Some Possibilities of High-temperature Steaming in Textile Printing

JOURNAL O F THE S O C I E T Y O F D Y E R S A N D C O L O U R I S T S Volume 83 June 1967 Number 6

Proceedings of the Society Some Possibilities of High-temperature Steaming in Textile Printing

A. P. LOCKETT Imperial Chemical Industries Ltd, Dyestufs Division, P.O. Box 42, Hexagon House, Blackley, Manchester 9

Presented at a Symposium on 'High-temperature Textile Treatments' held by the Manchester Region at the University of Manchester Institute of Science and Technology, on 25 March 1966, Mr H. R. Hadjeld in the chair; and at a meeting of the London Region, held at the Royal Society, Burlington House, London WI, on 2 December 1966, Mr R. F. York in the chair

A description is given of the use for dye fixation of high-temperature steam, i.e. superheated steam at atmospheric pressure but at temperatures above 100°C. Quantitative details are given for two important outlets in textile printing, VIZ. Procion (ICI) reactive dyes on cellulosic materials and disperse dyes on man-made fibres, e.g. triacetate and Terylene. The mechanism of high-temperature steaming is outlined and the economics of different steaming processes are discussed to show the potential advantage of the new process.

Introduction The textile-printing industry has been aware for many years

that the steaming operation, which is essential for the fixation of the dye, is both a production bottleneck and a relatively expensive process in terms of capital and labour costs.

Developments in recent years that have created a demand for new dyefixation techniques in textile printing include-

(a) the introduction of man-made fibres on which dyes cannot easily be fixed by conventional steaming methods,

(b) the introduction of new classes of dyes, e.g. Procion reactive dyes, that may be fixed by conventional steaming as well as by novel methods, and

(c) the continuing demand for increased productivity coupled with low capital and labour costs (it is now recognised that the smaller the floor space occupied by the machinery the lower generally is the overhead cost in a modem factory.)

In textile printing, the printing paste, containing dye and other essential ingredients, is applied to the material by well-known methods, such as screen and roller. The dye is thickened so that the printed 'mark' is sharp, and, after drying, the dye must be made to transfer to the fibres by a diffusion process from within the printed area.

From the earliest days of textile printing it has been known that various factors markedly influence the rate at which the dye diffuses. Koechlin (I), in 1828, stated that moisture was essential for the efficient steaming of cotton prints. Fixation processes have evolved, and today three main methods are used by the textile printer to fix dyes on natural and man-made fibres.

The oldest, and still the most popular, method is by passage through a festoon steamer or a roller ager in which the printed goods are treated at atmospheric pressure in steam at 100-105°C (212-220°F). These machines, which hold from 50 to lo00 yd of cloth, require a time of passage ranging from 10 min to as long as 60-90 min. The process is continuous, but it is expensive in steam, capital outlay, and floor space occupied. Another consideration with this type of steaming equipment is the time needed to establish satisfactory steaming conditions; because of their large size, heating-up times are lengthy and time is required to fill and empty the steamer. Further, the large amount of cloth in the steamer at any given time implies that, in case of accident, spoilage rates will be high.

Another popular steaming method, favoured by the printer of synthetic polymer fibres, is the use of the non-continuous pressure steamer. This is a development from the earliest types

of steamer ever used, the star and the cottage steamers. The cottage steamers were operated at atmospheric or higher pressures and were capable of achieving steaming temperatures above 100°C. Various devices were used to move the cloth to stop marking off; the cloth was batched with back greys or rotated continuously by various mechanical methods, whereas in the star steamer the cloth was hung on a star frame and steamed at atmospheric pressure.

The modern pressure star steamer now operates at high pressures, for example, 20 lb/in2 (1 -3 atm), giving a temperature of 125°C (255°F). The printed cloth is loaded on to star frames, which are then placed inside the steamer. The pressure is raised to the desired level and maintained there for up to 30 minutes. This process, which is non-continuous, requires two to four operatives and, because of the frequent need for the pressure to be released as one batch is finished and then to be built up again for a new batch, is extremely expensive in steam. In spite of these disadvantages, steamers of this type have been installed in many printing works throughout the world.

The most recent method, developed principally for man-made fibres, entails thermofixation. With this method, when either a continuous baker or a heat-setting stenter is used, it is possible to fix disperse dyes on Terylene (ICI) and other polyester fibres in times as short as 30-60 s at temperatures in the range 180- 210°C. This technique suffers from the disadvantages of high capital cost and high running costs, and the machinery occupies a large space. Further, the production rate may be low, since the average stenter is only 20-25 yd long and so is not capable of high production rates.

