Method of producing a friction texturized polyester filament yarn and yarn made thereby

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
1 shows the basic elements of an apparatus 10 for performing the method of the invention.
This apparatus includes a squeezing twister 12 for twisting the yarn and a heater 14.
The yarn 32 is fed from a supply bobbin 35 around a first shaft S1 through the heater 14 and then through the squeezing twister 12 where it is twisted upstream and detwisted downstream.
In the preferred embodiment the yarn is advantageously a flat polyester filament yarn with at least 80% by weight of ethylene terephthalate units and a titre from 400 to 600 dtex.
Then after passing through the squeezing twister 12 the detwisted yarn passed around a second shaft S2.
After passing around the second shaft S2 the yarn is friction texturized polyester filament yarn 37 having a crimpability of at least 45%.
The yarn is held against both shafts S1 and S2 by rollers R.
The temperatures in the heater 14 are over 200.
degree.
C.
, advantageously about 230.
degree.
C.
A preferred squeezing twister 12 is shown in more detail in FIG.
2.
It comprises two rotating cylindrical members 16,17 on each side of the yarn 33.
The multifilament yarn is twisted when the surfaces of the rotating cylindrical members 16,17 contact the side surfaces of the yarn 33.
These rotating members are mounted so that they can be pushed against and from the yarn 33 as it rotates on a mounting means M.
Also the contact or disk angle .
alpha.
with the yarn 33 can be changed.
A means for supplying forced air 22 can be used to forced the rotating member 17 against the yarn 33.
The pressure of the rotating member 17 can be controlled by controlling the means for supplying the air pressure 22.
The desired friction texturized polyester filament yarn 37 can be obtained by controlling the process parameters including the disk angle .
alpha.
shown in FIG.
3 and the air pressure for the air supplied by the means for supplying the air pressure 22.
It is essentially that the process parameters be controlled so that the ratio of the yarn tension immediately after or downstream of the squeezing twister 12 to that immediately before or upstream is less than one