Protective film for wavelength conversion sheet, wavelength conversion sheet, and backlight unit

Abstract

The invention provides a protective film for a wavelength conversion sheet, a wavelength conversion sheet, and a backlight unit. The protective film for a wavelength conversion sheet has a structure in which a first barrier layer-side surface of a first film comprising a first substrate and a first barrier layer and one surface of a second film comprising a second substrate are bonded with an adhesive layer interposed therebetween, the first substrate being made of a polyethylene terephthalate film or a polyethylene naphthalate film, and the first barrier layer being made of a polyethylene terephthalate film or a polyethylene naphthalate film. The first substrate is made of a polyethylene terephthalate film or a polyethylene naphthalate film, the second substrate is made of a polyethylene terephthalate film or a polyethylene naphthalate film, the thickness of the first substrate is larger than that of the second substrate, and a coating layer is arranged on one surface of the protective film for the wavelength conversion sheet. The protective film for a wavelength conversion sheet has a coefficient of thermal expansion in the TD direction in a temperature range of 30-90 DEG C of-0.8 * 10-4 / K or more and 0.5 * 10-4 / K or less.

Description

[0001] This application is a divisional application of Chinese application No. 201610806051.2, whose application date is September 6, 2016 and whose invention name is “Protective film for wavelength conversion sheet and its manufacturing method, as well as wavelength conversion sheet and backlight unit”. Technical Field

[0002] The present invention relates to a protective film for a wavelength conversion sheet and a method for manufacturing the same, as well as a wavelength conversion sheet and a backlight unit. Background Art

[0003] A liquid crystal display is a display device that controls the orientation state of liquid crystal by applying voltage, and displays images by transmitting or blocking light in each area. As a light source for the liquid crystal display, a backlight disposed on the back of the liquid crystal display is used. Cold cathode tubes have been used in the backlight so far, but recently, LEDs (light emitting diodes) have gradually been used to replace cold cathode tubes due to their long life and color development advantages.

[0004] Among the LEDs used in backlights, white LED technology is of great importance. As for white LED technology, the following method is generally used: a cerium-doped YAG:Ce (yttrium aluminum garnet:cerium) down-conversion phosphor is excited by a cyan (450nm) LED chip. In this case, the cyan light of the LED is mixed with the yellow light with a wide wavelength range generated by the YAG:Ce phosphor to form white light. However, this white light often has a little cyan, which often gives the impression of "cold" or "cool" white.

[0005] Therefore, in recent years, nano-sized phosphors using quantum dots have been commercialized. The so-called quantum dots are luminescent semiconductor nanoparticles with a diameter range of about 1 to 20 nm. Quantum dots can be used as phosphors for LED wavelength conversion because they display a wide range of excitation spectra and have high quantum efficiency. Furthermore, they have the following advantages: the wavelength of light emission can be completely adjusted in the entire visible region by simply changing the dot size and the type of semiconductor material. Therefore, it can be said that quantum dots actually hide the possibility of producing all colors, especially the warm white color that the lighting industry strongly desires. In addition, by combining the three dots corresponding to the luminous wavelength of red, green, and cyan, white light with different color rendering ratings can be obtained. In this way, for liquid crystal displays using backlights generated by quantum dots, compared with previous liquid crystal displays, the color tone is improved without increasing the thickness, power consumption, cost, and manufacturing process, and a large number of colors that people can recognize can be displayed.

[0006] The backlight using the white LED described above has the following structure: a phosphor with a specified emission spectrum (quantum dots and YAG:Ce, etc.) is diffused in a film, its surface is sealed with a protective film, and a wavelength conversion sheet that sometimes also seals the edges is combined with an LED light source and a light guide plate.

[0007] The protective film is formed by evaporation on the surface of a substrate such as a plastic film to prevent the penetration of deterioration factors in the atmosphere such as moisture and gas (e.g., oxygen). For example, Japanese Patent Publication No. 2011-013567 and International Publication No. 2014 / 113562 propose a wavelength conversion sheet having a structure in which a phosphor is sandwiched between protective films (barrier films) in order to suppress the degradation of the phosphor and a backlight using the same. Summary of the invention

[0008] However, the inventors of the present invention have found that even in a wavelength conversion sheet having a structure in which a phosphor is sandwiched between protective films for the wavelength conversion sheet, if the wavelength conversion sheet is exposed to a high temperature of 85°C or higher for a long time, the luminous efficiency of the phosphor is partially reduced, and an abnormality called black streaks may occur. If black streaks occur in the wavelength conversion sheet, problems such as poor color tone and poor display may occur when the wavelength conversion sheet is mounted on a display.

[0009] The present invention is completed in view of the problems of the above-mentioned prior art, and its purpose is to provide a protective film for a wavelength conversion sheet and a manufacturing method thereof, which can suppress the generation of black stripes even when the wavelength conversion sheet is exposed to high temperature for a long time when the wavelength conversion sheet is formed, as well as a wavelength conversion sheet and a backlight unit using the above-mentioned protective film for the wavelength conversion sheet.

[0010] In order to achieve the above object, the present invention provides a protective film for a wavelength conversion sheet, which has a structure in which a surface of a first film including a first substrate and a first barrier layer on the first barrier layer side is bonded to one surface of a second film including a second substrate via an adhesive layer, and has a thermal expansion coefficient in the TD direction within a temperature range of 30 to 90° C. of 1.0×10 -4 / K or less.

[0011] The inventors of the present invention have repeatedly conducted in-depth studies on the causes of the black stripes, and found that the black stripes extend from the ends of the wavelength conversion sheet, and that linear abnormalities (cracks) occur in the protective film for the wavelength conversion sheet at positions corresponding to the positions where the black stripes occur. In other words, it is believed that by exposing the wavelength conversion sheet to high temperatures for a long time, the barrier layer of the protective film for the wavelength conversion sheet cracks in stripes, and the oxygen that invades from the cracked parts degrades the phosphor, resulting in black stripes. In addition, it was found that the stripe-shaped cracks extend along the MD direction of the protective film for the wavelength conversion sheet. It is believed that the expansion and contraction of the film caused by heat is largely involved in the generation of cracks, such as Figure 7As shown in , by heating the wavelength conversion sheet protective film 20A, the wavelength conversion sheet protective film 20B expands more in the TD direction than in the MD direction, is stretched in the TD direction, and cracks (cracks) 30 are generated in the barrier layer. In addition, cracks in the barrier layer may be generated by heat during the manufacture of the wavelength conversion sheet, such as when laminating the wavelength conversion sheet protective film and the phosphor.

[0012] In contrast, the protective film for a wavelength conversion sheet according to the present invention has a structure in which the first and second films are laminated, and the thermal expansion coefficient in the TD direction in the temperature range of 30 to 90° C. is 1.0×10 -4 / K or less, thereby reducing the tensile stress in the TD direction and suppressing the generation of stripe-shaped cracks in the barrier layer. When a wavelength conversion sheet is formed, the generation of black stripes can be suppressed even when exposed to high temperature (for example, above 85°C) for a long time.

[0013] In the protective film for the wavelength conversion sheet of the present invention, the second film further comprises a second barrier layer, and the surface of the second film on the second barrier layer side may be in contact with the adhesive layer. In this case, a more excellent barrier property can be obtained, and the generation of black streaks can be further suppressed when the wavelength conversion sheet is formed.

