JP2017136737A - Protective film for fluophor and wavelength conversion sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective sheet for fluophor high in barrier property and excellent in appearance without wrinkle or the like.SOLUTION: There is provided a protective film for fluophor for protecting the fluophor using quantum dot, which has one or more barrier layer arranged on at least one surface of a polyethylene terephthalate film, wherein the polyethylene terephthalate film has elongation when measured at temperature rise rate of 5°C/min. while applying tensile 50 mN load in width (TD) direction by a thermomechanical property test machine of 0.2% or less at 80°C. The elongation is (length at 80°C-length at -15°C)/length at 15°Cx100%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a protective film for phosphor and a wavelength conversion sheet using the same.

  A liquid crystal display is a display device in which a liquid crystal composition is used for display. Liquid crystal displays are used as display devices in various devices, particularly information display devices and image display devices.

  The liquid crystal display displays an image by transmitting and blocking light for each region based on application of a voltage. Therefore, external light is required to display an image on the liquid crystal display. As a light source for that purpose, a backlight provided on the back surface of the liquid crystal display is used. Conventionally, a cold cathode tube is used for the backlight. Recently, LEDs (light-emitting diodes) have been used in place of cold-cathode tubes for reasons such as long life and good color development.

  In white LED technology, which occupies a great importance in displays, a method of exciting a cerium-doped YAG (yttrium, aluminum, garnet), Ce down-conversion phosphor with a blue (450 nm) LED chip is generally used. ing. The blue light of the LED and the yellow light having a wide wavelength range generated from the YAG phosphor are mixed to become white light. However, this white light is often somewhat bluish and is often considered “cold” or “cool” white.

  By the way, in recent years, nano-sized phosphors using quantum dots have been commercialized mainly by foreign venture companies. A quantum dot is a luminescent semiconductor nanoparticle, and the range of a diameter is 1-20 nm. The unique optical and electronic properties of quantum dots are being used in many applications such as flat panel displays and various color illuminations (lights) in addition to fluorescent imaging in the fields of biology and medical diagnostics.

  Since quantum dots show a wide excitation spectrum and high quantum efficiency, they can be used as phosphors for LED wavelength conversion. Furthermore, the wavelength of light emission can be completely adjusted over the entire visible range simply by changing the dot size or the type of semiconductor material. As a result, quantum dots have the potential to create virtually any color, especially the warm white that is highly desired in the lighting industry. In addition, it is possible to obtain white light having different color rendering indexes by combining three types of dots whose emission wavelengths correspond to red, green, and blue. In this way, a display using a quantum dot backlight improves color tone and expresses up to 65% of human-identifiable colors without increasing the thickness, power consumption, cost, and manufacturing process of conventional LCD TVs. It becomes possible.

  Backlights with quantum dots are those in which quantum dots with red or green emission spectrum are diffused in the film, and the outer surface is sealed with a barrier film or a laminate, and depending on the form, the edges are also sealed. There is also.

  Here, a barrier film forms a thin film by vapor deposition etc. on the surface of base materials, such as a plastic film, and prevents permeation | transmission of a water | moisture content or gas. In addition to barrier properties, barrier films are required to have appearance and transparency without scratches and wrinkles, but conventional barrier films are used as packaging materials for food and medical products and packaging materials for electronic devices. Therefore, there has been a problem that satisfactory performance cannot be obtained for phosphor protection.

  In particular, wrinkles that have not been a problem when used as packaging materials for foods and the like are a problem. That is, the barrier film used for the protective film for phosphors has the problem of suppressing wrinkles that are likely to occur due to cooling after heating in the barrier property imparting process such as vapor deposition and baking after coating, and having sufficient barrier properties. Met.

  In order to solve such a problem, several methods can be considered. For example, Patent Document 1 proposes a backlight sandwiched between barrier films in order to suppress phosphor deterioration. Patent Document 2 proposes coating with a barrier film in order to ensure the reliability of the organic EL element.

