DYEING OF POLYESTER WITH DISPERSE DYES:-
Description of Disperse Dyes which is used in Poleyster Dyeing:-
Polyester.
Figure: Dyeing Curve
Figure: Dyeing Curve.
Figure: Fire retardant fabric
A dye that is almost totally insoluble in water. Disperse dye exist in the dye bath as a suspension or dispersion of microscopic particles, with only a tiny amount in true solution at any time. They are the only dyes that are effective for “Normal” polyester. Some types are used for Nylon and Acetate. Polyester is dyed with disperse dyes by boiling with carrier chemicals or by heating the liquor to about 130°C which requires elevated pressure (Like a pressure cooker).
Where the fabric is padded with dye liquor then dried and heated to about 200°C for about 90 seconds, is also used for polyester and for coloring the polyester component of polycotton blends. Disperse dyes are also used for sublimation printing of synthetic fibres and are the colorant used in crayons and inks sold for making “Iron-ON” transfers.
The first dyes for cellulose acetate fibres were water soluble. The dye molecules contained a methylamino sulphonate group (-NHCH2SO3Na) introduced by reaction of a primary amino group with formaldehyde and sodium bisulphate (Ionamine dyes, 1922). During dyeing, this group hydrolysed to the less soluble parent amine.
Dye-NH-CH2SO3Na (aq) + H2O → Dye-NH2(s) + CH2O(aq) + NaHSO3(aq)
It was soon recognized that it was this compound that the cellulose acetate absorbed. The first true disperse dyes were simple, relatively insoluble azo and anthraquinone compounds dispersed in water using the sodium salt of sulphated ricinoleic acid.
Dye(s) ↔ Dye (aq) ↔ Dye(fiber)
Many of these dyes are obsolete but their development provided the technology for preparing fine aqueous dispersions by grinding the dye with dispersing agents. A fine dispersion is essential for rapid dyeing and avoids deposition of larger dye particles on the material.
Classification of Disperse Dye for Ployester:-
Disperse dyes for a compound shade on polyester can have quite incompatible dyeing properties. The SDC classification of disperse dyes is based on migration ability during exhaust dyeing, colour build-up, sensitivity to changes in temperature and the rate of dyeing.
This type of dye is often classified on the basis of dyeing rate and sublimation fastness, particularly for polyester dyeing. These two properties are a function of molecular weight and the number of polar groups in the dye molecule. The most common classifying is given bellow:
1) Low energy.
2) Medium energy.
3)High energy.
Low Energy Disperse Dye:-
Most dyeing and fastness properties change gradually with increase in molecular size. Small dye molecules with low polarity are leveling, rapid dyeing dyes with poor heat resistance. These are called low energy disperse dye.
Medium Energy Disperse Dye:-
Most of the dyeing and fastness properties change gradually with increase in molecular size. Moderate dye molecules with moderate polarity are leveling, rapid dyeing dyes with moderate heat resistance. These are called medium energy disperse dye.
High Energy Disperse Dye:-
More popular, higher molecular weight dye has low dyeing rates, poor migration during dyeing but good heat and sublimation fastness. These constitute the high energy disperse dye.
Selection Properties:-
Disperse dyes have some general properties which are given bellow –
Solubility:-
Disperse dyes are insoluble in water or slightly soluble in water. It makes fine dispersion with water with water with dispersing agent. Dissolves in organic solvents like benzene, toluene etc.
Fastness to washing: The fabric dyes with disperse dyes shows moderate to good washing fastness.
Light Fastness:-
Most of the disperse are very fast to washing. The minimum light fastness rating is 4-5.
Sublime ability:-
Due to stable electronic arrangement disperse dyes have good sublime ability.
Gas Fading: Fabrics dyed with certn blue & violet disperse dyes containing anthraquinone structure become fade in presence of nitrous oxide. This nitrous oxide may be made in nature from various sources such as open gas fire, electric heating arrangement.
Commercial (Trade name) Name of Disperse Dyes:-
Terasil.
Foron.
Palanil.
Resolin.
Samaron.
Dispersal.
