Process for spinning of core/mantle yarns and yarn products

A process for the production of a core/mantle yarn, in which a core thread is continuously conducted through a spinning zone in a gap formed between two adjacent and oppositely moving surfaces; staple fibers are fed into the path of the core thread and come into frictional contact with the moving surfaces in said zone to spin the staple fibers about the core thread; the core thread is preferably stretched during the spinning in order to bring about a defined, predetermined elastic stretch of the core thread in the spinning zone; and the core thread has a roughened surface which may be obtained by using a staple fiber yarn or thread obtained by texturizing, weaving, twisting, etc. The invention is especially characterized by an improved adherence of the fibers of the mantle to the core thread by pre-coating the core thread with an adhesive, or preferably by preapplying colloidal silicic acid to the core thread.

BACKGROUND OF THE INVENTION 
German published patent specification OS 24 64 400 discloses a process for 
the production of a yarn by winding of continuous filament yarns about 
staple fiber bands. The breaking stretch of the winding filament yarn is 
at least equal to the breaking stretch of the spun fibers. The strength 
elongation characteristic of the spun fibers and that of the winding 
filament yarn are to be attuned to one another in the sense that the 
initial modulus of the winding filament yarn is great and thereby in 
stretch stress of the filament yarn there is rapidly built up a 
sufficently high tension. This leads to filament yarns consisting of 
smooth fibers, which correspondingly leads to textile disadvantages. The 
strength factor of the winding filaments, therefore is very low, and 
therefore, they contribute little to the strength properties of the 
core/mantle yarn. 
It is further known from German published patent specification OS 26 27 220 
that endless threads (filament yarns) can be joined together with staple 
fibers (spinning fibers). 
It has proved it hitherto was possible, to be sure, to attain an 
improvement of the textile properties of the filament yarn, but it was not 
possible to bring about any appreciable increase of the strength 
properties. It was not possible to bring the strength properties of the 
core thread in harmony with the strength properties of the spun fibers 
(staple fibers) in such a way that a summation takes place of the strength 
properties. 
Attainment of core/mantle yarns with improved strength properties is the 
basic objective of this inventiion. 
BRIEF DESCRIPTION OF THE INVENTION 
The invention herein provides processes and apparatus for the production of 
a core/mantle yarn, in which the core thread is drawn at a constant rate 
through a spinning zone and staple fibers are spun thereabout to form a 
mantle. The core thread is pre-stretched in the spinning zone to such an 
extent that, at the desired reference strength of the finished core/mantle 
yarn, the specific strength of the core thread is greater than or equal to 
the specific reference strength of the finished core/mantle yarn. 
The core thread in the sense of this invention may be a filament yarn 
or--which equivalent--a multifilament yarn of endless monofilaments, 
preferaby textile polymer filaments. The core thread, however, may also be 
a thread spun from textile fibers--or what is equivalent--a thread spun 
from staple fibers. Here, natural fibers or textile polymer fibers can be 
used. 
The mantle fibers are in any case staple or spinnable fibers. It is a 
matter of choice whether they are natural fibers, such as, for example, 
cotton, or textile synthetic polymer fibers. 
The process of the invention assures that, on the one hand, a very high 
yarn strength is achieved through summation of the strength properties of 
both yarn constituents. On the other hand, the exterior of the core mantle 
thread can be modified in such a way that improvements in appearance and 
feel or other excellent textile properties can be realized. 
By reference strength and reference elongation in the sense of this 
invention there is meant the force that is required to elongate the 
finished core/mantle yarn by a certain prescribed amount, the reference 
elongation. 
The reference elongation is there a value selected by the yarn producer or 
processor, which is selected in the scope of the possibilities imparted to 
the material by the processsing conditions--for example tensile and 
stretch strains in the weaving machine--and to strains occurring in use in 
such a way that there are attained the optimum processing and/or use 
properties. 
Preferably the reference force lies in the range of 20% to 80% of the 
tearing strength of the finished core mantle thread. In the determination 
of the reference stretch it is very essential also to take into account 
the composition of the core/mantle thread. If the core mantle thread 
contains substantial components of natural fibers, for example cotton, the 
reference stretch--depending on the type of cotton--can amount to 6% to 
12% at the upper limit and ca. 2% at the lower limit. 