[0014] The present invention also provides a method for manufacturing a protective film for a wavelength conversion plate, which is a method for manufacturing a protective film for a wavelength conversion plate having a structure in which a surface on the first barrier layer side of a first film comprising a first substrate and a first barrier layer is bonded to a surface of a second film comprising a second substrate by means of an adhesive layer, and when the second film is bonded to the first film by means of the adhesive layer, the tension applied to the second film is less than 50 N / m.

[0015] In the case of industrially producing the protective film for a wavelength conversion sheet having the above-mentioned structure, when the first film and the second film are bonded together, for example, a laminating device is used to unwind the first film from a roll film, an adhesive is applied to the film being transported, and the second film unrolled from the roll film is bonded together. Tension is applied to the first and second films in the transporting process in the transporting direction (MD direction) by the laminating device, so that the films are stretched in the MD direction and compressed in the direction perpendicular to the MD direction (TD direction). Therefore, in the obtained protective film for a wavelength conversion sheet, there is a compressive internal stress in the MD direction and a tensile internal stress in the TD direction. According to the manufacturing method of the protective film for a wavelength conversion sheet of the present invention, when the second film and the first film are bonded together by an adhesive, by making the tension applied to the second film 50N / m or less, the tensile internal stress generated in the TD direction can be sufficiently reduced, and as a result, the thermal expansion coefficient of the obtained protective film for a wavelength conversion sheet in the TD direction can be reduced. Therefore, in the obtained wavelength conversion sheet protective film, the generation of stripe-shaped cracks in the barrier layer is suppressed, and when the wavelength conversion sheet is formed, the generation of black stripes can be suppressed even when exposed to high temperature for a long time. In addition, in the manufacturing method of the wavelength conversion sheet protective film of the present invention, when the first film and the second film are bonded together, a laminating device may not necessarily be used, and the bonding may be performed by a method that can make the tension applied to the second film 50N / m or less during bonding. For example, bonding may be performed manually without using a laminating device.

[0016] In the method for manufacturing a protective film for a wavelength conversion sheet of the present invention, it is preferred that the second film further comprises a second barrier layer, and in the protective film for a wavelength conversion sheet, the surface of the second film on the second barrier layer side is in contact with the adhesive layer. In this case, the obtained protective film for a wavelength conversion sheet can obtain a more excellent barrier property, and when a wavelength conversion sheet is formed, the generation of black streaks can be further suppressed even when exposed to high temperature for a long time.

[0017] The present invention also provides a wavelength conversion sheet comprising: a phosphor layer containing a phosphor; and the protective film for the wavelength conversion sheet of the present invention. According to the wavelength conversion sheet, the generation of black streaks can be suppressed even when the wavelength conversion sheet is exposed to high temperature for a long time.

[0018] The present invention also provides a backlight unit comprising: an LED light source; the wavelength conversion sheet of the present invention; and a light guide plate for allowing light from the LED light source to enter the wavelength conversion sheet. According to the backlight unit, the generation of black streaks can be suppressed even when exposed to high temperatures for a long time.

[0019] According to the present invention, a wavelength conversion sheet protective film and a method for manufacturing the same, as well as a wavelength conversion sheet and a backlight unit using the wavelength conversion sheet protective film can be provided, which can suppress the generation of black streaks even when the wavelength conversion sheet is exposed to high temperature for a long time when the wavelength conversion sheet is formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic cross-sectional view of a wavelength conversion sheet according to the first embodiment of the present invention.

[0021] Figure 2 This is a schematic cross-sectional view of a protective film for a wavelength conversion sheet according to one embodiment of the present invention.

[0022] Figure 3 This is a schematic cross-sectional view of a protective film for a wavelength conversion sheet according to one embodiment of the present invention.

[0023] Figure 4 It is a schematic cross-sectional view of a wavelength conversion sheet according to a second embodiment of the present invention.

[0024] Figure 5 A cross-sectional schematic diagram of a backlight unit according to an embodiment of the present invention

[0025] Figure 6 It is a schematic diagram which shows an example of the laminating apparatus which can be used when bonding the 1st film and the 2nd film together.

[0026] Figure 7 This is an explanatory diagram for explaining the mechanism of crack generation in the protective film for a wavelength conversion sheet.

[0027] Figure 8 This is a graph showing the relationship between the thermal expansion coefficient in the TD direction of the wavelength conversion sheet protective films of Examples 1 and 2 and the temperature.

[0028] Fig. 9 This is a graph showing the relationship between the thermal expansion coefficient in the MD direction of the wavelength conversion sheet protective films of Examples 1 and 2 and the temperature.

[0029] Fig.10 It is a graph showing the relationship between the thermal expansion coefficient in the TD direction of the wavelength conversion sheet protection films of Example 2 and Comparative Example 1 and the temperature.

[0030] Fig.11 It is a graph showing the relationship between the thermal expansion coefficient in the MD direction of the wavelength conversion sheet protection films of Example 2 and Comparative Example 1 and the temperature.

[0031] [Explanation of Reference Numerals]

[0032] 1 phosphor layer, 3 phosphor, 4 sealing resin, 5 first film, 6 adhesive layer,

[0033] 7 second film, 8 coating layer, 9 first substrate, 10 first barrier layer,

[0034] 11 inorganic thin film layer, 12 gas barrier coating layer, 14 second substrate,

[0035] 15 second barrier layer, 16 inorganic thin film layer, 17 gas barrier coating layer,

[0036] 18LED light source, 19light guide plate, 20, 21, 22protective film for wavelength conversion sheet,

[0037] 52 first film, 54 second film, 56 laminating film, 62 first unwinding roller,

[0038] 64 second unwinding roller, 66 winding roller, 72 adhesive coating device, 74 guide roller,

[0039] 76 rollers, 82 ovens, 100, 200 wavelength conversion sheets, 500 backlight units,

[0040] T1 first unwinding tension, T2 oven tension, T3 second unwinding tension, T4 winding tension. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the accompanying drawings, the same or corresponding parts are marked with the same symbols, and repeated descriptions are omitted. In addition, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0042] The protective film for a wavelength conversion sheet of the present invention is characterized in that it has a structure in which a surface of a first film including a first substrate and a first barrier layer on the first barrier layer side is bonded to one surface of a second film including a second substrate via an adhesive layer, and the thermal expansion coefficient of the protective film for a wavelength conversion sheet in the TD direction within a temperature range of 30 to 90° C. is 1.0×10 -4 / K or less. In addition, the wavelength conversion sheet of the present invention comprises: a phosphor layer containing a phosphor; and the protective film for the wavelength conversion sheet of the present invention. An embodiment of the protective film for the wavelength conversion sheet and the wavelength conversion sheet having such a configuration is described below.

[0043] <Wavelength conversion sheet according to the first embodiment>

[0044] First, a first embodiment of the present invention will be described. Figure 1 It is a schematic cross-sectional view of a wavelength conversion sheet according to the first embodiment of the present invention. Figure 1 The wavelength conversion sheet shown in contains fluorescent materials such as quantum dots, and can be used in a backlight unit for converting LED wavelengths, for example.

