Wavelength conversion film, wavelength conversion sheet, backlight, and display device

Abstract

To provide a film for wavelength conversion sheets when being used as a wavelength conversion sheet, exerting further excellent adhesion with a phosphor layer, a wavelength conversion sheet including the film, backlight including the wavelength conversion sheet and a display device.SOLUTION: A film 10 for wavelength conversion sheets comprises a primer layer 30 on a base material 20, where the primer layer 30 includes a cured product of a resin composition containing a polyurethane resin, and a softening point of the cured product is 250°C or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a film used in a wavelength conversion sheet. This disclosure also relates to a wavelength conversion sheet having the film, and to a backlight and display device equipped with the wavelength conversion sheet. [Background technology]

[0002] In recent years, the demand for liquid crystal displays (LCDs) has increased due to the development of personal computers, particularly portable personal computers. Furthermore, with the recent rise in the penetration rate of LCD televisions for home use, and the widespread adoption of smartphones and tablet devices, the market for LCDs is expanding.

[0003] Such liquid crystal display devices generally have a liquid crystal cell section, which consists of a color filter, a counter substrate, and a liquid crystal layer sandwiched between them, and also have a light source called a backlight section.

[0004] Recently, development of backlight components using quantum dot technology has also progressed. Quantum dots are nanometer-sized semiconductor particles. Furthermore, due to the quantum confinement effect (quantum size effect), in which electrons and excitons are confined within a tiny nanometer-sized crystal, the emission wavelength of quantum dots can be adjusted across the entire visible region. Because quantum dots can generate strong fluorescence in a narrow wavelength band, display devices can be illuminated with primary color light with excellent color purity. Therefore, backlights using quantum dots can be used to create display devices with excellent color reproduction.

[0005] The wavelength conversion sheet used as the backlight light source for this display device has a configuration that combines a phosphor layer in which nanometer-sized semiconductor phosphor particles are dispersed in a resin layer, a film formed on the surface of the phosphor layer to protect it, and an LED light source. The film has water vapor barrier properties to suppress the degradation of the phosphor layer. For example, a wavelength conversion sheet has been developed in which a barrier film is laminated on a phosphor layer containing phosphors, and the barrier film is a barrier layer laminated on one side of a predetermined polyethylene terephthalate film, and a backlight unit using the same has been developed (Patent Document 1).

[0006] To further suppress the penetration of water vapor into the phosphor layer, attempts have been made to improve the adhesion between the phosphor layer and the barrier film. For example, Patent Documents 2 and 3 disclose a barrier film that exhibits excellent adhesion to the phosphor layer even in high-temperature and high-humidity environments by using a primer layer containing a polyurethane resin composition. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2015 / 037733 [Patent Document 2] Japanese Patent Publication No. 2018-13724 [Patent Document 3] Japanese Patent Publication No. 2019-126924 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] The wavelength conversion sheets described in Patent Documents 2 and 3 maintained excellent adhesion to the phosphor layer even after being left in a 60°C, 90% RH environment for 500 hours. However, if left in the above environment for an extended period, delamination occurred between the wavelength conversion sheet and the phosphor layer. This delamination allowed oxygen and water vapor to penetrate the interior of the wavelength conversion sheet, causing deterioration of the phosphor layer, which was a problem. This disclosure has been made in view of the above-mentioned problems, and aims to provide a film for wavelength conversion sheets that has superior adhesion to a phosphor layer when used as a wavelength conversion sheet, a wavelength conversion sheet having the film, a backlight and a display device having the wavelength conversion sheet. [Means for solving the problem]

[0009] The inventors evaluated the relationship between the physical properties of films with primer layers of various formulations and their adhesion to the phosphor layer after long-term environmental testing. As a result, they found that when a polyurethane resin composition with a softening point above a predetermined value after curing is used, excellent adhesion to the phosphor layer can be ensured even when left for a long period of time exceeding 500 hours in an environment of 60°C and 90% RH, leading to the completion of this disclosure. In other words, in order to solve the above problems, this disclosure provides the following [1] to

[10] . [1] A film for wavelength conversion sheets having a primer layer on a substrate, wherein the primer layer contains a cured product of a resin composition containing a polyurethane resin, and the softening point of the cured product is 250°C or higher. [2] The film for wavelength conversion sheets according to [1], wherein the resin composition has a molar ratio of isocyanate groups to hydroxyl groups (NCO / OH ratio) of 1.1 or more. [3] The film for wavelength conversion sheets according to [1] or [2], wherein the polyurethane resin comprises a polyurethane resin obtained by the reaction of a polyfunctional isocyanate having a (meth)acrylic group with a hydroxyl group-containing compound. [4] A film for wavelength conversion sheets according to any one of [1] to [3], wherein the resin composition comprises a silane coupling agent. [5] A film for wavelength conversion sheets according to any one of [1] to [4], further comprising a barrier layer between the substrate and the primer layer. [6] The film for wavelength conversion sheets according to [5], wherein the barrier layer comprises an inorganic oxide layer and an organic coating layer, and the organic coating layer is in contact with the primer layer. [7] The film for wavelength conversion sheet according to [5], wherein the barrier layer is a layer containing a reaction product of a composition containing a metal oxide and a phosphorus compound. [8] A wavelength conversion sheet, wherein the film according to any one of [1] to [7] is provided such that the primer layer and the phosphor layer are in contact with at least one surface side of the phosphor layer containing a phosphor. [9] A backlight including at least one light source that emits primary light, an optical plate disposed adjacent to the light source for light guiding or diffusion, and a wavelength conversion sheet disposed on the light emitting side of the optical plate, wherein the wavelength conversion sheet is the wavelength conversion sheet according to [8].

[10] A display device including a backlight and a liquid crystal panel, wherein the backlight is the backlight according to [9]. [Advantages of the Invention] [[ID=A]] [[ID=B]]

[0010] According to the present disclosure, it is possible to obtain a wavelength conversion sheet that has excellent adhesion to the phosphor layer even when left in a high temperature and high humidity environment for a long time and can suppress the deterioration of the phosphor layer. By using the wavelength conversion sheet, it is possible to obtain a backlight and a display device in which deterioration of the phosphor layer hardly occurs. [Brief Description of the Drawings]

[0011] [Figure 1] It is a schematic cross-sectional view for schematically explaining an embodiment of the film for wavelength conversion sheet of the present disclosure. [Figure 2] It is a schematic cross-sectional view for schematically explaining an embodiment of the wavelength conversion sheet of the present disclosure. [Figure 3] It is a cross-sectional view showing an embodiment of the backlight of the present disclosure. [Figure 4] It is a cross-sectional view showing another embodiment of the backlight of the present disclosure. [Embodiments for Carrying Out the Invention]

[0012] The wavelength conversion sheet film of this disclosure will be described in detail below. In this specification, the numerical range notation "AA~BB" means "AA or greater and BB or less".

[0013] [Film for wavelength conversion sheets] The film for the wavelength conversion sheet protects the phosphor layer of the wavelength conversion sheet and prevents oxygen and water vapor from entering the wavelength conversion sheet from the external environment and reaching the phosphor layer, thereby preventing the phosphor layer from degrading. The wavelength conversion sheet film of the present disclosure has a primer layer on a substrate, the primer layer contains a cured product of a resin composition containing a polyurethane resin, and the softening point of the cured product is 250°C or higher.

[0014] Figure 1 is a schematic cross-sectional view illustrating one embodiment of the wavelength conversion sheet film of the present disclosure. The wavelength conversion sheet film 10 has a primer layer 30 on a substrate layer 20. As shown in Figure 1, the wavelength conversion sheet film 10 may have a barrier layer 40 between the substrate layer 20 and the primer layer 30. As shown in Figure 1, a diffusion layer 50 may be provided on the surface of the substrate layer 20 opposite to the surface on which the primer layer 30 is formed.

[0015] The wavelength conversion sheet film of this disclosure preferably has a high total light transmittance, as measured according to JIS K 7361-1:1997, in order to efficiently convert light from a light source when used as a wavelength conversion sheet. Specifically, the wavelength conversion sheet film of this disclosure preferably has a total light transmittance of 85% or more, and more preferably 90% or more, as measured according to JIS K 7361-1:1997.

