Advancements in Reactive Textile Dyes

Development in the Dyeing Process

Trichromatic Dyeing by the Exhaust Process

Economic consideration, equality and ecologist and ecological arguments are the major factors about the ideal dyeing process and optimum dyestuff selection.

In the dying process, over 60% of reactive dyes are applied by the exhaust dyeing method. The remainders are applied by padding. The selection of the basic trichromatic system is of fundamental importance to dyers when they select their reactive dye range for the exhaust process. Combining a yellow, a red and a blue dye can dye a wide range of shades.¹⁸

Another major demand made for the trichromatic combination is good reproducibility, both when recipes are transferred from the laboratory to pilot or bulk. Condition and from one batch to another, even of dying here to be performed on different units and dyeing conditions cannot be dyeing be held constant.

To sum up, the main demands made in trichromatic reactive combination are reliable dyeing results, high cost-effectiveness, good reproducibility of shade even if dyeing condition vary, good levelness, good fastness properties flexible possibilities of application.

The new Remazol trichromatic system comprises:

• Remazol Yellow RR
• Remazol Red RR
• and Remazol Blue RR

These dyes are supplied as low dusting granules which are free-flowing and are suitable for use on automatic dosing units and for manual addition.

Remazol RR dyes have very good build-up on cotton and regenerated cellulosic only small dyes amount are needed to dye deep shades. The good build-up of these products makes them highly economical Remazol RR dyes can be used to dye a wide range of shades including a large number of trichromatic fashion shades. As well as being suitable for medium and deep shades, in many instances, Remazol RR dyes meet the requirements made on pale shades.

Homogeneous Exhaust Dyeing Behaviour

To achieve optimum reliability and reproducibility of dying, two main criteria have to be met.

• The best possible balance needs to be found between the properties of the trichromatic combinations, that is substantive, diffusion properties fixation behaviour and washing-off properties.
• Normal fluctuations in dyeing conditions should not affect reproducibility.

The hydrophilic sulpho groups in the masked reactive group and hydrophilic groups in the chromophore give the Remazol RR dyes excellent solubility. They can, therefore, apply also in ultra-short liquor ratio.

In standard dyeing condition in a neutral liquors ratio is like 2 % dye, 50gpl salt, liquor ratio 10:1, and at 60⁰C. Remazol RR dyes have medium substantively. The dyes have very good diffusion properties in fibres. This ensures good penetration of the foods and thus level of dying, an equilibrium between substantively and diffusion is achieved very quickly so the neutral dyeing phase can be relatively short.

Since Remazol RR dyes are only moderately reactive, since the dyes have exhausted on to the fibres they have enough time to migrate into them, even in alkaline conditions before fixation occurs. Progressive dosing of alkali can be used to regulate the second exhaustion phase and fixation rate. It is not easy to give fixation data, which is, depends on the dyeing conditions. As a rule of thumb the lower the dyestuff concentration, the higher the salt load, the shorter the liquor ratio and the higher the affinity for the goods to be dyed the higher the fixation yield.

The relatively small amount of dyestuff required to dye specific shades and the comparatively high fixation yield is positive ecological attributes and help minimize the cost of wastewater treatment.

Dyeing Procedure

Progressive addition of the alkali has a significant impact on dying and allows optimum regulation of the exhaust process. This does not apply to vinyl sulphone dyes. The advantages of the automat system are now well known. Optimum fixation profile, excellent reproductively, excellent levelness, shortness dyeing times, automated dyeing process, fever rejects and fever operators required. The temperature of dying is adjusted at 60⁰C. Following pretreatment of the goods, the salt and auxiliaries are pre-run in the bath and dyes are the entered into the liquor using a miner dosing system. After a short diffusion phase, the alkali dosing programmed can be started. This should be followed by a final fixation period.

By varying dyeing parameters such as the salt load, type and amount of alkali, addition profile and duration of individual steps in the dying process, the dyeing method can be adjusted to suit virtually all article qualities and depths of shades, including articles made of regenerated cellulosic fibers such as viscose, modal, polynosic, lyocell and cupra.

The fixation yield obtained with Remazol RR dyes is roughly the same when using both soda ash \ caustic soda solution and soda ash on its own. A combination is used in Europe because alkali costs are lower, the procedure is relatively simple and advanced dosing technology is available.

By contrast, most dye house in Asia still use traditional dyeing methods, that is soda ash is as used as the fixation alkali. In this region, the use of a caustic soda solution is frequently rejected on safety grounds because the alkali is added manually.

All this show that the Remazol RR trichromatic system is a convincing and cost-effective solution.