Dispersing Agent:-
The actual disperse dye is formed as relatively large particles and, in this form, it is unsuitable for application on hydrophobic fibers. If these big particles are used in dyeing as such, they produce uneven and specky dyeing and their full colour value is not realized. In order to ensure uniform dyeing, the dye should be present in the dye bath in a uniform and very fine form, which should be stable under dyeing condition. This requires a large amount of suitable dispersing agents followed by grinding. The dispersing agent should be effective under the dyeing conditions and should be stable to hard water, high temperature and other dyeing assistants.
CSoap powder, Turkey Red Oil, Alkylsulphates, Alkylarylsulphonates, Fatty Alcholethylene Oxide condensates, Naphthalene-β-sulphonate and formaldehyte etc are the recommended dispersing agent performs many functions. It assists the process of particle size reduction of the dye. It also enables the dye to be formed in the powder form. When the powder is added to the dye bath, it facilitates the recon version of the powder in to a dispersion, it is required for carrying out the dyeing. Finally, it maintains the dispersion in a fine form in the dye bath throughout the dyeing process. Dispersing agents increase the solubility of the disperse dye in water. It is seen that solubility of the dye in water is considerably increased by the dispersing agent and that different dispersing agents affect the solubility to different extents. It can be noted that the dyeing rate increase with increasing solubility the dyeing rate actually decreases. Where the solubility is very high as in the case of direct dyes, practically no dyeing takes place.
Commercial (Trade name) Name of the Dispersing agent:
Setamol -BASF.
Edalon -Sandoz.
Calsolene Oil HS –A.C.I.
Hipogal –Hoechst.
Point Consideration for Textile Coloration:-
Textile Materials:-Textile (Fabric/Yarns/Fibres/Garments)
Dyes/Pigment
Chemicals (Common salt, Caustic, Soda ash etc.)
Auxiliaries (Leveling agent, wetting agent, sequestering agent etc.)
Machinery
Utilities:
Electricity
Water
Steam
Compressed air
Gas
Controlling Parameters:
Temperature
Time
Concentration of dyes and chemical
pH
M:L ratio
Pressure
Man power
Dyeing Mechanism of Disperse Dye:-
The dyeing of hydrophobic fibres like polyester fibres with disperse dyes may be considered as a process of dye transfer from liquid solvent (water) to a solid organic solvent (fibre). Disperse dyes are added to water with a surface-active agent to form an aqueous dispersion. The insolubility of disperse dyes enables them to leave the dye liquor as they are more substantive to the organic fibre than to the inorganic dye liquor. The application of heat to the dye liquor increases the energy of dye molecules and accelerates the dyeing of textile fibres.
Heating of dye liquor swells the fibre to some extent and assists the dye to penetrate the fibre polymer system. Thus, the dye molecule takes its place in the amorphous regions of the fibre. Once taking place within the fibre polymer system, the dye molecules are held by hydrogen bonds and Van Der Waals’ force.
The dyeing is considered to take place in the following simultaneous steps:
Diffusion of dye in solid phase into water by breaking up into individual molecules. This diffusion depends on dispersibility and solubility of dyestuff and is aided by the presence of dispersing agents and increasing temperature.
Adsorption of the dissolved dye from the solution onto the fibre surface. This dyestuff adsorption by fibre surface is influenced by the solubility of the dye in the dye bath and that in the fibre.
Diffusion of the adsorbed dye from the fibre surface into the interior of the fibre substance towards the center. In normal condition, the adsorption rate is always higher than the diffusion rate. And this is the governing step of dyeing.
When equilibrium dyeing is reached, the following equilibria are also established:
Dye dispersed in the bath
Dye dissolved in the bath
Dye adsorbed on the fibre
Dye diffused in the fibre
Effect of Various Condition on Disperse Dyeing:
Effect of Temperature:-
In case of dyeing with disperse dye, temperature plays an important role. For the swelling of fibre, temperature above 100°C is required if high temperature dyeing method is applied. Again, in case of carrier dyeing method, this swelling occurs at 85-90°C. If it is kept for more time, then dye sublimation and loss of fabric strength may occur.
Effect of pH:
For disperse dyeing the dye bath should be acidic and pH should be in between 4.5-5.5. For maintaining this pH, generally acetic acid is used at this pH dye exhaustion is satisfactory. During colour development, correct pH should be maintained otherwise fastness will be inferior and colour will be unstable.
