Since the PBT resin has excellent mechanical characteristics, electrical characteristics, heat resistance, weatherability, water resistance, chemical resistance, and solvent resistance, the resin is widely used in various applications as engineering plastics, in automobile parts, electrical and electronic parts, and the like. Although there have been developed many kinds of technologies relating to the improvement in fire retardancy, their reports on achieving the improvement in the fire retardancy, Comparative Tracking Index (CTI), and other characteristics specified by UL-94 Standard of Underwriter's Laboratories Inc., and very few reports deal with IEC60695-2 Standard of International Electrotechnical Commission (IEC). IEC60695-2 Standard requests the insulating material parts used for electrical and electronic equipment to have durability to ignition and flame propagation during working thereof. Specifically, regarding the equipment parts working without operator, there has been increasing the request for the safety of electrical insulating material part which supports a connection section exceeding 0.2 A of rated current or which is located within 3 mm from the connection section. As a result, it is required to satisfy 850° C. or higher glow-wire flammability index (GWFI) and 775° C. or higher glow-wire ignition temperature (GWIT) according to IEC60695-2 Standard. For a thermoplastic resin to satisfy specifically the GWIT standard is very difficult even in materials having V—O in the evaluation of fire retardancy of UL-94 Standard. Accordingly, there has been increasing the development of flame retardant technology to further improve the conventional technologies in recent years.
As a tendency of actual GWIT evaluations, good result has been obtained at a thickness not allowing the penetration of glow-wire during 30 seconds of contact, (a thickness of 3 mm of fiber-reinforced material, for example), and at a very thin material. For the fiber-reinforced PBT resins, it has been accepted that a thicknesses of 1 to 2 mm are specifically difficult to attain good evaluation result.
Since the resin materials under study are not limited in the product thickness in using in the market, these materials have to satisfy the flame test over the entire applicable thickness range.
Furthermore, these materials are requested to have, in addition to durability to the flame test, a good balance of fire retardancy, tracking resistance, and mechanical properties.
As a known method to impart fire retardancy to a PBT resin, there is a resin composition using a bromine-based flame retardant, antimony trioxide, and melamines in combination (JP-A 3-195765). JP-A 3-195765, however, does not suggest the glow-wire test.
Other than the above, the improvement in GWIT is carried out by an insulating material part which has a resin molded section formed using a resin composition composed of a PBT resin with the addition of polyhalogenated benzyl (meth)acrylate and antimony pentoxide. The insulating material part improves GWIT specified by IEC60695-2-13 Standard at the resin section with a thickness of 2 mm or smaller by combining an insulating plate made of metal or the like. The insulating material part, however, does not satisfy the Standard as a sole PBT resin composition, (JP-A 2005-232410).
Furthermore, the improvement in GWIT is carried out by an insulating material part which has a resin molded section formed from a resin composition composed of a PBT resin with a bromine-based flame retardant, antimony oxides, a glycidyl group-containing copolymer composed of an α-olefin and a glycidyl ester of α,β-unsaturated acid and a normal-chain olefin resin having a molecular weight of 10 thousand to 1 million, (JP-A 2006-45544). The evaluation of GWIT is, however, conducted at a thickness of 3 mm, and the patent disclosure does not suggest the evaluation at a thickness of 0.75 mm or 1.5 mm, which are the thickness recommended by IEC.
USPTO Backgrounds
USPTO Backgrounds