JP2012145938A - Manufacturing method of patterned retarder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a patterned retarder which enables mass production and increases productivity.SOLUTION: A manufacturing method of a patterned retarder includes a light alignment stage to position, on an alignment layer, a polarization filter 20 with light shielding parts 21 and wire grid pattern parts 22 repeatedly formed and to apply light from above the polarization filter 20 for alignment.

Description

  The present invention relates to a manufacturing method of a patterned retarder that can be applied to a stereoscopic image display device using a polarized glasses method, a transflective LCD, or the like.

  Recently, various types of image display devices such as liquid crystal display devices (LCD), electroluminescence (EL) display devices, plasma displays (PDP), field emission display devices (FED), etc. In particular, the paradigm for a super space type three-dimensional (3D) image display device has been changed.

  In general, 3D images that represent three dimensions are based on the principle of stereo vision through two human eyes, using binocular parallax that occurs because the two eyes are approximately 65 mm apart. This is a method for realizing a three-dimensional effect.

  The principle of binocular parallax is the separation of the left eye image viewed by the viewer through the left eye and the right eye image viewed through the right eye at different angles with at least two 3D image acquisition cameras, and then separated. This is a method of transmitting to the viewer's eyes. This is possible because the two human eyes receive objects through the retina at different angles, and these two images are synthesized by the two brains.

  Three-dimensional stereoscopic image technology can be broadly divided into a binocular parallax scheme and an autostereoscopic scheme. The binocular parallax method uses parallax images of the left and right eyes with the largest stereoscopic effect, and includes a polarized glasses method and a no-glasses method.

  A polarized glasses type three-dimensional stereoscopic image device described in Japanese Patent Laid-Open No. 10-232365 and Korean Patent Publication No. 2008-0108034 will be described as follows.

  A liquid crystal panel having a right eye image region R and a left eye image region L, a polarizing plate disposed on the entire surface of the liquid crystal panel, a polarization of the right eye image and the left eye image disposed on the polarizing plate and passing through the polarizing plate A three-dimensional stereoscopic image apparatus including a patterned retarder that emits circularly polarized light whose axis rotation directions are opposite to each other is provided. In addition, polarization glasses are provided that allow the right-eye image and the left-eye image emitted from the stereoscopic image device to be viewed as a stereoscopic image.

  There are many known patterned retarders and manufacturing methods applied to 3D stereoscopic video devices. As disclosed in US Pat. No. 5,327,285, a photoresist is coated on a polarizing film in which a TAC (triacetylcellulose) film and an iodine-treated stretched PVA (polyvinyl alcohol) film are laminated, and a predetermined portion. Is exposed to light and then treated with a potassium hydroxide solution to eliminate a certain portion of the retardation retardation function.

  On the other hand, in Korean Patent Application No. 2000-0087186, a phase retardation material is coated on a transparent substrate, and the phase retardation material is partially exposed to light through a mask to modulate the chiral characteristics. A method of manufacturing a stereoscopic image display device is proposed in which an optical filter (optical film) is formed in which a portion where the original characteristics are maintained and a portion where the original characteristics are maintained are arranged.

  However, the manufacturing method of US Pat. No. 5,327,285 is problematic because of the complicated manufacturing stage by chemical etching, and the high manufacturing cost and low productivity associated therewith. In the manufacturing method of polarizing filter of Korean Patent Application No. 2000-0087186, it is practically difficult to adjust the chiral property of the retarding substance with the intensity of light, so the yield is low and the instability due to temperature etc. There are problems.

  In order to improve the above problems, Korean Patent Publication No. 2010-0089782 discloses that a light transmission region and a light blocking region are selectively passed through the upper part of the polymer film. Is disposed on the upper and lower sides of the pattern mask 50, and a polarizing plate 60 having two distinct regions that transmit different polarized light is positioned above the pattern mask 50. Presents a photo-alignment method in which the polymer film is irradiated with ultraviolet rays to form alignment films having different alignment directions in a micro area of the polymer film (FIG. 5).

  However, in the photo-alignment method disclosed in Korean Patent Publication No. 2010-0089782, light loss occurs due to light scattering and interface reflection at the optical interface between the polarizing plate and the pattern mask. In addition, since the light irradiation process is performed twice, there is a problem that processability and productivity are low.

