PS and CTP printing plates are two important kinds of printing plate in commercial printing. What are they and their difference? How to choose aluminum plate substrates? Learn more.

1. PS and CTP Printing Plates
Abstract: PS and CTP printing plates are two important kinds of printing plate in commercial
printing. What are they and their difference? How to choose aluminum plate substrates? Learn
more.
The PS And CTP Printing Plates in China
The PS and CTP printing plates for offset printing features high printing quality, strong printing
resistance, environmental protection, reasonable cost, high resolution, clear writing, fast speed
and strong reproducibility. The aluminum plate base is 1050, 1060, 1070 and 1052 alumnum
plate, of which the aluminum content is ≥ 99.50%, ≥ 99.60%, ≥ 99.70% and ≥ 99.52%
respectively.
Aluminum plate base has the advantages of low
density, high strength, moderate wear
resistance, easy processing, good shape, good
hydrophilicity, high stability, good surface
treatment, strong recyclability, easy
regeneration, abundant resources
andreasonable price, etc,, which makes it an
indisputable high-quality PS/CTP plate
substrate.
The average annual growth rate of China’s
PS/CTP plate output from 2005 to 2011 was
21.32%. The growth rate of the domestic
production from 2011 to 2015 was 11.2%. At
present, China has become a net exporter of
PS/ CTP plate.
For PS plate making, there are two kinds of raw materials: the continuous cast-rolling strip and
the ingot hot-rolled strip. The PS plate quality made of them are almost equal. For CTP pringting
plates, the better choice is to use the ingot hot-rolled aluminum.
In the production of CTP plates, the pure stretch straightening production line is indispensable. It
plays a very important role in ensuring product flatness and performance. Up to now, many CTP
plates manufacturers such as Haomei Aluminum has such production line.
As for the composition of the alloy, there is still a lot of work to be done. Although the aluminum
base plate used in PS/ CTP plate are 1000 series aluminum, from our work experience and
metallological principles, we should regard this type of alloy as Al- Fe-Si alloys. The Fe/Si value
must reach a certain ratio in order to produce high-quality aluminum sheet. It is better that the
Fe/Si value is between 2.5 to 3.5.

2. What Is PS Plate
PS plate, the abbreviation of "Presensitized Plate", is a a lithographic printing plate pre-coated
with a photosensitive resin layer on the aluminum plate substrate. The high-quality aluminum
plate for PS plate is processed by electrolytic grinding and anodizing.
The PS plate features flat coating, uniform thickness, relatively good hydrophilicity, abrasion
resistance, and chemical stability, so its printing resistance is very high, which is suitable for
printing high, precise and fine products.
The commonly used PS aluminum plate substrate is generally 1050 and 1060 aluminum sheet
with H18 temper. In addition to the
production of PS plates, 1060
aluminum plate is also widely used
in positive PS plates, thermal CTP
plates, photosensitive CTP plates,
UV-CTP plates, etc.
The width range of Haomei
aluminum plate for PS plate making
is generally 400-1600mm, and the
conventional thickness is
0.10-0.50mm. The aluminum base
plate should be of high surface
quality and flatness. Therefore, in
order to obtain a high-quality
alumnum sheet, a special
straightening method must be
adopted after cold rolling.
With an advanced straightening processing technology, Haomei aluminum plate substrate can
avoid such defects like hard scratches, leveling marks, and shock marks. In addition, the
electrostatic spraying technology on the matte surface makes the air between the film and the PS
plate during printing smoothly drawn out, so that the vacuuming time is shortened by two-thirds
compared with the PS plate without the matte surface, thereby reducing the plate making time.
Advanced multi-layer sand mesh technology can help the PS plate base to improve the printing
durability. It is composed of sand meshes of different sizes (large waves, medium waves, and
small waves). Each size of the sand mesh shares important performance, so as to well realize the
balance of printing resistane and stain resistance.
How to Choose PS Plate Substrate
PS plate for offset printing is made up of two parts: the photosensitive layer that forms the
graphic part in printing and the aluminum plate that forms the hydrophilic blank part. It features
excellent printing quality, high printing endurance, safety and low cost.
The PS plate substrate is usually 1050 aluminum sheet. The thickness is 0.30mm, 0.27mm and
0.15 mm. The aluminum plate surface is not to have cracks, scratches, oil marks,etc. The gap

