JP7614857B2 - Optical pressure-sensitive adhesive sheet, laminate, and laminated structure - Google Patents

Description

The present invention relates to an optical adhesive sheet, a laminate comprising the optical adhesive sheet, and a laminated structure comprising the optical adhesive sheet.

An optical adhesive sheet is an adhesive sheet used to bond optical components. An example of the use of an optical adhesive sheet is to bond a display panel, such as a liquid crystal panel, to a cover panel provided on the outermost surface of the display device within a display device. The optical adhesive sheet fills the space between the display panel and the cover panel, thereby improving the visibility of the screen of the display panel. Optical adhesive sheets are usually required to have excellent transparency, and transparent optical adhesive sheets are also called optically clear adhesive (OCA) sheets.

For example, the following patent documents disclose prior art in the field related to optical adhesive sheets. Patent Document 1 discloses an optical adhesive containing an adhesive resin (A) with a weight average molecular weight of 200,000 to 2,000,000, a pigment (B), a dispersant (C), and a curing agent (D), and an optical adhesive sheet having an adhesive layer formed from the optical adhesive. It is disclosed that the optical adhesive has a color correction function for adjusting the color tone of optical components such as displays, is easy to form into a thin film, can maintain high adhesive strength and pigment dispersibility even when exposed to high temperature and high humidity environments for a long period of time, and has excellent transparency.

JP 2013-067782 A

Optical adhesive sheets used to bond optical components such as display panels, cover panels, and touch panels require high adhesive strength, as well as a thickness sufficient to cover the step formed by the bezel, and excellent flexibility to deform to conform to the step.

When a display panel, cover panel, touch panel, etc. are bonded together with an optical adhesive sheet and left in a high temperature and high humidity environment, for example at a temperature of 85°C and humidity of 85%, delay bubbles are generated and the adhesive interface between the optical adhesive sheet and the adherend may peel off. Bubbles that are not present immediately after the optical adhesive sheet is bonded to the adherend, but that subsequently form at the adhesive interface between the optical adhesive sheet and the adherend, are called delayed bubbles (delay bubbles). Delay bubbles are thought to be caused by the phenomenon in which a surface with weak adhesive strength peels off due to the pressure of water vapor generated from an adherend such as a cover panel such as a resin panel.

In addition, when a transparent optical adhesive sheet is used to bond optical components such as a display panel, a cover panel, or a touch panel, the boundary between the frame area of the display panel and the display screen can be easily noticeable, especially when the display panel is not lit. The present inventor investigated how to make the boundary between the frame area of the display panel and the display screen less noticeable by producing an optical adhesive sheet with reduced visible light transmittance by adding a pigment. However, it was found that even if the visible light transmittance of the optical adhesive sheet is adjusted by adding a pigment, the color tone of the optical adhesive sheet can change, which can affect the design of the display panel.

The present invention has been made in consideration of the above-mentioned current situation, and aims to provide an optical pressure-sensitive adhesive sheet that suppresses the generation of delay bubbles, is a thick film, has high conformability to an adherend, and maintains a suitable transmittance when used to bond optical components without impairing design, a laminate including the optical pressure-sensitive adhesive sheet, and a bonded structure including the above.

The inventors have investigated ways to realize a thick optical adhesive sheet that has the ability to conform to an adherend and suppresses delay bubbles, and have noticed that a thick film can be achieved by using a polyurethane layer as the middle layer, and that the occurrence of delay bubbles can be suppressed by placing an acrylic adhesive layer on the surface of the polyurethane layer.

The present inventors have studied a method for adjusting the visible light transmittance of an optical adhesive sheet in which an acrylic adhesive layer is disposed on the surface of the polyurethane layer. First, the inventors have studied the addition of carbon black as a black pigment to the acrylic adhesive layer on the surface. However, it has been confirmed that adding carbon black to the acrylic adhesive layer increases the yellowness and reduces the designability, although the visible light transmittance of the optical adhesive sheet can be adjusted. According to the inventors' studies, a light-shielding portion is generally provided in the frame area of a display panel by decorative printing or the like, and the light-shielding portion is often bluish black. Therefore, it has been found that the optical adhesive sheet used for bonding display panels and the like is also preferably bluish, and that if the yellowness is too high, the boundary between the frame area and the display screen becomes more noticeable and the designability is reduced. The inventors have further studied and found that by using a complex oxide pigment as a black pigment, the visible light transmittance can be adjusted without increasing the yellowness, and have completed the present invention.

The optical adhesive sheet of the present invention has a first surface acrylic adhesive layer, an intermediate polyurethane layer, and a second surface acrylic adhesive layer in this order, and at least one of the first surface acrylic adhesive layer and the second surface acrylic adhesive layer contains a complex oxide pigment.

The above-mentioned composite oxide pigment is preferably a black pigment.

The above-mentioned composite oxide pigment preferably contains at least one of iron and manganese.

The visible light transmittance is preferably 30% or more and 80% or less.

The total thickness is preferably 200 μm or more and 2000 μm or less.

The laminate of the present invention is characterized in that it is a laminate of the optical adhesive sheet of the present invention, a first release film covering one side of the optical adhesive sheet, and a second release film covering the other side of the optical adhesive sheet.

The laminated structure of the present invention is characterized by comprising a first adherend, a second adherend, and the optical adhesive sheet of the present invention that bonds the first adherend and the second adherend.

The present invention can provide an optical pressure-sensitive adhesive sheet that suppresses the generation of delay bubbles, has a thick film, has high conformability to an adherend, and maintains a suitable transmittance when used to bond optical components without impairing design, as well as a laminate and bonded structure that include the optical pressure-sensitive adhesive sheet.

1 is a cross-sectional view illustrating an example of the optical pressure-sensitive adhesive sheet of the present invention. FIG. 1 is a cross-sectional view illustrating a schematic example of a laminate of the present invention. FIG. 1 is a cross-sectional view illustrating a schematic example of a display device with a touch panel using the optical pressure-sensitive adhesive sheet of the present invention.

[Optical adhesive sheet]
The optical adhesive sheet of the present invention is characterized in that it has a first surface acrylic adhesive layer, an intermediate polyurethane layer, and a second surface acrylic adhesive layer in this order, and at least one of the first surface acrylic adhesive layer and the second surface acrylic adhesive layer contains a complex oxide-based pigment.

