JP7472093B2 - Front panel, optical laminate and image display device - Google Patents

Description

The present invention relates to a front panel, an optical laminate, and an image display device.

As a front panel, for example, a front panel having a hard coat layer made of acrylic resin and a resin film made of polyimide resin has been proposed (for example, see Patent Document 1 below).

JP 2017-102443 A

In recent years, there has been a demand for even higher quality front panels.

The present invention provides a high-quality front panel, optical laminate, and image display device.

The present invention (1) includes a front panel having a protective resin layer and a hard coat layer in that order in the thickness direction, and the difference in refractive index between the protective resin layer and the hard coat layer is 0.04 or less.

In this front panel, the difference in refractive index between the protective resin layer and the hard coat layer is small, at 0.04 or less, so the front panel is of high quality and does not suffer from unevenness problems caused by refractive index differences.

The present invention (2) includes the front panel described in (1), in which the molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer is 5.0 mol % or less.

In this front panel, the molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer is low at 5.0 mol % or less, so the high quality of the front panel can be more reliably ensured.

The present invention (3) includes the front panel according to (1) or (2), in which the material of the protective resin layer is an acrylic resin or a polycarbonate resin, and the material of the hard coat layer is an acrylic resin.

In this front panel, the material of the protective resin layer is acrylic resin or polycarbonate resin, and the material of the hard coat layer is acrylic resin, so that the refractive index of the protective resin layer and the refractive index of the hard coat layer are similar, and the difference between the refractive index of the protective resin layer and the refractive index of the hard coat layer is reliably reduced, ensuring that high quality is maintained.

The present invention (4) further includes the front panel according to any one of (1) to (3), which further includes a substrate and an adhesive layer, the substrate, the adhesive layer, the protective resin layer, and the hard coat layer being arranged in that order in the thickness direction, and the substrate including a thin glass plate.

This front panel further comprises a substrate and an adhesive layer, with the substrate, adhesive layer, protective resin layer, and hard coat layer being arranged in that order in the thickness direction, and the substrate including a thin glass plate, which suppresses the occurrence of marks (such as wrinkles) left after bending, and allows high quality to be maintained.

The present invention (5) includes an optical laminate having a polarizing film and a front panel described in any one of (1) to (4) in that order toward the viewing side.

This optical laminate has the front panel described above, so it is of high quality.

The present invention (6) includes an image display device having an image display member and the optical laminate described in (5) in this order toward the viewing side.

This image display device is equipped with the optical laminate described above, so it is of high quality and does not suffer from unevenness caused by refractive index differences.

The front panel, optical laminate, and image display device of the present invention are of high quality and do not suffer from unevenness problems caused by refractive index differences.

FIG. 1 is a cross-sectional view of an organic EL display device as an embodiment of the image display device of the present invention. FIG. 2 is a cross-sectional view of one embodiment of the optical laminate of the present invention. FIG. 3 is a cross-sectional view of one embodiment of the front plate of the present invention. FIG. 4 is a cross-sectional view illustrating the bent state of the front panel in the bending test.

[Organic EL display device]
An organic electroluminescence display device, which is one embodiment of an image display device of the present invention, will be described with reference to Fig. 1. Hereinafter, the organic electroluminescence display device will be abbreviated as an organic EL display device.

The organic EL display device 1 has, for example, a flat plate shape, and is preferably configured to be bendable around a bending portion 25 located between two opposing sides 27 spaced apart in the surface direction (direction perpendicular to the front-to-back direction), and more preferably configured to be foldable. Each of the components described below is preferably configured to be bendable, and more preferably configured to be foldable.

As shown in FIG. 1, the organic EL display device 1 includes an image display member 3 and an optical laminate 2, arranged in that order toward the viewing side. In other words, in this organic EL display device 1, the optical laminate 2 and the image display member 3 are arranged in that order toward the side opposite the viewing side, which is the side viewed by the user. In the organic EL display device 1, the viewing side corresponds to the front side, and the side opposite the viewing side corresponds to the back side.

[Optical laminate]
The optical laminate 2 includes a front plate 4 and a polarizing film 5 in this order toward the back side.

[Front panel]
The front panel 4 is sometimes called a cover window or a window film. The front panel 4 includes a protective member 6 and a substrate 7 in this order toward the back side.

[Adhesive layer and layer structure]
The organic EL display device 1 also includes an adhesive layer 8 located between adjacent members in the front-back direction. The adhesive layer 8 includes a first adhesive layer 9 as an example of an adhesive layer, a second adhesive layer 10, and a third adhesive layer 11, in that order toward the back side. Therefore, in the organic EL display device 1, the protective member 6, the first adhesive layer 9, the substrate 7, the second adhesive layer 10, the polarizing film 5, the third adhesive layer 11, and the image display member 3 are arranged in that order toward the back side.

[Protective material]
The protective member 6 protects the front side of the substrate 7. The protective member 6 has a flat plate shape extending in the planar direction. The protective member 6 includes a protective resin layer 12 and a hard coat layer 13, which are arranged in this order toward the front side.

[Protective resin layer]
The protective resin layer 12 forms the back surface of the protective member 6. The protective resin layer 12 extends in the planar direction. The material of the protective resin layer 12 is not particularly limited as long as it is a resin that satisfies the in-plane retardation Re(550) and thickness direction retardation Rth(550) described later.

The molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer 12 is, for example, 10 mol% or less, preferably 5.0 mol% or less, more preferably 3.0 mol% or less, even more preferably 2.0 mol% or less, and most preferably 0.0 mol%. If the molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer 12 is equal to or less than the above-mentioned upper limit, the high quality of the front panel 4 can be more reliably maintained.

The molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer 12 is measured, for example, as follows. The protective resin layer 12 is decomposed into structural units by a known decomposition method. For example, it is immersed in an alcohol solvent (e.g., methanol) to obtain the soluble portion as a decomposition product. The structural units of the decomposition product (soluble portion) are then identified by a known analytical method (e.g., gas chromatography-mass spectrometry (GC-MS)).

Separately, the protective resin layer 12 is subjected to ¹ H-NMR measurement. Specifically, the protective resin layer 12 is dissolved in a solvent for ¹ H-NMR to prepare a solution containing the main component of the protective resin layer 12. The solution is then subjected to ¹ H-NMR measurement. Next, based on the structural units identified by the above analysis method, the molar ratio of structural units derived from aromatic compounds and the molar ratio of structural units derived from non-aromatic compounds are determined from the integral ratio of protons directly connected to aromatic rings and the integral ratio of other protons. An aromatic compound is a compound having at least one aromatic ring. A non-aromatic compound is a compound having no aromatic ring. Then, the ratio of the number of moles of structural units derived from aromatic compounds in the main component of the material of the protective resin layer 12 is determined as a percentage.

