U.S. patent application number 10/072457 was filed with the patent office on 2002-11-28 for self-aligned aperture masks having high definition apertures.
This patent application is currently assigned to Corning Precision Lens Incorporated. Invention is credited to Brady, Michael D., Guermeur, Celine C., Nedelec, Yann P. M..
Application Number | 20020177082 10/072457 |
Document ID | / |
Family ID | 23017059 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020177082 |
Kind Code |
A1 |
Brady, Michael D. ; et
al. |
November 28, 2002 |
Self-aligned aperture masks having high definition apertures
Abstract
Self-aligned aperture masks are produced using a positive-acting
photoresist (18) which is developed with a liquid developer. The
apertures (30) of the mask have lower levels of inter-aperture
variability than masks produced using mechanical transfer of toner
particles (FIGS. 4-5 and 7-8), both for the apertures of a given
mask and between masks.
Inventors: |
Brady, Michael D.; (Painted
Post, NY) ; Guermeur, Celine C.; (Chartrettes,
FR) ; Nedelec, Yann P. M.; (Avon, FR) |
Correspondence
Address: |
Maurice M. Klee, Ph.D.
Attorney at Law
1951 Burr Street
Fairfield
CT
06430
US
|
Assignee: |
Corning Precision Lens
Incorporated
|
Family ID: |
23017059 |
Appl. No.: |
10/072457 |
Filed: |
February 7, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60267037 |
Feb 7, 2001 |
|
|
|
Current U.S.
Class: |
430/320 ;
156/240; 205/667; 430/300 |
Current CPC
Class: |
G03B 21/60 20130101;
G02B 3/0056 20130101; G02B 3/0031 20130101; G02B 3/0012
20130101 |
Class at
Publication: |
430/320 ;
156/240; 205/667; 430/300 |
International
Class: |
B44C 001/00 |
Claims
What is claimed is:
1. A method for making an aperture mask for a screen comprising:
(a) providing a substrate having a first side and a second side,
the first side having an array of lenses associated therewith; (b)
applying a positive-acting photoresist to the second side of the
substrate, said photoresist comprising at least one pigment
dispersed in a photosensitive matrix which, upon exposure to
actinic radiation, becomes soluble in a developer solution, said at
least one pigment absorbing light in the visible range; (c)
exposing the positive-acting photoresist by passing actinic
radiation through the array of lenses to form an exposure pattern
in the positive-acting photoresist, said exposure pattern being a
function of the optical properties of the lenses; and (d)
developing the positive-acting photoresist using the developer
solution to remove photoresist which has been exposed to the
actinic radiation and thus form apertures in the photoresist which
will transmit visible light to a greater extent than regions of the
photoresist that have not been exposed to the actinic
radiation.
2. The method of claim 1 wherein the array of lenses is an array of
microlenses.
3. The method of claim 2 wherein the array of microlenses is formed
in the first side of the substrate.
4. The method of claim 3 wherein the substrate comprises a first
layer and a second layer and the array of microlenses is formed by
embossing the first layer of the substrate.
5. The method of claim 4 wherein the first layer is a photocurable
resin.
6. The method of claim 2 wherein the array of microlenses is
applied to the first side of the substrate.
7. The method of claim 6 wherein the array of microlenses is
applied to the first side of the substrate using an adhesive.
8. The method of claim 6 wherein the array of microlenses is molded
onto the first side of the substrate.
9. The method of claim 1 wherein the at least one pigment comprises
pigment particles having a mean diameter below 500 nanometers.
10. The method of claim 1 wherein the at least one pigment
comprises carbon black particles.
11. The method of claim 1 wherein the photosensitive matrix
comprises the reaction product of a resin and a diazo oxide.
12. The method of claim 1 wherein the actinic radiation is UV
radiation.
13. The method of claim 1 wherein the actinic radiation has a
spatial distribution corresponding to the spatial distribution of
visible light which will pass through the lenses during use of the
screen.
14. The method of claim 1 wherein the developer solution is an
aqueous solution having a pH of 9 or higher.
15. The method of claim 1 wherein the apertures have at least one
cross-sectional dimension of less than 100 microns.
16. The method of claim 1 wherein the apertures have at least one
cross-sectional dimension of less than 50 microns.
17. The method of claim 1 wherein the apertures have a low level of
inter-aperture variability.
