GB1596740A

GB1596740A - Continuous dyeing of textile materials

Info

Publication number: GB1596740A
Application number: GB51363/76A
Authority: GB
Original assignee: Mather and Platt Ltd
Current assignee: Mather and Platt Ltd
Priority date: 1976-12-09
Filing date: 1976-12-09
Publication date: 1981-08-26
Also published as: CH621032GA3; DE2755579A1; CH621032B

Abstract

In a process for pad-dyeing textile material in sheet form on a pad-mangle having a short-liquor trough using aqueous padding liquors which in addition to dyeing assistants contain dyes which develop an affinity for the fibre only on heating of the padding liquor to temperatures above 60 DEG C, the cold padding liquor is passed on the way to the pad-mangle trough through a continuous heater, raising it to the treatment temperature which is above 60 DEG C. A short-liquor (economy) pad-mangle usable for this purpose has a continuous heater situated in the liquor feed line between the reservoir tank and the short-liquor trough and is provided with a means for setting the temperature of the padding liquor flowing out of the continuous heater into the short-liquor trough. The process is of special relevance for the continuous pad-dyeing of cotton textiles, since it makes it possible, despite the single-stage method of operation, to achieve the same success as requires a multi-stage treatment in the case of conventional pigment padding processes.

Description

(54) IMPROVEMENTS RELATING TO THE CONTINUOUS DYEING OF TEXTILE MATERIALS (71) We, MATHER & PLATT LIMITED, a British Company of Park Works, Manchester, M10 6BA, do hereby declare the invention, for which we praythat a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to the dyeing of, for example, fabric, film, felt, paper or yarn, hereinafter and in the claims referred to as textile material, in which the textile material is saturated by a heated dye liquor, the textile material being treated continuously by passage through the dye liquor.

The term textile material is intended to include cellulose, whether natural or regenerated, alone or in admixture with other fibres and the term is not intended to restrict the textile material to woven material.

This invention relates especially to the continuous dyeing of cotton textile material by the so-called vat type of dyestuff without being restricted to this type of textile material or to this type of dyestuff.

An object of the present invention is to improve the quality and the uniformity of dyeing of textile materials. A further object is to improve the economics of the dyeing process by reducing the amount of equipment required to carry out continuous dyeing and reducing the comsumption of energy, materials and labour per unit of textile material processed. An especially valuable feature of the present invention is the versatility of the process and apparatus which not only permits dyestuffs of widely varying affinities within the vat dyestuff group to be applied simultaneously in a uniform manner, but which in addition permits dyestuffs of quite different groups and with different chemical reactions to be applied on the same apparatus.

For example, whereas the present invention is especially directed to the application of vat dyestuffs to cotton textile material it has been found that dyestuffs of other groups may be uniformly applied to cellulose textile materials, such as, for example, dyestuffs of the following groups: Solubilised vat dyestuffs, Sulphur dyestuffs, Reactive dyestuffs.

It is known to dye a textile material continuously in a wide variety of ways but in order to achieve uniformity of dyeing it has long been a common feature of such methods to apply the dyestuff by saturating the textile material in a dye bath in which the dyestuff has, by intent, little or no affinity for the textile material during the period of saturation.

After saturation of the textile material by an aqueous solution or dispersion of the dyestuff in such a condition, affinity is then conferred upon the dyestuff within the textile material by subsequent chemical means usually accompanied by heat and/or moisture whereby the dyestuff then dyes the textile fibres and subsequently becomes fixed therein.

Such a method is that employed in the well known "pad-steam" process, and in the case of vat dyestuffs on cotton a common sequence of process and apparatus is as follows: 1. The cotton textile material is impregnated with a suspension of the pigment form of the dyestuff in water by passage through a suitable dye bath followed by squeezing off excess dye liquor by means of a padding mangle.

2. The impregnated material is partially dried by passage through an infra-red heating device.

3. The impregnated partially dried material is dried by passage through an air dryer, usually of the so-called hot-flue type, whereby the moisture content is reduced to approximately regain moisture level.

4. The dried material is then impregnated by a solution of a strong alkali and a reducing agent and excess liquor squeezed from the textile material by a padding mangle.

5. The material from stage 4 is then passed continuously through a steaming chamber filled with dry saturated steam at atmospheric pressure at 1000C.

The time of passage of material through the steamer is usually within the range 2W60 seconds.

