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Modern Technology of Textile Dyes & Pigments (2nd Revised Edition)

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Modern Technology of Textile Dyes & Pigments (2nd Revised Edition)

Author: Dr. H. Panda
Format: Paperback
ISBN: 9789381039717
Code: NI67
Pages: 512
Price: Rs. 1,675.00   US$ 150.00

Published: 2016
Publisher: NIIR PROJECT CONSULTANCY SERVICES
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Dyestuff sector is one of the core chemical industries in India. There are two types of colorants dyes and pigments. Dyes are soluble substances used to pass color to the substrate and find applications primarily in textiles and leather. Pigments are coloring materials, which are water insoluble. Key end-user industries of pigments include wood-coloring, stone, textiles, paints & coatings, food and metals. Pigment are usually manufactured as dry colorants and grounded into fine powder. The dyes market, meanwhile, largely depends upon the fortunes of its principal end-user, textiles, which account for about 70 percent of the total demand. Their importance has grown in almost every area of an economic activity.

In the colorants market, Asia-Pacific accounts for the largest share. This region is one of the key markets for dyes and pigments production. In the Asia-Pacific, India and China are the important countries contributing towards the growth of colorants market. Rising consumer spending will drive increased demand for colorants in textiles. Increases in value demand will reflect the growing importance of expensive, higher value dyes and pigments that meet increasingly stringent performance standards. Growing demand for high-quality value-added pigments is one of the key factors expected to result in a spurt in growth.

This book describes the various formulae, manufacturing processes and photographs of plant & machinery with supplier’s contact details. The major contents of the book are metal pigments, black pigments, inorganic colour pigments, organic colour pigments, extender pigments, white pigments, photocatalytic activity of titanium dioxide pigment, azo pigments, bisazo pyridine pigments, high grade organic pigments, high temperature stable inorganic pigments, anti corrosive pigments, metals and metal ions in pigmentary systems, control of organic pigment dispersion properties, pigments for plastics, rubber & cosmetics, pigments for printing inks, vat dyes, reactive dyes, disperse dyes, direct dyes and sulphur dyes etc.

It will be a standard reference book for professionals, entrepreneurs, those studying and researching in this important area and others interested in the field of textile dyes & pigments.


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Contents

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1. Metal Pigments
Aluminium Powder and Paste
Zinc Powder Pigments
Lead Powder and Paste

2. Black Pigments
Carbon Black

3. Inorganic Colour Pigments
Colour in Pigments
Crystal Form and Shape
Hiding Power and Opacity
Tinting Strength
General Characteristics
Manufacture of Colour Pigments

4. Organic Colour Pigments
Toners and Lakes
General Characteristics
Colour in Organic Materials
Manufacture of Organic Pigments
Spot Tests for Colour Pigments
Commercial Pigments
Lightfastness in Tints

5. Extender Pigments
Type of Extenders

6. White Pigments
General Comparison of White Pigments
White lead Pigments

7. Photocatalytic Activity of Titanium Dioxide Pigment
Experimental
Pigment Samples
Florida Exposure Series
Statistical Procedures
Results & Discussion
Acrylic Paints
Alkyd Paints
Summary

8. Use of Flocculation Gradient in Determining the Efficiency of Titanium Dioxide Utilisation in Paint
States of dispersion
Flocculation
Assessment of degree of flocculation
Conclusion

9. Titanium Dioxide Pigments in Water-reducible and Water soluble vehicles
Procedure of the evaluation
Preliminary tests
Results of the investigation
Optical properties of TiO2 pigments
Conclusions

10. Azo Pigments
Red Pigments
Permanent Reds
The Pyrazolone Red
Yellow Pigments
Manufacture of azo pigments
Coupling Component
Coupling preparation
Diazotization
Preparation of Coupling component

11. Bisazo Pyridone Pigments
Experimental

12. Novel Gold Colours and Effects with Environmentally Safe-to-use Mica Pigments
New Golden Pearl Lustre Pigment
Gold Colours and Effects
Other Colours Shades

13. Fluorescent Pigments
Pigment Manufacture
Photostability of Fluorescent Pigments
Fluorescent Application
Phosphorescent Luminous Pigments
Properties and Characteristics
Pearl Luster Pigments

