Abstract:
A light-emitting diode (LED) lighting apparatus is provided. The LED lighting apparatus includes at least one LED, and a wavelength conversion member spaced apart from the LED and configured to convert a wavelength of light emitted from the LED. The wavelength conversion member includes a light-transmitting member, and a transfer molded wavelength conversion layer disposed on at least one surface of the light-transmitting member. The transfer molded wavelength conversion layer includes a resin and a phosphor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and the benefit of Korean Patent Application No. 10-2012-0047882, filed on May 7, 2012, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light-emitting diode (LED) lighting apparatus and a method for fabricating a wavelength conversion member which is spaced apart from an LED in the LED lighting apparatus and converts a wavelength of light emitted from the LED. 
     2. Description of the Related Art 
     As light sources for illumination, fluorescent lamps and incandescent bulbs have been widely used. Incandescent bulbs have low efficiency and economic feasibility due to their high power consumption. For this reason, the demand for incandescent bulbs tends to significantly decrease. It is expected that such a decreasing trend will continue in the future. On the contrary, since fluorescent lamps have about ⅓ of power consumption of incandescent bulbs, they are high-efficient and cost-efficient. However, since fluorescent lamps are blackened by application of high voltage, the lifespan of fluorescent lamps is short. In addition, fluorescent lamps are environmentally unfriendly because they use a vacuum glass tube into which mercury being a heavy metal is injected together with argon gas. 
     Recently, the demand for LED lighting apparatuses has been rapidly increasing. LED lighting apparatuses have a long lifespan and are driven with low power. In addition, LED lighting apparatuses are environmentally friendly because they use no environmentally harmful substances such as mercury. A typical LED lighting apparatus includes an LED module, and the LED module includes package-level or chip-level LEDs, and a printed circuit board (PCB) on which the LEDs are mounted. Each of the LEDs includes an LED chip configured to emit light in a specific wavelength range, and a wavelength conversion material (for example, a phosphor) configured to generate desired color light, especially white light, by converting a wavelength of light emitted from the LED chip. Generally, the wavelength conversion material is included in an encapsulation material covering the LED chip, or is directly formed on the LED by conformal coating. 
     In the LED lighting apparatus, much heat is generated when the LEDS are supplied with power and operated. This heat has a bad influence on the wavelength conversion material included in the encapsulation material covering the LED chip or directly formed on the LED chip. That is, the encapsulation material including the wavelength conversion material may be separated from the surface of the LED chip by heat, and the original characteristic of the wavelength conversion material may be changed by heat. Therefore, feature values, such as color coordinates or color temperature of light generated by the LED lighting apparatus, may deviate from an originally intended or designed range. 
     In this regard, there has been proposed an LED lighting apparatus configured such that an optical member or an optical cover spaced apart from LEDs includes phosphors. Since the optical member is spaced apart from the LEDs, the phosphors included in the optical member may not be badly affected by heat generated from the LEDs. As a method of adding the phosphors to the inside of the optical member, there are a method of molding an optical member with a resin material mixed with phosphors, and a method of coating a phosphor on one surface of an optical member in a printing technique. Since the former method is limited to the molding technique using the resin material, it is difficult to apply to an optical member such as a glass. In addition, air bubbles may be formed within the optical member together with the phosphors. According to the latter method, the phosphor layer is formed on one surface of the optical member. The phosphor layer is formed with an uniform surface in the early stage, but the surface of the phosphor layer may be rough as times goes by. In worse cases, the phosphor layer may be separated from the surface of the optical member. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is directed to provide a method for fabricating a wavelength conversion member reliably at low cost, in which the wavelength conversion member is used for an LED lighting apparatus and includes a uniform and dense wavelength conversion layer on at least one surface thereof. 
     Another aspect of the present invention is directed to provide an LED lighting apparatus that can improve reliability by covering LEDs with a wavelength conversion member including a uniform and dense wavelength conversion layer on at least one surface thereof, and can always emit light in an intended color coordinate or color temperature range, in spite of passage of time. 
     According to an aspect of the present invention, an LED lighting apparatus includes at least one LED, and a wavelength conversion member spaced apart from the LED and configured to convert a wavelength of light emitted from the LED. The wavelength conversion member includes a light-transmitting member, and a wavelength conversion layer formed on at least one surface of the light-transmitting member. The wavelength conversion layer includes a resin and a phosphor, and is formed by a transfer molding. 
     According to one embodiment, the light-transmitting member may include a glass or a plastic material. 
     According to one embodiment, the light-transmitting member may include an uneven pattern. The uneven pattern may be formed in a region which is covered with the wavelength conversion layer or a region which is not covered with the wavelength conversion layer. 
     According to another aspect of the present invention, there is provided a method for fabricating a wavelength conversion member to be applied to an LED lighting apparatus. The method for fabricating the wavelength conversion member includes: preparing a light-transmitting member; arranging a mold to cover one surface of the light-transmitting member and; performing a transfer molding process to soften a solid molding material, including a phosphor and a resin, by heating and pressurizing the solid molding material, and fill a gap between the mold and the light-transmitting member with the softened molding material. 
