JP2007188678A - Organic el element for printer head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element for a printer head capable of easily suppressing color mixture of emitted light. <P>SOLUTION: This organic EL element 1 for a printer head is composed by stacking, on a substrate 2, a translucent reflecting film 3, a positive electrode layer 4, a hole injection layer 5, a hole transport layer 6, a luminescent layer 7, an electron transport layer 8, and a negative electrode layer (equivalent to a reflecting film as defined in a claim) 9. The translucent reflecting film 3 is formed by allowing a part of light emitted from the luminescent layer 7 to be transmitted, and the negative electrode layer 9 is formed by allowing the light emitted from the luminescent layer 7 to be totally reflected. The translucent reflecting film 3 and the negative electrode layer 9 are arranged to allow the light emitted by the luminescent layer 7 to resonate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic EL element for a printer head for exposing photosensitive paper or a photosensitive drum.

  Currently, an optical printer for printing an image by exposing a photosensitive member such as photosensitive paper or a photosensitive drum is known. Lasers and LEDs (light emitting diodes) are known as techniques for exposing a photoreceptor.

  In the case of an optical printer in which a photosensitive member is exposed by a laser, the photosensitive member must be exposed by scanning the laser by the width of the photosensitive member. Therefore, there is a problem that a driving means for driving the laser is required, and the size of the optical printer is increased.

  Therefore, an optical printer having a printer head in which LEDs are arranged corresponding to the width of the photoreceptor is known. In the case of the printer head in which the LEDs are arranged in this way, it is not necessary to scan the printer head in accordance with the width of the photosensitive member, so that the driving means for driving the printer head can be omitted. This has the advantage that the optical printer can be miniaturized.

  However, when LEDs are arranged on the same substrate in accordance with the width of the photoconductor, a large substrate is required, which increases the manufacturing cost of the substrate. Also known is a technique in which an LED array in which LEDs are arranged on a plurality of substrates is produced, and the LED array is arranged in accordance with the width of the photoconductor. However, it is difficult to align the LED arrays. In addition, there is a problem that it is difficult to increase the density of LEDs due to a gap formed between the LED arrays.

  Therefore, attention has been paid to an optical printer including a printer head in which organic EL elements that can be formed on an inexpensive substrate such as glass are arranged.

  In an optical printer having an organic EL element, an organic EL element arranged on a printer head is caused to emit light according to the width of the photosensitive paper, and the photosensitive paper is exposed to, for example, three colors of RGB by the emitted light. To print.

  However, as a matter of course, the organic EL element does not emit only light of a single wavelength, but emits light mixed in color with a certain emission spectrum. When the photoreceptor is exposed to light having a broad emission spectrum in this way, a mixed color is printed in the same manner as the emission spectrum.

  Therefore, Patent Document 1 discloses a technique for suppressing color mixture of light emitted from an organic EL element.

In the technique of Patent Document 1, a color filter is arranged in the irradiation direction of an organic EL element that emits blue and green light, and light of mixed color components can be removed by this color filter.
JP 2005-67026 A

  However, in the technique of Patent Document 1, since the color filter must be prepared as a separate part, there is a problem that the number of parts increases and the configuration of the optical printer becomes complicated. In addition, when the color filter is a separate component, alignment between the color filter and the organic EL element is required, and there is a problem that the manufacturing process becomes complicated.

  The present invention has been made in order to solve the above-described problems, and an object thereof is to provide an organic EL element for a printer head capable of easily suppressing color mixture of emitted light.

  In order to achieve the above object, the invention described in claim 1 is a light-emitting layer, a reflective film capable of totally reflecting light emitted from the light-emitting layer, and a side opposite to the reflective film across the light-emitting layer. And a translucent reflective film capable of reflecting a part of the light emitted from the light emitting layer, and the reflective film and the translucent reflective film are disposed so as to resonate the emitted light. An organic EL element for printer heads.

  According to the present invention, since the light emitted from the light emitting layer can resonate between the reflective film and the translucent reflective film, the desired light out of the light emitted from the light emitting layer can be resonated. In addition to being able to enhance, light other than the desired light can be attenuated. Thereby, after resonating, it is possible to easily suppress the color mixture of light irradiated from the translucent reflective film to the outside.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional structure of an organic EL element for a printer head (hereinafter referred to as an organic EL element) according to the present invention.

