JP2018124164A - Deterioration evaluation method of optical wavelength conversion sheet, optical wavelength conversion sheet, backlight device, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration evaluation method of an optical wavelength conversion sheet capable of performing quantitative deterioration evaluation having high correlation with visual evaluation.SOLUTION: A deterioration evaluation method of an optical wavelength conversion sheet 10 having host matrix and dispersed quantum dots in a host matrix, includes: a step of measuring a brightness distribution of at least a part of the other surface 10B opposite to one surface 10 in an optical wavelength conversion sheet 10 in a state that light capable of changing a wavelength by the quantum dots is irradiated on one surface 10A of the optical wavelength conversion sheet 10; a step of obtaining a distribution of a brightness change amount based on the measured distribution of the brightness change amount; a step of detecting a minimum value adjacent to a maximum value; a step of obtaining a width between a position at which the maximum value is obtained and a position at which the minimum value is obtained; and a step of evaluating deterioration of the optical wavelength conversion sheet based on the width.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light wavelength conversion sheet deterioration evaluation method, a light wavelength conversion sheet, a backlight device, and an image display device.

  2. Description of the Related Art A transmissive image display device such as a liquid crystal display device generally includes a backlight device that is disposed on the back side of a transmissive image display panel such as a liquid crystal display panel and illuminates the transmissive image display panel.

  Currently, in order to improve color reproducibility, it has been studied to incorporate an optical wavelength conversion sheet including an optical wavelength conversion layer containing quantum dots and a binder resin into a backlight device (see, for example, Patent Document 1). Quantum dots can absorb light (primary light) and emit light of different wavelengths (secondary light). The wavelength of light emitted from the quantum dot mainly depends on the particle diameter of the quantum dot. Therefore, in the backlight device incorporating the light wavelength conversion sheet, various colors can be reproduced while using a light source that projects light in a single wavelength region. For example, when a light source that emits blue light is used, the light wavelength conversion sheet can absorb blue light and emit green light and red light. Since the backlight device in which such a light wavelength conversion sheet is incorporated has excellent color purity, an image display device using this backlight device has excellent color reproducibility.

JP 2015-1111518 A

  In the light wavelength conversion sheet, the quantum dots are deteriorated by moisture and oxygen, and the light emission efficiency may be lowered. Therefore, a barrier film for suppressing the transmission of moisture and oxygen is provided on both surfaces of the light wavelength conversion layer. Provided. Since the barrier film is provided so as to sandwich the light wavelength conversion layer, the light wavelength conversion sheet usually has a structure in which a barrier film, a light wavelength conversion layer, and a barrier film are laminated in this order.

  However, even the light wavelength conversion sheet having the structure as described above is usually cut because the light wavelength conversion sheet is cut into a desired size with the barrier films provided on both sides of the light wavelength conversion layer. There is no barrier film on the side surface of the light wavelength conversion sheet, and the light wavelength conversion layer is exposed. For this reason, the quantum dot of the edge part of a light wavelength conversion sheet tends to deteriorate compared with the center part of a light wavelength conversion sheet. When the quantum dot at the end of the light wavelength conversion sheet deteriorates, the end has a color different from the color at the center during light emission.

  At present, the deterioration evaluation of the light wavelength conversion sheet is visually performed. However, a skilled technique is required to visually evaluate the deterioration of the light wavelength conversion sheet with a certain objectivity. For this reason, the deterioration evaluation method of the optical wavelength conversion sheet which has high correlation with visual evaluation and can be quantified is required. In addition, the quantitative degradation evaluation method of the light wavelength conversion sheet has not been established yet.

  The present invention has been made to solve the above problems. It is an object of the present invention to provide a degradation evaluation method for an optical wavelength conversion sheet capable of quantitative degradation assessment having a high correlation with visual assessment. Another object of the present invention is to provide a light wavelength conversion sheet in which a color change due to deterioration of quantum dots is difficult to be confirmed when visually evaluated during light emission, and a backlight device and an image display device including such a light wavelength conversion sheet. To do.

  According to one aspect of the present invention, there is provided a degradation evaluation method for an optical wavelength conversion sheet comprising an optical wavelength conversion layer including a host matrix and quantum dots dispersed in the host matrix, the optical wavelength conversion sheet Measuring a luminance distribution of at least a part of the other surface opposite to the one surface of the light wavelength conversion sheet in a state in which light that can be converted by the quantum dots is irradiated to the one surface of the light wavelength; Obtaining a luminance variation distribution based on the measured luminance distribution; detecting a maximum value from the obtained luminance variation distribution; and a minimum value adjacent to the maximum value; and the maximum value A deterioration evaluation method for an optical wavelength conversion sheet, comprising: obtaining a width from a position where the minimum value can be obtained to a position where the minimum value is obtained, and evaluating deterioration of the optical wavelength conversion sheet based on the width. It is subjected.

  In the degradation evaluation method for the optical wavelength conversion sheet, the step of measuring the luminance distribution is a step of measuring the luminance of at least an end portion of the optical wavelength conversion sheet, and the step of obtaining the luminance variation distribution is the light It may be a step of obtaining a luminance change amount at the end of the wavelength conversion sheet.

  In the degradation evaluation method of the light wavelength conversion sheet, the light wavelength conversion sheet further includes a step of arranging the light wavelength conversion sheet on a light emitting surface of a direct type backlight device before the step of measuring the luminance distribution. The size of the light emitting surface may be smaller than the size of the light emitting surface, and the light emitted in the step of measuring the luminance distribution may be light emitted from the backlight device.

  In the degradation evaluation method for the light wavelength conversion sheet, a barrier film that suppresses permeation of moisture and oxygen may be further provided on at least one surface of the light wavelength conversion layer.

  In the degradation evaluation method for the light wavelength conversion sheet, the light that can be wavelength-converted by the quantum dots is blue light, the quantum dots convert the blue light into green light, and the blue light. It may include a second quantum dot that converts to red light.

  According to another aspect of the present invention, a light wavelength conversion sheet comprising a light wavelength conversion layer comprising a host matrix and quantum dots dispersed in the host matrix, wherein the light wavelength conversion sheet is 60 ° C. with respect to the light wavelength conversion sheet. In addition, a durability test is performed for 500 hours in a 90% relative humidity environment, and after the durability test, the width when the deterioration of the light wavelength conversion sheet is evaluated by the deterioration evaluation method is 5 mm or less. An optical wavelength conversion sheet is provided.

  The light wavelength conversion sheet may further include a barrier film that suppresses transmission of moisture and oxygen on at least one surface of the light wavelength conversion layer.

  In the light wavelength conversion sheet, the quantum dot may include a first quantum dot that converts the blue light into green light and a second quantum dot that converts the blue light into red light.

  According to the other aspect of this invention, a backlight apparatus provided with a light source and said light wavelength conversion sheet which receives the light from the said light source is provided.

  According to another aspect of the present invention, there is provided an image display device comprising the above backlight device and a display panel disposed on the light output side of the backlight device.

  According to the deterioration evaluation method for a light wavelength conversion sheet of one aspect of the present invention, quantitative deterioration evaluation having a high correlation with visual evaluation is possible. Further, according to another aspect of the present invention, a light wavelength conversion sheet in which a color change due to deterioration of quantum dots is difficult to be confirmed when visually evaluated during light emission, and a backlight device and an image including such a light wavelength conversion sheet are provided. A display device can be provided.

It is a figure for demonstrating the degradation evaluation method of the optical wavelength conversion sheet which concerns on embodiment. It is a figure at the time of measuring the luminance distribution of the light wavelength conversion sheet which concerns on embodiment. It is a schematic block diagram of the light wavelength conversion sheet which concerns on embodiment. It is a figure which shows the effect | action of the light wavelength conversion sheet which concerns on embodiment. 1 is a schematic configuration diagram of an image display device including a backlight device according to an embodiment. It is a perspective view of the lens sheet shown by FIG. It is sectional drawing along the II line of the lens sheet of FIG. It is a schematic block diagram of the other backlight apparatus which concerns on embodiment. 5 is a graph showing a luminance distribution of a light wavelength conversion sheet according to Sample 2. 5 is a graph showing a luminance variation distribution of a light wavelength conversion sheet according to Sample 2. It is the graph which expanded a part of luminance variation distribution of FIG.

  Hereinafter, a method for evaluating deterioration of a light wavelength conversion sheet, a light wavelength conversion sheet, a backlight device, and an image display device according to an embodiment of the present invention will be described with reference to the drawings. In this specification, terms such as “sheet” and “film” are not distinguished from each other only based on the difference in designation. Thus, for example, “sheet” is used to include a member that may also be referred to as a film, and “film” is used to include a member that may also be referred to as a sheet. FIG. 1 is a view for explaining a degradation evaluation method for a light wavelength conversion sheet according to the embodiment, FIG. 2 is a view for measuring a luminance distribution of the light wavelength conversion sheet according to the embodiment, and FIG. It is a schematic block diagram of the light wavelength conversion sheet | seat which concerns on this embodiment, FIG. 4 is a figure which shows the effect | action of the light wavelength conversion sheet | seat which concerns on this embodiment.

<<< Degradation Evaluation Method of Light Wavelength Conversion Sheet >>>
When evaluating the deterioration of the light wavelength conversion sheet, first, as shown in FIG. 1, the deterioration evaluation apparatus 1 and the light wavelength conversion sheet 10 to be measured are prepared. The degradation evaluation apparatus 1 is disposed directly above the direct-type backlight device 2 and the backlight device 2 and is electrically connected to the luminance meter 3 and the luminance meter 3 for measuring the luminance of the light wavelength conversion sheet 10. And a processing device 4.

<< Backlight device >>
The backlight device 2 includes a light source 5 and a light diffusion plate 6 that is disposed on the light source 5 and has a function of diffusing light from the light source 5. The backlight device 2 may include a lens sheet and a reflective polarization separation sheet on the light diffusion plate 6 in addition to the light source 5 and the light diffusion plate 6. The light emitting surface 2A of the backlight device 2 shown in FIG. 1 is composed of a light exit surface of a light diffusing plate.

