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Konica Minolta Inc : Patent Application Titled “Manufacturing Method for Light Emitting Device and Phosphor Mixture” Published Online

Written on:January 17, 2014
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By a News Reporter-Staff News Editor at Politics & Government Week — According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Washizu, Takashi (Hachioji-shi, JP); Hatano, Takuji (Suita-shi, JP); Taguchi, Yoshihito (Kawasaki-shi, JP), filed on February 15, 2012, was made available online on January 2, 2014.

The assignee for this patent application is Konica Minolta , Inc.

Reporters obtained the following quote from the background information supplied by the inventors: “Hitherto, there has been developed, to be used for an illuminator or the like a light emitting device which produces white light by making phosphor emit, light by using light emitted from a light emitting element such as an LED element as excitation light.

“As such a light emitting device, there is known, for example, a light emitting device which produces white light by using phosphor which emits yellow light through blue light emitted from a light emitting element and mixing the colors of light or a light emitting device which produces white light by using phosphor which emits blue light, green light and red light through ultraviolet light emitted from a light emitting element and mixing the three colors of light.

“As a light emitting device having such a configuration, there has been developed a light emitting device in which a light emitting element is directly sealed with curable resin in which phosphor is dispersed. Uses of light emitting devices have expanded to a field which requires high brightness such as a headlight for a car. Because of this and so forth, in recent years, light emitting elements have been high-powered ones and accordingly generate heat. Therefore, when phosphor is provided directly on a light emitting element in such a way as to be dispersed in a sealing agent as described above, the sealing agent may deteriorate by heat generated by the light emitting element.

“In order to solve this problem, there is proposed in Patent Document 1 a technique to prevent deterioration of a sealing agent, the technique by which phosphor is dispersed not in resin but in a ceramic solution (ceramic precursor solution) so that a light emitting element is sealed with ceramics which do not deteriorate much by heat.

“Although the technique disclosed in Patent Document 1 can provide durability for a light emitting element, when phosphor is mixed with a ceramic precursor solution and the liquid mixture is applied onto a light emitting element, the phosphor precipitates in the liquid mixture because the specific gravity of phosphor is high. Hence, it is difficult to make phosphor evenly exist on a light emitting element, so that released white light is uneven, and accordingly chromaticity varies between light emitting devices.

“Further, when an application liquid, in which phosphor is dispersed in a ceramic precursor solution is applied, to a package on which a light emitting element is mounted, a mask component is usually used so that an application region for the application liquid is limited to a predetermined region. However, the phosphor adhering onto a mask component is often discarded. Because phosphor is expensive in general, it is desired that the phosphor adhering onto a mask component is also collected and reused.

“The inventors of the present invention gave consideration to this problem and found that the viscosity of an application liquid was able to be increased, phosphor thereof was able to be prevented from precipitating, and evenness of the application was able to be obtained by using polyhydric alcohol having a valence of two or more as a solvent of the application liquid and mixing certain particles therewith. Although, a technique using polyhydric alcohol is introduced in Patent Document 2, the technique disclosed in Patent Document 2 uses polyhydric alcohol as a mere additive (surface hardening retarder) (Paragraphs 0012-0014, 0021, etc.), which is totally different in purpose from the case where polyhydric alcohol is used as a solvent of an application liquid.

“However, in the technique by which polyhydric alcohol is used as a solvent of an application liquid in which phosphor is dispersed in a ceramic precursor solution, the phosphor adhering onto a mask component was covered with ceramics formed by the ceramic precursor solution and accordingly fixed onto the mask component, so that the phosphor was not able to be collected or reused.

“Then, consideration was given again, and it was decided to apply phosphor and a ceramic precursor solution separately.

“More specifically, it was decided (i) to apply onto a light emitting element and dry a liquid mixture in which phosphor is dispersed in polyhydric alcohol to form a phosphor layer and then (ii) to apply onto the phosphor layer and fire a ceramic precursor solution to fix the phosphor of the phosphor layer onto the light emitting element.

“By this two-step application, before a ceramic precursor solution was applied, a mask component was collected, and accordingly phosphor was able to be collected from the mask component to be reused.”

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors’ summary information for this patent application: “The Problems to be Solved by the Invention

“However, at the second step at which a ceramic precursor solution was applied to a phosphor layer, when the phosphor layer did not have a certain degree of strength, a phenomenon of separation, of the phosphor layer occurred.

“For example, when a liquid mixture of the first step was applied with a spray, and then a liquid mixture of the second step was applied with the spray, a phosphor layer was separated from a light emitting element because of the air pressure of the spray.

“In order to increase the strength of phosphor layers, typical oxide fine particles or the like was mixed, into a liquid mixture. However, the strength of phosphor layers was not increased. Further, a polymer additive was mixed therein. However, coloring occurred at the time of heating, and accordingly the chromaticity of the luminous color itself varied.

“Therefore, a main object of the present invention is to provide a manufacturing method for a light emitting device and a phosphor mixture suitably used in the manufacturing method each of which can prevent separation of a phosphor layer formed at a first step and reduce the chromaticity variation when an application liquid is applied at two steps, namely, the first step of applying a liquid mixture containing phosphor and the second step of applying a liquid mixture containing a ceramic precursor.

“Means for Solving the Problems

“In order to solve the above-described problems, according to an aspect of the present invention, there is provided a manufacturing method for a light emitting device including a light emitting element and a wavelength converting part which converts light emitted from the light emitting element into light of another wavelength, the manufacturing method including:

“a step of applying onto the light emitting element and drying a first liquid mixture in which phosphor and plate-like particles are dispersed in polyhydric alcohol having a valence of two or more to form a phosphor layer; and

“a step of supplying onto the phosphor layer and firing a second liquid mixture in which a translucent ceramic precursor is dispersed in a solvent to form the wavelength converting part.

“According to another aspect of the present invention, there is provided a phosphor mixture used in a manufacturing method for a light emitting device, the manufacturing method including: a step of applying onto the light emitting element and drying a first liquid mixture to form a phosphor layer; and a step of applying onto the phosphor layer and,firing a second liquid mixture in which a translucent ceramic precursor is dispersed in a solvent to form the wavelength converting part, wherein

“the phosphor mixture is a liquid mixture in which phosphor and plate-like particles having a particle size smaller than a particle size of the phosphor are dispersed in polyhydric alcohol having a valence of two or more and is used as the first liquid mixture.

“Advantageous Effects of the Invention

“According to the present invention, particular plate-like particles are contained in the first liquid mixture or the phosphor mixture, so that the strength of phosphor layers is increased and separation of the phosphor layers can be prevented, and by extension, the chromaticity variation of manufactured light emitting devices can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

“FIG. 1 is a cross-sectional view schematically showing the configuration of a light emitting device.

“FIG. 2 is a schematic view for explaining a manufacturing device (application device) and a manufacturing method for the light emitting device.”

For more information, see this patent application: Washizu, Takashi; Hatano, Takuji; Taguchi, Yoshihito. Manufacturing Method for Light Emitting Device and Phosphor Mixture. Filed February 15, 2012 and posted January 2, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=2527&p=51&f=G&l=50&d=PG01&S1=20131226.PD.&OS=PD/20131226&RS=PD/20131226

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