Process for texturizing polyester yarn and yarn

A process for the preparation of texturized multifilamentary polyester yarn possessing a stable crimp, in which the yarn passes first through a crimping device comprising an injector where the yarn is subjected to a stream of hot fluid which separates the filaments, and thereafter through a stacking nozzle to cause crimping, characterized in that the fluid is fed in at a temperature below the second order transition temperature of the polyester yarn, which feeding temperature is usually between 95.degree. and 220.degree. C., and in that the stack, after it issues from the nozzle is kept in the compressed state, subjected in this state to a high pressure of the order of 20 to 200 kg/cm.sup.2, and kept at ambient temperature or subjected to a heat treatment at a temperature below the second order transition temperature of the polyester yarn, which is usually at a temperature of up to about 220.degree. C., for a period of time ranging from one minute to 150 minutes. Polyester yarn possessing a stable crimp and fiber prepared by cutting the said yarn, as well as the textile articles comprising this yarn are also disclosed.

The present invention relates to a process for texturizing polyester yarn 
and the yarn obtained by this process. 
Continuous polyester yarns are often texturized with a view of using them 
in the weaving industry and in the hosiery trade; this texturizing 
generally makes use of the false twist process which makes it possible to 
prepare a yarn which possesses a certain elasticity, the bulk of the yarn 
making it possible to improve the handle of the article. For some 
applications, however, the main property sought is bulk, manifesting 
itself in a puffed-out appearance of the yarn, particularly when it is 
desired to produce floor coverings. 
It is known to crimp polyester yarns by means of other processes such as 
the pneumatic process described, for example, in U.S. Pat. No. 3,438,105 
assigned to the present applicants' assignee, in which the multi-filament 
yarn is subjected to a stream of hot fluid which separates the filaments 
and then stacks the whole in a restricted space from which it issues 
freely in the crimped state; however, the treatment with the hot fluid 
causes considerable shrinkage of the filaments, and this changes their 
tensiometric characteristics in such a way that their elongation at break 
increases greatly and their tensile strength is consequently reduced. This 
change manifests itself in subsequent deformations of the articles in the 
form of knitted or woven fabrics produced by means of the yarns; moreover, 
these deformations remove the crimp of the yarns and thus present the 
danger of cancelling out the desired effect; furthermore, because of the 
fragile nature of the crimp, which can be removed by simply exerting a 
tensile force on the yarn, great care must be taken when handling the said 
yarn when it is being wound up continuously in accordance with the above 
mentioned process, and during subsequent conversion operations. 
The present invention provides a process which makes it possible to avoid 
the above mentioned disadvantages and to prepare a texturized polyester 
yarn possessing a stable crimp. 
This process is characterized in that after having texturized the polyester 
yarn by means of a fluid as disclosed in the above-mentioned patent and 
wherein the fluid is kept below the second order transition temperature of 
the polyester yarn, usually at a temperature between 95.degree. and 
220.degree. C., the stack obtained is kept under compression, subjected to 
a high pressure, preferably between 20 and 200 kg/cm.sup.2, and kept at 
ambient temperatures or subjected to an elevated temperature still below 
the second order transition temperature of this polyester yarn, such as up 
to about 220.degree. C., for a period of time ranging from one minute to 
150 minutes. After this treatment, the mass of stacked yarn has become 
homogeneous and compact. This compact homogenerous mass can be delivered 
directly to the customer who can draw from it the yarn which can be used 
for textile operations; it is also possible to draw the yarn from the 
compact homogeneous mass and to wind it up in a conventional manner. The 
operations described above, of stacking, compressing and heat-treating the 
yarn can be carried out continuously or discontinuously. When they are 
carried out continuously, it is possible to thereafter knit or weave the 
yarn drawn from the compressed package. 
By "polyester yarn", there is to be understood a yarn which is wholly or 
partially stretched. This stretching process can be carried out in one or 
more operations, continuously or discontinuously, when the yarn is being 
manufactured. The polyester used in preferably that obtained by 
polymerizing ethylene glycol terephthalate, but other stretched or 
partially stretched polyester yarn can be used. The yarn is of any gauge 
or cross-section, and may or may not be colored. 
