JP2004351667A - Manufacturing method for uniaxial diffusion surface, light guide plate for liquid crystal display device manufactured using it, diffusion sheet and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a uniaxial diffusion surface, capable of completing processing for a short time at a low cost. <P>SOLUTION: In the method for manufacturing the uniaxial diffusion surface, the uniaxial diffusion surface for diffusing transmitting light in a specific direction is formed on a transparent material. Concretely, first, a grindstone wheel 2 and a mold 1 are relatively moved so that the grindstone wheel 2 is reciprocated in the direction crossing the diffusion direction of light almost at a right angle in the state that the grindstone wheel 2 is brought into contact with the mold 1 to form a fine uneven surface for forming the uniaxial diffusion surface. Next, the mold 1 having the fine uneven surface formed thereto is used to form the uniaxial diffusion surface on the transparent material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a uniaxial diffusion surface of a transparent material, and a light guide plate, a diffusion sheet, and a liquid crystal display for a liquid crystal display device manufactured by using the manufacturing method.
[0002]
[Prior art]
In recent years, liquid crystal display devices have become widespread. In particular, a liquid crystal display device is used as a core device also in a portable information terminal such as a mobile phone, a PDA, and a smartphone whose market is rapidly expanding. Since the liquid crystal display device itself does not emit light, an illumination unit called a backlight or a front light is attached. The illumination unit generally includes a light guide plate, and the light guide plate transmits light from a light source such as an LED or a fluorescent tube provided on a side surface of the light guide plate, and emits the light from an emission surface on the liquid crystal substrate side. At this time, the surface of the light guide plate is provided with a diffusive property for the purpose of increasing the viewing angle, relaxing the bright lines and dark lines, or a diffusion sheet is inserted between the light emitting surface of the light guide plate and the liquid crystal substrate.
[0003]
On the other hand, the present inventors have proposed an invention relating to uniaxial diffusion in Japanese Patent Application No. 2002-265815 as a technique for suppressing the light loss by specifying the diffusion direction of light and providing diffusion only in a desired direction. Since such an application has not been published yet, it is not a known technique. However, as a reference example for the method of manufacturing a uniaxial diffusion surface according to the present invention, the manufacturing method disclosed in the application will be described below.
[0004]
First, for example, a parallel flat glass plate such as an optical glass plate is polished smoothly, and a photoresist is coated on the glass plate with a uniform thickness by a spin coating method. Next, the photoresist on the glass plate is exposed to laser light using a drawing apparatus in which the table on which the glass plate is mounted can move in the XY directions or the laser exposure unit can move in the XY directions. At this time, an infinite number of straight lines are drawn at a random pitch in order to have uniaxial diffusion. For example, when one line is drawn, the pitch is formed by forming a sine wave and randomly changing the amplitude and frequency. It is desirable to change. In addition, by setting the amplitude to 200 μm or less, an apparently uniaxial straight line can be obtained. Next, by developing the exposed photoresist with a developing solution, a linear fine uneven surface can be obtained. If the photoresist used is a positive type, the exposed portions are washed away during development to form unexposed portions. Conversely, if the photoresist used is a negative type, the unexposed portions are washed away during development to form the exposed portions. A conductive thin film is formed on the conductive thin film by using a sputtering method or a vacuum evaporation method, and thereafter, a Ni plating or the like is thickly plated on the conductive thin film, and finally, the resist is peeled off to form a linear fine uneven surface. Can be created. Then, a uniaxial diffusion surface is formed on the transparent material by injection molding using this mold.
[0005]
Note that a conventional method for manufacturing a light guide plate is disclosed in Patent Document 1. However, a diffusion surface is formed in the light guide plate manufactured in this document, but it is not a uniaxial diffusion surface.
[0006]
[Patent Document 1]
JP-A-2002-303734
[Problems to be solved by the invention]
As described above, forming a uniaxial diffusion surface requires a large amount of capital investment and man-hours, so that high costs have to be achieved.
[0008]
The present invention has been made to solve such a problem, and an object of the present invention is to provide a method of manufacturing a uniaxial diffusion surface which can be processed at low cost and in a short time. A further object of the present invention is to provide a method of manufacturing a uniaxial diffusion surface which can reduce light loss as compared with graining or the like and can diffuse light effectively.
