JP2014199299A - Method for manufacturing patterned retardation film and exposure device for patterned retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a patterned retardation film to be applied to a passive type image display device, in which strip-like regions corresponding to the setting of pixels in an image display panel are formed with high accuracy.SOLUTION: While a transparent film material 2 is wound and conveyed by a conveyance roll 21, the film is exposed by using a mask 16 held to oppose to the conveyance roll 21. The mask 16 includes slits which are to be used for the exposure of a photo-alignment material film and which extend in the conveyance direction of the transparent film material 2 and are repeatedly formed in a direction orthogonal to the extending direction. A gap between the mask 16 and the conveyance roll 21 is 100 μm or more and 300 μm or less; the slit has a length of 5 mm or more and 50 mm or less; and the conveyance roll 21 has a diameter of 100 mm or more and 500 mm or less.

Description

The present invention relates to a pattern retardation film according to a passive three-dimensional image display device.

  In recent years, an image display device that displays a three-dimensional image by a passive method has been provided. Here, FIG. 7 is a schematic view showing a passive type image display apparatus using a liquid crystal display panel. The passive-type image display apparatus sequentially assigns pixels of the liquid crystal display panel that are continuous in the vertical direction or the horizontal direction (vertical direction in the example of FIG. 7) to the right eye and the left eye, respectively. Driving with the image data for the left eye, thereby displaying the image for the right eye and the image for the left eye simultaneously. In addition, a pattern retardation film is arranged on the panel surface (viewer side) of the liquid crystal display panel so that the light emitted from the right-eye pixel and the left-eye pixel is linearly polarized light having different directions for the right-eye and left-eye. Convert to As a result, in the passive method, glasses equipped with corresponding polarizing filters are worn, and a right-eye image and a left-eye image are selectively provided to the viewer's right and left eyes, respectively, and a three-dimensional image is displayed. To do.

  Therefore, in the pattern retardation film, two types of band-like regions in which the slow axis direction (direction in which the refractive index is maximized) are orthogonal to each other are sequentially formed corresponding to the setting of the pixels in the liquid crystal display panel. Thus, in the passive method, glasses equipped with corresponding polarizing filters are worn, and a right-eye image and a left-eye image are selectively provided to the viewer's right eye and left eye, respectively. Here, as the slow axis direction of the adjacent band-like region, a combination of +45 degrees and −45 degrees, or 0 degrees and +90 degrees with respect to the horizontal direction is usually employed. In the example of FIG. 7, the long side direction of the screen is shown as the horizontal direction in accordance with the name in the normal image display apparatus.

  This passive method can also be applied to an image display device having a slow response speed, and can display three-dimensionally with a simple configuration using a pattern retardation film and circularly polarized glasses. In the passive type image display device, a method of sequentially assigning pixels continuous in the horizontal direction to the right eye and the left eye in place of the vertical direction in the example of FIG. 7 is also employed.

  The pattern phase difference film according to this passive method requires a pattern-like phase difference layer that gives a phase difference to transmitted light corresponding to the allocation of pixels. With respect to this pattern retardation film, Patent Document 1 discloses a method of forming a retardation layer by forming a photo-alignment layer on a glass substrate with controlled alignment regulating force and patterning the alignment of liquid crystals with this photo-alignment layer. Is disclosed. Patent Document 2 discloses a method of forming a photo-alignment layer in which a fine uneven shape is formed on the peripheral side surface of a roll plate by laser irradiation, and the uneven shape is transferred to control the alignment regulating force in a pattern shape. Has been.

  Such a pattern retardation film needs to accurately create a band-like region corresponding to the pixel setting in the image display panel. Specifically, when the boundary width of the belt-like region becomes large or varies, light leakage or pitch deviation occurs. Note that the pitch deviation is a phenomenon in which the arrangement of regions in the pattern retardation film is deviated from the arrangement of pixels in the image display panel. If the light leakage and the pitch shift become significant, the image display device may cause problems such as crosstalk and color misregistration. Crosstalk is a phenomenon in which light emitted from the image display panel to be selectively supplied to the right and left eyes of the viewer leaks into the left and right eyes. In the three-dimensional image display, when the crosstalk becomes intense, the stereoscopic effect is remarkably impaired.

