The fiber which is made of polyethylene terephthalate or the polyester in which this is the main component has various excellent properties and so it is widely used not only in apparel but also in industrial materials.
As the method of making the polyester which is used for such industrial materials in the past, the two-process method in which polyester polymer is melt spun, the spun fiber yarn is passed through a heated cylinder installed directly under the face of spinning die and then is cooled and solidified, imparted with oil agent and taken up to obtain undrawn fiber yarn and then this is first taken up and then is drawn or the direct spinning-drawing method in which the undrawn fiber yarn is continuously drawn without taking up was used. Particularly the direct spinning-drawing method can enhance productivity and so it is used widely. However, it was difficult to make by the direct spinning-drawing method the fiber for industrial materials which require, in particular, low heat shrinkage and dimensional stability. For example, the polyester fiber which is used in resin-coated fabric or V belt, conveyer belt is required to have high strength and low heat shrinkage and, when it is attempted to make such polyester fiber by the direct spinning-drawing method, the heat treatment effect to the drawn fiber is inadequate because the drawing is done at a high speed and so the low heat shrinkage property could not be satisfied. As a means of complementing this, the surface temperature of the roller at the final drawing was raised to the level which is close to the melting of running fiber yarn and the time of heat treatment of the running fiber yarn was prolonged by adding one or 2 stages of drawing rollers, in practice. However, in these methods, the surface temperature of drawing roller is high and so the life of the bearing of the drawing roller is shortened, causing non-uniform rotation of the drawing roller or generating mechanical troubles such as unexpected stoppage during the operations. This also generated problems of increased facility cost because of the increased number of the drawing rollers and lower workability because of the enlarged apparatus.
This invention is intended to provide the method of efficient production, by the direct spinning-drawing method, of polyester fiber which has high strength, low heat shrinkage, excellent dimensional stability and is particularly suitable for use in resin-coated fabrics, V belt and conveyer belt applications.