Examples of materials for the protective resin layer 12 include resins such as acrylic resins and polycarbonate resins. As materials for the protective resin layer 12, acrylic resins and polycarbonate resins are preferably used from the viewpoint of reducing the in-plane retardation Re(550) and thickness retardation Rth(550), and more preferably, acrylic resins are used from the viewpoint of suppressing the fluctuation of the in-plane retardation Re(550) and the fluctuation of the thickness retardation Rth(550) before and after bending in the bending portion 25. In addition, the above-mentioned resins preferably do not have structural units derived from aromatic compounds.

The acrylic resin has, for example, glutarimide units and unsaturated carboxylic acid alkyl ester units. The acrylic resin preferably does not have structural units derived from aromatic compounds. Specifically, the acrylic resin has structural units of glutarimide units represented by the following formula (1) and unsaturated carboxylic acid alkyl ester units represented by the following formula (2).

(In formula (1), ^R1 and ^R2 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. ^R3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms.)

(In formula (2), ^R4 and ^R5 each represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

In formula (1), examples of the alkyl group having 1 to 8 carbon atoms represented by R ¹ and R ² include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl.

^R1 is preferably methyl.

^R2 is preferably a hydrogen atom.

Examples of the alkyl group having 1 to 18 carbon atoms represented by ^R3 include nonyl, decyl, dodecyl, undecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl, in addition to the alkyl groups having 1 to 8 carbon atoms. Examples of the cycloalkyl group having 3 to 12 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclodecyl. Examples of the aryl group having 6 to 10 carbon atoms include phenyl and naphthyl. ^R3 is preferably an alkyl group, and more preferably methyl.

In formula (2), examples of the alkyl group having 1 to 6 carbon atoms represented by R ⁴ and R ⁵ include methyl, ethyl, propyl, butyl, and pentyl, and the alkyl group is preferably methyl.

^R4 is preferably a hydrogen atom.

^R5 is preferably methyl.

The content of glutarimide units in the acrylic resin is, for example, 5 mol% or more, preferably 15 mol% or more, and, for example, 50 mol% or less, preferably 40 mol% or less. If the content of glutarimide units is equal to or more than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the phase difference can be reduced.

The imidization rate of the acrylic resin is the ratio of imide carbonyl groups to all carbonyl groups, and is, for example, 2.5% or more, and, for example, 7.5% or less, preferably 5.0% or less. If the imidization rate of the acrylic resin is equal to or higher than the above-mentioned lower limit, the deterioration of heat resistance and the deterioration of transparency can be suppressed. If the imidization rate of the acrylic resin is equal to or lower than the above-mentioned upper limit, the resin has excellent moldability and transparency. The imidization rate of the acrylic resin can be measured by the NMR spectrum, IR spectrum, etc. of the acrylic resin.

The content of the unsaturated carboxylic acid alkyl ester units in the acrylic resin is the remainder of the content of the glutarimide units, and is, for example, 50 mol% or more, preferably 60 mol% or more, and for example, 95 mol% or less, preferably 85 mol% or less. The content of the acrylic acid ester units in the acrylic resin (specifically, the acrylic acid ester units in the total amount of the glutarimide units, the methacrylic acid units, and the acrylic acid ester units) is, for example, less than 1 mass%, preferably less than 0.5 mass%. If the content of the acrylic acid ester units is equal to or less than the above-mentioned upper limit, the acrylic resin has excellent thermal stability and can suppress the deterioration of the physical properties of the acrylic resin during resin production or molding processing. The acid value of the acrylic resin is, for example, 0.10 mmol/g or more, for example, 0.50 mmol/g or less. If the acid value is within the above range, an acrylic resin with an excellent balance of heat resistance, mechanical properties, and molding processability can be obtained.

The acid value of an acrylic resin is the content of carboxylic acid units and carboxylic anhydride units in the acrylic resin. The acid value can be calculated, for example, by the titration method described in WO2005-054311 or the titration method described in JP2005-23272A.

The acrylic resin may contain other copolymerizable vinyl monomer units other than those mentioned above. Examples of other vinyl monomers include alkenyl aromatic monomers such as styrene, α-methylstyrene, vinyltoluene, and divinylbenzene.

The weight average molecular weight of the acrylic resin is, for example, 1,000 or more, preferably 5,000 or more, more preferably 10,000 or more, and, for example, 2,000,000 or less, preferably 1,000,000 or less, more preferably 500,000 or less. The weight average molecular weight of the acrylic resin is determined in terms of polystyrene using a gel permeation chromatograph (GPC system).

The polycarbonate resin contains, for example, a structural unit derived from a dihydroxy compound. The structural unit derived from a dihydroxy compound contains, for example, a structural unit derived from an isosorbide-based dihydroxy compound and a structural unit derived from at least one first dihydroxy compound selected from the group consisting of an alicyclic diol, an alicyclic dimethanol, a di-, tri- or polyethylene glycol, and an alkylene glycol or a spiro glycol. The first dihydroxy compound excludes an isosorbide-based dihydroxy compound.
Furthermore, the structural unit derived from the dihydroxy compound may contain a structural unit derived from a fluorene-based dihydroxy compound. Preferably, the structural unit derived from the dihydroxy compound does not contain a structural unit derived from a fluorene-based dihydroxy compound. In this case, the ratio of the structural unit derived from the aromatic ring compound in the protective resin layer 12 can be reduced or zero. Therefore, the quality of the protective resin layer 12 can be improved. The ratio of the isosorbide-based dihydroxy compound in the dihydroxy compound is, for example, 40 mol% or more, preferably 55 mol% or more, and, for example, 90 mol% or less, preferably 75 mol% or less. The ratio of the first dihydroxy compound in the dihydroxy compound is, for example, 60 mol% or less, preferably 45 mol% or less, and, for example, 10 mol% or more, preferably 25 mol% or more. The ratio of the fluorene-based dihydroxy compound in the dihydroxy compound is, for example, 25 mol% or less, preferably 10 mol% or less, more preferably 0 mol%.

The thickness of the protective resin layer 12 is, for example, 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and is, for example, 150 μm or less, preferably 100 μm or less, more preferably 80 μm or less. If the thickness of the protective resin layer 12 is equal to or greater than the above-mentioned lower limit, a decrease in impact resistance can be suppressed when the substrate 7 is a thin glass plate. If the thickness of the protective resin layer 12 is equal to or less than the above-mentioned upper limit, foldability can be improved.

The total light transmittance of the protective resin layer 12 is, for example, 85% or more, preferably 88% or more, more preferably 90% or more, and is, for example, 100% or less. The total light transmittance of the protective resin layer 12 is determined in accordance with JIS K 7361-1. The total light transmittance of the other members is determined in the same manner as above.

