tn' - _T0 ')/( _Tn - _T0 )
δTn=(T _n '/ΣT _i ')/(T _n /ΣT _i ) where i=1 to 4

The adhesive composition of each adhesive sheet and the evaluation results are shown in Table 1. The numerical values for the adhesive composition in Table 1 are the blending amounts (parts by weight). Note that for Comparative Example 2, the weather resistance test showed that Δb ^* exceeded 5%, indicating poor weather resistance, and therefore the moist heat test was not performed.

As shown in Table 1, the pressure-sensitive adhesive sheets of Examples 1 to 3 had small Δb ^* and good weather resistance, and ΔT _n and δT _n were close to 1.00 for all n = 1 to 4, the polarizer fading was small, and the sheets had excellent moist heat resistance.

REFERENCE SIGNS LIST 10 Polarizing plate 11 Polarizer 15 Optical layer 21, 22 Adhesive sheets 81, 82 Polarizing plate with adhesive 60 Image display cell 70 Cover window 100 Image display device

Claims (8)

A polarizing plate with a pressure-sensitive adhesive comprising: a polarizer having a first main surface and a second main surface; and a first pressure-sensitive adhesive sheet arranged in contact with the first main surface of the polarizer,
the first adhesive sheet is used for bonding to a cover window of an image display device,
the first pressure-sensitive adhesive sheet is made of a pressure-sensitive adhesive composition including an acrylic base polymer and 0.05 to 10 parts by weight of an ultraviolet absorber relative to 100 parts by weight of the acrylic base polymer;
The acrylic base polymer contains a nitrogen-containing monomer, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer in a total amount of 8 parts by weight or less relative to 100 parts by weight of the total of the monomer components,
A polarizing plate with a pressure-sensitive adhesive, in which all of ΔT ₁ , ΔT ₂ , ΔT ₃ and ΔT ₄ represented by the following formulae satisfy 1.0 to 1.2 when subjected to a moist heat test in which the plate is left in an environment of a temperature of 85° C. and a relative humidity of 85% for 100 hours:
ΔT _n = (T _n '-T ₀ ')/(T _n - T ₀ )
n is an integer from 1 to 4,
_T0 is the 100 μm equivalent transmittance at a wavelength of 380 nm before the wet heat test,
_T1 is the 100 μm equivalent transmittance at a wavelength of 450 nm before the wet heat test,
_T2 is the 100 μm equivalent transmittance at a wavelength of 520 nm before the wet heat test,
_T3 is the 100 μm equivalent transmittance at a wavelength of 580 nm before the wet heat test,
_T4 is the 100 μm equivalent transmittance at a wavelength of 660 nm before the wet heat test,
T ₀ ' is the 100 μm equivalent transmittance at a wavelength of 380 nm after the wet heat test,
T ₁ ' is the 100 μm equivalent transmittance at a wavelength of 450 nm after the wet heat test;
_T2 ' is the 100 μm equivalent transmittance at a wavelength of 520 nm after the wet heat test,
T ₃ ' is the 100 μm equivalent transmittance at a wavelength of 580 nm after the wet heat test,
T ₄ ' is the 100 μm equivalent transmittance at a wavelength of 660 nm after the wet heat test,
The 100 μm converted transmittance T (%), the total thickness L (μm) of the pressure-sensitive adhesive sheet and the polarizer, and the measured transmittance t (%) are
log ₁₀ (T/100) = (100/L) x log ₁₀ (t/100)
Satisfy the relationship. A polarizing plate with a pressure-sensitive adhesive comprising: a polarizer having a first main surface and a second main surface; and a first pressure-sensitive adhesive sheet arranged in contact with the first main surface of the polarizer,
the first adhesive sheet is used for bonding to a cover window of an image display device,
the first pressure-sensitive adhesive sheet is made of a pressure-sensitive adhesive composition including an acrylic base polymer and 0.05 to 10 parts by weight of an ultraviolet absorber relative to 100 parts by weight of the acrylic base polymer;
The acrylic base polymer contains a nitrogen-containing monomer, a hydroxyl group-containing monomer, and a carboxyl group-containing monomer in a total amount of 8 parts by weight or less relative to 100 parts by weight of the total of the monomer components,
A pressure-sensitive adhesive composition, in which all of δT ₁ , δT ₂ , δT ₃ and δT ₄ represented by the following formula are 0.95 to 1.05 when the composition is left for 100 hours in an environment having a temperature of 85° C. and a relative humidity of 85%:
δT _n =(T _n '/ΣT _i ')/(T _n /ΣT _i )
n and i are integers from 1 to 4;
_T0 is the 100 μm equivalent transmittance at a wavelength of 380 nm before the wet heat test,
_T1 is the 100 μm equivalent transmittance at a wavelength of 450 nm before the wet heat test,
_T2 is the 100 μm equivalent transmittance at a wavelength of 520 nm before the wet heat test,
_T3 is the 100 μm equivalent transmittance at a wavelength of 580 nm before the wet heat test,
_T4 is the 100 μm equivalent transmittance at a wavelength of 660 nm before the wet heat test,
T ₀ ' is the 100 μm equivalent transmittance at a wavelength of 380 nm after the wet heat test,
T ₁ ' is the 100 μm equivalent transmittance at a wavelength of 450 nm after the wet heat test;
_T2 ' is the 100 μm equivalent transmittance at a wavelength of 520 nm after the wet heat test,
T ₃ ' is the 100 μm equivalent transmittance at a wavelength of 580 nm after the wet heat test,
T ₄ ' is the 100 μm equivalent transmittance at a wavelength of 660 nm after the wet heat test,
The 100 μm converted transmittance T (%), the total thickness L (μm) of the pressure-sensitive adhesive sheet and the polarizer, and the measured transmittance t (%) are
log ₁₀ (T/100) = (100/L) x log ₁₀ (t/100)
Satisfy the relationship. 3. The polarizing plate with a pressure-sensitive adhesive according to claim 1, wherein the acrylic base polymer contains 0.1 parts by weight or more of a hydroxyl group-containing monomer relative to 100 parts by weight of the total of monomer components. The polarizing plate with the pressure-sensitive adhesive according to claim 3 , wherein the acrylic base polymer has a crosslinked structure formed by an isocyanate crosslinking agent. The polarizing plate with adhesive according to any one of claims 1 to 4 , further comprising a second adhesive sheet on a second main surface side of the polarizer. The polarizing plate with adhesive according to claim 5 , wherein the second adhesive sheet is laminated in contact with a second main surface of the polarizer. The polarizing plate with adhesive according to claim 5 , wherein the second adhesive sheet is laminated on a second main surface of the polarizer via another layer. An image display device comprising a second adhesive sheet, the adhesive-attached polarizing plate according to any one of claims 1 to 7 , and a cover window, in this order, on a surface of an image display cell,
The image display device, wherein the first adhesive sheet of the adhesive-attached polarizing plate is attached to the cover window .

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