Thursday, August 5, 2010

Cotfix Bifuntional Dyestuffs - for better exhaustion - most suitable dyes for knits.

Cotfix Bi-functional Dyes

The poor exhaustion and fixation properties of Vinylsulphone dyes that lead to lot of dyestuff wastage have given birth to the bi-functional dyes with medium exhaustion and better fixation properties.

Bifunctional dyes have filled a big vacuum of various hues of bright shades, which were not possible with vinyl sulphone type. The dyes were conventional Dichlorotriazine type, with the end condensation of ß-sulphato ethyl sulphone to have different type of reactive group in a single molecule. Being a dual reactive, the primary mode of fixation is from vinyl sulphone group and the dyeing temperature is same as vinyl-sulphone, which enables good, inter compatibility in between the two classes.

Methods of dyeing:

These bifunctional dyes are most suitable for exhaust dyeing and Pad Batch and continuous. Can be freely mixed in combinations with Vinyl Sulphone dyes.

Cotfix High Exhaust (HE) dyes - most suitable for garment dyeing!

Cotfix HE Dyes

Cotfix HE dyes are basically bis monochlorotriazine reactive dyes with low reactivity and high substantivity. These dyes are characterized by high but slow exhaustion and high fixation values. Washing off of dyed goods is easier due to higher fixation.

Due to the high fixation (85% and more) pollution problems are also minimized since the drained liquor contains minimal of unfixed dyes.

Characteristics of Cotfix HE dyes:

• Better reproducibility and hence batch to batch variation is minimized.

• High tinctorial value due to excellent build up properties

• Eco friendly due to higher fixation values.

• Better fastness properties.

• Wide range of application since it is suitable for all types of cellulosic materials like yarn, fiber, piece dyeing and garments.

Cotfix HE dyes are most suitable for garment dyeing, because of their high exhaustion and fixation properties at higher temperature (80°C) that facilitate uniform and level dyeing of stitched garments on all its parts like collar, scuffs and stitched yarn. Moreover because these dyes posses outstanding fastness characters when compared to other class of reactive dyes.

These dyes are most suitable for exhaust dyeing and in particular in that machinery where you can easily achieve and maintain the 80°C on the fabric.

Cotfix Hot Brands - Printing Dyes

Our cyanuric chloride based, Cotfix 'H' brand dyes forms various chemical linkage with hydroxyl groups of cellulose. These dyes are low substantive and high fixation dyes most suitable for dyeing and printing of cotton, viscose, cuprammonium rayon and natural silk. The dyeing temperature is 80°C.

METHOD OF DYEING: By Exhaust Dyeing:
Take well pre-scoured fabric and ensure that the pH of the fabric is 7, if require adjust pH by adding Acetic Acid. Take soft water for dyeing, if the water is hard, add sequestering agent to achieve best result.
Set the dye bath at 50ºC and add pre-dissolve dye in two portion and run for 10 min.
Add 5 gms./lit. Common salt for deep shade (2.5 gms./lit. for pale shade) and run for 10 min. start raising temperature to 80ºC - 85ºC in 30 min.
During raising temperature, 20 gms./lit. Common salt (10 gms./lit. for pale shade) after first 10 min. and add 25 gms./lit. Common salt (8 - 10 gms./lit. for pale shade) after another 10 min. and continue dye for 15 min. after reaching the temperature to 80ºC - 85ºC.
Add Alkali slowly in 15 min. and continue dyeing for further 45 - 75 min.

In conventional one-step printing with reactive dyes, urea is used to increase solubility of the dyestuffs and to improve dyestuff migration from the printing paste to the textile fiber.
Minimization or even substitution of urea is possible in the one-step method by controlled addition of moisture.
Another option is the two-step printing method, involving the following steps:
• Padding of the printing paste
• Intermediate drying
• Padding with alkaline solution of fixating agents (especially water-glass)
• Fixation by means of overheated steam
• Washing steps (to remove thickeners and improve fastness properties).
The process is carried out without urea.
A typical recipe for the printing paste is given below:
Thickening stock solution:
Fixation is carried out by means of overheated steam (90 °C to 125 °C).

Cotfix Cold Brand Dyes - Bright shades for hand dyeing

Cold Brand Dyestuff –Dichloro-triazine Based

These dyes are of particular interest in the dyeing and printing of cellulosic fibers, such as Cotton, Linen, Viscose, Cup ammonium and Polynosic rayons.