The in-plane retardation Re(550) of the protective resin layer 12 is, for example, 10 nm or less, preferably 5 nm or less, and particularly preferably 0 nm, i.e., no in-plane retardation Re(550). The thickness direction retardation Rth(550) of the protective resin layer 12 is, for example, 30 nm or less, preferably 10 nm or less, and particularly preferably 0 nm, i.e., no thickness direction retardation Rth(550).

If the in-plane retardation Re(550) and thickness retardation Rth(550) of the protective resin layer 12 are each equal to or less than the upper limit described above, the in-plane retardation Re(550) and thickness retardation Rth(550) (described below) of the front panel 4 including the protective resin layer 12 can be set within the desired range.

Note that "in-plane retardation Re(550)" means the in-plane retardation Re measured with light having a wavelength of 550 nm. "Thickness retardation Rth(550)" means the thickness retardation Rth measured with light having a wavelength of 550 nm. Even if the number 550 in parentheses varies, the definition of retardation is the same as above.

The in-plane retardation Re(550) and thickness retardation Rth(550) are measured with a retardation measuring device. The subsequent retardations are also measured with a retardation measuring device.

The refractive index of the protective resin layer 12 is appropriately adjusted so that the refractive index difference Δ with the hard coat layer 13 described below is within the desired range. Specifically, if the protective resin layer 12 is isotropic, its refractive index n is, for example, 1.40 or more, preferably 1.48 or more, and for example, 1.60 or less, preferably 1.55 or less, more preferably 1.53 or less, and even more preferably 1.52 or less.

The protective resin layer 12 is soft, specifically, its pencil hardness is, for example, 6B or less. The pencil hardness is measured in accordance with JIS K 5400-5-4. However, if the pencil hardness of the protective resin layer 12 is equal to or less than the upper limit described above, the front panel 4 is also soft, that is, the pencil hardness of the front panel 4 is also likely to decrease, for example, to 2B or less. However, in this embodiment, the front panel 4 includes a substrate 7 made of a thin glass plate having excellent hardness, and such a thin glass plate can reinforce the front panel 4, so that the front panel 4 has excellent hardness, specifically, the front panel 4 has a pencil hardness of, for example, B or more, preferably H or more, and more preferably 2H or more.

The composition, physical properties, and manufacturing method of the protective resin layer 12 are described in detail in, for example, JP 2016-151696 A.

[Hard coat layer]
The hard coat layer 13 is a protective member that suppresses damage caused by friction on the surface of the organic EL display device 1. For example, in the case where the optical laminate 2 is manufactured by roll-to-roll, when the optical laminate 2 is laminated in the radial direction of the rolls, the hard coat layer 13 suppresses damage caused by pressing or friction during lamination.

The hard coat layer 13 forms the surface of the protective member 6. The hard coat layer 13 is disposed on one side in the thickness direction of the protective resin layer 12. Specifically, the hard coat layer 13 is in contact with the surface (one side in the thickness direction) of the protective resin layer 12. The hard coat layer 13 extends in the planar direction.

The hard coat layer 13 is made of, for example, a cured product of a curable composition or a molded product of a thermoplastic composition. In other words, the material of the hard coat layer 13 can be, for example, a curable composition or a thermoplastic composition. The material of the hard coat layer 13 is preferably a curable composition, more preferably an active energy ray curable composition, and even more preferably an ultraviolet ray curable composition.

The main component of the material of the hard coat layer 13 does not have an aromatic ring, for example. The main component is the component that is contained in the largest amount in the hard coat layer 13, or the component that occupies 25% or more of the hard coat layer 13.

Specifically, the hard coat layer 13 is preferably made of a cured product of a curable composition (cured resin), and more preferably made of a cured product of a curable acrylic composition (cured acrylic resin).

The curable composition includes a UV-curable compound. The curable compound may be a monomer, an oligomer, or a prepolymer.

Specifically, examples of the curable compound include acrylic compounds (monomers and/or oligomers) having multiple ultraviolet-polymerizable functional groups, and preferably curable compounds having multiple (meth)acryloyl groups. The number of functional groups ((meth)acryloyl groups) in the curable compound is, for example, 3 or more, preferably 5 or more, and, for example, 30 or less, preferably 20 or less.

Furthermore, the curable compound preferably further contains a hydroxyl group in the molecule.

Examples of the curable compound that is a monomer include tricyclodecane dimethanol diacrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane triacrylate, pentaerythritol tetra(meth)acrylate, dimethylolpropane tetraacrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol (meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, dipropylene glycol diacrylate, isocyanuric acid tri(meth)acrylate, ethoxylated glycerin tri(meth)acrylate, ethoxylated pentaerythritol tetraacrylate, and oligomers or prepolymers thereof. These can be used alone or in combination.

Examples of the curable compound that is a monomer or oligomer include urethane (meth)acrylate and/or urethane (meth)acrylate oligomer. The number of (meth)acryloyl groups in the urethane (meth)acrylate and/or urethane (meth)acrylate oligomer is, for example, 3 or more, preferably 4 or more, more preferably 6 or more, and, for example, 25 or less, preferably 20 or less.

The weight average molecular weight (or theoretical molecular weight) of the urethane (meth)acrylate and/or urethane (meth)acrylate oligomer is, for example, 3000 or less, preferably 2500 or less, more preferably 2000 or less, and for example, 500 or more, preferably 800 or more. When the urethane (meth)acrylate and/or urethane (meth)acrylate oligomer is a commercially available product, the theoretical molecular weight described in the catalog attached to the commercially available product is used.

To form the hard coat layer 13, if the hard coat layer 13 is a cured body, a varnish containing a curable composition is applied, and then the curable composition is cured. Alternatively, the hard coat layer 13 made of a thermoplastic resin is directly molded from the thermoplastic composition.

The tensile storage modulus E' of the hard coat layer 13 at 25°C is, for example, 3 GPa or less, preferably 2.5 GPa or less, and for example, 1.5 GPa or more, preferably 2 GPa or more. The tensile storage modulus E' of the hard coat layer 13 at 25°C is obtained by measuring the dynamic viscoelasticity in a temperature dispersion mode under conditions of a frequency of 1 Hz and a heating rate of 5°C/min. If the tensile storage modulus E' of the hard coat layer 13 is equal to or less than the upper limit described above, the bending property (foldability) is excellent. If the tensile storage modulus E' of the hard coat layer 13 is equal to or more than the lower limit described above, damage to the protective resin layer 12 due to friction can be effectively suppressed.

The pencil hardness of the hard coat layer 13 is, for example, F or more, more preferably H or more, and even more preferably 2H or more. The pencil hardness is measured in accordance with JIS K 5400-5-4. If the pencil hardness of the hard coat layer 13 is equal to or greater than the above-mentioned lower limit, damage to the protective resin layer 12 due to friction can be effectively suppressed.

