KR20070018110A - Method for making tools for micro replication - Google Patents

Abstract

A method comprising electromechanically engraving a three-dimensional molding pattern (N) on a rigid surface. The rigid surface is configured to finely replicate according to the molding pattern (N). The rigid surface may be a pattern roller. The molding pattern may be for fine copying the optical element 5 in the light redirecting film 2.

Description

3D molding pattern engraving method, optical device micro-replication method and apparatus {METHOD FOR MAKING TOOLS FOR MICRO REPLICATION}

The present invention provides a continuous material web in which the reversed phase of the three-dimensional pattern is formed by electromechanically engraving a molding pattern consisting of small individual cavities on a rigid surface (for example, gravure electro-mechanical engraving). To a specific purpose method for micro replication.

Films with patterned surfaces are made for a variety of applications. For example, the photo paper may include a matte finish or a gloss finish film. This matte finish or gloss finish can give the photograph a desirable effect when viewed by an ordinary observer. Glossy or matte finishes require certain tolerances (ie, a certain level of precision) in the photo paper manufacturing process. The tighter the tolerances of the manufacturing process, the more complex and expensive the manufacturing process is in general. That is, the tolerances required to produce the pattern film for photo paper may be significantly lower than the tolerances required to produce a light redirecting film film for liquid crystal displays.

Light redirecting films can be used for a variety of applications. For example, light redirecting films can be used as part of a liquid crystal display (LCD) to increase the power efficiency of the LCD. The increase in power efficiency of LCDs (or other similar displays) can be significant. Liquid crystal displays are provided in battery operated mobile devices (e.g., cell phones, laptop computers, digital cameras, etc.). It is desirable for these mobile devices to maximize the operating time of their batteries. Although battery technology is improving, one way to increase the battery life of a mobile device is to reduce the device's power consumption without compromising quality. By manufacturing the liquid crystal display device more efficiently, the battery life of the mobile device can be extended, which is quite advantageous for the user.

The optics of the light redirecting film are very specific and detailed compared to the optics of a glossy or matte finish to the photograph. Thus, the precision of the manufacturing method for processing a photo paper with a gloss or matte finish may be unsuitable for the purpose of producing a light redirecting film. For example, the manufacturing method used to make other patterned films may not adequately reproduce the optical elements of the light redirecting film, or may provide the uniform film thickness required for the light redirecting film to be usable. Can't. Incompatibility of such existing manufacturing processes is a serious problem for the production of light redirecting films.

Summary of the Invention

Exemplary embodiments of the present invention relate to a method comprising electromechanically engraving a molding pattern on a rigid surface (eg, a pattern roller). Another exemplary embodiment of the present invention is directed to a method comprising microcopying an optical element on a light redirecting film. Another embodiment of the invention is directed to a device having a rigid surface. Molding patterns are formed on rigid surfaces and are formed by electromechanical pieces (eg, gravure electromechanical pieces).

The molding pattern is a three-dimensional surface shape formed on the rigid surface, so that the negative of the three-dimensional surface shape is exactly given to the surface of the object molded from the rigid surface. The molding pattern in the present invention includes a plurality of cavities that are well cut and formed on a rigid surface.

According to an exemplary embodiment of the present invention, the manufacturing method can produce molding patterns for light redirecting films that can be used in various applications. For example, by using a manufacturing method according to an exemplary embodiment of the present invention, a light redirecting film can be produced by accurate replication of a particular optical element. Such replication of certain optical elements enables films that can significantly increase the efficiency of liquid crystal displays. Thus, this increase in efficiency can extend the battery life of mobile devices (eg, mobile phones, laptop computers, digital cameras, etc.). The manufacturing method of an exemplary embodiment will enable the manufacture of thin films with separate optical elements. Light redirecting films that do not have separate optical elements will not be effective in increasing the efficiency of the display device without degrading display quality.

1 is a schematic side shaving of a light redirecting film system according to an exemplary embodiment of the present invention;

2 is an enlarged partial side view of a portion of a backlight and light redirecting film system in accordance with an exemplary embodiment of the present invention;

3 and 4 are schematic side views of a light redirecting film system according to an exemplary embodiment of the present invention;

5 is a diagram of a typical image cut by an electromechanical engraving machine, with cavities arranged in a regular offset grid, FIG.