Japanese Laid-Open Patent Publication No. 10-232365 Republic of Korea Patent Publication No. 2008-0108034 US Pat. No. 5,327,285 Korean Patent Application No. 2000-0087186 Korean Patent Publication No. 2010-0089782

  The present invention can minimize light loss due to light scattering and interface reflection at the optical boundary surface, and can form alignment films having different alignment directions in a photo-alignment process by one light irradiation. Since a separate mask is not provided, an exposure apparatus is simplified, and an attempt is made to provide a method for manufacturing a patterned retarder with improved mass production and productivity.

  The method of manufacturing the patterned retarder according to the present invention for solving the above-mentioned problem is to place a polarizing filter in which a light blocking part and a wire grid pattern part are repeatedly formed on the alignment film, and A photo-alignment step of aligning by irradiating light from above is included.

  The alignment film is aligned in a certain direction, and may include a photo-alignment step for aligning in a direction different from the alignment direction of the alignment film.

  The wire grid pattern part may have a straight shape.

  Furthermore, the method of manufacturing the patterned retarder according to the present invention includes a first polarizing filter unit in which a first light blocking unit and a first wire grid pattern unit are repeatedly formed on an alignment film, a second light blocking unit, and a second light blocking unit. Positioning a polarizing filter including a second polarizing filter part formed by repeatedly forming a second wire grid pattern part in a different direction from the pattern of the one wire grid pattern part, and orienting by irradiating light from the upper part of the polarizing filter A photo-alignment step.

  The polarizing filter may be formed such that the first light blocking unit of the first polarizing filter unit and the second wire grid pattern unit of the second polarizing filter unit are adjacent to each other.

  The alignment film may be non-oriented.

  Each of the first wire grid pattern part and the second wire grid pattern part may be a straight line.

  A step of forming a liquid crystal coating layer on the photo-aligned alignment film may be included.

  The photo-alignment step is a pattern that transmits the light irradiated at the film contact portion and the light emitting portion that moves while the film is in close contact with the film portion that is in close contact with the film contact portion to form a polarization pattern on the film portion. It can be performed by an exposure system including a forming unit.

  The pattern forming unit may include a polarizing filter.

  The distance between the curved surface of the polarizing filter and the roller curved surface provided in the pattern forming unit can be kept constant within a range of 50 to 150 μm.

  The present invention has a merit of excellent light efficiency because the use of a single polarizing filter causes little light loss due to scattering, interface reflection and the like, and the amount of light reaching the alignment film is high.

  Furthermore, according to the present invention, alignment films having different alignment directions can be formed in a photo-alignment process by a single light irradiation.

  Since the pattern mask required at the time of the one light irradiation process is not provided, the exposure equipment can be simplified.

  In addition, the present invention can produce a patterned retarder in a continuous process, enables mass production, and increases productivity.

1 shows a polarizing filter of the present invention. 1 shows a polarizing filter of the present invention. An example of the polarizing filter located on the alignment film by this invention is shown. An example of the polarizing filter located on the alignment film by this invention is shown. A mask and a polarizer positioned on an alignment film according to a comparative example (Korea Patent Publication No. 2010-0089782) are shown. 1 shows a configuration of a patterned retarder manufacturing apparatus according to an example of the present invention. 1 shows a configuration of an exposure system according to an example of the present invention. In the said comparative example, the captured image which captured the image which passes a polarizing plate and a patterned retarder with the microscope is shown. In the example of this invention, the captured image which captured the image which passes a polarizing plate and a patterned retarder with the microscope is shown.

  The present invention can minimize light loss due to light scattering and interface reflection at the optical boundary surface by using a single polarizing filter, and has different alignment directions in one photo-alignment process by light irradiation. The present invention relates to a method for manufacturing a patterned retarder capable of forming an alignment film.

  Hereinafter, the present invention will be described in detail.

  In the method of manufacturing a patterned retarder according to the present invention, a polarizing filter in which a light blocking portion and a wire grid pattern portion are repeatedly formed is positioned on an alignment film, and the light is irradiated from above the polarizing filter to be aligned. Including a photo-alignment step.

  The polarizing filter in the present invention can form light that vibrates in many directions into polarized light that vibrates only in a limited direction after passing through the polarizing filter, and only a part of the polarizing filter is formed. An optical element that can be formed into polarized light that vibrates in the same direction.

