U.S. patent application number 09/748915 was filed with the patent office on 2002-06-27 for electroplating of gravure cylinders.
Invention is credited to Smith, Robert.
Application Number | 20020079228 09/748915 |
Document ID | / |
Family ID | 25011447 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020079228 |
Kind Code |
A1 |
Smith, Robert |
June 27, 2002 |
Electroplating of gravure cylinders
Abstract
The present invention relates to an apparatus and method for
electroplating gravure cylinders that are used for gravure
printing. The apparatus and method preferably utilize rectifiers
that are able to pulse direct current several hundred times per
second in order to repeatedly and intermittently establish an
electric field between a supply of plating material and the gravure
cylinder.
Inventors: |
Smith, Robert; (Nashotah,
WI) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH, LLP
100 E WISCONSIN AVENUE
MILWAUKEE
WI
53202
US
|
Family ID: |
25011447 |
Appl. No.: |
09/748915 |
Filed: |
December 27, 2000 |
Current U.S.
Class: |
205/134 ;
204/224R |
Current CPC
Class: |
C25D 5/18 20130101; C25D
7/04 20130101; C25D 5/617 20200801 |
Class at
Publication: |
205/134 ;
204/224.00R |
International
Class: |
C25D 005/02; C25D
017/00 |
Claims
What is claimed is:
1. An apparatus for electroplating a cylinder used in gravure
printing, the apparatus comprising: a container; an ionic fluid
bath stored within said container such that the gravure cylinder is
at least partially submerged within the ionic fluid bath; a supply
of plating material within the ionic fluid bath; and an electrical
power source operatively connected with the gravure cylinder and
the supply of plating material, wherein said power source cycles
current at different levels through the ionic fluid to establish
different electric fields between the supply of plating material
and the gravure cylinder.
2. The apparatus of claim 1 wherein said supply of plating material
is stored on a reservoir that is submerged within the ionic
fluid.
3. The apparatus of claim 1 wherein said electrical power source is
a pulsing direct current rectifier.
4. The apparatus of claim 1 wherein said electrical power source
cycles current at two levels.
5. The apparatus of claim 4 wherein one of said current levels is
substantially near zero current.
6. The apparatus of claim 1 wherein said electrical power source
cycles current at different levels at least several hundred times
per second.
7. The apparatus of claim 1 further comprising a filter, wherein
said ionic fluid bath is circulated through said filter to remove
contaminants in said ionic fluid bath.
8. The apparatus of claim 1 wherein said container and said ionic
fluid bath are sized such that the gravure cylinder is wholly
submerged within said ionic fluid bath.
9. A method of electroplating a gravure cylinder comprising:
partially submerging the gravure cylinder with an ionic fluid bath;
submerging a supply of plating material within the ionic fluid
bath; and pulsing different levels of current between the supply of
plating material and the gravure cylinder.
10. The method as claimed in claim 9 wherein the gravure cylinder
is submerged wholly within the ionic fluid bath.
11. The method as claimed in claim 9 wherein the ionic fluid bath
is kept at temperature between 28 and 32 degrees Centigrade.
12. The method as claimed in claim 9 wherein the current is cycled
between two different levels.
13. The method as claimed in claim 12 wherein one of the current
levels is substantially near zero.
14. The method as claimed in claim 12 wherein one of the current
levels is zero.
15. The method of claim 9 wherein the current flows in one
direction.
16. The method of claim 9 wherein the current alternately flows in
opposite directions.
17. The method of claim 9 wherein the current primarily flows in
one direction and is periodically reversed in an opposite
direction.
18. The method of claim 17 wherein the current is pulsed at
different levels when the current is periodically reversed in the
opposite direction.
19. The method of claim 9 wherein the current is cyclically pulsed
in a forward direction for 16 milliseconds and then turned
substantially off for 8 milliseconds.
20. The method of claim 19 wherein the current is reversed every
1500 cycles.
21. The method of claim 20 wherein the current is reversed for 1
second.
22. The method of claim 9 wherein the current is cyclically pulsed
in a forward direction for 50 milliseconds and then turned
substantially off for 10 milliseconds.
23. The method of claim 22 wherein the current is reversed every
1500 cycles.
24. The method of claim 23 wherein the current is reversed for 1
second.
25. The method as claimed in claim 9 further comprising rotating
the cylinder within the ionic fluid bath.
26. The method as claimed in claim 25 wherein the cylinder is
rotated at 70 revolutions per minute.