6 is a view of another portion of a typical image cut by an electromechanical engraving machine, wherein the cavity is cut to varying depths, sizes, and shapes;

7 is a diagram of an irregular or random pattern of intersecting cavities,

8A-8C illustrate various forms of adjacent overlapping cavities,

9 is a cross-sectional view of the individual cavities showing how the individual cavities are cut to a predetermined final depth in multiple stages;

10A and 10B are views of a cylinder structure including a small cavity in accordance with an exemplary embodiment of the present invention.

The use of a cylinder having a small cavity pattern on its surface is versatile. Typically these cylinders are used to replicate the cavity pattern of its surface to other materials in a continuous manufacturing method. In gravure printing, for example, a series of cavities formed in a predetermined pattern on the cylinder surface is used to collect ink or coating material and transfer it onto the surface of the continuous web.

Patterned cylinders can also be used in the micro replication method. In ultraviolet (UV) cured replication, the material is applied in a manner that fills a cavity in the cylindrical surface, and the UV cured material cures by ultraviolet exposure and then separates from the cylinder. Other examples of fine replication methods include hot embossing and continuous extrusion. In hot embossing, the patterned cylinder is pressed against the preformed polymer web under high pressure and high temperature to produce a homogeneous product with a microstructured surface. In continuous extrusion, a thin layer of molten polymer is pressed against a patterned cylinder to produce a homogeneous product with a microstructured surface. A unique attraction of patterned cylinders is their ability to continuously manufacture products regardless of how they are used. Continuous methods can provide lower manufacturing costs compared to batch methods.

Given the attractiveness of the continuous manufacturing method, it is possible to efficiently create a cylinder having a predetermined pattern of small cavities. In addition to generating accurate patterns of small cavities, the time required to generate certain patterns on large surface areas must be rationalized. The surface area to be patterned into the small cavity is usually from 0.03 m 2 to 2.2 m 2 and most preferably from 0.32 m 2 to 1.0 m 2. It is desirable that the method required to produce the small cavity pattern can be achieved within three days.

While various techniques for producing patterned cylinders are known in the art, the lifetime of these techniques is shorter when a given pattern has some optical use. The field of application of replica patterns of small cavities with optical applications varies. These applications include, but are not limited to, holograms used in security and packaging applications, microlens arrays for communications and imaging systems, and light redirecting films used in backlight display systems. Examples of light redirecting films include diffusers, light collecting films, polarization recovery and regeneration films.

Diamond tools can be used to achieve the surface quality and roughness features required for the generation of optical features. Precisely shaped and polished diamond tools can be combined with the cylindrical surface using any of a variety of techniques to remove, form or form material on the cylindrical surface. Since diamond tools are expensive, more universal and less expensive alternative tool materials are preferred. Alternative tool materials, such as carbon steel or high speed steel, cannot produce optical quality features due to the relatively large material particle size. This large particle size will result in the production of fine chips along the cutting edge, which will produce surfaces with unacceptable roughness properties and therefore do not meet the requirements for surfaces with optical applications. To generate optical quality features directly in the cylinder, the features can be cut, formed, scribed, ruled or otherwise generated using a diamond tool or stylus.

There is an alternative for indirectly creating a cylinder having a predetermined pattern of small cavities. For example, a predetermined pattern can be created on a flat workpiece, and subsequent work can produce a flexible copy of the original that can be wrapped around a cylindrical surface. The use of this technique will form a seam or line that can be easily detected on the finished product whose frequency is the same as the circumference of the cylinder. This may be acceptable in some applications, but not in many applications. This is especially true when the finished product produced by replication or material transfer has a length greater than the circumference of the cylinder.

It is well known that the time it takes to create a cylinder with a predetermined pattern of small cavities is an important limitation of various alternative methods for patterning such cylinders. In particular, the time taken to create cylinders with a predetermined pattern of small cavities can make the creation of such cylinders very expensive. All alternative methods have the ability to produce 1 to 10 features per second. At this rate, the time required to pattern the average cylinder used in the continuous manufacturing method will be measured on a monthly basis. For example, if a pattern consists of 3,875 cavities per square centimeter and the surface area to be patterned is 1.0 m 2, at a speed of 10 features per second, the time required to pattern the cylinder is approximately 43 days.

