JP6716870B2 - Quantum dot sheet, backlight and liquid crystal display device - Google Patents

Description

The present invention relates to a quantum dot sheet, a backlight and a liquid crystal display device.

Development is underway to improve the light emission efficiency and color rendering of liquid crystal display backlights and lighting devices. In recent years, in order to realize such a light emitting device, a light source that generates primary light (a blue LED that emits blue light, etc.) and a quantum dot phosphor made of semiconductor particles (hereinafter, referred to as “quantum dot”) are combined. Light emitting devices are being developed.

The quantum dots are, for example, nano-sized compound semiconductor fine particles composed of a semiconductor fine particle composed of a core of CdSe and a shell of ZnS, and a ligand covering the periphery of the shell. Since the particle size of the quantum dot is smaller than the Bohr radius of excitons of the compound semiconductor, the quantum confinement effect appears. Therefore, the luminous efficiency of the quantum dots is higher than that of a conventionally used phosphor (rare earth phosphor) having an activator of rare earth ions, and a high light emission efficiency of 90% or more can be realized.
Further, since the emission wavelength of the quantum dot is determined by the band gap energy of the compound semiconductor fine particles quantized in this way, an arbitrary emission wavelength, that is, an arbitrary emission spectrum can be obtained by changing the particle size of the quantum dot. You can By combining these quantum dots with a blue LED or the like, it is possible to realize a backlight with high luminous efficiency and high color rendering (for example, see Patent Documents 1 to 3).

The method of incorporating the quantum dots into the backlight device includes an on-chip method of incorporating the quantum dots in the light source, an on-edge method of arranging a transparent tube containing the quantum dots between the light source and the light guide plate, and a light exit side of the light guide plate. Also known is an on-surface method in which a sheet containing quantum dots (quantum dot sheet) is arranged on a light source.
However, in the on-chip method, since the quantum dots are incorporated in the light source, the quantum dots are exposed to high temperatures, and the conversion efficiency of the quantum dots is poor. Further, in the on-edge method, the transparent tube containing the quantum dots is arranged between the light source and the light guide plate, so that the size becomes large. In particular, mobile devices are required to be downsized, and it is difficult for the on-edge method to deal with them.
On the other hand, the on-surface method does not have the above-mentioned problems, and it is possible to use the backlight device which has been used conventionally. Under these circumstances, it is currently under consideration to incorporate quantum dots into a backlight device by an on-surface method.

International Publication No. 2012/132239 JP, 2005-18131, A JP, 2015-28139, A

Quantum dots are sensitive to oxygen and humidity. Therefore, the quantum dot sheet used in the on-surface type backlight preferably has a laminated structure in which a layer containing quantum dots (quantum dot containing layer) is sandwiched between barrier films.
However, the laminated quantum dot sheet sometimes lacks in-plane brightness uniformity.
In view of the above problems, it is an object of the present invention to provide a quantum dot sheet, a backlight, and a liquid crystal display device that have good in-plane brightness uniformity.

In order to solve the above problems, the present invention provides a quantum dot sheet, a backlight and a liquid crystal display device of the following [1] to [9].

[1] A quantum dot-containing layer containing a quantum dot and a binder resin that absorbs primary light and emits secondary light, a layered product A arranged on one surface of the quantum dot-containing layer, and the quantum. And a laminated body B arranged on the other surface of the dot-containing layer,
The laminated body A and the laminated body B are configured to have at least a barrier layer, a light diffusion layer, and one or more light transmissive base materials,
A quantum dot sheet in which the layered product A and the layered product B are arranged so as to have a layer configuration that is vertically symmetrical with respect to the quantum dot-containing layer in the thickness direction.
[2] The quantum dot sheet according to the above [1], wherein the quantum dot-containing layer is in close contact with the laminate A and the laminate B without an adhesive layer.
[3] The quantum dot sheet according to the above [1] or [2], wherein the binder resin is a cured product of a composition containing a compound having an ionizing radiation curable functional group.
[4] The quantum dot sheet according to the above [3], wherein the compound having an ionizing radiation-curable functional group contains a monofunctional monomer in an amount of 40% by mass or more.
[5] Any one of the above [1] to [4], wherein both sides of the quantum dot sheet have an arithmetic average roughness Ra of 0.1 to 10 μm with a cutoff value of 0.8 mm according to JIS B0601:2001. The described quantum dot sheet.

[6] At least one light source that emits primary light, an optical plate arranged adjacent to the light source for guiding or diffusing light, and a quantum dot sheet arranged on the light emission side of the optical plate. In the provided backlight, the quantum dot sheet is the quantum dot sheet according to any one of the above [1] to [5].
[7] A liquid crystal display device including a backlight and a liquid crystal panel, wherein the backlight is the backlight according to the above [6].

[8] A method for manufacturing a quantum dot sheet, which sequentially includes the following steps (a) to (c).
(A) A step of stacking at least a barrier layer, a light diffusing layer, and one or more light transmissive base materials to obtain a stack A and a stack B.
(B) A quantum dot-containing layer coating liquid containing a quantum dot and a binder resin component that absorbs primary light and emits secondary light is provided on one surface of either one of the laminate A and the laminate B. The process of applying and forming a quantum dot containing layer.
(C) A layered body in which the quantum dot-containing layer is not formed in the step (b) and a surface of the layered body in which the quantum dot-containing layer is formed in the step (b) on the quantum dot-containing layer side are a quantum dot-containing layer. The step of laminating the layers so as to have a vertically symmetrical layered structure in the thickness direction.
[9] An adhesive is provided between the layered product in which the quantum dot-containing layer is not formed in the step (c) and the quantum dot-containing layer side surface of the layered product in which the quantum dot-containing layer is formed in the step (b). The method for producing a quantum dot sheet according to the above [8], which comprises laminating without interposing a layer.

INDUSTRIAL APPLICABILITY The quantum dot sheet, backlight and liquid crystal display device of the present invention can improve in-plane brightness uniformity.

It is sectional drawing which shows one Embodiment of the quantum dot sheet of this invention. It is sectional drawing which shows other embodiment of the quantum dot sheet of this invention. It is sectional drawing which shows one Embodiment of the backlight of this invention. It is sectional drawing which shows other embodiment of the backlight of this invention. It is a sectional view showing one embodiment of a liquid crystal display of the present invention.

Hereinafter, embodiments of the present invention will be described.
[Quantum dot sheet]
The quantum dot sheet of the present invention comprises a quantum dot containing layer containing a quantum dot and a binder resin that absorbs primary light and emits secondary light, and a laminate formed on one surface of the quantum dot containing layer. A, and a laminated body B arranged on the other surface of the quantum dot-containing layer,
The laminated body A and the laminated body B are configured to have at least a barrier layer, a light diffusion layer, and one or more light transmissive base materials,
The laminated body A and the laminated body B are arranged so as to have a vertically symmetrical layered structure with respect to the quantum dot-containing layer in the thickness direction.

1 and 2 are cross-sectional views showing an embodiment of the quantum dot sheet of the present invention. As shown in FIGS. 1 and 2, the quantum dot sheet of the present invention has a laminated body A and a laminated body B arranged in a vertically symmetrical layered structure with a quantum dot-containing layer as a center. is there.

Usually, a quantum dot sheet having a laminated structure is manufactured by the following steps (1) to (3).
(1) a step of producing the laminated body A and the laminated body B, (2) a step of forming a quantum dot containing layer in the laminated body A, (3) a laminated body A having a quantum dot containing layer formed therein, and a laminated body B. The step of laminating the adhesive layer via the adhesive layer, the quantum dot sheet manufactured by the steps (1) to (3) above has the adhesive layer in contact with the quantum dot-containing layer formed on only one side, The layer structure is not vertically symmetrical with respect to the thickness direction of the quantum dot-containing layer.

