JP2005093359A - Ac-operated electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an improvement of luminescence brightness without increasing manufacturing costs, and realize the suppression of power consumption and a longer-life of the elements in an AC-operated electroluminescent element provided with an insulating layer where high dielectric particles are dispersed. <P>SOLUTION: In the insulating layer 16 installed on at least one side of a light-emitting layer 14, at least a first high dielectrics particle group and a second high dielectrics particle group of which sizes are different are filled at a filling factor of 70% or more. An average particle diameter of the first high dielectrics particle group is to be 150 nm or more and an average particle diameter of the second high dielectrics particle group is to be 1/2 or less of that of the first high dielectrics particle group. A thickness of the insulating layer 16 is to be 0.5 μm or more and 20 μm or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an alternating current operation electroluminescence element, and more particularly to an alternating current operation electroluminescence element provided with an insulating layer in which high dielectric particles are dispersed.

  The electroluminescence element is expected to be used as a new display element or the like that does not require a separate light source as a self-luminous surface light source. There are two types of conventional electroluminescence elements, “dispersion type” and “thin film type”. In addition, although a direct-current drive electroluminescent element has been proposed, research and development is proceeding focusing on a more practical alternating-current drive. First, the basic structure, light emission mechanism, and features of each of the conventional dispersion-type and thin-film-type AC operation electroluminescent elements described in Non-Patent Document 1 and the like will be schematically described below.

  As shown in FIG. 3, the dispersion type AC operation electroluminescence element typically has a transparent electrode 32 formed on a transparent substrate 30 such as glass or a polyethylene terephthalate (PET) sheet by applying a transparent conductive film. Further, a light emitting layer 34, an insulating layer 36, and a back electrode 38, which are formed by a technique such as coating or screen printing, in which phosphor particles 34a are freely dispersed in a binder 34b, which is a dielectric, are laminated thereon. Has a structure. Furthermore, an additional layer such as a surface protective layer may be provided. When an AC voltage is applied between the transparent electrode 32 and the back electrode 38, the phosphor particles 34 a inside the light emitting layer 34 exhibit electroluminescence, and the light is extracted through the transparent electrode 32 and the transparent substrate 30. The insulating layer 36 is for blocking a current path and applying a stable high electric field to the light emitting layer 34, and is provided only on one side of the light emitting layer 34 in FIG. 3, but may be provided on both sides. . If the structure shown in FIG. 3 using different types of phosphor particles corresponding to a plurality of colors is overlapped and all the intermediate electrodes are made transparent, application to a color display or the like is possible.

  As the phosphor particles of the distributed alternating-current operation electroluminescence element, particles obtained by adding an activator for determining the emission color to the phosphor base material are used. A typical example is ZnS: Cu, Cl that emits blue-green light. In addition, ZnS: Cu, Al (green) or ZnS: Cu, Cl, Mn (orange yellow) depending on the desired emission color. ) Etc. are used. The light emission of the distributed alternating-current operation electroluminescence element is due to the fact that the element added as the activator acts as a donor and acceptor and recombination occurs. For example, in the case of the above ZnS: Cu, Cl, Cl acts as a donor and Cu acts as an acceptor. From such a light emitting mechanism, it is said that the activator needs to contain copper. Furthermore, the types of base materials to which copper can be added are limited, and only practical materials are ZnS, CaS, and SrS. Due to the limitations of these materials and the like, it is considered that the particle diameter of about 20 μm is optimal for the phosphor particles of the dispersed AC operation electroluminescence element. Phosphor particles slightly smaller than this may be used, but it is known that when the particle diameter is smaller than 2 to 3 μm, the emission luminance is remarkably lowered.

