Monday, November 16, 2009
Mineral colors
Mineral color contains metallic insoluble precipitates, which are deeply colored. These insoluble precipitates have found great application as pigment for paint. For other purposes of dyeing, the precipitates themselves are not used but they actually created in and on the fibers from the soluble substances
Examples:
Mineral colors are very limited, only about half a dozen are valuable to dyes or printers:
• Chrome yellow
• Chrome orange
• Chrome green
• Iron buff
• Prussian blue
• Manganese blue
Requirements for dyeing with mineral color
• They should be dyed under special conditions avoiding metallic contact
• They shouldn’t be wet handled
• They must be padded evenly.
• They shouldn’t have any crease before drying.
• During production of mineral khaki metal surface is used, acidity must be well controlled and pH must be adjusted to 4.
Advantages
• Very simple to apply
• Lower cost
• Easily available
Disadvantages
• Less affinity to fibers, so mechanical pressures in between the roller is required
• For commercialization some technical experience is required
• Tendering may happen due to uncontrolled pH
Mineral Khaki
A combination of iron buff and chrome green in proper proportions produces mineral khaki, which is extensively used for military uniforms. It has excellent fastness to light and wash.
Dyeing procedure
• The cotton is padded with solution containing FeSO4
• Now treated with boiling solution of Na2CO3.
• Now wash
FeSO4 + 2NaOH Fe(OH)2 + Na2SO4
Cr2(SO4)3 + 6NaOH Cr(OH)3 + 3Na2SO4
• Now the fabric is aired for the conversation of Chromium hydroxide to Chromium oxide and Ferrous hydroxide into Ferric oxide by atmospheric oxygen.
Cr(OH)3 [O] Cr2O3
Fe(OH)2 [O] Fe2O3
These oxides then combine to give khaki shade.
Recipe:
For 1% shade of khaki or Procion Yellow M4GS: 0.25%
Indanthrene yellow FSI : 0.5% Procion Blue M85GS: 0.50%
Indanthrene Black Brown NI: 0.5% Procion Brown: 0.25%
NaOH: 16 gm/L NaCl: about 35g/L
Hydrose: 5 gm/L Na2CO3: 3 gm/L
M:L = 1:5
Temp: 80 – 100°C
Time: 60- 90 min
Posted by Chariots of knowledge
Oxidation color
Some dyestuffs like aromatic amine, diamine, aminophenol etc found as intermediate compounds, which rapidly produce the final color through oxidation in the fiber substances; this class of dye is known as oxidation colors.
Oxidation colors high molecular wt., water insoluble ingrain colors. Water insoluble species is produced by oxidation reaction performed on aromatic amines and diamines.
Important Oxidation colors:
1. Aniline black
2. Diphenyl black
3. Solaniline black
4. paramine brown
5. Fuscamine brown
Why oxidation color is called ingrain dye?
Ingrain dyes are, by definition, any water insoluble colors formed in situ (on the fabric) from water soluble intermediate i.e. the dyes which are developed on fiber but they are not readymade.
The oxidation colors are formed from water soluble oxidation amines, which formed the final color on fabric through oxidation. Thus they are not readily available, but as intermediate compounds. Hence they are called ingrain dyes.
Aniline Black
Aniline black, the oxidation product is the important member of oxidation color for textile use. It is called oxidation aniline color. It is invented in 1863 with sodium chlorate and copper sulfate etc.
Aniline black dyeing and prints produce some of the most intense blacks: These colors are almost completely color stable to acids, bases and exposure to light. By far, the greatest use of aniline black is dyeing and calico printing for cotton. Silk and wool are dyed only when extensive precautions are taken against tendering.
Reagent used for dyeing
1. Soluble sat of aromatic amine: aniline or n aminophenylamine, anyline hydrochlorides
2. oxidising agents: NaClO3, KClO3, NaHCO3, KMnO4 etc.
