JPH0632306B2 - EL light emitting element - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an improvement in a panel-shaped EL light emitting device, and more particularly to an EL light emitting device in which pigment particles are mixed with phosphor particles.

[Prior art]

Recently, a thin-type dispersed EL light-emitting device, which is convenient for mounting, has been attracting attention as a backlight for liquid crystal displays and the like. This dispersion type EL light emitting device comprises a light emitting layer in which phosphor particles are dispersed in an organic binder such as cyanoethyl cellulose,
A high dielectric constant dielectric such as cyanoethyl cellulose is mixed with a white high dielectric constant dielectric powder such as barium titanate powder, a reflective insulating layer, a transparent electrode such as ITO, a back electrode such as aluminum, and a nylon such as nylon. It is composed of a moisture absorption layer made of a transparent resin film, and a moisture-proof outer resin film that hermetically surrounds the moisture absorption layer, the transparent electrode, the light emitting layer, the reflective insulating layer and the back electrode. In the light emitting layer of such an EL light emitting device, as shown in US Pat. No. 2,924,732, a red organic dye made of rhodamine is mixed with a blue green light emitting phosphor made of copper activated zinc sulfide. , A technique for obtaining white light has been developed.

[Problems to be Solved by the Invention]

Further, as disclosed in Japanese Patent Laid-Open No. 61-8896,
A technique has also been developed in which pigment particles are used instead of organic dyes to change the emission color of phosphor particles. However, when pigment particles are mixed with phosphor particles, there is a drawback that uneven light emission occurs. This is because in an EL light-emitting device in which pigment particles are not mixed in the light-emitting layer, the phosphor particles emit light over the entire surface of the light-emitting layer, so that light can be emitted uniformly over the entire surface without unevenness of light emission. This is because the light emission luminance of is low, and a portion having high light emission luminance and a portion having low light emission luminance can be formed. Therefore, the luminescent layer mixed with the pigment particles has a feature that the luminescent color can be changed by the pigment, but the luminescent state on the surface is significantly deteriorated. Moreover, in the EL light emitting device, generation of light emission spots cannot be eliminated in principle as long as pigment particles are mixed. Luminous spots due to pigment particles are luminescent parts distributed in a dot pattern,
This can be blindly done by reducing the area of the low light emitting portion. The minimum unit of the light emitting portion is determined by the size of the phosphor particles, and the minimum unit of the low light emitting portion is determined by the size of the pigment particles. The size of the phosphor particles affects the light emission characteristics and cannot be made smaller than necessary. Even if the pigment particles are small, the characteristics of the pigment are not adversely affected. Therefore, in the conventional EL light emitting device, fine particles are used as the pigment particles. For example, in the EL light emitting device described in the above-mentioned Japanese Patent Laid-Open No. 61-8896, pigment particles having a small particle diameter of 3 μm or less are mixed in phosphor particles having a large particle diameter. However,
EL manufactured by mixing 1.8 μm pigment particles with a phosphor
The light emitting element has a very noticeable luminescence that is clearly visible to the naked eye, and has a drawback that a light source of uniform planar light emission cannot be obtained. By the way, the pigment particles added to the light emitting layer are added to change the emission color of the phosphor particles. The pigment particles are
It absorbs the emission color from the phosphor particles and converts it to a different color. Therefore, by adding pigment particles to the light emitting layer, it is possible to obtain an EL light emitting element having a light emission color that cannot be emitted only by the phosphor. Pigment particles that absorb the light emitted from the phosphor particles and convert the wavelength of the absorbed light to emit light have a lower emission brightness than the phosphor particles. This is because the pigment particles absorb part of the incident light and emit part of the absorbed light energy as a different luminescent color. For this reason, it is impossible in principle for the EL light-emitting device in which pigment particles are added to the phosphor particles to have no emission spots. In the light emitting layer, light emission is strong in the phosphor particle portion and weak in the pigment particle portion. If the pigment particles can have the same emission brightness as that of the phosphor particles, it is possible to eliminate the emission unevenness. However, this is not possible due to the luminescence principle of the pigment particles. Therefore, as long as pigment particles are added to the light emitting layer, it is always possible to produce light emission spots, regardless of whether or not they can be visually discriminated. Since the emission unevenness is caused by the local difference in emission intensity, it is possible to reduce the particle diameters of the phosphor particles and the pigment particles, and to uniformly disperse the small phosphor particles and the pigment particles. It can be reduced in principle. However, the EL light-emitting element has the following important characteristics that are more important than reducing unevenness in light emission.
Higher emission brightness is required. To make matters worse, the emission luminance and the emission unevenness are contradictory characteristics, and it is extremely difficult to satisfy both at the same time. For example, if the particle size of the phosphor particles is increased, the emission brightness is increased, but the emission spots are increased. On the other hand, when phosphor particles having a small particle size are used, the unevenness of light emission is reduced, but the brightness of light emission is lowered. Therefore, it is extremely difficult for the EL light emitting element to increase the light emission brightness and reduce the light emission unevenness. Nevertheless, the EL light emitting element is required to have high light emission luminance and small light emission unevenness. An EL light emitting device with low emission brightness can be used only under restricted conditions. Especially,
The EL light emitting element has a lower light emission luminance per area than other illuminations, and it is difficult to obtain sufficient luminance in a bright place. In the EL light emitting device described in Japanese Patent Laid-Open No. 61-8896, the pigment particles are fine particles in order to reduce unevenness in light emission. It is presumed that the pigment particles, which are fine particles, reduce luminescent spots. The present inventor first thought that it is possible to reduce the unevenness of light emission by making the pigment particles into fine particles, and repeated enormous experiments to fabricate an extremely large number of EL light emitting devices. However, it is not possible to put an EL light-emitting device in which emission unevenness is sufficiently reduced to practical use by reducing the pigment particles. An EL light-emitting element was also manufactured in a state in which the pigment particles were made as small as possible, that is, using a soluble pigment, rhodamine. However,
Also in this EL light emitting device, the unevenness of light emission could not be sufficiently reduced. Therefore, as described in this publication, an EL light-emitting device in which large-sized phosphor particles are mixed with fine-particle pigment particles is no matter how fine-particle pigment particles are added, as long as the pigment is added. , It is not possible to eliminate the light emission spots. The present invention was developed for the purpose of solving these drawbacks, and an important object of the present invention is to provide an EL light emitting device capable of eliminating light emission unevenness and increasing the light emission brightness.

