Wavelength converting member and method of producing the same

A method of producing a wavelength converting member is provided. The method includes forming a quantum dot layer on a bottom organic layer, and forming a top organic layer on the quantum dot layer. The quantum dot layer includes quantum dots. A moisture vapor transmission rate of the top organic layer and the bottom organic layer is at least 0.006 g/(m2·day) and less than 9 g/(m2·day).

TECHNICAL FIELD

The present invention relates to a wavelength converting member used for a back light etc. and to a method of producing the same.

BACKGROUND ART

For example, JP 2013-544018 A (PTL 1) below discloses an invention relating to quantum dot films and lighting devices using the same.

For example, PTL 1 discloses inFIG. 6A, a lighting device600having a QD (quantum dot) phosphor material604and barrier layers620and622placed on both sides of the material. The barrier layers are provided, thereby ensuring the photostability of QDs and protecting the QDs from elevated temperatures, moisture, and other harmful environmental conditions (see [0072] etc. of PTL 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the invention according to PTL 1 does not refer in particular to the relationship between the structure of the barrier layers and change in the light emission intensity over time. In other words, PTL 1 does not limit the structure of the barrier layers in terms of change in the light emission intensity over time.

The present invention is made in consideration of the above, in particular with a view to providing a wavelength converting member which can reduce change in the light emission intensity over time as compared with conventional members and a method of producing the wavelength converting member.

Solution to Problem

A wavelength converting member according to the present invention includes a quantum dot layer having quantum dots; and at least one barrier layer formed on at least both sides of the quantum dot layer. The moisture vapor transmission rate of the barrier layer is lower than 9 g/(m2·d). Thus, change in the light emission intensity over time can be effectively inhibited as compared with conventional techniques.

In the present invention, the moisture vapor transmission rate is preferably 0.1 g/(m2·d) or less.

Further, in the present invention, the barrier layer is preferably formed around the entire periphery of the quantum dot layer.

Preferably, in the present invention, a wrap starting end and a wrap finishing end of the barrier layer are joined at edge on one side of the quantum dot layer.

Preferably, in the present invention, barrier layers are placed on both the top and bottom of the quantum dot layer and are joined at edges on sides of the quantum dot layer.

Further, in the present invention, the quantum dot layer is preferably formed from a molding or formed by inkjet printing.

Further, in the present invention, the barrier layer is preferably formed to have at least an organic layer. This facilitates the handling of the barrier layer (improvement in the handling).

Preferably, in the present invention, the barrier layer has a layered structure, in which the organic layer is formed as the innermost layer facing the quantum dot layer. This allows the quantum dot layer to be easily formed on the barrier layer, and the adhesion between the barrier layer and the quantum dot layer can be improved.

Preferably, in the present invention, in the barrier layer, an inorganic layer is provided outside the innermost layer. This can effectively improve the barrier properties of the barrier layer.

Preferably, in the present invention, a plurality of the organic layers are provided, and an inorganic layer is sandwiched between the organic layers. With such a structure including three or more layers in which the innermost layer and the outermost layer in the barrier layer are organic layers and an inorganic layer is sandwiched between the organic layers, the handling, the barrier properties, the adhesion between the barrier layer and the quantum dot layer, etc. can effectively be improved. In the present invention, the inorganic layer is preferably formed from a SiO2layer.

Further, in the present invention, the organic layer is preferably formed in contact with the quantum dot layer.

Further, in the present invention, the organic layer is preferably formed from a PET film.

Further, in the present invention, the quantum dot layer preferably contains a thickening agent. For example, since the viscosity would likely be reduced when a dispersant is added to improve the dispersibility of quantum dots, a thickening agent is added to adjust the viscosity. This allows the quantum dot layer to be formed with a certain uniform thickness, thereby achieving good fluorescence properties.

Further, in the present invention, the quantum dot layer may contain a light-scattering agent. Further, a surface of the barrier layer may be matted. Thus, adding a light-scattering agent to the quantum dot layer or matting a surface of the barrier layer can promote light scattering.

In a method of producing a wavelength converting member according to the present invention, the barrier layer made of a material having a moisture vapor transmission rate of less than 9 g/(m2·d) is formed on at least both sides of a quantum dot layer having quantum dots. In the present invention, the barrier layer made of a material having a moisture vapor transmission rate of less than 9 g/(m2·d) is prepared, and the barrier layer is formed on at least both sides of the quantum dot layer. This makes it possible to produce a wavelength converting member which allows for easier production process and allows change in the light emission intensity to be effectively inhibited as compared with conventional techniques.

Further, in the method of producing a wavelength converting member of the present invention, the entire periphery of the quantum dot layer having quantum dots is covered by the barrier layer. This makes it possible to produce a wavelength converting member which allows change in the light emission intensity to be more effectively inhibited as compared with conventional techniques.

Further, in the present invention, the method preferably includes the steps of; forming a plurality of the quantum dot layers at intervals on a lower barrier layer; forming an upper barrier layer over a surface of the lower barrier layer and surfaces of the plurality of the quantum dot layers; and isolating the quantum dot layers by cutting the lower barrier layer and the upper barrier layer between the quantum dot layers. Thus, a plurality of wavelength converting members can be obtained at the same time.

Further, in the present invention, the quantum dot layer is preferably formed from a molding or formed by inkjet printing.

Preferably, in the present invention, the barrier layer has an organic layer, and the organic layer is provided on the innermost side to face the quantum dot layer. Thus, while the adhesion between the barrier layer and the quantum dot layer can be improved, high wettability of a surface of the organic layer can be achieved, and the quantum dot layer can be formed more easily.

Preferably, in the present invention, the barrier layer has a plurality of organic layers and an inorganic layer sandwiched between the organic layers, and the innermost layer of the barrier layer facing the quantum dot layer and the outermost layer thereof are constituted by the organic layers. The organic layers on both sides of the barrier layer allows for good handling, making it easier to form the quantum dot layer. Further, the inclusion of inorganic layer allows the barrier properties of the barrier layer to be effectively improved.

Further, in the present invention, the quantum dot layer preferably contains a thickening agent. This allows the viscosity of the quantum dot layer to be adjusted, which facilitates the formation of the quantum dot layer having a given thickness on the surface of the barrier layer.

Advantageous Effects of Invention

Thus, in accordance with the wavelength converting member of the present invention, change in the light emission intensity over time can effectively be inhibited as compared with conventional techniques.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention (hereinafter simply referred to as “(disclosed) embodiments”) will now be described in detail. The present invention is not limited to the following embodiments and can be variously altered without departing from the spirit of the present invention.

FIGS. 1A to 1Care longitudinal sectional views of a wavelength converting member exemplifying a first embodiment of the present invention. As shown inFIG. 1A, a wavelength converting member1includes a quantum dot layer2having quantum dots, barrier layers3and4formed on both sides of the quantum dot layer2. As shown inFIG. 14, the wavelength converting member1is for example a sheet member shaped like a thin plate. In general, a “sheet” is defined as a structure having a thickness that is small relative to the length and the width. The wavelength converting member1may or may not be flexible, but is preferably flexible. The wavelength converting member1is sometimes simply called a sheet, or may be called a film or a film sheet. However, a “film” herein is defined as a flexible sheet product. Further, the wavelength converting member1may be formed with a uniform thickness, or may have a structure in which the thickness varies from point to point in the member, varies gradually in the length direction or the width direction, or varies in stages. The length dimension L, the width dimension W, and the thickness dimension T of the wavelength converting member1are not limited, and may be varied depending on the product. For example, the wavelength converting member can be used for a back light of a large product such as a TV set, or can be used for a back light of a small portable device such as a smartphone. Accordingly, the size of the wavelength converting member is determined in accordance with the size of the product.

The quantum dot layer2includes numerous quantum dots, and may also include a fluorescent pigment, a fluorescent dye, or the like in addition to the quantum dots.

Although the structure and the material of the quantum dots are not limited; for example, a quantum dot in this embodiment can have a semiconductor core having a diameter of two nanometers to several tens of nanometers. Further, a quantum dot can have, in addition to the core consisting of a semiconductor particle, a shell part covering the circumference of the core. The diameter of the core consisting of a semiconductor particle may be 2 nm to 20 nm, preferably, 2 nm to 15 nm. This does not limit the material of the core. For example, the core can use a core material containing at least Zn and Cd; a core material containing Zn, Cd, Se, and S; ZnCuInS; CdS; ZnSe; ZnS; CdSe; InP; CdTe; or a composite thereof.

