TWI889876B - Adhesive composition, adhesive sheet, polarizing plate with adhesive, and image display device - Google Patents

Abstract

The adhesive composition of the present invention is used to make an adhesive sheet, which is used to bond a polarizing element to a cover window and is positioned in contact with the polarizing element. When samples containing the adhesive sheet in contact with the polarizing element were subjected to a 100-hour humidity test at 85°C and 85% relative humidity, the change in transmittance before and after the test remained within a specified range.

Description

Adhesive composition, adhesive sheet, polarizing plate with adhesive, and image display device

The present invention relates to an adhesive sheet and an adhesive composition for forming an adhesive sheet for forming an image display device. Furthermore, the present invention relates to a polarizing plate with an adhesive and an image display device.

Liquid crystal displays (LCDs) or organic EL (electroluminescence) displays are widely used in various image display devices, including mobile phones, smartphones, car navigation systems, personal computer monitors, and televisions. Based on their display principle, LCDs employ polarizers on the viewing surface of the liquid crystal cell. In self-luminous displays, such as organic EL, circularly polarizing plates (a laminate of a polarizer and a quarter-wavelength plate) are placed on the viewing surface of the cell to prevent external light from being reflected by the metal electrode (cathode) and thus appearing as a mirror.

To prevent damage to the image display panel caused by external impact, a transparent front panel (also known as a "cover window"), such as a transparent resin sheet or glass sheet, is installed on the viewing side of the image display device. The cover window is bonded to the polarizing plate on the viewing side of the image display panel via an adhesive sheet.

Polarizing plates typically consist of a laminated structure with transparent protective films laminated to both sides of a polarizing element. However, to achieve thinner and more flexible image display devices, there are proposals for structures that omit the transparent protective films on one or both sides of the polarizing element. For example, Patent Document 1 discloses a structure in which a cover window is laminated via an adhesive sheet positioned in contact with the polarizing element. [Prior Art Document] [Patent Document]

[Patent Document 1] International Publication No. 2017/216886

[Identify the problem you want to solve]

An image display device having a cover window attached by an adhesive sheet arranged in contact with the viewing side surface of a polarizing element is used in various environments and is required to have high durability even under humid conditions. In view of the above problem, the object of the present invention is to provide an adhesive sheet arranged adjacent to a polarizing element, and an adhesive composition used to form the adhesive sheet. [Technical means to solve the problem]

One embodiment of the present invention is an adhesive composition used to form an adhesive sheet. The adhesive sheet is used to bond a polarizing element to a cover window of an image display device, and is arranged in contact with the polarizing element. When a sample with the adhesive sheet in contact with the polarizing element was subjected to a heat and humidity test at 85°C and 85% relative humidity for 100 hours, preferably, ΔT ₁ , ΔT ₂ , ΔT ₃ , and ΔT ₄ all met 1.0 to 1.2, and more preferably, δT ₁ , δT ₂ , δT ₃ , and δT ₄ all met 0.95 to 1.05.

_ΔTn = ( _Tn ' - _T0 ') / ( _Tn - _T0 ) _δTn = ( _Tn ' / _ΣTi ') / ( _Tn / _ΣTi ) In the above formulas, n and i are integers from 1 to 4.

_T0 is the transmittance at a wavelength of 380 nm at 100 μm before the humidity and heat test; _T1 is the transmittance at a wavelength of 450 nm at 100 μm before the humidity and heat test; _T2 is the transmittance at a wavelength of 520 nm at 100 μm before the humidity and heat test; _T3 is the transmittance at a wavelength of 580 nm at 100 μm before the humidity and heat test; and _T4 is the transmittance at a wavelength of 660 nm at 100 μm before the humidity and heat test. T ₀ ' is the transmittance at a wavelength of 380 nm at 100 μm after the humidity and heat test; T ₁ ' is the transmittance at a wavelength of 450 nm at 100 μm after the humidity and heat test; T ₂ ' is the transmittance at a wavelength of 520 nm at 100 μm after the humidity and heat test; T ₃ ' is the transmittance at a wavelength of 580 nm at 100 μm after the humidity and heat test; and T ₄ ' is the transmittance at a wavelength of 660 nm at 100 μm after the humidity and heat test.

The 100 μm-equivalent transmittance T (%), the combined thickness L (μm) of the adhesive sheet and the polarizer, and the measured transmittance t (%) satisfy the relationship log ₁₀ (T/100) = (100/L) × log ₁₀ (t/100).

The adhesive composition preferably contains a UV absorber.

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

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

One embodiment of the present invention is an image display device, which has a second adhesive sheet, a polarizing element including a polyvinyl alcohol film containing iodine, a first adhesive sheet, and a cover window in sequence on the surface of the image display unit, and the first adhesive sheet is the above-mentioned adhesive sheet, which is arranged in contact with the polarizing element. [Effects of the Invention]

An image display device in which the adhesive sheet of the embodiment of the present invention is arranged in contact with the viewing side surface of the polarizing element has durability against ultraviolet rays from the outside and can also exhibit high durability in a humid environment.

One embodiment of the present invention is an adhesive sheet disposed in contact with the viewing surface of a polarizing element in an image display device and an adhesive composition used to form the adhesive sheet. The adhesive sheet is used to bond the polarizing element to a cover window.

Figure 1 is a cross-sectional view of an image display device having a cover window on its viewing side. Image display device 100 includes a polarizing plate 10 attached to the surface of an image display unit 60 via an adhesive sheet 22, and a cover window 70 attached to polarizing plate 10 via an adhesive sheet 21 according to an embodiment of the present invention.

The polarizing plate 10 includes a polarizing element 11 comprising a polyvinyl alcohol film containing iodine. An appropriate optical layer 15 may be provided on the second principal surface of the polarizing element 11 (the surface facing the image display unit 60). An adhesive sheet 21 according to an embodiment of the present invention is disposed on the first principal surface of the polarizing element 11 (the surface facing the viewing side) in contact with the polarizing element 11. By disposing the adhesive sheet 21 on the viewing side of the polarizing element 11 without intervening optical layers, the image display device can be made thinner or more flexible.

[Moisture and heat resistance of adhesive sheet (transmittance change)] The adhesive sheet 21 of the embodiment of the present invention is used to bond the polarizing element 11 to the cover window 70 of the image display device, and is arranged in contact with the polarizing element 11. The adhesive sheet 21 is formed using the adhesive composition described below.

The adhesive sheet 21 of the embodiment of the present invention is characterized in that when a sample with the adhesive sheet in contact with a polarizing element is subjected to a heat and humidity test at a temperature of 85°C and a relative humidity of 85% for 100 hours, the transmittance changes little over a wide range of visible light.

Transmittance variation is evaluated based on the 100 μm-equivalent transmittance, which converts the measured transmittance t(%) of the laminate of the polarizer and adhesive sheet into the transmittance at a thickness of 100 μm. When the combined thickness of the adhesive sheet and polarizer is L(μm) and the measured transmittance is t(%), Lambert's law states that the 100 μm-equivalent transmittance T(%) satisfies the following relationship with t(%) and L(μm): log ₁₀ (T/100) = (100/L) × log ₁₀ (t/100)

Transmittance changes are evaluated using the 100 μm-equivalent transmittance (T _{0 )} at a wavelength of 380 nm, the 100 μm-equivalent transmittance (T _{1 )} at a wavelength of 450 nm, the 100 μm-equivalent transmittance (T _{2 )} at a wavelength of 520 nm, the 100 μm-equivalent transmittance (T ₃ ) at a wavelength of 580 nm, and the 100 μm-equivalent transmittance (T _{4 )} at a wavelength of 660 nm. The wavelength of 380 nm is in the ultraviolet region, the wavelength of 450 nm is equivalent to blue light, the wavelength of 520 nm is equivalent to green light, the wavelength of 580 nm is equivalent to yellow light, and the wavelength of 660 nm is equivalent to red light.

The laminate of the polarizing element and adhesive sheet was subjected to a heat and humidity test at 85°C and 85% relative humidity for 100 hours. The transmittance at wavelengths of 380 nm, 450 nm, 520 nm, 580 nm, and 660 nm at 100 μm was measured as T ₀ ', T ₁ ', T ₂ ', T ₃ ', and T ₄ ', respectively.