27. A method of electroplating a gravure cylinder comprising:
partially submerging the gravure cylinder within an ionic fluid
bath; submerging a supply of plating material within the ionic
fluid bath; rotating the cylinder within the ionic fluid bath; and
cycling current between the supply of plating material and the
gravure cylinder where the current is cycled in one direction
between substantially zero current and some higher level of
current.
28. The method as claimed in claim 27 wherein the current is
periodically reversed in an opposite direction.
29. The method as claimed in claim 28 wherein the current is
reversed every 1500 cycles.
30. The method of claim 27 wherein the current is cycled several
hundred times per second.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus and method for
electroplating gravure cylinders, and more particularly to an
apparatus and method for electroplating gravure cylinders using
current pulses.
BACKGROUND OF THE INVENTION
[0002] Electroplating has been historically used to coat gravure
cylinders with materials such as copper or chrome because of the
efficiency associated with providing a thin uniform coating of an
engraveable material on the gravure cylinders by electroplating
when compared with other methods. Gravure cylinders are plated with
a thin layer of material of engraveable material so that the
desired print can be etched, engraved or embossed into/onto the
deposited layer of plating material. The body of the gravure
cylinders are typically steel or aluminum and are used to provide a
sturdy and less expensive substrate for supporting the layer of
plated material. Due to the cost associated with producing gravure
cylinders, the cylinders are typically reconditioned after the
completion of each print run. Reconditioning a cylinder allows a
different print to be etched, engraved or embossed into/onto the
cylinder for a subsequent print run.
[0003] The reconditioning process typically involves removing at
least enough material from the outer surface of the cylinder to
partially remove the existing etching or engraving and then
electroplating a new layer of material onto the cylinder. Once the
new layer of material is deposited onto the cylinder, new etching
or engraving for a subsequent print run can be applied into the new
plating material.
[0004] Gravure cylinders are plated by partially submerging a
cylinder within an ionic fluid bath that includes ions of the
material which are to be deposited onto the cylinder. The partially
submerged cylinder is rotated so that the entire outer surface of
the cylinder periodically enters and exits the ionic fluid bath. A
supply of plating material is submerged within the ionic fluid and
once an electrical field is established between the cylinder and
the supply of plating material ions within the fluid bath are
deposited onto the cylinder. These deposited ions are continuously
replaced within the ionic fluid bath because additional ions break
free from the supply of plating material and enter the ionic fluid
bath.
[0005] The apparatus includes a container for holding the ionic
fluid bath and a reservoir for holding the plating material in
fluid communication with the ionic fluid bath. An electrical power
source is connected to the plating material and the cylinder to
establish the electric field between the plating material and the
cylinder. The electrical power source includes rectifiers that
apply a constant direct current such that the plating material is
continuously deposited from the ionic fluid onto the gravure
cylinder.
[0006] In many applications the cylinder surface is bombarded with
ultrasonic implosions in an attempt to improve the electroplating
process. Additional rectifiers may also be added to the electrical
power source to intermittently reverse the current for several
seconds. A seldom used process facilitates removing the old
engraving by reversing the current for long periods (e.g., 10-20
minutes). The engraving is more commonly removed by machining and
then reversing the current for a few seconds prior to plating to
facilitate better adhesion between the copper substrate and the new
coating.
[0007] Electroplating gravure cylinders in order to recondition the
cylinders for future print jobs is a cost effective way to provide
a smooth, uniform surface on a gravure cylinder which is suitable
for etching or engraving and then subsequent gravure printing.
Therefore, any improvement in the devices or processes related to
reconditioning gravure cylinders by electroplating would be
desirable.
SUMMARY OF THE INVENTION
[0008] The present invention relates to an apparatus and method for
electroplating gravure cylinders that are used for gravure
printing. The apparatus and method preferably utilize rectifiers
that are able to pulse direct current several hundred times per
second in order to repeatedly and intermittently establish an
electric field between a supply of plating material and the gravure
cylinder. Pulsing current several hundred times per second in order
to repeatedly establish a field between the supply of plating
material and the gravure cylinder significantly reduces the plating
duration and minimizes the surface pitting and nodules that are
present using conventional electroplating processes and
equipment.
[0009] The present invention is directed to an apparatus for
electroplating a cylinder that is used in gravure printing. The
apparatus includes a container and an ionic fluid bath stored
within the container such that the gravure cylinder can be at least
partially submerged within the ionic fluid bath. A supply of
plating material is submerged within the ionic fluid bath and an
electrical power source is operatively connected between the
gravure cylinder and the supply of plating material. The power
source cycles current at different levels, preferably several
hundred times per second, to the ionic fluid bath in order to
establish different electric fields between the supply of plating
material and the gravure cylinder. The electric power source is
preferably a periodic abrupt current change between a high level of
current and a substantially lower level of current. However, other
non-abrupt current variation over time at several times per second
can also be applied without departing from the scope of the present
invention.
