ABSTRACT

Production of carbon black from novel sources like spent automobile tyre, anthracite coal, furnace soot and graphite rod and subsequent use in the production of offset printing inks has been investigated. Carbon black from these sources were obtained by pyrolysis of shredded spent tyre and coal samples at 750-900^oC in an electrical furnace, isolation of furnace carbon black and graphite rod from dry cell, drying and pulverization of the resulting samples. Acid demineralization of the samples for 24hr followed with distilled water rinsing and oven drying at 110^oC for 12 hr were also carried out before sieving. The production of offset printing ink from the synthesized carbon black samples each of particles <37µm was done by oleoresinous varnish preparation method using a product formula. Viscosities of the produced ink were measured at room temperature (18000 mPa.s) and viscosity-temperature variation of the ink was determined as well. The ink showed viscosity–temperature stability at higher temperature (≥ 35^oC). Tests such as viscosity, dispersion, shade, drying, adhesion, scratch resistance, gloss, flexibility, water resistance, heat resistance, opacity, transparency, and tack were carried out, being dictated by their end use. Printability and product consistency with imported black ink were verified. The produced ink quality showed a little variation with the imported ink. However, the results indicate that inks of carbon black from furnace and tyre <37µm size gave the best result besides their blends whereas carbon black from coal and graphite rod of the same size gave fair results.

 

 

TABLE OF CONTENTS

Title page        –           –           –           –           –           –           –           –           –           –           i

Approval page –           –           –           –           –           –           –           –           –           –           ii

Certification    –           –           –           –           –           –           –           –           –           –           iii

Dedication      –           –           –           –           –           –           –           –           –           –           iv

Acknowledgement      –           –           –           –           –           –           –           –           –           v

Table of contents        –           –           –           –           –           –           –           –           –           vi

List of tables   –           –           –           –           –           –           –           –           –           –           ix

List of figures –           –           –           –           –           –           –           –           –           –           x

List of abbreviations, symbols and notations –           –           –           –           –           –           xi

Abstract          –           –           –           –           –           –           –           —          –           –           xii

Chapter 1: INTRODUCTION

Historical overview     –           –           –           –           –           –           –           –           –           1

Writing ink and preservation  –           –           –           –           –           –           –           –           5

Ink composition          –           –           –           –           –           –           –           –           –           7

Printing ink     –           –           –           –           –           –           –           –           –           –           17

Printing ink and processes      –           –           –           –           –           –           –           –           18

Manufacturing process description     –           –           –           –           –           –           –           23

Statement of problems            –           –           –           –           –           –           –           –           28

Aim/objectives of the study    –           –           –           –           –           –           –           –           28

Scope/limitation of the study  –           –           –           –           –           –           –           –           28

CHAPTER 2: LITERATURE REVIEW

Background    –           –           –           –           –           –           –           –           –           –           29

Carbon black   –           –           –           –           –           –           –           –           –           –           30

Conversion of waste tyre into carbon black   –           –           –           –           –           –           34

Reprocessing of used tyres into activated carbon and other products           –           –           35

The Improvement of carbon black from waste tyres for offset printing ink

using coupling agent   –           –           –           –           –           –           –           –           –           38

Ink chemistry and processes   –           –           –           –           –           –           –           –           38

The science of colours –           –           –           –           –           –           –           –           39

Pigments         –           –           –           –           –           –           –           –           –           –           42

Pigments and dyes      –           –           –           –           –           –           –           –           –           53

Linseed oil      –           –           –           –           –           –           –           –           –           –           54

Drying oils for printing inks    –           –           –           –           –           –           –           –           57

Chemistry of drying oils         –           –           –           –           –           –           –           –           58

Drying process of printing ink            –           –           –           –           –           –           –           60

CHAPTER 3: MATERIALS AND METHODS

Materials/Apparati      –           –           –           –           –           –           –           –           –           66

Reagents and chemicals          –           –           –           –           –           –           –           –           67

Methods          –           –           –           –           –           –           –           –           –           –           67

Ink manufacture          –           –           –           –           –           –           –           –           –           70

Ink printing tests         –           –           –           –           –           –           –           –           –           71

Images of instruments used and processes     –           –           –           –           –           –           72

CHAPTER 4: RESULTS AND DISCUSSION

Carbon black samples images as obtained                  –           –           –           –           –           75

Properties of carbon black produced  –           –           –           –           –           –           –           77

Viscosity results          –           –           –           –           –           –           –           –           –           80

Press ink test results    –           –           –           –           –           –           –           –           –           81

Effect of temperature on printing performance         –           –           –           –           –           81

Effect of temperature on viscosity     –           –           –           –           –           –           –           82

Temperature effects on ink flow         –           –           –           –           –           –           –           83

Mathematical model   –           –           –           –           –           –           –           –           –           84

Viscosity-temperature model  –           –           –           –           –           –           –           –           84

Conclusion/summary   –           –           –           –           –           –           –           –           –           85

Glossary          –           –           –           –           –           –           –           –           –           –           87

References      –           –           –           –           –           –           –           –           –           –           89

 

 

CHAPTER ONE

1.0       INTRODUCTION

Ink is a liquid or paste that contains pigments and or / dyes and is used to colour a surface to produce an image, text or design. Ink is used for drawing and / or writing with pen, brush, or quill. Thicker inks, in paste form, are used extensively in letter press and lithographic printing. Chemists view it as a colloidal system of fine pigment particles dispersed in a solvent¹. The pigment may or may not be coloured, and the solvent may be aqueous or organic.

Ink can be a complex medium, composed of solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, flourescers, and other materials. The components of inks serve many purposes; the ink’s carrier, colourants and other additives control flow and thickness of the ink and its appearance when dry.

1.1       HISTORICAL OVERVIEW

The origins of printing can be traced back several centuries. Pictorial prints were produced from cut wood blocks in Japan during the tenth century and probably earlier in China. The first movable type, moulded in clay, can be traced to China in the eleventh century, and wooden type appeared in China in the fourteenth century. In Europe, book production from wood blocks was seen early in the fifteenth century, and Gutenberg introduced cast metal type in the middle of the fifteenth century. These inventions were the basis of the original printing method, namely letterpress printing.