The change in transmittance before and after the humidity and heat test is primarily due to discoloration of the polarizer. In iodine-containing polyvinyl alcohol (PVA) polarizers, the polyvinyl alcohol polymer chains form complexes with polyiodine ions (I ₃ ^- and I ₅ ^- ). By aligning the polymer chains in a specific direction, the polyiodine ions align, exerting polarization properties. Exposure to high temperature and high humidity can cause discoloration of the polarizer due to structural changes in the polyiodine ions (e.g., from I ₅ ^- to I ₃ ^- ), disrupted orientation of the polyiodine ions, and iodine release (e.g., sublimation of I ₂ ). If the adhesive sheet placed in contact with the polarizing element has UV absorption properties, the transmittance change in the ultraviolet region due to discoloration of the polarizing element is minimal. Therefore, the 100 μm-equivalent transmittance T ₀ of the sample at a wavelength of 380 nm before the humidity and heat test and the 100 μm-equivalent transmittance T ₀ ' of the sample after the humidity and heat test can serve as the benchmark for evaluating changes in visible light transmittance.

The transmittance variation of visible light can be evaluated based on the metric _ΔTn = ( _Tn ' - _T0 ') / ( _Tn - _T0 ). n is an integer between 1 and 4. When n = 1, the transmittance variation is evaluated at a wavelength of 450 nm. When n = 2, the transmittance variation is evaluated at a wavelength of 520 nm. When n = 3, the transmittance variation is evaluated at a wavelength of 580 nm. When n = 4, the transmittance variation is evaluated at a wavelength of 660 nm.

For example, the change in transmittance at a wavelength of 450 nm (when n = 1) can be evaluated using the indicator ΔT ₁ = (T ₁ '-T ₀ ') / (T ₁ -T ₀ ). (T ₁ -T ₀ ) is the difference in transmittance at 450 nm and 380 nm at 100 μm before the humidity and heat test, while (T ₁ '-T ₀ ') is the difference in transmittance at 450 nm and 380 nm after the humidity and heat test. If this ratio, ΔT ₁ , is 1, it means that the transmittance difference between 450 nm and 380 nm has not changed since before and after the humidity and heat test. When ΔT ₁ is greater than 1, it means that after the humidity and heat test, the transmittance difference between the wavelengths of 450 nm and 380 nm increases. When ΔT ₁ is less than 1, it means that after the humidity and heat test, the transmittance difference between the wavelengths of 450 nm and 380 nm decreases.

As mentioned above, when the adhesive sheet has UV absorption, the change in transmittance at a wavelength of 380 nm before and after the humidity and heat test is minimal. If the polarizing element fades, the transmittance of visible light increases, so the difference between the transmittance at a wavelength of 380 nm and the transmittance after the humidity and heat test tends to increase. Therefore, _ΔTn is generally above 1.00. The smaller _ΔTn (the closer to 1.00), the less discoloration of the polarizing element.

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

When _ΔTn is 1.0-1.2, degradation of the polarizing element caused by external UV radiation, heat, or humidity is suppressed, resulting in excellent durability. Therefore, it can be used under various conditions, and even in humid conditions, it exhibits high durability.

To achieve a _ΔTn of 1.20 or less, the adhesive composition can be adjusted, for example. For example, the base polymer composition can be adjusted. In acrylic adhesives, it is preferable to reduce the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl-containing monomers in the base polymer. Furthermore, incorporating a UV absorber into the adhesive composition is also effective in achieving a _ΔTn of 1.20 or less.

As described above, the change in transmittance before and after the humidity and heat test can be evaluated using _ΔTn . On the other hand, even when _ΔTn is large, if the ratio of transmittance change at each visible light wavelength remains constant, the hue of the transmitted light will not change significantly. Conversely, even when _ΔTn is small for each visible light wavelength, if the variation in _ΔTn across wavelengths is large, the hue of the transmitted light will change significantly, potentially causing degradation in visibility, such as coloration, in image display devices.

The ratio of the transmittance at a specific wavelength to the transmittance of all visible light is expressed as _Tn / _ΣTi . Where _i is an integer from 1 to 4, ΣTi = _T1 + _T2 + _T3 + _T4 . For example, _T1 / _ΣTi is the ratio of the 100 μm-equivalent transmittance at a wavelength of 450 nm to the sum of the 100 μm-equivalent transmittances at wavelengths of 450 nm, 520 nm, 580 nm, and 660 nm.

The ratio of the transmittance ratio of a specific wavelength after the humidity and heat test ( _Tn '/ _ΣTi ') to the transmittance ratio of a specific wavelength before the humidity and heat test ( _Tn /ΣTi ₎ , _δTn = ( _Tn '/ _ΣTi ')/( _Tn / _ΣTi ), indicates how the ratio of the transmittance of a specific wavelength to the total visible light has changed. If _δTn is 1, the ratio of the transmittance of a specific wavelength (for example, 450 nm when n = 1) to the total visible light does not change before and after the humidity and heat test.

When δT ₁ is greater than 1, the transmittance at a wavelength of 450 nm increases after the humidity and heat test. When δT ₁ is less than 1, the transmittance at a wavelength of 450 nm decreases after the humidity and heat test. The closer δT _n is to 1.00 for each wavelength, the smaller the color change of the transmitted light caused by fading of the polarizing element.

For n=1-4 (i.e., wavelengths of 450 nm, 520 nm, 580 nm, and 660 nm), _δTn is preferably 0.95-1.05, more preferably 0.97-1.03, further preferably 0.98-1.02, and particularly preferably 0.99-1.01.

If _δTn is 0.95-1.05, degradation of the polarizing element caused by external UV radiation, heat, or humidity can be further suppressed, further improving durability. This allows for use in a wide range of conditions, and even in humid conditions, further demonstrating enhanced durability.

To achieve a _δTn within the range of 0.95-1.05, for example, the adhesive composition can be adjusted. For example, the composition of the base polymer in the adhesive composition can be adjusted. In acrylic adhesives, it is preferable to reduce the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl-containing monomers in the base polymer. Furthermore, incorporating a UV absorber into the adhesive composition is also effective in achieving a _δTn within the range of 0.95-1.05.

As described above, for n = 1 to 4, a smaller _ΔTn (closer to 1.00) indicates a smaller change in transmittance before and after the humidity and heat test, and a closer _δTn is to 1.00 indicates a smaller change in the color of the transmitted light. For samples bonded to a polarizing element in contact with an adhesive sheet made using the adhesive composition of the present invention, preferably, for n = 1 to 4, both _ΔTn and _δTn are within the above ranges.

[Adhesive Composition] The adhesive composition constituting the adhesive sheet 21 is not particularly limited in composition, as long as the sample obtained by laminating a polarizing element in contact with an adhesive sheet produced using the composition exhibits the aforementioned _ΔTn and/or _δTn . To achieve _ΔTn and/or _δTn within the aforementioned ranges, the adhesive composition preferably exhibits UV shielding properties. For example, by incorporating a UV absorber into the adhesive composition, UV-absorbing properties can be achieved, thereby enabling UV shielding.

<Base polymer>  Adhesive compositions generally contain a base polymer. Examples of base polymers include acrylic, silicone, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy, fluorine, and rubber polymers.

In particular, acrylic adhesives containing an acrylic polymer as a base polymer are preferred due to their excellent optical transparency and adhesion. In acrylic adhesives, the aforementioned _ΔTn can be reduced to 1.20 or less by reducing the ratio of polar monomers such as hydroxyl-containing monomers and nitrogen-containing monomers in the base polymer. Furthermore, in acrylic adhesives, the aforementioned _ΔTn can be reduced to a range of 0.95 to 1.05 by reducing the ratio of polar monomers such as nitrogen-containing monomers and hydroxyl-containing monomers in the base polymer.