The EL light-emitting device of the present invention comprises a light-emitting layer formed by dispersing phosphor particles and pigment particles in a binder, and a light-emitting layer sandwiched between the light-emitting layers. A panel-like overall shape is formed of two translucent electrode layers and a moisture-proof film covering the outer surface. The average particle size of the phosphor particles dispersed in the binder of the light emitting layer is specified in the range of 13 ± 7 μm, and the average particle size of the pigment particles is specified in the range of 4 ± 2 μm. The ratio of the average particle size of the particles is limited to the range of 1.5-6.

【Example】

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Example 1 The EL light emitting device shown in this figure has a light emitting layer 1, an insulating layer 2 located on the back surface thereof, and the light emitting layer 1 and the insulating layer 2.
A pair of electrode layers 3 and 4 which are sandwiched between the electrode layers 3 and 4 and are arranged to face each other, moisture-proof films 5 and 6 for surrounding the electrode layers 3 and 4 to block the outside air, and enclose the whole in an airtight manner. It is composed of moisture-proof outer films 7 and 8. The light-emitting layer 1 includes 100 parts by weight of a blue-green light-emitting phosphor having an equivalent surface sphere-equivalent average particle size (simply referred to as an average particle size in the present specification) of 6 μm, and an average particle size of 4 μm red manufactured by Sinlohi Co., Ltd. 10 parts by weight of the pigment (Shin-Hiroi FA-001) are evenly dispersed in an organic binder of cyanoethyl cellulose, applied on an insulating layer that reflects light and dried to form a light emitting layer having a thickness of about 70 μm. The optimum thickness of the light emitting layer 1 is preferably about 3 phosphor particles.
It is adjusted so that it is applied in a layered manner. Therefore, the thickness of the light emitting layer 1 is optimally about 3 times the diameter of the phosphor particles. If the light emitting layer 1 is too thick as compared with the phosphor particles, the electrode 3
The distance between Nos. 4 and 4 becomes wider, the dielectric constant of the light emitting layer 1 also decreases, the capacitance between the electrodes decreases, and the emission brightness decreases. On the other hand, if it is too thin, luminescent spots will appear. The blue-green light emitting phosphor particles have an x value of 0.
191, yS value is 0.365, ZnS: Cu, Cl
Phosphors are used. The insulating layer 2 is formed by applying powder of a ferroelectric substance such as BaTiO ₃ dissolved in an organic binder solution similar to the organic binder solution of the light emitting layer 1 to the electrode layer 4 and drying it. The lower surface of the insulating layer 2, that is, the electrode layer 4 located on the non-fluorescent surface is
A copper or aluminum plate can be used, and the electrode 3 located on the fluorescent surface that is the upper surface of the light emitting layer 1 is an electrode having electrical conductivity and translucency, such as In ₂ O ₃ on the lower surface of a polyester sheet,
A transparent conductive film such as SnO ₂ or Sb ₂ O ₃ may be used. Lead wires are connected to the electrode layers 3 and 4, and the lead wires are planar and insulated from each other, and are hermetically sandwiched between the moisture-proof outer skin films 7 and 8 and guided to the outside. In the moisture-proof films 5 and 6, upper and lower layers are connected at the peripheral edges of the electrode layers 3 and 4 to form a closed space, and the electrode layers 3 and 4, the light emitting layer 1 and the insulating layer 2 are hermetically sealed in the closed space. It is stored in. For the moisture-proof films 5 and 6, nylon sheets whose inner surfaces are coated with polyethylene are used. The upper and lower nylon sheets are polyethylene-heated and heat-sealed at the periphery of the electrodes. With this structure, the nylon sheet can be heat-sealed easily and reliably. However, as the moisture-proof films 5 and 6, it is also possible to use a sheet made of a moisture-absorbing material such as silica gel, activated alumina, magnesium oxide, molecular sieve, or synthetic zeolite formed with a binder. The moisture-proof outer films 7 and 8 are made of, for example, a thermoplastic synthetic resin having a good moisture-proof property and a light-transmitting property such as a trifluoroethylene chloride film whose inner surface is coated with polyethylene, and the peripheral portion of the moisture-proof film 5 is heated. Is heat sealed by. In the EL light-emitting device thus configured, when an AC electric field is applied to the electrode layers 3 and 4 from the external AC power source through the lead wire, the phosphor of the light-emitting layer 1 emits electroluminescence, and a uniform surface without light emission spots. In addition, as shown in the table of FIG. 3, as compared with the conventional comparative example 2 described in the above-mentioned JP-A-61-8896, the luminous brightness was 4.2% higher. . [Examples 2, 3, 4, 5, 6, 7] The average particle diameter of the phosphor particles in the light emitting layer 1 is 7.5 μm in order.