[0016] The gas barrier properties of the wavelength conversion sheet film disclosed herein can be set according to requirements that take into account the degradation of the phosphor, as described later. Specifically, if the phosphor used in the wavelength conversion sheet is prone to degradation by oxygen, water vapor, etc., it is preferable that the wavelength conversion sheet film has high gas barrier properties. On the other hand, if the phosphor is not prone to degradation, high gas barrier properties are not required for the wavelength conversion sheet film. The oxygen permeability value for wavelength conversion sheet film according to JIS K 7129-2:2006 is 20 cc / m 2 It is preferable that it is less than or equal to 10cc / m³ / day·atm. 2 It is more preferable that it be less than or equal to 5cc / m 2 It is even more preferable that it be less than or equal to day·atm, which is 2cc / m 2 It is particularly preferable that the humidity is less than or equal to 1 / day·atm. Furthermore, the water vapor transmission value for the wavelength conversion sheet film according to JIS K 7129:2008 Method B should be 20 g / m². 2 It is preferable that it be less than 10 g / m². 2 It is more preferable that it be less than 5 g / m². 2 It is even more preferable that it be less than or equal to 2 g / m². 2 It is especially preferable that it be less than or equal to one day. Oxygen permeability can be measured, for example, using the "OX-TRAN" oxygen permeability meter manufactured by MOCON Corporation (MOCON method). Similarly, water vapor permeability can be measured, for example, using the "PERMATRAN" water vapor permeability meter manufactured by MOCON Corporation. The conditions for measuring oxygen permeability are a temperature of 23°C and a relative humidity of 90%. The conditions for measuring water vapor permeability are a temperature of 40°C and a relative humidity of 90%.

[0017] The following describes each layer of the film for the wavelength conversion sheet. [Base material layer] The substrate layer primarily serves as a support for the primer layer. The substrate layer is preferably one with high light transmittance. Specifically, the substrate layer is preferably of 85% or higher, and more preferably of 90% or higher, in accordance with JIS K 7361-1:1997.

[0018] The material of the base layer is not particularly limited, as long as it is a resin film that does not impair the function of the wavelength conversion sheet. Examples of resins that can be used as the base layer include polyimide (PI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyethylene butyrate (PBT), polypropylene (PP), nylon resin, amorphous polyarylate, polysulfone, polyethersulfone, polyetherimide, fluororesin, and liquid crystal polymer. To obtain transparency, heat resistance, etc., it is preferable to use polyethylene naphthalate (PEN) or polyethylene terephthalate (PET) as the base layer. Furthermore, to obtain the oxygen permeability and water vapor permeability mentioned above, it is preferable to use polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP), or nylon resin as the base layer.

[0019] The base layer may be a single-layer resin film, or it may be a plurality of resin films bonded together via an adhesive layer. In the example shown in Figure 1, the base layer 20 is formed by bonding a first base material 20-1 and a second base material 20-2 via an adhesive layer 22. In this case, the first base material 20-1 serves as a support when forming the primer layer 30. The second base material 20-2 increases the overall thickness of the base layer 20 and provides rigidity to the wavelength conversion sheet film 10.

[0020] The overall thickness of the substrate layer is not particularly limited, but it is preferably 8 μm to 200 μm, and more preferably 8 μm to 150 μm. When the film for wavelength conversion sheets is manufactured by a winding method, the overall thickness of the substrate layer is preferably 125 μm or less. On the other hand, by increasing the overall thickness of the substrate layer, gas barrier properties against oxygen and water vapor can be obtained by the substrate layer. In this case, the barrier layer can be omitted. In order to ensure the required gas barrier properties by the substrate layer without providing a barrier layer, the overall thickness of the substrate layer is preferably 50 μm or more, and more preferably 75 μm or more.

[0021] When the substrate layer is constructed from multiple resin films, the thickness of the first substrate, which serves as the support for the primer layer, is preferably 8 μm to 50 μm, more preferably 8 μm to 25 μm, and even more preferably 8 μm to 20 μm. When the first substrate has the above thickness, handling is improved when manufacturing the primer layer by winding. Furthermore, the thickness of the second substrate is preferably 8 μm to 150 μm, and more preferably 8 μm to 100 μm. When the second substrate has the above thickness, appropriate rigidity can be given to the film for the wavelength conversion sheet. Furthermore, when manufacturing the film for the wavelength conversion sheet by winding, handling is improved. When gas barrier properties are ensured by the substrate layer as described above, the thickness of the second substrate is preferably 40 μm or more, and more preferably 50 μm or more.

[0022] The adhesive constituting the adhesive layer 22 is not particularly limited as long as it provides good adhesion between the substrate layers and satisfies the optical performance required for the wavelength conversion sheet. For example, the adhesive can be a polyvinyl acetate adhesive; a polyacrylic acid ester adhesive consisting of homopolymers such as ethyl acrylate, butyl acrylate, 2-ethylhexyl ester, or copolymers thereof with methyl methacrylate, acrylonitrile, styrene, etc.; a cyanoacrylate adhesive; an ethylene copolymer adhesive consisting of copolymers of monomers such as vinyl acetate, ethyl acrylate, acrylic acid, methacrylic acid, etc., and ethylene; a cellulose adhesive; a polyester adhesive; a polyamide adhesive; a polyimide adhesive; an amino resin adhesive consisting of urea resin or melamine resin, etc.; a phenol resin adhesive; an epoxy adhesive; a polyurethane adhesive; a reactive (meth)acrylic adhesive; a rubber adhesive consisting of chloroprene rubber, nitrile rubber, styrene-butadiene rubber, etc.; a silicone adhesive; or an inorganic adhesive consisting of alkali metal silicate, low-melting-point glass, etc. The composition system of the adhesive constituting the adhesive layer may be any composition form such as aqueous, solution, emulsion, or dispersion, and its properties may be any form such as film, sheet, powder, or solid, and the bonding mechanism may be any form such as chemical reaction, solvent evaporation, thermal melting, or hot pressure. Alternatively, instead of the adhesives mentioned above, the adhesive layer may be formed using, for example, a thermosetting resin or a thermoplastic resin containing a crosslinking agent. Alternatively, a thermoplastic resin such as EVA, ionomer, polyvinyl butyral (PVB), or polyethylene resin may be extruded between the substrates by extrusion lamination to form the adhesive layer.

[0023] The surface of the substrate layer on the side where the primer layer is provided may be subjected to a desired surface treatment in advance to improve adhesion with the primer layer or barrier layer. Examples of surface treatments include corona discharge treatment, ozone treatment, low-temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, and oxidation treatment using chemicals.

[0024] Furthermore, as a method to improve adhesion with the primer layer or barrier layer, a base layer such as an anchor coating layer or an adhesive layer may be formed in advance. As the base layer, for example, a resin composition can be used in which polyester resin, polyamide resin, polyurethane resin, epoxy resin, phenolic resin, (meth)acrylic resin, polyvinyl acetate resin, polyolefin resin such as polyethylene or polypropylene, copolymers or modified resins thereof, cellulose resin, and others are the main components of the vehicle.

[0025] [Barrier layer] The barrier layer is a layer that imparts gas barrier properties to the film for wavelength conversion sheets. The barrier layer is a layer that can be optionally provided depending on the gas barrier properties required for the film for wavelength conversion sheets. The barrier layer may be provided on the side of the substrate layer opposite the primer layer, or between the substrate layer and the primer layer. In order to prevent damage to the barrier layer during the manufacturing process of the film for wavelength conversion sheets and the manufacturing process of the wavelength conversion sheets, and to suppress deterioration of the phosphor layer from the sheet edges when a wavelength conversion sheet is formed, it is preferable that the barrier layer be provided between the substrate layer and the primer layer. In the example shown in Figure 1, the barrier layer 40 is constructed by laminating an inorganic oxide layer 42 and an organic coating layer 44 in that order from the substrate layer 20 side. The organic coating layer 44 is in contact with the primer layer 30. The barrier layer of this disclosure is not limited to the laminated configuration shown in Figure 1. The layers constituting the barrier layer include "an inorganic oxide layer formed by vapor deposition of an inorganic oxide," "an inorganic oxide layer formed by the sol-gel method," "an organic coating layer formed by applying a coating agent containing a water-soluble polymer such as polyvinyl alcohol," and "a layer containing a reaction product of a composition containing a metal oxide and a phosphorus compound (hereinafter referred to as the "metal phosphate reaction product layer")." The configuration of the barrier layer in this disclosure includes a single layer of a single type selected from the group consisting of these layers, a layer formed by laminating multiple single types selected from the group, and a layer formed by alternately laminating two or more types selected from the group. Among these, a configuration in which an inorganic oxide layer and an organic coating layer are laminated, or a single layer configuration of a metal phosphate reaction product layer, as shown in Figure 1, is preferred.