When the amount of hydroxyl-containing monomers used in the base polymer is high, the polarity of the polymer increases, and the hydrophilicity and moisture permeability of the adhesive sheet increase. Polarizing elements placed in contact with the adhesive sheet under high temperature and high humidity conditions are prone to fading. High hydrophilicity and moisture permeability of the adhesive sheet allow moisture from the external environment to easily reach the polarizing element. This moisture can disrupt the alignment of the polymer chains that comprise the polarizing element, or cause polyiodine ions to dissociate from the polymer chains. This is believed to be a cause of polarizing element fading. Furthermore, increasing the amount of nitrogen-containing monomers used in the base polymer increases the tendency of polarizing elements placed in contact with the adhesive sheet to discolor. Since nitrogen atoms easily coordinate with iodine, if the amount of nitrogen atoms contained in the base polymer of the adhesive sheet increases, the iodine fixed to the polymer chain of the polarizing element will coordinate with the nitrogen atoms of the adhesive, thereby detaching from the polymer chain. This is believed to be one of the causes of discoloration of the polarizing element.

By reducing the amount of hydroxyl-containing monomers and nitrogen-containing monomers in the base polymer, discoloration of the polarizing element can be suppressed, thereby making it possible to keep _ΔTn and _δTn within the above ranges.

Acrylic-based polymers contain an alkyl (meth)acrylate as a primary monomer component. In this specification, "(meth)acrylic acid" refers to acrylic acid and/or methacrylic acid. Alkyl (meth)acrylates having an alkyl group with 1 to 20 carbon atoms are particularly suitable. Alkyl (meth)acrylates may have a branched or cyclic alkyl group (alicyclic alkyl group).

Specific examples of the alkyl (meth)acrylate having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-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, nonyl (meth)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, eicosyl (meth)acrylate, and the like.

Specific examples of the alkyl (meth)acrylate having an alicyclic alkyl group include cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylates having a dicyclic aliphatic hydrocarbon ring such as isobutyl (meth)acrylate; and (meth)acrylates having a tricyclic or more aliphatic hydrocarbon ring such as dicyclopentyl (meth)acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may be one having a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate.

The amount of the alkyl (meth)acrylate is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, further 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, relative to 100 parts by weight of the total monomer components constituting the acrylic-based polymer.

The acrylic base polymer preferably contains an acrylic monomer with a crosslinkable functional group as a copolymer component. By providing the base polymer with a crosslinkable functional group, the base polymer can react with the crosslinking agent, thereby increasing the cohesive force of the adhesive and improving bonding reliability.

Examples of acrylic monomers with crosslinkable functional groups include hydroxyl-containing monomers and carboxyl-containing monomers. For example, when using an isocyanate crosslinking agent, a crosslinking structure is introduced through the reaction between hydroxyl groups and isocyanate groups. When using an epoxy crosslinking agent, a crosslinking structure is introduced through the reaction between carboxyl groups and epoxy groups. As described below, from the perspective of making the adhesive acid-free, it is preferred to use a hydroxyl-containing monomer as a copolymer component of the base polymer and to introduce a crosslinking structure using an isocyanate crosslinking agent. When the base polymer contains a hydroxyl-containing monomer as a monomer component, the crosslinking properties of the base polymer are enhanced, and the turbidity of the adhesive in high temperature and high humidity environments tends to be suppressed, resulting in an adhesive with higher transparency.

Examples of hydroxyl-containing monomers include (meth)acrylates 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. Of these, 2-hydroxyethyl acrylate (homopolymer Tg: -15°C) and 4-hydroxybutyl acrylate (homopolymer Tg: -32°C) are preferred because they contribute significantly to improved adhesion and can suppress whitening of the adhesive sheet in high-humidity environments.

The amount of hydroxyl-containing monomer is preferably at least 0.1 parts by weight, more preferably at least 0.5 parts by weight, and even more preferably at least 0.8 parts by weight, relative to 100 parts by weight of the total monomer components constituting the acrylic-based polymer. It can also be at least 1 part by weight, 1.5 parts by weight, or 2 parts by weight. Increasing the amount of hydroxyl-containing monomer reduces the number of unreacted functional groups in the crosslinking agent, thereby increasing the degree of crosslinking with a smaller amount of crosslinking agent and improving bonding reliability.

On the other hand, if the amount of hydroxyl-containing monomer used in the base polymer is too high, the polarity of the adhesive increases, and the polarizing element 11 placed in contact with the adhesive sheet 21 tends to fade. Consequently, _ΔTn and _δTn tend to deviate from 1.00. Therefore, the amount of hydroxyl-containing monomer is preferably 8 parts by weight or less, more preferably 7 parts by weight or less, and can also be 6 parts by weight or less, or 5 parts by weight or less, per 100 parts by weight of the total monomer components constituting the acrylic base polymer.

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

Acrylic-based polymers may contain nitrogen-containing monomers as monomer components. Examples of nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperidone, vinylpyrrolidone, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxamides, N-vinylcaprolactam, acrylonitrile, and methacrylonitrile.

As the amount of nitrogen-containing monomer used increases, the polarizing element 11 disposed in contact with the adhesive sheet 21 tends to discolor more easily, and _ΔTn and _δTn tend to deviate from 1.00. Therefore, the amount of nitrogen-containing monomer, relative to 100 parts by weight of the total 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 also 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 also contain no nitrogen-containing monomer as a monomer component.

If the acid components contained in the adhesive sheet are transferred to the polarizing element, it will promote the hydrolysis of polyvinyl alcohol, which may become the cause of the deterioration of the polarizing element. Therefore, the adhesive sheet 21 preferably has a lower content of organic acid monomers such as (meth) acrylic acid (free organic acid). In thermosetting or light-curing polymers, the presence of unreacted residual monomers is inevitable. Therefore, in order to reduce the acid monomer content in the adhesive sheet, it is better to reduce the amount of organic acid monomer components such as (meth) acrylic acid in the monomer components constituting the base polymer. Relative to 100 parts by weight of the total amount of monomer components constituting the acrylic base polymer, the content of carboxyl-containing monomers is preferably less than 1 part by weight, more preferably less than 0.5 parts by weight, and further preferably less than 0.1 parts by weight. The acrylic acid-based polymer preferably does not contain a carboxyl group-containing monomer as a monomer component.

To suppress fading of the polarizing element 11 in high-temperature, high-humidity environments and maintain _ΔTn and _δTn close to 1.00, the base polymer constituting the adhesive sheet 21 disposed in contact with the polarizing element 11 preferably has low polarity. To reduce the polarity of the base polymer, the content of polar monomers such as nitrogen-containing monomers, hydroxyl-containing monomers, and carboxyl-containing monomers as constituent monomers is preferably low. The content of polar monomers is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 8 parts by weight or less, and can be 6 parts by weight or less, or 5 parts by weight or less, relative to 100 parts by weight of the total monomer components of the acrylic base polymer.

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

The acrylic-based polymer is obtained by polymerizing the above-mentioned monomer components using various well-known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. Solution polymerization is preferred as the polymerization method, based on the balance between adhesive properties such as adhesion and retention, and cost considerations. Ethyl acetate, toluene, and the like are commonly used as solvents for solution polymerization. The solution concentration is generally between about 20% and 80% by weight. Thermal polymerization initiators such as azo initiators, peroxide initiators, and redox initiators combining peroxides and reducing agents (e.g., combinations of persulfate and sodium bisulfite, or combinations of peroxide and sodium ascorbate) are preferred as polymerization initiators. The amount of the polymerization initiator used is not particularly limited. For example, it is preferably about 0.005 to about 5 parts by weight, and more preferably about 0.02 to about 3 parts by weight, relative to 100 parts by weight of the total monomer components forming the base polymer.

Chain transfer agents can be used to adjust the molecular weight of the base polymer. Chain transfer agents can accept free radicals from the growing polymer chain, halting polymer elongation. The chain transfer agent then attacks monomers with the free radicals, restarting polymerization. Therefore, the use of chain transfer agents can suppress the increase in molecular weight of the base polymer without reducing the free radical concentration in the reaction system. Suitable chain transfer agents include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, hydroxyacetic acid, 2-hydroxyethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dihydroxy-1-propanol.

There is no particular limit on the amount of chain transfer agent used. However, if the amount is too high, the molecular weight of the base polymer may decrease, which may reduce the processability and dimensional stability of the adhesive sheet before photocuring. 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, further preferably 0.15 parts by weight or less, and particularly preferably 0.1 parts by weight or less, based on 100 parts by weight of the total 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. Furthermore, when a crosslinking structure is introduced into the acrylic base polymer, the molecular weight of the base polymer refers to the molecular weight before the crosslinking structure is introduced.