  As shown in FIG. 4, the thin-film AC operation electroluminescence element typically has a transparent electrode 42 formed on a transparent substrate 40 in the same manner as the dispersion type, and the first insulating layer 44a is formed thereon. The phosphor light-emitting layer 46, the second insulating layer 44b, and the back electrode 48, which are formed into a thin film by a technique such as vacuum deposition or sputtering, are stacked. Furthermore, an additional layer such as a surface protective layer or a buffer layer between the light emitting layer and the insulating layer may be provided. In general, each layer other than the light emitting layer 46 is also formed by a thin film forming technique such as vacuum deposition. Therefore, although the element of FIG. 4 is drawn to a thickness substantially the same as that of the element of FIG. It is about 1/100. When an AC voltage is applied between the transparent electrode 42 and the back electrode 48, the light emitting layer 46 exhibits electroluminescence, and the light is extracted through the transparent electrode 42 and the transparent substrate 40. A typical phosphor material used for the light emitting layer 46 is ZnS: Mn in which Mn serving as an emission center is doped in a base material ZnS, which emits orange-yellow light. In the case of the thin film type, a configuration called “dual pattern method” or “triple pattern method” in which light emitting portions doped with different types of light emission centers corresponding to a plurality of colors are arranged two-dimensionally, Application to a color display or the like is possible by overlapping the structure shown in FIG. 4 corresponding to a plurality of colors.

  Dispersive AC operating electroluminescent devices emit light by recombination between donor and acceptor, whereas thin film AC operating electroluminescent devices emit light by collisional excitation of emission centers by hot electrons running in the base material. It is said that. When an alternating voltage is applied, the hot electrons are generated when electrons injected into the light emitting layer 46 from the interface between the light emitting layer 46 and the insulating layers 44a and 44b and / or traps in the light emitting layer 46 are accelerated under a high electric field. It has been done.

  Comparing the distributed type and thin film type AC electroluminescent elements, each has advantages and disadvantages. The advantages of the distributed type include that the manufacturing process is simple and does not include vacuum deposition, etc., so that the manufacturing cost is low, the element can be easily enlarged, and a flexible element having flexibility can be manufactured. Is mentioned. Disadvantages are lower brightness than a thin film type, less color diversity, and larger particle size of dispersed phosphor particles, which is not suitable for applications such as high-definition displays. On the other hand, the advantages of the thin film type include that it is brighter and brighter than the dispersion type, that there are many variations of the light emission center that determines the color, that various colors can be expressed, and that high-definition display is possible. Disadvantages include complicated manufacturing processes and high costs.

  On the other hand, in Patent Documents 1 and 2, etc., while adopting a dispersive-like structure similar to the structure shown in FIG. There has also been proposed an alternating-current operation electroluminescence element using a phosphor material containing a luminescent center containing a luminescent center that is collisionally excited by hot electrons. In this AC electroluminescence device, electrons are injected into the phosphor particles from the interface between the phosphor particles and the surrounding dielectric and / or traps in the phosphor particles, and the electrons are accelerated. It is considered that a light emission mechanism similar to a conventional thin film type is realized by collision excitation of the emission center in the phosphor particles as hot electrons. Therefore, while enjoying the advantages of the conventional thin film type such as high brightness and color diversity, the basic structure itself is the same as that of the conventional distributed type, so that the manufacturing cost can be kept low.

Here, the insulating layer in the various AC operation electroluminescence elements described above may be formed by a vacuum deposition method or a sputtering method, or may be formed by a simpler and lower cost method such as coating or screen printing. As a specific example of the latter method, for example, a material in which high dielectric particles such as BaTiO ₃ (barium titanate) are dispersed in an organic binder having a relatively high dielectric constant such as cyanoethyl cellulose is layered. The method of apply | coating and drying is mentioned. In particular, in a distributed alternating current operation electroluminescent device in which the light emitting layer is formed by a simple method such as coating, if the insulating layer is formed by the same method, the manufacturing process of the entire device can be simplified and the cost can be reduced. Great effect.

In order to realize a high light emission luminance by applying a stable high electric field to the light emitting layer, it is necessary to increase the dielectric constant of the entire insulating layer. For example, in Patent Document 3, a dispersion type in which a fibrous high dielectric is used in place of a particulate high dielectric, the ratio of the high dielectric to the binder in the insulating layer is increased, and the dielectric constant of the insulating layer is improved. An AC-operated electroluminescence element has been proposed.
International Publication No. 02/080626 Pamphlet Japanese Patent Laid-Open No. 2000-195664 JP-A-5-326150 Toshio Higuchi, “Electroluminescent Display”, first edition, Sangyo Tosho Co., Ltd., July 25, 1991

  As described above, in order to realize a high luminance by applying a stable high electric field to the light emitting layer in an AC-operated electroluminescence element, it is necessary to increase the dielectric constant of the entire insulating layer. However, when a fibrous high dielectric is used in the insulating layer formed by coating or the like, the high dielectric is dispersed in the binder as compared with the case where the particulate high dielectric is used. It is easy to happen and difficult to handle. In particular, when a flexible element is formed using a flexible substrate, the dielectric constant of the insulating layer increases as the element is repeatedly bent and stretched by using a fibrous high-dielectric material. It will change.