3. between plate and horizontal plane is less than 3mm, wave number is less than 3/m and the
diagonal difference is less than 1 mm. Its qualiy has great effect on the quality of PS plate.
1. The surface quality of the aluminum plate
In the making process of aluminum plate, a layer of oxide film will be formed on its surface. At
the same time, the rolling oil and other impurities such as dust will inevitably remain. If it is not
removed, it will directly affect the electrolytic grit shape and anodizing effect, which will finally
influence the printing quality.
Therefore, we must strictly control the surface quality of the aluminum sheet, that is, the defects
depth of the surface and the degree of residual oil stains.
2. The flatness of the aluminum plate
If the flatness of the aluminum sheet is not good or the waves aare large, the distance between
the polar plate and the aluminum
plate is not uniform. Then, the
flow of charged electrolyte
between the two is different. The
electric quantity of the aluminum
plate above the base surface is
very different, thus leading to the
different electrolysis reaction.
The resulting grit size is uneven.
Fine sand meshes have little water
storage and cannot meet the
printing requirements; coarse sand
meshes store a lot of water, and
the blank part of the printing plate
is easy to get dirty. Besides, the
large waves of the aluminum base
plate will result in uneven spray
volume, nozzle cracks and the damage of the pringting equipment.
3. The thickness difference of aluminum plate
The relative elongation of the PS plate is restricted by the thickness of the aluminum base plate.
And the thickness difference of the PS plate will inevitably lead to uneven deformation and cause
inaccurate overprinting during printing.
Therefore, the thickness of the PS plate should be moderate and the thickness difference should
be uniform. Only in this way can it be ensured that it is strong enough and will not cause
excessive deformation.
CTP Printing Plates VS PS Plate
With the rapid development of CTP printing technology and the the continuous decline of CTP
plates price, the usage of CTP pringting plates is also rapidly catching up with the traditional PS
plates. The printing has high overall requirements for plate materials. To ensure the quality of the
printing plate, the apparent quality of the plate base is the prerequisite.
The apparent performance of aluminum sheet

4. The CTP plates have higher requirements on the aluminum sheet such as free of cracks, corrosion
pits, spots, scratches, oil marks and no slight color difference. The PS plate can ignore the above
problems. The main reason is that the CTP equipment uses scanning imaging. The PS plate uses a
vacuum method to make the plate and the film close.
The geometric size requirements of aluminum sheet
The aluminum plate thickness for CTP plate is generally 0.280mm, which is slightly thicker than
that of the PS plate. The thickness of the PS plate substate is 0.270mm±0.005mm. Some printing
companies also use the CTP plate of 0.275mm thickness. The thick aluminum plate is not easy to
bend.
The width tolerance of the CTP plate substrate is required to be ≤±0.5mm, preferably without
tolerance. There are also clear requirements
for the cutting quality of aluminum coils, that
is, there should be no burrs and curling edge
on the both sides after cutting.
The longitudinal and lateral thickness
tolerances of the aluminum plate base should
be ≤±0.005mm. The thickness deviation will
affect the plate making, and the parameters
set by the CTP plate making machine are
generally not allowed to be adjusted casually.
The electrolytic performance requirements of
aluminum sheet
Because CTP printing plates are mostly used
for high-end color printing, the sand mesh
value of CTP plates is smaller than that of PS
plates. The grit value Ra of the CTP plate is
generally 0.45-0.60 μm while the grit value Ra
of the PS plate is generally 0.60-0.80 μm.
Haomei Aluminum has different kinds of printing plates such as PS plate wholesale, CTP plates
and CTCP plate. Welcome to send inquire to dolly@alumhm.com.