JPS6259879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distributed AC electroluminescent device. More specifically, a dispersed AC electroluminescent device (hereinafter referred to as a dispersed EL (hereinafter referred to as "element").

Dispersed EL elements emit light by applying an electric field to a light-emitting layer in which phosphors are dispersed in a matrix resin with a high dielectric constant.The light-emitting layer is formed in a film shape, making it easy to thin the layer and making it flexible. and
Furthermore, it has the advantage that the area can be freely selected. Attempts are being made to utilize this advantage to put displays into practical use. The higher the dielectric constant of the matrix resin used as the dispersion medium for the phosphor, the higher the brightness, which is advantageous, but simply having a high dielectric constant is not enough.In order to increase the brightness, it must be transparent and durable. It must have voltage. Even more decentralized
It must not impair the flexibility, which is a characteristic of EL devices.

Epoxy resins, cyanoethyl cellulose, and the like have been proposed as such matrix resins. However, the former is not very preferable due to its low dielectric constant. Cyanoethyl cellulose depends on the degree of cyanation, but those with 80% or more cyanation have an extremely high dielectric constant of 15 or more, so they are extremely advantageous in terms of dielectric constant and are the most commonly used. has been done.

However, when making an EL device, an electrode is required to apply a voltage to the luminescent layer, which is formed by dispersing phosphor in a matrix resin. For example, a transparent electrode such as ITO or tin oxide is used as the electrode on the side), but it is also necessary to tightly adhere this electrode to the luminescent layer. In addition, although the back side of the light emitting layer may be in direct contact with the electrode, the light emitting layer in which phosphors are dispersed in a matrix resin is non-uniform and it is difficult to apply a uniform voltage. A voltage-resistant reflective layer is provided in which a white powder such as titanium oxide powder is dispersed in a resin. Close contact with this back layer is also required. When providing a voltage-resistant reflective layer, it is possible to use a voltage-resistant reflective layer whose matrix resin is a resin that has good adhesion to the light-emitting layer, so that adhesion is not a big problem. However, if the luminous layer has good adhesion, a transparent high dielectric constant dielectric film can be used instead of the voltage-resistant reflective layer, and a reflective metal such as nickel or aluminum can be deposited on the back of the film to create a mirror surface. This is even more advantageous since the dielectric film becomes a withstand voltage layer and the mirror surface of the vapor-deposited metal becomes a reflective surface. However, the cyanoethylcellulose mentioned above
It has poor adhesion with transparent electrodes such as ITO and tin oxide, as well as polymeric substances, and a light-emitting layer using cyanoethyl cellulose as a matrix resin tends to form gaps between the light-emitting layer and the transparent electrode layer. There are many cases where it is not possible to apply

The present invention uses a cyanoethylated ethylene vinyl alcohol copolymer, which has excellent dielectric constant and adhesive properties with transparent electrodes, as a highly dielectric resin component, for example, as a matrix resin component of a luminescent layer. The present invention provides an EL device with a high quality. The present invention will be explained in detail below.

The ethylene-vinyl alcohol copolymer used for cyanoethylation is usually obtained by saponifying ethylene-vinyl acetate copolymer.
The degree of saponification can be selected arbitrarily. However, since the alcohol group is cyanoethylated and a high dielectric constant is obtained, it is preferable that the degree of saponification is high, and the copolymer is generally saponified by 50% or more, more preferably 80% or more. Also, this ethylene
Regarding the degree of cyanoethylation of the vinyl alcohol copolymer, it is not necessary that all of the OH groups in the vinyl alcohol bonding groups are cyanoethylated, but in order to maintain the high dielectric constant required for EL devices, the OH Preferably, 40% or more of the groups are cyanoethylated. More preferably 50
% or more. Furthermore, the ethylene group is necessary to impart flexibility, adhesiveness, and thermal stability to the cyanoethylated ethylene-vinyl alcohol copolymer, and is 10 mol% or more and 70 mol% of the copolymer constituent groups.
The following are desirable. If it is less than 10 mol%, the cyanoethylated ethylene-vinyl alcohol copolymer will have poor adhesion to the electrode and poor thermal stability;
Exceeding this is not preferable because the content of cyanoethyl groups will be small and the dielectric constant will be low.

