JPH08100173A - White fluorescence conversion film and white light emitting element containing the film - Google Patents

Abstract

PURPOSE: To prepare the subject conversion film capable of converting the emission color of a blue light-emitting organic EL element into white color in high efficiency, producible at a low cost, enabling the reduction of the size and the thickness of the element and useful e.g. as a back light of an OA instrument, watch, etc., by dispersing a specific fluorescent dye in a light-transmitting medium. CONSTITUTION: This white fluorescence conversion film having a light transmittance of preferably <=50% at wavelength of 460nm is produced by dispersing (A) a white fluorescent material expressed by the formula (Ar<1> and Ar<2> are each an aryl; R<1> to R<5> are each H or a 1-3C alkyl; R<6> is a 1-3C alkyl), e.g. 2- 2-[4-(N,N-diphenylamino)phenyl]ethenyl}-4-dicyanomethylene-6-methyl-4H -pyran in (B) a light-transmitting medium such as polyvinyl pyrrolidinone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white fluorescent conversion film and a white light emitting device using the same, and more specifically, it is a highly efficient white light emission color of a blue light emitting organic electroluminescent (hereinafter abbreviated as EL) device. The present invention relates to a white fluorescent conversion film capable of converting into white light, and a white light emitting element including the light emitting element portion and the white fluorescent conversion film, capable of generating white light of high efficiency and high quality, inexpensive, downsizing, and thinning.

[0002]

2. Description of the Related Art When a light emitting element is used for applications such as a back light for office automation equipment, a back light for watches, and a back light for various displays, white is most preferable as a light emitting color. However, since a single light emitting device that emits white light is not generally known, a method for obtaining white light emission by combining a light emitting layer with a fluorescent layer or a complementary color light emitting layer in a light emitting device having an emission color other than white. Are being tried.
For example, when a fluorescent layer is arranged in the EL light emitting layer in the stacking direction,
A method of changing the color tone of the emitted light in various ways (Japanese Patent Publication No. 63-1).
8319 gazette), in a dispersion type EL device, a light emitting layer and a complementary color light emitting layer are arranged between a transparent electrode and a counter electrode,
Method for obtaining white light emission (Japanese Patent Application Laid-Open No. 5-174974,
JP-B-5-33514 and JP-B-5-32879) are disclosed. However, these methods have drawbacks that the manufacturing process is complicated and the life of the obtained element is short.

Therefore, in order to prolong the life of the device and simplify the manufacturing method, a method of laminating a phosphor layer on the opposite side of the transparent electrode has been attempted. For example, a method of obtaining white light emission by arranging a complementary color fluorescent layer on the opposite side of a transparent electrode of an EL element has been proposed (Japanese Patent Publication No. 63-18).
319, Japanese Patent Application Laid-Open No. 63-19796, Japanese Utility Model Application Laid-Open No. 63-77299), specifically, orange-yellow light emission E.
Method of using blue light emitting fluorescent dye for L element
No. 2-90897), a blue-green light emitting EL element has a yellow color,
A method using an orange or red light emitting fluorescent dye (Japanese Patent Laid-Open Publication No. 6-58242)
2-104000, Japanese Utility Model Laid-Open No. 2-95197, Japanese Utility Model Laid-Open No. 3-104997), a method of using a pink fluorescent pigment in a blue-green light emitting EL element (Japanese Patent Application Laid-Open No. 6-163159), and the like.

However, these methods are applicable only to the orange-yellow EL element and the blue-green EL element, and there is a problem that the emission color of the blue-EL element cannot be converted to white. Further, a method of obtaining white light emission by laminating fluorescent stripe layers of two or three colors on the opposite side of the transparent electrode and turning on the stripes of all colors (JP-A-60-84580 and JP-A-1-48580). 1
No. 4,269,94 and Japanese Patent Application Laid-Open No. 5-258860) are known, but in this case, the manufacturing method of the element is complicated and an inexpensive element cannot be manufactured. On the other hand, formula (II)

Embedded image 2- [2- [4- (N, N-dimethylamino) phenyl] ethenyl] -4-dicyanomethylene-6 represented by
It is known to use -methyl-4H-pyran (abbreviated as DCM) dispersed in polymethylmethacrylate (abbreviated as PMMA) as a fluorescence conversion film (JP-A-3-152897). However, according to the study by the present inventors, this fluorescence conversion film (DCM / PMM
A) is a blue light emitting organic EL device (chromaticity: x = 0.14, y =
Even when superposed on 0.20, emission maximum wavelength: 482 nm, yellow-green (chromaticity: x = 0.40, y = 0.58) emission is only obtained with 5% efficiency, and white light is obtained. I couldn't do it.