It is during stage 5 that the chemical reactions occur which promote the dyeing of the cotton fibre by the vat dyestuff.

Subsequent to this stage the dyed material is treated in sequence to a known series of operations which include rinsing, oxidising, soaping and washing.

It is a characteristic of this present invention, and with special reference to the application of vat dyestuffs to cotton textile material that saturation of the textile material with the dye liquor takes place almost simultaneously with dyeing of the textile material, by reason of the dyestuffs being present in the dye bath in aqueous solution at an elevated temperature, and in which the dyestuff possesses optimum affinity for the textile material.

In consequence of this present invention and by comparison with the example of a "pad-steam" sequence in common use, the 5 stages referred to for typical "pad-steam" working are reduced to a single stage in which saturation and dyeing take place together, being then usually followed by the known methods of rinsing, oxidising, soaping and washing as earlier described.

It is known that different classes or groups of dyestuffs require the additions of differing chemical substances, generally known as dyeing assistants or dyeing auxiliaries in order that the dyestuff may be made fully soluble and/or rendered of optimum affinity for the textile material. It is equally known that the rate of dyeing usually increases with increase in temperature of the dyeing reaction.

Reference has been made to dyestuffs being present in a dyebath in a state of optimum affinity for the textile material, and in the case of vat dyestuffs, and most sulphur dyestuffs, the dyestuffs as purchased and stocked prior to use are insoluble in water and possess no affinity for cotton textile material. Both groups of dyestuffs are rendered soluble in water by the addition of a strong alkali and a chemical reducing agent. Along with the combined influence of time and temperature the insoluble dyestuff is not only converted to the so-called "soluble reduced" or "leuco" state but also then possess a strong affinity for a cellulosic textile material.

Of the two groups of dyestuffs, vat and sulphur, the vat group is the more important, but also the soluble vat "leuco" product is the more unstable.

They become progressively more unstable with increase in temperature and the leuco product may be easily over reduced, hydrolised or molecularly re-arranged or may crystallise, and in addition the leuco vat solutions are frequently sensitive to strong light.

It has thus been the custom to apply the leuco vat dyestuffs to cellulosic textile material by a batch technique, in which bath temperatures are kept below 50"C, thus permitting dyeing to take place for the necessary time without the dyebath becoming too unstable. Such batch process times vary from 30 to 60 minutes.

Continuous dyeing from a leuco dyebath implies dyeing times of generally less than 1 minute with the consequent necessity to increase the rate of dyeing by increasing the dyebath temperature to over 500 C; and the technical literature gives many examples of failures to achieve satisfactory working by continuous leuco techniques.

Unsatisfactory because resultant dyeings are invariably lacking in uniformity of shade over the dyed length, the dye yield is poor and the resultant fastness properties of the dyed material fall far short of those to be expected from vat dyestuffs.

All these handicaps of a continuous leuco process which arise by virtue of the difficulty of balancing a rapid rate of dyeing against dyebath stability were overcome by the pad steam process referred to in which the problem of dyetlth stability was avoided by applying the insoluble dyestuff to the fabric and subsequently converting to the leuco state in situ.

We have now discovered that a cellulosic textile material may be dyed with vat dyestuffs to the highest standards of quality by immersion in a dyebath containing the leuco dyestuff at a temperature exceeding 60"C, but generally between 800C and 950C for a period not exceeding 5 seconds, but generally less than 2 seconds. Under such conditions, saturation of the textile material by the leuco dye liquor takes place almost simultaneously with dyeing or fixation due to the extremely rapid rate of dyeing which is achievable at such temperatures.

It is a preferred characteristic of this invention that the dyebath liquor contents be continuously fed to the dyebath in the completely soluble state, (which means that the original insoluble pigment dyestuff has been converted to the fully reduced or soluble leuco state) at the selected working temperature above 60"C, such a feed liquor having been stored in bulk at room temperature, at which temperature it is stable, being heated and mixed to the working temperature by passage through a mixer/heat exchanger situated adjacent to the dyebath, and by passage through the said mixer/heat exchanger the dye feed liquor is converted to the fully reduced leuco state.It should be noted that whereas this invention is especially applicable to those groups of dyestuff which are made soluble by virtue of chemical reduction, there are groups of dyestuffs which are normally soluble in water but which do not initially posses affinity for the textile material, and affinity is conferred by some chemical means other than by reduction.