<Crosslinking Structure of Base Polymer> An acrylic base polymer preferably has a crosslinking structure. Methods for introducing a crosslinking structure into a base polymer generally include: (1) polymerizing a base polymer having functional groups capable of reacting with a crosslinking agent, then adding a crosslinking agent to allow the base polymer to react with the crosslinking agent; and (2) introducing a branched structure (crosslinking structure) into the polymer chain by including a photopolymerizable polyfunctional compound in the polymerization components of the base polymer.

In the adhesive composition constituting the adhesive sheet 21 configured in contact with the polarizing element 11, the acrylic base polymer preferably has a crosslinking structure introduced by the method of (1) above. Alternatively, the adhesive composition constituting the adhesive sheet 21 may contain a photopolymerizable multifunctional compound and a photopolymerization initiator, and then photocuring may be performed after the adhesive sheet 21 is attached to the cover window 70, thereby introducing the crosslinking structure of (2) above. That is, the adhesive composition constituting the adhesive sheet 21 preferably has a base polymer having a crosslinking structure formed by a (thermal) crosslinking agent such as an isocyanate crosslinking agent, and further, it is also possible to introduce a crosslinking structure formed by a photopolymerizable multifunctional compound (photocrosslinking agent) by photocuring.

<Adhesive Composition> The adhesive composition is prepared by mixing a crosslinking agent, a photopolymerizable multifunctional compound, a photopolymerization initiator, and, if necessary, oligomers or various additives with an acrylic base polymer. The adhesive composition preferably has a viscosity suitable for coating on a substrate (e.g., approximately 0.5 Pa·s to approximately 20 Pa·s). The viscosity of the 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, and the composition, molecular weight, and amount of other components (e.g., oligomers). Thickening additives may be used to adjust the viscosity.

(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 surface of the viewing side of the polarizing element, degradation of the polarizing element caused by ultraviolet rays incident from outside the display device is usually suppressed by making the transparent protective film have ultraviolet absorbing properties. On the other hand, in a structure in which the adhesive sheet 21 is arranged in contact with the surface of the viewing side of the polarizing element 11, since no transparent protective film is provided on the viewing side of the polarizing element, it is preferable to make the adhesive sheet 21 have ultraviolet absorbing properties to prevent light degradation of the polarizing element 11 caused by ultraviolet rays (for example, color change of the polarizing element accompanied by structural change of polyiodine ions (from I ₅ ^- to I ₃ ^- )).

In order to impart UV absorption to the adhesive sheet 21, the adhesive composition preferably contains a UV absorber. Examples of UV absorbers include benzotriazole-based UV absorbers, benzophenone-based UV absorbers, tris(III)-based UV absorbers, salicylate-based UV absorbers, and cyanoacrylate-based UV absorbers. Based on the viewpoints of high UV absorption, excellent compatibility with acrylic polymers, and the ease of obtaining highly transparent acrylic adhesives, tris(i)-based UV absorbers and benzotriazole-based UV absorbers are preferred. Among them, tris(i)-based UV absorbers containing a hydroxyl group and benzotriazole-based UV absorbers having one benzotriazole skeleton per molecule are particularly preferred.

As the ultraviolet absorber, commercially available products can be used. Examples of commercially available trisoxane-based ultraviolet absorbers include: the reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-trioxane-2-yl)-5-hydroxyphenyl and [(alkoxy)methyl]oxirane ("TINUVIN 400" manufactured by BASF), the reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-trioxane and glycidyl (2-ethylhexyl) ester ("TINUVIN 405"), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-trisinol ("TINUVIN 460" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-trisinol-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-trisinol ("TINUVIN 479”), 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-tri-2,4-diyl]diphenol ("Tinosorb S" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-tri-2-yl)-5-[2-(2-ethylhexyloxy)ethoxy]-phenol ("ADK STAB LA-46" manufactured by ADEKA), etc.

Examples of commercially available benzotriazole-based UV absorbers include 2-(2H-benzotriazole-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 928" manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole ("TINUVIN PS" manufactured by BASF), 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol ("TINUVIN 900" manufactured by BASF), 2-(2H-benzotriazole-2-yl)-6-dodecyl-4-methylphenol ("TINUVIN 571), 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 328" manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol ("TINUVIN 329”), ester compound of phenylpropionic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyl (C7-C9 side chain and linear alkyl) (“TINUVIN 384-2” manufactured by BASF), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) propionate and polyethylene glycol (“TINUVIN 1130” manufactured by BASF), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl) propionate and polyethylene glycol 300 (“TINUVIN 213”), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole (Sumisorb 250 manufactured by Sumitomo Chemical), etc.

The amount of the UV absorber in the adhesive composition is approximately 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, relative to 100 parts by weight of the base polymer. By maintaining the UV absorber content within this range, a decrease in transparency caused by UV absorber leakage can be suppressed. Furthermore, the adhesive sheet 21 has UV shielding properties, thereby improving weather resistance and suppressing optical degradation of the polarizing element caused by external UV radiation.

(Crosslinking Agent) As mentioned above, the acrylic base polymer preferably has a crosslinked structure. This crosslinking structure is introduced into the base polymer by adding a crosslinking agent to the adhesive composition and, if necessary, heating it. While crosslinking with isocyanate-based crosslinking agents is sometimes referred to as "thermal crosslinking" to distinguish it from crosslinking introduced with photopolymerizable polyfunctional compounds, crosslinking with a crosslinking agent can be introduced without heating. The introduction of thermal crosslinking into the acrylic base polymer tends to improve the cohesiveness and adhesion of the adhesive sheet.

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 crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. Among these, isocyanate crosslinking agents are preferred due to their high reactivity with the hydroxyl groups of the base polymer and their ease of introducing a crosslinked structure.

As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups in one molecule can be used. Examples of the isocyanate crosslinking agent include lower aliphatic polyisocyanates such as butyl diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentyl diisocyanate, cyclohexyl diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylenediisocyanate; trihydroxymethylpropane/toluene diisocyanate trimer adduct (e.g., "Coronate L" manufactured by Tosoh Corporation), trihydroxymethylpropane/hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL"), trihydroxymethylpropane adduct of xylylenediisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals), isocyanurate of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh Corporation), and other isocyanate adducts.

By adjusting the amount of crosslinking agent added, the cohesive force or adhesion 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 part by weight, and even more preferably 0.1 to 0.5 part by weight, relative to 100 parts by weight of the base polymer.

(Photopolymerizable Multifunctional Compound) To impart photocurability to the adhesive sheet, the adhesive composition preferably contains a photopolymerizable multifunctional compound. A photopolymerizable multifunctional compound has two or more photopolymerizable functional groups per molecule. The photopolymerizable functional groups can be free radical, cationic, or anionic. Due to their excellent reactivity, free radical polymerizable functional groups with unsaturated double bonds (ethylenic unsaturated groups) are preferred. As photopolymerizable multifunctional compounds, multifunctional (meth)acrylates are preferred due to their high compatibility with acrylic-based polymers, and multifunctional acrylates are particularly preferred due to their high photoradical reactivity.

Examples of the multifunctional (meth)acrylate 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, alkylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerol di(meth)acrylate. Difunctional (meth)acrylates such as bis(trihydroxymethylpropane) tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; trifunctional (meth)acrylates such as bis(trihydroxymethylpropane) tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and pentafunctional or higher (meth)acrylates such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

To improve the bonding 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 weight (g/eq) of the multifunctional compound is preferably 50-500, more preferably 70-300, and even more preferably 80-200. To exhibit appropriate compatibility with the base polymer, the photopolymerizable multifunctional compound is preferably 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 further preferably 1 to 5 parts by weight relative to 100 parts by weight of the acrylic base polymer. When the content of the photopolymerizable multifunctional compound is small, the adhesive sheet after photocuring tends to have insufficient bonding reliability. On the other hand, when the content of the photopolymerizable multifunctional compound is too large, the ratio of the base polymer in the adhesive sheet (adhesive composition) before photocuring decreases, and the processability or processing dimensional stability of the adhesive sheet may be reduced. Furthermore, when the content of the photopolymerizable multifunctional compound is too large, the adhesive sheet after photocuring becomes hard, and the adhesive sheet 21 may have insufficient bonding strength or impact resistance at low temperatures.