[0045] Figure 1The wavelength conversion sheet 100 shown in FIG. 1 is roughly constituted by a phosphor layer (wavelength conversion layer) 1 containing a phosphor and protective films for the wavelength conversion sheet (hereinafter also referred to as "protective films") 20, 20 respectively provided on one surface 1a and the other surface 1b of the phosphor layer 1. Thus, the phosphor layer 1 is enclosed (i.e., sealed) between the protective films 20, 20. Among them, since the phosphor layer 1 must be given a barrier property, it is desirable to have a structure in which the phosphor layer 1 is sandwiched by a pair of protective films 20, 20. The following describes in detail each layer constituting the wavelength conversion sheet 100.

[0046] (Phosphor layer)

[0047] The phosphor layer 1 is a thin film with a thickness of tens to hundreds of μm including a sealing resin 4 and a phosphor 3. As the sealing resin 4, for example, a photosensitive resin or a thermosetting resin can be used. The sealing resin 4 is sealed in a state where one or more phosphors 3 are mixed inside. The sealing resin 4 plays a role of filling the gaps between the phosphor layer 1 and a pair of protective films 20, 20 when they are stacked. In addition, the phosphor layer 1 can be formed by stacking more than two layers of phosphor layers in which only one phosphor 3 is sealed. The two or more phosphors 3 used in these one or more phosphor layers are selected to have the same excitation wavelength. The excitation wavelength is selected based on the wavelength of the light irradiated by the LED light source. The fluorescent colors of the two or more phosphors 3 are different from each other. When a cyan LED (peak wavelength of 450nm) is used as the LED light source and two phosphors 3 are used, each fluorescent color is preferably red and green. The wavelength of each fluorescence and the wavelength of the light irradiated by the LED light source are selected based on the spectral characteristics of the color filter. The peak wavelength of fluorescence is, for example, 610 nm for red and 550 nm for green.

[0048] Next, the particle structure of the phosphor 3 is described. As the phosphor 3, it is preferred to use quantum dots that have high color purity and can be expected to have improved brightness. As quantum dots, for example, quantum dots in which a core as a light-emitting portion is coated with a shell as a protective film can be listed. As the above-mentioned core, for example, cadmium selenide (CdSe) and the like can be listed, and as the above-mentioned shell, for example, zinc sulfide (ZnS) and the like can be listed. By coating the surface defects of CdSe particles with ZnS having a large band gap, the quantum efficiency is improved. In addition, the phosphor 3 may be a core doubly coated with a first shell and a second shell. In this case, CdSe can be used for the core, zinc selenide (ZnSe) can be used for the first shell, and ZnS can be used for the second shell. In addition, as phosphors 3 other than quantum dots, YAG:Ce and the like can also be used.

[0049] The average particle size of the phosphor 3 is preferably 1 to 20 nm. The thickness of the phosphor layer 1 is preferably 1 to 500 μm.

[0050] The content of the phosphor 3 in the phosphor layer 1 is preferably 1 to 20% by mass, more preferably 3 to 10% by mass, based on the total amount of the phosphor layer 1 .

[0051] As the sealing resin 4, for example, a thermoplastic resin, a thermosetting resin, an ultraviolet curing resin, etc. can be used. These resins can be used alone or in combination of two or more.

[0052] As the thermoplastic resin, for example, cellulose derivatives such as acetyl cellulose, nitro cellulose, acetyl butyl cellulose, ethyl cellulose and methyl cellulose; vinyl resins such as vinyl acetate and its copolymers, vinyl chloride and its copolymers, and vinylidene chloride and its copolymers; acetal resins such as polyvinyl formal and polyvinyl butyral; acrylic resins such as acrylic resin and its copolymers, methacrylic resin and its copolymers; polystyrene resins; polyamide resins; linear polyester resins; fluororesins; and polycarbonate resins.

[0053] Examples of the thermosetting resin include phenol resins, urea-melamine resins, polyester resins, and silicone resins.

[0054] As the ultraviolet curable resin, there can be mentioned photopolymerizable prepolymers such as epoxy acrylate, urethane acrylate and polyester acrylate. In addition, these photopolymerizable prepolymers can be used as the main component and monofunctional or polyfunctional monomers can be used as diluents.

[0055] (Protective film for wavelength conversion sheet)

[0056] The protective film 20 for a wavelength conversion sheet includes: a first film 5 including a first substrate 9 and a first barrier layer 10, an adhesive layer 6, and a second film 7 including a second substrate 14. The first film 5 and the second film 7 are laminated so that the surface of the first film 5 on which the first barrier layer 10 is formed faces the second substrate 14 via the adhesive layer 6. Furthermore, a coating layer 8 is provided on one surface 14a of the second substrate 14 as required. In other words, when the side away from the phosphor layer 1 is the second substrate 14 and the side close to the phosphor layer 1 and on which the barrier layer is laminated is the first substrate 9, a film including the second substrate 14 and the coating layer 8 provided on one surface 14a of the second substrate 14 and a film including the first substrate 9 and the first barrier layer 10 provided on one surface 9a of the first substrate (first film 5) are laminated via the adhesive layer 6 so that the second substrate 14 and the surfaces of the first substrate 9 on which the first barrier layer 10 is formed face each other. With such a configuration, it is possible to prevent the first barrier layer 10 from being damaged during production, and to suppress a decrease in barrier properties due to defects in the barrier layer.

[0057] like Figure 1 As shown in FIG. 1 , the first film 5 includes a first substrate 9 and a first barrier layer 10 provided on one surface 9 a of the first substrate 9 .

[0058] The first and second substrates 9 and 14 are not particularly limited, but preferably have a total light transmittance of 85% or more. For example, polyethylene terephthalate films and polyethylene naphthalate films can be used as substrates having high transparency and excellent heat resistance.

[0059] In order to obtain excellent barrier properties, the thickness of the second substrate 14 is preferably 12 μm or more. The thickness of the first substrate 9 is not particularly limited, but is preferably 80 μm or less in order to reduce the total thickness of the wavelength conversion sheet 100 .

[0060] The thickness of the second substrate 14 is preferably smaller than the thickness of the first substrate 9. By increasing the thickness of the first substrate 9, the thermal shrinkage of the first substrate 9 caused by the thermal history when the first barrier layer 10 is formed, which is the cause of the uneven thickness of the first film 5, can be suppressed, and by relatively reducing the thickness of the second substrate 14, the overall transmittance of the protective film 20 for the wavelength conversion sheet can be prevented from decreasing, and as a result, the uneven brightness and color can be reduced.

[0061] Specifically, the thickness D2 of the second substrate 14 is preferably in the range of 4 to 30 μm, and the thickness D1 of the first substrate 9 is preferably in the range of 16 to 80 μm. In addition, the difference D1-D2 between the thickness of the second substrate 14 and the thickness of the first substrate 9 is preferably in the range of 5 to 76 μm. By setting D2 to 4 to 30 μm, shape defects during lamination can be suppressed. By setting D1 to 16 to 80 μm, curling of the protective film 20 for the wavelength conversion sheet can be suppressed. Furthermore, in order to achieve a thin protective film 20 for the wavelength conversion sheet of less than 50 μm, the thickness D2 of the second substrate 14 is more preferably in the range of 4 to 20 μm, and the thickness D1 of the first substrate 9 is more preferably in the range of 16 to 45 μm. In addition, the difference D1-D2 between the thickness of the second substrate 14 and the thickness of the first substrate 9 is more preferably in the range of 5 to 45 μm.