The stacking process if preferably carried out at a temperature of between 
95.degree. and 220.degree. C., but in any event below the second order 
transition temperature of the polyester yarn, in order to heat the yarn to 
a sufficient extent to make it easier to fold over the strands and to 
stack the whole. The stacked yarn is subjected thereafter to a pressure 
treatment and optionally a heat treatment, the pressure treatment and the 
heat treatment being carried out simultaneously or successively, 
continuously or discontinuously. 
The purpose of the pressure treatment is to keep the length of the yarn 
constant, so as to prevent it from shrinking during the heat treatment. 
Consequently, the heat treatment for stabilizing the crimp has the same 
effect as a conventional heat treatment for effecting dimensional 
stabilization under tension. The pressure device can be of any known type, 
such as pistons, endless belts, calenders, mechanical presses, inflatable 
chambers and the like. 
The yarn obtained possesses a crimped and puffed-out appearance; the 
filaments of which it is formed possesses deformations which are 
distributed at random and are of several types, namely the crimps which 
are distributed along the yarn and are grouped in zones separated by zones 
of flatter yarn, on the one hand, and the deformations due to the effect 
of the pressure means on the yarn, on the other hand. The yarn can also 
possess deformations in its transverse cross-section. It is found that the 
heat treatment of the yarn stabilizes the latter dimensionally, although 
this treatment of the yarn is carried out on the said yarn in the folded 
state, due to the blocking by the pressure exerted.

Referring to FIGS. 1 to 3, the yarn 1, coming from a feed device which is 
not represented, enters an injector 2 in which it is subjected to a stream 
of hot fluid 3 which opens the filaments, but is not at a temperature 
higher than the second order transition temperature of the yarns or 
filaments. The filaments then enter a nozzle 4 which has orifices 5 
pierced through its side; a part of the fluid escapes through these 
orifices and the other part ensures that the stack 6 is formed in and 
moves forward through the nozzle. At the outlet of the nozzle, the said 
stack is deposited in a cylindrical receptacle 7 (FIG. 1); when the 
receptacle is full, it is placed under the platen of a press 8 (FIG. 2) 
which converts the stacked packet of yarn into a compressed package. The 
receptacle and the package, kept under compression, are then subjected to 
heat treatment to a temperature below the second order transition 
temperature of the polyester yarn, in an oven 9 (FIG. 3). The latter 
heating treatment may be omitted. After the treatment and after cooling, 
the package of stacked yarn is withdrawn from the receptacle. The yarn is 
drawn from the package obtained; it has the appearance shown in FIG. 4. 
The texturized yarn thus obtained can be used in the form of continuous 
yarn or can be cut up and used in the form of fiber, for any textile 
applications. 
The following examples are provided to further illustrate the present 
invention only, and the invention is in no way to be deemed as limited 
thereby. 
EXAMPLE 1 
A poly(ethylene glycol terephthalate) yarn, of 167 dtex/30 strands, 
stretched in a ratio of 4.5 supplies a crimping device as described in 
U.S. Pat. No. 3,438,105 which description is incorporated here by 
reference under the following conditions: 
Rate of Feed--500 meters/minute 
Nature of the fluid--steam 
Pressure of the fluid--3 kg/cm.sup.2 
Diameter of the nozzle--3 mm 
Rate at which the stack issues--6 meters/minute. 
At the outlet of the nozzle the stack is deposited at the rate of 15 
meters/minute in a container consisting of a metal cylinder of diameter 72 
mm and height 40 cm, and is then subjected to a pressure of 130 
kg/cm.sup.2 ; the compressed package obtained is then heat-treated in a 
hot air medium for 60 minutes at 200.degree. C. After the homogeneous hard 
compact package obtained has been cooled, the yarn is drawn off. The 
comparative properties of the treated yarn and of an untreated control 
yarn are as shown in the following Table I. 