As examples of the above methods employed for the fixation of specific ranges of dyes, the following may be cited-

(a) Procion H Dyes Printed on Mercerised Cotton Fixation of these dyes can be achieved either

(i) by steaming for 10-15 min in a festoon steamer at 100-

(ii) by baking for 2-5 min at 150°C (30O"F), or (iig by flash ageing, in which the alkali-padded cloth is

steamed for 30 s. Method (iii) gives a high production rate, but it has disadvantages, e.g. the necessity for washing-off immediately after steaming, and there may be difficulty in maintaining a good printed mark.

105°C (212-20OoF), or

21 3

21 4 JSDC JUNE 1967; LOCKET

(b) Disperse Dyes Printed on Terylene Fixation of the dye can be achieved by any of the following

four methods. ( i ) Steaming is carried out in a continuous festoon steamer

at 100-105°C (212-220°F) for long periods, e.g. 45 min, or even for up to 90 min (by passing the cloth through twice) at a low speed.

(ii) Steaming is carried out in a continuous festoon steamer at 100-105"C (212-220°F) in the presence, in the print paste, of special assistants termed 'carriers'. They facilitate diffusion of dye into the fibre, and their use enables the time of steaming to be reduced to 3 M 5 min. On the other hand, they are expensive and specific, and in some cases they impair the light fastness of the printed dyes; they may also affect the printing paste adversely, owing to crystallisation during storage before printing.

(iii) A pressurised star steamer is used-with all the disadvantages outlined previously.

(iv) Thermofixation is carried out on a heat-setting stenter, but with low production rates and high cost, as indicated previously. Treatment times of 30-60 s, at 180-200°C (355--390"F), are commonly employed.

The methods of fixation for printed reactive dyes and disperse dyes, outlined above, indicate the two major factors that have influenced the development of improved methods. These two factors, which markedly affect the rate of fixation of dyes of widely different chemical types on a variety of fibres, are-

(1) temperature, which must be raised to increase the fixation rate, and

(2) the presence of additives which facilitate diffusion of the dye into the fibre and so decrease the fixation time.

With these factors in mind, an investigation was undertaken into the use, for dye fixation, of superheated steam ('high- temperature' steam), i.e. steam at temperatures above 100°C but at atmospheric pressure. This steam will be unsaturated, whereas steam at the same temperature but under pressure, e.g. in a pressure steamer, will usually be saturated. These conditions obviate the need for pressure seals, which in the past has been the stumbling block for continuous pressure steamers, in which temperatures up to about 140°C have been achieved by using pressures around 40 lb/in2 (3 atm).

Experimental Two main design problems were encountered in the construc-

tion of a laboratory high-temperature steamer. Firstly, it was difficult to achieve and control the desired temperature, at the same time avoiding temperature gradients. Secondly-and perhaps of greater importance, as later results will indicate-the air content of the steam had to be reduced to as low a level as practicable. Both these factors are important if consistent and useful results are to be obtained.

LABORATORY HIGH-TEMPERATURE STEAMERS

The most convenient source of external heat was found to be high-pressure steam. This allows the temperature to be controlled by varying the pressure of steam supplied to the closed inner and outer chambers, whose walls heat the live steam injected into the steaming chamber, which is not under pressure.

The laboratory high-temperature (HT) steamer constructed for this investigation is illustrated in Figure I . The steamer consists of a cylindrical, double-jacketed vessel sealed at one end and open at the other. A rectangular pressure vessel is located in the centre of the cylindrical vessel. A guide roller at the top of the pressure vessel enables the cloth to pass through the steaming zone in a continuous manner. The steamer is open to the atmosphere, suitable mouthpieces permitting entry and exit of the cloth. A perforated pipe, the full height of the steamer,

enables compressed air, steam-air mixtures, or steam alone to be blown on to the inside surface of the outer vessel, thus filling the steaming zone and preventing the entry of air during experiments.

W I Inner pressure vessel 2 Outer pressure vessel 3 Cloth 7 Pressure gauge 4 High-pressure steam supply

5 Low-pressure steam supply 6 Thermometer

8 Mouthpieces

Figure I--laboratory high-temperature steamer

The inner and outer pressure vessels are connected to a high- pressure steam supply through a pressure-reduction valve, so it is possible to obtain the temperature required by selecting the appropriate steam pressure. Thermometers are located in the steaming zone, and preliminary trials confirmed that there were no significant temperature gradients and that it was possible to obtain a 100% atmosphere of steam at any desired temperature. Obviously, the temperature range is dependent on the maximum steam pressure available and on the safe working pressure of the inner and outer vessels.

