JP2010070608A - Acrylic film for optical use, light guide plate, and backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic film for optical use with improved transparency. <P>SOLUTION: The acrylic film for optical use comprises a resin composition (C) containing an acrylic polymer (A) and a fluorine-based resin (B), wherein a mass ratio (A/B) of the acrylic polymer (A) to the fluorine-based resin (B) is in the range from 30/70 to 99.9/0.1. Brightness of the light, entering the end face of the acrylic film and emitting from the face opposite the end face, is greater than that of the film consisting of the acrylic polymer (A) alone, as measured under the same conditions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical acrylic film suitable for an optical film that requires high transparency, a light guide plate using the same, and a backlight unit, and particularly for use in a light guide plate that requires high transmittance and thinning. The present invention relates to a suitable optical acrylic film.

  Polarizer protective film, diffuser protective film, light guide film, microlens array, various optical members such as antireflection base materials, building materials such as interior materials, automobile members, reflective materials used for road signs, etc. A highly transparent resin film is used in various applications.

  In particular, the amount of resin films used for liquid crystal displays is increasing year by year, and higher total light transmittance and lower haze are required.

  Among them, since the light guide plate used in the backlight unit of the liquid crystal device is used in a long optical path, the resin film used in such a light guide plate can have transmission loss due to light absorption, scattering, reflection, etc. as much as possible. Less is required. Conventionally, a film (acrylic film) made of an acrylic resin having a high total light transmittance, particularly a cast sheet of polymethyl methacrylate has been used for such a resin film.

  On the other hand, in recent years, in order to reduce power consumption, as a primary light source of a liquid crystal display device, a point-like one such as a light emitting diode (LED) is widely used instead of a linear or rod-like one such as a fluorescent lamp. . Since LEDs having small dimensions can be formed, there is a demand for further thinning of liquid crystal display devices using such LEDs. In addition, with the expansion of the field of use of liquid crystal display devices, there is a strong demand for thin backlight units, particularly for small liquid crystal display devices, and thinning of light guide plates used in backlight units is also being promoted. .

  However, as the light guide plate becomes thinner, the number of times the light traveling in the light guide plate is reflected on the surface of the light guide plate increases. Therefore, even if the composition is the same, the light transmission loss increases and the luminance increases. There is a problem that it tends to decrease, and a material having higher transparency has been demanded as a material used for the light guide plate.

  Patent Document 1 discloses a light guide plate made of a composition comprising an acrylic resin and an aliphatic polyester resin, having a small retardation and a small refractive index, suppressing reflection of light on the incident surface, and loss of light. It is described that can be reduced.

On the other hand, Patent Document 2 discloses an impact-resistant film made of an acrylic resin mainly composed of methyl methacrylate, an acrylic elastomer, and a fluororesin mainly composed of vinylidene fluoride. No. 3 discloses a cover film for an optical recording medium comprising a polymethacrylic resin and a polyvinylidene fluoride resin.
JP 2008-20747 A JP-A-3-124754 JP 61-78857 A

  However, the light guide plate using a resin composition made of an acrylic resin and an aliphatic polyester resin described in Patent Document 1 has a problem of low brightness because the compatibility between the resins is not sufficient.

  The impact resistant film described in Patent Document 2 has a problem that the luminance is lowered when used in a long optical path because of its large haze.

  The film described in Patent Document 3 is a cover film for an optical recording medium, and there is no description about the transmittance when used in a long optical path.

  An object of the present invention is to provide an optical acrylic film with improved transparency, and a thin and high-intensity light guide plate and backlight unit.

According to one aspect of the present invention, an acrylic film comprising a resin composition (C) containing an acrylic polymer (A) and a fluororesin (B),
The mass ratio (A / B) between the acrylic polymer (A) and the fluororesin (B) is in the range of 30/70 to 99 / 0.1,
For optical use, light is incident from the end face of the acrylic film, and the brightness of the light emitted from the opposite end face facing the end face is greater than the brightness of the film made of only the acrylic polymer (A) measured under the same conditions. An acrylic film is provided.

  According to the other aspect of this invention, the light-guide plate formed by providing uneven | corrugated shape to both surfaces or one side of said acrylic film is provided.

  According to another aspect of the present invention, a backlight unit incorporating the light guide plate is provided.

  According to the present invention, an acrylic film with improved transparency can be obtained. By using this acrylic film, a thin and high-intensity light guide plate and backlight unit can be provided.

  The acrylic film which is one Embodiment of this invention consists of a resin composition (C) containing an acrylic polymer (A) and a fluorine resin (B). This acrylic film is particularly suitable for light guide plate applications.

  The mass ratio (A / B) of the acrylic polymer (A) and the fluororesin (B) is preferably in the range of 30/70 to 99.9 / 0.1.