After Treatments

The high fixation yield of Remazol RR dyes means that only small amounts of hydrolysate need to be washed off. Since second exhaustion is generally over 90% most of the hydrolysate is removed with the dye liquor when it is drained out of the bath. The first after treatment bath serves two purposes: it reduces the salt concentration, then by reducing the substantivity of unfixed dyestuff, and washes off the alkali. In the second bath, the goods are acidified to prevent partial hydrolysis fixed dyes during the subsequent soaping stage.

The hot bath brings the unfixed dyes to the surface of the fibre so that they can be washed out and removed with the liquor when it is drained from the bath. Because of the low quality of hydrolysis and the good washing off properties of Remazol RR dyes, after treatment to obtain the required level of wet fastness can be performed quickly and requires relatively little energy and water.

Fastness Properties

With Remazol RR dyes, it is possible to obtain fastness properties that are the demands normally made on sports and leisure wear. Here two features of the fastness property outline.

• Lightfastness: Remazol RR dyes have unusual properties when exposed to light although the dying light fastness somewhat, the basic shade remains unchanged. This is an advantage for dyes and end user alike and means that the light fastness of pale shades is acceptable for most articles. For example, If Remazol Blue RR is replaced by Blue dye with high lightfastness such as Remazol Brilliance BB the dyeing exhibits of shade after exposure to light and is no better than the result obtained with the original dye.
• Stability to Acids: The dyestuff-fibre bond formed by Remazol RR dyes is extremely suitable to acids. So Remazol RR dyes are ideal for dyeing Polyester/Cellulose by the reverse dyeing process.

Low Salt Reactive Dyeing

A new range of reactive dyes for cotton based on the very well established bifunctional Sumifix Supra dyes from Sumitomo offers the two advantages of excellent exhaustion and fixation and is suitable for a low salt application. ¹⁹

With the increase of reactive used it has become necessary to counter the damage by reactive dyeing there is a large volume of coloured wastewater due to low exhaustion and fixation and high salt content is wastewater from large quantities of salt and alkali.

As well as environment pressure the production cost needs to be reduced where possible without compromising overall productivity.

The advantage of low salt dyeing includes:

• High productivity
• Low dyeing cost
• Good levelling
• Good migration
• Easy wash-off

The advantage of new dyes is that they show a very small variation in fixation and exhaustion at conventional and low salt application. All have similar for selecting product suitable for a low salt application.

The reduced quantities of salt required to enable the optimum method of addition of salt to be selected. When adding 50gpl salt, machine limitation often force pre-salting this can cause unleveled dyeing. In critical cases where liquid salt addition is necessary the lower quantities make it possible without altering both volumes greatly. Low salt addition saves time and assist level dyeing and result in less re-dyes.

Low salt dyeing is also easier to wash off in comparison to those dyeing carried out a conventional quantity of salt. This is because the washing off the property of reactive dyes is related to it’s substantive to cellulose the lower the substantively the easier. It is to remove the hydrolysed dyestuff easier washing off save time. Basically, a saving of salt between 30% and 50% is possible.

There are two methods that can be used for law salt dyeing.

Temperature Raise Method

This method gives higher dyeing affinity than adding the salt at a high temperature. This method produces the highest colour yield due to the gradual build-up with the increase in temperature.

Constant Temperature dyeing method

This method to decreased affinity at a high-temperature result improves the migration. This dyeing method is suitable for high-density fabric and yarn dyeing.

The range of Sumicix, EX-F and HE dyes, plus some other Sumfix Supra dyes suitable for low salt application is as follows.

Other ranges of low salt reactive dyes are as follows:

CIBACRON LS range

This range utilizes several different reactive groups in a number of different arrangements.²⁰ the bulk is bifunctional, usually bis-monoflurotrizines ^21,22. Other groups or combination of groups are also used, including monoflurotriazine and monochlorotriazine in combination with vinyl sulphone as well as a trifunctional dye.⁶

As is usual with batch wise dying of other reactive dyes, the CIBACRON dying is applied in the presence of an electrolyte, albeit reduced levels, typically for 30 min, followed by addition of alkali to effect fixation, generally over 60 min.

Remazol EF range

These dyes are essentially conventional vinyl sulphones. This particular reactive group is somewhat different from the halotriazine, which is generally less substantive than the reactive dye itself, and easily wash out after completion of dying. In this dyeing two ureido groups have been claimed by Dystar to fix and to build up well in the presence of a reduced concentration of the electrolyte.²³ In this case, the ureido groups might be expected to contribute to increased substantively, leading to a lower salt requirement ⁶

No Salt Dyeing

Several approaches have been in vogue in practice to achieve optimum results:

• Use of high fixation reaction dyes
• Increasing the dye exhaustion

High fixation reactive dyes have several reactive groups and thus offers increased chances of dying of reactive dyes with dye-fibre bonding. However, for obtaining heavier shades it becomes extremely difficult to control the hydrolysis.