Figure 2 illustrates a further design, in which, three heating plates are used instead of the inner and outer pressure vessels. These plates may be heated by high-pressure steam, by electricity, or by circulating hot oil or any other heat-transfer fluid.

P

Q

I High-pressure steam supply or other suitable heating source 2 Rectangular heating vessels 3 Cloth 4 Low-pressure steam supply 5 Fluon-coated top roller

Figure 2-Mark II laboratory high-temperature steamer

H IGH-TEM PERATURE STEAM1 N G IN TEXT1 LE PRI NTI NG 21 5

The two steamers proved very satisfactory for laboratory use, in that they were simple to control over a wide range of operating temperatures.

QUANTITATIVE DETERMINATION OF EXTENT OF FIXATION

Procion Dyes The percentage fixation achieved was determined by extraction

of unfixed dye from a measured area of printed and steamed fabric, by repeated treatments with water at 80°C. The previously shredded fabric, after extraction, was filtered-off on a Hirsch funnel, a glass-fibre filter pad being used to avoid dye uptake by the filtering medium. A final treatment for 5 min at the boil removed the last traces of dye. The solution of extracted dye was diluted to a volume suitable for optical-density measure- ments. Extraction of an equal area of printed pattern that had not been steamed served as a control and enabled the amount of dye fixed under a given set of steaming conditions to be determined.

Disperse Dyes The technique for estimating disperse dyes entailed Soxhlet

extraction of the steamed and washed-off print with a suitable solvent, an unsteamed unwashed print of the same dimensions being extracted to provide the value for the total dye applied. From the two values obtained, the percentage fixation was determined. Chlorobenzene was used for Terylene prints and methanol for cellulose triacetate prints.

Results and Discussion In order to evaluate the possibilities of HT steaming, experi-

ments were performed in which different printed materials were treated under a variety of steaming conditions. In view of the promising results obtained in these qualitative experiments, a series of quantitative experiments was next carried out. The results of these experiments are given below.

PROCION DYES PRINTED ON CELLULOSIC SUBSTRATES

Procion H and other reactive dyes were subjected to HT steaming after being printed on mercerised cotton and on viscose rayon staple, using the normal recipes associated with conventional steaming and fixation by baking. Four important facts emerged, viz.-

(a ) Very short HT steaming times gave a fixation at least equal to that of conventional methods.

(b) Compared with baking, HT steaming gave much more rapid fixation at the same temperature and equally rapid fixation at a temperature lower than that used for baking.

(c) It was possible to achieve high levels of fixation on viscose rayon in short steaming times, the level of fixation being much higher and more consistent than that obtained by baking.

(d) Addition of 20 % of urea to the printing paste was necessary in order to achieve satisfactory dye fixation.

Figures 3 and 4 illustrate the rates of fixation of two Procion H dyes printed on mercerised cotton and viscose rayon. Tables 1 and 2 give the comparative levels of fixation for six reactive dyes applied to the same fabrics and then fixed by different methods. These data serve to confirm the conclusions summarised above.

0 I .o 5.0 10.0 Time, min

High-temperature steaming at 150°C Mercerised cotton Viscose rayon

Conventional steaming at 102°C 0 Mercerised cotton 0 Viscose rayon

Figure 3-Comparison of fixation of Procion Golden Yellow H-RS by conventional stearning and by high-temperature steaming

loo

75

s 5 a '= 50

e

25

0

1 I I .o 5 .O

Time, min

10.0

High-temperature steaming at 150°C Mercerised cotton Viscose rayon

Conventional steaming at I W C 0 Mercerired cotton 0 Viscose rayon

Figure 4-Comparison of fixation of Procion Brilliant Red H-3BNS by conventional steaming and by high-temperature steaming

Procion Brilliant Yellow HdGS Procion Golden Yellow H-RS Procion Scarlet H-RNS Procion Brilliant Red H3BNS Procion Brilliant Blue H-GRS Procion Black H-NS

TABLE 1

Fixation of Procion Dyes on Viscose Rayon

Colour Index

steaming for HT steaming at HT steaming at C.I. Reactive 10 min 150°C for 30 s 150°C for 60 s

