Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B21/00—Projectors or projection-type viewers; Accessories therefor
  • G03B21/54—Accessories
  • G03B21/56—Projection screens
  • G03B21/60—Projection screens characterised by the nature of the surface
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0006—Arrays
  • G02B3/0012—Arrays characterised by the manufacturing method
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0006—Arrays
  • G02B3/0012—Arrays characterised by the manufacturing method
  • G02B3/0031—Replication or moulding, e.g. hot embossing, UV-casting, injection moulding
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0006—Arrays
  • G02B3/0037—Arrays characterized by the distribution or form of lenses
  • G02B3/0056—Arrays characterized by the distribution or form of lenses arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses

Definitions

• 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.
• 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.
• 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.
• 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. Patent No. 2,338,654, U.S. Patent No. 2,618,198, U.S. Patent No. 5,870,224, PCT Patent Publication No.
• WO 99/36830 EPO Patent Publication No. 1 014 169 Al, Japanese Patent Publication No. 2000-147662, and Japanese Patent Publication No. 2000-147663.
• 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.
• the apertures are produced first and are subsequently used to produce microlenses (see U.S. Patent 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. Patent No. 4,666,248).
• 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.
• 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.
• 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 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.
• the Cromalin® 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® 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.
• Cromalin® 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.
• Cromalin® A further problem with the Cromalin® system arises from the fact that the high pressures used in the toner transfer step can damage the lens array portion of the laminate.
• the present invention is designed to overcome these problems with the Cromalin® system. SUMMARY OF THE INVENTION
• the mask comprises apertures of high definition;
• 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;
• 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;
• the mask is produced by a process which does not apply excessive pressure to a lens array used to produce the self-aligned apertures
• the mask does not substantially deteriorate with age; and (6) the mask can be produced economically on a continuous basis.
• the present invention provides self-aligned aperture masks which have some and preferably all of the foregoing six properties.
• the invention provides 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;
• 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;
• the invention provides apparatus (a screen subassembly) comprising:
• an aperture mask on the second side of the substrate comprising:
• 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.
• 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.
• FIGS. 1A through IE are schematic diagrams which illustrate the basic steps of the process of the invention.
• Figure 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.
• Figure 2B shows the same structure as Figure 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.
• Figure 3 is a schematic diagram illustrating a representative continuous production embodiment of the invention.
• Figures 4A and 4B are photomicrographs of portions of aperture masks prepared using the process of the present invention.
• Cromalin® process respectively, at a magnification of 20X.
• the aperture dimensions are approximately 40 microns by 20 microns in each case.
• Figures 5A and 5B are photomicrographs of portions of aperture masks prepared using the process of the present invention and the Cromalin® process, respectively, at a magnification of 50X.
• the maximum short-axis aperture dimension is approximately 30 microns in each case.
• Figure 6 shows the layout of the microlens array through which UV light was passed to produce the aperture masks of Figures 4 and 5.
• Figures 7A and 7B are binary (black and white) pictures showing the apertures of Figures 4A and 4B, respectively, except for the merged aperture at (row 1- column 6) and (row 2 - column 5) of Figure 4A, which was not included in the quantitative analysis.
• Figures 8A and 8B show the perimeters of the apertures of Figures 7A and 7B, respectively, These figures also include the aperture numb'ers of Tables lA and lB.
• the reference numbers used in the drawings correspond to the following:
• substrate 12 first side of substrate 14 second side of substrate 16 lenses
• pigmented photosensitive layer i.e., photosensitive matrix having at least one pigment dispersed therein
• non-pigmented photosensitive layer i.e., photosensitive matrix per se
• Figure 1 illustrates the basic steps of the process of the invention.
• Figure 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.
• 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 O33 patent application.
• the lenses can be formed separately and applied to the first side of the substrate using, for example, a suitable adhesive.
• the lenses can be formed onto the first side using a molding process. See, for example, U.S. Patent No. 5,264,063.
• the lenses can be formed directly in the first side of the substrate using an embossing process.
• the substrate preferably includes first and second layers, the first layer being relatively soft at room temperature so that it can be easily embossed.
• the first layer should be hardenable, e.g., through UV, e-beam, or thermal curing.
• an acrylic-based resin which is UV curable can be used for the first layer.
• 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.
• the substrate and the array of lenses can be formed simultaneously using a web extrusion process. See, for example, U.S. Patents Nos. 4,601,861 and 4,486,363.
• the substrate with its associated lenses is then combined with a positive-acting photoresist 18 (see Figure IB).
• FIG. 2A shows a representative structure for photoresist 18 prior to exposure to actinic radiation.
• 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.
• photoresist 18 can be used in the practice of the invention.