Figure 1 is a cross-sectional view showing a schematic example of an optical adhesive sheet of the present invention. As shown in Figure 1, the optical adhesive sheet 10 of the present invention has a first acrylic adhesive surface layer 11, an intermediate polyurethane layer 12, and a second acrylic adhesive surface layer 13, in this order. The intermediate polyurethane layer 12 is preferably thicker than the first acrylic adhesive surface layer 11 and the second acrylic adhesive surface layer 13.

The optical adhesive sheet 10 ensures the flexibility and conformability of the optical adhesive sheet 10 by the intermediate polyurethane layer 12, while the occurrence of delay bubbles can be suppressed by disposing the first and second surface acrylic adhesive layers on the surface of the intermediate polyurethane layer 12. In particular, display panels for vehicles are sometimes used in high-temperature environments and are prone to the occurrence of delay bubbles, but by using the optical adhesive sheet of the present invention to bond display panels for vehicles and the like, the occurrence of delay bubbles can be suppressed even in high-temperature environments.

The thickness (total thickness) of the optical adhesive sheet 10 of the present invention is preferably 200 μm or more and 2000 μm or less. By making the total thickness 200 μm or more, in addition to being able to cover the steps of the adherend, the sheet can also be suitably used for bonding a curved display having a curved display screen. If the thickness is less than 200 μm, the flexibility of the optical adhesive sheet 10 decreases, and when one side of the optical adhesive sheet is attached to the surface of an optical member, the optical adhesive sheet cannot cover the unevenness or steps present on the surface of the optical member, and the other side of the optical adhesive sheet and the surface of the other optical member cannot be bonded with sufficient adhesive strength. A more preferred lower limit of the thickness of the optical adhesive sheet 10 is 300 μm, an even more preferred lower limit is 500 μm, and a particularly preferred lower limit is 700 μm. The thickness of each layer and the total thickness can be measured, for example, using a displacement sensor ZW-S20 manufactured by Omron Corporation.

The visible light transmittance of the optical adhesive sheet 10 is preferably 30% or more and 80% or less. By having the visible light transmittance of 30% or more and 80% or less, when the optical adhesive sheet 10 is used to bond optical components such as a display panel, the boundary between the frame region of the display panel and the display screen can be made less noticeable when the display panel is turned off while suppressing the influence on the image display when the display panel is turned on. If the visible light transmittance is less than 30%, the display image when the display panel is turned on may be difficult to see, and it may be necessary to increase the brightness of the light source of the display device. In addition, since it is necessary to increase the amount of colorant added, there is a concern that the adhesive strength may decrease. On the other hand, if the visible light transmittance exceeds 80%, the boundary between the frame region of the display panel and the display screen becomes more easily visible. The visible light transmittance is a transmittance measured by a method conforming to the "visible light transmittance test" specified in JIS A 5759. The wavelength range of visible light in this test is 380 to 780 nm.

The optical adhesive sheet 10 preferably has b* of 1 or less in the L*, a*, b* color system. When the b* is 1 or less, the optical adhesive sheet 10 is visually recognized as having a bluish color tone with a low yellowness, and when the optical adhesive sheet 10 is used to bond optical components such as a display panel, the boundary between the frame region and the display screen can be made less noticeable. On the other hand, when the b* exceeds 1, the yellowness is strongly perceived, the boundary between the frame region and the display screen is easily noticeable, and the design may be deteriorated. The L*, a*, b* color system is a value measured by a method conforming to JIS K 7105. The L*, a*, b* color system can be measured using a color difference meter (CM-3700A, manufactured by Konica Minolta, Inc.).

<Surface acrylic adhesive layer>
The first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 are both layers constituting the outermost surface of the optical pressure-sensitive adhesive sheet 10. At least one of the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 contains a complex oxide pigment. The complex oxide pigment is an inorganic pigment in which two or more metal oxides are chemically bonded by high heat or the like. Only one of the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 may contain a complex oxide pigment, or both the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 may contain a complex oxide pigment. When it is desired to lower the visible light transmittance of the optical pressure-sensitive adhesive sheet 10, the complex oxide pigment can be added separately to the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13, so from the viewpoint of suppressing the ejection of the complex oxide pigment, it is preferable that both the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 contain a complex oxide pigment.

The optical adhesive sheet 10 of the present invention can obtain step-following properties by forming the intermediate polyurethane layer 12 thick, but by adding a complex oxide pigment to at least one of the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13, the visible light transmittance and color tone of the optical adhesive sheet 10 can be adjusted without being affected by the thickness of the intermediate polyurethane layer 12. In addition, by using a complex oxide pigment as a colorant, the visible light transmittance can be controlled without increasing the yellowness (b* value when expressed in the L*, a*, b* color system) of the optical adhesive sheet 10. It is believed that the complex oxide pigment contains multiple types of metal oxides, which can suppress the yellowness. On the other hand, carbon black has a large absorption of short wavelengths (blue region), so it is believed that the yellowness is strongly perceived.

The above-mentioned composite oxide pigment is preferably a black pigment. When the optical adhesive sheet 10 is used to bond optical components such as a display panel, it is preferable to use a black pigment, which is an achromatic color, in consideration of the small effect on the color tone of the displayed image when the display panel is turned on and the harmony between the display screen and the frame area when the display panel is turned off.

The above-mentioned complex oxide pigment preferably contains at least one of iron and manganese. Examples of the above-mentioned complex oxide pigment include complex oxide pigments containing iron and manganese, complex oxide pigments containing iron, cobalt and chromium, and complex oxide pigments containing copper, chromium and manganese. Of these, complex oxide pigments containing both iron and manganese are more preferred. A specific example of a colorant containing the above-mentioned complex oxide pigment containing iron and manganese is "NSP-AY 805B BLACK" manufactured by Nikko Bix Co., Ltd. The above-mentioned colorant may contain resin, solvent, additives, etc. in addition to the complex oxide pigment.

The content of the above-mentioned complex oxide pigment per 100 parts by weight of the acrylic resin is preferably 0.1 parts by weight or more and 1.5 parts by weight or less. A more preferred lower limit of the content of the above-mentioned complex oxide pigment per 100 parts by weight of the acrylic resin is 0.3 parts by weight, and a more preferred upper limit is 0.9 parts by weight.

