Phosphor sheet, a diffusion plate, an illuminating device, and a display  unit

A phosphor sheet having a laminated structure including a first barrier material, a first barrier material, a first color conversion layer, a second color conversion layer, and a second barrier layer and a display unit and an illuminating device including display unit is provided. A diffusion plate and a display unit including a diffusion plate are also provided.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority Patent Application JP 2009-159042 filed in the Japan Patent Office on Jul. 3, 2009, the entire contents of which is hereby incorporated by reference.

BACKGROUND

The present application relates to a color conversion element used for a liquid crystal display or the like and a display unit.

In the past, as a thin display unit, a liquid crystal display (LCD) has been used. In the liquid crystal display, a backlight irradiating the whole area of a liquid crystal panel from behind is used. The liquid crystal displays are classified broadly into direct lighting type and edge lighting type according to the structure of the backlight. In the edge lighting type, after light entering from the side face of a light guide plate is propagated inside the light guide plate, the light is extracted from the top face of the light guide plate. Meanwhile, in the direct lighting type, for example, a plurality of fluorescent lamps such as a CCFL (Cols Cathode Fluorescent Lamp) are arranged on a substrate, and thereby surface light emission is made as a whole (for example, see Japanese Unexamined Patent Application Publication No. 2005-108635).

In recent years, the liquid crystal display has been gotten larger, thinned, and lightened, and the life thereof has been lengthened. Further, in terms of improving moving picture characteristics by blinking control, a light emitting unit for performing surface light emission by arranging a plurality of light emitting diodes (LED) on a substrate has attracted attention. In such a light emitting unit, the following two methods are mainly used for extracting white light. In the first method, light emitting diodes that respectively emit each color of three colors R, G, and B are arranged, such light emitting diodes are concurrently lighted, and thereby the three color light is synthesized to obtain white light. In the second method, for example, a blue light emitting diode chip is surrounded by a resin containing a phosphor, and blue light is color-converted to white light.

However, in the foregoing second method, potting of the phosphor is made for a minute area of the light emitting diode chip. Thus, it is difficult to evenly and uniformly form the resin containing the phosphor. Thus, in recent years, as the third method replacing the second method, a method of color-converting blue light by using a material in which the resin containing the phosphor is sandwiched between a sheet base material (hereinafter referred to as a phosphor sheet) has attracted attention.

Meanwhile, in general, the phosphor is weak to oxygen and moisture vapor. When the phosphor is exposed to oxygen, moisture vapor and the like, the characteristics thereof are deteriorated. Thus, in the case where the phosphor sheet is used for the backlight, luminance and chromaticity deteriorates. Such deterioration of the phosphor is particularly significant under high temperature and high humidity environment. Thus, in the foregoing phosphor sheet, high moisture vapor barrier properties, high gas barrier properties and the like are needed for the sheet base material.

Thus, a method of providing a protective layer composed of a silicon compound or the like on the resin containing the phosphor (see Japanese Examined Patent Application Publication No. 6-58440) and a method of directly coating the surface of the resin containing the phosphor with a protective embrocation (refer to Japanese Unexamined Patent Application Publication No. 59-42500) have been proposed. Further, a method of sealing the resin containing the phosphor by sandwiching with two pieces of glass plates has been also proposed (see Japanese Unexamined Patent Application Publication No. 2007-23267).

SUMMARY

However, in the case where the methods of Japanese Examined Patent Application Publication No. 6-58440, Japanese Unexamined Patent Application Publication Nos. 59-42500, and 2007-23267 described above are used, for the purpose of protecting the phosphor, an expensive material such as a special protective layer and a glass plate should be used, resulting in a disadvantage of increased manufacturing cost. Thus, it is aspired that in an optical member in which color conversion is made by the phosphor such as a phosphor sheet, deterioration of the phosphor is prevented while an inexpensive material widely used for food packaging or the like is used as a sheet base material.

In view of the foregoing, in an embodiment, it is desirable to provide a color conversion element with which deterioration of a phosphor is able to be prevented at low cost and a display unit including the color conversion element.

According to an embodiment, there is provided a phosphor sheet having a laminated structure in which a first color conversion layer is provided on a first barrier material, the first color conversion layer includes a first color phosphor dispersed in a first resin layer, a second color conversion layer is provided on the first color conversion layer, the second color conversion layer includes a second color phosphor dispersed in a second resin layer, and a second barrier material is provided on the second color conversion layer.

According to an embodiment, there is provided a display unit comprising a display panel, a light source, and a phosphor sheet through which light emitted from the light source passes to illuminate the display panel, in which the phosphor sheet has a laminated structure including a first color conversion layer provided on a first barrier material, the first color conversion layer includes a first color phosphor dispersed in a first resin layer, a second color conversion layer is provided on the first color conversion layer, the second color conversion layer includes a second color phosphor dispersed in a second resin layer, and a second barrier material is provided on the second color conversion layer.

According to an embodiment, there is provided an illuminating device comprising a light source and a phosphor sheet through which light emitted from the light source passes, in which the phosphor sheet has a laminated structure including a first color conversion layer provided on a first barrier material, the first color conversion layer includes a first color phosphor dispersed in a first resin layer, a second color conversion layer is provided on the first color conversion layer, the second color conversion layer includes a second color phosphor dispersed in a second resin layer, and a second barrier material is provided on the second color conversion layer.

According to an embodiment, there is provided a diffusion plate including a first barrier material, a second barrier material, and a laminated structure provided between the first and second barrier materials, in which the laminated structure includes a first color conversion diffusion plate and a second color conversion diffusion plate provided on the first color conversion diffusion plate, a first adhesive layer provided on a top face of the laminated structure to seal the laminated structure to the first barrier material, and a second adhesive layer provided on a bottom face of the laminated structure to seal the laminated structure to the second barrier material, and in which the first color diffusion plate includes a first color phosphor dispersed therein and the second color diffusion plate includes a second color phosphor dispersed therein.