[0026] <Inorganic oxide layer> Examples of inorganic oxide layers include layers composed of aluminum oxide, silicon oxide, magnesium oxide, or mixtures thereof. From the viewpoint of gas barrier properties, transparency, and productivity, the inorganic oxide layer is preferably a thin film layer mainly composed of aluminum oxide or silicon oxide.

[0027] Methods for forming an inorganic oxide layer include methods for forming it by depositing inorganic oxides and methods for forming it by the sol-gel method. Examples of methods for forming deposited films include physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, or chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition.

[0028] The thickness of the inorganic oxide layer is not particularly limited, but is preferably between 5 nm and 500 nm. A thickness of 5 nm or more ensures uniformity of the inorganic oxide layer, providing sufficient gas barrier properties to the wavelength conversion sheet film. Considering gas barrier properties, the inorganic oxide layer is more preferably 8 nm or more, and even more preferably 10 nm or more. Furthermore, a thickness of 500 nm or less allows for sufficient flexibility in the inorganic oxide layer, reducing the occurrence of scratches and cracks in each inorganic oxide layer. Considering transparency and productivity, the inorganic oxide layer is more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 20 nm or less. When multiple inorganic oxide layers are provided, it is preferable that each inorganic oxide layer falls within the above thickness range.

[0029] <Organic coating layer> The organic coating layer prevents various secondary damages in subsequent processes and provides high gas barrier properties to the film for the wavelength conversion sheet. Furthermore, by positioning the inorganic oxide layer between the substrate layer and the organic coating layer, the occurrence of scratches and cracks in the inorganic oxide layer can be reduced. In addition, by providing the organic coating layer in contact with the primer layer, good adhesion between the primer layer and the barrier layer of this disclosure can be achieved.

[0030] The organic coating layer is formed by applying a coating solution containing, for example, a water-soluble polymer and an aqueous solution or water / alcohol mixture containing at least one of one of a metal alkoxide and its hydrolysate, or tin chloride, as a gas barrier composition. The organic coating layer preferably contains at least one component selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, metal alkoxide hydrolysates, and metal alkoxide polymers. Examples of water-soluble polymers used in the organic coating layer include polyvinyl alcohol, polyvinylpyrrolidone, and ethylene-vinyl alcohol copolymers. In particular, excellent gas barrier properties can be obtained when polyvinyl alcohol and / or ethylene-vinyl alcohol copolymers are used. The content of polyvinyl alcohol resin and / or ethylene-vinyl alcohol copolymer is preferably in the range of 5 to 500 parts by mass, and more preferably in the range of 20 to 200 parts by mass, per 100 parts by mass of the total amount of the above-mentioned alkoxides.

[0031] The gas barrier composition may also contain silane coupling agents. Known organic reactive group-containing organoalkoxysilanes can be used as silane coupling agents. In this disclosure, organoalkoxysilanes having epoxy groups are particularly preferred, and examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. One or more of the above silane coupling agents may be used in combination. In this disclosure, the amount of the above silane coupling agent used is preferably 1 to 20 parts by mass per 100 parts by mass of the above alkoxysilane.

[0032] The thickness of the organic coating layer is not particularly limited, but is preferably between 100 nm and 500 nm. A thickness of 100 nm or more of the organic coating layer provides sufficient gas barrier properties to the film for the wavelength conversion sheet. Considering gas barrier properties, the organic coating layer is more preferably 120 nm or more, and even more preferably 150 nm or more. Furthermore, a thickness of 500 nm or less of the organic coating layer ensures sufficient transparency. Considering transparency and productivity, the organic coating layer is more preferably 300 nm or less, and even more preferably 200 nm or less. When multiple organic coating layers are provided, it is preferable that each organic coating layer is within the above thickness range.

[0033] <Metal Phosphate Reaction Layer> An example of a layer containing a reaction product of a composition comprising a metal oxide and a phosphorus compound (metal phosphorus reaction product layer) is the layer described in International Publication WO2011 / 122036. Aluminum is preferred as the metal. The thickness of the metal phosphate reactant layer is not particularly limited, but is preferably between 100 nm and 2000 nm. A thickness of 100 nm or more in the metal phosphate reactant layer provides sufficient gas barrier properties to the film for wavelength conversion sheets. Considering gas barrier properties, the thickness of the metal phosphate reactant layer is more preferably 200 nm or more, and even more preferably 300 nm or more. Furthermore, a thickness of 2,000 nm or less in the metal phosphate reactant layer suppresses cracking during film formation. Considering flexibility and other factors, the thickness of the metal phosphate reactant layer is more preferably 1,000 nm or less, and even more preferably 900 nm or less.

[0034] [Primer layer] The primer layer ensures good adhesion with the phosphor layer when used as a wavelength conversion sheet, preventing delamination between the wavelength conversion sheet film and the phosphor layer even in high-temperature and high-humidity environments, and thus preventing degradation of the phosphor layer.

[0035] In this disclosure, the primer layer contains a cured product of a resin composition containing a polyurethane resin. The presence of a polyurethane resin in the primer layer can be confirmed by detecting urethane bonds using methods such as X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and gas chromatography-mass spectroscopy (GCMS).

[0036] In this disclosure, the softening point of the cured product of the resin composition constituting the primer layer is 250°C or higher. The softening point of the cured product is a value measured by local thermal analysis using a thermal probe. In local thermal analysis using a thermal probe, the thermal probe is brought into contact with the surface of the primer layer, and the displacement of the thermal probe from before heating is measured while the temperature is increased to obtain a thermal expansion curve. Specifically, the thermal probe is pushed up as the resin of the primer layer expands due to heating. As the resin of the primer layer softens, the tip of the thermal probe penetrates into the resin, causing the thermal probe to descend. The point where the displacement of the thermal probe changes from upward to downward corresponds to the peak of the thermal expansion curve. The temperature at the peak of the thermal expansion curve is defined as the softening point of the cured resin composition constituting the primer layer. In this invention, the softening point is the average value of measurements taken at 10 arbitrary locations on the surface of the primer layer.

[0037] By including a cured product of a resin composition containing polyurethane resin in the primer layer, the peel strength between the primer layer and the phosphor layer is high when used as a wavelength conversion sheet, resulting in good adhesion before exposure to high temperature and high humidity environments (sometimes referred to as "initial adhesion"). If the softening point of the cured resin composition constituting the primer layer is below 250°C, even if the initial adhesion is good, delamination will occur between the primer layer and the phosphor layer if left in a high-temperature, high-humidity environment (e.g., 60°C, 90% RH). In other words, leaving it in a high-temperature, high-humidity environment reduces adhesion (sometimes referred to as "adhesion over time" or "longitudinal adhesion"). By having a softening point of 250°C or higher for the cured resin composition constituting the primer layer, it is possible to suppress a decrease in peel strength, i.e., a decrease in adhesion over time, even if left in a high-temperature, high-humidity environment for a long period exceeding 500 hours. The softening point is preferably 270°C or higher, and more preferably 280°C or higher.

[0038] The following is an inference regarding the influence of the softening point of the cured resin composition constituting the primer layer on the delamination state (adhesion) between the primer layer and the phosphor layer when exposed to a high-temperature, high-humidity environment. First, the initial adhesion can be inferred as follows: As described later, the phosphor layer of the wavelength conversion sheet is formed by applying a resin composition that serves as a precursor to the phosphor layer to the surface of the primer layer of the film for the wavelength conversion sheet, and then curing the resin composition. On the phosphor layer side of the primer layer, shrinkage stress is generated as the phosphor layer shrinks. On the other hand, on the side of the primer layer opposite the phosphor layer, since it is in contact with the substrate layer or barrier layer, no shrinkage stress is generated when the phosphor layer is cured. In other words, the formation of the phosphor layer creates a stress distribution in the thickness direction of the primer layer, and strain is generated inside the primer layer. If the initial adhesion between the phosphor layer and the primer layer is weak, delamination will occur between the phosphor layer and the primer layer due to the strain inside the primer layer. If a wavelength conversion sheet is left in a high-temperature, high-humidity environment for a long period of time, the resin composition constituting the primer layer will be affected by heat and water vapor, even if its softening point is higher than the ambient temperature. If the softening point of the cured product is below 250°C, the properties of the resin are easily altered by heat and water vapor. Possible changes in resin properties include hydrolysis and softening of polyurethane resins. Therefore, even if the initial adhesion is good, the stress balance inside the primer layer may change, or the primer layer may deteriorate at the interface with the phosphor layer, leading to a decrease in adhesion and delamination. On the other hand, if the softening point of the cured product is 250°C or higher, changes in the properties of the resin are less likely to occur, thus suppressing changes in stress balance and deterioration of the primer layer. As a result, it is possible to maintain high adhesion between the phosphor layer and the primer layer even when left in a high-temperature, high-humidity environment.