<Light source>
The light source 5 emits light whose wavelength is converted by a quantum dot 17 described later. The light source 5 is not particularly limited as long as it irradiates light that is wavelength-converted by the quantum dots 17, but for example, a fluorescent lamp such as a linear cold cathode tube, a point light emitting diode (LED), or the like Incandescent light bulbs are listed. When the quantum dot 17 includes a first quantum dot that converts blue light into green light and a second quantum dot that converts blue light into red light, the light source 2 includes a light source that emits blue light, A blue light emitting diode is particularly preferable. In this specification, “blue light” is light having a wavelength range of 380 nm or more and less than 480 nm, “green light” is light having a wavelength range of 480 nm or more and less than 590 nm, and “red light” is It is light having a wavelength range of 590 nm to 750 nm.

<Light diffusion plate>
The light diffusing plate 6 has a light incident surface 6A constituted by one surface on the light source 5 side and a light outgoing surface 6B constituted by the other surface on the light wavelength conversion sheet 10 side. The light that has entered the light diffusion plate 6 from the light incident surface 6A is diffused in the light diffusion plate 6 and emitted from the light output surface 6B.

  The light diffusing plate 6 is not particularly limited as long as the light from the light source 5 can be diffused. For example, a plate in which light diffusing particles are dispersed in a transparent material can be used. Although it does not specifically limit as a transparent material, For example, transparent resin, inorganic glass, etc. are mentioned. As the transparent resin, a transparent thermoplastic resin is suitably used because it is easy to mold. The transparent thermoplastic resin is not particularly limited. For example, polystyrene resin, styrene-methyl methacrylate copolymer resin, styrene-methacrylic acid copolymer resin, styrene-maleic anhydride copolymer resin. Methacrylic resin, acrylic resin, polycarbonate resin, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), AS resin (acrylonitrile-styrene copolymer resin), polyolefin resin (polyethylene resin, polypropylene resin, etc.) and the like. . One of these may be used, or two or more of these may be mixed and used. Examples of the light diffusing particles in the light diffusing plate 6 include light diffusing particles generally used as a light diffusing plate.

<< Brightness meter >>
The luminance meter 3 measures the luminance distribution of the other surface 10B on the side opposite to the one surface 10A on the backlight device 2 side of the light wavelength conversion sheet 10. The luminance meter may be a surface luminance meter that measures the luminance distribution of the entire surface. The luminance meter 3 is not particularly limited, and a commercially available product can be used. Examples of commercially available luminance meters include UA-200 (manufactured by Topcon Techno House). The distance (focal length) from the surface 10B of the light wavelength conversion sheet 10 to the luminance meter 3 can be adjusted as appropriate.

<< Processing equipment >>
The processing device 4 has a function of acquiring the luminance distribution measured by the luminance meter 3 as data and obtaining the luminance change amount distribution based on the acquired luminance distribution. Further, the processing device 4 may have a function of extracting a luminance distribution in a designated portion (for example, a straight portion from any one edge of the light wavelength conversion sheet to the other edge).

<< Light wavelength conversion sheet >>
The light wavelength conversion sheet 10 to be measured is a sheet for converting the wavelength of some of the incident light to other wavelengths and emitting the other part of the incident light and the wavelength-converted light. is there. The size of the light wavelength conversion sheet 10 is preferably smaller than the size of the light emitting surface 2 </ b> A of the backlight device 2. By using the light wavelength conversion sheet 10 having such a size, it is possible to evaluate not only the deterioration of the central portion side than the end portion of the light wavelength conversion sheet 10 but also the deterioration of the end portion of the light wavelength conversion sheet 10. it can. The “deterioration of the end portion” in the present specification means that the quantum dots existing at the end portion of the light wavelength conversion sheet deteriorate.

  As shown in FIG. 3, the light wavelength conversion sheet 10 includes a light wavelength conversion layer 11, barrier films 12 and 13 provided on both surfaces of the light wavelength conversion layer 11, and light wavelength conversion layers in the barrier films 12 and 13. The light diffusion layers 14 and 15 are provided on the surface opposite to the surface on the 11th side. In the light wavelength conversion sheet 10, the surfaces of the light diffusion layers 14 and 15 constitute the surface of the light wavelength conversion sheet 10.

  The light wavelength conversion sheet 10 has a structure of a light diffusion layer 14 / barrier film 12 / light wavelength conversion layer 11 / barrier film 13 / light diffusion layer 15, but the light wavelength conversion sheet has a light wavelength conversion layer. If so, the structure of the light wavelength conversion sheet is not particularly limited. For example, the light wavelength conversion sheet is a light diffusion layer / barrier film / light wavelength conversion layer / barrier film, barrier film / light wavelength conversion layer / barrier film, light transmissive substrate / light wavelength conversion layer / light transmissive substrate. The light diffusion layer / overcoat layer / light wavelength conversion layer / overcoat layer / light diffusion layer, or overcoat layer / light wavelength conversion layer / overcoat layer may be employed.

  In the light wavelength conversion sheet 10, as shown in FIG. 4, when light is incident from the surface 10 </ b> A of the light wavelength conversion sheet 10, the light L <b> 1 incident on the quantum dots 17 in the light wavelength conversion layer 11 is It is converted into light L2 having a wavelength different from that of the light L1, and is emitted from the surface 10B. On the other hand, even when light is incident from the surface 10A, the light L1 passing between the quantum dots 17 in the light wavelength conversion layer 11 is emitted from the surface 10B without being wavelength-converted.

  The thickness of the light wavelength conversion sheet 10 is preferably 10 μm or more and 500 μm or less. If the average thickness of the light wavelength conversion sheet 10 is in this range, it is suitable for weight reduction and thinning of the backlight device in which the light wavelength conversion sheet 10 is incorporated.

  The thickness of the light wavelength conversion sheet 10 is obtained by photographing a cross section of the light wavelength conversion sheet 10 using a scanning electron microscope (SEM), measuring the thickness of the light wavelength conversion sheet 10 in 20 positions in the image of the cross section, Let it be the average value of the thickness of 20 places. Among these, considering that the film thickness of the light wavelength conversion sheet 10 is on the order of μm, it is preferable to use SEM. In the measurement with the SEM, it is preferable that the acceleration voltage is 30 kV and the magnification is 1000 to 7000 times.

Since the optical wavelength conversion sheet 10 includes the barrier films 12 and 13, the entire sheet has a water vapor transmission rate (WVTR) of 0.1 g / (m at 40 ° C. and a relative humidity of 90%. ² · 24h) is preferable. The water vapor transmission rate is a numerical value obtained by a method based on JIS K7129: 2008. The water vapor transmission rate can be measured using a water vapor transmission rate measuring device (product name “PERMATRAN-W3 / 31”, manufactured by MOCON). The water vapor transmission rate is an average value of values obtained by measuring three times.

Since the optical wavelength conversion sheet 10 includes the barrier films 12 and 13, the oxygen transmission rate (OTR: Oxygen Transmission Rate) at 23 ° C. and a relative humidity of 90% is 0.1 cm ³ / (m. ² · 24 h · atm) is preferable. The oxygen permeability is a numerical value obtained by a method based on JIS K7126: 2006. The oxygen permeability can be measured using an oxygen gas permeability measuring device (product name “OX-TRAN 2/21”, manufactured by MOCON). The oxygen transmission rate is the average of the values obtained by measuring three times.

In the light wavelength conversion sheet 10, the water vapor transmission rate at 40 ° C. and a relative humidity of 90% is preferably 1.0 × 10 ⁻² g / (m ² · 24 h) or less. The oxygen transmission rate at 23 ° C. and 90% relative humidity is preferably 1.0 × 10 ⁻² cm ³ / (m ² · 24 h · atm) or less.

<Light wavelength conversion layer>
The light wavelength conversion layer 11 includes a host matrix 16 and quantum dots 17 dispersed in the host matrix 16. The light wavelength conversion layer 11 preferably contains light scattering particles 18 in order to increase wavelength efficiency. Further, the light wavelength conversion layer 11 preferably contains an additive for suppressing the deterioration of the quantum dots 17. Both surfaces of the light wavelength conversion layer 11 are covered with the barrier films 12 and 13, but the side surfaces of the light wavelength conversion layer 11 are exposed.

  The film thickness of the light wavelength conversion layer 11 is preferably 10 μm or more and 200 μm or less. If the average thickness of the light wavelength conversion layer 11 is within this range, it is suitable for reducing the weight and thickness of the backlight device. The film thickness of the light wavelength conversion layer 11 is obtained by photographing a cross section of the light wavelength conversion layer 11 using a scanning electron microscope (SEM), and measuring the film thickness of the light wavelength conversion layer 11 in 20 positions in the image of the cross section. , And the average value of the film thickness at the 20 locations. The upper limit of the average film thickness of the light wavelength conversion layer 11 is more preferably less than 170 μm.

(Host matrix)
The host matrix 16 is not particularly limited, and examples thereof include at least one of binder resin, glass such as silica glass, and silica gel. Although it does not specifically limit as binder resin, The polymer of a polymeric compound is mentioned. The polymerizable compound (curable compound) is a polymerizable compound, and examples thereof include an ionizing radiation polymerizable compound (ionizing radiation curable compound) and a thermopolymerizable compound (thermosetting compound). Examples of the ionizing radiation in this specification include visible light, ultraviolet rays, X-rays, electron beams, α rays, β rays, and γ rays.

  The ionizing radiation polymerizable compound has at least one ionizing radiation polymerizable functional group in the molecule. Examples of the ionizing radiation polymerizable functional group include ethylenically unsaturated groups such as a (meth) acryloyl group, a vinyl group, and an allyl group. The “(meth) acryloyl group” means to include both “acryloyl group” and “methacryloyl group”.

  Examples of the ionizing radiation polymerizable compound include an ionizing radiation polymerizable monomer, an ionizing radiation polymerizable oligomer, and an ionizing radiation polymerizable prepolymer, and these can be appropriately adjusted and used. As the ionizing radiation polymerizable compound, a combination of an ionizing radiation polymerizable monomer and an ionizing radiation polymerizable oligomer or an ionizing radiation polymerizable prepolymer is preferable.

  Examples of the ionizing radiation polymerizable monomer include monomers containing a hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and ethylene glycol di (meth) acrylate. , Diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, tetramethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylol ethanetri (meth) ) Acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaeryth Ritorutetora (meth) acrylate, dipentaerythritol hexa (meth) acrylate, glycerol (meth) (meth) acrylic acid esters such as acrylate.