3. Catalyst/Oxidation carrier: CuSO4, CuS, FeCl3, potassium ferricyanide
4. Hygroscopic agent: NH4Cl
5. Migration inhibitor: Na-alginate, gum etc
6. Acid liberating agent: HCl
Classification of Aniline Black:
Based on method of dyeing and chemical used:
1. Prussiate Black/Steam Aniline Black:
Oxidation catalyst: Na4[Fe(CN)6] sodium Ferro cyanide (yellow prucciated of soda, hence the name)
Oxidation by NaClO3
Color produced by steaming (> 98ºC, 5min)
2. Diphenyl Black/Copper Sulfide Aniline Black
CuS as catalyst
NaClO3 as oxidizing agent
3. Chromate Aniline
4. Aged Aniline black
Dyeing Method
Recipe:
Aniline Black 8-10%
HCl: 15%
K2Cr2O7: 10%
CuSO4: 4%
Temperature: 100C
Time 90min
M:L = depends on machine
Procedure:
• First make solution with aniline and hydrogen chloride (sometimes paste preparation). Add water to make proper solution; if necessary boil to make clear solution.
• Potassium dichromate solution is made and added to dyebath
• The material is impregnated with this solution at room temperature for 30min
• CuSO4 solution is made and is added to dyebath
• Temperature rises slowly to boiling and dyeing for 30-45min
• The substance is hot air aged with removal of the hydrogen chloride fumes. There are also emissions of volatilized amine. Temperature should not be violently fluctuated
• Oxidation occurs during drying process and the dye becomes fixed.
• Good penetration is possible since the salt of dyestuffs has no fiber affinity.
After treatment
1-2% soaping at 100°C for 10 -15min
Wash and dry
For aniline black: 5gm/L solution of dichromate or bisulfite is necessary which will not develop green tint and also molecular wt is increased by 10%.
Thus dyeing of aniline black on cellulosic fiber fabric includes four steps:
1. impregnation with the aniline liquor
2. Drying of the impregnated fabric
3. developing either by ageing or steaming
4. after treatment
Defects
1. Tendering: Presence of mineral acid causes formation of oxycellulose and hydrocellulose
2. Greeninsh color: lack of proper oxidation
Remedies - a chroming treatment with sulfuric acid
3. Bronziness: presence of excess acid causes reddish tone turn the black shade bronzy.
Remedies – treatment with a dilute solution (0.05%) of tannic acid and then dried without washing
Advantages
• Jet black dyeing on cellulose are main use
• can produce more deep color
• for some shade, vat black are 5-10% expensive by weight
• less tendering than sulfur and vat black
• Rapid color develops during steaming
• No corrosion of boiler
• almost completely color stable to acids, bases and exposure
• reduction of time
Disadvantages
• Loss of cellulosic strength due to sulfuric acid form
• effluent treatment is difficult
• more chemical may cause dyeing problem
• dye range is limited
Mordant Dyeing
The term ‘mordant’ is derived from the Latin ‘mordeo,’ which means to bite or to take hole of. Mordant dye have no affinity to textile fiber, they are attached by a mordant, which can be an organic or inorganic substances. The most commonly used mordant is inorganic chromium, so sometimes this dye is called chrome dyes. Other inorganic mordants are Al, Cu, Fe and organic mordant. Tannic acid is rarely used.
Mordant improves the fastness of the dye on the fibre such as water, light and perspiration fastness. The choice of mordant is very important as different mordants can change the final colour significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. Fiber most readily dyed with mordant dyes are the natural protein fibers, particularly wool and sometime synthetic fibers modacrylic and nylon.
It is often noted that when a mordant dye forms a lake with a metal, there is a strong colour change. This is because metals have low energy atoms. The incorporation of these low energy atoms into the delocalised electron system of the dye causes a bathochromic shift in the absorption. It is this delocalised electron system which is fundamentally responsible for colour in dyes. Since different metal atoms have differing energy levels, the colour of the lakes may also differ.
The most commonly used mordant dye is undoubtedly hematein (natural black 1), whose status as a natural product supercedes its mode of dyeing, apparently. Others are eriochrome cyanine R (mordant blue 3) and celestine blue B (mordant blue 14), both used as substitutes for alum hematoxylin but with a ferric salt as the mordant. Alizarin red S (mordant red 3) is valuable for the demonstration of calcium, particularly in embryo skeletons
Reason for so named
Some natural and synthetic dyes can be applied or fixed on wool and other textile fibers with the help of an auxiliary chemical called a mordant. These dyes are therefore called mordant dyes.
