of the free formaldehyde contents of these raw materials in their studies?

Dr Patel: All the resins used in the work were commercial products, but no attempt was made to measure the free formaldehyde contents.

Disperse Dyes for Polyester - A New Approach to Compatibility David Blackburn and Victor C. Gallagher" Yorkshire Chemicals Ltd Kirkstall Road Leeds LS3 1LL

Vic Gallagher gained a BSc in the Colour Chemistry and Dyeing Department of Leeds University. He joined Yorkshire Chemicals Ltd in 1968 and was based in their Technical Service department. He was later made responsible for the development of textile auxiliaries together with associated quality control and manu- facturing techniques. Mr Gallagher transferred to the

After graduating in Natural Sciences from Cambridge University, Mr D Blackburn worked for 12 years in the Dyeing Research laboratories of Courtaulds Limited at Droylsden, where he was heavily involved in the develop- ment of Courtelle acrylic fibre. He then became Technical Manager of the Droylsden and Kirklees dyehouses and was particularly concerned with the yarn dyeing of textured Celon and Tricel. After a period as Dyehouse Manager at Furzebrook Knitting Company, Aintree, Mr Blackburn joined Yorkshire Chemicals L td as Chief Colourist in 1972. Since that time he has been principally involved in disperse dyes for polyester and basic dyes for acrylic fibres and has lectured on both subjects in the UK and in Europe.

The factors affecting rate compatibility and on-tone build-up when applying mixtures of disperse dyes to polyester are discussed. A method of predicting the compatibility o f the dyes in a given recipe is described. It is concluded that it is not possible for three individual dyes of different colour (e.g. yellow, red and blue) to be rate-compatible over a wide range of depths (com- binations). An alternative approach is suggested in which each of three dyes is itself a primary combination of individual dyes of similar hues but having different

Chief ColourlstO department in 1973 and has since worked on new dyeing techniques, rapiddyeing methods, and in particular on problems associated with disperse dye com- patibility. After a short period with Batoyle L td, Milnsbridge, Mr Gallagher has recently joined Patco Chemicals Ltd, Bolton

dyeing rates. It is shown that such primary combinations are capable of being used together to give on-tone build-up over a wide colour range. Further they offer advantages as regards their suitability for use in rapid- dyeing cycles.

INTRODUCTION Many of the principal classes of dye can be sub-divided according to their application properties. For example, acid dyes can be grouped according to whether they require strongly acid, weakly acid or neutral conditions for applica- tion to wool [l I . Basic dyes are considered in terms of their dyeing properties as characterized by their compatibility value [2] on acrylic fibres. In 1977, the Society of Dyers and Colourists published [31 recommended methods for assessing the dyeing properties of disperse dyes on polyester.

Although these methods provide useful information about the behaviour of disperse dyes, they do not enable the dyer to choose rate-compatible mixtures for dyeing polyester in the way that the compatibility value tests do for basic *Present address: Patco Chemicals Ltd, Smiths Road, Bolton

JSDC Volume 96 May 1980 237

dyes on acrylic fibres. In fact there is no simple system for formulating rate-compatible recipes for dyeing polyester materials with disperse dyes, although Saville et al. [41 described a categorizing test which was useful in this respect.

Very considerable effort has, however, been expended in the investigation of methods of reducing dyeing cycle times in polyester dyeing, and many of these have involved some attempt to categorize disperse dyes. These are well summar- ized in a recent paper by Siegrist [5], and it i s apparent that one of the main difficulties in defining "optimized dye cycles" arises from the fact that the rate of dyeing of a disperse dye on polyester is very much a function of the depth of dyeing, i.e. of the concentration of dye in the bath.

RATE OF DYEING AND DEPTH OF COLOUR When dyeing polyester with a combination of dyes, it i s advantageous to use dyes which, when used in the amount required, have similar rates of dyeing. This ensures an on-tone build up of the colour and simplifies the control of rate of exhaustion, since the dyes tend to behave as one. It is, however, much easier to state this objective than to achieve it.