18. Apparatus comprising: (a) a substrate having a first side and a
second side; (b) an array of lenses associated with the first side
of the substrate; and (c) an aperture mask on the second side of
the substrate comprising: (i) a pigmented polymer layer comprising
at least one pigment dispersed substantially uniformly throughout
the layer, said pigment absorbing visible light, said pigmented
polymer layer being either an unexposed positive-acting photoresist
or an exposed, but not developed, positive-acting photoresist; and
(ii) a plurality of apertures which pass through the pigmented
polymer layer, the locations of the apertures being based on the
optical properties of the array of lenses; wherein the apertures
transmit visible light to a greater extent than the pigmented
polymer layer.
19. The apparatus of claim 18 wherein the array of lenses is an
array of microlenses.
20. The apparatus of claim 19 wherein the substrate comprises a
first layer and a second layer with the array of microlenses being
formed in the first layer.
21. The apparatus of claim 20 wherein the first layer is a
photocurable resin.
22. The apparatus of claim 19 further comprising an adhesive layer
between the array of microlenses and the first side of the
substrate.
23. The apparatus of claim 18 wherein the at least one pigment
comprises particles having a mean diameter below 500
nanometers.
24. The apparatus of claim 18 wherein the at least one pigment
comprises carbon black particles.
25. The apparatus of claim 18 wherein the pigmented polymer layer
comprises the reaction product of a resin and a diazo oxide.
26. The apparatus of claim 18 wherein the apertures have at least
one cross-sectional dimension of less than 100 microns.
27. The apparatus of claim 18 wherein the apertures have at least
one cross-sectional dimension of less than 50 microns.
28. The apparatus of claim 18 wherein the apertures have a low
level of inter-aperture variability.
29. The apparatus of claim 18 wherein the aperture mask further
comprises a non-pigmented polymer layer which is either an
unexposed positive-acting photoresist or an exposed, but not
developed, positive-acting photoresist, said non-pigmented polymer
layer being closer to the second side of the substrate than the
pigmented polymer layer.
30. The apparatus of claim 29 further comprising an adhesive layer
between the non-pigmented polymer layer and the second side of the
substrate.
31. The apparatus of claim 18 further comprising an adhesive layer
between the pigmented polymer layer and the second side of the
substrate.
32. A rear projection television comprising the apparatus of claim
18.
Description
FIELD OF THE INVENTION
[0001] This invention relates to self-aligned aperture masks used
in rear projection screens and, in particular, to self-aligned
masks which achieve high definition of the individual apertures
making up the mask.
BACKGROUND OF THE INVENTION
[0002] Rear projection televisions are widely used as consumer
products and are becoming ever more popular as computer monitors. A
critical component of such televisions is the rear projection
screen upon which the user views the ultimate image. Such screens
need to satisfy a number of stringent criteria.
[0003] For example, to provide a bright image, the screen should
control the distribution of light in viewer space so that as much
light as possible is directed to the places where the user is
likely to be. Arrays of either cylindrical lenses or microlenses
can be used for this purpose. Co-pending U.S. Patent Application
No. 60/222,033, filed Jul. 31, 2000, and entitled "Structured
Screens for Controlled Spreading of Light," the contents of which
are incorporated herein by reference, discloses particularly
preferred microlens arrays for this purpose. This application is
referred to hereinafter as the "'033 patent application".
[0004] To achieve high contrast, rear projection screens have
typically included an aperture mask designed to prevent ambient
light from entering the projection television. Such light can
reflect from structures internal to the television and become
redirected to the viewer. This redirected light reduces the
contrast of the image since it can appear at, for example, places
where the image should be black.
[0005] In their most simple form, aperture masks can be prepared by
printing a black matrix on one of the surfaces making up the rear
projection screen. Beginning with arrays of cylindrical lenses and
continuing through to arrays of microlenses, workers in the art
have used self-alignment techniques to form such aperture masks.
See, for example, U.S. Pat. No. 2,338,654, U.S. Pat. No. 2,618,198,
U.S. Pat. No. 5,870,224, PCT Patent Publication No. WO 99/36830,
EPO Patent Publication No. 1 014 169 A1, Japanese Patent
Publication No. 2000-147662, and Japanese Patent Publication No.
2000-147663.
[0006] The goal of these self-alignment techniques is to ensure
that the apertures of the mask correspond to the locations where
light will be focused by the lens array. In some cases, the
apertures are produced first and are subsequently used to produce
microlenses (see U.S. Pat. No. 5,897,980, EPO Patent Publication
No. 0 753 791, PCT Patent Publication No. WO 99/36830) and in other
cases, the lenses are prepared first and then used in the
production of the apertures (see U.S. Pat. No. 4,666,248).
[0007] The present invention is concerned with the second approach,
i.e., the approach in which an array of lenses is produced first
and then used to create a self-aligned aperture mask.