On the other hand, in the present invention, as shown in FIGS. 1 and 2, the quantum dot-containing layer is used as a center and has a vertically symmetrical layer structure in the thickness direction. With such a configuration, the quantum dot sheet of the present invention can improve the uniformity of in-plane brightness. The reason for this is considered as follows.
First, by making the quantum dot sheet have a vertically symmetrical layer structure, the strain due to expansion and contraction of each layer of the quantum dot sheet can be evenly dispersed. If the strain is evenly distributed, the flatness of the quantum dot sheet can be improved, and at the same time, it can be specified among multiple interfaces existing in the quantum dot sheet (for example, the interface between the quantum dot containing layer and the light transmissive substrate). It is possible to prevent the strain from concentrating on the interface.
If the quantum dot sheet has good flatness, the amount of light leaking between the optical plate and the quantum dot sheet, which will be described later, may be reduced, or the angle of light emitted from the quantum dot sheet may be higher than it should be. Can be prevented. As a result, the in-plane brightness uniformity of the quantum dot sheet can be improved.
Further, when strain is prevented from concentrating on a specific interface among a plurality of interfaces existing in the quantum dot sheet, peeling of the interface can be prevented. Delamination of the interface leads to deterioration of various functions. Therefore, by making the quantum dot sheet have a vertically symmetrical layered structure, it is possible to suppress the functional deterioration of the quantum dot sheet at the initial stage and with time.

It is to be noted that the layer configuration that is vertically symmetrical in the thickness direction means that the number of layers and the type of layers are the same in the upper and lower portions, and that the thickness of each layer is substantially the same. In order that the thicknesses can be said to be substantially the same, the ratio of the thicknesses of the upper and lower layers in the target relationship is preferably in the range of 0.95 to 1.05, and is in the range of 0.97 to 1.03. Is more preferable.
The thickness of each layer can be calculated, for example, by measuring the thickness at 20 locations from an image of a cross section photographed using a scanning transmission electron microscope (STEM) and averaging the values at 20 locations. The accelerating voltage of STEM is preferably 10 kv to 30 kV and the magnification is preferably 1000 to 7000 times. When the thickness is nano-order, the STEM magnification is preferably 50,000 to 300,000 times.
Moreover, it is preferable that the layers having a symmetrical relationship have substantially the same composition. For example, it is preferable that the light diffusion layer of the laminate A and the light diffusion layer of the laminate B have substantially the same composition. In order to say that the compositions are substantially the same, 90% by mass or more of the constituent components of the layer are preferably the same, more preferably 95% by mass or more, and more preferably 99% by mass or more. More preferable.

Quantum dot-containing layer The quantum dot-containing layer contains quantum dots that absorb primary light and emit secondary light, and a binder resin.
The quantum dots include a first quantum dot that absorbs primary light having a wavelength corresponding to blue and emits secondary light having a wavelength corresponding to red, and a first quantum dot that absorbs primary light having a wavelength corresponding to blue and corresponds to green. It is preferable to include at least one kind of second quantum dots that emits secondary light having a wavelength of, and more preferable to include both the first quantum dots and the second quantum dots.
The peak wavelength of the primary light having a wavelength corresponding to blue is preferably in the range of 380 to 480 nm, more preferably 450 nm. The secondary light having a wavelength corresponding to green preferably has a peak wavelength in the range of 495 to 570 nm, more preferably a peak wavelength of 528 nm. The secondary light having a wavelength corresponding to red preferably has a peak wavelength in the range of 620 to 750 nm, more preferably 637 nm.

The quantum dots (first quantum dot and second quantum dot) will be described below.
Quantum dots are semiconductor nanometer-sized fine particles, which have a unique optical and electrical property due to the quantum confinement effect (quantum size effect) in which electrons and excitons are confined in small nanometer-sized crystals. It exhibits properties and is also called semiconductor nanoparticles or semiconductor nanocrystals.
The quantum dots are semiconductor nanometer-sized fine particles, and are not particularly limited as long as they are materials that produce a quantum confinement effect (quantum size effect). For example, there are semiconductor fine particles whose emission color is regulated by their particle size and semiconductor fine particles having a dopant as described above. As the quantum dots in the present invention, both semiconductor fine particles whose emission color is regulated by their particle size and semiconductor fine particles having a dopant can be used, and both can obtain excellent color purity.

The quantum dots have different emission colors depending on their particle diameters. For example, in the case of quantum dots composed only of a core made of CdSe, the particle diameters are 2.3 nm, 3.0 nm, 3.8 nm, and 4 nm. The peak wavelengths of the fluorescence spectrum at 0.6 nm are 528 nm, 570 nm, 592 nm and 637 nm. That is, the particle size of the quantum dots that emit the secondary light with the peak wavelength of 637 nm is 4.6 nm, and the particle size of the quantum dots that emit the secondary light with the peak wavelength of 528 nm is 2.3 nm.
The quantum dot-containing layer may contain quantum dots that emit secondary light having a wavelength corresponding to red and quantum dots other than quantum dots that emit secondary light having a wavelength corresponding to green.
The quantum dot content is appropriately adjusted according to the thickness of the quantum dot containing layer, the light recycling rate in the backlight, the desired tint, and the like. If the thickness of the quantum dot-containing layer is within the range described later, the quantum dot content is about 0.01 to 1.0 part by mass with respect to 100 parts by mass of the binder resin in the quantum dot-containing layer.

Specific examples of the material to be the core of the quantum dot include MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS. , II-VI semiconductor compounds such as HgSe and HgTe, AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs and TiSb. A semiconductor compound or a semiconductor crystal containing a semiconductor, such as a group V semiconductor compound, a group IV semiconductor such as Si, Ge, and Pb, can be exemplified. Alternatively, a semiconductor crystal containing a semiconductor compound containing three or more elements such as InGaP can be used.
Further, as the quantum dot composed of semiconductor fine particles having a dopant, a semiconductor crystal obtained by doping the above semiconductor compound with a cation of a rare earth metal such as Eu ³⁺ , Tb ³⁺ , Ag ⁺ , and Cu ⁺ or a cation of a transition metal is used. It can also be used.
As the material for the core of the quantum dot, semiconductor crystals such as CdS, CdSe, CdTe, InP and InGaP are used from the viewpoints of ease of production, controllability of particle size capable of obtaining light emission in the visible region, and fluorescence quantum yield. Is preferred.

The quantum dot may be composed of one kind of semiconductor compound or may be composed of two or more kinds of semiconductor compounds, and for example, a core composed of a semiconductor compound and a shell composed of a semiconductor compound different from the core. It may have a core-shell structure having and.
When a core-shell type quantum dot is used, as the semiconductor that constitutes the shell, by using a material with a bandgap higher than that of the semiconductor compound that forms the core so that excitons are confined in the core, the emission efficiency of the quantum dot Can be increased.
Examples of the core-shell structure (core/shell) having such a band gap magnitude relation include CdSe/ZnS, CdSe/ZnSe, CdSe/CdS, CdTe/CdS, InP/ZnS, Gap/ZnS, Si/ZnS, InN/GaN, InP/CdSSe, InP/ZnSeTe, InGaP/ZnSe, InGaP/ZnS, Si/AlP, InP/ZnSTe, InGaP/ZnSTe, InGaP/ZnSSe, etc. may be mentioned.

The size of the quantum dots may be appropriately controlled depending on the material forming the quantum dots so that light having a desired wavelength can be obtained. The quantum dot has a larger energy band gap as the particle size becomes smaller. That is, as the crystal size decreases, the quantum dot emission shifts to the blue side, that is, to the high energy side. Therefore, by changing the size of the quantum dot, the emission wavelength can be adjusted over the entire wavelength range of the spectrum of the ultraviolet region, the visible region, and the infrared region.
Generally, the particle size (diameter) of the quantum dots is preferably in the range of 0.5 to 20 nm, and particularly preferably in the range of 1 to 10 nm. The narrower the size distribution of the quantum dots, the clearer the emission color can be obtained.
The shape of the quantum dot is not particularly limited, and may be, for example, a spherical shape, a rod shape, a disk shape, or another shape. The particle size of the quantum dot can be a true spherical value having the same volume when the particle dot is not spherical.
The quantum dots may be coated with resin. Further, the refractive index of the binder resin of the quantum dot containing layer and n _A, the refractive index of the resin (coating resin) for covering the quantum dots upon the n _B, n _{B /} n _A is 1.02 or more, or 0 It is preferable to satisfy the relationship of 0.98 or less. The quantum dots coated with the resin can improve the durability of the quantum dots. When the refractive index of the binder resin and the refractive index of the coating resin satisfy the above relationship, the resin-coated quantum dots function as internal diffusion particles described later.
In the present invention, the refractive index is based on light having a wavelength of 450 nm.