[0039] The polyurethane resin composition includes a one- or two-component polyurethane resin obtained by the reaction of a polyfunctional isocyanate with a hydroxyl group-containing compound. The softening point of the cured resin composition constituting the primer layer can be changed by altering the combination of polyfunctional isocyanates and hydroxyl group-containing compounds, the blending ratio of polyfunctional isocyanates and hydroxyl group-containing compounds, the combination and blending ratio of multiple hydroxyl group-containing compounds with different softening points, the NCO / OH ratio in the polyurethane resin, and the molecular weight of the polyurethane resin. Furthermore, the softening point of the cured resin composition constituting the primer layer can also be altered by adding a tackifying resin (tackyfire) with a different softening point than the polyurethane resin.

[0040] Polyfunctional isocyanates and hydroxyl group-containing compounds may be used individually or in combination. Examples of polyfunctional isocyanates include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenylene polyisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate. The polyfunctional isocyanate may be used as a high molecular weight modified form such as an adduct, burette, or isocyanurate, or as a block form. The modified and block forms may have functional groups such as hydroxyl groups, carboxyl groups, epoxy groups, amino groups, mercapto groups, vinyl groups, acryloyl groups, and methacryloyl groups. Among these, it is preferable to use a (meth)acrylic group-containing polyisocyanate. That is, the polyurethane resin of this disclosure includes a polyurethane resin obtained by the reaction of a polyfunctional isocyanate having a (meth)acrylic group with a hydroxyl group-containing compound. Examples of hydroxyl group-containing compounds include polyether polyols, polyester polyols, polyester polyurethane polyols, and polyacrylate polyols.

[0041] The NCO / OH ratio is preferably 1.1 or higher, more preferably 1.2 or higher, and even more preferably 1.3 or higher. An NCO / OH ratio of 1.1 or higher results in excellent initial adhesion and a softening point of 250°C or higher. However, a high NCO / OH ratio causes the primer layer to become tacky. For this reason, the NCO / OH ratio is preferably 4.0 or lower, and more preferably 3.0 or lower. Depending on the type of polyfunctional isocyanate and hydroxyl group-containing compound, the higher the molecular weight of the polyurethane resin, the higher the softening point of the polyurethane resin. As a result, the softening point of the cured resin composition tends to be 250°C or higher. The molecular weight (weight-average molecular weight) of the polyurethane resin is preferably between 100 and 100,000.

[0042] The cured product of the above polyurethane resin composition is preferably contained in an amount of 40% by mass or more, and more preferably 70% by mass or more, of the total amount of the primer layer. By including 40% by mass or more of the polyurethane resin, the initial adhesion and adhesion over time between the primer layer and the phosphor layer can be improved.

[0043] In this disclosure, the primer layer preferably further contains a silane coupling agent. The inclusion of a silane coupling agent has the effect of suppressing the decrease in adhesion over time, which occurs when the urethane bonds in the polyurethane resin are hydrolyzed when left in a high-temperature, high-humidity environment for a long period of time. Furthermore, in a configuration in which a barrier layer is provided, the adhesion between the primer layer and the barrier layer (especially the organic coating layer) can be improved.

[0044] Silane coupling agents undergo hydrolysis of a functional group at one end of the molecule, typically a chloro, alkoxy, or acetoxy group, to form a silanol group (Si-OH). This modifies the resin composition of the primer layer with covalent bonds, forming strong bonds. Therefore, hydrolysis of urethane bonds in high-temperature and high-humidity environments is suppressed, and the deterioration of adhesion over time can be prevented. Furthermore, organic functional groups such as vinyl, methacryloxy, amino, epoxy, or mercapto at the other end of the silane coupling agent can improve the adhesion between the primer layer and the phosphor layer, as well as the adhesion between the barrier layer and the primer layer.

[0045] As silane coupling agents, one or more organically functional silane monomers having binary reactivity can be used, such as γ-chloropropyltrimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyl-tris(β-methoxyethoxy)silane, γ-methacrylateoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-mercaptopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-ureidopropyltriethoxysilane, bis(β-hydroxyethyl)-γ-aminopropyltriethoxysilane, and aqueous solutions of γ-aminopropyl silicane.

[0046] The silane coupling agent described above is preferably contained in an amount of 1% by mass or more, and more preferably 2% by mass or more, of the total amount of the primer layer. When the silane coupling agent content is within the above range, the initial adhesion between the primer layer and the phosphor layer, and the adhesion between the barrier layer and the primer layer can be further improved. In addition, good adhesion can be maintained between the primer layer and the phosphor layer over time. Furthermore, in order to improve the extensibility of the primer layer and suppress the occurrence of cracks in the primer layer, the silane coupling agent is preferably contained in an amount of 30% by mass or less, and more preferably 20% by mass or less, of the total amount of the primer layer.

[0047] Furthermore, in this disclosure, after forming the primer layer, the surface of the primer layer (the contact surface with the phosphor layer) may be subjected to surface treatments such as corona discharge treatment, ozone treatment, low-temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, or oxidation treatment using chemicals.

[0048] In this disclosure, the primer layer may further contain a filler. The filler plays a role in adjusting the viscosity of the coating solution for forming the primer layer and improving coating suitability. Examples of fillers that can be used include powders such as calcium carbonate, barium sulfate, alumina white, silica, talc, and glass frit, as well as resin powders.

[0049] The primer layer may further contain additives such as stabilizers, crosslinkers, lubricants, UV absorbers, and others, as needed.

[0050] The thickness of the primer layer is not particularly limited, but it is preferably 0.05 μm or more, and more preferably 0.1 μm or more. A relatively thick primer layer is preferable in order to minimize strain within the primer layer. However, if the primer layer is too thick, handling and productivity will decrease, so the thickness of the primer layer is preferably 10 μm or less, and more preferably 3 μm or less.

[0051] The primer layer according to this embodiment preferably has a high total light transmittance, as measured according to JIS K 7361-1:1997, in order to efficiently convert light from a light source. Specifically, the primer layer according to this embodiment preferably has a total light transmittance of 85% or more, and more preferably 90% or more, as measured according to JIS K 7361-1:1997, when the primer layer is formed on a PET film (film thickness: 12 μm).

[0052] [Diffusion layer] The diffusion layer is a layer provided for the purpose of reducing the anisotropy of the light emission angle distribution and preventing adhesion, and is an optional layer in this disclosure. The diffusion layer includes a binder resin and a filler. By embedding the filler itself in the binder resin, and by exposing at least a portion of the filler from the binder resin to the layer surface, an uneven shape is created on the diffusion layer surface, thereby reducing the anisotropy of the light emission angle distribution. Furthermore, the uneven surface of the diffusion layer prevents the films or sheets from sticking together during the manufacturing process of the wavelength conversion sheet film or the wavelength conversion sheet itself. For example, when manufacturing the films or sheets using a winding method, handling of the films or sheets becomes easier, and surface scratches can be suppressed. In addition, when used as a display device, it prevents the light guide plate or diffuser plate from sticking to the wavelength conversion sheet, suppressing scratches caused by friction between the light guide plate or diffuser plate and the wavelength conversion sheet, and reducing the occurrence of defects in the appearance of the display device.

[0053] The binder resin for the diffusion layer is not particularly limited, as long as it satisfies the specifications required for the film and wavelength conversion sheet. For example, acrylic resins, epoxy resins, urethane resins, polyester resins, polyester acrylate resins, polyurethane acrylate resins, acrylic urethane resins, epoxy acrylate resins, etc., can be used. From the viewpoint of having high hardness, the binder resin is preferably an acrylic resin.

[0054] From the viewpoint of the optical performance required for the film for the wavelength conversion sheet and the wavelength conversion sheet, the filler is preferably a resin filler. Examples of resins used for the filler include acrylic resins and polystyrene resins. From the viewpoint of improving the scratch resistance of the diffusion layer, an acrylic resin filler is particularly preferred. Here, acrylic resin refers to a polymer containing as a monomer component an ethylenically unsaturated monomer having at least one carboxyl group or carboxylic acid ester group selected from the group consisting of methacrylic acid, acrylic acid, methacrylic acid esters, and acrylic acid esters. The refractive index difference between the filler and the resin binder is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less.