As the first printing was a development from writing and drawing/painting, it was natural that the first printing inks would be based on writing inks and paints. They were composed of lampblack or coloured minerals dispersed in water-soluble gum. However, Gutenberg soon found that the aqueous gum solution-based inks did not wet metal type surfaces satisfactorily. The composition of the inks developed by Gutenberg is not known with certainty but was probably derived from the artists’ paints of the time. These were based upon vegetable oils, such as linseed or nut oil, which were heated to increase their viscosity and fortified with natural rosin; to accelerate drying, metal salts were added. The first clear records of compositions of printing inks date from the seventeenth century and are of this nature.²

 

Until the middle of the eighteenth century, printers made their own inks. When the specialist industry of ink manufacture began to develop, the ink supplied was little more than concentrated pigment dispersion. Any skilled printer considered that he was a craftsman and would modify the ink that he purchased with his own ‘secret’ additives to give the printing properties that he wanted. During the eighteenth century, there were many publications of printing ink formulations. They all followed the same basic composition but included the use of other vegetable oils and natural resins, gave more details about the pigments used and focused on the details of the manufacturing methods. Throughout this period, a significant hazard to the ink makers (in terms of fires, vapours and spills) was in the heating of the various oils. Some of the processing even required the hot oils to be ignited and then extinguished with a metal cover.

The lithographic (or litho) process was introduced in 1796 in Germany by Alois Senefelder. This process relied upon a particular type of hydrophilic limestone upon which images were drawn with greasy inks. These images were then receptive to oil-based inks, while the remainder of the surface was not. The first lithographic inks were composed of beeswax, tallow soap and lampblack, again produced by heating and burning.

Gradually, the basic composition of letterpress and litho inks began to converge, with

rosin-fortified linseed oil being the basis of most coloured inks and rosin oil or mineral oils being the basis of blacks. The difference between the inks for the two processes was minor, but important; the litho inks contained additives and had a substantially higher viscosity.

The invention of phenol-formaldehyde resins and the introduction of oil-soluble formulations in the 1920s initiated the era of synthetic resin media. Then in 1936, petroleum distillates were introduced to create the two-phase quick-setting mechanism that is the basis of the majority of conventional letterpress and litho inks used today.² Although printing was carried out by letterpress for many centuries, this process has declined rapidly in the last two decades and is now limited to a few specialist applications and those sectors where older equipment has yet to be replaced.

Rotary letterpress printing from rubber printing plates (stereos) originated around

1890 and took the name ‘aniline printing’ from the aniline-derived dyes that were dissolved in water or alcohol to make the ink. The crude process has been refined since then, particularly over the last 30 years, and has developed into a discrete process in its own right under the name of flexographic (or flexo) printing. The basic dyes still have limited use but modern inks are based upon synthetic pigments in a wide range of synthetic media dissolved in volatile solvents, such as industrial methylated spirits (denatured ethanol).

The intaglio process, in which the image is engraved as a recess in a metal plate, was probably first used for printing purposes in the fifteenth century. A very viscous ink, which was likely to be similar to the letterpress inks of the time, was wiped over the surface so that it filled the recesses but was removed from the surface. A much refined form of this basic process is still in limited use for high-security printing such as the printing of bank notes.

An evolution of ‘the intaglio process occurred in 1852 with the introduction of a method of etching the image into the plate rather than relying on the highly skilled art of engraving. This has led to the rotogravure or gravure process of today. A coating of dichromated gelatin was exposed to sunlight and then etched with a solution of ferric chloride. A variety of techniques’ were used over the years to control the depth of the etching and thus the strength of the print produced. Modern production is by mechanical or laser engraving so that the light-sensitive coatings and etchants have largely fallen out of use. In the early days, the gravure inks were similar to those of intaglio printing. By the end of the eighteenth century, metal ‘doctor blades’ had been introduced to replace the wiping of the surplus ink with a cloth, but the inks remained the same. It was not until the end of the nineteenth century that the ‘liquid’ inks were introduced. The earliest of these were water-based and probably similar to the aniline inks of the time. These were later abandoned in favour of inks containing hydrocarbon solvents and natural or synthetic resins.

Screen printing is a small segment of the printing industry, for which the history is less well recorded. As a development of stenciling, the process has been in use for many centuries, primarily for the decoration of textiles. In the 1920s, it started to attract attention as a convenient way of producing short runs of posters and for printing on difficult surfaces such as glass. The process has developed as a means of depositing heavy films of ink upon a wide variety of substrates, often of difficult shape. In the early days, no suitable inks were available for screen printing, and use was made of ordinary decorative paints. Modern screen printing inks are based on a wide range of synthetic resins and polymers in a range of sol vents with suitable volatility.

At the end of the 1960s, a totally new technology, ultraviolet (UV) ³ curing, was introduced into printing ink formulation.^{4, 5}

These 100%-solids systems polymerize by mechanisms of free radicals or acid catalysis initiated by irradiation with suitable wavelengths of UV radiation. The technology was initially developed for litho and letterpress printing but soon spread to screen ink formulations and is now being introduced to flexo and gravure printing.

Although the smallest companies and industries in lesser developed regions may still use older technologies, the printing and printing ink industries today are generally very different from those of 50 years ago. Rapidly changing technologies, automation and computer control, and safer materials and processes characterize the industries today in the developed countries.

Today’s inks are divided into two classes – printing inks and writing inks. Printing inks are further broken down into two sub-classes: ink for conventional printing, in which a mechanical plate comes in contact with or transfers an image to the paper or object being printed on; and ink for digital non-impact printing, which includes ink-jet and electro-photographic technologies.⁶

Colour printing was made primarily with linseed oil, soybean oil, or a heavy petroleum distillate as the solvent (called the vehicle) combined with organic pigments. The pigments are made up of salts of nitrogen-containing compounds (dyes) such as yellow lake, peacock blue, phthalocyanine green, and diarylide orange. Inorganic pigments also are used in printing inks to a lesser extent. Some examples are chrome green (Cr₂O₃), Prussian Blue [Fe₄ [Fe(CN)₆]₃], Cadmium yellow (CdS), and Molybdate orange ( a mix of lead chromate , molybdate, and sulfate).

Black ink is made using carbon black. White pigments, such as titanium dioxide are used either by themselves or to adjust characteristics of coloured inks. Inks also contain additives such as waxes, lubricants, and drying agents to aid printing and to impart any desired special characteristics.⁶

The use of soy bean oil-based inks has gained in popularity in reducing their volatile organic content which was considered a major threat to the atmosphere. The American Soybean Association was very effective in the late 1980s at promoting the use of soy oils in printing inks. The extent to which soybean oil can replace the petroleum oil varies with the kind of ink, the greatest proportion (about 50%) being possible with news ink. Reports were made on black and coloured inks consisting of 100% vegetable oil-based vehicles which met the industry standards for lithographic and letterpress newsprint applications.^7,8 In Europe, alkyd drying oils are progressively replaced by rapeseed or sunflower alkyds. Furthermore, fatty methyl esters from these oils have been also investigated.⁸In 2000, the soy ink’s U.S. market share reached about 22 percent and it was estimated that the full potential could consume 40 million bushels of soybeans annually. Furthermore, 25 percent of the colour newsprint in Japan is now soy ink.