TABLE I 
__________________________________________________________________________ 
Shrin- 
Gauge kage Crimp, 
dtex/ in number 
number 
Tensile 
Elon- 
boiling 
Elas- of 1/2 
of strength 
gation 
water 
ticity 
Bulk 
waves/ 
Yarn strands 
g/den 
% % % cm.sup.3 /g 
cm 
__________________________________________________________________________ 
Control 
yarn 167/30 
4.8 18.9 
7.75 0.88 
1.95 
Textu- 
rized 
yarn 199/30 
3.2 25.4 
0.45 45 6.39 
11 
__________________________________________________________________________ 
It is thus seen that the properties have been changed to give practically 
zero shrinkage in boiling water but high elasticity and high bulk; the 
yarn, blocked dimensionally because of the violent transverse compression 
force and the heat treatment, possesses a stable crimp which is removed 
only when a very high tensile force is exerted on this yarn. The purpose 
of the tests, the results of which are indicated below in Table II, is to 
illustrate this crimp stability; they compare the crimp stability, under 
different loads, of the yarn obtained according to the present process and 
of the yarn taken from the stack at the outlet of the crimping device. 
TABLE II 
__________________________________________________________________________ 
Load in g/dtex 0 0.5 0.75 1 1.25 1.5 
__________________________________________________________________________ 
Yarn taken 
at the out- 
Crimp -3.7 -1 -0.2 +0.3 +2 +2 
let of the 
contrac- 
device tion 
% 
Yarn accor- 
ding to present 
-47.3 
-35 -14.6 
-28 -14 -55 
process 
__________________________________________________________________________ 
The crimp contraction is measured in accordance with a method wherein a 
skein is prepared having a length of 50 cm by coiling 8 turns of yarn, 
each of one meter, under a tension of 0.1 g/dtex. A load is applied for 
one minute, consisting of a weight suspended at one end of the skein, that 
is to say, in the case of a skein of yarn of 167 dtex/30 strands at 1 
g/dtex, the corresponding load is 2,672 g. 
The load is removed after one minute; the skein is immersed for five 
minutes in a graduated wide-mouthed vessel containing water at 90.degree. 
C., and the difference in length between the length of the skein before 
applying the load and the length of the skein after immersion in water is 
measured and multiplied by two in order to bring the said measurement to 
one meter. 
By examining the results, it can be seen easily that the crimp in the yarn 
of this invention persists while the yarn taken at the outlet of the 
crimping device begins to flow under a load of between 0.75 and 1 g/dtex. 
EXAMPLE 2 
A poly(ethylene glycol terephthalate) yarn, of 550 dtex/60 strands, 
stretched in a ratio of 4.5, is introduced into and texturized in a 
crimping device like that described in U.S. Pat. No. 3,438,105, under the 
following conditions: 
Rate at which the yarn is fed to the injector--2,000 meters/minute 
Nature of the fluid--saturated steam 
Pressure of the fluid--5 kg/cm.sup.2 
Diameter of the nozzle--8 mm 
Rate at which the stack issues--30 meters/minute 
At the outlet of the nozzle, the stack is deposited at a rate of 35 
meters/minute in a receptacle consisting of a cylinder of diameter 72 mm 
and height 40 cm, and is then subjected to a pressure of 140 kg/cm.sup.2 ; 
the compressed package obtained is then heat-treated at 145.degree. C., in 
saturated steam for 20 minutes. After cooling the package obtained, the 
yarn is drawn off. The comparative properties of the yarn before and after 
treatment are as shown in the following Table III. 
TABLE III 
__________________________________________________________________________ 
Gauge Crimp, 
dtex/ shrinkages % number 
number Elon- Boil- Dry Elas- of 1/2 
of Strength 
gation 
ing Steam air ticity 
Bulk waves 
Yarn strands 
R.k.m. 
% water 130.degree. C. 
150.degree. C. 
% % cm. 
__________________________________________________________________________ 
Control 
550 dtex/ 
yarn 60 strands 
35 15 8 13 9 -- -- -- 
Treated 
574 dtex/ 
yarn 60 strands 
22 20.4 0.3 0.8 0.2 27.1 3.96 7 
__________________________________________________________________________ 
While the present invention has been illustrated primarily with regard to 
the foregoing exemplification, it should be obvious that the present 
invention is not in any way to be deemed as limited thereto, but must be 
construed as broadly as all or any equivalents thereof.