1. Field of the Invention
The present invention relates to a light emitting device that can be used in a liquid crystal backlight, an illumination light source, and various types of indicators, displays and traffic signal lights, and relates particularly to a light emitting device with improved levels of heat resistance and light resistance.
2. Description of the Prior Art
In light emitting devices that use a light emitting element such as an LED, the light emitting element is typically coated with a layer comprising a phosphor for converting the wavelength of the light, or an organic resin layer with a high degree of optical transparency that functions as a lens or the like. When current flows through the light emitting element, the element heats up to a temperature of 100° C. to 130° C. Furthermore, light emitting elements that emit blue light or ultraviolet light from the short wavelength region are now being used, meaning resin layers that not only exhibit excellent heat resistance, but also exhibit excellent light resistance to ultraviolet light and the like are now being demanded. Conventionally, epoxy resins have been widely used as the material for the resin layer, but recently, silicone-based resins, which are known to offer excellent ultraviolet light resistance and heat resistance, have started being used.
However, with short wavelength LEDs such as blue LEDs and ultraviolet LEDs now being developed, the resin layer now requires a tougher material that is not only capable of withstanding heat generation, but is also able to withstand this type of high energy, short wavelength light. Previously proposed silicone resins have been addition curable resins that use a hydrosilylation reaction, meaning the proportion of silethylene linkages within the cured product is high. Because silethylene linkages are prone to cleavage by light or heat, the main skeleton within the cured product is prone to deterioration, and the resin is prone to bleed-out of low molecular weight, fluid, oily silicone. As a result, the mechanical strength of the cured product falls, and the resin is more likely to become brittle and prone to heat deformation. Furthermore, the low molecular weight silicone components that bleed out can cause a variety of faults. In addition, if the resin reaches this state, then color irregularities and tone variation are more likely to occur during light emission, meaning the color tone characteristics of the light emitting element may be affected.
Furthermore, conventionally used resins generally exhibit poor adhesion to metal members, and are prone to peeling.