[0009]
[Means for Solving the Problems]
The method for producing a uniaxial diffusion surface according to the present invention is a method for producing a uniaxial diffusion surface for forming a uniaxial diffusion surface for diffusing transmitted light in a specific direction on a transparent material, in a state where a grindstone is brought into contact with a mold. Forming a fine uneven surface for forming the uniaxial diffusion surface by relatively moving the grindstone and the mold so that the grindstone reciprocates in a direction substantially perpendicular to the light diffusion direction, Forming the uniaxial diffusion surface on the transparent material using a mold on which the fine uneven surface is formed. According to such a method, processing can be completed at low cost and in a short time. In addition, light loss is smaller than in graining or the like, and light can be diffused effectively.
[0010]
It is desirable that the grinding wheel is a grinding wheel that grinds the surface by sliding the surface of the grinding wheel with respect to a mold. In this case, since the grinding wheel moves relatively to the mold in a rotating state, the area of the grinding surface of the grinding wheel to be contacted differs depending on the surface area of the mold. Therefore, a slightly different grinding process is performed on the ground surface of the mold at a portion, and the surface can be randomly processed.
[0011]
Further, the rotation axis of the grinding wheel is preferably substantially parallel to the light diffusion direction. With this arrangement, the direction of grinding by the grinding wheel and the direction of grinding by the relative movement of the entire grinding wheel and the mold can be matched, and the diffusivity and the anisotropy with the orthogonal direction are improved. be able to.
[0012]
In a preferred embodiment, the maximum surface roughness Rt when scanning in a direction orthogonal to the reciprocating direction of the grindstone of the mold is 1 μm to 50 μm or the average surface roughness Ra is in a range of 0.1 μm to 5 μm. .
[0013]
A light guide plate for a liquid crystal display device in which a uniaxial diffusion surface manufactured by the above manufacturing method is formed on an emission surface, and a main traveling direction of light of the light guide plate and a grinding direction for reciprocating the grindstone substantially match. Good. With such a configuration, the emission angle can be efficiently widened without obstructing the progress of light propagating in the light guide plate. In other words, in the traveling direction of light, the behavior of light is the same as that of smooth surface reflection, and in the direction orthogonal to this, the behavior of light of diffuse surface reflection is exhibited.
[0014]
Further, the uniaxial diffusion surface manufactured by the above manufacturing method may be formed on a diffusion sheet for a liquid crystal display device. Further, the uniaxial diffusion surface manufactured by the above-described manufacturing method may be formed on a light incident end surface of a light guide plate for a liquid crystal display device. At this time, it is preferable that the thickness direction of the light guide plate and the reciprocating direction of the grindstone substantially match.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, a cavity or a core surface forming a product surface of a mold is machined in a specific direction for controlling light by grinding using a grindstone. The cavity refers to the female (concave) mold insert of the mold, and the core refers to the male (convex) mold insert of the mold.
[0016]
There are various types of grinding methods. In the present invention, a so-called surface grinding method is used in which a disk-shaped grinding wheel that rotates at a high speed is used, and a work is scraped by reciprocating a table. FIG. 1 shows a main part of a grinding apparatus for performing the surface grinding method. As shown in the figure, a work 1 of a mold cavity or a mold core is fixed on a table 3 with a magnet or a fixing jig. Then, the table 3 is reciprocated in the left-right direction in the drawing while the disc-shaped grinding wheel 2 rotating at a high speed is in contact with the surface of the work 1. At this time, the feed speed of the table 3 is, for example, 1.5 m / sec. The reciprocating operation is a repetition of acceleration, constant speed, and deceleration, and processing is performed at a constant speed portion. For example, the rotation direction of the grinding wheel 2 is clockwise, and the grinding is performed when the table 3 moves from left to right in the figure. This is called an upcut. Conversely, cutting when the table 3 moves from right to left is called downcut. Since the relative speed differs between the case of up-cutting and the case of down-cutting, the processing conditions will be slightly different, but there is no problem in either processing.