JP 2011-013567 A JP 2009-018568 A

  However, when a display in which quantum dots are sealed with an existing barrier film with reference to Patent Documents 1 and 2 is manufactured, the lifetime of white light obtained due to insufficient barrier properties is short, and scratches and However, there is a problem that the uniformity of color (light) occurs in the white LED due to the pattern of the quantum dots, and the uniformity is deteriorated.

  This invention is made | formed in view of this situation, and it aims at providing the protective film for fluorescent substances excellent in the external appearance without barrier property, wrinkles, etc., and the wavelength conversion sheet obtained using the same. .

In order to solve the above problems, the present invention described in claim 1 is a phosphor protective film for protecting a phosphor using quantum dots,
Comprising one or more barrier layers provided on at least one surface of the polyethylene terephthalate film;
The polyethylene terephthalate film is
With a thermomechanical property tester, the elongation when measured at a heating rate of 5 ° C./min while applying a tensile 50 mN load in the width (TD) direction was 80 ° C.
A protective film for a phosphor, characterized by being 0.2% or less.
Here, the elongation is (length at 80 ° C.−length at 15 ° C.) / Length at 15 ° C. × 100%. Here, when the elongation rate is a negative value, it indicates contraction, and when it is a positive value, it indicates expansion.

  The present invention according to claim 2 is characterized in that the one or more barrier layers are alternately laminated in order of an inorganic thin film layer and a gas barrier coating layer from a side close to the polyethylene terephthalate film. The phosphor protective film according to claim 1.

  The present invention described in claim 3 is the phosphor protective film according to claim 2, wherein the inorganic thin film layer includes at least one deposited film of silicon oxide and aluminum oxide. .

  The present invention according to claim 4 is characterized in that the gas barrier coating layer has as a component at least one of a hydroxyl group-containing polymer compound, a metal alkoxide, a metal alkoxide hydrolyzate, and a metal alkoxide polymer. The phosphor protective film according to claim 2 or 3, wherein

  According to a fifth aspect of the present invention, there is provided the phosphor according to any one of the first to fourth aspects, on a phosphor layer containing a phosphor using quantum dots and on at least one surface of the phosphor layer. A wavelength conversion sheet characterized by comprising a body protective film.

  The protective film for a phosphor of the present invention is excellent in appearance because generation of wrinkles and the like can be suppressed even by cooling after heating in a barrier property imparting step such as vapor deposition or baking after coating. Moreover, since not only an inorganic thin film layer but a gas barrier coating layer is provided, the barrier property is excellent. Therefore, in the wavelength conversion sheet of the present invention using this, the deterioration of the characteristics of the quantum dots is suppressed, and a backlight unit with little decrease in luminous efficiency over a long period of time is obtained, and a highly uniform light emitting surface is obtained even on the display. be able to.

It is a schematic cross section which shows the structure of the protective film for fluorescent substances which is 1st Embodiment to which this invention is applied, and the wavelength conversion sheet of 1st Embodiment using the same. It is a schematic cross section which shows the structure of the protective film for fluorescent substances which is 2nd Embodiment to which this invention is applied, and the wavelength conversion sheet of 2nd Embodiment using the same. It is a schematic cross section which shows the structure of the protective film for fluorescent substances which is 3rd Embodiment to which this invention is applied, and the wavelength conversion sheet of 3rd Embodiment using the same. It is explanatory drawing which shows the longitudinal direction (MD) and width direction (TD) of a transparent plastic film (base material). It is a characteristic view which shows the result of having measured the elongation rate about the polyethylene terephthalate film of Examples 1-3 and Comparative Examples 1-2 with the thermomechanical property tester.

  Hereinafter, the first to third embodiments of a phosphor protective film to which the present invention is applied and a wavelength conversion sheet using the same will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner, and the dimensional ratios of the respective components are not always the same as the actual ones. .