The in-plane retardation Re(550) of the hard coat layer 13 is, for example, 10 nm or less, preferably 5 nm or less. The thickness direction retardation Rth(550) of the hard coat layer 13 is, for example, 30 nm or less, preferably 10 nm or less.

The refractive index of the hard coat layer 13 is adjusted as appropriate so that the refractive index difference Δ with the protective resin layer 12 described below is within the desired range. Specifically, if the protective resin layer 12 is isotropic, its refractive index n is, for example, 1.40 or more, preferably 1.48 or more, and for example, 1.60 or less, preferably 1.53 or less.

The thickness of the hard coat layer 13 is, for example, 5 μm or more, preferably 7 μm or more, and, for example, 30 μm or less.

The total light transmittance of the hard coat layer 13 is, for example, 85% or more, preferably 90% or more, and, for example, 100% or less.

The composition, properties, and manufacturing method of the hard coat layer 13 are described in detail in, for example, JP 2016-151696 A.

[Properties of protective material]
The protective member 6 has a thickness of, for example, 15 μm or more, preferably 35 μm or more, and for example, 170 μm or less, preferably 130 μm or less, more preferably 90 μm or less.

The total light transmittance of the protective member 6 is, for example, 85% or more, preferably 90% or more, and, for example, 100% or less.

The in-plane retardation Re(550) of the protective member 6 is, for example, 10 nm or less, preferably 5 nm or less. The thickness direction retardation Rth(550) of the protective member 6 is, for example, 30 nm or less, preferably 10 nm or less.

With the hard coat layer 13 facing inward and with a diameter of 4 mm, the protective member 6 is fixed in a bent state at 180 degrees and placed in an environment of 85°C and 85% RH for 100 hours. After that, the protective member 6 is opened and the difference Δ between the in-plane retardation Re(550) of the bent portion 25 and the in-plane retardation Re(550) of the bent portion 25 before the bending test is, for example, 10 nm or less, and the difference Δ between the thickness direction retardation Rth(550) of the bent portion 25 after the bending test and the thickness direction retardation Rth(550) of the bent portion 25 before the bending test is, for example, 30 nm or less. Details of the bending test will be described later in [Another feature of one embodiment].

[substrate]
The substrate 7 forms the rear surface of the front panel 4. The substrate 7 is adhered to the protective resin layer 12 via a first adhesive layer 9, which will be described later. The substrate 7 is, for example, flexible.

The substrate 7 may be, for example, a resin film such as a polyimide film, or a thin glass plate. From the viewpoint of obtaining excellent bendability, as well as excellent foldability, hardness, and transparency, a thin glass plate is preferably used as the substrate 7. In this embodiment, the substrate 7 is preferably made of a thin glass plate.

The substrate 7 ensures the mechanical strength and toughness of the front panel 4. The substrate 7 supports the protective member 6 from the back side. The substrate 7 has a flat plate shape that extends in the surface direction.

The thickness of the substrate 7 is, for example, 10 μm or more, and, for example, 100 μm or less, preferably 80 μm or less.

The total light transmittance of the substrate 7 is, for example, 80% or more, preferably 85% or more, and, for example, 95% or less.

The thin glass plate is preferably isotropic. The refractive index n of the thin glass plate is, for example, 1.45 or more and, for example, 1.55 or less. If the thin glass plate is isotropic, it does not have an in-plane retardation Re(550) and a thickness retardation Rth(550).

[Polarizing film]
The polarizing film 5 is disposed on the back side of the front plate 4. As a result, the polarizing film 5 is protected by the front plate 4. The polarizing film 5 is adhered to the substrate 7 via a second adhesive layer 10 described below. The polarizing film 5 has a flat plate shape extending in the surface direction.

The thickness of the polarizing film 5 is, for example, 15 μm or more, preferably 25 μm or more, and, for example, 300 μm or less, preferably 250 μm or less. The total light transmittance of the polarizing film 5 is, for example, 40% or more, preferably 42% or more, and, for example, 45% or less.

The polarizing film 5 comprises, in order toward the back side, a polarizer protection film 17, a polarizer 18, and an optical compensation layer 19.

[Polarizer protective film]
The polarizer protective film 17 forms the surface of the polarizing film 5. The polarizer protective film 17 extends in the plane direction. The polarizer protective film 17 protects the polarizer 18, which will be described next, from the front side.

The material of the polarizer protective film 17 is not particularly limited, and examples thereof include polyethylene terephthalate resin, polyethylene naphthalate resin, acetate resin, polyethersulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyamideimide resin, polyolefin resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polyarylate resin, polyphenylene sulfide resin, and the like. These can be used alone or in combination. As a material for the polarizer protective film 17, from the viewpoint of making the optical laminate 2 high quality, an acrylic resin can be used, and more preferably, an acrylic resin having an unsaturated carboxylic acid alkyl ester unit and a glutarimide unit can be used, and specifically, the acrylic resin exemplified for the protective resin layer 12 can be used.

The thickness of the polarizer protective film 17 is, for example, 10 μm or more, and, for example, 100 μm or less, preferably 80 μm or less. The in-plane retardation Re(550) and thickness retardation Rth(550) of the polarizer protective film 17 are, for example, 10 nm or less, preferably 5 nm or less. If the polarizer protective film 17 is isotropic, its refractive index n is, for example, 1.40 or more, preferably 1.48 or more, and, for example, 1.60 or less, preferably 1.53 or less.

The composition, physical properties, and manufacturing method of the polarizer protective film 17 are described in detail, for example, in JP 2016-151696 A.

[Polarizer]
The polarizer 18 is in contact with the rear surface of the polarizer protective film 17. The polarizer 18 has a flat plate shape extending in the surface direction. Examples of the polarizer 18 include a film obtained by dyeing and stretching a hydrophilic film such as a PVA film, a film obtained by dehydrating a PVA film, and a film obtained by dehydrochlorinating a polyvinyl chloride film. The polarizer 18 is a single layer or a multilayer. The thickness of the polarizer 18 is, for example, 1 μm or more, preferably 3 μm or more, and, for example, 15 μm or less, preferably 10 μm or less. The material, composition, physical properties (birefringence, phase difference, refractive index, etc.), manufacturing method, etc. of the polarizer 18 are described in detail in, for example, JP 2016-151696 A.