The quantum dots include, for example, quantum dots having a fluorescence wavelength of approximately 520 nm (green) and those having a fluorescence wavelength of approximately 660 nm (red). Accordingly, when blue light enters the light entrance plane1aas shown inFIGS. 1A to 1C, the quantum dots convert part of the blue light into green or red light. Thus, white light can be obtained from the light exit plane1b.

For example, the quantum dot layer2is formed by coating the surface of a film like barrier layer with a resin composition in which quantum dots are dispersed, or by previously shaping the resin composition into a predetermined shape.

As shown inFIG. 1A, the barrier layers3and4are individually placed on both sides of the quantum dot layer2. As shown inFIG. 1B, the barrier layers3and4can be joined to both surfaces of the quantum dot layer2with adhesive layers7provided therebetween. Thus provided barrier layers3and4protect both surfaces of the quantum dot layer2, leading to improved resistance to environment (durability). Such a structure in which barrier layers are placed on both sides of a quantum dot layer has conventionally been studied (PTL 1). However, the structure does not limit the structure of the barrier layers in terms of inhibiting change in the light emission intensity of the wavelength converting member over time.

This being the case, in this embodiment, the moisture vapor transmission rate of the barrier layers3and4is set to lower than 9 g/(m2·d), Here, the “moisture vapor transmission rate” can be Measured based on JIS K7129 (:2008). Specifically, the moisture vapor transmission rate can be measured using, without limitation, a humidity sensor method, an infrared sensor method, or a gas chromatography method. In this embodiment, the moisture vapor transmission rate of the barrier layers3and4is preferably 5 g/(m2·d) or less, more preferably 3 g/(m2·d) or less, still more preferably 1 g/(m2·d) or less, yet more preferably 0.1 g/(m2·d) or less, and even more preferably 0.01 g/(m2·d) or less. The moisture vapor transmission rate is most preferably 6×10−3g/(m2·d) or less.

Thus, change in the light emission intensity over time can be effectively inhibited as compared with conventional techniques by controlling the moisture vapor transmission rate of the barrier layers3and4. For example, as shown in the experimental results described below, when quantum dots having a green fluorescence wavelength were used, for a sample in which barrier layers having a moisture vapor transmission rate of 9 g/(m2·d) were used, the light emission intensity of the blue fluorescence wavelength (incident light) gradually increased over time while the light emission intensity of the green fluorescence wavelength decreased rapidly. For endurance test conditions, the temperature was set at 60° C., and the humidity was set at 90%.

The high moisture vapor transmission rate of the barrier layers3and4increases the amount of water vapor reaching the quantum dot layer2, so that the quantum dots contained in the quantum dot layer2are likely to deteriorate. To address this problem, in this embodiment, the moisture vapor transmission rate of the barrier layers3and4is set to lower than 9 g/(m2·d) so as to protect the quantum dots from the adverse environment or rapid changes in the environment. Thus, deterioration of the quantum dots can be suppressed and change in the light intensity over time can be effectively inhibited. The experiments described below proved that change in the light emission intensity over time could effectively be inhibited when the moisture vapor transmission rate of the barrier layers3and4was 0.1 g/(m2·d) or less.

InFIG. 1B, the quantum dot layer2is joined to the barrier layers3and4with the adhesive layers7therebetween; alternatively, as shown inFIG. 1C, the barrier layers3and4can be directly jointed to both sides of a quantum dot layer2′ without providing the adhesive layers7.

In the structure ofFIG. 1C, for example, when an adhesive component is contained in the quantum dot layer2′, the barrier layers3and4can be joined to both surfaces of the quantum dot layer2′. This makes it possible to reduce the sheet thickness of the wavelength converting member1; for example, the thickness can be adjusted to 100 μm or less.

Even for the structure in which the adhesive layers7are provided as shown inFIG. 1B, for example, when the quantum dot layer2is formed by calendaring a substrate for supporting the quantum dot layer2is not required; in addition, the quantum dot layer2can be formed with a thin sheet thickness, specifically of approximately 70 μm or less, which allows the wavelength converting member1to be formed with a thin sheet thickness.

Next, in addition to the fact that the moisture vapor transmission rate of the barrier layers3and4is less than 9 g/(m2·d), the material and structure of the barrier layers3and4that are preferred in this embodiment will be described. Note that the following embodiment does not limit the presence or absence of the adhesive layers or the state of the quantum dot layer to those inFIG. 1BandFIG. 1C.

InFIG. 2, the barrier layers3and4are each formed as a single layer of an organic layer S. The organic layer5constitutes a resin film, and the barrier layers3and4are present as resin films, which results in easier handling of the barrier layers3and4. Further, inFIG. 2, the organic layer5abuts the quantum dot layer2. Here, since the surface of the organic layer5is excellent in wettability, when the quantum dot layer2is formed by application, the quantum dot layer2can easily be formed with a given thickness on the surfaces of the barrier layers3and4. Further, the adhesion between the quantum dot layer2and the organic layer5can be improved by thermocompression bonding, etc. In this embodiment, the organic layer5is preferably a PET (polyethylene terephthalate) film. This allows for high light transmittance, and can effectively improve the above-described handling and the adhesion between the organic layer and the quantum dot layer2.

Further, inFIG. 3, the barrier layers3and4are each formed to have a layered structure composed of the organic layer5and an inorganic layer6. In this case, the organic layers5are formed as the innermost layers in the barrier layers3and4that are in contact with the quantum dot layer2, and the inorganic layers6are formed on the outer sides of the innermost layers (as the outermost layers). The organic layers S are preferably PET (polyethylene terephthalate) films. The inorganic layers6are preferably SiO2layers. Further, the inorganic layer6may be a layer of silicon nitride (SiNx), aluminum oxide (Al2O3), titanium oxide (TiO2), or silicon oxide (SiO2), or a laminate thereof. The provision of such organic layers5facilitates the handling of the barrier layers3and4. Further, since the organic layers5are placed inside in the barrier layers3and4, the organic layers5can abut the quantum dot layer2. Accordingly, as withFIG. 2, when the quantum dot layer2is formed by application, the formation can be facilitated, and the adhesion between the quantum dot layer2and the organic layers5can be improved. Further, inFIG. 3, the inorganic layers6are provided in the barrier layers3and4, resulting in excellent barrier properties even when the barrier layers3and4are thin. The barrier properties here refer to water vapor transmission properties and gas barrier properties. In this embodiment, the moisture vapor transmission rate of the barrier layers3and4can be made lower than 9 g/(m2·d) even when the thickness of the barrier layers3and4is as small as several tens of micrometers. The gas barrier properties may be evaluated with oxygen transmission rate. InFIG. 3, the barrier layers3and4each have a two-layer structure having a single layer of the organic layer5and a single layer of the inorganic layer6; alternatively, they may each have a structure in which a plurality of the organic layers5and a plurality of the inorganic layers6alternately stacked (provided that the innermost layers of the barrier layers3and4are preferably the organic layers5).

InFIG. 4A, the barrier layers3and4are each formed with a layered structure composed of a plurality of the organic layers5and the inorganic layer6sandwiched between the organic layers5. The organic layers5are preferably PET (polyethylene terephthalate) films. Further, the organic layers5preferably contain a diffusion agent. Alternatively, a diffusion promoting layer can be formed between the quantum dot layer2and the organic layers5. The inorganic layer6is preferably a SiO2layer. Further, the inorganic layer6may be a layer of silicon nitride (SiNx), aluminum oxide (Al2O3), titanium oxide (TiO2), or silicon oxide (SiO2), or a laminate thereof. InFIG. 4A, the barrier layers3and4each have a three-layer structure composed of two organic layers5and one inorganic layer6; alternatively, they may each have a structure composed of five or more layers.

InFIG. 4A, both the benefits from the barrier structure shown inFIG. 2and the benefits from the barrier structure shown inFIG. 3can be achieved. Specifically, as shown inFIG. 4A, the innermost layers and the outermost layers in the barrier layers3and4are formed from the organic layers5. Accordingly, the handling of the barrier layers3and4can be more effectively facilitated. In addition, this makes it possible to effectively achieve higher adhesion between the barrier layers3and4and the quantum dot layer2, easier formation of the quantum dot layer2, and higher barrier properties of the barrier layers3and4.

Note that as an alternative to the structure inFIG. 4A, for example, the barrier layers3and4may each have a layered structure of inorganic layer6-organic layer5-inorganic layer6. In this geometry, a plurality of the inorganic layers6are placed in each of the barrier layers3and4, which allows the barrier layers3and4to have more excellent barrier properties.

In the above structure, the barrier layers3and4are each placed on either side of the quantum dot layer2. Specifically, the barrier layers3and4can each have a different layered structure such as the single layer structure shown inFIG. 2or the layered structures shown inFIG. 3andFIG. 4A; and the barrier properties, typified by the moisture vapor transmission rate, of the barrier layers3and4may have the nominal values, for example.