[0008] The earliest self-aligned aperture masks were based on
photographic emulsion technology. This approach has a number of
disadvantages including low transparency of the apertures and poor
age performance. If a photographic emulsion were to be used to
produce an aperture mask for a projection television, the age
performance problem would only become worse in view of the heat
which such televisions generate.
[0009] Recently, proposals have been made to use DuPont's
Cromalin.RTM. system to produce aperture masks. See, for example,
Japanese Patent Publication No. 09-269546 and U.S. Pat. No.
5,870,224.
[0010] As discussed in these references, in the first step of the
process, a laminate of (1) a tacky, photosensitive, transparent
layer and (2) a lenticular lens array is prepared. Thereafter, the
photosensitive layer is exposed with UV light through the lens
array. The UV light causes the photosensitive layer to polymerize
and lose its tackiness in the exposed regions. A backing film
carrying toner particles is then applied to the photosensitive
layer and through the application of pressure (e.g., pressure up to
700 kg/cm.sup.2), toner particles are transferred to the unexposed
and thus still tacky regions of the photosensitive layer. The
backing film is then mechanically pulled away from the
photosensitive layer with toner particles remaining on the layer at
the tacky regions.
[0011] As illustrated by the comparative example set forth below,
the Cromalin.RTM. system has the serious drawback that it produces
apertures of low definition, i.e., rather than having
cross-sectional perimeters of the desired design shape, the
apertures have ragged, uneven perimeters. Moreover, the
Cromalin.RTM. system for producing aperture masks exhibits a high
level of variability in the shapes of the apertures, both among the
apertures of a given screen and between screens.
[0012] An additional problem with the Cromalin.RTM. system arises
from the fact that the apertures are filled with polymerized
material. Such material may vary from aperture to aperture in, for
example, the degree of polymerization, which can produce
uncontrollable variations in the optical path for light passing
through the finished screen. For example, the surface curvature of
the polymerized material filling the apertures can vary in an
uncontrollable manner from aperture to aperture.
[0013] Further variability in masks produced using the
Cromalin.RTM. system can result from different amounts of toner
being transferred to the regions of the mask which are intended to
block visible light.
[0014] A further problem with the Cromalin.RTM. system arises from
the fact that the high pressures used in the toner transfer step
can damage the lens array portion of the laminate.
[0015] The present invention is designed to overcome these problems
with the Cromalin.RTM. system.
SUMMARY OF THE INVENTION
[0016] In view of the foregoing, there is a need in the art for a
self-aligned aperture mask having some and preferably all of the
following properties:
[0017] (1) the mask comprises apertures of high definition;
[0018] (2) the mask is produced by a process with low variability
both for the apertures of an individual mask and between masks in
terms of aperture configuration and optical properties;
[0019] (3) the mask is produced by a process which produces
essentially the same level of blackness at all parts of the mask
which are intended to block light;
[0020] (4) the mask is produced by a process which does not apply
excessive pressure to a lens array used to produce the self-aligned
apertures;
[0021] (5) the mask does not substantially deteriorate with age;
and
[0022] (6) the mask can be produced economically on a continuous
basis.
[0023] The present invention provides self-aligned aperture masks
which have some and preferably all of the foregoing six
properties.
[0024] In accordance with one of its aspects, the invention
provides a method for making an aperture mask for a screen
comprising:
[0025] (a) providing a substrate having a first side and a second
side, the first side having an array of lenses associated
therewith;
[0026] (b) applying a positive-acting photoresist to the second
side of the substrate, said photoresist comprising at least one
pigment dispersed in a photosensitive matrix which, upon exposure
to actinic radiation, becomes soluble in a developer solution, said
at least one pigment absorbing light in the visible range;
[0027] (c) exposing the positive-acting photoresist by passing
actinic radiation through the array of lenses to form an exposure
pattern in the photoresist, said exposure pattern being a function
of the optical properties of the lenses; and
[0028] (d) developing the positive-acting photoresist using the
developer solution to remove photoresist which has been exposed to
the actinic radiation and thus form apertures in the photoresist
which will transmit visible light to a greater extent than regions
of the photoresist that have not been exposed to the actinic
radiation.
[0029] In accordance with another of its aspects, the invention
provides apparatus (a screen subassembly) comprising:
[0030] (a) a substrate having a first side and a second side;
[0031] (b) an array of lenses associated with the first side of the
substrate; and
[0032] (c) an aperture mask on the second side of the substrate
comprising:
[0033] (i) a pigmented polymer layer comprising at least one
pigment dispersed substantially uniformly throughout the layer,
said pigment absorbing visible light, said pigmented polymer layer
being either an unexposed positive-acting photoresist or an
exposed, but not developed, positive-acting photoresist; and
[0034] (ii) a plurality of apertures which pass through the
pigmented polymer layer, the locations of the apertures being based
on the optical properties of the array of lenses;
[0035] wherein the apertures transmit visible light to a greater
extent than the pigmented polymer layer.