  Furthermore, considering the improvement of the performance of the entire device, the insulating layer has a high dielectric constant and contributes to high-luminance light emission, and does not increase the power consumption of the device or reduce the light emission lifetime. preferable.

  In view of the above circumstances, the present invention provides an AC-operated electroluminescence device having an insulating layer that contributes to high-luminance light emission of the device while being easy to form, and also contributes to suppression of power consumption and longer life of the device. It is intended to do.

  That is, the AC operation electroluminescent element of the present invention includes a light emitting layer that exhibits electroluminescence between a pair of electrodes, and an insulating layer provided on at least one side of the light emitting layer, and the insulating layer has an average of A layer having a layer thickness of 0.5 μm or more and 20 μm or less including at least a first high dielectric particle group and a second high dielectric particle group having different particle diameters with a filling ratio of 70% or more, The average particle size of the dielectric particle group is 150 nm or more, and the average particle size of the second high dielectric particle group is ½ or less of the average particle size of the first high dielectric particle group. To do.

  Here, the first high dielectric particle group and the second high dielectric particle group may be particle groups made of different types of high dielectric substances.

  Moreover, in the AC operation electroluminescent element of the present invention described above, the total volume of the first high dielectric particle group is in the range of 70% to 90% of the total volume of all the high dielectric particles in the insulating layer. Is preferred.

  Further, in the above-described AC operation electroluminescent device of the present invention, at least the first high dielectric particle group and the second high dielectric particle group are in a binder having a relative dielectric constant of 15 or less in the insulating layer. It is preferably dispersed. Moreover, it is preferable that the weight change when the whole element is left to stand for 48 hours in an environment of an air temperature of 25 ° C. and a humidity of 60% and then dried at 120 ° C. for 4 hours is 0.5% or less.

  Moreover, in the above-mentioned AC operation electroluminescent element of the present invention, it is preferable that the light emitting layer is a layer in which phosphor particles containing light emission centers that are collisionally excited by hot electrons are dispersed.

  In the AC operation electroluminescence device of the present invention, since the insulating layer is filled with at least two high dielectric particle groups having different sizes at a high filling rate, a particulate high dielectric material that is easy to handle is used. High luminance can be realized by applying a stable high electric field to the light emitting layer. In addition, since the insulating layer thickness is reduced in a range that does not cause a short circuit, the ratio of the voltage applied to the light emitting layer is increased to further increase the light emission luminance, and the dielectric loss in the insulating layer is reduced to reduce consumption. The power can be suppressed and the lifetime of the element can be increased. In addition, since such an insulating layer can be formed by a simple technique such as coating, the manufacturing process can be simplified and the cost can be reduced.

  In addition, when a binder having a relative dielectric constant of 15 or less is used in the insulating layer, or when the entire device is left for 48 hours in an environment of an air temperature of 25 ° C. and a humidity of 60% and then dried at 120 ° C. for 4 hours. When the weight change is adjusted to be 0.5% or less, it is possible to further reduce power consumption and extend the life of the element.

  Furthermore, the light emitting layer of the above-mentioned AC operation electroluminescent device of the present invention is collision-excited by hot electrons, which is particularly important for increasing the ratio of voltage applied to the light emitting layer and reducing the dielectric loss in the insulating layer. In the case of a layer in which phosphor particles containing luminescent centers are dispersed, the above-described effects of the present invention are better utilized. In addition, since such a light emitting layer can be formed by a simple technique such as coating like the above insulating layer, the entire element can be formed by a simple technique, and the overall manufacturing process is simplified. There is also an advantage that the cost and cost can be reduced. In addition, a large element or a flexible element can be manufactured.

  Hereinafter, exemplary embodiments of the present invention will be described in detail.