[Optical compensation layer]
The optical compensation layer 19 is in contact with the rear surface of the polarizer 18. The optical compensation layer 19 has a flat plate shape extending in the surface direction. The optical compensation layer 19 is a retardation film, specifically, functions as a λ/4 plate. As a result, the polarizing film 5 including the polarizer 18 and the optical compensation layer 19 has excellent circular polarization. Examples of the material of the optical compensation layer 19 include materials having the following optical properties, such as polycarbonate resin, polyvinyl acetal resin, cycloolefin resin, acrylic resin, cellulose ester resin, etc. Preferably, it is a polycarbonate resin. The polycarbonate resin includes, for example, a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of an alicyclic diol, an alicyclic dimethanol, a di-, tri- or polyethylene glycol, and an alkylene glycol or a spiro glycol.

The in-plane retardation Re(550) of the optical compensation layer 19 is, for example, 100 nm or more, preferably 135 nm or more, and, for example, 180 nm or less, preferably 155 nm or less. The in-plane retardation Re(550) of the optical compensation layer 19 is greater than the in-plane retardation Re(450) and less than the in-plane retardation Re(650). Specifically, Re(450)/Re(550) is, for example, less than 1, preferably 0.95 or less, and, for example, 0.8 or more. Re(550)/Re(650) is, for example, less than 1, preferably 0.97 or less, and, for example, 0.8 or more.

The composition, physical properties, and manufacturing method of the optical compensation layer 19 are described in detail in, for example, JP 2017-102443 A.

The substrate 7 and polarizing film 5 having the polarizer protective film 17, the polarizer 18, and the optical compensation layer 19 are described in detail in JP 2017-102443 A.

[Adhesive layer]
The adhesive layer 8 is an adhesive layer that adheres (pressure-sensitively bonds) the above-mentioned members in the front-back direction. The adhesive layer 8 includes the first adhesive layer 9, the second adhesive layer 10, and the third adhesive layer 11, as described above.
Each of the first adhesive layer 9, the second adhesive layer 10, and the third adhesive layer 11 extends in the planar direction. The thickness of each of the first adhesive layer 9, the second adhesive layer 10, and the third adhesive layer 11 is, for example, 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and for example, 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less.

The total light transmittance of each of the first adhesive layer 9, the second adhesive layer 10, and the third adhesive layer 11 is, for example, 85% or more, preferably 88% or more, more preferably 90% or more, and is, for example, 100% or less.

In particular, the in-plane retardation Re(550) of the first adhesive layer 9 is, for example, 10 nm or less, and the thickness retardation Rth(550) is, for example, 30 nm or less.

The composition, physical properties, and manufacturing method of the adhesive layer 8 including the first adhesive layer 9 are described in detail in, for example, JP 2018-28573 A.

[First adhesive layer]
The first adhesive layer 9 adheres in the front-back direction between the protective member 6 and the substrate 7. Specifically, the first adhesive layer 9 contacts (adheres to) the back surface of the protective resin layer 12 and the front surface of the substrate 7.

[Second adhesive layer]
The second adhesive layer 10 adheres the front plate 4 and the polarizing film 5 in the front-back direction. Specifically, the second adhesive layer 10 contacts (adheres to) the back surface of the substrate 7 and the front surface of the polarizer protective film 17.

[Third adhesive layer]
The third adhesive layer 11 adheres the optical laminate 2 and the image display member 3 in the front-back direction. Specifically, the third adhesive layer 11 contacts the back surface of the optical compensation layer 19 and the front surface of the optical laminate 2.
[Adhesive layer material]
Examples of the materials for the first adhesive layer 9, the second adhesive layer 10, and the third adhesive layer 11 include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine adhesives, epoxy adhesives, and polyether adhesives.

In particular, the material of the first adhesive layer 9 is preferably an acrylic adhesive, from the viewpoint of reducing the in-plane retardation Re(550) and thickness retardation Rth(550) of the front panel 4.

Examples of acrylic adhesives include crosslinked adhesives in which a copolymer of an alkyl (meth)acrylate containing an alkyl portion having 3 to 8 carbon atoms and a hydroxyalkyl (meth)acrylate containing a hydroxyalkyl portion having 3 to 8 carbon atoms is crosslinked with a crosslinking agent.

Examples of alkyl (meth)acrylates containing an alkyl portion having 3 to 8 carbon atoms include n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-octyl (meth)acrylate. A preferred example of the alkyl (meth)acrylate is n-butyl (meth)acrylate.

Examples of hydroxyalkyl (meth)acrylates containing a hydroxyalkyl moiety having 3 to 8 carbon atoms include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate. A preferred example of the hydroxyalkyl (meth)acrylate is 4-hydroxybutyl (meth)acrylate. The number of parts by mass of the hydroxyalkyl (meth)acrylate relative to 100 parts by mass of the alkyl (meth)acrylate is, for example, 0.5 parts by mass or more and, for example, 5 parts by mass or less.

Examples of crosslinking agents include isocyanate-based crosslinking agents, peroxide-based crosslinking agents, epoxy-based crosslinking agents, and imine-based crosslinking agents. These can be used alone or in combination. Preferably, an isocyanate-based crosslinking agent and a peroxide-based crosslinking agent are used in combination. Examples of isocyanate-based crosslinking agents include bifunctional and trifunctional agents, preferably trifunctional agents, and specifically, trimethylolpropane adducts of xylylene diisocyanate. Examples of peroxide-based crosslinking agents include acyl peroxides, preferably benzoyl peroxide. The ratio of the crosslinking agent is, for example, 0.01 parts by mass or more, and, for example, 1 part by mass or less, relative to 100 parts by mass of the copolymer. In addition, when an isocyanate-based crosslinking agent and a peroxide-based crosslinking agent are used in combination, the number of parts by mass of the isocyanate-based crosslinking agent is, for example, 0.05 parts by mass or more and less than 0.2 parts by mass, and the number of parts by mass of the oxide-based crosslinking agent is, for example, 0.2 parts by mass or more and 0.5 parts by mass or less, relative to 100 parts by mass of the copolymer.

[Image display section]
The image display member 3 forms the back surface of the organic EL display device 1. The image display member 3 is disposed on the back side of the optical laminate 2 via a third adhesive layer 11. The image display member 3 has a substantially flat plate shape extending in the surface direction, and specifically, an organic EL element can be mentioned. For example, although not shown, the image display member 3 includes a display substrate, two electrodes, an organic EL layer sandwiched between the two electrodes, and a sealing layer. The thickness of the image display member 3 is, for example, 1 μm or more, for example, 100 μm or less. The configuration, physical properties, manufacturing method, etc. of the image display member 3 are described in detail in, for example, JP 2018-28573 A.

[Touch panel input display device]
1, the organic EL display device 1 can further include a conductive layer 15 and a concealing layer 16. This allows the organic EL display device 1 to function as a touch panel type input display device.

