Silk Fibre Dyeing

Dyeing of silk fiber

 Like wool, silk is a protein fibre and can therefore be dyed using the same methods as for wool dyeing (Õ Dyeing of wool). As silk is considerably more resistant to alkali than wool, dyeing processes which are carried out under weakly alkaline conditions are also used. In this regard, it must also be borne in mind that under alkaline conditions, high temperatures and conditions of high mechanical stress at the same time, individual fibres (fibrils) can split away from the silk filaments giving the material a fluffy and rough appearance. Compared to wool, silk also has a distinctly lower affinity because of its weaker acid binding capacity. Additional factors influencing the affinity of silk are its origin, extent of degumming, the yarn quality (tram silk, organize) and whether the silk has been weighted or not. In general, it can be said that under the same dyeing machine conditions, level dyeing are less problematic to produce on silk than on wool. The dyeing temperature should not exceed a maximum of 80°C since temperatures at the boil have a negative influence on the luster and handle of silk.

Silk is dyed in all its commercial forms but is best dyed in the form of hanks (yarn) and piece goods. In principle, all the well-known types of dyeing machine can be used if they have been suitably modified to take into account the sensitivity of silk to tension and mechanical stress.

The most important types of dyeing machine for silk fibre dyeing include:

Hank dyeing machines: no hank deformation (with double stick systems), no filament splitting, level dyeings obtainable provided the rate of liquor circulation is adequate;

Spray type dyeing machines for hank yarn: good liquor circulation and therefore hardly any leveling problems, hank deformation and filament splitting is possible; particularly suitable for high-twist and folded yarns;

Package dyeing machines for cross-wound packages: short liquor ratio, no levelling problems with adequate liquor circulation, no filament splitting, uniform winding of packages important because of the risk of channeling;

Star frame dyeing machine: suitable for all types of woven silk fabrics, no chafe marks, low productivity, high energy and water consumption (liquor ratio 100–300:1);

Winch dyeing machine: good levelness is possible, high productivity, average liquor ratio, high risk of chafe marks,

Jigger dyeing machine: high productivity possible, extremely short Dyeing of polyester/polyester copolymer liquor ratio, risk of moiré formation, good leveling resp. slow-exhausting dyes are an advantage here;

Jet-dyeing machines: good levelness, high productivity, short to medium liquor ratio, especially suitable for jersey and crêpe fabrics (due to the virtual absence of fabric tension), possibility of chafe marks;

Beam dyeing machines: good to excellent levelness, short liquor ratio 10–20 : 1, no chafe marks, especially suitable for heavy and smooth silk qualities, risk of moiré formation.

Tab.: Fields of application, advantages and disadvantages and fastness properties of various dye classes suitable for dyeing silk.

Practically all classes of dye can be used for colouring silk (see Table). There is hardly any other textile fibre for which this is possible. Nowadays, silk fibre is mainly dyed with direct, acid, metal-complex or reactive dyes.

 Metal-complex and acid dyes for silk: from the dye classes listed in the Table the 1: 2 metal-complex and acid dyes are the most important in practice. Apart from a few exceptions in the acid dye range, they can all be applied from a weakly acidic bath (Fig. 1) and exhibit good levelling properties. By careful selection, all fashion shades, including those specific to silk, can be dyed although, from time to time, the colour fastness has to take second place. Thus, for the brilliant shades, red, blue, turquoise and green, often only moderate light fastness ratings and, in deep shades, only moderate wet fastness ratings are achieved (e.g. colour fastness to water severe, alkaline perspiration and washing at 40°C).

Fig. 1: Method and dyeing recipes for dyeing silk with metal complex and acid dyes (Ciba-Geigy). - - pale shades;  dark shades

Reactive dyes for silk: These are being used to an increasing extent (Fig. 2). They are characterised by their brilliance, high degree of fixation, high light fastness and outstanding wet fastness properties. In general, they are not very substantive although differences exist between the individual types. Consequently, the aim should be to use the shortest possible liquor ratios for these dyes. Dyeing is carried out first of all in a neutral bath with the addition of sodium sulphate at tempera tures of 60–70°C, with the exception of black dyeing which are dyed at 90°C. Only in the last 15–20 min. at the end temperature is an addition of sodium carbonate made to adjust the pH of the dyebath to 8–8.5 for dye fixation. After rinsing, the dyeing must still be soaped in order to remove the unfixed dye which is not covalently bound to the substrate (source: Flensberg and Hammers).