<First Embodiment>
(Protective film for phosphor)
The part of the code | symbol 3 of FIG. 1 has shown typically the cross-sectional structure of the protective film 3 for fluorescent substance which is 1st Embodiment to which this invention is applied. The phosphor protective film 3 of the present embodiment is a barrier film having a transparent plastic film 5 and a barrier layer 6.
In the configuration of FIG. 1, the barrier layer 6 is provided on one side of the transparent plastic film 5, but may be provided on both sides.

  As a production process of the phosphor protective film 3, first, the inorganic thin film layer 7 is formed on at least one surface of the transparent plastic film 5 by, for example, vapor deposition. Next, the gas barrier coating layer 8 is laminated on the surface of the inorganic thin film layer 7 by a coating + firing method or the like. Thereby, the protective film 3 for fluorescent substance with which the barrier layer 6 which consists of the inorganic thin film layer 7 and the gas-barrier coating layer 8 was provided on the transparent plastic film 5 is obtained.

  In FIG. 4, the figure for demonstrating the longitudinal direction and width direction of the transparent plastic film (base material) used with the protective film for fluorescent substance of this invention is shown. In the present invention, it is assumed that the web-like transparent plastic film is a take-up roll, and the running direction (MD) of the transparent plastic film is the longitudinal direction. On the other hand, the direction perpendicular to the longitudinal direction MD (TD) is the width direction. Note that MD is an abbreviation for Machine Direction, and TD is an abbreviation for Transverse Direction.

  Generally, when a barrier film is produced industrially, the film is unwound from a web-shaped roll, and after a barrier layer is formed on the film, the film is wound as a barrier film. During these steps, an external force in the mechanical tension direction is applied to the film in the transported (running) state in order to transport the film in a stretched state. In consideration of these external forces, the present invention achieves a reduction in the occurrence of wrinkles and the like of the protective film for a phosphor by defining a suitable range for the thermal elongation rate of the transparent plastic film.

  The thickness of the transparent plastic film 5 is not particularly limited, but in order to maintain the barrier property of the wavelength conversion sheet 1 described later and to prevent the total thickness from being increased, the thickness may be in the range of 12 to 100 μm. desirable. As the transparent plastic film 5, a polyethylene terephthalate film is preferably used from the viewpoint of dimensional stability and processability.

  In the phosphor protective film of the present invention, the elongation when measured at a heating rate of 5 ° C./min while applying a tensile 50 mN load in the width (TD) direction by a thermomechanical property tester, At 80 ° C., a polyethylene terephthalate film of 0.2% or less is used. Here, the elongation is (length at 80 ° C.−length at 15 ° C.) / Length at 15 ° C. × 100%. When the elongation is a negative value, it indicates contraction, and when it is a positive value, it indicates expansion. Here, the reason why the tensile load is applied is to simulate the tensile external force applied to the polyethylene terephthalate film which is in the conveying state in the process as described above. Moreover, the reason for using 80 ° C. as a standard is that the temperature is a suitable temperature that is considered necessary and sufficient from the viewpoint of the use environment and production conditions of the phosphor protective film. The reason why an elongation of 0.2% or less is suitable is shown in the examples. The lower limit is not particularly limited as long as the elongation is 0.2% or less, but is 0% or more for a general polyethylene terephthalate film.

  In order to adjust the elongation percentage of the polyethylene terephthalate film to the above-mentioned preferable range, for example, the molecular chain in the film is oriented by stretching, and the stretched film is further heated. When heating the stretched film, the heating temperature is set in consideration of the glass transition temperature and melting point of polyethylene terephthalate. By heating the stretched film at an appropriate temperature, it becomes possible to control the crystal structure by various methods such as promoting or relaxing the molecular chain orientation obtained by stretching and fixing the crystal structure. As a result, the thermal elongation in the TD direction of the polyethylene terephthalate film can be adjusted.