The mantle fibers serve above all the purpose of influencing in a favorable 
manner the appearance, the feel and the wear properties of the core/mantle 
yarn and of the products made from it. Preferably they are natural fibers, 
in particular cotton. Also possible, however, is the use of spinnable 
fibers (staple fibers) of synthetic polymers used in textiles. For this, 
endless filaments can be supplied as a band to a tearing or cutting 
mechanism used for direct conversion into staple fibers, which are fed to 
the spinning installation. 
Of spinning processes for the practice of the process of the invention 
several processes are available. They are open-end spinning processes, 
such as, for example, air turbulence processes or processes in which 
spinning fibers are twisted together on one or more moving surfaces into a 
fiber yarn. In particular, a process according to the disclosure of our 
aforesaid U.S. application as well as in German application P 26 56 787.3, 
are preferred. 
The use of such spinning processes in conjunction with the process of this 
invention leads, therefore, to an especially favorable combination, 
because this spinning process in no way influences the course of the core 
thread. Further, the combination of the process of the invention with the 
spinning process according to the aforesaid patent disclosures makes 
possible in an especially suitable manner the prestretch of the core 
thread in the spinning zone, since both processes make possible a straight 
course of the core thread through the fiber spinning zone. 
The core thread is such that the mantle fibers adhere well to it. For this 
reason preferably core threads with roughened surface are used. It is 
possible, for example, to use as the core thread a staple fiber yarn which 
is spun in a continuous process operated in association with the process 
of the invention. 
The spinning rollers may also be hyperboloids, especially asymmetric 
hyperboloids, the core thread running axially from the largest end to the 
smallest end of the asymmetric hyperboloids. 
For the increase of the strength and stretch properties of the core/mantle 
yarn it is suggested, as preferred, a texturized synthetic polymer thread 
be used as the core thread. The texturizing can be achieved, in 
particular, by false twisting. It is also possible to carry out the 
false-twist texturizing continuously just ahead the spinning process of 
the invention. As usual, the core thread is conducted over a heating 
arrangement, thereupon twisted and then conducted through a false-twist 
apparatus. The core thread is then spun after the false twister. The zone 
in which the false twist occurs may run back also the stretching into the 
stretching zone. 
Another possiblity for the texturizing is, in particular, the stuffing 
chamber or the air nozzle texturizing. A roughened surface is obtained on 
the filament thread also by the means that using an air stream impinging 
transversely on the filaments in a manner wherein they become interlaced 
with one another. Such processes are sometimes called "tangle" processes. 
A further possiblility for the roughening of the surface lies in twisting 
the core thread. 
All these possibilites listed for the roughening of the surface are 
essentially determined by processing and use conditions for the 
core/mantle yarn generated. It may also be expedient to use a smooth core 
thread, which is first preheated with an adhesive that can be washed out. 
This results in a well sheathed and durable core/mantle yarn which has 
good working properties. Only after incorporating of the yarn into a 
textile structure by weaving, knitting, fine-knitting or the like is the 
adhesive washed out, since then the cohesion between core and mantle 
fibers is assured in another manner. 
Especially for the production of carpet yarns it is useful to supply an 
electrically conducting core thread--possibly together with other treated 
core threads--as described earlier--to the spinning zone. 
It was further found that the process of the invention, through a heat 
treatment of the freshly spun core/mantle yarn, preferably by heating the 
finished core/mantle yarn passing over a heated surface, e.g., a hot 
contact plate, provides yarns with special effects. In particular, the 
shrinkage properties of the core thread and of the mantle fibers can be 
adapted to one another, or through different shrinkage properties, special 
swelling effects result or that the stretch (elongation) properties can be 
influenced in a special way. Use of these process modifications are 
greatly dependent on the desired structure of the core/mantle yarn and on 
its intended processing and use. 
A further object of the invention is to provide a core/mantle yarn which 
can be produced in particular by the processes described herein. This 
core/mantle thread yarn is characterized in that the core thread is 
multifile synthetic polymer which is crimped, preferably 
three-dimensionally crimped, and is twisted about the staple fibers. The 
specific strength of the core thread at reference stretch of the 
core/mantle yarn is greater than the specific reference strength of the 
core/mantle yarn. 
The specific strength in the sense of this invention is a fineness-referred 
tensile strength, which is given, for example, as tearing length in the 
dimension: 
##EQU1## 
To determine the prestretch of the core thread in the spinning zone, 
therefore, according to the invention, first the desired reference stretch 
and the desired reference strength of the finished core/mantle yarn are 
determined. There is then determined in the force-stretch diagram of the 
core thread, for a specific strength which is greater than the reference 
strength of the finished core/mantle yarn, the appertaining stretch 
(elongation). This stretch minus the reference stretch then yields the 
prestretch at which the core thread is conducted in the spinning zone. 