Wish you good luck-------------------------------------------
You Should read more related post to gain more knowldge.

Polyester and natural fibre dyeing | Blebds Dye

Dyeing of polyester fibres

-->

Polyester fibres are hydrophobic, have a very low swelling capacity and, with the exception of copolymer fibres, have no reactive groups and no affinity for water-soluble dyes. Dye accessibility must be achieved by the addition of carriers or the use of high temperatures (Õ High-temperature dyeing). The heat-setting of polyester before dyeing has a considerable influence on dye affinity, especially in exhaust dyeing with carriers. Oligomers also have an effect on the dyeing results. Exhaust processes are of importance for disperse dyes and naphthol-based diazo combinations. In continuous dyeing processes, pigments are used for pastel shades whilst vat and vat leuco ester dyes are likewise only used for pale shades. In general, disperse dyes are applied by the heat-set thermofixation process. For dyeing polyester loose fibre and card sliver, HT circulating liquor dyeing machines with the material press-packed into cages are used; card sliver can also be dyed by continuous methods. Smooth yarns in the form of cross wound packages and textured yarns in the form of cross-wound muffs loaded on to spindles are likewise dyed in HT circulating liquor dyeing machines. For woven and knitted fabrics, HT winches or HT jet and HT beam dyeing machines are available. Thermosol plants are used for the continuous dyeing of woven fabrics. Polyester copolymer fibres (modified polyester) contain anionic groups and can therefore be dyed with cationic dyes as well. Optimal batchwise polyester dyeing processes are characterised by coordinated temperature control and liquor circulation. In this connection, it should be noted that an increased rate of liquor circulation leads to improved levelness. As a result, the critical rate of dyeing increases in proprtion to the rate of liquor circulation. However, an increased rate of liquor circulation through the textile material only leads to optimum levelness up to a certain limit. Moreover, with increased liquor throughput, increasingly unlevel results are observed. The conditions for this minimum unlevelness are to a large extent independent of the rate of heating.

Dyeing of acrylic polyester blends Single-bath and two-bath exhaust processes are used with disperse dyes for the polyester and cationic dyes for the acrylic fibres.

Dyeing of cotton or regenerated cellulose and polyester blends

These mixtures occupy a very large share of the market, and the blend ratio is nearly always 67% polyester and 33% cotton; with regenerated cellulose, the ratio is often 70 : 30 in many cases.

Disperse dyes are almost exclusively used for the polyester component and reactive, vat, vat leuco ester or sulphur dyes for the cellulosic component. Direct dyes are used only occasionally. In most cases, a tone-in-tone dyeing of both types of fibre is required, for which special ranges of pre-mixed dyes are available from different manufacturers. The formulation of these mixed dyes has been fine-tuned so that both fibre components can be dyed to the same shade by exhaust as well as continuous dyeing methods.

I. Exhaust method: for the dyeing of yarns this process is only of secondary importance. Dyeing is carried out on cross-wound yarn packages or warp beams by the single-bath single-stage or single-bath two-stage process. Direct dyes can be used for cotton in the single-bath single-stage process provided they have sufficient resistance to carriers. With the single-bath two stage process, the cellulosic component is dyed first in the case of reactive dyes whereas the polyester component is dyed first in the case of vat dyes. In two-bath processes, the polyester is likewise dyed first followed by the cellulose with appropriate dyes for each fibre.

Where the cellulosic fibres are too heavily stained with the disperse dyes, an intermediate reduction clear with dithionite must be given (as well as for processes involving the use of carriers in order to remove carrier residues). The exhaust method is also used for light weight woven fabrics as well as knitgoods. Dyeing equipment as for 100% polyester fabrics.

II. Continuous method: this process is used for all other qualities and offers numerous possibilities. Intermediate drying is critical as a certain amount of dye migration can take place at this stage. Most of the disperse dye on the cellulose is transferred by diffusion on to the polyester component during thermofixation.

Polyester natural silk blend Dye

The polyester component is dyed first with disperse dyes in a single-bath two-stage or two-bath process, followed by an intermediate reduction clear if necessary. Finally, the silk is dyed with acid dyes.

Polyester or polyester copolymer (cationic dyeable) Dyeing

This mixture is only seldom encountered. Disperse dyes are used for the polyester and cationic dyes for the modified polyester fibres in a single-bath two-stage or a two-bath process. For continuous dyeings, the modified polyester fibres are pre-dyed with cationic dyes on the pad-steam range, then disperse and vat dyes are applied on the padder followed by thermofixation and development on the pad-steam range. In the knitgoods sector, two-colour effects are produced as well as solid shades. Acid-modified polyester with a high rate of dyeing: carrier-free dyeing at the boil with suitable disperse and cationic dyes.

