U.S. patent application number 11/292444 was filed with the patent office on 2007-06-07 for electroform, methods of making electroforms, and products made from electroforms.
Invention is credited to Paul William Buckley, Dennis Joseph Coyle, Michael J. Davis, Richard Edwards, Kenneth Paul Zarnoch.
Application Number | 20070125651 11/292444 |
Document ID | / |
Family ID | 38117624 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070125651 |
Kind Code |
A1 |
Buckley; Paul William ; et
al. |
June 7, 2007 |
Electroform, methods of making electroforms, and products made from
electroforms
Abstract
In one embodiment, the method for making a product comprises:
contacting a surface of the electroform with a solution having a pH
of less than or equal to 6, applying a cathodic current to the
electroform, applying a product material to the electroform, curing
the product material, and removing the cured material from the
electroform to form the product.
Inventors: |
Buckley; Paul William;
(Scotia, NY) ; Coyle; Dennis Joseph; (Clifton
Park, NY) ; Davis; Michael J.; (Mt.Vernon, IN)
; Edwards; Richard; (Huntsville, AL) ; Zarnoch;
Kenneth Paul; (Scotia, NY) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
38117624 |
Appl. No.: |
11/292444 |
Filed: |
December 2, 2005 |
Current U.S.
Class: |
205/67 |
Current CPC
Class: |
B29C 33/3842 20130101;
C25D 1/10 20130101; B29L 2031/3475 20130101; C25D 11/02
20130101 |
Class at
Publication: |
205/067 |
International
Class: |
C25D 1/00 20060101
C25D001/00 |
Claims
1. A method for making a product from an electroform, comprising:
contacting a surface of the electroform with a solution having a pH
of less than or equal to 6, wherein the surface comprises features
to be replicated; applying a cathodic current to the electroform;
applying a product material to the electroform; curing the product
material; and removing the cured material from the electroform to
form the product.
2. The method of claim 1, wherein the pH is less than or equal to
about 5.
3. The method of claim 1, wherein the pH is about 2 to about 5.
4. The method of claim 1, wherein the cathodic current is applied
at a current density of about 1 ASF to about 60 ASF.
5. The method of claim 4, wherein the current density is about 2
ASF to about 30 ASF.
6. The method of claim 5, wherein the current density is about 2
ASF to about 10 ASF.
7. The method of claim 1, wherein, after the product has been
removed, further comprising contacting the surface with a caustic
media.
8. The method of claim 7, wherein the caustic media has a pH of
greater than or equal to about 8.
9. The method of claim 8, wherein the pH is about 8 to about
14.
10. The method of claim 9, wherein the pH is about 12 to about
14.
11. The method of claim 7, further comprising rinsing the
electroform with deionized water and applying a cathodic current to
the electroform.
12. The method of claim 1, wherein the product comprises
microstructures and/or nanostructures.
13. The method of claim 1, wherein the electroform comprises
nickel.
14. The method of claim 1, wherein the product material comprises
an acrylate.
15. The method of claim 14, wherein curing the product material
comprises ultraviolet curing of the product material.
16. The method of claim 1, wherein applying a product material
further comprises pressing the product material into the
electroform with a backing film.
17. The method of claim 16, wherein the backing film is selected
from the group consisting of polycarbonate, polyester, and so
forth, as well as reaction products comprising at least one of the
foregoing, and combinations comprising at least one of the
foregoing.
18. A product formed from the method of claim 1, wherein the
product has microstructures with nanoscale resolution.
19. The product of claim 18, wherein the product is a film.
20. A light management article comprising the film of claim 19.
21. The article of claim 20, wherein the article is a backlight
computer display.
Description
BACKGROUND
[0001] This disclosure generally relates to electroforming and
methods for forming an electroform.
[0002] Electroforming involves an electrochemical process that uses
an anode (which may supply metal for deposition), an electrolyte,
and a substrate (which acts as a cathode). An electrical current to
the anode and cathode is controlled to manage the deposition of the
metal onto the substrate to create a metal replica of various
shapes and textures. In another example, electroforms can be made
from a complex micromachined master. The replicas (or micromachined
master) can be used to mass-produce plastic articles with precise
microstructure using processes such as printing, embossing, and
casting. For example, these replicas can be employed in the
production of data storage media such as CDs, DVDs, and the
like.
[0003] In backlight computer displays or other display systems,
optical films are often used to direct light. For example, in
backlight displays, light management films use prismatic structures
(often referred to as microstructure) to direct light along a
viewing axis (i.e., an axis substantially normal to the display).
Directing the light enhances the brightness of the display viewed
by a user and allows the system to consume less power in creating a
desired level of on-axis illumination. Films for turning or
directing light can also be used in a wide range of other optical
designs, such as for projection displays, traffic signals, and
illuminated signs. The prismatic structures are generally formed in
a display film by replicating a metal tool, mold, or electroform
having prismatic structures disposed thereon, via processes such as
stamping, molding, embossing, or UV-curing. It is generally
desirable for the display film and the mold to be free from defects
so as to facilitate a uniform luminance of light. Since such
structures serve to strongly enhance the brightness of a display,
any defects, even if they are small (on the order of 10 microns),
can result in either a very bright or very dark spot on the
display, which is undesirable. The mold and the display films are
therefore inspected to eliminate defects.
[0004] Molds such as, for example, electroforms are generally used
for manufacturing light management films such as prism sheets for
use in liquid crystalline displays. In general, such light
management films have at least one microstructured surface that
refracts light in a specific way to enhance the light output of the
display. Since these films serve an optical function, the surface
features must be of high quality with no roughness or other
defects. This microstructure is first generated on a master, (e.g.,
a silicon wafer, glass plate, metal drum, or the such) and is
created by one of a variety of processes such as photolithography,
etching, ruling, diamond turning, or others. Since this master
tends to be expensive to produce and fragile in nature, tooling or
molds are typically reproduced off of this master, which in turn
serve as the molds from which plastic microstructured films are
mass-produced. These tools can be metal copies grown via
electroforming processes, or plastic copies formed via molding-type
processes. Tools copied directly from the master are called
1.sup.st-generation (sub-master), copies of these tools are called
2.sup.nd-generation (sub-master), etc. In general, multiple copies
can be made of every tool made at any generation, leading to a
geometric growth in number of tools with each generation--i.e. a
"tooling tree" is produced. Each generation is an inverted image of
the previous generation. If the desired final product is a
"positive" geometry, then any generation of tooling that is a
negative can be used as a mass-production replication tool. If the
master is manufactured as a negative, then any even-generation mold
can be used for mass-production.
[0005] One difficulty always present when a manufacturing process,
such as the optical display film manufacturing process, uses a
component or subprocess in a subsequent step of the process is the
systemic defect. If a major component, such as a shim tool or a
master tool, is defective, then every subsequent mold and film
replicated from those components will be defective. In prior
attempts to alleviate this problem, the optical display film
manufacturing process has been separated into three
semi-independent manufacturing processes, the master tool, the shim
tool and the display film manufacturing processes. Each primary
manufacturing process has had an independent inspection and defect
correction process that identifies a defective component or product
at that particular step in the process and then removes it from the
process chain. These processes are intended to prevent a defective
master tool from being made into a defective shim tool, a defective
shim tool from being made into defective film samples, and
defective film samples from being sold.
[0006] Depending upon the size of the replica, the size, geometry,
and amount of features to be replicated, and the materials of the
master and sub-master, the degree of successful replication can
vary greatly. There is a constant need to make the electroplating
process more efficient (e.g., reduce the plating time), and more
effective (e.g., improve the accuracy of the replication, enhance
the separation of sub-master from master, and reduce the amount of
yield loss). These needs are especially difficult when the articles
made from the electroform serve an optical function, making
tolerances critical and very small defects unacceptable.
