JP2009070897A - Organic electroluminescence device and method for producing the same - Google Patents

Abstract

An object of the present invention is to improve display defects of an organic electroluminescence device manufactured by a relief printing method.
An organic electroluminescence device manufactured by a relief printing method, and at least a layer formed by the relief printing method has a concentration of a metal or a metal compound composed of chromium, iron, nickel, cobalt of 100 ppm or less. To do. The anilox roll 12 and the doctor blade 13 used in the printing apparatus for achieving the above object are designed so that the Vickers hardness and the contact angle satisfy a predetermined relationship.
[Selection] Figure 1

Description

  The present invention relates to an organic electroluminescence element and a method for producing the same, and more particularly to an organic electroluminescence element for improving display defects in a display of an organic electroluminescence element produced by using a relief printing method and a method for producing the same. It is.

  An organic electroluminescence element (organic EL element) is a light emitting element having a structure in which an organic light emitting layer is sandwiched between an anode and a cathode. When a voltage is applied, holes are injected from the anode and electrons are injected from the cathode. It is an element that takes out the energy generated as a result of recombination of a hole-electron pair on or inside the organic light emitting layer as light. Organic electroluminescence devices using organic substances in the light emitting layer have been studied for a long time, but their practical application has not progressed due to the problem of light emission efficiency. In contrast, in 1987, C.I. W. Tang proposed an organic electroluminescent device with a laminated structure in which the organic light emitting layer is divided into two layers, a light emitting layer and a hole transport layer, and confirmed high-efficiency light emission at low voltage (see Non-Patent Document 1, etc.). Since then, research on organic electroluminescence devices has been actively conducted.

  Organic materials used for the light emitting layer of the organic EL element are classified into low-molecular materials and high-molecular materials. The method for forming the light emitting layer varies depending on the material. For low molecular weight materials, a method of forming a film mainly by vapor deposition is used, and for high molecular weight materials, a method of dissolving or dispersing in a solvent and applying on a substrate is performed. In addition, as a means for patterning the light emitting layer in order to make the organic EL element full color, when using a low molecular weight material, a mask having a pattern according to a desired pixel shape is used, and different light emitting colors are used. A method of depositing and forming a light emitting material on a portion corresponding to a desired pixel is performed. This method is an excellent method for uniformly forming a thin film in a desired shape, but there is a problem that it is difficult to form a pattern when the substrate to be deposited becomes large in terms of mask accuracy.

  On the other hand, in the case of using a polymer material, a pattern formation mainly by an ink jet method and a pattern formation method by printing have been proposed. For example, in the inkjet method disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 10-12377), a light emitting layer material dissolved in a solvent is ejected from an inkjet nozzle onto a substrate and dried on the substrate to obtain a desired pattern. Is the way to get.

  However, since the ink droplets ejected from the nozzle have a spherical shape, the ink spreads in a circular shape when landing on the substrate, and the formed pattern lacks linearity or the landing accuracy is poor. There is a problem that linearity cannot be obtained. On the other hand, for example, in Patent Document 2 (Japanese Patent Laid-Open No. 2002-305077), a bank is formed in advance on a substrate with a material having ink repellency using photolithography or the like, and ink droplets are landed on the bank. Thus, a method is disclosed in which the ink repels according to the bank shape and a linear pattern is obtained. However, when the repelled ink returns to the inside of the pixel, the ink swells inside the pixel, and there remains a problem that the film thickness of the organic light emitting layer in the pixel varies.

  Therefore, instead of low-molecular-weight organic light-emitting materials, a method has been proposed in which organic polymer light-emitting materials are dissolved or dispersed in a solvent to make ink, and this ink is patterned by a printing method. A printing method, a screen printing method, and the like have been proposed. In particular, letterpress printing is excellent in pattern formation accuracy, film thickness uniformity, and the like, and is suitable as a method for producing an organic electroluminescence element by a printing method.