[Conductive layer]
The conductive layer 15 is provided in the optical laminate 2, and specifically, is disposed on the back side of the third adhesive layer 11. The conductive layer 15 is embedded, for example, in a middle portion in the front-back direction of the third adhesive layer 11 (a middle portion in the thickness direction).

Examples of materials for the conductive layer 15 include metal oxides, conductive fibers (fibers), and metals.

Examples of metal oxides include composite oxides such as indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), indium gallium oxide (IGO), indium tin oxide (ITO), and antimony tin oxide (ATO). The total light transmittance of the conductive layer 15 made of a metal oxide is, for example, 85% or more, preferably 88% or more, more preferably 90% or more, and is, for example, 100% or less.

Examples of conductive fibers include metal nanowires and carbon nanotubes.

Metals include gold, platinum, silver, copper, etc. When the material of the conductive layer 15 is a metal, the conductive layer 15 is a metal mesh having a mesh shape in a planar view. The width of the lines constituting the mesh is, for example, 100 μm or less, preferably 30 μm or less, more preferably 10 μm or less, and is, for example, 1 μm or more.

Details of the conductive layer 15 are described in, for example, JP 2017-102443 A, JP 2014-113705 A, and JP 2014-219667 A. The conductive layer 15 integrally includes a sensor electrode portion 20 located at the center in the surface direction and a lead-out wiring portion (not shown) located around the sensor electrode portion 20.

[Concealing layer]
The concealing layer 16 is provided on the front panel 4, and specifically, is disposed (specifically, printed) on the periphery of the back surface of the protective resin layer 12. The concealing layer 16 has a pattern including the lead-out wiring portion (or the lead-out wiring) of the conductive layer 15 in a plan view. Examples of the material of the concealing layer 16 include a composition containing a black component and a resin. The total light transmittance of the concealing layer 16 is, for example, 10% or less, preferably 5% or less. The concealing layer 16 is a layer in the organic EL display device 1 that prevents a user from viewing the lead-out wiring portion (not shown) from the viewing side. When projected in the thickness direction, the optical laminate 2 includes a non-display region 21 that overlaps with the concealing layer 16, and a display region 22 that does not overlap with the concealing layer 16 and overlaps with the sensor electrode portion 20 of the conductive layer 15. When the concealing layer 16 is provided on the front panel 4, the in-plane retardation Re(550) and thickness direction retardation Rth(550) of the front panel 4 are the in-plane retardation Re(550) and thickness direction retardation Rth(550) measured in the display area 22 of the front panel 4.

Salient Features of One Embodiment
Next, prominent features of this embodiment will be described.

The difference Δ between the refractive index n of the protective resin layer 12 and the refractive index n of the hard coat layer 13 is, for example, 0.04 or less, preferably 0.03 or less, and more preferably 0.02 or less.

<1> More specifically, if both the protective resin layer 12 and the hard coat layer 13 are isotropic, the difference Δ between the refractive index n of the protective resin layer 12 and the refractive index n of the hard coat layer 13 is 0.04 or less, preferably 0.03 or less, and more preferably 0.02 or less.

<2> If both the protective resin layer 12 and the hard coat layer 13 are birefringent, the difference Δ in the refractive index nx in their slow axis direction is 0.04 or less, preferably 0.03 or less, more preferably 0.02 or less, and even more preferably 0.01 or less, and the difference Δ in the refractive index in their fast axis direction is 0.04 or less, preferably 0.03 or less, and more preferably 0.02 or less.

<3> If one of the protective resin layer 12 and the hard coat layer 13 is isotropic and the other is birefringent, the difference Δ between the refractive index n of one and the refractive index nx of the other in the slow axis direction is 0.04 or less, preferably 0.03 or less, and more preferably 0.02 or less.

If the refractive index difference Δ exceeds the upper limit, a high-quality front panel 4, a high-quality optical laminate 2, and a high-quality organic EL display device 1 cannot be obtained, and problems with unevenness due to the refractive index difference Δ occur.

Other Features of an Embodiment
The in-plane retardation Re(550) of the front panel 4 is 10 nm or less, and the thickness direction retardation Rth(550) of the front panel 4 is 30 nm or less.

If the in-plane retardation Re(550) of the front panel 4 exceeds 10 nm, or if the thickness retardation Rth(550) of the front panel 4 exceeds 30 nm, it may not be possible to obtain a high-quality front panel 4.

The in-plane retardation Re(550) of the front panel 4 is preferably 5 nm or less, more preferably 1 nm or less. The thickness retardation Rth(550) of the front panel 4 is preferably 15 nm or less, more preferably 10 nm or less.

In addition, the front panel 4 is fixed in a bent state at 180 degrees with the hard coat layer 13 facing inward and with a diameter of 4 mm, and then placed in an environment of 85°C and 85% RH for 100 hours. After that, the front panel 4 is opened, and the difference Δ between the in-plane retardation Re(550) of the bent portion 25 and the in-plane retardation Re(550) of the bent portion 25 before the bending test is, for example, 10 nm or less, and the difference Δ between the thickness direction retardation Rth(550) of the bent portion 25 after the bending test and the thickness direction retardation Rth(550) of the bent portion 25 before the bending test is, for example, 30 nm or less.

In the bending test, as shown in FIG. 4, the front panel 4 is bent while being supported from the back side by two glass plates 35 so that the hard coat layer (not shown in FIG. 4) of the front panel 4 faces inward. At that time, the distance L between the surfaces of the front panel 4 facing each other in the thickness direction is 4 mm. In other words, if the bent portion 25 is semicircular, its diameter (inner diameter) is 4 mm.

The absolute value of the photoelastic coefficient of the front panel 4 at 23°C is, for example, 150.0 x ^{10-13 cm2} /dyn or less, preferably 100.0 x ^{10-13 cm2} /dyn or less, more preferably 50.0 x ^{10-13 cm2} /dyn or less, particularly preferably 30.0 x ^{10-13 cm2} /dyn or less, and most preferably 10.0 x ^{10-13 cm2} /dyn or less. If the absolute value of the photoelastic coefficient of the front panel 4 is equal to or less than the upper limit described above, the difference Δ in Re(550) and the difference Δ in Rth(550) before and after the bending test can be set to equal to or less than the upper limit described above. Therefore, the front panel 4 has excellent bending properties and further excellent foldability.

[Effects of one embodiment]
In the front panel 4 of this organic EL display device 1, the difference Δ between the refractive index of the protective resin layer 12 and the refractive index of the hard coat layer 13 is small, at 0.04 or less, so that the front panel 4 is of high quality without causing problems with unevenness due to the refractive index difference Δ.

In addition, in this front panel 4, if the molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer 12 is low, at 5.0 mol % or less, the high quality of the front panel 4 can be more reliably ensured.