The first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 are layers containing an acrylic resin. The acrylic resin is obtained by curing an acrylic resin composition. Examples of the acrylic resin composition include those containing a (meth)acrylic acid ester polymer or a copolymer thereof (hereinafter also referred to as a (meth)acrylic copolymer) and a crosslinking agent.

The (meth)acrylic copolymer may be, for example, a copolymer of an alkyl (meth)acrylate ester and a carboxyl group-containing monomer.

The above-mentioned (meth)acrylic acid alkyl esters include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 18 carbon atoms (CH ₂ ═CR ¹ -COOR ² ; R ¹ is a hydrogen atom or a methyl group, and R ² is an alkyl group with 1 to 18 carbon atoms), and the number of carbon atoms in the alkyl group is preferably 4 to 12.

Examples of (meth)acrylic acid alkyl esters having an alkyl group of 1 to 18 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. These may be used alone or in combination of two or more.

The above-mentioned carboxyl group-containing monomers include, for example, carboxyl group-containing (meth)acrylates such as β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, succinic acid mono(meth)acryloyloxyethyl ester, and ω-carboxypolycaprolactone mono(meth)acrylate; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. These may be used alone or in combination of two or more.

The crosslinking agent may be, for example, a component capable of undergoing a crosslinking reaction with the crosslinkable functional group derived from the crosslinkable functional group-containing monomer contained in the (meth)acrylic copolymer. Specific examples of the crosslinking agent include isocyanate compounds, metal chelate compounds, and epoxy compounds. The crosslinking agents may be used alone or in combination of two or more kinds.

The first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 are preferably moisture permeable. When the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 are moisture permeable, water vapor, which is thought to be the cause of delay bubble generation, is less likely to accumulate at the adhesive interface with the adherend, and the generation of delay bubbles can be further suppressed.

The moisture permeability of the first surface acrylic pressure-sensitive adhesive layer 11 and the second surface acrylic pressure-sensitive adhesive layer 13 is preferably 400 to 800 g/m ² ·h. This is because when the moisture permeability is in the above range, the occurrence of delay bubbles can be sufficiently suppressed when a laminated structure using the optical pressure-sensitive adhesive sheet 10 is placed in a high temperature and high humidity environment (temperature 85°C, humidity 85%) for a long period of time (for example, 1000 hours). A more preferable lower limit of the moisture permeability is 500 g/m ² ·h, and a more preferable upper limit is 750 g/m ² ·h.

The moisture permeability is measured based on the A-1 method (calcium chloride method) of JIS L1099 (2012) "Test method for moisture permeability of textile products". In the measurement of moisture permeability, a test specimen is prepared by attaching a test piece to a test cup containing about 33 g of moisture absorbent (calcium chloride) and sealing it, and the test specimen is placed in a thermo-hygrostat at a temperature of 40°C ± 2°C and a humidity of 90 ± 5% RH at a position where the wind speed does not exceed 0.8 m/s about 10 mm above, and the mass a1 (unit: g) of the test specimen is measured immediately after removal after one hour. After measuring the mass a1, the test specimen is again placed in the same position in the thermo-hygrostat, and the mass a2 (unit: g) of the test specimen is measured immediately after removal after one hour. Then, the moisture permeability is calculated by the following formula.
Moisture permeability [unit: g/ ^m2 ·h] = (a2-a1)/moisture permeability area [unit: ^m2 ]

The moisture permeability can be adjusted by the composition of the acrylic resin that constitutes the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13. For example, a commonly known method is to construct the acrylic resin as a copolymer and adjust the ratio of components that contribute to moisture permeability (see JP 2015-227395 A and JP 5920519 B).

The thickness of the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 is preferably 10 μm or more and 100 μm or less. If the thickness is less than 10 μm, there is a risk that sufficient adhesive strength cannot be obtained to sufficiently suppress delayed bubbles. On the other hand, if the thickness exceeds 100 μm, there is a risk that the flexibility (step followability) sufficient to follow the steps present on the surface of the adherend to which the optical adhesive sheet is attached cannot be obtained. In addition, when the optical adhesive sheet is used to bond substrates having different elasticity when the environment changes, such as bonding a glass substrate and a resin substrate, the optical adhesive sheet may not be able to follow the dimensional change of the substrate when the environment changes, and may peel off. From the viewpoint of further suppressing the generation of delayed bubbles, the thickness of the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 is more preferably 20 μm or more. Considering flexibility, the more preferred upper limit of the thickness of the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 is 80 μm, and the even more preferred upper limit is 50 μm.

<Intermediate polyurethane layer>
The intermediate polyurethane layer 12 is a layer containing polyurethane. By containing polyurethane in the intermediate polyurethane layer 12, an intermediate polyurethane layer 12 having excellent transparency and conformability can be obtained. Since polyurethane is flexible, the optical adhesive sheet 10 of the present invention stretches well and is very difficult to tear when a tensile stress is applied. Therefore, it can be peeled off without leaving any adhesive residue. Furthermore, since polyurethane has a high dielectric constant, the optical adhesive sheet 10 can obtain a high electrostatic capacitance, and can be suitably used for bonding capacitive touch panels.

The intermediate polyurethane layer 12 is preferably a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component. Thermosetting polyurethane can be formed into a film without using a solvent, which allows the intermediate polyurethane layer 12 to be made thick. In addition, since the intermediate polyurethane layer 12 contains thermosetting polyurethane, it is possible to obtain a highly reliable intermediate polyurethane layer 12 that has excellent flexibility and transparency even when formed into a thick film, and is less likely to whiten even in high temperature and high humidity environments. The above-mentioned thermosetting polyurethane is obtained, for example, by reacting a polyol component with a polyisocyanate component, and preferably has a structure shown in the following formula (A).

In the above formula (A), R represents the portion of the polyisocyanate component excluding the NCO group, R' represents the portion of the polyol component excluding the OH group, and n represents the number of repeating units.

The thermosetting polyurethane is preferably not acrylic-modified, and preferably does not contain any moiety derived from acrylic acid ester, methacrylic acid ester, or the like in the main chain. When the thermosetting polyurethane is acrylic-modified, it is hydrophobic, and therefore water is more likely to aggregate in a high-temperature, high-humidity environment. This water aggregation can cause whitening, foaming, or the like, and impair the optical properties. Therefore, by making the thermosetting polyurethane not acrylic-modified, it is possible to prevent the deterioration of the optical properties due to whitening, foaming, or the like in a high-temperature, high-humidity environment. In the thermosetting polyurethane, the total amount of the monomer units derived from the polyol component and the monomer units derived from the polyisocyanate component is preferably 80 mol % or more of the monomer units constituting the entire thermosetting polyurethane.