Heat setting Process:-
Heat setting of synthetic fabrics eliminates the internal tensions within the fiber generated during manufacture and the new state can be fixed by rapid cooling. This heat setting fixes the fabrics in the relaxed state and thus avoids subsequent shrinkage or creasing of fabric. Presetting of goods make it possible to use higher temperature for setting without considering the sublimation properties of dyes and also has a favorable effect on dyeing behavior and running properties of goods. On the other hand, post setting can be combined with some other operations such as thermosol dyeing or optical brightening of polyester, post setting as a final finish is useful to get a high dimensional stability along with desired handle.
The application of heat in heat setting can be done by hot air, on a pin stenter at 220c for 20-30 seconds for polyester goods and at a lower temperature range of 190-225C for 15 -20 seconds for polyamides. Acrylics may be heat set partially at 170-190 c for 15-60 seconds to reduce formation of running creases. but higher temperature should be avoided to prevent yellowing.
Hydro setting is so rarely used particularly to get fuller and softer handle on polyamides at 125-135c in autoclaves for 20-30 minutes. It can be combined with dyeing or optical brightening.
Steam setting can be done by saturated or super-heated steam. During steaming, uniform treatment can be ensured by initial sequence of alternate short steaming and vacuum application for 20-30 min at 130C under pressure. Super-heated steam can be used in stenters and setting time is 25% shorter than for hot air on account of quicker heating up rate. Acrylic fibers have to be protested as some may undergo excessive shrinkage or loss of handle. Before the material is heat set, it should be thoroughly washed to remove spin preparations, lubricants, sizing agents and impurities as these are likely to be burned in drying heat setting making their removal difficult.
MERHOD OF THE DYEING OF SYNTHETIC FIBRE WITH DISPERSE DYES:
There are three common method of dyeing with disperse dyes which are as follows:-
Carrier method of dyeing.
High temperature dyeing.
The thermosol process of dyeing.
Carrier Dyeing Method:-
Commercial (Trade name) Name of Carrier:
Tumescal –A.C.I.
Matexil –A.C.I.
Levagol –Bayer.
Dilatin –Sandoz.
Invalon –Ciba.
Hisogal –Hoechst.
Recipe:
Dye:
-For light shade<0.5%
-For medium shade 0.5-1.5%
-For deep shade >1.5%
Carrier (Phenol): 3 gm/lit
Acetic Acid: 1 gm/lit
Dispersing Agent: 2gm/lit
Salt: 1-2 gm/lit
PH: 4-4.5
M: L: 1:10
Time: 60 min
Temperature: 90°C
Dyeing Sequence of Polyester is given
Below:-
Carrier and vessel washed by hydrose and caustic at 1000C for 20 min
↓
Load the package in the carrier and feed in the vessel
↓
Add washing agent and run at 800C for 20 min
↓
Dyeing period
↓
Add leveling agent and acid, run at 600C for 10 min
↓
pH check
↓
Color mixing at 700C for 40 min
↓
Color dosing at 600C for 20 min
↓
Polyester dyeing at 1350C at 20 gradient for 50 min
↓
Sample check
↓
Ok
↓
Temperature cool down at 780C and drain
↓
Hot wash for 10 min
↓
Rinse for 15 min for light shade and 25 min for dark shade
↓
Add hydrose, soda ash, run at 800C for 20 min
↓
Drain
↓
Rinse for 10 min
↓
Neutralization by acetic acid at 500C 20 min
↓
Finishing.
Procedure:-
At first, a paste of dye and dispersing agent is prepared and then water is added to it.
Dye bath is kept at 60°C temperature and all the chemicals along with the material are added to it. Then the bath is kept for 15 min without raising the temperature.
pH of bath is controlled by acetic acid at 4-5.5.
Now temperature of dye bath is raised to 90°C and at that temperature the bath is kept for 60 min.
Then temperature is lowered to 60°C and resist and reduction cleaning is done if required. Reduction cleaning is done only to improve the wash fastness.
Material is again rinsed well after reduction cleaning and then dried.
High Temperature Dyeing Method:
Pretreatment:-
Pretreatment of polyester fabric is a must before starting the dyeing operation. The pretreatment is essential to remove the lubrication oils and other auxiliaries used during spinning and weaving or knitting operation. This following simple treatment is enough to remove those impurities.