Information such as the particle size, shape, and dispersion state of the quantum dots can be obtained with a transmission electron microscope (TEM). The crystal structure and particle size of the quantum dots can be obtained by X-ray crystal diffraction (XRD). Furthermore, it is possible to obtain information on the particle size and surface of the quantum dots by the ultraviolet-visible (UV-Vis) absorption spectrum.

Examples of the binder resin for the quantum dot-containing layer include thermoplastic resins, cured products of thermosetting resin compositions, and cured products of ionizing radiation curable resin compositions. Among these, from the viewpoint of durability, a cured product of the thermosetting resin composition and a cured product of the ionizing radiation curable resin composition are preferable, and a cured product of the ionizing radiation curable resin composition is more preferable.

The thermosetting resin composition is a composition containing at least a thermosetting resin and is a resin composition that is cured by heating.
Examples of the thermosetting resin include acrylic resin, urethane resin, phenol resin, urea melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. In the thermosetting resin composition, a curing agent is added to these curable resins as needed.

The ionizing radiation curable resin composition is a composition containing a compound having an ionizing radiation curable functional group (hereinafter, also referred to as “ionizing radiation curable compound”). Examples of the ionizing radiation-curable functional group include (meth)acryloyl group, vinyl group, ethylenically unsaturated bond group such as allyl group, and epoxy group, oxetanyl group and the like, and among them, ethylenically unsaturated bond group is preferable. .. Further, among the ethylenically unsaturated bond groups, a (meth)acrylate group is preferable. Hereinafter, the ionizing radiation curable compound having a (meth)acryloyl group is referred to as a (meth)acrylate compound.
In addition, in this specification, "(meth)acrylate" refers to methacrylate and acrylate. In addition, in the present specification, “ionizing radiation” refers to an electromagnetic wave or a charged particle beam having an energy quantum capable of polymerizing or cross-linking a molecule, and usually an ultraviolet ray (UV) or an electron beam (EB) is used. Besides, electromagnetic waves such as X-rays and γ-rays, and charged particle beams such as α-rays and ion rays can also be used.

The ionizing radiation curable compound may be a monofunctional ionizing radiation curable compound having only one of the above functional groups, or a polyfunctional ionizing radiation curable compound having at least two of the above functional groups. , Or a mixture thereof.
Further, the ionizing radiation curable compound may be a monomer, an oligomer, a low molecular weight polymer, or a mixture thereof.
Among the ionizing radiation curable compounds, the monofunctional monomer can suppress the polymerization shrinkage and improve the flatness of the quantum dot sheet, and improve the adhesiveness of the quantum dot-containing layer to improve the quantum dot sheet initial stage and time course. It is suitable in that it suppresses various functional deteriorations. In particular, when the thickness of the quantum dot-containing layer is large, the above-mentioned effect when the monofunctional monomer is used becomes remarkable.
Further, when the adhesion of the quantum dot containing layer is improved by using a monofunctional monomer, the quantum dot containing layer can be brought into close contact with the laminate A and the laminate B without interposing the adhesive layer. That is, by improving the adhesiveness of the quantum dot-containing layer by using a monofunctional monomer, it is possible to easily make the structure of the quantum dot sheet vertically symmetrical with respect to the quantum dot-containing layer in the thickness direction. Further, the quantum dot-containing layer is brought into close contact with the stacked body A and the stacked body B without the adhesive layer interposed therebetween, whereby the moisture resistance and oxygen resistance of the quantum dots can be improved.
The proportion of the monofunctional monomer in the total ionizing radiation-curable compound is preferably 40% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, and 90% by mass or more. Is more preferable, and 100% by mass is most preferable.

Further, since quantum dots are weak against humidity, it is preferable to use, as a main component, an ionizing radiation curable compound having no hydroxyl group in the molecule. Specifically, the ratio of the ionizing radiation curable compound having no hydroxyl group in the molecule to the total ionizing radiation curable compound is preferably 80% by mass or more, more preferably 90% by mass or more, and 100 More preferably, it is mass %.

Examples of the ionizing radiation-curable compound having no hydroxyl group in the molecule include ethyl (meth)acrylate, butyl (meth)acrylate, ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate, octyl (meth)acrylate, dicyclopentenyl ( Monofunctional (meth)acrylate compounds such as (meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth) Acrylate, tricyclodecane dimethanol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxytri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, Examples thereof include polyfunctional (meth)acrylate compounds such as ditrimethylolpropane tetra(meth)acrylate.

Further, the ionizing radiation-curable compound preferably has a total carbon number of 8 or more from the viewpoint of increasing hydrophobicity and improving moisture resistance of the quantum dots. Considering the adhesiveness of the quantum dot-containing layer in addition to the moisture resistance, the total carbon number of the ionizing radiation curable compound is more preferably 8-20. For example, examples of the monofunctional (meth)acrylate monomer having a total carbon number of 8 to 20 include ethylhexyl (meth)acrylate and octyl (meth)acrylate.

The molecular weight of the ionizing radiation-curable compound is preferably 100 to 2000, more preferably 120 to 1000, and even more preferably 150 to 500. When the molecular weight of the ionizing radiation-curable compound is 100 or more, it is possible to easily prevent liquid dripping during production, and when the molecular weight is 2000 or less, quantum due to the pressure at the time of bonding in the step (c) described later. The thickness of the dot-containing layer can be easily made uniform.
When a monofunctional monomer is used as the ionizing radiation-curable compound, the molecular weight of the monofunctional monomer is 100 from the viewpoint of preventing dripping during production, making the thickness of the quantum dot-containing layer uniform, and adhering the quantum dot-containing layer. It is preferably -500, more preferably 120-400, and even more preferably 150-250.

When the ionizing radiation curable compound is an ultraviolet curable compound, the ionizing radiation curable composition preferably contains additives such as a photopolymerization initiator and a photopolymerization accelerator.
Examples of the photopolymerization initiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyl oxime ester, thioxanthones and the like.
These photopolymerization initiators preferably have a melting point of 20° C. or lower. This is because when the melting point is 20° C. or lower, it can be easily dissolved at room temperature when added to the above ionizing radiation-curable compound during production.
Further, the photopolymerization accelerator is capable of reducing the polymerization inhibition by air during curing and accelerating the curing rate, and, for example, from p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester and the like. At least one selected from the above is included.

Internal Diffusion Particles The quantum dot-containing layer may contain internal diffusion particles. By including the internal diffusing particles, the primary light can be made closer to uniform diffusion for the following reasons, and the angle dependence of the tint can be suppressed.
Of the light emitted from the quantum dot sheet, the secondary light is evenly diffused, while the primary light has directivity. Therefore, bringing the primary light closer to uniform diffusion leads to suppression of the angle dependence of the tint. Further, the directivity can be made close to uniform diffusion by strong diffusion, and the diffusion by the internal diffusion particles can diffuse the light to a large angle. Therefore, the inclusion of the internal diffusion particles leads to suppression of the angle dependence of the tint.
In addition, the secondary light that is uniformly diffused diffuses a large proportion of light up to a high angle, and while the light easily leaks from the edge area of the quantum dot sheet, the primary light has a small proportion of diffused light at a high angle, which is Light does not easily leak from the area. Therefore, the edge region has a large proportion of primary light, and tends to have a tint of primary light (bluish when the primary light is blue), but by including internal diffusion particles in the quantum dot-containing layer, It is possible to make the edge region less likely to be colored with the primary light.

As the internal diffusion particles, both organic particles and inorganic particles can be used. Examples of the organic particles include particles made of polymethylmethacrylate, acryl-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone resin, fluorine resin and polyester. .. Examples of the inorganic fine particles include fine particles made of silica, alumina, zirconia, titania and the like.
Examples of the shape of the internal diffusion particles include a spherical shape, a disk shape, a rugby ball shape, and an amorphous shape.
The internal diffusion particles may be any of hollow particles, porous particles and solid particles.