  As the ionizing radiation polymerizable oligomer, a polyfunctional oligomer having two or more functional groups is preferable, and a polyfunctional oligomer having three (trifunctional) or more ionizing radiation polymerizable functional groups is more preferable. Examples of the polyfunctional oligomer include polyester (meth) acrylate, urethane (meth) acrylate, polyester-urethane (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, and isocyanurate. (Meth) acrylate, epoxy (meth) acrylate, etc. are mentioned.

  The ionizing radiation polymerizable prepolymer has a weight average molecular weight exceeding 10,000, and the weight average molecular weight is preferably 10,000 or more and 80,000 or less, and more preferably 10,000 or more and 40,000 or less. When the weight average molecular weight exceeds 80,000, the viscosity is high, so that the coating suitability is lowered, and the appearance of the obtained light wavelength conversion layer may be deteriorated. For this reason, when the ionizing radiation polymerizable prepolymer having a weight average molecular weight exceeding 80,000 is used, it is preferable to mix and use the polymerizable monomer and the polymerizable oligomer. Examples of the polyfunctional polymerizable prepolymer include urethane (meth) acrylate, isocyanurate (meth) acrylate, polyester-urethane (meth) acrylate, and epoxy (meth) acrylate.

  The thermopolymerizable compound has at least one thermopolymerizable functional group in the molecule. Examples of the thermally polymerizable functional group include cyclic ether groups such as epoxy groups and oxetanyl groups, vinyl ether groups, and the like.

  Examples of the thermopolymerizable compound include cyclic ether compounds having at least one cyclic ether group in the molecule such as epoxy compounds and oxetane compounds, and vinyl ether compounds. As the cationically polymerizable compound, from the viewpoint of further suppressing the occurrence of tunneling, a cyclic ether compound is preferable, and among the cyclic ether compounds, an epoxy compound is preferable.

  An epoxy compound is a compound having one or more epoxy groups in the molecule. Although it does not specifically limit as an epoxy compound, For example, a bisphenol A type epoxy compound, a bisphenol F type epoxy compound, a bisphenol S type epoxy compound, a biphenyl type epoxy compound, a fluorene type epoxy compound, a novolak phenol type epoxy compound, a cresol novolak type epoxy Compounds, aromatics such as modified products thereof, or alkylene glycol diglycidyl ethers such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether or 1,6-hexanediol diglycidyl ether, glycerin or alkylene oxide adducts thereof Polyglycidyl ethers of polyhydric alcohols such as di- or triglycidyl ethers, polyethylene glycols or alkylene glycols thereof Diglycidyl ether side adduct, polypropylene glycol or polyalkylene glycol diglycidyl ether diglycidyl ether of alkylene oxide adduct thereof, and aliphatic, such as alkylene oxide. Here, as the alkylene oxide, aliphatic epoxy compounds such as ethylene oxide and propylene oxide, 3 ′, 4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl methacrylate and the like Examples thereof include alicyclic epoxy compounds containing one or more epoxy groups and one or more ester groups in the molecule. Among these, alicyclic epoxy compounds such as 3 ′, 4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and 3,4-epoxycyclohexylmethyl methacrylate are preferable in terms of adhesive strength and curability. .

(Quantum dot)
The quantum dots 17 are nano-sized semiconductor particles having a quantum confinement effect. The particle diameter and average particle diameter of the quantum dots 17 are, for example, 1 nm or more and 20 nm or less. When the quantum dot 17 absorbs light from the excitation source and reaches an energy excitation state, the quantum dot 17 emits energy corresponding to the energy band gap of the quantum dot. Therefore, by adjusting the particle size of the quantum dots 17 or the composition of the substance, the energy band gap can be adjusted, and energy in various levels of wavelength bands can be obtained. In particular, the quantum dots 17 can generate strong fluorescence in a narrow wavelength band.

  Specifically, the energy band gap of the quantum dots 17 increases as the particle diameter decreases. That is, as the crystal size decreases, the light emission of the quantum dots 17 shifts to the blue side, that is, to the high energy side. Therefore, by changing the particle diameter of the quantum dots 17, the emission wavelength can be adjusted over the entire wavelength range of the ultraviolet region, the visible region, and the infrared region. For example, when the quantum dot 17 is composed of CdSe / ZnS described later, blue light is emitted when the particle diameter of the quantum dot 17 is 2.0 nm or more and 4.0 nm or less, and the particle diameter of the quantum dot 17 is Green light is emitted when 3.0 nm or more and 6.0 nm or less, and red light is emitted when the particle diameter of the quantum dots 17 is 4.5 nm or more and 10.0 nm or less. In the above, the particle diameter range of the quantum dot emitting blue light and the particle diameter range of the quantum dot emitting green light partially overlap, and the particle diameter of the quantum dot emitting green light and the red light Although the range of the particle diameter of the emitted quantum dots partially overlaps, even if the quantum dots have the same particle diameter, the emission color may vary depending on the size of the quantum dot core, so there is no contradiction. Not what you want.

  Although one kind of quantum dot may be used as the quantum dot 17, two or more kinds of quantum dots each having an emission band in a single wavelength region can be used depending on the particle diameter or material. is there. Specifically, the optical wavelength conversion assembly layer 11 may include a first quantum dot 17A and a second quantum dot 17B having an emission band in a wavelength region different from that of the first quantum dot 17A. .

  The quantum dot 17 can generate strong fluorescence in a desired narrow wavelength region. For this reason, the backlight device using the light wavelength conversion sheet can illuminate the display panel with light of three primary colors having excellent color purity. In this case, the display panel has excellent color reproducibility.

  The quantum dot 17 includes, for example, a core made of a first semiconductor compound, a shell made of a second semiconductor compound that covers the core and is different from the first semiconductor compound, and a ligand bonded to the surface of the shell. It is configured.

  Examples of the first semiconductor compound constituting the core include MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, II-VI semiconductor compounds such as HgS, HgSe and HgTe, III such as AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs and TiSb A semiconductor crystal containing a semiconductor compound or a semiconductor such as a group V semiconductor compound, a group IV semiconductor such as Si, Ge, and Pb can be given. Alternatively, a semiconductor crystal including a semiconductor compound containing three or more elements such as InGaP can be used. Among these, semiconductor crystals such as CdS, CdSe, CdTe, InP, and InGaP are preferable from the viewpoints of ease of production and controllability of particle diameters that can obtain light emission in the visible range.

  As the second semiconductor compound constituting the shell, a semiconductor compound having a band gap higher than that of the first semiconductor compound constituting the core is preferably used so that excitons are confined in the core. Thereby, the luminous efficiency of a quantum dot can be improved. Examples of the second semiconductor compound constituting the shell include ZnS, ZnSe, CdS, GaN, CdSSe, ZnSeTe, AlP, ZnSTe, and ZnSSe.

  As a specific combination of the core-shell structure (core / shell) composed of a core and a shell, for example, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, Gap / ZnS, Si / ZnS, Examples include InN / GaN, InP / CdSSe, InP / ZnSeTe, InGaP / ZnSe, InGaP / ZnS, Si / AlP, InP / ZnSTe, InP / ZnSSe, InGaP / ZnSTe, and InGaP / ZnSSe.

  The ligand is for stabilizing unstable quantum dots. Examples of the ligand include sulfur compounds such as thiols, phosphorus compounds such as phosphine compounds or phosphine oxides, nitrogen compounds such as amines, and carboxylic acids.

  The shape of the quantum dot 17 is not particularly limited, and may be, for example, a spherical shape, a rod shape, a disk shape, or other shapes. When the shape of the semiconductor nanoparticles is not spherical, the particle diameter of the semiconductor nanoparticles can be a true spherical value having the same volume.

  Information such as the particle diameter, average particle diameter, shape, and dispersion state of the quantum dots 17 can be obtained by a transmission electron microscope or a scanning transmission electron microscope. The average particle diameter of the quantum dots can be obtained as an average value of the diameters of 20 quantum dots measured by observation with a transmission electron microscope or a scanning transmission electron microscope. Further, since the emission color of the quantum dot 17 changes depending on the particle diameter, the particle diameter of the quantum dot can be obtained from the confirmation of the emission color of the quantum dot 17. Further, the crystal structure and crystallite size of the quantum dots 17 can be known by X-ray crystal diffraction (XRD). Furthermore, the information regarding the particle diameter etc. of a quantum dot can also be obtained with an ultraviolet-visible (UV-Vis) absorption spectrum.

  The content of the quantum dots 17 in the light wavelength conversion layer 11 is preferably 0.01% by mass or more and 2% by mass or less, and more preferably 0.03% by mass or more and 1% by mass or less. If the content of the light wavelength conversion particles is less than 0.01% by mass, sufficient light emission intensity may not be obtained, and if the content of the light wavelength conversion particles exceeds 2% by mass, sufficient excitation will occur. There is a possibility that the transmitted light intensity of light cannot be obtained. In addition, the mass% of the quantum dot in the light wavelength conversion layer which is hardened | cured material, and the mass% of the light-scattering particle mentioned later can be calculated roughly with the following method. First, at least a part of the light wavelength conversion layer is sampled from the light wavelength conversion sheet, and its mass is measured. Next, the host matrix contained in the sampled portion is dissolved in a solvent or incinerated by combustion to remove the components of the host matrix. When removing the host matrix components, the quantum dots and the light scattering particles are not removed, and the quantum dot and light scattering particle components have large particle sizes. Separate components of scattering particles. Next, the component mass of the separated quantum dots and the component of the light scattering particles are measured. And the ratio of the mass of the quantum dot contained in at least one part of the sampled light wavelength conversion layer based on the mass of the sampled light wavelength conversion layer and the mass of the quantum dot is calculated. Further, the ratio of the mass of the light scattering particles contained in at least a part of the sampled light wavelength conversion layer is calculated based on the mass of at least a part of the sampled light wavelength conversion layer and the mass of the light scattering particles.

(Light scattering particles)
The light-scattering particles 18 are particles having an action of changing the traveling direction of light by scattering the light that has entered the light wavelength conversion layer 11.