JP 2005-49865 A JP 2010-152296 A

  The present invention has been made in view of such a situation, and relates to a pattern retardation film applied to a passive image display device, and creates a band-like region corresponding to the setting of a pixel of an image display panel with high accuracy. For the purpose.

  In order to solve the above-mentioned problems, the present inventor has conducted intensive research to reduce the distance between the mask and the object to be exposed and to adjust the length of the slit provided in the mask. It came to the idea of restricting the thickness, and completed the present invention.

(1) In the manufacturing method of the pattern phase difference film which processes sequentially while conveying the transparent film material by elongate, and produces a pattern phase difference film,
A photo-alignment material film production step for producing a photo-alignment material film on the transparent film material,
An exposure process for producing an alignment film by applying a photo-alignment technique by exposing the photo-alignment material film using a mask; and
On the alignment film, a retardation layer is formed by a right-eye region that gives a phase difference corresponding to right-eye transmitted light and a left-eye region that gives a phase difference corresponding to left-eye transmitted light. A phase difference layer manufacturing process,
The exposure step includes
While transporting the transparent film material by a transport roll, exposure processing is performed using the mask held to oppose the transport roll,
For the mask,
A slit used for exposure of the photo-alignment material film, the slit extending in the transport direction of the transparent film material is repeatedly formed in a direction orthogonal to the extension direction,
An interval between the mask and the transport roll is 100 μm or more and 300 μm or less,
The slit has a length of 5 mm or more and 50 mm or less,
A diameter of the transport roll is set to 100 mm or more and 500 mm or less.

  According to (1), even at the center of the slot and at the upper and lower ends of the slot, the transmitted light of the slot can be used for exposure before spreading greatly, thereby reducing the variation in boundary width, It is possible to prevent the boundary width from increasing, and as a result, it is possible to create a band-like region corresponding to the setting of the pixels of the image display panel with high accuracy.

(2) In (1),
The exposure step includes
The mask is held by a frame made of a material having a linear expansion coefficient of 0 to 12.4 × 10 ⁻⁶ / ° C. or less.

  According to (2), even when the temperature rises due to exposure, it is possible to prevent warpage of the mask due to thermal expansion of the frame and the like so that the distance between the mask and the object to be exposed does not change. , The accuracy can be further improved.

(3) In an exposure apparatus for a pattern retardation film that is used for production of a pattern retardation film by carrying out an exposure process while conveying a long transparent film material on which a photo-alignment material film has been created,
While carrying the transparent film material by a roll for conveyance, using a mask held so as to oppose the roll for conveyance, exposure processing is performed,
For the mask,
A slit used for exposure of the photo-alignment material film, the slit extending in the transport direction of the transparent film material is repeatedly formed in a direction orthogonal to the extension direction,
An interval between the mask and the transport roll is 100 μm or more and 300 μm or less,
The slit has a length of 5 mm or more and 50 mm or less,
The diameter of the conveyance roll is 100 mm or more and 500 mm or less.

  According to (3), even at the center of the slot and at the upper and lower ends of the slot, it can be used for exposure before the transmitted light of the slot spreads greatly, thereby reducing the variation in boundary width, It is possible to prevent the boundary width from increasing, and as a result, it is possible to create a band-like region corresponding to the setting of the pixels of the image display panel with high accuracy.

(4) In (3), the mask is held by a frame made of a material having a linear expansion coefficient of 0 to 12.4 × 10 ⁻⁶ / ° C. or less.

  According to (4), even when the temperature rises due to exposure, warpage of the mask due to thermal expansion of the frame body can be prevented so that the distance between the mask and the exposure target does not change, and as a result. , The accuracy can be further improved.

  With regard to a pattern retardation film applied to a passive type image display device, it is possible to create a band-like region corresponding to the pixel setting of the image display panel with high accuracy, and to sufficiently reduce light leakage and pitch deviation. .

It is a figure which shows the confirmation result of the stripe in the image display apparatus by a passive system. It is a flowchart which shows the manufacturing process of the pattern phase difference film of FIG. It is a figure where it uses for description of the exposure process of FIG. It is a figure which shows the mask used for the exposure process of FIG. It is a figure where it uses for description of an exposure process. It is a figure where it uses for description of the boundary of a pattern phase difference film. It is a figure where it uses for description of the three-dimensional image display by a passive system.