[0055] The average particle size of the filler is preferably 1 μm or more and 50 μm or less, and more preferably 1.5 μm or more and 10 μm or less. When the average particle size of the filler is 1 μm or more, at least a portion of the filler is exposed more from the surface of the diffusion layer, providing appropriate light diffusion and more effectively suppressing adhesion. When the average particle size of the filler is 50 μm or less, the filler is less likely to detach from the diffusion layer, suppressing deterioration of the diffusion layer's function and damage caused by detached filler. In this disclosure, the average particle size refers to the mass-average value d50 obtained by particle size distribution measurement using laser diffraction.

[0056] The filler content is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less, relative to the total amount of the diffusion layer. A content of 5% by mass or more provides appropriate light diffusion and effectively prevents adhesion. A content of 50% by mass or less makes it easier to meet the optical properties required for wavelength conversion sheets and wavelength conversion sheets, and also improves the film formation properties of the diffusion layer.

[0057] The diffusion layer may optionally contain additives such as stabilizers, curing agents, crosslinking agents, lubricants, UV absorbers, and others, as needed.

[0058] The thickness of the diffusion layer is not particularly limited and can be set appropriately according to the average particle size of the filler, the specifications required for the wavelength conversion sheet film and the wavelength conversion sheet itself. For example, the thickness of the diffusion layer is preferably 1.0 μm or more and 50.0 μm or less, and more preferably 1.5 μm or more and 10.0 μm or less. Note that the thickness of the diffusion layer refers to the thickness of the resin portion other than the filler in the diffusion layer, and does not include the portion of the filler that protrudes above the resin. The thickness of the diffusion prevention layer can be measured, for example, by observing the cross-section with a scanning electron microscope.

[0059] [Method for manufacturing film for wavelength conversion sheets] The wavelength conversion sheet film of this disclosure is manufactured by the following process.

[0060] (1) Barrier layer formation process A barrier layer is formed on one surface of the substrate layer (or the first substrate). Note that the barrier layer formation step can be omitted.

[0061] As illustrated in Figure 1, when an organic coating layer and an inorganic oxide layer are used as barrier layers, first an inorganic oxide layer is formed on a substrate layer (or a first substrate), and then an organic coating layer is formed on the inorganic oxide layer. Furthermore, the surface on which the barrier layer of the base material layer (or the first base material) is formed may have the above-described surface treatment applied in advance, or a base layer may have been formed thereon.

[0062] Inorganic oxide layers can be formed by vapor deposition or sol-gel methods. Methods for vapor deposition of inorganic oxides include physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, or chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition.

[0063] The organic coating layer can be formed by applying a coating agent containing the above-mentioned gas barrier composition and curing it by heating. The coating agent is prepared by adding a solvent to the gas barrier composition to obtain the desired gas barrier properties, thickness, viscosity, etc. Methods for applying the coating agent include roll coating, gravure coating, knife coating, dip coating, spray coating, and other coating methods.

[0064] The metal phosphate reactant layer can be formed by the method described in International Publication WO2011 / 122036.

[0065] (2) Primer layer formation process A primer layer is formed on the substrate layer or barrier layer. The primer layer can be formed by applying a coating agent of a resin composition containing the polyurethane resin and curing it by heating. The coating agent is prepared by adding a solvent to the coating agent to obtain the desired thickness, viscosity, etc. Methods for applying the coating agent include roll coating, gravure coating, knife coating, dip coating, spray coating, and other coating methods. The heating temperature is preferably in the range of 50°C to 180°C.

[0066] As shown in Figure 1, when the substrate layer is constructed by laminating multiple substrates, the method for manufacturing a wavelength conversion sheet film according to this disclosure further includes (3) an adhesion step after (2) a primer layer formation step. (3) Adhesion process In the bonding process, the side of the first substrate opposite the barrier layer and the second substrate are laminated together with an adhesive layer in between. Specifically, the adhesive described above is applied to the surface of the first substrate, the second substrate is placed on top, and the adhesive layer is cured. Alternatively, a coating agent containing a crosslinking agent and resin is applied to the surface of the first substrate, the second substrate is placed on top, and the coating agent is crosslinked by heat or other means. The adhesive or coating agent can be applied by roll coating, gravure coating, knife coating, dip coating, spray coating, other coating methods, or printing methods. Alternatively, molten thermoplastic resin may be poured between the first and second substrates by extrusion lamination, and then cooled to form an adhesive layer.

[0067] Furthermore, if a diffusion layer is provided as shown in Figure 1, it is preferable that the diffusion layer is already formed on the base layer or the second base layer. Specifically, a coating agent containing resin, filler, solvent, etc., can be applied to the surface opposite to the surface where the barrier layer of the base material or second base material is provided, and then cured to form the coating. Methods for applying the coating agent include roll coating, gravure coating, knife coating, dip coating, spray coating, and other coating methods.

[0068] [Applications of films for wavelength conversion sheets] The wavelength conversion film of this disclosure can be used, for example, as a wavelength conversion film for a surface light source. Examples of surface light sources include backlight light sources for display devices such as liquid crystal displays, and backlight light sources for inspection equipment. In other words, the wavelength conversion film of this disclosure can be used as a "wavelength conversion film for a backlight light source of a display device," a "wavelength conversion film for a backlight light source of inspection equipment," and so on. Furthermore, the wavelength conversion film of this disclosure can also be used as a "wavelength conversion film for horticultural applications." Examples of horticultural wavelength conversion sheets include sheets that have the function of converting ultraviolet light to wavelengths suitable for plant growth. Wavelengths suitable for plant growth include wavelengths suitable for photosynthesis. Horticultural wavelength conversion sheets can be installed, for example, on the ceilings of horticultural facilities such as greenhouses and glasshouses.

[0069] [Wavelength Conversion Sheet] Figure 2 is a schematic cross-sectional view illustrating one embodiment of the wavelength conversion sheet of the present disclosure. The wavelength conversion sheet 100 in Figure 2 comprises the wavelength conversion sheet film 10 (10a, 10b) shown in Figure 1 on both surfaces of the phosphor layer 60. The configuration of the wavelength conversion sheet of the present disclosure is not limited to Figure 2. The wavelength conversion sheet of the present disclosure may, for example, have the wavelength conversion sheet film shown in Figure 1 on one surface side and the wavelength conversion sheet film of the present disclosure having a different laminated configuration on the other surface side. Examples of the wavelength conversion sheet film of the present disclosure having a different laminated configuration include, for example, a wavelength conversion sheet film without a barrier layer, or a wavelength conversion sheet film with a different barrier layer configuration. Furthermore, the wavelength conversion sheet film 10 of this disclosure may be provided on at least one surface side of the phosphor layer 60. That is, the wavelength conversion sheet film 10(10a) of this disclosure may be provided on one surface side of the phosphor layer 60, and another wavelength conversion sheet film other than the wavelength conversion sheet film of this disclosure described above may be provided on the other surface side of the phosphor layer 60.

[0070] [Phosphor layer] The phosphor layer is a layer used to adjust the emission wavelength of light emitted from a backlight source. The phosphor layer can be formed by laminating a encapsulating resin containing phosphors. For example, it can be formed by applying a mixture containing phosphors and encapsulating resin to the surface of a substrate layer and curing it. The phosphor layer contains one or more phosphors consisting of quantum dots.

[0071] Quantum dots that form phosphors are semiconductor particles of a predetermined size that exhibit the quantum confinement effect. When a quantum dot absorbs light from an excitation source and reaches an energetically excited state, it releases energy corresponding to its energy band gap. By adjusting the size of the quantum dot or the composition of the material, the energy band gap can be adjusted, and energy levels across various wavelength bands can be obtained. In particular, quantum dots can generate strong fluorescence in a narrow wavelength band. Therefore, display devices can be illuminated with light of the three primary colors with excellent color purity, resulting in display devices with excellent color reproduction. Preferably, the quantum dots include quantum dots that emit secondary light at a wavelength corresponding to red, quantum dots that emit secondary light at a wavelength corresponding to green, and combinations thereof. However, the quantum dots may also include quantum dots other than those that emit secondary light at a wavelength corresponding to red or green.

