Offset Plate
Technology
Surface Chemists
Overview
• Offset Plate Production requires multiple steps or phases in
the manufacturing process. Material handling and inspection
to specific tolerances is critical for successful output. The
following components apply:
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Coil Inspection
Degrease / Clean coils
Graining
Anodizing
Post Treatment
Coating
Converting
Packaging
The Manufacturing Process
• Manufactures of offset printing plates “alter the surface of
aluminum” to produce products that meet specific
requirements for imaging quality and printing performance.
• The process requires producing plates from coils of aluminum
that are supplied from aluminum mills. Aluminum is supplied
in specific mill gauges, holding metallurgical tolerances for
tinsel strength, elongation, hardness, flatness, etc….
• Litho sheet is a highly specialized product (represents 1% of
the total aluminum industry) that must be devoid of surface
imperfections. After the coating process, the material must be
void free from the factory to deliver the best quality products.
Aluminum Coils
Coils of aluminum are mounted to a continuous production process.
Cleaning Coils
• At the rolling mills an oil
lubricant is applied to the
coils of aluminum. The
first phase in the process
of creating an offset
plate is to degrease or
clean the coils with a
cleaning agent like
Trisodium Phosphate
(TSP).
Graining
• The grain of the plate acts as the foundation of an offset plate.
There are different methods of graining which include
mechanical, chemical, electrochemical and a combination of a
mechanical/electrochemical process.
• Producers increase the surface area of the plate adding
“teeth” or “peaks and valleys” to the smooth surface of
aluminum.
• This permits subsequent chemistries to adhere to the surface
and makes the plate more abrasion resistant to stand up to
the “hostile printing press”.
• Graining helps the plate surface carry water.
Micro Photo Grain 300X
Micro Photo Grain 1000X
Electrochemical Graining
Anodizing
• Anodizing provides the ability to obtain longer run-lengths or
physical impressions from the plate. The following
characteristics are improved via anodizing:
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A) Abrasion resistance
B) Scratch resistance
C) Corrosion resistance
D) Improves the water carrying or hydrophilic properties of the plate.
• Anodizing places a controlled oxide layer in/on the surface of
aluminum, which is more uniform and consistent then what
exists in nature. In the anodizing process, we essentially strip
off the existing oxide layer (provided by nature) and replace it.
Anodizing continued….
• Anodizing is like a “hard ceramic porous sponge” sitting in/on
the aluminum. In the process, a hot water seal closes the
pores trapping the anodic layer in the pores of the aluminum.
• Manufactures control the thickness and hardness of the oxide
layer by adjusting the concentration of acid (sulfuric acid,
phosphoric acid) and amount or electrical energy used in the
process.
• On a scale from 1-10 with talc being a 1…and 10 being a
diamond, the anodic layer is in the range of an 8 similar to the
hardness of a Sapphire stone.
Anodizing
Post Treatments
• Post treatments are used after the anodizing process to create
a barrier layer between the hydrophilic anodized aluminum
and the subsequent coatings applied for imaging.
• There are multiple options available to manufactures for the
post treatment process including Sodium Silicate, Polyvinyl
Phosphonic Acid (PVPA), Phosphate Fluoride and others.
• The post treatment process creates a photo glue, allowing
analog and digital coatings to adhere to the surface of the
plate for imaging.
Monitoring the process
• During the manufacturing
process, automated
systems are in place to
monitor tank
concentrations,
temperature, line speed,
electrical current, etc.,
while surface topography
and coatings are
inspected utilizing video
and laser inspection
systems.
Coatings
• Plate manufactures apply specifically tuned coatings to the
plate for the creation of plate products.
• The spectral sensitivity of plates are designed to be receptive
to specific wave-lengths.
• Analog plates = 360-380nm
• Violet CTP plates = 405nm
• Thermal CTP plates – 830nm
• The process involves applying specific coat weights and must
be very tightly controlled and monitored. The amount of
energy required for imaging is directly related to the speed
and sensitivity of the coatings being applied.
Coating line
Converting
• All suppliers of plate products convert coils of coated product
into sheet form to meet your pressroom requirements. Plates
are converted holding specific tolerances for length, width,
burr, flatness and squareness.
• Every package of printing plates includes a package ID number
or in some cases a bar code that correlates to the internal
manufacturing records of the supplier.
• Packaging specifications are supplier specific, but for the most
part the delivery of plates to the end user is pretty straight
forward.
Converting
Questions?
J. Faulkner
National Accounts Manager
Anocoil Corporation