ES353310A1 - Self-bulking conjugate filaments - Google Patents

Abstract

A conjugate filament comprises at least two components, one of said components being polypropylene homopolymer having a density of at least 0À88 and the or each other of said components being a copolymer of propylene and up to 25% of a second alpha-olefin having 2 to 6 carbon atoms, the or each said copolymer having a density of at least 0À88. A copolymer component may be either a random copolymer containing 2 to 5% ethylene, or a block copolymer containing 3 to 25% ethylene. The components of the filaments may be disposed in side-by-side or in sheath-and-core relationship, the former being preferred. The ratio of the components in the conjugate filaments can vary from about 1: 4 to 4: 1, but generally the filaments will be comprised of about equal portions of each component. After spinning through a suitable spinneret, the orienting draw is conducted at a temperature below the melting point of the polypropylene in order to develop the optimum properties of the filaments at above the temperature at which either of the components forms voids. Preferably, the drawing temperature will be between about 80 and 110 C. A draw to a draw ratio of at least 2À5 is required to produce sufficient shrinkage to result in useful crimped filaments. In some cases, the stretched filaments crimp spontaneously as soon as the stress imposed by the drawing operation is relaxed. In other cases, the crimp is developed by applying heat to the filaments in a relaxed state, causing the same to shrink, bringing the differential shrinkage effect into play. Such heat treatment is preferably effected in a batch operation, as with boiling water or an oven, at a temperature above that where the copolymer component shrinks, but below that at which substantial shrinkage of the homopolymer component takes place. Normally this will be between about 90 and 150 C. The specific temperature selected is also dependent upon the ethylene content of the copolymer component, higher temperatures being preferred at the lower levels of ethylene content. Heat treatment is preferably carried out for about 0À2 to 10 minutes. The heat treatment may also be effected continuously by bringing the yarn, moving suitably at 100 to 1000 metres per minute, into contact with a hot plate or through a heated zone. In such continuous operation, treatment times of the order of 0À01 second to about 1 minute are employed, and the heat source or zone can be at a temperature as high as 300 C. Filaments so made have a crimp frequency of about 5 to 100 crimps per inch. In Example 1, a conjugate filament yarn is spun from propylene homopolymer and a random copolymer of ethylene and propylene containing about 2À4% ethylene, the components being disposed in side-by-side relationship. Spinning is effected at 250 C. at a linear rate of 665 metres per minute to form a spun yarn which is drawn about 3À5 times at about 100 C. and develops crimps on subsequent heating in the tensionfree state by placing a skein of the same on a metal grating in an oven at 125 C. for two minutes. In example 2, example 1 is repeated, using the same homopolymer in combination with an end block copolymer containing about 25 % ethylene. The resulting yarn is heat treated in boiling water for five minutes to develop the crimp. In Example 3, the same homopolymer as before is used with a 3-block copolymer containing 3% ethylene. In further experiments the same homopolymer is used with a random copolymer of propylene and about 3À2% butene- 1. The resulting yarn is heat-treated at 125 C. for 5 minutes to develop the crimp. Filaments having more than two components, e.g. a homopolymer and two copolymer components, may be made, and conjugate filaments may also be prepared with polypropylene in one component and a mixture of copolymers in the other components, e.g., a mixture of ethylene-propylene and butene-propylene copolymers.