Known techniques exist for creating continuous optical grooves on cylinders using diamond tools. In this way, the non-rotating diamond tool is engaged with the rotating cylinder. Typically the symmetric tool is coupled perpendicular to the surface of the cylinder to form a symmetric groove consisting of two or more angled surfaces. Although coupled with the cylinder, it can also be moved further into the surface or retracted from the surface of the cylinder to change the feature depth. If this is done in a continuous nonlinear motion, the resulting groove will consist of two or more curved surfaces. U. S. Patent No. 6,581, 286 (Campbell et al.) Discloses a method for forming simple continuous features by thread cutting. The grooves produced by this method are symmetrical and continuous and consist of two curved surfaces.

In other applications the diamond tool is moved parallel, perpendicular or at an angle to the axis of rotation of the cylinder or workpiece while being engaged. Any or all combinations of these movements can be made simultaneously, and the choice of movement selected is a function of the desired shape of the cavity being manufactured. Exemplary applications of this method include the production of individual segments of large mirror assemblies.

Exemplary embodiments of the present invention provide a molding pattern for microreplication comprising a special purpose metal cylinder for patterning into small individual three-dimensional cavities by electromechanical engraving to replicate the reversed phase of the three-dimensional pattern into a continuous material web. Create

1 and 2 schematically illustrate one form of a light redirecting film system 1 according to an exemplary embodiment of the present invention. The light redirecting film system 1 may include a light redirecting film 2 that redistributes most of the light emitted by the backlight BL (or other light source) in a direction more perpendicular to the surface of the film. The film 2 can be used to redistribute light within a certain viewing angle from any light source for illumination. For example, the film 2 can be used with the display D (eg in liquid crystal displays used in laptop computers, word processors, aviation displays, cell phones, PDAs) to make the display brighter. The liquid crystal display comprises a transmissive liquid crystal display schematically illustrated in FIGS. 1 and 2, a reflective liquid crystal display illustrated schematically in FIG. 3, or a transflective liquid crystal display illustrated schematically in FIG. 4. It may be in any form.

The reflective liquid crystal display D schematically illustrated in FIG. 3 may include a rear reflective film 40 on the rear surface for reflecting ambient light entering the display from the display to increase the brightness of the display. The light redirecting film 2 according to an exemplary embodiment of the present invention is redirected into the display in a direction perpendicular to the film plane such that ambient light (or light from the front light) is reflected by the rear reflection film within a predetermined viewing angle. It can be placed near the top of the reflective liquid crystal display to increase the brightness of the display. The light redirecting film 2 may be attached, laminated, or held in place relative to the top of the liquid crystal display.

The transflective liquid crystal display D illustrated by way of example in FIG. 4 has a transreflector (T) disposed between the display and the backlight BL, which is adapted to enter the front of the display. Is reflected from the display to increase the brightness of the display in a lighted environment and also transmit light out of the display from the backlight through a trans reflector to brighten the display in a dark environment. In an exemplary embodiment, the light redirecting film 2 redirects or redistributes the ambient light and / or the light from the backlight more perpendicular to the film plane, making the light output distribution more permissible to allow movement through the display. In order to increase the brightness of the display, it may be placed near the top or near the bottom of the display, or both, as shown schematically in FIG. 4.

The light redirecting film 2 is an individual of well defined shape on the light exit surface 6 of the film to deflect the incident light distribution such that the light leaving the film is distributed in a direction more perpendicular to the film surface. A thin transparent film or substrate 8 having a pattern of the optical element 5 can be provided.

Each individual optical element 5 may have a width and length several times smaller than the width and length of the film, and may be formed concave or convex on the exit surface of the film. These individual optical elements 5 may have at least one inclined surface for refracting incident light in a direction perpendicular to the light exit surface. The optical element 5 may have an aspect ratio of 0.5 or more. The optical element 5 may have a depth of at least 15 micrometers. These optical elements can take a variety of different shapes. US Patent Application Publication No. US 2001/0053075 A1, entitled “Light Redirecting Film and Film System”, is incorporated herein in its entirety. This patent application discloses various modifications of the optical element. However, those skilled in the art will recognize other variations of the optical elements of the light redirecting system covered by embodiments of the present invention.