On the other hand, inFIG. 4B, a plurality of barrier layers3,4,3′, and4′ are stacked on both sides of the quantum dot layer2. For example, the barrier layers3,4,3′, and4′ are each formed with a single layer structure or a layered structure shown inFIG. 2,FIG. 3, andFIG. 4A. The barrier layer3is joined to the barrier layer3′ and the barrier layer4is joined to the barrier layer4′ using an adhesive or the like. For example, the barrier layers3,4,3′, and4′ each have a layered structure of organic layer (for example, a PET film) inorganic layer (for example, SiO2). In the laminate, the inorganic layers are provided inside to be closer to the quantum dot layer2, whereas the organic layers are provided on the outer sides. Specifically, inFIG. 4B, for example, the laminate has barrier layer4′ (organic layer-inorganic layer), barrier layer4(organic layer-inorganic layer), quantum dot layer2, barrier layer3(inorganic layer-organic layer) and barrier layer3′ (inorganic layer-organic layer), stacked in this order from the lower side to the upper side in the diagram.

When the plurality of the barrier layers3,4,3′, and4′ are stacked as described above, variations can be reduced and the barrier properties can be steadily improved even when the barrier layers3,4,3′, and4′ used have low barrier properties.

Further, in the above structures, the barrier layers placed on both sides of the quantum dot layer2have symmetric layered structures; alternatively, the barrier layers may have asymmetric structures.

In addition, the following processes may be performed to improve the light scattering capability of the wavelength converting member1. Specifically, in the embodiment shown inFIG. 5, surfaces of the barrier layers3and4are matted. For example, the barrier layers3and4can be each formed as a laminate of inorganic layer-organic layer-matted layer. In such a structure, surfaces3aand4aof the respective barrier layers3and4have irregularities. Alternatively, a surface of one of the barrier layer3and the barrier layer4may be matted. Yet alternatively, a light-scattering agent8may be contained in the quantum dot layer2as shown inFIG. 6. Examples of the material of the light-scattering agent8can include, but not limited to, fine particles of BN, AIN, or the like. By way of example, the light-scattering agent8may be contained at 1 wt % to 10 wt % with respect to the quantum dot layer2. Further, the light-scattering agent8may be contained in the barrier layers3and4. In this case, the concentration of the light-scattering agent8contained in the quantum dot layer2may be equal to or different from the concentration of the light-scattering agent contained in the barrier layers3and4. The barrier layers3and4shown inFIG. 5andFIG. 6may have any one of the structures inFIG. 2toFIG. 4B. For example, a surface of one of the barrier layer3and the barrier layer4may be matted; the quantum dot layer2may contain the light-scattering agent8; and the barrier layer3or the barrier layer4may contain the light-scattering agent8.

In another embodiment shown inFIG. 7, the quantum dot layer2contains a thickening agent9. Examples of the thickening agent9can include, but not limited to, carboxyvinyl polymers-based, carboxymethyl cellulose-based, methyl ether acrylate copolymers-based; and bentonite (aluminum silicate)-based or hectorite (magnesium silicate)-based additives. When the thickening agent9is contained, the viscosity of the resin composition forming the quantum dot layer2can be appropriately adjusted, and the quantum dot layer2can easily be formed with a given thickness and a given shape.

Further, in this embodiment, the quantum dot layer2preferably contains a dispersant to improve the dispersibility of the quantum dots contained in the quantum dot layer2. Examples of the material of the dispersant used include, but not limited to, additives of epoxy resins, polyurethanes, polycarboxylates, acid-formaldehyde condensate polymers of naphthalenesulfonic, polyethylene glycols, compounds of partial alkyl ester of a polycarboxylic acid, polyethers, polyalkylene polyamines, alkyl sulfonate salts, quaternary ammonium salts, higher alcohol alkylene oxides, polyhydric alcohol esters, alkyl polyamines, or polyphosphates. DISPERBYK® available from BYK Japan KK can be given as a specific example.

As shown in Table 1 below, when quantum dots were mixed and dispersed in a liquid resin, the viscosity was found to decrease. When the viscosity was measured, the shear rate was 15/s to 500/s. The unit of the viscosity shown in the table is (mPa·s).

TABLE 1Resin only (without quantum dots)Quantum dots mixed in Resin6603317089063367

Accordingly, in order to keep the viscosity within a predetermined range for facilitating the formation of the quantum dot layer2, the viscosity is preferably adjusted for example by adding the above thickening agent. Note that the values of the viscosity shown in Table 1 are mere examples, and the viscosity can be adjusted to a required level as appropriate.

In the embodiments shown inFIG. 1AtoFIG. 7, the barrier layers are placed at least on both the top and bottom of the quantum dot layer2, and no limitation is placed on the provision of the barrier layers at edges on the sides of the quantum dot layer2(the right and left sides of the quantum dot layer2in the diagram). On the other hand, in structures described below, a barrier layer is formed around the entire periphery of the quantum dot layer2. FIG.8is a longitudinal sectional view of a wavelength converting member exemplifying an eighth embodiment of the present invention. The entire periphery of the quantum dot layer2is covered with the barrier layer81, which allows the entire periphery of the quantum dot layer2to be protected. Accordingly, the durability can be improved as compared with the case where only both the top and bottom of the quantum dot layer2are protected as shown inFIGS. 1A to 1C. Thus, deterioration of the quantum dot layer2can suitably be suppressed. As shown inFIG. 8, a wrap starting end82and a wrap finishing end83of the barrier layer81overlap on a top surface80of the quantum dot layer2. It will be appreciated that the position where the wrap starting end82and the wrap finishing end83overlap may be on any one of the top surface80, the bottom surface, the right side, and the left side of the quantum dot layer2. For the region where the wrap starting end82and the wrap finishing end83overlap, the wrap starting end82and the wrap finishing end83are joined for example by thermocompression bonding and bonding. In the structure shown inFIG. 8, the wrap starting end82and the wrap finishing end83overlap in a position facing one face of the quantum dot layer2, so that the barrier layer81can be used without waste.

Without limiting the overall shape of a wavelength converting member60shown inFIG. 8, the wavelength converting member60may be shaped like a stick, a block, or a chip, or may be shaped like a sheet obtained by extending the length dimension of the quantum dot layer2in the lateral direction in the diagram shown inFIG. 8,

FIG. 9is a longitudinal sectional view of a wavelength converting member exemplifying a ninth embodiment of the present invention. InFIG. 9, the barrier layer81covers the entire periphery of the quantum dot layer2, and the wrap starting end82and the wrap finishing end83of the barrier layer81are joined for example by thermocompression bonding at an edge on one side of the quantum dot layer2(the right side of the quantum dot layer2in the diagram). Thus, the structure in which the wrap starting end82and the wrap finishing end83of the barrier layer81are joined at an edge on one side of the quantum dot layer2allows the wrap starting end82and the wrap finishing end83to be joined in a region without affecting the quantum dot layer2. For example, when the wrap starting end82and the wrap finishing end83are joined by thermocompression bonding, the quantum dot layer2can be prevented from being heated, and thermal effects on the quantum dot layer2can be suppressed. Alternatively, the wrap starting end82and the wrap finishing end83may be joined by bonding.

FIG. 10is a longitudinal sectional view of a wavelength converting member exemplifying a tenth embodiment of the present invention. InFIG. 10, the quantum dot layer2is provided on a lower barrier layer85, and an upper barrier layer86is provided to cover the lower barrier layer85and the quantum dot layer2. The barrier layers85and86placed on both the top and bottom of the quantum dot layer2are joined to each other at edges on the sides of the quantum dot layer2(the right and left sides of the quantum dot layer2in the diagram) for example by bonding or thermocompression bonding. Since the barrier layers85and86are joined to each other at the edges of the quantum dot layer2, effects of the joining process on the quantum dot layer2can be suppressed. Further, in the structure ofFIG. 10, unlike inFIG. 8andFIG. 9, the barrier layers85and86are two separate layers, and the quantum dot layer2is sandwiched between the barrier layers85and86. Accordingly, it is not necessary to wrap the entire periphery of the quantum dot layer2with the barrier layer81as in the structures shown inFIG. 8andFIG. 9. Therefore, the wavelength converting member60can easily be formed with the barrier layers being formed on the entire periphery of the quantum dot layer2, and the structure shown inFIG. 10is suitable for mass production of the wavelength converting member60.