The rate of exhaustion of disperse dyes on polyester i s very dependent on the depth of the dyeing. Figure 1 shows the exhaustion rate of Serilene Dark Red FL (YCL) (C.I. Disperse Red 65) a t three depths on textured polyester fabric when the rate of rise of temperature i s I o C per minute. It can be seen that by the time the bath has reached 12OoC, the exhaustion is over 90% for a 0.12% dyeing, whereas for a 1.2% dyeing it i s 54%, and for a 2.4% dyeing it i s 34%. Therefore, it is not possible to say that a given pair of dyes are compatible in dyeing rate -they will probably be so over a limited range of respective concentration, but be incompat- ible outside it. This is shown by considering the two recipes A and B below,

A B 1. Serilene Yellow 3GL 150% - YCL 0.6% 0.05%

2. Serilene Blue 3RLN - YCL 0.4% 4.8% ((2.1. Disperse Yellow 54)

(C.1. Disperse Blue 64)

Figures 2 and 3 show the rate of exhaustion of each dye in the two mixtures, and it i s apparent that in A the rates are similar, whereas in B they are markedly different. Thus, as expected, recipe A gives an on-tone build up as the dyeing proceeds, whereas with recipe B, the dyeing is initially very yellow and builds up bluer.

100

/

M 8ol / / / I

/ 1

20! / I O I 60 70 80 90 100 110 120 130°C 0 10 20 30 40 50 60 70 rnin

Figure 1 - Relationship between rate of dyeing and depth of colour for Serilene Dark Red F L

238 JSDC Volume 96 May 1980

0 60 120min

Figure 2 - Recipe A. Rates of dyeing of yellow ( 1 ) and blue (2) components

100 I

0 70 100 130 "C

Figure 3 - Recipe B. Rates of dyeing of yellow ( I ) and blue (2) components

It i s necessary, therefore, to know in some detail the relation between depth of dyeing and rate of dyeing for al l the dyes being considered. This knowledge has been accumul- ated for a l l the YCL disperse dyes and the information is given in graphical form as shown in Figure 5, showing two dyes as examples. The V number i s a numerical value given to the rate of dyeing and is explained in detail below.

MEASUREMENT OF RATE OF DYEING IN TERMS OF THE V NUMBER The rate of dyeing of each disperse dye a t five depths was determined on scoured, unset, double-jersey, textured poly- ester fabric at a liquor ratio of 20:l using the following dyebath:

x% dye 1 g/I Dyapol DL (anionic dispersing agent) 1 % acetic acid

Dyeing was commenced a t 7OoC in a laboratory high- temperature dyeing machine, the temperature raised a t I0C/min to 13OoC and dyeing continued a t this temperature for 60 minutes. By removing samples a t appropriate tempera- tures and using a combination of reflectance spectrophoto- metry on the dyed fabric, and absorption measurements on the dye solutions, the rate-of-dyeing curve was plotted. From this, the time taken to reach half the final exhaustion ( t ~ ) i s read off. This i s converted to the V number using the following relationship:

70 - t x v = - 10

Within the experimental conditions used, V i s always a positive number, in fact always greater than 1. The higher the V number, the faster the rate of dyeing.

An example of the rate curves, and the values for t X and V number for a dye applied a t five depths is given in Figure 4. For each dye a plot of V number against depth of dyeing is obtained, using a logarithmic scale (see Figure 5) because of the rapid increase in V number a t depths below 1%. However, as a result of experimental difficulties, when the amount of dye applied is below about 0.05% the accuracy of the measurement i s reduced, but, because of the definition of V number, it has a limiting maximum value of 7.0 at zero dye concentration and a l l the graphs therefore tend to this value.

USE OF THE V NUMBERS Consider the following recipes A, 6 and C, each of which gives a grey, the three dyeings being similar in hue and depth:

Commercial Name (YCL) C.I. Disperse V

A 0.18% Serilene Golden Yellow 2R-LS Orange 93 3.3 0.25% Serilene Red 3B-LS Red 82 3.2 0.80% Serilene Blue CB-LS Blue 153 3.0

B 0.4% Serilene Golden Yellow T-FS Yellow 70 2.6 0.1% Serilene Rubine 4B-LS Red 272 3.4 0.7% Serilene Blue CB-LS Blue 153 3.1

C 0.19% Serilene Golden Yellow 2R-LS Orange 93 3.3 0.13% Serilene Red 3B-LS Red 82 3.5 0.30% Serilene Navy Blue G-LS Blue 171 1.6

The greatest difference between V number (AV) in Recipe A is 0.3, for Recipe B AV i s 0.8, and for Recipe C AV i s 1.9. Compatibility tests were carried out on these three recipes using a l0C/min rate of rise and sampling a t 10°C intervals. These clearly showed that Recipe A gave on-tone build up. Recipe B was less satisfactory, the earlier dyeings being more violet. Recipe C was markedly incompatible, giving virtually a brown in the early stages of dyeing. This clearly demonst- rates that compatibility can be expected if al l the compon- ents in a recipe have similar V numbers.