Such would include the solubilised vat dyes and the reactive dyes and the principles of this invention may be used to apply these groups of dyestuffs to textile materials.

The manner in which the objects of this present invention are to be achieved is now set forth.

In accordance with the present invention we provide a process of continuous dyeing of a textile material by passing it through a small volume dye bath so that it is saturated with an aqueous liquor containing dyestuff and chemical assistant medium in complete solution and at an optimum temperature such as to render the dyestuff of optimum affinity for the textile material following which saturation the textile material is withdrawn from the dye bath and excess liquor immediately removed from it, the process being characterised by feeding the dye liquor which is stored under conditions of minimum affinity for the textile material through a mixer/heat exchanger before delivery of said dye liquor to the dye bath, and from which mixer/heat exchanger the liquor emerges as a homogeneous solution at a higher temperature than its inlet temperature, the residence time for the liquor in the mixer/heat exchanger being between 2 and 60 seconds.

Preferably the dye bath is of a very small volume, so that the contents would be rapidly consumed by the passage of textile material through it, whereas in fact the volume is kept substantially constant by feeding dye liquor to the dye bath at the rate at which it is being consumed.

It is an essential step in the working of this invention that the dye bath feed liquor passes through a mixer/heat exchanger in which thorough mixing and heating takes place, the dwell time of any particle of liquor passing through the mixer/heat exchanger, irrespective of rate of flow being sufficient to ensure mixing, heating and solubilisation without being so long as to disturb the stability of the dye solution and its affinity for the textile material.

It is convenient to combine the functions of mixing and heating within one unit of auxiliary equipment, but it is to be understood that the mixing and the heating may take place in two separate stages, provided the liquor dwell time is not thereby excessive.

In the application of vat dyes to cotton textile materials according to this invention, it has been found that saturation and actual dyeing are substantially completed between the textile material entering the dye bath and leaving the point at which excess liquor is removed from the textile material, and it has been found that the time between the two such points need not exceed 5 seconds and in some cases is as little as 1 second.

After the removal of excess liquor from the textile material there is normally little advantage in prolonging the reaction outside the dye bath, and the usual course is then to rinse and treat in a known sequence of rinsing and oxidising, soaping and washing steps.

Oxidation may be assisted by an air passage of textile material outside a treatment step.

In certain cases however, it may be beneficial to extend the reaction time after the removal of excess dye liquor by steaming the textile material prior to aeration and prior to the first washing step.

For vat dyes steaming would be in the absence of air, and may be saturated steam at atmospheric pressure, or saturated steam at pressures above atmospheric pressure, the purpose being to assist any dye particles on the surface of heavy or dense textile material to diffuse inwards.

The length of dwell time in such cases is not likely to exceed 15 seconds at atmospheric pressure, or 5 seconds at 2 atmospheres gauge pressure.

In the case of dyestuffs other than vat dyestuffs the steaming period may be beneficially extended. For example, in the application of reactive dyestuffs the steaming step is primarily a dye fixation stage rather than a dye diffusion process, and as such dyestuffs are not applied in a state of chemical reduction there is no danger of loss of stability by prolonged steaming nor is the presence of air a handicap, so that steaming may in fact be beneficially performed by superheated steam over 100"C but at atmospheric pressure.

However, it should again be understood that the process and apparatus of this invention are directed primarily to satisfying the more critical conditions of vat dyeing.

We have discovered for the working of this invention that the dwell time for dye liquors passing from entry to exit point of the mixer/heat exchanger lies between 2 seconds and 60 seconds, depending on the dye constitution and its ease of reduction to the soluble form, its subsequent stability, and the depth of shade which is required.

The depth of shade to be produced is almost solely dependent on the concentration of dyestuff in the dye liquor, provided the chemical and physical conditions selected and provided render the dyestuff completely and uniformly reduced to the soluble form, and the concentration at any one time must be uniform throughout the dye bath.

The precise quantity of dye liquor left within the textile material after removing the excess, must vary with a given textile material, density and structure, and the means selected to remove the excess. The greater the excess removed the more economical the process, but the greater the risk with vat dyes of premature oxidation of the reduced dyestuff.Thus we provide a process of continuous dyeing of a textile material by passing it through a dyebath for an immersion period not exceeding 5 seconds, so that it is saturated with an aqueous dye liquor containing dyestuff(s) and chemical assistants in complete solution and maintained at an temperature above 60"C, such as to render the dyestuff(s) of optimum affinity for the textile material, following which saturation the textile material is withdrawn from the dyebath and excess liquor removed from it, the process being characterised by passing the dye liquor which is stored in bulk supply under conditions of minimum affinity for the textile material through a mixer/heat exchanger before delivery for said liquor to the dye bath, and from which mixer/heat exchanger the liquor or liquors fed to it emerge as a homogeneous solution at a temperature between 600C and the boiling point of the solution and with a dwell time for any particle of liquor within the mixer/heat exchanger between 2 seconds and 60 seconds.