According to an embodiment, there is provided a display unit including a display panel, a light source, and a diffusion plate through which light emitted from the light source passes to illuminate the display panel, in which the diffusion plate comprises a first barrier material, a second barrier material, a laminated structure provided between the first and second barrier materials, and in which the laminated structure includes a first color conversion diffusion plate and a second color conversion diffusion plate, a first adhesive layer provided on a top face of the laminated structure to seal the laminated structure to the first barrier material, and a second adhesive layer provided on a bottom face of the laminated structure to seal the laminated structure to the second barrier material, the first color diffusion plate including a first color phosphor dispersed therein and the second color diffusion plate including a second color phosphor dispersed therein.

According to an embodiment, deterioration of the phosphor is easily inhibited. Thereby, deterioration of the phosphor is able to be inhibited even if an inexpensive material that is widely used for a food packaging or the like is used as the pair of base materials. Thus, deterioration of the phosphor is able to be inhibited at low cost.

DETAILED DESCRIPTION

The present application will be hereinafter described in detail with reference to the drawings according to an embodiment. The description will be given in the following order:

1. First embodiment (phosphor sheet): example of separately coated two layer structure with an interlayer barrier film

2. First modified example: example without the interlayer barrier film

3. Second modified example: example that an adhesive corresponding to the phosphor type is used

4. Third modified example: example that an adhesive corresponding to the phosphor type is used (without the interlayer barrier film)

5. First to third application examples: examples of a display unit and a illuminating device including the phosphor sheet

6. Second embodiment (diffusion plate): example of a three-layer laminated structure sealed by using the same adhesive for both the upper side and the lower side

7. Fourth modified example: example of a two-layer laminated structure sealed by using respectively different adhesives for the upper side and the lower side

First Embodiment

Structure of phosphor sheet10A

FIG. 1schematically illustrates a cross sectional structure of a phosphor sheet10A according to a first embodiment. In the phosphor sheet10A, a red conversion layer12and a green conversion layer11are sealed between barrier films13A and13B (a pair of base materials). The red conversion layer12is a color conversion layer for converting part of blue light to red light, and the green conversion layer11is a color conversion layer for converting part of blue light to green light, respectively. That is, the phosphor sheet10A has a laminated structure in which each layer separately exists for every phosphor type. In this embodiment, a description will be given of a two layer structure composed of the red conversion layer12and the green conversion layer11as an example.

The red conversion layer12contains a resin layer12band a red phosphor12athat is dispersed and contained in the resin layer12b. The red phosphor12acolor-converts, for example, blue light as exciting light to red light. For example, the red phosphor12ais (Ca, Sr, Ba)S:Eu2+, (Ca, Sr, Ba)2Si5N8:Eu2+, CaAlSiN3:Eu2+or the like. The red phosphor12ais composed of powdery particles. Thus, the red phosphor12ais fixed and held on a face of a barrier film13B by the resin layer12bas a binder resin. Examples of material of the resin layer12binclude an ink paste binder resin such as a polyvinyl butyral resin, a polyvinyl acetal resin, a phenol resin, an epoxy resin, and a melamine resin. In addition, for example, an adhesive functioning as a binder resin such as the following examples may be used. Examples include a urea resin system, a melamine resin system, a phenol resin system, a resorcinol resin system, an epoxy resin system, a polyurethane resin system, a polyimide system, a polybenzimidazole system, a polyester resin system, a vinyl acetate resin system, a polyvinyl acetal system, a polyvinyl alcohol system, a vinyl chloride resin system, a cyanoacrylate system, a polyether acrylate system, a polyethylene system, a cellulose system, a chloroprene rubber system, a nitrile rubber system, an SBR system, an SIS system, a polysulfide system, a butyl rubber system, a silicone rubber system, vinylphenolic, epoxyphenolic, chloroprenephenolic, nirilephenolic, nylon epoxy, and nitrile epoxy.

The green conversion layer11contains a resin layer11band a green phosphor11athat is dispersed and contained in the resin layer11b. The green phosphor11acolor-converts, for example, blue light as exciting light to green light. For example, the green phosphor11ais SrGa2S4:Eu2+, Ca3Sc2Si3O12:Ce3+or the like. The green phosphor11ais composed of powdery particles as the red phosphor12a. Thus, the green phosphor11ais fixed and held on a face of the barrier film13A by the resin layer11bas a binder resin. As a material of the resin layer11b, the resins listed in the foregoing resin layer12bare used. A resin used for the resin layer11bmay be identical with or may be different from a resin used for the resin layer12b. However, though details will be described later, a resin selected according to the phosphor type in each color conversion layer is desirably used.

The barrier films13A and13B are a base material sheet to support the red conversion layer12and the green conversion layer11, and function as a protective layer of the red conversion layer12and the green conversion layer11. Examples of material of the barrier films13A and13B include a thermoplastic resin such as polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polystyrene (PS), polyether sulfone (PES) and cyclic amorphous polyolefin, and a transparent resin such as multifunctional acrylate, multifunctional polyolefin, unsaturated polyester, and an epoxy resin. A material having relatively low barrier performance such as moisture vapor transmittance of the barrier films13A and13B of about from 0.05 to 5 g/m2/day, for example, about 0.1 g/m2/day is suitably used. The thickness is, for example, from 10 μm to 1000 μm both inclusive.

In this embodiment, a barrier film13C (interlayer barrier film) is further provided between the red conversion layer12and the green conversion layer11. The material, the thickness, and the moisture vapor transmittance of the barrier film13C are similar to those of the barrier films13A and13B.

Such a phosphor sheet10A is able to be formed, for example, as follows. That is, first, the red phosphor12ais mixed in a solvent containing a binder resin. A face of the barrier film13B is coated or printed with the resultant mixed solution, and then dried. Thereby, the red conversion layer12is formed on the face of the barrier film13B (the red phosphor is fixed thereon). Similarly, the green phosphor11ais mixed in a solvent containing a binder resin. A face of the barrier film13A is coated or printed with the resultant mixed solution, and then dried. Thereby, the green conversion layer11is formed on the face of the barrier film13A (the green phosphor is fixed thereon). The red conversion layer12and the green conversion layer11formed as above are bonded with each other by using an adhesive or the like with the barrier film13C in between. In the case where an adhesive is used as a binder resin, fixing each color phosphor onto each barrier film and bonding each barrier film with each other are concurrently made by using the adhesive. At this time, fixing and bonding are made according to a curing method of the adhesive (for example, thermal curing type, ultraviolet curing type or the like). Thereby, the phosphor sheet10A is formed.