[0036] As used herein, the term positive-acting photoresist means a
photoresist having the characteristic that development of the
photoresist causes removal from the photoresist of those portions
of the photoresist that have been exposed to actinic radiation.
[0037] Additional features and advantages of the invention are set
forth in the detailed description which follows, and in part will
be readily apparent to those skilled in the art from that
description or recognized by practicing the invention as described
herein.
[0038] It is to be understood that both the foregoing general
description and the following detailed description are merely
exemplary of the invention, and are intended to provide an overview
or framework for understanding the nature and character of the
invention as it is claimed.
[0039] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
various embodiments of the invention, and together with the
description serve to explain the principles and operation of the
invention. The drawings are not intended to indicate scale or
relative proportions of the elements shown therein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIGS. 1A through 1E are schematic diagrams which illustrate
the basic steps of the process of the invention.
[0041] FIG. 2A is a schematic diagram illustrating a representative
structure for a positive-acting photoresist suitable for use with
the present invention prior to exposure to actinic radiation.
[0042] FIG. 2B shows the same structure as FIG. 2A after (1)
lamination of photoresist 18 to the second side of substrate 10,
(2) removal of carrier sheet 20, and (3) actinic radiation exposure
and development. Only one aperture 30 is shown in this figure, it
being understood that in practice a plurality of apertures will be
formed in the photoresist.
[0043] FIG. 3 is a schematic diagram illustrating a representative
continuous production embodiment of the invention.
[0044] FIGS. 4A and 4B are photomicrographs of portions of aperture
masks prepared using the process of the present invention and the
Cromalin.RTM. process, respectively, at a magnification of
20.times.. The aperture dimensions are approximately 40 microns by
20 microns in each case.
[0045] FIGS. 5A and 5B are photomicrographs of portions of aperture
masks prepared using the process of the present invention and the
Cromalin.RTM. process, respectively, at a magnification of
50.times.. The maximum short-axis aperture dimension is
approximately 30 microns in each case.
[0046] FIG. 6 shows the layout of the microlens array through which
UV light was passed to produce the aperture masks of FIGS. 4 and
5.
[0047] FIGS. 7A and 7B are binary (black and white) pictures
showing the apertures of FIGS. 4A and 4B, respectively, except for
the merged aperture at (row 1-column 6) and (row 2-column 5) of
FIG. 4A, which was not included in the quantitative analysis.
[0048] FIGS. 8A and 8B show the perimeters of the apertures of
FIGS. 7A and 7B, respectively, These figures also include the
aperture numbers of Tables 1A and 1B.
[0049] The reference numbers used in the drawings correspond to the
following:
[0050] 10 substrate
[0051] 12 first side of substrate
[0052] 14 second side of substrate
[0053] 16 lenses
[0054] 18 positive-acting photoresist
[0055] 20 base carrier sheet or film
[0056] 22 release layer
[0057] 24 pigmented photosensitive layer, i.e., photosensitive
matrix having at least one pigment dispersed therein
[0058] 26 non-pigmented photosensitive layer, i.e., photosensitive
matrix per se
[0059] 28 adhesive layer
[0060] 29 actinic radiation
[0061] 30 aperture
[0062] 32 feed roll for lens array
[0063] 34 feed roll for positive-acting photoresist
[0064] 36 assembly station
[0065] 38 peeling station
[0066] 40 initial UV exposure station
[0067] 42 development station
[0068] 44 development solution application and brushing
substation
[0069] 46 rinsing substation
[0070] 48 drying substation
[0071] 50 final UV exposure station
[0072] 52 protective coating station
DETAILED DESCRIPTION OF THE INVENTION
[0073] FIG. 1 illustrates the basic steps of the process of the
invention. In particular, FIG. 1A shows a substrate 10 having a
first side 12 and a second side 14, the first side having
associated therewith an array of lenses 16.
[0074] The substrate can be composed of various materials known in
the art such as polycarbonate, polyester, etc. The lenses 16 can be
cylindrical lenses or microlenses, microlenses being preferred. In
either case, the lenses can have a variety of configurations,
preferred configurations being those disclosed in the
above-referenced '033 patent application.
[0075] The lenses can be formed separately and applied to the first
side of the substrate using, for example, a suitable adhesive.
Alternatively, the lenses can be formed onto the first side using a
molding process. See, for example, U.S. Pat. No. 5,264,063.