Further, as the internal diffusion particles, those in which n _B /n _A is 1.02 or more or 0.98 or less when the refractive index of the binder resin is n _A and the refractive index of the internal diffusion particles is n _B are used. It is preferable. n _B /n _A is a relative refractive index between the binder resin and the internal diffusion particles, and by setting n _B /n _A to 1.02 or more or 0.98 or less, light is diffused to a high angle, The angle dependence of tint can be easily suppressed. Further, by setting n _B /n _A to 1.02 or more or 0.98 or less, the probability that primary light collides with the quantum dots increases, and the usage amount of the quantum dots can be reduced.
n _B /n _A is more preferably 1.10 or more or 0.95 or less, or 1.15 or more, or from the viewpoint of strong diffusivity, suppression of light leakage of the polarizing plate, and balance of front luminance. It is more preferably 0.90 or less.
The refractive index of the internal diffusion particles can be measured by the Becke method, and the refractive index of the binder resin can be measured by the Abbe method.

The content of the internal diffusion particles is preferably 1 to 40 parts by mass and more preferably 3 to 30 parts by mass with respect to 100 parts by mass of the binder resin. By setting the content of the internal diffusing particles within the above range, light can be diffused to a high angle, and at the same time, the light leakage of the polarizing plate and the decrease in front luminance can be suppressed.

The average particle size of the internal diffusion particles is preferably 10 μm or less, and more preferably 3 μm or less, from the viewpoint of increasing the number of particles per content and achieving uniformity of diffusion. The lower limit of the average particle size of the internal diffusion particles is about 0.1 μm.

The average particle diameter of the internal diffusion particles can be calculated by the following operations (1) to (3).
(1) A transmission observation image of the quantum dot-containing layer is taken with an optical microscope. The magnification is preferably 500 to 2000 times.
(2) Arbitrary 10 particles are extracted from the observed image, the major axis and the minor axis of each particle are measured, and the particle diameter of each particle is calculated from the average of the major axis and the minor axis. The major axis is the longest diameter on the screen of each particle. In addition, the minor axis means a distance between two points where a line segment orthogonal to the midpoint of the line segment forming the major axis is drawn and the orthogonal line segment intersects with particles.
(3) The same operation is performed 5 times on the observation image of another screen of the same sample, and the value obtained from the number average of the particle diameters of 50 particles in total is taken as the average particle diameter of the internal diffusion particles.
The average particle size of the diffusing particles of the light diffusing layer, which will be described later, can also be calculated according to the above operation.

The thickness of the quantum dot-containing layer is preferably 10 to 200 μm, more preferably 20 to 150 μm, and further preferably 30 to 130 μm. When the thickness of the quantum dot-containing layer is within this range, it is suitable for weight reduction and thinning of the display device, and color unevenness due to thickness fluctuation (manufacturing tolerance) of the quantum dot-containing layer can be suppressed.

The quantum dot-containing layer is preferably in close contact with the laminate A and the laminate B without an adhesive layer. With such a structure, the structure of the quantum dot sheet can be easily made vertically symmetrical with respect to the quantum dot-containing layer in the thickness direction, and the moisture resistance and oxygen resistance of the quantum dots can be easily improved.
From the viewpoint of improving the moisture resistance and oxygen resistance of the quantum dots, the surfaces of the laminates A and B that are in close contact with the quantum dot-containing layer are preferably light transmissive base materials or barrier layers.

Laminate A and Laminate B
The laminate A and the laminate B are configured to have at least a barrier layer, a light diffusion layer, and one or more light transmissive base materials.

When the laminated body A and the laminated body B are formed into a quantum dot sheet, the laminated body has a layer structure that is vertically symmetrical with respect to the quantum dot-containing layer in the thickness direction.
The layer configuration that is vertically symmetrical in the thickness direction means that the number of layers is the same and the thickness and composition of the symmetrical layers are substantially the same. Therefore, the laminated body A and the laminated body B have the same number of layers, and have substantially the same thickness and composition of symmetrical layers.

Light-Transparent Substrate The number of light-transmissive substrates of the laminate A and the laminate B may be only one as shown in FIG. 1 or two or more as shown in FIG.
The light transmissive substrate is not particularly limited, but it is preferable that it has heat resistance and is excellent in smoothness, elasticity and mechanical strength. Examples of such transparent substrates include polyester, triacetyl cellulose (TAC), cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyether sulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal. , Polyetherketone, acrylic, polycarbonate, polyurethane, and amorphous olefins (Cyclo-Olefin-Polymer: COP).
Among the above, polyesters (polyethylene terephthalate, polyethylene naphthalate) that have been stretched, especially biaxially stretched, are preferable from the viewpoints of mechanical strength, dimensional stability, and heat resistance.

The thickness of the light-transmissive substrate is preferably 10 to 200 μm, more preferably 20 to 150 μm, and further preferably 30 to 100 μm, from the viewpoint of the balance between mechanical strength, stiffness and thinning. When the layered product A and the layered product B have two or more light transmissive substrates, the thickness of each light transmissive substrate is preferably within the above range.
In order to improve the adhesiveness, a physical treatment such as corona discharge treatment or oxidation treatment, or a coating called an anchor agent or a primer may be applied to the surface of the light-transmitting substrate in advance.

Barrier Layer The barrier layer has the role of improving the moisture resistance and oxygen resistance of the quantum dots.
The position of the barrier layer in the laminated body A and the laminated body B is not particularly limited, but in the case of the quantum dot sheet, it is preferable to be the position closer to the quantum dot containing layer side than the light diffusion layer.

The barrier layer is preferably made of an inorganic substance or an inorganic oxide, and examples thereof include a vapor deposition film of an inorganic substance or an inorganic oxide and a hydrolysis film of an inorganic alkoxide. From the viewpoint of moisture resistance and oxygen resistance, the barrier layer is preferably a vapor deposited film of an inorganic material or an inorganic oxide.
The barrier layer can be formed by a known method using a known inorganic material, inorganic oxide, inorganic alkoxide, etc., and the composition and the forming method are not particularly limited. The barrier layer may be a single layer or two or more layers. When two or more barrier layers are provided, they may have the same composition or different compositions.

The material of the vapor deposition film is silicon (Si), aluminum (Al), magnesium (Mg), calcium (Ca), potassium (K), tin (Sn), sodium (Na), boron (B), titanium (Ti). , Lead (Pb), zirconium (Zr), yttrium (Y), and the like, oxides of these, and those in which organic substances are mixed.
The inorganic alkoxide that is the material of the hydrolysis film is also called a metal alkoxide, and examples thereof include silicon alkoxides such as tetraalkoxysilane, titanium alkoxide, and aluminum alkoxide.

The thickness of the barrier layer is preferably 5 to 1000 nm, more preferably 10 to 700 nm, and more preferably 10 to 500 nm from the viewpoint of the balance among moisture resistance, oxygen resistance, crack suppression and light transmission. More preferable. When the barrier layer is a vapor deposition film, the thickness of the barrier layer is preferably 5 to 30 nm, more preferably 7 to 25 nm, and further preferably 10 to 20 nm.
Examples of a method for forming a vapor deposition film as a barrier layer include physical vapor deposition (PVD) such as vacuum vapor deposition, sputtering, and ion plating, plasma chemical vapor deposition, and thermochemical vapor deposition. Examples thereof include a chemical vapor deposition method (CVD method) such as a growth method and a photochemical vapor deposition method.

Light Diffusing Layer The light diffusing layer has the role of strengthening the diffusion of the quantum dot sheet and suppressing the angular dependence of tint.
The light diffusion layer is preferably arranged at the outermost layer of the quantum dot sheet or at a position where it can be identified with the outermost layer. The position that can be equated with the outermost layer means the position of the light diffusion layer when a thin film (a layer having a thickness of 100 nm or less) that does not substantially affect the surface unevenness of the light diffusion layer is formed on the light diffusion layer. Says the position.

The light diffusion layer preferably has an outer diffusion due to surface irregularities. By disposing such a light diffusion layer at the outermost layer or at a position that can be identified with the outermost layer, it is possible to prevent the quantum dot sheet from coming into close contact with a member (such as a brightness enhancement sheet) that comes into contact with the quantum dot sheet.
The light diffusion layer can be formed of, for example, a binder resin and diffusion particles.

Examples of the binder resin of the light diffusion layer include a thermoplastic resin, a cured product of a thermosetting resin composition, and a cured product of an ionizing radiation curable resin composition. Among these, from the viewpoint of scratch resistance, a cured product of a thermosetting resin composition and a cured product of an ionizing radiation curable resin composition are preferable, and a cured product of an ionizing radiation curable resin composition is more preferable.
As the thermosetting resin composition and the ionizing radiation curable resin composition, the same ones as exemplified for the quantum dot containing layer can be used.