  The average particle size of the light-scattering particles 18 is preferably 20 times or more and 2000 times or less, more preferably 50 times or more and 1000 times or less than the average particle size of the quantum dots 17. If the average particle size of the light scattering particles is less than 20 times the average particle size of the quantum dots, sufficient light scattering performance may not be obtained in the light wavelength conversion layer, and the average particle size of the light scattering particles is If the average particle diameter exceeds 2000 times the average particle diameter of the quantum dots, the number of light-scattering particles decreases even if the addition amount is the same, so that the number of scattering points may decrease and a sufficient light scattering effect may not be obtained. . The average particle diameter of the light scattering particles 18 can be measured by the same method as the average particle diameter of the quantum dots 17 described above.

  Further, the average particle diameter of the light scattering particles 18 is preferably 1/300 or more and 1/20 or less, and 1/200 or more and 1/30 or less of the average film thickness of the light wavelength conversion layer 11 described later. Is more preferable. If the average particle diameter of the light scattering particles is less than 1/300 of the average film thickness of the light wavelength conversion layer, sufficient light scattering performance may not be obtained in the light wavelength conversion layer. If the particle diameter exceeds 1/20 of the average film thickness of the light wavelength conversion layer, the ratio of light scattering particles to the light wavelength conversion layer decreases even if the addition amount is the same. Light scattering effect cannot be obtained.

  Specifically, the average particle diameter of the light-scattering particles 18 is preferably, for example, from 0.1 μm to 10 μm, and more preferably from 0.3 μm to 5 μm. If the average particle diameter of the light scattering particles is less than 0.1 μm, the light wavelength conversion efficiency of the light wavelength conversion sheet may be insufficient. In order to obtain sufficient light scattering properties, It is necessary to increase the amount of addition. On the other hand, if the average particle diameter of the light-scattering particles exceeds 10 μm, the number of light-scattering particles is reduced even if the addition amount (% by mass) is the same, so that the number of scattering points is reduced and a sufficient light-scattering effect is obtained. I can't get it.

  The shape of the light-scattering particle 18 is not particularly limited. For example, the shape is spherical (true sphere, substantially true sphere, elliptic sphere, etc.), polyhedral, rod-like (cylindrical, prismatic, etc.), flat, flake-like, indefinite. Examples include shape. In addition, when the shape of the light scattering particles is not spherical, the particle diameter of the light scattering particles can be a true spherical value having the same volume.

  The light scattering particles 18 are preferably surface-treated with a silane coupling agent from the viewpoint of firmly fixing the light scattering particles 18 in the host matrix 16. By being surface treated with a silane coupling agent, it can be chemically bonded to the host matrix 16.

  The light scattering particles 18 may be organic particles such as acrylic resin particles, styrene resin particles, melamine resin particles, and urethane resin particles, but the luminance change rate before and after the wet heat resistance test can be reduced. Moreover, since it becomes possible to scatter suitably the incident light to the light wavelength conversion sheet and to improve the light wavelength conversion efficiency with respect to this incident light, inorganic particles are preferable.

Inorganic particles include aluminum-containing compounds such as Al ₂ O ₃ , zirconium-containing compounds such as ZrO ₂ , tin-containing compounds such as antimony-doped tin oxide (ATO) and indium tin oxide (ITO), and magnesium-containing materials such as MgO and MgF _2. At least one compound selected from the group consisting of compounds, titanium-containing compounds such as TiO ₂ and BaTiO ₃ , antimony-containing compounds such as Sb ₂ O ₅ , silicon-containing compounds such as SiO ₂ , and zinc-containing compounds such as ZnO Particles. Since these inorganic particles can increase the difference in refractive index with the binder resin, they are also preferable from the viewpoint of obtaining a large Mie scattering intensity. Since the light wavelength conversion efficiency with respect to the incident light by the light wavelength conversion sheet 10 can be improved more suitably, the light scattering particles 18 may be made of two or more materials.

  The content of the light scattering particles 18 in the light wavelength conversion layer 11 is preferably 1% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 30% by mass or less. If the content of the light scattering particles is less than 1% by mass, the light scattering effect may not be sufficiently obtained, and if the content of the light scattering particles exceeds 50% by mass, Mie scattering occurs. Since it becomes difficult, the light scattering effect may not be sufficiently obtained, and the processability may be deteriorated because there are too many light scattering particles.

  From the viewpoint of obtaining sufficient light scattering, the absolute value of the difference in refractive index between the light-scattering particles 18 and the host matrix 16 is preferably 0.05 or more, and more preferably 0.10 or more. Note that either the refractive index of the light scattering particles 18 or the refractive index of the host matrix 16 may be larger. Here, as a method for measuring the refractive index of the light-scattering particles before being included in the light wavelength conversion layer, for example, the Becke method, the minimum deflection angle method, the deflection angle analysis, the mode line method, the ellipsometry method, etc. can do. In addition, the refractive index of the host matrix 16 in the light wavelength conversion layer 11 is determined by, for example, extracting ten pieces of the host matrix 16 from the light wavelength conversion layer 11 by cutting or the like. Each of the refractive indexes of the host matrix 16 is measured, and the average value of ten measured refractive indexes of the host matrix 16 can be obtained. Further, the refractive index of the light scattering particles 18 is determined by, for example, taking out a piece of a part of the surface of the light scattering particle 18 exposed from the host matrix 16 by cutting out from the light wavelength conversion layer 11 and taking out the piece. The refractive index of each of the ten light scattering particles 18 whose surfaces are exposed by the Becke method can be measured, and the average value of ten refractive indexes of the measured light scattering particles 18 can be obtained. The Becke method uses a refractive index standard solution with a known refractive index. Place the above piece on a glass slide, drop the refractive index standard solution on the sample, and immerse the piece in the refractive index standard solution. When the surface of the binder resin or light-scattering particle is different from the refractive index of the refractive index standard solution, the bright line (Becke line) generated on the surface of the binder resin or light-scattering particle cannot be visually observed. In this method, the refractive index of the refractive index standard solution is used as the refractive index of the host matrix or light scattering particles. If the surface of the light-scattering particles is not exposed in the removed piece, the surface of the light-scattering particles is covered with the host matrix, so that the host matrix existing around the light-scattering particles and There is no difference in refractive index. For this reason, it is possible to determine whether or not a part of the surface of the light scattering particles is exposed by measuring the refractive index difference with the host matrix existing around the light scattering particles by the Becke method or the like. . In addition, the refractive index difference between the binder resin and the light scattering particles is measured using a phase shift laser interference microscope (such as a phase shift laser interference microscope manufactured by FK Optical Laboratory or a two-beam interference microscope manufactured by Mizoji Optical Industry Co., Ltd.). can do.

(Additive)
Although it does not specifically limit as an additive, The compound which suppresses the oxidation and deterioration of a quantum dot is preferable. Examples of the compound that suppresses oxidation and deterioration of the quantum dots include phenolic compounds, amine compounds, sulfur compounds, phosphorus compounds, hydrazine compounds, amide compounds, and hindered amine compounds. The additive may be combined with the host matrix.

<Barrier film>
The barrier films 12 and 13 are films for suppressing the permeation of moisture and oxygen and protecting the quantum dots 17 from moisture and oxygen. Here, the “barrier film” in the present specification is a single member and has a water vapor transmission rate of less than 0.1 g / (m ² · 24 h) at 40 ° C. and a relative humidity of 90%, and at 23 ° C. and a relative humidity. It shall mean a film having an oxygen permeability at 90% of less than 0.1 cm ³ / (m ² · 24 h · atm). The barrier film includes not only a single layer structure film but also a multilayer structure film. The durability of the quantum dots 17 can be further improved by installing the barrier films 12 and 13 while sandwiching the light wavelength conversion layer 11. The barrier films 12 and 13 shown in FIG. 3 are provided on the light transmissive base materials 19 and 20 and the light wavelength conversion layer 11 side of the light transmissive base materials 19 and 20 and suppress the transmission of moisture and oxygen. And barrier layers 21 and 22 having a function.

The water vapor transmission rate (WVTR: Water Vapor Transmission Rate) of the barrier films 12 and 13 is 1.0 × 10 ⁻² g / (m ² · 24 h) or less at 40 ° C. and a relative humidity of 90%. Is more preferable. The water vapor transmission rate can be measured using a water vapor transmission rate measuring device (product name “PERMATRAN-W3 / 31”, manufactured by MOCON). The water vapor transmission rate is an average value of values obtained by measuring three times.

The oxygen transmission rate (OTR: Oxygen Transmission Rate) of the barrier films 12 and 13 is 1.0 × 10 ⁻² cm ³ / (m ² · 24 h · atm) or less at 23 ° C. and a relative humidity of 90%. More preferably it is. The oxygen permeability can be measured using an oxygen gas permeability measuring device (product name “OX-TRAN 2/21”, manufactured by MOCON). The oxygen transmission rate is the average of the values obtained by measuring three times.

(Light transmissive substrate)
The thickness of the light transmissive base materials 19 and 20 is not particularly limited, but is preferably 10 μm or more and 300 μm or less. If the thickness of the light-transmitting base materials 19 and 20 is less than 10 μm, the light wavelength conversion sheet may be assembled or wrinkled or broken during handling, and if it exceeds 300 μm, the weight of the display and the thin film may be reduced. There is a risk that it may not be suitable. The more preferable lower limit of the thickness of the light-transmitting substrates 19 and 20 is 50 μm or more, and the more preferable upper limit is 200 μm or less.

  The thickness of the light transmissive base materials 19 and 20 is a cross section of the light transmissive base materials 19 and 20 using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM). The thickness of the light-transmitting base materials 19 and 20 is measured at 20 points in the cross-sectional image, and the average value of the film thicknesses at the 20 points is obtained.

  Examples of constituent materials for the light-transmitting substrates 19 and 20 include polyester (for example, polyethylene terephthalate, polyethylene naphthalate), cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, and polysulfone. , Thermoplastic resins such as polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, polymethyl methacrylate, polycarbonate, or polyurethane. As a constituent material of the light-transmitting substrates 12 and 13, preferably, polyester (for example, polyethylene terephthalate, polyethylene naphthalate) is used.

  The light transmissive base materials 19 and 20 may be composed of a single base material, but may be a laminated base material composed of a plurality of base materials. Such a laminated base material may be composed of a plurality of layers composed of the same kind of constituent raw material layers, or may be composed of a plurality of layers composed of different kinds of constituent raw material layers, depending on the application. Good.