[0072] The core of a quantum dot is a nanometer-sized semiconductor particle, and is not particularly limited as long as it is a material that exhibits a quantum confinement effect (quantum size effect). Examples of quantum dots include semiconductor particles whose emission color is regulated by their own particle size, and semiconductor particles having a dopant. Examples of core materials include semiconductor compounds or semiconductor crystals containing semiconductors such as: Group II-VI semiconductor compounds like MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe; Group III-V semiconductor compounds like AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs, and TiSb; and Group IV semiconductors like Si, Ge, and Pb. Furthermore, semiconductor crystals containing semiconductor compounds with three or more elements, such as InGaP, can also be used. Furthermore, as the quantum dots composed of semiconductor fine particles having a dopant, Eu can be added to the above semiconductor compound. 3+ Tb 3+ Ag + Cu + A semiconductor crystal doped with a cation of a rare earth metal or a cation of a transition metal such as these can also be used. As the material for the core of the quantum dots, semiconductor crystals such as CdS, CdSe, CdTe, InP, and InGaP are suitable from the viewpoints of ease of production, controllability of the particle size for obtaining light emission in the visible region, and fluorescence quantum yield.

[0073] The quantum dots may be composed of one kind of semiconductor compound or two or more kinds of semiconductor compounds.For example, the quantum dots may have a structure (core-shell structure) in which the core as the light-emitting part is covered with a protective layer (shell). When using core-shell type quantum dots, as the semiconductor constituting the shell, by using a material having a higher band gap than the semiconductor compound forming the core so that excitons are confined in the core, the light emission efficiency of the quantum dots can be increased. Examples of such a core-shell structure (core / shell) having a relationship of the magnitude of the band gap include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, Gap / ZnS, Si / ZnS, InN / GaN, InP / CdSSe, InP / ZnSeTe, InGaP / ZnSe, InGaP / ZnS, Si / AlP, InP / ZnSTe, InGaP / ZnSTe, InGaP / ZnSSe, and the like.

[0074] The size of the quantum dots may be appropriately controlled depending on the material constituting the quantum dots so that light of a desired wavelength can be obtained.As the particle size of the quantum dots becomes smaller, the energy band gap becomes larger.That is, as the crystal size becomes smaller, the light emission of the quantum dots shifts toward the blue side, that is, toward the high energy side. Generally, the particle size (diameter) of the quantum dots is preferably in the range of 0.5 nm to 20 nm, and particularly preferably in the range of 1 nm to 10 nm. Furthermore, the narrower the size distribution of the quantum dots, the more vivid the emission color can be obtained. The shape of the quantum dot is not particularly limited and may be spherical, rod-shaped, disc-shaped, or other shapes. If the quantum dot is not spherical, the particle size of the quantum dot may be the same as that of a perfectly spherical dot with the same volume. Quantum dots may be coated with resin.

[0075] The quantum dot content is adjusted as appropriate depending on the thickness of the phosphor layer, the light recycling rate in the backlight, the desired color, etc. If the thickness of the phosphor layer is within the range described later, it is preferable that the quantum dot content is 0.01 parts by mass or more and 1.0 part by mass or less per 100 parts by mass of the sealing resin of the phosphor layer.

[0076] Examples of encapsulating resins for the phosphor layer include cured products of thermosetting resin compositions and cured products of ionizing radiation-curable resin compositions. Among these, from the viewpoint of durability, cured products of thermosetting resin compositions and cured products of ionizing radiation-curable resin compositions are preferred, and cured products of ionizing radiation-curable resin compositions are more preferred.

[0077] A thermosetting resin composition is a composition containing at least a thermosetting resin, which hardens upon heating. Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, and silicone resins. These may be used individually or in combination of one or more. A curing agent may be added to these curable resins in the thermosetting resin composition as needed.

[0078] The ionizing radiation-curable resin composition is a composition containing a compound having an ionizing radiation-curable functional group (hereinafter also referred to as "ionizing radiation-curable compound").

[0079] Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups, with ethylenically unsaturated bonding groups being preferred. Among ethylenically unsaturated bonding groups, (meth)acryloyl groups are preferred. Hereinafter, ionizing radiation-curable compounds having (meth)acryloyl groups will be referred to as (meth)acrylate compounds. That is, it is preferable that the sealing resin contains a cured product of a composition containing (meth)acrylate compounds. In this specification, "(meth)acrylate" refers to methacrylate and acrylate. In this specification, "ionizing radiation" refers to electromagnetic waves or charged particle beams that have energy quanta capable of polymerizing or crosslinking molecules, and usually ultraviolet (UV) or electron beams (EB) are used, but other electromagnetic waves such as X-rays and gamma rays, and charged particle beams such as alpha rays and ion beams can also be used.

[0080] The ionizing radiation-curable compound may be a monofunctional ionizing radiation-curable compound having only one of the above-mentioned functional groups, or a polyfunctional ionizing radiation-curable compound having two or more of the above-mentioned functional groups, or a mixture thereof. Among these, polyfunctional ionizing radiation-curable compounds are preferred, and polyfunctional (meth)acrylate compounds having two or more (meth)acryloyl groups are more preferred. That is, the encapsulating resin preferably contains a cured product of a polyfunctional ionizing radiation-curable compound, and more preferably contains a cured product of a polyfunctional (meth)acrylate compound.

[0081] The polyfunctional (meth)acrylate compounds may also have alkylene oxy groups. As for the alkylene oxy group, for example, an alkylene oxy group having 2 to 4 carbon atoms is preferred, an alkylene oxy group having 2 or 3 carbon atoms is more preferred, and an alkylene oxy group having 2 carbon atoms is even more preferred.

[0082] A polyfunctional (meth)acrylate compound having an alkylene oxy group may also be a polyfunctional (meth)acrylate compound having a polyalkylene oxy group containing multiple alkylene oxy groups. When a polyfunctional (meth)acrylate compound has alkylene oxy groups, the number of alkylene oxy groups in one molecule is preferably 2 to 30, more preferably 2 to 20, even more preferably 3 to 10, and even more preferably 3 to 5.

[0083] When a polyfunctional (meth)acrylate compound has an alkylene oxy group, it is preferable that it has a bisphenol structure. This tends to improve the heat resistance of the cured product. Examples of bisphenol structures include bisphenol A structure and bisphenol F structure, with bisphenol A structure being preferred. Among the polyfunctional (meth)acrylate compounds having an alkylene oxy group, ethoxylated bisphenol A type di(meth)acrylate, propoxylated bisphenol A type di(meth)acrylate, and propoxylated ethoxylated bisphenol A type di(meth)acrylate are preferred, with ethoxylated bisphenol A type di(meth)acrylate being more preferred.

[0084] Furthermore, the ionizing radiation-curable compound may be a monomer, an oligomer, a low molecular weight polymer, or a mixture thereof.

[0085] When the ionizing radiation-curable compound is an ultraviolet-curable compound, the ionizing radiation-curable composition preferably contains additives such as photopolymerization initiators and photopolymerization accelerators.

[0086] The phosphor layer may contain internally diffusing particles. The internally diffusing particles can be either organic or inorganic. Examples of organic particles include those made of polymethyl methacrylate, acrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone resin, fluororesin, and polyester. Examples of inorganic fine particles include those made of silica, alumina, zirconia, and titania. The shape of the internally diffusing particles can be spherical, disc-shaped, rugby ball-shaped, or irregular. Furthermore, the internally diffusing particles may be hollow particles, porous particles, or solid particles.

[0087] The content of internally diffusing particles is preferably 1 to 40 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of the sealing resin.

[0088] The average particle size of the internally diffusing particles is preferably 1 μm or more and 7 μm or less, and more preferably 1 μm or more and 3 μm or less.

[0089] The thickness of the phosphor layer is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and even more preferably 30 μm to 130 μm.

[0090] [Manufacturing method for wavelength conversion sheets] The wavelength conversion sheet of this disclosure can be manufactured using at least one wavelength conversion sheet film manufactured by the manufacturing method described above. Below, as shown in Figure 2, a method for manufacturing a wavelength conversion sheet having a phosphor layer sandwiched between the wavelength conversion sheet films of this disclosure will be given as an example. Specifically, a mixture (ink) containing a phosphor and a sealing resin is applied to the surface of the primer layer of the wavelength conversion sheet film of this disclosure. Methods for applying the mixture (ink) include roll coating, gravure coating, knife coating, dip coating, spray coating, and other coating methods. Then, the phosphor layer is brought into contact with the primer layer of another wavelength conversion sheet film according to this disclosure. After that, the mixture (ink) is cured by heat or the like to obtain a wavelength conversion sheet.