[0005]

SUMMARY OF THE INVENTION Under the circumstances, the present invention provides a white fluorescent conversion film capable of converting the emission color of a blue light emitting organic EL element to white with high efficiency, and high efficiency and high quality white light. It is an object of the present invention to provide a white light emitting device that is capable of producing a light emitting element, is inexpensive, and can be downsized and thinned.

[0006]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, the above formula (II)
A compound related to DCM represented by
A film in which a fluorescent dye having a structure in which one substituent is an aryl group instead of a methyl group is dispersed in a light transmissive medium can convert the emission color of a blue light emitting organic EL device to white with high efficiency,
It has been found that an element composed of this film and a light emitting element section can generate white light of high efficiency and high quality, and can be inexpensive, downsized, and thinned. The present invention has been completed based on such findings. That is, the present invention has the general formula (I)

[0007]

Embedded image

(In the formula, Ar ¹ and Ar ² each represent an aryl group, which may be the same or different, and R ^{1 to} R ⁵ are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Group, which may be the same or different from each other, and R ⁶ represents an alkyl group having 1 to 3 carbon atoms.) White fluorescent obtained by dispersing a fluorescent dye represented by A white light emitting device including a conversion film and the white fluorescence conversion film and a light emitting device part is provided.
The white fluorescence conversion film of the present invention comprises a fluorescent pigment dispersed in a light transmissive medium, and the fluorescent pigment is represented by the general formula (I).

[0009]

[Chemical 4]

A pyran derivative having a structure represented by the following is used. In the general formula (I), Ar ¹ and Ar ² are
Each represents an aryl group. A substituent such as a lower alkyl group, for example, a methyl group, an ethyl group, an n-propyl group or an isopropyl group may be introduced into the aryl group. Specific examples of Ar ¹ and Ar ² include phenyl group and 2
-Methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 1-naphthyl group, 2-naphthyl group, 1-
Examples thereof include anthranyl group. This Ar ¹ and Ar
^{The two} may be the same or different. R ^{1 to} R ⁵
Are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and as the alkyl group having 1 to 3 carbon atoms, a methyl group,
Examples thereof include ethyl group, n-propyl group and isopropyl group. R ^{1 to} R ⁵ may be the same or different. R ⁶ is an alkyl group having 1 to 3 carbon atoms and represents a methyl group, an ethyl group, a propyl group or an isopropyl group.

Examples of the pyran derivative represented by the above general formula (I) include those having the following structures.

[0012]

Embedded image

[0013]

[Chemical 6]

[0014]

[Chemical 7]

[0015]

Embedded image

Of these, particularly Ar ¹ and Ar ² in the general formula (I) are both phenyl groups, R ¹ , R ² ,
2- [2- [4- (N, N-diphenylamino) phenyl] ethenyl] -4-dicyanomethylene-6 in which R ³ , R ⁴ and R ⁵ are both hydrogen atoms and R ⁶ is a methyl group
-Methyl-4H-pyran is preferred in terms of performance and ease of manufacture. Further, in the present invention, one kind of fluorescent dye composed of the pyran derivative represented by the general formula (I) may be used, or two or more kinds thereof may be used in combination.
On the other hand, the light-transmitting medium is not particularly limited as long as it has light-transmitting property and film-forming property.
For example, polymer compounds, inorganic glass, and printing media are used. Here, as the polymer compound, for example, polyvinylpyrrolidinone, polyacrylonitrile, poly (N, N-dimethylacrylamide), poly (N, N-dimethylmethacrylamide), polyvinyl alcohol, polymethylmethacrylate, polystyrene,
Examples thereof include polycarbonate, polyvinyl acetate, polyvinyl chloride, polybutene, polyethylene glycol, and copolymers thereof, and examples of the inorganic glass include borate glass and silica glass. Among these light transmissive media, polyvinylpyrrolidinone is particularly preferable in terms of light transmissivity, film forming property, and other physical properties. In addition, in the present invention, the light-transmitting medium may be used alone or in combination of two or more kinds.