BRIEF SUMMARY
[0007] Disclosed herein are methods for making electroforms,
electroforms formed therefrom, methods for making product with
those electroforms, and products made therefrom.
[0008] In one embodiment, the method for making a product
comprises: contacting a surface of the electroform with a solution
having a pH of less than or equal to 6, applying a cathodic current
to the electroform, applying a product material to the electroform,
curing the product material, and removing the cured material from
the electroform to form the product.
[0009] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Refer now to the figures, which are exemplary, not limiting,
and wherein like numbers are numbered alike.
[0011] FIG. 1 is one embodiment of an electroforming process
map.
[0012] FIG. 2 is a cross sectional view of a backlight display
device.
[0013] FIG. 3 is a perspective view of an optical substrate
comprising a surface characterized by a cross section of a prism
having a curved sidewall or facet.
[0014] FIG. 4 is a first cross sectional view of an optical
substrate comprising a surface characterized by a cross section of
a prism having a curved sidewall or facet.
[0015] FIG. 5 is a second cross sectional view of an optical
substrate comprising a surface characterized by a cross section of
a prism having a curved sidewall or facet.
[0016] FIG. 6 is a cross sectional view of a compound angle prism
and of the geometric parameters of the curved sidewall or facet of
FIGS. 4 and 5 as described by a segment of a polynomial
function.
DETAILED DESCRIPTION
[0017] Ranges disclosed herein are inclusive and combinable (e.g.,
ranges of "up to about 25 wt %, or, more specifically, about 5 wt %
to about 20 wt %", is inclusive of the endpoints and all
intermediate values of the ranges of "about 5 wt % to about 25 wt
%," etc). Furthermore, the terms "first," "second," and the like,
herein do not denote any order, quantity, or importance, but rather
are used to distinguish one element from another, and the terms "a"
and "an" herein do not denote a limitation of quantity, but rather
denote the presence of at least one of the referenced item. The
modifier "about" used in connection with a quantity is inclusive of
the stated value and has the meaning dictated by the context,
(e.g., includes the degree of error associated with measurement of
the particular quantity). The suffix "(s)" as used herein is
intended to include both the singular and the plural of the term
that it modifies, thereby including one or more of that term (e.g.,
the colorant(s) includes one or more colorants).
[0018] FIG. 1 is a process map of one embodiment of an
electroforming process for making a sub-master and a 2.sup.nd
generation sub-master. The process comprises forming a master drum
having a pattern disposed in an external surface thereof. The
pattern can be produced in various fashions, e.g.,
photolithography, machining, etching, cutting, milling, scribing,
among other techniques. The master can be cleaned, e.g., washed
with organic solvents, water, acid, and/or base. To enable the
removal of the electrodeposited layer from the master, a release
point can be formed and the drum can be passivated. The release
point can be an area of the master that is masked, such as with
tape, to prevent metal deposition on that area. The area is chosen
to be outside of the pattern, and has a length to facilitate
removal of the layer from the drum. For example, the tape can be
disposed longitudinally across the master such that, once the layer
has been disposed on the master, the tape can be removed, exposing
an edge of the sub-master. The sub-master can then be removed by
peeling it from around the drum. It is desirable to uniformly
remove the sub-master from the drum without twisting or torquing
the sub-master. Twisting, torquing, and other non-uniform removal
can damage the pattern on the surface of the sub-master and
potentially even damage the surface of the master.
[0019] To further facilitate the separation, the surface of the
master can be passivated which helps to prevent the replica (i.e.,
sub-master) from adhering to the surface of the master. Possible
passivation techniques include the formation of a separation layer
(such as an oxide and/or hydroxide layer) over the master surface,
electrostatic cleaning, and/or by chemical passivation techniques.
Formation of a separation layer can comprise an electrolytic
oxidation process wherein the electrolytic current and voltage are
applied to form a controlled thickness separation layer. Chemical
passivation can comprise immersing the master surface in a solution
for a controlled period of time. The particular solution is
dependent upon the master composition. Some possible solutions
include alkali metal hydroxide solutions, chromate (such as
potassium dichromate), among others.
[0020] For example, the surface of the master can optionally be
rinsed with Simple Green solution (commercially available from
Sunshine Makers, Inc., located in Huntington Beach, Calif.) and
then sprayed with a saponin solution to promote wetting of the
surface. A potassium dichromate solution (e.g., about 5 grams per
liter (g/l)) can be applied to the surface of the master (e.g.,
poured over the surface). The potassium dichromate is then rinsed
from the master surface to form a passivated master. Optionally,
the saponin and potassium dichromate applications can be repeated
as desired.
[0021] The passivated master can then be plated in various
processes, including an electroforming process. The electroforming
process can be performed in an electroforming tank where the outer
surface of the master functions as the cathode through electrical
contacts. The anode can be constructed from various metals,
including the metal to be deposited during metallization. For
example, a nickel anode or nickel alloy can be used if nickel is
the desired metal in the metallization process. For example, the
passivated master can be placed into an electroforming solution and
optionally rotated (e.g., up to about 10 revolutions per minute
(rpm) or so) to more uniformly deposit the metal. A rectifier in
electrical communication with the anode and cathode can be
maintained constant during this process or it can be adjusted. The
electroforming can be accomplished in up to about 24 hours.
[0022] The solution in the electroforming tank can be an aqueous
solution comprising a surfactant agent, a pH of less than or equal
to about 6, and optionally a hardening agent. The solution will
further comprise the metal(s) to be deposited. One embodiment of a
solution can comprise about 60 grams per liter (g/l) to about 100
g/l of metal sulfamate (e.g., the metal to be deposited),
sufficient acid to attain a pH of less than or equal to about 6, a
sufficient amount of surfactant agent to affect wetting of the
metallic surface to be coated, and optionally a hardening agent,
e.g., to control stress in the deposit. For example, the solution
can comprise about 70 g/l to about 90 g/l nickel sulfamate, about
25 g/l to about 35 g/l boric acid, and sufficient sulfamic acid to
attain a pH of about 2 to about 5.0.
[0023] When a current is applied to the system, the anodic metal
oxidizes to form metal ions which then flow to the cathode (the
outer surface of the passivated master) and deposit thereon. The
cathode then reduces the metal ion into elemental metal. The
following shows the reactions at the anode and cathode for nickel:
anode: Ni.sup.0-2e.sup.-.fwdarw.Ni.sup.2+ cathode:
Ni.sup.2++2e.sup.-.fwdarw.Ni Electroforming of other metals also go
through similar reactions at the anode and cathode. Some of the
possible metals for the electroforming process include, but are not
limited to, nickel (Ni), cobalt (Co), copper (Cu), silver (Ag),
iron (Fe), aluminum (Al), titanium (Ti), iridium (Ir), gold (Au),
chromium (Cr), beryllium (Be), tungsten (W), tantalum (Ta),
molybdenum (Mo), platinum (Pt), palladium (Pd), gold (Au), among
others, as well as alloys comprising at least one of the foregoing
metals, and mixtures comprising at least one of the foregoing
metals. Some possible alloys include a nickel-phosphorus (NiP)
alloy, a palladium-phosphorus (PdP) alloy, a cobalt-phosphorus
(CoP) alloy, a nickel-cobalt (NiCo) alloy, a gold-cobalt alloy
(AuCo), and a cobalt-tungsten-phosphorus (CoWP) alloy.