  Although it does not specifically limit as the inorganic thin film layer 7, For example, it is preferable to use aluminum oxide, silicon oxide, magnesium oxide, or a mixture thereof. However, it is particularly preferable to use aluminum oxide or silicon oxide from the viewpoint of barrier properties and productivity.

  The film thickness of the inorganic thin film layer 7 is preferably in the range of 10 to 500 nm, and more preferably in the range of 50 to 300 nm. Here, when the film thickness is less than 10 nm, the film thickness is too thin, so that a uniform film cannot be obtained or the function as a gas barrier material cannot be sufficiently achieved. On the other hand, when the film thickness exceeds 500 nm, the thin film cannot be kept flexible, and the thin film may be cracked due to external factors such as bending and pulling after the film formation.

  The gas barrier coating layer 8 is provided to prevent various secondary damages in the subsequent process and to provide high barrier properties. The gas barrier coating layer 8 desirably has at least one of a hydroxyl group-containing polymer compound, a metal alkoxide, a metal alkoxide hydrolyzate, and a metal alkoxide polymer as a component.

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

The metal alkoxide is a compound represented by a general formula, M (OR) _n (M: metal such as Si, Ti, Al, Zr, R: alkyl group such as CH ₃ , C ₂ H ₅ ). Specific examples include tetraethoxysilane [Si (OC ₂ H ₅ ) ₄ ] and triisopropoxyaluminum [Al (O-iso-C ₃ H ₇ ) ₃ ], among which tetraethoxysilane and triisopropoxyaluminum. Is preferable because it is relatively stable in an aqueous solvent after hydrolysis. Examples of the hydrolyzate and polymer include silicic acid (Si (OH) ₄ ) as a tetraethoxysilane hydrolyzate and polymer, and aluminum hydroxide (Al (OH) ₃ ) and the like.

  A catalyst such as tin chloride may be added to the gas barrier coating layer 8 in order to decompose the aforementioned metal alkoxide. For example, it may be stannous chloride, stannic chloride or a mixture thereof, and may be an anhydride or a hydrate.

(Phosphor layer)
The phosphor layer (also referred to as a wavelength conversion layer. Reference numeral 2 in FIG. 1) is a thin film of several tens to several hundreds μm made of phosphor and a sealing resin. As the sealing resin, for example, a photosensitive resin or a thermosetting resin made of an acrylic resin, an epoxy resin, or a polyolefin resin can be used. Inside the sealing resin, a phosphor made of quantum dots is sealed in a mixed state of one or two kinds. The phosphor layer 2 may be a laminate in which two or more phosphor layers in which only one kind of phosphor is sealed are laminated. Those phosphors having the same excitation wavelength are selected. The excitation wavelength is selected based on the wavelength of light emitted by the LED light source. The fluorescent colors of the two types of phosphors are different from each other. Each fluorescent color is red and green. The wavelength of each fluorescence and the wavelength of light emitted from the LED light source are selected based on the spectral characteristics of the color filter. The peak wavelengths of fluorescence are, for example, 610 nm for red and 550 nm for green.

  The particle structure of the phosphor will be described. As the phosphor, a core-shell type quantum dot having particularly good luminous efficiency is preferably used. The core-shell type quantum dot is obtained by coating a semiconductor crystal core as a light emitting portion with a shell as a protective film. For example, cadmium selenide (CdSe) can be used for the core and zinc sulfide (ZnS) can be used for the shell. Quantum yield is improved by coating the surface defects of the CdSe particles with ZnS having a large band gap. In addition, the phosphor may be one in which the core is doubly coated with the first shell and the second shell. 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 the phosphor layer 2, each phosphor that converts blue light from a light source into red, green, or the like may be dispersed in a single layer, or may be laminated as a separate layer to form a multilayer phosphor layer. .