The ratio of the average particle diameter of the diffusion particles to the thickness of the light diffusion layer (average particle diameter of diffusion particles/thickness of light diffusion layer) is preferably 0.10 to 2.00, and 0.15 to 1 It is more preferably 0.50 and even more preferably 0.20 to 1.00.
By setting the ratio of the average particle diameter of the diffusing particles in the light diffusing layer on the light emitting surface side to the thickness of the light diffusing layer to 0.10 or more, strong outdiffusion can be imparted. Further, by setting the ratio of the average particle size of the diffusion particles in the light diffusion layer on the light incident surface side to the thickness of the light diffusion layer to 0.10 or more, retroreflectivity is imparted and the light recycling rate is increased. Thus, it becomes possible to reduce the content of the quantum dots. Further, by setting the ratio of the average particle diameter of the diffusing particles to the thickness of the light diffusing layer to be 2.00 or less, the diffusing particles can be sufficiently held in the light diffusing layer.
Further, from the viewpoint of easily obtaining the effect based on the above ratio, the average particle diameter of the diffusion particles in the light diffusion layer is preferably 1 to 20 μm, and more preferably 1 to 10 μm.

As the diffusing particles, both organic particles and inorganic particles can be used, and the same particles as those exemplified as the internal diffusing particles of the quantum dot-containing layer can be used.

The thickness of the light diffusion layer is preferably 1 to 30 μm, and more preferably 3 to 20 μm, from the viewpoint of holding power of the diffusion particles and external diffusibility.
From the viewpoint of the balance between diffusivity and coating film strength, the diffusion particles of the light diffusion layer are preferably 10 to 200 parts by mass, and more preferably 30 to 170 parts by mass with respect to 100 parts by mass of the binder resin. It is more preferably 50 to 150 parts by mass.

Adhesive Layer In order to stack the respective layers constituting the laminated body A and the laminated body B, an adhesive layer may be interposed between the respective layers. For example, in FIG. 2, the adhesive layer is provided between the light-transmitting substrate and the barrier film and between the barrier film and the diffusion film.
The adhesive layer can be formed from a general-purpose pressure-sensitive adhesive (adhesive), thermosetting adhesive, or ionizing radiation curable adhesive.
The thickness of the adhesive layer is preferably 0.5 to 20 μm, and more preferably 1 to 10 μm from the viewpoint of adhesive strength and thinning.

The quantum dot sheet may have functional layers other than the above, such as an antireflection layer and an antistatic layer.
The total thickness of the quantum dot sheet is not particularly limited, but is about 100 to 700 μm.

Manufacturing Method of Quantum Dot Sheet Although the manufacturing method of the quantum dot sheet is not particularly limited, for example, the quantum dot sheet can be manufactured in the following order (a) to (c).
(A) A step of stacking at least a barrier layer, a light diffusing layer, and one or more light transmissive base materials to obtain a stack A and a stack B.
(B) A quantum dot-containing layer coating liquid containing a quantum dot and a binder resin component that absorbs primary light and emits secondary light is provided on one surface of either one of the laminate A and the laminate B. The process of applying and forming a quantum dot containing layer.
(C) A layered body in which the quantum dot-containing layer is not formed in the step (b) and a surface of the layered body in which the quantum dot-containing layer is formed in the step (b) on the quantum dot-containing layer side are a quantum dot-containing layer. The step of laminating the layers so as to have a vertically symmetrical layered structure in the thickness direction.

The laminated body A and the laminated body B produced in the step (a) have the same number of layers and substantially the same thickness and composition of symmetrical layers.
As the binder resin component in the step (b), any one of a thermoplastic resin, a cured product of a thermosetting resin composition, and an ionizing radiation curable resin composition, or a mixture thereof can be used.

In the step (c), the layered body in which the quantum dot-containing layer is not formed in the step (b) and the surface on the quantum dot-containing layer side of the layered body in which the quantum dot-containing layer is formed in the step (b) are bonded together. In this case, as shown in FIGS. 1 and 2, it is preferable to bond the quantum dot-containing layer without using an adhesive layer from the viewpoint of vertically symmetric structure in the thickness direction.

When the binder resin component of the step (b) is an ionizing radiation curable resin composition, the following method should be adopted in order to bond the two laminates together without the adhesive layer in the step (c). Is preferred.
First, the ionizing radiation curable resin composition preferably contains a monofunctional monomer.
Secondly, when forming the quantum dot-containing layer in the step (b), the ionizing radiation is not irradiated or the irradiation amount of the ionizing radiation is suppressed to leave an uncured portion in the ionizing radiation curable resin composition. It is preferable that the ionizing radiation is irradiated after the step (c) so that the curing of the ionizing radiation curable resin composition proceeds.
The combination of the first method and the second method is preferable in that the workability of bonding the two laminated bodies together in the step (c) without interposing an adhesive layer is further improved.

Transmittance The total light transmittance of JIS K7361-1:1997 of the quantum dot sheet of the present invention is not particularly limited, but is usually about 40% or more.

Surface Roughness In the quantum dot sheet of the present invention, the arithmetic average roughness Ra of both surfaces is preferably 0.1 to 10 μm, more preferably 0.2 to 8 μm, and 0.5 to 5 μm. Is more preferable. Ra on both surfaces of the quantum dot sheet is preferably substantially the same. Specifically, when Ra on the surface of the laminate A side is Ra _A and Ra on the surface of the laminate B side is Ra _B , Ra _A /Ra _B is in the range of 0.9 to 1.1. It is preferable.
By setting Ra to 0.1 μm or more, it is possible to prevent the quantum dot sheet from coming into close contact with a member that comes into contact with the quantum dot sheet. Examples of the member in contact with the quantum dot sheet include a prism sheet located on the light emitting side of the quantum dot sheet, and an optical plate for guiding or diffusing located on the light incident side of the quantum dot sheet. Further, by setting Ra to 10 μm or less, it is possible to suppress light leakage of the polarizing plate and a decrease in front luminance.
Further, by controlling the intensity of diffusion, from the viewpoint of balancing the suppression of the angle dependence of the tint, the suppression of the tint of the edge region, the light leakage of the polarizing plate, and the suppression of the decrease in the front luminance, Ra is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. Further, by setting Ra on the light incident surface side to 1 μm or more, retroreflectivity is imparted, the recycling rate of light is increased, and the content of quantum dots can be reduced.
In addition, Ra and Rz _JIS described later are based on JIS B0601:2001, and are average values when measured 20 times at a cutoff value of 0.8 mm.

The quantum dot sheet of the present invention has a ten-point average roughness Rz _JIS on both surfaces of preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and 0.5 to 8 μm. Is more preferable. Rz _{JIS on} both surfaces of the quantum dot sheet is preferably substantially the same. Specifically, when Rz _JIS on the surface on the laminate A side is Rz _A and Rz _JIS on the surface on the laminate B side is Rz _B , Rz _A /Rz _B is within the range of 0.9 to 1.1. Is preferred.
When the Rz _JIS satisfies the above range, it indicates that the surface roughness of the quantum dot sheet has a certain randomness and that the roughness is not extremely biased. Therefore, when Rz _JIS satisfies the above range, it is possible to reduce the bias of diffusion and prevent local adhesion.
Further, by controlling the intensity of diffusion, from the viewpoint of balancing the suppression of the angle dependence of the tint, the suppression of the tint of the edge region, the light leakage of the polarizing plate, and the suppression of the decrease in the front luminance, Rz _JIS is preferably 1 to 10 μm, and more preferably 2 to 8 μm.
In order to set Ra and Rz _JIS within the above range, a light diffusion layer described below may be positioned on the outermost surface of the quantum dot sheet.

[Backlight]
The backlight of the present invention includes at least one light source that emits primary light, an optical plate that is arranged adjacent to the light source, for guiding or diffusing light, and a quantum plate that is arranged on the light emission side of the optical plate. In a backlight including a dot sheet, the quantum dot sheet is the quantum dot sheet of the present invention described above.

As an example of the backlight of the present invention, an edge light type backlight as shown in FIG. 3 or a direct type backlight as shown in FIG. 4 can be adopted.