Dyeing of wool and polyester blends 

The blend ratio is mainly 55% polyester and 45% wool. For the highest quality it is recommended to dye each fibre separately.

Optimum fibre protection is not possible. As there is nothing to be gained by two-bath dyeing, it has been substituted by single-bath processes. A major disadvantage in dyeing this fibre blend is the fact that disperse dyes result in a more or less pronounced staining of the wool component and this staining has no colour fastness to speak of. A strict selection of those dyes which exhibit the least possible staining on wool is therefore necessary. Dyeing is carried out by the exhaust process at 105–107°C if possible, and with reduced amounts of carrier. Disperse dyes are used for the polyester and 1 : 2 metal-complex dyes for the wool. Pre-mixed dyes are also available from a few manufacturers.

Dyeing of polyvinylchloride (PVC)

 fibres Polyvinylchlorid fibres are mainly dyed with disperse dyes. Cationic or metal-complex dyes are also frequently used. Pigments are seldom and naphthol dyes only occasionally used. The dyes must be carefully selected and, depending on the type of fibre, are dyed with or without the addition of a swelling agent (carrier) or dyeing is carried out under HT conditions, whereby polyvinylchloride filament yarns have a considerably lower dye affinity than polyvinylchloride staple fibres.

Dyeing of regenerated cellulose fibres

(Viscose, cupro fibres, high wet modulus /polynosic fibres). In principle, all dyes used for dyeing cotton are suitable for dyeing regenerated cellulose fibres (Õ Dyeing of cotton). The most important dyes are substantive and reactive dyes, with preference being given to hot dyeing types. The affinities of fibres produced by various manufacturers differ and can even vary from batch to batch from the same manufacturer. Textiles made from these materials are sensitive to pressure, friction and tension and this must be taken into account during the dyeing process. A well-known fault is the streaky appearance of woven or knitted fabrics due to slight variations in fibre manufacture. This streakiness can be avoided to some extent by selection of suitable dyes. The pronounced swelling properties of these fibres must be taken into account from the dyeing kinetics point of view (exothermic swelling) so that a fibre specific processing sequence is necessary.


Wish you good luck-------------------------------------------
You Should read more related post to gain more knowldge.

-->

Dyeing of jute, flex, modacrylic, polyamide fibres and their blends

Dyeing of hemp fibre

 This is of no significance as the products manufactured from hemp fibre are almost exclusively used for technical textile purposes (fire-engine hoses and belts, etc.).

Dyeing of hat trimmings of straw, panama and Sisal for hemp

1. For dyeing straw: acid and 1: 1 metal-complex dyes

2. For dyeing panama: disperse and cationic dyes

3. For dyeing sisal: direct, acid, and 1: 1 and 1: 2 metal complex dyes.

Iridescent effects by piece-dyeing

 A prerequisite is that the warp and the weft have different affinities – usually acetate/triacetate or triacetate mixtures. Single-bath dyeing can be carried out with direct and disperse dyes, usually giving contrasting shades.

Jute fibre Dyeing

The jute fibre dyeing is similar like cotton fibre dyeing.  The high proportion of non-cellulosic material gives jute an affinity for cationic dyes (mordant unnecessary) and acid dyes. Unlike cotton, jute is sensitive to alkalis. The light fastness of jute dyeings is poorer than on cotton.

Dyeing of leather(goods) Because of the wool like chemical nature of leather, appropriately modified dyeing methods are used depending on the type of tanning process. The usual treatment with aqueous dye solutions given to new articles (by brushing on or dipping) has only a limited application for second-hand goods (garment dyeing). For expediency, dyeing is carried out using tried and tested commercially available

Dyeing of linen (flax) fibre

 In principle, dyeing is carried out using all the dye classes that are suitable for cotton (Õ Dyeing of cotton). Dye penetration is generally more difficult, especially in the case of vat dyes. The best penetration and levelness is achieved with reactive dyes.

Loose material (loose stock, loose fibre) Dyeing, 
Advantages: Any unlevelness in dyeing is evened out during the subsequent spinning process, large quantities can be produced to one shade by blending several batches and a low liquor ratio is possible in dyeing.