14. High Grade Organic Pigments
Azo Condensation
Vat Pigments and Related Compounds
Thioindigo Pigments
Immersion Processes
Perylene-Perinone pigments
Toning White Enamels
Phthalocyanine

15. Phthalocyanines
Methods for formation of pigments from crude
Acid pasting
Concentration of the sulfuric acid
Amounts of the sulfuric acid
Production of b-form pigment by salt grinding
Manufacture of metal free phthalocyanine
Phthalocyanine complexes from metals other than copper
Flocculation, flotation and flooding
Flotation
Application of phthalocyanine pigments
Phthalocyanine dyes of Textile materials
Phthalocyanine reactive dyes

16 High Temperature Stable Inorganic Pigments

17. New Metal Complex Pigments
Experimental
Metal complex formation
Results and Discussion

18. Latest Developments in Organic Pigments for Automotive Finishes
Violet
Advantages of using Mica Pearl

19. Preparation of Iron Oxide Pigment from Industrial Waste
Preparation of the pigment

20. Anti Corrosive Pigments
Electrochemical theory of Corrosion
Anticorrosive Pigments
Anti corrosive properties of Zinc Dust
Zinc Dust Pigmented coating
Corrosion mechanism
Corrosion mechanism
Good Inter coat Adhesion
Mechanism of Corrosion
Corrosion Control
Preparation of Anti corrosive Pigment Strontium Chromate
Synthetic Lamellar Iron Oxide: a New Pigment for
Anti-corrosive Primers
The need for an improved barrier pigment
Comparisons with traditional iron oxides
Summary and general conclusions

21. An Overview of Aluminium Pigment Technologies
Colour and Sparkle
Distinctness of Image—DOI
Tint strength
Particle size distribution

22. Metals and Metal Ions in Pigmentary Systems

23 Control of Organic Pigment Dispersion Properties
Experimental
Results and Discussion

24 Advances in the Science and Technology of Pigments
Arylamide Azo Yellows
Azo Red Pigments
Heterocyclic Pigments
Metal Complex Pigments
Surfaces treatment
Environmentally safe chemistry
Novelty and profitability pressures

25 Pigments for Plastics, Rubber and Cosmetics
Selection of pigment
Colouring Techniques
Colouring Thermoplastics
Polyethylene
Vulcan Fast and Vulcan Pigments

26. Pigments for Printing Inks
Fastness to Light
Organic pigment for printing ink should offer

27. Vat Dyes
Indigoid Dyes
Indigo
Thioindigoid Dyes
Anthraquinone Vat Dyes
Chemical Constitution of Quinone Vat Dyes
The Reduction of Quinone Vat Dyes
Vat Dye Dispersions
Reducing Vat Dyes with Hydros
Scheme 1
Scheme 2
Manufacture of Common Vat Dyes
CI Vat Brown 1 CAS 2475-33-4
CI Vat Yellow 2 CAS No. 129-09-9
CI Vat Yellow 4 CAS No. 128-66-5
CI Vat Orange 1 CAS No. 1324-11-4
CI Vat Orange 15 CAS No. 128-70-1 6
CI Vat Blue 20 CAS No. 116-71-2
CI Vat Green 1 CAS No. 128-58-5
Waste Streams of Vat Dye Manufacture

28. Reactive Dyes
Nucleophilic Substitution Systems
Trichloropyrimidine Dyes
The Chloropyridazine Systems
Quinoxaline Derivatives
Chloroacetyl and Bromoacetyl Derivatives
Vinylsulphone Dyes
Acrylamide Dyes
Evidence for Chemical Combination Cellulose
Properties of Reactive Dyes
Types of Reactive Dyes
Reactive Dye Structure
Properties

29. Disperse Dyes
Azo Dyes
Anthraquinone Disperse Dyes
Miscellaneous Disperse Dyes
Methine or Styryl Dyes
Coumarm Dyes
Formazine Dyes
Chemical Constitutions of Disperse Dyes
Disperse Dye Dispersions
Fastness Properties of Disperse Dyes
Manufacturing Process

30. Direct Dyes
Chemical Constitution of Direct Dyes
Major Types of Direct Dyes
Cationic Direct Dyes
Anionic Direct Dyes
Classification According to Dyeing Behaviour
Class A
Class B
Class C

31. Sulphur Dyes
Introduction
Properties of Sulphur Dyes
Sulphurised Vat Dyes
Ready-reduced and Solubilised Sulphur Dyes

32. Photographs of Plant & Machinery with Supplier’s Contact Details

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Sample Chapters


(Following is an extract of the content from the book)
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Metal Pigments

Certainly there is no resemblance or connection between metal

pigments and metallic stearates. It was merely a matter of convenience

to group these two short subjects together in one chapter.