  The alignment film used is aligned in a certain direction. The alignment film is formed by applying a normal alignment film-forming composition on the film and then drying it.

  The formation method of the alignment film oriented in the above-mentioned fixed direction is not particularly limited, but a non-contact method such as polarized light exposure is preferable compared to a contact method such as a rubbing roll on the coating surface.

  In the photo-alignment step using the alignment film oriented in a certain direction, the light blocking part 21 and the wire grid pattern part 22 of FIG. 1 are repeatedly formed on the film 5 on which the alignment film is formed as shown in FIG. The polarizing filter 20 is positioned and oriented in a direction different from the orientation direction of the orientation film.

  The method using the polarizing filter 20 according to the present invention can improve the reduction in the resolution of the exposure light as compared with the conventional method in which the polarizing plate 60 and the pattern mask 50 are separated. Specifically, conventionally, since the polarizing plate 60 and the pattern mask 50 are separated and only the distance between them is diffracted while the exposure light travels, the resolution of the exposure light is lowered. Since the exposure light passes through one polarizing filter 20, the problem with respect to this reduction in resolution is not considered.

  Furthermore, the method for manufacturing a patterned retarder according to the present invention includes a first polarizing filter unit in which a first light blocking unit and a first wire grid pattern unit are repeatedly formed on an alignment film, and a second light blocking unit. Position the polarizing filter including the second polarizing filter part in which the second wire grid pattern part in a different direction from the pattern of the first wire grid pattern part is repeatedly formed, and irradiate light from above the polarizing filter. A photo-alignment step of aligning;

  At this time, a non-oriented alignment film is used as the alignment film.

  In the photo-alignment step using the non-oriented alignment film, the first light blocking part 23 and the first wire grid pattern part 24 of FIG. 2 are repeatedly formed on the film 5 on which the alignment film is formed, as shown in FIG. The polarizing filter 20 including the first polarizing filter unit 40, the second light blocking unit 25, and the second polarizing filter unit 41 in which the second wire grid pattern unit 26 is repeatedly formed is used.

  At this time, the second wire grid pattern portion 26 is patterned in a direction different from the pattern of the first wire grid pattern portion 24 and is oriented so that the alignment films have alignment regions in different directions.

  In the polarizing filter 20, the first polarizing filter unit 40 and the second polarizing filter unit 41 are aligned in the traveling direction of the alignment film, and the first light blocking unit 23 and the second polarizing filter unit 41 of the first polarizing filter unit 40 are arranged. The second wire grid pattern portions 26 are formed adjacent to each other.

  When the polarizing filter 20 of FIG. 2 is used for an alignment film oriented in a certain direction, use an alignment film formed by an alignment film forming composition composed of components whose alignment direction is not fixed by light exposure. Is preferred.

  The light blocking unit 21, the first light blocking unit 23, and the second light blocking unit 25 are structures that absorb and reflect incident light so as not to reach the alignment layer, and the wire grid pattern The portion 22, the first wire grid pattern portion 24, and the second wire grid pattern portion 26 have a structure that polarizes incident light and reaches the alignment film.

  The shapes of the wire grid pattern part 22, the first wire grid pattern part 24, and the second wire grid pattern part 26 are each a straight line, and specifically, a plurality of metal wires protruding in a parallel straight line have a predetermined cycle. Arranged in The metal wire is formed from aluminum (Al), silver (Ag), chromium (Cr), copper (Cu), nickel (Ni), Ti (titanium), gold (Au) or at least two alloys thereof. .

  As a method of forming the wire grid pattern part 22, the first wire grid pattern part 24, and the second wire grid pattern part 26, a common method in this field can be used. For example, after forming a master pattern, it is manufactured using a mold that is an inverse image of the formed master pattern, and a metal layer and a polymer layer are sequentially laminated on a transparent protective film or a glass substrate, and then a mold is used. A pattern is formed on the polymer layer. A metal grid can then be deposited on the shaped pattern through gradient deposition to form a wire grid pattern. Alternatively, a method of etching a polymer layer of a formed pattern, forming a metal pattern by dry etching or wet etching of a metal layer exposed on the surface, and then removing the polymer remaining on the formed metal pattern A wire grid pattern can also be formed.