  In order to realize a high light emission luminance by applying a stable high electric field to the light emitting layer in an AC operation electroluminescence element, it is necessary to increase the dielectric constant of the entire insulating layer. Here, in the case of an insulating layer formed by a simple coating method or the like, the dielectric constant of the binder, which is generally an organic substance, is a high dielectric that is dispersed in the binder even if a relatively high dielectric constant is selected. It is only about 1/100 of the dielectric constant. Therefore, in order to increase the dielectric constant of the entire insulating layer, it is necessary to increase the filling factor of the high dielectric material.

  Therefore, in the AC operation electroluminescent device of the present invention, at least two high dielectric particle groups having different sizes are used as the high dielectric material dispersed in the insulating layer. As a result, if the size of each high-dielectric particle group is appropriately selected, the small high-dielectric particles enter between the large high-dielectric particles. It is possible to increase the filling rate of the high dielectric material in the insulating layer and contribute to improvement of the luminance of the element.

  Furthermore, considering the improvement of the performance of the entire device, it is preferable that the insulating layer not only has a high dielectric constant but also has a low dielectric loss. This is because if the dielectric loss in the insulating layer is large, heat is generated and the power consumption of the device increases, leading to a decrease in the light emission lifetime due to the deterioration of the binder and the deterioration of the material constituting the device. This heat generation becomes more and more serious as the applied voltage and frequency are increased in order to increase the light emission luminance of the device.

  In order to reduce the dielectric loss in the insulating layer, it is considered preferable to reduce the absolute amount of the dielectric loss by reducing the thickness of the insulating layer. In addition, it is preferable to reduce the thickness of the insulating layer from the viewpoint of increasing the ratio of the voltage applied to the light emitting layer in the applied AC voltage and increasing the light emission luminance. However, since the insulating layer plays a role of blocking the current path and preventing the short circuit of the element, it should not be so thin as to cause a short circuit.

  In terms of power consumption and light emission lifetime, the insulating layer preferably has a low moisture content and low hygroscopicity. If moisture and volatile components in the insulating layer are vaporized due to heat generated during electroluminescence, the light emitting performance deteriorates due to the formation of vacancies in the device and the vaporized component reacting with the phosphor in the light emitting layer. It is.

  Here, it is a binder part that contains moisture or a volatile component in the insulating layer. As described above, if the packing ratio of the high dielectric particles is increased by using at least two high dielectric particle groups having different sizes in the insulating layer, the proportion of the binder in the insulating layer is reduced. Although the rate and hygroscopicity can be reduced, the effect of further reducing the moisture content and hygroscopicity can be obtained by selecting an appropriate binder type. In general, a binder having a high dielectric constant is considered to have a tendency to easily contain water and absorb moisture due to its high polarity. From the viewpoint of increasing the voltage ratio applied to the light emitting layer and increasing the light emission luminance, it is preferable that the binder has a high dielectric constant, but the insulating layer is filled with high dielectric particles with a considerably high filling rate. If this is the case, the problem of lowering the brightness due to the use of a binder having a low dielectric constant is small, and the problems of water content and moisture absorption are more serious. Furthermore, the moisture content can be controlled by the drying conditions in the device manufacturing process. Therefore, it is considered preferable to employ a binder having a relatively low dielectric constant and low moisture content and moisture absorption in the element of the present invention.

  From the above, regarding the insulating layer of the AC operation electroluminescence element, at least two high dielectric particle groups having different sizes are used, and the size of each high dielectric particle group and the thickness of the insulating layer are adjusted. Thus, it is considered that the insulating layer contributes to high-luminance light emission of the element while being easily formed, and further contributes to suppression of power consumption and long life of the element. At the same time, it is considered that by using an appropriate binder having a relatively low dielectric constant and low moisture content and moisture absorption, it is possible to further reduce power consumption and extend the life of the device.

Therefore, as a result of verification by experiments to be described later, as shown in Table 1 below, as to the size of each high dielectric particle group, the average particle diameter of the first high dielectric particle group is 150 nm or more, and the second high dielectric particle group The average particle diameter of the dielectric particle group is set to ½ or less of the average particle diameter of the first high dielectric particle group, and is included in the insulating layer at a filling rate of 70% or more in total, preferably 75% or more. I understood that it was good. Moreover, about the layer thickness of the insulating layer, it turned out that a minimum is 0.5 micrometer or more, and an upper limit is 20 micrometers or less, More preferably, it is 10 micrometers or less, More preferably, 5 micrometers or less are good.

