PRODUCTION OPTIMIZATION AND APPLICATION OF PRINTING INK FROM WASTE CARBON SOURCES

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.

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