[0010] In another form, the present invention is directed to a
method of electroplating a gravure cylinder. The method includes
partially submerging the gravure cylinder within an ionic fluid
bath; submerging a supply of plating material within the ionic
fluid bath; and pulsing different levels of current between the
supply of plating material and the gravure cylinder.
[0011] In the preferred form of the method, the current is
periodically reversed after cycling the current at several
different levels in the forward direction. Periodically reversing
the current between several cycles of current at different levels
in the forward direction facilitates removing imperfections from
the outer surface of the gravure cylinder. In addition, reversing
current also helps to maintain a supply of copper in the immersion
layer (i.e., the layer near the cylinder).
[0012] Pulsing direct current with or without periodically
reversing current improves the ability to engrave the cylinder by
reducing the grain size of the plating material that is deposited
on the gravure cylinder and improves leveling across the cylinder
surface. In addition, using pulsing rectifiers reduces the
coplating of hydrogen and minimizes the hardness differences
between individual cylinders that are plated at different times and
the hardness variation caused by the differences between cylinder
suppliers.
[0013] Other features and advantages of the invention are set forth
in the following drawings, detailed description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will hereafter be described with reference to
the accompanying drawings wherein like numerals denote like
elements.
[0015] FIG. 1 is a section view showing a gravure cylinder
partially submerged within an ionic fluid bath.
[0016] FIG. 2 is a top plan view illustrating the apparatus of the
present invention with the gravure cylinder that is to be plated
removed from the apparatus.
DETAILED DESCRIPTION
[0017] The apparatus and method of the present invention are shown
in FIG. 1. A plating tank 10 includes a container 18 that is filled
with an ionic fluid bath 14. A supply of plating material 12 is
held submerged within the ionic fluid bath 14 by a reservoir 20
such that the plating material 12 is in continuous fluid
communication with the ionic fluid bath 14. An electrical power
source 22 is connected positively to the plating material 12 and
negatively to a cylinder 16. The electrical power source 22
includes pulsing direct current rectifiers 23 (e.g., Power Pulse
Model PEXXXX) that are preferably manufactured by
Plating-Electronic GmbH, Marie-Curie-Strasse, Denzlingen, Germany,
although other rectifiers could be used without departing from the
scope of the present invention.
[0018] The supply of plating material 12 may be any type of
material that is commonly used in electroplating processes. The
material must be able to undergo ionization within the ionic fluid
bath 14 in order to replenish the ions that are plated onto the
outer surface of the cylinder 16. Copper is one of the materials
that is commonly used in plating and will be used as the primary
example throughout this description without implying any
limitations as to the type of plating material which might be used
in the apparatus and process of the present invention. Other
examples of plating material include chromium (trivalent or
hexavalent), nickel and nickel alloys.
[0019] Copper ions have a positive charge so that the power source
22 in forward current mode must supply a negative charge to the
cylinder 16 and a positive charge to the copper plating material 12
in order to coat the cylinder 16 with copper. The negatively
charged cylinder attracts the positively charged ions such that the
copper ions are deposited on the surface of the cylinder 16. As the
copper ions are deposited on the cylinder 16 they are removed from
the ionic fluid bath 14. Additional copper ions are induced by the
electrical potential present between the cylinder 16 and the copper
plating material 12 to separate from the copper plating material 12
and enter the ionic fluid bath 14 thereby replacing the ions which
have been deposited onto the cylinder 16.
[0020] The gravure cylinder 16 includes a longitudinal axis 37 and
the cylinder 16 rotates about the longitudinal axis 37 during the
electroplating process. The cylinder 16 rotates on a shaft 36 such
that only a portion of this cylinder 16 is submerged within the
ionic fluid 14 at any given time. Therefore, rotating the cylinder
16 through the ionic fluid bath 14 permits all parts of the
cylinder 16 to be coated with copper ions from the ionic fluid bath
14.
[0021] The reservoir 20 which holds the plating material 12 within
the ionic fluid bath 14 includes a titanium base tray 40 that is
mounted on a support 42. A plastic liner 46 and a plurality of
upper bars 48 are disposed between the base tray 40 and the plating
material 12 such that the copper bars 48 are in contact with the
plating material 12. The liner 46 is perforated in order to allow
the ionic fluid to pass through to the base tray 40 where the fluid
can exit through the base tray 40 via a drainage conduit 50 into a
fluid supply 28.
