Inks ???
What are they ?
How are they used ?
Halftone and Colour Printing
Links
Have you ever thought why your wallpaper has a pattern ?
How you can get thursty of just looking at a sixpack ? Why your furniture looks like expensive
wood where it's only cheap chipboard ? Why your handbag looks like lizzard leather where in fact
it's only ordinary plastic ? up
It's a fascinating job working in this industry ! up
That is the classical way with very "thick" inks, having a consistence
somewhere between toothpaste and peanut butter and due to their consistence also called
"paste inks" or "fatty inks". A more modern way is so called FLEXO printing, where the
printing surface is made from rubber or photopolymer plastics and the image can be laser
engraved or produced by applying a strong light source onto the photopolymers, washing away the
non exposed parts and hardening the remains. In this case, the inks are much "thinner", between
water and, let's say, salad dressing and quite logically are called "liquid inks".
In industrial printing, Intaglio can be diverted in two classes:
1) The real Intaglio that is mainly used for banknote printing:
A very deep engraving and consequently a very thick layer of ink so that the blind can "touch"
the banknote similar to braille and due to some specific spots on the note can recognize the
value of it. Inks for this application are of the "paste ink" type and have to withstand all
possible and impossible attacks.
2) The industrial printing for long runs: Where letterpress, flexo and offset are either to
slow or the materials (rubber clichés in flexo, offset plates etc.) are not resistant enough,
you go to gravure. Making a steel cylinder, covering it with copper, polishing it, engraving it
and protecting it with chromium costs a lot of money and is too expensive for short runs, but
if you want to print some millions of magazines, it's still the cheapest way ! The inks for
industrial gravure printing are from the "liquid" type.
*Wiping: On real Intaglio banknote printing, the wiping is done either with a roll of tissue
that runs against the rotation direction of the printing cylinder or with a roll of paper. The
use in both cases is similar to the use of toilet paper: you wipe (and throw away) the surplus,
in this case quite a lot of ink ! Is that one of the reasons why banknotes are so expensive ?
In industrial gravure, where liquid inks are used, you just let rotate the cylinder in a bath
of ink and then clean the surface by the means of a so called "doctor blade". That's some kind
of a very thin knife that scratches over the cylinder, and as the ink is liquid, it will drop
down again into the bath.
The basic principle of lithographic (or planographic) printing is that a flat (plane) printing
surface is devided into areas accepting the ink and others refusing the ink without cutting
or etching the surface. The inventor, Alois Sennefelder from Bavaria is therefore called the
father of the offset process. He found that if you draw on a polished limestone with a greasy
pen or crayon, then rinse the limestone with water, roll over it with a greasy ink, the ink
will adhere on the spots where the limestone was covered with the greasy crayon, but will be
repelled on the spots where the limestone was wetted with water. After putting a paper over
the inked limestone, you get a mirror image of the limestone on your paper. Artists still do it
that way producing the so called "litho's" but for industrial printing the limestone is since
long replaced by metallic "offset plates". Nevertheless, the principle is similar: You first
dampen your (chemically treated) plate, then try to ink it. Where the plate is wet, it will
refuse the ink. Theoretically, you can print from the plate, but to give a better print, you
first transfer the contents on the surface of the plate (including the water film) onto a soft
rubber blanket which then will give a better transfer onto the relatively rough surface of the
paper. In doing so, you will also print a negative image with water, but this water is a)
invisible, and b) first penetrating very quickly into the pores of the paper and later on
evaporating. It sounds logical that this can be done only with greasy (fatty) inks.
(The other way would be possible too:) Draw with a water based pen, then dampen the non
printing areas with a volatile solvent e.g. white spirit and cover the printing areas with a
water based ink, but this process would be far to dangerous for industrial use !!!
The principle of screen printing is that you have "a screen", in flatbed screen printing
normally a fine synthetic fabric, in rotary screen some kind of a metallic drum with a lot of
holes in it. A photopolymer coating is applied over the whole surface, then exposed and the
surplus washed away. So you can "block" parts of the screen where you don't want to print.
When you put the screen onto a paper, pour the ink over the screen and press it through the
holes with a squeegee, you will get an impression of the non-blocked holes on your paper. This
kind of printing is widely used under artists (think at the Marilyn series of Andy Warhol or
the Austrian artist F. Hundertwasser) Industrial applications of flatbed screen are mostly for
very small runs where it's not worth the money to use more refined technics.
A variation of screen printing is the so called "pad printing" where you first do a screen print
on a very flexible surface and then press this surface as long as the ink is still fresh and wet
against the stuff to be printed. This is generally used for irregular non-flat surfaces like
plastic bottles etc. A good simulation of pad printing can be found on one of the links.
Other applications of screen- and padprinting with VERY SPECIAL INKS which are no classic
printing inks and I therefore don't go into the details are:
a)printing of integrated circuits e.g. motherboards for PC's and b) printing on glass, china or
ceramics where the print then is burnt in. upPrinting inks
Most people think at the word "ink" about something to fill their fountain
pen with, or, looking very far, at newspapers, where in the past they got black fingers from
reading. But inks go much further !
Because all this stuff is printed !
What are they ?