(Wavelength conversion sheet)
1 is a schematic cross-sectional view showing a configuration of a wavelength conversion sheet 1 according to a first embodiment to which the present invention is applied. As shown in FIG. 1, the wavelength conversion sheet 1 of the present embodiment includes a phosphor layer 2 including a phosphor using quantum dots, and a phosphor protective film 3 provided on both surfaces of the phosphor layer 2. , And is configured. When the wavelength conversion sheet 1 of the present embodiment is configured, the barrier layers 6 of the respective phosphor protective films 3 are laminated so as to face the phosphor layer 2. As a result, the phosphor layer 2 is enclosed between the phosphor protective films 3 on both sides.

  Although the production process of the wavelength conversion sheet 1 is not particularly limited, for example, after applying a mixed liquid prepared by dispersing a phosphor material in a sealing resin on the surface of the barrier layer 6 of one phosphor protective film 3 The wavelength conversion sheet 1 can be manufactured by laminating the phosphor layer 2 so that the surface of the barrier layer 6 of the other phosphor protective film 3 and the phosphor layer 2 are in contact with each other, followed by UV curing or thermosetting.

  Hereinafter, the second embodiment and the third embodiment of the phosphor protective film and the wavelength conversion sheet using the same according to the present invention will be described respectively, but the same components as those in the first embodiment are denoted by the same reference numerals. And the description thereof is omitted.

<Second Embodiment>
(Protective film for phosphor)
The part of the code | symbol 23 of FIG. 2 has shown typically the cross-sectional structure of the protective film 23 for fluorescent substance which is 2nd Embodiment to which this invention is applied. The phosphor protective film 23 of the present embodiment is a barrier film having the transparent plastic film 5 and the barrier layer 26.

  The barrier layer 26 includes the inorganic thin film layer 7 and the gas barrier coating layer 8. Further, as shown in FIG. 2, the barrier layer 26 has an inorganic thin film layer 7 formed on one surface of the transparent plastic film 5, and a gas barrier coating layer 8 is laminated on the inorganic thin film layer 7. Furthermore, the inorganic thin film layer 7 is laminated on the gas barrier coating layer 8, the gas barrier coating layer 8 is laminated on the inorganic thin film layer 7, and so on, and the inorganic thin film layer 7 and the gas barrier coating layer 8 are alternately laminated. It is configured.

(Wavelength conversion sheet)
The code | symbol 21 which shows the whole of FIG. 2 is a schematic cross section which shows the structure of the wavelength conversion sheet | seat 21 which is 2nd Embodiment to which this invention is applied. As shown in FIG. 2, the wavelength conversion sheet 21 of the present embodiment includes a phosphor layer 2 including a phosphor using quantum dots, and a phosphor protective film 23 provided on both surfaces of the phosphor layer 2. , And is configured. When configuring the wavelength conversion sheet 21 of the present embodiment, the respective protective films 23 for phosphors are laminated with the barrier layer 26 facing the phosphor layer 2. As a result, the phosphor layer 2 is enclosed between the phosphor protective films 23 on both sides.

<Third Embodiment>
(Protective film for phosphor)
The part of the code | symbol 33 of FIG. 3 has shown typically the cross-sectional structure of the protective film 33 for fluorescent substance which is 3rd Embodiment to which this invention is applied. The phosphor protective film 33 of this embodiment is a barrier film in which a barrier layer 36 is sandwiched between two transparent plastic films 5.

  The barrier layer 36 is laminated via the adhesive layer 9 so that the barrier layer 6 in the first embodiment is opposed to the barrier layer 36. Therefore, in other words, the phosphor protective film 33 has the adhesive layer 9 so that the gas barrier coating layer 8 faces the phosphor protective film 3 of the first embodiment comprising the transparent plastic film 5 and the barrier layer 6. It is a laminate film laminated through.

  Although it does not specifically limit as the contact bonding layer 9, Adhesives and adhesives, such as an acryl-type material, a urethane type material, and a polyester-type material, can be used. Specifically, any of an acrylic resin-based pressure-sensitive adhesive, a urethane-based adhesive, and an ester-based adhesive can be used.