Disadvantages: satisfactory processing in spinning isusually only achieved through the application of spinning oils and dressings. The spinning of coloured yarns demands total separation of different shades in spinning and laborious cleaning is necessary when changing colours. Unavoidable co-processing of short fibres and dyeable impurities. Continuous dyeing can be carried out by a pad steam process (e.g. the Smith Piston Pad Dyeing Machine).

Dyeing of modacrylic (acid dyeable) and wool fibre blends

This modacrylic and woo fibre blend can only be dyed in solid shades with dyeing difficulty because of the considerably higher affinity of the acid dyes for the wool fibre component. The best possible solid shade dyeings are achieved with the Chem Acryl process and other process variants (manufacturer: Chemstrand Corp., Decatur, Alabama/USA).

An addition of the following dyeing auxiliaries is necessary: cationic and non-ionic dyeing assistants which retard the exhaustion of selected acid dyes and bring about a satisfactory balance between the dye on both fibre components in the sulphuric acid bath.

Modacrylic fibre dye

Dyeing of ombré or shadow effects, shadow dyeing on one and the same hank, e.g. by hand using square or U-section rods. Firstly, the palest colour is dyed from a full vat dye then, after dropping a little of the dyebath, a dye addition is made and a somewhat darker shade is dyed – this procedure is repeated with the increase in depth of shade becoming less and less as ever smaller additions of dye are made. In this way, light to dark shadow effects of the same colour, i.e. so-called tonal gradations, are obtained. Ombré variations are produced by using different dyes. Excellent ombré dyeing are obtained on thoroughly pretreated dry goods by employing a material-specific dye selection (hot and cold dyeing types and no pre-mixed dyes if possible) as well as the absence of wetting agent (undesired upward migration of dye) with, if necessary, controlled additions of salt and temperature regulation. The most efficient results are obtained on the hank dyeing machine where good dye penetration is achieved by raising and lowering the entire yarn carrier assembly. With increasing depth of shade, the hanks are lowered to a lesser and lesser extent into the dye liquor which is correspondingly increased in strength with additions of dye. By dropping the liquor level approx. 5 cm for each individual shade a reduced depth of immersion is achieved.

After reaching half the original bath volume, the yarn carrier assembly is lowered to a reduced depth. For piece goods, dyeing on the star frame is very practical (star dyeing machine) by continually raising and lowering the frame with the aid of a beam assembly (a cable running over a boom-arm); this method has proved particularly suitable for sensitive qualities (e.g. pure silk).

Polyamide fibre dye

Various dye classes of dye are suitable for dyeing polyamide fibres, and dye selection is based on the form of the material, the fastness requirements and the dyeing properties.

I. Disperse dyes: these dyes have good affinity and levelling properties. Affinity differences in the fibre are easily levelled out. The wet fastness properties of medium to deep dyeings are unsatisfactory.

II. Acid dyes: the most widely used class of dyes for dyeing polyamide fibres. They offer a wide colour gamut and good fastness properties, especially following an aftertreatment with products to improve the wet fastness. For combination dyeings it is essential to use dyes with similar rates of exhaustion. The selected dyes must not exhibit any blocking action. In order to cover up affinity differences in the material, anionic leveling agents, which possess an affinity for the fibre, are used in the dyebath.

III. Metal-complex dyes: these dyes have good light and wet fastness properties. Their use is limited (except for black) since differences in the polyamide material cannot be levelled out in most cases. Fastness properties can be improved with a tannin/tartar emetic (potassium antimony(III) tartrate) aftertreatment. IV. Metal-containing disperse dyes: the fastnesses properties are the same as those of the metal-complex dyes. Material-dependent affinity differences are largely covered in dark shades. Improved fastness properties are possible with a tannin/(tartar emetic) (potassium antimony(III) tartrate) aftertreatment.

V. Reactive disperse dyes: dyeable as disperse dyes; chemical bonding with the fibre takes place following an alkaline aftertreatment thereby giving good wet fastness properties.

VI. Direct dyes: the selection is limited: used chiefly for reasons of shade and price.

VII. Naphthol dyes: of no importance.

VIII. Chrome dyes: of interest only for black shades (applied by the so-called Metachrome process in which dye and mordant are applied simultaneously from a single bath).

IX. Reactive dyes: the light fastness of these dyes varies appreciably on polyamide. Wet fastness properties are good. Any affinity differences that may arise are not covered in all cases. Combination dyeings are only possible to a limited extent. The build-up is also limited.

X. Logwood black: This dye is of interest for reasons of shade and fastness but, the method of dyeing is very involved.

Wish you good luck-------------------------------------------
You Should read more related post to gain more knowldge.