Operation and Effect of Phosphor Sheet10A

In this embodiment, in the case where blue light enters a face of the phosphor sheet10A, for example, the barrier film13B side of the phosphor sheet10A, the incident blue light sequentially passes the red conversion layer12and the green conversion layer11. In the course of light passing, part of the blue light is color-converted to red light and green light, respectively, which is emitted from the barrier film13A side. The green light and the red light are mixed with blue light that has not been color-converted and has passed the fluorescence sheet10A, and thereby white light is obtained.

A description will be given of phosphor sheets100A and100B according to Comparative examples 1 and 2 with reference toFIGS. 2A and 2B. As illustrated inFIG. 2A, the phosphor sheet100A of Comparative example 1 has a color conversion layer101between a pair of base material sheets102A and102B. In the color conversion layer101, a green phosphor101aand a red phosphor101bare mixed and held in a resin layer101c. However, a phosphor such as the green phosphor101aand the red phosphor101bis generally weak to moisture vapor, oxygen or the like. Thus, there is a possibility that the phosphor is deteriorated by gas G such as moisture vapor passed the pair of base material sheets102A and102B.

Thus, it is necessary that the color conversion layer101is sandwiched between high barrier films103A and103B having high gas barrier characteristics as the phosphor sheet100B according to Comparative example 2 illustrated inFIG. 2B. The high barrier films103A and103B have a significantly high barrier function with a moisture vapor transmission of 0.05 g/m2/day or less. In such high barrier films103A and103B, a plurality of inorganic films composed of silicon oxide (SiOx), aluminum oxide (Al2O3) or the like are layered on a resin film such as a PET. Further, in some cases, an inorganic film and an organic film are layered. Further, in some cases, a glass substrate or the like is used. Thereby, passing of the gas G is able to be effectively prevented, and deterioration of the phosphor is able to be suppressed. However, for such high barrier films103A and103B, development thereof is significantly difficult, the material cost is high, and the manufacturing cost mounts.

Meanwhile, in this embodiment, each layer separately exists for every phosphor type (the red phosphor12aand the green phosphor11b). That is, the color conversion layer is divided into the red conversion layer12and the green conversion layer11, and the barrier film103C is provided therebetween. Thereby, compared to the case that the green phosphor101aand the red phosphor101bthat are mixed in the same layer is sealed with the base material sheets102A and102B as in Comparative example 1, deterioration of the phosphor is easily suppressed.

As described above, in this embodiment, the color conversion layer is divided into the red conversion layer12containing the red phosphor12aand the green conversion layer11containing the green phosphor11a. Thus, compared to the case that the foregoing phosphors are mixed in the same layer, deterioration of the respective phosphors is easily suppressed. Specifically, in the red conversion layer12, entering of moisture vapor or the like from the barrier film13B (bottom face) side is inhibited by the barrier film13B, while entering of moisture vapor or the like from the barrier film13A (top face) side is inhibited by the barrier films13A and13C. Similarly, in the green conversion layer11, entering of moisture vapor or the like from the barrier film13A (top face) side is inhibited by the barrier film13A, while entering of moisture vapor or the like from the barrier film13B (bottom face) side is inhibited by the barrier films13B and13C.

Thus, deterioration of the phosphor is able to be inhibited while an inexpensive barrier film (for example, a film in which alumina or silica is layered on PET or PEN) that is widely used for a food packaging or the like is used as the barrier films13A to13C sandwiching the red conversion layer12and the green conversion layer11. Thus, deterioration of the phosphor is able to be inhibited at low cost. Further, by inhibiting deterioration of the phosphor, chromaticity change and luminance change after long time usage are able to be decreased.

Samples (samples 1 to 3) of the following phosphor sheets were practically formed, and deterioration of the phosphor (chromaticity change) was examined. Specifically, Sample 1 as illustrated inFIG. 3Aas Comparative example 1-1 and Sample 2 as illustrated inFIG. 3Bas Comparative example 1-2 were formed. Sample 3 as illustrated inFIG. 3Cwas formed as Example 1. Sample 1 corresponds to the structure of Comparative example 2 described above, and had a structure that the color conversion layer101in which the green phosphor101aand the red phosphor101bwere mixed and contained was sandwiched between high barrier films103A1and103B1(moisture vapor transmittance: 0.01 g/m2/day). Sample 2 had a structure that the color conversion layer101in which the green phosphor101aand the red phosphor101bwere mixed and contained was sandwiched between low barrier films103A2and103B2(moisture vapor transmittance: 0.1 g/m2/day). Sample 3 had a structure that the red conversion layer12containing the red phosphor12aand the green conversion layer11containing the green phosphor11awere sandwiched between low barrier films13A1and13B1, and a low barrier film13C1was provided between the red conversion layer12and the green conversion layer11. The moisture vapor transmittance of the low barrier films13A1,13B1, and13C1was respectively 0.1 g/m2/day. In Samples 1 to 3, a phosphor emitting red light with the use of blue light as exciting light was used as a red phosphor; and a phosphor emitting green light with the use of blue light as exciting light was used as a green phosphor, respectively. In both the foregoing phosphors, deterioration under high temperature and high humidity was large. As an exciting light source, a blue LED was used. Samples 1 to 3 were left for 300 hours under environment of 60 deg C. and 90% RH, and the chromaticity change amount (Δu′, v′) from the initial point was measured. The results are illustrated inFIG. 4.