InFIG. 1AtoFIG. 10, for example, the quantum dot layer2is formed from a molding. Specifically, the quantum dot layer2is formed for example by injection molding, and the barrier layer(s) are provided on the molding of the quantum dot layer2. When the quantum dot layer2is formed from a molding, wavelength converting members having various shapes can be easily and suitably formed. In this embodiment, the quantum dot layer2is not necessarily formed from a molding, and may be formed by application. In the case of application, a barrier layer is previously prepared, and the quantum dot layer2is applied to the barrier layer. The application can be performed for example by inkjet printing or a dispenser method. In particular, inkjet printing is preferred.

InFIG. 11toFIG. 13, a quantum dot layer62is formed by inkjet printing, in a wavelength converting member61shown inFIG. 11, the quantum dot layer62is formed by inkjet printing, and the structure of the barrier layer81provided on the quantum dot layer62is the same as that inFIG. 8. Further, in the wavelength converting member61shown inFIG. 12, the quantum dot layer62is formed by inkjet printing, and the structure of the barrier layer81provided on the quantum dot layer62is the same as that inFIG. 9. Further, in the wavelength converting member61shown inFIG. 13, the quantum dot layer62is formed by inkjet printing, and the structure of the barrier layers81provided on the quantum dot layer62is the same as that inFIG. 10.

When the quantum dot layer62is formed by inkjet printing, the quantum dot layer62can be formed with a significantly thin thickness. As a result, as shown inFIG. 11toFIG. 13, a surface61aof the wavelength converting member61can be planarized.

For example, the wavelength converting members1,60, and61of the disclosed embodiments can each be incorporated into a back light unit55shown inFIG. 15. InFIG. 15toFIG. 17, the wavelength converting member1is illustrated as an example. InFIG. 15, the back light unit55is configured to have a plurality of light emitting devices20(LEDs) and the wavelength converting member1of this embodiment that faces the light emitting devices20. As shown inFIG. 15, the light emitting devices20are supported on a surface of a support52. InFIG. 15, the back light unit55is placed on the back side of a display area54of, for example, a liquid crystal display, and constitutes part of a display device50.

Although not shown inFIG. 15, in addition to the wavelength converting member1, a diffuser panel for diffusing light, and other sheets may be provided between the light emitting devices20and the display area54.

When the wavelength converting member1is formed like a sheet as shown inFIG. 14, the wavelength converting member1in the form of a single sheet may be placed between the light emitting devices20and the display area54as shown inFIG. 15. Alternatively, for example, a plurality of the wavelength converting members1may be joined together to achieve a predetermined size. A structure in which the plurality of wavelength converting members1are joined together by tiling is hereinafter referred to as a compound wavelength converting member.

Here, a structure in which the compound wavelength converting member is placed instead of the wavelength converting member1of the display device50inFIG. 15, and a diffuser panel is placed between the light emitting devices20and the compound wavelength converting member, that is, a structure of light emitting devices20-diffuser panel-compound wavelength converting member-display area54will be discussed. With such a structure, light emitted from the light emitting devices20and diffused by the diffuser panel enters the compound wavelength converting member. Since the light diffused by the diffuser panel enters the compound wavelength converting member, the distribution of the light intensity depending on the distance from the light emitting devices20can be reduced. The distance between the light emitting devices20and the compound wavelength converting member is longer than in the case where the diffuser panel is not provided, which reduces effects of heat radiated from the light emitting devices20on the quantum dots contained in the compound sheet.

On the other hand, as shown inFIG. 16, the structure may have light emitting devices20-compound wavelength converting member21-diffuser panel22-display area54placed in this order. Accordingly, even when irregular reflection occurs at the joints between the wavelength converting members1or the emission color varies due to deterioration of quantum dots caused by water vapor having entered through the joints, color unevenness in the display of the display area54can be suitably reduced. Specifically, since the light output from the compound wavelength converting member21is diffused by the diffuser panel22and then enters the display area54, color unevenness in the display of the display area54can be reduced.

When the compound wavelength converting member21is used, a diffuser panel is preferably placed on the light emission side of the compound wavelength converting member21not only when the compound wavelength converting member21is used for the display device shown inFIG. 16, but also when the compound wavelength converting member21is used for example for a lighting.

Alternatively, as shown inFIG. 17, the wavelength converting member1of this embodiment may be provided at least either on a surface of a light guide plate40or between the light guide plate40and light emitting devices20to serve as a light guide member. As shown inFIG. 17, the light emitting devices20(LEDs) are placed to face the light guide plate40. Note that the use of the wavelength converting member1of the embodiments is not limited to those shown inFIG. 15,FIG. 16, andFIG. 17.

In the disclosed embodiments, change in the light emission intensity of the wavelength converting member1over time can effectively be reduced as compared with conventional techniques. Accordingly, when the wavelength converting member1of the disclosed embodiments is used for the back light unit55, the light guide member, etc., the wavelength conversion characteristics can be made stable and the lifespan of the back light unit55and the light guide member can be extended.

Further, the wavelength converting member i of this embodiment can be flexible. This allows the wavelength converting member1to be suitably placed for example on a curved surface.

Note that the wavelength converting member1of this embodiment can also be used for a lighting device, a light source unit, a light diffusion apparatus, a light reflector system, etc. other than the back light unit or the light guide member described above.

Further, inFIG. 15,FIG. 16, andFIG. 17, a wavelength converting member61in which one of the quantum dot layers62shown inFIG. 11toFIG. 13is formed by inkjet printing can be used. The wavelength converting members1,60, and61shown inFIG. 1toFIG. 13may each be placed inside a glass capillary.

FIG. 18is a conceptual diagram for illustrating apparatus for producing a wavelength converting member of this embodiment. A shown inFIG. 18, the apparatus is configured to have a first web roll30for feeding a resin film10to be the barrier layer3and a second web roll31for feeding a resin film11to be a barrier layer4, a take-up roll32, and a pressure contact portion35composed of a pair of nip rolls33and34, a coating means36, and a heating unit38.

As shown inFIG. 18, the resin film10having a moisture vapor transmission rate of less than 9 g/(m2·d) is fed from the first web roll30, and a surface of the resin film10is coated with a resin composition37containing quantum dots using the coating means36. The resin composition37can be applied for example by an application method using a known application coater or an impregnation coater. Examples of the coater include a gravure coater, a dip coater, and a comma knife coater. Alternatively, the resin composition37can be applied by inkjet printing.

As shown inFIG. 18, the resin film10of which surface is coated with the resin composition37is heated by the heating unit38provided with heaters, etc. This leads to evaporation of a solvent contained in the resin composition37, and the quantum dot layer2is solidified to a certain extent at this time.

Subsequently, as shown inFIG. 18, the resin film11having a moisture vapor transmission rate of less than 9 g/(m2·d) fed from the second web roll31abuts an exposed surface of the quantum dot layer2, and a layered structure of resin film11-quantum dot layer2-resin film10is pressured and welded between the nip rolls33and34composing the pressure contact portion35. In the pressure contact portion35, the boundaries of the quantum dot layer2and the resin films10and11are fixed by thermocompression bonding.

A sheet member39composed of resin film11-quantum dot layer2-resin film10is wound on the take-up roll32. The wound sheet member39is cut into a predetermined size, thereby obtaining the wavelength converting member1shaped like a sheet.

In the above production method, the quantum dot layer2is formed by application on the resin film10, and the thickness of the quantum dot layer2formed can be roughly from 10 μm to 500 μm. Further, the thickness of the resin films10and11is roughly from a few tens of micrometers to 1000 micrometers, so that the thickness of the wavelength converting member1is roughly from 50 μm to 2500 μm. Note that the thickness of the quantum dot layer2and the thickness of the wavelength converting member1are not limited.

The resin films10and11illustrated inFIG. 18each have a single layer of the organic layer5shown inFIG. 2or a layered structure having the organic layer5and the inorganic layer6shown in one ofFIG. 3andFIGS. 4A and 4B. Preferably, the inorganic layer6is provided between the plurality of organic layers5as shown inFIG. 4A. Specifically, the resin films10and11preferably each have a layered structure of PET film-SiO2layer-PET film.

Alternatively, a stack of a plurality of resin films can be fed to be placed on both surfaces of the quantum dot layer to provide a structure in which the a plurality of barrier layers are placed on both sides of the quantum dot layer as shown inFIG. 4B.

The matting process shown inFIG. 5is performed on one or both of the surfaces of the sheet member39wound on the take-up roll32shown inFIG. 18or is performed on both surfaces of the wavelength converting member1shown inFIG. 14, formed by cutting the sheet member39into a predetermined size.

