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°C 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
110C 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 (> 35C). 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.
CHAPTER 1
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 solvent’. 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 ofprinting 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 Alo is 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. 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. Modem 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
res1ns.
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. Modem 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.°
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 (Cr0O9), Prussian Blue [Fe, [Fe(CN)]], 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.” 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.’ 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.”
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.” 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.14Iron gall inks requrre storage mn 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.’
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 O. l-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
1. Channel Black, surface area 110 m2/g
11. Furnace Black, surface area 80 m2/g
111. Acetylene Black, surface area 65 m2/g lV. Lamp Black, surface area 20 m2/g V. Blacking, surface area 15 m2/g
Inks generally fall into four classes;
A. Aqueous
B. Liquid
C. Paste
D. 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.
This material content is developed to serve as a GUIDE for students to conduct academic research
PRODUCTION OPTIMIZATION AND APPLICATION OF PRINTING INK FROM WASTE CARBON SOURCES>
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