(Example 2), 9.0 μm (Example 3), 10.5 μm
(Example 4), 12.0 μm (Example 5), 15.0 μm
m (Example 6) and 18.0 μm (Example 7) were replaced by the same procedure as in Example 1 to fabricate an EL light emitting device. As shown in FIG. 3, the obtained EL light emitting device becomes a planar light emitting panel of uniform light emission without light emission unevenness.
The emission brightness was improved by 5.3 to 7.2% as compared with Comparative Example 2. [Examples 8 and 9] The average particle diameter of the pigment particles was 2 μm (Example 8) and 6 μm.
An EL light emitting device was manufactured as in Example 1 except that (Example 9) was used. In the obtained EL light emitting device, when the average particle size of the pigment particles is larger than 2 μm and 6 μm or less, there is little or no luminescent spot visually, and it becomes a uniform planar light emitting body, and the emission brightness is , The pigment particle size is 2
In the range of 6 μm, a favorable emission luminance of 105.4 to 107.6% was exhibited. [Comparative Example 1] The same as in Example 1 except that the average particle diameter of the pigment particles is increased, and the average particle diameter of the phosphor particles is changed from 4 µm to 8 µm in Example 1 to 12.0 µm. E
An L light emitting device was manufactured as a prototype. This EL light emitting element has uneven light emission on the surface and cannot realize a uniform light emitting surface. [Comparative Example 2] The average particle diameter of the pigment particles was changed from Example 1 and 4 µm to 1.8.
and the average particle size of the phosphor particles is 32.8μ.
Same as Example 1 except that m
A conventional EL light-emitting device described in Japanese Patent Publication No. 1994-242242 was prototyped. This EL light emitting element had light emission unevenness on the surface, and the light emission luminance was lower than that of the present invention. In the EL light emitting device described above, ZnS: Cu, Cl is formed in the light emitting layer 1.
Phosphor particles are used, and red pigment (Shinhiroi FA-001) manufactured by Sinlohi Co., Ltd. is used for the pigment particles. For the phosphor particles, for example, (ZnS: Cu, Al, Cl), (ZnS:
S: Mn, Cu, Cl), (ZnS: Cu, Br),
(ZnS: Cu, Mn, Br), (ZnCdS: Cu,
Br) or other phosphor particles having an average particle diameter of 6 to 20.
The pigment particles having an average particle diameter of 2 to 6 μm can be used. By the way, the EL light emitting device of the present invention realizes uniform planar light emission and excellent light emission brightness by specifying the average particle diameters of the pigment particles and the phosphor particles within the above range. When the pigment particle size is smaller than 2 μm, the brightness of the EL light emitting element is lowered, and in the range other than 2 to 6 μm, uniform planar light emission without light emission unevenness cannot be realized. Therefore, preferably, the average particle diameter of the pigment particles is adjusted within the range of 3 to 5 μm. When the average particle diameter of the phosphor particles is smaller than 6 μm, the life of the EL light emitting element is shortened, and when it is larger than 20 μm, uniform planar light emission cannot be realized and the emission brightness is also lowered. To do. Therefore, preferably, the average particle size of the phosphor particles is adjusted in the range of 8 to 16 μm. Further, the insulating layer 2 includes, for example, Y ₂ O ₃ , TiO ₂ , Al ₂
O ₃ , ZnO, BaTiO ₃ , PbTiO ₃ , SrTiO ₃
It is possible to use a single ferroelectric substance or a mixture of plural types of ferroelectric substances such as those dispersed in a high dielectric constant organic resin. As the moisture-proof outer film 8 covering the back surface of the electrode 4, a film in which a metal foil such as an aluminum foil is sandwiched between polyesters and the inner surface of which is coated with polyethylene can be used.