[0017]
Next, the movement of the three axes will be described. Here, as shown in FIG. 1, the reciprocating direction of the table 3 is an X axis, the direction orthogonal to the main plane of the table 3 is the Y axis, and the vertical direction, that is, the direction perpendicular to the main plane of the table 3 is the Z axis. I do. At this time, when the grinding wheel 2 makes one reciprocation in the X-axis direction, the table 3 moves in the Y-axis direction by one pitch. When the grinding wheel 2 moves to the end of the processing work 1 by moving in the Y-axis direction, that is, after processing the entire processing work 1, the grinding wheel 2 cuts in a desired depth in the Z-axis direction. The relative positional relationship between the processing work 1 and the table 3 in the Z-axis direction when processing the entire surface of the processing work 1 is fixed. The movement in the Y-axis direction is also fixed when the grinding wheel 2 makes one reciprocation in the X-axis direction. The relative movement between the grinding wheel 2 and the table 3 in the Y-axis direction and the Z-axis direction is performed when the grinding wheel 2 is off the work 1. In this example, relative movement between the grinding wheel 2 and the table 3 in the Z-axis direction is realized by the movement of the grinding wheel 2.
[0018]
When the reciprocating direction of the table is the grinding direction, (1) the mold is processed by setting the direction perpendicular to the direction in which diffusion is desired to be imparted to the grinding direction. By performing such processing, a fine uneven surface formed of fine uneven streaks is formed on the surface of the mold in the grinding direction. A uniaxial diffusion surface can be formed on a transparent material by injection molding using a mold having such a fine uneven surface. At this time, the uniaxial diffusion surface has a diffusion property in a direction substantially orthogonal to the grinding direction. Here, in the embodiment of the present invention, the “uniaxial diffusion surface” indicates a diffusivity only in one direction with respect to two axes orthogonal to each other. When the luminance of the emitted light is obtained by entering from the linear direction, the normal direction to the exit surface is defined as an angle of 0 degree, and the luminance at the measurement angle is orthogonal to two orthogonal directions if there is no anisotropy. The values at each angle in the two directions are equal. On the other hand, on the surface provided with the uniaxial diffusivity, in the diffusion direction, the luminance near 0 degrees decreases, and the luminance at the peripheral angles increases. On the other hand, in the orthogonal direction, although the luminance at 0 degrees slightly decreases, the luminance tendency for each angle does not change.
[0019]
The surface roughness of the mold when scanned in a direction perpendicular to the grinding direction is desirably in the range of a maximum surface roughness Rt of 1 μm to 50 μm or an average surface roughness Ra of 0.1 μm to 5 μm. The definition of the surface roughness here is based on the JIS-B0601 standard. Examples of such a surface roughness measuring device include TOPY-2D / 3D manufactured by WYKO using a phase difference method, Surfcom 920A manufactured by Tokyo Seimitsu using an astigmatism method, and Nano Scope manufactured by Digital Instruments, an atomic force microscope. A stylus type P12EX manufactured by Tencor can be used. Here, P12EX manufactured by Tencor is used as an example. Roughness measurement conditions were as follows: scanning distance: 1000 μm, scanning speed: 5 μm / sec, sampling frequency: 200 Hz, stylus weight: 5 mg, stylus tip shape: 45 °, 2 μmR, cutoff filter: Gaussian, short wavelength cutoff The filter is 24 Hz, and the long-wavelength cutoff filter is 167 μm.
[0020]
The surface of the transparent material formed using such a mold also has the same surface roughness. The grinding wheel 2 is made of hard abrasive grains such as aluminum oxide and silicon carbide mixed with a binder and solidified. Since the grinding wheel 2 moves relatively to the processing workpiece 1 in a rotating state, the area of the grinding surface of the grinding wheel 2 to contact differs depending on the surface area of the processing workpiece 1. Therefore, the surface of the ground work 1 is subjected to a slightly different grinding at a part. That is, they are processed at random.
[0021]
By using the mold obtained in this way to form a light emitting surface, a light incident surface, and a diffusion surface such as a diffusion sheet of a light guide plate, it is possible to add a diffusion function in a specific direction while suppressing light loss. Can be. The transparent material forming the uniaxial diffusion surface by the manufacturing method according to the present invention may be not only a completely transparent material but also a translucent material. The transparent material includes, for example, a synthetic resin such as methacrylic resin, polycarbonate, and polystyrene, and a glass material.