[First Embodiment]
FIG. 1 is a view showing a pattern retardation film according to the first embodiment of the present invention. In the image display device according to the first embodiment, the pixels of the liquid crystal display panel that are continuous in the vertical direction (left-right direction in FIG. 1) are alternately displayed in order of the right-eye pixel and the left-eye pixel. They are distributed to the left-eye pixels that display the video, and are driven by right-eye and left-eye image data, respectively. As a result, the image display apparatus alternately divides the display screen into a band-like region for displaying the right-eye image and a band-like region for displaying the left-eye image, and separates the right-eye image and the left-eye image. Display at the same time. In this image display device, the pattern phase difference film 1 shown in FIG. 1 is disposed on the panel surface of the liquid crystal display panel, and the pattern phase difference film 1 corresponds to light emitted from pixels for the right eye and the left eye, respectively. To give the phase difference. Thereby, this image display apparatus displays a desired three-dimensional image by a passive method.

  In the pattern retardation film 1, for example, an alignment film 3 and a retardation layer 4 are sequentially formed on a substrate 2 made of a transparent film material such as triacetyl cellulose. In the pattern retardation film 1, the retardation layer 4 is formed of a liquid crystal material, and the alignment of the liquid crystal material is patterned by the alignment regulating force of the alignment film 3. The orientation of the liquid crystal molecules is indicated by a long and narrow ellipse in FIG. By this patterning, the pattern phase difference film 1 is formed in a band shape alternately with the right-eye area A and the left-eye area B sequentially with a certain width corresponding to the pixel assignment in the liquid crystal display panel. A phase difference corresponding to each of the light emitted from the right-eye and left-eye pixels is given.

  In the pattern retardation film 1, after a photo-alignment material film made of a photo-alignment material is produced, the alignment film 3 is formed by irradiating the photo-alignment material film with ultraviolet rays by linearly polarized light by a so-called photo-alignment technique. Here, the ultraviolet rays applied to the photo-alignment material film are set so that the direction of polarization is different by 90 degrees between the right-eye region A and the left-eye region B, whereby the liquid crystal material provided in the retardation layer 4 , Liquid crystal molecules are aligned in the corresponding directions in the right-eye region A and the left-eye region B, and a phase difference corresponding to transmitted light is given.

FIG. 2 is a flowchart showing manufacturing steps of the pattern retardation film 1. In the manufacturing process of the pattern retardation film 1, the base material 2 is provided by a long film wound around a roll, and the photo-alignment material film is sequentially produced by feeding the base material 2 out of the roll (steps SP1-SP2). . Here, although various manufacturing methods can be applied to the photo-alignment material film, in this embodiment, a film-forming liquid in which the photo-alignment material is dispersed in a solvent such as benzene is applied by a die and then dried. Is produced. In addition, although various materials to which the photo-alignment technique can be applied can be applied as the photo-alignment material, in this embodiment, the alignment is not changed by ultraviolet irradiation after the alignment, for example, a light dimerization type. Use materials. For this light dimerization type material, see “M. Schadt, K. Schmitt, V. Kozinkov and V. Chigrinov: Jpn. J. Appl. Phys.,
31, 2155 (1992), '' M. Schadt, H. Seiberle and A.
Schuster: Nature, 381, 212 (1996) ", and the like, for example, already marketed under the trade name" ROP-103 ".

  Subsequently, in this manufacturing process, a photo-alignment film is produced by irradiating ultraviolet rays in the exposure process (step SP3). Subsequently, in this manufacturing process, after the liquid crystal material is applied by a die or the like in the retardation layer manufacturing process, the liquid crystal material is cured by irradiation with ultraviolet rays, and the retardation layer 4 is manufactured (step SP4). Subsequently, in this manufacturing process, after performing an antireflection film manufacturing process or the like as necessary, in the cutting process, the pattern phase difference film 1 is manufactured by cutting out to a desired size (steps SP5 to SP6).

  FIG. 3 shows the details of this exposure process. This manufacturing process is performed by irradiating ultraviolet rays (polarized ultraviolet rays) by linearly polarized light through a mask 16 that shields a portion corresponding to the region A for the right eye or the region B for the left eye, For the left-eye region B or the right-eye region A, the photo-alignment material film is oriented in a desired direction (FIG. 3A). Thereby, this manufacturing process executes the first exposure process. Subsequently, this manufacturing process irradiates the entire surface with ultraviolet light with linearly polarized light whose polarization direction is 90 degrees different from that of the first exposure process, and the unexposed area A for the right eye or the area for the left eye in the first exposure process. For B, the photo-alignment material film is oriented in a desired direction (FIG. 3B). Thus, in this manufacturing process, the alignment film 3 is produced by sequentially exposing the right eye region A and the left eye region B by two exposure processes.

