JPH11214158A - El element for back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a translucent scattering layer which excels in close adhesion property, has high transmissivity when light is emitted, is white when light is not emitted with high shielding property. SOLUTION: A light emitting layer 4 formed by adding a pink pigment 4c so as to make blue-green color look white presents pink color when light is not emitted, but looks white by a translucent scattering layer 1. The translucent scattering layer 1 is formed by titanium oxide coated mica 1a which is obtained by coating titanium oxide on a base material, mica, and has a particle size of 10 to 60 μm and a binder 1b. When the shielding property is to be increased 40% or less of titanium oxide is added to the titanium oxide coated mica 1a. The translucent scattering layer 1 provides transmissivity of 55 to 80% when its average film thickness is 3 to 20 μm so that desired transmissivity when light is emitted and desired shielding property when light is not emitted are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight EL device.

[0002]

2. Description of the Related Art As is well known, a display medium such as a liquid crystal panel includes:
When the outside world is bright, a reflective plate is arranged on the back side to reflect light from the front side so that the display can be viewed. However, since it cannot be seen when the outside is dark, a backlight is required. Therefore, in the prior art, as shown in FIG. 4, a semi-transmissive scattering plate b is arranged on the back of a display medium (liquid crystal panel) a, and an EL element c is arranged behind the plate. Thus, when the outside is bright, the liquid crystal display is made visible by reflecting the light from the outside by the light semi-transmissive scattering plate b.
By causing the L element c to emit light and using this as a backlight, the display on the display medium a can be viewed.

As an example of the EL element c, a transparent electrode layer 43 such as ITO is provided on one surface of a transparent electrode base film 42.
A light emitting layer 44, a high dielectric layer 45, and a back electrode layer 4 formed by adding a light emitting body 44a doped with copper of zinc sulfide (ZnS).
6 are sequentially laminated.

Since the emission color of a normal EL element is blue-green, the display surface of the transmission type display medium a also takes on a blue-green color. However, generally, white is preferred for the display surface. Therefore, as a means for causing the EL element to emit white light, a pink (see FIG. 4) pigment 44b having a complementary color relationship of blue-green is mixed into the light emitting layer.

However, when a pink pigment is added to the light-emitting layer, the EL element emits white light, but when no light is emitted, the display surface of the display medium looks like a pink color. It will be different. Therefore, in order to suppress this color, a white printed film is formed on a surface of a transparent electrode base film serving as a display surface, or a white filter is provided.

[0006]

When a white filter is provided as a means for suppressing the pink color during non-emission, or a white ink containing titanium oxide or aluminum powder is printed to form the filter. In the case of formation, since the film thickness to be formed is only several μm, there is a problem that the color at the time of non-emission changes due to a slight change in the film thickness, and it is difficult to control the film thickness.

Further, this thin film has poor adhesion to PET (polyethylene terephthalate) or the like used as a display surface (transparent electrode film) of an EL element, and is liable to be damaged. It is difficult to obtain a material having high smoothness.

[0008]

In order to solve the above problems, an EL device for a backlight according to the present invention comprises a light transmissive scattering layer composed of mica as a base material and coated with titanium oxide. It is formed by kneading titanium oxide coated mica having a particle size of 60 μm and, if necessary, kneading titanium oxide together with a binder at a weight ratio of 0 to 40%.

[0009] While titanium oxide-coated mica enhances light scattering, titanium oxide lowers the reflection density and enhances shielding properties, so that the reflection ratio depends on the mixing ratio of titanium oxide-coated mica and titanium oxide. It is easy to adjust density and gray scale.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A backlight EL device of the present invention comprises a transparent electrode layer on one surface of a transparent electrode base film.
A light-emitting layer, a dielectric layer, and a back electrode layer are sequentially laminated, and a white light-semi-transmissive scattering layer is formed on the other surface of the transparent electrode base film. It is characterized in that light transmission is sometimes high, and when light is not emitted, the reflection density is reduced so that the display surface of the EL element can be shielded.