As exemplarily shown in FIG. 2, the light incident surface 7 of the film 2 is an optical coating 25 (eg, an antireflective coating, a reflective polarizer, a retardation coating or a polarizer). ] May be provided. Further, in the exemplary embodiment, the light incident surface 7 may be provided with a matte or diffuse texture, depending on the visual appearance desired. The matte finish can produce softer images that are not bright. The combination of the flat and curved surfaces of the individual optical elements 5 of the exemplary embodiment of the present invention impinges on the flat and curved surfaces to produce a smoother image without the need to further diffuse or matte the incident surface of the film. It can be configured to redirect some of the rays in different directions. The individual optical elements 5 of the light redirecting film 2 can overlap in a staggered, interlocked and / or intersecting structure with each other to produce an optical structure with an appropriate surface area coverage.

The individual optical elements 5 can have various shapes and sizes on the light redirecting film 2. Individual optical elements 5 may also be arranged on the surface in an irregular pattern in which the spacing between adjacent elements varies. For example, randomly or pseudo-random placement of the individual optical elements 5 on the light redirecting film 2 may result in the light redirecting film being assembled with other optical components. May be useful to avoid moire patterns or other optical effects.

Irregular patterns include a number of cavities that are arranged so as not to follow a regular pattern such as matrix, grid or linear arrangement. The random pattern includes cavities having positions selected by a random method.

The backlight BL may be almost flat or curved. The backlight BL may be a single layer or a multilayer and may have different thicknesses and shapes. The backlight BL may be flexible or rigid, and may be made of various composites. In addition, the backlight may be hollow, filled with liquid, air, or solid, and may have holes or ridges.

Light source 26 may be in any suitable form (eg, incandescent lamp, lens end bulb, line light, halogen lamp, light emitting diode (LED), chip from LED, which may be colored, filtered, or painted by an arc lamp). , Neon bulb, cold cathode fluorescent lamp, fiber optical photoconductor from a remote light source, laser or laser diode, or any other suitable light source. In addition, light source 26 may be a combination of multiple colored LEDs or multiple color radiation sources to provide a predetermined color or white light output distribution. For example, single LEDs with different color (e.g. red, blue, green) or multiple color chips to produce white or any other color light output distribution by varying the intensity of each individual color light. The same number of colored lights can be used.

As illustrated schematically in FIGS. 1 and 2, a rear reflective film 40 may be attached or disposed on one side of the backlight BL, in which light emitted from the side through the backlight is opposite to the opposite side. It is to improve the light output efficiency of the backlight by reflecting to be emitted through. In addition, optical modifications may be made on one or both sides of the backlight to change the light path as illustrated schematically in FIGS. 1 and 2 such that the internal critical angle is exceeded and a portion of the light exits from one or both sides of the backlight. The pattern of 50 can be provided.

Thermoplastic films with textured surfaces have applications from packaging to optical films. The texture may be created in a casting nip consisting of a pressure roller and a pattern roller. Depending on the pattern transferred to the thermoplastic film, it may be difficult to obtain a uniform degree of replication over the width of the film. Obtaining this uniform degree of replication and having a smooth backside to the film can also be difficult.

Conventional extrusion roll forming systems include an extruder that extrudes a molten polymer material into a nip. The nip is formed between the forming roller and the pressure roller. The molten polymer is pressed into the forming roller pattern by the pressure roller and cooled. The polymer exits the nip into a semisolid to solid state. Rubber pressure rollers can be used to provide a relatively uniform pressure across the casting nip since the covering can be modified to accommodate any thickness non-uniformity in the melt curtain. This thickness non-uniformity may be due to the presence of thick edges due to neck-in or other causes of non-uniform flow from the extrusion die. However, the rubber covering may not have a surface with insufficient roughness to produce a glossy (eg smooth) backside.

Exemplary embodiments of the present invention relate to a method of electromechanically engraving a molding pattern on a rigid surface. The molding pattern may be for finely replicating the optical element during the manufacture of the light redirecting film. The electromechanical piece may be a gravure electromechanical piece. Gravure electromechanical engraving processes have been used to make printing rollers in the printing industry. However, exemplary embodiments of the present invention use gravure electromechanical engraving for a completely different purpose, such as the manufacture of molding patterns.

In a typical electromechanical piece, the cavities formed on the cylinder are arranged in a regular pattern. 5 is a view of a portion of a typical image cut by an electromechanical engraving machine, in which a cavity N having a center point M is arranged in a regular offset grid and there is a constant spacing X and Y between the centers of the cavity It shows what to do. The vertical direction is aligned around the cylinder and the horizontal direction is aligned with the axis of the cylinder. The intervals X and Y define the screen and angle of the electromechanically carved image and are constant over the image. The image is sculpted by engraving one column of cavities in a single rotation of the cylinder and then moving the engraving head by a distance X along the axis of the cylinder and then carving and repeating the next row of cavities.