[0076] As a further alternative, the lenses can be formed directly
in the first side of the substrate using an embossing process. In
this case, the substrate preferably includes first and second
layers, the first layer being relatively soft at room temperature
so that it can be easily embossed. Further, once embossed, the
first layer should be hardenable, e.g., through UV, e-beam, or
thermal curing. For example, an acrylic-based resin which is UV
curable can be used for the first layer.
[0077] Direct embossing without the use of a separate soft layer
can also be used if the lenses have relatively low heights, e.g.,
if the lens effect is achieved through holography.
[0078] As a still further alternative, the substrate and the array
of lenses can be formed simultaneously using a web extrusion
process. See, for example, U.S. Pat. Nos. 4,601,861 and
4,486,363.
[0079] However obtained, the substrate with its associated lenses
is then combined with a positive-acting photoresist 18 (see FIG.
1B).
[0080] FIG. 2A shows a representative structure for photoresist 18
prior to exposure to actinic radiation. As shown therein, the
photoresist can include a base carrier sheet or film 20, a release
layer 22, a layer 24 comprising a photosensitive matrix and at
least one pigment (e.g., carbon black having a mean particle size
of less than 500 nanometers, preferably, 300 nanometers or less)
dispersed substantially uniformly throughout the matrix, a layer 26
comprising a non-pigmented photosensitive matrix, and a thermal
adhesive layer 28. The photosensitive matrix is preferably the
reaction product of a resin with a diazo oxide.
[0081] Detailed descriptions of suitable photoresists 18 having the
foregoing structure can be found in, for example, U.S. Pat. No.
4,260,673, the contents of which is incorporated herein by
reference. Commercially, such photoresists are available from
Imation Inc., Oakdale, Minn., and are sold under the trademark
MATCHPRINT. Particularly suitable MATCHPRINT products for use in
the process of the present invention are those referred to as
"black U.S. standard" and "black Euro standard."
[0082] Other configurations for photoresist 18 can be used in the
practice of the invention. For example, non-pigmented layer 26 can
be removed if desired. Also, the content of black pigment can be
made higher than that used in the U.S. and Euro standard products,
if desired. Alternatively, an enhanced optical density can be
achieved by increasing the thickness of pigmented layer 24.
[0083] Photoresist 18 can be applied to second side 14 of substrate
10 in a variety of ways. Preferably, thermal adhesive layer 28 of
the commercially available MATCHPRINT product is used for this
purpose. Alternatively, a pressure sensitive adhesive can be
employed either alone or in combination with a thermal
adhesive.
[0084] As shown in FIG. 1C, the photoresist/substrate/lens array
assembly, however prepared, is exposed to actinic radiation 29
through lenses 16 to produce an exposure pattern of exposed and
non-exposed regions in the positive-acting photoresist. Exposure
through the lenses produces the desired self-alignment of the
aperture mask with the lenses.
[0085] Various types of actinic radiation can be used to perform
the exposure depending on the characteristics of the
positive-acting photoresist. Examples include UV radiation, IR
radiation, and visible light, UV radiation being preferred. In
particular, UV radiation having a wavelength in the range of
360-410 nanometers is preferred when the positive-acting
photoresist is the MATCHPRINT product discussed above.
[0086] The exposure with actinic radiation should have a spatial
distribution which corresponds to the spatial distribution of
visible light which will pass through the lenses during use of the
finished rear projection screen. In particular, the actinic
radiation needs to be spatially distributed by the lenses of the
lens array in a manner which is similar to the manner in which
visible light will be distributed by those lenses during use of the
finished screen. This needs to take into account the variation of
the index of refraction of the lenses with wavelength as well as
the wavelength range of the actinic radiation and of the visible
light which will be passing through the screen during use. The
configuration of the incoming actinic radiation beam is adjusted to
achieve this desired correspondence of spatial distributions.
Commercially available optical design programs can be used to
determine lens systems which will cause the actinic radiation to
have the desired spatial distribution.
[0087] After UV exposure, the photoresist/substrate/lens array
assembly is developed to remove the regions of the photosensitive
matrix (both pigmented and non-pigmented in FIG. 2) which have been
exposed to the actinic radiation and thus form the desired
self-aligned apertures (see FIG. 1D). A variety of developer
solutions can be used depending on the particular photoresist
employed, water-based developers being preferred because of their
ease of handling and disposal. For the MATCHPRINT system discussed
above, the developer has a pH of 9 or higher so that it can
dissolve the exposed regions of the photosensitive matrix. This
developer also dissolves release layer 22 so that the developer
solution can reach photosensitive layers 24 and 26.