Optionally, the textile material may be steamed immediately after removal of excess liquor by passage through a steaming chamber in the absence of air within the chamber, but in the presence of saturated steam at atmospheric pressure or saturated steam at excess atmospheric pressure, or in selected cases with superheated steam at atmospheric pressure. Thereafter the textile material may be treated by a suitable combination af known srinsing, oxidising soaping snd washing processes.

Also in accordance withthis invention we Olid6 apparatus for se in continuous i:ingzfa1-tileinaftrii with heated aqueous dye liquor, comprising at least one tank for storing cold dye liquor, a smallvolume dye bath, means for delivering the cold dye liquor to the dye bath via a mixer/heat exchanger having a flow path therein which constrains the dye liquor to a residence time within the mixer/heat exchanger of between 2 and 60 seconds, means for immediately removing excess liquor from the textile material as it egresses from the dye bath, means for controlling the level of dye liquor in the dye bath, and means for controlling the temperature of the dye liquor delivered from the mixer/heat exchanger to the dye bath.

Means is preferably provided to maintain the concentration of dyestuffs within the dye bath uniform by suitable mechanical agitation and/or circulation.

Optionally, a steaming chamber is provided through which the textile material may pass immediately after removal of excess dye liquor and in which the textile material is subjected to heat and moisture with or without the presence of air and at atmospheric pressure or at excess atmospheric pressure.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing of apparatus suitable for carrying out the dyeing process according to the present invention.

The apparatus comprises a pair (although there may be more than two) of bulk cold dye liquor storage tanks 5, the outlet/inlet of each of which is valve-controlled as indicated at 6. The tanks 5 can be replenished via a valve-controlled supply pipe 7.

The dye liquor bath is indicated at 8 and is of small volume It contains a displacement block 9 which is used, when desired, to further reduce the volume.

Dye liquor is fed to the bath 8 from tanks 5 by a pump 10 driven by a motor 11.

The dye liquor passes through a mixer/heat exchanger 12 prior to entering the dye liquor bath 8.

The rate of flow of dye liquor into the bath 8 is controlled by a level controller 13 which operates a dye liquor modulating valve 14 upstream of the mixer/heat exchanger 12 in the direction of dye liquor flow.

The temperature of dye liquor fed from the mixer/heat exchanger 12 to the bath 8 is controlled by a dye liquor thermostat 15 in the bath 8 and which controls a modulating valve 16, in turn, controlling steam supply into the mixer/heat exchanger 12.

The dye liquor level in bath 8 is indicated at 17.

The fabric being dyed is indicated at 18 and passes over a guide roller 19 into the dye liquor, around a guide roller 20 in the bottom of the bath 8 and then out of the latter and between a lower metal padding roller 21, which may be heated separately to bath temperature, and an upper rubbercovered squeezing roller 22.

A spare rubber-covered, turret-type squeezing roller is indicated at 23.

A doctor blade is indicated at 24 and this co-operates with padding roller 21 to guide dye liquor expressed at the nip back into the bath 8.

It will be manifest from earlier description of the way in which the abovedescribed apparatus is utilised in carrying out the dyeing process of the present invention.

When it is desired to change from one dye shade to a different shade, the following sequence takes place. The apparatus is stopped on completion of the first dye run, with a tape or wrapper through the dye liquor bath assemble ready to draw the next material forward. Pump 10 is stopped, and the dye liquor tank 8, mixer/heat exchanger 12 contents dropped to drain. Dye feed tanks 5 are shut off, the level controller 13 is neutralised and the contents of a cleaning solution tank 24A are now pumped via the mixer/heat exchanger 12 to dye liquor tank 8.

Since the level controller 13 is neutralised the cleaning solution overflows into an extension 25 of the tank 8 and there takes up level 26 and overflows back to tank 24.

Padding roller 21 is now dipping into the cleaning solution, which roller on rotation also cleans roller 22; (a clutch permits the padding roller 21 to rotate while the other apparatus components are stationary).