The method for producing the white fluorescence conversion film of the present invention is not particularly limited, and various methods can be used. For example, the fluorescent dye represented by the general formula (I) is mixed with a light-transmissive medium, and then the casting method, spin coating method, printing method, bar coating method, extrusion molding method, roll molding method, pressing method is used. A desired white fluorescence conversion film can be obtained by forming a film using a method such as a spray method or a roll coating method. When an organic solvent is used in these film forming methods, examples of the organic solvent include 1,2-dichloroethane; chloroform; acetone;
Cyclohexanone; toluene; xylene; N, N-dimethylformamide; dimethylsulfoxide; 1,2-dimethoxyethane; diethylene glycol dimethyl ether and the like can be used. These solvents may be used alone or in combination of two or more. For example, when a film is formed by the casting method, an appropriate solvent is selected from the above solvents, and the solution obtained by dissolving the fluorescent dye and the light transmissive medium in this is gently placed on a substrate such as a glass substrate. A thin white fluorescence conversion film can be obtained by gently allowing the solvent to gradually evaporate with a pallet, a petri dish, or the like.

The white fluorescent conversion film of the present invention has a wavelength of 460n.
The light transmittance at m is preferably 50% or less. When this light transmittance exceeds 50%, the blue region (4
20 to 485 nm) and the converted white light is difficult to obtain. The preferable light transmittance is in the range of 0 to 50%, and particularly preferably in the range of 5 to 20%. Since the light transmittance depends on the extinction coefficient of the fluorescent dye used and the film thickness of the white fluorescence conversion film, the necessary fluorescent dye concentration is determined from the extinction coefficient and the film thickness so that the concentration is obtained. The fluorescent dye may be dispersed in the light transmissive medium. The thickness of the white fluorescence conversion film is usually 1 to 1000 μm, preferably 2 to 100 μm. The white light emitting element of the present invention comprises the white fluorescence conversion film thus obtained and the light emitting element section, and as the light emitting element section, for example, a blue light emitting diode or a blue light emitting organic EL element is used. Among these, an organic thin film EL element having an emission maximum wavelength of 420 to 485 nm is preferable among them. If the maximum emission wavelength of the light emitting element section deviates from the range of 420 to 485 nm, it is difficult to obtain good white light even with the configuration of the present invention.

The blue light emitting organic thin film EL device having the maximum emission wavelength of 420 to 485 nm is disclosed in, for example, Japanese Patent Laid-Open No. 3-4.
No. 7890, No. 3-231970, No. 5-17765, No. 5-135878, No. 5-140145, No. 5-247.
It can be produced according to the methods disclosed in Japanese Patent Application Laid-Open No. 458, No. 5-247459, No. 6-100857, No. 6-13080, and the like. To give an example, a transparent supporting substrate made of a glass substrate having an ITO electrode formed thereon has 4,4′-bis [N-phenyl-N- (3-methylphenyl) amino] biphenyl (TPD); 4,4 ′. A blue light emitting organic thin film EL device is obtained by sequentially vacuum-depositing -bis (2,2-diphenylvinyl) biphenyl (DPVBi) and Mg-Ag electrodes and stacking them. FIG. 1 is a schematic diagram showing the configuration of the white light emitting element of the present invention, in which the emission color from the light emitting element section A is converted into white light by the white fluorescence conversion film B.

