A METHOD OF DYEING A WEB OF FABRIC ON A JIGGER AND A JIGGER TO CARRY OUT THE METHOD

Abstract: Optimum evenness of coloration is obtained on a jigger which operates with increasing speed of the web of fabric during a passage by carrying out a suction out of liquid from the web of fabric at a point between the winding off roll of fabric and the liquid bath so that every part of the web of fabric enters the liquid bath with substantially the same liquid content.

Description: Title: A method of dyeing a web of fabric on a ijgger and a jigger to carry out the method. Technical Field The present invention relates to a method of dyeing a web of fabric on a jigger where the web of fabric is al¬ ternately wound on and unwound from the two rolls of the jigger and during the passage between the rolls passes through a.dye bath and where the speed of the web of fabric increases during a passage. The invention also relates to a jigger to carry out the method. Background Art A jigger is a machine for liquid treatment of a web of fabric in which the web of fabric is alternately wound on and unwound from the two rolls of the j igger and during the passage between the rolls passes through a liquid bath. The liquid bath may possibly be replaced by other systems for replacement of the liquid, e.g. spraying of the liquid. The function of the jigger is of particularly critical importance for dyeing a web of fabric because the object here is to obtain a uniform colour of the entire web of fabric. The first known mechanized jiggers were equipped with a simple driving mechanism which drove the wind-up roll at a constant speed of rotation, so that both the speed of the web of fabric and the centrifugal force on the outer¬ most layers of the rolls of fabric increase proportional to the diameter of the roll of f bric. Later on jiggers were developed, the two rolls of which were driven through a common differential so that the sum of the speeds of rotation of the rolls remained constant whereby the course of the speed in a passage of fabric describes a symmetrical curve having its maximum in the middle of the passage where the speed of the web of fabric is about 50% higher than at the two ends. The jiggers which today practically control the market in the Western world are driven in such a way that the speed of the web of fabric remains constant or as constant as possible, e.g. with a driving mechanism as decribed in Danish patent No. 81,440 and the numerous variations of this principle, described e.g. in Danish Patents Nos . 98,233; 98,422 and 140,765. Most recently it has been realized that the principle of the constant speed of the web of fabric is wrong and in disagreement with the theory about how a web of fabric takes up dyestuff from a dye bath. It is not the brief stay of the web of fabric in the bath which is important to the picking up of dyestuff, and the speed of the web of fabric through the bath, therefore, need not be con¬ stant, but on the contrary can be increased during a passage like in the first known mechanical jiggers and thereby be utilized to obtain optimum dyeing rate and evenness. Thus, according to French published application No. 2,615,213 the speed of the web of fabric is increased by driving the jigger in such a manner that the centrifugal force on the outermost layers of the winding up roll of fabric is kept constant. Thereby is obtained a reduction of the time of treatment seeing that it is possible to operate with a higher average speed of the web of fabric than when the speed is kept constant or when it varies symmetrically like in the jiggers which are driven through a differential. The theory behind the use of a constantly increasing speed of fabric during a passage is as follows. The very passage of the bath takes only a few seconds, whereas the web of fabric is for many minutes on a rotating rool, and the proper dyeing process takes place in the fabric roll. During its passage through the bath the textile materiale receives a certain amount of fresh dye liquid, and dyestuff therein then migrates into the sur¬ rounding fibres . The rate of migration varies for a given textile material from one dyestuff to another, and the process can last from some seconds to a few minutes. When equilibrium has been established essentially nothing takes place until the next passage of the bath. Only at the ends of the web of fabric can the time difference between two passages of the bath be so short that not all the dyestuff has time to migrate into the fabric which may result in a more light colouration. However, what is of primary importance is the amount of liquid which the web of fabric takes up during the passage of the bath, and the centrifugal force plays an essential role for this. A liquid layer at the outer side of the roll is under the influence of two forces: the gravity which in the top of the roll acts on the liquid in the direction of the centre and which in the bottom of the roll acts on the liquid in the direction away from the centre so that as a consequence of the constant rotation of the roll the force of gravity will be neutral as far as the distribution of liquid is concerned, and the cen¬ trifugal force which everywhere acts on the liquid in the direction away from the centre and which .may become several times greater than the force of gravity and may have the effect that liquid is hurled away from the surface of the roll. If such uncontrolled hurling away of liquid from the outermost layers of fabric happens the supply of dyestuff is of course no longer constant during a passage, and the dyeing can become uneven. But provided there is no hurling away of liquid the cen¬ trifugal -force has the effect that there is a constant transport of liquid from the innermost layers of the roll outward. The transport depends on the size of the cen¬ trifugal force and the nature of the fabric but will normally result in only insignificant changes in the outermost layers of fabric within the necessary migration times for dyestuffs. During the operation there will be a change in moisture content from the innermost to the outermost layers of fabric both in the winding up and the winding off roll, and this may be of importance to the picking up of fresh dye liquid during the passage of the bath. Normally, the exchange of dye liquid during the passage of the bath takes place in the way that a certain per¬ centage of the free liquid content