Process for simultaneous dyeing and bonding of sewing silks made from polyester filaments

By the use of acrylic resins capable of being cross-linked under the effect of heat, and of disperse dyestuffs in the same padding bath, subsequent drying and thermosol treatment of the padded threads (twist) with subsequent reductive purification and application of a fiber preparation, bonding and simultaneous fast dyeing of sewing silks consisting of polyester multifilaments is achieved, which meets the requirements of the practice with respect to this article. The process is carried out continuously during rewinding.

The present invention relates to a process for simultaneous dyeing and 
bonding of sewing silk consisting of filaments of linear polyesters. 
Twisted endless filaments (multifilaments) are generally used as sewing 
silks. The silk processing industry requires for this article, among other 
things, good running i.e. sliding properties at high sewing speed. 
However, at the usually high sewing speed which cannot be compared with 
those of household sewing machines, high mechanical stress by friction and 
heating occurs at the places of thread guidance, especially at the eye of 
the needle. Therefore, attention must be paid that the sewing silk is not 
damaged on sewing, i.e. that the twisted thread is not split into 
individual filaments. 
For this reason, as protection against such harmful influences, sewing 
silks consisting of polyamide material, for example, have been bonded 
(sheathed) with a plastic film and simultaneously dyed and acid dyestuffs 
according to the acid shock method. Sewing silks of polyamide filaments, 
however, have the disadvantage of softening at a relatively low 
temperature and subsequently stretching or even melting, which leads to 
breaking of the thread. From this point of view, sewing silks consisting 
of polyester filaments are in a very high demand because of their 
excellent technological properties. Their special advantage, compared with 
silks of polyamide filaments, is the higher softening or melting point of 
the polyester material and the lower elongation when sewing on machines. 
Thus, both factors allow higher sewing speeds. 
Up to now, no process has been known for simultaneously bonding and dyeing 
such polyester filaments for sewing silks. The bonding products and 
dyestuffs used for this purpose on polyamide material are unfit for 
polyester material. 
From German Offenlegungsschrift No. 2,638,237, however, a process is known, 
according to which filament bundles, which are intended for the 
manufacture of technical ribbons or safety belts and which consist of 
polyester monofilament, are dyed with disperse dyestuffs according to a 
thermosol process, with the assistance of the effect of an accompanying 
synthetic resin. The auxiliary cover of the synthetic resin, in this case, 
has mainly the objective of protecting the disperse dyestuff which is not 
yet fixed, but already applied to the filaments, especially against 
abrasion during the weaving of the ribbons. Real fixation of the textiles, 
together with the dyestuffs applied, is only performed by the thermosol 
operation after weaving. 
In contrast thereto, when bonding sewing silk made from multifilaments, 
other circumstances, however, must be taken into consideration, which 
simultaneously outline the objects of the present invention. 
The following requirements have to be met: 
(a) Sewing silk (of polyester filament) is to be fast-dyed. In the case of 
polyester material this can only be achieved by disperse dyestuffs. 
Moreover, the dyeing must be repurified by reduction, in order to remove 
dyestuff which has been superficially deposited on filaments. 
(b) The individual filaments of the sewing silk must have corresponding 
technological properties, that means, they must have a predetermined 
shrinkage and elongation behavior. These qualifications can only be 
provided by a thermofixation process. 
(c) The sewing silk must stand the high mechanical stress of sewing and for 
this end it must have certain characteristics. Above all, splitting of the 
twisted sewing silk into individual filaments, for example, on tearing of 
one individual filament in the multifilament, must be prevented. Moreover, 
the so-called snarling, i.e. the formation of little loops when entagling 
the threads in the seams, is to be avoided. Electrostatic charge of the 
filaments is not desirable, either, abrasion is to be reduced and the 
strength of the thread is not to be diminished. Bonding gives the sewing 
silk these intended properties. 
Thus, it was object of the present invention to dye and simultaneously to 
bond polyester filaments for use in sewing silks, and to ensure at the 
same time that the bonding does not adversely affect the properties of the 
dyeing and, on the other hand, that the requirements for the dyeing do not 
impair the bonding, either. 
This object is achieved in accordance with the invention by continuously 
padding the twisted multifilament, during the rewinding operation, with an 
aqueous dispersion containing one or more disperse dyestuffs, a binder 
system of one or more polymerizable acrylic compounds capable of being 
thermally cross-linked and a catalyst which promotes cross-linking, at a 
liquor pick-up of 15 to 25% (of the weight of the dry filament material), 
subsequently drying the padded threads, subjecting them for 15 to 60 
seconds to a heat treatment with hot air of 190.degree.-225.degree. C., 
repurifying by reduction of the sewing silk so treated before winding it 
up again and finally applying on to it a usual fiber preparation. 
In the practice, the process as claimed is advantageously carried out as 
follows: 
During the rewinding, the sewing silk of polyester filaments is 
continuously forwarded from a beaming creel or warp beam support over a 
foulard, in which the padding liquor is applied with, for example, a 
liquor pick-up of about 20% (of the weight of the dry filament material), 
to the dryer, preferably a cylinder dryer. From there the threads which 
were dried at at least 110.degree. C. are passed through the hot air zone, 
where simultaneously the polyester filament material is fixed and 
stabilized, the dyeing is fixed and the acrylic resin is set. Via cooling 
rolls, which are also intended to serve as tension compensators, the 
sewing silk which now is dyed and bonded is passed to the aftertreatment. 
The washing machine should have 4 baths, one for the reductive, alkaline 
aftertreatment, one for rinsing, one for the neutralization and one for 
the preparation. Next, the substrate is dried again (cylinder drier or hot 
air zone) and then the dyed and bonded sewing silk is wound up. 
In the new process, the amount and composition of the dispersion of the 
polymerizable acrylic compounds capable of being crosslinked are of 
special importance. In general, 200-400 g/l of these resin-forming 
substances are used, preferably a copolymer of ethyl acrylate, 
N-methylol-acryl-amide and acrylonitrile. 
As catalyst which promotes cross-linking and has acidic action only under 
heat, substances of the type of alkylolamine hydrochlorides, especially 
aminopropanol hydrochloride, are used in accordance with the invention. 
In view of the large amount of cross-linkable acrylic compounds used, it 
was surprising that the hardening expected as a consequence of the resin 
formation has not impaired the suppleness of the silk, but has caused the 
desired bonding effect, that means the bonding of the individual 
filaments, without reducing the flexibility of the fiber. Moreover, it was 
not to be expected that this bonding itself is not impaired by the 
subsequent reductive aftertreatment of the dyed product in intensively 
alkaline medium at an elevated temperature, which is absolutely necessary 
for the fastness of the dyeing, and that the desired smoothing and glueing 
of the individual filaments is maintained. 
The technological properties of the finished sewing silk depend 
substantially on the precise supervision of the drying and fixation 
conditions. Depending on the titer of the individual filaments and on 
their number in the silk, the length of time for passing through the 
heating zone must be adapted to be between 15 to 60 seconds. 
Moreover, selection of a suitable fiber preparation is also decisive for 
achieving good running properties of the silk on sewing. In this respect, 
plasticizers on the basis of oleylsarcoside, paraffin oil emulsions and 
products on the basis of silicone oil or mixtures of these products have 
prooved to be suitable.