It should be emphasized that, although the practical work involved in determining V numbers is reproducible to a satisfactory degree, the use of the V number system is based on a number of assumptions and approximations which

70 100 1 3 O C 120min 0 60

Figure 4 - Rate curves, values for t x and values for V, for Serilene Golden Yellow T-FS applied at five depths

reduce the absolute accuracy of the system. The influence of changes in dyeing procedure, such as rate of rise of temperature, carriers and liquor ratio are discussed later, but clearly they too must give rise to some variations in interpretation of AV. However, in general terms, if AV is less than 0.5, a compatible combination showing on-tone build up is almost assured. If AV i s between 0.5 and 1.2, some incompatibility may be expected, but it is probably worth- while to carry out a compatibility tes t under the conditions to be used in bulk, to determine the extent of the incompatibility. If AV i s greater than 1.2, then it i s highly likely that a markedly off-tone build up will be obtained.

USE OF THE V NUMBER TO CONTROL THE DYEING RATE As can be seen from Figure 4, tX occurs in the middle of the steepest part of the exhaustion curve. If the temperature corresponding to t X i s called the critical temperature ( T c ) , then it can be seen that, over the temperature range (TC-15)OC to (TC+15)OC, approximately 80% of the dye is absorbed. A 1"Clmin rate of rise through this 3OoC section of the dyeing cycle is probably adequate to ensure level dyeing in most types of modern dyeing equipment, although the actual rate is dependent on the machine and the material to be dyed, Outside this temperature region the rate of rise can be increased considerably, thus reducing the total time of the dyeing cycle without increasing the chance of unlevel dyeing.

Because of the way in which the V number i s calculated, there is a simple relationship between V and T, which is

7 .O 6.0 5 .O

4.0

f 3.0

B Serilene Golden Yellow T-FS

L

z Z >

2.0

1 .o 0.01 0.02 0.03 0.04 0.05 0.1 0.2 0.3 0.4 0.5 1 .o 2.0 3.0 4.0 5.0

Dye in bath, %

Figure 5 - V number against depth of dyeing for Serisol Fast Yellow PL 150% and Serilene Golden Yellow T-FS

JSDC Volume 96 May 1980 239

shown in Figure 6. Thus, for a dye with a given V number, the corresponding T, can be read from the graph and the critical temperature region is thus known. Unfortunately, this relationship is only strictly applicable under the dyebath conditions defined earlier. Minor variations in dyeing condi- tions will probably only alter the critical temperature region by about 5OC. For example, increasing the rate of rise to 2'C/min increases T, by about 5OC. More specific effects will be described below.

~~

70 80 90 100 110 120 13OoC +10min Critical tern peratu re ( Tc), O C

Figure 6 - Relationship between Vand T, at l°C/min rate of rise of temperature

EFFECT OF CHANGES IN THE DYEING SYSTEM The V number is defined under the precise conditions described earlier and is therefore a constant. The time of half-dyeing, however, and hence T,, will vary i f the condi- tions are changed. The extent of the change in T, has been investigated for the following variables, altering each in turn:

Rate of rise of temperature Use of carrier Use of levelling agents Liquor ratio Change in fibre type

Rate of Rise of Temperature Increasing the rate of rise of ->mperature increases the critical temperature and, although there are some variations from dye to dye, the general effect i s as shown in Figure 7. Thus, if a dye at a particular concentration has a V number of 3, then T, would be 1 10°C for a 1°C/min rate of rise, but would be 125OC for a 5'C/rnin rate of rise. (Note that the corresponding values of t x under these conditions are 40 minutes and 11 minutes, respectively.)

Use of Carriers The presence of carriers reduces T, as i s shown in Table 1. The alkyl naphthalene carrier (Optinol MNS) has a greater effect than the ortho-phenylphenol carrier (Optinol 6).

71\

6-

5-

B 4- L

5 : 3- 2-

1-

Figure 7 - Relationship between V and T, at different rates of rise of temperature

Use of Levelling Agents Levelling agents based on non-ionic products give somewhat different results with different dyes but, in general, their effect on T, is less than that of carriers, as can be seen from Table 2. I t i s significant, however, that in some cases there i s a slight increase in T,, possibly due to dye solubilization.

Liquor Ratio The effect on T, of changes in liquor ratio i s shown in Table 3. It can be seen that shorter liquor ratios decrease Tc and larger liquor ratios increase T,, but the changes are relatively small.