【The invention's effect】

The EL light-emitting device of the present invention can solve the problem of light emission unevenness and further increase the light emission brightness by a completely opposite idea that cannot be imagined by the conventional technical idea. That is, unlike the conventional EL light-emitting device, the EL light-emitting device of the present invention does not mix pigments having a small particle size. On the contrary, the average particle size of the pigment particles is as large as 4 ± 2 μm, Moreover, the present invention is characterized in that the average particle size of the pigment particles is set close to the phosphor particles, while the phosphor particles are restricted to a limited range of 13 ± 7 μm. Increasing the average particle size of the pigment particles is usually considered to increase the unevenness of light emission. On the other hand, the EL light emitting device of the present invention is unexpectedly
The large pigment particles are used to significantly reduce the emission unevenness. That is, the ratio of the average particle diameter of the pigment particles and the phosphor particles is set to a specific range, and the particle diameter of the pigment particles is brought close to the phosphor particles, whereby in addition to the dispersibility of the pigment particles, the phosphor particles The dispersed state of the particles is also improved, both the phosphor particles and the pigment particles are uniformly dispersed, the emission unevenness is eliminated, and the emission brightness is improved. As described above, the light emitting layer in which the particle diameters of the phosphor particles and the pigment particles are specified within a specific range is similar to the internal structure of hardened concrete. Concrete cannot be made sufficiently strong by mixing sand with large-particle aggregate. It has been demonstrated that the addition of medium particle aggregates in addition to large particle aggregates and sand increases strength. This is because the aggregate of medium particles is uniformly dispersed in the voids of the aggregate of large particles to form hard concrete. The EL light emitting device of the present invention has a structure similar to this to improve both characteristics of light emission unevenness and light emission intensity. That is, as shown in FIG. 2, by uniformly dispersing the pigment particles in the voids of the phosphor particles, not only the pigment particles but also the phosphor particles are uniformly dispersed. Therefore, both the phosphor particles and the pigment particles are uniformly dispersed,
This is to eliminate the light emission spots. The uniform dispersion of both pigment particles and phosphor particles is demonstrated by the higher emission brightness. As shown in FIG. 2, the pigment particles that are uniformly dispersed in the gaps between the phosphor particles are excited by the light emitted from the phosphor particles in the vicinity to emit light of different wavelengths. That is, the pigment particles dispersed in the voids of the phosphor particles are very efficiently excited by the light of the adjacent phosphor particles and efficiently emit light of different colors. On the other hand, in the EL light emitting device using the minute pigment particles, the minute pigment particles can be aggregated among the phosphor particles.
The aggregated pigment particles cannot efficiently excite the light of the phosphor particles. The agglomerated pigment particles are in a state in which the surface of the pigment particles is covered with a large number of pigment particles, that is, the pigment particles are coated with other pigment particles. However, the central pigment particles are not excited by light. This is because the light emitted from the phosphor particles is absorbed by the pigment particles that coat the surface. In this state, the pigment particles added to the light emitting layer are all particles efficiently,
Cannot be excited by light. Therefore, all the pigment particles added to the light emitting layer are not effectively used for the function of converting the emission color of the phosphor particles. The pigment particles added to the light emitting layer in a state where the emission color of the phosphor particles is not converted,
Since it does not emit light by itself, the emission brightness is reduced. That is, the pigment particles that are not excited by the emission of the phosphor particles,
