JP4961694B2 - Manufacturing method of organic EL element - Google Patents

Description

  The present invention relates to a method for producing an organic EL device comprising a light emitting medium layer including a transparent electrode, a counter electrode, and an organic light emitting layer, and causing the organic light emitting layer to emit light by passing a current from both electrodes to the organic light emitting layer. The present invention relates to a manufacturing method for forming a medium layer by a relief printing method.

  In recent years, with the diversification of information equipment, there has been a growing need for flat display elements that consume less power and occupy a smaller area than conventional CRTs. As one of such flat display elements, an electroluminescence element is required. (EL elements) are attracting attention.

  An EL element is an element that is excited by applying a voltage to a conductive luminescent material to emit light. It is divided into an inorganic EL element using an inorganic compound as a luminescent material and an organic EL element using an organic compound.

  Although some display devices using inorganic EL elements have been put into practical use from an early stage, their use has been slow due to problems such as the drive voltage being too high.

On the other hand, since organic EL elements exhibit high luminous efficiency, it is expected that research and development will be actively conducted for practical use in the future. The structure of this organic EL element is, for example, formed on a transparent substrate such as glass, a transparent hole (hole) injection electrode such as indium oxide doped with tin, and a hole injection electrode. A hole transport layer containing triphenyldiamine and the like, a luminescent medium layer containing a luminescent material such as an aluminum quinolinol complex laminated on the hole transport layer, and a metal electrode (electron injection electrode) having a low work function such as sodium As basic components. And, by applying a voltage of about 10 volts between the hole injection electrode and the electron injection electrode, it has a feature that extremely high luminance of several hundred to several tens of thousands of cd / m ² can be obtained. Such an organic EL element is expected to be applied to a color display device.

  As a method for forming a light emitting medium layer, thin film formation has been proposed by a vacuum process such as vacuum deposition. The method of forming a thin film by a vacuum process has the advantage that the film thickness of the thin film can be accurately controlled, but has a problem of poor throughput. Further, when a thin film is patterned in a vacuum process, it is common to use a mask having a desired pattern. However, this method has a problem that the patterning accuracy becomes difficult as the substrate becomes larger.

  Therefore, recently, a method for forming a thin film by a wet process such as a wet coating method or a printing method has been tried. Thin film formation by these wet processes has the advantage that film formation under atmospheric pressure is possible and the equipment cost is low.

  As the wet coating method, there are a spin coating method, a bar coating method, a protruding coating method, a dip coating method, and the like. However, in order to perform patterning with high definition or separate application to RGB three colors, these wet coating methods are used. It is difficult to form a thin film by a printing method that is good at painting and patterning.

  Examples of the printing method include various printing methods such as intaglio printing, relief printing, planographic printing, and screen printing. Gravure printing, which is representative of intaglio printing, is a metal plate, and its cost is high, replacement is not easy, it is a metal plate, so it can not handle glass substrates, the plate touches the base material and scratches etc. There is. Screen printing is not only suitable in terms of viscosity, but also has a problem that it is difficult to produce a thin film having a thickness of 0.1 μm.

  On the other hand, the relief printing method is a printing method suitable for organic EL that is compatible with the viscosity region of the organic light emitting ink and does not damage the substrate. The production of the organic EL element using the relief printing method can greatly speed up the production of the organic EL element. In addition, since a very expensive organic EL light emitting material can be printed only on a necessary portion, the material has a feature that only a necessary minimum amount of material is used.

  In a broad sense, the letterpress printing method is a printing method in which the image area is a convex plate, i.e., a letterpress, supplying ink to the convex part of the letterpress, and transferring and printing the ink on the convex part to the substrate. is there. In the printing industry, one using rubber letterpress is called flexographic printing, and one using resin letterpress is distinguished from resin letterpress printing. In the present invention, the letterpress printing method is called without any particular distinction.