[0062] In addition, as a wavelength conversion plate 100, the upper and lower protective films 20, 20 are arranged in a manner such that the first film 5 having the first barrier layer 10 is located closer to the phosphor layer 1 than the second film 7, so that the distance between the first barrier layer 10 and the phosphor layer 1 can be as close as possible, thereby improving the sealing effect of the phosphor layer 1 generated by the protective film 20.

[0063] The first barrier layer 10 is not particularly limited, but preferably includes an inorganic thin film layer 11 and a gas barrier coating layer 12. Examples of the configuration of the barrier layer include the following: Figure 1 As in the first barrier layer 10 shown in FIG. 1 , an inorganic thin film layer 11 is stacked on one surface (single surface) 9 a of the first substrate 9 , and a gas barrier coating layer 12 is stacked on the inorganic thin film layer 11 .

[0064] The inorganic thin film layer (inorganic oxide thin film layer) 11 is not particularly limited, and for example, aluminum oxide, silicon oxide, magnesium oxide, or a mixture thereof can be used. Among these, aluminum oxide or silicon oxide is preferably used from the viewpoint of barrier properties and productivity.

[0065] The thickness (film thickness) of the inorganic thin film layer 11 is preferably in the range of 5 to 500 nm, and more preferably in the range of 10 to 100 nm. Among them, if the film thickness is 5 nm or more, there is a tendency to easily form a uniform film and to be able to more fully exert the function as a gas barrier material. On the other hand, if the film thickness is 500 nm or less, sufficient flexibility can be maintained through the film, and there is a tendency to more reliably prevent cracks from occurring in the film due to external factors such as bending and stretching after film formation.

[0066] The gas barrier coating layer 12 is provided to prevent various secondary damages in the subsequent process and to impart high barrier properties. From the viewpoint of obtaining excellent barrier properties, the gas barrier coating layer 12 preferably contains at least one selected from a hydroxyl-containing polymer compound, a metal alkoxide, a metal alkoxide hydrolyzate, and a metal alkoxide polymer as a component.

[0067] Specific examples of the hydroxyl group-containing polymer compound include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and starch. In particular, when polyvinyl alcohol is used, the barrier property is most excellent.

[0068] In metal alkoxides, the general formula is: M(OR) n (M represents a metal atom such as Si, Ti, Al, Zr, etc., R represents an alkyl group such as -CH3, -C2H5, and n represents an integer corresponding to the valence of M). Specifically, tetraethoxysilane [Si(OC2H5)4], triisopropoxyaluminum [A1(O-iso-C3H7)3], etc. can be listed. Tetraethoxysilane and triisopropoxyaluminum are relatively stable in aqueous solvents after hydrolysis, so they are preferred. In addition, as hydrolyzates and polymers of metal alkoxides, for example, as hydrolyzates and polymers of tetraethoxysilane, silicic acid (Si(OH)4) and the like can be listed; as hydrolyzates and polymers of triisopropoxyaluminum, aluminum hydroxide (Al(OH)3) and the like can be listed.

[0069] The thickness (film thickness) of the gas barrier coating layer 12 is preferably in the range of 50 to 2000 nm, more preferably in the range of 100 to 500 nm. If the film thickness is 50 nm or more, there is a tendency to obtain more sufficient gas barrier properties, and if it is 2000 nm or less, there is a tendency to be able to maintain sufficient flexibility through the film.

[0070] Figure 2 1 is a diagram showing a modified example of the protective film for the wavelength conversion sheet in this embodiment. Figure 2 Like the protective film 21 for a wavelength conversion sheet of the present invention, the barrier layer may be provided on the other surface 14b of the second substrate 14 provided with the coating layer 8 on one surface 14a. That is, the second film 7 may include: the second substrate 14; and the second barrier layer 15 including the inorganic thin film layer 16 and the gas barrier coating layer 17 formed on the surface 14b of the second substrate 14 opposite to the coating layer 8. In this way, the first and second barrier layers 10 and 15 are sandwiched between the first substrate 9 and the second substrate 14, and by arranging the second barrier layer 15 at a position closer to the phosphor layer 1, even if, for example, a tiny pinhole or other defect is generated in the first barrier layer 10 or the second barrier layer 15, the barrier performance can be more effectively exerted. The inorganic thin film layer 16 and the gas barrier coating layer 17 may have the same structure as the inorganic thin film layer 11 and the gas barrier coating layer 12 described above.

[0071] Figure 3 FIG. 2 is a diagram showing another modified example of the protective film for the wavelength conversion sheet in the present embodiment. Figure 3 Like the protective film 22 for the wavelength conversion plate, the first barrier layer 10 may have a structure in which a plurality of inorganic thin film layers 11 and gas barrier coating layers 12 are stacked. In particular, by alternately stacking the inorganic thin film layers 11 and the gas barrier coating layers 12, the presence of the gas barrier coating layers 12 and other inorganic thin film layers 11 can prevent defects such as tiny pinholes in the inorganic thin film layer 11, thereby improving the barrier performance.

[0072] The first barrier layer 10 and the second barrier layer 15 may contain an anchor coating layer as required. In order to improve the adhesion between the first and second substrates 9, 14 and the inorganic thin film layers 11, 16, the anchor coating layer is provided between them. In addition, the anchor coating layer may also have a barrier property to prevent the penetration of moisture and oxygen.

[0073] The anchor coating layer can be formed using, for example, a resin selected from polyester resins, isocyanate resins, polyurethane resins, acrylic resins, polyvinyl alcohol resins, ethylene-vinyl alcohol resins, vinyl-modified resins, epoxy resins, resins containing oxazoline groups, modified styrene resins, modified silicone resins, or alkyl titanates. The anchor coating layer can be formed using any of the above resins alone or using a composite resin obtained by combining two or more of the above resins.

[0074] The thickness of the anchor coating is preferably in the range of 5 to 500 nm, more preferably in the range of 10 to 100 nm. If the thickness is 5 nm or more, the adhesion between the first and second substrates 9, 14 and the inorganic thin film layers 11, 16 and the barrier properties to moisture and oxygen tend to be improved; if the thickness is 500 nm or less, a uniform layer in which the internal stress caused by the thick film is sufficiently suppressed tends to be formed.

[0075] like Figures 1 to 3 As shown in FIG. 1 , in order to laminate the first film 5 and the second film 7, the adhesive layer 6 is provided between the first film 5 and the second film 7. The adhesive layer 6 is not particularly limited, and an adhesive or a binder such as an acrylic material, a polyurethane material, or a polyester material can be used. More specifically, any of an acrylic adhesive, an acrylic adhesive, a polyurethane adhesive, and an ester adhesive can be used.

[0076] The thickness of the adhesive layer 6 is not particularly limited, but is preferably 10 μm or less to reduce the total thickness of the wavelength conversion sheet protective film and the wavelength conversion sheet. On the other hand, the thickness of the adhesive layer 6 is preferably 3 μm or more to obtain better adhesion.

[0077] In order to exert one or more optical functions and antistatic functions, the coating 8 is provided on the surfaces of the two wavelength conversion sheet protective films 20, 20, that is, on both surfaces of the wavelength conversion sheet 100. Among them, the optical function is not particularly limited, and can include anti-interference fringe (moire fringe) function, anti-reflection function, diffusion function, etc. Among these, the coating 8 preferably has at least an anti-interference fringe function as an optical function. In this embodiment, the case where the coating 8 has at least an anti-interference fringe function is described.