Each of the alternating-current-operation electroluminescent elements according to the examples and comparative examples described in Table 1 has a structure as shown in FIG. 1 and is manufactured as follows. As the substrate 10, a 350 μm thick BaSO ₄ kneaded white polyethylene terephthalate (PET) sheet exhibiting light scattering reflectivity was used. On this substrate 10, a light transmissive electrode 12 in which conductive particles such as In ₂ O ₃ and SnO ₂ were dispersed in a resin was formed. Next, a material obtained by dispersing phosphor particles 14a made of ZnS: Mn having an average particle diameter of 0.5 μm, prepared by spray pyrolysis and annealing with a muffle furnace, in a solution of cyanoethyl cellulose constituting the binder 14b, The light emitting layer 14 was formed by coating in a 2 μm thick layer. On the light-emitting layer 14, a paste in which ultrafine particles of BaTiO ₃ as high dielectric particles are dispersed in the same cyanoethyl cellulose solution as described above is applied for different elements, dried, and insulated. Layer 16 was formed. At this time, by adjusting the mixing ratio of the high dielectric particles and the binder, the filling rate of the entire high dielectric particles in the insulating layer 16 is 73% in the elements 1 to 14 in Table 1 and 67% in the element 15. In the element 16, it was set to 78%. Further, a carbon paste was applied on the insulating layer 16 so as to have a thickness of about 50 μm to form a back electrode 18. In addition, the relative thickness of each layer illustrated in FIG. 1 is for explanation, and is different from the actual thickness described above.

  Here, when the insulating layer 16 is formed, for the elements 1 to 4 in Table 1, only one type of high dielectric particle 20 having a uniform size is dispersed in the binder 22, and (a) of FIG. An insulating layer 16 as shown in FIG. For the other elements 5 to 17, a first high dielectric particle group consisting of high dielectric particles 20a having a large average particle diameter and a second high dielectric particle group consisting of smaller high dielectric particles 20b are used. The insulating layer 16 as shown in FIG. 2B was formed by mixing and dispersing in the binder 22. The average particle diameter of the first high dielectric particle group and the average particle diameter of the second high dielectric particle group in each element are as shown in Table 1. Further, the mixing ratio of the first high dielectric particle group and the second high dielectric particle group is about 3: 1 in volume ratio, that is, the total volume of the first high dielectric particle group is The total volume of all high dielectric particles in the insulating layer was set to about 75%.

  About each produced element, the Sawyer-Power circuit was assembled and the brightness | luminance and power consumption at the time of applying the alternating voltage of 250V and 1kHz were evaluated. The evaluation results are shown in Table 1. Here, the power consumption shown in Table 1 is a relative value when the element 1 is 100.

Looking at the evaluation results in Table 1, first, in the elements 1 to 4 using only one kind of high dielectric particles having a uniform size, even if the insulating layer is made as thin as 5 μm, it is 300 cd / m ^2. Only the brightness before and after was obtained and the power consumption was high.

Next, when the evaluation results of the elements 5 to 8 using the first and second high dielectric particle groups are compared, in the elements 5 to 7 in which the average particle diameter of the first high dielectric particle group is 150 nm or more, In both cases, a luminance exceeding 600 cd / m ² was obtained, and the power consumption was suppressed to a low level of 70 or less as a relative value. However, in the element 8 in which the average particle diameter of the first high dielectric particle group is 130 nm, the luminance falls to 350 cd / m ^{2 at} each stage, and the power consumption increases.

On the other hand, even if the average particle diameter of the first high dielectric particle group is set to 150 nm or more, the average particle diameter of the second high dielectric particle group is more than 1/2 of the average particle diameter of the first high dielectric particle group. In the large element 9, the luminance was as low as 360 cd / m ² and the power consumption was high.

Next, when comparing the evaluation results of the elements 10 to 15 in which the average particle diameters of the first and second high dielectric particle groups are fixed to 200 nm and 60 nm, respectively, and the layer thickness of the insulating layer is changed, the layer thickness is In each of the elements 11 to 14 in the range of 0.5 μm or more and 20 μm or less, high luminance of about 600 cd / m ² or more was obtained, and power consumption was suppressed to a low level of 70 or less in relative value. However, in the element 10 in which the thickness of the insulating layer was increased to 23 μm, the luminance dropped to each stage to 210 cd / m ² and the power consumption increased. On the other hand, in the element 15 in which the thickness of the insulating layer was reduced to 0.3 μm, the element was short-circuited and did not emit light.