Comparative fixation (%) after number conventional

Yellow 18 100 87 110 orange 12 Red 33 Red 29

100 100 100

Blue 5 100

75 64 60 60

95 100 90 90

Black 8 100 64 100

baking at 150°C for 5 min

86 68 40 20 20 40

21 6

TABLE 2 Fixation of Procion Dyes on Mercerised Cotton

JSDC JUNE 1967; LOCKETT

Colour Index number

C.I. Reactive Procion Brilliant Yellow H-4GS Yellow 18 Procion Golden Yellow H-RS Orange 12 Procion Scarlet H-RNS Red 33 Procion Brilliant Red H3BNS Red 29 Procion Brilliant Blue H-GRS Blue 5 Procion Black H-NS Black 8

Dye

Comparative fixation (%) after conventional steaming for HT steaming at HT steaming at

100 112 115 100 90 100 100 84 112 100 103 105 100 85 100 100 93 107

10 min 150°C for 30 s 150°C for 60 s

The results of these experimental studies enabled the following general recommendations to be made for the application of Procion H dyes to cotton and viscose rayon fabrics. For comparison, times and temperatures for conventional steaming and baking are included.

Mercerised or Causticised Cotton HT steam-30 s at 150°C (300°F) or 60 s at 130°C (265°F) Conventional steam-10 min at 100-105°C (212-220°F) Baking-5 rnin at 150°C (300°F) or 2 rnin at 180°C (355°F) Viscose Rayon HT steam-60 s at 150T (300°F) or 90 s at 130°C (265°F) Conventional steam-10 min at 100-105”C (212-220°F) Baking-not usually employed owing to low and irregular yields

The advantages of the HT process are discussed later in detail, but it is here seen that, in comparison with conventional methods, very much higher production rates are possible.

of fixed dye.

DISPERSE DYES PRINTED ON MAN-MADE FIBRES

Initially, prints were prepared with a few disperse dyes on four different man-made fibres, viz. cellulose acetate, cellulose triacetate, Terylene, and nylon 6.6. The prints were subjected to HT steaming, and various additions were made to the printing pastes to determine their ‘carrier’ effect. The following compounds were examined : benzyl alcohol, DEGDA, Glyezin PFD (BASF), Polyethylene Glycols P200-600, Solution Salt BN (ICI), thiourea, triacetin, Tumescal PH (ICI), and urea.

The carriers examined proved to be specific in their action under HT steaming conditions, i.e. not all dyes were affected in the same way; some showed vastly improved fixation, whereas others were virtually unaffected. It was found that an addition of 20 % of urea to the printing paste gave the best over-all results. Larger amounts were needed than with the usual carriers, but urea was effective with all the dyes examined. Urea is cheap and readily available and it does not have the disadvantage of poor solubility in the printing paste associated with some carriers. Furthermore, urea is readily removed from steamed fabric by washing and it has no adverse effect on light fastness.

TABLE 3 Fixation of Dispersol Fast Orange B Liquid (C.I. Disperse Orange 13)

Steaming Temp. 0.5 1 2 4 30 45 60 90 method (“C) min min min min min min min min

Cellulose Triacetate Conventional 100 46 48 80

Fixation (%) after steaming for

Pressure

High- 150 69 82 temperature 170 66 74

180 69 Terylene

Conventional 100 42 44 48

(10 Ib/inz) 115 75

Pressure (20 Ib/in*) 125 High- 150 85 88 temperature 170 73 87

180 88

90

baking at 150°C for 5 min

115 91

110 104 98

104

A series of qualitative experiments was carried out in order to determine the times and temperatures needed for different fibres. These experiments were followed by a more detailed quantitative study of the fixation of disperse dyes on Terylene and cellulose triacetate, the results of which are given in Tables 3-8.

TABLE 4 Fixation of PQ Dispersol Fast Yellow T Paste (C.I. Disperse Yellow 42)


Cellulose Triacetate 50 55 65 Conventional 100


Pressure (10 Ib/inz) 115 85 High- 150 72 78 temperature 170 60 82

180 63 Terylene

Conventional 100 Pressure (20 Ib/inz) 125 High- 160 76 91 temperature 170 78 93

180 94

10 11 12

95

TABLE 5 Fixation of Disperse Dyes on Cellulose Triacetate

Fixation (%) after steaming for Steaming Temp. 0.5 1 2 30 45 60 method (“C) min min min min rnin min