In addition, in this front panel 4, if the material of the protective resin layer 12 is acrylic resin or polycarbonate resin and the material of the hard coat layer 13 is acrylic resin, the refractive index of the protective resin layer and the refractive index of the hard coat layer are similar, and the difference Δ between the refractive index of the protective resin layer 12 and the refractive index of the hard coat layer 13 can be reliably reduced, thereby reliably maintaining high quality.

On the other hand, as described above, the protective resin layer 12 made of acrylic resin or polycarbonate resin (particularly acrylic resin) has a low tensile storage modulus E', which reduces the mechanical strength and is likely to cause a reduction in the strength of the front panel 4.

However, in this organic EL display device 1, if the substrate 7 is made of a thin glass plate, the protective resin layer 12 can be reinforced, so that the reduction in strength of the front panel 4 can be suppressed.

Furthermore, this front panel 4 includes a substrate 7 including a thin glass plate, and a first adhesive layer 9. The substrate 7, the first adhesive layer 9, the protective resin layer 12, and the hard coat layer 13 are arranged in order in the thickness direction, which suppresses the occurrence of traces (such as wrinkles) left after bending and maintains high quality.

This optical laminate 2 and organic EL display device 1 are equipped with the front panel 4 described above, and therefore are of high quality without the problem of unevenness caused by the refractive index difference Δ.

[Modification]
In the following modifications, the same reference numerals are used for the same components and steps as those in the above-mentioned embodiment, and detailed descriptions thereof will be omitted. In addition, each modification can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and its modifications can be appropriately combined.

Although not shown, the back surface of the conductive layer 15 may be in direct contact with the surface of the image display member 3.

In one embodiment, an organic EL display device 1 is illustrated as an example of an image display device of the present invention, but the present invention is not limited to this, and examples thereof include liquid crystal display devices (LCDs).

The protective member 6 may further include a second hard coat layer 14. The second hard coat layer 14 is disposed on the surface of the hard coat layer 13. That is, the protective member 6 includes the protective resin layer 12, the hard coat layer 13, and the second hard coat layer 14 in this order toward the front side. The second hard coat layer 14 has the same physical properties and thickness as the hard coat layer 13, except for the following differences. The tensile storage modulus E' of the second hard coat layer 14 at 25°C is, for example, lower than the tensile storage modulus E' of the second hard coat layer 14. The tensile storage modulus E' of the second hard coat layer 14 at 25°C is, for example, less than 2 GPa, preferably less than 1.5 GPa, and is, for example, 0.5 GPa or more, preferably 1 GPa or more. The tensile storage modulus E' of the second hard coat layer 14 at 25°C is obtained by measuring the dynamic viscoelasticity in a temperature dispersion mode under conditions of a frequency of 1 Hz and a heating rate of 5°C/min.

As shown in FIG. 2, the optical laminate 2 of this modified example is not provided on the image display member 3, and does not have to constitute the organic EL display device 1. In more detail, the optical laminate 2 is one component for producing the organic EL display device 1, and is not yet adhered to the optical laminate 2. In this case, a release sheet 26 shown by the phantom line is laminated on the back surface of the third adhesive layer 11. The optical laminate 2 is a device that is distributed as a component alone and can be used industrially.

Although not shown, the front panel 4 may not be provided on the polarizing film 5 and may not constitute the optical laminate 2. More specifically, the front panel 4 is a component for producing the optical laminate 2 and is not yet adhered to the polarizing film 5. The front panel 4 may be provided with a second adhesive layer 10. The front panel 4 is a device that is distributed as a component alone and can be used industrially.

As shown in FIG. 3, the front panel 4 of the modified example may not include a substrate 7 and may only include a protective member 6. Specifically, the front panel 4 shown in the modified example of FIG. 3 does not include a first adhesive layer 9 and a substrate 7, and is composed of only a protective member 6.

Preferably, the front panel 4 further includes a first adhesive layer 9 and a substrate 7, and the substrate 7 further includes a thin glass plate. This configuration makes it possible to suppress the occurrence of marks (such as wrinkles) left after bending (and further folding), and maintain high quality.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is in no way limited to the examples and comparative examples. In addition, the specific numerical values of the compounding ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding compounding ratio (content ratio), physical property value, parameter, etc. described in the above "Form for carrying out the invention".

First, the method for measuring the physical properties of each layer is explained below.

[Refractive index]
The refractive index of each layer at a wavelength of 589 nm was measured using an Abbe refractometer (model number: DR-M2, manufactured by Atago Co., Ltd.) at a temperature of 23° C.

[Measurement of the molar proportion of structural units derived from aromatic compounds in the protective resin layer 12]
[Identification of structural units]
The protective resin layer 12 was immersed in methanol. The methanol soluble matter (decomposition products) was measured by GC-MS. As a result, the structural unit of the protective resin layer 12 was identified.

[Measurement of the proportion of aromatic compounds based on integrals]
The protective resin layer 12 was dissolved in deuterated chloroform to prepare a solution. This was subjected to ¹ H-NMR measurement. In the ¹ H-NMR measurement, based on the structural units identified by the GC-MS measurement, the molar ratio of structural units derived from aromatic compounds and the molar ratio of structural units derived from non-aromatic compounds were calculated from the integral ratio of protons directly connected to aromatic rings and the integral ratio of other protons, respectively. Thereafter, the ratio of the number of moles of structural units derived from aromatic compounds in the protective resin layer 12 was calculated as a percentage. In the ¹ H-NMR measurement, an NMR evaluation device (AVANCEIII-600 with Cryo Probe, manufactured by Bruker Biospin) was used.

[Example 1]
A coating agent was prepared by mixing 100 parts by mass of a multifunctional acrylate (manufactured by AICA Kogyo Co., Ltd., product name "Z-850-16"), 5 parts by mass of a leveling agent (manufactured by DIC Corporation, product name: GRANDIC PC-4100), and 3 parts by mass of a photopolymerization initiator (manufactured by Ciba Japan Co., Ltd., product name: Irgacure 907), and diluting the mixture with methyl isobutyl ketone to a solid content concentration of 50% by mass.

Separately, a protective resin layer 12 was prepared, which was made of an acrylic film manufactured by Nitto Denko Corporation (product name "HX-40N", thickness 40 μm). The refractive index of the protective resin layer 12 was 1.51. The molar ratio of structural units derived from aromatic compounds in the protective resin layer 12 was 0.0 mol%.

A coating agent was applied to one side of the prepared protective resin layer 12 to form a coating layer, and the coating layer was heated together with the protective resin layer at 90°C for 2 minutes. Next, the coating layer was irradiated with ultraviolet light using a high-pressure mercury lamp at an integrated light amount of 300 mJ/ ^cm2 to form a hard coat layer 13. The thickness of the hard coat layer 13 was 10 μm. The refractive index of the hard coat layer 13 was 1.49. As a result, as shown in FIG. 3, a protective member 6 including the protective resin layer 12 and the hard coat layer 13 was produced. In other words, a front panel 4 including the protective member 6 was produced.