The polyol component and the polyisocyanate component can be liquid at room temperature (23°C), and a thermosetting polyurethane can be obtained without using a solvent. Other components such as a tackifier can be added to either the polyol component or the polyisocyanate component, and are preferably added to the polyol component. When producing the intermediate polyurethane layer 12, there is no need to remove the solvent, so a uniform sheet can be formed with a large thickness. In addition, the intermediate polyurethane layer 12 can be made thick and is flexible, so it has excellent impact resistance.

The optical adhesive sheet with the intermediate polyurethane layer 12 can be used to bond a transparent member having a transparent conductive film on its surface to a cover panel, and when other members are used, it can also be used to bond a display panel or a transparent member having a transparent conductive film on its surface to other members. When the optical adhesive sheet with the intermediate polyurethane layer 12 is used to bond a display panel to a transparent member having a transparent conductive film on its surface (touch panel), the step formed by the bezel arranged on the outer edge of the display panel can be covered by the optical adhesive sheet.

The intermediate polyurethane layer 12 containing thermosetting polyurethane can maintain its optical properties even when formed thick, so by forming the intermediate polyurethane layer 12 thick, a thick optical adhesive sheet 10 can be created without changing the visible light transmittance or color. On the other hand, since thermosetting polyurethane is a solvent-free system, it is difficult to mix it uniformly with a powder colorant. In addition, it is difficult to add a colorant containing a solvent to the intermediate polyurethane layer 12 because the solvent separates from the thermosetting polyurethane composition. For these reasons, in the present invention, a colorant is added to at least one of the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13, rather than to the intermediate polyurethane layer 12.

The polyol component may, for example, be polyolefin polyol, polyether polyol, polycaprolactone polyol, polycarbonate polyol, polyester polyol, etc. These may be used alone or in combination of two or more kinds. Of these, it is preferable to use polyolefin polyol, etc. Specific examples of the polyolefin polyol include Epol (manufactured by Idemitsu Kosan Co., Ltd.).

The polyol component preferably contains 50% by weight or more of a polyol component having an olefin skeleton, and more preferably consists only of a polyol component having an olefin skeleton.

The polyolefin polyol has an olefin skeleton. In other words, it is preferable that the main chain is composed of polyolefin or a derivative thereof. The polyolefin polyol contains at least a polyol component having an olefin skeleton. Examples of the polyol component having an olefin skeleton include polybutadiene-based polyols such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, 1,2-polychloroprene polyol, and 1,4-polychloroprene polyol, polyisoprene-based polyols, and polyols in which the double bonds are saturated with hydrogen or halogen. The polyol component having an olefin skeleton may be a polyol obtained by copolymerizing an olefin compound such as styrene, ethylene, vinyl acetate, or acrylic ester with a polybutadiene-based polyol, or a hydrogenated product thereof. The polyol component having an olefin skeleton may have a linear structure or a branched structure. The polyol component having an olefin skeleton may be one type or two or more types.

As the polyisocyanate component, either one or both of hydrophilic polyisocyanate and hydrophobic polyisocyanate may be used. The hydrophilic polyisocyanate is a polyisocyanate having a hydrophilic unit, and the hydrophobic polyisocyanate is a polyisocyanate not having the hydrophilic unit. The hydrophilic polyisocyanate having the hydrophilic unit does not mean a polyisocyanate having improved hydrophilicity only by a structure derived from an isocyanate group, such as an isocyanurate structure or a biuret structure, but a polyisocyanate having a functional group (hydrophilic unit) that enhances hydrophilicity. The inclusion of a hydrophilic unit in the polyisocyanate component provides an effect of suppressing whitening due to moisture absorption.

The polyisocyanate component preferably contains a hydrophilic polyisocyanate and a hydrophobic polyisocyanate. By containing both a hydrophilic polyisocyanate and a hydrophobic polyisocyanate in the thermosetting polyurethane composition, the balance between hydrophilicity and hydrophobicity of the intermediate polyurethane layer 12 can be adjusted. When only a hydrophobic polyisocyanate is used, the intermediate polyurethane layer 12 may whiten due to moisture absorbed from the outside after the optical adhesive sheet is manufactured. On the other hand, when only a hydrophilic polyisocyanate is used, although whitening due to moisture absorption can be suppressed, it becomes difficult to mix with the polyol component, and transparency may decrease.

The hydrophilic units contained in the hydrophilic polyisocyanate are preferably polyalkylene oxide units. Examples of polyalkylene oxide units include polyethylene oxide units and polypropylene oxide units.

Hydrophilic units other than polyalkylene oxide units include, for example, units containing a carboxylic acid group, an alkali metal base of a carboxylic acid, a sulfonic acid group, an alkali metal base of a sulfonic acid, a hydroxyl group, an amide group, an amino group, etc. More specifically, examples include polyacrylic acid, an alkali metal salt of a polyacrylic acid, a copolymer containing a sulfonic acid group, an alkali metal salt of a copolymer containing a sulfonic acid group, polyvinyl alcohol, polyacrylamide, carboxymethylcellulose, an alkali metal salt of carboxymethylcellulose, polyvinylpyrrolidone, etc.

The hydrophilic polyisocyanate is preferably a modified polyisocyanate containing an ethylene oxide unit obtained by reacting an aliphatic and/or alicyclic polyisocyanate having an isocyanate group with an ether compound having a polyalkylene oxide unit. By using an aliphatic and/or alicyclic polyisocyanate, coloring and discoloration are less likely to occur, and the transparency of the optical adhesive sheet can be more reliably ensured over a long period of time. In addition, by reacting an ether compound having a polyalkylene oxide unit to form a modified product, the polyisocyanate component can suppress whitening due to the action of the hydrophilic portion (polyalkylene oxide unit), and can exhibit compatibility with low-polarity tackifiers, plasticizers, etc. due to the action of the hydrophobic portion (other units).

Specific examples of modified polyisocyanates containing ethylene oxide units include Tosoh's Coronate 4022, Aquanate 130, and Aquanate 140.