The fact that the fixation of reactive of reactive dyes on substrates containing amino groups is much higher than on cellulosic fibres has been responsible for initiating a large amount of work in introducing amino residues in cellulosic fibres.

Treating the cellulose with, for example, N-2-sulphatoethylpiperazine in a padding process, in the present of sodium hydroxide, and heating to 150⁰C  for 2.5 min achieve this. The resulting modified cellulose, possessing many covalently bound piperazine units, was then reacted with conventional reactive dyes without any additional alkali. ²⁴

Modification with glycidyl trimethylammonium chloride

Glycidyl trimethylammonium chloride or its precursor 1-chloro-2-hydroxy-3-trimethylammonium propane was used to modify cellulose.

The modification has been recommended in a pad-bake or in an alkaline pad-batch process. Since the structure (II) is predominantly prevalent the anionic sulfonated reactive dye is initially absorbed on to the fibre by ionic attraction to the quarternary ammonium residue.²⁵

Modification with N, N-dymethylazetidinium chloride (DMMAAC)

This DMMAAC fixes covalently to cotton by an alkali-catalysed pad-dry-bake procedure leading to the structure as follows:

Dyeing with Neutral Reactive Dye

Ordinary reactive dyes contain cyanuric chloride (halogen substitution dyes) react with cellulosic fibre by substitution reaction liberating strong acids eg. HCl, HF.

To neutralize as these liberated acids during dyeing and fixation process alkali is added.

Liberating salts are necessary as an acid binding process has various disadvantages for example; use of high concentration of alkali makes effluent containing a high concentration of chemicals in the dying of blends. Therefore process becomes time-consuming.

Thus if dyeing can be carried out at neutral pH, these problems can be minimized. As we saw before that Kayaceion reactive dyes to react with cellulosic fibre at neutral pH. It must contain the ammonium group as a reactive group and must be designed to increase the affinity for cellulose.

Dyeing Procedure

These dyes are dissolved in hot salt water. pH adjusted to 6.5 to 7.5 by adding a buffering solution. Glauber’s salt is added after dissolving dyes. The amount of Glauber’s salt required varies depending upon the concentration of dyes.

• 10 to 40gpl for a pale shade
• 40 to 80gpl for medium shades
• 80gpl for dark shades

Dyeing time and temperature depend upon the depth of shade and of dyeing machine, which can be normal Jigger or Jet dyeing machine. Dyeing can be carried at the desired temperature, for example, 80⁰C or 130⁰C as per the machine. If dyeing time is to be shortened fixation can be carried out in alkaline pH.

After dyeing rinsing with cold water, hot water rinsing soaping and again cold water rinsing is carried out to remove unfixed dyes. Cationic dyes fixing agents can be used to improve wash fastness properties for medium and dark shades.

As neural reactive dyes are applied at high temperature under neutral pH, a mixture of these dyes with disperse dyes are very suitable for dyeing of polyester/cotton in one bath. Other blends like acrylic/cotton, nylon/viscose rayon can be carried out in one bath.

Advantages of using neutral reactive dyes over conventional reactive dyes:

• Easy of dyeing proves by adding all dyes and chemicals prior to heating
• Levelling and fixation is better
• Excellent reproducibility
• Increased productivity
• Cleaner effluent and eco-friendly.

Short Time Dyeing

Currently undergoing extensive will test is a method to shorten the dyeing cycle.

The Sumifix Supra E-EC dyes have a high rate within an adequate contract of levelling and excellent dyeing compatibility in trichromatic combustion. These for it is possible to decrees the dyeing rate this is done by a split addition of a new alkali initial addition of soda ash 1 to 3gpl followed by the addition of the new alkali blend to increases the pH in the dye bath to approximately 12.5. This results in an increase in the dyeing even dark shade after 40 minutes in the alkali cycle rather than 60 minutes at pH 11.5.²⁶

All dyestuff suitable for low salt dyeing can be used in short time dying.

Wool Dyeing

As hydroxyl groups in cellulosic fibres, amino, a thiol and hydroxyl group in wool is a potential reactive system capable of incorporation in a reactive dye molecule.

Reactive dyes used for wool dyeing are of two types: a system that reacts by nucleophilic substitution reaction and those that react by the Michael addition reaction.

Specific reactive dyes for wool are as follows.²⁷

Reactive dyes current account for about 5 % if the wool dyes market. The largest dye group is the chrome dye class with 31 % of the market but globally there are increasing concerns about the environmental impact of the group of the dyes they have excellent fastness properties however and only the reactive class comes close in the regard.