The optical plate 120 used for the edge light type backlight of FIG. 3 is an optical member for guiding the primary light emitted from the light source 110, and is a so-called light guide plate. The light guide plate has, for example, a substantially flat plate shape that is formed so that at least one surface thereof serves as a light incident surface and one surface substantially orthogonal thereto serves as a light emitting surface.

The light guide plate is mainly made of a matrix resin selected from highly transparent resins such as polymethylmethacrylate. If necessary, resin particles having a different refractive index from the matrix resin may be added to the light guide plate. Each surface of the light guide plate may not have a uniform flat surface but a complicated surface shape, and may be provided with a dot pattern or the like.

The optical plate 120 used for the direct type backlight of FIG. 4 is an optical member (light diffusing material) having a light diffusing property for making the pattern of the light source 110 difficult to see. Examples of the light diffusing material include a milky white resin plate having a thickness of about 1 to 3 mm.

In addition to the above-mentioned light source, optical plate and quantum dot sheet, the edge light type and the direct type backlight include a reflection plate, a light diffusion film, a prism sheet, a brightness enhancement film (BEF) and a reflection type, depending on the purpose. It may include one or more members selected from a polarizing film (DBEF) and the like. The reflecting plate is arranged on the side opposite to the light emitting surface side of the optical plate. The light diffusion film, the prism sheet, the brightness enhancement film, and the reflective polarizing film are arranged on the light emitting surface side of the optical plate. To provide a backlight excellent in balance of front brightness, viewing angle, etc. by including one or more members selected from a reflector, a light diffusion film, a prism sheet, a brightness enhancement film, a reflective polarizing film, etc. You can

In the edge light type and the direct type backlight, the light source 110 is a light emitting body that emits primary light, and it is preferable to use a light emitting body that emits primary light having a wavelength corresponding to blue. The peak wavelength of the primary light having a wavelength corresponding to blue is preferably in the range of 380 to 480 nm, more preferably 450 nm. As the light source 110, an LED light source is preferable, and a monochromatic blue LED light source is more preferable, from the viewpoint that a device in which a backlight is installed can be simplified and downsized. There is at least one light source 110, and a plurality of light sources 110 are preferable from the viewpoint of emitting sufficient primary light.
In the case where only one of the first quantum dot and the second quantum dot is contained in the quantum dot containing layer of the quantum dot sheet, in addition to the primary light source including a light emitting body that emits primary light of a wavelength corresponding to blue, It is preferable to have an auxiliary light source. Specifically, when the quantum dot containing layer contains only the first quantum dots, it is preferable to use a light emitting body that emits light having a wavelength corresponding to green as an auxiliary light source. Further, when only the second quantum dots are contained in the quantum dot containing layer, it is preferable to use a light emitting body which emits light having a wavelength corresponding to red as an auxiliary light source.

Since the backlight of the present invention uses the quantum dot sheet of the present invention described above, it is possible to improve the tint of the edge region of the backlight and the angle dependence of the tint.

[Liquid crystal display]
The liquid crystal display device of the present invention is a liquid crystal display device including a backlight and a liquid crystal panel, and the backlight is the backlight of the present invention described above.

FIG. 5 is a sectional view showing an embodiment of the liquid crystal display device of the present invention. The liquid crystal display device 300 of FIG. 5 includes a backlight 200 and a liquid crystal panel 210. Further, the backlight 200 and the liquid crystal panel 210 are incorporated and fixed in a holder 220.

The liquid crystal panel includes a polarizing plate (not shown), a color filter (not shown), and the like. The liquid crystal panel is not particularly limited, and those generally known as liquid crystal panels for liquid crystal display devices can be used. For example, a liquid crystal panel having a general structure in which the upper and lower sides of a liquid crystal layer are sandwiched by glass plates, specifically, a display type such as TN, STN, VA, IPS and OCB can be used.

The polarizing plate is not particularly limited as long as it has a desired polarization characteristic, and generally known polarizing plates for liquid crystal display devices can be used. Specifically, for example, a polarizing plate formed by stretching a polyvinyl alcohol film and containing iodine is preferably used.

The color filter is not particularly limited, and, for example, a generally known color filter for liquid crystal display devices can be used. The color filter is usually composed of a transparent coloring pattern of each color of red, green and blue, and each of the transparent coloring patterns is composed of a resin composition in which a colorant is dissolved or dispersed, preferably pigment fine particles are dispersed. ..
The color filter is formed by adjusting an ink composition colored in a predetermined color and printing it by each color pattern, or a paint-type photosensitive resin composition containing a colorant of a predetermined color. A method of forming an object by a photolithography method can be used.

The display image of the liquid crystal display device is displayed in color by the white light emitted from the backlight passing through the color filter. The liquid crystal display device can realize a display that is excellent in brightness and efficiency and that generates a very clear color by using a color filter that matches a spectrum of a backlight formed by quantum dots.

The liquid crystal panel may have a structure in which an arbitrary layer is formed on the color filter in a single layer or multiple layers. The optional layer is not particularly limited, for example, a sensor layer for a touch panel, a hard coat layer, an antistatic layer, a low refractive index layer, a high refractive index layer, an antiglare layer, an antifouling layer, an antireflection layer, a high dielectric constant. Examples thereof include a body layer, an electromagnetic wave shielding layer, an adhesive layer and the like.

Since the liquid crystal display device of the present invention uses the above-described backlight of the present invention, it is possible to improve the tint of the edge region of the display image and the angle dependence of the tint.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In addition, "part" and "%" are based on mass unless otherwise specified. Unless otherwise specified, the refractive index is 450 nm.

1. Measurement and Evaluation of Physical Properties of Quantum Dot Sheets Physical properties of quantum dot sheets and liquid crystal display devices of Examples and Comparative Examples were measured and evaluated as follows. The results are shown in Table 1.

1-1. Surface Roughness Using a surface roughness measuring instrument (model number: SE-3400/manufactured by Kosaka Laboratory Ltd.), in accordance with JIS B0601:2001, under the following measurement conditions, Ra on both surfaces of the quantum dot sheet and Rz _JIS was measured. Table 1 shows the average values of 20 measurements.
[Stylus of surface roughness detector]
Product name SE2555N manufactured by Kosaka Research Institute (tip curvature radius: 2 μm, apex angle: 90 degrees, material: diamond)
[Measurement conditions of surface roughness measuring instrument]
・Reference length (cutoff value λc of roughness curve): 0.8 mm
-Evaluation length (reference length (cut-off value λc) x 5): 4.0 mm
・Feeding speed of stylus: 0.5 mm/s
・Spare length: (cutoff value λc) x 2
・Vertical magnification: 2000 times ・Horizontal magnification: 10 times

1-2. Planarity The planarity of the quantum dot sheet immediately after manufacturing was visually evaluated. As a result, “A” indicates that waviness on the surface of the quantum dot sheet and rising of the end portion of the quantum dot sheet are not observed, and “C” indicates that at least one of waviness and rising edge of the quantum dot sheet is observed.

1-3. Luminance uniformity The liquid crystal display produced in "4" below was turned on, and the in-plane luminance uniformity was visually evaluated. One point is one that does not bother the brightness unevenness in the plane at all, and two points that is a level that does not cause any practical problems, but a level where the brightness unevenness is large in the plane. The following points were evaluated by 20 subjects, and the average score was calculated. Those with an average score of less than 1.25 points are "AA", those with an average score of 1.25 points or more and less than 1.50 points are "A", those with an average point of 1.50 points or more and less than 2.00 points "B", and those having an average score of 2.0 or more were designated as "C".

1-4. Adhesion When producing the quantum dot sheets of Examples and Comparative Examples, a laminate A having a width of 25 mm and a length of 170 mm and a laminate B having a width of 25 mm and a length of 150 mm were produced. A quantum dot layer is formed only in a region 150 mm from one end of the biaxially stretched PET film side surface of the laminate A, and the laminate B is attached to the portion where the quantum dot layer is formed from the biaxially stretched PET film side. After they were combined, they were irradiated with ultraviolet rays to obtain samples for measuring adhesion of Examples and Comparative Examples.
The protruding portion of the laminate A of the measurement sample was fixed to a chucking jig attached to a tensile tester (manufactured by A&D Company, trade name: Tensilon), and the peeling angle was 180°. The protruding portion fixed to was pulled, and the force (peeling force) required to peel off the biaxially stretched PET film of the laminate A from the quantum dot-containing layer was measured. The measurement was performed at room temperature under the condition of a pulling speed of 0.3 m/min. As a result, the biaxially stretched PET cannot be peeled off and the biaxially stretched PET is broken, and the peeling force cannot be measured as "A", 10N/25 mm or more as "B", and 10N/25 mm or less as "C". And When the base material is destroyed, it means that the adhesion is so good that the base material is destroyed.