Hydrophobic polyisocyanates include IPDI (isophorone diisocyanate)-based polyisocyanates and HDI (hexamethylene diisocyanate)-based polyisocyanates. A specific example of an IPDI-based polyisocyanate is Desmodur I manufactured by Sumika Bayer Urethane Co., Ltd. A specific example of an HDI-based polyisocyanate is HC-247 manufactured by Nippon Polyurethane Industry Co., Ltd.

The α ratio of the intermediate polyurethane layer 12 (molar number of OH groups derived from the polyol component/molar number of NCO groups derived from the polyisocyanate component) is preferably 1.0 or more and 1.8 or less. The lower the α ratio, the harder the intermediate polyurethane layer 12 is, and the higher the α ratio, the softer the intermediate polyurethane layer 12 is. By setting the α ratio of the intermediate polyurethane layer 12 to 1.0 or more and 1.8 or less, it is possible to suppress the generation of delay bubbles and ensure the flexibility of the optical adhesive sheet. A more preferable upper limit of the α ratio is 1.5. If the α ratio is less than 1.0, the amount of the polyisocyanate component is excessive relative to the amount of the polyol component, so that the intermediate polyurethane layer becomes hard. If the intermediate polyurethane layer becomes hard, it may be difficult to ensure the flexibility required for the optical adhesive sheet. In addition, if the α ratio is less than 1.0, the adhesive strength required for the optical adhesive sheet may not be ensured. If the α ratio exceeds 1.8, the thermosetting polyurethane composition may not be sufficiently cured.

The thermosetting polyurethane composition may further contain a plasticizer. The plasticizer is not particularly limited as long as it is a compound used to impart flexibility to the thermosetting polyurethane, but from the viewpoints of compatibility and weather resistance, it is preferable that the plasticizer contains a carboxylic acid-based plasticizer.

The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is a catalyst used in a urethanization reaction, and examples thereof include organic tin compounds such as di-n-butyltin dilaurate, dimethyltin dilaurate, dibutyltin oxide, and tin octanoate; organic titanium compounds; organic zirconium compounds; tin carboxylates; bismuth carboxylates; and amine catalysts such as triethylenediamine.

The thickness of the intermediate polyurethane layer 12 is preferably 100 μm or more and 2000 μm or less. The intermediate polyurethane layer 12 can be thickened by containing polyurethane, and when used for bonding touch panels and the like, it can sufficiently cover steps such as bezels. If the thickness is less than 100 μm, the flexibility of the optical adhesive sheet as a whole decreases, and when one side of the optical adhesive sheet is bonded to the surface of an optical member, the unevenness or steps present on the surface of the optical member cannot be covered, and the optical member and other members cannot be bonded with sufficient adhesive strength via the optical adhesive sheet. A more preferred lower limit of the thickness of the intermediate polyurethane layer 12 is 200 μm, a further more preferred lower limit is 300 μm, and a particularly preferred lower limit is 500 μm. A more preferred upper limit of the thickness of the intermediate polyurethane layer 12 is 1800 μm, a further more preferred upper limit is 1500 μm, and a particularly preferred upper limit is 1000 μm.

The optical adhesive sheet 10 may have a first surface acrylic adhesive layer 11, an intermediate polyurethane layer 12, and a second surface acrylic adhesive layer 13 in this order, and the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 may be located on the outermost surface (the surface in contact with the adherend) of the optical adhesive sheet 10. The optical adhesive sheet 10 may further have other layers, but preferably has a three-layer structure of the first surface acrylic adhesive layer 11, the intermediate polyurethane layer 12, and the second surface acrylic adhesive layer 13. That is, it is preferable that the first surface acrylic adhesive layer 11 and the intermediate polyurethane layer 12 are in contact with each other, and it is preferable that the second surface acrylic adhesive layer 13 and the intermediate polyurethane layer 12 are in contact with each other.

The thermosetting polyurethane composition may contain various additives such as tackifiers (tackifiers), stabilizers, antioxidants, antifungals, and flame retardants, as necessary, to the extent that they do not impair the required properties of the optical adhesive sheet.

<Method of manufacturing optical pressure-sensitive adhesive sheet>
The method for laminating the first surface acrylic adhesive layer 11, the intermediate polyurethane layer 12, and the second surface acrylic adhesive layer 13 in this order is not particularly limited, and examples include a method in which the first surface acrylic adhesive layer 11, the second surface acrylic adhesive layer 13, and the intermediate polyurethane layer 12 are separately prepared and then bonded together.

The method for producing the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 is not particularly limited, and may be, for example, a method in which an acrylic resin, a complex oxide pigment, etc. are mixed to obtain an acrylic resin composition, and then the acrylic resin composition is formed into a film using a general-purpose film-forming device or film-forming method such as various coating devices, bar coaters, doctor blades, etc. Also, the first surface acrylic adhesive layer 11 and the second surface acrylic adhesive layer 13 may be produced using a centrifugal molding method.

The method for producing the intermediate polyurethane layer 12 is not particularly limited. For example, when the intermediate polyurethane layer 12 is a cured product of a thermosetting polyurethane composition, the method preferably includes a step of preparing a thermosetting polyurethane composition by stirring and mixing a polyol component and a polyisocyanate component, and a step of curing the thermosetting polyurethane composition. The thermosetting polyurethane composition may further contain a tackifier.

When the intermediate polyurethane layer 12 is a cured product of a thermosetting polyurethane composition, a specific example of the manufacturing method is to mix a polyol component, a polyisocyanate component, and, if necessary, other components such as a catalyst, and stir them with a mixer or the like to obtain a liquid or gel-like thermosetting polyurethane composition. When a tackifier is contained, the tackifier is added to the polyol component in advance, and a master batch is prepared by heating and stirring to dissolve the tackifier, and then mixed with other materials. The thermosetting polyurethane composition is then immediately put into a molding device, and the thermosetting polyurethane composition is moved while sandwiched between a pair of release films, causing a curing reaction (crosslinking reaction) to occur, whereby the thermosetting polyurethane composition is semi-cured, and a sheet integrated with the pair of release films is obtained. The intermediate polyurethane layer 12 is then obtained by causing a crosslinking reaction in an oven for a certain period of time.