As illustrated inFIG. 4, comparing Sample 1 to Sample 2, the chromaticity change in Sample 1 using the high barrier film was smaller than that of Sample 2 using the low barrier film. Meanwhile, in Sample 3 (Example 1), though the low barrier film was used, the chromaticity change was suppressed to the same degree as that of Sample 1 using the high barrier film. From the foregoing results, it was found that in the case where each color conversion layer separately existed for every phosphor type, and the barrier film was provided between the respective layers, deterioration of the phosphor was able to be effectively inhibited while an inexpensive low barrier film was used.

Next, a description will be given of modified examples (first to third modified examples) of the foregoing first embodiment. For elements similar to those of the first embodiment, the same referential symbols will be affixed thereto, and the description will be omitted as appropriate.

FIRST MODIFIED EXAMPLE

FIG. 5schematically illustrates a cross sectional structure of a phosphor sheet10B according to the first modified example. As the phosphor sheet10A of the foregoing first embodiment, the phosphor sheet10B has a two layer structure composed of the red conversion layer12and the green conversion layer11between the pair of barrier films13A and13B. The phosphor sheet10B of this modified example is different from the phosphor sheet10A of the foregoing first embodiment, in that the barrier film (barrier film13C) is not provided between the red conversion layer12and the green conversion layer11. The phosphor sheet10B is able to be formed, for example, as follows. That is, in the same manner as that of the foregoing first embodiment, after the green conversion layer11is formed on one face of the barrier film13A and the red conversion layer12is formed on one face of the barrier film13B, respectively, the red conversion layer12and the green conversion layer11are oppositely bonded with each other.

As described above, the barrier film (barrier film13C) is not necessarily provided between the red conversion layer12and the green conversion layer11. Even if such a barrier film does not exist, by forming the laminated structure in which each layer respectively exists for every phosphor type, deterioration of the phosphor is able to be easily inhibited. In the case where a phosphor having normalized light emitting spectrum peak of 600 or more is used as the red phosphor12a, and a phosphor having normalized light emitting spectrum peak from 500 to 600 both inclusive is used as the green phosphor11a, respectively, for example, white light having chromaticity (0.20 and 0.14) showing spectrum as illustrated inFIG. 6is able to be obtained.

SECOND MODIFIED EXAMPLE

FIG. 7schematically illustrates a cross sectional structure of a phosphor sheet10C according to the second modified example. As the phosphor sheet10A of the foregoing first embodiment, the phosphor sheet10C has a two layer structure composed of a red conversion layer42containing the red phosphor12aand the green conversion layer41containing the green phosphor11abetween the pair of barrier films13A and13B. However, the phosphor sheet10C of this modified example is different from the phosphor sheet10A of the foregoing first embodiment, in that adhesive layers41band42brespectively containing different adhesives are provided as a resin layer for retaining each phosphor in the green conversion layer41and the red conversion layer42.

That is, in this modified example, though the green conversion layer41contains the green phosphor11a, the green phosphor11ais fixed and held on a face of the barrier film13A by the adhesive layer41b. The adhesive layer41bcontains an adhesive that is compatible with the green phosphor11aand effectively inhibits deterioration of the green phosphor11a(compatible with the green phosphor11a). Meanwhile, the red conversion layer42contains the red phosphor12a. The red phosphor12ais fixed and held on a face of the barrier film13B by the adhesive layer42b. The adhesive layer42bcontains an adhesive that effectively inhibits deterioration of the red phosphor11a(compatible with the red phosphor11a).

Examples of materials of the adhesive layers41band42binclude an adhesive functioning as a binder resin of each phosphor such as a urea resin system, a melamine resin system, a phenol resin system, a resorcinol resin system, an epoxy resin system, a polyurethane resin system, a polyimide system, a polybenzimidazole system, a polyester resin system, a vinyl acetate resin system, a polyvinyl acetal system, a polyvinyl alcohol system, a vinyl chloride resin system, a cyanoacrylate system, a polyether acrylate system, a polyethylene system, a cellulose system, a chloroprene rubber system, a nitrile rubber system, an SBR system, an SIS system, a polysulfide system, a butyl rubber system, a silicon rubber system, vinylphenolic, epoxyphenolic, chloroprenephenolic, nitrilephenolic, nylon epoxy, and nitrile epoxy.

However, in this modified example, an adhesive selected according to the phosphor type is used in the adhesive layers41band42b, since a compatible combination of a phosphor and an adhesive and an incompatible combination of a phosphor and an adhesive exist. For example, in the green conversion layer41, as a material of the adhesive layer41b, an adhesive capable of effectively inhibiting deterioration of the green florescence substance11asuch as an acrylic adhesive is used. In the red conversion layer42, as a material of the adhesive layer42b, an adhesive capable of effectively inhibiting deterioration of the red florescence substance12asuch as a butyl rubber adhesive is used. The acrylic adhesive and the butyl rubber adhesive may be heat curing type or ultraviolet curing type. As an adhesive used for the adhesive layers41band42b, an adhesive functioning as a binder resin as described above may be used, or other type of adhesive may be used. In the latter case, in addition to the foregoing adhesive, other resin material functioning as a binder resin (not illustrated inFIG. 7), for example, an ink paste binder resin such as a polyvinyl butyral resin, a polyvinyl acetal resin, a phenol resin, an epoxy resin, and a melamine resin is used.

For examining deterioration behavior difference according to the combinations of a phosphor and an adhesive as described above, samples were formed. At this time, two types of samples were formed. One thereof was obtained by printing a green phosphor (SrGaS4:Eu) on a PET film by using an acrylic adhesive (ultraviolet curing type). The other thereof was obtained by printing the green fluorescence (SrGaS4: Eu) on a PET film by using a butyl rubber adhesive (heat curing type). Two types of samples were left under environment of 85 deg C. and 85% RH. Similarly, two types of samples were formed for the red phosphor (CaS:Eu), and left under similar environment. Temporal change of luminance of these samples (relative luminance in the case where the initial luminance is 1) is illustrated inFIGS. 8A and 8B.