In the production of organic electroluminescent elements by letterpress printing, organic polymer light-emitting materials are dissolved or dispersed in a solvent and converted into ink, and arranged in a matrix of fine square or hexagonal lattices called anilox rolls. It is applied to a roll surface having a concave hole. Further, the ink applied per unit area of the anilox roll is made uniform by scraping off excess ink on the surface with a doctor blade. Next, the ink on the anilox is transferred to a relief plate corresponding to the shape of the pixel. Finally, the ink on the letterpress is transferred onto the substrate to form the organic light emitting layer of the organic electroluminescence element.
However, when an organic light emitting layer is formed by letterpress printing, the anilox roll and doctor blade for supplying ink to the letterpress with a desired pixel pattern are constantly rubbed during the printing process. Wear occurs, and foreign matter generated by the wear is mixed in the ink and taken into the printed organic light emitting layer. The foreign matter taken into the organic light emitting layer may cause a short circuit, a non-emission point (dark spot), or a point that shines stronger than the other part of the pixel (bright spot) when the element emits light. Pixels will not light up.
Japanese Patent Laid-Open No. 10-12377 JP 2002-305077 A C. W. Tang, S.M. A. VanSlyke, Applied Physics Letters, 51, 913, 1987

  This invention is made | formed in view of the above-mentioned situation, The objective is to improve the light emission defect of the organic electroluminescent element which provided the organic light emitting layer with the relief printing method.

As a result of intensive studies for overcoming the above-mentioned problems, the present inventor has obtained the present invention.
The invention according to claim 1 includes at least one organic light emitting layer having a light emitting region on a substrate, an anode for injecting holes into the organic light emitting layer, and a cathode for injecting electrons into the organic light emitting layer. And at least one of the organic light-emitting layers is formed by a relief printing method, and the concentration of the metal or metal compound in the organic light-emitting layer formed by the relief printing method is It is an organic electroluminescence element characterized by being 100 ppm or less (hereinafter also referred to as a first embodiment).
The invention according to claim 2 is characterized in that the metal or metal compound is derived from an anilox roll in a relief printing method and a doctor blade for removing unnecessary ink on the anilox roll. Item 2. The organic electroluminescence device according to Item 1 (hereinafter also referred to as a second embodiment).
According to a third aspect of the present invention, the metal element contained in the metal and the metal compound is selected from the group consisting of chromium, iron, nickel and cobalt, and the concentration is the concentration of the metal or metal compound composed of these elements. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a total.
According to a fourth aspect of the present invention, there is provided a step of forming one or more organic light emitting layers having a light emitting region on a substrate, a step of forming an anode for injecting holes into the organic light emitting layer, and the organic light emission. Forming a cathode for injecting electrons into the layer, wherein at least one of the organic light emitting layers is formed by a relief printing method and used in the relief printing method When the Vickers hardness of the anilox roll is Ha and the Vickers hardness of the doctor blade for removing unnecessary ink on the anilox roll is Hb, the organic light emitting layer formed by the relief printing method satisfies the following relationship: A method for producing an organic electroluminescence device, wherein the concentration of the metal or metal compound is 100 ppm or less There (hereinafter, also referred to as a third embodiment).
Ha> Hb ≧ 700 Hv
The invention according to claim 5 is characterized in that the angle formed by the doctor blade and the upstream of the rotation direction in the tangential surface of the anilox roll at the place where the anilox roll and the doctor blade are in contact is an acute angle of 5 to 75 °. It is a manufacturing method of the organic electroluminescent element of Claim 4 (henceforth the 4th form).

  According to this invention, the light emission failure of the organic electroluminescent element which provided the organic light emitting layer with the relief printing method is improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram for explaining an example of a manufacturing process of an organic electroluminescence element by a relief printing method.
In FIG. 1, a fine and uniform for supplying a constant amount of ink to an ink fountain 11 filled with an ink in which a light emitting material for forming an organic light emitting layer is dissolved in a solvent (hereinafter referred to as light emitting layer ink). A part of the surface of the anilox roll 12 on which the concave pattern is formed is immersed. The fine and uniform concave patterns formed on the surface of the anilox roll 12 are generally arranged in a square, rhombus or hexagonal lattice matrix, but irregular when moire from the anilox roll occurs. There may be used one having a concave hole (however, the total volume (cell volume) of the holes per unit area is constant). The size of the concave pattern is usually represented by the value of the number of lines in the matrix per unit length and is called the number of lines. Also, the larger the number of lines, the smaller the concave pattern on the anilox, and the cell volume decreases.