[0024] Electroforming process parameters include solution
temperature, composition, and rectifier voltage. Regarding the
temperature, the solution in the electroforming tank can optionally
be heated to about 30.degree. C. to about 80.degree. C., or, more
specifically, about 35.degree. C. to about 60.degree. C., or, even
more specifically, about 40.degree. C. to about 50.degree. C. The
rectifier can be used to apply a sufficient voltage to the
electrodes to induce an electric current to cause anodic oxidation
of the metal to be deposited, and to reduce the metal ions at the
cathode. For the formation of a Ni or Ni alloy layer, for example,
the current density can be about 2 amperes per square foot (ASF) to
about 100 ASF or so, or, more specifically, about 5 ASF to about 60
ASF or, even more specifically, about 10 ASF to about 30 ASF.
[0025] The exposure time in the electroforming tank while the
current is applied can be determined based upon the particular
metal layer to be formed and the desired thickness of that layer.
The layer thickness can be based upon a desired structural
integrity to enable the layer to be removed from the master as well
as to be used to produce next generation sub-masters, and based
upon the size of the features formed in the surface of the layer.
Thicknesses can be up to and exceeding about 500 micrometers
(.mu.m) or so, or, more specifically, about 50 .mu.m to about 400
.mu.m, or, even more specifically, about 100 .mu.m to about 300
.mu.m, and, yet more specifically, about 150 .mu.m to about 250
.mu.m.
[0026] By controlling the processing parameters of the
electroplating, the thickness of the deposited metal layer can be
adjusted. The thickness of this metal layer can be calculated from
the equation: T = ( M I t Z .times. F .times. .times. .rho. .times.
.times. A ) ##EQU1## [0027] where: T=thickness of the electroformed
layer; [0028] M=the molar mass of the metal; [0029] I=the current;
[0030] t=the time of electroformation; [0031] |Z|=the absolute
value of the valence of the metal; [0032] F=Faraday constant;
[0033] .rho.=the density of the metal; and [0034] A=the surface
area to be covered by the metal. This equation gives a theoretical
maximum thickness assuming 100% efficiency of the cathode. However,
because electrodes are not always 100% efficient, the actual
thickness is usually less than that calculated by the equation.
Generally, the efficiency of an electrode is about 95% to about 99%
depending on the material used as well as other factors.
[0035] Once the desired thickness is achieved, rectifier is
switched off and the cylinder is removed from the electroforming
tank. Optionally, the coated master is rinsed, e.g., with water
(such as deionized water (i.e., water that has been treated with an
ion exchange resin to remove ions therefrom)), and retained in an
inert environment (e.g., an environment that does not chemically
interact with the sub-master surface to change the surface
chemistry under the environmental conditions). Some possible inert
environments include nitrogen, argon, helium, vacuum, and others,
depending upon the environment.
[0036] The sub-master, comprising a negative of the structures on
the master, can be separated from the master. For example, if a
separation tape (also know as plater's tape) has been disposed on
the master, the tape can be removed from the master, exposing the
master as well as an edge of the sub-master. The sub-master can
then be peeled from the master. The master can again be used to
produce additional generations of sub-masters by repeating the
masking, passivation, plating, and separation.
[0037] The sub-master thus produced, can then be used to make next
generation sub-masters (e.g., shims). Prior to employing the
sub-master in the plating process, the sub-master can optionally be
annealed. The annealing can be employed to flatten the sub-master
into a sheet-like form, for example, for ease in production of a
subsequent generation of sub-masters. The sub-master, once removed
from the master, has a rounded shape, e.g., a partial cylinder.
Therefore, the sub-master can be heated to a sufficient temperature
to change the shape of the sub-master from a cylinder-like to a
sheet or plate-like sub-master. The particular annealing
temperature is based upon the sub-master composition as well as the
annealing time. The particular temperature employed is sufficiently
high to soften the sub-master such that it forms a sheet in a
chosen time, while sufficiently low to avoid undesirable surface
reactions as well as adversely affecting the sub-master's surface
features. The upper temperature limit is based upon the melting
temperature of the sub-master material, as well as the possible
reactions and adverse effects that the heat may have on the surface
features, while the lower temperature limit is based upon a
practical amount of time to convert the overall shape of the
sub-master to a sheet-like form. At the higher temperatures, an
inert environment can be employed.
[0038] With Ni and Ni alloy sub-masters, for example, annealing can
be accomplished at a temperature of about 200.degree. C. to about
400.degree. C., or, more specifically, about 200.degree. C. to
about 300.degree. C., or, even more specifically, about 225.degree.
C. to about 275.degree. C. These temperatures can be employed for
periods of time of about 3 hours to about 10 hours, or, more
specifically, about 4 hours to about 7 hours.
[0039] Optionally, the annealed sub-master can be mounted to a
stiffener plate to enhance the structural integrity of the
sub-master. The stiffener plate can comprise any material that will
provide the desired structural integrity to the sub-master, will
not react with the plating solution and/or the sub-master under the
plating conditions. Possible stiffener plates include materials
such as aluminum, ferrous materials (e.g., stainless steel), and so
forth, as well as combinations comprising at least one of the
foregoing materials.
[0040] The sub-master can be mounted to the stiffener plate with
various adhesives, such as a non-conductive vinyl adhesive,
double-faced tape (e.g., pressure sensitive, double-faced tape).
The tape adhesive can comprise rubber, acrylic, silicone, and
combinations comprising at least one of the foregoing adhesives.
The adhesives can be applied to the plate and contacted with a
rubber roll to attain good adhesion. Optionally, the plate can then
be placed in a vacuum bag where a vacuum can be applied to evacuate
air from the space between the sub-master and the plate,
eliminating air voids. In other words, the pressure in the bag can
be reduced to below the pressure of the atmosphere surrounding the
bag.
[0041] In another embodiment, the sub-master can be attached to the
stiffener plate using magnetic force. For example, the plate could
have permanent and/or electro-magnets imbedded therein, and/or
magnetic sheeting (e.g., vinyl magnetic sheeting) can be adhered to
the surface of the stiffener plate.
[0042] The mounted sub-master can then be masked to prevent the
subsequent deposition of the metal layer onto the stiffener plate,
as well as onto undesirable areas of the sub-master. Various
masking materials compatible with the plating environment as well
as the stiffener plate and sub-master, can be employed. Some
exemplary materials include vinyl tape, polyimide tape, and
polyester tape, among others. The polyester tape has been found to
be chemically resistant and consequently reusable for several
plating cycles. The adhesive on the tape can comprise various
adhesives compatible with the plating environment, such as
silicone. The mask can be applied to the back of the plate and the
perimeter of the front of the plate to define the plating area for
the electroforming step.
[0043] Connection areas can then be cut through the tape, e.g., at
the short edges of the sub-master, to expose the mounting plate.
Conductive material can then be employed to connect the stiffener
plate and the sub-master. The conductive material can be a metal
such as nickel, aluminum, stainless steel, copper, and combinations
comprising at least one of the foregoing metals. For example, metal
foil tape can be applied to the connection area and conductive
sealer (e.g., conductive paint) can be disposed around the copper
tape to ensure conductivity between the sub-master and the
stiffener plate (wherein the foil tape has a conductive
adhesive).
[0044] In order to form sub-masters with a taping area, e.g., to
inhibit surface area yield loss in the subsequent generations of
sub-masters, the sub-master can optionally be mounted on an
oversized stiffener plate. This stiffener plate can have a larger
surface area than the sub-master such that, on the side of the
stiffener plate where the sub-master is mounted with adhesive
(e.g., double-faced tape), there is an area of stiffener plate
surface that extends beyond the perimeter of the sub-master; e.g.,
that forms a boarder around the sub-master. The size of the desired
border is application dependent. A border can be formed having a
width of up to about 5 inches (12.7 centimeters (cm) or so, or,
more specifically, about 0.25 inches (0.6 cm) to about 4 inches
(10.2 cm), or, even more specifically, about 0.5 inches (1.3 cm) to
about 3 inches (7.6 cm), and, yet more specifically, about 1 inch
(2.5 cm) to about 2 inches (5.1 cm).