1-5. Blocking With respect to the backlight manufactured in “4” below, occurrence of blocking was visually evaluated between the quantum dot sheet and the light guide plate and between the quantum dot sheet and the prism sheet. As a result, "A" means that no blocking occurs and "C" means that blocking occurs.

1-6. Angle Dependency of Color Tone The backlight of the example prepared in “4” below was turned on, and the color near the center of the backlight was visually evaluated from various directions. One point is one where the change in hue due to the angle is completely unnoticeable, and two points are those where there is a slight concern about the change in shade due to the angle, but there is no problem in practical use. Twenty subjects were evaluated on the basis of the evaluation criteria that the problematic level was 3 points, and the average score was calculated. Those with an average score of 1.50 or less are "AA", those with an average score of more than 1.50 and 2.00 or less are "A", those with an average score of more than 2.00 and less than 2.50. "B", and those having an average score of 2.5 or more were "C".

2. Production of Quantum Dots InP/ZnS core-shell type quantum dots (quantum dot A having a peak wavelength of 637 nm of a fluorescence spectrum are referred to by referring to a method described in a technical document “Journal of American Chemical Society. 2007, 129, 15432-15433”. ), and an InP/ZnS core-shell quantum dot (quantum dot B) having a peak wavelength of 528 nm in the fluorescence spectrum.

3. Preparation of quantum dot sheet [Example 1]
A barrier layer having a film thickness of 20 nm made of silicon oxide was formed on one surface of the biaxially stretched PET film having a thickness of 12 μm by the PVD method to obtain a barrier film. Then, on one surface of a biaxially stretched PET film having a thickness of 50 μm, a light-diffusing layer coating solution a1 having the following formulation was applied so as to have a thickness after drying of 11 μm, dried, and then irradiated with ultraviolet rays to obtain a light-diffusing layer. Was formed to obtain a light diffusion film. Next, the light diffusion film, the barrier film, and the biaxially stretched PET film having a thickness of 50 μm were laminated in this order through the adhesive layer having a thickness of 3 μm to obtain a laminate A (see FIG. 2 ). The barrier film and the light diffusion film were attached so that the surfaces of the two films on the side of the biaxially stretched PET film faced each other. Then, a laminate B was obtained by the same operation as above.
Next, the biaxially stretched PET film side surface of the laminate A was coated with a quantum dot-containing layer coating solution b1 having the following formulation so that the thickness after drying would be 100 μm, and dried to contain ion dots not irradiated with quantum dots. Layers were formed.
Then, the quantum dot-containing layer that has not been irradiated with ionizing radiation and the surface of the laminated body B on the side of the biaxially stretched PET film are opposed to each other and bonded to each other, and ultraviolet rays are irradiated from the light diffusion layer side of the laminated body A to generate ionizing radiation. Curing of the curable resin composition proceeded to obtain the quantum dot sheet of Example 1.

<Light diffusion layer coating liquid a1>
-Pentaerythritol triacrylate 30 parts (KAYARAD-PET-30 manufactured by Nippon Kayaku Co., Ltd.)
・Urethane acrylate 70 parts (Nippon Gosei Kagaku KK, UV1700B)
-Photopolymerization initiator 5 parts (BASF, Irgacure 184)
・Silicone-based leveling agent 0.1 part (manufactured by Momentive Performance Materials, TSF4460)
・Urethane resin-based diffusion particles 100 parts (average particle diameter 3 μm)
・Diluting solvent 500 parts

<Quantum dot-containing layer coating solution b1>
・Isononyl acrylate 100 parts (monofunctional monomer, refractive index 1.45)
-Photopolymerization initiator 5 parts (BASF, Irgacure 184)
・Quantum dot A 0.2 parts ・Quantum dot B 0.2 parts ・Diluting solvent 5 parts

[Example 2]
Example 2 was repeated in the same manner as in Example 1 except that 20 parts of internal scattering particles (true spherical alumina, average particle diameter 1.5 μm, refractive index 1.76) were added to the quantum dot-containing layer coating solution 1a. A quantum dot sheet was obtained.

[Comparative Example 1]
A laminate A and a laminate B were prepared in the same manner as in Example 1. Next, the biaxially stretched PET film side surface of the laminate A was coated with the quantum dot-containing layer coating solution b1 so that the thickness after drying was 100 μm, dried, and then irradiated with ultraviolet rays from the quantum dot-containing layer side. .. The irradiation amount of ultraviolet rays was the theoretical amount at which the ionizing radiation curable resin composition was completely cured.
Next, a urethane two-component curing type adhesive was applied to the surface of the laminate B on the side of the biaxially stretched PET film so that the thickness after drying was 10 μm, and dried to form an adhesive layer.
Next, the quantum dot-containing layer formed in the layered product A and the adhesive layer formed in the layered product B were opposed to each other and bonded to each other to obtain a quantum dot sheet of Comparative Example 1.

[Comparative example 2]
A quantum dot sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that the layered product B was changed to the following layered product B-1.
(Laminate B-1)
A barrier layer having a film thickness of 20 nm made of silicon oxide was formed on one surface of the biaxially stretched PET film having a thickness of 12 μm by the PVD method to obtain a barrier film. Then, on one surface of a biaxially stretched PET film having a thickness of 50 μm, a blocking prevention layer coating solution c1 having the following formulation was applied so that the thickness after drying was 3 μm, dried, and then irradiated with ultraviolet rays to prevent the blocking layer. To form an anti-blocking film. Next, the anti-blocking film, the barrier film, and the biaxially stretched PET film having a thickness of 50 μm were laminated in the above-mentioned order via the adhesive layer having a thickness of 3 μm to obtain a laminate B-1. The barrier film and the anti-blocking film were bonded together such that their biaxially oriented PET film side surfaces face each other.

<Blocking prevention layer coating liquid c1>
-Pentaerythritol triacrylate 30 parts (KAYARAD-PET-30 manufactured by Nippon Kayaku Co., Ltd.)
・Urethane acrylate 70 parts (Nippon Gosei Kagaku KK, UV1700B)
-Photopolymerization initiator 5 parts (BASF, Irgacure 184)
・Silicone-based leveling agent 0.1 part (manufactured by Momentive Performance Materials, TSF4460)
・Urethane resin particles 10 parts (average particle diameter 3 μm)
・Diluting solvent 500 parts

4. Production of Backlight and Liquid Crystal Display Device A commercially available liquid crystal display device (diagonal 7 inches) using a blue LED as a light source was disassembled and the backlight was taken out. The backlight was an edge light type, and had a reflection plate below the light guide plate, a light diffusion film above the light guide plate, and two prism sheets. The two prism sheets had lower stripes and upper stripes with stripe lines orthogonal to each other.
The light diffusion film was removed from the backlight, and the quantum dot-containing sheets of Examples 1 and 2 and Comparative Examples 1 and 2 were placed between the light guide plate and the prism sheet to obtain Examples 1 and 2 and Comparative Example 1. A backlight of ~2 was obtained.
Then, the backlights of Examples 1 and 2 and Comparative Examples 1 and 2 were returned to the places where the backlights of the disassembled liquid crystal display device were installed, and the liquid crystal display devices of Examples 1 and 2 and Comparative Examples 1 and 2 were returned. Got

As is clear from the results in Table 1, the quantum dot sheets of Examples 1 and 2 were excellent in flatness and therefore excellent in in-plane brightness uniformity. Moreover, the quantum dot sheets of Examples 1 and 2 were excellent in adhesiveness, and were able to suppress the functional deterioration in the initial stage and over time.