     According to one embodiment, the mold may include a transfer port, and a runner extending from the transfer port to the gap. The transfer molding process may include putting the solid molding material into the transfer port, pressurizing the solid molding material with a plunger, and injecting the softened molding material into the gap through the runner. 
     According to one embodiment, the transfer port and the runner may be disposed in a region right above the light-transmitting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an LED lighting apparatus according to an embodiment of the present invention. 
         FIG. 2  is a plan view illustrating a state in which a mold for molding a wavelength conversion layer is disposed to cover one surface of a light-transmitting member. 
         FIG. 3  is a cross-sectional view taken along line I-I of  FIG. 2 . 
         FIGS. 4 and 5  are diagrams for describing a transfer molding process of forming the wavelength conversion layer on one surface of the light-transmitting member by using the mold illustrated in  FIGS. 2 and 3 . 
         FIG. 6  is a cross-sectional view of a wavelength conversion member in which the wavelength conversion layer is formed on one surface of the light-transmitting member in the transfer molding process illustrated in  FIGS. 4 and 5 . 
         FIGS. 7A to 7D  are cross-sectional views illustrating various modifications of the wavelength conversion member. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. In the drawings, the widths, lengths and thicknesses of elements may be exaggerated for clarity. Throughout the drawings and description, like reference numerals will be used to refer to like elements. 
       FIG. 1  is a cross-sectional view of an LED lighting apparatus according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the LED lighting apparatus  1  includes a plurality of LEDs  2 , and a wavelength conversion member  10  spaced apart from the LEDs  2  and covering top sides of the LEDs  2 . The plurality of LEDs  2  are mounted on a printed circuit board (PCB). In addition, the PCB  3  is attached on a heat sink  5  and thermoconductively connected to the heat sink  5 . The heat sink  5  may include a plurality of heat dissipation fins  51 . In addition, the LED lighting apparatus  1  may include a housing  6  for accommodating the above-described LEDs  2  inside. 
     Although not illustrated, the LED lighting apparatus  1  may include circuits and parts for driving the LEDs  2 . The LED  2  may include an LED chip and an encapsulation material encapsulating the LED chip. The LED chip may be directly mounted on the PCB  3 , or may be disposed on the PCB  3  while being embedded in a package with lead terminals. 
     The LEDs  2  may include a GaN-based LED chip configured to emit blue light, and an LED chip with a wavelength of about 430 μm to 470 μm, which includes an InGaN-based active layer. In addition, the wavelength conversion member  10  includes a light-transmitting member  11  configured to transmit light, and a wavelength conversion layer  12  formed on the surface of the light-transmitting member  11 . The wavelength conversion member  10  includes a phosphor that converts blue light generated by the LED  2  into long-wavelength light, and the phosphor may be a yellow phosphor or a combination of a green phosphor and a red phosphor. 
     After light passes through the wavelength conversion member  10 , the wavelength-converted long-wavelength light and the non-wavelength-converted blue light may be mixed to generate white light. Since the phosphor within the wavelength conversion layer  12  provided in the wavelength conversion member  10  is spaced apart from the LED  2 , the characteristic or performance of the wavelength conversion member  10  is not deteriorated by heat and/or light generated by the LED  2 . 
     The light-transmitting member  11  may be made of a plate type transparent glass or a plastic. However, the light-transmitting member  11  may be made of light-transmitting materials other than glass. In addition, the wavelength conversion member  10  illustrated in  FIG. 1  includes the wavelength conversion layer  12  only on the bottom surface of the light-transmitting member  11 , but the wavelength conversion layer  12  may be formed only on the top surface of the light-transmitting member  11  or may be formed on both the top surface and the bottom surface. The wavelength conversion layer  12  is formed on the surface of the light-transmitting member  11  to a predetermined thickness by the transfer molding, and has a uniform phosphor distribution. 
     A method for fabricating the wavelength conversion member by forming the wavelength conversion layer  12  on one surface of the light-transmitting member  11  by the transfer molding will be described in more detail. 
       FIG. 2  is a plan view illustrating a state in which a mold  80  is disposed to cover one surface of the light-transmitting member  11  in order for the transfer molding of the wavelength conversion layer  12  (see  FIG. 1 ).  FIG. 3  is a cross-sectional view taken along line I-I of  FIG. 2 . 
     Referring to  FIGS. 2 and 3 , the plate type mold  80  is disposed to cover one surface of the light-transmitting member  11  having an area equal to or smaller than that of the mold  80 . In  FIG. 2 , the light-transmitting member  11  is covered with the plate type mold  80  and is indicated by a hidden line. The plate type mold  80  includes one or more resin injection portions  81 . The mold  80  having an appropriate number of the resin injection portions  81  may be selected and used according to the area of one surface of the light-transmitting member  11  or the area of the wavelength conversion layer  12  (see  FIG. 1 ) formed on one surface of the light-transmitting member  11  by the transfer molding. In this case, a circumference of a gap between the light-transmitting member  11  and the plate type mold  80  is filled. 
