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Rockyphot S, Rockyphot
K, Rockyphot XN, Rockyphot GN 20
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are negative working light
sensitive coatings for use on metals. The coating are particularly
suitable for rotogravure cylinders and plates and are very resistant
against chemical and mechanical strain. The coated material may be
stored in the dark for approx. 6 weeks without suffering from variations
in temperature and air humidity.
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Properties
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Properties
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Rockyphot S
spray- and whirler coating
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Rockyphot K
dip coating
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Rockyphot XN
dip coating
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Rockyphot GN 20
spray-, dip- and whirler coating
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main purpose
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rotogravure package printing
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textile printing, embossing
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rotogravure package printing
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rotogravure printing
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optimum coating thickness
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1,8 - 2 µm
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3 µm
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1,8 - 2 µm
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2 - 3 µm package printing
up to 5 µm textile printing
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resolution
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approx. 4 µm at 2 µm coating thickness
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6 µm at 3 µm coating thickness
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approx. 4 µm at 2 µm coating thickness
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approx. 2 µm at 2,5 µm coating thickness
approx. 8 µm at 5 µm coating thickness
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etching depth
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up to 50 µm ( 70 l/cm gravurescreen)
160 µm (linework)
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up to 180 µm (linework)
up to 50 µm ( 70 l/cm gravurescreen)
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up to 50 µm ( 70 l/cm gravurescreen)
up to 120 µm (linework)
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up to 50 µm ( 70 l/cm gravurescreen)
up to 180 µm (linework)
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drying time
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less than 5 min. at 25ƒC
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minimum 10 min. at 25 ƒC
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approx. 5 min. at 25 ƒC
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minimum 10 min. at 25 ƒC
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viscosity at 20 ƒC
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16,7 - 21,5 mPas
(undiluted)
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40,5 - 46,8 mPas
(undiluted)
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19,1 - 23,5 mPas
(undiluted)
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n/a
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thinner
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Thinner for Rockyphot S
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Thinner for Rockyphot K
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Thinner for Rockyphot XN
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Thinner for Rockyphot GN 20; Special Spray Thinner vor Rockyphot
GN 20
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developer
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Green Developer
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Green Developer
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Blue Developer
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Developer for Rockyphot GN 20 (colouring: blue to black)
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hardening time
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20 min. after development at room temperature
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20 min. after development at room temperature
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10 min. after development at room temperature
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10 min. after development at room temperature
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spectral sensitivity
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370 - 410 nm
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370 - 410 nm
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370 - 410 nm
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300 - 400 nm
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specific features
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Very good contrast after development.
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Very good homogenity after application of coating and very
good contrast after development.
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Particularly suitable for screenwork on engraves cylinders
where such halftones cannot be applied through engraving and
adheres to the engraved parts very well and does not show comets
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Particularly suitable to coat steel and very good resistance
against plating baths.
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Preparation
Preparation of the metal
surface
To achieve an optimum adhesion
of the coating, the metal surface has to be cleaned and slightly roughened.
It is especially important to remove oil and grease residues. The
surface which is to be coated should undergo two preparation steps:
1. To remove dirt, oxides
and irregularities rub the surface with descumming chalk or very fine
wet sand paper. Then the surface has to be rinsed with water and wiped
off with a clean cotton pad under running water. Dry with a hot-air
blower or oil-free compressed air.
2. Chemical preparation of
the surface depends on the metal which is to be coated. The following
list shows which chemical is to be used for which metal. Chemical
preparation is not always necessary and depends on the purpose intended.
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Metal
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Preparation Chemical
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Temperature
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Time
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Copper
Brass
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1 part Hydrochloric acid (37%) + 10 parts water
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room temperature
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30 sec.
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Magnesium
Zinc
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Phosphoric acid (2%)
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room temperature
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30 sec. - 1 min.
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Aluminium
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1) Sodiumhydroxid solution (2%) +
2) Trisodiumphosphate solution (18%)
3) neutralize in 1 part Nitric acid (65%) + 10 parts water
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room temperature
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1 - 2 min.
30 sec.
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Steel
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Due to the differences of steel alloys we cannot give precise
preparation hints for steel materials.
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After treating the metal chemically,
rinse the metal thoroughly with lukewarm water (25 ƒC). It is important
that the material is completely dried with oil free compressed air
or with a hot air blower prior to coating. Do not wipe dry. Best coating
temperature is 25 ƒC.
Coating
Dip coating
For most dip coating operations
Rockyphot K and Rockyphot XN can be used unthinned. Since come types
of coating equipment do no have a suitable pull speed, the original
coatings might have to be thinned. Rockyphot K and Rockyphot XN are
usually not thinned more than 3 parts of coating to 1 part of thinner.
Rockyphot GN 20 is usually not thinned more than 2 parts of coating
: 1 part of thinner. The precise ratio has to be determined by the
user himself.