[0091] [Backlight] The backlight of the present disclosure comprises at least one light source that emits primary light, an optical plate disposed adjacent to the light source for light guidance or diffusion, and a wavelength conversion sheet (quantum dot sheet) disposed on the light-emitting side of the optical plate, wherein the wavelength conversion sheet is the wavelength conversion sheet of the present disclosure described above.

[0092] The backlight 200 of this disclosure can be either an edge-lit backlight as shown in Figure 3 or a direct-lit backlight as shown in Figure 4.

[0093] The optical plate 120 used in the edge-lit backlight 201 shown in Figure 3 is an optical component for guiding the primary light emitted from the light source 110, and is a so-called light guide plate 121. The light guide plate 121 has a substantially flat shape, for example, formed such that at least one surface is the light incident surface and one surface substantially perpendicular to it is the light emission surface.

[0094] The light guide plate is mainly composed of a matrix resin selected from highly transparent resins such as polymethyl methacrylate. The light guide plate may also contain resin particles with different refractive indices from the matrix resin, as needed. Each surface of the light guide plate may not be a uniform plane but may have a complex surface shape, and may be provided with a dot pattern or the like.

[0095] The optical plate 120 used in the direct-lit backlight 202 shown in Figure 4 is an optical component (light diffusing material 122) that has light-diffusing properties to make the pattern of the light source 110 difficult to see. Examples of the light diffusing material 122 include a milky white resin plate with a thickness of about 1 to 3 mm.

[0096] Edge-lit and direct-lit backlights may, in addition to the light source, optical plate, and wavelength conversion sheet described above, include one or more components selected from reflectors, light-diffusing films, prism sheets, brightness-enhancing films (BEF), and reflective polarizing films (DBEF), depending on the purpose. The reflector is positioned on the side opposite to the light-emitting surface of the optical plate. The light-diffusing film, prism sheet, brightness-enhancing film, and reflective polarizing film are positioned on the light-emitting surface side of the optical plate. By including one or more components selected from reflectors, light-diffusing films, prism sheets, brightness-enhancing films, and reflective polarizing films, a backlight with an excellent balance of front brightness, viewing angle, etc., can be made.

[0097] In edge-lit and direct-lit backlights, the light source 110 is a light emitter that emits primary light, and it is preferable to use a light emitter that emits primary light with a wavelength corresponding to blue. The primary light with a wavelength corresponding to blue preferably has a peak wavelength in the range of 380 nm to 480 nm. More preferably, the peak wavelength is 450 nm ± 7 nm, more preferably 450 nm ± 5 nm, more preferably 450 nm ± 3 nm, and more preferably 450 nm ± 1 nm. From the viewpoint of simplifying and miniaturizing the device for installing the backlight, the light source 110 is preferably an LED light source, and more preferably a monochromatic blue LED light source. Alternatively, a red phosphor may be coated on a monochromatic blue LED light source to create a light source that emits both blue and red light. There is at least one light source 110, and from the viewpoint of emitting sufficient primary light, there are preferably multiple light sources.

[0098] [Display device] Examples of display devices include liquid crystal displays. A liquid crystal display device comprises a backlight and a liquid crystal panel. The backlight is the backlight of the present disclosure described above.

[0099] The liquid crystal panel is not particularly limited, and a general-purpose liquid crystal panel for a liquid crystal display device can be used. For example, a liquid crystal panel having a common structure in which a liquid crystal layer is sandwiched between glass plates, specifically those with display methods such as TN, STN, VA, IPS, and OCB, can be used.

[0100] The liquid crystal display device further includes a polarizing plate and a color filter, etc. General-purpose polarizing plates and color filters can be used.

[0101] The wavelength conversion sheet of this disclosure exhibits particularly excellent adhesion between the film for the wavelength conversion sheet and the phosphor layer. Therefore, when the wavelength conversion sheet of this disclosure is applied to a display device (liquid crystal display device), degradation of the phosphor layer due to the intrusion of water vapor and oxygen from the external environment can be effectively suppressed. As a result, a display device with a backlight source exhibiting excellent environmental stability can be created. [Examples]

[0102] Next, the present disclosure will be described in more detail by reference to examples, but the present disclosure is not limited in any way by these examples.

[0103] 1. Evaluation and Measurement The following measurements and evaluations were performed on wavelength conversion film and wavelength conversion sheet manufactured using the method described below. The results are shown in Table 1. Unless otherwise specified, and unless the tests were conducted under specific environmental conditions, the atmosphere during each measurement and evaluation was 23±5°C and 40-65% relative humidity. Before starting each measurement and evaluation, the target sample was exposed to the aforementioned atmosphere for at least 30 minutes.

[0104] 1-1. Softening point measurement The softening point of the primer layer was measured for the wavelength conversion sheet films of the examples and comparative examples by the following process. The nanoTA measuring device manufactured by ANASYS INSTRUMENTS was used, and the PR-EX-AN2-300-5 thermal probe manufactured by ANASYS INSTRUMENTS was used. Before measurement, calibration was performed using the following procedure. As standard samples, BRUKER nanoTA Calibration Samples were prepared. These standard samples contained polycaprolactone (softening point: 55°C), polyethylene (softening point: 116°C), and polyethylene terephthalate (softening point: 235°C), all of which have known softening points. Each standard sample was heated while in contact with a thermal probe. During heating, the thermal expansion directly beneath the thermal probe was measured, and a graph representing the Deflection (displacement) against Voltage (potential) was obtained. The measurement conditions set on the instrument were as follows. Measurement start temperature: 0.1V Measurement end temperature: 10V Heating rate: 0.2V / sec Using the softening points of each standard sample, the graph representing the displacement of the thermal probe against potential was converted into a graph representing the displacement against temperature.

[0105] After calibration, the thermal probe was brought into contact with the surface of the primer layer of the wavelength conversion sheet films of the examples and comparative examples. Then, with the thermal probe in contact, the films were heated under the following conditions, and a graph (thermal expansion curve) representing the displacement of the thermal probe with respect to temperature was obtained. If the surface of the primer layer is not exposed, the primer layer may be measured from a cross-section formed with a diamond knife manufactured by DiATOME after embedding the sample in resin. Measurement start temperature: 40℃ Measurement end temperature: 350℃ Heating rate: 5°C / sec The temperature at which the curve peaked was obtained in the resulting thermal expansion curve. The above measurement was performed at 10 arbitrary locations on the surface of the primer layer of the wavelength conversion sheet film in the examples and comparative examples. The average of the obtained temperatures was defined as the softening point. The results are shown in Table 1.

[0106] 1-2. Initial adhesion evaluation After preparing the wavelength conversion sheets for the examples and comparative examples, 25 mm × 150 mm test pieces were cut from three arbitrary locations on the wavelength conversion sheets. Using a benchtop material testing machine (STA-1150, manufactured by Takachiho Seiki Co., Ltd.), a peeling test was performed under the following conditions: temperature of 23°C, tensile speed: 300 mm / min, peeling direction: 180°, chuck distance: 15 mm. The peel strength between the wavelength conversion sheet film (primer layer) and the phosphor layer was measured for each test piece. The average value of the obtained peel strengths was taken as the initial peel strength (before the high temperature and high humidity test). The results are shown in Table 1.

[0107] 1-3. Evaluation of adhesion over time The wavelength conversion sheets of the examples and comparative examples were placed in a constant temperature and humidity chamber adjusted to 60°C and 90%RH. After 250 hours and 500 hours, the wavelength conversion sheets were removed from the constant temperature and humidity chamber. The peel strength of each specimen of the extracted wavelength conversion sheet was measured according to the procedure described in 1-2 above. The average of the peel strengths of the specimens obtained from any three locations was used as the peel strength at each elapsed time. The results are shown in Table 1.

[0108] 2. Sample preparation 2-1. Preparation of films for wavelength conversion sheets <Example 1> As the first substrate, an aluminum oxide thin film (AlOx, target thickness: 8 nm) was deposited onto a PET film (thickness: 12 μm) by vacuum deposition to form an inorganic oxide layer.