Change in Fibre Type With the range of normal commercial polyester fibres examined, the variations in T, have been found to be relatively small except for such unusual fibre variations as the so-called "non-carrier dyeable polyesters". Results for three different textured polyester fibres are shown in Table 4.

Some of these variables are seen to have a significant effect on T,, but it is the difference between the V numbers of a given dye combination which determines the compatibility, not t x or Tc. A large number of dye combinations have been examined in compatibility tests in which the factors above were varied. In virtually a l l cases, dye formulations, chosen to be compatible on the basis of the V numbers derived from the graphs, retained their compatibility despite large varia- tions in dyeing conditions. Similarly, formulations predicted to be incompatible on the basis of their V numbers, remained incompatible under the various conditions examined. This shows the system to be quite robust as regards the type of variations in dyeing conditions likely to be found in practice.

TABLE 1

Effect of Carriers on T, ("C)

Carrier W e % No Addition Optinol MNS Optinol B

Serilene Yellow 3GL 150% 0.2 103 90 103 2.0 117 104 111

Serilene Red 36-LS 0.2 107 93 103 2.0 117 114 117

Serilene Navy Blue G-LS 0.2 123 95 105 2.0 129 118 119

240 JSDC Volume96 May 1980

Fig. 8

“C

90

100

110

120

130

130 60 m

I Compatibility test

Grey Exhaust

S using Primary Comb

Old Gold Exhaust

iations

Green Exhaust

Fig. 9 Compatibility tests on various recipes

Customer’s recipe ‘Random’ combination Primary Combination

Exhaust Exhaust Exhaust 0 -

1

90

100

110

120

130

130 60 m

Fig.10 Compatibility tests on various recipes

Customer's recipe 'Random' combination Primary Combination o f - Exhaust Exhaust Exhaust b

90

100

110

120

130

130 60 m

Fig. 11 Compatibility tests on various recipes

"C

90

100

110

120

130

130 60m

Recipe A Exhaust

Recipe 6

Exhaust

Recipe C

Exhaust

TABLE 2

Effect of Levelling Agents on T, ("C)

Levelling Agent % No Addition Dyapol G Dyapol N

Serilene Yellow 3GL 150% 0.2 103 106 107 2.0 117 114 115

Serilene Red 3B-LS 0.2 107 111 109 2.0 117 120 120

Serilene Navy Blue G-LS 0.2 123 114 113 2.0 129 124 124

TABLE 3

Effect of Liquor Ratio on T, ("C)

Serilene Yellow 5R

Serilene Yellow 5R

Liquor %Dye Ratio

0.2 10 20 35

1.0 10 20 35

Serisol Brilliant Red X3B 200% 0.2 10 20 35

Serisol Brilliant Red X3B 200% 1.0 10 20 35

Serilene Navy Blue G-LS

Serilene Navy Blue G-LS

TABLE 4

Effect of Fibre Type on T, ("C)

Commercial Fibre (Textured Yarn)

Terylene Asahi Kasei Unitika Ester

Tc("C)

91 93 94

1 04 105 108

105 106 107

112 113 118

0.2 10 120 20 123 35 124

1.0 10 127 20 129 35 130+

T, of 0.5% Serilene Red 3B-LS

112 110 107

EXAMPLES OF THE USE OF V NUMBERS An olive green is required on a normal textured polyester fabric to be dyed at 130°C. Two recipes are available which give, approximately, this colour :

V Recipe A 1.00% Serisol Fast Yellow PL 150% 2.5

0.13% Serilene Red 2BL 4.1 0.30% Serilene Blue 2GL 200% 3.4

Recipe B 0.60% Serilene Yellow 5 R 3.9 0.12% Serilene Red 2BL 4.2 0.25% Serilene Blue RL 3.9

AV = 1.6

AU = 0.3

From this information it would be expected that Recipe B is much more compatible than Recipe A, because it has a smaller AV, and is therefore to be preferred. Because the V numbers for Recipe B are so close together, one can work on the basis that the V number is 4.0. This corresponds to a T, of 100°C and the critical temperature region i s therefore 85-1 15°C. A suitable dyeing cycle would therefore be:

Prepare bath a t 60-70°C Raise quickly to 85°C Raise a t 1°C/min to 115°C Raise quickly to 130°C Maintain for 30 min a t 130°C Cool and wash off, etc.