[0045] A conductive rim can then be disposed on the exposed surface
of the stiffener plate, overlaying the edges of the sub-master. The
conductive rim can be formed with any conductive material that is
compatible with the plating environment and materials, and that can
be adhered to the stiffener plate. Possible conductive materials
include stainless steel, copper, nickel, and silver, among other
conductive materials. Possible forms for the conductive material
include sheets, tapes (such as pressure sensitive tape), paintable
liquids and/or pastes containing metals, among others.
[0046] If the adhesive on the tape used to form the conductive rim
is not electrically conductive, a conductive material such as a
conductive paint can be applied to the seam between the sub-master
and the conductive rim. The conductive material can be dried
(actively or passively), sanded smooth to remove over-painted
regions, thereby forming an extended sub-master. The mounted
sub-master can then be masked as described above, leaving at least
a portion of the conductive rim exposed. Here, due to the presence
of the conductive rim, when the electroform is deposited (e.g., via
chemical vapor deposition, plasma spraying, in an electroforming
bath, or otherwise), the next generation sub-master produced will
have a non-surface feature area that forms a periphery or frame
around the surface feature area. This periphery can then be used
for the masking and adhesion in the production of subsequent
generations of sub-masters whereby the loss of surface area in the
surface feature region is minimized because the non-surface feature
frame can be sacrificed if trimming of the periphery is needed.
[0047] The mounted sub-master can be connected to electrode(s)
through the back of the stiffener plate. For example, copper
electrode(s) can be secured to the back of the stiffener plate with
copper screws.
[0048] The masked sub-master can then optionally be disposed in a
box (e.g., a frame such that the mounted sub-master forms the back
of the box), where the edges of the frame are sealed to the plate
with sealant. For example, the mounted sub-master is placed in a
box (such as a pre-machined box formed from an electrically
non-conductive material such as glass, plastic (e.g., polyvinyl
fluoride), and/or the like) and sealed to the masked sub-master
with sealant such as a silicone sealant. The frame may help
facilitate the even distribution of the metal layer on the
sub-master, inhibiting buildup at the edges thereof.
[0049] The sub-master can be used in the plating process to create
additional electroforms so long as the surface to be plated is
properly passivated. As noted above, passivation helps to prevent
the next generation sub-master from adhering to the surface of the
prior generation sub-master once formed. Controlling various
parameters of the passivation layer affect the life of the
sub-master (e.g., the number of copies that can be made from the
sub-master while retaining macroscale, microscale, and nanoscale
resolution). Macroscale refers to the reproduction in the next
generation sub-master of the overall geometry of the replica, such
as flatness and visual uniformity. This macrostructure has a size
of approximately 1 millimeter (mm) to about 1 meter (m) or the
entire size of the part being formed; i.e. of a size scale easily
discerned by the human eye. Microscale refers to the reproduction
in the next generation sub-master of microstructures on the
surface, such as hemispheres, corner-cubes, microlenses, prisms,
and so forth, as well as combinations comprising at least one of
the foregoing. These microstructures have a size of less than or
equal to about 1 mm, or, more specifically, greater than 100
nanometers (nm) to about 1 mm. Nanoscale resolution refers to the
reproduction in the next generation sub-master of nanostructures
forming part of a surface feature, such as at or near corners or a
peak or valley of a surface feature, or the optical smoothness of a
facet of a feature. These nanostructures have a size of less than
or equal to about 500 nm, or, more specifically, less than or equal
to about 100 nm, or, even more specifically, less than or equal to
about 20 nm, and yet more specifically, about 0.5 nm to 10 nm.
[0050] The parameters that can be controlled that can affect the
life of the sub-master include the chemical composition, the
thickness, density, and distribution of the passivation layer. By
controlling the passivation layer, greater than or equal to about
50, or, more specifically, greater than or equal to about 75, or,
even more specifically, greater than or equal to about 100, and
even expect hundreds of sub-masters from nickel alloy electroform
replicas having the nanoscale resolution can be produced.
[0051] The particular passivation employed for the sub-master is
dependent upon the sub-master material. Passivation can be
accomplished, for example, by contacting the sub-master with a
solution (e.g., an aqueous solution) and anodically charging the
sub-master. The aqueous solution can comprise a surfactant and be
alkaline (e.g., have an alkalinity of greater than or equal to pH
8, or, more specifically, greater than or equal to about 10, or,
even more specifically, a pH of about 12 to about 14).
[0052] The surfactant can be any material that reduces the surface
tension of water and aids the wetting of the metal surface.
Possible surfactants include cationic, non-ionic, anionic, as well
as combinations comprising at least one of the foregoing
surfactants. Anionic surfactants include, for example,
carboxylates, sulfonates, sulfates, and phosphate esters. Cationic
surfactants include, for example, amines and quaternary salts.
Non-ionic surfactants include, for example, polyoxyethylene
derivatives of fatty alcohols, carboxylic esters, and carboxylic
amides.
[0053] The alkalinity can be attained with a material capable of
promoting or causing the formation of metal oxides and/or metal
hydroxides on the surface of the sub-master, e.g., an oxidation
species. Some possible oxidation species that can be employed
include alkali metal hydroxides (such as sodium hydroxide,
potassium hydroxide, and the like), as well as combinations
comprising at least one of the foregoing.
[0054] Once the sub-master is disposed in the aqueous solution, it
is anodically charged to convert metallic components on the surface
thereof to metal oxides and/or metal hydroxides, thereby forming a
passivation layer. The sub-master can be charged until the
passivation layer has a thickness of about 10 Angstroms (.ANG.) to
about 500 .ANG., or, more specifically, about 15 .ANG. to about 60
.ANG., or, even more specifically, about 20 .ANG. to about 40
.ANG.. The amount of current applied to the sub-master can be about
1 ASF to about 40 ASF, or, more specifically, about 5 ASF to about
25 ASF, or, even more specifically, about 5 ASF to about 10 ASF.
This current can be applied for a period of about 1 minute to about
5 minutes, or, more specifically, about 1 minute to about 3
minutes.
[0055] This passivation technique has been found particularly
useful with Ni containing sub-masters (e.g., comprising Ni and/or a
Ni alloy (e.g., NiCo, NiCr, among others)). For the Ni containing
sub-masters, a greater number of successful replication of the
nanostructures was achieved when employing a solution comprising an
alkali metal hydroxide instead of a chromate. Possible alkali metal
hydroxides include sodium hydroxide, potassium hydroxide, and the
like, as well as combinations comprising at least one of the
foregoing.
[0056] Once passivated, the sub-master can optionally be dried
(passively and/or actively), and then plated. Plating can be in
various fashions that are capable of applying a layer of metal onto
the surface of the electroform and thereby replicating the surface
features thereof. For example, the passivated electroform can be
placed in a solution in the electroforming tank. Electrical
connection is made to the surface of the sub-master comprising the
surface features so that it becomes the cathode. This solution in
the electroforming tank can comprise about 60 g/l to about 100 g/l
of metal sulfamate (e.g., the metal to be deposited), sufficient
acid to attain a pH of less than or equal to about 6, a sufficient
amount of surfactant agent to affect wetting of the metallic
surface to be coated, and optionally a hardening agent, e.g., to
control stress in the deposit. For example, the solution can
comprise about 70 g/l to about 90 g/l metal alloy sulfamate (e.g.,
nickel-cobalt sulfamate, cobalt-tungsten sulfamate, and so forth),
about 25 g/l to about 35 g/l boric acid, and sufficient sulfamic
acid to attain a pH of about 2 to about 5.0. The anode, as stated
above, optionally comprises the metal or metals to be deposited on
the sub-master surface.