  The organic EL element 1 includes a translucent reflective film 3, an anode layer 4, a hole injection layer 5, a hole transport layer 6, a light emitting layer 7, an electron transport layer 8, a cathode layer (on the reflective film according to the claims) on a substrate 2. Equivalent) 9 are stacked.

  Since the organic EL element 1 is configured such that light is emitted from the substrate 2 side, the substrate 2 is a transparent substrate that can transmit light, such as a glass substrate.

  The translucent reflective film 3 is made of Ag, Al, Cr, a compound thereof, or a dielectric multilayer film. This translucent reflective film 3 is configured to have a reflectance of about 50%. Therefore, half of the light emitted from the light emitting layer 5 is transmitted by the translucent reflective film 3 and half of the light is reflected toward the cathode layer 9.

  The anode layer 4 is made of a transparent electrode such as ITO having a thickness of about 100 nm that can transmit the light emitted from the light emitting layer 7.

  The hole injection layer 5 improves the injection rate of holes injected from the anode layer 4 and is made of copper phthalocyanine (CuPc). The hole transport layer 6 is for transporting holes injected from the anode layer 4 through the hole injection layer 5 to the light emitting layer 7 and is made of NPB.

The light emitting layer 7 is configured to emit light by injected electrons and holes. The electron transport layer 8 is for smoothly transporting the electrons injected from the cathode layer 9 to the light emitting layer 7 and is made of Al ₃ .

  The cathode layer 9 is made of a reflective film such as Al that can totally reflect the light emitted by the light emitting layer 7.

  Here, the combined thickness of the organic layer 10 of the organic EL element 1 composed of the hole injection layer 5 to the electron transport layer 8 and the anode layer 4 is configured to resonate the light emitted by the light emitting layer 7. ing. Specifically, the optical distance from the upper surface of the translucent reflective film 3 calculated from the thickness of the organic layer 10 and the anode layer 4 to the lower surface of the cathode layer 9 (the actual distance multiplied by the refractive index of the substance) ) L is configured to satisfy either L = kλ / 2n (there is no phase shift on the reflection surface) or L = kλ / 4n (the reflection surface has a half-wavelength shift). Here, k is an integer, and λ is the peak wavelength of the emission spectrum emitted from the light emitting layer 7.

  Therefore, the light emitted by the light emitting layer 7 resonates between the translucent reflective film 3 and the cathode layer 9. A part of the resonated light passes through the translucent reflective film 3 and the substrate 2 and is emitted to the outside. An image can be printed on the photosensitive paper by exposing the photosensitive paper with the light emitted to the outside.

  Thus, by resonating the light emitted by the light emitting layer 7 between the translucent reflective film 3 and the cathode layer 9, it is possible to intensify the light having the peak wavelength of the emission spectrum, and other wavelengths. Can weaken the light. Thus, after resonating, most of the light that is transmitted to the outside through the substrate 2 and the translucent reflective film 3 can be constituted by light of a desired wavelength, and light of other wavelengths is reduced. Therefore, color mixing of light can be suppressed.

  Next, the results of experiments conducted to prove the effect of the organic EL element according to the present invention will be described.

  First, the effect of reducing the color mixture will be proved using the emission spectrum.

  First, an experimental result of an organic EL element capable of emitting blue light will be described with reference to FIG. In FIG. 2, the solid line shows the experimental result of the organic EL element capable of resonating according to the present invention. In FIG. 2, the alternate long and short dash line indicates the experimental result of the organic EL element according to the comparative example in which the light cannot be resonated. In FIG. 2, the dotted line shows the result of simulation of the organic EL element that can resonate. 2 is a result of experiment using the organic EL element 1 in which the thickness of the organic layer 10 is set to about 120 nm and the thickness of the anode layer 4 is set to about 100 nm.

  As is clear from the comparison of the emission spectrum according to the present invention (solid line) shown in FIG. 2 and the emission spectrum according to the comparative example (one-dot chain line), it can be seen that the emission spectrum having a wavelength of about 470 nm or more is greatly reduced. . From this, it can be seen that color mixing due to light other than the peak wavelength of about 410 nm can be greatly reduced.

In a simulation using a blue organic EL element that can resonate as a model, the color mixture ratio with green light was as low as about 3.5%. Here, the color mixing ratio is a ratio of different colors (green and red in the case of a blue organic EL element) in an emission spectrum obtained by simulation. Specifically, the color mixing ratio of green in the blue organic EL element is
Color mixing ratio = (area of blue emission spectrum × green filter characteristic) / area of blue emission spectrum.