of the textile material is exchanged with fresh liquid. If the textile material has lost liquid on account of the liquid transport there will be not only an exchange during the passage of the bath but also a supplementation with fresh dye liquid so that the liquid content is again brought to the original level. Thus, hereby the textile material gets an increased dyestuff supply compared to a material which has not lost liquid due to the centrifugal force, and this gives rise to an uneven colouration. Therefore, even though advantages can be obtained by operating with increasing speed of the web of fabric on a jigger, this method can also result in uneven colouration. DK patent application No. 6212/68 and the French Patents Nos. 1,118,921 and 1,403,791 describe jiggers which in the bath have suction means with the object of obtaining the highest possible exchange of the liquid in the web of fabric while it passes the bath. With suction means si¬ tuated in this place only a certain percentage is always exchanged and the system therefore cannot equalize dif¬ ferences caused by varying moisture content at the time of immersion. From German patent No. 3,239,450 is known a igger which has one suction means situated between the bath and the winding up roll with the object of reducing the water content of the web of fabric before drying after the last passage. Disclosure of Invention The drawbacks of the known jiggers are obviated according to the present invention by carrying out a suction out of liquid from the web of fabric at a point between the winding off roll of fabric and the liquid bath so that every part of the web of fabric enters the liquid bath with substantially the same liquid content. Brief Description of the Drawings The invention is further illustrated in the drawing, in which Fig. 1 is a sketch of the principle of the jigger, Figs. 2-5 are graphs of the speed and acceleration of the fabric when dyeing a web of fabric by various known meth¬ ods . Best Mode for Carrying out the Invention In Fig. 1 1 is the winding up roll in the situation under consideration, and 2 is the winding off roll. The web of fabric 3 travels through a dye bath 4 during the passage between the rolls, and the liquid in the rolls of fabric on the two rolls is exposed to the centrifugal force as indicated by the arrows. To equalize the difference in liquid content which the web of fabric can obtain as a result of the centrifugal force the invention provides for a suction out of liquid from the web of fabric at a point between the winding off fabric roll and the liquid bath, two suction means 5 which extend over the entire width of the web of fabric being situated between the rolls 1 and 2 and the liquid bath 4, and of these only the right hand suction means is active in the situation under consideration. Fig. 2 is a graph of the speed and acceleration of the web of fabric on the winding up roll as a function of the percentage amount of wound up (or wound off) fabric when dyeing on a directly driven jigger. The ordinate indicates both the speed and the acceleration when they are expressed V 2 - Λ as respectively V-100 m/min and r . 10" J m/miii', where r is the radius of the roll of fabric. Fig. 3 is a similar graph of the speed and acceleration of the web of fabric on the winding up roll when dyeing on a jigger with a differential drive. Here the ordinate also indicates the percentage variation of the speed. Fig. 4 is a similar graph of the speed and acceleration of the web of fabric on the winding up roll when dyeing with constant speed of the web of fabric. Here the speed curve is a straight line coinciding with the abscissa axis. Fig. 5 is a similar graph of the speed and acceleration of the web of fabric on the winding up roll when dyeing with constant acceleration. The invention relates to a method in which the speed of the web of fabric increases during a passage, e.g. as illustrated in Figs. 2 and 5, i.e. has a higher value at the end of a passage than at the beginning of the passage, but does not necessarily increase continuously as shown in Figs. 2 and 5. The suction out of liquid from the web of fabric to adjust the amount of liquid in the web of fabric can also in an embodiment according to the invention be supplemented with the measure of periodically reducing the speed of the web of fabric or keeping it constant. Moreover, the suction out of liquid from the winding off roll of fabric can be increased or reduced during the passage and thereby have an equalizing effect on light ends which can arise on account of a rapidly following second passage of the bath. The invention also relates to a jigger for carrying out the described method which jigger is of the kind which has such driving means that the speed of the web of fabric increases during a passage and which has a suction means between a roll and the dye bath, and the igger is cha¬ racterized in that it has suction means between both the rolls and the dye bath which extend over the entire width of the web of fabric.

Claims: Claims : 1. A method of dyeing a web of fabric on a jigger where the web of fabric is alternately wound on and unwound from the two rolls of the jigger and during the passage between the rolls passes through a dye bath, and where the speed of the web of fabric increases during a passage, c h a r a c t e r i s e d in that a suction out of liquid from the web of fabric is carried out at a point between the winding off roll of fabric so that every part of the web of fabric enters the liquid bath with substantially the same liquid content. 2. A method as claimed in claim 1, c h a r a c - t e r i s e d in that the speed of the web of fabric is periodically reduced or kept constant. 3. A method as claimed in claims 1 and 2, c h a r a c¬ t e r i s e d in that the suction out of liquid from the web of fabric is increased or reduced in the course of the passage. 4. A jigger for carrying out the method as claimed in claim 1 having such driving means that the speed of the web of fabric increases during a passage and having a suction means between a roll and the dye bath, c h a r- a r a c t e r i s e d in that it has suction means between both the rolls and the dye bath which extend over the entire width of the web of fabric.

Inventors: HENNINGSEN ERIK, HENNINGSEN, ERIK
Applicants: HENRIKSEN VALD AS, VALD. HENRIKSEN A/S
Application year: 1990
Main classification: D06B3
IPC codes: D06B3