[0020]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Production Example 1 2- [2- [4- (N, N-diphenylamino) phenyl] ethenyl] -4-dicyanomethylene-6-methyl-
Preparation of 4H-pyran 4-dicyanomethylene-2,6-dimethyl-4H-pyran 0.6 g (3.7 mmol) and 4- (N, N-diphenylamino) benzaldehyde 1.0 g (3.7 mmol). Dissolve in 50 ml of refluxing ethanol, piperidine
0.2 ml was added and the mixture was refluxed intermittently for 25 hours.
The reaction mixture was allowed to cool to room temperature, the solid formed was filtered off, and ethanol / dichloromethane (weight ratio 1/2) 5
By recrystallization from 0 ml, 0.3 g (yield 12%) of a by-product was obtained as black green needle crystals. After evaporating the solvent from the recrystallization filtrate, the residue was purified by column chromatography (silica gel / dichloromethane) to obtain 0.6 g of the desired product as red needle crystals (yield 38%). The melting point (mp), ¹ H-NMR, UV-visible absorption spectrum and fluorescence spectrum of this product were measured. The results are shown below. mp: 217-218 ° C. ¹ H-NMR (CDCl ₃ , tetramethylsilane (TM
S) standard): 2.38 (3H, s), 6.4 to 6.6 (3H,
m), 7.0-7.5 (15H, m) UV-visible absorption spectrum (in 1,2-dichloroethane,
Concentration 1.4 × 10 ^-6 mol / liter), λmax (log
ε): 467 nm (4.62) Fluorescence spectrum (in 1,2-dichloroethane, excitation wavelength 450 nm, concentration 1.4 × 10 ^-6 mol / liter), fluorescence maximum wavelength: 581 nm

Production Example 2 Preparation of organic thin film EL element ITO on a glass substrate of 25 mm × 75 mm × 1.1 mm
The transparent support substrate was prepared by forming an electrode with a thickness of 100 nm. The transparent support substrate was ultrasonically cleaned with isopropyl alcohol for 5 minutes, then with pure water for 5 minutes, and again with isopropyl alcohol for 5 minutes. Next, this transparent support substrate was fixed to a substrate holder of a vacuum vapor deposition apparatus, and 4,4'-bis (N-phenyl-N- (3-methylphenyl) amino] was added to a molybdenum resistance heating boat.
200 mg of biphenyl (TPD) is put into another boat for resistance heating made of molybdenum and 200 mg of 4,4'-bis (2,2-diphenylvinyl) biphenyl (DPVBi).
Then, the inside of the vacuum chamber was depressurized to 1 × 10 ⁻⁴ Pa. A boat containing TPD was heated to 215 to 220 ° C., TPD was deposited on the substrate at a vapor deposition rate of 0.1 to 0.3 nm / sec, and a hole injection layer having a thickness of 60 nm was formed. At this time, the substrate temperature was room temperature. Without removing the obtained hole injection layer from the vacuum chamber, DPV
Bi at a boat temperature of 250 ° C and a vapor deposition rate of 0.1 to 0.2 nm /
It was deposited on the substrate for 2 seconds to form a light emitting layer having a film thickness of 40 nm. This was taken out of the vacuum chamber, a stainless steel mask was placed on the light emitting layer side, and it was fixed again to the substrate holder. Next, 0.5 g of silver (Ag) wire was put into a tungsten basket, 1 g of magnesium (Mg) ribbon was put into a boat made of molybdenum, and the inside of the vacuum chamber was decompressed to 1 × 10 ⁻⁴ Pa, Mg (deposition rate,
8 nm / sec) and Ag (vapor deposition rate, 0.1 nm / sec) were simultaneously vapor-deposited to form a negative electrode to prepare an organic thin film EL device.