(Barrier layer)
The barrier layers 21 and 22 are composed of vapor deposition layers having a function of suppressing the permeation of moisture and oxygen. A vapor deposition layer is a layer formed by vapor deposition methods, such as physical vapor deposition (PVD) methods, such as sputtering method and an ion plating method, and chemical vapor deposition (CVD) method, for example. A vapor deposition layer has the advantage that barrier property can be improved.

  The material for forming the vapor deposition layer is not particularly limited as long as it can be vapor-deposited by a vapor deposition method and has barrier properties, and examples thereof include inorganic oxides such as silicon oxide and aluminum oxide, metals, and the like.

  Although the film thickness of a vapor deposition layer is not specifically limited, It is preferable that they are 0.01 micrometer or more and 1 micrometer or less. If the thickness of the deposited layer is less than 0.01 μm, the barrier performance of the deposited layer may be insufficient, and if it exceeds 1 μm, the barrier performance may be easily deteriorated due to cracks in the deposited layer. is there. The minimum with more preferable thickness of a vapor deposition layer is 0.03 micrometer or more, and a more preferable upper limit is 0.5 micrometer or less.

  The film thickness of the vapor deposition layer is obtained by photographing a cross section of the light wavelength conversion sheet 60 using a scanning electron microscope (SEM), measuring the film thickness of the vapor deposition film at 20 positions in the image of the cross section, and measuring the film at the 20 positions. Use the average thickness. Moreover, a single layer may be sufficient as a vapor deposition layer, and what laminated | stacked the several layer may be sufficient as it. When a plurality of vapor deposition layers are laminated, each layer constituting the vapor deposition layer may be directly laminated or bonded.

<Light diffusion layer>
The light diffusion layers 14 and 15 have a concavo-convex shape on the surface, and the light that enters and exits the light wavelength conversion sheet 10 can be diffused by the concavo-convex shape. By providing the light diffusion layers 14 and 15, the light wavelength conversion efficiency in the light wavelength conversion sheet 10 can be further increased. The light diffusion layers 14 and 15 contain light scattering particles and a binder resin.

(Light scattering particles)
The light-scattering particles in the light diffusion layers 14 and 15 are mainly for forming a concavo-convex shape on the surfaces of the light diffusion layers 14 and 15 and exhibiting a light-scattering function.

  The average particle diameter of the light-scattering particles in the light diffusion layers 14 and 15 is preferably 10 to 20,000 times, more preferably 10 to 5000 times the average particle diameter of the quantum dots 17 described above. preferable. If the average particle size of the light-scattering particles is less than 10 times the average particle size of the quantum dots, sufficient light diffusibility may not be obtained in the light diffusion layer, and the average particle size of the light-scattering particles may be If it exceeds 20,000 times the average particle diameter of the quantum dots, the light diffusion performance of the light diffusion layer will be excellent, but the light transmittance of the light diffusion layer will be greatly reduced. In addition, the average particle diameter of light-scattering particle | grains can be measured by the method similar to the average particle diameter of the quantum dot 17 mentioned above.

  Specifically, the average particle diameter of the light scattering particles in the light diffusion layers 14 and 15 is, for example, preferably 1 μm to 30 μm, and more preferably 1 μm to 20 μm. If the average particle diameter of the light scattering particles is less than 1 μm, the light wavelength conversion efficiency of the light wavelength conversion sheet may be insufficient, and the amount of light scattering particles added to provide sufficient light diffusibility. Need to be more. On the other hand, when the average particle diameter of the light scattering particles exceeds 30 μm, the light diffusion performance is excellent, but the light transmittance of the light diffusion layer is likely to be greatly reduced.

  The absolute value of the difference in refractive index between the light-scattering particles and the binder resin in the light diffusion layers 14 and 15 is preferably 0.02 or more and 0.15 or less. If it is less than 0.02, the light diffusibility due to the refractive index of the light scattering particles cannot be obtained optically, and the improvement of the light wavelength conversion efficiency of the light wavelength conversion sheet may be insufficient. If it exceeds 15, the transmittance of the light diffusion layer may be lowered. The more preferable lower limit of the difference in refractive index between the light-scattering particles and the binder resin is 0.03 or more, and the more preferable upper limit is 0.12. Note that either of the refractive index of the light-scattering particles and the refractive index of the binder resin may be larger. The refractive indexes of the light-scattering particles and the binder resin can be measured by the same method as the refractive indexes of the light-scattering particles 18 and the binder resin.

  Since the shape of the light-scattering particles in the light diffusion layers 14 and 15 is the same as the shape of the light-scattering particles 18 in the light wavelength conversion layer 11, description thereof will be omitted here. The light scattering particles in the light diffusion layers 14 and 15 are preferably chemically bonded to the binder resin from the viewpoint of firmly fixing the light scattering particles in the binder resin. This chemical bonding can be realized by using light scattering particles whose surface is modified with a silane coupling agent.

  The light scattering particles may be particles made of an organic material or particles made of an inorganic material. The organic material constituting the light scattering particles is not particularly limited. For example, polyester, polystyrene, melamine resin, (meth) acrylic resin, acrylic-styrene copolymer resin, silicone resin, benzoguanamine resin, benzoguanamine / formaldehyde condensation resin , Polycarbonate, polyethylene, polyolefin and the like. Of these, a crosslinked acrylic resin is preferably used. Moreover, it does not specifically limit as an inorganic material which comprises the said light-diffusion particle | grains, For example, inorganic oxides, such as a silica, an alumina, a titania, a tin oxide, an antimony dope tin oxide (ATO), a zinc oxide fine particle, etc. are mentioned. Of these, silica and / or alumina is preferably used.

(Binder resin)
As the binder resin, a polymer of a polymerizable compound can be used. As the polymerizable compound, since the same compound as the polymerizable compound described in the column of the light wavelength conversion layer can be used, the description is omitted here.

  After preparing the degradation evaluation device 1 and the light wavelength conversion sheet 10, the light wavelength conversion sheet 10 is placed on the light emitting surface 2A of the backlight device 2 (the light exit surface 3B of the light diffusion plate 6). Next, light that can be converted in wavelength by the quantum dots 17 is irradiated from the light source 5 of the backlight device 2 to the surface 10 </ b> A of the light wavelength conversion sheet 10. In this state, the luminance distribution of at least a part of the surface 10B of the light wavelength conversion sheet 10 is measured by the luminance meter 3. When a surface luminance meter is used as the luminance meter 3, the luminance of the entire surface 10B of the light wavelength conversion sheet 10 is measured.

  The luminance distribution measured by the luminance meter 3 is taken into the processing device 4 as data. In the processing device 4, the luminance change amount distribution is obtained based on the luminance distribution taken in as data. Specifically, for example, in the luminance distribution, the luminance distribution is standardized so that the maximum luminance is 100%, the unit is converted to%, and the luminance variation distribution is obtained from the luminance distribution. The luminance change amount is a difference in luminance at every measurement interval when measuring luminance. The measurement interval is preferably 0.5 mm or less, and more preferably 0.2 mm or less. When a surface luminance meter is used as the luminance meter 3, when the size of the light wavelength conversion sheet 10 is smaller than the size of the light emitting surface 2A, not only the luminance of the entire surface 10B of the light wavelength conversion sheet 10 is obtained. Since the luminance of the light emitting surface 2A outside the light wavelength conversion sheet 10 can also be measured, in the processing device 4, any point A on the light emitting surface 2A outside the light wavelength conversion sheet 10 as shown in FIG. If the straight line portion from the light wavelength conversion sheet 10 across the light wavelength conversion sheet 10 to another arbitrary point B on the light emitting surface 2A outside the light wavelength conversion sheet 10 is specified, The luminance distribution in the selected portion is extracted, and the luminance change amount distribution in the designated portion is obtained. Thus, the light wavelength conversion sheet 10 is traversed along one side of the light wavelength conversion sheet 10 from an arbitrary point A on the light emitting surface 2A outside the light wavelength conversion sheet 10, and outside the light wavelength conversion sheet 10. By obtaining the luminance change amount distribution to another arbitrary point B on the light emitting surface 2A, the end portions 10C, 10D of the light wavelength conversion sheet 10 can also be accurately evaluated. Therefore, the end portions 10C of the light wavelength conversion sheet 10, Not only the deterioration of the portion inside 10D but also the deterioration of the end portions 10C and 10D of the light wavelength conversion sheet 10 can be evaluated.

  Then, a maximum value and a minimum value adjacent to the maximum value are detected from the obtained luminance change amount distribution. The “maximum value” in the present specification means a point at which the luminance change amount is changed from an increase to a decrease, and the luminance change amount is 1.5% or more. Further, the “minimum value” in this specification means that the luminance change amount is changed from a decrease to an increase, and the luminance change amount is −1.5% or less. When the maximum value or the minimum value is not detected, it is determined that there is no deterioration of the light wavelength conversion sheet in this portion.

  When a maximum value and a minimum value are detected, a width from a position at which the maximum value is obtained to a position at which the minimum value is obtained (hereinafter, this width is referred to as “degradation width”) is obtained, and based on this deterioration width. To evaluate the deterioration of the light wavelength conversion sheet. Specifically, for example, the deterioration of the light wavelength conversion sheet can be evaluated based on whether or not the deterioration width is within a predetermined range. For example, when the deterioration width is 5 mm or less, even if the color change of the light wavelength conversion sheet is visually evaluated, the change in the color is not noticed. Therefore, the deterioration width of the light wavelength conversion sheet is 5 mm or less. In this case, it can be determined that the portion where the deterioration of the light wavelength conversion sheet is evaluated is not deteriorated. For this reason, it is possible to evaluate the deterioration of the light wavelength conversion sheet depending on whether or not the deterioration width is 5 mm or less.

  The deterioration width indicates how much the deterioration of the quantum dots is widened, and the larger the deterioration width, the wider the area where the quantum dots are deteriorated. Here, human eyes tend to detect deterioration of the light wavelength conversion sheet when the luminance change is locally large, but tend not to be detected when the deteriorated region of the light wavelength conversion sheet is narrow. is there. For this reason, in the human eye, when the luminance change is locally large and the degradation region of the light wavelength conversion sheet is wide, the degradation of the light wavelength conversion sheet can be detected, but the luminance change locally. Even if it is large, when the region where the light wavelength conversion sheet is deteriorated is narrow, the deterioration of the light wavelength conversion sheet cannot be detected. On the other hand, in this embodiment, since deterioration of the light wavelength conversion sheet is evaluated based on the above-described deterioration width, quantitative deterioration evaluation having a high correlation with visual evaluation can be performed.