[Laminate]
A release film may be attached to both sides of the optical pressure-sensitive adhesive sheet of the present invention. FIG. 2 is a cross-sectional view showing an example of the laminate of the present invention. A laminate 20 (hereinafter also referred to as the "laminate of the present invention") in which the optical pressure-sensitive adhesive sheet 10 of the present invention, a first release film 21 covering one side of the optical pressure-sensitive adhesive sheet 10, and a second release film 22 covering the other side of the optical pressure-sensitive adhesive sheet 10 are laminated is also one aspect of the present invention. According to the laminate of the present invention, the first release film and the second release film can protect both sides of the optical pressure-sensitive adhesive sheet of the present invention until just before it is attached to the adherend. This prevents a decrease in adhesion to the optical pressure-sensitive adhesive sheet of the present invention and adhesion of foreign matter. In addition, the optical pressure-sensitive adhesive sheet of the present invention is prevented from sticking to anything other than the adherend, thereby improving handleability.

The first release film and the second release film can be, for example, a PET film. The material and thickness of the first release film and the second release film may be the same or different.

The bonding strength (peel strength) of the optical adhesive sheet and the first release film of the present invention is preferably different from the bonding strength (peel strength) of the optical adhesive sheet and the second release film of the present invention. By having the bonding strengths different from each other in this way, it becomes easy to peel only one of the first release film and the second release film (the release film with the lower bonding strength) from the laminate of the present invention, bond the exposed first surface of the optical adhesive sheet to the first adherend, and then peel the other of the first release film and the second release film (the release film with the higher bonding strength) and bond the exposed second surface of the optical adhesive sheet to the second adherend.

At least one of the surface of the first release film that contacts the optical pressure-sensitive adhesive sheet of the present invention and the surface of the second release film that contacts the optical pressure-sensitive adhesive sheet of the present invention may be subjected to an easy-peel treatment (release treatment). Examples of easy-peel treatments include silicone treatment.

[Laminated structure]
A laminated structure comprising a first adherend, a second adherend, and the optical adhesive sheet of the present invention that bonds the first adherend and the second adherend (hereinafter also referred to as the "laminate structure of the present invention") is also an aspect of the present invention.

The application of the laminated structure of the present invention is not particularly limited, and may be a display panel such as a liquid crystal panel and a cover panel laminated together with an optical adhesive sheet. By laminating the display panel and the cover panel together with an optical adhesive sheet and eliminating the air layer between the display panel and the cover panel, the visibility of the display panel can be improved. When the display panel is disposed in a housing (bezel) having an opening in the display section, the bezel is disposed on the outer edge of the display panel. Therefore, a step corresponding to the thickness of the bezel is formed. The method of laminating the display panel and the cover panel by overlapping the optical adhesive sheet not only in the center of the display panel but also in the area where the bezel is disposed is also called "bezel-on lamination". The laminated structure formed by bezel-on lamination is also called "bezel-on lamination structure".

The optical adhesive sheet used in the present invention is flexible and can be made thick, making it suitable for bezel-on lamination. The laminated structure of the present invention may have a bezel-on lamination structure, and may have, for example, a structure in which an optical adhesive sheet and a support member are provided between a first adherend and a second adherend, the support member having a step-forming portion disposed on the outer edge of the first adherend, and the optical adhesive sheet may include a thick film portion that bonds the first adherend and the second adherend, and an end portion sandwiched between the step-forming portion and the second adherend. The resin substrate may be the first adherend or the second adherend.

Figure 3 is a cross-sectional view showing a schematic example of a display device with a touch panel using the optical adhesive sheet of the present invention. The display device with a touch panel is a laminated structure having a bezel-on laminated structure. The laminated structure 50 shown in Figure 3 has a configuration in which an optical adhesive sheet 10 and an upper bezel (support member) 41 are provided between a first adherend 51 and a second adherend 52, and may be, for example, a part of an electronic device such as a display device. The upper bezel 41 is integrated with the lower bezel 42 to form a housing (bezel) that houses the first adherend 51.

In the laminated structure 50, the optical adhesive sheet 10 includes a thick film portion that bonds the first adherend 51 and the second adherend 52, and an end portion sandwiched between the step-forming portion of the upper bezel 41 and the second adherend 52. The end portion of the optical adhesive sheet 10 is sandwiched between the second adherend 52 and the step-forming portion of the upper bezel 41, and is therefore difficult to peel off. In addition, since the optical adhesive sheet 10 reaches the step-forming portion of the upper bezel 41, the entire upper surface of the first adherend 51 is covered by the step-forming portion of the upper bezel 41 or the optical adhesive sheet 10, and moisture absorption of the first adherend 51 can be prevented. When a polarizing plate is located on the upper surface of the first adherend 51, moisture absorption of the polarizing plate can be prevented. If the polarizing plate absorbs moisture, performance deterioration may be accelerated, or the absorbed moisture may evaporate in a high-temperature environment, causing delayed bubbles.

The combination of the first adherend 51 and the second adherend 52 is not particularly limited, and examples include various members constituting a display device, such as a display panel, a touch panel (a glass substrate with an ITO transparent conductive film), and a cover panel (cover glass). The first adherend 51 may be a display panel or a touch panel, and the second adherend 52 may be a cover panel, or the first adherend 51 may be a display panel and the second adherend 52 may be a touch panel.

The type of display panel is not particularly limited, and examples include a liquid crystal panel and an organic electroluminescence panel (organic EL panel). A polarizing plate, a retardation film, etc. may be disposed on the surface of the display panel to which the optical adhesive sheet 10 is attached. By bonding various components within the display device using the optical adhesive sheet 10, it is possible to eliminate the air layer (air gap) within the display device, and to improve the visibility of the display screen. Furthermore, when a polarizing plate is disposed, the optical adhesive sheet 10 can effectively prevent the polarizing plate from absorbing moisture.

When viewed in a plane, the upper bezel 41 is a frame-shaped member arranged around the optical adhesive sheet 10, and at least a portion of it is arranged on the outer edge of the first adherend 51. The side of the portion (step-forming portion) arranged on the outer edge of the first adherend 51 forms a step. The shape of the side of the step-forming portion is not particularly limited, and the side of the step-forming portion may be perpendicular to the upper surface of the first adherend 51. When the first adherend 51 is a display panel, the upper bezel 41 is arranged in the frame region of the display device, and a light-shielding portion 52A may be provided on the outer edge of the first adherend 51 so that the upper bezel 41 is not visible to the user of the display device. The material of the upper bezel 41 is not particularly limited, and examples include metal, resin, etc.