  In the wire grid pattern part 22, the first wire grid pattern part 24, and the second wire grid pattern part 26, the width of each metal wire (pattern width), height (pattern height), and the interval between metal wires ( The value of the period of the pattern can be adjusted by optical design related to polarization characteristics such as transmittance and reflectance. For example, the pattern width can be 150 nm or less, preferably 10 to 100 nm, the pattern height can be 600 nm or less, preferably 50 to 500 nm, and the pattern period can be 300 nm or less, preferably 20 to 200 nm. .

  The length of the polarizing filter 20 and the lengths of the first polarizing filter part 40 and the second polarizing filter part 41 can be adjusted by the size of the alignment film and the moving direction. In addition, the sizes of the light blocking unit 21 and the wire grid pattern unit 22, the first light blocking unit 23 and the first wire grid pattern unit 24, the second light blocking unit 25 and the second wire grid pattern unit 26, and their sizes The spacing between can be adjusted by the desired patterned retarder.

  The light is not particularly limited, but an electron beam, an ion beam, a plasma beam, radiation, or the like can be used, and it is preferable to use ultraviolet rays that are easy to handle.

  The patterned retarder manufactured according to the present invention is preferably subjected to a photo-alignment step so that the alignment directions are perpendicular to each other. At this time, the term “vertical” includes not only a state where two lines form 90 ° but also a case where a substantially vertical effect can be shown.

  The liquid crystal coating layer is formed after the alignment layer is cured by performing the photo-alignment step. The liquid crystal coating layer is formed by applying and drying a liquid crystal coating layer forming composition containing a liquid crystal compound having optical anisotropy and crosslinkability by light on the cured alignment film. The liquid crystal compound is a substance having a refractive index anisotropy of 0.05 or more, and for example, a reactive liquid crystal compound (RM) is preferably used.

  The dried coating layer is photocured to produce a patterned retarder in which liquid crystals are aligned according to the alignment direction of the alignment film.

  In the present invention, the portions other than the photo-alignment step performed using the specific polarizing filter 20 on the alignment film, for example, the types of the alignment film and the liquid crystal coating layer, the formation method, the characteristics such as the thickness, the photo-alignment conditions, etc. are described above. In addition to the above, it can be appropriately selected and applied so as to exhibit optical characteristics generally required in the art.

  On the other hand, the patterned retarder according to the present invention can be manufactured using an apparatus generally used in this field.

  For example, as shown in FIG. 6, a transfer unit 11 for unwinding and / or winding and transferring a roll film, an alignment film forming unit (not shown) for forming an alignment film on the transferred film, and the film Forming a patterned retarder that forms a patterned retarder by irradiating light after forming a liquid crystal coating layer on the alignment film and irradiating light onto the alignment film formed thereon to align the light. A manufacturing apparatus including part 3 can be used.

  The first roll 7 and the second roll 9 of the transfer unit 11 are independently connected to a driving source (not shown) such as a motor by a power transmission member (not shown) such as a belt or a chain, and the driving force is transmitted. It is preferably arranged to rotate. In addition, a plurality of guide rolls (not shown) for maintaining the tension and stable film transfer and accumulators (accumulator, not shown) for controlling the film transfer amount according to the process can be provided. Further, it is preferable that the film 5 on which the alignment film is formed is moved by a normal roll-to-roll method.

  The alignment film can be formed in the process immediately before the alignment by the alignment film forming unit, and in some cases, the alignment film can be formed on the film through a separate alignment film forming step. Further, if necessary, an ordinary drying apparatus can be used for curing the formed alignment film in the alignment film forming portion.

  The patterned retarder forming unit 3 includes a mixed solution application unit 31, a mixed solution drying unit 33, and a curing unit 35.

  Furthermore, the present invention can perform defect inspection of the patterned retarder including the defect inspection section (not shown) after the patterned retarder forming section 3. The defect inspection unit scans an optical filter to identify the specified defect, and displays the specified defect using a marking device such as ink marking or bar code marking, or the defect information in a separate storage unit ( (Form, size, position) can be stored and applied to a stereoscopic image display device.

  The exposure system used in the photo-alignment unit 1 can be performed while the film is in close contact with the cylindrical roller 160 as shown in FIG. it can.

  Specifically, the exposure system transmits the light irradiated by the film contact portion and the light emitting portion (light source) 110 that moves while the film is in close contact with the film portion that is in close contact with the film close contact portion. A pattern forming unit 150 for forming a polarization pattern may be included.