[Example 2]
A front panel 4 shown in Fig. 3 was produced in the same manner as in Example 1. However, the protective resin layer 12 was changed to a polycarbonate film produced in the following manner.

81.98 parts by mass (0.56 mol parts) of isosorbide (manufactured by Rocket Fleuret, product name "POLYSORB"), 47.19 parts by mass (0.24 mol parts) of tricyclodecane dimethanol, 175.1 parts by mass (0.81 mol parts) of diphenyl carbonate (manufactured by Mitsubishi Chemical Corporation), and 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst were charged into a reaction vessel, and in a nitrogen atmosphere, the heating tank temperature was heated to 150°C as the first step of the reaction, and the raw materials were dissolved (about 15 minutes) while stirring as necessary. Next, the pressure was changed from normal pressure to 13.3 kPa, and the heating tank temperature was raised to 190°C over one hour, while the generated phenol was extracted from the reaction vessel. After the entire reaction vessel was kept at 190°C for 15 minutes, the pressure in the reaction vessel was set to 6.67 kPa, the heating tank temperature was raised to 230°C in 15 minutes, and the generated phenol was extracted outside the reaction vessel as the second step. As the stirring torque of the stirrer increased, the temperature was raised to 250°C in 8 minutes, and the pressure in the reaction vessel was allowed to reach 0.200 kPa or less in order to remove the further generated phenol. After reaching a predetermined stirring torque, the reaction was terminated, and the reaction product was extruded into water to obtain polycarbonate resin pellets. The obtained polycarbonate resin was vacuum-dried at 80°C for 5 hours, and then a protective resin layer 12 made of a polycarbonate film having a thickness of 135 μm was produced using a film-forming device equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder setting temperature: 250°C), a T-die (width 300 mm, setting temperature: 250°C), a chill roll (setting temperature: 120 to 130°C), and a winder. The refractive index of the protective resin layer 12 was 1.51. The molar ratio of structural units derived from aromatic compounds in the protective resin layer 12 was 1.0 mol%.

[Example 3]
A front panel 4 shown in Fig. 3 was produced in the same manner as in Example 1. However, the protective resin layer 12 was changed to a polycarbonate film produced in the following manner.

38.06 parts by weight (0.059 mol parts) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 53.73 parts by weight (0.368 mol parts) of isosorbide (manufactured by Rocket Fleuret, trade name "POLYSORB"), 9.64 parts by weight (0.067 mol parts) of 1,4-cyclohexanedimethanol (cis, trans mixture, manufactured by SK Chemical Co., Ltd.), 81.28 parts by weight (0.379 mol parts) of diphenyl carbonate (manufactured by Mitsubishi Chemical Co., Ltd.), and 3.83×10 ⁻⁴ parts by weight (2.17×10 ⁻⁶ mol parts) of calcium acetate monohydrate as a catalyst were charged into a reaction vessel, and the inside of the reaction vessel was replaced with nitrogen under reduced pressure. The raw materials were dissolved under stirring at 150° C. for about 10 minutes under a nitrogen atmosphere. In the first step of the reaction, the temperature was raised to 220°C over 30 minutes, and the reaction was carried out at normal pressure for 60 minutes. The pressure was then reduced from normal pressure to 13.3 kPa over 90 minutes, and the pressure was maintained at 13.3 kPa for 30 minutes to extract the generated phenol from the reaction system. In the second step of the reaction, the heat transfer medium temperature was raised to 240°C over 15 minutes, while the pressure was reduced to 0.10 kPa or less over 15 minutes to extract the generated phenol from the reaction system. After reaching a predetermined stirring torque, the pressure was restored to normal pressure with nitrogen to stop the reaction, and the generated polyester carbonate was extruded into water, and the strands were cut to obtain polycarbonate resin pellets. Next, a polycarbonate film was produced from the obtained polycarbonate resin pellets. The refractive index of the obtained polycarbonate film (unstretched) was 1.53. The obtained polycarbonate film was stretched 2 to 3 times in an oblique direction. The stretching direction was set to 45° with respect to the longitudinal direction of the film. In this way, a protective resin layer 12 made of a polycarbonate film was produced. The refractive index of the protective resin layer 12 was 1.53. The molar ratio of structural units derived from aromatic compounds in the protective resin layer 12 was 6.6 mol %.

[Comparative Example 1]
A front panel 4 shown in Fig. 3 was produced in the same manner as in Example 1. However, the protective resin layer 12 was changed to a polyethylene terephthalate film (product name: T912E50-N) manufactured by Mitsubishi Chemical Corporation. The refractive index of this protective resin layer 12 was 1.57. The molar ratio of structural units derived from aromatic compounds in the protective resin layer 12 was 50 mol%.

[evaluation]
The following items were evaluated for the front panels 4 of Examples 1 to 3 and Comparative Example 1. The evaluation results are shown in Table 1.

[Refractive index difference]
The difference between the refractive index of the protective resin layer 12 and the refractive index of the hard coat layer 13 was calculated.

[Quality]
A black acrylic plate was attached to the protective resin layer 12 of the front panel 4 via an acrylic adhesive. Next, the surface of the hard coat layer 13 was visually observed under a three-wavelength fluorescent lamp. The surface was evaluated as ⊚ when almost no unevenness in appearance was visible, ◯ when unevenness in appearance was slightly visible, and × when unevenness in appearance was clearly visible.

1. Organic EL display device
2 Optical laminate
3 Image display member
4 Front panel
6 Protective member
7. Substrate
9 First adhesive layer
12 Protective resin layer
13 Hard coat layer

Claims (5)

The substrate is provided with a substrate, an adhesive layer, a protective resin layer, and a hard coat layer in this order in a thickness direction,
a difference between a refractive index of the protective resin layer and a refractive index of the hard coat layer is 0.04 or less;
the substrate comprises a thin glass plate;
The thickness of the protective resin layer is 10 μm or more and 150 μm or less,
A front panel, characterized in that the protective resin layer has a pencil hardness of 6B or less. The front panel according to claim 1, characterized in that the molar ratio of structural units derived from aromatic compounds in the main component of the material of the protective resin layer is 5.0 mol % or less. The front panel according to claim 1 or 2, characterized in that the material of the protective resin layer is an acrylic resin or a polycarbonate resin. A polarizing film;
4. An optical laminate comprising: a front plate according to claim 1; and a front plate according to claim 2, in that order toward a viewing side. An image display member;
An image display device comprising: the optical laminate according to claim 4 in this order toward a viewing side.