Conventional 100 83 86 Pressure

High- 150 69 84 89 temperature 1 60 87 94

170 89 93 96 180 91 93

Dispersol Fast Scarlet TR Liquid

(10 Ib/inZ) 115 95

Duranol Blue G Liquid (C. I . Disperse Blue 26) 42 46 Conventional 100

Pressure (10 Ib/inz) 115 60 High- 150 26 46 49 temperature 160 49 53

170 48 62 69 I80 62 68

TABLE 6 Fixation of Disperse Dyes on Terylene


Conventional 100 29 30 35 Pressure (20 Ib/inz) 125 92 High- 150 60 71 temperature 170 73 90


Dispersol Fast Ruhine BT Liquid (C.I. Disperse Violet 33)

180 83

HIGH-TEMPERATURE STEAMING IN TEXTILE PRINTING 21 7

TABLE &continued

Steaming Temp. 0.5 1 2 4 30 45 60 90 method ("C) min min min min min min min min

Dispersol Fast Red TB Liquid (C.I. Disperse Red 131) Conventional 100 40 49 58 Pressure (20 Ib/inz) 125 93 High- 150 85 88 temperature 170 80 93

180 88


TABLE 7 Fixation of Duranol Blue TR 300 Powder Fine (C.I. Disperse Blue 56)

on Terylene

Steaming Temp. 0.5 1 2 4 30 45 60 90 method ("C) min min min min min min min min Conventional 100 25 29 34


Pressure (20/in2) 115 High- 150 62 12 temperature 170 61 82

180 75

7s

TABLE 8 Fixation of Dispersol Fast Yellow G Liquid (C.I. Disperse Yellow 3)

on Cellulose Triacetate Fixation (%) after steaming for

Steaming Temp. 0.5 1 2 30 45 60 method ("C) min min min min min min Conventional 100 84 89 Pressure (10 lb/in2) 115 82 High- 150 53 87 89 temperature 160 94 95

170 94 98 95 180 95 98

The results of the qualitative and quantitative work on cellulose triacetate and Terylene (Tables 3-8) led to the following conclusions-

(a) Fixation of disperse dyes on cellulose acetate, cellulose triacetate, nylon, and Terylene may be achieved in very much shorter steaming times than is possible with conventional fixation methods, e.g. steaming at atmospheric pressure in the presence of carriers or steaming under pressure.

(b) An addition of 20% of urea to the printing paste is essential if good results are to be obtained.

(c) With Terylene, it is possible to achieve fixation of disperse dyes in times similar to those employed for thermofixation, but at lower temperatures, e.g. 170°C instead of 200°C.

These experiments enabled the following general recommendations to be made for the application of Duranol and Dispersol dyes-

cellulose acetate 1-2 rnin at 130-150°C (265-300°F)

Sminat lSO"C(300"F); 1 minat 180°C(355"F) cellulose triacetate Ter ylene nylon

The practical advantages of the HT process are examined in more detail later, but it is already clear that the possibility of using a continuous high-production process for the above dye- fibre systems should have an immediate appeal to fabric printers-faced, as they are, with increasing demands for printed fabrics produced from these fibres.

MECHANISM OF THE PROCESS

Rate of Heating Numerous attempts have been made to determine the rate of

heating of textile materials in different heating media. There are many difficulties, the most important being that the rates obtained are applicable only to the particular piece of equipment studied (2-4).

Figure 5 shows the approximate rate of heating of a textile material in hot air and in superheated steam, both at 180°C. In hot air the cloth is gradually heated to the ambient temperature. In superheated steam, immediate contact of the fibres with the steam causes condensation to occur, resulting in virtually instantaneous heating to 100°C. Next follows a short dwell (at loOOC) during which the condensed water is evaporated, and then the temperature rises to 180°C. The difference in rate of heating is only slight; for example, for a modified baking system (2), a delay of 3 s was found for hot air, as compared with superheated steam. Contrary to the generally accepted belief, the heat-transfer rates of hot air and superheated steam are very similar (4), so it is unlikely that the slight increase in heating rate produces the increase in dye-fixation rate that occurs in superheated steam.

/ / / /

/ /

/ /

/ /

/ /

Figure 5-Rateof heating of textile substrate in hot air and in superheated steam

Condensation When the cloth, normally at room temperature, enters the HT

steamer, water condenses on to it and heats it rapidly to 100°C. The amount of water condensing may be calculated, and for the fibre itself it is 5.5%. If the presence of a dried-out film of printing paste is allowed for, between 5 . 5 % and 10% of water condenses on to the substrate.