[0057] When a current is applied to the system, the anodic metal
oxidizes to form metal ions which then flow to the cathode (the
surface of the passivated sub-master) and deposit thereon. The
cathode then reduces the metal ion into elemental metal. Once the
desired thickness of the deposited metal has been achieved, the
current is ceased and the plated sub-master is removed from the
tank.
[0058] The thickness of the layer formed on the sub-master, which
is a positive of the sub-master, is dependent on its use, for
example, to produce further generations of sub-masters or to
produce final product. The thickness can be greater than the depth
of the features on the sub-master and sufficient to attain the
structural integrity for its intended use. The layer thickness can
be based upon a desired structural integrity to enable the layer to
be removed from the master as well as to be used to produce next
generation sub-masters. Thicknesses can be up to and exceeding
about 500 micrometers (.mu.m) or so, or, more specifically, about
50 .mu.m to about 400 .mu.m, or, even more specifically, about 100
.mu.m to about 300 .mu.m, and, yet more specifically, about 150
.mu.m to about 250 .mu.m.
[0059] In some applications it may be desirable to form a
multi-layer electroform, e.g., for the final generation tooling
(i.e., the electroform employed to make final product such as
prismatic films). For example, a single electroform that is
produced with layers of different compositions. Each layer can have
the same or a different thickness. For example, the surface layer
(i.e., the layer the side of the electroform comprising the surface
features), can be a material that enhances the release of the final
product from the electroform, and/or that inhibits undesired
reactions on the surface, while the back layer can be a material
that enhances the structural integrity of the electroform. One or
more intermediate layers can also be employed, e.g., to enhance the
bonding of the other layers.
[0060] For example, a surface layer comprising gold (e.g., gold, a
gold alloy, or a gold mixture) can be plated onto a sub-master, and
then backing layer comprising nickel (e.g., nickel, a nickel alloy,
or a nickel mixture) can be overplated (plated over the gold). In
this process, the sub-master is passivated as described above. The
passivated sub-master can then be disposed into an electroplating
bath comprising the desired surface-layer material (e.g., gold).
The surface layer can then be formed utilizing the sub-master as
the cathode in the electroplating process. Once the desired surface
layer thickness has been achieved, the sub-master can then be
disposed in a second electroplating solution to form the second
layer onto the surface layer. Again, the sub-master can be used as
the cathode in the electroplating process. The thickness of the
second layer is dependent upon a desired overall electroform
thickness and the function of this second layer, e.g., as an
intermediate layer or as the backing layer. Although passivation of
the sub-master between the electroplating solutions is possible,
the various layers can be formed without this passivation so that
each layer of the multilayer electroform is firmly bonded to the
next.
[0061] The thickness of the surface layer is dependent upon the
particular application. The surface layer can have a thickness of
millimeters in some applications, while it can be nanometers thick
in others. For example, where the surface layer is employed to
attain a chemical inertness on the surface of the electroform while
controlling the costs of the layer (e.g., while limiting the amount
of gold in the layer), the surface layer can have a thickness of up
to about 10 .mu.m or so, or, more specifically, about 1 nm to about
1 .mu.m, or, even more specifically, about 5 nm to about 500 nm,
and yet more specifically, about 10 nm to about 100 nm. An
intermediate layer can have a thickness of up to about 50
micrometers (.mu.m) or so, or, more specifically, about 1 nm to
about 25 .mu.m, or, even more specifically, about 10 nm to about 1
.mu.m. The backing layer can have a thickness of up to about 500
micrometers (.mu.m) or so, or, more specifically, about 50 .mu.m to
about 400 .mu.m, or, even more specifically, about 100 .mu.m to
about 300 .mu.m.
[0062] For example, a passivated sub-master can be passivated in an
alkaline solution by anodically charging the sub-master. Once a
passivation layer has been formed, the passivated electroform can
be removed from the alkaline solution and optionally rinsed. The
passivated electroform can then be disposed in the surface layer
electroplating solution comprising gold cyamide, silver cyamide,
and so forth. A current is applied, and, with the passivated
electroform acting as the cathode, metal ions (e.g., gold, silver,
cobalt, nickel, and so forth, depending on the composition of the
solution) are deposited on the surface of the sub-master.
[0063] Once a desired surface layer thickness has been attained,
the coated electroform is moved to the next electroplating solution
comprising the metals to be disposed in the subsequent layer (e.g.,
comprising nickel, cobalt, and so forth). Optionally, the coated
electroform can be rinsed (e.g., with deionized water) prior to
entering the subsequent electroplating solution. Furthermore,
maintenance of the coated electroform in an inert environment can
be desirable (i.e., an environment that will not cause a reaction
on the surface layer). In the subsequent electroplating solution,
the coated sub-master again functions as the cathode and receives
metal ions on its surface. This process can be repeated until the
desired number of layers and layer thicknesses has been
attained.
[0064] It has been discovered that the formation of an inert
coating layer on the surface of the final generation sub-master
enhances the life of the sub-master. For example, a surface layer
comprising gold (e.g., a gold-cobalt surface layer with a
nickel-cobalt backing layer) is particularly useful with acrylate
coating material. Not to be bound by theory, where the acrylate
coating material would react with the surface of a nickel-cobalt
electroform, causing building-up nodules of solid crosslinked
coating on the surface of the tool. These nodules grow in size and
number over successive copies of the tool on the coater. They are
also replicated on the films produced with that electroform. Even
when the nodules are less than 100 nm in size (as measured along a
major access), they can adversely effect the replication of
nanostructures from the electroform. When the grow to about 200 nm
to about 400 mn in size, they are large enough to scatter light
(preferentially scattering blue light) and give the film product a
blue hazy appearance. At this point, for a product requiring
nanostructure replication, the product is rejected and the tool is
scrapped. Depending on the coating formulation, the failure point
can be as little as 100 copies or as many as a few thousand copies,
where manufacturing efficiency requires tens of thousands of
copies, and even hundreds of thousands of copies from a single
electroform to be efficient and production viable. By employing the
inert surface layer on the electroform, using the same product
coating formulation that caused failure of a single layer
electroform after 100 copies, 30,000 copies were produced with no
nodule formation (as confirmed with a high resolution scanning
electron microscope (SEM)).
[0065] A further advantage of the multilayer electroform is its
surface properties are changes which gives enhanced release of the
coating (e.g., plastic replication material) from the electroform
in the plastic replication process. For example, a cured acrylate
coating peeled off of the multilayer electroform with less force
than from a single layer electroform. If the coating sticks to the
electroform it can tear, leading to a point defect forming on the
tool where a bit of the plastic material stuck to the sub-master.
This debris replicates into every subsequently-produced plastic
film, causing rejection of all products thus formed and production
must be stopped and the tool discarded. When forming single layer
electroforms, defects could be developed within the making of 300
to 2,000 plastic films, while, with the use of multilayer
electroforms (e.g., with a surface layer comprising gold), at least
about 20,000 to about 30,000 plastic films could be made without
the formation of point defects.
[0066] Since the plated sub-master is flat, separation of the
2.sup.nd generation sub-master can be accomplished by peeling the
electroform (i.e., the plating) from the sub-master. As noted above
it is desirable to uniformly remove the sub-master from the
substrate without twisting or torquing the sub-master. Twisting,
torquing, and other non-uniform removal can damage the pattern on
the surface of the next generation sub-master and potentially even
damage the surface of the sub-master being replicated.