(Photopolymerization initiator) The photocurable adhesive composition containing a photopolymerizable multifunctional compound preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzoyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and 9-oxosulfonium-based photopolymerization initiators. The photopolymerization initiator is a photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, etc. 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, relative to 100 parts by weight of the base polymer.

(Oligomer) The adhesive composition may contain various oligomers for purposes such as adjusting the adhesive sheet's adhesion and viscosity. Oligomers with a weight-average molecular weight of approximately 1,000 to 30,000 are suitable. Acrylic oligomers are preferred due to their excellent compatibility with the acrylic-based polymer.

Acrylic oligomers contain an alkyl (meth)acrylate as a main monomer component. Preferred monomer components include an alkyl (meth)acrylate having a chain alkyl group (chain alkyl (meth)acrylate) and an alkyl (meth)acrylate having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of chain alkyl (meth)acrylates and cyclic alkyl (meth)acrylates are as exemplified above as monomer components of the acrylic base polymer.

The glass transition temperature of the acrylic oligomer is preferably above 20°C, more preferably above 50°C, even more preferably above 80°C, and particularly preferably above 100°C. The combined use of a low-Tg base polymer with a crosslinked structure and a high-Tg acrylic oligomer tends to improve the adhesion of the adhesive sheet. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is generally below 200°C, preferably below 180°C, and more preferably below 160°C. The glass transition temperature of the acrylic oligomer is calculated using the aforementioned Fox equation.

Among the exemplified alkyl (meth)acrylates, methyl methacrylate is preferred as a chain alkyl (meth)acrylate due to its high glass transition temperature and excellent compatibility with the base polymer. Preferred cycloalkyl (meth)acrylates are dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. Specifically, the acrylic oligomer preferably contains methyl methacrylate and one or more monomers selected from the group consisting of dicyclopentyl acrylate, dicyclopentyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate as constituent monomer components.

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

The weight average molecular weight of the acrylic oligomer is preferably 1000 to 30000, more preferably 1500 to 10000, and even more preferably 2000 to 8000. Using an acrylic oligomer having a molecular weight within this range tends to improve the adhesion or retention of the adhesive sheet.

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

When the adhesive composition contains an oligomer component such as an acrylic oligomer, its content is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the base polymer. When the oligomer content in the adhesive composition is within this range, improved adhesion can be expected.

(Silane Coupling Agent) A silane coupling agent may be added to the adhesive composition for purposes such as adjusting adhesion. The amount of silane coupling agent added to the adhesive composition is typically about 0.01 to 5.0 parts by weight, preferably about 0.03 to 2.0 parts by weight, per 100 parts by weight of the base polymer.

(Antioxidant) The adhesive composition may contain an antioxidant. This antioxidant can inhibit the reaction or degradation of the curing component caused by heat or light in the storage or use environment of the adhesive composition or adhesive sheet. Examples of antioxidants include amine-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and phenol-based antioxidants. Among these, amine-based and phenol-based antioxidants, which act as free radical chain inhibitors, are preferred, with phenol-based antioxidants having a hindered phenol structure being particularly preferred.

An antioxidant having a hindered phenol structure is one in which a sterically hindered group such as a tert-butyl group is bonded to at least one of the carbon atoms adjacent to the carbon atom on the aromatic ring bonded to the OH group of the phenol. Examples of antioxidants with a hindered phenol structure include butylated hydroxytoluene (BHT), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] ("Irganox 1010" manufactured by BASF), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ("Irganox 1076" manufactured by BASF), 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol ("Irganox 1330), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-tris(2,4,6(1H,3H,5H)-trione ("Irganox 3114" manufactured by BASF), tris[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate ("Irganox 3125" manufactured by BASF), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] ("ADK STAB" manufactured by ADEKA), AO-60”), 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane (ADK STAB AO-80 manufactured by ADEKA), 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate (Sumilizer GS manufactured by Sumitomo Chemical), 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate (Sumilizer GM"), 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diylbis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] (Sumilizer GA-80 manufactured by Sumitomo Chemical), 1,3,5-tris(3-hydroxy-4-tert-butyl-2,6-dimethylbenzyl)-1,3,5-tris(2,4,6(1H,3H,5H)-trione) (Cyanox 1790 manufactured by Cytec), etc.

When the adhesive composition contains an antioxidant, from the perspective of suppressing undesirable curing reactions or degradation, the antioxidant content is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and even more preferably 0.1 parts by weight or more, and can also 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. On the other hand, excessive amounts of antioxidant may hinder curing during light curing of the adhesive sheet. Therefore, the antioxidant content 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 ingredients listed above, the adhesive composition may contain additives such as chain transfer agents, adhesion promoters, plasticizers, softeners, degradation inhibitors, fillers, colorants, surfactants, and anti-static agents.

[Adhesive Sheet Formation] The adhesive composition is applied to a substrate and, if necessary, the solvent is dried to remove it, thereby forming an adhesive sheet on the substrate. Any suitable substrate can be used to form the adhesive sheet. The substrate may also be a release film having a release layer on the surface of a resin film.

Examples of resin materials for release films include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether sulfone 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, more preferably 25 to 150 μm. Examples of materials for the release layer include silicone release agents, fluorine release agents, long-chain alkyl release agents, and fatty acid amide release agents. The thickness of the release layer is typically about 10 to 2000 nm.

The adhesive composition can be applied to the substrate by various methods, including roller coating, contact roller coating, gravure coating, reverse coating, brush coating, spray coating, dip roller coating, rod coating, doctor blade coating, air knife coating, curtain coating, die lip coating, and die nozzle coating.

When the adhesive composition contains a solvent, it is preferred to dry the solvent after applying the adhesive composition to the substrate. A suitable drying method can be employed depending on the intended purpose. The heating drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. The drying time can be appropriately selected. 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, a cover sheet is preferably added to protect the surface of the adhesive sheet. As the cover sheet, a release film having a release layer on the surface in contact with the adhesive sheet is preferred, similar to the base film.

After applying the adhesive composition to the substrate, heating is performed as needed to introduce crosslinks into the base polymer. The heating temperature and duration are appropriately adjusted based on the type of crosslinking agent used, typically ranging from 20°C to 160°C for approximately 1 minute to 7 days. The heating used to dry the solvent can also serve as the crosslinking agent. As previously mentioned, the introduction of crosslinks does not require heating.

To promote the formation of crosslinked structures, a crosslinking catalyst can be used. For example, examples of isocyanate-based crosslinking agents include metal-based crosslinking catalysts (particularly tin-based crosslinking catalysts) such as tetra-n-butyl titanium, tetra-isopropyl titanium, iron(III) acetylacetonate, butyltin oxide, dioctyltin dilaurate, and dibutyltin dilaurate.

By laminating a release film to the surface of an adhesive sheet, you can create an adhesive sheet with release films temporarily attached to both sides. Alternatively, the base material or cover sheet used to form the adhesive sheet can be used directly as the release film.

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

The thickness of the adhesive sheet 21 used to bond the polarizing element 11 to the cover window 70 is preferably 30 μm or greater, more preferably 40 μm or greater, and even more preferably 50 μm or greater. Increasing the thickness of the adhesive sheet 21 tends to improve impact resistance. Furthermore, when the cover window 70 has printing steps resulting from decorative printing, the adhesive sheet 21 can be made to absorb the steps. There is no particular upper limit on the thickness of the adhesive sheet 21. Based on 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, more preferably 90% or more. The haze of the adhesive sheet is preferably 1.5% or less, more preferably 1% or less.

The transmittance of light at a wavelength of 380 nm through the adhesive sheet 21 is preferably 5% or less, more preferably 4% or less, and may be 3% or less. Improving the UV shielding properties of the adhesive sheet 21 improves weather resistance and suppresses photodegradation of the polarizing element 11, such as yellowing, caused by incident UV light. As described above, by including a UV absorber in the adhesive composition, the adhesive sheet 21 maintains visible light transparency while also imparting UV absorptivity.