The principal metal pigments are those made from aluminium,

zinc and mixtures of copper and zinc which range from 100% copper

to about 70% copper and 30% zinc. Pigments from the copper-zinc

alloys are known as “bronze powders.” Metal lead pigments are

available and metal silver pigments have specialized uses such as

conductive coatings for printed circuits. Similarly, nickel and stainless

steel pigments find use where a combination of metallic appearance

and alkali resistance is required.

The metal industry produces fine particle size metals in both

powder and flake forms which are used in a variety of industries. The

paint industry uses chiefly the flake form of aluminium and bronze

and zinc in the powder form. Since metal, even as very thin foil, is

completely opaque to visible and ultraviolet light, it could be anticipated

that metal pigments would have exceptionally good hiding power.

However, they have relatively low tinting strength and for some finishes

they are coloured with various amounts of colour pigments.

Finely divided metals react with moisture, and hydrogen gas is

one of the products. If this reaction occurs in tightly closed containers

it may develop sufficient pressure to bulge or rupture the container.

Therefore, every effort must be made to store metal pigments under dry

conditions and to use paint vehicles which are as nearly anhydrous

as possible. In many cases two containers are used to ship metallic

paints. One container has the metal pigment and the other contains

the remainder of the paint. Shortly before application the metal pigment

is mixed into contents of the second container.

Metal pigments fulfill several important functions in coatings.

Bronze powders are widely used for decorative coatings. Aluminium

pigments also are used for decorative purposes; in addition, they impart

heat reflective properties, reduced permeability to moisture, and good

durability to coatings. Zinc dust contributes corrosion- inhibitive

properties in primers for iron and steel and excellent adhesion in primers

for galvanized iron. The many applications for metal pigments and

metallic stearates are discussed in later chapters. This chapter outlines

the types, method of manufacture, and general properties of the principal

metal pigments and metallic stearates available at present.

The lubricant is added to prevent the aluminium particles from

being mechanically welded together under impact and also to develop

a bright metallic lustre on the flakes. Usually, the lubricant is stearic

acid but other fats and oils may be used, such as tallow and olive and

rapeseed oils. It is believed that chemical reaction occurs between

stearic acid and aluminium during the milling operation to form a

strongly adhering coating of aluminium stearate on the finished flake.

This coating makes possible the leafing action of the flakes in a paint

film with the resulting brilliant metallic finish. The coating is quite

stable under conditions of normal use, but it may be loosened or

removed at temperatures above 180oF, also by certain solvents, and by

chemical reaction with materials such as lead driers and free acids in

vehicles. Further discussion of conditions for proper leafing is given

later under physical and chemical properties.

The liquid medium for wet milling usually is mineral spirits, but

liquids such as solvent naphtha or certain plasticisers are used for

specific applications. The mill is run until test shows the required

degree of fineness has been attained; then the paste is washed from the

mill with mineral spirits. The batch is filtered and adjusted to the

specified solid content either by drying or by addition of liquid medium.

The solid content of commercial aluminium pastes usually is 65%, but

special grades may be as high as 73.5%. Flake aluminium powders are

produces by complete drying of the paste through evaporation of the

mineral spirits under vacuum. The foregoing process produces the

leafing type of aluminium pigments. These may be treated to convert

them into the non-leafing type, or a special lubricant may be used

which produces the non-leafing type directly.

An indirect indication of the particle size is obtained from the

water-covering test. A weighed amount of powder is dusted on to the

surface of a rectangular pan of water as uniformly as possible between

two movable baffles. The layer of powder then is manipulated by means

of the baffles to produce as extensive an area as possible and still

maintain a continuous layer. The area of this layer is measured, and

the results are expressed as square centimenters covered per gram of

powder. The coverage ranges from about 8000-10,000 sq cm/gm for

the coarse grades, 14,000-18,000 sq cm/gm for the lining grades, and

25,000-30,000 sq cm/gm for the extra fine lining grades.