  The film contact portion is a cylindrical roller 160, and the film 5 on which the alignment film is formed preferably moves while being in close contact with the curved surface of the roller.

  The pattern forming unit 150 serves to transmit light emitted from the light emitting unit (light source) 110 toward the rotation axis of the roller 160. The pattern forming unit 150 includes the polarizing filter 20 according to the present invention, and the distance between the curved surface of the polarizing filter 20 provided in the pattern forming unit 150 and the curved surface of the roller 160 is constant (AA ′ = BB ′ = CC ′). To be maintained.

  The distance between the curved surface of the polarizing filter 20 provided in the pattern forming unit 150 and the curved surface of the roller 160 is preferably 50 to 150 μm, and preferably 50 to 100 μm.

  Furthermore, the pattern forming unit 150 may be positioned without any particular limitation such as an inlet portion, a central portion, and an outlet portion of the roller 160 as long as it can form a pattern.

  In addition, the pattern forming unit 150 preferably includes a chamber in which the internal pressure is adjusted in order to adjust the curved surface of the polarizing filter 20.

  The surface of the roller 160 is preferably subjected to non-reflective or non-scattering treatment.

  The exposure system of the present invention further includes a first reflecting unit 120 that reflects light output from the light emitting unit (light source) 110, and a condensing unit that collects and transmits the light reflected by the first reflecting unit 120. And a second reflection unit 140 that reflects the light transmitted from the condenser 130 by the pattern forming unit 150.

  At this time, the pattern forming unit 150 can directly receive the light emitted from the light emitting unit (light source) 110 and transmit the light to the film portion in close contact with the film contact portion.

  Hereinafter, preferred embodiments will be presented for the understanding of the present invention. However, the following embodiments are examples of the present invention, and various changes and modifications can be made within the scope and technical idea of the present invention. It will be obvious to those skilled in the art, and such variations and modifications are, of course, within the scope of the claims.

Example 1
The triacetyl cellulose film was transferred by the transfer unit 11 as in the manufacturing apparatus of FIG. An acrylate-based alignment liquid was applied onto the transferred film and dried with hot air at 40 ° C. for 120 seconds to form an alignment film having a thickness of 1,000 mm. Thereafter, an alignment film oriented in a certain direction was formed on the alignment film by irradiating polarized light with a 14 mW exposure lamp.

While the film 5 on which the alignment film is formed moves, UV light of 20 mW / cm ² is continuously moved while moving the substrate at a speed of 4 m / min for 1 second in the optical alignment unit 1 in which the polarizing filter 20 of FIG. 1 is disposed. It was formed so that the light passed through only the wire grid pattern portion 22 and had an orientation direction different from the orientation film.

  After the alignment film was cured, the composition for forming a liquid crystal coating layer was applied, preliminarily dried at 80 ° C. for 20 seconds, and then dried at 110 ° C. for 5 seconds to form a coating layer having a thickness of 1.5 μm. . Then, the patterned retarder was manufactured by photocuring with ultraviolet rays for 500 seconds with a 14 mW exposure lamp. The production rate of the patterned retarder was 4 m / min.

(Example 2)
Although it implemented like the said Example 1, the patterned retarder was manufactured using the non-orientated alignment film and the polarizing filter 20 of FIG. The production rate of the patterned retarder was 8 m / min.

(Example 3)
Although it implemented similarly to the said Example 1, as shown in FIG. 7, the patterned retarder was manufactured using the exposure system by which a film photoaligns, closely_contact | adhering to the cylindrical roller 160. As shown in FIG. At this time, the distance between the curved surface of the polarizing filter 20 provided in the pattern forming unit 150 and the curved surface of the roller 160 was maintained at 70 μm. The production rate of the patterned retarder was 8 m / min.

(Comparative example)
As in FIG. 5, a pattern mask 50 in which a light transmission region and a light blocking region are repeatedly formed on the alignment film and a region that transmits different polarized light on the pattern mask are formed as shown in FIG. The patterned retarder was manufactured by positioning the polarizer 60 having the same. The production rate of the patterned retarder was 4 m / min.

(Test example)
The optical loss by the manufacturing method of the patterned retarder of the said Example and a comparative example was measured with the following method, and the result was shown in following Table 1.