The cyanoethylated ethylene-vinyl alcohol copolymer used in the present invention is thermoplastic and soluble in solvents, so it can be easily formed into a film, and this film has an extremely high dielectric constant and strong adhesion to electrodes. have For example, a resin film with an ethylene content of 68 mol% and a degree of cyanoethylation of about 90% exhibits a dielectric constant of about 20 at 25° C. and 1 KHz. In addition, since it has an ethylene group, it has excellent fluidity when melted and has excellent thermal stability. Furthermore, since this cyanoethylated copolymer is apparently insoluble in water and hardly swells, it is thought to have low water absorption. However, because it dissolves well in polar solvents such as acetone, methyl ethyl ketone, dimethyl formamide, acrylonitrile, nitromethane, and other polar solvents, it is possible to easily form cast films using these solvents, and this film can also be formed on glass plates or aluminum plates. The material that is cast or thermally welded onto the surface is extremely strongly adhered to the extent that it cannot be easily peeled off.

A known phosphor can be used as the phosphor dispersed in the matrix resin. For example, using ZnS as a matrix, it can be used alone or in addition to Cu, I, Cl, Al,
A typical example is one to which at least one of Mn, NdF ₃ and the like is added.

The volume ratio of phosphor and matrix resin is
There should be 10 to 300 parts of matrix resin per 100 parts, preferably 50 to 200 parts. If the amount of resin exceeds this range, the brightness will be low because there are few fluorescent sources, and if it is below, there will be too much phosphor and pinholes will easily occur, making it impossible to increase the applied electric field, resulting in low brightness. It is for the sake of becoming.

The method of mixing the phosphor and matrix resin to form the phosphor layer is arbitrary, such as directly kneading the matrix resin and the phosphor and extruding it into a film, or press-molding it. Due to the excellent fluidity of the resin, it is possible to make a uniformly mixed film for the luminescent layer. Alternatively, a uniform luminescent layer film can be formed by casting a mixture of a phosphor and a matrix resin in a resin solvent to form a film.

The cyanoethylated ethylene-vinyl alcohol copolymer used in the present invention as a highly dielectric resin component of the dispersed AC electroluminescent device, for example, as a matrix resin for the luminescent layer, has extremely excellent transparency, and the thickness of the luminescent layer Even if the resin is relatively thick, the light in the lower layer is hardly attenuated in the resin. The appropriate thickness of the luminescent layer is usually in the range of 5 to 100 microns.

The structure of the element of the present invention can be configured arbitrarily. For example, if necessary, a voltage-resistant reflective layer or a transparent dielectric layer is provided on the base electrode, the above-mentioned light-emitting layer is adhered thereon, and a transparent electrode such as ITO is further applied thereon. The transparent electrode may be provided directly on the light emitting layer by vapor deposition, sputtering, coating, etc., or for example, the surface of the transparent electrode such as ITO applied on the surface of a film such as polyester or polycarbonate may be bonded under high temperature. . Further, when using a high dielectric constant film coated with a transparent electrode such as ITO, the surface of the film opposite to the ITO may be adhered to the light emitting layer.

The simplest method is to replace the above-mentioned film for the light-emitting layer, which is made of phosphor and matrix resin, with an ITO vapor-deposited film (the ITO surface can be arbitrarily selected on either the light-emitting layer side or the opposite side). The light-emitting layer can be brought into close contact with the ITO vapor-deposited film and the lower electrode very easily simply by sandwiching it between the lower electrode layer having the voltage layer and heat-pressing it. Furthermore, instead of using a film-formed luminescent layer, if the luminescent layer is formed by a casting method on an ITO vapor-deposited film or a lower electrode layer, even if the solvent is evaporated at a temperature close to room temperature, Good adhesion can be obtained with the ITO vapor deposited film or the lower electrode.

In addition, if the polymer film surface of the ITO vapor-deposited film is in contact with the luminescent layer, it is necessary to use a polymer film with a high dielectric constant as much as possible, and make sure that sufficient voltage is applied to the luminescent layer. . As such a high dielectric constant film, for example, a vinylidene fluoride polymer or a copolymer film containing vinylidene fluoride as a main component and a monomer copolymerizable with the vinylidene fluoride polymer is preferably used. The cyanoethylated ethylene-vinyl alcohol copolymer used in the present invention adheres extremely well to these vinylidene fluoride polymers or copolymers.