  The light emitting layer ink is applied to the surface of the anilox roll 12 that has passed through the ink fountain, and then the excess light emitting layer ink on the anilox roll 12 is scraped off by a doctor blade 13 that is in contact with the tangent line of the anilox roll at a certain angle. A uniform liquid film with an ink amount appropriately regulated by the volume is obtained. The anilox roll 12 on which an appropriate amount of the luminescent layer ink is placed is pressed against the relief plate 14 on which a desired pattern wound around the surface of the plate cylinder 16 is formed, and the luminescent layer ink moves to the relief plate surface at a certain rate. Subsequently, the light emitting layer ink 17 on the surface of the letterpress is pressed against the substrate 15, the light emitting layer ink is transferred to the substrate 15 side, and dried to form a pattern of the organic light emitting layer on the substrate 15.

  However, since the rotating anilox roll 12 and the doctor blade 13 are constantly rubbing inside the relief printing apparatus, the anilox roll or the doctor blade is worn. For this reason, foreign matter generated by abrasion is mixed into the ink and taken into the printed organic light emitting layer. The foreign matter taken into the organic light emitting layer may cause a short circuit, a non-emission point (dark spot), or a point that shines stronger than the other part of the pixel (bright spot) when the element emits light. Pixels sometimes stopped lighting.

  In particular, anilox rolls have innumerable fine concave surfaces on the surface due to their properties, and can be regarded as rough surfaces. In general, wear due to friction with a rough surface is greater than wear due to friction between smooth surfaces, so the anilox roll cell is preferably as fine and smooth as possible (the number of lines is large), but if the number of lines is too large, the cell The volume is insufficient and the film thickness of the resulting pattern is insufficient. Therefore, in order to obtain a printed film having a uniform organic light emitting layer, the number of anilox rolls is appropriately 300 to 900 per inch in the case of a hexagon (honeycomb).

  In order to remove foreign substances such as metal or metal fine particles generated from an anilox roll or a doctor blade due to wear, the light emitting layer ink inside the ink fountain 11 may be circulated and filtered to remove foreign substances. In addition, if the generated foreign matter has magnetism, a mechanism for collecting the foreign matter by a magnet can be installed inside the printing apparatus, and the foreign matter can be removed by this mechanism.

Still, among the generated foreign matter, minute or ionized particles cannot be completely removed from the light emitting layer ink even by filtration or the like, and are taken into the light emitting layer pattern formed by printing.
As a countermeasure against foreign matter, it is most preferable not to increase the concentration of foreign matter in the luminescent layer ink by frequently replacing the luminescent layer ink used for printing with a new liquid. Not only is this time consuming, but the loss of ink in which the expensive organic light emitting layer material is dissolved increases.

  Therefore, the present inventor, in the production of organic electroluminescent elements by the relief printing method, the hardness and contact angle of the anilox roll and doctor blade of the printing apparatus, the concentration of foreign matter in the organic light emitting layer and the display failure of the organic electroluminescent element. As a result of intensive studies focusing on the relationship, the present invention has been achieved.

  In the first and second embodiments, at least the organic light-emitting layer formed by the relief printing method among the organic electroluminescence elements created by the relief printing method has a concentration of foreign matter of metal or metal compound contained in the layer of 100 ppm or less. Is defined as In particular, the anilox roll and the doctor roll in the apparatus used in the letterpress printing process are always rubbed and thus easily wear, and become a main source of foreign substances of metal or metal compound. By satisfying the requirements of the first form and the second form, the display defect of the pixel of the organic electroluminescence element produced by the relief printing method is improved.

  In addition, although there are several modes for pixel display defects of the organic electroluminescence element, the following can be cited from the appearance of the light emitting defect portion. A display defect called a dark spot is a minute non-light emitting point generated in the light emitting surface, and in some cases, the size thereof may increase with time. Moreover, the point that brightly shines than the other part of the pixel (bright spot) is caused by a local change in the film thickness of the organic light emitting layer or a projection of a transparent electrode such as ITO, which causes a current leak. May be accompanied. Furthermore, if the size of the foreign matter mixed in is large and the foreign matter is conductive, the cathode and the anode of the organic electroluminescence element may be short-circuited.

