Patent ID: 8124550

Claim:
A filter medium for gas or liquid including a thermally bonded nonwoven fabric containing a low-shrinkage dual-component core-sheath fiber composed of a crystalline polyester core consisting of polyethylene terephthalate (PET) and a crystalline polyester sheath consisting of polybutylene terephthalate (PBT), the sheath having a melting point at least 10° C. lower than the core, the heat-shrinkage of the fiber being less than 10% at 170° C., wherein said sheath polyesters have a heat of fusion of >40 J/g and a width at the base of the sheath melting peak via Differential Scanning Calorimetry occurring within <40° C. at 10° C./minute, wherein the sheath of the low-shrinkage dual-component core-sheath fiber comprises >95% of a homogeneous polyester polymer which is not a copolymer and the height of the melting peak of the Differential Scanning Calorimetry curve for said PET core is greater than the height of the melting peak of the Differential Scanning curve for said PBT sheath.