The importance of a high steam content in a superheated steam atmosphere has already been mentioned. In the results for Procion dyes on mercerised cotton and staple viscose rayon given in Tables 1 and 2, the effect of air and steam at 150°C on the levels of fixation is shown. Table 9 shows the effect of

21 8 JSDC JUNE 1967; L O C K E T

increasing steam content on the fixation of three disperse dyes applied to Terylene and cellulose triacetate. From these results and from further larger-scale work, it appears imperative to maintain the steam content as near to 100% as possible. Once the steam content falls below 90-95%, over-all dye fixation begins to fall off sharply, especially on cellulose triacetate. The steam-air content of the steamer was measured with a wet- and dry-bulb thermometer system and this system was used to control the steaming conditions (4).

TABLE 9

Effect of Steam Content on Fixation of Disperse Dyes on Cellulose Triacetate and Terylene*

Steam content

(%)

Fixation (%) with Dispersol Fast

Air Yellow G Liquid Dispersol Fast

(%) Yellow 3) TR Liquid content (C.I. Disperse Scarlet

Cellulose Triacetate 0 100 54 60

50 50 80 14 I 0 0 0 92 89

0 100 88 88 50 50 89 90

100 0 92 95

Terylene

*All prints treated at 160°C for 1 min

Duranol Blue G Liauid

(C.I. Disperse Blue 26)

29 39 48

65 I9 90

Effect of Printing Assistants From the above results and the discussion, it is apparent that

urea plays an important part in HT steaming. Table 10 shows the effect of urea on the fixation of three disperse dyes on Terylene and cellulose triacetate. The effect of urea and its uses in textile processing have been investigated (5), and it has been shown-again contrary to the commonly expressed opinions- that urea is not hygroscopic.

TABLE 10 Effect of Urea on Fixation of Disperse Dyes*

Fixation (%) with Dispersol Fast Duranol Blue

Fibre Urea Yellow G Liquid Dispersol Fast G Liquid (%) (C.I. Disperse Scarlet (C.I. Disperse

Yellow 3) TR Liquid Blue 26) Terylene 0 56 68 51

20 91 98 94

Cellulose 0 6 14 triacetate 20 89 89

*All prints fixed by HT steaming at 150°C for 2 rnin

13 49

During the present work, urea has been shown to be capable of combining with water to form a eutectic mixture at high temperatures. Table 11 shows the effect of small additions of water in lowering the melting point of the eutectic melt; the effect of two disperse dyes on the melting point of urea is also indicated.

TABLE 11 Effect of Additions on Melting Point of Urea Addition Amount added M.p.

( %) (“C) None - 13i Water 5 105 Water 10 50 Duranol Blue TR 300 Pdr Fine

(C.I. Disperse Blue 56) 50 106 Duranol Brilliant Violet BR 300

Pdr Fine 50 110

It follows that the rate-of-heating characteristics illustrated by Figure 5 must now be altered, because some of the condensed water is not evaporated. The rate of heating in the presence

and absence of urea is shown in Figure 6. These results have been verified by experiments (4) which show that, at 100°C in the presence of urea, the time taken for evaporation to occur is reduced, so the rate of heating is again slightly increased, compared with that for hot air alone. The temperature reached by the cloth in the presence of urea is slightly lower in steam than in air, and this is most probably caused by slow decom- position and evaporation of the molten urea at the high temperature employed.

I80

V

f E x I00 $ c 0 6

0 15 30

H o t air - Superheated steam in the absence of urea - - - Superheated steam in the presence of urea

Time, s _ _ _ _ _ _ _ _ _ _

Figure 6-Rate of heating of textile substrate in hot air and in superheated steam in the presence and absence of urea

The mechanism of HT steaming may be summarised as follows. In the presence of superheated steam, water condenses on to the fabric, raising its temperature to 100°C. The condensed water and the urea present form a eutectic melt in which the dye dissolves, and this melt increases significantly the rate at which the dye diffuses into the fibre substrate.

OTHER OUTLETS FOR HT STEAMING

Flash Ageing of Vat Dyes and Reactive Dyes In flash ageing, wet cloth enters the steamer and remains at

100°C until it is dry. Flash ageing is usually complete in 30-40 s, which is less than the time taken to dry the cloth in a HT steamer, even at ISO’C, so the advantage of using superheated steam in a flash ager will be small. One advantage, however, is the elimination of ‘flushing’ of heavily covered prints, because of the slight drying effect in the superheated steam.