The light transmissive scattering layer is composed of titanium oxide coated mica having a particle size of 10 to 60 μm by coating mica with titanium oxide, and titanium oxide added to the mica as needed. May be added in an amount of 40% or less by weight with respect to the titanium oxide-coated mica, and a binder may be mixed with the ink to form the ink.

The light transmissive scattering layer has a light transmittance of 55 to 8 when the average film thickness in a dry state is 3 to 20 μm.
It is set to be 0%.

[0013]

Next, an embodiment of the present invention will be described with reference to the drawings and tables. As shown in FIG. 1, the present invention comprises a light-emitting surface of a normal EL element c on which a light transflective layer 1 described later is formed. As an example of the EL element c, the following layers are laminated on one surface of a transparent electrode film 2 made of a PET (polyethylene terephthalate) sheet. The first layer is a transparent electrode layer 3 formed by depositing ITO. The light emitting layer 4 is formed as the second layer. The light emitting layer 4 is made of a phosphor 4a in which zinc sulfide (ZnS) is doped with copper.
Is dispersed in a high-dielectric resin binder 4b such as a fluororesin, and printed with an ink made by kneading a mixture to which a pink pigment 4c is added. On the third layer, a dielectric layer 5 is formed. The dielectric layer 5 is made of barium titanate (TiB) which is a high dielectric substance in a high dielectric binder.
aO ₃ ) is printed with ink dispersed therein.
On the fourth outer layer, a back electrode layer 6 formed by printing carbon ink is formed.

The light-emitting layer 4 comprises a mixture of a zinc sulfide (ZnS) -based phosphor 4a and a fluororesin binder 4b in a ratio of 7: 4, and a pink pigment (Sinloich FA-00).
1. Product name: Shinloich Co., Ltd.) 4c 2.5wt
% Is formed by kneading the kneaded mixture. The color of the light emitted by the light emitting layer is relatively strong in pink, but the ratio of the phosphor to the fluororesin binder is 5: 3. 75, to which 2 wt% of the above-mentioned pink pigment is added and kneaded to form an ink.

Since the EL element c has a pink pigment added thereto, it exhibits a white color due to a complementary color to the blue-green color when emitting light, but has a pink color when not emitting light. By forming the above-mentioned semi-transmissive scattering layer 1 on the other surface of the EL element c, it becomes white when viewed from the front in both light emission and non-white light.

Next, the light semi-transmissive scattering layer 1 will be described in detail. The light semi-transmissive scattering layer 1 is composed of a mica powder, a mica powder coated with titanium oxide (TiO ₂ , Ti ₂ O _3, etc.), a titanium oxide-coated mica 1a having a particle size of 10 to 60 μm, and a polyester resin. It is formed by screen printing using an ink produced by adding and kneading a binder 1b composed of a solvent such as isophorone or tetralin. In this embodiment, the ratio of (titanium oxide-coated mica) :( polyester resin) :( solvent) is set to 15:25:60.

[0017] The titanium oxide-coated mica alone may not have sufficient shielding properties for concealing the color on the back side. In such a case, however, if necessary, 40 wt% or less based on the titanium oxide-coated mica. The reflection density is increased by adding titanium oxide. Therefore, in this case, the above three parties (titanium oxide coated mica, polyester resin, solvent)
The ratio is (titanium oxide coated mica + titanium oxide):
(Polyester resin): Ratio of (solvent) among the three is 1
5:25:60.

The thickness of the coating of titanium oxide on mica can be determined by the mixing ratio of mica and titanium oxide. In the above embodiment, the ratio of titanium oxide was set to 2
8 wt%, 35 wt% for small particle size, and 16 wt% for large particle size.