[0109] Solution A was prepared by mixing tetraethoxysilane with a solution (pH 2.2) of water, isopropyl alcohol, and 0.5N hydrochloric acid while cooling to 10°C. Separately, Solution B was prepared by mixing polyvinyl alcohol with a saponification value of 99% or more and isopropyl alcohol. Solution A and Solution B were mixed to prepare a coating solution for forming an organic coating layer (solid content: 5%). Next, a coating solution for forming an organic coating layer was applied onto the inorganic oxide layer by gravure printing, and the layer was heated at 180°C for 60 seconds to form an organic coating layer with a thickness of 180 nm.

[0110] Next, a primer layer-forming coating solution was prepared according to the following formulation. The NCO / OH ratio of the coating solution was 1.3. • Acrylic polyol resin 150 parts by mass • Modified polyisocyanate having acrylic groups: 80 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0111] Next, a primer layer-forming coating solution was applied to the organic coating layer. The amount of coating solution applied was 0.5 g / m². 2 Then, it was dried at 80°C for 60 seconds to form a primer layer with a thickness of 0.4 μm.

[0112] A urethane-based adhesive (manufactured by Rock Paint Co., Ltd., product names "RU-004, H-1") was applied by gravure printing to the surface of the first substrate opposite to the surface where the inorganic oxide layer and primer layer were formed, and then dried to form an adhesive layer with a thickness of 4 μm.

[0113] Next, a PET film (thickness: 100 μm) was placed as the second substrate on the adhesive layer side of the first substrate, and the first and second substrates were bonded together under conditions of nip pressure: 0.2 MPa and line speed: 50 m / min to produce the wavelength conversion sheet film of Example 1.

[0114] <Example 2> The barrier film of Example 2 was prepared using the same procedure as in Example 1, except that the primer layer-forming coating solution of the formulation described below was used. The NCO / OH ratio of the coating solution was 1.3. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 1 40 parts by mass • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 70 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0115] <Example 3> The barrier film of Example 3 was prepared using the same procedure as in Example 1, except that the primer layer-forming coating solution of the formulation described below was used. The NCO / OH ratio of the coating solution was 4.0. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 1 15 parts by mass • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 60 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0116] <Example 4> The barrier film of Example 4 was prepared using the same procedure as in Example 1, except that the primer layer-forming coating solution of the formulation described below was used. The NCO / OH ratio of the coating solution was 1.3. The amount of coating solution applied was 0.5 g / m². 2 Therefore, acrylic polyol resin 2 is a resin with a larger molecular weight than acrylic polyol resin 1. • Acrylic polyol resin 2 30 parts by mass • Polyester urethane resin 20 parts by mass 40 parts by mass of modified polyisocyanate having acrylic groups • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass <Example 5> The barrier film of Example 5 was prepared using the same procedure as in Example 1, except that the primer layer-forming coating solution of the formulation described below was used. The NCO / OH ratio of the coating solution was 4.0. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 2 10 parts by mass • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 30 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0117] <Comparative Example 1> A barrier film of Comparative Example 1 was prepared using the same procedure as in Example 1, except that a primer layer-forming coating solution with the formulation described below was used. The NCO / OH ratio of the coating solution was 1.3. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 5 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0118] <Comparative Example 2> A barrier film of Comparative Example 2 was prepared using the same procedure as in Example 1, except that a primer layer-forming coating solution with the formulation described below was used. The NCO / OH ratio of the coating solution was 8.0. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 30 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0119] <Comparative Example 3> A barrier film of Comparative Example 3 was prepared using the same procedure as in Example 1, except that a primer layer-forming coating solution with the formulation described below was used. The NCO / OH ratio of the coating solution was 1.3. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 1 15 parts by mass • Polyester urethane resin 20 parts by mass • Modified polyisocyanate having acrylic groups: 20 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0120] <Comparative Example 4> A barrier film of Comparative Example 4 was prepared using the same procedure as in Example 1, except that a primer layer-forming coating solution with the formulation described below was used. The NCO / OH ratio of the coating solution was 1.3. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 2 10 parts by mass • Polyester urethane resin 20 parts by mass 10 parts by mass of modified polyisocyanate having acrylic groups • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0121] <Comparative Example 5> A barrier film of Comparative Example 5 was prepared using the same procedure as in Example 1, except that a primer layer-forming coating solution with the formulation described below was used. The NCO / OH ratio of the coating solution was 4.0. The amount of coating solution applied was 0.5 g / m². 2 That's what I decided. • Acrylic polyol resin 1 15 parts by mass • Polyester urethane resin 20 parts by mass • Modified polyisocyanate without acrylic groups: 40 parts by mass • Silane coupling agent (3-glycidoxypropyltrimethoxysilane) 2.0 parts by mass • Silica powder (average particle size 3 μm) 2.0 parts by mass

[0122] 2-2. Fabrication of Wavelength Conversion Sheets A phosphor (quantum dot with an average particle size of 3-5 nm) consisting of a cadmium selenide (CdSe) core and a zinc sulfide (ZnS) shell was mixed with a sealing resin (ionizing radiation-curable urethane acrylate resin) in a ratio of 1 part by mass of phosphor to 100 parts by mass of sealing resin to prepare a phosphor layer forming mixture (ink).

[0123] The above ink was applied to the primer layer of the wavelength conversion sheet film of the examples and comparative examples to form a phosphor layer with a thickness of 100 μm (after drying). The wavelength conversion sheets of other examples and comparative examples (each the same as the barrier film coated with the above ink) were laminated on the phosphor layer so that the primer layer was in contact with the phosphor layer. Then, the wavelength conversion sheets of Examples 1-5 and Comparative Examples 1-5 were prepared by UV curing the sealing resin of the phosphor layer.

[0124] 3.Results [Table 1]

[0125] In Examples 1 and 4, no peak was observed in the curve within the measured temperature range. Therefore, it was determined that the primer layers in Examples 1 and 4 had a curing point exceeding 350°C. In all of Examples 1-5, the softening point of the cured resin composition of the primer layer was 250°C or higher. The wavelength conversion sheets in Examples 1-5 showed improved adhesion from the initial adhesion after 250 hours. Furthermore, high adhesion was maintained even after 500 hours. In contrast, Comparative Examples 1-5 had a low softening point for the cured resin composition of the primer layer. Although the wavelength conversion sheet of Comparative Examples 1-5 had similar initial adhesion to that of Examples 1-5, its adhesion decreased significantly after 250 hours. [Explanation of symbols]

[0126] 10 (10a, 10b) Wavelength conversion sheet film 20 Base material layer 20-1 First substrate 20-2 Second substrate 22 Adhesive layer 30 Primer layer 40 Barrier layer 42 Inorganic oxide layer 44 Organic coating layer 50 Diffusion layer 60 Phosphor layer 100 Wavelength Conversion Sheet 110 Light source 120 Optical plate 121 Light guide plate 122 Diffuser 130 Reflector 140 Prism Sheets 200 Backlight 201 Edge-lit backlight 202 Direct-lit backlight

Claims

1. The substrate has a primer layer, The primer layer contains a cured product of a resin composition including a polyurethane resin, The polyurethane resin includes a polyurethane resin obtained by the reaction of a polyfunctional isocyanate having a (meth)acrylic group with a hydroxyl group-containing compound. A film for wavelength conversion sheets, wherein the softening point of the cured product is 250°C or higher.

2. The film for wavelength conversion sheets according to claim 1, wherein the resin composition has a molar ratio of isocyanate groups to hydroxyl groups (NCO / OH ratio) of 1.1 or more.

3. The film for wavelength conversion sheets according to claim 1 or claim 2, wherein the resin composition comprises a silane coupling agent.

4. The wavelength conversion sheet film according to any one of claims 1 to 3, further comprising a barrier layer between the substrate and the primer layer.

5. The film for wavelength conversion sheets according to claim 4, wherein the barrier layer comprises an inorganic oxide layer and an organic coating layer, and the organic coating layer is in contact with the primer layer.

6. The wavelength conversion sheet film according to claim 4, wherein the barrier layer is a layer containing a reaction product of a composition comprising a metal oxide and a phosphorus compound.

7. A wavelength conversion sheet comprising a film according to any one of claims 1 to 6, provided on at least one surface side of a phosphor layer containing a phosphor, such that the primer layer and the phosphor layer are in contact.

8. A backlight comprising at least one light source that emits primary light, an optical plate disposed adjacent to the light source for light guidance or diffusion, and a wavelength conversion sheet disposed on the light-emitting side of the optical plate, A backlight in which the wavelength conversion sheet is the wavelength conversion sheet described in claim 7.

9. A display device comprising a backlight and a liquid crystal panel, wherein the backlight is the backlight described in claim 8.

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