(Rather dry stuff !) As a general rule, most
of the modern printing inks are composed of a) carrier composed of a resin and a solvent to
dissolve this resin, b) a "pigment" to give it a color and c) some additives. The oldest resins
are natural products like tree gum, tar pitch, derivates of boiled linseed oil etc. The first
solvents were vegetable oils, still used frequently today in modern offset inks. Later came
mineral spirits and for liquid inks organic solvents like alcohol (that's why some printers are
always so happy), but the future for liquid inks is WATER ! The first pigments were natural
ones like the mineral pigments earth yellow, iron oxyde red, ultramarine- and cobalt blue and -
most important - lamp black.Nowadays, with the exception of vegetable oils in offset inks and
tar pitch as a cost reducer for cheap newspaper inks all the ingredients are manmade, even the
lamp black and specially the colored pigments. All this stuff is - simply said -
mixted together in specially designed mills and whoop: the ink is
ready ! Modern printing inks have to withstand a lot of attacks from different mediums without
being damaged, just think about the banknote you forgot in your shirt and that went into the
laundry or the inks used for the furniture industry where you can buy one table today, a second
one after 5 years; and if they are printed with a good ink, you won't see the difference. But
you also have the opposite side, for instance inks for checks which fade or change colors if
you try to fiddle with the check.
How are they used ?
You can get a printed image in the
classical way of "printing" in four different ways, which i'll name according to the main
principles:
a) Relief Printing
This is the oldest method of printing: The artist draws a pattern on
any suitable surface, then cuts away a portion of the surface so that only the desired image
remains on the surface. When inking the surface, only the parts which are not cut away can
accept the ink and later on transfer it to the paper. Just think at the potato stamping we all
did as kids. Look also on the net for "wood engraving", "wood cut" or "lino cut". You can cut
letters (or drawings) out of wood, linoleum or do it the other way round: cut the desired
image into a soft form and fill that up with hot, liquid lead. After cooling down and removing
the lead from the form, you have a "letter", that's why this process is also called
"letterpress"
b) Intaglio Printing
Intaglio printing is the opposite of relief printing: the image to be printed is "cut" into
a surface (mostly copper), the surface is covered with ink in a way to assure that all "holes"
are filled with ink, then the surface is wiped* clean so that only the ink in the engraved
parts is left over and then is transferred onto the paper. This "cutting" can be done really by
cutting with a needle, (in modern gravure mostly with a diamond) or chemically by etching. On
etching, you cover the plate or cylinder with an inert material and then use an etching needle
to draw your pattern in this material. Then you put the plate into a bath filled with a strong
acid which will attack the plate on the spots where it is not protected, but will not attack
the protection layer. After that, you wash away the protection layer with a suitable solvent.
The "hottest" new way in the real meaning of the word is burning in with a laser, but that's
only in an experimental stage at the moment. After one of the above mentioned processes, the
plate or cylinder theoretically can be used, but as copper is a very soft metal, normally it's
covered with a very fine layer of some mils of the very hard metal chromium to assure a longer
life of the copper image before being "erased" by the friction of the wiping* devices. Classical
masters of etching are Leonardo da Vinci and Albrecht Duerer (who doesn't know his praying hands ?),
but it's still today a very frequently used expression of art.
c) Lithographic Printing
d) Screen Printing
Rotary screen is mainly used for textile printing and (in a minor amount) also for vinyl wall
and floor covering.
SOME GOOD LINKS :
Website of the Museum Plantin-Moretus, a 16th century print shop in Antwerp, very interesting !
More details about etching and "dry point" in the time of Rembrandt
There are some interesting sites at the university of Delaware over color printing in the 19th century.
Have a look at:
Intaglio processes (with nice prints)
b) artistic
"Nature Printing" How to use a natural object as a printing plate
How the photogravure printing process works on an artist's press with a good description and photos
c) technical
The Philadelphia Printshop has a very good reference library covering nearly all possible
questions concerning printing. You MUST go to the link "What is a print ?"
The company Kingvideo tries to sell you their videos about printing, but also has some extracts
of these videos on the net. Try:
"Halftone" - An initiation in the raster process or
"Printing Press" describing in detail the offset process on a four color press
An animated demo how the pad printing process works
The department where I'm responsable for: click on "industrial"
Banknotes in detail
The reference library of another printing ink company with a lot of hyperlinks for professionals
b) artistic
"Nature Printing" How to use a natural object as a printing plate
How the photogravure printing process works on an artist's press with a good description and photos
c) technical
The Philadelphia Printshop has a very good reference library covering nearly all possible
questions concerning printing. You MUST go to the link "What is a print ?"
The company Kingvideo tries to sell you their videos about printing, but also has some extracts
of these videos on the net. Try:
"Halftone" - An initiation in the raster process or
"Printing Press" describing in detail the offset process on a four color press
An animated demo how the pad printing process works
The department where I'm responsable for: click on "industrial"
Banknotes in detail
The reference library of another printing ink company with a lot of hyperlinks for professionals
c) technical
The Philadelphia Printshop has a very good reference library covering nearly all possible
questions concerning printing. You MUST go to the link "What is a print ?"
The company Kingvideo tries to sell you their videos about printing, but also has some extracts
of these videos on the net. Try:
"Halftone" - An initiation in the raster process or
"Printing Press" describing in detail the offset process on a four color press
An animated demo how the pad printing process works
The department where I'm responsable for: click on "industrial"
Banknotes in detail
The reference library of another printing ink company with a lot of hyperlinks for professionals
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