Example 1 To 1.8 mg of 2- [2- [4- (N, N-diphenylamino) phenyl] ethenyl] -4-dicyanomethylene-6-methyl-4H-pyran obtained in Preparation Example 1 was obtained. , Polyvinylpyrrolidinone [manufactured by Kanto Chemical Co., Inc., molecular weight about 360,000
] 0.85 g and dichloromethane 8.5 ml were added and dissolved. Then add this solution to 25 mm x 75 mm
Cast on × 1mm glass substrate, air-dry for 12 hours, then 5
A fluorescent conversion film was prepared by vacuum drying at 0 ° C. 460 nm
The dye concentration for achieving a transmittance of 50% or less in Lambert-Beer rule [-log (T / 10
0) = εbc, where T is the transmittance in%, b is the film thickness,
ε is a molecular extinction coefficient of 4.2 × 10 ⁴ cm ⁻¹ M ⁻¹ , c
Is the required dye concentration. ] It calculated according to. The thickness of this fluorescence conversion film was 50 μm as measured by a micrometer, and the transmittance at 460 nm was 9%.
Met. Organic thin film EL device obtained in Production Example 2 (chromaticity x = 0.161, y = 0.150, blue, emission maximum wavelength 46
(0 nm) was caused to emit light under the conditions of voltage 7 V and current density 4.2 mA / cm ² , and the conversion film was superposed thereon to form a white light emitting device, and the output light was measured by a luminance meter (CS-100 manufactured by Minolta). The brightness of the blue light before the conversion film is stacked is 100
While it was cd / m ² , chromaticity x = 0.340, y =
White light of 0.313 was obtained at a luminance of 60 cd / m ² .
The conversion efficiency was 60%.

Example 2 To 3.0 mg of 2- [2- [4- (N, N-diphenylamino) phenyl] ethenyl] -4-dicyanomethylene-6-methyl-4H-pyran obtained in Preparation Example 1 was obtained. 1.5 g of a printing medium [S-800 manufactured by Toyo Ink Co., Ltd.] was added and dissolved. Using this, 25mm x 75mm x 1mm
The film is prepared on the glass substrate of
After air-drying for an hour, it was vacuum dried at 50 ° C. to prepare a fluorescence conversion film. The film thickness of this fluorescence conversion film was 56 μm as measured by a micrometer, and the transmittance at 460 nm was 8%. Organic thin film EL obtained in Production Example 2
When the output film was measured with a luminance meter (CS-100 manufactured by Minolta Co., Ltd.) by stacking the conversion film on the device to form a white light emitting device, the brightness of the blue light before the conversion film was stacked was 100 cd.
/ M ² , whereas chromaticity x = 0.350, y = 0.4
20 white lights were obtained with a brightness of 60 cd / m ² . The conversion efficiency was 60%. The chromaticity of the emission color of each of the organic thin film EL device obtained in Production Example 2 and the white light emitting devices obtained in Examples 1 and 2 was plotted in the chromaticity coordinate diagram of FIG.

[0024]

The white fluorescence conversion film of the present invention can convert the emission color of the blue light emitting organic EL element into white with high efficiency, and the white fluorescence conversion film and the light emitting element section of the present invention. The white light emitting element emits white light with high efficiency and high quality, and is inexpensive and can be downsized and thinned. Therefore, the white light emitting element of the present invention is suitably used, for example, in a backlight for office automation equipment, a backlight for watches, a backlight for various displays, a dot matrix display and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a white light emitting element of the present invention.

FIG. 2 is a chromaticity coordinate diagram showing areas of each color.

[Explanation of symbols]

 A light emitting element part B white fluorescent conversion film

Claims (6)

[Claims] 1. A compound of the general formula (I) (In the formula, Ar ¹ and Ar ² each represent an aryl group, which may be the same or different from each other;
^{1 to} R ⁵ each represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, which may be the same or different from each other, and R ⁶ represents an alkyl group having 1 to 3 carbon atoms. ) A white fluorescence conversion film obtained by dispersing the fluorescent dye represented by the formula (3) in a light transmissive medium. 2. The fluorescent dye is 2- [2- [4- (N, N-
Diphenylamino) phenyl] ethenyl] -4-dicyanomethylene-6-methyl-4H-pyran.
The white fluorescence conversion film described. 3. The white fluorescence conversion film according to claim 1, wherein the light transmissive medium is polyvinylpyrrolidinone. 4. The light transmittance at a wavelength of 460 nm is 5
The white fluorescence conversion film according to claim 1, which is 0% or less. 5. A white light emitting element comprising the white fluorescence conversion film according to claim 1 and a light emitting element section. 6. The white light emitting element according to claim 5, wherein the light emitting element section is an organic thin film electroluminescent element having an emission maximum wavelength of 420 to 485 nm.