[0078] The coating layer 8 is composed of a binder resin and microparticles. In addition, microparticles can be embedded in the binder resin so that a part of the microparticles is exposed from the surface of the coating layer 8, thereby generating fine concavities and convexities on the surface of the coating layer 8. By providing the coating layer 8 on the surfaces of the wavelength conversion sheet protective films 20, 20, that is, both surfaces of the wavelength conversion sheet 100, the generation of interference fringes such as Newton rings can be more fully prevented, and as a result, a high-efficiency, high-definition, and long-life display can be obtained. Furthermore, the coating layer 8 can be provided only on the surface of one side of the wavelength conversion sheet protective film 20, that is, one side of the wavelength conversion sheet 100, and the above-mentioned effect can be obtained even in this case.

[0079] As the binder resin, there is no particular limitation, and resins with excellent optical transparency can be used. More specifically, for example, thermoplastic resins such as polyester resins, acrylic resins, acrylic urethane resins, polyester acrylate resins, polyurethane acrylate resins, polyurethane resins, epoxy resins, polycarbonate resins, polyamide resins, polyimide resins, melamine resins, phenolic resins, thermoplastic resins, ionizing radiation curing resins, etc. can be used. Among these, acrylic resins with excellent light resistance and optical properties are preferably used. These are not only one kind, but also a plurality of combinations can be used.

[0080] The microparticles are not particularly limited, and for example, inorganic microparticles such as silicon dioxide, clay, talc, calcium carbonate, calcium sulfate, barium sulfate, titanium oxide, aluminum oxide, and organic microparticles such as styrene resin, polyurethane resin, silicone resin, and acrylic resin can be used. These microparticles can be used not only as one kind but also as a combination of a plurality of kinds.

[0081] The average particle size of the fine particles is preferably 0.1 to 30 μm, more preferably 0.5 to 10 μm. If the average particle size of the fine particles is 0.1 μm or more, there is a tendency to obtain an excellent interference fringe prevention function, and if it is 30 μm or less, there is a tendency to further improve transparency.

[0082] The content of the microparticles in the coating 8 is preferably 0.5 to 30% by mass, more preferably 3 to 10% by mass, based on the total amount of the coating 8. If the content of the microparticles is 0.5% by mass or more, the light diffusion function and the effect of preventing the generation of interference fringes tend to be further improved, while if it is 30% by mass or less, the brightness will not be reduced.

[0083] The wavelength conversion sheet protective film 20 having the above-mentioned structure must have a thermal expansion coefficient in the TD direction within a temperature range of 30 to 90° C. of 1.0×10 -4 That is, the maximum value of the thermal expansion coefficient in the TD direction within the temperature range of 30 to 90°C must be 1.0×10-4 / K or less. The thermal expansion coefficient in the TD direction can be measured by TMA (thermomechanical analysis). The measurement conditions can be, for example, load: 50 mN, heating rate: 5°C / min, set temperature: 30-150°C. The thermal expansion coefficient is 1.0×10 -4 / K or less, the generation of stripe-shaped cracks in the barrier layers (the first barrier layer 10 and the second barrier layer 15) can be suppressed, and when the wavelength conversion sheet 100 is formed, the generation of black stripes can be suppressed even when exposed to high temperatures for a long time. From the viewpoint of more fully achieving the above-mentioned effects, the above-mentioned thermal expansion coefficient is preferably 0.8×10 -4 / K or less, more preferably 0.5×10 -4 / K or less, more preferably 0.3×10 -4 / K or less. In addition, there is no particular lower limit on the thermal expansion coefficient, but the thermal expansion coefficient is usually -0.8×10 -4 / K or above.

[0084] In order to more fully suppress the generation of black streaks when exposed to high temperature for a long time, the thermal expansion coefficient of the wavelength conversion sheet protective film 20 in the TD direction in the temperature range of 30 to 110° C. is preferably 1.0×10 -4 / K or less, more preferably 0.8×10 -4 / K or less, more preferably 0.5×10 -4 / K or less, particularly preferably 0.3×10 -4 / K or less.

[0085] The thermal expansion coefficient of the wavelength conversion sheet protective film 20 in the MD direction within the temperature range of 30 to 90° C. is not particularly limited, but is generally -1.5×10 -4 / K or above and 1.5×10 -4 / K or less.

[0086] By using the wavelength conversion sheet protection film 20 having the above-described structure as a protection film for protecting the phosphor of the wavelength conversion sheet 100 , the performance of the wavelength conversion sheet 100 using phosphors such as quantum dots can be maximized.

[0087] Next, a method for manufacturing the wavelength conversion sheet 100 of the present embodiment will be described. In the method for manufacturing the wavelength conversion sheet 100 of the present embodiment, for example, the phosphor layer 1 can be laminated between a pair of wavelength conversion sheet protective films 20 and 20 according to the following procedure.

[0088] (Process for Manufacturing the Protective Film 20 for Wavelength Converting Sheet)

[0089] In the manufacturing process of the wavelength conversion sheet protective film 20, 20, first, the coating layer 8 is formed on one surface 14a of the second substrate 14. Specifically, the coating layer 8 is formed by applying a coating liquid mixed with a binder resin, fine particles, and a solvent as needed on one surface 14a of the second substrate 14 and drying the mixture.

[0090] In addition, an inorganic thin film layer 11 is laminated on one surface 9a of the first substrate 9 by, for example, a vapor deposition method. Next, a coating agent containing an aqueous solution or a water / alcohol mixed solution containing at least one component selected from a hydroxyl-containing polymer compound, a metal alkoxide, a metal alkoxide hydrolyzate, and a metal alkoxide polymer as a main agent is applied to the surface of the inorganic thin film layer 11 and dried to form a gas barrier coating layer 12. Thus, a first film 5 is obtained in which a first barrier layer 10 composed of an inorganic thin film layer 11 and a gas barrier coating layer 12 is provided on one surface of the first substrate 9.

[0091] Next, the film on which the coating layer 8 is formed and the first film 5 on which the first barrier layer 10 is formed are laminated using the adhesive layer 6. Specifically, the second substrate 14 (second film 7) on which the coating layer 8 is provided is made to face the barrier layer-formed surface of the first film 5, and laminated using the adhesive layer 6. As the adhesive layer 6, any one of acrylic adhesive, acrylic adhesive, polyurethane adhesive, and ester adhesive can be used. Thus, the protective film 20 for the wavelength conversion sheet formed by laminating two films is obtained.

[0092] Furthermore, in the present embodiment, an example of forming the coating layer 8 is first described, but the timing of forming the coating layer 8 is not particularly limited, and for example, the coating layer 8 may be formed on the surface 14a of the second substrate 14 after laminating two films before forming the coating layer 8. Of course, when the coating layer 8 is not formed, this step is not required.

[0093] In the present embodiment, the first film 5 and the second film 7 are bonded together under the condition that the tension applied to the second film is 50 N / m or less. As a result, the protective film 20 for the wavelength conversion sheet can be obtained in which the internal stress of the stretch generated in the TD direction is sufficiently reduced, the thermal expansion coefficient in the TD direction is reduced, and the generation of stripe-shaped cracks in the barrier layer can be suppressed. From the viewpoint of more fully obtaining the above-mentioned effects, the tension applied to the second film is preferably 30 N / m or less, and more preferably 15 N / m or less. The lower limit of the tension applied to the second film is not particularly limited, and for example, it can be 0 N / m or 10 N / m.