  FIG. 4 is a plan view showing a mask used for the first exposure process. The mask 16 is formed by the width of the base material 2 having a long length, and slits having an elongated rectangular shape extending in the transport direction of the base material 2 are sequentially provided at regular intervals. Thereby, in this manufacturing process, during the period when the base material 2 is conveyed under the slit, the base material 2 is irradiated with light from the light source, and the first exposure process is executed. Here, the mask 16 is formed by providing a light shielding portion 16B made of chromium or the like on the surface of a transparent plate-like support member 16A made of quartz glass or the like (see FIG. 5).

FIG. 5 is a view showing an exposure apparatus used in an exposure process using the mask 16. In FIG. 5, light used for exposure is indicated by arrows. The exposure apparatus 20 conveys the substrate 2 by being wound around a backup roll 21 that is a conveyance and exposure roll. In the exposure apparatus 20, the mask 16 is held by a mask holder 22 so as to face the backup roll 21. The mask holder 22 is a frame that holds the mask 16 by holding the transparent plate-like support member 16A. In this embodiment, the mask holder 22 is made of microgranite having a small linear expansion coefficient. By configuring the mask holder 22 with a material having a small linear expansion coefficient in this way, in this embodiment, even when the temperature of the mask 16 changes greatly due to the irradiation of ultraviolet rays, the mask 16 does not deform such as warpage. Thus, the distance between the mask 16 and the surface of the backup roll 21 is prevented from changing. For the mask holder 22, various materials can be applied as long as the linear expansion coefficient is 0 to 12.4 × 10 ⁻⁶ / ° C. or less. For example, instead of microgranite, invar, superinvar, Cobalt, quartz glass, and ceramics may be applied.

  The mask 16 is arranged so that the vertical line from the surface of the mask 16 substantially intersects with the rotation axis of the backup roll 21 at substantially the center in the longitudinal direction of the slit. As a result, when the distance from the mask 16 to the surface of the backup roll 21 is viewed in the vertical direction from the surface of the mask 16, the distance to the surface of the backup roll 21 is the smallest at the center of the slit, and It is held so that the distance to the surface of the backup roll 21 at the end is the largest. The backup roll 21 is called a cooling roll, and is provided with a cooling pipe or the like for reducing a temperature rise due to ultraviolet irradiation.

  The exposure apparatus 20 guides the ultraviolet rays emitted from the lamp unit 23 to the mask 16 through the mirror unit 24, the linear polarizing plate 25, and the mirror unit 26, and performs an exposure process with the transmitted light of the mask 16. Here, in the lamp unit 23, ultraviolet irradiation lamps are arranged side by side in the direction along the rotation axis of the backup roll 21, so that the ultraviolet rays for exposure are emitted with a substantially uniform light amount in the rotation axis direction of the backup roll 21. Eject. The mirror unit 24 is emitted by bending the optical path of the ultraviolet light emitted from the lamp unit 23 by approximately 90 degrees by a mirror 24A extending along the rotation axis direction of the backup roll 21, and the linear polarizing plate 25 is provided by the exposure apparatus. The outgoing light from the mirror unit 24 is emitted by the polarization plane corresponding to the area A or the area B related to the exposure processing 20. The mirror unit 26 bends the optical path of the ultraviolet light emitted from the linearly polarizing plate 25 by about 90 degrees by the mirror 26 </ b> A and emits the light toward the mask 16. Here, the mirror 26 </ b> A is a cylindrical concave mirror in which the rotation axis direction of the backup roll 21 is an extension direction, and thereby emits light with reduced divergence in the direction perpendicular to the rotation axis direction of the backup roll 21.

  By the way, when the emitted light from the lamp unit 23 in which the lamps are arranged along the rotation axis direction of the backup roll 21 in this way is guided to the mask 16 through the mirror 26A or the like, the light used for the exposure by the ideal parallel light is used. It is difficult to guide to the mask 16, and the light emitted from the mask 16 diverges to some extent. Further, since the arrangement direction of the slits in the mask 16 is the arrangement direction of the lamps in the lamp unit 23, the emitted light from the mask 16 diverges the transmitted light in the direction along the rotation axis that is the arrangement direction of the lamps. The degree of will change.