10: quantum dot containing layers 21a, 21b, 31a, 31b, 41a, 41b: light transmissive substrates 30a, 30b: barrier films 32a, 32b: barrier layers 40a, 40b: light diffusion films 42a, 42b: light diffusion layer 51a , 51b, 52a, 52b: adhesive layer 61: laminated body A
62: laminated body B
100: quantum dot sheet 110: light source 120: optical plate 130: reflection plate 140: prism sheet 200: backlight 210: liquid crystal panel 220: holder 300: liquid crystal display device

Claims (11)

A quantum dot-containing layer containing a quantum dot that absorbs primary light and emits secondary light and a binder resin, a stack A formed on one surface of the quantum dot-containing layer, and the quantum dot-containing layer And a laminated body B arranged on the other surface of
The laminated body A and the laminated body B are configured to have at least a barrier layer, a light diffusion layer, and one or more light transmissive base materials,
The laminated body A and the laminated body B are arranged so as to have a vertically symmetrical layered structure with respect to the quantum dot-containing layer in the thickness direction,
The binder resin is a cured product of a composition containing a compound having an ionizing radiation curable functional group,
The compound having an ionizing radiation-curable functional group contains 100 % by mass of a monofunctional monomer,
The quantum dot-containing layer further contains internal diffusion particles, and when the refractive index of the binder resin is n _A and the refractive index of the internal diffusion particles is n _B , n _B /n _A is 1.02 or more, or A quantum dot sheet having 0.98 or less. A quantum dot-containing layer containing a quantum dot that absorbs primary light and emits secondary light and a binder resin, a stack A formed on one surface of the quantum dot-containing layer, and the quantum dot-containing layer And a laminated body B arranged on the other surface of
The laminated body A and the laminated body B are configured to have at least a barrier layer, a light diffusion layer, and two or more light transmissive base materials,
The laminated body A and the laminated body B are arranged so as to have a vertically symmetrical layered structure with respect to the quantum dot-containing layer in the thickness direction,
The binder resin is a cured product of a composition containing a compound having an ionizing radiation curable functional group,
In the compound having an ionizing radiation-curable functional group, 40% by mass or more of a monofunctional monomer,
The quantum dot-containing layer further includes internal diffusion particles, and has a refractive index n of the binder resin. _A , The refractive index of the internal diffusion particles is n _B And then n _B /N _A Is 1.02 or more or 0.98 or less, a quantum dot sheet. A quantum dot-containing layer containing a quantum dot that absorbs primary light and emits secondary light and a binder resin, a stack A formed on one surface of the quantum dot-containing layer, and the quantum dot-containing layer And a laminated body B arranged on the other surface of
The laminated body A and the laminated body B are configured to have at least a barrier layer, a light diffusion layer, and one or more light transmissive base materials,
The light diffusion layer contains diffusion particles and a binder resin, the content of the diffusion particles contained in the light diffusion layer is 10 to 200 parts by weight with respect to 100 parts by weight of the binder resin contained in the light diffusion layer,
The laminated body A and the laminated body B are arranged so as to have a vertically symmetrical layered structure with respect to the quantum dot-containing layer in the thickness direction,
The binder resin contained in the quantum dot-containing layer is a cured product of a composition containing a compound having an ionizing radiation curable functional group,
In the compound having an ionizing radiation-curable functional group, 40% by mass or more of a monofunctional monomer,
The quantum dot-containing layer further includes internal diffusion particles, and has a refractive index n of the binder resin. _A , The refractive index of the internal diffusion particles is n _B And then n _B /N _A Is 1.02 or more or 0.98 or less, a quantum dot sheet. The quantum dot containing layer, the quantum dot sheet according to any one of claims 1 to 3 comprising in close contact with the laminate A and the laminate B without interposing an adhesive layer. The quantum dots according to any one of claims 1 to 4, wherein both surfaces of the quantum dot sheet have an arithmetic average roughness Ra of a cutoff value of 0.8 mm in accordance with JIS B0601:2001 of 0.1 to 10 µm. Sheet. A back including at least one light source that emits primary light, an optical plate that is arranged adjacent to the light source, for guiding or diffusing light, and a quantum dot sheet that is arranged on the light emission side of the optical plate. in light, the quantum dot sheet is a quantum dot sheet according to any one of claims 1-5 backlight. A liquid crystal display device comprising a backlight and a liquid crystal panel, wherein the backlight is the backlight according to claim 6 . The manufacturing method of the quantum dot sheet which performs the following processes of (a)-(c) in order.
(A) A step of stacking at least a barrier layer, a light diffusing layer, and one or more light transmissive base materials to obtain a stack A and a stack B.
(B) A quantum dot-containing layer coating liquid containing a quantum dot and a binder resin component that absorbs primary light and emits secondary light is provided on one surface of either one of the laminate A and the laminate B. The coating, the binder resin is a cured product of a composition containing a compound having an ionizing radiation-curable functional group, wherein the compound having an ionizing radiation-curable functional group contains 100 % by mass of a monofunctional monomer, The quantum dot-containing layer further contains internal diffusion particles, and when the refractive index of the binder resin is n _A and the refractive index of the internal diffusion particles is n _B , n _B /n _A is 1.02 or more or 0. A step of forming a quantum dot-containing layer, which is not more than 0.98.
(C) A layered body in which the quantum dot-containing layer is not formed in the step (b) and a surface of the layered body in which the quantum dot-containing layer is formed in the step (b) on the quantum dot-containing layer side are a quantum dot-containing layer. The step of laminating the layers so as to have a vertically symmetrical layered structure in the thickness direction. The manufacturing method of the quantum dot sheet which performs the following processes of (a)-(c) in order.
(A) A step of stacking at least a barrier layer, a light diffusing layer, and two or more light transmissive base materials to obtain a stack A and a stack B.
(B) A quantum dot-containing layer coating liquid containing a quantum dot and a binder resin component that absorbs primary light and emits secondary light is provided on one surface of either one of the laminate A and the laminate B. The binder resin is a cured product of a composition containing a compound having an ionizing radiation-curable functional group, and the binder resin contains 40% by mass or more of a monofunctional monomer in the compound having an ionizing radiation-curable functional group, The quantum dot-containing layer further includes internal diffusion particles, and has a refractive index n of the binder resin. _A , The refractive index of the internal diffusion particles is n _B And then n _B /N _A Is 1.02 or more or 0.98 or less, the process of forming a quantum dot containing layer.
(C) A layered body in which the quantum dot-containing layer is not formed in the step (b) and a surface of the layered body in which the quantum dot-containing layer is formed in the step (b) on the quantum dot-containing layer side are a quantum dot-containing layer. The step of laminating the layers so as to have a vertically symmetrical layered structure in the thickness direction. The manufacturing method of the quantum dot sheet which performs the following processes of (a)-(c) in order.
(A) at least a barrier layer, a light diffusion layer and one or more light transmissive substrates are laminated, the light diffusion layer contains diffusion particles and a binder resin, and the content of the diffusion particles contained in the light diffusion layer is A step of obtaining a layered product A and a layered product B which are 10 to 200 parts by mass with respect to 100 parts by mass of the binder resin contained in the light diffusion layer.
(B) A quantum dot-containing layer coating liquid containing a quantum dot and a binder resin component that absorbs primary light and emits secondary light is provided on one surface of either one of the laminate A and the laminate B. The binder resin applied and contained in the quantum dot-containing layer is a cured product of a composition containing a compound having an ionizing radiation-curable functional group, and a monofunctional monomer in the compound having an ionizing radiation-curable functional group. Of 40% by mass or more, the quantum dot-containing layer further contains internal diffusion particles, and the refractive index of the binder resin is n. _A , The refractive index of the internal diffusion particles is n _B And then n _B /N _A Is 1.02 or more or 0.98 or less, the process of forming a quantum dot containing layer.
(C) A layered body in which the quantum dot-containing layer is not formed in the step (b) and a surface on the quantum dot-containing layer side of the layered body in which the quantum dot-containing layer is formed in the step (b) are a quantum dot-containing layer. The step of laminating the layers so as to have a vertically symmetrical layered structure in the thickness direction. In the step (c), the layered product in which the quantum dot-containing layer is not formed and the surface of the layered product in which the quantum dot-containing layer is formed in the step (b) on the side of the quantum dot-containing layer are provided with an adhesive layer therebetween. The method for producing a quantum dot sheet according to any one of claims 8 to 10, wherein the quantum dot sheet is bonded without being attached.