The matting process cart be performed for example by sandblasting the sheet surface, or by coating the sheet surface with a mat layer, but is not limited thereto. Further, as shown inFIG. 6, in order to obtain the quantum dot layer2containing the light-scattering agent8, the light-scattering agent8can be added to the resin composition37to be applied with the coating means36shown inFIG. 18. When the thickening agent9is contained in the resin composition37to be applied with the coating means36shown inFIG. 18, the viscosity of the resin composition37can be suitably adjusted. The viscosity can be adjusted to, for example, around several hundreds of mPa·s to several thousands of mPa·s, without limitation. Suitably adjusting the viscosity of the resin composition37to optimize the fluidity of the resin composition37allows for the formation of the quantum dot layer2with a generally uniform thickness on a surface of the resin film10.

In the production process shown inFIG. 18, the quantum dot layer2is formed by application to a surface of the resin film10; alternatively, the resin films10and11may be stuck to both surfaces of the molding of the quantum dot layer2having previously been formed. The quantum dot layer2may be formed using a method such as injection molding, extrusion molding, blow molding, thermoforming, compression molding, calendaring, blown film extrusion, or casting. The thickness of the molding of the quantum dot layer2cart be around 10 μm to 500 μm. For example, the molding of the quantum dot layer2can be formed with a thickness of approximately 300 μm. The resin films10and11can be stuck to both sides of the molding of the quantum dot layer2by thermocompression bonding, etc. Note that adhesive layers may be provided between the quantum dot layer2and the resin films10and11.

Methods for making the wavelength converting member1into a film include methods using a coating machine and methods using a molding machine. Curing methods using a coating machine include UV curing and heat curing.

In this embodiment, the resin films10and11having a moisture vapor transmission rate of less than 9 g/(m2·d) can suitably and easily be placed on both sides of the quantum dot layer2. This makes it possible to easily produce a wavelength converting member1which allows change in the light emission intensity to be effectively inhibited as compared with conventional techniques.

Next, a method of producing the wavelength converting member inFIG. 8will be described with reference toFIG. 19.FIG. 19is a conceptual diagram for illustrating a method of producing a wavelength converting member of the eighth embodiment of the present invention. As shown in the left diagram inFIG. 19, for example, the quantum dot layer2is formed from a molding. Next, in the middle diagram inFIG. 19, the barrier layer81is placed on the entire periphery of the quantum dot layer2. Further, as shown in the right diagram inFIG. 19, the wrap starting end82and the wrap finishing end83overlap on one side (top surface80inFIG. 19) of the quantum dot layer2and the wrap starting end82and the wrap finishing end83are thermocompression bonded using a thermocompression bonding member90. Thermocompression bonding can be performed for example by while heating, pressing the wrap starting end82and the wrap finishing end83or joining them under pressure using rollers. Alternatively, the wrap starting end82and the wrap finishing end83can be joined using an adhesive instead of thermocompression bonding. The production method shown inFIG. 19enables easily and suitably covering the entire periphery of the quantum dot layer2with the barrier layer81.

A method of producing the wavelength converting member inFIG. 9will be described with reference toFIG. 20.FIG. 20is a conceptual diagram for illustrating a method of producing a wavelength converting member of the ninth embodiment of the present invention. As shown in the left diagram inFIG. 20, for example, the quantum dot layer2is formed from a molding. In the middle diagram inFIG. 20, with the wrap starting end82of the barrier layer81being located at an edge on one side of the quantum dot layer2, the barrier layer81is wrapped around the quantum dot layer2, and the wrap starting end82and the wrap finishing end83overlap at the edge of the quantum dot layer2as shown in the right diagram ofFIG. 20. The wrap starting end82and the wrap finishing end83are then thermocompression bonded using thermocompression bonding member90. As shown inFIG. 20, the wrap starting end82and the wrap finishing end83of the barrier layer81overlap at an edge on one side of the quantum dot layer2, which can reduce effects caused by joining the wrap starting end82and the wrap finishing end83for example by thermocompression bonding on the quantum dot layer2(thermal effects, etc.). Thus, the quantum dot layer2can be prevented from being deteriorated in the step of forming the barrier layer81. Note that the wrap starting end82and the wrap finishing end83may be joined by bonding.

A method of producing the wavelength converting member inFIG. 10will be described with reference toFIG. 21.FIG. 21is a conceptual diagram for illustrating a method of producing a wavelength converting member of the tenth embodiment of the present invention. In the step shown inFIG. 21A, a plurality of the quantum dot layers2are placed at intervals on the barrier layer85. For example, the quantum dot layers2are each formed from a molding, and the plurality of the quantum dot layers2are arranged on the barrier layer85. Here, the quantum dot layers2are preferably fixed to the barrier layer85by bonding.

Subsequently, in the step shown inFIG. 21B, the barrier layer86is placed over the surface of the barrier layer85and the quantum dot layers2. Preferably, an adhesive layer is previously applied to the inner surface of the barrier layer86(facing the barrier layer85and the quantum dot layers2), and the barrier layer85is stuck to the barrier layer86with the quantum dot layers2therebetween. Alternatively, the barrier layer85and the barrier layer86can be stuck together by thermocompression bonding. As shown by the chain lines inFIG. 21B, the joined barrier layers85and86are cut between the adjacent quantum dot layers2thereby isolating the quantum dot layers2. Thus, a plurality of the wavelength converting members60can be obtained at the same time.

According to the method of producing the wavelength converting member60shown inFIG. 21, since the barrier layers85and86overlap, the barrier layers can be placed on the entire periphery of the quantum dot layers2, so that the wavelength converting members60in each of which the barrier layer is formed on the entire periphery of the quantum dot layers2can be easily and suitably produced, and the method is suitable for mass production of the wavelength converting members60.

Using the production methods shown inFIG. 19toFIG. 21, the entire periphery of the quantum dot layer(s)2can be covered by the barrier layer, the entire periphery of the quantum dot layer(s)2can be suitably protected by the barrier layer(s), and the durability can be more effectively improved. Thus, deterioration of the quantum dot layer(s)2can be more suitably suppressed.

For example, the quantum dot layers(s)2shown inFIG. 19toFIG. 21are formed from a molding; alternatively, the quantum dot layer(s)2may be formed by inkjet printing as shown inFIG. 11toFIG. 13. In the case of inkjet printing, a resin composition in which quantum dots are dispersed is discharged onto the top of the barrier layer by inkjet printing. The discharged resin composition is preferably heated for stabilization. The heating temperature is preferably 30° C. to 80° C. and more preferably 30° C. to 50° C.

In this embodiment, the resin films10and11(barrier layers) each have an organic layer, and it is preferable that the organic layer abuts the quantum dot layer(s)2in the production process. Thus, the quantum dot layer(s)2can be formed on a surface of the organic layer with high wettability, the quantum dot layer(s)2can be formed more easily, and the adhesion between the barrier layer and the quantum dot layer(s)2can be improved due to the affinity therebetween.

Further, the layered structure of the resin films10and11each having a plurality of organic layers and an inorganic layer provided between the organic layers allows the organic layers to be placed on both surfaces of the resin films10and11. This improves handling, and allows for easier formation of the quantum dot layer2on the surfaces of the resin films10and11. In addition, the inorganic layers included in the barrier layers make it possible to effectively improve barrier properties of the resin films10and11(barrier layers).

Alternatively, the resin films10and11can each have a layered structure composed of a plurality of inorganic layers and an organic layer provided between the inorganic layers. Further, a plurality of resin films can be placed by being stacked. In this case, the resin films10and11can be joined by sticking them together using an adhesive or by thermocompression bonding.

EXAMPLES

The present invention will be described in detail below with Examples and Comparative Examples performed to demonstrate the effects of the present invention. Note that the present invention is not limited to the following examples.

In Sample 1 to Sample 8 of Examples, an elastomer was dissolved in organosilane, thereby obtaining a QD ink (resin composition) in which quantum dots having a fluorescence wavelength of approximately 520 nm (green) (also referred to as “green quantum dots”) were dispersed. For the elastomer, HYBRAR® 7311 from KURARAY CO., LTD. was used.

A laminate of glass-QD ink-barrier layer was obtained. Heat treatment was performed to evaporate the solvent of the QD ink, thereby obtaining a quantum dot layer. In this case, the following structure was employed for the barrier layer.

A barrier layer formed as a film having a three-layer structure of PET film-SiO2layer-PET film with a moisture vapor transmission rate of 6×10−3g/(m2·d). The thickness of the barrier layer was 49 μm,

A barrier layer having a three-layer structure of PET film/SiO2layer/PET film with a moisture vapor transmission rate of 9 g/(m2·d). The thickness of the barrier layer was 50 μm.