‘S’ Finish for Cellulose Triacetate Fabric A hot alkaline hydrolysis is recommended if the best fastness

and wearing properties are to be obtained. This is usually carried out, e.g. on a jig, for long periods (6). It has been found that the ‘S’ finish can be produced in a continuous manner by padding in a solution of sodium hydroxide and steaming for 2 min at 150°C.

H IG H-TEM PERATU RE STEAM1 NG IN TEXT1 LE PRINTING 21 9

Other Applications Stabilised azoic dyes can be developed in short steaming

times, e.g. 30 s, at 150°C. The time needed for the fixation of basic dyes on acrylic fibres

is reduced significantly by HT steaming. Many of the printing processes described above may be

converted into continuous dyeing processes, and development work is being carried out in this field.

BULK-SCALE STEAMERS

The laboratory studies indicate the need for a bulk-scale machine in which the temperature is readily controllable and (of greater importance) the amount of air can be kept to a minimum. Attempts have been made to introduce steam into heat-setting stenters, but without much success in terms of extra dye fixation (4); the amount of air present is considered to be too great. However, development work is in hand, in conjunction with several well-known textile-machinery makers. Various prototype development and full-scale HT steamers have been constructed and are now in commercial production in different parts of the world.

The experimental results and forecasts for HT steaming outlined in this paper have been fully borne out in that these steamers have been operating for some time with both technical and commercial satisfaction.

ADVANTAGES OF THE ICI HT STEAMING PROCESS

Of the many advantages to be gained from employing this

(1) higher production rates, particularly where a continuous

(2) lower operating costs, including reduced use of steam; (3) lower manpower requirements; and (4) smaller requirements for floor space. In Table 12, three processes commonly recommended for the

application of Procion and other reactive dyes to cellulose are compared with HT steaming. The ICI HT steaming process has obvious advantages. It is a single-phase process, i.e. no padding liquor is required. A high throughput is achieved and the results, especially on viscose rayon, are more consistent than those obtained by baking.

In Table 13, the two processes frequently adopted for the fixation of disperse dyes on man-made fibres are compared in detail with high-temperature steaming. It is evident that the HT process, being continuous, gives high production rates, overcomes the need for expensive carriers, and offers large savings in steam and labour costs.

In Figure 7, the HT steaming process is compared with other fixation processes, for a number of important dye-fibre systems. A logarithmic scale is used in order to emphasise the shorter fixation time (and correspondingly by increased output) in HT steaming.

technique, the following are the most important-

process replaces a non-continuous one;

TABLE 12 Comparison of Different Fixation Processes for Procion Dyes Printed on Cellulosic Fibres

Fixat ion Cloth content Steaming time Additional Production Production process (yd) (min) chemical costs (yd/h) per 12-h shift:

(yd) Roller baker 80 5 < 10% 960 11,500

(urea) Festoon steamer 600 15 - 2,400* (1 end) 27,600-82,800

HT steamer 60 0.5-1 ‘0 10% 3,600* 41,400-82,800

Flash ager 10-30 0.5 (padding 1,200 13,800-41,400

*Viscose rayon t Mercerised or causticised cotton $Allowance included for filling and emptying steamers of 600-yd capacity

4,800 (2 ends) 7,200t (3 ends)

(urea) 7,200t

liquor) 3,600

TABLE 13 Comparison of Different Fixation Processes for Disperse Dyes Printed on Man-made Fibres

Festoon steamer Pressure High-temperature steamer steamer

Cloth content (yd): 600 500 60 Steaming time (min): 30 60 20-30 1 Cloth speed (yd/h) 1 end: 1,200 600 750-1 ,000 3,600

Approx. steam consumption (Ib/h) : 5,000 - 600

2 ends: 2,400 1,200 Production per 12-h shift (yd): 26,400 12,000* 9,000-12,000 43,200 ..