1.2.      WRITING INK AND PRESERVATION

Older style writing inks, such as in fountain pens, use a fluid water-based dye system. But in the 1950’s, when ballpoint pens became fashionable, the writing ink industry shifted to paste-like oil-based dye systems. The thick consistency allows capillary action to keep the ink flowing well, and the inks generally are non-smearing and quicker drying than water-based systems. Dyes tend to be preferred over pigments for writing inks because pigments cannot be dispersed minutely enough and tend to clog the pen tip. Water-based dye or pigment systems are still used for markers, highlighters, and roller ball pens. A few pen manufacturers, such as ‘BIC’ (which sell about three million pens per day), make their own ink, but most pen manufacturers buy their ink.⁶       

The two most used black writing inks in history are carbon inks and iron gall inks. Both types create problems for preservationists. A Chinese ink-stick made in the form of lotus leaves and flowers is shown in figure 1.1 below.

 

Figure 1.1   Chinese ink sticks; carbon-based and made from soot and animal glue.

Carbon inks were commonly made from lampblack or soot and a binding agent such as gum Arabic or animal glue. The binding agent keeps the carbon particles in suspension and adhered to paper. The carbon particles do not fade over time even when in sunlight or when bleached. One benefit of carbon ink is that it is not harmful to the paper. Over time, the ink is chemically stable and therefore does not threaten the strength of the paper. Despite these benefits, carbon ink is not ideal for permanence and ease of preservation. Carbon ink has a tendency to smudge in humid environments and can be washed off a surface. The best method of preserving a document written in carbon ink is to ensure it is stored in a dry environment.⁹ Recently, carbon inks made from carbon nanotubes have been successfully created. They are similar in composition to the traditional inks in that they use a polymer to suspend the carbon nanotubes. These inks can be used in inkjet printers and produce electrically conductive patterns.¹⁰

1.2.1    Iron Gall

Iron gall inks became prominent in the early 12th century. They were used for centuries and were widely thought to be the best type of ink. However, iron gall ink is corrosive and damages the paper it is on.¹¹ Items containing this ink can become brittle and the writing fades to brown. The original scores of Johann Sebastian Bach are threatened by the destructive properties of iron gall ink. The majority of his works are held by the German State Library, and about 25% of those are in advanced stages of decay.¹² The rate at which the writing fades is based on several factors, such as proportions of ink ingredients, amount deposited on the paper, and paper composition.⁹ Corrosion is caused by acid catalyzed hydrolysis and iron (II)-catalyzed oxidation of cellulose.¹³

Treatment is a controversial subject. No treatment undoes damage already caused by acidic ink. Deterioration can only be stopped or slowed. Some  think it best not to treat the item at all for fear of the consequences. Others believe that non-aqueous procedures are the best solution. Yet others think an aqueous procedure may preserve items written with iron gall ink. Aqueous treatments include distilled water at different temperatures, calcium hydroxide, calcium bicarbonate, magnesium carbonate, magnesium bicarbonate, and calcium phytate. There are many possible side effects from these treatments. There can be mechanical damage, which further weakens the paper. Paper colour or ink colour may change, and ink may bleed. Other consequences of aqueous treatment are a change of ink texture or formation of on the surface of the ink.¹⁴

Iron gall inks require storage in a stable environment, because fluctuating relative humidity increases the rate that formic acid, acetic acid, and furan derivatives form in the material the ink was used on. Sulphuric acid acts as a catalyst to cellulose hydrolysis, and iron (II) sulphate acts as a catalyst to cellulose oxidation. These chemical reactions physically weaken the paper, causing brittleness.¹⁵

1.2.2    Indelible Ink

Indelible means “un-removable”. Some types of indelible ink have a very short shelf life because of the quickly evaporating solvents used. India, Mexico, Indonesia and other developing countries have used indelible ink in the form of electoral stain to prevent electoral fraud. The Election Commission in India has used indelible ink for many elections. Indonesia used it in their last election in Aceh. In Mali, the ink is applied to the fingernail. Indelible ink itself is not infallible as it can be used to commit electoral fraud by marking opponent party members before they have chances to cast their votes. There are also reports of ‘indelible’ ink washing off voters’ fingers.¹⁶

1.3       Ink Composition

Ink formulations vary, but commonly involve four components;

• Colourants
• Vehicles (binders)
• Additives
• Carrier substances.¹⁷

Colourants: are used more frequently than dyes because they are more colour fast, but they are also more expensive, less consistent in colour and have less of a colour range than dyes.¹⁷

Pigments: pigments are solid, opaque particles suspended in ink to provide colour. Pigment molecules typically link together in crystalline structures that are 0.1-2µm in size and comprise 5-30% of the ink volume.¹⁷ Qualities such as hue, saturation and lightness vary depending on the source of pigment. In printing inks, pigments are used almost exclusively, save with flexo inks.

Pigments, by their chemical nature, are further divided into

• Inorganic pigments
• Organic pigments.

Furthermore, there are metallic pigments, pearlescent pigments, fluorescent pigments, and others more. Pigments are usually referred to by their Colour Index name or formula number
(e.g. P.Y. 12, CI No. 21090 = Pigment Yellow 12, formula number 21090). Inorganic pigments account for the achromatic inks.

The most important white pigment is titanium dioxide, which serves to make white inks; calcium carbonate, also a white pigment, is only used as an extender. The most important pigment at all is carbon black, as it is the only pigment used in the manufacture of the most important printing ink, the black one. There are several processes to form carbon black; they all rely on the thermal decomposition or the incomplete burning of hydrocarbons such as fuel oil or natural gas. “Furnace black” and “channel black” are produced most frequently.

Particle size in some carbon black pigment

			i.		Channel Black,	surface area	110 m²/g
			ii.		Furnace Black,	surface area	80 m²/g
			iii.		Acetylene Black,	surface area	65 m²/g
			iv.		Lamp Black,	surface area	20 m²/g
			v.		Blacking,	surface area	15 m²/g

Inks generally fall into four classes;

1. Aqueous
2. Liquid
3. Paste
4. Powder

Liquid inks are employed in gravure and flexo printing, while paste inks are used in letterpress and lithography. Screen inks are intermediate between paste and liquid inks. As inks containing carbon black as the only pigment show a brown shade, Milori Blue or methylene Blue is added to counter that.¹⁸Table 1.2 below shows various kinds of pigments and their industrial applications.