[0094] The method for laminating the first film 5 and the second film 7 is not particularly limited as long as it satisfies the above conditions. The lamination can be performed manually. In the case of industrial production of the protective film 20 for a wavelength conversion sheet, for example, Figure 6The lamination was carried out using the lamination apparatus shown in FIG.

[0095] Figure 6 Schematic diagram showing an example of a laminating device that can be used when bonding the first film 5 and the second film 7. Figure 6 In the case of the laminating device shown in , lamination (lamination process) is performed according to the following procedure. First, an adhesive (adhesive) is applied to the barrier layer forming surface of the first film 52 unwound from the first unwinding roller 62 by the adhesive coating device 72. The first film 52 coated with the adhesive is introduced into the oven 82 through the guide roller 74 to dry the adhesive. The temperature in the oven 82 can usually be changed in stages using three units, and each can be set to 25 to 200° C. After drying, the first film 52 is introduced into the guide roller 74 and transported to the nip roller 76. On the other hand, the second film 54 unwound from the second unwinding roller 64 is transported to the nip roller 76 and laminated to the adhesive-coated surface of the first film 52 between the nip rollers 76, 76. The pressure when the first film 52 and the second film 54 are laminated between the nip rollers 76, 76 can usually be set to 0.05 to 0.2 MPa. Then, the bonded film 56 in which the first film 52 and the second film 54 are bonded together via an adhesive is wound up on the winding roll 66 .

[0096] In the above-mentioned bonding process, the tensions T1, T2, T3 and T4 applied to the transported film are adjusted to the desired range. In the present embodiment, among these tensions, the second unwinding tension T3 applied to the second film 54 when the second film 54 is unwound and bonded to the first film 52 is set to 50 N / m or less. The second unwinding tension T3 must be 50 N / m or less, preferably 10 to 50 N / m, more preferably 10 to 30 N / m, and further preferably 10 to 15 N / m. By making the second unwinding tension T3 within the above-mentioned range, the protective film 20 for the wavelength conversion sheet in which the tensile internal stress generated in the TD direction is sufficiently reduced, the thermal expansion coefficient in the TD direction is reduced, and the generation of stripe-shaped cracks in the barrier layer can be suppressed can be obtained.

[0097] The first unwinding tension T1 applied to the first film 52 when unwinding the first film 52 is preferably 10 to 100 N / m, more preferably 10 to 30 N / m, and even more preferably 10 to 15 N / m.

[0098] The oven tension T2 applied to the first film 52 when passing through the oven 82 is preferably 10 to 100 N / m, more preferably 10 to 60 N / m, and even more preferably 10 to 40 N / m.

[0099] The winding tension T4 applied to the sticking film 56 when winding up the winding roll 66 is preferably 10 to 150 N / m, more preferably 10 to 100 N / m, and even more preferably 10 to 60 N / m.

[0100] The conveyance speed of each film can be generally set to 5 to 100 m / min.

[0101] The aging temperature is preferably appropriately selected according to the material, and is preferably, for example, 40 to 60° C. and 1 to 3 days.

[0102] (Process for Manufacturing Phosphor Layer 1)

[0103] In the manufacturing process of the phosphor layer 1, first, the phosphor 3 and the sealing resin 4 are mixed with a solvent used as needed to prepare a mixed solution. Next, the prepared mixed solution is applied to the surface of the side of the protective film 20 for the wavelength conversion sheet where the coating 8 is not provided. Next, another protective film 20 for the wavelength conversion sheet produced separately is laminated. At this time, the surfaces 1a and 1b of the phosphor layer 1 and the surfaces of the sides of the two protective films 20 for the wavelength conversion sheet where the coating 8 is not provided are respectively arranged opposite to each other. Next, in the case where the sealing resin 4 is a photosensitive resin, the photosensitive resin is cured by irradiation with ultraviolet rays (UV curing), so that the wavelength conversion sheet 100 of this embodiment can be obtained. In addition, as for the photosensitive resin, it can be further thermally cured after UV curing. In addition, as the sealing resin 4, in addition to the photosensitive resin, a thermosetting resin, a chemically curing resin, etc. can also be used.

[0104] UV curing can be performed at 100 to 1000 mJ / cm 2 In addition, thermal curing can be performed at, for example, 60 to 120° C. for 0.1 to 3 minutes.

[0105] In this embodiment, an example is described in which the phosphor layer 1 is formed on the surface of one wavelength conversion plate protective film 20 where the coating layer 8 is not provided, and then another wavelength conversion plate protective film 20 is stacked on the surface of the phosphor layer 1, but the present invention is not limited to this.

[0106] <Wavelength conversion sheet according to the second embodiment>

[0107] Next, a second embodiment of the present invention will be described. Figure 4 2 is a cross-sectional schematic diagram of a wavelength conversion sheet according to a second embodiment of the present invention. The wavelength conversion sheet 200 according to the second embodiment differs from the wavelength conversion sheet 100 according to the first embodiment only in the configuration of the wavelength conversion sheet protective film 23. Therefore, for the wavelength conversion sheet 200 according to the second embodiment, the same reference numerals are used for the same components as those in the first embodiment, and description thereof is omitted.

[0108] like Figure 4As shown in FIG. 1 , the wavelength conversion sheet 200 of the present embodiment is roughly configured by including a phosphor layer (wavelength conversion layer) 1 containing a phosphor and wavelength conversion sheet protective films 23, 23 respectively provided on one surface 1a and the other surface 1b of the phosphor layer 1. Thus, the phosphor layer 1 is enclosed (sealed) between the wavelength conversion sheet protective films 23, 23.

[0109] (Protective film for wavelength conversion sheet)

[0110] The protective film 23 for a wavelength conversion sheet of the present embodiment includes: a first film 5 including a first substrate 9 and a first barrier layer 10, an adhesive layer 6, a second substrate 14 (second film 7), and a coating layer 8. In addition, the first substrate 9 having the coating layer 8 provided on one surface 9b has the first barrier layer 10 provided on the other surface 9a of the first substrate 9, and the first barrier layer 10 is stacked facing the second substrate 14 via the adhesive layer 6. In other words, when the side away from the phosphor layer 1 is the first substrate 9 and the side close to the phosphor layer 1 is the second substrate 14, the first substrate 9, the film (first film 5) including the coating layer 8 provided on one surface 9b of the first substrate 9 and the first barrier layer 10 provided on the other surface 9a of the first substrate, and the second substrate 14 are stacked via the adhesive layer 6 so that the second substrate 14 faces the first barrier layer 10. According to the structure of the protective film 23 for the wavelength conversion plate, since the second substrate 14 is arranged between the first barrier layer 10 and the protected phosphor layer 1, even if there are bumps and foreign matter on the phosphor layer 1, the impact can be mitigated by the second substrate 14, and damage to the first barrier layer 10 can be suppressed.

[0111] Furthermore, when the wavelength conversion sheet 200 of this embodiment is constructed, Figure 4 As shown in , the respective wavelength conversion sheet protective films 23, 23 are stacked so that the second substrate 14 faces the phosphor layer 1 side. More specifically, in the wavelength conversion sheet 200, the wavelength conversion sheet protective films 23, 23 are stacked so that the second substrate 14 sandwiches the phosphor layer 1. In the present embodiment, the coating layer 8 is also provided on the surface of each of the wavelength conversion sheet protective films 23, 23, and is provided on both surfaces of the wavelength conversion sheet 200.