  As a result, as shown in FIG. 6, the width of the boundary 36 between the right eye region A and the left eye region B varies in the pattern retardation film 1. Here, when the pattern retardation film 1 is sandwiched between linear polarizing plates having a crossed Nicol arrangement and the right-eye area A and the left-eye area B are set to the extinction position, light is transmitted at the boundary 36. As a result, when the width of the boundary 36 is varied and further increased, the accuracy of the pattern retardation film is lowered to cause light leakage and pitch deviation. As a result, crosstalk and the like become remarkable.

  Therefore, in this embodiment, the distance between the mask 16 and the backup roll 21 is reduced so that the light emitted from the mask 16 is subjected to exposure before it spreads greatly. However, simply reducing the distance between the mask 16 and the backup roll 21 may cause the base material 2 used for the exposure process to come into contact with the mask 16. Therefore, in this embodiment, the space between the mask 16 and the backup roll 21 is reduced within a range in which the base material 2 does not contact the mask 16, and sufficient increase in productivity is achieved, and the increase in boundary width and variation are reduced. .

  More specifically, if the distance between the mask 16 and the backup roll 21 is smaller than 100 μm, the substrate 2 may come into contact with the mask 16. Further, when the interval is 500 μm or more, the emitted light spreads greatly, and the boundary width increases and the variation becomes remarkable.

  Even if the distance between the exposure object and the mask is simply reduced, the spread of light used for exposure in the direction of the rotation axis of the backup roll 21 differs greatly at the upper and lower ends of the slit. However, if the length H of the slit is simply shortened, the amount of light used for exposure is insufficient. Thus, in this embodiment, the length H of the slit (see FIG. 4) is also limited within a range in which the amount of light used for exposure can be sufficiently secured, thereby further increasing the boundary width and reducing variations, Improve the production accuracy of the band-like region.

  More specifically, when the length H of the slit is larger than 50 mm, the spread of light used for exposure at the upper and lower ends of the slit increases, and as a result, the boundary width increases and the variation becomes significant. However, when the slit length H is shorter than 5 mm, the amount of light used for exposure is insufficient.

  The distance between the mask 16 and the backup roll 21 and the slit length S are based on the assumption that the backup roll 21 has a diameter of 100 mm or more and 500 mm or less. The backup roll needs to have a diameter of 100 mm or more and 500 mm or less from the viewpoint of improving productivity by keeping the tension to the base material to be exposed to a constant value stably.

  As a result, the backup roll 21 has a diameter of 100 mm or more and 500 or less, the distance between the mask 16 and the backup roll 21 is set to 100 μm or more and 300 μm or less, and the slit length H in the mask is 5 mm. As described above, the boundary width is set to 50 mm or less, and the boundary width can be made sufficiently small in practice, and further, the variation in the boundary width can be reduced.

  Note that the boundary width is a peak of transmitted light amount by scanning across the regions A and B in a state where the pattern retardation film is sandwiched between the linear polarizing plates by the crossed Nicol arrangement and the regions A and B are set to the extinction position. As the value was detected, detection was performed based on the distance between the parts where the transmitted light amount was about 5% of the peak value.

  Specifically, in this embodiment, for the backup roll 21 having a diameter of 100 mm, the distance between the mask 16 and the backup roll 21 (almost central portion of the slit) is set to 200 μm, and the slit length H is set to 10 mm. . Thereby, a pattern phase difference film can be produced with sufficient accuracy for practical use.

  Moreover, the pattern retardation film used for the measurement of the boundary of the boundary width in this way is arranged on the liquid crystal display panel, and the strength of the streaks observed when displaying the three-dimensional image is determined to determine whether it is practically used. . Here, when produced under the conditions according to this embodiment, in the pattern retardation film 1, the average value of the boundary width is 16.7 μm, and the relative standard deviation value (standard deviation / average value) of the boundary width is 8.0. %, And it was found to be sufficiently practical. Incidentally, when the material of the mask holder 22 is returned to a material having a large linear expansion coefficient (stainless steel), the average value of the boundary width is 17.5 μm, and the relative standard deviation value (standard deviation / average value) of the boundary width is 8. In this case, it was found that it could not be put to practical use according to strict judgment.