After two or three minutes circulation of cleaning solution through the system previously occupied by dye liquor, the cleaning solution is dropped to drain and the normal dye feed cycle begins with next and different dye liquor.

A specific apparatus constructed similar to the schematic arrangement illustrated comprised a pneumatically loaded padding mangle, with a lower heated metal roller and an upper rubber covered roller, operating at a 450 angle to the lower roller, a heated dye liquor tank was disposed adjacent to the metal roller with one edge acting as a doctor blade to guide liquor expressed from the squeezing nip back into the dye liquor tank. Textile material was continouosly treated by passing through dye liquor in the tank with excess liquor expressed at the nip returning to the dye tank; a variable speed allowed different immersion times and pre-heated dye liquor at a selected temperature and with the dye and chemical assistant in wholly soluble form was fed into the dye liquor tank (in the case of vat and sulphur dyes the dyes were in the completely reduced or leuco state).

Textile material emerging form the dye pad nip could then be rinsed, oxidised, soaped and washed in conventional apparatus.

Example 1 A bleached cotton repp furnishing fabric of weight 250 gms/sq metre was passed continuously through the apparatus at a speed to give a dwell time in the dye liquor of 1 second the dye liquor temperature was 95"C with the following composition.

7.5gms/litre Vat Dyestuff-Colour Index vat red 34 24.0gms/litre Caustic Soda 100" Thr.

30.0gms/litre Sodium Hydrosulphate.

1.0gms/litre Commercial wetting agent.

The load on the pad nip was such as to give a liquor expression of 90%.

Fabric emerging from the pad nip was immediately rinsed in cold water, and oxidised, soaped, washed and dried in a conventional manner.

The resultant deep rose shade fabric was then tested for fastness according to the standard methods for the Determination of Colour Fastness of Textiles. 3rd Editions published by The Society of Dyers, Colourists, Bradford.

a) Colour Fastness to washing (150.4) b) Colour Fastness to rubbing BS 2677 In both methods of test the fastness was equivalent to that obtained by dyeing vat red 34 by a conventional vat dyeing method.

Example 2 The procedure of Example 1. was repeated but using a bleached cotton corduroy fabric. Weight 260 gms/sq metre.

Dye liquor composition.

7.SgmsAitre Vat dyestuff Colour Index vat brown 1 30.0gms/litre Caustic Soda 100" Thr.

50.0gms/litre Sodium Hydrosulphite 1.0gms/litre Commercial wetting agent.

Immersion time 2 seconds.

Dye bath temperature 95"C.

Liquor Expression 105% The resultant dark fawn shade likewise possessed normal fastness properties.

Example 3 The procedure of Example 1 was repeated, but using a blend suiting fabric composed of 67% polyester fabric and 33% cotton. Weight 180gms/sq metre.

The polyester content had been commercially dyed to a purple shade using disperse dyestuff and leaving the cotton undyed. Dye liquor composition.

5.0gms/litre Vat Purple 4R 30.0gms/litre Caustic Soda 100" Thr.

50.0gms/litre Sodium Hydrosulphite.

1.0gms/litre Commercial Wetting Agent.

Immersion time 2 seconds.

Dye bath temperature 70"C.

Liquor Expression 65% The resultant fabric was "solid" shade of purple, free from any uneven appearance and meeting the commercial standards of factries expected.

WHAT WE CLAIM IS: 1. A process of continuous dyeing of a textile material by passage through a small volume dye bath so that it is saturated with an aqueous liquor containing dyestuff and chemical assistant medium in complete solution and at an optimum temperature such as to render the dyestuff of optimum affinity for the textile material, following which saturation the textile material is withdrawn from the dye bath and excess liquor immediately removed from it, the process being characterised by feeding the dye liquor which is stored under conditions of minimum affinity for the textile material through a mixer east exchanger before delivery of such liquor to the dye bath, and from which mixer/heat exchanger the liquor emerges as a homogeneous solution at a higher temperature than its inlet temperature, the residence time for the liquor in the mixer/heat exchanger being between 2 and 60 seconds.

2. A process as claimed in Claim 1, in which the aqueous liquor containing dyestuff and chemical assistant medium in complete solution is completely in the chemically reduced or leuco state.

3. A process as claimed in Claim 2, residence time of the liquor in the mixer/heat exchanger is reduced by the employment of a chemical reduction accelerator medium in the liquor.