The thickness of the upper bezel 41 (the size of the step) is not particularly limited, but is, for example, 200 to 1000 μm. If the thickness of the upper bezel 41 exceeds 200 μm, the thickness of the optical adhesive sheet 10 needs to be 300 μm (0.3 mm) or more, so an optical adhesive sheet thicker than a normal optical adhesive sheet is used.

The thickness of the thick film portion of the optical adhesive sheet 10 is preferably 1.5 times or more, and more preferably 2 times or more, the thickness of the step-forming portion of the upper bezel 41. This ensures sufficient thickness at the end of the optical adhesive sheet 10 sandwiched between the step-forming portion of the upper bezel 41 and the second adherend 52, and prevents peeling of the end. The thickness of the thick film portion of the optical adhesive sheet 10 in the laminated structure 50 is substantially the same as the thickness of the optical adhesive sheet 10 before lamination. In other words, the thickness of the optical adhesive sheet 10 before lamination is preferably 1.5 times or more, and more preferably 2 times or more, the thickness of the upper bezel 41.

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

(Raw material blend)
In the following examples and comparative examples, the compounding raw materials used to prepare the thermosetting polyurethane compositions are as follows:
(A) Polyol component: Polyolefin polyol (EPOL (registered trademark)) manufactured by Idemitsu Kosan Co., Ltd.
(B) Polyisocyanate Component (B-1) Hydrophilic polyisocyanate Modified polyisocyanate containing ethylene oxide units ("Coronate 4022" manufactured by Tosoh Corporation)
(B-2) Hydrophobic polyisocyanate IPDI (isophorone diisocyanate)-based polyisocyanate ("Desmodur I" manufactured by Sumika Bayer Urethane Co., Ltd.)
(B-3) Isocyanate-based curing agent ("DY-70" manufactured by Soken Chemical Industries, Ltd.)
(C) Tackifire "Imarve P-100" manufactured by Idemitsu Kosan Co., Ltd.
(D) Catalyst Dimethyltin Dilaurate ("Fomrez catalyst UL-28" manufactured by Momentive)
(E) Acrylic resin (E-1) "SK1838" manufactured by Soken Chemical Industries, Ltd.
(E-2) "SK1875" manufactured by Soken Chemical Industries, Ltd.
(F) Colorant (F-1) Colorant containing a composite oxide pigment ("NSP-AY 805B BLACK" manufactured by Nikko Bix Co., Ltd.) (content of composite oxide pigment: 10 to 15% by weight)
(F-2) Carbon black pigment (solvent dispersion type) ("MHI Black #220" manufactured by Mikuni Pigment Co., Ltd.)

<Intermediate polyurethane layer>
(Production Example 1)
A thermosetting polyurethane composition having an α ratio of 1.5 was prepared by mixing and stirring 100 parts by weight of a polyol component (A), 4.7 parts by weight of a hydrophilic polyisocyanate (B-1), 4.7 parts by weight of a hydrophobic polyisocyanate (B-2), 10 parts by weight of a tackifier (C) and 0.01 parts by weight of a catalyst (D) using a reciprocating rotary mixer Aziter.

Tosoh's "Coronate 4022" is obtained by reacting a polyisocyanate made from hexamethylene diisocyanate and/or hexamethylene diisocyanate monomer as the starting material with an ether polyol having an average of three or more ethylene oxide units per molecule.

Then, the obtained thermosetting polyurethane composition was sandwiched between a pair of release films (PET films with a release-treated surface) and transported while being crosslinked and cured at an oven temperature of 50 to 90°C for several minutes to obtain a sheet with a release film. Then, a crosslinking reaction was carried out in a heating device for 10 to 15 hours to produce an intermediate polyurethane layer (thermosetting polyurethane layer) with release films on both sides.

(Production Example 2)
An intermediate polyurethane layer with a release film according to Production Example 2 was produced in the same manner as Production Example 1, except that a composite oxide pigment was added to the thermosetting polyurethane composition. In order to mix with the solventless thermosetting polyurethane composition, NSP-AY 805B BLACK was dried by volatilizing the solvent contained therein, and 0.01 part by weight of the composite oxide pigment was added per 100 parts by weight of the polyisocyanate component.

<Acrylic adhesive layer>
(Production Example 3)
(E-1) and (E-2) were blended at a solid content ratio of 5:5 to prepare an acrylic resin, and 0.6 parts by weight of an isocyanate-based curing agent (B-3) and 3 parts by weight of a colorant (F-1) containing a complex oxide-based pigment were added to 100 parts by weight of the acrylic resin to prepare an acrylic resin composition. The obtained acrylic resin composition was applied to a release film using a comma coater, dried in a drying oven at 80 to 120°C, and then a release film was placed on the coated surface. Then, the composition was heated at 40°C for one week to complete curing, and an acrylic pressure-sensitive adhesive layer with a release film according to Production Example 3 was prepared.

(Production Example 4)
An acrylic pressure-sensitive adhesive layer with a release film according to Production Example 4 was prepared in the same manner as in Production Example 3, except that 6 parts by weight of colorant (F-1) containing a complex oxide pigment was added to 100 parts by weight of the acrylic resin.

(Production Example 5)
An acrylic pressure-sensitive adhesive layer with a release film according to Production Example 5 was produced in the same manner as in Production Example 3, except that no colorant containing a complex oxide pigment was added.

(Production Example 6)
An acrylic pressure-sensitive adhesive layer with a release film according to Production Example 6 was prepared in the same manner as in Production Example 3, except that 0.24 parts by weight of a carbon black pigment (F-2) was added per 100 parts by weight of the acrylic resin instead of the colorant containing a complex oxide pigment.

The moisture permeability of the acrylic pressure-sensitive adhesive layers according to Production Examples 3 to 6, measured based on the A-1 method of JIS L1099 (2012), was 560 g/ ^m2 ·h.