ADVANTAGES AND DISADVANTAGES OF THE V NUMBER SYSTEM There is no doubt that use of a recipe in which al l the components dye a t similar rates offers considerable advant- ages. The principal gains from choosing compatible recipes are maximum chance of level dyeing and the narrowing of the critical temperature region, leading to shorter dyeing cycles. Using the V number system, it is possible to te l l by inspection if any given recipe is likely to be compatible. In very extensive laboratory work, and considerable industrial experience, it is our finding that mixtures, predicted to be compatible by the V number system, remain compatible even when relatively large changes are made in the conditions of dyeing .

It is probable that there will be some exceptions to this general observation, due to specific interaction between dyes or between a dye and an auxiliary product, but our experience suggests that this will be very infrequent. A disadvantage of the system i s that the actual formulation of compatible recipes can be tedious if trial and error methods have to be used. There may also be cases where, because of colour or fastness requirements, it is not possible to obtain a truly compatible recipe. It is also likely that, in order to select compatible combinations over a wide shade range, a dyer will have to stock a larger number of individual dyes than would normally be the case.

AN ALTERNATIVE APPROACH The ideal situation would be to have a small range of disperse dyes which, when used to produce any colour on polyester, give even, on-tone build-up to give a dyeing of acceptable fastness. These dyes would be expected to give level dyeings in any dyeing system and to offer savings in time and energy by facilitating the design of an optimum dyeing process.

When formulating compatible recipes for any given colour using the V number system, it i s essential to arrive at a recipe in which all the components have a similar V number. Because the V number is primarily dependeni on the depth of dyeing, it i s fundamentally impossible to obtain a "trichromatic" combination of homogeneous dyes which will be compatible when used to produce a wide range of colours.

JSDC Volume 96 May 1980 241

Taking the more simple case of recipes based on a yellow

(a) With a yellowish green, the blue being present in

(b) with a neutral green, the two dyes may be compatible

(c j with a bluish green, the yellow being present in lower

and a blue dye, it i s possible that

lower quantity may be absorbed more rapidly

and build-up may be on tone

quantity may be absorbed more rapidly.

It i s conceivable that if, instead of using a single yellow and a single blue, one were to use three yellow dyes, whose V numbers a t the relevant concentrations differ significantly, and three blue dyes, whose V numbers differ in like manner, the V numbers of the yellow element as a whole could overlap with the V numbers of the blue element as a whole. If this were the case one might expect some improvement in compatibility compared with (a) and (c) above.

For the sake of clarity, it i s convenient to call mixtures of dyes of similar hue 'primary' combinations. It should be possible to produce yellow, red and blue primary combina- tions, mixtures of which could then be used to reproduce a given colour and, if the theoretical conclusions are valid, dyeings of these mixtures should build-up reasonably on- tone. These suppositions were investigated by studying the V numbers of al l YCL disperse dyes a t a range of depths, and primary combinations were formulated based on dyes whose V numbers range from relatively low to relatively high. Examples of the range of V numbers of individual com- ponents within the stated percentage depths of three such primary combinations are given in Table 5.

TABLE 5

Range of V numbers in Primary Combinations

Primary Combinations 0.1% 0.5% 2.0%

Yellow I 2.3-+5.2 1.W4.5 1.7+3.6 Red I 3.7+5.0 2.W4.1 2.W3.5 Blue I 3.4-+5.1 1.W4.1 1.5+2.8

Since the individual components are deliberately picked to have different V numbers, and hence different critical dyeing temperatures, it i s impossible to assign a V number as such to the primary combinations, or a specific value for T,. For these primary combinations, it i s necessary to think in terms of a range of V numbers or of a broad band of critical dyeing temperatures. Incompatibility arises through large differences between V numbers, i.e. in rate of dyeing, of the individual dyes used for a particular dyeing, and these differences are likely to be reduced considerably when primary combinations having a broad band of V numbers, i.e. rates of dyeing, are used. A detailed investigation of the compatibility of primary combinations, such as those quoted in Table 5, was carried out by dyeing many tertiary mixtures of them on polyester fabric in a laboratory high-temperature dyeing machine a t a liquor ratio of 20:l. Dyeings were removed at 80"C, 90°C, 100°C, l lO°C, 12O"C, 130"C, and after 60 minutes a t 13OoC. After the fabric was removed from each pot, a furtherpiece of polyester fabric was entered and dyed for 30 minutes a t 130°C to indicate the amount of each dye remaining in the residual liquor - these are referred to as exhaust dyeings. Three tertiary dyeing were produced as follows:

The results of the compatibility tests are illustrated in Figure 8.