6 is a diagram of another portion of a typical image cut out by a gravure electromechanical engraving machine. The cavity N is cut to different depths in the surface of the cylinder, resulting in a change in cavity size and shape. A cavity depth change is provided to transfer a varying amount of material, such as ink or coating material, to that point in the image. However, the cavity positions are still arranged in rows with constant spacing X. An electromechanical engraver always moves a distance from one column to the next. Repetitive patterns of optical elements having a constant offset between the cavity rows, which will be produced by conventional electromechanical engraving methods, may have deleterious optical effects such as moiré when the product is placed assembled with other optical components.

Exemplary embodiments of the present invention significantly modify the electromechanical engraving method to provide cavity irregular positioning for replicating three-dimensional fine features. The electromechanical engraver can be modified to allow any irregular or random cavity position, to allow for variable offsets between the cavity rows. Any irregular or random cavity position can also cause multiple cavities to intersect and interlock in any irregular or random manner. 7 is an illustration of an irregular or pseudo-random pattern of cross cavities that can be cut in accordance with one embodiment of the present invention. 7 shows a cavity with a gap in between for simplicity of illustration. The cavity position is also irregular or random, but can substantially cover the surface of the cylinder. Any irregular or random cavity positions and intersections can have a beneficial effect on products molded from cylinders, including reduced moiré effect in the optical substrate.

The variable offset between the rows of cavities can also be zero, which causes the electromechanical engraver to engrave multiple rows of cavities at the same X position. This ability can be useful in a variety of ways to make tools for fine replication. The edges of adjacent cavities that are sequentially carved by an electromechanical engraver cannot have sharp edges between them because of the momentum between the engraving head and the stylus. 8A is a side view of two adjacent overlapping cavities F1, F2. In FIG. 8B, these cavities will have a rounded intersection point Q1 when continuously engraved by an electromechanical engraver. However, as shown in Fig. 8C, by sculpting adjacent features F1 and F2 in two rows at the same location, a sharp transition Q2 can be achieved between the two cavities.

Tools for fine replication may need to have deeper cavities than can be cut in a single cut, or are usually made of a material such as nickel or nickel-phosphorus alloy that is harder than electromechanically carved It may need to be. Engraving deep features in these rigid materials may stress the diamond stylus and destroy it, or optical-quality surfaces can no longer be achieved. Engraving multiple rows of cavities at the same X position can solve these problems by cutting the cavities by increasing depth in each row. For example, as shown in FIG. 9, the first row of pieces may cut (C1) the cavity to 50% of its final depth, and the second row of pieces at the same location may cut the cavity of its final depth. Cutting C2 up to 90% and the final third row of pieces at the same location may cut the cavity C3 to its final depth. As a result, the features can be cut to any depth, the stylus is subjected to lower cutting forces, and the surface finish of the cavity can be of optical quality.

10A and 10B are illustrations of cylinder 310 in which a predetermined pattern of cavities can be generated, in accordance with an exemplary embodiment of the present invention. The structure of the cylinder can vary considerably and is sometimes tailored to the particular end use. In all structures the cylinder has a nominal diameter 334 in association with the nominal face length 330. The cylinder may have a shaft 338 or tapered mounting hole 340 that defines the axis of rotation 324 at the end of the nominal diameter. If the cylinder does not have a shaft, the total length of the cylinder 336 may be equal to the face length. More typically the cylinder has a shaft whose length is included in the entire length of the cylinder.

The cylinder may be hollow or solid, but in either case the cylindrical surface will have some associated thickness of the particular material needed to achieve the desired result. In particular, if the desired pattern of cavities has optical applications, the cylindrical surface will be a non-ferrous material or alloy, and thus can be successfully processed using diamond tools. It is also desirable for the material to have a very small particle structure or to be amorphous and free of inclusions, pits, voids and other defects that will affect the optical use of a given pattern. Examples of such materials include, but are not limited to, copper and copper-nickel alloys, nickel and nickel-phosphorus alloys, and high purity aluminum.