[0019]

[Table 1]

Table 1 shows the particle diameter of titanium oxide-coated mica, the reflection density and the tristimulus value (X, Y,
Z) and the measurement results of the chromaticity coordinate values (x, y). Of the above three stimuli, X and Z have no significant meaning here, but the Y value is a value obtained when a so-called full color is converted to a gray scale. It has a blackening property. As for the chromaticity coordinate value (x, y), it can be seen that the values near x = 0.3 and y = 0.3 in the xy chromaticity diagram shown in FIG. 3 are white.

In the light semi-transmissive scattering layer of the present invention, the x and y values are each close to 0.3 in order to make the object color itself white, and the Y value is made as large as possible to produce whiteness as reflected and scattered light. Is required. Therefore, when the values in Table 1 are overviewed, it can be said that among them, the medium grain size type having 150 mesh is the most suitable.

Incidentally, when titanium oxide is added to titanium oxide-coated mica, it can be seen that the Y value decreases as the amount of addition increases. Further, those having a large particle size of mica have a large Y value, but are not suitable for adoption because the film thickness is too large and the light transmittance is reduced.

The light-semitransmissive scattering layer 1 transmits light emitted from the light-emitting layer during light emission, and further transmits light of a transmissive display medium (not shown).
Is required to transmit light from the back side to the front side.

FIG. 2 shows the drying after drying of the light-semitransmissive scattering layer formed by printing with the titanium oxide-coated mica alone, that is, without the addition of titanium oxide. (Dry) shows the relationship between film thickness and light transmittance. As can be seen from this figure, the transmittance is d
The thickness of the ry film becomes smaller as the film thickness increases, but by setting the average film thickness to 3 to 20 μm and the transmittance in the range of 55 to 80%, the specification generally satisfies the light transflective scattering layer. More preferably, it is preferable that the average film thickness is 7 to 15 μm and the transmittance is in the range of 60 to 70%.

Here, as for the thickness of the above-mentioned light semi-transmissive scattering layer, the particle size of the titanium oxide-coated mica 1a is 10 to 60.
μm, the surface of the light semi-transmissive scattering layer in a dry state is uneven, but not the maximum value or the minimum value of the unevenness, but the average value as a whole, that is, the average film thickness. Describes the characteristics.

[0026]

According to the present invention, since the ink having high adhesion to the EL light emitting surface is used, it is easy to form a semi-transmissive scattering layer, and it is possible to obtain an EL element for a backlight which is hardly defective. it can. In addition, when the light is not emitted, the display surface is made white with suppressed pink color, and when the light is emitted, high-luminance white EL emission with high transmittance can be used for the backlight.

Further, by forming the light semi-transmissive scattering layer of the present invention so as to have an average film thickness of 3 to 20 μm in a dry state, the light transmittance becomes 55 to 80%, which is a general practical range. Will be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment.

FIG. 2 is a diagram showing a relationship between a dry film thickness and light transmittance.

FIG. 3 is an xy chromaticity diagram as a reference diagram.

FIG. 4 is a sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semi-transmissive scattering layer 1a Titanium oxide coat mica 1b Binder 2 Transparent electrode base film 3 Transparent electrode layer 4 Light emitting layer 5 Dielectric layer 6 Back electrode layer

Claims (2)

[Claims] 1. A transparent electrode layer, a light emitting layer, a dielectric layer, and a back electrode layer are sequentially laminated on one surface of a transparent electrode base film, and the other surface of the transparent electrode base film has a white color. A light-semitransmissive scattering layer is formed, the light-semitransmissive scattering layer is a titanium oxide-coated mica having a particle size of 10 to 60 μm obtained by coating mica with titanium oxide;
A backlight EL comprising a titanium oxide having a weight ratio of 40% or less based on the titanium oxide-coated mica, which is added as necessary, and a binder.
element. 2. The method according to claim 1, wherein the light transflective layer has an average thickness of 3 to 20 μm in a dry state.
An EL element for a backlight, wherein light transmittance is 55 to 80%.