Leafing grades may be distinguished from the non-leafing grades

by mixing a small amount of paste or powder with mineral spirits of

xylene. The leafing grades produce the familiar metallic surface on the

liquid, whereas the non-leafing graders yield a gray suspension. This

test does not give satisfactory results with liquids having surface tension

values of less than 25. For example, VM&P naphtha does not permit

satisfactory leafing because of its low surface tension values. The extent

of leafing of aluminium pigments is measured by the spatula immersion

test. A polished spatula of standard dimensions is dipped in a specific

mixture of pigment and coumarone resin solution, withdrawn rapidly,

and allowed to drain in a cylinder for three minutes. The coating then

is examined for extent of leafing over the total depth of immersion. The

ratio of the depth of the fully leafed portion to the total depth is

calculated and expressed as percent leafing. This test may be used to

determine possible loss of leafing of an aluminium paint on aging.

Handling and Storage. Aluminium pastes and powders should

be stored in closed containers at normal temperatures. Open containers

permit loss of volatile liquid from pastes with consequent drying and

uncertainty of composition. Free access of pigments to air and moisture

should be avoided. Long exposure to air produces oxidation of the

metal with a consequent loss of adhesion of the stearate layer and

reduction of leafing property. Moisture reacts chemically with finely

divided aluminium with a resulting production of hydrogen gas and

loss of leafing property. The use of paste eliminate the dust hazard

connected with the powder type. In addition, paste has a higher

apparent density, therefore it occupies less space and mixes with paint

vehicles more easily than powder.

 

Black Pigments

Charred bones and soot from smoky fires were used as black

colouring materials by pre-historic man. Modern man also uses bone

black and soot as black pigments for paints and printing inks, but he

has wide range of types and grades of black pigments for specific

applications. In addition to the blacks composed chiefly of carbon, he

used certain inorganic blacks in which good filling properties are more

important than depth of colour. The general types of black pigments

are listed in Table 1 together with their raw materials and approximate

range of composition.

Bone black is obtained by pulverizing carbonized bones. It has

good blackness and also low oil absorption and good filling properties.

Vegetable black is obtained by carbonizing wood and other plant

products. At present it finds-only limited use in coatings, and it is

being replaced by blacks having more uniform composition varies with

source and type of raw material, and they may be replaced with greater

uniformity with mixtures of extender pigments and carbon black.

Mineral black is used in coatings such as freight car paints and metal

primers and surfacers. The natural and synthetic black oxides of iron

are described. They are used where good filling properties are more

imortant than blackness of colour. Antimony sulfide is used almost

excliusively in camouflage paints, since it reflects the same as green

foliage when photographed with infrared film. Black toners are organic

compounds used in conjunction with carbon black to increase the

blackness of specialty finishes. An apprarent increase in blackness of

finishes made with certain standard carbon blacks may be obtained by

addition of up to 25% of in iron blue. The type of iron blue generally

used is the toning blue.

In addition to the black pigments listed in Table 1 the paint

industry uses a variety of bituminous materials such as pitches,

asphalts, and gilsonite in black and dark coloured coatings.

Furnace Black. The furnace process not only give higher yields of

carbon, but also the plant occupies much less space and is free from

the smoke nuisance associated with burner houses. Also, the furnace

process may be adjusted to use either gas or oil as the raw material.

Continued improvements since the furnace process was inaugurated

have produced smaller size particles with better blackness, but it

remains to be seen whether this trend can be continued to produce

colour equal to the better grades of channel black.

In the furnace process the same operations of partial combustion

to produce the necessary temperature and thermal decomposition of

the remainder take place, but a single large flame replaces the large

number of small flames of the channel process. Gas and air are admitted

separately to a firebrick-lined furnace which operates at a temperature

of about 2400oF. Through controlled air supply and the particular

design of the inlet ports, a large portion of the gas is decomposed

instead of being burned completely. The hot gases from the furnace,

carrying the black in suspension, are cooled by water sprays. Then the

products pass through an electrostatic field which agglomerates the

carbon particles so that they may be collected in cyclone collectors,

and the exhaust gases are vented to the atmosphere. From the collectors

the black may be bagged or routed through pelletizing equipment. The

variables in the furnace process are:

Thermal Black. Thermal black represents only a small percentage

of carbon black production. Two general types are produced; one is

based on natural gas as the raw material and the other on acetylene.