  Light is incident from the end face of this acrylic film, the brightness of the light emitted from the opposite end face facing this end face is L1, and the brightness of the film consisting only of the acrylic polymer (A) measured under the same conditions is L2. Then, the luminance ratio (L1 / L2) of these films is preferably greater than 1, more preferably 1.05 or more, and even more preferably 1.1 or more. As will be described later, the luminance ratio (L1 / L2) is obtained particularly in a film having a film thickness of 350 μm and a distance of 20 cm from the end face (I) to the end face (O) and having a square planar shape. It is preferred that

  Hereinafter, preferred embodiments of the present invention will be described in detail.

[Acrylic polymer (A)]
The acrylic polymer (A) is a polymer comprising 50 to 100% by mass of an alkyl methacrylate unit having an alkyl group having 1 to 4 carbon atoms and 0 to 50% by mass of another vinyl monomer unit copolymerizable therewith. Is preferred. The content of the alkyl methacrylate unit is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more from the viewpoint of obtaining desired properties of the acrylic polymer (A).

  Examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate and the like.

  Here, “polymer” means a homopolymer or a copolymer. When the acrylic polymer (A) is a homopolymer, it is, for example, polymethyl methacrylate, and when it is a copolymer, it is, for example, a copolymer of methyl methacrylate and a vinyl monomer other than methyl methacrylate.

  Examples of other vinyl monomers copolymerizable with the above alkyl methacrylate include alkyl acrylates having 1 to 8 carbon atoms in the alkyl group such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate. ; Alkyl methacrylate having 1 to 4 carbon atoms of alkyl group such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate (other than the above alkyl methacrylate); aromatic methacrylate such as phenyl methacrylate, benzyl methacrylate, isobornyl Alicyclic methacrylates such as methacrylates; Aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene; Bis such as acrylonitrile and methacrylonitrile Lucian compounds and the like, may be used in combination of two or more of these.

  Among these, from the viewpoint of compatibility with the fluororesin (B), transparency of the resulting film, heat resistance, and weather resistance, the co-polymerization of methyl methacrylate and alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. A coalescence is preferable, and a copolymer of methyl methacrylate and methyl acrylate is more preferable. The composition of this copolymer is preferably 80 to 99% by mass of methyl methacrylate units and 1 to 20% by mass of alkyl acrylate units, 90 to 99% by mass of methyl methacrylate units, and 1 to 10% by mass of alkyl acrylate units. % Is more preferable.

  The weight average molecular weight of the acrylic polymer (A) is preferably in the range of 50,000 to 200,000. If the weight average molecular weight is too small, good mechanical strength cannot be obtained, and if it is too large, melt molding becomes difficult. The weight average molecular weight is more preferably 70,000 to 170,000, and further preferably 80,000 to 120,000.

  The polymerization method for obtaining the acrylic polymer (A) is not particularly limited, and various methods such as a usual suspension polymerization method, emulsion polymerization method, bulk polymerization method and the like can be applied. From the viewpoint of excellent properties, it is preferable to use a suspension polymerization method or a bulk polymerization method.

  As the acrylic polymer (A), the Dainar (registered trademark) BR series manufactured by Mitsubishi Rayon Co., Ltd. and the Acrypet (registered trademark) series manufactured by Mitsubishi Rayon Co., Ltd. can be suitably used and are industrially available. Is possible.

[Fluorine resin (B)]
As the fluororesin (B), one having a sufficiently high compatibility with the acrylic polymer (A) is used. The compatibility of the fluororesin (B) and the acrylic polymer (A) is determined by measuring the glass transition point in accordance with JIS K7121 under the blending conditions of the film to be formed, and the acrylic polymer (A) and the fluororesin ( It is preferable that the two glass transition points derived from B) are not detected and only one glass transition point is detected.

  In addition, the fluororesin (B) is a melting peak derived from the crystal structure of the fluororesin (B) in the measurement of the melting temperature based on JIS K7121 under the blending conditions of the film to be formed with the acrylic polymer (A). Is preferably not observed at all.

  As the fluororesin (B), trifluoroalkyl methacrylate homopolymer, tetrafluoroalkyl methacrylate homopolymer, pentafluoroalkyl methacrylate homopolymer, octafluoroalkyl methacrylate homopolymer, heptadecafluoroalkyl methacrylate homopolymer, Fluorinated alkyl methacrylate polymer such as fluorinated alkyl methacrylate / alkyl methacrylate copolymer; trifluoroalkyl α-fluoroacrylate homopolymer, tetrafluoroalkyl α-fluoroacrylate homopolymer, pentafluoroalkyl α-fluoroacrylate only Polymer, octafluoroalkyl α-fluoroacrylate homopolymer, heptadecafluoroalkyl α-fluoroacrylate homopolymer, etc. Any α-fluoromethacrylate polymer; vinylidene fluoride homopolymer, vinylidene fluoride / tetrafluoroethylene copolymer, vinylidene fluoride polymer such as vinylidene fluoride / hexafluoropropylene copolymer, etc. A mixture of two or more of these may be used.

  Among these, from the viewpoint of transparency when blended with the acrylic polymer (A), a vinylidene fluoride polymer is preferable, and a vinylidene fluoride homopolymer is more preferable.

[Resin composition (C)]
The acrylic film of the present invention comprises a resin composition (C), and the resin composition (C) can be formed by blending an acrylic polymer (A) and a fluororesin (B).