 

 

Table 1.1   Use of inorganic pigments18
titanium oxide
iron oxides		–				–		–
carbon black							–
chromate pigments					–	–	–	–	–
molybdenum red pigments			–	–	–	–	–	–	–
zinc pigments		–			–		–	–
cadmium pigments		–			–	–	–	–	–
chromium oxide pigments		–	–		–	–		–	–
ultramarine blue		–			–	–	–	–	–
iron blue			–	–	–		–	–	–

	very important
	medium importance
	rarely used
–	not used

Inorganic coloured pigments are very rarely used nowadays, as they usually contain toxic heavy metals (chromium, cadmium, lead, etc.). For green and blue shades, phtalocyanine pigments are employed. These molecules contain a very stable system of aromatic rings. For red and yellow inks, azo pigments are most frequently used. Their formula contains the azo group, -N=N-. Organic pigments account for the coloured inks.

The human body is able to cleave the azo group into the compounds which it is made of, and thus producing aromatic amines, some of which are carcinogenic. The simplest examples to illustrate this are poly-enes of the type;

Obviously the wave-length of maximum absorption is the longer the more expanded the conjugated system is. If it is big enough, enters the visible region. Then the molecule shows the colour complementary to the colour absorbed. Figure 1.2 below shows some pigments for coloured printing ink like yellow, magenta and cyan colours.

 

yellow (azo pigment)

Magenta (lithol pigment) Cyan (copper phthalocyanine) – form

Figure 1.2       Pigments for Coloured Printing Inks¹⁷

Special pigments: Pigments for metallic inks consist of small metal flakes, which act as tiny mirrors. They are, however, larger than usual pigments (several µm as opposed to fractions of a µm). “Silver” pigments are made of aluminium, while “gold” pigments are made of brass or dyed aluminium. Pearlescent pigments are coated with very thin layers of titanium dioxide, some silicate material, etc. The thickness of these layers is only fractions of the wave-length of visible light, so parts of the reflected light are extinguished by interference.

Fluorescent pigments give extremely brilliant inks. They absorb light of the visible or UV-range and emit it again at some other, longer wave-length. Hence, most fluorescent pigments are red or yellow. They are most effectual when illuminated in the dark with ultraviolet light. They may also be employed for security purposes (stamps, banknotes, etc.).

Dyes (or dye stuff): These are soluble in the material they are used in. They are rather scarce in printing inks, but they are of some importance in flexo inks and for some special applications, e.g. heat transfer printing, invisible (i.e. fluorescent) inks, and cheque security inks. Some of these dyestuffs, called basic dyes, are quite popular because of their high tinctorial strength and brilliant shades, but they soon fade when exposed to light. They also need some mordant, which helps to make the prints more resistant to water. As basic dyes usually are soluble in water; and they are a bit more frequent in water-based inks than elsewhere. One of the most popular dyes is eosine, which is well known from the teachers’ red fountain pen ink and it also shows a strong yellow-green fluorescence.

Dye-based inks are generally much stronger than pigment-based inks and can produce much more colour of a given density per unit of mass. However, because dyes are dissolved in the liquid phase, they have a tendency to soak into paper, making the ink less efficient and potentially allowing the ink to bleed at the edges of an image.

To circumvent this problem, dye-based inks are made with solvents that dry rapidly or are used with quick –drying methods of printing, such as blowing hot air on the fresh print. Other methods include harder paper sizing and more specialized paper coatings. The latter is particularly suited to inks used in non-industrial settings (which must conform to lighter toxicity and emission control) such as inkjet printer inks. Another technique involves coating the paper with a charged coating. If the dye has the opposite charge, it is attracted to and retained by this coating, while the solvent soaks into the paper. Cellulose, the wood-derived material most paper is made of, is naturally charged, and so a compound that complexes with both the dye and the paper’s surface aids retention at the surface. Such a compound is commonly used in ink-jet printing inks.

An additional advantage of dye-based ink systems is that the dye molecules interact chemically with other ink ingredients. This means that they can benefit more than pigmented ink from optical brighteners and colour-enhancing agents designed to increase the intensity and appearance of dyes. Because dyes get their colour from the interaction of electrons in their molecules, the way the electrons can move is determined by the charge and extent of electron delocalization in other ink ingredients. The colour emerges as a function of the light energy that falls on the dye. Thus, if an optical brightener or colour enhancer absorbs light energy and emits it through or with the dye, the appearance changes, as the spectrum of light re-emitted to the observer changes.

A more recent development in dye-based inks are dyes that react with cellulose to permanently colour the paper. Such inks are not affected by water, alcohol, and other solvents. As such, their use is recommended to prevent frauds that involve removing signatures, such as check washing. This kind of ink is most commonly found in gel inks and in certain fountain pen inks.

Vehicles or varnishes: They serve to bring the pigment in a printable form and fix it onto the printing stock. The use of the terms “vehicle”, “varnish” and “binder” is somewhat confusing. Some say, a varnish is made up of a binder and a vehicle; others say, vehicle and varnish are the same. The components of the vehicle mainly depend on the drying process and hence on the printing process envisaged.

Binders refers to that part of the vehicle which remains on the printing stock, may be

• just dissolved in some suitable solvent, which is removed after printing (suitable substances usually are called resins),
• formed from the vehicle or parts of it by means of a chemical reaction, or
• a mixture of both.

Resins are the comprehensive expression for a broad selection of naturally occurring, semi-synthetic or synthetic materials which are employed as (e.g.) binders for printing inks. Chemically, they are polymers. They are solids or rather viscous liquids. Most of them are of a non-crystalline structure. Natural resins include;

• Rosin from pine trees, which can be separated into turpentine oil and colophony. Colophony is amber, hard and brittle substance. Its main constituent is abietic acid.
  It cannot be used as such, but must be chemically modified, e.g. esterified with glycerol or reacted with maleic or fumaric acid anhydrides.
• Asphalt, which is the residue when crude oil or coal tar are distilled. They are very dark and hence can only be used for black inks. There are naturally occurring materials of a similar composition (e.g. Gilsonite).
• Shellac is made from the secretion of an insect. Its special property is its solubility in methylated spirit and, after saponification, in water. Its importance has declined.

Semi-synthetic resins include:

1). Alkyd esters. These are polyesters made of (e.g.) phthalic acid esters and glycerol, which are modified with some fatty acid. Depending on the fatty acid employed, the alkyd may be “drying” or “non-drying”.

2). Chemically modified cellulose, such as

1. nitrated cellulose
2. ethyl cellulose
3. Sodium carboxymethyl cellulose, etc.

Synthetic resins are virtually innumerable. Important examples include;

1. acrylic resins
2. polyvinyl acetate
3. polyvinyl alcohol
4. polyamide resins
5. polyurethane resins
6. epoxy resins, etc.,

Solvents are used to dissolve the binders of printing inks. They are also used, by the manufacturer and by the printer, to adjust the viscosity of the ink to the printer’s requirements. The solvents used in printing inks include mineral oil, other aliphatic and aromatic hydrocarbons, ketones, esters, and alcohols. These substances do not take part in any chemical reaction.