[0067] The 1.sup.st generation sub-master can be employed to make
additional 2.sup.nd generation sub-masters by repeating the
passivation, plating, and separation. Depending upon the materials
used for the mounting and masking, one or several 2.sup.nd
generation sub-master may be produced prior to replacing those
materials.
[0068] The 2.sup.nd generation sub-master can be employed to make
3.sup.rd generation sub-masters or to make final product, e.g.,
film with microstructures having nanoscale resolutions, and in
particular, films comprising light-reflecting elements (e.g.,
retroreflective elements). Possible microstructures include
light-reflecting elements such as cube-corners (e.g., triangular
pyramid), trihedral, hemispheres, prisms, ellipses, tetragonal,
grooves, channels, microlenses, and others, as well as combinations
comprising at least one of the foregoing.
[0069] The particular post-treatment(s) employed prior to using a
sub-master in the production of product are dependent upon the
particular product to be formed. For example, to produce an
acrylate film comprising the desired nanoscale resolution, the
surface energy of the sub-master can be reduced (e.g., of a nickel
containing sub-master). Desirably, the post-treatment renders the
surface of the electroform hydrophobic, and as such; will not
attract polar molecules such as organic monomers and in particular
acrylate monomers.
[0070] High surface energy surfaces can attract polar molecules and
become wetted with them. In the case of water being the polar
species, the surface is wetted with water, there being a low
wetting angle, and the surface is said to be "hydrophilic." Low
surface energy surfaces will not attract polar molecules and will
not become wetted with them. If the surface is rendered to be of a
low surface energy then polar species like water will bead-up on
the surface, and the surface is said to be "hydrophobic."
[0071] The surface energy of the sub-master surface can be reduced
by treating the sub-master with a solution having a pH of less than
or equal to 6, or, more specifically, less than or equal to about
5, or, even more specifically, about 2 to about 5. Optionally, a
cathodic current can be applied. The cathodic current can have a
current density of about 1 ASF to about 60 ASF, or, more
specifically, about 2 ASF to about 30 ASF or, even more
specifically, about 2 ASF to about 10 ASF.
[0072] The sub-master can also, optionally, be treated to remove
particulate(s) and/or staining (e.g., after the sub-master has been
used to make product). This treatment can be before the sub-master
has been used to produce product, and/or to refurbish the
sub-master. This post-treatment can comprise rinsing the sub-master
with water (e.g., deionized water), acidic media, and/or caustic
media. For example, the sub-master can be placed in a bath
containing deionized water, aqueous acid (e.g., a pH of less than
or equal to about 6, or, more specifically, a pH of about 2 to
about 5), and/or caustic media (e.g., a pH of greater than or equal
to about 8, or, more specifically, a pH of about 8 to about
14).
[0073] Once removed from the bath, the sub-master can be rinsed
with water (e.g., deionized water), for example, to remove
particulates and metal salts. The sub-master can then be actively
(e.g., contacted the heat, gas, and/or another method of
facilitating drying) and/or passively dried. Optionally, the
sub-master can be oven dried at a temperature that does not
adversely affect the surface features or surface chemistry.
[0074] When used to make a product (e.g., to mass produce product
such as LCD displays to diffuse or collimate light), the
electroform (e.g., an electroform that has been post-treated with a
cathodic current), can be attached to a calendaring roll. Product
material can then be applied to the electroform. For example, a
desired film material(s) can be extruded (or co-extruded) such that
the material that will comprise the surface feature is disposed in
direct physical contact with the electroform. The material can be
cured and removed from the electroform to form the product. As an
alternative, and/or in addition to the extrusion, preformed film(s)
can be employed. Here, the film to be imprinted with the surface
features can be sufficiently heated to enable the formation of the
surface features into the film surface.
[0075] Possible product materials include plastics (e.g.,
thermoplastics and/or thermosets), such as acrylates,
polycarbonates, polyesters, terephthalates (e.g., poly(ethylene
terephthalate)), polyimides (e.g., polyetherimides), polystyrenes
(e.g., ABS, ASA, and so forth), polyolefins, polyacrylonitrile
(PAN), polyamide (PA), polyvinyl chloride (PVC), resorcinol,
polyarylenes (e.g., polyarylene ether), polyacrylonitrile,
polyethers, as well as combinations comprising at least one of the
foregoing plastics. Various plastics can be combined in a single
layer. These plastics can also be disposed in separate layers to
form the product wherein one of the layers comprises the desired
surface features. If multilayers are employed, adjacent layers
comprise materials that provide sufficient adhesion between the
layers for the desired application (e.g., that will not delaminate
under use conditions for the product). Optionally, coatings and the
like can be applied to the product after the surface features have
been disposed in the surface thereof. Possible films that can be
produced with the present process include those disclosed in U.S.
Published Application No. 2003/0214728 A1 to Olczak, U.S. Published
Application No. 2004/0109663 A1 to Olczak, and others.
[0076] In FIG. 2 a cross sectional view of a backlight display
device 100 is shown. The backlight display device 100 comprises an
optical source 102 for generating light 104. A light guide 106
guides the light 104 therealong by total internal reflection (TIR).
The light guide 106 contains disruptive features that cause the
light 104 to escape the light guide 106. A reflective substrate 108
positioned along the lower surface of the light guide 106 reflects
any light 104 escaping from the lower surface of the light guide
106 back through the light guide 106 and toward an optical
substrate 110. At least one optical substrate 110 is receptive of
the light 104 from the light guide 106. The optical substrates 110
comprise a three-dimensional surface 112 defined by prismatic
structures 116 (FIGS. 3, 4, 5, and 6).
[0077] The optical substrates 110 may be positioned, one above the
other, in a crossed configuration wherein the prismatic structures
116 are positioned at an angle with respect to one another (e.g.,
90 degrees). The prisms 116 have a prescribed peak angle, .alpha.,
a height, h, a length, 1, and a pitch, p and one or both of the
prismatic surfaces 112 may be randomized in their peak angle,
.alpha., height, h, length, 1, and pitch, p. Yet further, one or
both sides of the substrates 110 may have the prisms 116. In FIGS.
3, 4, and 5 the sidewall or facets 132 of the prisms 116, which
comprise the surface 112, are curved. The curvature can be
described as a segment of a parabola, or more generally as a
polynomial surface given by the sag equation: z = cr 2 1 + 1 - ( 1
+ k ) .times. c 2 .times. r 2 + dr 2 + er 4 + fr 6 + Higher .times.
.times. order .times. .times. terms .times. .times. in .times.
.times. r ( 2 ) ##EQU2## where z is the perpendicular deviation (or
"sag") in microns of the sidewall or facet 132 of the prisms 116
from a straight reference line 128, originating at a first
reference point (b) at a base of the prism and terminating at a
second reference point (a) near the peak of the prism and c-1 is
the radius of curvature of the facet. Here the coefficients of the
polynomial may have the following approximate ranges:
-20<c<20, -10<d<10, -10<e<10, -10<f<10, and
-1<k or less than or equal to zero, wherein r is a radial
coordinate or distance from an optical axis in microns. It is noted
that c.sup.2r.sup.2 is greater than or equal to zero and less than
or equal to 1. Odd order terms in r (e.g., r.sup.1, r.sup.3,
r.sup.5, r.sup.7, etc.) with appropriately chosen coefficients may
also be used as in Eq. 2. The higher order terms for the even and
odd order terms have appropriately chosen coefficients. Terms other
than the first r.sup.2 term may be written as: i = 1 N .times. a i
.times. r i . ##EQU3##
[0078] Linear segments or other approximations to the polynomial
described by Eq. 2 may also be used. Linear segments result in a
compound angle prism having a first facet 126 at an angle of
.theta. and a second facet 124 at an angle of .beta.. As best
understood from FIG. 6, the curvature of the curved sidewall or
facet 132 of the prisms 116 can be either convex or concave. In
FIG. 6, the side facets of the prism are positioned so as to form
one or more compound facets 124, 126, respectively subtending an
angle of .beta. or .theta. with the base of the prism.