In the third embodiment of the present invention, regarding the anilox roll 12 and the doctor blade 13, when the Vickers hardness of the anilox roll is Ha and the Vickers hardness of the doctor blade is Hb, the following relationship should be satisfied.
Ha> Hb ≧ 700 Hv
That is, the Vickers hardness of the doctor blade is set to be lower than the Vickers hardness of the anilox roll, and the damage of the anilox roll is suppressed by setting the Vickers hardness (Hv) to 700 Hv or more, and the wear of the doctor blade is minimized. I can do it. When the Vickers hardness of the anilox roll is lower than that of the doctor blade, the anilox roll is more easily worn by rubbing. Anilox rolls originally have uneven surfaces and are easily chipped at the edge, and when chipping occurs due to wear, the wear must be avoided because it is more expensive than a doctor blade and requires time for replacement. Further, in the present invention, the hardness of the doctor blade is defined to be lower than the hardness of the anilox roll, so that the abrasion is caused by the doctor blade, but the Vickers hardness is 700 Hv as defined in the present invention. With the above configuration, almost no wear occurs and contamination of the light emitting layer ink can be suppressed, and the doctor blade is relatively easy to replace and is inexpensive. As soon as it occurs, it can be replaced with a new doctor blade.

  In addition, specific materials for anilox rolls and doctor blades suitable for satisfying the above formula are shown below. An anilox roll is completed by creating an iron core according to the printing width and printing length and polishing it, forming a surface layer, engraving the required number of concave holes, and finally polishing the surface. In this case, the Hv of the anilox roll is defined by the material and forming method of the surface layer, but generally, a method of forming a hard chromium plating layer and then mechanically engraving to form an anilox concave hole is performed. It has been broken. Moreover, a surface layer can be formed by spraying a ceramic material such as a metal oxide, carbide, or nitride on an iron core, and an anilox recess can be formed by laser engraving on the surface layer. In any method, it is possible to obtain a Vickers hardness of 700 Hv or more as defined in the present invention.

  In addition, the doctor blade is generally widely used a carbon tool steel called SK material and a steel plate called Swedish steel, but in order to increase rust prevention, martensitic stainless steel such as SUS420, In order to obtain corrosion resistance, austenitic stainless steel such as SUS301 is also used. A material obtained by cutting these materials according to the printing width and uniformly polishing the surface is used for the doctor blade. Further, in order to improve the uniformity of the doctor ring or extend the life of the blade, a shape process such as a taper or a step is applied to the portion of the blade edge. A doctor blade having a thickness of about 0.1 mm to 0.3 mm is widely used. If the plate thickness is less than 0.1 mm, the doctor blade is too stiff and an appropriate pressure on the anilox roll cannot be obtained, and if it is greater than 0.3 mm, it is often difficult to process the doctor blade. However, doctor blades made of these materials all have Vickers hardness of 400 Hv to 600 Hv, which is inappropriate in the third embodiment of the present invention.

As the material of the doctor blade that satisfies the third aspect of the present invention, the surface of the steel or stainless steel is subjected to composite nickel plating, or a ceramic material such as metal oxide, carbide or nitride is sprayed and coated. Can be mentioned.
In composite plating, one or more kinds of fine particles are co-deposited in a metal matrix formed by plating to form a plating film as a composite material. In general, the matrix metal for plating is nickel and the plating bath is electroless or An electrolytic nickel plating bath in which fine particles are dispersed is used. Fine particles dispersed in the nickel plating bath include ceramics such as silicon carbide and resin fine particles such as PTFE (polytetrafluoroethylene). Silicon carbide itself has a high hardness and can increase the hardness of the doctor blade in combination with the hardness of nickel. On the other hand, although the PTFE fine particles themselves do not have hardness, the frictional resistance of PTFE can reduce the frictional resistance, and as a result, the wear resistance can be improved as compared with normal nickel plating. The content rate of these fine particles in the matrix is not particularly defined, but if the content rate is too low, the effect of the composite particles is thin, and if it is too high, the adhesion of the matrix becomes weak and the matrix is easily peeled off. The content is adjusted to an appropriate value depending on the type and particle size of the particles. A plating film having a thickness of 10 to 20 μm is widely used. If the plating film is thinner than this, the fine particles in the plating film are exposed excessively and are easily peeled off. If the plating film is too thick, the plating film itself is easily peeled off by the stress of the plating film. In addition, a known surface treatment can be applied to the substrate for the purpose of improving the adhesion between the plating film and the substrate.
By nickel composite plating, it is possible to obtain a doctor blade with a Vickers hardness of 700 Hv or higher, and particularly with silicon carbide composite plating, a high hardness of 900 Hv or higher can be obtained.
In addition to composite plating, a steel blade or a stainless steel substrate coated with a ceramic material such as metal oxide, carbide, or nitride by thermal spraying can be used as the doctor blade used in the present invention. Examples of the ceramic material to be sprayed include a tungsten carbide / cobalt composite film, a tungsten carbide / cobalt-chromium alloy composite film, a nickel oxide film, and an aluminum oxide film. These sprayed coatings have a very high Vickers hardness of 950 Hv or more and are suitable for the third embodiment of the present invention.

