1. Basic principles of offset
printing
The principle of oil-water
immiscibility;
The principle of selective adsorption of
plate;
The principle of dot forming;
The principle of indirect printing.
2. Choice of overprint or trapping
in book printing china
If the overprint is not accurate, it is
easy to show white and affect the beauty, and overprint is easy to rub the back
due to the thick ink layer, so the monochrome press dry printing tends to use
overprint, and the multi-color machine wet press tends to use trapping;
Wet press overprint must consider the
nature of the ink, the viscosity and adhesion of the first printing ink must be
greater than that of the later printing ink, otherwise the latter printing ink
will appear reverse overprint phenomenon. After printing ink must also have a
high transparency; When printing
gold ink and silver ink on coated paper, the color obtained by trapping gold
ink and silver ink on white paper is thicker and purer than printing on other
background colors; When
printing black, if there are only large field images on the black plate, the
trapping method is used to increase the ink amount of the black plate, and the
ink color obtained by printing on white paper is thicker than that by
overprinting on other field background colors. But the fine lines are usually
overprint of book printing china.
In order to ensure that the plate is
covered by the back ink layer, the trapping amount is usually increased by 0.03
~ 0.05mm on the basis of the registration accuracy of the equipment. If the
registration accuracy is 0.15 mm, then the trapping part is generally 0.18 ~
0.20 mm larger.
3. Precautions of book printing china
a. Color block overprint color to try to
avoid the use of a small percentage of the dot, such as 20% below the flat
screen dot. Because the color block composed of small dots is easy to cause
partial light shading due to insufficient air suction or fine particles adhered
to the glass of negative film and plate printing machine when printing, it is
easy to drop the plate due to excessive moisture, dirty blanket or plate wear.
The above two reasons can cause uneven ink color. As for less than 5% of the
dot, ordinary offset printing process is difficult to restore, should be
avoided.
b. At the same time, color block overprint
color to try to avoid the use of a large percentage of the dot, such as more
than 80% of the flat screen dot. Because the color block composed of large dot
in the printing water supply is slightly insufficient or the blanket is dirty,
it is easy to paste the plate. More than 95% of the outlets should be
avoided.
c. To avoid too many color number of the
field or a high number of dot overprint color block, as easy as the ink layer
is too thick and cause back rub dirty.
d. When using spot color printing process,
try not to select the color blocks that need to be mixed by too many basic
color inks. Too many kinds of ink mixing will make the allocation of ink more
difficult, not only increase the ink mixing time, but also difficult to deploy
the color of similar hue.
e. When printing a large area of a certain
color with spot color, try to avoid printing small anti white words and lines
with the same color. Because of the large area printing is inclined to increase
the thickness of the ink layer, thick ink layer is easy to spread, but it will
lead to small anti white text and line paste.
f. For the text, in the field in the middle
of the printing anti white small characters, should try to advise customers to
choose bold type.
g. When printing a full plate on the spot,
you can use the plate left after the last printing, and stop water supply
instead of special plate making. However, there is a slight difference in the
adsorption capacity between the photosensitive glue on the graphic part and the
alumina in the blank part on the PS plate. When printing the color with strong
color rendering property (such as dark blue), it is better to select the fully
folded plate.
4. Printing color sequence arrangement in book printing china
Generally, under the condition of wet
pressing, the color of the first printing ink is dominant. For example, if you
print cyan first and then magenta, the overlay color will be cyan; if you print
magenta first and then cyan, the overlay color will be red. And in the case of
wet press dry, it is after printing ink color is dominant. From the point of
view of optics, CMYK color sequence should be used in lithography.
Generally speaking, the color sequence of
warm tone prints based on figure painting should be black, green, magenta and
yellow;
The printing color sequence should be
black, magenta, cyan and yellow for prints with cold colors such as landscape
paintings and snow scenes;
The color sequence of two-color machine
printing is cyan + magenta, black + yellow, while the color sequence of
monochrome printing is cyan, magenta, yellow, black or black, cyan, magenta and
yellow (generally, when the black plate is a skeleton version, black is printed
in front); In order to
facilitate overprint of book printing
china, the color order should be arranged according to the thickness of the
ink layer from small to large, such as black ink 0.8um-cyan 0.9um-magenta
1.0um-yellow ink 1.1um;
Arrange the printing color sequence
according to the order of ink viscosity from large to small, such as black ink
1188pa. S - green ink 488pa. S - magenta ink 477pa. S - yellow ink 147pa. S. if
the ink viscosity can not meet the arrangement requirements, the ink viscosity
can be adjusted in advance;
In book
printing china, the ink with small covering area should be printed first,
and the dark ink should be printed first (because of its high viscosity and
covering power, avoid sticking on the back);
UV ink printing, because of its absorption
of UV photons, resulting in different curing speed, so the color sequence
should be black green yellow fuchsin.