As illustrated inFIGS. 8A and 8B, in both the green phosphor11aand the red phosphor12a, deterioration behavior in the case where the acrylic adhesive was used was different from deterioration behavior in the case where the butyl rubber adhesive was used. As illustrated inFIG. 8A, in the green phosphor11a, luminance lowering degree in the case where the acrylic adhesive was used was smaller than that in the case where the butyl rubber adhesive was used, and it was found that deterioration of phosphor was effectively inhibited. Meanwhile, as illustrated inFIG. 8B, in the red phosphor12a, luminance lowering degree in the case where the butyl rubber adhesive was used was smaller than that in the case where the acrylic adhesive was used, and it was found that deterioration of the phosphor was effectively inhibited. The reason thereof may be as follows. In the case where an incompatible adhesive is used, the phosphor is deteriorated and decomposed, and thereby pH of the ambient surrounding is changed to acidic property and alkaline property. Such environment change causes deterioration of the adhesive, which further accelerates deterioration of the phosphor. Such vicious circle may be the reason thereof. As described above, in terms of inhibiting deterioration of the phosphor, it is found that a suitable combination of the phosphor type (the green phosphor11aand the red phosphor12a) and the adhesive type exists.

Thus, in this modified example, by focusing attention on the fact that a suitable combination of a phosphor and an adhesive exists, in the two layer structure composed of the green conversion layer41and the red conversion layer42, different adhesives are used in the green conversion layer41and the red conversion layer42. That is, while the green phosphor11ais diffused (contained) in the adhesive layer41bmade of the acrylic adhesive in the green conversion layer41, the red phosphor12ais diffused (contained) in the adhesive layer42bmade of the butyl rubber adhesive in the red conversion layer42. Thereby, the difference among respective deterioration rates of respective fluorescence types, that is, the difference among respective deterioration rates of respective colors is decreased, and temporal change in chromaticity of white light is inhibited. Thus, deterioration of the phosphor is able to be more effectively inhibited than in the foregoing first embodiment.

THIRD MODIFIED EXAMPLE

FIG. 9schematically illustrates a cross sectional structure of a phosphor sheet10D according to the third modified example. As the phosphor sheet10A of the foregoing first embodiment, the phosphor sheet10D has a two layer structure composed of the red conversion layer42containing the red phosphor12aand the green conversion layer41containing the green phosphor11abetween the pair of barrier films13A and13B. Further, as in the foregoing second modified example, in the green conversion layer41and the red conversion layer42, as a resin layer for retaining each phosphor, different adhesive layers41band42bare provided. However, in this modified example, the structure is different from that of the foregoing second modified example in that a barrier film is not provided between the green conversion layer41and the red conversion layer42.

As above, an adhesive corresponding to each phosphor may be used for the adhesive layers41band42bin the green conversion layer41and the red conversion layer42in the structure in which the barrier film is not provided between the green conversion layer41and the red conversion layer42. In the case where the interlayer barrier film is not provided, barrier performance is low compared to the case that the interlayer barrier film is provided. However, by using an adhesive capable of effectively inhibiting deterioration of a phosphor for every phosphor type, such lowering of barrier performance is able to be compensated.

In the foregoing second and third modified examples, phosphor sheet samples (samples A and B) were practically formed, and deterioration of the phosphor (chromaticity change) was examined. Sample A had the structure according to the second modified example (including the barrier film13C). Sample B had the structure according to the third modified example (not including the barrier film13C). However, in the samples A and B, a phosphor emitting red light with the use of blue light as exciting light was used as a red phosphor; and a phosphor emitting green light with the use of blue light as exciting light was used as a green phosphor, respectively. For both the foregoing phosphors, a sulfide system phosphor whose deterioration was large under high temperature and high humidity was used. As an exciting light source, a blue LED was used. Samples A and B were left under environment of 60 deg C. and 90% RH, and the chromaticity change amount (Δu′, v′) from the initial point was measured. The results are illustrated inFIG. 10. As illustrated inFIG. 10, in particular, in the phosphor sheet10C of the second modified example having the barrier film13C, chromaticity change was not almost shown even after 500 hours elapsed.

In the foregoing first embodiment and the foregoing first to the third modified examples, the description has been given of the two layer structure composed of the red conversion layer containing the red phosphor and the green conversion layer containing the green phosphor as an example. However, a laminated structure composed of three or more layers may be used. In this case, two types of color conversion layers respectively containing each phosphor may be alternately layered by using two types of phosphors. Otherwise, three types or more of color conversion layers may be layered by using three types of phosphors.

FIRST APPLICATION EXAMPLE

FIG. 11schematically illustrates a cross sectional structure of a display unit1according to an application example (first application example) of the foregoing phosphor sheets10A to10D. However, a description will be given of the phosphor sheet10A as a representative. The display unit1is, for example, a liquid crystal display. The display unit1includes a display panel26and a light source21as a backlight for illuminating the display panel26. The display unit1sequentially includes the phosphor sheet10A, a diffusion plate22, a diffusion film23, a lens film24, and a reflective polarizing film25between the display panel26and the light source21.

In the light source21, a plurality of LEDs21aare arranged on the substrate20. The phosphor sheet10A is arranged on the light emitting side of the light source section21. The LED21ais, for example, a blue light emitting diode.

The diffusion plate22and the diffusion film23diffuse incident light to uniformize the intensity distribution. Examples of material used for the diffusion plate22include a thermoplastic resin such as polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polystyrene, polyether sulfone, and cyclic amorphous polyolefin, multifunctional acrylate, multifunctional polyolefin, unsaturated polyester, and an epoxy resin. In particular, a material whose deterioration due to a blue light emitting diode or a near-ultraviolet diode is slight is desirable. The thickness of the diffusion plate22is, for example, about from 1 mm to 3 mm both inclusive. The lens film24has a structure in which, for example, a plurality of projections in a state of a prism (in a state of a triangle pole) stand in line in the same plane. The lens film24has a function to focus incident light in the front face direction, for example. The reflective polarizing film25transmits one polarized light and reflects the other polarized light downward (light source section21side) to contribute to reusing light. The reflective polarizing film25is provided to improve light usage efficiency.