`M' Brand Dyes are highly reactive requiring comparatively milder conditions in dye fixation.  They are primarily of interest in dyeing at normal room temperature (about 25-35ºC) using Soda Ash or Sodium Bicarbonate.

`M' Reactive Dyes are applicable to cellulosic textiles by Batch - wise, semi-continuous and Continuous methods in conventional textile machinery like Open-vat, Package, Jet, Jig, Winch and Padding Mangle.

Some important considerations in Reactive cold brand dyeing:

Effect of Ca ++ and Mg ++ on Reactive Dyestuffs.

Reduced Solubility
Particularly with Greens and Turquoises
Can cause dye spotting

Unlevel dyeing

Loss of dye from recipe (economy)

Difficulties in washing-off (reduced fastness)

Staining machinery (and subsequent fabric batches)

Reduced “RFT”; and increased possibility of customer complaint.
Increased Aggregation

Can cause dye spotting

Unlevel dyeing

Loss of dye from recipe (economy)

Difficulties in washing-off (reduced fastness)

Staining machinery (and subsequent fabric batches)

Reduced “RFT”; and increased possibility of customer complaint.
Inadequate removal from within the fiber during preparation
Can cause “cloudy” dyeing or even white precipitates on the fiber
Unlevel dyeing

Reduced “RFT”; and increased possibility of customer complaint.


 Bicarbonate in the Dye bath:

It is quite common, many dye house managements ignore the testing of hardness of water time to time. They just find fault either with process chemicals or dyes but just ignore the potential dangers of bicardbonate in process water!.
Practical Dangers to “Right First Time” Dyeing of Bicarbonate:
Bicarbonate turns to carbonate on heating (equation 1)
The exhaustion and migration phase which should be under neutral conditions is alkaline
Premature hydrolysis with loss of economy of recipe.

More loose dye than expected to wash-off after dyeing; with loss of wet fastness
Bicarbonate turns to carbonate on heating (equation 1)
The exhaustion and migration phase which should be under neutral conditions is alkaline
Premature Fixation before Migration.

Unlevel dyeing ; expensive re-processing.

Unpredictable bicarbonate content

Poor shade reproducibility in terms of both Lab – Bulk; and Bulk - Bulk
Expensive Shading Additions.

Loss of time, “RFT” and money.

a.      The residual Peroxide and chlorine on the bleached fabric will yield poor depths due to the destruction of dyestuff molecules.

b.      Higher moisture content of the dyestuff i.e., more than 3.5%, also yields poor depth of shades.

c.      A good neutralization with acetic acid after dyeing is necessary.

d.      Use Non-ionic low foaming detergents for soaping.

Chemical requirements: (For MLR 1:7 to 1:15)

0.1 – 0.5%
30 gms/liter
3 gms/liter
0.5 –1.0%
35 gms/liter
4 gms/liter
40 gms/liter
5 gms/liter
55 gms/liter
7 gms/liter
Above 4%
70 gms/liter
10 gms/liter

Dye Dissolution:

The dissolving of cold brand dyes is a crucial step, which determines the colour yield, repeatability and lab to bulk reproducibility.

  1. If the shade we are going to be dyed is a tri-chromatic one, i.e., a combination of three dyes, each dyestuff in the combination should be weighed separately and put into separate containers.
  2. Each dye should be dissolved separately using 1:15 MLR ratio i.e., for 1 kg of dye 15 liters of water should be used.
  3. First the dye should be pasted thoroughly, with a little cold water into a uniform colloidal mass. Then add hot water of 60°C and dilute.
  4. Filter through fine bolting cloth and the mix the three dyes.
  5. Do not add urea directly to the solid dye powder. If large quantities
Of dyestuff is dissolved, add 1/10th by weight of urea to dissolved solution to improve dissolution.

Sampling/Shading/Addition of Dyes during dyeing (Sampling procedure):

1.     Do not compare any sample taken just after the addition of salt against the standard shade. This will mislead you.
2.     Take sample 30 minutes after the addition of soda for light & medium shades and 45 minutes for dark and v.dark shades.
3.     Wash              Cold-  ½ minute
4.     Wash Hot –     60°C- ½ minute
5.     Neutral soap – boil – ½ minute
6.     Neutral soap – boil – ½ minute
7.     For dark and very dark shades, do 6 soaping of ½ minute duration.
8.     Cold wash.
10. Check shade.
11.If shade is not matching, and if you want to make 10 or 20 or 30% addition in total, drain the running bath up to ½ volume, refill with fresh water, then add the required dye (pre-dissolved, filtered) in two portions, continue dyeing for another ½ half. Do not make any addition of salt or soda into the bath.