All these mixtures are seen to be very compatible, giving even, on-tone build-up through the temperature range, and in addition the exhaust dyeings show no marked hue change. The grey was also dyed a t a rate of temperature rise of 5'C/rnin and the result was just as satisfactory as the others carried out a t 1°C/min rate of rise. Thus, these three primary combinations gave good results in a range of colours where a great deal of careful formulation and matching would normally be required to obtain such compatible recipes, and, even with the aid of the V number system, it is almost certain that more than three dyes would be required overall.

JUST1 FlCATlON OF PRIMARY COMBINATIONS It might be suggested that the very good compatibility observed above is due simply to the increased number of dyes being used in the recipe, and that increasing, a t random, the total number of dyes used for a particular dyeing would result in a similar improvement in compatibility. This possibility was examined by studying the compatibilities of three recipes for each of two colours submitted by a customer. With these there were problems of unlevel dyeing, believed to be due to incompatibility in the customer's recipes. They were therefore rematched using -

(a) primary combinations as defined previously (b) alternative random combinations not chosen on the

basis of V numbers.

(These alternative combinations were mixture dyes, each containing a t least three components, and sold commercially as mixtures to obtain particular colours. Therefore, as regards V numbers, they are random mixtures, but are commercially acceptable mixtures and are not technically outrageous!)

The two colours were a brown and a beige, and the compatibilities of the various recipes were checked by carrying out a series of dyeings and sampling them a t various temperatures as described earlier. The results for the brown are shown in Figure 9 and for the beige in Figure 10. In each case, it can be seen that the original three component recipes were markedly incompatible, that the "random" combina- tions show a distinct improvement in compatibility, and that the use of carefully selected primary combinations has resulted in almost completely compatible recipes.

Further work was aimed a t determining just how carefully the primary combination must be chosen in order to give satisfactory results over a wide colour range. A number of other primary combinations were formulated, s t i l l using the V-number principle, but varying the range of V numbers covered by the components of a particular primary combination. Various colours were then produced using tertiary mixtures of several alternative primary methods described previously. On the whole, the results suggested that any primary combination so based would exhibit good compatibility with other similar primary combinations. However, some primary combinations are better than others in that they give almost perfect compatibility with each other. An example of this i s illustrated in Figure 11, where a brown was approximately matched with the following three recipes, in which the dyes in A and B are primary combinations -

Primary Recipe Combination Grey Old Gold Green

Yellow II 0.18% 0.7% 0.4% Red I 0.21% 0.12% 0.05% Blue I 0.48% 0.05% 0.5%

242 JSDC Volume 96 May 1980

A B C Yellow II 0.6% Yellow Ill 0.6% Serilene Yellow 3GL 150% 0.25% Red I 0.5% Red II 0.5% Serilene Red 2BL Blue I 0.2% Blue I 0.2% Serilene Blue RL

Recipe C was included to indicate the compatibility of a typical three-colour combination and uses three dyes which are often (wrongly) claimed to be compatible. It can be seen that recipe C is markedly incompatible, recipe B shows quite good compatibility and recipe A almost perfect compa- tibility. The spread of V numbers in these recipes is indicated diagramatically in Figure 12 which shows that the greatest degree of overlap of V numbers between the three elements occurs with recipe A.

Recipe A V Number Recipe B V Number Recipe 3

Figure 12 - Range of V number for three recipes for a brown dyeing

Although this theoretical type of approach, using such diagrams, proved very useful in helping to formulate the best primary combinations, it needed to be validated by actual compatibility tests. This is hardly surprising in view of the fact that the V number itself is an attempt to described a fairly complex rate-of-dyeing curve by means of a single parameter, and as such is not ideally suited for the ultimate "fine-tuning" of formulations of primary combinations. Nevertheless, it i s the V numbers of the individual com- ponents of the primary combinations which determine the overall compatibility of a particular recipe and thus the individual components have to be chosen with considirable care,

RATE OF DYEING OF PRIMARY COMBINATIONS The V number relationship is, as described earlier, deter- mined by actually measuring the rate of dyeing of an individual dye a t several depths (see Figure 4). If the rate curves for the individual components of a primary combina- tion are drawn on one graph, as in Figure 13, a considerable spread in dyeing rate can be seen. Figure 13 depicts the rate curves for the individual dyes in a 4-component yellow primary combination (each component dyed a t 0.06%). If the rates of exhaustion of the individual components a t a given temperature are averaged, it i s possible to use these points to construct a theoretical average rate-of-dyeing curve for the primary combination (dyed at 0.24% depth). This i s clearly not strictly accurate as it assumes equal colour value from a l l 4 components. However, the general shape does reflect the observed behaviour of the primary combination.