The cylindrical surface to be machined can be wrought or plated. In the forged form the material may comprise the entire cylindrical surface, or may be pressed or otherwise sleeve-fitted onto an existing cylindrical surface made of less expensive material. In plating, an electrochemical method or the like is used to transfer a predetermined material to a thin layer uniformly on the outside of the cylindrical surface. This plating method may also be done on the mandrel to produce a thin sleeve of the desired material. This sleeve can then be patterned into a predetermined cavity or groove and then transferred to a desired cylinder for use in replication or material transfer. This sleeve can also be removed from the mandrel and transferred to the desired cylinder prior to the formation of the desired cavity.

After the cavity formation of the desired pattern, the sleeve can be removed and used as a belt in a replication or material transfer process. The sleeve can also be cut to any size and used in a flat state for replication methods such as injection molding or thermoforming.

Claims (26)

A method comprising electromechanically engraving a three-dimensional molding pattern on a rigid surface, The rigid surface is configured to finely replicate in accordance with the three-dimensional molding pattern. 3D molding pattern engraving method. The method of claim 1, The electromechanical piece is a gravure electromechanical piece 3D molding pattern engraving method. The method of claim 1, The electromechanical piece, Moving the rigid surface at a constant speed; Moving a diamond stylus in and out of the rigid surface by applying an alternating voltage to a series of magnets to create a torsional motion in the rod, The diamond stylus is attached to the rod to cumulatively create a cavity in accordance with the three-dimensional molding pattern. 3D molding pattern engraving method. The method of claim 1, The rigid surface is the surface of the pattern roller having the three-dimensional molding pattern 3D molding pattern engraving method. The method of claim 1, The rigid surface is configured to finely replicate individual optical elements in accordance with the three-dimensional molding pattern. 3D molding pattern engraving method. The method of claim 5, The rigid surface is configured to finely replicate the optical element on a light redirecting film. 3D molding pattern engraving method. The method of claim 6, The optical element has a well defined shape for redistributing light passing through the light redirecting film in a direction perpendicular to the light redirecting film. 3D molding pattern engraving method. The method of claim 5, At least some of the optical elements overlap 3D molding pattern engraving method. The method of claim 5, The individual optical elements are carved into columns, Spacing between columns is uneven 3D molding pattern engraving method. The method of claim 5, The individual optical element is carved into rows, The rows are engraved on the pattern roller at the same axial position 3D molding pattern engraving method. The method of claim 5, The individual optical elements are arranged in an irregular or pseudo-random pattern. 3D molding pattern engraving method. The method of claim 5, The individual optical elements are arranged in rows, The electromechanical engraving includes cutting individual optical elements of the row to a depth below the final depth, and then cutting the individual optical elements of the row to the final depth. 3D molding pattern engraving method. A method comprising microcopying an optical element onto a light redirecting film, the method comprising: The optical element fine copy uses a pattern roller having a pattern representing the optical element, The pattern of the pattern roller is formed by a gravure electro-mechanical engraving process Optical device microcopy method. The method of claim 13, The fine replication step includes extrusion roll molding Optical device microcopy method. The method of claim 14, The extrusion roll forming forms the light redirecting film in a nip between the pattern roller and the pressure roller. Optical device microcopy method. The method of claim 13, The fine replication step comprises ultraviolet (UV) curing Optical device microcopy method. The method of claim 13, The method comprises an embossing step Optical device microcopy method. In a device comprising a rigid surface, A three-dimensional molding pattern is formed on the rigid surface, The three-dimensional molding pattern is formed by an electromechanical piece, The rigid surface is configured to finely replicate in accordance with the three-dimensional molding pattern. Device. The method of claim 18, The electromechanical piece is a gravure electromechanical piece Device. The method of claim 18, The rigid surface is the surface of the pattern roller having the molding pattern Device. The method of claim 18, The rigid surface is configured to finely duplicate an optical element in accordance with the three-dimensional molding pattern. Device. The method of claim 21, The rigid surface is configured to finely replicate the optical element on the light redirecting film. Device. The method of claim 21, The optical element is of a well defined shape to redistribute light passing through the light redirecting film in a direction perpendicular to the light redirecting film Device. The method of claim 21, The optical element is an individual optical element, At least some of the optical elements overlap Device. The method of claim 21, The optical element is an individual optical element, The gap between the individual optical elements in the pattern roller axial direction varies Device. The method of claim 21, The optical element is an individual optical element, The individual optical elements are arranged in an irregular or pseudo-random pattern Device.

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