New Reactive Range For Wool

Lanasol CE Range

The Lanasol CE range of wool dyes has been developed to give customers the option of cost-effectively replacing chrome dyes by metal-free reactive dyes. The range comprises a trichromatic system plus a black and navy blue dye, which can be used either alone or in combination with other dyes of the Lanasol range.²⁸

The Lanasol CE trichromatic system is based on the same α-bromo-acrylamide reactive group as the classic Lanasol range. Dyes are applied by standard Lanasol dyeing procedure and can be shared with other Lanasol dyes. This new system is a supplement for deep shades recommended whenever chrome dyes have to be replaced cost-effectively.

The range has been specially designed for wool dyeing. Excellence wet fastness, very good light fastness; high-cost effectiveness makes the dye particularly suitable for deep shades in replacement of chrome dyes.

The new Lanasol CE range consists of five new products, the trichromatic system comprising Lanasol Yellow CE, Red CE, and Blue CE and two further products Lanasol Navy CE and Lanasol Black CE.

Lanasol Yellow CE has brilliant slightly reddish yellow shade. The dye has good lightfastness and fair levelness. It is suitable for application at a temperature above the boil.

Lanasol Red CE has a brilliant red shade. Fibre levelness is fair to good. Although the dye has good solubility, it should not be dissolved at a temperature above 60⁰C.

Lanasol Blue CE has a dull green-blue shade. Lightfastness is good and levelness in the pale shade is moderate. The dye is suitable for application at a temperature above the boil. Unlike the other products of the range, Lanasol Blue CE is not dischargeable.

Lanasol Navy CE is the latest addition to the range. This is a cost-effective alternative to the navy dyes in the Lansol range. Its shade is close to that of Lanasol Navy B. it has good lightfastness, although that of Lanasol Navy CE is not suitable as a trichromatic dye or for blue. It can be used for dying at temperatures above the boil. It is suitable for discharge printing only with coloured illuminants.

Lanasol Black CE achieves deep black shades very cost-effectively. This dye is not suitable for trichromatic dyeing or for grey shades. Lightfastness is good. The dye is suitable for application at temperatures above the boil.

The dyeing procedure recommends a 15-minute temperature hold at 70⁰C for yarn and piece dyeing. For shrink-resist wool, a starting temperature of 30⁰C and a 15-minute temperature hold at 60⁰C are recommended.

Three auxiliaries are used in conjunction with the dyes. These are Albegal FFA, Cibaflow CIR, and Albegal B.

Albegal FFA has outstanding penetration-promoting action that ensures easy wetting and de-aeration of the goods. It promotes uniform liquor circulation and so improves levelness. The product is particularly recommended for use in circulating liquor dyeing machines.

Cibaslow CIR is a penetration accelerant for use in exhaust dyeing. It has a combined wetting, de-aerating and durable antifoam action. The product is particularly recommended for use in circulating-liquor machine and Jets.

Albegal B is a levelling agent. It promotes migration and has surface levelness on goods at all stages of processing and fibre levelness of tippy wool.

The advantages in the use of this new range are that combines cost effectiveness, high fastness and fixation, and thus excellent reproducibility.

Realan Range

Nearly 50 % of the reactive dye marked for two shades black and navy accounted for wool. To develop dyes for this shade, which performed to marked exception reaction, navy blue BG has excellent colour strength and is very economical. It is a metal-free Tungsten shade with high fastness properties. These two main dyes were complemented by the rest of the realan rang to cover a wide gamut.

These are large molecular acid dyes with two or three sulphonic group and a reaction system. This reactive group is able to form a covalent bond with an amino group of wool to gives the high fastness level.²⁹

These dyes are applicable to loose stock top yarn and price with very high fastness requirement. They are also especially suitable for the shrink to resist wool, as well as silk blends.

The dyeing method for Realan dyes on untreated wool uses the recipe:

• X gpl – Realan dye
• 1-2 gpl – Na-sulphate anhydrous
• Xgpl – Acetic acid 60%
• 1-2 gpl – Avolone Ren or 0.5-1 % engonal WR
• pH – 4.5-5

The auxiliaries and pH are set, the dye is added and the dye bath ramped at 1⁰C/Min to 98^oC/Min held at this temperature for 30 to 90 min after cooling, ammonia, after treatment is applied.

Both Realan black G gran and Realan navy blue BG, show excellent build-up and fixation on wool, compared with combative dyes. Top optimum fastness levels, it is essential to use ammonia after treatment with the black and navy dyes.

The trends toward ecologically safe textile and environmentally friendly textile processing had stimulated the development of a new range of reactive dyes for wool.

Realan reactive dyes range is as follows.