The spinning device of the invention is an open-end spinning device with an 
open-end spinning zone through which the core thread can travel, 
especially a spinning device as disclosed in the aforesaid U.S. and German 
applications. The spinning device according to the invention is 
characterized by having its spinning zone located between two thread 
delivery mechanisms that are driven at a constant, adjustable translation 
ratio. 
For the production of a core thread of staple fibers--be it natural fibers 
or synthetic polymer fibers--there can be provided ahead of the spinning 
device of the invention another spinning device. For the modification of a 
core thread which consists of endless filaments, the spinning device of 
the invention can have ahead of its inlet side a texturizing unit. This 
texturizing unit may be positioned before the first delivery mechanism. 
The process of the invention and the appratus in its further development 
offers, however, the advantageous possibility of arranging both the 
texturizing arrangement and also the spinning device between the two 
delivery mechanisms, thereby providing a simple and economical machine 
construction. 
For the production of the mantle fibers there can be arranged in front of 
the spinning device of the invention a tearing or cutting mechanism for 
endless synthetic polymer filaments. In this development of the spinning 
device of the invention it is possible, avoiding any intermediate 
processing, to spin a core/mantle yarn, starting with endless polymer 
filaments, on a single spinning machine. 
The process of the invention permits conducting the core thread through the 
spinning zone (where spinning fibers or staple fibers are spun thereabout) 
at a precalculated stretch and tension. For production of core/mantle 
yarns with prescribed properties, it is especially advantageous if the 
core thread is pretwisted in the spinning zone to such an extent that, at 
the desired reference stretch of the finished core/mantle yarn, the 
specific strength of the core thread is greater than or equal to the 
specific reference strength of the finished core/mantle yarn, whereby the 
core thread is subject to approximately the same stretch relations as the 
mantle and, in the process, takes over the main loads imposed on the yarn. 
A possibility of exerting the necessary pull force on the core thread in 
the spinning zone exists also with the use of hyperboloids as spinning 
rollers, which are adjusted in such a way that they exert an axial 
conveying force on the core thread. 
It has proved especially advantageous if the core thread is pretreated 
after the first delivery mechanism and before the entry into the spinning 
zone with a colloidal silicic acid, i.e., (H.sub.2 Si.sub.2 O.sub.5).sub.x 
in colloidal solution, a commercially available composition. The colloidal 
silicic acid preferably has a 50 to 90% water content. It is applied 
preferably in amounts calculated as dry substance, of less than 0.5% of 
the thread weight, most preferably less than 0.3% by weight. The applied 
amount of colloidal silicic acid preferably can be controlled by 
conducting the thread at a certain encircling arc over a finishing roller 
driven in rotation, which dips in part into a container with the 
application medium (silicic acid) and which is driven at a controllable 
speed of rotation. For example, the colloidal silicic acid may be applied 
to the core thread by means of a rotably driven finishing roller which 
dips into a container of the acid as a thread finishing fluid, the core 
thread contacting said roller circumferentially outside of the container 
over an angle of more than 30.degree., and the finishing roller being 
rotatably driven at a controllable predetermined circumferential velocity. 
By the application of colloidal silicic acid to the thread the quality of 
the core/mantle yarn can be very substantially improved. In particular, 
hereby the so-called "push-on tendency" is reduced to virtually to zero. 
By "push-on tendency" there is meant the following: 
In the wrapping of a core thread with staple fibers there is present the 
danger that part of the mantle, consisting of staple fibers, upon running 
through thread-guide elements--such as are usual and necessary in yarn 
working and yarn processing (especially in weaving and knitting)--is 
pushed or slid on the core thread to form an acummulation of thickening of 
mantle fibers. Thereby the core thread becomes partially denuded of mantle 
fibers. The accumulation of the mantle fibers leads, in the case of yarn 
treatment or processing, very easily to yarn breakage and results, in the 
finished textile structure (knit or woven) to an uneven appearance. It, 
therefore, becomes necessary to reduce the push-on tendency, i.e., by 
improving the adhesion of the mantle fibers to the core thread. One 
measure for determining the push-on tendency is the so-called "push-on 
length". This is determined by conducting the core thread through a narrow 
gap, in front of which the spun fibers of the mantle are restrained. The 
core thread is then loaded with a weight which amounts to approximately 
half the tearing strength of the core/mantle yarn. In consequence of this 
weight load, the core thread tends to be drawn by a certain amount through 
the gap, while it is held fast by the restrained mantle fibers. The weight 
also is fastened to a gap plate, the gap of which corresponds 
approximately to the diameter of the core thread. Ahead of this gap plate 
occurs an accumulation of stripped-off mantle fibers. The length of core 
thread bared in this way of mantle fibers is called the "push-on length". 