The black from natural gas has the largest particle size and greyest

colour of the carbon blacks, and the black from acetylene is intermediate

in size and colour between furnace and channel black. Thermal black

is produced by thermal decomposition without simultaneous

combustion.

In the natural gas process the thermal decomposition takes place

in an insulated chamber containing a network of firebrick. First, the

chamber is heated to 1800-2500oF direct combustion of an air-gas

mixture. Then the combustion is stopped, and a charge of “make-gas”

is passed through the heated chamber. The resulting carbon and spent

gases are cooled by water sprays, and the carbon collected in bag

filters. This process gives a high yield of carbon, but the particle size is

large and the colour is quite grey. Somewhat smaller particle size may

be obtained by diluting the make-gas with spent flue gases.

The carbon content of bone black is about 20% that of carbon

black. Since the hiding power and tinting strength depend on the carbon

content, it will be apparent that bone black is much weaker than carbon

black in these respects. However, bone black is much lower in oil

absorption, therefore a greater percentage can be incorporated in a

formulation without developing excessive consistency. This feature is

desirable in the production of low-sheen black finishes or when good

filling properties are required, such as in leather finishing. Its particle

size, relatively large, is expressed as percent retained on a 325-mesh

screen. When used with other colours it shows less tendency to float

than carbon black because of the larger particle size. Bone black is

fairly easy to disperse in coating vehicles and is wetted by water much

easier than regular carbon black. For this reason it finds use in tinting

calcimine, casein and latex paints, and water base inks. Generally,

bone black is considered too abrasive for lithographic inks, but is used

in artists colours and many standard coatings.

Vegetable Black. Vine black was produced originally from stems

and twigs of grape and hop vines and from organic wastes of the wine

industry. It is the most important member of the family of “vegetable”

blacks which are produced from many kinds of cellulosic materials

obtained from plants and trees. Vegetable blacks are made by dry

distillation and carbonization of the vegetable material in the absence

of air. They range from 30-70% in carbon content, the remainder being

a mixture of calcium and potassium carbonates. As may be expected,

vegetable blacks show an alkaline reaction. They are somewhat low in

colour value and in oil absorption. At present they find very limited

application in coatings and have been replaced to a great extent by

mixtures of furnace black and black iron oxides.

Mineral blacks are coarse pigments with low oil absorption and

good filling properties. They may be used in coatings such as freight

car paints and sanding surfacers. In view of the availability at low

cost of carefully classified extended pigments described, and of the

newer furnace blacks, it would appear that combinations of these

materials could be made by paint manufacturers to meet the

requirements of mineral blacks with possible improvement in

performance.

Antimony Trisulfide. Antimony sulfide occurs in nature as the

grayblack mineral known as stibnite. It may be pulverized to the

required particle size and used as a pigment in camouflage paints.

When such paints are photographed with infrared film, the antimony

sulfide gives the same reflection characteristics as green foliage.

Antimony sulfide may be made by reaction between antimony

and sulfur or by precipitation from solution of antimony trichloride

with hydrogen sulfide. The natural products range from 64-66% Sb2S3,

and the technical grade of precipitated material contains about 94%

Sb2S3. Owing to its low colour value, its use in paints is limited almost

entirely to the camouflags type.      

Extender Pigments

Introduction

Extender pigments are much lower in price than prime pigments

and are used in paints primarily to reduce cost. However, by careful

selection of the partiuclar type of extender for specific paints, it is often

possible to improve certain properties of the paint or the dry coating.

Proper choice of extender may improve properties such as consistency,

leveling, and pigment settling in the paint. Certain extenders reinforce

the structure of the dry coating mechanically, while others increase its

resistance to the transmission of moisture.

Flat finish and semi-gloss paints are produced by using pigment

concentrations high enough to prevent the formation of a layer of clear

oil or resin in the surface of the coating which would give it gloss.

When pigment particles are in the surface they diffuse the light and

prevent specular or glossy reflection. In paints with high pigment

concentration sufficient hiding may be obtained by replacing some of

the opaque pigment with extender pigment. Since extenders are lower

in price than opaque pigments, a reduction in material cost will result.