Laminates using the barrier layers of Sample 1 to Sample 3 above were subjected to an endurance test under conditions of temperature: 60° C. and humidity: 90%. The light emission intensity was measured using a total luminous flux measurement system available from Otsuka Electronics Co., Ltd. by measuring the total luminous flux of the light caused in each sample by blue (wavelength: 450 nm) LED excitation light.

FIG. 23is a graph showing the relationship the elapsed time and the blue light intensity (450 nm area) for each sample. Here, the blue light intensity corresponds to the area of the emission peak observed at a wavelength of 450 nm.

As shown inFIG. 23, the blue light intensity (450 nm area) was found to gradually increase over time in Sample 2 and Sample 3. In other words, that the intensity of blue light was found to increase over time in Sample 2 and Sample 3. On the other hand, it was found that the blue light intensity (450 nm area) was constant in Sample 1, and the light intensity of blue light did not change over time. Further, it was found for Sample 1 that while the initial blue light intensity (time: 0 h) and the blue light intensity after 150 hours were 0.0075 (time: 0 h) and 0.0070 (150 h), respectively; thus, the blue light intensity hardly changed, and the change in the blue light intensity was within 10%. Here, the change in the blue light intensity is represented by [(initial blue light intensity−blue light intensity after 150 hours)/initial blue light intensity]×100(%) (absolute value).

FIG. 24is a graph showing the relationship the elapsed time and the green light intensity (green area) for each sample. Here, the green light intensity corresponds to the area of the emission peak observed at a wavelength of 520 nm. As shown inFIG. 24, in Sample 2 an Sample 3, the green light intensity (green area) was found to rapidly decrease over time. The increased blue light intensity and the reduced green light intensity as in Sample 2 and Sample 3 mean that the green quantum dots deteriorated over time. On the other hand, it was found for Sample 1 that the blue light intensity (450 nm area) did not change over time, and the reduction in the green light intensity (green area) over time was successfully made smaller compared with Sample 2 and Sample 3. Further, it was found for Sample 1 that the initial green light intensity (time: 0 h) and the green light intensity after 150 hours were 0.0078 (time: 0 h) and 0.0039 (150 h), respectively; thus, the change over time was smaller compared with Sample 2 and Sample 3, and the change in the green light intensity was within 50%. Here, the change in the green light intensity is represented by [(initial green light intensity−green light intensity after 150 hours)/initial green light intensity]×100(%) (absolute value).

The measurement results presented inFIG. 23andFIG. 24show that deterioration of the quantum dots can be suitably suppressed with the use of the barrier layer of Sample 1, thereby effectively inhibiting the change in the light emission intensity over time. Based on the measurement results shown inFIG. 23andFIG. 24, the moisture vapor transmission rate of the barrier layer was set to a value lower than 9 g/(m2·d). Further, the moisture vapor transmission rate range of the barrier layer of Sample 1, that is, 6×10−3g/(m2·d) or less is assumed to be the most preferable range.

Subsequently, the barrier films were evaluated. In the evaluation, barrier layers of Sample 1 above, Sample 5 in which the moisture vapor transmission rate was 1.6×10−2g/(m2·d), and Sample 6 in which the moisture vapor transmission rate was 8.4×10−3g/(m2·d) were used. The light transmittance (%) was 86.8 (total light) for Sample 1, 92.5 (wavelength: 450 nm) for Sample 5, and 90.6 (wavelength: 450 nm) for Sample 6.

FIG. 25is a graph showing the relationship the elapsed time and the x-coordinate of the CIE color space chromaticity diagram for each sample. Sample 4 is a sample without barrier layers (the quantum dot layer formed from a molding).

In the evaluation, both sides of the quantum dot layer were sandwiched between the barrier films of the above samples, and light emitting devices (LEDs) were placed on the side of one of the barrier films with a diffuser panel provided therebetween. Measurements were performed from the side of the other barrier film using a spectrometer.

FIG. 22is a schematic view of a light emission testing unit used in experiments. Part of the light emission testing unit is shown by a longitudinal sectional view. As shown inFIG. 22, a light emission testing unit56was provided with the light emitting devices20(LEDs) and Sample S being placed in a position facing the light emitting devices20. Each sample in the experiments was a sheet, in which a quantum dot layer was sandwiched between the above barrier films, and the end faces of the barrier films were bonded for example with an epoxy bond and stuck together using aluminum tape. The light emitting devices20were supported on a surface of the support52, and a diffuser panel22was provided between the light emitting devices20and Sample S. All sides of the light emitting devices20were surrounded by a cylindrical reflective sheet23, and the diffuser panel22was placed on the top of the reflective sheet23. The light emitted from the light emitting devices20was diffused by the diffuser panel22and entered Sample S. The reflective sheet23had a box shape with an opening of for example 3 cm square, and the reflective sheet23had a height (distance of the diffuser panel22from the support52) of for example 4 cm. The light emitted from the light emitting devices20was then made to enter Sample S through the diffuser panel22, and the light output from the top of Sample S was measured using the total luminous flux measurement system. Note that the experiment was performed under conditions of temperature: 60° C. and humidity: 90%. Using the light emission testing unit56shown inFIG. 22, the light emission intensity of the light emitting devices20through Sample S can be accurately measured.

As shown inFIG. 25, the x-coordinate did not change over time for Samples 1, 5, and 6 except for Sample 4 without barrier layers. In Sample 1 and Sample 5, the initial x-coordinate (time: 0 h) and the x-coordinate after 200 hours were 0.208 (time: 0 h) and 0.210 (200 h), respectively; thus, the change in the x-coordinate was found to be within 1%. in Sample 6, the initial x-coordinate (time: 0 h) and the x-coordinate after 200 hours were 0.210 (time: 0 h) and 0.213 (200 h), respectively; thus, the change in the x-coordinate was found to be within 2%. Here, the x-coordinate change is represented by [(initial x-coordinate−x-coordinate after 200 hours)/initial x-coordinate]×100(%) (absolute value)

FIG. 26is a graph showing the relationship the elapsed time and the y-coordinate of the CIE color space chromaticity diagram for each sample. As shown inFIG. 26, the y-coordinate did not change over time in Samples 1, 5, and 6 except for Sample 4 without barrier layers. In Sample 1 and Sample 5, the initial y-coordinate (time: 0 h) and the y-coordinate after 200 hours were 0.170 (time: 0 h) and 0.190 (200 h), respectively; thus, the change in the y-coordinate was found to be within 15%. In Sample 6, the initial y-coordinate (time: 0 h) and the y-coordinate after 200 hours were 0.170 (time: 0 h) and 0.195 (200 h), respectively; thus, the change in the y-coordinate was found to be within 15%. Here, the y-coordinate change is represented by [(initial y-coordinate−y-coordinate after 200 hours)/initial y-coordinate]×100(%) (absolute value).

FIG. 27is a graph showing the relationship the elapsed time and the normalized illumination for each sample. As shown inFIG. 27, the normalized illumination did not change over time in Samples 1, 5, and 6 except for Sample 4 without barrier layers. In this result, the normalized illumination changed by ±30% over 200 hours.

Next, a barrier layer having a moisture vapor transmission rate of 10−2g/(m2·d) was used as Sample 7, and a barrier layer having a moisture vapor transmission rate of 10−1g/(m2·d) was used as Sample 8. The moisture vapor transmission rates of the barrier layers had the nominal values. Further, a sheet described in the description ofFIG. 22above was formed and the spectrum was measured over time using the light emission testing unit ofFIG. 22.

FIG. 28is a graph showing the relationship the elapsed time and the x-coordinate of the CIE color space chromaticity diagram for each sample. In the experiments, in addition to Sample 7 and Sample 8, Sample 1 and Sample 2 described above were used.