Polarizing Plate <Polarizing Element> Polarizing plate 10 includes polarizing element 11. Polarizing element 11 is, for example, a polyvinyl alcohol film containing iodine. Polyvinyl alcohol or its derivatives can be used as the material for the polyvinyl alcohol film used in the polarizing element. Examples of polyvinyl alcohol derivatives include polyvinyl formal and polyvinyl acetaldehyde. Other examples include those modified with alkenes such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, or their alkyl esters, or acrylamide. Polyvinyl alcohols typically used have a degree of polymerization of approximately 1,000 to 10,000 and a saponification degree of approximately 80 to 100 mol%.

A polarizing element is obtained by subjecting a polyvinyl alcohol film to iodine dyeing and stretching. The thickness of the polarizing element is preferably about 1 to about 50 μm. A thin polarizing element having a thickness of 10 μm or less may also be used as the polarizing element. Examples of thin polarizing elements include those described in Japanese Patent Publication No. 51-069644, Japanese Patent Publication No. 2000-338329, WO2010/100917, Japanese Patent No. 4691205, and Japanese Patent No. 4751481. Such a thin polarizing element can be obtained, for example, by a manufacturing method comprising stretching a polyvinyl alcohol resin layer and a stretching resin substrate in a laminated state and then performing an iodine dyeing step.

Optical Layer An optical layer is not provided on the first principal surface (the viewing side) of the polarizing element 11. As mentioned above, an adhesive sheet 21 is provided in contact with the polarizing element 11. The polarizing plate 10 may consist solely of the polarizing element 11, or an appropriate optical layer 15 may be provided on the second principal surface (the surface facing the image display unit 60) of the polarizing element 11.

Optical layer 15 can be a transparent protective film used to protect polarizing element 11, an optical compensation layer for purposes such as widening the viewing angle, or a quarter-wave plate used to form a circularly polarizing plate together with polarizing element 11. Optical layer 15 can also function as both a transparent protective film and a phase difference plate.

Materials constituting the optical layer 15 include, for example, resin materials with excellent transparency, mechanical strength, and thermal stability. Specific examples of such resin materials include cellulose resins such as triacetylcellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (northene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The optical layer 15 may also be a liquid crystal material. For example, a liquid crystal layer in which liquid crystal molecules are aligned in a specific direction can be used as the optical layer 15 .

The optical layer 15 can be directly in contact with the second principal surface of the polarizing element 11 or bonded thereto via an appropriate adhesive layer. The optical layer 15 can be a laminate of two or more layers. For example, the optical layer 15 can be a laminate of two or more films, a laminate comprising a liquid crystal layer on a film substrate, or a laminate of two or more liquid crystal layers. The optical layer 15 can include an alignment film for aligning liquid crystal molecules in a specific direction.

[Polarizing Plate with Adhesive] As shown in Figure 2, the adhesive sheet 21 can be provided as a polarizing plate with adhesive 81, formed as a single-volume layer with the polarizing plate 10. In the polarizing plate with adhesive, the adhesive sheet 21 is positioned in contact with the first principal surface of the polarizing element 11. In Figure 2, the optical layer 15 is provided on the second principal surface of the polarizing element 11. However, as mentioned above, the polarizing plate 10 does not need to have an optical layer on the second principal surface of the polarizing element.

There is no particular limitation on the method of attaching the adhesive sheet 21 to the first main surface of the polarizing element 11. The adhesive sheet 21 may be bonded to the polarizing element 11 by prefabricating it on a substrate, or the adhesive sheet 21 may be formed using the polarizing element 11 as the substrate.

In the adhesive-attached polarizing plate 81, a release film 41 is preferably releasably attached to the adhesive sheet 21. The release film protects the exposed surface of the adhesive sheet 21 until it is attached to the cover window 70. Alternatively, the base material used for forming (coating) the adhesive sheet can be directly used as the release film 41 on the adhesive sheet 21.

As shown in Figure 3, a polarizing plate with adhesive can be a double-sided adhesive plate, with an adhesive sheet 21 on the viewing side of the polarizing plate 10, which contacts the polarizing element 11, and another adhesive sheet 22 on the other side of the polarizing plate. Preferably, a release film 42 is releasably attached to the adhesive sheet 22.

In the adhesive-attached polarizing plate 81 shown in FIG3 , the polarizing plate 10 includes an optical layer 15 on the second principal surface of the polarizing element 11, and an adhesive sheet 22 is disposed on the optical layer 15. Alternatively, the adhesive sheet 22 may be laminated on the second principal surface of the polarizing element 11 so as to be in contact with the polarizing element 11 without intervening any other layers.

If a double-sided adhesive polarizing plate with adhesive layers pre-attached on both sides of the polarizing plate 10 is used as described above, the step of attaching another adhesive sheet to the polarizing plate can be omitted after the polarizing plate is attached to the surface of the image display unit, thereby simplifying the manufacturing steps of the image display device.

The adhesive sheet 22 is used to bond the polarizing plate 10 to the image display unit 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. Various adhesives suitable for bonding polarizing plates to image display units can be used for the adhesive sheet 22. Acrylic adhesives are preferred as the adhesive for the adhesive sheet 22.

A polarizing plate with adhesive, having adhesive sheet 21 disposed in contact with one side of polarizing element 11, preferably exhibits ΔT 1 , ΔT ₂ , ΔT ₃ , and ΔT ₄ within a range of 1.00 to 1.20 when subjected to a humidity and heat test at 85°C and 85% relative humidity for 100 hours. ΔT ₁ , _{ΔT 2 , ΔT 3 , and} ΔT ₄ are as defined above. For each of n = 1 to 4, ΔT _n of the polarizing plate with adhesive 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. A ΔT _n closer to 1.00 indicates less discoloration of the polarizing element and superior humidity and heat resistance.

A polarizing plate with an adhesive having an adhesive sheet 21 disposed in contact with one side of the polarizing element 11 preferably exhibits δT ₁ , δT ₂ , δT ₃ , and δT ₄ within a range of 0.95 to 1.05 when subjected to a 100-hour humidity test at a temperature of 85°C and a relative humidity of 85%. δT ₁ , _{δT 2 , δT 3 ,} and δT ₄ are as defined above. The polarizing plate with an adhesive preferably has a δT _n of 0.97 to 1.03, more preferably 0.98 to 1.02, and even more preferably 0.99 to 1.01 for n = 1 to 4. A δT _n closer to 1.00 indicates a smaller color shift in the transmitted light.

The polarizing plate with an adhesive having an adhesive sheet 21 disposed in contact with one side of the polarizing element 11 preferably has _ΔTn within the above range and _δTn within the above range.

[Image Display Device] As shown in FIG1 , the image display device 100 has a cover window 70 attached to the viewing side of the polarizing plate 10 via an adhesive sheet 21. An image display unit 60 such as a liquid crystal unit or an organic EL unit is attached to the other side of the polarizing plate 10 via an adhesive sheet 22. The image display unit 60 may be bendable.

A transparent plate with suitable mechanical strength and thickness can be used as the cover window 70. Examples of such a transparent plate include a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate. If the image display unit 60 is bendable, the cover window 70 may also be bendable. The cover window can be formed by laminating multiple transparent films with an adhesive or bonding agent, and may also include a touch panel sensor. The touch panel sensor can be any type of touch panel, such as a resistive film type, an electrostatic capacitance type, an optical type, or an ultrasonic type.

The order of laminating the polarizing plate 10 and the cover window 70 using the adhesive sheet 21 and laminating the adhesive sheet 22 and the image display unit 60 is not particularly limited. As described above, a polarizing plate with an adhesive agent pre-attached to the surface of the polarizing plate can be used.

After laminating the polarizing plate 10 to the cover window 70 via the adhesive sheet 21, defoaming can be performed to remove bubbles at the laminating interface or near the printing steps. Suitable defoaming methods include heating, pressurization, and decompression. For example, lamination can be performed under reduced pressure/heating to suppress bubble incorporation. To further suppress and delay bubble formation, pressure can be applied simultaneously with heating, such as through autoclaving.