The refractive indexes of extender pigments range from 1.55 to

1.65, and since these values are only slightly different from those for

oils and resins, extenders generally do not contribute to the hiding

power of paints. In special cases, such as their use in wood fillers and

flat varnishes, lack of opacity is desirable to prevent a “muddy” effect

in clear furniture finishes. Certain chemically prepared extenders such

as Micro-Cel pigments have refractive indexes in the range of those for

oils and resins, but in combination with while opaque pigments they

contribute slightly to hiding power. The reson for this phenomenon is

not clearly understood at characteristics, and the effect of these factors

on the scattering of light in the coating. Detailed knowledge of the

various types and grades of extenders will enable the paint formulator

to produce paints having maximum properties at minimum costs.

Type of Extenders

Extender pigment are obtained from two general sources: (1) by

pulverization of certain rocks and sedimentary deposits; (2) by chemical

precipitation. The two types are referred to as natural and precipitated

extenders respectively. The natural deposits such as limestone, quartz,

and clay are found in various parts of the country, and the pigments

usually are processed at the deposits. The markets are supplied from

local deposits whenever possible, because the low price of extender

pigments will not permit high freight charges. There may be

considerable variation in composition and properties of natural

deposits with corresponding differences in extender pigments obtained

from them. Therefore paint manufacturers having plants in eastern,

central, and western states may have to adjust their formulations

containing extenders to accommodate variations in extenders supplied

to the different plants.

Extender pigments also may be used to advantage to increase the

consistency of paints. Some extenders that have much higher oil

absorption values than white pigments may be employed to increase

the consistency of white paints without raising the cost. The oil

absorption of a particular pigment is directly proportional to its

available surface; therefore the grade having finer particle size usually

has higher oill absorption. Since oil absorption also is affected by the

nature of the pigment surface, the oil absorption values vary among

the different type of extender pigments because their different surface

characteristics as discussed before.

Extender pigments are marketed as white powders, but because

of their low refractive indexes they do not contribute whiteness or high

reflectance to oleoresinous paints. However, some grades of natural

extenders contain traces of metallic oxides, such as iron oxide, which

cause slight discolouration or reduction in reflectance of white paints.

Such grades should not be used for flat or semi-gloss white finishes

but would be entirely satisfactory for coloured finishes or in metal

primers and surfacers.

Extender pigments may vary considerably in characteristics such

as reactivity with components of paint vehicles, sensitivity to and

solubility in water, and in the pH of water slurries. Their reactivity is

due in part to variations in origin and methods of processing, but

some of the reactivity is inherent in the particular extenders. For

example, barytes is very inert chemically and not sensitive to moisture

adsorption, whereas calcium carbonate is more readily affected by acidic

conditions. Calcium sulfate may adsorb sufficient moisture in humid

weather to change the consistency characteristics of a paint. The pH

and specific resistance of water slurries of extenders are important if

these pigments are to be used in water-dispersed paints; they should

be checked carefully. Some extenders have sufficient solubility in water

to liberate enough cations to affect the stability of latex or other types

of emulsion paints.

Calcium Carbonate Extenders. Calcium carbonate extender

pigments are very widely used and are frequently referred to as whiting.

They are available as both natural and precipitated types and in a

wide range of particle size. The very coarse grades are preferred for

putty and glazing compounds, the intermediate sizes for oleoresinous

flat and semi-gloss finishes and caulking compounds, and ultrafine

precipitated grades are available for gloss finished and printing inks.

Natural whiting is obtained from two main sources: limestone

and chalk. Limestone is widely distributed throughout the world and

is found in most of the states of the United States. Limestone and the

related rocks, marble and calcite, are crystalline and were formed in

the earth’s crust by reactions between calcium salts and water

containing carbon dioxide. When magnesium salts were present, a

mixture of magnesium and calcium carbonates were precipitated which

is known as dolomite limestone. Chalk is an oolitic variety of calcium

carbonate and was formed by deposition of shells and marine animals.

Natural whitings are made by quarrying the rock, crushing and

grinding it, and then classifying the powdered material for particle

size requirement. The grinding process may be either dry or wet. In dry

grinding the screened crushed rock is powdered with a hammer or

roller mill and classfied for particle size by the air-flatation process. A

stream of compressed air passes through the mill and carries out the

particles which are small enough to “float” on it; the larger particles

drop back into the mill. The rate of air flow is a factor in the particle

size obtained in the product.