Important examples include;

• toluene, xylene
• mineral oil 280/310 (boiling point range, °C)
• mineral spirits 80/110, 100/140
• acetone, methyl ethyl ketone (MEK)
• methyl isobutyl ketone (MIBK)
• ethyl acetate, isopropyl acetate
• n-propyl acetate, isobutyl acetate
• methoxy propane, ethoxy propane
• methanol, ethanol, iso-propanol, n-propanol
• water

Next to their chemical nature and, hence, their solubilizing properties, the boiling point is the most crucial property when choosing suitable solvents.

For printing inks, the following boiling point ranges are common:

Flexo and gravure   ——      80- 140^oC

Screen printing        —-        130 – 210^oC

Heat-set web-offset   —       240 – 280^oC

Cold-set web-off-set, letterpress —-280 – 320^oC

In a sense, the “drying oils” in chemically drying inks and the reactive fluids in UV-curing systems also are solvents. They serve every purpose of a non-reactive solvent, although in the end they are not removed, but become part of the binder. Evaporating solvents are a major source of environmental pollution by printing plants. They should be recovered or, at least, destroyed. The following combinations of binders and solvents in table 1.2 below are common for printing inks:

TABLE 1.2: SOLVENT AND BINDER COMBINATIONS¹⁸

Process	Binder	Solvent
Newsprint	Hydrocarbon resins e.g. asphalt	Mineral oil
Offset	Drying oils, alkyd resins, modified rosin, hydrocarbon resins	Mineral oil
Metal decorating	Alkyd resins, melamine resins	Mineral oil
Publication gravure	Modified rosin, hydrocarbon resins	Toluene
Flexo, packaging gravure	Nitrated cellulose, polyvinyl acetate, polyamide resins	Alcohols, esters, ketones, mineral spirits
Water based flexo, packaging gravure	Maleic resins, acrylic resins shellac	Water, alcohols

 

 

 

 

Additives: make up only a few percent of the total ink, but may have tremendous effects on the performance of the ink. They are the best part of the manufacturers’ know how.

Additives include:

• Optical brighteners
• Driers
• Anti-skinning agents
• Thixotropy promoters
• Adhesion promoters
• Waxes
• Plasticizers
• Surfactants
• Defoaming agents
• Biocides
• Deodorants
• Micro-encapsulated perfumes

Optical brighteners: are used to make inks more brilliant. They are fluorescent chemicals similar to fluorescent pigments. They absorb ultraviolet light and usually transform the energy contained into blue or bluish-green light. As the eye (or the brain) regards bluish white as particularly white, such inks are perceived as extremely brilliant.

Driers: usually are cobalt or manganese compounds. These heavy metals act as catalysts to accelerate oxidative drying.

Anti-skinning agents: are employed to prevent the ink from drying on the printing machine. For this purpose, among others, phenols are employed. These chemicals are more readily oxidized than the drying oils contained in the ink and consume the oxygen. So the drying of the ink does not start until the anti-skinning agent is exhausted – even if the printer would like them to do so now.

Adhesion promoters: Titanium chelates, among others, form chemical bonds between binder and printing stock. Both must contain hydroxyl (-OH) groups.

Waxes: may be natural or synthetic in nature. They are employed to improve mar-resistance, slip and water repellency of the print. The term “wax” is used for any material suitable for these purposes, whatever its chemical nature (polyethylene waxes, other hydrocarbon waxes, Teflon waxes, beeswax, carnauba wax, etc.). Waxes are usually employed as pastes.

Plasticizers: They are used to make the dried film of printing ink more flexible. Their mode of action has been explained in the general polymer section. The plasticizers used in printing inks usually are esters of medium sized alcohols with phthalic acid, dioctyl phthalate, (DOP), being the most important of all, citric acid, stearic acid, etc.

Surfactants: These are employed to reduce surface tension and thus to minimize wetting problems, especially with difficult printing stocks.

Defoaming agent: They may become necessary if surfactants are contained in the ink. Usually silicones are employed.

Biocides: These prevent microbial degradation of printing inks. Conditions in a printing ink are not so hostile to microbial life as one might expect. This is particularly true for water-based inks.

Deodorants: They do not prevent, but mask unpleasant odours. Some manufacturers even add peppermint, lavender, or vanillin aroma to their inks.

Micro-Encapsulated Perfumes: These may be liberated by rubbing the print with one’s nail. They are usually contained in coatings. So a print of roses smells of roses etc. These inks, however, lose their fragrance fairly quick.

 

1.4       Printing Ink

Printing inks are a mixture of pigments, oils, resins, solvents, and driers. The fluid component of the ink, made of binders (oils and resins) and solvents, is called the vehicle. The vehicle serves as the dispersing and carrying agent for the pigment particles and gives the ink the required rheological properties of flow and plasticity. Vehicles carry pigments through printing presses and transfer and bind the ink to the surface to be printed.^{19, 20}

Pigments are the solid, coloured part of printing inks which are visible to the eye when viewing printed material. As in paints, pigments provide inks with colour, opacity, durability, and body or consistency. Pigments, as well as binders, determine whether or not a print will bleed in water, oil, alcohol, fats, acid, or alkali. Thus, pigments are partially responsible for determining the end use of the ink. Ink pigments, like paint pigments, may be classified as either organic or inorganic and natural or manufactured.^{19, 20} Oils serve as one of the film-forming agents in letterpress, lithographic, and offset inks.

Most oils used in the manufacture of printing inks are classified by their origin as mineral oils, vegetable oils, animal oils, and synthetic oils. Vegetable oils are further categorized into the drying oils and the non-drying oils. Non-drying oils are used in vehicles which dry by the absorption of the vehicle into the paper. These oils penetrate the substrate, soft absorbent papers such as news and comic paper, rather than evaporate from the substrate’s surface. Drying oils dry by oxidation.²⁰ Vegetable drying oils are most often used in printing inks. The primary vegetable drying oils are linseed oil, China wood oil, perilla oil, and soya bean oil. Steadily replacing the natural oils are synthetic oils such as dehydrated castor oil, re-esterified fish oil, acids, and long-oil alkyds.¹⁹

Resins are one of the primary components in printing ink vehicles. Along with oils, they serve as film-forming ingredients (binders) and impart to the ink gloss, drying speed, improved hardness, toughness, and scuff-resistance. Resins are divided into two classes: natural resins and synthetic resins. All natural resins, with the exception of shellac, are formed by solidifying the viscous sap of trees. Fresh sap contains both resins and volatile oils. Although the oils are normally removed by distillation or evaporation, residual volatiles may remain in the treated resin and eventually contribute to the volatile content of the ink product. Several synthetic resins include phenol formaldehyde resins, alkyds, polyesters, vinyls, silicones, and polyurethanes.¹⁹