     The resin injection portion  81  includes a transfer port  812  and a runner  814  having a cross-sectional area smaller than that of the transfer port  812 . The runner  814  extends from the transfer port  812  to a space covering one surface of the light-transmitting member  11 , and may include a runner of a narrow sense, a gate and/or a sprue. In this embodiment, both the transfer port  812  and the runner  814  of the resin injection portion  81  are disposed in a region right above the light-transmitting member  11 . 
     In this embodiment, a gap between one surface of the light-transmitting member  11  and the mold  80  facing each other becomes a space in which the wavelength conversion layer  12  is to be formed by the transfer molding. The runner  814  extends from the transfer port  812  to the space. 
     As illustrated in  FIGS. 2 and 3 , before the mold is arranged, a solid molding material  70  mixed with a phosphor is prepared in a tablet form. The solid molding material  70  may be prepared in a tablet form by pressing a powder in which a phosphor and a powder-type resin are uniformly mixed. As the resin used herein as the solid molding material  70 , epoxy, especially epoxy molding compound (EMC) having excellent absorption resistance, may be advantageously used. 
       FIGS. 4 and 5  are diagrams for describing the transfer molding process of forming the wavelength conversion layer on one surface of the light-transmitting member by using the above-described mold. 
     Referring to  FIGS. 4 and 5 , under a high-temperature and high-pressure condition, the transfer molding process is performed to inject the phosphor-containing resin into the gap (or space) between the light-transmitting member  11  and the mold  80  through the resin injection portion  81 . More specifically, the tablet-shaped solid molding material  70  is put into the transfer port  812  of the resin injection portion  81 . While raising a temperature, a plunger  60  disposed in the transfer port  812  moves vertically downward to pressurize the solid molding material  70 . The molding material  70 , which is heated at a high temperature and pressurized at a high pressure, is softened into a gel phase or a liquid phase. The molding material  70  is densely filled into the gap between the light-transmitting member  11  and the mold  80  through the runner  814  and is then cured. 
     In this manner, the wavelength conversion layer  12  with the phosphors uniformly distributed is formed on the surface of the light-transmitting member  11  to a uniform thickness. In a case where the resin injection portion  81  is provided in plurality (see  FIG. 2 ), the plungers  60  are provided as many as the number of the resin injection portions  81 , and the plungers  60  are vertically moved in synchronization. A heating unit such as a heater for heating the molding material  70  may be installed in the plunger  60  or the mold  80 . 
       FIG. 6  is a cross-sectional view of the wavelength conversion member with the wavelength conversion layer formed on one surface of the light-transmitting member by the transfer molding step. 
     Referring to  FIG. 6 , the light-transmitting member  11  with the wavelength conversion layer  12  is separated from the mold  80 . The cured resin r, which exists in the runner  814  (see  FIGS. 2 to 5 ), may remain in the wavelength conversion layer  12 . In this case, this resin r is removed. As a result, it is possible to fabricate the wavelength conversion member  10  in which the wavelength conversion layer  12  is uniformly formed on one surface of the light-transmitting member  11  by the transfer molding. 
     The structure or shape of the mold  80  can be variously modified. For example, the transfer port  812  of the resin injection portion  81  may be disposed at a position deviating from the light-transmitting member  11 , and the runner  814  may extend to the lateral space of the light-transmitting member  11  instead of the upper space of the light-transmitting member  11 . 
     Various modifications of the wavelength conversion members  10  according to the present invention are provided. 
     A wavelength conversion member  10  illustrated in  FIG. 7A  includes a pair of wavelength conversion layers  12  formed by a transfer molding on two opposite surfaces of a light-transmitting member  11 , that is, top and bottom surfaces thereof. The pair of wavelength conversion layers  12  may include the same phosphor or may include different phosphors. In a wavelength conversion member  10  illustrated in  FIG. 7B , a wavelength conversion layer  12  is formed on one surface of a light-transmitting member  11 , and an uneven pattern  13  for light diffusion or scattering is formed on an opposite surface of the light-transmitting member  11 . The uneven pattern  13  diffuses or scatters light so that wavelength-converted light and non-wavelength-converted light can be mixed more efficiently. Therefore, more uniform white light can be obtained. In a wavelength conversion member  10  illustrated in  FIG. 7C , an uneven pattern  13  is formed on one surface of a light-transmitting member  11 , and a wavelength conversion layer  12  is formed by a transfer molding to cover the uneven pattern  13 . A wavelength conversion member  10  illustrated in  FIG. 7D  includes a curved portion, and a wavelength conversion layer  12  is formed on the surface of the curved portion. 
     While the embodiments of the present invention have been described with reference to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.