By application of colloidal silicic acid to the core thread, even with less 
than the aforesaid 0.3% applied amount, based on the core thread weight, 
it was possible to reduce the push-on length of a thread having no finish 
application from one in the range of 40 cm to an immeasurably small 
push-on length for the colloidal silicic acid-coated-core thread. 
ILLUSTRATED EMBODIMENTS 
Preferred forms of the invention are described below, in conjunction with 
the drawings, wherein:

In FIG. 1 there schematically shown is the spinning device which--as in the 
aforesaid U.S. and German applications--consists of two air permeable, 
rotatable perforated drums 1 that are journalled in bearings 2 and are 
driven via drive belt 5 by motor 4 in the same direction. The side-by-side 
drums are provided with many perforations 6. By the suction arrangement 7 
an air stream is drawn into each drum in the region of the fiber spinning 
zone in the gap between the drums. For further details reference is made 
to the above-mentioned U.S. application. 
The core thread 3, in which thread is drawn off from the run-off bobbin 15, 
is supplied to the spinning device. Further modifications for the 
production of the core thread are represented in FIGS. 2 to 5. The core 
thread is conducted through (or at least a short distance in) the 
narrowest gap formed between the two drums 1. To this gap there are also 
fed the staple fibers supplied from the resolving and feeding unit 10. 
From the can 9 the fiber or filament cable 8 is drawn off by means of the 
roller mechanism 11 and fed to the resolving roller 12. The fiber cable is 
resolved by the toothed roller 12 into individual, discrete fibers. The 
individual fibers are conveyed in an airstream through the fiber feed 
channel 13 into the gap between the rollers 1 and, namely, in such a way 
that in the process they are straightened as much as possible. The 
finished spun core/mantle yarn is drawn off by delivery mechanism 16 from 
the spinning zone and, with reciprocation by the transverse unit 18, is 
wound on the winding bobbin 17. 
The delivery mechanisms 14 and 16 are operatively connected through gear 
19. Gear 19 is adjustable so that the desired translation ratio between 
the delivery mechanisms 14 and 16 can be set selectively. 
The unit of FIG. 2 may be substituted for the parts enclosed in block A of 
FIG. 1 and illustrates the production of a core thread of staple fibers in 
a continuous process to be used in association with the production of the 
core/mantle yarn according to this invention. 
A spun fiber or filament cable 21 is drawn off from the can 22 by means of 
the resolving and feed unit 20. The resolving and feed unit 20 is 
constructed like the resolving and feed unit 10 in FIG. 1. The descrete 
fibers are fed to the spinning unit 25 of like construction to the 
spinning unit of FIG. 1. The perforate drums are driven by motor 23 and 
contain like suction arrangements 24. The core thread 3 is generated by 
the spinning unit 25, which is drawn off by the delivery mechanism 
14--identical with the delivery mechanism 14 in FIG. 1--and is supplied to 
the spinning unit represented in FIG. 1 as core thread. 
In FIG. 3, another combination useful as the block A in FIG. 1 provides a 
texturizing of the core thread of filament yarn. The core thread is drawn 
off from the bobbin 15. In the texturizing unit, (for example, a 
compression or stuffing chamber, an air crimping unit or a tangle unit) 
imparts texture to the thread being drawn therethrough by the first 
delivery mechanism 14, which is also represented in FIG. 1. 
The apparatus shown in FIG. 4 may be used as the block A in FIG. 1 to 
attain false-twist texturizing of the core thread. The core thread 3 is 
drawn off from the bobbin 15 through the first delivery mechanism 14 and 
thereupon guided over the heating plate 26 as well as through the false 
twister 27 before it runs into the spinning device represented in FIG. 1. 
The heating plate 26 is heated by the vapor condensation heating 
principle. In the lower part of the heating system forming a closed cavity 
there is a fluid which is heated by an electric heating resistance. The 
pressue in the system is adjustable. Twist is applied by the known 
disc-type twisting unit 27. 