The ink industry refers to solvents as any organic liquid used to dissolve film-forming materials and keep them in solution until the ink is applied to the surface to be printed. When the ink has been applied, the solvent should be removed quickly to allow the ink to dry. Ink formulators use a number of different solvents including ketones, ethers, esters, alcohols, alcohol ethers, chlorinated compounds (methylene chloride, carbon tetrachloride, and trichloroethylene), and some aromatic hydrocarbons such as toluene and xylene.¹⁹

Driers are used in inks which contain oxidizable oils or vehicles which form films by oxidation. The driers, most often organic salts of metals such as lead, manganese, and cobalt, act as catalysts and are added to drying oils to increase their normal drying rate. The metal constituent imparts the drying action, while the organic portion of the salt carries the metal into solution, or dispersion, with the oil. Too much drier causes the ink to skin and dry on the press, fill in halftones, and causes the sheets to stick and offset in the pile.^{19, 20}

Inks, like paints, may contain small concentrations of additives. Additives perform a special function or impart a certain property to the coating. Additives include biocides, surfactants, antifoams, and waxy or greasy components. The waxy and greasy components are used to improve the working and setting qualities of the ink, and to eliminate offsetting, sticking, and picking problems. Waxes may be cooked directly into the vehicle, or prepared as a compound and added to the ink.^{19, 20}

Inks may also be classified by use and according to the type of vehicle used in the formulation. The four primary types of inks are letterpress inks, lithographic and offset inks, gravure inks, and flexographic inks. Typically, flexographic and rotogravure inks employ a solvent carrier, while letterpress, lithographic, and offset inks are of an oil or paste base.

 

1.5       Printing Inks and Processes

1.5.1    Lithographic (offset) inks

The broad spectrum of applications for lithography requires a wide variety of inks to serve the needs of the offset printing industry.^{21, 22, 23, 24} Table 1.3 outlines the various printing processes, drying systems and vehicles.

Table 1.3        Printing ink, drying systems and vehicles

S/N	Drying System	Printing Process	Type of Vehicle	Example
1	Absorption	Newspaper printing (letterpress or cold-set web offset)	Non-drying oil	High boiling petroleum oils (mineral oil, b.p. 280-350°C)
2	Solvent Evaporation	Heat-set /web off set	Solvent/ Resin	Lower boiling petroleum distillates (b.p within 240-300°C) with resins and drying oils
		Gravure	Solvent/ Resin	Toluene (Publication gravure),or ethyl acetate and alcohols(packaging gravure) with resins
		Flexography	Solvent/Resin	Alcohol, ethyl acetate or water and resins
3	Oxidation	Letterpress, Offset,Intaglio	Drying oil/Resin	Linseed oil varnish with resins and driers (Cobalt or Manganese soaps)
4	Precipitation	Letterpress (Specialty)	Glycol/Resin	Moisture-set inks(glycol solvent with water-soluble resins binder)
5	Radiation Curing (UV or electron beam)	All Processes	Monomers	Acrylate or Vinyl ether epoxy resins for the oligomers, reactive resins and  monomers(with photo-initiators for UV curing)
6	Quick-Setting	Litho, Letterpress	Drying oil/resins distillate	Linseed oil/resin with petroleum distillate (b.p 260-280°C)

Adapted from National Association of Printing Ink Manufacture²¹, Kübler ²², Bassemir et al.²³ and Williams²⁵

 

Newspaper offset (cold-set) printing inks are typically very simple. Blacks are carbon black in a high-boiling mineral oil with asphaltic material (Bitumen, Gilsonite).²⁶ Such inks could consist of up to 70% mineral oil²⁷ which, in the past, might have contained up to 15% aromatic hydrocarbons. During the last decade, these mineral oils have been replaced with grades that have about 5% aromatics, of which less than 0.1 % are polycyc1ic aromatic hydrocarbons (PAHs).²⁸ Coloured inks generally have a Soya bean oil vehicle instead of mineral oil. For recycling of newsprint, the ink must be removable and therefore these inks do not contain binders that undergo significant oxidative cross-linking.

Heat-set web offset inks are designed to produce high-gloss printed images (magazines, books). They contain lower-boiling mineral oils that are removed (within 1 sec) as the printed roll (web) passes through a hot air oven. A typical formulation might be: organic pigments (15-25 wt %), hard resins (25-35 wt %), soft resins and drying oils (5-15 wt %), mineral oil (B.P. 240-260 °C; 25-40 wt %) and additives (5-10 wt %). ^{22, 25}

Sheet-fed offset inks are used in commercial litho presses for printing, for example, advertising brochures, business papers and packaging, on individual sheets rather than long rolls. Inks are based on phenolic or maleic acid-modified rosin ester and alkyd resins in vegetable drying oils (linseed, soya, Tung) diluted with mineral oil. Inks dry by quick-setting, i.e. by absorption and oxidation. A typical formulation would be: organic pigments (12-20 wt %), hard resins (20-25 wt %), soft resins and drying oils (20-30 wt %), mineral oil (b.p. 250-300 °C; 20-30 wt %) and additives (5-10 wt %). ²²

Radiation-cured offset inks, which are based on acrylate or vinyl/ether monomers, are becoming very important in both sheet-fed and web offset processes. The printed substrate is exposed to UV radiation or an electron beam at the end of the press, and the ink sets within a fraction of a second. To exclude the oil-based ink from the hydrophilic areas of the printing plate, all offset litho printing processes require water-based fountain or dampening solutions. These solutions are typically slightly acidic aqueous solutions (pH 3.5-5.5) containing small amounts of buffers, alcohols, surfactants, hydrophilic polymers (gum Arabic or cellulose derivatives), complexing agents ethylene di-amine tetra acetic acid, (EDTA) and preservatives.

 

1.5.2    Letterpress inks

While letterpress is being replaced by other printing processes, it is still used to a limited extent to produce newspapers, magazines, self-adhesive labels, packaging and other printed products ^{21, 22, 23, 25}. Letterpress news ink is similar to web offset inks used to print newspapers.

