A polybutylene terephthalate resin is excellent in an injection molding property, mechanical characteristics, a heat resistance, electric characteristics, a resistance to chemicals, etc. Utilizing these properties, the polybutylene terephthalate resin has been widely utilized as products by an injection molding in fields of automobile parts, machine parts, electro-communication parts, etc. Further, it is also excellent in a mold transfer property and is advantageously used also in lamp members such as extension uses of automobiles for which a good external appearance is particularly demanded. Furthermore, in view of its use, it is necessary to highly control the heat resistance of the resin, and a suppression of gas generation (low gas emission) upon the molding, etc.
On the other hand, an LED light has been installed for headlamps of high-class automobiles in recent years and a lamp design has been also started in a drastic change from the former one. For example, in a reflector type (a type wherein a light from a light source is irradiated by means of reflection using a reflector), it is necessary that an area around the light source is metallized with aluminum. Recently, a new design has been appearing wherein the reflector type is changed to a projector type (a type wherein the light from the light source is irradiated by condensing to a front lens) and the area around the light source is changed to a black colored design. However, due to this change, there has been resulted a problem of condensation of a sunlight. That is, when the sunlight is reflected by a projector lens and is condensed to a surrounding black area, a temperature of the condensed area becomes very high whereby a surface melting occurs. (Such a phenomenon itself has been known from old time already but, up to now, it has not caused any particular problem in view of a lamp design.) Taking such a problem into consideration, there has been a demand for materials which transmit infrared light so that the temperature does not increase even by the condensation of the sunlight and also for materials which have a heat resistance resulting in no surface melting even at the high temperature.
As to a technique for transmitting the infrared light, there are disclosures, for example, in Patent Documents 1 to 3 for a resin composition containing a resin consisting of polybutylene terephthalate or of polybutylene terephthalate and a polybutylene terephthalate copolymer together with a noncrystalline resin such as a polycarbonate resin, a styrene acrylonitrile resin, a polyester resin containing 1,4-cyclohexanedimethanol ingredient, etc. However, although this technique is useful for enhancing the infrared light transmittance of the resin of a polybutylene terephthalate type, a heat deflection temperature significantly lowers by addition of the noncrystalline resin. Accordingly, it is difficult to practically use this resin composition particularly as a lamp part.
In addition, as to a technique for preparing a black colored polyester resin composition which suppresses a temperature rise due to irradiation of a sunlight, there is disclosed, for example, in Patent Document 4 for a polyethylene terephthalate resin composition which does not contain carbon black but contains a pigment which is made into black color by mixing several pigments. According to this invention, it is possible to lower a temperature corresponding to a heat quantity accumulated by an infrared light-absorbability of carbon black, as a result of the use of the pigment of a non-carbon black type. However, an effect of suppressing the temperature rise thereby is small and, accordingly, there is yet a room for improvement.