The following examples illustrate the invention. 
EXAMPLE 1 
150 kg of twisted multifilament of dtex 226 f 64.times.3 of linear 
polyesters (sewing silk) on bobbins of 2.5 kg each, are creeled on a 
beaming creel, warped while being unwound and padded on a foulard at room 
temperature and with 20% liquor pick-up (of the weight of the material) 
with an aqueous liquor of the following composition: 
600 g/l of an aqueous, 40% dispersion of a copolymer of 
84% of ethyl acrylate, 
11% of N-methylol acrylamide and 
5% of acrylonitrile (percentages are given by weight) 
30 g/l of aminopropanol hydrochloride (catalyst), 
9.7 g/l of the disperse dyestuff 
2,6-dicyano-4-nitro-2'-acetylamino-4'-diethylamino-azobenzene, 
4.14 g/l of the disperse dyestuff of the formula 
##STR1## 
and 10.68 g/l of the disperse dyestuff of the formula 
##STR2## 
After padding the wet filament material is dried on drying cylinders at 
about 110.degree. C. and then subjected to hot air treatment at 
210.degree. C. for 25 seconds. After cooling, the dyeing thus obtained is 
continuously repurified on cooling rolls. The temperature of the reductive 
repurification bath is 85.degree. C.; per 1 kg of polyester filament in 1 
liter of water there have to be employed: 
24 cm.sup.3 of sodium hydroxide solution (32.5%) 
24 g of sodium dithionite and 
6 g of a detergent on the basis of a nonylphenol oxyethylated with 20 mols 
of ethylene oxide per mol. 
Subsequently, the dyeing is rinsed with hot water at 70.degree. C., 
neutralized with acetic acid and furnished with a preparation in the last 
bath. The preparation bath contains in 1 liter of water: 
6 g/l of oleylsarcoside and 
2 g/l of an emulsifiable mineral oil paraffin preparation. 
The coat of this preparation is 20% of the weight of the material. 
Subsequently, the dyed and bonded polyester filaments are dried and wound 
up. 
A sewing silk dyed black with good running properties on sewing, good 
strength and sufficient elongation is obtained. 
EXAMPLE 2 
When using instead of the dyestuffs on Example 1 the following dyestuff 
combination 
4.85 g/l of the disperse dyestuff 
2,6-dicyano-4-nitro-2'-acetylamino-4'-diethylaminoazobenzene 
2.07 g/l of the disperse dyestuff of the formula 
##STR3## 
5.34 g/l of the disperse dyestuff of the formula 
##STR4## 
6.75 g/l of the disperse dyestuff of the formula 
##STR5## 
and for the rest carrying out the process as described in Example 1, a 
dark blue sewing silk with good wear characteristics is obtained. 
EXAMPLE 3 
The process is carried out exactly as in Example 1, but instead of the 
dyestuff combination mentioned in Example 1, the following dyestuffs are 
used: 
1 g/l of the dyestuff Disperse Blue 56 C.I. No. 63 285 
4 g/l of the disperse dyestuff of the formula 
##STR6## 
6 g/l of the disperse dyestuff of the formula 
##STR7## 
After dyeing, bonding and aftertreatment, a brown sewing silk with the 
required behavior on sewing is obtained. 
The same result as in the Examples 1 to 3 is obtained when using instead of 
polyester multifilament of dtex 226 f 64, three times twisted, a polyester 
multifilament of the same titer and the same number of filaments, which, 
however, is twisted twice. 
Corresponding results can also be obtained when using sewing silk of 
multifilament of dtex 74 f 16 or f 24, twisted two or three times, or of 
dtex 455 f 96, twisted two or three times, and when subjecting the sewing 
silk for fixation to a hot air treatment for 15 or 60 seconds.