In Patent Document 1, when an organic EL layer is formed by a printing method using an organic EL coating liquid (ink), the vapor pressure is 500 Pa or less for the purpose of preventing drying of the coating liquid generated in the printing process. An organic EL coating liquid characterized by containing at least one kind of a certain solvent has been proposed. Furthermore, there is a description that 250 Pa or less is preferable from the viewpoint of the surface property of the film. Moreover, when using the mixed solution of 2 or more types of solvent, it is described that it is preferable that the solvent whose vapor pressure in the temperature at the time of forming a film by a printing method is 500 Pa or less contains 50 wt% or more. .
JP 2001-155861 A

  However, when a high boiling point solvent is used for the ink, it becomes difficult to remove the high boiling point solvent in the organic light emitting medium layer after forming the organic light emitting medium layer on the substrate. If the solvent in the luminescent medium layer cannot be removed sufficiently and a residual solvent is present in the layer, there is a problem in that the emission intensity is reduced and the element is deteriorated. In addition, as a method for removing the solvent, heating drying, vacuum drying, vacuum heating drying, and the like are conceivable. However, in order to remove the high boiling point solvent, it is necessary to heat the substrate at a high temperature during drying, and the high boiling point solvent is sufficiently removed. When trying to remove, there is a problem that the element is deteriorated by heat. That is, when a high boiling point solvent is used for the ink, although drying of the ink during printing can be prevented, there has been a big problem in terms of solvent removal after printing. Therefore, an object of the present invention is to form a light emitting medium layer without using a high boiling point solvent when forming a light emitting medium layer using a relief printing method, and to obtain a good organic EL element.

In order to solve the above-mentioned problems, the invention according to claim 1 is composed of a light emitting medium layer including a transparent electrode, a counter electrode, and an organic light emitting layer, and causing the organic light emitting layer to emit light by flowing current from both electrodes to the organic light emitting layer. A method for producing an organic EL device, wherein the light-emitting medium layer is formed by transferring ink that has been converted into an ink using a solvent that dissolves or disperses the light-emitting medium material onto a substrate to be printed using a relief printing apparatus. In the method of manufacturing an organic EL element, the relief printing apparatus includes at least an ink supply unit, an anilox roll, and a relief printing, and the step of forming the light emitting medium layer using the relief printing apparatus includes the ink Supplying the ink from the supply unit onto the anilox roll, then supplying the ink on the anilox roll onto the relief plate, and The ink on the plate has, and supplying to the printing substrate, in the step of forming the light emitting medium layer by using the relief printing device, dissolving or dispersing the light emitting medium material in said ink by spraying fine droplets of the solvent have a step of applying to one of said anilox ink supplied onto a roll, or an ink which is supplied onto the relief plate, dissolve the luminescent medium material in said ink Or the solvent to disperse | distribute consists of a solvent with a boiling point of 200 degrees C or less, It was set as the manufacturing method of the organic EL element characterized by the above-mentioned.

  According to the present invention, when a low-boiling point solvent is used when making a luminescent medium material into an ink, it becomes possible to transfer the ink on the plate onto the printing substrate without drying the ink during relief printing. The pattern formation by flexographic printing could be performed accurately. Therefore, it was possible to produce an organic EL element free from unevenness and blurring. In addition, by using an ink composed of a low-boiling solvent, the heating step is eliminated in the drying step after pattern formation, or the solvent in the ink can be sufficiently removed under mild heating conditions. It was possible to manufacture an organic EL element with good luminous efficiency while suppressing deterioration of the constituent materials.

  The method for producing an organic EL device of the present invention is a method for producing an organic EL device comprising a transparent substrate and a luminescent medium layer composed of at least a single layer or a plurality of layers and a counter electrode on a support substrate, At least one of the luminescent medium layers is formed using a relief printing method using an ink composed of a solvent having a boiling point of 200 ° C. or lower. Hereinafter, an example of the organic EL element according to the present invention will be described with reference to FIG. The present invention is not limited to the configuration shown in FIG.

  The support substrate 1 that can be used in the present invention is a role of holding the electrode and the polymer light emitting medium layer during the production of the polymer EL element, and after completion of the polymer EL element, one side of the element is sealed, It plays a role of preventing deterioration of the element constituent material.