Carrier cost per 100 Ib paste: 3s. 4d. (10% ureat) no addition 6s. 8d. (20% ureat) 30s. ( 5 % p-phenylphenol:)

Steam usage (Ib/yd cloth steamed): 2.08 4.16 approx. 3.0 0.17 Operatives per steamer: 1-2 Approx. floor area (ftz): 300 Approx. ratio of total steaming costs (HT steaming as unity): *Allowance included for filling and emptying time ?At 4d. per Ib $At 6s. per Ib

5 .O

3 4 1-2 400 90

7.5-10.0 1 *o

220 JSDC JUNE 1967; SHAH

Dye class Fibre Fixation time, min (log. scale) 120 60 30 15 8 4 2 1 0.5

r - 7 1 1 I I I l l Azoic

composition Cotton . 0

Reactive Cotton . c, 0 and viscose rayon

Vat Cotton . and viscose rayon 0

Nylon . 0 Acetate . 0

A 0 Disperse Triacetate . rn (with carrier) . (with carrier) 0

7 Polyester . A

Basic Acrylic .. 0 High-temperature steaming Fluh ageing . Conventional steaming (roller, festoon) 7 Thermosol

@ Baking A Pressure steaming

Figure 7-Comparison of processing times of conventional and HT steaming processes

Conclusions Obviously, the techniques of textile printing are similar in

many ways to those used in textile dyeings-for example, the local application of a suitable dye solution in printing and

over-all application in padding; in both cases the fabrics are then dried and finally subjected to the fixation processes,

Recent development work has, in fact, shown that, where a heat treatment or baking process can be replaced by a high-temperature steaming treatment, considerable advantages can be obtained, shortening of the treatment time and lowering of the fixation temperature being among the most important.

This development work has led to the publication of recommendations for various uses of high-temperature steaming in textile printing and dyeing (7).

The ICI HT steaming process offers a new and simple method of achieving rapid fixation of many different classes of dye applied by printing and dyeing techniques to a wide variety of textile substrates in a more economical manner than has hitherto been possible.

* * * The author acknowledges the help of Mr W. Beaumont and

Mr B. Glover in the experimental work, and thanks numerous colleagues in the AR.TS Department for their encouragement and assistance. ’

(MS. received 19 September 1966)

References I Koechlin, H., Bull. SOC. industr. Mulhouse (1828). 2 Ulrich, P., and Niederer, H., S.V.F. Fachorgan, 20 (1965) 712. 3 Marshall, W. J., unpublished work. 4 Artos Forschung Maschen, unpublished work. 5 Baumgarte, U., Melliund Textilber., 46 (1965) 851. 6 Courtaulds Ltd, Trice1 Technical Service Manual. 7 ICI, Technical Information (Dyehouse) No. 898, 899, 920 and 923.

Review Pa per Recent Developments in Organic Pigments

N. V. SHAH Colour-Chem Ltd, Thana, Bombay, India

Azo, vat and phthalocyanine pigments are discussed briefly. The demand for high-grade pigments has led to the development of new classes of organic pigments, viz. quinacridone, dioxazine, perylene-perinone, fluorubine, pyrrocoline, and isoindolinone pigments. The preparation and properties of these pigments are discussed, particular attention being paid to the range of colours and the

fastness properties obtained and to the prospects of commercial development.

Introduction Pigments have achieved a significant position in modern

industry, as is evident from their use, for example, in the colora- tion of paints, printing inks, plastics, rubber and textile fabrics. It was only after the discovery of copper phthalocyanine that chemists realised that it was possible to produce high-grade organic pigments that could adequately satisfy industrial requirements. This led to research into the improvement of existing classes of pigments and to the discovery of new classes that gave a wider colour range and also met the required fastness standards of the different industries.

In an earlier review (I), Gaertner described the general development of high-grade organic pigments. The present paper deals mainly with the methods of synthesis of these compounds.

Before the new classes of pigments are discussed, brief reference will be made to pigments that have been commercially exploited over the past fifty years.

AZO PIGMENTS

At present, most of the pigments produced are azo compounds, yellows, oranges and reds being derived from azo compounds containing acetoacetarylide, pyrazolone and naphthol groups (or

derivatives of such groups), respectively. If certain solubilising groups are present, it may be possible to form metal chelates, which are used as pigments.

The classical am pigments have poor fastness properties but, because they are cheap, they are widely used. However, the new azo condensation pigments have overcome these fastness problems. They are high-molecular-weight pigments and their preparation and properties are described in the patent literature (2). Only those azo condensation pigments that have been formed by the condensation of two azo molecules of similar chemical structure have been commercially exploited. It would, therefore, be interesting to investigate the condensation of two azo molecules of different chemical structure.

VAT PIGMENTS

This group of pigments can be divided into three main types, viz.

( i ) anthraquinone. (ii) thioindigo, and

(iii) perylene-perinone. The last type will be discussed in the section dealing with newly developed pigments.

Documents

Some Possibilities of High-temperature Steaming in Textile Printing