(Light loss)
The patterned retarder produced above was placed on a polarizing plate having absorption axes orthogonal to each other, and an image passing through the polarizing plate and the patterned retarder was captured with a microscope (Olympus). The captured image was measured for luminance in a certain region using a digital video analysis program.

  At this time, in the captured image, as shown in FIG. 8 and FIG. 9 (FIG. 8—Comparative Example, FIG. 9—Example 1), a portion where light leakage occurs is indicated by a surface shape or a line shape (interval between patterns). . In the following captured image, the black portion is in a state where the orientation is well formed, and the clouded portion is formed in a double orientation due to the diffraction phenomenon, and the orientation direction is unknown. At this time, in the comparative example, a pattern is formed in the vertical direction, and in Example 1, the pattern is formed in a direction from the upper right part toward the lower left part.

  In the example, the boundary between patterns is narrow and clear, but in the comparative example, the boundary between patterns is wide. Therefore, it can be confirmed that the accuracy of the patterned retarder is lowered.

  If the luminance was 0, the image was considered to be completely black and the light loss was 0%. If the luminance was 100, the image was considered to be completely white and the light loss was considered to be 100%.

  As shown in the above table, Examples 1 to 3 according to the present invention showed a production rate equivalent to or higher than that of the comparative example and confirmed that the optical loss was remarkably low.

1: Photo-alignment part 3: Patterned retarder forming part 5: Film on which an alignment film is formed 7: First roll 9: Second roll 11: Transfer part 13: Light source 20: Polarizing filter 21: Light blocking part 22: Wire Grid pattern unit 23: first light blocking unit 24: first wire grid pattern unit 25: second light blocking unit 26: second wire grid pattern unit 31: mixed solution applying unit 33: mixed solution drying unit 35: curing unit 40 : First polarizing filter unit 41: Second polarizing filter unit 50: Pattern mask 60: Polarizing plate 110: Light source 120: First reflecting unit 130: Concentrator 140: Second reflecting unit 150: Pattern forming unit 160: Roller

Claims (12)

On top of the alignment film,
Position the polarizing filter on which the light blocking part and the wire grid pattern part are repeatedly formed,
A method for producing a patterned retarder, comprising a photo-alignment step of aligning by irradiating light from above the polarizing filter.   The method for manufacturing a patterned retarder according to claim 1, wherein the alignment film is aligned in a certain direction.   The method for producing a patterned retarder according to claim 2, further comprising a photo-alignment step of aligning in a direction different from the alignment direction of the alignment film.   The method for manufacturing a patterned retarder according to claim 1, wherein the shape of the wire grid pattern portion is a straight line. On top of the alignment film,
The first polarizing filter part in which the first light blocking part and the first wire grid pattern part are repeatedly formed, and the second wire grid pattern part in a direction different from the pattern of the second light blocking part and the first wire grid pattern part are repeated. Position the polarizing filter including the formed second polarizing filter part,
A method for producing a patterned retarder, comprising a photo-alignment step of aligning by irradiating light from above the polarizing filter.   6. The patterning according to claim 5, wherein the polarizing filter is formed such that the first light blocking part of the first polarizing filter part and the second wire grid pattern part of the second polarizing filter part are adjacent to each other. Retarder manufacturing method.   6. The method of manufacturing a patterned retarder according to claim 5, wherein the alignment film is non-oriented.   6. The method of manufacturing a patterned retarder according to claim 5, wherein each of the first wire grid pattern part and the second wire grid pattern part is a straight line.   6. The method for producing a patterned retarder according to claim 1, further comprising a step of forming a liquid crystal coating layer on the photo-aligned alignment film.   The photo-alignment step includes a film contact portion that moves while the film is in close contact; and a light that is emitted from the light emitting portion is transmitted to the film portion that is in close contact with the film contact portion, thereby forming a polarization pattern on the film portion. 6. The method of manufacturing a patterned retarder according to claim 1, wherein the patterning retarder is performed by an exposure system including a forming unit.   The method of manufacturing a patterned retarder according to claim 10, wherein the pattern forming unit includes a polarizing filter.   The method for producing a patterned retarder according to claim 11, wherein the distance between the curved surface of the polarizing filter provided on the pattern forming unit and the curved surface of the roller is kept constant within a range of 50 to 150 µm. .

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