  Examples of the support substrate 1 include glass, a thin metal plate, and a plastic film. As the plastic film, polyethylene terephthalate, polypropylene, cycloolefin polymer, polyamide, polyether sulfone, polymethyl methacrylate, polycarbonate and the like can be used.

  Since the light emitting medium layer is a very thin film and even a slight unevenness causes pinholes, it is preferable to perform a smoothing treatment on the light emitting medium layer lamination side. If a flexible substrate such as a plastic substrate is selected, a flexible polymer EL element that can be bent can be manufactured. In addition, since the organic EL element can be manufactured while winding, continuous production is possible, which is advantageous in terms of cost.

  When using a water vapor permeable material such as a plastic film, it is necessary to have scratch resistance, reflection resistance, and oxidation resistance, so it is necessary to have a ceramic vapor deposited film, polyvinylidene chloride, polyvinyl chloride, ethylene-acetic acid. A gas barrier film such as a saponified vinyl copolymer may be laminated. Moisture resistance can also be imparted by performing a process such as vapor deposition or coating of an inorganic thin film.

  When the light extraction direction of the element is performed from the lower surface (bottom emission method) or both upper and lower surfaces (transparent organic EL element), it is preferable to select a translucent support substrate. From the viewpoint of translucency and moisture resistance, a glass substrate is preferable.

  A transparent electrode 2 is formed on the support substrate 1 as an anode. The transparent electrode 2 is not particularly limited as long as it is a conductive substance capable of forming a transparent or translucent electrode. Specifically, a composite oxide of indium and tin (hereinafter referred to as ITO) can be preferably used. A film can be formed on the support substrate 1 by vapor deposition or sputtering. Alternatively, a precursor such as indium octylate or indium acetone can be formed on the base material by a coating pyrolysis method in which an oxide is formed by thermal decomposition. Alternatively, a material in which a metal such as aluminum, gold, or silver is vapor-deposited in a translucent state can be used. Alternatively, an organic semiconductor such as polyaniline can also be used.

  The transparent electrode 2 may be patterned by etching as necessary, or may be activated by UV treatment, plasma treatment, or the like. When the light extraction direction is the top surface (top emission method), the transparent electrode is formed on the light emitting medium layer.

  After forming the transparent electrode, an insulating partition wall 6 is formed between adjacent patterned transparent electrodes by a photolithography method using a photosensitive material, if necessary. The photosensitive material for forming the insulating partition 6 may be either a positive type resist or a negative type resist, and may be a commercially available one, but it must have insulating properties. In the case where the partition has no insulating property, a current flows through the partition to the adjacent pixel electrode, resulting in a display defect. Specific examples include polyimide, acrylic resin, and novolac resin. Further, for the purpose of improving the display quality of the organic EL element, a light shielding material may be contained.

  Next, the light emitting medium layer 3 is formed on the conductive layer. The light emitting medium layer has a laminated structure including a hole injection layer, a hole transport layer, an electron block layer, a hole block layer, an electron transport layer, and an electron injection layer in addition to the organic light emitting layer containing an organic light emitting material, if necessary. It is possible to take. In addition, when a hole injection layer, a hole transport layer, an electron block layer, a hole block layer, an electron transport layer, and an electron injection layer are provided in the light emitting medium layer, the present invention can be applied to the formation of these layers. It is possible to apply a manufacturing method.

  The hole injection layer, the hole transport layer, and the electron block layer are layers having a material having a hole transport property and / or an electron block property, and each has a hole injection barrier from the anode to the organic light emitting medium layer. It is a layer that plays a role of lowering, advancing holes injected from the anode toward the cathode, and preventing electrons from traveling toward the anode while passing through the holes. The hole blocking layer and the electron transporting layer are layers having a material having an electron transporting property and / or a hole blocking property, and each forwards electrons injected from the cathode toward the anode. It is a layer that plays a role of preventing holes from traveling in the direction of the cathode while passing electrons. The electron injection layer is a layer having a material having an electron injection property, and is a layer that plays a role of lowering an electron injection barrier from the cathode to the organic light emitting medium layer. Here, a light emitting medium layer composed of the hole transport layer 3a and the organic light emitting layer 3b is shown.