[0079] The light-redirecting structure can be created, for example,
by applying the curable coating to the base film and casting the
desired light-redirecting structure in the curable coating, by
hot-embossing the structure directly onto the base film, or the
like. While the base film material can vary depending on the
application, suitable materials include those base film materials
discussed in published U.S. Patent Application No. 2003/0108710 to
Coyle et al. More specifically, the base film material of the
brightness enhancement film can comprise metal, paper, acrylics,
polycarbonates, phenolics, cellulose acetate butyrate, cellulose
acetate propionate, poly(ether sulfone), poly(methyl methacrylate),
polyurethane, polyester, poly(vinylchloride), polyethylene
terephthalate, and the like, as well as blends copolymers, reaction
productions, and combinations comprising at least one of the
foregoing.
[0080] The following examples are provided merely to further
illustrate the electroforms and the methods described herein, and
are not intended to limit the scope hereof.
EXAMPLES
Example 1
Passivation in a Caustic Solution with Anodic Current
[0081] Sample 1, a nickel sub-master electroform having a
microstructure comprising a plurality of channels and grooves of
about 1 .mu.m to about 37 .mu.m in depth, was passivated by
immersion into an aqueous solution for 4 minutes at 25.degree. C.
while applying an anodic current density of 4 ASF. The aqueous
solution comprised 20 g/l potassium hydroxide and 0.5 g/l sodium
lauryl sulfate and had a pH of 13.5. The sub-master was removed,
rinsed with deionized water, and then dried. The sub-master was
then plated with a nickel-cobalt (NiCo) alloy by electroforming a
layer that was about 100 .mu.m in thickness. After electroforming,
the plated sub-master was rinsed and dried, and the nickel-cobalt
electroform was readily peeled from the sub-master, showing
complete removal and no visible damage to the microstructures when
examined under a microscope at up to 40.times.. It is also noted
that samples have been examined to a magnification of 100.times.X
without visible damages, and even passed SEM (scanning electron
microscope) review at 100K.times.(100,000.times.).
Example 2
Passivation in a Caustic Solution with Anodic Current
[0082] Sample 2, a nickel sub-master electroform having a
microstructure comprising a plurality of channels and grooves of
about 1 .mu.m to about 37 .mu.m in depth, was passivated by
immersion into an aqueous solution for 4 minutes at 35.degree. C.
while applying an anodic current density of 4 ASF. The aqueous
solution comprised 20 g/l of StamperPrep (a high alkalinity (pH
greater than 13), low foaming, cleaning agent comprising sodium
hydroxide commercially available from DisChem, Inc., Ridgway, Pa.),
and had a pH of greater than 13.5. The sub-master was removed,
rinsed with deionized water, and then dried. The sub-master was
then plated with a nickel-cobalt alloy by electroforming a layer
that was about 100 .mu.m in thickness under the same conditions as
in Example 1. After electroforming, the plated sub-master was
rinsed and dried, and the nickel-cobalt electroform was readily
peeled from the sub-master, showing complete removal and no visible
damage to the microstructures when examined under a microscope.
Example 3
Passivation of a Nickel Containing Sub-master
[0083] Sample 3, a nickel sub-master electroform having a
microstructure comprising a plurality of channels and grooves of
about 1 .mu.m to about 37 .mu.m in depth, was passivated by
immersion into an aqueous solution for 30 seconds at 35.degree. C.
while applying an anodic current density of 35 ASF. The aqueous
solution comprised 90 g/l of StamperPrep, and had a pH of greater
than 13.5. The sub-master was removed, rinsed with deionized water,
and then dried. The sub-master was then plated with a nickel-cobalt
alloy by electroforming a layer that was about 100 .mu.m in
thickness under the same conditions as in Example 1. After
electroforming, the plated sub-master was rinsed and dried, and the
nickel-cobalt electroform was readily peeled from the sub-master,
showing complete removal and no visible damage to the
microstructures when examined under a microscope.
Example 4
Passivation of a Nickel Containing Sub-master
[0084] Sample 4, a production-size nickel-cobalt sub-master
electroform (a nominal size of 40 centimeters (cm) by 65 cm),
having a microstructure comprising a plurality of channels and
grooves of about 1 .mu.m to about 37 .mu.m in depth, was passivated
by immersion into an aqueous solution for 4 minutes at 35.degree.
C. while applying an anodic current density of 4 ASF. The aqueous
solution comprised 20 g/l of StamperPrep, and had a pH of greater
than 13.5. The sub-master was removed, rinsed with deionized water,
and then dried. The sub-master was then plated with a nickel-cobalt
alloy by electroforming a layer that was about 200 .mu.m in
thickness under the same conditions as in Example 1. After
electroforming, the plated sub-master was rinsed and dried, and the
nickel-cobalt electroform was readily peeled from the sub-master,
showing complete removal and no visible damage to the
microstructures when examined under a microscope.
[0085] Sample 4 was then recycled through the passivation step and
electroforming step a total of 57 times, thus generating 57
electroforms all of which separated cleanly and wholly, showing
complete removal and no visible damage to the microstructures when
examined under a microscope.
Example 5
Passivation of a Nickel Containing Sub-master
[0086] Sample 5, a production-size nickel-cobalt sub-master
electroform (a nominal size 40 cm by 65 cm), having a
microstructure comprising a plurality of channels and grooves of
about 1 .mu.m to about 37 .mu.m in depth, was passivated by
immersion into an aqueous solution for 4 minutes at 35.degree. C.
while applying an anodic current density of 4 ASF. The aqueous
solution comprised 20 g/l of StamperPrep, and had a pH of greater
than 13.5. The sub-master was removed, rinsed with deionized water,
and then dried. The sub-master was then plated with a nickel-cobalt
alloy by electroforming a layer that was about 200 .mu.m in
thickness under the same conditions as in Example 1. After
electroforming, the plated sub-master was rinsed and dried, and the
nickel-cobalt electroform was readily peeled from the sub-master,
showing complete removal and no visible damage to the
microstructures when examined under a microscope.
[0087] Sample 5 was then recycled through the passivation step and
electroforming step a total of 65 times, thus generating 65
electroforms all of which separated cleaning and wholly showing
complete removing and with no visible damage to the microstructures
when examined under a microscope.
Example 6
Passivation of a Nickel Containing Sub-master with a Solution
Comprising Dichromate
[0088] A nickel-cobalt sub-master electroform having a
microstructure comprising a plurality of channels and grooves of
about 1 .mu.m to about 37 .mu.m in depth was passivated by
immersion into an aqueous solution comprising 5 g/l potassium
dichromate for 5 minute at 25.degree. C. while agitating the
solution. The sub-master was removed and rinsed with deionized
water. The sub-master was then plated with a nickel-cobalt alloy by
electroforming a layer that was about 100 .mu.m in thickness. After
electroforming, the plated sub-master was rinsed and dried, and the
nickel-cobalt electroform was peeled from the sub-master.
Examination under a microscope showed the microstructures to be
partially damaged, whereas the very finest structures at the
sharpest comers of the peaks were torn from the electroform and
remained on the sub-master, thus causing visible defects and loss
of optical performance. The dichromate passivation process was
inadequate to passivate the nickel containing sub-master in that
not all areas (in particular, the deepest valleys on the
sub-master), were passivated sufficiently to allow complete removal
of the entire electroform copy.
