Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – With crimping or crinkling of strands of filaments
Patent
1998-08-31
2000-09-26
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
With crimping or crinkling of strands of filaments
26417713, 26421114, 26421117, 425464, D01D 522, D01D 5253, D02G 100
Patent
active
061238864
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the production of crimped filaments made from long chain molecule thermoplastics materials and relates particularly, but not exclusively to fibres made from polypropylene.
2. Description of Related Art
Filaments made from long chain molecule thermoplastics materials are well known in the art and are generally extruded through holes in a spinneret plate from a body of the molten plastics material above the spinneret plate. When produced in this manner, the filaments are essentially straight and without crimp. Whilst continuous straight filaments, without crimp, can be used for a number of commercial processes, a crimping of the filament is highly desirable for a number of commercial applications, in particular in the clothing or woven material industries.
One known method for applying a crimp to a continuous filament is to pass the filament, in heated conditions, between a pair of meshing gear wheels but the crimp obtained by the gear wheels is very limited and lies in only one plane of the filament. If the filament is rotated about its axis whilst passing through the gear wheels a helical crimp can be produced but said crimp will require the additional expense of providing a means of rotating each filament and the crimp is relatively weak.
In another known method for crimping filaments the filaments, whilst in heated condition, are cooled on one side and, as the filaments cool, differential stresses will be induced across the diameter of the filaments. When the drawing tension is released from such filaments a wavy, or helical, crimp will develop but, in practise, the degree of crimp applied to and retained by such filaments is relatively small.
SUMMARY OF THE INVENTION
Preferred embodiments of the present invention seek to provide a method for making filaments wherein the filaments have a substantial, generally helical crimp therein.
According to the present invention there is provided a method for producing a substantial helical crimp in a continuous filament, the method comprising the steps of generating a turbulence in a thermoplastic material intended to form the filament whilst the thermoplastics material is in its glass transition phase and maintaining stresses induced in the formed filament by said turbulence whilst the filament material passes into its crystallised phase.
Viewed from another direction the present invention provides a method for inducing a substantial helical crimp in a continuous filament of a thermoplastics material comprising the steps of inducing turbulence in the polymer flow immediately prior to, or at the point of, formation of the filament.
Preferably the turbulence is concentrated towards one side of the cross-section of the filament.
In a preferred embodiment, the molten filaments are rapidly cooled to solidification so that the disturbance of the molecular structure is locked into the crystallised polymer.
During subsequent processing of the filaments when the axial tension is removed from the filaments, the stresses induced into the filaments before or on leaving the spinneret plate cause uneven tensions in the filaments to be relieved which results in distortion of the filaments and produces a pronounced helical crimp effect in each filament.
In a preferred embodiment, the method further comprises the step of extruding the filaments through holes in a spinneret plate wherein each hole makes an angle, preferably an angle of substantially 45.degree., to an external face of the spinneret plate.
Alternatively, or in addition, the turbulence in the molten plastics may be generated by a change of the cross-sectional area of each hole through the spinneret plate.
In a preferred embodiment the change of cross-sectional area of each hole through the spinneret plate is in the form of a step.
In one embodiment the hole through the spinneret plate from which the filament is drawn is of different cross-sectional areas, with the smallest cross-sectional area at that end of the hole from which the fil
REFERENCES:
patent: 3781949 (1974-01-01), Breen et al.
Abstract of Japan 47-24963 B (1972).
SCS Consultancy Services
Tentoni Leo B.
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