JPH05335085A - Electroluminescent element and drive method therefor - Google Patents

Abstract

PURPOSE:To provide an electroluminescent element having reduced self-capacity and high luminous brightness, and enable the element to be driven while reducing a drive frequency disagreeable to the ears by making a luminous element of an organic dispersion type electroluminescent element to drive a luminous layer within the predetermined frequency, and keeping the dielectric constant of a binder for the luminous layer equal to or below the predetermined value. CONSTITUTION:A luminous element comprises a transparent glass substrate 2, a transference electrode layer 4, a luminous layer 6 formed with fluorescent particles dispersed in a binder made of epoxy resin, a reflective insulation layer 8 with BaTiO3 dispersed in epoxy resin, a back electrode layer 10, and a moisture-proof film 12, respectively stacked in order. The binder in the layers 8 and 10 is epoxy resin and has a dielectric constant equal to or less than 15. Also, the layers 4 and 10 are connected to an inverter to drive the layer 6 via an electrode lead led from the sealing peripheral end of the substrate 2 and the film 12. A drive frequency for the inverter is between 6 and 10kHz.

Description

Detailed Description of the Invention

[001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic dispersion type electroluminescent device driven at a high driving frequency and an electroluminescent device applicable not only to a dispersion type but also to all thin film type, enamel type etc. The present invention relates to a driving method.

[002]

2. Description of the Related Art Generally, an electroluminescent element is thin and can obtain uniform surface emission with low power consumption. Therefore, it is used for a backlight of a liquid crystal display device or an eraser of a copying machine. In recent years, the applications have been expanding more and more, and thinner and lighter ones are required as the needs.

By the way, in an inverter for driving the light emitting layer, in most cases, the drive frequency is currently 500 Hz to
1 kHz, and in part only 3-4 kHz. Such a low drive frequency is generally
This is because there is an inverse relationship between the driving frequency and the life time of the electroluminescent element, but the low frequency inevitably causes a problem of increasing the transformer size volume in the inverter.

In general, the frequency band of 500 Hz to 4 kHz is said to be the region of highest sensitivity for human hearing, and especially for audio equipment, telephones, etc., where low noise is preferable, it is uncomfortable. It is disliked as "peeping" noise, and despite the noise countermeasures such as attaching a third electrode to the electroluminescent element to cancel the vibration, it has a high sound pressure level of 40 dB and is used in a quiet office or the like. It has become a problem, and its countermeasures have been desired.

[0095]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electroluminescent device with reduced noise and reduced volume to enhance the emission brightness, and to "feel the ear" for human hearing. The present invention provides a novel method for driving an electroluminescent element, which drives the electroluminescent element with a minimum drive frequency.

[0096]

DISCLOSURE OF THE INVENTION In general, the inventor has found that, for human hearing, 500 Hz-
The present invention was completed by finding out that the fact that it becomes smaller near 8 kHz higher than 4 kHz (see, for example, Tokyo Observatory Polar Science Department chronological table, page 490) is applied to an electroluminescent device, and by conducting various experiments. ..

First, the electroluminescent device of the present invention has a frequency of 6 to.
An organic dispersion type EL device that drives a light emitting layer at 10 kHz, characterized in that the binder of the light emitting layer has a relative dielectric constant of 15 or less.

The binder is preferably made of epoxy resin. The reflective insulating layer laminated on the light emitting layer is made of epoxy resin.

The driving method of the electroluminescent element of the present invention is characterized in that the driving frequency of the electroluminescent element is set to 6 to 10 kHz.

The driving frequency is preferably around 8 kHz.

[0111]

According to the method of the present invention, the driving frequency of the electroluminescent element is set to 6 to 10 kHz, preferably around 8 kHz. Therefore, even if the sound pressure level is the same, the conventional frequency is 500 Hz to 4 kHz. It sounds like a small sound to human hearing, about 10 to 20 horns. Also,
In the conventional drive at a frequency of 500 Hz or 1 kHz,
The third high frequency is in a high sensitivity band for all human ears and is heard as a squeaky sound, whereas when the driving frequency is 6 to 10 kHz, the second and third high frequencies are 12 to 20 kHz, The frequency becomes 18 to 30 kHz, which is very insensitive to the human ear or completely outside the audible frequency range. That is, noise can be significantly reduced.

Further, according to the electroluminescent device of the present invention, the frequency is set to 6 to 10 kHz, so that when the same output is obtained,
The higher the frequency, the smaller the transformer can be used, which allows the inverter to have a smaller volume. This is particularly effective for equipment that requires a small size.

Further, conventionally, from the relationship between the lighting frequency and the life time, the lower the frequency, the more advantageous the life is. On the other hand, in the electroluminescent element of the present invention, even if the frequency is increased, Its packaging technology provides excellent moisture protection and does not reduce the required life. In other words, except for extreme usage examples, generally, the actual usage time is 10
It can withstand between 00 and 2000 hours.

By driving the light emitting layer at a high frequency of 6 to 10 kHz, the dielectric constant of the binder can be lowered as the frequency is increased, even though the same current is passed between the electrodes. It is not necessary to use a high dielectric constant material such as cyanoethyl-based binder (relative dielectric constant 20 to 30) of
Epoxy resin (relative permittivity around 4) or the like can be used as a binder or the like. Moreover, for example, a cyanoethyl-based binder contains a large amount of water, whereas a low-dielectric-constant resin such as an epoxy-based resin has a small water content, so that the life can be improved.