Subsequently, when the evaluation results of the elements 16 and 17 in which the total filling rate of the high dielectric particles in the insulating layer is changed, the brightness of the element 16 in which the total filling rate is less than 70% is 390 cd / m ² . It is low and power consumption is high. On the other hand, in the element 17 in which the total filling rate was 78%, extremely good results were obtained in both light emission luminance and power consumption.

When the above evaluation results are combined, in the element having the insulating layer including the first and second high dielectric particle groups having different sizes, the average particle diameter of the first high dielectric particle group is 150 nm or more, the second The average particle diameter of the high dielectric particle group is set to ½ or less of the average particle diameter of the first high dielectric particle group, and is included in the insulating layer at a filling rate of 70% or more in total. It can be seen that when the layer thickness is 0.5 μm or more and 20 μm or less, high luminance of about 600 cd / m ² or more can be obtained, and the power consumption of the element can be suppressed low. The total filling rate is more preferably 75% or more. Moreover, about the upper limit of the layer thickness of an insulating layer, 10 micrometers or less are more preferable, and 5 micrometers or less are further more preferable.

  Here, from the total filling rate of 70% or more as described above, it is considered that the high dielectric particles are in close contact with each other in the insulating layer of the AC operation electroluminescent element of the present invention.

  There is no particular limitation on the lower limit of the size of the second high dielectric particle group, but if the size is too small, the particles themselves cannot obtain a stable dielectric constant, and they may easily aggregate and become difficult to handle. In consideration of the above, it is preferable to be about 1/100 of the first high dielectric particle group.

In the elements of the above embodiments, BaTiO ₃ particles are used as the particles forming the first and second high dielectric particle groups, but different types of high dielectric particles are used. Also good. For confirmation, a device similar to the device 7 in Table 1 in which the particles constituting the first high dielectric particle group were changed from BaTiO ₃ particles to SrTiO ₃ particles was evaluated for luminance and power consumption. Good results similar to those for element 7 were obtained. Further, in the first high dielectric particle group and / or in the second high dielectric particle group, a plurality of types of high dielectric particles having a uniform average particle diameter may be mixed and used.

Further, as a result of verification by another experiment described later, as shown in Table 2 below, in the AC operation electroluminescent device of the present invention, as a binder filling the space between the high dielectric particles in the insulating layer, the relative permittivity It has been found that it is preferable to use a material having 15 or less, more preferably 5 or less. Also, the entire element should be adjusted so that the weight change when dried at 120 ° C for 4 hours after being left for 48 hours in an environment of 25 ° C and 60% humidity is 0.5% or less. Was found to be preferable.

  Each element shown in Table 2 has a structure including the substrate 10, the light transmissive electrode 12, the light emitting layer 14, the insulating layer 16, and the back electrode 18 shown in FIG. The manufacturing method is also the same as that of the elements of the examples in Table 1. However, in any element, the average particle diameter of the first high dielectric particle group is 200 nm, the average particle diameter of the second high dielectric particle group is 90 nm, the total filling rate is 73%, and the layer thickness of the insulating layer Was 2 μm. Further, the mixing ratio of the first high dielectric particle group and the second high dielectric particle group is about 4: 1 in volume ratio, that is, the total volume of the first high dielectric particle group is The total volume of all high dielectric particles in the insulating layer was set to about 80%. Regarding the insulating layer, for elements 1 to 3 in Table 2, the same cyanoethyl cellulose as the element of each example of Table 1 was used as a binder for the insulating layer, but for element 4, non-vulcanized fluororubber was used. For No. 5, a thermoplastic cycloolefin resin was used as a binder for the insulating layer. The relative dielectric constants of the cyanoethyl cellulose, the non-vulcanized fluororubber and the thermoplastic cycloolefin resin used were 20, 13 and 3.5, respectively. In addition, by changing the drying conditions of each element at the time of forming the insulating layer, the residual amount of moisture and volatile components in the element (mainly in the insulating layer) was made different for each element.