The appropriate pull speed
to achieve an optimum coating thickness is 10 - 15 cm/min. for Rockyphot
K and 20 - 30 cm/min. for Rockyphot XN. At a pull speed of approx.
35 cm/min. the appropriate coating thickness for textile printing
will be achieved with undiluted Rockyphot GN 20. Rockyphot GN 20 thinned
according to the ratio 2 parts coating : 1 part thinner will give
you the appropriate coating thickness for package printing at the
same time pull speed.
Thicker coatings can be made
with higher pull speed; less thick coatings can be made with lower
pull speed or by thinning.
Over time the coating material
may change viscosity due to evaporation of volatile solvents. Since
the viscosity of the coating affects coating thickness, we recommend
checking the viscosity of the coatings from time to time. The flow
time is a sufficient relative index of viscosity. We recommend a DIN
cup with a nozzle diameter of 2 mm. Changes in flow time of more than
3 - 4 % should be corrected with Thinner for Rockyphot.
Caution: For uniform
coating it is absolutely necessary that a complete mixture of thinner
and coating is achieved.
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Spray coating
Spray coating with Rockyphot
S can be performed with common spray coating equipment. The following
data have been evaluated on a certain type of equipment and should
work as a guideline for similar spray coating equipment.
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Thinning ratio
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2 parts Rockyphot S + 1 part Thinner
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Nozzle diameter
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0,4 mm
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Spraying pressure
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0,5 bar
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Rotation speed of cylinder
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120 rpm
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Shear
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0,8 mm/revolution
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Diameter of cylinder
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200 mm
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Distance of spraygun
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40 mm
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Angle of spraygun in shear direction
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40ƒ
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Coating quantity
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3 - 3,5 ml/dm¾
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For spray coating Rockyphot GN 20 has to be first thinned with Thinner
for Rockyphot GN 20. Then, according to the type of spray coating
equipment the thinning ratio with Special Spray Thinner for Rockyphot
GN 20 can be: 1 part Rockyphot GN 20 (thinned 2:1) : 1 part Special
Spray Thinner for Rockyphot GN 20.
The correct setting has to
be determined by the user himself because the change of only one parameter
changes the other parameters.
Whirler-coating
For the coating of plates we recommend a heated whirler. The rotation
of the plates which have to be coated depends on the size of the plates.
With a rotation speed of 150 rpm the optimum coating thickness of
2 µm for plates of 20 x 30 cm will be achieved with Rockyphot S. Same
rotation speed gives a coating thickness of approx. 4 µm with Rockyphot
GN 20. Leave the plate in the whirler for 3 - 4 min. at 50 ƒC. The
plate will be ready for exposure after cooling off. For larger plate
sizes Rockyphot has to be thinned to avoid streaks during whirler-coating.
Exposure
The spectral sensitivity of Rockyphot lies in the near ultraviolet
range, 300 - 420 nm. Any copy lamp is suitable for exposure provided
that is has an UV output. Because of the differences in light source
and equipment it is not possible to give a firm value for optimum
exposure time. This must be determined by test exposures on each piece
of equipment. For this we recommend the use of a 21 step Stouffer
scale. We recommend the following values:
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Linework
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Gray scale density 0,65 Step 5 solid
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Screenwork up to 70 l/cm
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Gray scale density 0,50 Step 4 solid
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Screenwork up to 120 l/cm
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Gray scale density 0,35 Step 3 solid
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Developing
Development time, depending on coating thickness, lies in the
range between 1,5 - 2 min. Development can be performed through dip
tank development or by splashing the rotogravure cylinder with developer
several times. Using either method the
cylinder has to be rinsed
with fresh developer approx. 30 sec. before development is concluded
to make sure that even the finest screen work develops clearly. After
development the developer must be washed off with a fairly strong
spray of water
with a side to side motion.
Then rinse for an additional 30 sec. and dry with compressed air.
If after drying there is modest amount of scum visible, this can be
washed off with alcohol. Material beeing coated with Rockyphot GN
20 is not allowed to be washed with ethyl-alcohol.
Caution: If you are
developing in a dip tank do not allow water to get into the developer.
Do not dry the plate before washing off with water.
Retouching
For retouching use Freundorfer Retouching Varnish Red.
Attention: Do not use retouching inks containing toluene or
xylol!
Removal
After etching the
coating can be removed with Freundorfer Stripper 10.
Rockyphot GN 20 coatings can also be removed with toluene and xylol.
Safety instructions
Coating and Developer
contain flammable solvents. These products should not be used in the
vicinity of open flames. Prolonged exposure to skin as well as prolonged
inhalation of the vapors should be avoid; therefore it is good to
have adequate ventilation in the room and good ventilation in the
immediate work place. Eye protection is recommended.
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