[0088] The developer solution is applied to release layer 22 and a
mild brushing is used to help remove the exposed regions of the
photoresist. Thereafter, excess developer and dissolved
photosensitive resin is washed from the surface using water,
following which the developed photoresist/substrate/lens array
assembly is passed through low pressure rollers to squeeze off
remaining liquid. Finally, the assembly is dried using, for
example, hot air. FIG. 2B shows the structure of the
photoresist/substrate combination at this stage of the process.
[0089] To stabilize the color of the assembly, a second exposure
with actinic radiation is performed as shown in FIG. 1E. Since the
development process has been completed at this point in the
process, this exposure does not result in a change in the
configuration of the photoresist, i.e., the photoresist continues
to have the self-aligned apertures surrounded by a resin
matrix.
[0090] To protect the finished photoresist/substrate/lens array
assembly, a plastic protective layer, e.g., a thermoplastic acrylic
layer, can be applied to the finished assembly. Alternatively, the
assembly can be mounted to a support sheet, e.g., a sheet of
polycarbonate or PMMA, using an appropriate adhesive.
[0091] FIG. 3 shows a representative continuous process for
practicing the steps of FIG. 1. As shown therein, feed roll 32
provides substrate 10 with preformed arrays of lenses 16 and feed
roll 34 provides unexposed photoresist 18. The substrate and
photoresist are combined together at assembly station 36, and layer
20 of FIG. 2A is removed at peeling station 38. Assembly station 36
includes an appropriate heating system (not shown) to activate the
thermal adhesive of layer 28.
[0092] The photoresist is exposed with the desired aperture pattern
at initial UV exposure station 40. If desired, station 40 can be
located upstream of peeling station 38 since the UV exposure takes
place through the array of lenses. In either case, the exposed
photoresist is developed in development station 42 which includes
substations 44, 46, and 48 for development solution application and
brushing, rinsing, and drying, respectively.
[0093] The developed photoresist then passes through final UV
exposure station 50 which exposes the remaining photoresist and
thus stabilizes the color of the aperture mask. Finally, a
protective layer is applied at station 52. Alternatively, a support
sheet can be applied at this point in the process as discussed
above.
[0094] For a flexible protective layer, the finished
photoresist/substrate/lens array assembly can be collected on a
roll for later use in constructing a finished rear projection
screen. If a support sheet is used for protection, the finished
assembly can be cut and stacked for later use. Alternatively, in
either case, further processing can take place immediately after
the application of the protective layer or sheet.
COMPARATIVE EXAMPLE
[0095] FIGS. 4A and 4B are photomicrographs of portions of aperture
masks prepared using the process of the present invention and the
Cromalin.RTM. process, respectively, at a magnification of
20.times.. FIG. 6 shows the layout of the microlens array through
which UV light was passed to produce the aperture masks of this
figure.
[0096] The individual microlenses were anamorphic microlenses
having a diameter of 50 microns and a center-to-center spacing of
43.3 microns. The lenses had parabolic profiles along both their
fast (horizontal) and slow (vertical) axes. The microlenses were
randomized in accordance with the above-referenced '033 patent
application. In particular, the radius of curvature along the fast
axis was chosen to be between 8 and 9 microns with a uniform
probability density function, while for the slow axis, the radius
of curvature was chosen to be between 33 and 36 microns, again with
a uniform probability density function. The total depth of the
microlenses was 36 microns.
[0097] The thickness of the substrate which carried the microlenses
was chosen to place the photosensitive layer in each case between
the fast axis and slow axis focal planes of the microlenses. In
particular, the thickness was chosen so that the photosensitive
layer was approximately at the location of the circles of least
confusion of the microlenses. This location minimized the spot
sizes of the UV light used to expose the photosensitive layer. For
the above microlenses, the distance between the apices of the
microlenses and the photosensitive layer was approximately 75
microns.
[0098] The masks of FIGS. 4A and 4B were prepared by passing
collimated UV light through the microlenses with the collimation
angle and other exposure conditions being the same in each case
except for exposure time which was separately optimized for the two
photosensitive materials. Other than the use of collimated light,
the Cromalin.RTM. and MATCHPRINT photosensitive materials were used
in accordance with the respective manufacturer's instructions.
[0099] As can be seen in FIG. 4, the process of the present
invention produced significantly better apertures than those
produced by the Cromalin.RTM. process. In particular, the apertures
of the invention have substantially better definition than those of
the Cromalin.RTM. process. Also, the variation between apertures is
substantially less for the process of the invention than for the
Cromalin.RTM. process. A high level of variation from run to run
was also seen with the Cromalin.RTM. process, while the process of
the invention produced essentially identical apertures each time it
was performed.