The false twister may be any known type, e.g., as described in German 
published patent specification OS 22 13 881. 
In FIG. 5, which again has apparatus useful as block A in FIG. 1, there is 
likewise shown apparatus for the false-twist texturizing of the core 
thread 3 as in FIG. 4. The difference lies in that in FIG. 5 an 
unstretched core thread, for example of polyethylene terephthalate, is 
presented. This is simultaneously stretched and false-twist texturized 
between the delivery mechanisms 28 and 14. The delivery mechanism 14 is 
identical with that represented in FIG. 1. The delivery mechanisms 14 and 
28 are, moreover, likewise in operative connection with adjustable 
translation ratio by the gear 19. 
FIG. 6 shows alternative apparatus for that in block B in FIG. 1 for the 
production of the discrete polymer fibers from a cable 29 of the synthetic 
fibers. The cable 29 is drawn off from the can 30 and converted in the 
tearing mechanism 31, which has a usual construction type, into a spinning 
cable 8. The spinning fiber cable 8 is then--as represented in FIG. 
1--supplied to the feed and resolving unit 10. The tearing mechanism 31 
consists in the case represented of the two roller mechanism 32 and 33, 
between which extends the conveyor belt 34. 
FIGS. 7 and 8 show heating units serving as alternatives in block C in FIG. 
1 and provide for modification of the freshly spun core/mantle yarn by a 
heat treatment. According to FIG. 7 the heat treatment takes place by 
means of a contact-free passage of the yarn through the heater 35 just 
ahead of the delivery mechanism 16. Such a heat treatment is useful, for 
example, to render the core/mantle yarn tension-free. 
In FIG. 8 the heat treatment occurs between the delivery mechanism 16 
(represented also in FIG. 1) and a further delivery mechanisms 36, which 
are operatively connected at an adjustable translation ratio. In FIG. 8 
there is used a contact heating plate 37. The contact heating plate is 
likewise heated according to the vapor condensation principle. This 
arrangement according to FIG. 8 has the special advantage that the heat 
treatment of the finished core mantle thread can take place under a 
tension that is independent of the tension prevailing in the spinning 
zone. In particular, tensions can also be exerted on the mantle fibers, 
which at first is not the case in the spinning zone. 
According to the invention, the core thread is conducted in the spinning 
zone between the delivery mechanism 14 and 16 by corresponding adjustment 
of the translation ratio with a certain prestretch. This prestretch is 
determined by first establishing the reference stretch of the finished 
core/mantle yarn. The core/mantle yarn has a certain tearing stretch, 
which corresponds to a tearing strength. Obviously, the core/mantle yarn 
must not be strained to the tearing point either in the processing or in 
use. Since the core/mantle yarn is composed of various components, there 
must be established, on the contrary, a reference stretch and a reference 
strength corresponding to this, which assures that no damage will take 
place to one of the components. Otherwise reference stretch and reference 
strength, however, also present a measure for the normal strains occurring 
in processing and use. The establishment of reference stretch and 
reference strength are in the province of problems of yarn producers and 
yarn processors. 
The prestretch setting in the spinning about of the core thread should, 
according to the invention, be so great that in the case of normal load, 
therefore at reference stretch of the core/mantle yarn, the core thread 
absorbs the essential load. 
In comparative tests that are yielded from the following table, a core 
thread of polyethylene terephthalate 16 7 dtex=60 Nm was streteched in 
apparatus according to FIG. 5 in conjunction with FIG. 1, texturized and 
worked with cotton fibers, staple length 40 mm 1.7 dtex individual denier, 
Nm 40 into a core/mantle yarn Nm 24. The reference stretch of the finished 
core/mantle yarn was established at 8.5% with a reference strength of 18 
km. The core thread was conducted in the first test with by-passing of the 
delivery mechanism 14. It proved that only a very poor and irregular 
adherence of the mantle fibers to the core threads occurred. The breaking 
stretch of the core thread was 31.5%. The specific tearing strength was, 
however, to only 16.3 km, and was thereby considerably worse than in the 
case of the core/mantle yarn. 
In the parallel test, the core thread was prestretched between the delivery 
mechanism 14 and 16. Previously there had been determined the 
strength-stretch diagram of the core thread according to FIG. 9. 
