Poly(trimethylene terephthalate) (also referred to as “3GT” or “PTT”) has recently received much attention as a polymer for use in textiles, flooring, packaging and other end uses.  Textile and flooring fibers have excellent physical and chemical properties. 
It is known that bicomponent fibers wherein the two components have differing degrees of orientation, as indicated by differing intrinsic viscosities, possess desirable crimp contraction properties which lead to increased value in use for said fibers. 
U.S. Pat.  No.  6,692,687 discloses a spinning process for the production of side-by-side or eccentric sheath-core bicomponent fibers, the two components comprising poly(ethylene terephthalate) and poly(trimethylene terephthalate), respectively.  Due to the poly(ethylene terephthalate), fibers and fabrics made from them have a harsher hand than poly(trimethylene terephthalate) monocomponent fibers and fabrics.  In addition, due to the poly(ethylene terephthalate) these fibers and their fabrics require high-pressure dyeing. 
U.S. Pat.  Nos.  4,454,196 and 4,410,473, which are incorporated herein by reference, describe a polyester multifilament yarn consisting essentially of filament groups (I) and (II).  Filament group (I) is composed of polyester selected from the group poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly(tetramethylene terephthalate), and/or a blend and/or copolymer comprising at least two members selected from these polyesters.  Filament group (II) is composed of a substrate composed of (a) a polyester selected from the group poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly(tetramethylene terephthalate), and/or a blend and/or copolymer comprising at least two members selected from these polyesters, and (b) 0.4 weight % to 8 weight % of at least one polymer selected from the group consisting of styrene type polymers, methacrylate type polymers and acrylate type polymers.  The filaments can be extruded from different spinnerets, but are preferably extruded from the same spinneret.  It is preferred that the filaments be blended and then interlaced so as to intermingle them, and then subjected to drawing or draw-texturing.  The Examples show preparation of filaments of type (II) from poly(ethylene terephthalate) and polymethylmethacrylate (Example 1) and polystyrene (Example 3), and poly(tetramethylene terephthalate) and polyethylacrylate (Example 4).  Poly(trimethylene terephthalate) was not used in the examples.  These disclosures of multifilament yarns do not include a disclosure of multicomponent fibers. 
U.S. Pat.  Nos.  3,454,460 and 3,671,379 disclose bicomponent polyester textile fibers. 
JP 11-189925, describes the manufacture of sheath-core fibers comprising poly(trimethylene terephthalate) as the sheath component and a polymer blend comprising 0.1 weight % to 10 weight %, based on the total weight of the fiber, polystyrene-based polymer as the core component.  According to this application, processes to suppress molecular orientation using added low softening point polymers such as polystyrene did not work. ( Reference is made to JP 56-091013 and other patent applications.)  It states that the low melting point polymer present on the surface layer sometimes causes melt fusion when subjected to a treatment such as false-twisting (also known as “texturing”).  Other problems mentioned included cloudiness, dye irregularities, blend irregularities and yarn breakage.  According to this application, the core contains polystyrene and the sheath does not.  Example 1 describes preparation of a fiber with a sheath of poly(trimethylene terephthalate) and a core of a blend of polystyrene and poly(trimethylene terephthalate), with a total of 4.5% of polystyrene by weight of the fiber. 
JP 2002-56918A discloses sheath-core or side-by-side bicomponent fibers wherein one side (A) comprises at least 85 mole % poly(trimethylene terephthalate) and the other side comprises (B) at least 85 mole % poly(trimethylene terephthalate) copolymerized with 0.05–0.20 mole % of a trifunctional comonomer; or the other side comprises (C) at least 85 mole % poly(trimethylene terephthalate) not copolymerized with a trifunctional comonomer wherein the inherent viscosity of (C) is 0.15 to 0.30 less than that of (A).  It is disclosed that the bicomponent fibers obtained were pressure dyed at 130° C.
Japanese unexamined patent application 2002-30527 discloses side by side type polyester-based conjugated fiber obtained by conjugating polyesters having different viscosities in a conjugating ratio of 65:35–35:65, comprising component A including poly(trimethylene terephthalate) as a main constituent and component B including poly(butylene terephthalate) as a main constituent, the intrinsic viscosities of the component A and B satisfy the formula 1.5≦Ia/Ib≦2.5 (Ia is the intrinsic viscosity of component A and Ib is the intrinsic viscosity of component B), and the fiber has the following characteristics: elongation rate of crimp ≦20%, elongation rate of stretching ≧10%, stretch modulus of elongation ≧90%, and Uster irregularity ≦2.0%. 
Co-owned U.S. Pat.  No.  6,641,916 and co-owned, co-pending U.S. Patent Application No.  2004/0084796, which are incorporated by reference, disclose a side-by-side or eccentric sheath-core bicomponent fiber wherein each component comprises a different poly(trimethylene terephthalate) composition and wherein at least one of the compositions comprises styrene polymer dispersed throughout the poly(trimethylene terephthalate). 
It is desirable to produce bicomponent fibers of poly(trimethylene terephthalate) and poly(tetramethylene terephthalate) having soft hand and high dye uptake.  It is also desirable to dye such bicomponent fibers at atmospheric pressure.