It was shown in Figure 1 that the rate of dyeing is very dependent on depth of dyeing. If one considers the 4-component primary combination shown in Figure 13, then the curve for a 0.24% dyeing of this Combination, which is in fact equivalent to a 0.06% dyeing of each individual dye,

0.65% 0.18%

1001

m

temperature - 1"C/min

Theoretical average for primary combination

n o o n 3 3 TirnelTemperature

Figure 13 - Rates of dyeing of components of a primary combination

should be more relevantly compared against the curve for a 0.24% dyeing of an individual dye. The 0.24% curve for the individual dye will l ie to the right (i.e. a t higher tempera- tures) of those a t 0.06%, as i s shown in Figure 4. Clearly it i s likely that a primary combination will exhaust a t lower temperatures than the equivalent amount of many individual dyes.

This point was examined further by measuring the exhaustion of a primary combination after dyeing for 1 hour at 11O"C, 120°C and 130"C, respectively. The results are shown in Table 6, where they are compared with comparable results for Serilene Yellow 5R (C.I. Disperse Yellow 71, a dye known to exhibit a particularly low degree of temperature sensitivity. It can be seen that, even a t this relatively heavy depth, the primary combination shows only slight reduction in yield at the lower temperatures.

TABLE 6

Effect of Dyeing Temperature on Yield

% Exhaustion after 1 hour a t 110°C 120°C 130°C

3% Yellow II 87 91 95 3% Serilene

Yellow 5R 90 91 92

Although other primary combinations show rather greater temperature sensitivity than that of Yellow II, it does appear to be the case that primary combinations generally respond to time and temperature variations during applica- tion in a similar manner to equivalent depths of "low energy" dyes rather than of "high energy" dyes, even though they may contain a "high energy" component. This is presumably because the individual components are absorbed independently, and each is present in relatively small amount.

Nevertheless, as with a l l polyester dyeing, it is necessary to dye for sufficient time, a t a sufficiently high temperature, in order to obtain a degree of filament penetration which will ensure the expected colour yield and colour fastness.

JSDC Volume 96 May 1980 243

FASTNESS PROPERTIES OF PRIMARY COkIBINATIONS The components of primary combinations are chosen primarily on the basis of their dyeing rates, as indicated by their V numbers. It is almost certain that a satisfactory primary combination will contain dyes differing widely in fastness properties - particularly as regards sublimation fastness - because this tends to be closely associated with dyeing rate. It is very unlikely, therefore, that primary combinations can be produced which have the highest level of sublimation fastness. Other fastness properties, such as light, washing and perspiration, can, however, be taken into account to some extent when formulating a primary com- bination, although the optimum spread of V numbers remains the primary consideration. Table 7 gives some indication of the fastness properties of the three most widely used primary combinations. The 2% dyeings are usually slightly stronger than 1/1 standard depth and it is apparent that fastness properties are generally good up to this depth of dyeing.

INDUSTRIAL USE OF PRIMARY COMBINATIONS Problems of unlevelness or poor colour reproducibility of dyeings on polyester tend to be most prevalent with pale-to-medium-depth dyeings using three-colour combina- tions. It is in exactly such circumstances that the primary combinations described earlier might be expected to be of the greatest advantage. The on-tone build-up in a wide range of colours and the relatively low degree of temperature sensitivity tend to reduce the risk of either of the above faults occurring. By contrast, deep dyeings, such as navy blues and blacks, rarely exhibit unlevelness and dyes tend to be chosen on grounds of fastness properties or economy.

Industrial trials have therefore been concentrated on producing pale-to-medium-depth dyeings on piece, and have sought to exploit the advantages of primary combinations, either to overcome unlevelness or to use a rapid dyeing cycle. An example of the first type was the dyeing of a warp-knit textured polyester fabric on a pressure beam dyeing machine to a medium olive-brown. Unlevel results had frequently been obtained using a normal three-colour combination, and it was therefore rematched using primary combinations a t about 4% total depth. The new recipe gave level and satisfactory results in bulk and the on-tone build-up was confirmed by taking liquor samples a t intervals throughout the dyeing and carrying out exhaust dyeings. An example of a successful "rapid dyeing" was the dyeing of a pale fawn, matched with primary combinations a t about 0.2% total depth, on a Ventura Sprint jet-dyeing machine. The cycle