After Treatments:

  1. After dyeing is over, drain the bath.
  2. Do one cold wash – overflow.
  3. Do one cold wash.
  4. Do one Hot wash @ 50°C
  5. Neutral soap 0.5 to 1.0 g/l at 80 to 90°C for 15 minutes.
  6. Hot wash at 80°C – 10 minutes.
  7. Cold wash – 10 minutes.
  8. Softening treatment (Cationic if necessary) 1 – 2%
(All the above information were given under good faith and does not carry any warranty)

Monday, August 2, 2010

How to really economize your product cost?

Cotfix economizes your consumption of water, chemicals and dyestuff to a large extent.

Nuchem Dyestuffs P Ltd., (NDPL), offers many solutions for economizing your product and process cost, without compromising the quality. NDPL moves with changes and always has a constant policy of WIN-WIN. Only when our customers win, we feel that we too have attained success.

When there is an advancement in technology, it is wise to make a change to adopt to the new technology.We help our customers to save cost with the help of emerging technologies and not by cutting short of any process or product.

How to economize your processing?
•    Not by just directly comparing the product costs!
•    Not by selecting a local company or supplier who can give you cheaper products!
•    Not by selecting inferior quality of dyes and chemicals!
•    Not by eliminating the right process or reducing time and energy!

Then, what is the Right Way to reduce cost?
•    By selecting the better technology!
•    By selecting better dyes and chemicals!
•    By including energy saving techniques!
•    By right training and development of human resources.

NDPL offers all the above positive things to all her customers.

We have a strong technical team that suggests ways and means to solve your existing problems and suggests, be with you, take trials and prove practically how much one can save men and money.

We can supply tailor made products that suits particularly to your environment and requirement. Now NDPL can supply as a package;

•    All your auxiliary chemicals right from pretreatment to effluent treatment
•    All your colorant needs – Direct, Reactive, Disperse and Pigments.
•    Technical expertise to match your requirements.

Dyes and Chemicals:

To reduce the total cost of production without sacrificing the quality, NDPL ventured to start manufacturing selective important auxiliaries that are really a must for processing. These auxiliaries are highly concentrated, eco friendly products that work in minimal concentrations.

Similarly NDPL has highly concentrated reactive dyestuff ranges that would replace ordinary V.S. dyes and Bifuntional dyes almost in 1:3 ratio, saving dyes and chemicals cost to a marked extent. In fact one can get better all round fastness properties too.

The above figure clearly shows how much is saving dyestuff and chemical, by just changing your class of dyestuff from V.S. or Bi-functional. This is just one area of saving and one concrete example to quote.

Similarly there are techniques that can really increase the dyestuff depth by 20 to 30%. Using this new dyeing technique we not only save the dyestuff consumption, but also get excellent rubbing and washing fastness properties.

Sunday, August 1, 2010

Viscose Dyeing - Method & Tips for yarn and fabric

Dyeing Yarn:
Without salt, swelling of viscose increases with temperature. This must be remembered in package dyeing where high swelling and high pump pressure can lead to flattening of the yarn cross section at cross over points. Flow should be predominantly IN to OUT so that the yarn layers float apart and the liquor can circulate more easily. With OUT to IN flow the yarn layers are compressed and flow is reduced. OUT to IN flow cycles should therefore only be 30 seconds or so.

Conical cones:
The cones must be homogeneously wound to ensure an even dye result and the bobbin edges should be carefully rounded off (bumped). The winding hardness should be approx. 25 Shore. Taking the relatively highswelling of the material into account this equals a volume of approx. 360 – 380 g/l. Due to the higher swelling of the material we recommend that the windingdiameter is limited to 160mm.  Dyeing problems have been experienced where the yarn tube diameter has reached 170mm (approximately 850g / cone).

Cylindrical Cones:
Lighter dyeing results on the edges can be avoided by using winding hardness's of approx. 25 Shore and a pressure rate of 20 %.

Dyeing Fabric:
As viscose is a high affinity fibre, special consideration must be given to the choice of dyestuff and exhaust application technique. Hot dyeing reactive dyes are preferred for exhaust application in order to secure the highest migration and diffusion through the high

affinity fibre when dyeing in rope form. Dye suppliers will thus generally recommend a migration technique to give levelness and reproducibility. This technique offers high dye mobility at temperatures as high as 110° C before cooling to 80° C for optimum fixation of the reactive dye to the cellulose chain.