[0115]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 First, the structure of the electroluminescent element will be described. As shown in FIG. 1, the electroluminescent element comprises a transparent glass substrate 2, a transparent electrode layer 4 such as ITO, and a phosphor particle made of epoxy. A light emitting layer 6 formed by dispersing it in a binder made of a resin (trademark Epicoat 1004 butyl cartol solution), a reflective insulating layer 8 formed by dispersing BaTiO3 in the same solution as the above epoxy resin, Back electrode layer 10 such as a metal film, and moisture-proof film 12
Are sequentially laminated. The moisture-proof film 12 includes a pair of polyester films 14 and 14, a metal layer 16 such as an aluminum foil sandwiched between the polyester films 14 and 14, and a sealing layer 18 of a thermoplastic resin such as modified polyethylene. And this moisture-proof film 1
The periphery of 4 is hermetically sealed to the transparent substrate 2 via a suitable adhesive.

Particularly noteworthy in this embodiment is that the binder in the light emitting layer 6 and the reflective insulating layer 8 is an epoxy resin and has a relative dielectric constant of 4. The binder preferably has a relative dielectric constant of about 3 to 15 and low dielectric loss.
This is because if the relative permittivity is 15 or more, the dielectric loss generally increases and the efficiency decreases.

Although not shown, the transparent electrode layer 4 and the back electrode layer 10 drive the light emitting layer 6 through the electrode leads led from the sealing peripheral portion of the transparent glass substrate 2 and the moisture-proof film 12. It is connected to the inverter for the drive frequency.
This is due to the use of an inverter operating at Hz. The inverter can be easily constructed by changing the winding of the transformer and the circuit constant.

In the electroluminescent element thus constructed, the light emitting layer 6 is driven through the inverter, the transparent electrode layer 4 and the back electrode layer 10.

Importantly, when the driving frequency is set to 8 kHz, the luminous efficiency of the light emitting layer 6 becomes lower as compared with the epoxy type because the cyanoethyl type is lowered as described below.

For comparison, a conventional electroluminescent device was prepared in which the binders of the light emitting layer 6 and the reflective insulating layer 10 were used alone with cyanoethyl pullulan. With respect to the luminous efficiency of the conventional one, in terms of the luminous efficiency in relation to the driving frequency, the luminous efficiency of the conventional cyanoethyl-based binder is good up to the driving frequency of 6 kHz, but conversely, the driving frequency is 6 kHz. Beyond that point, the luminous efficiency of the epoxy binder of this example is good. It is considered that this is because the current increases as the driving frequency increases, and the luminous efficiency decreases in the cyanoethyl system, which has a large inductive loss.

The emission brightness of both electroluminescent elements was set to 20.
When the noise level was measured according to the nit, the conventional electroluminescent device using cyanoethyl pullulan alone as the binder of the light emitting layer 6 and the reflective insulating layer 10 had a driving frequency of 1 kHz.
In the case of z, it was 29.8 dB, but in the present embodiment, it can be remarkably reduced to 21.3 dB at the drive frequency of 8 kHz.

Further, in the electroluminescent device of the present invention, the same brightness can be obtained, but a smaller input is required as the luminous efficiency is increased. Further, an electroluminescent element having a high moisture-proof effect is provided by a transparent glass substrate and the moisture-proof film 12 including the metal layer 16 as compared with a case where the whole is surrounded by a light-transmitting moisture-proof film such as trifluoroethylene chloride resin. Therefore, in the electroluminescent device of the present invention,
There is no big difference with about 2000 hours.

Example 2 Unlike the example 1, the light emitting layer 6
Also, a conventional electroluminescent device using cyanoethyl pullulan alone without using an epoxy resin as the binder of the reflective insulating layer 10 was used, and the driving frequency was 8 k as in Example 1.
Driven as Hz.

The noise level was measured by adjusting the light emission luminance to 20 nits. When the driving frequency was 1 kHz, 29.
While it was 8 dB, in the present embodiment, the drive frequency was 8
It was 24.4 dB at kHz.

[0266]

EFFECT OF THE INVENTION In an organic dispersion type EL device for driving a light emitting layer at a frequency of 6 to 10 kHz, the binder of the light emitting layer has a relative dielectric constant of 15 or less to reduce noise and reduce the volume of the inverter. It is possible to provide an electroluminescent device in which the emission brightness is improved by reducing

Further, the driving frequency of the electroluminescent element is set to 6 to 10.
By setting the frequency to kHz, it is possible to provide a novel method for driving an electroluminescent element, which drives the electroluminescent element with a drive frequency that is “audible to human hearing” as small as possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing an electroluminescent device according to an embodiment of the present invention.

[Explanation of symbols]

 2 transparent glass substrate 4 transparent electrode layer 6 light emitting layer 8 reflective insulating layer 10 back electrode layer 12 moisture-proof film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masafumi Asada 100 491, Oka, Kaminaka-cho, Anan City, Tokushima Prefecture Nichia Kagaku Kogyo Co., Ltd.

Claims (5)

[Claims] 1. An electroluminescent element, which is an organic dispersion type EL element for driving a light emitting layer at a frequency of 6 to 10 kHz, wherein a binder of the light emitting layer has a relative dielectric constant of 15 or less. 2. An electroluminescent device, wherein the binder is made of epoxy resin. 3. An electroluminescent device, wherein the reflective insulating layer laminated on the light emitting layer is made of epoxy resin. 4. The driving frequency of the electroluminescent device is 6 to 10 k.
A method for driving an electroluminescent device, characterized in that the frequency is set to Hz. 5. A method of driving an electroluminescence device, wherein the driving frequency is around 8 kHz.