[Example 1]
One intermediate polyurethane layer (thickness 450 μm) with the release film according to Production Example 1 and two acrylic pressure-sensitive adhesive layers (thickness 25 μm) with the release film according to Production Example 3 were prepared. The release films arranged on both sides of the intermediate polyurethane layer with the release film were peeled off, and one release film of the acrylic pressure-sensitive adhesive layer with the release film was peeled off. Then, the acrylic pressure-sensitive adhesive layer with the release film from which one release film was peeled off was laminated on both sides of the intermediate polyurethane layer so that the surface of the acrylic pressure-sensitive adhesive layer from which the release film was peeled off was in contact with the surface of the intermediate polyurethane layer. In this way, an optical pressure-sensitive adhesive sheet according to Example 1 having a total thickness of 500 μm and including a first surface acrylic pressure-sensitive adhesive layer, an intermediate polyurethane layer, and a second surface acrylic pressure-sensitive adhesive layer in this order, and a laminate according to Example 1 in which release films were arranged on both sides of the optical pressure-sensitive adhesive sheet were produced.

[Example 2]
An optical pressure-sensitive adhesive sheet and laminate according to Example 2 were produced in the same manner as in Example 1, except that the thickness of the intermediate polyurethane layer was changed to 950 μm.

[Example 3]
An optical adhesive sheet and laminate of Example 3 were prepared in the same manner as Example 1, except that one of the surface acrylic adhesive layers was replaced with an acrylic adhesive layer (thickness 25 μm) of Manufacturing Example 5 that did not contain a complex oxide-based pigment.

[Example 4]
An optical pressure-sensitive adhesive sheet and laminate of Example 4 were produced in the same manner as in Example 3, except that the thickness of the intermediate polyurethane layer was changed to 950 μm.

[Example 5]
The optical adhesive sheet and laminate of Example 5 were prepared in the same manner as Example 1, except that one each of the acrylic adhesive layer (thickness 25 μm) of Production Example 4 and the acrylic adhesive layer (thickness 25 μm) of Production Example 5 not containing a complex oxide-based pigment was used as the surface acrylic adhesive layer.

[Comparative Example 1]
An optical adhesive sheet and laminate of Comparative Example 1 were prepared in the same manner as in Example 1, except that two acrylic adhesive layers (thickness 25 μm) of Manufacturing Example 5, which did not contain a complex oxide-based pigment, were used.

[Comparative Example 2]
An optical adhesive sheet and laminate relating to Comparative Example 2 were prepared in the same manner as in Example 1, except that one acrylic adhesive layer (thickness 25 μm) from Production Example 6 containing a carbon black-based pigment and one acrylic adhesive layer (thickness 25 μm) from Production Example 5 not containing a complex oxide-based pigment were used as the surface acrylic adhesive layer.

[Comparative Example 3]
An optical adhesive sheet and laminate relating to Comparative Example 3 were prepared in the same manner as in Example 1, except that one intermediate polyurethane layer (thickness 450 μm) relating to Production Example 2 in which a carbon black-based pigment was added was used as the intermediate polyurethane layer, and two acrylic adhesive layers (thickness 25 μm) relating to Production Example 5 in which no complex oxide-based pigment was contained were used as the surface acrylic adhesive layers.

The optical adhesive sheets of the examples and comparative examples were evaluated using the following methods, and the results are summarized in Table 1 below.

<Dispersibility>
The optical pressure-sensitive adhesive sheets according to the examples and comparative examples were visually inspected, and a mark of "O" was given when no aggregation of the colorant was observed, and a mark of "X" was given when aggregation of the colorant was observed.

<Color Tone Evaluation>
Test pieces were prepared by sandwiching the optical pressure-sensitive adhesive sheets according to the examples and comparative examples between a pair of transparent glass plates, and the color tone of each test piece was measured using a color difference meter (Konica Minolta, CM-3700A) according to a method conforming to JIS K 7105. The color tone was expressed in the L*, a*, b* color system, with a value of ◯ when b* was 1 or less and a value of × when b* was greater than 1.

<Visible light transmittance>
Test pieces were prepared by sandwiching the optical pressure-sensitive adhesive sheets of the examples and comparative examples between a pair of transparent glass plates, and the visible light transmittance of each test piece was measured using a spectrophotometer (Nicolet 6700FTIR, manufactured by Thermo Scientific) in accordance with JIS A 5759.

As shown in Table 1, Examples 1 to 5, in which a composite oxide pigment was added to at least one of the first and second surface acrylic adhesive layers, had a color tone with a suppressed yellowish tinge while maintaining a suitable visible light transmittance. Comparing Examples 1 and 2, and Examples 3 and 4, it was confirmed that changing the thickness of the intermediate polyurethane layer did not affect the color tone or visible light transmittance.

On the other hand, Comparative Example 1, in which no oxide-based pigment was added to the surface acrylic adhesive layer, had too high a visible light transmittance, and when used to bond optical components, the boundary between the display area and the frame area of the display panel became noticeable. Comparative Example 2, in which a carbon black-based pigment was added to one of the surface acrylic adhesive layers, was able to suppress the visible light transmittance, but the b* value was high. Comparative Example 3, in which a complex oxide-based pigment was added to the intermediate polyurethane layer, was unable to mix the thermosetting polyurethane composition and the complex oxide-based pigment uniformly, and aggregation of the complex oxide-based pigment was observed.

10: Optical adhesive sheet 11: First surface acrylic adhesive layer 12: Intermediate polyurethane layer 13: Second surface acrylic adhesive layer 20: Laminate 21: First release film 22: Second release film 41: Upper bezel (support member)
42: Lower bezel 50: Laminated structure 51: First adherend 52: Second adherend 52A: Light shielding portion

Claims (6)

A first surface acrylic pressure-sensitive adhesive layer, an intermediate polyurethane layer, and a second surface acrylic pressure-sensitive adhesive layer in this order,
at least one of the first acrylic pressure-sensitive adhesive surface layer and the second acrylic pressure-sensitive adhesive surface layer contains a composite oxide pigment;
An optical pressure-sensitive adhesive sheet having a visible light transmittance of 30% or more and 80% or less . The optical adhesive sheet according to claim 1, characterized in that the composite oxide pigment is a black pigment. The optical adhesive sheet according to claim 1 or 2, characterized in that the composite oxide pigment contains at least one of iron and manganese. An optical adhesive sheet according to any one of claims 1 to 3, characterized in that the total thickness is 200 μm or more and 2000 μm or less. A laminate comprising an optical adhesive sheet according to any one of claims 1 to 4 , a first release film covering one side of the optical adhesive sheet, and a second release film covering the other side of the optical adhesive sheet. A laminated structure comprising a first adherend, a second adherend, and the optical pressure-sensitive adhesive sheet according to any one of claims 1 to 4 , which bonds the first adherend and the second adherend.

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