  Next, experimental results of the organic EL element for emitting green light will be described with reference to FIG. In FIG. 3, the solid line shows the experimental result of the organic EL element capable of resonating according to the present invention. In FIG. 3, an alternate long and short dash line indicates an experimental result of the organic EL element according to the comparative example in which the light is configured not to resonate. In FIG. 3, the dotted line shows the result of simulation of the organic EL element that can resonate. 3 is a result of an experiment using the organic EL element 1 in which the thickness of the organic layer 10 is set to about 160 nm and the thickness of the anode layer 4 is set to about 100 nm.

  As can be seen from the comparison of the emission spectrum according to the present invention shown in FIG. 3 (solid line) and the emission spectrum according to the comparative example (one-dot chain line), it can be seen that the emission spectrum having a wavelength of about 550 nm or more is greatly reduced. . From this, it can be seen that color mixing due to light other than the peak wavelength of about 520 nm can be greatly reduced.

  In a simulation using a resonating green organic EL element as a model, the color mixture ratio with red light was about 3.0% and the color mixture ratio with blue light was a low value of about 3.0%. .

Next, the effect of reducing the color mixture will be proved using chromaticity coordinates.

  Table 1 shows an organic EL element that emits green and blue light, an organic EL element of a comparative example that does not resonate, and an organic EL element that can resonate according to the present invention, and the respective chromaticity coordinates are examined. It is. For reference, chromaticity coordinates using liquid crystals are also listed. FIG. 4 is a plot of the experimental results shown in Table 1 on chromaticity coordinates, where ◯ indicates chromaticity coordinates according to the present invention, Δ indicates chromaticity coordinates according to a comparative example, and □ indicates chromaticity by liquid crystal. The coordinates are shown. The chromaticity coordinates referred to here are a mixture of emission spectra obtained through experiments.

 As shown in Table 1, in the case of an organic EL element that emits green light, the chromaticity coordinates of the organic EL element of the comparative example are (0.24, 0.43), whereas The chromaticity coordinates of the organic EL element are (0.22, 0.73). Thereby, as shown in FIG. 4, it turns out that the organic EL element of this invention is emitting deep green light with few color mixing compared with the organic EL element of a comparative example.

  Further, as shown in Table 1, in the case of an organic EL element that emits blue light, the chromaticity coordinates of the organic EL element of the comparative example are (0.16, 0.12). The chromaticity coordinates of the organic EL element according to the invention are (0.14, 0.08). Thereby, as shown in FIG. 4, it turns out that the organic EL element of this invention is emitting deep blue light with few color mixing compared with the organic EL element of a comparative example.

  Although the present invention has been described in detail using the above-described embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the embodiments described in this specification. The present invention can be implemented as modifications and changes without departing from the spirit and scope of the present invention defined by the description of the scope of claims. Therefore, the description of the present specification is for illustrative purposes and does not have any limiting meaning to the present invention. Hereinafter, modified embodiments in which the above-described embodiment is partially modified will be described.

  For example, the material which comprises each layer of the said embodiment is not limited to what was mentioned above, It can change suitably. Similarly, if the light emitted from the light emitting layer 7 can resonate, the thickness of each layer can be changed as appropriate.

1 shows a cross-sectional structure of an organic EL element for a printer head (hereinafter referred to as an organic EL element) according to the present invention. It is a figure showing the emission spectrum by the organic EL element which concerns on this invention which can light-emit blue light, a comparative example, and simulation. It is a figure showing the emission spectrum by the organic EL element which concerns on this invention which can light-emit green light, a comparative example, and simulation. It is a figure showing the chromaticity coordinate by the organic EL element which concerns on this invention which can light-emit blue and green light, a comparative example, and simulation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic EL element 2 Substrate 3 Translucent reflective film 4 Anode layer 5 Hole injection layer 6 Hole transport layer 7 Light emitting layer 8 Electron transport layer 9 Cathode layer 10 Organic layer

Claims (1)

A light-emitting layer, a reflective film capable of totally reflecting light emitted from the light-emitting layer, and a part of the light emitted from the light-emitting layer, located on the opposite side of the reflective film across the light-emitting layer. With a translucent reflective film capable of reflecting,
An organic EL element for a printer head, wherein the reflective film and the translucent reflective film are disposed so that the emitted light can resonate.

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