Moisture-set inks have been used for food packaging printing and contain maleic or fumaric acid-modified rosin products or modified phenolics as binders in glycol solvents. The printed surface is treated with steam or a fine mist of water, and the water-insoluble acidic binders precipitate, setting the ink. Water-miscible inks maintain the stability of the ink through an organic base that evaporates or is neutralized to induce drying. A variety of other ink types have been used in letterpress printing, inc1uding heat-set, quick-set, water-washable and high-gloss inks.²¹

 

1.5.3    Flexographic inks

Flexographic inks are liquid inks, rather than pastes, and are designed to dry quickly primarily by evaporation. Both solvent- and water-based ink systems are used extensively in flexography. Common solvents in the solvent-based inks inc1ude the lower alcohols (ethyl, n- propyl, isopropyl,²⁹ usually mixed with esters and sometimes small amounts of higher glycol ethers or aliphatic hydrocarbons to obtain optimum resin solubility, viscosity and drying speed. A wide variety of resins are used in solvent-based flexo inks, such as nitrocellulose, polyamides, cellulose esters, acrylics and various modified rosins. Although pigments are the most common colourants, there is some use of both basic and metal-complex dyes in flexographic inks. Because much of the flexographic printing is on non-absorbent flexible packaging (polyethylene ³⁰, polypropylene, ³¹ poly (vinyl chloride), ³² ink additives may inc1ude plasticizers to promote formation of a flexible ink film and waxes to add rub resistance. ^{21, 22, 23}

For environmental reasons, the solvents in ink are being increasingly replaced by water. Approximately 50% of all flexographic inks have water as their primary solvent.²³ Resins in these water-based formulations are generally acidic acrylates or fumaric acid-modified rosin or shellac, neutralized with ammonia or volatile amines, which evaporate from the printed substrate and thereby set the ink film. A typical water-based flexographic ink for paper or paperboard contains: organic pigments (12-15%), resins (10-25%) and additives (5-7%); the remainder is water. For printing on plastics, the ink usually contains a small amount of alcohol (2-5%) and more additives (6-10%).²²

Water-based flexographic printing also finds some application in newspaper printing, but it still represents only a small segment of the market (6-7% in the United States in 1992),²³ and removal of the ink from newsprint before recyc1ing the paper remains a problem. UV-cured inks are also beginning to be used in flexographic printing. Their composition is similar to the UV- cured offset litho inks although they are less viscous. ^{22, 33}

 

 

 

1.5.4    Gravure inks

Gravure inks are similar to flexographic inks except that ketones and aromatic hydrocarbons can be used as solvents, providing much greater latitude in the selection of binders.²³ In the United States, gravure inks are divided into 10 categories according to the type of binder or solvent. For example, aliphatic hydrocarbons (hexane, VM&P (varnish makers’ and painters’) naphtha, mineral spirits) are used mainly in type A, B and D inks; aromatic hydrocarbons (toluene, xylene) ³⁴ are used in types B, D, M and T; and ketones (acetone, methyl ethyl ketone) and esters (ethyl, isopropyl, n-propyl and butyl acetates) are required for type C ink.²³

Gravure inks also are c1assified according to the printed product. ‘Publication gravure’ (magazines, catalogues) utilizes hard resins dissolved in toluene and/or aliphatic solvents. Resins include maleic acid-modified rosin and phenolic resins, calcium and zinc resinates hydrocarbon resins and others. Polyethylene-based waxes are often added to improve abrasion resistance. A typical publication gravure ink might contain: pigments (8-15 wt %), resins (15-20 wt %), solvent (60-70 wt %) and additives (0.5- 5 wt %).²²

‘Packaging gravure’ does not use hydrocarbon solvents but rather uses esters and alcohols (type C inks in the United States nomenclature). For various packaging substrates, resins may inc1ude cellulose nitrate, maleic resins, acrylates resins, polyurethane resins and polyamide resins, or mixed polymers of vinyl chloride/vinyl acetate/vinyl alcohol. Plasticizers (phthalates, citrates, adipates) also may be required, especially with cellulose nitrate. Basic dyes are used occasionally, in addition to pigments, in gravure inks. More recently, water-based gravure inks (type W), with formulations very similar to the water-based flexographic inks, are finding increasing use in packaging gravure. ^{21, 22, 23}

A special application of gravure (as well as other processes) is in printing with transfer inks. Aqueous inks containing selected textile-disperse dyes are printed and dried on special papers. The printed image can then be transferred by sublimation to the textile materials (e.g. polyester fabric) by pressing at approximately 200°C.²² Intaglio is another specialized process using a higher-viscosity ink in which a high quality image is engraved on a steel plate. Inks often contain special high-durability pigments, filers to increase viscosity, drying oil vehic1e and a number of additives. This process is used in printing paper currency (bank-notes), postage stamps, stock certificates and similar products.^{22, 23}

1.5.5    Screen process inks

Screen printing is a highly versatile process that can apply a thicker film of ink to the substrate than other printing processes. A very wide range of ink formulations is available, depending on the substrate and the requirements for the printed product. Drying may be by evaporation, oxidation, radiation-curing or other processes. Any of the resin types found in litho, flexo and gravure inks may be used, and the solvents can be of almost any type as long as they evaporate at a suitable rate, which is slower than that required for flexo and gravure. Solvents (propylene glycol ethers, aromatic and aliphatic hydrocarbons and cyclohexanone) typically have somewhat higher boiling-points than those used in gravure printing, and inks are more viscous. ^{22, 23, 35} Although newly introduced product ranges are usually lead-free, screen printing is the one process that still makes significant use of lead chromate pigments. The use of n-vinyl pyrrolidone ³⁶ in UV-cured inks has declined.

 

1.6       MANUFACTURING PROCESS DESCRIPTION

Paint and ink facilities use similar manufacturing processes to produce their respective products. Most small plants (i.e., facilities employing less than 20 people) produce paint in 10 to 500 gallon batches, while larger facilities produce paint in 200 to 3,000 gallon batches with stock items made in 10,000 gallon runs.^{37, 38} Inks are produced in batches ranging from one gallon to over 1000 gallons.³⁸ The raw materials used in the manufacture of paints and inks include pigments, solvents, resins (or binders), and other additives. In most cases, the manufacturing facilities purchase these raw materials and then formulate, or blend, a finished product. Normally, no chemical reactions take place during the process. ³⁸

A batch process production of paint and ink involves four major steps: ^{39, 40, 41, 42}

• Preassembly and premix
• Pigment grinding/milling
• Product finishing/blending
• Product filling/packaging

The manufacturing process is summarized thus in figure 1.3;

1.6.1    Preassembly and Premix

The first step in the manufacturing process is preassembly and premix. In this step, the liquid raw materials (e.g., resins, solvents, oils, alcohols, and/or water) are “assembled” and mixed in containers to form a viscous material to which pigments are added. The pigment and liquid mixture forms a thicker material, which is then sent to the grinding operations. At this stage, the particles in the concentrate are rather large (250 pm) and not consistently mixed.³⁹ The premix stage results in the formation of an intermediate product which is referred to as the base or mill base. With further processing, this base with high pigment concentration may become any one of a variety of specific end products.^{39, 40}

a).        Resin production and cooking

Resin production is typically considered the first step in the manufacturing process. However, few paint facilities, and even fewer ink plants, currently manufacture their own resins. This step is now being accomplished in closed reactors in chemical plants. Once the resin has been manufactured, it must be cooked and then converted to a usable vehicle. Over the last decade, this step, like resin production, has become increasingly performed by chemical plants.