[0100] Analyses were performed to quantify the differences between
the apertures of FIGS. 4A and 4B and, in particular, the
differences in aperture variability between the two figures. The
procedures used were as follows.
[0101] Each image constituted 640.times.512 pixels representing a
sample size of 700 .mu.m.times.560 .mu.m. Each pixel corresponded
to 1.09375 .mu.m.times.1.09375 .mu.m. In order to perform the
calculations, the original images (FIGS. 4A and 4B) were
transformed to binary (black and white) pictures (FIGS. 7A and 7B)
by applying a threshold. The threshold used was 128 in a range of 0
to 255 gray steps. The internal perimeters of the apertures were
then extracted to produce FIGS. 8A and 8B.
[0102] The area (in pixels) and perimeter (in pixels) of each
aperture was measured from FIGS. 7A and 7B by counting the black
pixels in each domain. Some apertures of FIG. 7B are composed of
sub-apertures which were grouped together and considered as a
single aperture in the analysis.
[0103] The software used for the threshold and pixel counting was
NIH IMAGE (version 1.62) by Wayne Rasband, National Institutes of
Health, USA.
[0104] The "circularity" of each aperture (a unitless number) was
calculated as follows:
circularity=(perimeter).sup.2/(4.pi.(area)).
[0105] The fractal dimension of each aperture was calculated using
the Mass Radius Method and the on-line software FRACTOP V0.2,
available at http://life.csu.edu.au/fractop/. The following
parameters were used in the analysis:
[0106] (a) number of centers to average over: 20;
[0107] (b) number of regression points to use for the semi-log
graph regression: 10;
[0108] (c) centers limited within 0.3 times radius of gyration.
[0109] The results of the analysis are shown in Tables 1A and 1B
for the apertures of the present invention (MATCHPRINT) and the
prior art (Cromalin.RTM.), respectively. As can be seen in these
tables, the area, perimeter, circularity and fractal dimension
dispersions (i.e., standard deviation divided by mean) are lower
for the apertures of the present invention than for the apertures
of the prior art. Put another way, the data of Tables 1A and 1B
show that for a given microlens design, the process of the
invention leads to apertures with a higher level of homogeneity in
size and shape than the prior art process.
[0110] It should be noted that the apertures of FIGS. 4A and 4B
were formed using microlenses which were intentionally random in
shape, i.e., the microlenses varied in radius of curvature. Such
randomness automatically results in at least some variation in the
apertures formed. For this reason, absolute dispersion values are
not appropriate for distinguishing the apertures of the present
invention from those produced by the prior art. For example, the
apertures produced by the prior art method for a set of uniform
(non-random) microlenses could exhibit less dispersion than the
apertures produced by the present invention for a set of random
microlenses.
[0111] Relative values however can be determined. Thus, the ratio
of the dispersion values of Tables 1A to the dispersion values of
Table 1B for area, perimeter, circularity, and fractal dimension
are 0.35, 0.47, 0.37, and 0.46, respectively. Thus, in general, the
level of inter-aperture variability of the apertures of the
invention will be less than 50% of the level of inter-aperture
variability of the apertures of the prior art for a comparable set
of microlenses.
[0112] FIGS. 5A and 5B show a second set of self-aligned aperture
masks prepared using the same microlens array layout of FIG. 6, the
same microlens diameter of 50 microns, and the same
center-to-center spacing of 43.3 microns. The lenses had parabolic
profiles along their slow axes with the radius of curvature being
chosen to be between 16 and 26 microns with a uniform probability
function.
[0113] Along the fast axis, hybrid spherical/parabolic profiles
described by the following sag function, were used: 1 s ( x ) = ( R
s - R s 2 - x 2 ) + x 2 2 R p ,
[0114] where .alpha., R.sub.s, and R.sub.p are the adjustable
parameters of the profile. For the microlenses used to produce FIG.
5, R.sub.s was 25 microns, R.sub.p was chosen to be between 8 and
14 microns with a uniform probability function, and .alpha. was
chosen to be between 0.6 and 0.8, again with a uniform probability
function. The total microlens depth was 43 microns.
[0115] For these microlenses, the distance between the apices of
the microlenses and the photosensitive layer was approximately
80-85 microns which caused the apertures to overlap so that the
finished aperture mask, as shown in FIG. 5, is in the form of black
serpentine strips. The exposure protocol was the same as that used
for FIG. 4. Again, as in FIG. 4, the process of the present
invention produced superior apertures to those produced by the
Cromalin.RTM. process.