When the adhesive sheet 21 comprises a photocurable adhesive composition, the adhesive composition is photocured after the polarizing plate 10 and the cover window 70 are attached. The photopolymerizable multifunctional compound undergoes polymerization by light irradiation, thereby improving the adhesive sheet's bonding reliability.

The amount of light irradiated during photocuring is not particularly limited as long as it is within the range sufficient to photocure the adhesive sheet. For example, the accumulated light amount is approximately 50 mJ/ ^cm² to approximately 10,000 mJ/ ^cm² . The adhesive sheet 21 can be irradiated with light from either the polarizing plate 10 side or the cover window 70 side. However, to prevent degradation of the polarizing element 11 due to ultraviolet light, irradiation with ultraviolet light from the cover window 70 side is preferred. If the adhesive sheet 21 has ultraviolet shielding properties, even when irradiated with ultraviolet light for photocuring, the majority of the ultraviolet light is absorbed by the adhesive sheet 21, thereby reducing the amount of ultraviolet light irradiating the polarizing element.

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 polarizing element 11 has the characteristics described above. Therefore, even when the image display device having the adhesive sheet 21 is exposed to a high temperature and high humidity environment, or when it is exposed to external light for a long time, the polarizing element is less likely to deteriorate, such as fading or yellowing, and has excellent durability. [Example]

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

[Examples 1 to 3 and Comparative Examples 1 and 2] <Polymerization of base polymer> The monomer components in the ratios shown in Table 1 (a total of 100 parts by weight), azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate were placed in a reaction vessel equipped with a thermometer, a stirrer, a condenser, and a nitrogen inlet tube, and stirred for 1 hour in a nitrogen atmosphere at 23°C to perform nitrogen replacement. Then, the reaction was carried out at 56°C for 5 hours and then at 70°C for 3 hours to prepare an acrylic base polymer solution.

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

<Preparation of adhesive composition> To the acrylic base polymer solution obtained above, the following components were added in the amounts shown in Table 1 relative to 100 parts by weight of the base polymer, and then uniformly mixed to prepare an adhesive composition.   Isocyanate crosslinking agent: trihydroxymethylpropane adduct of benzyl diisocyanate  ("Takenate D110N" manufactured by Mitsui Chemicals)  Ultraviolet absorber: 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-tris-2,4-diyl]diphenol ("Tinosorb S" manufactured by BASF)

<Adhesive Sheet Preparation> The photocurable adhesive composition is applied to a release film (polyethylene terephthalate film with a silicone release layer on one side), heated at 100°C for 3 minutes to remove the solvent, and then another release film is attached to the surface. The laminate is aged at 25°C for 3 days to allow crosslinking, thereby obtaining an adhesive sheet with release films temporarily attached to both sides.

[Preparation of Adhesive Sheet A] 97 parts by weight of butyl acrylate and 3 parts by weight of acrylic acid as monomer components, 0.2 parts by weight of AIBN as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate were placed into a reaction vessel equipped with a thermometer, a stirrer, a condenser, and a nitrogen inlet tube. The mixture was stirred for 1 hour in a nitrogen atmosphere at 23°C and replaced with nitrogen. Then, the mixture was reacted at 60°C for 5 hours to obtain a solution of an acrylic acid-based polymer with a weight average molecular weight (Mw) of 1.1 million. To the base polymer solution, 0.8 parts by weight of trihydroxymethylpropane toluene diisocyanate ("Coronate L" manufactured by Nippon Polyurethane Industry) as an isocyanate-based crosslinking agent and 0.1 parts by weight of a silane coupling agent ("KBM403" manufactured by Shin-Etsu Chemical Industry) were added and uniformly mixed to prepare an adhesive composition solution.

The adhesive composition was applied to a release film to a dried thickness of 20 μm. The film was dried at 100°C for 3 minutes to remove the solvent, and then another release film was laminated to the surface. The laminate was aged at 50°C for 2 days to allow crosslinking, resulting in an adhesive sheet A with release films temporarily laminated on both sides.

[Evaluation] A polarizing element comprising a 25 μm thick stretched polyvinyl alcohol film impregnated with iodine was bonded to a first alkali-free glass plate via an adhesive sheet A. A second alkali-free glass plate was bonded thereto via the adhesive sheets of the embodiment and comparative example to produce evaluation samples.

Weathering test: Using a UV fade meter (Suga Test Instruments "U48AU"), the samples were exposed to carbon arc light from the second alkali-free glass plate for 100 hours at a temperature of 40°C and a relative humidity of 20%. The irradiance (integrated illuminance from 300 to 700 nm) was 500 ± 50 W/ ^m² . The difference between b ^* ₀ and b ^* ₁ of the transmitted light before and after the test was calculated as Δb ^* = b ^* ₁ - b ^* ₀ . b ^* is the chromaticity index b ^* in the CIE 1976 color space. The sample was placed on a backlight for measurement.

(Humidity and Heat Test) The transmittance spectrum of the evaluation samples was measured using a UV-visible spectrophotometer, and the initial transmittances (t _{0 )} , t ₁ , t ₂ , t ₃ , and t _{4 )} were recorded at wavelengths of 380 nm, 450 nm, 520 nm, 580 nm, and 660 nm. The evaluation samples were maintained in a constant temperature and humidity chamber at 85°C and 85% relative humidity for 100 hours to perform the humidity and heat test. The transmittance spectrum of the samples after the humidity and heat test was measured, and the transmittances (t ₀ ', t ₁ ', t 2 ', t ₃ ', and t ₄ ') were recorded at wavelengths of 380 nm, 450 nm, 520 nm, ₅₈₀ nm, and 660 nm.

Based on the measured transmittance value t, Lambert's law was used to calculate the transmittance T at 100 μm, which is the total thickness of the polarizer (25 μm) and the adhesive sheet (100 μm), L = 125 μm, converted to the transmittance at a thickness of 100 μm. This is log ₁₀ (T/100) = (100/L) × log ₁₀ (t/100).

T ₀ : Transmittance at 380 nm before the humidity and heat test (converted to 100 μm) T ₁ : Transmittance at 450 nm before the humidity and heat test (converted to 100 μm) T ₂ : Transmittance at 520 nm before the humidity and heat test (converted to 100 μm) T ₃ : Transmittance at 580 nm before the humidity and heat test (converted to 100 μm) T ₄ : Transmittance at 660 nm before the humidity and heat test (converted to 100 μm) T ₀ ': Transmittance at 380 nm after the humidity and heat test (converted to 100 μm) T ₁ ': Transmittance at 450 nm after the humidity and heat test (converted to 100 μm) T ₂ ': Transmittance at 520 nm after the humidity and heat test (converted to 100 μm) μm-converted transmittance T ₃ ': 100 μm-converted transmittance at a wavelength of 580 nm after the humidity and heat test. T ₄ ': 100 μm-converted transmittance at a wavelength of 660 nm after the humidity and heat test.

Based on the 100 μm equivalent transmittance T ₀ to T ₄ before the above-mentioned humidity and heat test and the 100 μm equivalent transmittance T ₀ ' to T ₄ ' after the humidity and heat test, calculate the following _ΔTn and _δTn (n = 1 to 4). ΔTn = ( _Tn ' - _T0 ') / ( _Tn - _T0 ) δTn = ( _Tn ' / _ΣTi ') / ( _Tn / _ΣTi ) Where, i = 1 to 4

The adhesive compositions and evaluation results for each adhesive sheet are shown in Table 1. The values in Table 1 represent the amounts (parts by weight) used for the adhesive compositions. Furthermore, for Comparative Example 2, the Δb ^* value exceeded 5% in the weathering test, indicating a weathering failure, so the wet heat test was not performed.