  The deterioration evaluation method of the present embodiment is particularly effective in a light wavelength conversion sheet having barrier films on both surfaces of a light wavelength conversion layer such as the light wavelength conversion sheet 10. That is, when the barrier film is provided on both surfaces of the light wavelength conversion layer, both surfaces of the light wavelength conversion layer are covered with the barrier film, but the edges of the light wavelength conversion layer are exposed. Therefore, the edge part (part containing an edge) of a light wavelength conversion layer tends to deteriorate. Here, in the light wavelength conversion sheet, when the end of the light wavelength conversion sheet is deteriorated, the light from the light source of the backlight device (for example, blue light) is absorbed and lost, so the end of the light wavelength conversion sheet In the area, the brightness is drastically decreased. For this reason, in the case where the size of the light wavelength conversion sheet is smaller than the light emitting surface of the backlight device, the light wavelength conversion sheet extends from an arbitrary point on the light emitting surface of the backlight device outside the light wavelength conversion sheet to one side of the light wavelength conversion sheet. Along the light wavelength conversion sheet, and when measuring the luminance change distribution to another arbitrary point on the light emitting surface outside the light wavelength conversion sheet, from this arbitrary point of the light wavelength conversion sheet Since there is a light diffusing plate that does not absorb light from the light source of the backlight device up to the edge of the light wavelength conversion sheet on the point side, the amount of change in luminance is almost constant, but enters the end of the light wavelength conversion sheet Since the brightness rapidly decreases, a minimum value appears in the brightness variation distribution. And if it passes the edge part which has deteriorated, since it will enter into the part which has not deteriorated of the light wavelength conversion sheet, the brightness increases rapidly, and the maximum value appears in the brightness change amount distribution. Furthermore, the luminance change amount is almost constant in the non-degraded portion of the optical wavelength conversion sheet, but the luminance decreases rapidly when entering the opposite end of the degradation, so the luminance variation distribution The minimum appears again at. And if it passes the edge on the opposite side to the said edge of a light wavelength conversion sheet | seat, since it will enter into a light diffusing plate, a maximum value will appear again in luminance variation distribution. Therefore, at the end portion of the light wavelength conversion sheet, it is possible to easily grasp how much deterioration has occurred from the end edge of the light wavelength conversion sheet toward the central portion by measuring the deterioration width.

  In the above, a light wavelength conversion sheet that is smaller than the light emitting surface of the backlight device is used. For example, the quantum dot may deteriorate in a spot shape in a portion other than the end of the light wavelength conversion sheet. In order to grasp the size of the spot where the light has deteriorated, the size of the light wavelength conversion sheet is not necessarily smaller than the light emitting surface of the backlight device.

  When the deterioration of the light wavelength conversion sheet 10 is evaluated by the deterioration evaluation method of the present embodiment, when the deterioration width of the light wavelength conversion sheet 10 is 5 mm or less, the visual evaluation at the time of light emission is performed for the reason described above. It is difficult to confirm a color change due to the deterioration of the quantum dots 17. In particular, a durability test is performed on the light wavelength conversion sheet 10 in an environment of 60 ° C. and a relative humidity of 90% for 500 hours, and the deterioration width of the light wavelength conversion sheet 10 after the durability test is 5 mm or less. Therefore, even after the durability test, it is difficult to confirm a color change due to deterioration of the quantum dots 17 by visual evaluation during light emission. Thereby, the light wavelength conversion sheet 10 in which the color change due to the deterioration of the quantum dots 17 is difficult to be confirmed during light emission can be provided. The light wavelength conversion sheet having a deterioration width of 5 mm or less can be achieved, for example, by adding the above-described additive for suppressing deterioration of quantum dots to the light wavelength conversion layer.

  The light wavelength conversion sheet 10 can be used by being incorporated in a backlight device and an image display device. Hereinafter, an example in which the light wavelength conversion sheet 10 is incorporated in a backlight device and an image display device will be described. FIG. 5 is a schematic configuration diagram of an image display device including a backlight device according to the present embodiment, FIG. 6 is a perspective view of the lens sheet shown in FIG. 5, and FIG. FIG. 8 is a cross-sectional view taken along line I, and FIG. 8 is a schematic configuration diagram of another backlight device according to the present embodiment.

<<< Image display device >>>
The image display device 30 shown in FIG. 4 includes a backlight device 40 and a display panel 80 disposed on the light output side of the backlight device 40. The image display device 30 has a display surface 30A for displaying an image. In the image display device 30 shown in FIG. 5, the surface of the display panel 80 is a display surface 30A.

  The backlight device 40 illuminates the display panel 80 in a planar shape from the back side. The display panel 80 functions as a shutter that controls transmission or blocking of light from the backlight device 40 for each pixel, and is configured to display an image on the display surface 70A.

<< Display panel >>
The display panel 80 shown in FIG. 5 is a liquid crystal display panel, and a polarizing plate 81 disposed on the light incident side, a polarizing plate 82 disposed on the light exit side, and between the polarizing plate 81 and the polarizing plate 82. The liquid crystal cell 83 is provided. Polarizing plates 81 and 82 decompose incident light into two linearly polarized light components (S-polarized light and P-polarized light) orthogonal to each other and vibrate in one direction (direction parallel to the transmission axis) (for example, P It has a function of transmitting a linearly polarized component (for example, S-polarized light) that transmits polarized light and vibrates in the other direction (direction parallel to the absorption axis) perpendicular to the one direction.

  The liquid crystal cell 83 is configured such that a voltage can be applied to each region where one pixel is formed. Then, the orientation direction of the liquid crystal molecules in the liquid crystal cell 83 changes depending on the presence or absence of voltage application. As an example, the linearly polarized light component in a specific direction transmitted through the polarizing plate 81 arranged on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal cell 83 to which a voltage is applied, When passing through the liquid crystal cell 83 to which no voltage is applied, the polarization direction is maintained. In this case, depending on whether or not a voltage is applied to the liquid crystal cell 83, the linearly polarized light component oscillating in a specific direction transmitted through the polarizing plate 81 is transmitted to the polarizing plate 82 or absorbed and blocked by the polarizing plate 82. it can. In this way, the display panel 80 is configured so that transmission or blocking of light from the backlight device 40 can be controlled for each pixel. The details of the liquid crystal display panel are described in various known literatures (for example, “Flat Panel Display Dictionary” (published by Tatsuo Uchida, Hiraki Uchiike), 2001, Industrial Research Council). The detailed description of is omitted.

<< Backlight device >>
The backlight device 40 shown in FIG. 5 is configured as an edge light type backlight device, and includes a light source 50, an optical plate 55 as a light guide plate disposed on the side of the light source 50, and a light output side of the optical plate 55. The light wavelength conversion sheet 10 disposed on the lens, the lens sheet 60 disposed on the light output side of the light wavelength conversion sheet 10, the lens sheet 65 disposed on the light output side of the lens sheet 60, and the light output side of the lens sheet 65. The reflection-type polarization separation sheet 70 disposed and the reflection sheet 75 disposed on the side opposite to the light output side of the optical plate 55 are provided. The backlight device 40 includes the optical plate 55, the lens sheets 60 and 65, the reflective polarization separation sheet 70, and the reflective sheet 75, but these sheets and the like may not be provided. In the present specification, the “light exit side” means a side from which light is emitted from each member in the direction of exiting the backlight device.

  The backlight unit 40 has a light emitting surface 40A that emits light in a planar shape. In the backlight device 40 shown in FIG. 5, the light exit surface of the reflective polarization separation sheet 70 is the light emitting surface 40 </ b> A of the backlight device 40.

  The surface on the optical plate 95 side in the light wavelength conversion sheet 10 is a surface 10A (light incident surface), and the surface on the lens sheet 60 side in the light wavelength conversion sheet 10 is a surface 10B (light exit surface).

<Light source>
Since the light source 50 is the same as the light source described above, the description thereof is omitted here.

<Optical plate>
The optical plate 65 as the light guide plate is formed in a square shape in plan view. The optical plate 65 extends between the light output surface 65A formed by one main surface on the display panel 80 side, the back surface 65B formed of the other main surface facing the light output surface 65A, and the light output surface 65A and the back surface 65B. And have side faces. Of the side surfaces, the side surface on the light source 50 side is a light incident surface 55 </ b> C that receives light from the light source 50. The light that has entered the optical plate 55 from the light incident surface 55C is guided through the optical plate in a direction (light guide direction) connecting the light incident surface 55C and the opposite surface facing the light incident surface 55C, and the light exit surface. It is emitted from 55A.

  As a material constituting the optical plate 55, a material that is widely used as a material for an optical sheet incorporated in an image display device and has excellent mechanical characteristics, optical characteristics, stability, workability, and the like, and can be obtained at low cost. For example, transparent resins mainly composed of one or more of acrylic resin, polystyrene, polycarbonate, polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate or urethane acrylate reactive resins (ionizing radiation curable resins, etc.) are preferably used. Can be done. If necessary, a light diffusing material having a function of diffusing light can be added to the optical plate 55. As the light diffusing material, for example, particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, or silicone resin having an average particle diameter of 0.5 μm to 100 μm are used. it can.

<< Lens sheet >>
The lens sheets 60 and 65 have a function of changing the traveling direction of the incident light and emitting it from the light output side. In the present embodiment, as shown in FIG. 7, the function of concentratingly improving the luminance in the front direction by changing the traveling direction of the light L3 having a large incident angle and emitting it from the light exit side (condensing function). In addition, it has a function (retroreflection function) of reflecting the light L4 having a small incident angle and returning it to the light wavelength conversion sheet 10 side. The lens sheets 60 and 65 include a light transmissive substrate 61 and a lens layer 62 provided on one surface of the light transmissive substrate 61.

<Light transmissive substrate>
Since the light transmissive substrate 61 is the same as the light transmissive substrates 12 and 13, the description thereof will be omitted here.