In the fourth embodiment of the present invention, the angle (θ in FIG. 1) formed by the doctor blade and the upstream of the anilox tangent surface at the location where the anilox roll 12 and the doctor blade 13 are in contact with each other is an acute angle of 5 to 75 °. Defined. If the angle θ formed by the anilox roll 12 and the doctor blade 13 exceeds 75 ° (becomes an obtuse angle), the doctor blade will not bend even if the pushing pressure of the doctor blade is increased. Since the cutting edge of the doctor blade faces, the cutting edge and the contour of the concave hole of the anilox roll (called a bank) collide with each other, and wear tends to occur.
When θ is nearly vertical, it is difficult to obtain a uniform pressing pressure in the axial direction of the anilox roll because the bending of the doctor blade cannot be used when the doctor blade is pressed against the anilox roll. By defining θ as an acute angle of 5 to 75 ° as defined in the fourth embodiment of the present invention, a uniform pressing pressure can be obtained by the deflection of the doctor blade when the doctor blade is pressed against the anilox roll. Also, if θ is less than 5 °, the contact area of the anilox roll becomes too large due to the deflection of the doctor blade when the pressing pressure is applied, the uniform pressing pressure cannot be obtained, and the printed film is uneven. appear.

  The more preferable θ is 15 to 65 °.

  In addition, it has been clarified by the present invention that metals and metal compounds generated from anilox rolls and doctor blades have a close relationship between the density in the printed organic light-emitting layer and display defects. Correlation with the concentration of chromium, iron, nickel and cobalt, which are components of a certain steel or stainless steel, is the most important. The concentration of the metal and the metal compound in the organic light emitting layer formed by the printing method can be quantified by atomic absorption spectrometry (AAS: Atomic Absorption Spectrometry). When a plurality of the metal elements are detected, the total concentration correlates with a display defect. In this case, the metal is detected as a metal compound such as fine particles of a single metal, fine particles in an alloy state, a metal in an ionic state, and an oxide.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

[Vickers hardness]
The Vickers hardness of the doctor blade and the anilox roll was measured under the following conditions.
Fischer Instruments: Fischer Scope HM2000
Test load: 200 mN, average of 3 measurement points was taken as Vickers hardness.
[Measurement of metals and metal compounds in organic light-emitting layers]
A light emitting layer ink prepared by dissolving PPV (polyparaphenylene vinylene), which is an organic light emitting layer forming material, is printed on an ITO substrate by a letterpress printing machine described in this specification, and dried, and then toluene is applied to the substrate. The ink was redissolved and recovered, and the solvent of the recovered liquid was volatilized to obtain a nonvolatile content. This nonvolatile content was analyzed by atomic absorption analysis (Perkin Elmer: SIMA6000), and the metal element concentration in the light emitting layer ink solid content was quantified.
[Creation of organic electroluminescence element]
On another ITO substrate, a PEDOT / PSS (polyethylenedioxyphenylene / polystyrene sulfonic acid) aqueous solution is spin-coated so as to have a dry film thickness of 50 nm. A printed light emitting layer having a thickness of 60 nm was formed. Then, a cathode was deposited on this substrate by vacuum deposition in the order of calcium (5 nm) and aluminum (150 nm), and sealing was further performed to obtain an organic electroluminescence device.

