2 :Printing is Process of Transferring an inked image from its carrier unto a substrate under impression.
TYPES OF PRINTING TECHNOLOGIES
1.Letterpress
2. Offset Lithography
Letterpress
The first ever press was a Letterpress. It basically uses stamps to
grab ink and place it on the paper (or other material). Think of a
typewriter, but doing whole pages in one press. Of course, this took
long to do as each page was setup before by hand and manually placing
these letter stamps in place. As time went on, full page stamps were
created instead to make the process easier (though still inefficient
compared to other methods). Today however, the Letterpress is not used
much as it is not an efficient and far too expensive method of printing.
Offset Lithography
This method of printing is the most common used today. It is also
one of the oldest. It works on the principle that water and oil (ink)
don't mix. Using metal or polyester sheets (called plates), image and
non-image areas are burned onto the plate using light to expose the
image areas. this plate is attached onto a cylinder that as it goes
around on the press, picks up water onto the non image areas. since
water and oil don't mix, when the plate comes into contact with the ink,
it only sticks to where the water isn't, our image area. The plate then
comes into contact with a rubber sheet (called a blanket) and it
transfers the image. The blanket them rotates around and presses to
image into the paper. This is where the offset term comes from. While
other methods can be done with offset theories, the Offset Lithography
is so common that when someone refers to offset printing, this is what
they mean.
Flexography
This is traditionally used to print labels. If you look at a bottle
of pop, the plastic or cellophane label on it was likely done by
flexography. It is the packaging industry who primarily uses
flexography. The idea behind flexography is similar to a Letterpress
where it uses a stamp, but this one is created with rubber etched with
tiny grooves that pick up ink. The rubber stamp (plate) wrapped around a
cylinder which rotates and picks up ink from a reservoir then presses
it into the printing material. This is often done on plastics, tissues,
labels, stickers and cardboard.
Gravure
This is a method usually used in printing long runs of magazines.
Much like flexography, gravure printing has a cylinder that picks up ink
in tiny etched grooves and places it on the paper. The difference is,
gravure doesn't use a plate. Its grooves are actually etched into the
cylinder. This allows it to last much longer and can be used for more
impressions (contacts with the paper/material) before it wears out.
Screen Printing
This is still a common method of printing. It is often used on all
the odd materials. Solid letters on plastics, T-shirts and clothing
materials, a lot of signs and others use screen printing. The idea
behind screen prints is basically a screened material such as silk or
nylon is stretched across a frame and fastened into place. A stencil,
cut my hand or made electronically, is placed over that screen to block
out non printing areas. Ink (often rubber based) is placed inside the
frame and scrapped across the stencil with a rubber squeegee. The ink
goes through the screen and onto the material.
Digital Printing
There are several way to do digital printing. Many methods try to
reproduce the effects of the previously described styles. There are
inkjet, laser and toner, and magnetic digital printers. In inkjet, the
ink cartridge holds liquid ink that is released in tiny sprays onto the
paper . It makes several dots, that when viewed without a magnifying
glass creates the illusion of your image. Laser and toner method uses a
laser to charge the paper in certain areas which will attract toner of
cymk colours to it. It then goes through a fuser which melts the toner
into the paper. Magnetic works in much the same way but instead of
electrical charges, it uses magnetic ones. It also passes through a
fuser to melt the toner.this is just rough and brief definitions of printing technologies, in the next articles I'll cover each printing technology in Depth.
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