In the display panel26, a liquid crystal layer is sealed between a drive substrate on which, for example, a TFT (Thin Film Transistor), various drive circuits, a pixel electrode and the like are formed and an opposed substrate on which a color filter, an opposed electrode and the like are formed (all elements are not illustrated). Each polarizing plate (not illustrated) is bonded to the light incidence side and the light emitting side of the display panel26.

In the display unit1, blue light emitted from the LED21apasses the phosphor sheet10A. At this time, the blue light entering the phosphor sheet10A is color-converted to red light and green light as described above, which is finally emitted from the phosphor sheet10A as white light. The white light emitted from the phosphor sheet10A sequentially passes the diffusion plate22, the diffusion film23, the lens film24, and the reflective polarizing film25, and illuminates the display panel26. The illuminated light is modulated based on image data in the display panel26, and thereby image display is performed. As described above, by converting the blue light from the light source section21to white light by using the phosphor sheet10A, chromaticity change and luminance change of illuminated light are able to be decreased.

In the foregoing first application example, the phosphor sheet10A is provided directly above the light source section21. However, the arrangement location of the phosphor sheet10A is not particularly limited. For example, as a display unit2illustrated inFIG. 12, a structure in which the phosphor sheet10A is located between the diffusion plate22and the diffusion film23may be also adopted.

SECOND APPLICATION EXAMPLE

FIG. 13schematically illustrates a cross sectional structure of a illuminating device (illuminating device3) according to an application example (second application example) of the foregoing phosphor sheets10A to10D. However, a description will be given of the phosphor sheet10A as a representative. The illuminating device3is, for example, a white LED. In the illuminating device3, the phosphor sheet10A is arranged directly above a diode chip30. The diode chip30is a light emitting element that emits blue light, and is electrically connected to a cathode frame32aand an anode frame32bby a wire bond31. The diode chip30and the phosphor sheet10A are hermetically sealed with a package cap33.

In the illuminating device3, blue light emitted from the diode chip30is color-converted in the phosphor sheet10A, which is emitted outside as white light. As described above, the phosphor sheet10A may be arranged directly above the diode chip30. Thereby, a white LED with small chromaticity change and small luminance change is able to be formed.

THIRD APPLICATION EXAMPLE

FIG. 14Aschematically illustrates a cross sectional structure of a illuminating device (illuminating device4) according to an application example (third application example) of the foregoing phosphor sheets10A to10D. However, a description will be given of the phosphor sheet10A as a representative. The illuminating device4is used, for example, as a backlight of a liquid crystal display or the like. For example, a blue LED35is arranged on the side face of a light guide plate34in the shape of a wedge. The shape of the light guide plate34is not limited to the wedge, but may be in a state of a parallel plate. Examples of material of the light guide plate34include a thermoplastic resin such as polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polystyrene, polyether sulfone, and cyclic amorphous polyolefin, multifunctional acrylate, multifunctional polyolefin, unsaturated polyester, and an epoxy resin as the material of the diffusion plate22of the foregoing first application example. A reflecting face S1of the light guide plate34is provided with, for example, groove process, dot process or the like for extracting light. The phosphor sheet10A is provided on a light emitting face S2of the light guide plate34.

In the illuminating device4, blue light entering from the blue LED35into the light guide plate34is totally reflected and propagated through the light guide plate34. After that, the total reflection condition is collapsed by process provided for the reflecting face S1, and the blue light is emitted from the light emitting face S2. The blue light emitted from the light guide plate34is color-converted in the phosphor sheet10A. Thereby, white light with small chromaticity change or the like is able to be obtained.

In the foregoing third application example, a description has been given of the example that the phosphor sheet10A is provided on the light emitting face S2of the light guide plate34. However, for example, as illustrated inFIG. 14B, the phosphor sheet10A may be bonded with the reflecting face S1of the light guide plate34. In this case, at the time when the total reflection condition of the blue light propagated in the light guide plate34is collapsed in the reflecting face S1, the blue light passes the phosphor sheet10A and is color-converted. Thus, white light with small chromaticity change or the like is able to be obtained.

Second Embodiment

Structure of Diffusion Plate50A

FIG. 15schematically illustrates a cross sectional structure of a diffusion plate (diffusion plate50A) according to the second embodiment. The diffusion plate50A is sealed in a state that a red conversion diffusion plate52and green conversion diffusion plates51A and51B are layered between barrier films53A and53B (a pair of base materials). The red conversion diffusion plate52functions as a color conversion layer for converting part of blue light to red light, and has a diffusion function to uniformly diffuse incident light. The green conversion diffusion plates51A and51B function as a color conversion layer for converting part of blue light to green light, and has a diffusion function to uniformly diffuse incident light. That is, as in the foregoing first embodiment, the diffusion plate50A has a laminated structure in which each layer separately exists for every phosphor type. In the following description, for elements similar to those of the phosphor sheet10A of the foregoing first embodiment, the same referential symbols are affixed thereto, and the description will be omitted as appropriate. The red conversion diffusion plate52and the green conversion diffusion plates51A and51B are a specific example of “color conversion layer” of the invention.

However, in this embodiment, the red phosphor12ais contained in the red conversion diffusion plate52, and the green phosphor11ais contained in the green conversion diffusion plates51A and51B, respectively. It is structured as a three layer laminated structure in which the green conversion diffusion plates51A and51B are provided to sandwich the red conversion diffusion plate52.

The red conversion diffusion plate52contains the red phosphor12ain a dispersed state. The red phosphor12ais kneaded in a resin material as the base material thereof in the course of formation of the red conversion diffusion plate52. Thereby, the red phosphor12ais dispersed and held in the red conversion diffusion plate52.

Similarly, the green conversion diffusion plates51A and51B respectively contain the green phosphor11ain a dispersed state. The green phosphor11ais dispersed and held in the green conversion diffusion plates51A and51B in the course of formation of the green conversion diffusion plates51A and51B.