As shown inFIG. 28, in Sample 2 having a barrier layer with a moisture vapor transmission rate of 9 g/(m2·d), the x-coordinate changed immediately after the start of the experiment. In Sample 1, Sample 7, an Sample 8, in each of which the barrier layer had a moisture vapor transmission rate of 10−1g/(m2·d) or less, change in the x-coordinate over time was not observed or was very small. In Sample 1 and Sample 8, the initial x-coordinate (time: 0 h) and the x-coordinate after 1100 hours were 0.220 (time: 0 h) and 0.225 (1100 h), respectively; thus, the change in the x-coordinate was found to be within 5%. In Sample 7, the initial x-coordinate (time: 0 h) and the x-coordinate after 1100 hours were 0.219 (time: 0 h) and 0.219 (1100 h), respectively; thus, the change in the x-coordinate was found to be 0%. Here, the x-coordinate change is represented by [(initial x-coordinate−x-coordinate after 1100 hours)/initial x-coordinate]×100(%) (absolute value)

FIG. 29is a graph showing the relationship the elapsed time and the y-coordinate of the CIE color space chromaticity diagram for each sample. As shown inFIG. 29, change in the y-coordinate over time was not observed or was very small in Samples 1, 7, and 8 except for Sample 2 having a barrier layer with a moisture vapor transmission rate of 9 g/(m2·d). In Sample 1 and Sample 8, the initial y-coordinate (time: 0 h) and the y-coordinate after 1100 hours were 0.190 (time: 0 h) and 0.210 (1100 h), respectively; thus, the change in the y-coordinate was found to be within 15%. In Sample 7, the initial y-coordinate (time: 0 h) and the y-coordinate after 1100 hours were 0.160 (time: 0 h) and 0.195 (1100 h), respectively; thus, the change in the y-coordinate was found to be within 25%. Here, the y-coordinate change is represented by [(initial y-coordinate−y-coordinate after 1100 hours)/initial y-coordinate]×100(%) (absolute value)

FIG. 30is a graph showing the relationship the elapsed time and the normalized illumination for each sample. As shown inFIG. 30, change in the normalized illumination over time was not observed or was very small in Samples 1, 7, and 8 except for Sample 2 having a barrier layer with a moisture vapor transmission rate of 9 g/(m2·d). In this result, the normalized illumination changed by ±30% over 200 hours.

From the above experiments, barrier layer(s) having a moisture vapor transmission rate of approximately 0.1 g/(m2·d) or more were found to sufficiently improve durability. Based on the above, the moisture vapor transmission rate of the barrier layer(s) was preferably set to 0.1 g/(m2·d) or less.

Next, experiments were performed using samples in which the barrier layer was formed around the entire periphery of the quantum dot layer(s). In Sample 9 to Sample 14, a QD ink (resin composition) obtained by dissolving an elastomer in organosilane and dispersing quantum dots having a fluorescence wavelength of approximately 520 nm (green) and quantum dots having a fluorescence wavelength of approximately 650 nm (red) (also referred to as “red quantum dots”) therein. For the elastomer, HYBRAR® 7311 from KURARAY CO., LTD. was used. Heat treatment was performed to evaporate the solvent of the QD ink, thereby obtaining a quantum dot layer. For the quantum dot layers used in the experiments, high concentration layers and low concentration layers were prepared. For the barrier layer, a sheet member in which a SiO2layer was formed on a PET film that had a moisture vapor transmission rate of approximately 10−3g/(m2·d) was used. The samples (wavelength converting members) used in the experiments had the following structures.

A wavelength converting member constituted by only a quantum dot layer without barrier layers.

The wavelength converting member shown inFIG. 8. Note that the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded in an overlapping manner on the top surface of the quantum dot layer.

The wavelength converting member shown inFIG. 10. Note that the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded in an overlapping manner at edges on the sides of the quantum dot layer.

The above samples were subjected to an endurance test under conditions of temperature: 60° C. and humidity: 90%. The light emission intensity was measured using a total luminous flux measurement system available from Otsuka Electronics Co., Ltd. by measuring the total luminous flux of the light caused in each sample by blue (wavelength: 450 nm) LED excitation light. First, the experimental results for Sample 9 to Sample 11 using the low concentration quantum dot layers are described.

FIG. 31is a graph showing the relationship the elapsed time and the blue light intensity (450 nm area) for Sample 9 to Sample 11. Here, the blue light intensity corresponds to the area of the emission peak observed at a wavelength of 450 nm.

As shown inFIG. 31, the blue light intensity (450 nm area) was found to gradually increase over time in Sample 9. In other words, the intensity of blue light was found to increase over time in Sample 9. On the other hand, it was found that the blue light intensity (450 nm area) stayed constant in Sample 10 and Sample 11, and the light intensity of blue light was kept unchanged over time. Further, the initial blue light intensity (time: 0 h) and the blue light intensity after 450 hours were 0.0049 (time: 0 h) and 0.0056 (450 h), respectively in Sample 10 and were 0.0053 (time: 0 h) and 0.0053 (450 h), respectively in Sample 11. It was found for Sample 10 and Sample 11 that the blue light intensity after 450 hours hardly changed from the initial blue light intensity (time: 0 h), and the change in the blue light intensity was within 15%. Here, the change in the blue light intensity is represented by [(initial blue light intensity−blue light intensity after 450 hours)/initial blue light intensity]×100(%) (absolute value).

FIG. 32is a graph showing the relationship the elapsed time and the green light intensity (green area) for Sample 9 to Sample 11. Here, the green light intensity corresponds to the area of the emission peak observed at a wavelength of 520 nm. As shown inFIG. 32, in Sample 9, the green light intensity (green area) was found to rapidly decrease in 100 hours from the start of the experiment. The increased blue light intensity and the reduced green light intensity as in Sample 9 mean that the green quantum dots deteriorated over time. On the other hand, it was found that the blue light intensity (450 nm area) did not change over time in Sample 10 and Sample 11, and the reduction in the green light intensity (green area) over time was made smaller compared with Sample 9. Further, the initial green light intensity (time: 0 h) and the green light intensity after 450 hours were 0.0017 (time: 0 h) and 0.0016 (450 h), respectively in Sample 10 and were 0.0022 (time: 0 h) and 0.0023 (450 h), respectively in Sample 11. Further, it was found for Sample 10 and Sample 11 that the change from the initial green light intensity (time: 0 h) to the green light intensity after 450 hours was smaller compared with Sample 9, and the change in the green light intensity was within 10%. Here, the change in the green light intensity is represented by [(initial green light intensity−green light intensity after 450 hours)/initial green light intensity]×100(%) (absolute value).

FIG. 33is a graph showing the relationship the elapsed time and the red light intensity (red area) for Sample 9 to Sample 11, Here, the red light intensity corresponds to the area of the emission peak observed at a wavelength of 650 nm. As shown inFIG. 33, in Sample 9, the red light intensity (red area) was found to rapidly decrease in 50 hours from the start of the experiment. The increased blue light intensity and the reduced red light intensity as in Sample 9 mean that the red quantum dots deteriorated over time. On the other hand, it was found that the blue light intensity (450 nm area) did not change over time in Sample 10 and Sample 11, and the reduction in the red light intensity (red area) over time was successfully made smaller compared with Sample 9. Further, the initial red light intensity (time: 0 h) and the red light intensity after 450 hours were 0.0017 (time: 0 h) and 0.0014 (450 h), respectively in Sample 10 and were 0.0022 (time: 0 h) and 0.0018 (450 h), respectively in Sample 11. It was found for Sample 10 and Sample 11 that the change from the initial red light intensity (time: 0 h) to the red light intensity after 450 hours was smaller compared with Sample 9, and the change in the red light intensity was within 25%, Here, the change in the red light intensity is represented by [(initial red light intensity−red light intensity after 450 hours)/initial red light intensity]×100(%) (absolute value).

The experimental results presented inFIG. 31toFIG. 33show that deterioration of quantum dots can be suitably suppressed by covering the entire periphery of the quantum dot layer with the barrier layer, thereby effectively inhibiting the change in the light emission intensity over time.

Subsequently, the barrier films were evaluated.FIG. 34is a graph showing the relationship the elapsed time and the x-coordinate of the CIE color space chromaticity diagram for Sample 9 to Sample 11.

As shown inFIG. 34, the x-coordinate did not change substantially over time in any of the samples. In Sample 10, the initial x-coordinate (time: 0 h) and the x-coordinate after 450 hours were 0.2013 (time: 0 h) and 0.1892 (450 h), respectively; thus, the change in the x-coordinate was found to be within 10%. In Sample 11, the initial x-coordinate (time: 0 h) and the x-coordinate after 450 hours were 0.2080 (time: 0 h) and 0.1998 (450 h), respectively; thus, the change in the x-coordinate was found to be within 5%. Here, the x-coordinate change is represented by [(initial x-coordinate−x-coordinate after 450 hours)/initial x-coordinate]×100(%) (absolute value).

FIG. 35is a graph showing the relationship the elapsed time and the y-coordinate of the CIE color space chromaticity diagram for Sample 9 to Sample 11. As shown inFIG. 35, the y-coordinate of Sample 9 that was not provided with barrier layers significantly changed over time as compared with Sample 9 and Sample 10 in which the entire periphery of the quantum dot layer was surrounded by the barrier layer. In Sample 10, the initial y-coordinate (time: 0 h) and the y-coordinate after 450 hours were 0.1428 (time: 0 h) and 0.1210 (450 h), respectively; thus, the change in the y-coordinate was found to be within 20%. In Sample 11, the initial y-coordinate (time: 0 h) and the y-coordinate after 450 hours were 0.1626 (time: 0 h) and 0.1635 (450 h), respectively; thus, the change in the y-coordinate was found to be within 1%. Here, the y-coordinate change is represented by [(initial y-coordinate−y-coordinate after 450 hours)/initial y-coordinate]×100(%) (absolute value).