  The hole transport material used for the hole transport layer 3a may be any material that is generally used as a hole transport material, such as copper phthalocyanine and its derivatives, 1,1-bis (4-di-p-tolylamino). Phenyl) cyclohexane, N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine, N, N'-di (1-naphthyl) -N , N′-diphenyl-1,1′-biphenyl-4,4′-diamine and other low molecular weight compounds such as aromatic amines can also be used. Among them, polyaniline, polythiophene, polyvinylcarbazole, poly (3,4-ethylenediene) An organic material such as a mixture of oxythiophene) and polystyrenesulfonic acid (PEDOT / PSS) is more preferable because it can be formed by a wet method.

  The hole transport layer forming material is dissolved or dispersed in a solvent to form a hole transport ink, which is formed on the substrate by a coating method using a slit coater, spin coater, bar coater, roll coater, die coater, gravure coater, etc. However, it can also be formed by the flexographic printing apparatus of the present invention. Moreover, after formation, it is dried to form a hole transport layer.

  As the solvent for dissolving or dispersing the hole transport material, for example, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, isopropyl alcohol, ethyl acetate, butyl acetate, water or the like alone or a mixture thereof A solvent etc. are mentioned. In particular, water or alcohols are suitable.

  Next, the organic light emitting layer 3b is formed on the hole transport layer 3a. The organic light emitting material used for the organic light emitting layer 3b may be any material generally used as an organic light emitting material. Coumarin-based, perylene-based, pyran-based, anthrone-based, porphyrene-based, quinacridone-based, N, N′— Fluorescent dyes such as dialkyl substituted quinacridone, naphthalimide, N, N'-diaryl substituted pyrrolopyrrole dissolved in polymers such as polystyrene, polymethyl methacrylate, polyvinyl carbazole, PPV and PAF Polyparaphenylene-based polymeric fluorescent materials can be used.

  The organic light emitting material is dissolved or dispersed in a solvent to form an organic light emitting ink, which is formed by the flexographic printing apparatus of the present invention.

  Solvents for dissolving or dispersing the organic light emitting material include, for example, toluene, xylene, anisole, mesitylene, tetralin, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, isopropyl alcohol, ethyl acetate, butyl acetate, water, benzoic acid Examples thereof include methyl acid, ethyl benzoate and the like alone or a mixed solvent thereof. Among these, xylene, anisole, and mesitylene are particularly preferable in terms of solvent removal after the formation of the organic light emitting layer because the organic light emitting material has good solubility and the boiling point at atmospheric pressure is 200 ° C. or less.

  Using these solvents, the organic light emitting ink is adjusted so that the solid content of the organic light emitting material is 0.8% to 2.5 wt%, and the viscosity of the organic light emitting ink is 10 mPa · s to 70 mPa at 25 ° C. It is preferably in the range of s, more preferably in the range of solid content of 1.0% to 2.0% and viscosity of 15 mPa · s to 60 mPa · s.

  Moreover, you may add surfactant, antioxidant, a viscosity modifier, a ultraviolet absorber, etc. to organic luminescent ink as needed.

  FIG. 2 shows a schematic diagram of a relief printing apparatus when pattern printing is performed on the substrate 24 to be printed with an ink made of an organic light emitting material. The printed substrate 24 has at least a transparent electrode and a hole transport layer formed on a support substrate. This manufacturing apparatus has a plate copper 18 on which an ink tank 10, an ink chamber 11, an anilox roll 13, and a relief plate 16 provided with projections are mounted. The ink tank 10 contains organic light-emitting ink, and the organic light-emitting ink is fed into the ink chamber 11 from the ink tank 10. The anix roll 13 is rotatably supported in contact with the ink supply part of the ink chamber 12.