The barrier films53A and53B are a protective sheet for sealing and protecting the red conversion diffusion plate52and the green conversion diffusion plates51A and51B. Examples of material of the barrier films53A and53B include a transparent resin similar to the material of the barrier films13A and13B of the foregoing first embodiment. A material having a relatively low barrier performance such as moisture vapor transmittance of about from 0.05 to 5 g/m2/day is suitably used.

In this embodiment, an adhesive layer54is provided to cover the top face and the bottom face of the laminated structure composed of the red conversion diffusion plate52and the green conversion diffusion plates51A and51B. The adhesive layer54is intended to seal the laminated structure between the barrier films53A and53B. Examples of material of the adhesive layer54include a urea resin system, a melamine resin system, a phenol resin system, a resorcinol resin system, an epoxy resin system, a polyurethane resin system, a polyimide system, a polybenzimidazole system, a polyester resin system, a vinyl acetate resin system, a polyvinyl acetal system, a polyvinyl alcohol system, a vinyl chloride resin system, a cyanoacrylate system, a polyether acrylate system, a polyethylene system, a cellulose system, a chloroprene rubber system, a nitrile rubber system, an SBR system, an SIS system, a polysulfide system, a butyl rubber system, a silicone rubber system, vinylphenolic, epoxyphenolic, chloroprenephenolic, nirilephenolic, nylon epoxy, and nitrile epoxy. A single half on the barrier film53A side of the adhesive layer54and a single half on the barrier film53B side of the adhesive layer54respectively correspond to “first adhesive layer” and “second adhesive layer” according to an embodiment.

However, as a material of the adhesive layer54, an adhesive capable of effectively inhibiting deterioration of phosphor according to each phosphor type (compatible adhesive) is desirably selected as in the foregoing second modified example.

Specifically, combination of the green phosphor11aand an acrylic adhesive, and combination of the red phosphor12aand a butyl rubber adhesive are respectively suitable. More specifically, an adhesive compatible with the phosphor arranged on the outermost side (the barrier film53A side and the barrier film53B side) in the laminated structure, in other words, an adhesive compatible with the phosphor contained in the diffusion plate adjacent to the adhesive layer54is selected. For example, the green conversion diffusion plates51A and51B containing the green phosphor11aare arranged on the outermost side. Thus, an adhesive compatible with the green phosphor11a, that is, the acrylic adhesive is desirably used.

Operation and Effect of Diffusion Plate50A

In this embodiment, in the case where blue light enters a face of the diffusion plate50A, for example, the barrier film53B side, the incident blue light sequentially passes the green conversion diffusion plate51B, the red conversion diffusion plate52, and the green conversion diffusion plate51A. In the course of light passing, part of the blue light is color-converted to red light and green light, respectively, which is emitted from the barrier film53A side. The green light and the red light are mixed with blue light that has not been color-converted and has passed, and thereby white light is obtained.

A description will be given of a diffusion plate104according to Comparative example 3 with reference toFIG. 16. The diffusion plate104has a color conversion diffusion plate105between a pair of high barrier films106A and106B. In the color conversion diffusion plate105, the green phosphor101aand the red phosphor101bare mixed and contained. The color conversion diffusion plate105is sealed between the high barrier films106A and106B with an adhesive layer107in between. That is, since the green phosphor101aand the red phosphor101bare mixed in the diffusion plate104of Comparative example 3, the material of the adhesive layer107is not able to be selected according to suitable combination of a phosphor and an adhesive as described above. Thus, the deterioration rate of the green phosphor101ais different from the deterioration rate of the red phosphor101b. In the result, temporal change of white chromaticity is increased in some cases. Thus, in the diffusion plate104, in order to inhibit deterioration of the phosphor, the expensive high barrier films106A and106B with moisture vapor transmittance of about 0.01 g/m2/day or less are desirably used.

Meanwhile, this embodiment had a laminated structure in which each layer separately exists for every phosphor type (red phosphor12aand the green phosphor11b), and the red conversion diffusion plate52is sandwiched between the green conversion diffusion plates51A and51B. By adopting such a laminated structure, an adhesive compatible with the phosphor that is arranged on the outermost side that is susceptible to moisture vapor or the like is able to be selected. Further, the internal layer of the laminated structure (red conversion diffusion plate52) is sandwiched between other diffusion plates (green conversion diffusion plates51A and51B) from above and from beneath. Thus, it becomes hard to be affected by moisture vapor, and the phosphor is hard to deteriorate. Thereby, the difference between respective deterioration rates of the respective fluorescence types, that is, the difference between respective deterioration rates of respective color is decreased, and temporal change of chromaticity of white light is inhibited.

As described above, this embodiment has the laminated structure composed of the red conversion diffusion plate52containing the red phosphor12aand the green conversion diffusion plates51A and51B containing the green phosphor11a. Thus, deterioration of the phosphor is easily inhibited by using effect of combination of the phosphor and the adhesive. Thereby, deterioration of the phosphor is able to be inhibited while for example, an inexpensive film (PET, PEN or the like) that is widely used for a food packaging or the like is used as the barrier films53A and53B sandwiching the laminated structure. Thus, deterioration of the phosphor is able to be inhibited at low cost. Further, by inhibiting deterioration of the phosphor, chromaticity change and luminance change after long time usage are able to be decreased.

In the foregoing second embodiment, the description has been given of the specific example of the three layer laminated structure in which the diffusion plate containing the red phosphor is sandwiched between two diffusion plates containing the green phosphor. However, the laminated structure of the diffusion plate is not limited thereto. For example, a structure in which n or more layers (n represents an odd number of 5 or more) of the two types of diffusion plates are alternately layered may be adopted. In the case where the number of phosphor types is two, and each diffusion plate containing each phosphor is alternately layered, if the number of layers is an odd number, the outermost two layers become a diffusion plate containing the same type of phosphor. Thus, in the same manner as that of the foregoing second embodiment, as the adhesive layer54, an adhesive compatible with the phosphor of the foregoing two layers may be selected.