<Lens layer>
As shown in FIGS. 6 and 7, the lens layer 62 includes a sheet-like main body 63 and a plurality of unit lenses 64 arranged side by side on the light output side of the main body 63.

  The main body 63 functions as a sheet-like member that supports the unit lens 64. As shown in FIGS. 6 and 7, the unit lenses 64 are arranged on the light output side surface 63 </ b> A of the main body 63 without leaving a gap. Accordingly, the light exit surfaces 60B and 65B of the lens sheets 60 and 65 are formed by lens surfaces. On the other hand, as shown in FIG. 7, the main body 63 has a smooth surface that forms the light incident side surface of the lens layer 62 as the light incident side surface 63B that faces the light output side surface 63A.

  The unit lenses 64 are arranged side by side on the light output side surface 63 </ b> A of the main body 63. As shown in FIG. 6, the unit lenses 64 extend linearly in the direction intersecting the arrangement direction AD of the unit lenses 64, particularly linearly in the present embodiment. In the present embodiment, a large number of unit lenses 64 included in one lens sheet 60, 65 extend in parallel with each other. Further, the longitudinal direction LD of the unit lenses 64 of the lens sheets 60 and 65 is orthogonal to the arrangement direction AD of the unit lenses 64 in the lens sheets 60 and 65.

  The unit lens 64 may have a triangular prism shape, a wavy shape, or a bowl shape such as a hemisphere. Specifically, examples of the unit lens include a unit prism, a unit cylindrical lens, and a unit microlens. Examples of the lens sheet having such a unit lens shape include a prism sheet, a lenticular lens sheet, and a microlens sheet. In the present embodiment, a triangular prism-shaped unit prism whose width becomes narrower toward the light output side will be described as a unit lens. The shape of the cross section (also referred to as the main cutting surface of the lens sheet) parallel to both the normal direction ND of the sheet surfaces of the lens sheets 60 and 65 and the arrangement direction AD of the unit lenses 64 is a triangular shape protruding to the light output side. ing. In particular, from the viewpoint of intensively improving the brightness in the front direction, the cross-sectional shape of the unit lens 64 at the main cut surface is an isosceles triangle shape, and the apex angle located between the equilateral sides is the light exit side surface 63A of the main body 63. Each unit lens 64 is configured to protrude from the light to the light exit side.

  The unit lens 64 preferably has an apex angle of 80 ° or more and 100 ° or less, and more preferably an apex angle of about 90 °, from the viewpoint of improving the light utilization efficiency. However, the tip of the unit lens 64 may be a curved surface in consideration of breakage of the tip of the unit lens at the time of winding the light wavelength conversion sheet.

  The dimensions of the lens sheets 60 and 65 can be set as follows as an example. First, as a specific example of the unit lens 64, the arrangement pitch of the unit lenses 64 (corresponding to the width of the unit lens 64 in the illustrated example) can be set to 10 μm or more and 200 μm or less. However, in recent years, the definition of the arrangement of the unit lenses 64 is rapidly increasing, and the arrangement pitch of the unit lenses 64 is preferably 10 μm or more and 50 μm or less. Further, the protruding height of the unit lens 64 from the main body portion 63 along the normal direction ND to the sheet surface of the lens sheets 60 and 65 can be set to 5 μm or more and 100 μm or less. Further, the apex angle θ of the unit lens 64 can be set to 60 ° or more and 120 ° or less.

  As can be understood from FIG. 5, the arrangement direction of the unit lenses 64 of the lens sheet 60 and the arrangement direction of the unit lenses 64 of the lens sheet 65 intersect, and more specifically, are orthogonal to each other.

<Reflection-type polarized light separation sheet>
The reflection-type polarization separation sheet 70 transmits only a first linearly polarized light component (for example, P-polarized light) out of the light emitted from the lens sheet 65 and is a second straight line orthogonal to the first linearly polarized light component. It has a function of reflecting a polarized component (for example, S-polarized light) without absorbing it. In the state where the second linearly polarized light component reflected by the reflective polarization separation sheet 70 is reflected again and the polarized light is canceled (including both the first linearly polarized light component and the second linearly polarized light component), The light again enters the reflective polarization separation sheet 70. Therefore, the reflective polarization separating sheet 70 transmits the first linearly polarized light component of the incident light again, and the second linearly polarized light component orthogonal to the first linearly polarized light component is reflected again. Hereinafter, by repeating the above process, about 70 to 80% of the light emitted from the lens sheet 65 is emitted as the light source light that has become the first linearly polarized light component. Therefore, by making the polarization direction of the first linearly polarized light component (transmission axis component) of the reflective polarization separation sheet 70 coincide with the transmission axis direction of the polarizing plate 121 of the display panel 80, the light emitted from the backlight device 40 is emitted. Can be used for image formation on the display panel 80. Therefore, even when the light energy input from the light source 50 is the same, it is possible to form an image with higher luminance than in the case where the reflective polarization separation sheet 70 is not disposed, and the energy utilization efficiency of the light source 50 is also improved. improves. In particular, the light reflected by the reflective polarization separation sheet 70 can be wavelength-converted by the light wavelength conversion sheet 10. Therefore, the wavelength conversion efficiency of the light wavelength conversion sheet 10 can be further increased by arranging the reflective polarization separation sheet 70. Therefore, further improvement in light utilization efficiency can be expected.

  As the reflective polarization separating sheet 70, “DBEF” (registered trademark) available from 3M Company can be used. In addition to “DBEF”, a high-intensity polarizing sheet “WRPS” available from Shinwha Intertek, a wire grid polarizer, or the like can be used as the reflective polarization separating sheet 90.

<Reflection sheet>
The reflection sheet 75 has a function of reflecting light leaking from the back surface 55 </ b> B of the optical plate 55 so as to enter the optical plate 90 again. The reflection sheet 75 includes a white scattering reflection sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, and the like. obtain. The reflection on the reflection sheet 75 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflection sheet 75 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection.

<< Other backlight devices >>
The backlight device incorporating the light wavelength conversion sheet 10 may be a direct type backlight device as shown in FIG. The backlight device 90 shown in FIG. 8 includes a light source 50, an optical plate 100 that receives light from the light source 50 and functions as a light diffusing plate, a light wavelength conversion sheet 10 that is disposed on the light output side of the optical plate 100, A lens sheet 60 disposed on the light output side of the light wavelength conversion sheet 10, a lens sheet 65 disposed on the light output side of the lens sheet 60, and a reflective polarization separation sheet 70 disposed on the light output side of the lens sheet 65. I have. In the present embodiment, the light source 50 is disposed not directly on the side of the optical plate 100 but directly below the optical plate 100. In FIG. 8, members denoted by the same reference numerals as those in FIG. 5 are the same as the members shown in FIG. Note that the backlight device 90 is not provided with the reflection sheet 75.

<Optical plate>
The optical plate 100 as a light diffusing plate is the same as the light diffusing plate 3, so the description thereof is omitted here.

  In order to describe the present invention in detail, examples will be described below, but the present invention is not limited to these descriptions.

<Preparation of composition for light wavelength conversion layer>
First, each component was mix | blended so that it might become a composition shown below, and the composition for optical wavelength conversion layers was obtained.
(Composition 1 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC Corporation): 92.5 parts by mass Triphenylphosphine (phosphine compound, product name “JC-263”, manufactured by Johoku Chemical Industry Co., Ltd.): 7. 5 parts by mass / green light emitting quantum dots (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 parts by mass / red light emitting quantum dots (Product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 part by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, Product name “Irgacure (registered trademark) 184”, manufactured by BASF Japan Ltd.): 0.2 parts by mass

(Composition 2 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC Corporation): 95 parts by mass Triphenylphosphine (phosphine compound, product name “JC-263”, manufactured by Johoku Chemical Industry Co., Ltd.): 5.0 mass Part / green light emitting quantum dot (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 part by weight / red light emitting quantum dot (product Name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 parts by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name) “Irgacure (registered trademark) 184” manufactured by BASF Japan Ltd.): 0.2 parts by mass

(Composition 3 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC Corporation): 50 parts by mass Trimethylolpropane tris (3-mercaptobutyrate) (product name “TPMB”, manufactured by Showa Denko KK): 50 parts by mass Green light emitting quantum dot (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 parts by mass Red light emitting quantum dot (product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 part by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “ Irgacure (registered trademark) 184 ", manufactured by BASF Japan Ltd.): 0.2 parts by mass

(Composition 4 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC): 70 parts by mass Trimethylolpropane tris (3-mercaptobutyrate) (product name “TPMB”, manufactured by Showa Denko KK): 30 parts by mass Green light emitting quantum dot (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 parts by mass Red light emitting quantum dot (product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 part by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “ Irgacure (registered trademark) 184 ", manufactured by BASF Japan Ltd.): 0.2 parts by mass

(Composition 5 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidick V-5500”, manufactured by DIC): 100 parts by mass Green emitting quantum dot (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS , Average particle size 3.3 nm): 0.2 parts by mass Red light emitting quantum dots (product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm) : 0.2 part by mass-radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “Irgacure (registered trademark) 184”, manufactured by BASF Japan Ltd.): 0.2 part by mass

(Composition 6 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC Corporation): 99.8 parts by mass Triphenylphosphine (phosphine compound, product name “JC-263”, manufactured by Johoku Chemical Industry Co., Ltd.): 0. 2 parts by mass / green emitting quantum dots (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 parts by mass / red emitting quantum dots (Product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 part by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, Product name “Irgacure (registered trademark) 184”, manufactured by BASF Japan Ltd.): 0.2 parts by mass

(Composition 7 for light wavelength conversion layer)
Epoxy acrylate (product name “Unidic V-5500”, manufactured by DIC): 97 parts by mass Trimethylolpropane tris (3-mercaptobutyrate) (product name “TPMB”, manufactured by Showa Denko KK): 3 parts by mass Green light emitting quantum dot (product name “CdSe / ZnS 530”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 3.3 nm): 0.2 parts by mass Red light emitting quantum dot (product name “CdSe / ZnS 610”, manufactured by SIGMA-ALDRICH, core: CdSe, shell: ZnS, average particle size 5.2 nm): 0.2 part by mass / radical polymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name “ Irgacure (registered trademark) 184 ", manufactured by BASF Japan Ltd.): 0.2 parts by mass

<Preparation of composition for light diffusion layer>
Each component was mix | blended so that it might become a composition shown below, and the composition 1 for light diffusion layers was obtained.
(Composition 1 for light diffusion layer)
Pentaerythritol triacrylate: 99 parts by mass Light scattering particles (crosslinked polystyrene resin beads, product name “SBX-4”, manufactured by Sekisui Plastics Co., Ltd., average particle size 4 μm): 158 parts by mass Photoinitiator (1-hydroxycyclohexyl phenyl ketone, product name “Irgacure (registered trademark) 184, manufactured by BASF Japan Ltd.): 1 part by mass / solvent (methyl isobutyl ketone: cyclohexanone = 1: 1 (mass ratio)): 170 parts by mass

<Sample 1>
First, two barrier films were produced by the following method. Polyethylene terephthalate as a light-transmitting substrate having a size of 7 inches and a thickness of 50 μm is generated in a chamber by applying a high-frequency power with a frequency of 13.56 MHz and a power of 5 kW to an electrode in a high-frequency sputtering apparatus. Forming a silica vapor deposition layer as a barrier layer having a thickness of 50 nm and a refractive index of 1.46 made of a target material (silica) on one side of a film (product name “Lumirror T60”, manufactured by Toray Industries, Inc.) Thus, two barrier films each having a silica vapor deposition layer formed on one surface of the polyethylene terephthalate film were formed.