It becomes a black spot and reduces the brightness of the EL light emitting element. Therefore, there is a drawback that a large number of spots that do not emit light are dispersed and the emission brightness is reduced. On the other hand, in the EL light emitting device of the present invention, spots that do not emit light are not seen, and it is possible to uniformly emit light throughout. Thus, the EL light emitting device of the present invention can emit light uniformly over the entire light emitting layer because almost all pigment particles are
The reason is that the pigment particles can be excited efficiently with the phosphor particles to emit light in different emission colors. By the way, the EL light emitting element has a characteristic that the emission brightness is lowered when the average particle diameter of the phosphor particles is reduced. However, in the EL light emitting device of the present invention, although the average particle size of the phosphor particles is specified to be in the range of 13 ± 7 μm and made smaller than that of the conventional product, the emission brightness has excellent characteristics superior to those of the conventional product. To realize. Even if the emission brightness of the phosphor particles decreases,
It will be demonstrated that the ability to increase the emission brightness of an EL light emitting device can improve the luminous efficiency of pigment particles. As described above, the EL light-emitting device of the present invention does not merely improve the dispersibility of the phosphor particles and the pigment particles to reduce the unevenness of light emission, but more efficiently converts the pigment particles into light, thereby reducing the light emission. The light emission output of the pigment particles, which are the portions, is increased to reduce light emission unevenness. Therefore, the EL light emitting elements of the present invention have mutually contradictory characteristics, and it is extremely difficult to satisfy them at the same time. In addition to eliminating unevenness in light emission, it is possible to achieve a truly ideal characteristic that the light emission brightness can be improved. Using a 4 μm red pigment for the pigment particles and changing the particle size of the blue-emitting zinc sulfide phosphor,
It is shown in the table of FIG. As is clear from this table, in the EL light emitting device of the present invention, by limiting the average particle size of the phosphor to a specific range, the emission brightness is improved by about 4% or more as compared with the conventional EL light emitting device. is doing. Particularly in the range of the phosphor particle diameter of 10 to 20 μm, the emission brightness is improved by 6% or more. In addition, the EL light emitting device of the present invention has a long life until the emission brightness is lowered to a certain level by increasing the initial emission brightness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an EL light-emitting device, FIG. 2 is an enlarged cross-sectional view of a light-emitting layer of the EL light-emitting device according to the present invention, and FIG. 3 is a table showing the relative luminance with respect to the particle diameter and the state of the light-emitting surface. 1 ... Emitting layer, 2 ... Insulating layer, 3 ... Electrode layer, 4 ... Electrode layer, 5 ... Moisture-proof film, 6 ... Moisture-proof film, 7 ... Moisture-proof outer film, 8 ... Moisture-proof outer film, 9 ... Phosphor particles, 10 ... Pigment particles.

Claims (3)

[Claims] 1. A light emitting layer in which phosphor particles and pigment particles are dispersed in a binder, two electrode layers which are superposed with at least one of the light emitting layers sandwiched between them, and an outer surface. In an EL light-emitting device having a panel-like overall shape including a moisture-proof film covering the above, the average particle diameter of the phosphor particles in the light-emitting layer is in the range of 13 ± 7 μm, and the average particle diameter of the pigment particles is 4 ±. An EL light-emitting element having a range of 2 μm and an average particle size ratio of phosphor particles / pigment particles of 1.5 to 6. 2. The phosphor particles have an average particle diameter of 8 to 15 μm.
The EL light-emitting device according to claim 1, wherein the pigment particles have an average particle diameter of 3 to 5 μm. 3. The EL light emitting device according to claim 1, wherein the light emitting layer contains 4 to 20 parts by weight of pigment particles with respect to 100 parts by weight of the phosphor particles.