The mordant have affinity both for a fiber can be applied by using a mordant.
In wool dyeing, only chromium salts are of importance and hence mordant dyes for wool are usually called chrome dyes.
Classification
On the basis of origin
1. Natural: Alizarine
2. Synthetic: Acid chrome
1. Natural Mordant dye
Alizarine: Alizarine is an example of natural mordant dye. It is obtained from the root of the madder. Alizarine is known as polygenetic mordant dye because it develops a variety of colors on different mordants.
Mordant Color
Al Red
Sn pink
Fe Brown
Cr puce brown
Cu yellowish brown
Haematin: this is extensively used before and only one still in use found from logwood. It yield navy blue or black colors of good fastness with chromium compounds. This is used in nylon and wool.
Recipe: haematin dye: 8-10%
Acetic acid: 1cc/l [pH 4-6]
temperature: 50-90°C
Time: 2hr
As it is time consuming process, the natural mordant dyes are used in lesser extent.
2. Acid mordant dyes:
Acid color + chromium = acid chrome
Few dihydroxy azo dyes could co-ordinate so easily with chromium and they could be dyed as acid dyes and mordanted by aftertreatment with K or Na dichromate. Such dyestuffs are known as the acid mordant dyes & are used extensively for wool & also for polyamide fibers.
They have good wet fastness and most of them possess satisfactory light fastness.
Methods of dyeing:
There are three general methods of application of mordant dyes as described below:
1. Chrome mordant process: two bath process
First bath: mordanting with insoluble chromium hydrate
2nd bath: dyeing
2. Afterchrome process: two bath/single bath process
First bath: dyeing
2nd bath: mordanting with chromium
3. Methachrome (or chromate) process
Dye + mordant (dichromate) in same bath
Mechanism of dyeing
Fig shows an example of mordant dye and shows the formation of dye mordant complex. The chromium cation has a valency of 6 (i.e. 6 bonds) which represented by six lines toward the chromium cation.
The mordant dye is shown to the Cr cation by three of the six bonds. The other three bonds have molecules of water attached to them. It is thought that the three molecules of water are there as an intermediate step only and will gradually be water replaced by another mordant dye anion. Thus two mordant dye molecules form a complex with the Cr cation to form a lake or a dye chromium complex. The formation of these relatively large complexes results in very good wash fastness of dye.
Dyeing procedure of Alizarine dyes
· Boil cotton fabric in solution of 1 part TR oil and
10 part water for 12 hrs
· Dry at 40-60°C
· Treat again with 10°Tw acetate at 60°C for 2hrs
· Dry at 40-60°C
· Again treat with 2 part Sodium phosphate
10 part water at 30-45°C
· Dye 1-1.5% shade with calcium acetate at room temperature for 20 mins
· Wash for 30 min at 70°C
· Soap wash, dry
Dyeing of wool with synthetic mordant:
Dyeing recipe
Dye 1-5%
Acetic acid (80%): 2-5% [pH 4-5]
Glauber salt: 10-25%
H2SO4: 1%
L:R= 1:20
Time 45-60 min
Mordanting recipe:
K dichromate: 2%
Temperature: 80-100°C
Time 45 min
M:L = 1:20
Dyeing procedure
· Prepare the dye bath with acetic acid and glauber salt.
· Temperature of the bath is raised to 50-60°C and the goods are entered
· The liquor is brought to boil for 30 min
· H2SO4 is now added to complete exhaustion and boiling is continued for another 30 mins
· When dye bath is exhausted and boiling has been continued for long enough for the color to be level, the temperature is allowed to drop and Potassium dichromate is added
· Chroming is continued at boil for 30 min
It is extremely important to make certain that goods are dyed uniformly before the dichromate is added because there will be no further migration afterward. The dye liquor must also be virtually exhausted before mordanting, because of dye remains in solution it will be precipitated on the surface of the fibers in form of its insoluble lake and cause poor rubbing fastness.
Disadvantages:
· Color matching is difficult as the process of mordanting means that the color builds up gradually
· Length periods of applications are both detrimental to protein and polyamide fibers and rather costly.
· Dichromate salts become pollutants once they are discharged into sewerage.
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