  When the relative standard deviation value of the boundary width is in the range of 8.2 to 13.6%, streak is not clarified by improving the positioning accuracy when arranged on the image display panel. However, when the positioning accuracy is improved step by step in this way, the productivity is remarkably lowered, and thus cannot be put to practical use. Further, when the relative standard deviation value of the boundary width is larger than 13.6%, even if the positioning accuracy is improved, the generation of streaks cannot be avoided, so that it cannot be put into practical use. Accordingly, it is desirable that the relative standard deviation value of the boundary width is smaller than 8.2%.

  Thereby, in this embodiment, the pattern retardation film 1 is created with an average value of 16.7 μm of boundary width and a relative standard deviation value (standard deviation / average value) of 8.0% of the boundary width, and has sufficiently high accuracy. Created by.

[Other Embodiments]
The specific configuration suitable for the implementation of the present invention has been described in detail above. However, the present invention can be variously combined or modified with the configuration of the above-described embodiment without departing from the spirit of the present invention. Can do.

  That is, in the above-described embodiment, the case where the light distribution film is manufactured by performing the exposure process on the entire surface after the exposure process using the mask has been described. However, the present invention is not limited to this, and conversely, the entire surface is processed. It can be widely applied to the case where a light distribution film is produced by performing an exposure process using a mask after the exposure process, and further to the case where a light distribution film is produced by repeating the exposure process using the mask. .

  In the above-described embodiment, the case where the mask holder is manufactured using a material having a small linear expansion coefficient has been described. However, the present invention is not limited to this, and when a practically sufficient characteristic can be secured, A mask holder made of a material may be applied.

DESCRIPTION OF SYMBOLS 1 Pattern phase difference film 2 Base material 3 Light distribution film 4 Phase difference layer 16 Mask 20 Exposure apparatus 21 Backup roll 22 Mask holder 23 Lamp unit 24, 26 Mirror unit 25 Linear polarizing plate

Claims (4)

In the manufacturing method of the pattern retardation film, which is sequentially processed while conveying the transparent film material by a long length,
A photo-alignment material film production step for producing a photo-alignment material film on the transparent film material,
An exposure process for producing an alignment film by applying a photo-alignment technique by exposing the photo-alignment material film using a mask; and
On the alignment film, a retardation layer is formed by a right-eye region that gives a phase difference corresponding to right-eye transmitted light and a left-eye region that gives a phase difference corresponding to left-eye transmitted light. A phase difference layer manufacturing process,
The exposure step includes
While transporting the transparent film material by a transport roll, exposure processing is performed using the mask held to oppose the transport roll,
For the mask,
A slit used for exposure of the photo-alignment material film, the slit extending in the transport direction of the transparent film material is repeatedly formed in a direction orthogonal to the extension direction,
An interval between the mask and the transport roll is 100 μm or more and 300 μm or less,
The slit has a length of 5 mm or more and 50 mm or less,
The manufacturing method of the pattern retardation film whose diameter of the said roll for conveyance is 100 mm or more and 500 mm or less. The exposure step includes
The method for producing a patterned retardation film according to claim 1, wherein the mask is held by a frame body made of a material having a linear expansion coefficient of 0 to 12.4 × 10 ⁻⁶ / ° C. or less. In the exposure apparatus of the pattern retardation film used for the production of the pattern retardation film by carrying out the exposure process while transporting the transparent film material by the length in which the photo-alignment material film is created,
While carrying the transparent film material by a roll for conveyance, using a mask held so as to oppose the roll for conveyance, exposure processing is performed,
For the mask,
A slit used for exposure of the photo-alignment material film, the slit extending in the transport direction of the transparent film material is repeatedly formed in a direction orthogonal to the extension direction,
An interval between the mask and the transport roll is 100 μm or more and 300 μm or less,
The slit has a length of 5 mm or more and 50 mm or less,
An exposure apparatus for a patterned retardation film, wherein the conveyance roll has a diameter of 100 mm or more and 500 mm or less. The pattern retardation film exposure apparatus according to claim 3, wherein the mask is held by a frame made of a material having a linear expansion coefficient of 0 to 12.4 × 10 ⁻⁶ / ° C. or less.

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