Recipe:-
Lissopal D paste: 2 gm/lit
Soda Ash: 2 gm/lit
Treat with the above recipe at 90~95°C for 20 minutes.
Drain-Hot wash @ 70°C for 10 minutes> cold wash > Neutralize with 1cc/lit Acetic Acid.
Cheak the PH- 5.5-6.0
Dyeing Process:
Polyester Texties require a Heat Setting operation before dyeing. Heat settings eliminates the internal tensions within the fibre generated during manufacture and the new state can be fixed by rapid cooling. This heat settings fixed the fabrics in the relaxed state and thus avoids subsequent shrinkage or creasing of fabric.
Dye bath setting and Dyeing:
Recipe:-
Lyogen DFT: 0.5 gm/lit
Sandozen PES: 1.0 gm/lit
Acetic Acid: 1 gm/lit
PH: 5.5-6.0
Temperature: 130°C
Time: 1 hr
Procedure:-
At first a paste of dye and dispersing agent is prepared and water is added to it.
PH is controlled by adding acetic acid.
This condition is kept for 15 minutes at temperature 60°C.
Then the dye bath temperature is raised to 130°C and this temperature is maintained for 1 hour. Within this time, dye is diffused in dye bath, adsorbed by the fibre and thus required shade is obtained.
The dye bath is cooled as early as possible after dyeing at 60°C.
The fabric is hot rinsed and reduction cleaning is done if required.
Then the fabric is finally rinsed and dried.
Dyeing of Polyester Fabric in Thermasol Dyeing Method:
Thermasol dyeing method is continuous methods of dyeing with disperse dye. Here dyeing is performed at high temperature like 180-220°C in a close vessel. Here time of dyeing should be maintained very carefully to get required shade and to retain required fabric strength.
Recepi
Dye: X gm/lit
Dispursing Agent: 2 gm/lit
Sodium Alginate Thickener: 5-10 gm/lit
Citric Acid to get PH: 4-5
Sequence:-
Pading- Drying- Thermofixing- Aftertreatment.
Procedure:
At first the fabric is padded with dye solution using above recipe in a three-bowl padding mangle.
Then the fabric is dried at 100°C temperature in dryer. For dyeing, infra-red drying method is an ideal method by which water is evaporated from fabric in vapor form. This eliminates the migration of dye particles.
Then the fabric is passed through thermasol unit where thermo fixing is done at about 205°C temp for 60-90 seconds depending on type of fibre, dye and depth of shade. In thermasol process about 75-90% dye is fixed on fabric.
After thermo fixing the unfixed dyes are washed off along with thickener and other chemicals by warm water.
Then soap wash or reduction cleaning is done if required. And finally the fabric is washed.
Textile Finishing:-
Textile finishing process is a separate subject a processor should be well versed. This is the end process that adds up value, quality and appearance to the final product.
Each substrate according the end use would finish differently.
Finishing operations can be widely divided into 2 classes;
1) Mechanical means of finishing or mechanical finishes or physical transformation of subtrate due to mechanical processes,
2) Chemical finishes.
Functional Finishes:-
The properties of synthetic fibers, most important among them being polyamide, polyester and polyacrilonitrile, are essentially different from those of natural cellulosic and wool fibers. Hence the sequence of finishing operations is likely to be different. While cellulosic’s require a resin finishing treatment to impart easy-care properties, synthetic fibers already have these easy-care criteria and require only a heat setting operation. The use of 100% synthetic textiles has increased considerably since the arrival texurised yarns consisting of filaments and the growing production of knit goods. The use of open weave has enabled production of lighter, air permeable, fabrics to ensure better wearing comfort.
Filling and Stifening Finishes:-
A stiffening effect is desirable in certain polyamides and polyester materials for petticoats, collar interlinings, etc., which can be done by reducing the mutual independence of structural element of fabric by polymer deposition on coating as a fine film. Some special Urea-formaldehyde pre-condensates have been found to be useful. Application of film-forming acrylates dispersions as well as latex rubber emulsions gives a fuller effect with sufficient stiffness.
When softening is desired it can be achieved by reducing the frictional coefficient between structural elements of fabrics, cationic long chain fatty derivatives and silicones may be used in conjunction with polymer forming agents. Recently some cationic softeners having reactive functional groups have been developed to get better fastness of finish.