Moreover, it was established according to the invention that the core 
thread in the case of load of the reference load was to absorb the greater 
load of 21 
##EQU2## 
From the strength-stretch diagram according to FIG. 9 for this load there 
can be derived a stretch of 12.5% as the reference stretch (elongation) of 
the core thread. 
The prestretch in the spinning zone was thereby determined as the 
difference between the reference stretches of the core/mantle yarn on the 
one hand and of the core thread on the other hand at 4% and 
correspondingly adjusted. The strength of the finished core/mantle yarn 
was thereby possible to increase beyond the prescribed reference strength. 
TABLE 
__________________________________________________________________________ 
Core thread 
Core/mantle yarn E 
B D Spec. G 
A Specif. 
C Spec. strength 
F Prestretch 
Ref. ref. Tearing 
tearing 
[Km] Stretch 
[%] 
stretch strength 
stretch 
strength 
at ref. 
[%] in spinning 
[%] [Rm] [%] [Km] stretch 
at force E 
zone 
__________________________________________________________________________ 
Determined 
Strength- Determined 
Strength- 
Type after stretch according 
stretch 
of material 
diagram 
Test Test to diagram of 
G = F - R 
determina- 
processing 
of the E &gt; B the core 
tion use K-M thread thread 
8.5 18 31.5 16.3 
State of unusable, 
Not Not 
the art since determined 
determined 
0 
D &lt; B 
New 8.5 18 12.9 25.1 21 12.5 4 
process good, 
since 
D &gt; B 
__________________________________________________________________________ 
In FIG. 10 there is illustrated a spinning device for the practice of the 
process of the invention, which device corresponds essentially to the 
device of FIG. 1. The same reference numbers as in FIG. 1, therefore, was 
retained insofar as the same designations apply. The core thread 3 is 
drawn off from the stationary delivery bobbin 15 through the first entry 
delivery mechanism 14 at a predetermined speed. The spinning device 1 
consists in the example represented of asymmetrical hyperboloid sieve 
rollers or drums, the gap between which is traversed by the core thread 3 
from the largest to the smallest end of the rollers or drums. Each of the 
hyperboloid rollers or drums is driven by a motor 4 of its own, the 
circumferential velocity of the two air permeable rollers being equal. The 
core mantle thread is drawn off by the delivery mechanism 16, is moved 
back and forth by traverse mechanism 18 and is wound on a cross-bobbin 17. 
The fibers for the mantle about the core thread are conducted as fiber 
cable 8 through the entry mechanism 11 and resolving roller 12 and then 
through fiber channel 13 into the narrow gap formed between the hyperbolic 
sieve drums or rollers. Air suction devices 7, the air entry orifices of 
which lie in the interior of each sieve drum, define the yarn formation 
line and zone. 
A special feature in FIG. 10 is the finishing roller 38 positioned between 
the first delivery mechanism 14 and the spinning device 1. The finishing 
roller 38 is driven in rotation and dips partially into the finish 
container 39 where it is moistened continuously over its circumference 
with a suitable fluid. The turning rate of the finish roller can be 
attuned via the gear 19 with the speed of the first delivery mechanism 14 
in such a way that a certain amount of fluid is constantly applied to the 
thread. It is worthwhile to apply only a small amount of fluid, in order 
to avoid any dirtying of the subsequent parts of the machine. In 
particular, use of colloidal silicic acid as application agent improves 
the properties of the core/mantle yarns and in particular, the push-on 
tendencies of the yarns are substantially improved, especially if amounts 
of less than 0.3% of the thread weight, calculated as dry colloidal 
silicic acid, is applied. 
In the application of colloidal silicic acid to the core thread immediately 
before the spinning it becomes possible to produce a core/mantle yarn 
having no push-on tendency at all and in which the mantle fibers have, 
under normal load conditions, an insoluble bond with the core thread. In 
like manner numerous other finish agents that are usual in the textile 
industry were investigated. In no case was it possible to achieve any 
substantial improvedment of the push-on tendency. Even the addition of 
collodial silicic acid to other usual finish agents failed to bring the 
desired success. Rather, a worsening the push-on tendency was the result 
so that it is to be assumed that the colloidal silicic acid has a 
determinative significance for the production of qualitatively high-value 
core/mantle yarns. The reason(s) for this surprising property of colloidal 
silicic acid has not yet been found. Possibly a role is played by an 
increase of the thread, thread friction between core thread and mantle 
fibers and/or a crystallization of the silicic acid.