[0022]
(2) In the case of forming on the emission surface of the light guide plate, the die is machined with the main traveling direction of the directional light and the grinding direction substantially coincide with each other. Thereby, the emission angle can be efficiently widened without obstructing the progress of light propagating in the light guide plate. Here, the main traveling direction of the directional light refers to the direction normal to the plane of incidence, and according to another aspect, the direction indicated by the maximum intensity of the light distribution defined by the International Commission on Illumination. In the case of perfect parallel light, it is defined as the traveling direction of light.
[0023]
FIG. 2 is a microscopic observation image of the uniaxial diffusion surface formed on the mold piece, and fine uneven streaks are formed on the upper and lower sides of the figure, and these streaks are in the grinding direction, and the direction perpendicular to this streak is It becomes the diffusion direction.
[0024]
(1st Embodiment)
FIG. 4 is a perspective view of the light guide plate of the first embodiment according to the embodiment of the present invention, and is an example in which a single-axis diffusion surface is formed on an emission surface of the light guide plate 10. The light guide plate 10 has a rectangular shape, and the light source chip 20 is disposed substantially at the center of one of two short sides. The diffusion direction on the uniaxial diffusion surface is substantially orthogonal to the main traveling direction of light from the light source chip 20. In this case, as shown in FIG. 4, a linear mark is observed in the main traveling direction of light. In the present invention, light emitted from the light source chip 20 propagates in the light guide plate 10 while being repeatedly reflected between the upper surface (emission surface) and the lower surface (reflection surface) of the light guide plate 10.
[0025]
Since the light guide plate 10 according to the embodiment of the present invention does not have a diffusivity in the traveling direction of the light, the light can efficiently pass through the light guide plate 10 without causing unnecessary diffusion when the light propagates. Will be propagated. In addition, the light exiting from the light exit surface when the light hits the reflection prism of the light guide plate 10 has a tendency that the direction orthogonal to the light propagation direction is narrow, but by having a diffusivity in this orthogonal direction, Light can be diffused efficiently.
[0026]
Next, a method for manufacturing a uniaxial diffusion surface according to an embodiment of the present invention will be described.
FIG. 3 is a perspective view showing a mold piece for obtaining the light guide plate shown in FIG. 4 by injection molding. Except for the thickness of the mold piece, the outer shape thereof is similar to that of the light guide plate shown in FIG. As a method of manufacturing the mold piece, first, HPM38 (HRC50) manufactured by Hitachi Powdered Metals Co., Ltd. is cut into a desired shape as a base material, and this is mounted on a surface grinder manufactured by Nagase Integrex Corporation using a magnet chuck and ground. Was done. The grinding direction is orthogonal to the diffusion direction shown in FIG. 3, and this direction is the reciprocating direction of the table shown in FIG. Here, it is selected that the grinding direction is made substantially coincident with the main traveling direction of the directional light. That is, a fine streak-shaped fine uneven surface is formed in the grinding direction, and a uniaxial diffusion surface having diffusivity in a direction orthogonal to the fine uneven surface can be formed. The grinding wheel is CXY60-J (Abrasive # 60) manufactured by Noritake Co., Ltd., the rotation speed of the grinding wheel is 2500 rpm, the feed pitch in the direction orthogonal to the grinding direction of the work is 1.5 mm, and the cutting amount of the grinding wheel is 0.02 mm / time. NK-55 manufactured by Noritake Cool Co. was used as the grinding fluid. The grinding width of the grinding wheel is about 30 mm.
[0027]
The grinding speed is determined by the relative speed difference between the feed speed of the table on which the workpiece is magnetically chucked and the number of revolutions of the grinding wheel.If the grinding speed is high, the surface roughness is rough, and if it is slow, the surface roughness is fine, The table feed speed was determined such that the surface roughness of the diffusion surface when scanned in the diffusion direction was in the range of Rt 1 μm to 50 μm and Ra 0.1 μm to 5 μm.
[0028]
By using the thus obtained mold, the light guide plate is molded by an injection molding method, whereby a light guide plate having a diffusion function added only in a desired direction can be obtained while suppressing light loss. it can.