[0112] In the wavelength conversion plate 200, by making the film thickness of the second substrate 14 thinner than the film thickness of the first substrate 9, in addition to the effect described in the first embodiment, the distance between the first barrier layer 10 and the phosphor layer 1 can be made closer, and the effect of suppressing the infiltration of oxygen and moisture into the phosphor layer 1 can be obtained.

[0113] The thickness of the first substrate 9 is preferably greater than that of the second substrate 14. By increasing the thickness of the first substrate 9, the thermal shrinkage of the first substrate 9 caused by the thermal history when the first barrier layer 10 is formed, which is the cause of the uneven thickness of the first film 5, is suppressed, and no inorganic thin film layer or gas barrier coating layer is formed on the second substrate 14, so that no thermal history is applied, and thermal shrinkage can be suppressed, and by making the thickness relatively small, the transmittance of the entire wavelength conversion sheet protective film 23 is prevented from being reduced, and as a result, brightness unevenness and color unevenness can be reduced.

[0114] As can be seen from the above, the thickness D2 of the second substrate 14 is preferably in the range of 4 to 20 μm, and the thickness D1 of the first substrate 9 is preferably in the range of 16 to 80 μm. By setting the thickness D2 of the second substrate 14 to 4 to 20 μm, the second substrate 14 can be used to mitigate the impact, thereby preventing the first barrier layer 10 from being damaged and preventing shape defects during lamination. By setting D1 to 16 to 80 μm, the curling of the wavelength conversion sheet protective film 23 can be suppressed.

[0115] In addition, the wavelength conversion sheet protective film 23 also satisfies the conditions of the thermal expansion coefficient in the TD direction in the temperature range of 30 to 90° C. described in the first embodiment, similarly to the wavelength conversion sheet protective film 20. Thus, it is possible to suppress the generation of stripe-shaped cracks in the barrier layer, and when the wavelength conversion sheet 200 is formed, the generation of black stripes can be suppressed even when it is exposed to high temperature for a long time.

[0116] In addition, Figure 3 Similarly, as for the first barrier layer 10, a plurality of inorganic thin film layers 11 and gas barrier coating layers 12 may be stacked. In particular, by alternately stacking the inorganic thin film layers 11 and the gas barrier coating layers 12, defects such as tiny pinholes of the inorganic thin film layer 11 can be prevented by the presence of the gas barrier coating layer 12 and the other inorganic thin film layers 11, and the barrier performance can be improved.

[0117] According to the wavelength conversion sheet 200 of the second embodiment described above, it is possible to obtain the same effects as those of the wavelength conversion sheet 100 of the first embodiment described above.

[0118] <Backlight Unit>

[0119] Figure 5 1 shows an embodiment of a backlight unit. The backlight unit 500 of this embodiment has an LED (light emitting diode) light source 18, a light guide plate 19, and a wavelength conversion sheet 100. In the backlight unit 500, a wavelength conversion sheet 200 can be used instead of the wavelength conversion sheet 100. Furthermore, the backlight unit 500 can have a reflector, a diffuser, a prism sheet, etc., but they are omitted in the figure.

[0120] The LED light source 18 is arranged on the side of the light guide plate 19, and the wavelength conversion sheet 100 is arranged on the light guide plate 19 (the direction of light travel). A plurality of LED elements with a cyan light emission color are arranged inside the LED light source 18. The LED element can be a purple LED, or can also be an LED with a lower wavelength. The LED light source irradiates light to the side of the light guide plate. In the case of a backlight unit using the wavelength conversion sheet 100 of the present embodiment, the irradiated light is incident on a layer (phosphor layer) 1 formed by mixing a resin such as acrylic or epoxy with a phosphor, for example, via the light guide plate.

[0121] The light guide plate 19 efficiently conducts the light irradiated from the LED light source 18, and a known material can be used. As the light guide plate 19, for example, an acrylic film, a polycarbonate film, a cycloolefin film, etc. are used. The light guide plate 19 can be formed by, for example, screen printing, injection molding, extrusion molding, or inkjet molding. The thickness of the light guide plate 19 is, for example, 100 to 1000 μm.

[0122] The preferred embodiments of the present invention have been described in detail above, but the technical scope of the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention. For example, the configurations of the wavelength conversion sheets 100 and 200, the wavelength conversion sheet protective films 20, 21, 22, and 23, and the backlight unit 500 of the above-mentioned first and second embodiments are examples and are not limited thereto.

[0123] In addition, in the wavelength conversion sheet of the present invention, as in the first and second embodiments described above, the phosphor layer 1 may be sandwiched between the same wavelength conversion sheet protective films 20 to 23 or between wavelength conversion sheet protective films having different structures.

[0124] In addition, the wavelength conversion sheet of the present invention may be configured such that either one of the wavelength conversion sheet protective films covering the phosphor layer 1 has the coating layer 8 , or both of the wavelength conversion sheet protective films have the coating layer 8 .

[0125] In addition, in the wavelength conversion plate of the present invention, the surface of the wavelength conversion plate protective film that contacts the phosphor layer 1 may be subjected to a modification treatment or an easy-adhesion layer made of a polyurethane resin or the like may be provided in order to improve the adhesion between the wavelength conversion plate protective film and the phosphor layer 1 .

[0126] in addition, Figure 1 and Figure 4In the wavelength conversion sheets 100 and 200 shown in the figures, the first barrier layer 10 includes one inorganic thin film layer 11 and one gas barrier coating layer 12, but at least one of the inorganic thin film layer 11 and the gas barrier coating layer 12 in the first barrier layer 10 may include two or more layers. In this case, the inorganic thin film layer 11 and the gas barrier coating layer 12 are preferably stacked alternately.

[0127] Furthermore, in Figure 1 and Figure 4 In the wavelength conversion sheets 100 and 200 shown in the figures, both end surfaces of the phosphor layer 1 (the left and right end surfaces in the figures not covered by the wavelength conversion sheet protective films 20 and 23) can be sealed with a sealing resin, and the entire phosphor layer 1 can also be covered with a sealing resin.

[0128] [Example]

[0129] The present invention will be described in more detail below based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0130] [Example 1]

[0131] (Production of protective film for wavelength conversion sheet)

[0132] On a single surface of a 25 μm thick polyethylene terephthalate film as a first substrate, silicon oxide was provided to a thickness of 0.05 μm as an inorganic thin film layer by vacuum evaporation, and a coating solution containing tetraethoxysilane and polyvinyl alcohol was further applied on the inorganic thin film layer by wet coating, and heated and dried at 150° C., thereby forming a gas barrier coating layer with a thickness of 0.45 μm. Thus, a first film was obtained in which a first barrier layer composed of an inorganic thin film layer and a gas barrier coating layer was provided on one surface of the first substrate.

[0133] Next, silicon oxide was provided as an inorganic thin film layer with a thickness of 0.05 μm on a single surface of a 15 μm thick polyethylene terephthalate film as the second substrate by vacuum evaporation, and a coating solution containing tetraethoxysilane and polyvinyl alcohol was further applied on the inorganic thin film layer by wet coating, and heated and dried at 150° C., thereby forming a gas barrier coating layer with a thickness of 0.45 μm. Thus, a second film was obtained in which a second barrier layer composed of an inorganic thin film layer and a gas barrier coating layer was provided on one surface of the second substrate.