  With the rotation of the anix roll 13, the ink 14 supplied to the surface of the anix roll is scraped off by the doctor 12 and formed into a uniform film thickness. The ink 14 is transferred to the convex portion of the relief plate 16 mounted on the plate cylinder 18 that is driven to rotate in the vicinity of the anix roll. On the flat table 20, the substrate to be printed 24 is transported to a printing position by the convex portion of the relief plate 16 by a transport means (not shown). And the ink in the convex part of the relief printing plate 16 is printed with respect to the to-be-printed substrate 24, and a pattern is formed.

  As the relief plate 16 provided with the projections, a metal plate is not suitable when the substrate is glass, and it is desirable to use a resin plate. In addition, when forming the organic light emitting layer, the solvent contained in the organic light emitting ink is an oil-soluble organic solvent. In order to prevent the swelling of the relief printing plate by this solvent and to enable accurate printing of the pattern, hydrophilic solvent is used. It is preferable to use a functional resin plate. Examples of such a relief plate include a water-developable resin relief plate obtained by applying a water-developable photocurable photosensitive resin to a plate substrate, and exposing and developing.

  The step of applying a liquid made up of fine droplets is performed on ink or a substrate to be printed before printing. The installation location of the liquid applicator is shown at 18a, 18b and 18c in FIG. It is preferable that the liquid application | coating process performed using a liquid application apparatus is performed with respect to the ink which exists on the letterpress 16 (18a). In addition, liquid may be applied to the ink on the anilox roll (18b). Also, when liquid is applied to the substrate to be printed before printing, the liquid is applied to the ink. (18c). Moreover, these may be performed simultaneously instead of individually. The liquid is applied to the ink in the form of fine droplets, ie, a mist. As a method for forming minute droplets, a spray method in which a liquid is passed through a minute hole while applying pressure, a heating evaporation method in which a liquid is heated to form a vapor, The ventilation system performed by blowing and vaporizing with respect to a liquid level is mentioned. Moreover, you may carry out by the combination of these. Furthermore, an air blowing mechanism may be provided to apply the liquid to a predetermined location.

  The liquid to be applied should have a boiling point of 200 ° C. or lower, and must be compatible with the ink. Preferably, the liquid is the same as the solvent contained in the ink or a liquid comprising at least one of the solvents contained in the ink. The ink on the liquid-applied plate or anilox roll in this manner can suppress an increase in viscosity due to drying of the ink, that is, evaporation of the solvent. That is, it is possible to compensate for the evaporation of the solvent in the ink in the printing process. Therefore, the ink can be stably transferred from the plate to the substrate to be printed, and the pattern formation by flexographic printing can be performed accurately. An organic EL element free from unevenness and blurring can be obtained.

  Further, these liquid application mechanisms (18a, 18b, 18c) can save space, can be attached to a commercially available flexographic printing apparatus, and can be implemented at low cost.

  As a method for drying the ink printed on the substrate to be printed, it may be heated or dried under reduced pressure, but it is more preferable to dry under heating and reduced pressure to remove the solvent. By using a solvent and a liquid having a boiling point of 200 ° C. or less, the solvent and the applied liquid can be sufficiently removed without heating at a high temperature.

  Next, the counter electrode 4 is formed as a cathode. As the counter electrode 4, a single metal such as Mg, Al, or Yb is used, or a compound such as Li or LiF is sandwiched by about 1 nm at the interface in contact with the light emitting medium material, and highly stable and conductive Al or Cu is laminated. And use. Alternatively, in order to achieve both electron injection efficiency and stability, an alloy system of a metal having a low work function and a stable metal, for example, an alloy such as MgAg, AlLi, or CuLi can be used. As a method for forming the cathode, a resistance heating vapor deposition method, an electron beam method, or a sputtering method can be used depending on the material. The thickness of the cathode is preferably about 10 nm to 1000 nm.

  Finally, in order to protect these organic EL laminates from external oxygen and moisture, an organic EL element can be obtained by hermetically sealing with a glass cap and an adhesive. Moreover, when a translucent board | substrate has flexibility, sealing sealing is performed using a sealing agent and a flexible film.