[0029]
(Second embodiment)
FIG. 5 is a perspective view of a light guide plate according to a second embodiment of the present invention, which is another example in which a light-scattering surface of the light guide plate 10 is formed with a uniaxial diffusion surface. The light guide plate 10 has a rectangular shape, and is different from the first embodiment in that a light source chip 20 is arranged at a corner. The direction of the uniaxial diffusing surface has diffusivity in the direction orthogonal to the main traveling direction of light from the light source chip 20 as in the first embodiment. Therefore, as shown in FIG. 5, oblique linear marks are observed. Other configurations follow the first embodiment, and the method of manufacturing the mold pieces also follows the first embodiment except that the grinding direction is different. Also in the present embodiment, it is possible to obtain a light guide plate having a diffusion function added only in a desired direction while suppressing light loss.
[0030]
(Third embodiment)
FIG. 6 is a perspective view of a third embodiment according to the present invention, and is an example in which the present invention is used for a diffusion sheet 30 placed on an emission surface on a light guide plate. In this example, since light does not need to propagate through the diffusion sheet 30, the diffusion direction can be set in a desired direction. A basic mold piece manufacturing method follows the first embodiment, and a sheet is manufactured using the obtained mold, whereby a diffusion sheet having uniaxial diffusivity can be obtained. As a material of the sheet, PC (polycarbonate) and PET (polyethylene terephthalate) are selected. Also in the present embodiment, it is possible to obtain a diffusion sheet having a diffusion function added only in a desired direction while suppressing light loss.
[0031]
(Fourth embodiment)
FIG. 7 is a perspective view of a light guide plate according to a fourth embodiment of the present invention, which is an example in which a uniaxial diffusion surface is formed on a light incident portion of the light guide plate. The light guide plate 10 has a rectangular shape, and a light source chip is disposed at substantially the center of one of two short sides. The direction of the uniaxial diffusion surface is selected so that the light from the light source chip which enters from the short side diffuses into the light guide plate surface, and does not diffuse in the thickness direction of the light guide plate. That is, as shown in FIG. 7, a linear mark is observed in the thickness direction of the light guide plate. Regarding the processing method, it is possible to manufacture according to the first embodiment except that the shape of the mold piece is reduced. Also in the present embodiment, it is possible to obtain a light guide plate having a diffusion function only in a desired direction while suppressing light loss.
[0032]
(Fifth embodiment)
FIG. 8 is a perspective view of a light guide plate according to a fifth embodiment of the present invention, which is used for a light guide plate having a different light incident portion shape from the light guide plate of the fourth embodiment. It is an example. The light guide plate 10 has a rectangular shape, and differs from the fourth embodiment in that a light source chip is arranged at a corner. The direction of the uniaxial diffusion surface is selected so that the light from the light source chip 20 entering from the corner diffuses into the light guide plate surface, and does not diffuse in the thickness direction of the light guide plate 10. That is, as shown in FIG. 8, a linear mark is observed in the thickness direction of the light guide plate 10. Here, since the light incident portion 11 is a circular arc having a curvature, the light receiving portion 11 is manufactured in accordance with the first embodiment except that the light incident portion 11 is processed using a copying grinding machine instead of a surface grinding machine. Also in the present embodiment, it is possible to obtain a light guide plate having a diffusion function only in a desired direction while suppressing light loss.
[0033]
(Sixth embodiment)
The sixth embodiment relates to a liquid crystal display device including the light guide plates according to the first, second, fourth, and fifth embodiments. 9, reference numeral 10 denotes a light guide plate, 11 denotes a light incident portion, 12 denotes a prism surface, 13 denotes an emission surface, 20 denotes a light source chip, 40 denotes a reflection sheet, 50 denotes a polarizing plate (including a retardation plate), and 60 denotes a transmission type. A liquid crystal plate, 100 is a planar light source, and 200 is a liquid crystal module.