[0134] Next, the first film and the second film are laminated using an adhesive in the following manner so that the respective barrier layers are facing each other. First, prepare the first film and the second film cut to A4 size. Apply an adhesive to the first barrier layer of the first film, heat it at 80°C for 1 minute, manually place the second film on the adhesive, and laminate it using a laminator at a laminating temperature of 60°C and a line speed of 1m / min (manual lamination). Then, age it in an oven at 50°C for 2 days to obtain a laminated film. In addition, as an adhesive, a mixture of 20 parts by mass of a main agent (trade name: X-313-405S, manufactured by SAIDEN Chemical Co., Ltd., acrylic resin, solid content of 60.0% by mass), 0.274 parts by mass of a curing agent (trade name: K-341, manufactured by SAIDEN Chemical Co., Ltd., isocyanate resin, solid content of 75.5% by mass), and 25 parts by mass of a solvent (ethyl acetate) was used.

[0135] Next, a coating solution containing an acrylic resin and silica particles (average particle size of 3 μm) was applied to the second substrate of the second film by wet coating to form a coating layer with a thickness of 5 μm. Thus, an A4-sized protective film for a wavelength conversion sheet was obtained. Two sheets of the protective film for a wavelength conversion sheet were prepared.

[0136] (Production of wavelength conversion sheet)

[0137] After mixing CdSe / ZnS 530 (trade name, manufactured by SIGMA-ALDRICH) as quantum dots with an epoxy-based photosensitive resin, the mixed solution was applied to the first substrate surface of the first film of the wavelength conversion sheet protective film, and a wavelength conversion sheet protective film of the same structure was stacked thereon, and UV curing lamination was performed to obtain a wavelength conversion sheet. The obtained wavelength conversion sheet has the following structure: Figure 1 The wavelength conversion sheet 100 shown in FIG. Figure 2 The wavelength conversion sheet protective film 21 was used instead of the wavelength conversion sheet protective film 20. The size of the obtained wavelength conversion sheet was A4 size.

[0138] [Example 2]

[0139] The first and second films were prepared in the same manner as in Example 1. The first and second films were bonded together using the same adhesive as in Example 1 in the following manner so that the barrier layers thereof faced each other. Figure 6 The laminating apparatus shown in was used, and the tension applied to the films was adjusted to the values ​​shown in Table 1, thereby laminating the first film and the second film (roll laminating). In addition, the laminating conditions other than the tension were as follows.

[0140] (Lamination conditions)

[0141] Version: Oblique line 90L 95μm

[0142] Reverse processing

[0143] Substrate width: 320mm wide

[0144] Pressurizing (pressurizing roller) width: 280mm

[0145] Processing speed: 10m / min

[0146] Oven temperature (set temperature of oven 3 units): 60℃-70℃-80℃ from the inlet side

[0147] Ripening: 50°C, 2 days

[0148] A protective film for a wavelength conversion sheet and a wavelength conversion sheet finally cut to A4 size were obtained in the same manner as in Example 1 except that the bonding was performed by the above-mentioned method.

[0149] [Comparative Example 1]

[0150] A protective film for a wavelength conversion sheet and a wavelength conversion sheet finally cut into A4 size were obtained in the same manner as in Example 2 except that the tension applied to the film during roll lamination was adjusted to the value shown in Table 1.

[0151] Table 1

[0152]

[0153] <Comparison of Thermal Expansion Coefficients>

[0154] The thermal expansion coefficients of the protective films for wavelength conversion sheets obtained in the examples and comparative examples were measured by TMA (thermomechanical analysis) in the MD direction and TD direction. The measurement conditions are as follows. The measurement results are shown in Figures 8 to 11 and Table 2. Among them, Figure 8 This is a graph showing the relationship between the thermal expansion coefficient in the TD direction and the temperature of the protective films for wavelength conversion sheets of Examples 1 and 2. Fig. 9 This is a graph showing the relationship between the thermal expansion coefficient in the MD direction and the temperature of the protective films for wavelength conversion sheets of Examples 1 and 2. Fig.10 Graph showing the relationship between the thermal expansion coefficient in the TD direction and the temperature of the protective films for wavelength conversion sheets of Example 2 and Comparative Example 1. Fig.11 It is a graph showing the relationship between the thermal expansion coefficient in the MD direction of the wavelength conversion sheet protection films of Example 2 and Comparative Example 1 and the temperature.

[0155] Table 2 shows the maximum values ​​of the thermal expansion coefficients in the TD direction within a temperature range of 30 to 90°C.

[0156] (Measurement conditions)

[0157] Load: 50mN

[0158] Heating rate: 5℃ / min

[0159] Set temperature: 30~150℃

[0160] <Black Stripe's Review>

[0161] The wavelength conversion sheet obtained in the embodiment and the comparative example was placed in an oven at 85°C for 100 hours and 1000 hours. Then, the surface of the wavelength conversion sheet was observed using a fluorescence microscope (industrial inspection microscope manufactured by Olympus, trade name: MX51) that can be observed with both white light and ultraviolet (UV) light to confirm the presence or absence of black streaks. Based on the confirmation results, the black streaks were evaluated according to the following evaluation criteria. The results are shown in Table 2.

[0162] A: Even after leaving it for 1000 hours, no black streaks were observed.

[0163] B: No black streaks were observed after leaving the sample for 100 hours, but black streaks were observed after leaving the sample for 1000 hours.

[0164] C: After being left for 100 hours, black streaks were observed.

[0165] Table 2

[0166]

[0167] Industrial Applicability

[0168] As described above, according to the present invention, a protective film for a wavelength conversion sheet capable of suppressing the generation of black streaks even when a wavelength conversion sheet is exposed to high temperature for a long time when the wavelength conversion sheet is formed and a method for manufacturing the same, as well as a wavelength conversion sheet and a backlight unit using the protective film for a wavelength conversion sheet can be provided. Thus, a high-definition display without problems such as poor color tone and poor display can be manufactured.

Claims

1. A protective film for a wavelength conversion sheet, comprising a structure in which a surface of a first film including a first substrate and a first barrier layer on the first barrier layer side is bonded to one surface of a second film including a second substrate via an adhesive layer, wherein: The first substrate is made of a polyethylene terephthalate film or a polyethylene naphthalate film, and the second substrate is made of a polyethylene terephthalate film or a polyethylene naphthalate film. The thickness of the first substrate is greater than the thickness of the second substrate, A coating layer is provided on one surface of the wavelength conversion sheet protective film, The thermal expansion coefficient of the protective film for the wavelength conversion sheet in the TD direction in the temperature range of 30 to 90° C. is -0.8×10 -4 / K or above and 0.5×10 -4 / K or less.

2. The protective film for a wavelength conversion sheet according to claim 1, wherein: The second film further includes a second barrier layer, and a surface of the second film on the second barrier layer side is in contact with the adhesive layer. 3 . A wavelength conversion sheet comprising: a phosphor layer containing a phosphor; and the protective film for a wavelength conversion sheet according to claim 1 . 4 . A backlight unit comprising: an LED light source; the wavelength conversion sheet according to claim 3 ; and a light guide plate that allows light from the LED light source to be incident on the wavelength conversion sheet.

Images