  Shows the material of anilox roll and doctor blade, printing conditions, results of appearance evaluation of the printed light-emitting layer film and the created device, and AAS analysis results (quantitative determination of iron, chromium, nickel and cobalt elements) of the light-emitting layer ink It is shown in 1.

[Details of experimental conditions]
The anilox roll and doctor blade are doctored at a peripheral speed of 100 mm per second during printing and transfer. Also, during standby (a time zone during which printing / transfer is not performed during substrate loading / unloading, alignment, etc.), doctoring is performed at a peripheral speed of 20 mm per second to prevent drying. If the ratio of the printing / transfer time and the waiting time in the printing process (the ratio of the driving speed at the peripheral speed of 100 mm and the driving speed at the time of 20 mm in the doctoring) is converted to an average of a fixed time, it is about 1: 9. . The anilox roll used in the printing machine of the present invention has a surface subjected to ceramic spraying (chromium oxide), laser engraving of honeycombs of various numbers of lines, and Vickers hardness is 1100 Hv.
[Details of evaluation of created element]
As for the printing result, the fluorescent pattern of the light emitting layer was visually confirmed with an ultraviolet lamp while the printing of the light emitting layer ink was finished. ○ is a state where there is no unevenness, × is a state where the printed pattern is uneven, and Δ is a state where there is a slight unevenness. Also, regarding the confirmation of the panel light emission state, after printing the light emitting layer on a substrate different from the substrate for confirming the printing unevenness, vapor deposition and sealing are performed to form a panel, and the dark spots are obtained after the electrodes are connected to emit light. The presence / absence of (DS), bright spot (BS), and short circuit was confirmed. In addition, the panel evaluation is not performed about the thing in which the printing nonuniformity is seen. In Table 1, the address is θ in FIG.

  In this invention, since the density | concentration of the metal or metal compound of an organic light emitting layer is 100 ppm or less, a display defect can be improved and it is useful for the display use etc. which used the organic electroluminescent element.

It is a figure for demonstrating an example of the manufacturing process of the organic electroluminescent element by a relief printing method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Inkwell, 12 ... Anilox roll, 13 ... Doctor, 14 ... Printing plate (letter plate), 15 ... Substrate, 16 ... Plate cylinder, 17 ... Top plate surface Light emitting layer ink.

Claims (5)

  An organic electroluminescent device comprising at least one organic light emitting layer having a light emitting region on a substrate, an anode for injecting holes into the organic light emitting layer, and a cathode for injecting electrons into the organic light emitting layer. And at least one of the organic light emitting layers is formed by a relief printing method, and the concentration of the metal or the metal compound of the organic light emitting layer formed by the relief printing method is 100 ppm or less. Organic electroluminescence device.   2. The organic electroluminescence device according to claim 1, wherein the metal or the metal compound is derived from an anilox roll in a relief printing method and a doctor blade for removing unnecessary ink on the anilox roll. .   The metal element contained in the metal and the metal compound is selected from the group consisting of chromium, iron, nickel and cobalt, and the concentration is the sum of the concentrations of the metal or metal compound consisting of these elements. Item 3. The organic electroluminescence device according to Item 1 or 2. Forming one or more organic light emitting layers having a light emitting region on a substrate; forming an anode for injecting holes into the organic light emitting layer; and forming a cathode for injecting electrons into the organic light emitting layer. A process for producing an organic electroluminescence device, wherein at least one layer of the organic light emitting layer is formed by a relief printing method, and the Vickers hardness of an anilox roll used in the relief printing method is Ha, When the Vickers hardness of the doctor blade for removing unnecessary ink on the anilox roll is Hb, the following relationship is satisfied, and the concentration of the metal or metal compound in the organic light emitting layer formed by the relief printing method is 100 ppm. The manufacturing method of the organic electroluminescent element characterized by the following.
Ha> Hb ≧ 700 Hv   5. The organic material according to claim 4, wherein the angle formed by the doctor blade and the upstream of the rotation direction of the tangential surface of the anilox roll at a position where the anilox roll contacts the doctor blade is an acute angle of 5 to 75 °. Manufacturing method of electroluminescent element.

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