[0022] Referring now also to FIG. 2, the reservoir 20 includes a
pair of exterior retaining walls 52 that extend upward from
opposing edges of the base tray 40. A pair of end walls 54 are
positioned at opposing ends of the exterior retaining walls 52 such
that the reservoir 20 forms an enclosure that is large enough to
receive the gravure cylinder 16.
[0023] A pair of interior retaining walls 56 are positioned
substantially parallel to and inwardly from the exterior retaining
walls 52. The pair of interior walls 56 extend upwardly from base
tray 40 such that the section of the reservoir 20 between the
interior retaining walls 56 is adapted to receive the entire supply
of plating material 12.
[0024] A pump 32 returns the drained fluid from the fluid supply 28
back to the ionic fluid bath 14 via a conduit 30. The conduit 30
extends through the base tray 40 such that the fluid is pumped into
the interior portions 71 of filter tubes 34. The filter tubes 34
extend longitudinally along the length of the reservoir 20 between
the interior retaining walls 52 and exterior retaining walls 56.
The filter tubes 34 are made up of a plurality of shorter filter
tubes 34a, 34b, 34c, 34d. The plurality of filter tubes 34a, 34b,
34c, 34d, are mounted on a plurality of brackets 58 that are
intermittently spaced along the length of the reservoir 20 (see
FIG. 2).
[0025] The filter tubes 34 promote uniform ionic fluid distribution
along the length of the reservoir 20. The filter tubes 34 are
preferably constructed of a polypropylene material which restricts
the flow of ionic fluid into the ionic fluid bath 14. The ionic
fluid 14 enters the hollow interior portions 71 of the filter tubes
34 and then flows radially outward through the polypropylene
material into the container 18. The restrictive polypropylene
filter tube ensures that the filter tubes 34 are at least partially
filled with ionic fluid 14 to promote the slow and even
distribution of ionic fluid along the length of the reservoir
20.
[0026] A capping member 60 that includes a plurality of orifices 62
connects the tops of the interior retaining walls 52 with the tops
of the exterior retaining walls 56 on the respective sides of the
reservoir 20. Each of the filter tubes 34a, 34b, 34c, 34d is
therefore enclosed by a capping member 60, an interior retaining
wall 52, an exterior retaining wall 56 and a portion of the liner
46.
[0027] A barrier 24 is positioned between the plating material 12
and the cylinder 16. The barrier 24 extends between the pair of
interior walls 52 and covers the plating material 12 which would
otherwise be exposed to the cylinder 16. Positioning the barrier 24
in this manner causes any ions that are given up by the plating
material 12 to pass through the barrier 24 before they can contact
the cylinder 16. The barrier 24 helps to prevent oxides and other
undesirable contaminates from coming into contact with the cylinder
16. The barrier 24 is preferably made from a sheet of polypropylene
that includes openings which are appropriately dimensioned to
permit passage of ionic fluid yet prohibit passage of copper oxides
and other contaminates. The fine mesh barrier allows positively
charged ions to float evenly from the supply material thereby
reducing valleys and peaks along the cylinder length and
facilitating uniform ionic dispersion by diffusion.
[0028] The barrier 24 acts as a diffusion member and preferably
includes a titanium grid 64 on which a polypropylene sheet 66 is
located on the material supply side. The titanium grid 64 is
mounted on a hinge 68 such that the barrier 24 can be pivoted away
from the plating material 12 in order to facilitate easy insertion
and removal of plating materials to/from the reservoir 20.
[0029] The titanium grid 64 includes apertures 70 such that the
ions pass through the apertures 70 when they flow through the grid
64. The spacing between the apertures 70 promotes diffusion of the
ions as they approach the cylinder 16. Diffusing the ions so that
they are more uniformly dispersed within the ionic fluid bath 14
distributes the ions onto the cylinder 16 in a more uniform
fashion. The apertures 70 are preferably circular and vary in size
with all of the apertures 70 being less than two inches in
diameter.
[0030] The ionic fluid bath 14 consists of a carrier fluid and ions
that are generally disbursed throughout the carrier fluid. Once
again referring to copper as an example, a copper sulfate is
typically mixed with a fluid such as water. It should be noted that
other additives which are commonly known in the art could also be
added to the fluid. The sulfate breaks into ions of copper and
sulfate with the copper ions having a positive charge and the
sulfate ions having a negative charge. When the electrical field is
established between the cylinder 16 and the plating material 12 the
positively charged copper ions are attracted toward the negatively
charged cylinder 16 while the sulfate ions move towards the
reservoir 20. The copper ions are deposited onto the outer surface
of cylinder 16 while the sulfate ions move into proximity with the
plating material 12 where the sulfate ions combine with naturally
occurring oxides in the copper. As the sulfate ions combine with
the oxides in the copper, a sludge is formed which drops into the
reservoir 20.