TABLE 7

Fastness Properties on Textured Polyester, Dyed a t 130OC. Reduction-deared a t 7OoC, and Stentered a t 160°C for 30 seconds before Testing

Sublimation

Dyeing (Xenon) CS PES Dye % Light 30 s @ 18OoC

Yellow II 0.2 6 5 5 2.0 6-7 5 3-4

Red I 0.2 5-6 5 5 2.0 6 5 4

Blue II 0.2 5-6 5 5 2.0 6 5 4

Washing I S 0 3

CS PA66

5 5 5 4 5 5 5 4-5 5 5 5 4

used is shown in Figure 14 and it can be seen that a 4"C/min rate of rise was employed, The total dyeing cycle was about 100 min and a level dyeing was achieved which also had the required fastness properties despite the shortened dyeing cycle.

20 + I 1 r 0 40 80 120 160 m

Time, min

Figure 14 - Rapid dyeing cycle on Ventura Sprint

Similar results with other colours have been obtained on different types of fabric in different types of machine. A wide range of dyeings has been produced, which have a l l exhibited a high degree of on-tone build-up, and for the most part only the three primary combinations quoted in Table 7 have been used viz. a golden yellow, a neutral red and a bright, but reddish, blue, and it has therefore been useful to formulate a fourth primary combination, a greenish-yellow, in order to obtain brighter greens than was possible with the golden yellow.

CONCLUSIONS It has been shown that the rate of dyeing of an individual, essentially homogeneous, disperse dye is very dependent on depth of dyeing and that it i s practicable and useful to characterize the rate of dyeing a t a particular depth by a single parameter (the V number) which i s based on time of half dyeing. If, in a given recipe, the component dyes have similar V numbers then the mixture will be rate-compatible and will build-up on tone. Furthermore, this predictability of compatibility has been shown to be largely unaffected by considerable changes in the dyeing conditions employed. These observations support the generally held belief [6,71

Perspiration PH 8

PES PA66

5 5 5 4-5 5 5 5 4 5 5 5 4-5

Notes: CS - Change of colour of dyeing PES - Staining of adjacent polyester PA66 - Staining of adjacent nylon 6.6

244 JSDC Volume96 May 1980

that disperse dyes applied in mixture behave essentially independently of one another.

It i s therefore evident that no combination of (say) three individual dyes of different colour can build up on-tone over a wide range of colours, i.e., where the relative concentration of the individual components vary greatly. It is, however, possible, from a knowledge of V numbers, to formulate rate-compatible recipes which will give on-tone build-up, although this entails the use of a large number of individual dyes and preferably the availability of instrumental match prediction or a well-stocked shade file.

An alternative approach is to prepare primary combina- tions of dyes of similar colour but of different dyeing rates [8]. This can best be done by studying the V number versus concentration (depth of dyeing) graphs for dyes of approxi- mately similar hue. It has been shown that when such primary combinations, e.g. yellow, red and blue, are used in mixtures, then on-tone build-up can be obtained over a wide range of colours. Thus a dyer need use, and stock, only a few primary combinations (say 3 or 4) in order to be able to match a wide gamut of colours and yet be confident of achieving on-tone build-up.

It has also been shown that such primary combinations dye quite quickly a t relatively low dyeing temperatures and give good exhaustion in relatively short times. These pro- perties are assumed to be due to the fact that the individual dyes, which form the basis of the primary combinations, are present in relatively small quantities as compared with a normal three-colour combination.

The combined advantages of on-tone build-up and relatively rapid exhaustion a t temperatures below 130°C means that primary combinations are very well suited for rapid-dyeing cycles. This is particularly true for the often difficult area of pale-to-medium mode colours and their use can lead to significant savings in time and in energy used for a given dyeing.

REFERENCES 1.

2.

3.

4.

5. 6. 7.

8.

Report of the Committee on the Dyeing Properties of Wool Dyes, J.S.D.C., 66 (1950) 213. Basic Dyes on Acrylic Fibres Committee, ibid., 88 (1972) 220. Report of the Committee on the Dyeing Properties of Disperse Dyes, ibid., 93 (1977) 228. Saville, Tandy and Walsh, Book of Papers, A.A.T.C.C. National Technical Conference, 1974. Siegrist, Rev. Prog. Coloration, 8 (1977) 24. Beckmann and Brieden, Chemiefasern, 20 (1970) 553. Tandy and Schuler, Dyes and Chemicals Technical Bulletin (Du Pont), 29 (Dec 1973) 114. British Patent Application, 25144/78.

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