  A 0.7 mm thick and 100 mm square glass substrate was used as the support substrate, and an ITO line with an 800 μm pitch (L / S = 700/100) was provided as the anode (conductive layer). Next, a reverse-tapered cathode (counter electrode) dividing partition 7 was formed by photolithography so as to be orthogonal to the ITO line.

  Thus, PEDOT / PSS was added to a 1 wt% aqueous dispersion of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT / PSS), which are hole transport materials, on the support substrate provided with the partition walls. A solution obtained by adding 0.5% amount of higher alcohol ether type surfactant: Emulgen 105 (manufactured by Kao Corporation, nonionic) so that the film thickness after drying is 180 nm by the slit coat method. Was applied to form a hole transport layer.

  On the hole transport layer thus formed, 1 of poly [2-methoxy-5- (2′-ethylhexyloxy) -1,4-phenylenevinylene] (MEH-PPV), which is a polymer light-emitting material, is formed. A .8 wt% o-xylene solution was formed to a thickness of 80 nm by flexographic printing. In order to prevent drying of the film during printing, o-xylene was sprayed on the plate and anilox roll by a spray method so that the spray amount / surface area = 0.005 ml / cm 2. The ink on the support substrate was dried at 120 ° C. under reduced pressure for 4 hours. Next, MaAg was formed into a pattern with a thickness of 200 nm by binary co-evaporation as the cathode layer 6 to produce a passive drive type organic EL device.

  The obtained passive drive type organic EL device was able to display only selected pixels without leak current, and showed 100 cd / m 2 at an applied voltage of 7.3V.

(Comparative Example 1)
As Comparative Example 1, an organic light emitting layer was formed in the same manner as in Example except that o-xylene was not sprayed. As a result, the ink was dried on the plate of the flexographic printing apparatus, and the ink on the plate could not be completely transferred onto the substrate to be printed (support substrate).

(Comparative Example 2)
As Comparative Example 2, formation of an organic light emitting layer in the same manner as in Example 1 except that triethylbenzene was used instead of o-xylene as a solvent for the organic light emitting material MEH-PPV, and liquid spraying was not performed. An organic EL element was created. As a result, the obtained organic EL element can emit only selected pixels with no leakage current and showed 100 cd / m 2 at an applied voltage of 9.5 V. ) Was confirmed.

It is sectional drawing of the organic EL element of this invention. It is the schematic of the relief printing apparatus of this invention.

Explanation of symbols

1 Support substrate 2 Transparent electrode (anode)
3a Hole transport layer 3b Organic light emitting layer 4 Counter electrode (cathode)
6 Insulating partition 10 Ink tank 11 Ink chamber 12 Doctor 13 Anilox roll 14 Ink 16 Letterpress 17 Plate cylinder 18a, 18b, 18c Liquid applicator 20 Flat table 24 Printed substrate

Claims (1)

A method of manufacturing an organic EL device comprising a light emitting medium layer including a transparent electrode, a counter electrode, and an organic light emitting layer, and causing the organic light emitting layer to emit light by passing an electric current from both electrodes to the organic light emitting layer. Alternatively, in the method for producing an organic EL element for forming the light-emitting medium layer by transferring ink inked using a solvent to be dispersed onto a substrate to be printed using a relief printing apparatus, the relief printing apparatus includes at least An ink supply unit, an anilox roll, and a letterpress;
The step of forming the light emitting medium layer using the relief printing apparatus includes:
Supplying the ink from the ink supply unit onto the anilox roll;
Next, supplying the ink on the anilox roll onto the relief plate,
Next, supplying the ink on the relief plate onto the substrate to be printed,
Have
Wherein in the step of forming the light emitting medium layer by using a relief printing device, supplied by the light emitting medium spraying fine droplets of solvent in which the material is dissolved or dispersed in said ink onto said anilox roll ink, or said fed onto the relief plate was have a step of applying any of the ink, the solvent for the luminescent medium material dissolved or dispersed in said ink organic EL characterized in that it consists of a boiling point 200 ° C. or less of the solvent Device manufacturing method.

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