Mineral colors

The word ‘Mineral’ indicates that these are inorganic in nature and these colors differ from all other classes of dyes, which are organic compound. Before introduction of the coal for dyes, these mineral colors formed an important section of the dyes.
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