[0116] Rather than placing the photosensitive layer at the circle
of least confusion as was done in preparing FIGS. 4 and 5, the
photosensitive layer can be placed at either the fast axis or the
slow axis focal plane. This location has the advantage of
increasing the area of the aperture mask which is light blocking
without unacceptably reducing the amount of light which passes
through the screen to the viewer during use of the projection
television.
[0117] For this case, when randomized microlenses are used, the
randomization should be constrained so that all of the microlenses
have a substantially common fast or slow focal plane. For example,
for a hybrid spherical/parabolic profile of the type described by
the equation set forth above, the randomization preferably is
performed so that the following relationship is satisfied: 2 R p R
s R p + R s = ( 1 - 1 2 n UV - 1 2 n max ) ,
[0118] where .tau. is the thickness of the substrate, n.sub.uv is
the index of refraction of the microlenses and the substrate during
UV exposure (the indices of refraction of the microlenses and the
substrate are preferably equal to avoid surface losses), and
n.sub.max is the effective index of refraction of the portions of
the screen upstream of the aperture mask (i.e., towards the light
source) for the longest wavelength of light that will pass through
the screen during use.
[0119] Although specific embodiments of the invention have been
described and illustrated, it will be apparent to those skilled in
the art that modifications and variations can be made without
departing from the invention's spirit and scope. The following
claims are thus intended to cover the specific embodiments set
forth herein as well as such modifications, variations, and
equivalents.
1TABLE 1A Present Invention Area Perimeter Circularity Fractal
Aperture # (pixel) (pixel) (unitless) dimension 1 2224 239 2.04
1.88 2 2916 320 2.79 1.85 3 2756 276 2.20 1.82 4 3044 276 1.99 1.83
5 2460 269 2.34 1.84 6 2907 327 2.93 1.78 7 2986 263 1.84 1.94 8
2787 290 2.40 1.89 9 3318 322 2.49 1.73 10 3451 324 2.42 1.74 11
2425 273 2.45 1.88 12 2631 262 2.08 1.9 13 2524 287 2.60 1.75 14
2740 281 2.29 1.87 15 2994 270 1.94 1.91 16 2712 299 2.62 1.8 17
2838 291 2.37 1.82 18 2567 292 2.64 1.9 19 2595 301 2.78 1.82 20
3190 302 2.28 1.81 21 2724 299 2.61 1.87 22 3699 317 2.16 1.83 23
2364 268 2.42 1.78 24 2633 275 2.29 1.76 25 3393 328 2.52 1.71 26
2715 273 2.18 1.86 27 2700 334 3.29 1.84 28 2675 289 2.48 1.84 29
2576 261 2.10 1.88 30 2811 267 2.02 1.83 31 2604 250 1.91 1.88 32
2464 292 2.75 1.9 33 2447 290 2.73 1.85 Total 91870 9507 Mean
2783.94 288.09 2.39 1.84 Std Dev 332.56 24.09 0.33 0.06 Std
Dev/Mean 0.119 0.084 0.136 0.031
[0120]
2TABLE 1B Prior Art Area Perimeter Circularity Fractal Aperture #
(pixel) (pixel) (unitless) dimension 1 1374 180 1.88 1.91 2 915 189
3.11 1.76 3 1039 222 3.77 1.66 4 1717 227 2.39 1.85 5 618 189 4.60
1.94 6 1542 219 2.48 1.88 7 2321 268 2.46 1.95 8 1128 191 2.57 1.82
9 1577 218 2.40 1.78 10 1589 265 3.52 1.79 11 1650 233 2.62 1.93 12
1300 213 2.78 1.81 13 555 184 4.85 1.57 14 1906 236 2.33 1.87 15
1428 240 3.21 1.89 16 788 228 5.25 1.85 17 972 172 2.42 2 18 907
226 4.48 1.66 19 2201 314 3.56 1.93 20 1294 218 2.92 1.86 21 1539
240 2.98 1.88 22 1291 182 2.04 1.93 23 198 118 5.60 2.3 24 1091 185
2.50 1.92 25 1785 251 2.81 1.89 26 1627 219 2.35 1.98 27 1116 201
2.88 1.91 28 1650 293 4.14 1.83 29 894 173 2.66 1.78 30 1547 246
3.11 1.9 31 1578 246 3.05 1.84 32 1634 227 2.51 1.86 33 1275 209
2.73 1.79 34 969 304 7.59 1.62 35 1788 251 2.80 1.89 Total 46803
7777 Mean 1337.23 222.20 3.24 1.86 Std Dev 456.24 39.80 1.18 0.12
Std Dev/Mean 0.341 0.179 0.365 0.067
* * * * *
References