High Temperature Stable Inorganic Pigments

 

The pottery industry has, for several thousand years, been using

high temperature stable inorganic pigments, which do not fade or

discolour even at the high temperatures (between 400o and 1400oC)

required for the maturing of enamels and glazes. Moreover, there are

many examples of beautiful colour and decoration work from as early

as the Shang dynasty in China (1500 B.C.), which have come down to

our period without much change in the shade or brightness of the

colours. While it is true, that the glaze substrate in which these pigments

are embodied, provides substantial protection from contact with air,

water, chemicals and other destructive elements, it is nevertheless also

true that the light-fastness of these pigments must be something fantastic

for them to have remained unchanged for periods of 3000 years and

more.

While the tinting power of many inorganic colours tends to the

rather less than that of organic pigments, inorganic pigments tend to

have greater opacity, hiding power, bleed resistance, and of course

light-fastness. They are more resistant to heat, and, being mostly ionic

bonded, are usually less reactive with the organic vehicles, which are

usually covalent bonded.

High temperature stable inorganic pigments can also be used for

normal temperature applications such as the pigmentation of rubbers,

plastics, paints, cements, etc. Almost any colour and shade, including

those shown in IS:5-1978 and many more not shown in the I.S. charts,

are obtainable with high temperature stable pigments.

High temperature stable pigments are mostly exides, sulphides

or silicates of various metals

Shades of red, yellow, pink and violet are also obtainable from

compounds of tin, copper and gold. Such compounds are, naturally,

quite expensive, but produce very attractive, long lasting shades. Blues

and violets are produced from compounds of vanadium, titanium,

uranium, copper and cobalt. Cobalt colours are, of course, fairly

expensive, but have excellent light-fastness and binding power. They

come mostly in the spinel crystalline form, which are stable upto

1600oC., and inert to acids and alkalies.

Because of chemical stability, light-fastness, resistance to dilute

acids and alkalies, dispersability and compatibility with other organic

and inorganic pigments, high temperature stable pigments make

excellent colours for.

Preparation of Iron Oxide Pigment from Industrial Waste

Paint is used for decoration, protection of metals and functional

applications. The constituents of a paint are vehicle, pigment, solvent

and additivies. Pigments are mainly used for giving body to the paint,

protection and for specialised functions. These are finely divided solids

of different shades used in the paint to give colour, hiding, consistency,

durability, build, etc. These particles are substantially insoluble in water.

Pigments may be classified as natural and synthetic, depending on

their origin.

Iron oxides are extensively used as inert pigments in the paint

industy. A dye intermediate manufacturing industry in the country

was faced with the problem of accumulation of huge volumes of slude

in their factory during the iron and acid reduction process. Efforts

have been made elsewhere to convert the sludge into useful pigment.

These results of the preliminary studies made in this direction are

reported in this paper.

Preparation of the pigment

The sample supplied by the firm contained total iron as Fe2O3-

90.5% and ferrous iron as FeO 3%. The colour of the product was

black. The sludge was washed first with water to remove the soluble

impurities such as chlorides, etc. This washed product was

subsequently subjected to the treatments as shown in Table 1 and visual

observations were made.

A water wash was given to remove the chloride present in the

sludge. It may be seen from the above table that the sludge heated to

500oC at the end of one hour only showed some slight change in the

colour. The temperature was gradually increased from 150oC and the

colour change was observed at 500oC only. The time of heating also

determined by increasing the duration from 30 minutes onwards and

changes could be seen only at the end of 60 minutes. Further heating

did not show any change. No change could be observed when the

slude was treated with different treatments as indicated in Sl. Nos. 2 to

6. When the chloride-free sludge was treated with 10% iron oxide or

pigment grade synthetic iron oxide, the colour of the sludge changed

to that of the pigment grade red oxide at 500oC itself. But the product

was heated to 700oC and maintained there for three hours for the

transformation to be completed. Thus the waste product was converted

into a pigment grade iron oxide.

The water extract of the waste as well as the treated products

were analysed for pH and chloride. It was found that the pH was

neutral i.e. 6.5-7.0 in all the cases except the sludge which was slightly

acidic (

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