Chemical facilities cook resins with oils, fatty acids, or alcohols in indirectly heated closed stainless steel vessels.⁴³These reactors are normally vented through a fractional distillation column and a condenser, so that vaporized compounds are recycled back into the reactor. After the resin has been cooked and then cooled, it is thinned with solvent to produce the vehicle.^{43, 44} The thinning stage is often the point at which paint and ink plants begin their manufacturing process.

1.6.2    Pigment Grinding or Milling

The incorporation of the pigment into the paint or ink vehicle to yield fine particle dispersion is referred to as pigment grinding or milling. This process occurs in three stages (i.e., wetting, grinding, and dispersion) which may overlap in any grinding operation. To wet the pigment particles, the wetting agent, normally a surfactant, must displace all contaminants (e.g., air, moisture, and gases) adsorbed on the surface of the pigment particles. The wetting process actually begins in the premix step, when the pigment is charged to the liquid vehicle.^{44, 45} Grinding is the mechanical breakup and separation of the pigment particle clusters into isolated primary particles. Dispersion is the movement of the wetted particles into the body of the liquid vehicle to produce a permanent particle separation.⁴⁵

The goal of pigment grinding is to achieve fine, uniformly-ground, smooth, round pigment particles which are permanently separated from other pigment particles. The degree to which this is realized determines the coating effectiveness and permanency of the ink. Grinding equipment must work effectively with the vehicle to accomplish this end. Just as there is a variety of pigment vehicles, so there is an array of dispersion (milling) equipment.

1.6.3    Product Finishing

Final product specifications are achieved in the product finishing step which consists of three intermediate stages: thinning, tinting and blending.

a).        Thinning (letdown)

Material letdown, or thinning, is the process by which a completed mill base dispersion is let down or reduced with solvent and/or binder to give a coating which is designed to provide a durable, serviceable film that is easily applied to the substrate. ⁴⁵ The volume of the ink may increase significantly at this point depending on the final product specifications.

b).        Tinting

Tinting is the process of adjusting the colour of completed mill base dispersions. Normally, an operator will collect a sample of the paint or ink once it exits the milling equipment. This sample will be taken to the laboratory and compared to the desired colour standard. Various combinations of pigments, solvents, resins, and pastes are added to the material to meet the colour requirements. ^{39, 40, 41}

c).        Blending

Blending operations occur once the necessary additions have been made to the completed mill base dispersion. Blending is the process of incorporating the additions into the material in order to meet the desired product specifications. In the case of batch operations, blending may simply consist of additional milling in a ball mill or added mixing and dispersing in a portable mix tank/high-speed disperser set-up. In other cases, the mill base dispersion is transferred to fixed agitated blend tanks or additional mix tank/disperser operations. In each case, material adjustments for thinning and tinting are added through top openings, agitated, and gravity fed or pumped out bottom or side spigots for filling operations.^{39, 40, 41, 42}

 

 

 

1.6.4    Product Filling

The final step in paint and ink manufacturing is product filling operations. After the material has been blended, it is transferred from the blend tanks into containers for product shipment. The transfer step normally involves product filtration and mass transfer.

a).        Filtering

Filtering acts to screen out impurities (e.g., dust, gelled resin, and pigment aggregates) and to enhance the quality and uniformity of the product. In the case of media mills, filters prevent the grinding media from exiting the mill and entering shipment containers.^{42, 46}

Paints and inks may be filtered in a variety of ways. Some facilities simply attach cheese cloth or cloth socks to the exiting blend tank spigot.^{39, 41, 42}Other plants use filtering equipment such as strainers or sieves. The Russel Finex strainer consists of a vibrated screen and hopper through which product flows prior to entering shipment containers. The screens may be either metal mesh, supported nylon, or another synthetic fiber. Another strainer, the Jenag strainer, has a vertical chamber holding fiber filters. The paint is fed by gravity or pump to the chamber and drawn through by vacuum.⁴⁶

High quality finishes, such as those used for automobiles and industrial products, may be pumped through wound polypropylene or other resin cartridge filters.^{40, 46} Bag filters, made from felts (rayon, polypropylene, or nylon) or gauzes (polypropylene, nylon, or polyester), can be attached to the flanged end of a supply line and supported by a vibrating wire basket. These bags are usually washable and used only for small batches.^{41, 46}

b).        Material transfer

Once the material has been filtered, it can be transferred into pails, drums, tote tanks, tote wagons, or another container for shipment. Although most paints are sold by volume, most manufacturing facilities find it more convenient to fill the shipping containers by weight using the specific gravity of the paint or ink. Filling may be accomplished either manually or mechanically depending on the number and size of the containers to be filled.^{40, 46}

 

 

 

 

 

1.7          STATEMENT OF PROBLEMS

Investigations of tyre pyrolysis and application of its by products are rarely found in the open literature. While some literatures can be found for the pyrolysis of waste tyre to obtain carbon black for other purposes like its use as an adsorbent there is a scarce application in printing ink production except in one, improvement of carbon black for offset printing ink. Presently, also, no work has been found for the production of printing ink using carbon black from spent carbon rod, furnace soot or coal dust.

Therefore, this research project shall be focusing on the novel approach for synthesis of carbon black from spent tyre, spent carbon rod, furnace soot and coal dust and its subsequent use for printing ink production.

This study shall seek to solve economic and environmental problems which include;

1. Printing inks used in Nigeria are imported from China, India, Europe, America etc.
2. The automobile spent tires take up large amounts of valuable landfill space and also represent a fire hazard and users in Nigeria have found no good means of disposal yet.

• Graphite rods from spent cell battery constitute a major domestic solid waste and users have found no better means of disposal.

1. High cost of printing ink for the printing industry.

 

1.8       AIM AND OBJECTIVES OF THE STUDY

The aim of this study is to carry out laboratory synthesis and production of carbon black from sources such as spent automobile tyre, coal, carbon rod and furnace soot and their use in printing ink industry. The specific objectives of the study are:

• Conversion of spent tyres, carbon rod, coal, furnace soot to carbon black
• Production of printing ink using carbon black
• Quality assessment of the printing ink against industry standard

 

1.9          SCOPE/LIMITATION OF THE STUDY

This research work would have its scope restricted to the production and use of carbon black from spent automobile tyre, graphite rod, and coal in production of offset printing ink (black) for the Nigerian printing industry.

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