When such a high dielectric constant film is placed between the transparent electrode and the light emitter layer, this film becomes a withstand voltage layer and the voltage distribution to the light emitter becomes uniform, so the withstand voltage between the lower electrode and the lower electrode increases. The voltage reflective layer or transparent dielectric layer can be omitted. the above
It is also possible to use cyanoethylated ethylene-vinyl alcohol copolymer as the high dielectric constant polymer film on which ITO is deposited. In this case, it is desirable for the polymer film to have a high dielectric constant as well as high insulation properties, and as a cyanoethylated ethylene-vinyl alcohol copolymer, it is recommended to increase the content of ethylene groups even if the dielectric constant is sacrificed. It is better to increase the dielectric strength. still,
When the ITO surface is directly bonded to the light emitter layer, the polymer film of the vapor-deposited film does not need to have a high dielectric constant, and may be a transparent film such as polyester resin or polycarbonate resin. The phosphor layer of the present invention also has extremely good adhesion to ITO.

The cyanoethylated ethylene-vinyl alcohol copolymer can be used as a matrix resin for a voltage-resistant reflective layer provided as necessary between the lower electrode and the transparent dielectric layer film.

The EL element of the present invention has extremely excellent adhesion, even when the luminescent layer is directly adhered to the electrode, or when a high dielectric constant resin layer is provided between the electrode and the extremely high dielectric constant. Since the phosphor is dispersed in the resin with high efficiency, a high voltage can be uniformly applied to the phosphor, and voltage emission with extremely high efficiency and high brightness can be achieved.

The light-emitting layer using the cyanoethylated ethylene-vinyl alcohol copolymer of the present invention as a matrix resin has sufficient adhesion to be applicable to all of these. The EL device of the present invention having such a structure takes advantage of the high dielectric constant of the matrix resin used in the light-emitting layer and its good adhesion to transparent electrodes, etc., to provide a high-luminance EL device.

The present invention will be explained below with reference to Examples.

Example Ethylene-vinyl alcohol copolymer (manufactured by Kuraray, EVAL EP-F ethylene content: 32 mol%) was cyanoethylated with acrylonitrile. N
The degree of cyanoethylation to vinyl alcohol was determined to be approximately 90%. The dielectric constant of this cast film showed a high value of 20 at 1KHz. This resin is soluble in polar solvents such as acetone, methyl ethyl ketone, and dimethyl formamide, and the film has extremely good transparency. In addition, it has extremely good adhesion to glass metals, etc., and to ITO transparent electrodes (polyester film vapor deposition).
Pressing at 200°C for 2 minutes made the adhesive adhere to such an extent that it would not come off at all.

On the other hand, ZnS/cyanoethylated resin = ZnS/cyanoethylated resin
The mixture was mixed in acetone in a volume ratio of 60/40, the latter was dissolved and then coated on 100μ Al foil, and the acetone was removed by drying. The thickness of the formed luminescent layer was 60μ.

The ITO electrode surface deposited on the polyester surface was adhered to the surface opposite to the Al foil at 200° C. and a pressure of 15 kg/cm ² to form a transparent electrode layer.

The adhesion between the Al foil and ITO surface and the EL light-emitting layer using cyanoethylated resin was so good that the Al foil would break if you tried to forcefully peel it off.

This element has a frequency of 1K for a light emitter thickness of 60μ.
When an electric field of Hz2Vrms/μm was applied and the brightness was measured, it was found to be 42 cd/m ² . As a comparative example,
A device completely identical to the example was prepared except that cyanoethyl cellulose was used instead of the cyanoethylated resin. This product also had poor adhesion between the ITO electrode and the light emitting body, resulting in uneven brightness within the light emitting surface. The brightness was 30 cd/ ^m2 .

From the above examples and explanations, it can be seen that the distributed EL device according to the present invention has high brightness, and has Al foil electrodes.
Because it has good adhesion with ITO electrodes, it is resistant to mechanical bending and is extremely useful industrially.

Although the present invention has been illustrated above, it will be understood that the above-mentioned examples can be further modified based on the technical idea of the present invention.

Claims (1)

[Claims] 1. A dispersed AC electroluminescent device characterized by using a cyanoelated ethylene-vinyl alcohol copolymer as a highly dielectric resin component.