Subsequently, the said composition for light diffusion layers was apply | coated to the surface on the opposite side to the surface at the side of the silica vapor deposition layer in both barrier films, and the coating film was formed. Next, the solvent in the coating film was evaporated by allowing the formed coating film to dry by passing dry air at 80 ° C. for 30 seconds. Then, the light diffusion layer with a film thickness of 10 μm was formed by irradiating with ultraviolet rays so that the integrated light amount was 500 mJ / cm ² to cure the coating film, thereby forming a barrier film with a light diffusion layer.

Subsequently, the composition 1 for light wavelength conversion layers was apply | coated to the silica vapor deposition layer side of one barrier film with a light-diffusion layer, it was made to dry at 80 degreeC, and the coating film was formed. And the other barrier film with a light-diffusion layer was laminated | stacked so that the silica vapor deposition layer might contact | connect the surface of the silica vapor deposition layer of the barrier film with a light-diffusion layer in a coating film. In this state, the coating film is cured by irradiating ultraviolet rays so that the integrated light quantity becomes 500 mJ / cm ² , thereby forming a light wavelength conversion layer having a thickness of 100 μm adhered to both barrier films with a light diffusion layer. did. This obtained the light wavelength conversion sheet which concerns on the sample 1 of length 10cm x width 10cm.

<Samples 2-7>
In Samples 2 to 7, light wavelength conversion sheets were produced in the same manner as Sample 1 except that each light wavelength conversion composition shown in Table 1 was used instead of the light wavelength conversion composition 1.

<Degradation evaluation of optical wavelength conversion sheet by degradation width>
In the light wavelength conversion sheets according to Samples 1 to 7, the light wavelength conversion sheet is subjected to a durability test for 500 hours in an environment of 60 ° C. and a relative humidity of 90%, and the light wavelength conversion sheet after the durability test is deteriorated. It was evaluated whether or not there is a part that is.

  Specifically, first, a backlight device including 21 blue light emitting diodes having an emission peak wavelength of 450 nm and a light diffusion plate arranged on the blue light emitting diode was prepared. The blue light emitting diodes were arranged in a plane shape at an equal interval of 7 × 3 in the vertical direction, and the size of the light diffusion plate was 25 cm in length × 15 cm in width. In addition, the light emission surface of the backlight apparatus was comprised from the light emission surface of the light diffusing plate.

  On the other hand, in the light wavelength conversion sheet according to Samples 1 to 7, a durability test was performed in which the light wavelength conversion sheet was left in an environment of 40 ° C. and a relative humidity of 90% for 300 hours. And the light wavelength conversion sheet | seat after a durability test was mounted on the light emission surface (light emission surface of a light-diffusion plate) of a backlight apparatus. Then, with the blue light emitting diode of the backlight device turned on, a light wavelength conversion sheet is used from above the light wavelength conversion sheet using a 2D color luminance meter (product name “UA-200”, manufactured by Topcon Technohouse). The luminance distribution of the entire surface on the 2D color luminance meter side and the light emitting surface outside the light wavelength conversion sheet was measured.

  After measuring the luminance distribution, the measured luminance distribution is imported into a personal computer as data, and the optical wavelength conversion is performed from an arbitrary point on the light emitting surface outside the optical wavelength conversion sheet from the acquired luminance distribution data. The light wavelength conversion sheet was traversed along one side of the sheet, and the luminance distribution of the straight line portion was extracted to another arbitrary point on the light emitting surface outside the light wavelength conversion sheet (see FIG. 9). Next, in this extracted luminance distribution, the luminance distribution is normalized so that the maximum luminance is 100%, the unit is converted to%, the luminance variation distribution is obtained from the luminance distribution, and the maximum is obtained from the luminance variation distribution. The value and the minimum value adjacent to the maximum value were detected (see FIGS. 10 and 11). The luminance measurement interval was set to 0.12 mm. And the degradation range which is the width | variety from the detected maximum value to the minimum value was calculated | required. In addition, since the light wavelength conversion sheet passes through the two end portions, in the luminance variation distribution, the maximum value and the minimum value may appear at one end portion, and the maximum value and the minimum value may appear at the other end portion. However, in this case, the deterioration width was obtained, and the larger deterioration width was defined as the deterioration width. In FIGS. 10 and 11, since the horizontal axis is the number of pixels, deterioration is caused by multiplying the absolute value of the difference between the pixel where the maximum value appears and the pixel where the minimum value appears by 0.12 mm which is the size of one pixel. The width dw was determined.

<Visual degradation evaluation of optical wavelength conversion sheet>
In the light wavelength conversion sheets according to Samples 1 to 7 after the durability test, whether or not there is a deteriorated portion was visually evaluated. Specifically, the light wavelength conversion sheet after the durability test was placed on a light diffusion plate on a blue light emitting diode having an emission peak wavelength of 450 nm. And the surface of the light wavelength conversion sheet | seat was visually evaluated in the state which turned on the blue light emitting diode. The evaluation criteria were as follows.
◯: Since the color at the end was the same as the color at the center, no deterioration at the end was confirmed.
X: Since the color of the edge part was different from the color of the center part, deterioration of the edge part was confirmed.

The results are shown in Table 1.

  The results will be described below. As shown in Table 1, the optical wavelength conversion sheets according to Samples 4 to 7 had a deterioration width exceeding 5 mm, and thus the deterioration of the end portion was also confirmed by visual evaluation. On the other hand, in the light wavelength conversion sheets according to Samples 1 to 4, since the deterioration width was 5 mm or less, deterioration of the end portion was not confirmed even by visual evaluation.

DESCRIPTION OF SYMBOLS 1 ... Degradation evaluation apparatus 2 ... Backlight apparatus 2A ... Light emission surface 3 ... Luminance meter 4 ... Processing apparatus 5 ... Light source 6 ... Light diffusing plate 10 ... Light wavelength conversion sheet 11 ... Light wavelength conversion layer 16 ... Binder resin 17 ... Quantum dot 30 ... Image display device 40, 90 ... Backlight device 80 ... Display panel

Claims (10)

A degradation evaluation method for an optical wavelength conversion sheet comprising an optical wavelength conversion layer comprising a host matrix and quantum dots dispersed in the host matrix,
A luminance distribution of at least a part of the other surface of the light wavelength conversion sheet opposite to the one surface in a state in which light that can be converted by the quantum dots is irradiated to the one surface of the light wavelength conversion sheet. Measuring the
Obtaining a luminance variation distribution based on the measured luminance distribution;
Detecting a local maximum value and a local minimum value adjacent to the local maximum value from the obtained luminance variation distribution;
A method for evaluating deterioration of a light wavelength conversion sheet, comprising: obtaining a width from a position where the maximum value is obtained to a position where the minimum value is obtained, and evaluating deterioration of the light wavelength conversion sheet based on the width.   The step of measuring the luminance distribution is a step of measuring at least the luminance of the end portion of the light wavelength conversion sheet, and the step of obtaining the luminance change amount distribution is a luminance change amount of the end portion of the light wavelength conversion sheet. The method for evaluating deterioration of a light wavelength conversion sheet according to claim 1, wherein the deterioration is obtained.   Before the step of measuring the luminance distribution, the method further comprises a step of disposing the light wavelength conversion sheet on a light emitting surface of a direct type backlight device, and the size of the light wavelength conversion sheet is smaller than the size of the light emitting surface. The deterioration evaluation method for a light wavelength conversion sheet according to claim 1, wherein the light irradiated in the step of measuring the luminance distribution is light irradiated from the backlight device.   The degradation evaluation method for a light wavelength conversion sheet according to claim 1, further comprising a barrier film that suppresses permeation of moisture and oxygen on at least one surface of the light wavelength conversion layer.   The light that can be wavelength-converted by the quantum dots is blue light, and the quantum dots convert the blue light into green light, and the second quantum dots convert the blue light into red light. The deterioration evaluation method of the optical wavelength conversion sheet of Claim 1 containing this.   An optical wavelength conversion sheet comprising an optical wavelength conversion layer comprising a host matrix and quantum dots dispersed in the host matrix, wherein the optical wavelength conversion sheet has a temperature of 60 ° C. and a relative humidity of 90% for 500 hours. A light wavelength conversion sheet, wherein a durability test is performed, and the width when the deterioration of the light wavelength conversion sheet is evaluated by the deterioration evaluation method according to claim 1 is 5 mm or less after the durability test.   The light wavelength conversion sheet according to claim 5, further comprising a barrier film that suppresses permeation of moisture and oxygen on at least one surface of the light wavelength conversion layer.   The light wavelength conversion sheet according to claim 6, wherein the quantum dots include a first quantum dot that converts the blue light into green light, and a second quantum dot that converts the blue light into red light. A light source;
A light wavelength conversion sheet according to claim 6, which receives light from the light source. The backlight device according to claim 9;
An image display device comprising: a display panel disposed on a light output side of the backlight device.

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