  Further, the thickness of the adhesive layer 9 is not particularly limited, but is desirably 20 μm or less in order to reduce the total thickness of the phosphor protective film 33 or the wavelength conversion sheet 31 described later.

(Wavelength conversion sheet)
The code | symbol 31 which shows the whole of FIG. 3 is a schematic cross section which shows the structure of the wavelength conversion sheet 31 which is 3rd Embodiment to which this invention is applied. As shown in FIG. 3, the wavelength conversion sheet 31 of the present embodiment includes a phosphor layer 2 including a phosphor using quantum dots, and a phosphor protective film 33 provided on both surfaces of the phosphor layer 2. , And is configured. Thus, the phosphor layer 2 is enclosed between the phosphor protective films 33 on both sides.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the wavelength conversion sheets of the first, second, and third embodiments, the example in which the phosphor protective film is provided on both surfaces of the phosphor layer 2 is shown. It may be a configuration.

  Further, as a developed form of the phosphor protective film 33 of the above-described third embodiment, the barrier layer 6 is made of the inorganic thin film layer 7 and the gas barrier coating like the barrier layer 26 of the second embodiment. The layer 8 and the inorganic thin film layer 7 and the gas barrier coating layer 8 may be alternately laminated. As described above, including the second embodiment, the phosphor protective film in which the inorganic thin film layers and the gas barrier coating layers are alternately laminated two or more layers can exhibit more excellent barrier performance. it can.

  Hereinafter, although the effect of the present invention is further explained using an example and a comparative example, the present invention is not limited to the following example.

<Example 1>
(Preparation of protective film for phosphor)
On one side of a 25 μm-thick polyethylene terephthalate film (elongation: 0.10%) as a substrate, silicon oxide is provided to a thickness of 25 nm by vacuum deposition to form an inorganic thin film layer, and from alkoxysilane and polyvinyl alcohol After applying the coating liquid to a thickness of 0.3 μm by wet coating, a heat treatment is performed to form a gas barrier film layer, and the phosphor protective film (reference numeral 3 in FIG. 1) of the first embodiment is formed. Produced. The measurement of the elongation rate will be described later.

(Production of wavelength conversion sheet)
The concentration of CdSe / ZnS 530 (manufactured by SIGMA-ALDRICH) as quantum dots was adjusted and dispersed in a solvent to obtain a phosphor solution. The phosphor solution was mixed with a photosensitive resin, and then applied to the gas barrier coating layer side of the prepared phosphor protective film to form a phosphor layer having a thickness of 100 μm.

  The phosphor protective film having the same structure as described above is laminated on the phosphor layer formed on the phosphor protective film as described above, and the wavelength conversion of the first embodiment of Example 1 is performed by UV curing lamination. A sheet (reference numeral 1 in FIG. 1) was produced.

<Example 2>
A phosphor protective film for the first embodiment was produced in the same manner as in Example 1 except that a polyethylene terephthalate film (elongation: 0.17%) was used as the base material. A wavelength conversion sheet according to the first embodiment of Example 2 was produced in the same manner.

<Example 3>
By applying an acrylic resin adhesive to the gas barrier coating layer of the phosphor protective film produced in Example 2, and then bonding another phosphor protective film having the same configuration as the phosphor protective film, A phosphor protective film (reference numeral 33 in FIG. 3) of the third embodiment was produced. Thereafter, a wavelength conversion sheet (reference numeral 31 in FIG. 3) of the third embodiment of Example 3 was produced in the same manner as in Example 1.

<Comparative Example 1>
A wavelength conversion sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that a polyethylene terephthalate film (elongation: 0.22%) was used as the substrate.

<Comparative example 2>
A wavelength conversion sheet of Comparative Example 2 was produced in the same manner as in Example 3 except that a polyethylene terephthalate film (elongation: 0.22%) was used as the substrate.

