## 1 Introduction  
As automotive lamps are highly integrated, the heat generated from bulbs reduces the light quantity and lifespan of the bulbs [1]. In addition, the surrounding parts are deformed by thermal shocks at higher temperatures. Among the automotive lamp modules, the part subjected to the highest heat is the reflector that reflects the light of the bulb outside [2]. To minimize the deformation of the reflector caused by thermal shocks, many studies have been actively conducted worldwide on heat dissipation design and material change for heat release [3; 4; 5; 6].  
As for studies on the geometry of the reflector, research has been conducted on the geometry that improves the heat dissipation performance by designing radiation fins on the reflector. The geometry that has the optimal heat dissipation performance was derived using the geometry of radiation fins as a design variable [7]. There are also cases where materials were changed to improve heat transfer. For the projection lamp reflector, the aluminum die casting method was applied to release the heat generated from the bulb. Although aluminum is a light metal with high thermal conductivity, it is heavier than polymer materials (specific gravity: approximately 2.7 g/cm\({}^{3}\)) and its molding process is limited. In addition, the cost of processing, such as anodizing, is high [8; 9]. Research on the development of light and thermally conductive polymer composites is underway to replace metal materials [10; 11]. Further, studies are being conducted on composites obtained by mixing lightweight, highly strong, and thermally conductive base materials and ceramic powders or fibers with appropriate particle sizes [12; 13; 14]. In previous studies on composites, however, the mechanical characteristics [15; 16] and thermal characteristics [17; 18] were analyzed in the composite specimen stage, and few studies were conducted on the actual products.  
Moreover, various methods [19; 20; 21] have been introduced for molding products using composites, and most of them require long production times and involve processes requiring high production costs. Among the various manufacturing methods, the method that uses injection molding is suitable for the mass production of products with the same geometry, and it is one of the methods selected for the manufacture of automotive parts considering economic efficiency and productivity.  
In this study, the mechanical, thermal, and morphological characteristics of polymer matrix composites containing alumina based on the alumina content were compared for their application to automotive lamp reflectors, and their flowability and injection moldability were analyzed. PBT and PB6 were used as the polymer matrix, and alumina was used as a thermally conductive filler. The various characteristics of composites according to the alumina content were analyzed. Among them, the case where 60% alumina was added to PA6 was selected.  
To compare the performances of the selected composites with that of the fog lamp reflector manufactured with conventional PBT, fog lamp reflectors were fabricated under the same conditions as the reflector injection conditions. Lamps were mounted on the fabricated two reflectors, and the temperature changes of the reflectors were analyzed by creating an environment similar to actual use conditions. When 60% alumina was added, the thermal conductivity was improved and thus the maximum temperature of the lamp reflector was reduced and the heat was well transferred to the surroundings, compared to the fog lamp reflector fabricated with conventional PBT.