[0031] The fluid level within the container 18 is maintained by an
overflow wall 72 which is positioned inward from an outer wall 74
on the container 18. The ionic fluid bath 14 is maintained at a
constant level since any excess ionic fluid 14 falls over the top
of the overflow wall 72 into a passage 76 that returns the
overflowing fluid to the fluid supply tank 28.
[0032] The power supply 22 preferably includes rectifiers 23 that
pulse high levels of direct current several hundred times per
second. Pulsing current in this type of application allows gravure
cylinders to be reconditioned much more efficiently and with less
waste of plating material. The power source 22 supplies a negative
charge to the gravure cylinder 16 and a positive charge to the
supply of plating material 12. The negative charge is applied to
the cylinder 16 through a connector 78 that is in contact with the
conductive shaft 36 attached to the cylinder 16. A positive charge
is applied to a buss 80 that is in contact with the supply of
plating material 12. The buss 80 preferably extends along the
length of the reservoir 22 generally parallel with the longitudinal
axis 37 of the cylinder 16.
[0033] An example of the operation of the plating tank is as
follows. However, the example is for illustration purposes and is
not intended on being limiting. A supply of copper plating material
12 in the form of oxygen-free copper nuggets that include
approximately 0.04% phosphorus by weight is submerged within the
ionic fluid bath 14. The ionic fluid bath 14 consists primarily of
water mixed with copper ions and sulfate ions. Solution
concentrations of the ionic fluid include 55-65 grams per liter of
reagent grade sulfuric acid and 170-200 grams of copper sulfate per
liter. The amount of total dissolved solids in the ionic fluid 14
is between 0-4 PPM and the amount of total chlorides in the ionic
fluid is between 50-70 PPM. The ionic fluid 14 is preferably kept
at a temperature between 28 and 32 degrees centigrade although
other temperatures could be used, and the cylinder 16 is preferably
rotated within the ionic fluid bath 14 by any conventional means at
approximately 10 to 100 revolutions per minute. The container 18
holds approximately 3,000 liters of ionic fluid 14 which is
recycled approximately 30 times per hour such that approximately
60,000 liters of ionic fluid 14 flows through the container 18 per
hour.
[0034] Although other cycle times could be used without departing
from the scope of the present invention, one known effective cycle
time for plating 0.050 millimeters of copper onto the outer surface
of the cylinder includes repeatedly pulsing the current on for 16
milliseconds and off for 8 milliseconds with one second of reverse
current every 1,500 cycles. This duty cycle should be approximately
65% of the rated capacity of the pulsing direct current rectifier.
The approximate current density generated with this type of duty
cycle is anywhere from 20 to 80 amperes per square decimeter. The
process is repeated until the desired plating thickness is
reached.
[0035] Another set of cycle times for plating approximately 0.050
millimeters of copper onto a gravure cylinder includes pulsing the
direct current rectifiers on for 50 milliseconds and off for 10
milliseconds repeatedly until the desired plating thickness is
reached. The pulsing direct current rectifiers are operating with
an 83% duty cycle using these cycle times and the current density
should be anywhere from 20 to 40 amperes per square decimeter.
[0036] Pulsing current several hundred times per second in order to
repeatedly establish a field between the supply of plating material
and the gravure cylinder significantly reduces the plating duration
and minimizes the surface pitting and nodules when they are present
using conventional electroplating processes and equipment. Pulsing
direct current also improves the ability to engrave the cylinder by
reducing the grain size of the plating material that is deposited
on the gravure cylinder and improves leveling the across the
cylinder surface. In addition, using pulsing rectifiers reduces the
copulating of hydrogen and minimizes the hardness differences
between individual cylinders that are plated at different
times.
[0037] The foregoing description the present invention has been
presented for purposes of illustration and description. The
description is not intended to limit the invention to the form
disclosed herein. Consequently, variations and modifications
commensurate with the above teachings, and the skill and knowledge
of the prior art, are within the scope of the present invention.
The embodiments and forms described herein are intended to explain
the best modes for practicing the invention and to enable others
skilled in the art to utilize the invention in the disclosed or
other embodiments and with various modifications required by the
particular applications or uses of the present invention. It is
intended that the appended claims be construed to include
alternative embodiments and forms to the extent permitted by the
prior art.
* * * * *