For higher substantivity dyes, the salt should be added gradually (over 30 mins) at 95° C, or at the highest temperature at which additions can be made.

The bath is set at 50° C with the required amount of electrolyte, auxiliaries and the pH adjusted with acetic acid to around pH 6.0. Predissolved dyes are then added in a linear manner over 15 – 20 minutes. The temperature is raised to 95° C (or even up to 110° C) at 1.5 to 2° C per min. and held for 20 minutes at 95° C before cooling back to 80° C at 1° C per min. Hold at 80° C for 10 minutes before adding the alkali in a linear manner over 15-20 minutes. Continue for 45-60 mins.

Further precautions
Under alkaline conditions, in enclosed machines, viscose is especially prone to cause problems of dye reduction. It is essential that viscose is thoroughly desulphurised, otherwise appreciable colour value will be lost. Mild peroxide bleaching and addition of reduction inhibitor Resistsalt  from the start of dyeing is recommended.

When dyeing in rope form, there must be sufficient displacement and this is best achieved for woven fabrics in jets with aerodynamic systems. The liquor temperature should not fall below 50° C and a suitable running  crease inhibitor should be used in all hot baths.In order to guard against the danger of formation of running creases, the size of the load should not exceed approx. 80% of the maximum load.

Fabric circulation speed should be set to between 80 – 120 seconds. To prevent abrasion marks, the slippage (difference between winch speed and fabric speed) should be as low as possible.
Levelling & migrating agent (yarn and fabric) can be used to increase migration – especially with difficult large molecule dyes.

If dyed viscose fabrics are allowed to begin to dry in patches – top of trolley – edges of folds – these areas may be visible as a physical/optical patch after finishing. Keep fabric thoroughly  wetted until drying machine/ stenter is available

Preventing predrying of the fabric is important, but it is far better to ensure that production flows quickly and fabric does not stand wet for a long time.

Dyeing - Summary
• Remove oils and waxes in preparation
• No twists in loading – load machine below capacity
• Sewing – sew more than once – at an angle
• Abrasion – avoid slippage – always run at 50° C or higher
• Cooling creases – cool at 1° C per minute
• Danger of sulphur residues and reduction
• Tension in dyeing machine – problems with shrinkage
• Migration of unfixed dye while waiting for drying
• Fabric drying out in patches – watermarks
(physical/optical effect). Keep fabric wet right up to
the dryer

Auxiliaries that goes smooth with Cotfix Dyes

In order to support the customers with a complete set of compatible auxiliary chemicals, Nuchem dyestuffs P Ltd/, has introduced the following products;

Auxiliary Chemicals from
Nuchem Dyestuffs P Ltd

Concentrated Alpha Amylase enzyme suitable for batch & continuous Desizing  processes
Nuprizyme –A400 = 0.5 to 1.0% w/w
Pad- Batch:
Nuprizyme –A400 = 3 to 6 gpl
Powerful, low foaming, APEO free Detergent & Wetting Agent - A Mixture of Ethoxylated Fatty Alcohols - Nonionic

Nunonwet-conc 1.0 – 2.0 gpl
Scouring & Bleaching- Exhaust
Nunonwet-conc 0.5 – 0.8%
Scouring & Bleaching- Continuous
Nunonwet-conc 3.0 – 5.0 gpl
A powerful sequestering agent
Neseq-conc 0.5 – 1.0 gpl
Scouring & Bleaching- Exhaust
Neseq-conc 0.5 – 1.0 gpl
Scouring & Bleaching- Continuous
Nuseq-conc 0.5 – 1.0 gpl
Nustabilize - NI
Organic Hydrogen Peroxide stabilizer
Peroxide Bleaching:
Nustabilize-NI = 1/5 th of Peroxide concentration.
Perox - K
A strong Peroxide killer of Stabilized Catalase Enzyme.
Peroxide Removal:
Perox – K = 0.3 – 1.0 gpl
Concentrated Amber colored Cellulase Enzyme for Biopolishing
Knit fabrics = 0.3 – 1.5% O.W.F.
Garments   = 0.05 – 0.6% O.W.F.
Denim Goods = 0.15 – 0.6%

A strong Anionic Mercerizing wetting agent
Nurcerol – 3.0 – 10 gpl
Nonionic Amino silicone softener ,in concentrated form