  About each produced element, the Sawyer-Tower circuit was assembled and the brightness | luminance, power consumption, and light emission lifetime at the time of applying 250V, 1kHz alternating voltage were evaluated. The evaluation results are shown in Table 2. Here, the power consumption shown in Table 2 is a relative value when the element 1 shown in Table 1 is 100. In addition, the light emission lifetime is a relative value when the element 1 shown in Table 1 is set to 1 for the time until the initial luminance becomes ½. Note that each element was sandwiched from above and below by a moisture-proof film until just before the evaluation.

  Furthermore, after removing the moisture-proof film from the elements similar to the above-described elements 1 to 4 whose luminance and the like were evaluated and leaving them in an environment of an air temperature of 25 ° C. and a humidity of 60% for 48 hours, 120 ° C. 4 Time drying was performed and the weight change before and after drying was evaluated. The smaller the change in weight at this time, the smaller the content of moisture and volatile components in the element (mainly in the insulating layer). The evaluation results are also shown in Table 2.

  Comparing the evaluation results of the elements 1 to 3 shown in Table 2, in the element 1 in which the weight change when the entire element is dried at 120 ° C. for 4 hours is 0.5% or less, the power consumption is kept low, It can be seen that the emission lifetime is also longer. Further, when comparing the elements 1, 4, and 5, which each have a weight change of 0.5% or less during drying, the elements 4 and 5 using a binder having a relative dielectric constant of 15 or less in the insulating layer are more It can be seen that significantly improved power consumption and emission lifetime are obtained. In the element 5 using a binder having a relative dielectric constant of 5 or less, the improvement effect is particularly high. This is considered to be due to the fact that the hygroscopic property afterwards is lower when a binder having a lower relative dielectric constant is used even if the initial moisture and volatile component contents of the device are the same. On the other hand, regarding the light emission luminance of the device, comparing the devices 4 and 5 with the device 1, it can be seen that the light emission luminance hardly decreases even when a binder having a low dielectric constant is used.

  From the above, in the AC operation electroluminescent element of the present invention, the use of a material having a relative dielectric constant of 15 or less, more preferably 5 or less as a binder in the insulating layer allows consumption without impairing high luminance. It has been found that the effect of suppressing power can be further enhanced, and that the lifetime of the device can be extended. Also, the entire element should be adjusted so that the weight change when dried at 120 ° C for 4 hours after being left for 48 hours in an environment of 25 ° C and 60% humidity is 0.5% or less. As a result, it was found that the effect of further reducing power consumption and extending the life of the device can be obtained.

  The constituent materials of the insulating layer and other layers are not limited to those used in the above embodiments.

In addition to BaTiO ₃ and SrTiO ₃ used in the above examples, the material of the high dielectric particles in the insulating layer is, for example, Y ₂ O ₃ , Ta ₂ O ₅ , BaTa ₂ O ₆ , TiO ₂ , Sr ( Zr, Ti) O ₃ , PbTiO ₃ , Al ₂ O ₃ , Si ₃ N ₄ , ZnS, ZrO ₂ , PbNbO ₃ , Pb (Zr, Ti) O _{3 and the} like can be used. In the above embodiment, the insulating layer is provided only on one side of the light emitting layer, but it may be provided on both sides.

Furthermore, each of the elements in the above examples had a light emitting layer in which phosphor particles made of ZnS: Mn were dispersed, but any other light emitting layer exhibiting appropriate electroluminescence could be used. It may be a thing. Here, since the insulating layer in the element of the present invention described above can be formed by a simple technique such as coating or screen printing with a dispersion in which high dielectric particles are dispersed in a binder, the light emitting layer is also used. If the phosphor particles are dispersed in the binder in the same manner as the devices in the above embodiments, the entire device can be formed by a simple method, and the manufacturing process can be simplified and the cost can be reduced. There are advantages. In addition, a large element or a flexible element can be manufactured. At this time, as phosphor particles in the light-emitting layer, ZnS: Cu, which is activated by copper and emits light by recombination between a donor and an acceptor, as used in a conventional distributed AC operation electroluminescence element. Phosphor particles such as Cl may be used, but the case where phosphor particles containing an emission center that is collision-excited by hot electrons, such as ZnS: Mn used in each of the above embodiments, is used. The effects of the present invention described above are better utilized. This is because, when phosphor particles containing a luminescent center that is collision-excited by hot electrons are used, the electric field intensity at which light emission starts is as high as about 0.1 to 1 MV / cm. This is because it is particularly important to increase the ratio of the voltage and to reduce the dielectric loss in the insulating layer. Examples of such phosphors include ZnS: Mn, BaAl ₂ S ₄ : Eu, CaS: Pb, SrS: Ce, CaGa ₂ S ₄ : Ce, ZnS: Tb, Ga ₂ O ₃ : Mn, CaS. _{: Eu, ZnS: Sm, F} , Ga 2 O 3: Cr, Zn 2 SiO 4: Mn, Zn 2 GaO 4: Mn, Y 2 O 3: Eu and _Y 2 _O 2 S: Eu, and the like.