[Table 1] Adhesive composition Weathering test Moisture and heat test transmittance Base polymer UV absorber ∆b* (%) Wavelength 380 nm 450 nm 520 nm 580 nm 660 nm Example 1 BA/2EHA/4HBA=68/31/1 Isocyanate crosslinker 0.3 0.6 2.5 Measured transmittance t 0.3% 44% 55% 54% 57% t' 0.3% 46% 57% 56% 59% 100 μm converted transmittance T 1% 52% 62% 61% 64% T' 1% 54% 64% 63% 66% ∆T 1.04 1.03 1.03 1.03 δT 1.01 1.00 1.00 1.00 Example 2 BA/2EHA/4HBA=66/31/3 Isocyanate crosslinker 0.3 0.6 2.7 Measured transmittance t 0.3% 43% 54% 55% 58% t' 0.3% 45% 56% 57% 59% 100 μm converted transmittance T 1% 51% 61% 62% 65% T' 1% 53% 63% 64% 66% ∆T 1.04 1.03 1.03 1.02 δT 1.01 1.01 1.01 0.99 Example 3 BA/2EHA/4HBA=65/30/5 Isocyanate crosslinker 0.3 0.6 2.4 Measured transmittance t 0.3% 45% 55% 54% 57% t' 0.3% 51% 62% 59% 63% 100 μm converted transmittance T 1% 53% 62% 61% 64% T' 1% 58% 68% 66% 69% ∆T 1.10 1.10 1.08 1.08 δT 1.01 1.01 1.00 1.00 Comparative example 1 BA/2EHA/4HBA=62/28/10 Isocyanate crosslinker 0.3 0.6 3.2 Measured transmittance t 0.3% 44% 55% 54% 57% t' 0.3% 51% 62% 65% 73% 100 μm converted transmittance T 1% 52% 62% 61% 64% T' 1% 58% 68% 70% 77% ∆T 1.11 1.10 1.15 1.21 δT 0.98 0.96 1.01 1.06 Comparative example 2 BA/2EHA/4HBA=68/31/1 Isocyanate crosslinker 0.3 0 5.3 Undetermined

As shown in Table 1, the adhesive sheets of Examples 1-3 exhibited relatively low Δb ^* and good weather resistance. Furthermore, _{both ΔTn} and _δTn were close to 1.00 when n = 1-4, resulting in minimal fading of the polarizing element and excellent moisture and heat resistance.

10: Polarizing plate 11: Polarizing element 15: Optical layer 21, 22: Adhesive sheet 41, 42: Release film 60: Image display unit 70: Cover window 81, 82: Polarizing plate with adhesive 100: Image display device

Figure 1 is a cross-sectional view schematically illustrating one embodiment of an image display device. Figure 2 is a cross-sectional view illustrating one embodiment of a polarizing plate with an adhesive. Figure 3 is a cross-sectional view illustrating one embodiment of a polarizing plate with an adhesive.

10:Polarizing plate

11: Polarizing element

15: Optical layer

21,22: Adhesive Sheet

60: Image display unit

70: Cover Window

100: Image display device

Claims (8)

A polarizing plate with an adhesive includes a polarizing element having a first principal surface and a second principal surface; and a first adhesive sheet disposed in contact with the first principal surface of the polarizing element. The first adhesive sheet is used for bonding to a cover window of an image display device. The first adhesive sheet comprises an adhesive composition containing an acrylic-based polymer and 0.05 to 10 parts by weight of a UV absorber per 100 parts by weight of the acrylic-based polymer. The acrylic-based polymer contains 8 parts by weight or less of nitrogen-containing monomers, hydroxyl-containing monomers, and carboxyl-containing monomers relative to 100 parts by weight of the total monomer components. When the polarizing plate with the adhesive is subjected to a humidity test at a temperature of 85°C and a relative humidity of 85% for 100 hours, ΔT ₁ , ΔT ₂ , ΔT ₃ , and ΔT ₄ expressed by the following formula all satisfy a range of 1.0 to 1.2: ΔT _n = (T _n '-T ₀ ')/(T _n -T ₀ ) where n is an integer from 1 to 4, T ₀ is the transmittance at a wavelength of 380 nm before the humidity test, measured at 100 μm, T ₁ is the transmittance at a wavelength of 450 nm before the humidity test, and T _T2 is the 100 μm-converted transmittance at a wavelength of 520 nm before the humidity and heat test, _T3 is the 100 μm-converted transmittance at a wavelength of 580 nm before the humidity and heat test, _T4 is the 100 μm-converted transmittance at a wavelength of 660 nm before the humidity and heat test, _T0 ' is the 100 μm-converted transmittance at a wavelength of 380 nm after the humidity and heat test, _T1 ' is the 100 μm-converted transmittance at a wavelength of 450 nm after the humidity and heat test, _T2 ' is the 100 μm-converted transmittance at a wavelength of 520 nm after the humidity and heat test, _T3 ' is the 100 μm-converted transmittance at a wavelength of 580 nm after the humidity and heat test, _T4 ' is the 100 μm-converted transmittance at a wavelength of 660 nm after the humidity and heat test. The 100 μm-equivalent transmittance at nm, the 100 μm-equivalent transmittance T (%), the combined thickness L (μm) of the adhesive sheet and the polarizing element, and the measured transmittance t (%) satisfy the relationship log ₁₀ (T/100) = (100/L) × log ₁₀ (t/100). A polarizing plate with an adhesive, comprising a polarizing element having a first principal surface and a second principal surface; and a first adhesive sheet disposed in contact with the first principal surface of the polarizing element. The first adhesive sheet is used for bonding to a cover window of an image display device. The first adhesive sheet comprises an adhesive composition containing an acrylic-based polymer and 0.05 to 10 parts by weight of a UV absorber per 100 parts by weight of the acrylic-based polymer. The total amount of nitrogen-containing monomers, hydroxyl-containing monomers, and carboxyl-containing monomers in the acrylic-based polymer is 8 parts by weight or less per 100 parts by weight of the total monomer components. When the polarizing plate with an adhesive is placed in an environment at a temperature of 85°C and a relative humidity of 85% for 100 hours, the following δT ₁ is expressed: , δT ₂ , δT ₃ and δT ₄ are all 0.95-1.05; δT _n = (T _n '/ΣT _i ')/(T _n /ΣT _i ) n and i are integers from 1 to 4, T ₀ is the 100 μm-converted transmittance at a wavelength of 380 nm before the humidity and heat test, T ₁ is the 100 μm-converted transmittance at a wavelength of 450 nm before the humidity and heat test, T ₂ is the 100 μm-converted transmittance at a wavelength of 520 nm before the humidity and heat test, T ₃ is the 100 μm-converted transmittance at a wavelength of 580 nm before the humidity and heat test, T ₄ is the 100 μm-converted transmittance at a wavelength of 660 nm before the humidity and heat test, T ₀ ' is the 100 μm-converted transmittance at a wavelength of 380 nm after the humidity and heat test. nm, the 100 μm-converted transmittance. T ₁ ' is the 100 μm-converted transmittance at a wavelength of 450 nm after the humidity and heat test. T ₂ ' is the 100 μm-converted transmittance at a wavelength of 520 nm after the humidity and heat test. T ₃ ' is the 100 μm-converted transmittance at a wavelength of 580 nm after the humidity and heat test. T ₄ ' is the 100 μm-converted transmittance at a wavelength of 660 nm after the humidity and heat test. The 100 μm-converted transmittance T (%), the combined thickness L (μm) of the adhesive sheet and the polarizing element, and the measured transmittance t (%) satisfy the relationship: log ₁₀ (T/100) = (100/L) × log ₁₀ (t/100). The polarizing plate with an adhesive according to claim 1 or 2, wherein the acrylic-based polymer contains 0.1 parts by weight or more of a hydroxyl monomer relative to 100 parts by weight of the total monomer components. The polarizing plate with an adhesive as claimed in claim 3, wherein the acrylic-based polymer has a crosslinked structure formed by an isocyanate-based crosslinking agent. The polarizing plate with adhesive according to claim 1 or 2 further comprises a second adhesive sheet on the second main surface side of the polarizing element. The polarizing plate with adhesive as claimed in claim 5, wherein the second adhesive sheet is laminated in contact with the second main surface of the polarizing element. The polarizing plate with adhesive as claimed in claim 5, wherein the second adhesive sheet is laminated on the second main surface of the polarizing element via other layers. An image display device comprises a second adhesive sheet, a polarizing plate with an adhesive as described in any one of claims 1 to 4, and a cover window on the surface of an image display unit in sequence, wherein the first adhesive sheet of the polarizing plate with an adhesive is adhered to the cover window.