Hdrophillic Finishes:-
On account of lower moisture and water absorption capacity synthetic fiber materials become uncomfortable in contact with skin. Certain products based on modified (oxy-ethylated) polyamides makes the wearing more pleasant by reducing the cohesion of water so that it spreads over a larger area and thus evaporates more rapidly.
Anti-pilling Finishes:-
Pilling is an unpleasant phenomenon associated with spun yarn fabrics especially when they contain synthetics. Synthetic fibers are more readily brought to the surface of fabric due to their smooth surface and circular cross section and due to their higher tensile strength and abrasion resistance, the pills formed take a long time to be abraded by wear. With knit fabric, two more problems occur, viz., “picking” where the abrasion individual fibers work themselves out of yarn loops onto the surface when garment catches a pointed or rough object. These two effects are more predominant in the weave, is more open and yarn is bulkier.
The finish has to cement the fibers within the yearn so that their dragging becomes more difficult, without affecting the handle adversely. Special polymer formers of acrylate type or latex type are useful but should form a film of good cohesion, should hydrophilic and should not form a tacky surface. padding in polymer dispersion or emulsion followed by drying at moderate temperature gives the desired effect.
Permanent Anti-static effects:
Anti-static effective chemicals are largely chemically inert and require Thermosol or heat treatment for fixing on polyester goods. Agents of polyether type are found to be useful but should not effect the dye-equilibrium on fiber otherwise the rubbing fastness is impaired. In general, Thermsolable anti-static agents also have a good soil release action which is as permanent as the anti-static effect. Anti-static finishes may also be of polyamide type being curable at moderate temperatures.
Non-Slip Finishes:
Synthetic warp and weft threads in loosely woven fabrics are particularly prone to slip because of their surface smoothness when the structure of fabric is disturbed and appearance is no loner attractive. To avoid these attempts are made to give the filaments a rougher surface. Silica-gel dispersions or silicic acid colloidal solutions are quite useful and they are used with advantage in combination with latex polymer or acrylates dispersions to get more permanent effect along with simultaneous improvement in resistance to pilling or snagging. These polymer finishes are also capable of imparting a soft and smooth handle to synthetic fabric without imparting water repellency.
Fire Resistant Finishes;
With synthetic fiber which melt on igniting by a flame, the molten moss is itself quite dangerous and a fire-resistant treatment is desirable for certain end uses. Polyester fabrics can be made flame resistant by treatment with an aqueous emulsion of xylene soluble 2,3-dibromopropyl phosphate in a pad-cure sequence. A semi-permanent effect can be produced by treating with a mixture of ammonium bromide and brominated phosphoric acid esters.
Polyamides can be made flame resistant by applying phosphorous tri-chloride ammonia reaction products or ammonium bromide with amino-triazine condensation products. For acrylics tris-dibromopropyl-phosphate as well as 2-cyanoethyl-tetramethyl-di-amino-phosphate is quite effective.
Anti-mirobial Finishes:
With the increasing use synthetic fibers for carpets and other materials in public places, anti-microbial finishes have assumed importance. A reduction in soiling tendency will along way in keeping textiles free from germs and usual soil repellant as well as soil release finishes are effective in some way. products which are commonly applied are brominated phenols, quaternary ammonium compounds, organo-silver and tin compounds which can be applied as solutions or dispersions. They can also be incorporated in a polymeric film deposited on the surface to get controlled release. Some reactive systems similar to those for reactive dyes have been recently tried to incorporate anti-microbial structural features.
Finishing of Elastometric Textiles:-
The heat sensitivity of electrometric fibers limits the choice of products and finishing process that can be employed. In order to eliminate the latent tensions, these electrometric textiles are simply steamed or treated with hot water. Dry curing or heat treatment is restricted to temperature below 140C, these fabrics have e to be dried and curd with minimum tension with over feed stenter. To groups of materials, viz., foundation fabric and knitted fabric for bathing suits are resin finished. Water proofing can be imparted by using Zirconium salts containing wax emulsions as it does not require a high temperature treatment. A filling treatment can be obtained with modified methylol-urea type products
Ref:-https://textilelearner.net.
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