When Sample 10 and Sample 11 were compared, better results were obtained overall with Sample 11 than with Sample 10. This is probably because in Sample 11, the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded at the edges of the quantum dot layer unlike in Sample 10, so that thermal effects on the quantum dot layer were reduced as compared with the structure of Sample 10.

Next, experimental results for Sample 12 to Sample 14 using the high concentration quantum dot layers are described.

A wavelength converting member constituted by only a quantum dot layer without barrier layers.

The wavelength converting member shown inFIG. 8. Note that the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded in an overlapping manner on the top surface of the quantum dot layer.

The wavelength converting member shown inFIG. 10. Note that the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded in an overlapping manner at edges on the sides of the quantum dot layer.

The above samples were subjected to an endurance test under conditions of temperature: 60° C. and humidity: 90%. The light emission intensity was measured using a total luminous flux measurement system available from Otsuka Electronics Co., Ltd. by measuring the total luminous flux of the light caused in each sample by blue (wavelength: 450 nm) LED excitation light.

FIG. 36is a graph of the measurements of the relationship the elapsed time and the blue light intensity (450 nm area) for Sample 12 to Sample 14.

As shown inFIG. 36, the intensity of blue light was found to increase over time in Sample 12. On the other hand, it was found that the blue light intensity (450 nm area) stayed constant in Sample 13 and Sample 14, and the light intensity of blue light was kept unchanged over time. Further, the initial blue light intensity (time: 0 h) and the blue light intensity after 189 hours were 0.0010 (time: 0 h) and 0.0013 (189 h), respectively in Sample 13 and were 0.0010 (time: 0 h) and 0.0009 (189 h), respectively in Sample 14. It was found for Sample 13 and Sample 14 that the blue light intensity after 189 hours hardly changed from the initial blue light intensity (time: 0 h), or the change in the blue light intensity was smaller than that in Sample 12, and the change in the blue light intensity was within 30%. Here, the change in the blue light intensity is represented by [(initial blue light intensity−blue light intensity after 189 hours)/initial blue light intensity]×100(%) (absolute value).

FIG. 37is a graph showing the relationship the elapsed time and the green light intensity (green area) for Sample 12 to Sample 14. Here, the green light intensity corresponds to the area of the emission peak observed at a wavelength of 520 nm. As shown inFIG. 36andFIG. 37, it was found that changes in the blue light intensity (450 nm area) and the green light intensity (green area) over time in Sample 13 and Sample 14 were successfully made smaller compared with Sample 12. Further, the initial green light intensity (time: 0 h) and the green light intensity after 189 hours were 0.0017 (time: 0 h) and 0.0019 (189 h), respectively in Sample 13 and were 0.0015 (time: 0 h) and 0.0018 (189 h), respectively in Sample 14. It was found for Sample 13 and Sample 14 that the change from the initial green light intensity (time: 0 h) to the green light intensity after 189 hours was within 20%. Here, the change in the green light intensity is represented by [(initial green light intensity−green light intensity after 189 hours)/initial green light intensity]×100(%) (absolute value).

FIG. 38is a graph showing the relationship the elapsed time and the red light intensity (red area) for Sample 12 to Sample 14. Here, the red light intensity corresponds to the area of the emission peak observed at a wavelength of 650 nm. As shown inFIG. 36andFIG. 38, it was found that changes in the blue light intensity (450 nm area) and the red light intensity (red area) over time were successfully made smaller in Sample 13 and Sample 14 compared with Sample 12. Further, the initial red light intensity (time: 0 h) and the red light intensity after 189 hours were 0.0038 (time: 0 h) and 0.0039 (189 h), respectively in Sample 13 and were 0.0037 (time: 0 h) and 0.0040 (189 h), respectively in Sample 14. It was found for Sample 13 and Sample 14 that the change from the initial red light intensity (time: 0 h) to the red light intensity after 189 hours was within 10%. Here, the change in the red light intensity is represented by [(initial red light intensity−red light intensity after 189 hours)/initial red light intensity]×100(%) (absolute value).

The experimental results presented inFIG. 36toFIG. 38show that deterioration of the quantum dots can be suitably suppressed by covering the entire periphery of the quantum dot layer with the barrier layer, thereby effectively inhibiting the change in the light emission intensity over time.

Subsequently, the barrier films were evaluated.FIG. 39is a graph showing the relationship the elapsed time and the x-coordinate of the CIE color space chromaticity diagram for Sample 12 to Sample 14. In Sample 13, the initial x-coordinate (time: 0 h) and the x-coordinate after 189 hours were 0.3729 (time: 0 h) and 0.3524 (189 h), respectively; thus, the change in the x-coordinate was found to be within 10%. In Sample 14, the initial x-coordinate (time: 0 h) and the x-coordinate after 189 hours were 0.3748 (time: 0 h) and 0.3811 (189 h), respectively; thus, the change in the x-coordinate was found to be within 5%. Here, the x-coordinate change is represented by [(initial x-coordinate−x-coordinate after 189 hours)/initial x-coordinate]×100(%) (absolute value).FIG. 40is a graph showing the relationship the elapsed time and the y-coordinate of the CIE color space chromaticity diagram for Sample 12 to Sample 14. In Sample 13, the initial y-coordinate (time: 0 h) and the y-coordinate after 189 hours were 0.3441 (time: 0 h) and 0.3301 (189 h), respectively; thus, the change in the y-coordinate was found to be within 5%. In Sample 14, the initial y-coordinate (time: 0 h) and the y-coordinate after 189 hours were 0.3347 (time: 0 h) and 0.3580 (189 h), respectively; thus, the change in the y-coordinate was found to be within 5%, Here, the y-coordinate change is represented by [(initial y-coordinate−y-coordinate after 189 hours)/initial y-coordinate]×100(%) (absolute value), As shown inFIG. 39andFIG. 40, changes in the x-coordinate and the y-coordinate over time were smaller in Sample 13 and Sample 14 in which the entire periphery of the quantum dot layer was surrounded by the barrier layer compared with Sample 12 that was not provided with barrier layers.

When Sample 13 and Sample 14 were compared, better results were obtained overall with Sample 13 than with Sample 14. This is probably because in Sample 14, the wrap starting end and the wrap finishing end of the barrier layer were thermocompression bonded at the edges on the sides of the quantum dot layer unlike in Sample 13, so that thermal effects on the quantum dot layer were reduced as compared with the structure of Sample 13.

FIG. 41toFIG. 43show the light emission spectrum of light output when blue light of 450 nm was applied to Sample 9 to Sample 11. The horizontal axis represents the wavelength, and the vertical axis represents the light intensity. Each diagram shows the spectra after 0 hours (immediately after the start of the experiment) and after 450 hours. As shown inFIG. 41, in Sample 9, significant change in the spectrum was observed in 450 hours from 0 hours. On the other hand, as shown inFIG. 42andFIG. 43, in Sample 10 and Sample 11, change in the spectrum in 450 hours from 0 hours was smaller compared with Sample 9. It was found for Sample 10 and Sample 11 that since the barrier layer covered the periphery of the quantum dot layer, deterioration of quantum dots was suitably suppressed; thus, change in the light emission intensity over time was effectively inhibited.

FIG. 44toFIG. 46show the light emission spectrum of light output when blue light of 450 rim was applied to Sample 12 to Sample 14. The horizontal axis represents the wavelength, and the vertical axis represents the light intensity. Each diagram shows the spectra after 0 hours (immediately after the start of the experiment) and after 189 hours. As shown inFIG. 44, in Sample 12, significant change in the spectra was observed in 189 hours from 0 hours. On the other hand, as shown inFIG. 45andFIG. 46, the change in the spectrum in 189 hours from 0 hours was found to be smaller in in Sample 13 and Sample 14 compared with Sample 12. It was found for Sample 13 and Sample 14 that since the barrier layer covered the periphery of the quantum dot layer, deterioration of quantum dots was suitably suppressed; thus, change in the light emission intensity over time was effectively suppressed.

INDUSTRIAL APPLICABILITY

The present invention can provide a wavelength converting member which makes it possible to effectively inhibit change in the light emission intensity over time; and a back light unit, a light guide member, a display device, and the like that have stable wavelength conversion characteristics can be obtained using the wavelength converting member of the present invention.

This application is based on Japanese patent application No. 2014-263785 filed on Dec. 26, 2014, the content of which is hereby incorporated in its entirety.