<Thermomechanical property tester (TMA) measurement>
About the polyethylene terephthalate film used in Examples 1 to 3 and Comparative Examples 1 to 2, a thermomechanical analyzer (measuring device: TMASS6100 manufactured by PerkinElmer, sample size: 4 × 15 mm, temperature condition: 15 to 100 ° C., The rate of elongation was measured using a heating rate of 5 ° C./min and a load condition (TD direction, tensile direction): 50 mN.

<Water vapor permeability measurement>
About the protective films for phosphors prepared in Examples 1 to 3 and Comparative Examples 1 to 2, the water vapor transmission rate was measured at a temperature of 40 ° C. using a water vapor transmission rate measuring device (measuring device: Aquatran manufactured by Modern Control). The humidity was measured under the condition of 90% RH.

<Appearance evaluation>
About the wavelength conversion sheet | seat produced in Examples 1-3 and Comparative Examples 1-2, in each process which produces a wavelength conversion sheet | seat, the LED light source is applied, the light emission state on a surface is confirmed, and unevenness, wrinkles, etc. are visually observed. The presence or absence was confirmed. The case where there was no occurrence of unevenness or wrinkles was evaluated as ◯, the case where there was no mark, and the case where there was particularly remarkable as XX.

The above measurement results, appearance evaluation results, and comprehensive determination results are shown in FIG.

  From Table 1, in the wavelength conversion sheet of Examples 1 to 3, the elongation rate when heated while applying a tensile load in the TD direction is small, and by using a polyethylene terephthalate film excellent in heating dimensional stability, excellent. Barrier properties and appearance can be obtained.

  On the other hand, in the wavelength conversion sheet using the polyethylene terephthalate film having a large elongation when heated while applying a tensile load in the TD direction and being inferior in heat dimensional stability, the barrier property is almost affected. Although there was no problem, there was a problem in the appearance of wrinkles in particular, and there were problems such as non-uniform surface emission and Newton rings.

  According to the present invention, a phosphor protective film having excellent appearance and barrier properties can be obtained, and deterioration of phosphor characteristics can be suppressed. Therefore, a backlight unit having good uniformity over a long period of time and less reduction in luminous efficiency can be obtained. can get. As a result, a display with high definition, high efficiency, and long life can be obtained.

1, 2, 31 ... wavelength conversion sheet 2 ... phosphor layers 3, 23, 33 ... phosphor protective film 5 ... transparent plastic films 6, 26, 36 ... barrier layer 7 ..Inorganic thin film layer 8 ... gas barrier coating layer 9 ... adhesive layer 40 ... unwinding part

Claims (5)

A protective film for a phosphor for protecting a phosphor using quantum dots,
Comprising one or more barrier layers provided on at least one surface of the polyethylene terephthalate film;
The polyethylene terephthalate film is
With a thermomechanical property tester, the elongation when measured at a heating rate of 5 ° C./min while applying a tensile 50 mN load in the width (TD) direction was 80 ° C.
A protective film for a phosphor, characterized by being 0.2% or less.
Here, the elongation is (length at 80 ° C.−length at 15 ° C.) / Length at 15 ° C. × 100%. From the side where the one or more barrier layers are close to the polyethylene terephthalate film,
The protective film for a phosphor according to claim 1, wherein the protective film is composed of an inorganic thin film layer and a gas barrier coating layer which are alternately laminated in this order.   The phosphor protective film according to claim 2, wherein the inorganic thin film layer includes a deposited film of at least one of silicon oxide and aluminum oxide.   4. The gas barrier coating layer according to claim 2, wherein the gas barrier coating layer has at least one of a hydroxyl group-containing polymer compound, a metal alkoxide, a metal alkoxide hydrolyzate, and a metal alkoxide polymer as a component. The protective film for fluorescent substance of description. A phosphor layer containing a phosphor using quantum dots;
A wavelength conversion sheet comprising the phosphor protective film according to any one of claims 1 to 4 on at least one surface of the phosphor layer.