Highly heat resistant nylon (polyamide) can be obtained by polycondensation of an aromatic dicarboxylic acid or an aromatic diamine. The highly heat resistant nylon can have a semi-aromatic structure and a semi-crystalline structure, and can be used in various fields requiring high heat resistance due to considerably higher heat resistance as compared with general nylon products.
In many electronic applications, the highly heat resistant nylon must be soldered by a lead-free solder at a surface temperature of about 260° C. without formation of blisters and must have no distortion even after absorption of water. Thus, the highly heat resistant nylon should exhibit excellent properties in terms of moisture absorption resistance, heat resistance, moldability and the like.
Examples of highly heat resistant nylon generally used in electronic and other applications include PA4T, PA6T, PA9T, PA10T, PA11T, PA12T, and the like. Highly heat resistant nylon using a C9 or longer chain diamine may be used directly as a homopolymer or may be used in the form of a copolymer using a small amount of a comonomer (dicarboxylic acid or diamine). Generally, PA4T and PA6T homopolymer cannot be processed due to the extremely high melting point thereof; thus, a large amount (dozens %) of the comonomer is introduced to improve melt processability.
In PA6T, examples of the comonomer include adipic acid, isophthalic acid and the like, which are generally used in the art, and may also include short-chain and long-chain aliphatic diamines, cyclic aliphatic diamines, branched aliphatic diamines, short-chain and long-chain aliphatic dicarboxylic acids, cyclic aliphatic dicarboxylic acids, branched aliphatic dicarboxylic acids, and the like. In addition, a cyclic aliphatic dicarboxylic acid may be used instead of an aromatic dicarboxylic acid to produce products with excellent optical and thermal properties, and copolymerization of a monomer capable of increasing glass transition temperature (Tg) may be performed to prevent deterioration in properties of nylon products at high temperature. However, such copolymerization cannot prevent discoloration of nylon upon exposure to air at high temperature.
Highly heat resistant polyester-based products can also be used for products requiring discoloration resistance instead of highly heat resistant nylon. Highly heat resistant polyester-based products, however, generally exhibit lower heat resistance than highly heat resistant nylon and can have drawbacks, such as poor moisture absorption resistance, moldability and the like under high humidity conditions, despite excellent discoloration resistance thereof.
Therefore, there is a need for polyamide ester resins (amide-ester hybrid resin) which can exhibit excellent heat resistance, discoloration resistance and the like, as compared with existing highly heat resistant nylon products, and can improve moisture absorption resistance, moldability, and the like, which are drawbacks of polyester products.