4. A process as claimed in Claim 2, residence time of the liquor is extended by the use of chemical stabilising agent medium in the liquor.

5. A process according to any one of Claims 1 to 4, in which the mixer/heat exchanger function is carried out by two or more separate units, either two or more combined mixer/heat exchangers or separate mixers and separate heat exchangers, the separate liquor feeds thereto being metered so as to maintain the desired proportions delivered and used within the dye bath.

6. A process according to any of the preceding Claims, in which the residence time of textile material within the dye bath tank is 5 seconds or less.

7. A process according to Claim 6, in which the temperature of the liquor within the dye bath tank is in excess of 60"C.

8. A process according to Claim 7, in which the temperature is between 80"C and 95"C.

9. A process according to any of the preceding Claims, in which an extended dyeing time, or extending diffusion time, or extended fixation time, is provided immediately after removal of excess dye bath liquor from the saturated textile material by treating the textile material with steam at atmospheric pressure either saturated or superheated.

10. A process according to claim 9, in which the steam is saturated steam above atmospheric pressure.

11. A process according to any of the preceding claims, in which the dyed material is dried immediately after leaving the means of expressing excess dye liquor from the textile material, or alternatively immediately after the textile material leaves a steamer.

12. A process according to any of the preceding claims, in which the dyed material is successively rinsed with water and/or oxidised and/or soaped and washed and dried.

13. A process of continuous dyeing of a textile material, substantially as hereinbefore described.

14. Textile material when dyed by the process claimed in any one of claims 1 to 13.

15. Textile material when dyed according to Example 1 or Example 2 or Example 3.

16. Apparatus for carrying out the process according to claim 1, comprising at least one tank for storing cold dye liquor, a small-volume dye bath, means for delivering the cold dye liquor to the dye bath via a mixer/heat exchanger, having a flow path therein which constrains the dye liquor to a residence time within the mixer/heat exchanger of between 2 and 60 seconds, means for immediately removing excess liquor from the textile material as it egresses from the dye bath, means for controlling the level of dye liquor in the dye bath, and means for controlling the temperature of the dye liquor delivered from the mixer/heat exchanger to the dye bath.

17. Apparatus according to claim 16, in which the level-controlling means comprises a level controller in the dye bath operatively connected to a valve controlling the flow of cold dye liquor to the mixer/heat exchanger.

18. Apparatus according to claim 16 or 17, in which the temperature-controlling means comprises a thermostat in the dye

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. disperse dyestuff and leaving the cotton undyed. Dye liquor composition. 5.0gms/litre Vat Purple 4R 30.0gms/litre Caustic Soda 100" Thr. 50.0gms/litre Sodium Hydrosulphite. 1.0gms/litre Commercial Wetting Agent. Immersion time 2 seconds. Dye bath temperature 70"C. Liquor Expression 65% The resultant fabric was "solid" shade of purple, free from any uneven appearance and meeting the commercial standards of factries expected. WHAT WE CLAIM IS:

1. A process of continuous dyeing of a textile material by passage through a small volume dye bath so that it is saturated with an aqueous liquor containing dyestuff and chemical assistant medium in complete solution and at an optimum temperature such as to render the dyestuff of optimum affinity for the textile material, following which saturation the textile material is withdrawn from the dye bath and excess liquor immediately removed from it, the process being characterised by feeding the dye liquor which is stored under conditions of minimum affinity for the textile material through a mixer east exchanger before delivery of such liquor to the dye bath, and from which mixer/heat exchanger the liquor emerges as a homogeneous solution at a higher temperature than its inlet temperature, the residence time for the liquor in the mixer/heat exchanger being between 2 and 60 seconds.

bath which operates a valve controlling flow of steam to the heat exchanger.

19. Apparatus according to any one of claims 16 to 18 in which a pad constituted by a lower metal padding roller and an upper resilient squeezing roller receives the dyed textile material on its egress from the dye bath, a doctor cooperating with the metal padding roller to guide expressed dye liquor back into the dye bath.

20. Apparatus according to any one of claims 1 to 19, comprising a tank for containing cleaning solution and coupled into the apparatus, in closed circuit between a point upstream of the mixer/heat exchanger and an extension of the dye bath.

21. Apparatus for carrying out the process claimed in Claim 1, substantially as hereinbefore described with reference to the accompanying diagrammatic drawing.