  As a material for the substrate, a flexible material such as the PET sheet used in the above embodiment may be used, or a glass substrate such as barium borosilicate glass or aluminosilicate glass may be used.

As the material of the transparent electrode, ITO (indium titanium oxide), ZnO: Al, Zn ₂ In ₂ O ₅ , (Zn, Cd, Mg) O— (B, Al, Ga, In, Y) ₂ O ₃ — ( Si, Ge, Sn, Pb, Ti, Zr) O ₂ , (Zn, Cd, Mg) O— (B, Al, Ba, In, Y) ₂ O ₃ — (Si, Sn, Pb) O, MgO— A material mainly containing In ₂ O ₃ , a GaN-based material, a SnO ₂ -based material, or the like can be used.

  A metal electrode such as an aluminum electrode may be used as the back electrode.

  In addition to the layer configuration of each of the above embodiments, an additional layer such as a surface protective layer may be provided.

  As mentioned above, although embodiment of this invention was described in detail, it cannot be overemphasized that these embodiment is only an illustration and the technical scope of this invention should be defined only by a claim. Yes.

Sectional drawing which shows the structure of each Example of an alternating current operation electroluminescent element which concerns on this invention, and a comparative example Sectional drawing of the insulating layer of the device of the comparative example and the device of the example of the present invention Sectional drawing which shows the basic structure of the conventional distributed AC operation electroluminescent element Sectional drawing which shows the basic structure of the conventional thin film type alternating current operation electroluminescent element

Explanation of symbols

10, 30, 40 Substrate 12, 32, 42 Transparent electrode 14, 34, 46 Light emitting layer 14a, 34a Phosphor particle 14b, 34b Light emitting layer binder 16, 36, 44a, 44b Insulating layer 18, 38, 48 Back electrode 20 20a, 20b High dielectric particles 22 Insulating layer binder

Claims (6)

Between a pair of electrodes, a light emitting layer exhibiting electroluminescence, and an insulating layer provided on at least one side of the light emitting layer,
The insulating layer is a layer having a layer thickness of 0.5 μm or more and 20 μm or less that includes at least a first high dielectric particle group and a second high dielectric particle group having a different average particle diameter at a filling rate of 70% or more in total. The average particle diameter of the first high dielectric particle group is 150 nm or more, and the average particle diameter of the second high dielectric particle group is 1 of the average particle diameter of the first high dielectric particle group. An AC-operated electroluminescence element characterized by being / 2 or less.   2. The alternating current operation electroluminescence device according to claim 1, wherein the first high dielectric particle group and the second high dielectric particle group are particle groups made of different types of high dielectric substances.   3. The alternating current according to claim 1, wherein a total volume of the first high dielectric particle group is in a range of 70% to 90% of a total volume of all the high dielectric particles in the insulating layer. Operating electroluminescence element.   The at least first high dielectric particle group and the second high dielectric particle group are dispersed in a binder having a relative dielectric constant of 15 or less in the insulating layer. The alternating current operation electroluminescent element of any one of Claims 1.   The weight change when the entire device is left to stand at an ambient temperature of 25 ° C and a humidity of 60% for 48 hours and then dried at 120 ° C for 4 hours is 0.5% or less. The alternating current operation electroluminescent element of any one of 1-4.   6. The alternating current operation electroluminescence device according to claim 1, wherein the light emitting layer is a layer in which phosphor particles including a light emission center that is collisionally excited by hot electrons are dispersed.

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