Further, a three layer laminated structure in which a diffusion plate containing a green phosphor is sandwiched between two diffusion plates containing a red phosphor may be adopted. In this case, the diffusion plate containing the red phosphor is adjacent to the adhesive layer54. Thus, as a material of the adhesive layer54, an adhesive compatible with the red phosphor such as a butyl rubber adhesive may be selected.

Next, a description will be given of a modified example (fourth modified example) of the foregoing second embodiment. For elements similar to those of the first embodiment and the second embodiment, the same referential symbols are affixed thereto, and the description thereof will be omitted as appropriate.

FOURTH MODIFIED EXAMPLE

FIG. 17schematically illustrates a cross sectional structure of a diffusion plate50B according to the fourth modified example. The diffusion plate50B is sealed in a state that a red conversion diffusion plate56and a green conversion diffusion plate55are layered between the barrier films53A and53B. The red conversion diffusion plate56has a color conversion function and a diffusion function similar to those of the red conversion diffusion plate52of the foregoing second embodiment. The green conversion diffusion plate55has a color conversion function and a diffusion function similar to those of the green conversion diffusion plates51A and51B of the foregoing second embodiment. That is, as in the foregoing first and the foregoing second embodiments, the diffusion plate50B has a laminated structure in which each layer separately exists for every phosphor type. However, the laminated structure of this modified example is a two layer structure composed of the red conversion diffusion plate56and the green conversion diffusion plate55. The green conversion diffusion plate55is arranged on the barrier film53A side, and the red conversion diffusion plate56is arranged on the barrier film53B side. Further, an adhesive layer57(first adhesive layer) is provided on the barrier film53A side, and an adhesive layer58(second adhesive layer) is provided on the barrier film53B side, respectively. For the adhesive layers57and58, different adhesives are used.

The adhesive layers57and58are intended to seal the laminated structure between the barrier films53A and53B. Examples of material of the adhesive layers57and58include a urea resin system, a melamine resin system, a phenol resin system, a resorcinol resin system, an epoxy resin system, a polyurethane resin system, a polyimide resin system, a polybenzimidazole system, a polyester resin system, a vinyl acetate resin system, a polyvinyl acetal system, a polyvinyl alcohol system, a vinyl chloride resin system, a cyanoacrylate system, a polyether acrylate system, a polyethylene system, a cellulose system, a chloroprene rubber system, a nitrile rubber system, an SBR system, an SIS system, a polysulfide system, a butyl rubber system, a silicon rubber system, vinylphenolic, epoxyphenolic, chloroprenephenolic, nirilephenolic, nylon epoxy, and nitrile epoxy. As in the foregoing second embodiment, an adhesive compatible with the phosphor contained in an adjacent diffusion plate is desirably selected. Specifically, an acrylic adhesive is desirably used as the adhesive layer57, and a butyl rubber adhesive is desirably used as the adhesive layer58.

As in this modified example, the laminated structure may be a two layer structure composed of the red conversion diffusion plate56and the green conversion diffusion plate55. In this case, by providing the adhesive layers57and58made of different adhesives on the respective sides of the barrier films53A and53B, effect equal to that of the foregoing second embodiment is able to be obtained.

In the foregoing fourth modified example, the description has been given of the specific example of the two layer laminated structure in which the diffusion plate containing the red phosphor and the diffusion plate containing the green phosphor are layered. However, the laminated structure of the diffusion plate is not limited thereto. For example, a structure in which m or more layers (m represents an even number of 4 or more) of the two types of diffusion plates are alternately layered may be adopted. In the case where the number of phosphor types is two, and each diffusion plate containing each phosphor is alternately layered, if the number of layers is an even number, the outermost two layers become a diffusion plate containing different types of phosphors. Thus, in the same manner as that of the foregoing fourth modified example, it is possible that the adhesive layers57and58made of different adhesives are provided on the respective sides of the barrier films53A and53B, and an adhesive compatible with each phosphor for the adhesive layers57and58is selected, respectively.

Further, in the foregoing second embodiment and the fourth modified example, the description has been given of the specific example of the structure in which two types of phosphors are contained in each diffusion plate different from each other, and the two types of diffusion plates are alternately layered. However, the diffusion plates are not necessarily alternately layered, and the number of phosphor types is not limited to two.

While the present application has been described with reference to the embodiments and the modified examples, the present application is not limited to the foregoing embodiments and the like, and various modifications may be made. For example, in the foregoing embodiments and the like, the description has been given of the case that the red phosphor and the green phosphor that use blue light as exciting light are used as an example. However, other type of phosphor may be used. For example, as a yellow conversion phosphor, (Y, Gd)3(Al, Ga)5O12:Ce3+(commonly called YAG: Ce3+), α-SiAlON:Eu2+or the like may be used. Further, as a yellow or green conversion phosphor, (Ca, Sr, Ba)2SiO4:Eu2+or the like may be used. Further, the number of phosphors to be used may be three or more.

Further, in the foregoing embodiments and the like, the description has been given of the blue LED as an exciting light source as an example. However, the light source is not limited thereto, and a light source emitting color light in a relatively short wavelength region such as a near-ultraviolet LED may be used. In this case, as a green conversion or yellow conversion phosphor, (Ca, Sr, Ba)2SiO4:Eu2+, BAM: Eu2+, Mn2+, α-SiAlON:Eu2+or the like may be used. As a red conversion phosphor, Y2O2S: Eu3+, La2O2S:Eu3+, (Ca, Sr, Ba)2Si5N8:Eu2+, CaAlSiN3:Eu2+, LiEuW2O8, Ca(Eu, La)4Si3O13, Eu2W2O9system, (La, Eu)2W3O12, (Ca, Sr, Ba)3MgSi2O8:Eu2+, Mn2+, CaTiO3:Pr3+, Bi3+or the like may be used. As a blue conversion phosphor, BAM:Eu2+, (Ca, Sr, Ba)5(PO4)3Cl:Eu2+or the like may be used. However, in terms of light emitting efficiency and weather resistance, the blue light emitting diode is preferably used.