[0034]
In the present embodiment, the reflection sheet 40 is disposed on the lower surface of the light guide plate 10, that is, on the side of the prism surface 12, to form the planar light source 100. On the emission surface 13 of the light guide plate 10, a uniaxial diffusion surface is formed by the manufacturing method described in the above embodiment. Since the configuration, function and effect of the reflection sheet 40 are well known, the description is omitted. Further, on the planar light source 100, a transmissive liquid crystal plate 60 provided with polarizing plates 50 (including a phase difference plate) on both surfaces was arranged. Here, the light emitted from the light source chip 20 enters the light guide plate 10 through the light incident portion 11, and is repeatedly reflected in the light guide plate 10 between the emission surface 13 and the prism surface 12 and propagates in the light guide plate 10. The light is reflected and deflected in the normal direction of the light exit surface 13 by the inclination angle formed on the prism surface 12 and exits from the light exit surface 13. Here, a reflection sheet 40 is provided on the prism surface 12 side, and light propagating in the light guide plate 10 exits from the exit surface 13 without leakage. Since the light exit surface 13 of the light guide plate 10 is formed with a uniaxial diffusion surface, the light is diffused, and the backlight type liquid crystal display panel is configured to illuminate the liquid crystal plate 60 via the polarizing plate 50. be able to.
[0035]
【The invention's effect】
According to the present invention, since processing is performed using a general-purpose surface grinding method, processing can be completed at low cost and in a short time. In addition, light loss is smaller than in graining or the like, and light can be diffused effectively.
[Brief description of the drawings]
FIG. 1 is a perspective view of a main part of a grinding device used in a method of manufacturing a uniaxial diffusion surface according to the present invention.
FIG. 2 is a view showing a microscope observation image of a mold piece manufactured by the method for manufacturing a uniaxial diffusion surface according to the present invention.
FIG. 3 is a perspective view of a mold piece processed by the manufacturing method according to the present invention.
FIG. 4 is a perspective view of a light guide plate manufactured by the manufacturing method according to the present invention.
FIG. 5 is a perspective view of a light guide plate manufactured by the manufacturing method according to the present invention.
FIG. 6 is a perspective view of a diffusion sheet manufactured by the manufacturing method according to the present invention.
FIG. 7 is an enlarged view near the incident surface of the light guide plate manufactured by the manufacturing method according to the present invention.
FIG. 8 is an enlarged view near the incident surface of the light guide plate manufactured by the manufacturing method according to the present invention.
FIG. 9 is a cross-sectional view of a liquid crystal display device including a light guide plate manufactured by the manufacturing method according to the present invention.
[Explanation of symbols]
Reference Signs List 1 processing work 2 grinding wheel 3 table 10 light guide plate 20 light source chip 30 diffusion sheet

Claims (8)

A method for manufacturing a uniaxial diffusion surface, wherein a uniaxial diffusion surface for diffusing transmitted light in a specific direction is formed on a transparent material,
To form the uniaxial diffusion surface by relatively moving the grindstone and the mold such that the grindstone reciprocates in a direction substantially perpendicular to the light diffusion direction with the grindstone in contact with the mold. Forming a micro-textured surface of
Forming the uniaxial diffusion surface on the transparent material using a mold having the fine uneven surface formed thereon. The method for manufacturing a uniaxial diffusion surface according to claim 1, wherein the grinding wheel is a grinding wheel that grinds the surface by sliding the surface with respect to a mold by rotating. 3. The method according to claim 2, wherein a rotation axis of the grinding wheel is substantially parallel to a diffusion direction of the light. The maximum surface roughness Rt when scanning in a direction orthogonal to the reciprocating direction of the grindstone of the mold is 1 μm to 50 μm or the average surface roughness Ra is in a range of 0.1 μm to 5 μm. 1. The method for producing a uniaxial diffusion surface according to 1. A light guide plate for a liquid crystal display device, wherein a uniaxial diffusion surface manufactured by the method for manufacturing a uniaxial diffusion surface according to claim 1 is formed on an emission surface, and a main traveling direction of light of the light guide plate. And a grinding direction in which the grinding wheel is reciprocated substantially coincides with the grinding direction. A diffusion sheet for a liquid crystal display device having at least one uniaxial diffusion surface produced by the method for producing a uniaxial diffusion surface according to claim 1. A light guide plate for a liquid crystal display device, wherein a uniaxial diffusion surface manufactured by the method for manufacturing a uniaxial diffusion surface according to any one of claims 1 to 4 is formed on a light incident end surface, wherein the light guide plate has a thickness direction and the thickness direction. A light guide plate wherein the reciprocating directions of the grindstones are substantially matched. A liquid crystal display device comprising the light guide plate according to claim 5.

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