• non-pigmented layer 26 can be removed if desired.
• the content of black pigment can be made higher than that used in the U.S. and Euro standard products, if desired.
• an enhanced optical density can be achieved by increasing the thickness of pigmented layer 24.
• Photoresist 18 can be applied to second side 14 of substrate 10 in a variety of ways.
• thermal adhesive layer 28 of the commercially available MATCHPRINT product is used for this purpose.
• a pressure sensitive adhesive can be employed either alone or in combination with a thermal adhesive.
• the photoresist/substrate/lens array assembly 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.
• 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.
• 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.
• 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.
• the photoresist/substrate/lens array assembly is developed to remove the regions of the photosensitive matrix (both pigmented and non-pigmented in Figure 2) which have been exposed to the actinic radiation and thus form the desired self-aligned apertures (see Figure ID).
• 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.
• 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.
• FIG. 2B shows the structure of the photoresist/substrate combination at this stage of the process.
• a plastic protective layer e.g., a thermoplastic acrylic layer
• the assembly can be mounted to a support sheet, e.g., a sheet of polycarbonate or PMMA, using an appropriate adhesive.
• FIG 3 shows a representative continuous process for practicing the steps of Figure 1.
• 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 Figure 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.
• 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. 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.
• 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.
• Figures 4A and 4B are photomicrographs of portions of aperture masks prepared using the process of the present invention and the Cromalin® process, respectively, at a magnification of 20X.
• Figure 6 shows the layout of the microlens array through which UV light was passed to produce the aperture masks of this figure.
• 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.
• 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.
• 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.
• 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.
• the distance between the apices of the microlenses and the photosensitive layer was approximately 75 microns.
• the masks of Figures 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.
• the Cromalin® and MATCHPRINT photosensitive materials were used in accordance with the respective manufacturer's instructions.
• the process of the present invention produced significantly better apertures than those produced by the Cromalin® process.
• the apertures of the invention have substantially better definition than those of the Cromalin® process.
• the variation between apertures is substantially less for the process of the invention than for the Cromalin® process.
• a high level of variation from run to run was also seen with the Cromalin® process, while the process of the invention produced essentially identical apertures each time it was performed. Analyses were performed to quantify the differences between the apertures of Figures 4A and 4B and, in particular, the differences in aperture variability between the two figures. The procedures used were as follows.
• Each image constituted 640 x 512 pixels representing a sample size of 700 ⁇ m x 560 ⁇ m. Each pixel corresponded to 1.09375 ⁇ m x 1.09375 ⁇ m.
• the original images Figures 4A and 4B
• 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 Figures 8A and 8B.
• the area (in pixels) and perimeter (in pixels) of each aperture was measured from Figures 7A and 7B by counting the black pixels in each domain.
• FIG. 7B Some apertures of Figure 7B are composed of sub-apertures which were grouped together and considered as a single aperture in the analysis.
• the software used for the threshold and pixel counting was NIH IMAGE (version 1.62) by Wayne Rasband, National Institutes of Health, USA.
• the apertures of Figures 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.
• the ratio of the dispersion values of Tables 1A to the dispersion values of Table IB for area, perimeter, circularity, and fractal dimension are 0.35, 0.47, 0.37, and 0.46, respectively.
• 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.
• Figures 5A and 5B show a second set of self-aligned aperture masks prepared using the same microlens array layout of Figure 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.
• ⁇ , R s , and R p are the adjustable parameters of the profile.
• R s was 25 microns
• R p was chosen to be between 8 and 14 microns with a uniform probability function
• ⁇ was chosen to be between 0.6 and 0.8, again with a uniform probability function.
• the total microlens depth was 43 microns.
• 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 Figure 5, is in the form of black serpentine strips.
• the exposure protocol was the same as that used for Figure 4. Again, as in Figure 4, the process of the present invention produced superior apertures to those produced by the Cromalin® process.
• 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.
• the randomization should be constrained so that all of the microlenses have a substantially common fast or slow focal plane.
• the randomization preferably is performed so that the following relationship is satisfied:
• ⁇ is the thickness of the substrate
• n 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)
• n 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.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Overhead Projectors And Projection Screens (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23017059

Family Applications (1)

Country Status (4)

Families Citing this family (19)

Citations (2)

Family Cites Families (32)

• 2002
  • 2002-02-07 JP JP2002563075A patent/JP4226329B2/ja not_active Expired - Lifetime
  • 2002-02-07 WO PCT/US2002/003665 patent/WO2002063392A1/en not_active Ceased
  • 2002-02-07 KR KR1020037010375A patent/KR100870800B1/ko not_active Expired - Lifetime
  • 2002-02-07 US US10/072,457 patent/US20020177082A1/en not_active Abandoned
• 2003
  • 2003-04-15 US US10/430,179 patent/US6770425B2/en not_active Expired - Lifetime

Patent Citations (2)

Also Published As

Similar Documents

Legal Events