Example 7
Post-treatment by Immersion in a Caustic Solution, Followed by
Rinsing and Drying
[0089] An electroform, such as Sample 1, can be immersed in a
caustic solution having a pH of about 8 to 14, at 40.degree. C.,
for 1 to 5 minutes, rinsed with deionized water, and dried. The
electroform can then be placed on a roll for use in the formation
of acrylate films. A liquid coating mixture, comprising UV-curable
acrylate monomer(s), oligomer, photoinitiator, and non-reactive
additive(s), can be pressed into the electroform surface by a
backing film, (e.g., a plastic film, such as polycarbonate,
polyester, and so forth, as well as reaction products comprising at
least one of the foregoing, and combinations comprising at least
one of the foregoing), and can be cured to fix the microstructures
into the surface. The film, with the cured acrylate
microstructures, can then be separated from the roll. It has been
observed that electroforms, such as Sample 1, (that have only been
rinsed, but not post-treated to reduce the surface energy), i.e.,
with a high surface energy, cause permanent sticking of minute
domains of the acrylate coating during the production of the
transparent film. These minute domains accumulate on the
electroform surface, ultimately changing the surface features, and
thereby effectively causing the loss of the desired nanoscale
resolution.
Example 8
Post-treatment by Immersion in an Acidic Solution and Application
of a Reverse Current (Cathodic Current)
[0090] Sample 7, a NiCo sub-master such as Sample 1, can be
post-treated, e.g., to reduce the surface energy. Sample 7 can be
immersed in an acidic solution for 1 to 5 min at 40.degree. C.,
while applying a cathodic current density of 4 ASF. The acidic
solution can comprise Citranox.TM., and can have a pH of about 4.
The electroform can then be placed on a roll for use in the
formation of acrylate films. A liquid coating mixture, comprising
UV-curable acrylate monomer(s), oligomer, photoinitiator, and
non-reactive additive(s), can be pressed into the electroform
surface by a backing film, (such as polycarbonate, polyester, and
so forth), and can be cured to fix the microstructures into the
surface. The film, with the cured acrylate microstructures, can
then be separated from the roll. This acrylate film has been
observed to have a nanoscale resolution.
Example 9
Treatment by Immersion in a Caustic Solution (After Production of
Product with the Electroform)
[0091] Sample 8, a NiCo sub-master such as Sample 1, can be
post-treated, e.g., to reduce the surface energy. Sample 8 can be
immersed in a caustic media for 1 to 5 min at 40.degree. C., while
applying a cathodic current density of 4 ASF. The caustic solution
can comprise StamperPre.TM., sodium hydroxide, etc., and can have a
pH of about 8 to about 14. The electroform can then be placed on a
roll for use in the formation of acrylate films. A liquid coating
mixture, comprising UV-curable acrylate monomer(s), oligomer,
photoinitiator, and non-reactive additive(s), can be pressed into
the electroform surface by a backing film, (such as polycarbonate,
polyester, and so forth), and can be cured to fix the
microstructures into the surface. The film, with the cured acrylate
microstructures, can then be separated from the roll. It was
further observed that the caustic soak and reverse current, when
applied to the nickel or nickel-cobalt electroforms, also
eliminated particulate and staining defects from the
microstructured electroform surface, which resulted in tool yield
improvements.
[0092] The electroforms prepared as described herein can be use to
produce acrylate films, e.g., display films with microscale
features. For such brightness enhancement films, the key optical
property to be measured is the on-axis luminance of these films in
an LCD backlight assembly, which was measured with using the
following protocol. A Teijin D120 (commercially available from
Tsujiden Co., Ltd., Japan) bottom diffuser was placed on backlight
(i.e., LG Phillips LP121X1 single CCFL notebook backlight), and a
vertical prism film was placed over the bottom diffuser (i.e., the
lower prism film was oriented with the prisms running vertically)
while the horizontal prism film was placed over the vertical prism
film (i.e., the upper film was placed with prisms running
horizontally). The inverter was a Taiyo Yuden LS 390 (commercially
available from Taiyo Yuden (U.S.A.) Inc., Schaumburg, Ill.). A
thermocouple was used to monitor the temperature of the active
backlight in real-time while letting the system equilibrate (until
the average temperature did not change more than 0. 1.degree. F.
over a 5 minute duration). Once equilibrium was attained, the
Microvision SS220 display analysis system (commercially available
from Microvision, Auburn, Caif.) output the luminance in units of
candelas per square meter (also known as "nits"). These units were
converted to "relative luminance units" compared with a BEF-II film
standard (commercially available from Minnesota Mining and
Manufacturing Co., St. Paul, Minn.). It is noted that the
Microvision software included: luminance uniformity--measured
on-axis luminance across 13 points of the backlight; and view
angle--measured luminance as a function of angle at the center
point of the backlight.
[0093] A 3.sup.rd-generation electroform designated M-1-1-1 (i.e.
the 1.sup.st 3.sup.rd-geneartion copy of the 1.sup.st
2.sup.nd-generation copy of the 1.sup.st 1.sup.st-generation copy
of the master "M") was prepared according to the process described
above to produce 67 4.sup.th-generation copies of itself. Copies
number 2 and 67 were used to produce display films that were tested
for luminance. The films from the 2.sup.nd copy had an average
normalized luminance of 103.5% with a standard deviation of 0.19%,
while the films from the 67.sup.th copy had an average normalized
luminance of 103.2% with a standard deviation of 0.22%, which makes
them statistically equal at a 95% confidence limit. In other words,
even after 67 production cycles, there was no decrease in quality
of the film produced.
[0094] The present electroplating process is more effective than
prior art processes, e.g., the replication accuracy has been
maintained for greater than or equal to about 100 replicas. For
example, due to the passivation process, the replicas (i.e., next
generation sub-masters) readily separate from the sub-master after
the plating process without loss of surface features.
[0095] Additionally, the post-treatment process for treating the
sub-master prior to using the sub-master in production of a product
(such as a display film), enables the reproducible production of a
more regular geometric pattern than when the sub-master has been
post-treated with deionized water and a caustic media (pH of about
8 to about 14). This post-treatment, which uses a cathodic current
and acidic media, is particularly useful on electroforms used in
the production of articles from a polar material. The caustic media
can be employed with the electroform between product production
runs, to reduce, and possibly eliminated particulate and staining
defects from the microstructured electroform surface; resulting in
tool yield improvements.
[0096] It is noted that the mounting techniques, and/or passivation
techniques disclosed above can be used with various processes for
producing an electroform (e.g. a sub-master), and are not limited
to the electroplating technique discussed herein. Other possible
processes for depositing the metal material onto the master or
sub-master to produce the next generation sub-master include plasma
spraying, vapor deposition (e.g., chemical vapor deposition),
electroless plating.
[0097] As previously noted, the electroforms can be used to produce
objects comprising microstructures with nanoscale resolution, such
as films. These films can be used in various applications, e.g., in
light management applications (e.g., as a part of a light
management article). For example, the film can be used in to
direct, diffuse, and/or polarize light. The films can be brightness
enhancement films used in backlight computer displays or other
display systems. Some other potential applications include
graphical applications (e.g., labels, flooring graphic
applications, and so forth), automotive overlays, instrument
clusters, tridimensional molded parts (e.g., with multicolor
graphics that can be backlit), and so forth. The films can be used
alone or in multilayer structures. For example, in applications
such as those described in U.S. Published Application No.
2004/0228141 A1 to Hay et al.
[0098] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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