  As a blending method, a commonly used method can be used. For example, there is a method of mechanically mixing with a mixer such as a Henschel mixer and then melt-kneading with a twin screw extruder, but the method is not limited thereto.

  The mixing ratio (A / B) of the acrylic polymer (A) and the fluororesin (B) is preferably in the range of 30/70 to 99.9 / 0.1.

  From the viewpoint of obtaining a sufficient transparency improvement effect of the fluororesin (B), the blending ratio of the fluororesin (B) is 100 parts by mass of the total of the acrylic polymer (A) and the fluororesin (B). Is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, further preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. That is, the mixing ratio (A / B) is preferably 99.9 / 0.1 or less, more preferably 99/1 or less, still more preferably 97/3 or less, and particularly preferably 95/5 or less.

  When there are too many fluororesins (B), crystallization of a fluororesin (B) will occur easily, the acrylic film obtained will become cloudy and light transmittance will fall easily.

  In general, the fluororesin (B) is slightly yellow, and when the amount of the fluororesin (B) added is increased, the yellowishness of the resulting acrylic film tends to increase. Particularly for display applications, it is desired that the yellow color of the film is small. Moreover, the glass transition temperature of a fluorine-type resin (B) is low compared with an acrylic polymer (A), and when there is much addition amount of a fluorine-type resin (B), the heat resistance of the acrylic film obtained will fall. More generally, the fluororesin (B) is very expensive as compared with the acrylic polymer (A), and the cost increases when the blending amount of the fluororesin (B) is increased. From these viewpoints, the blending ratio of the fluororesin (B) is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, further preferably 35 parts by mass or less, particularly preferably 25 parts by mass or less, and 20 parts by mass. The following are most preferred. That is, the mixing ratio (A / B) is preferably 30/70 or more, more preferably 30/70 or more, further preferably 65/35 or more, particularly preferably 75/25 or more, and most preferably 80/20 or more.

  Considering the above matters, the mixing ratio of the acrylic polymer (A) and the fluororesin (B) is 30 to 99.9 masses when the acrylic polymer (A) is 100 mass parts. Part, 0.1 to 70 parts by mass of the fluororesin (B) is preferable, 50 to 99 parts by mass of the acrylic polymer (A) is more preferable, and 1 to 50 parts by mass of the fluororesin (B) is more preferable. A) 65-97 parts by mass, fluorine-based resin (B) 3-35 parts by mass are more preferable, acrylic polymer (A) 75-97 parts by mass, fluorine-based resin (B) 3-25 parts by mass are particularly preferable, The acrylic polymer (A) is most preferably 80 to 95 parts by mass and the fluororesin (B) is 5 to 20 parts by mass. That is, the mixing ratio (A / B) can be set to satisfy, for example, 80/20 <A / B <95/5.

  The resin composition (C) preferably has an extrapolated glass transition start temperature of 70 ° C. or higher, more preferably 80 ° C. or higher, from the viewpoint of the heat resistance of the acrylic film. By using an acrylic film having sufficient heat resistance, a highly reliable display can be provided.

[Brightness of acrylic film]
The luminance of the acrylic film in the present invention indicates the luminance of light emitted from the end surface (O) facing the end surface (I) when light is incident from the end surface (I) of the acrylic film.

  In FIG. 1, sectional drawing along the advancing method of the light for demonstrating the measuring method of the brightness | luminance of an acrylic film is shown. In the figure, reference numeral 1 denotes an acrylic film, reference numeral 2 denotes a reflection sheet, reference numeral 3 denotes a light source, reference numeral 4 denotes an end face (I), and reference numeral 5 denotes an end face (O).

  When measuring the luminance of the acrylic film, the distance from the end surface (I) to the end surface (O) is 5 cm or more when the length of the light guide plate used in a small display such as a mobile phone or a game machine is assumed. It is preferable. Assuming that it is used for a larger screen, it is more preferably 10 cm or more, and further preferably 20 cm or more. When the distance from the end face (I) to the end face (O) is 20 cm or more, a slight difference in transmission loss due to light absorption, scattering, reflection or the like is observed as a large luminance difference. A film capable of obtaining high brightness even when the distance from the end face (I) to the end face (O) is long is particularly suitable for a light guide plate application used in a long optical path.

[Auxiliary]
In the resin composition (C) in the present invention, an auxiliary agent can be added to such an extent that the luminance is not impaired. Specifically, lubricants, plasticizers, antibacterial agents, antifungal agents, light stabilizers, ultraviolet absorbers, bluing agents, antistatic agents, heat stabilizers, and the like may be added.

[Thickness of acrylic film]
The thickness of the acrylic film of the present invention is preferably 500 μm or less. If it is 500 micrometers or less in thickness, the request | requirement of film thickness reduction is especially satisfy | filled and it can use suitably as a thin light-guide plate use. The thickness of the acrylic film is more preferably 50 to 500 μm, further preferably 50 to 400 μm, and particularly preferably 50 to 350 μm.

[Method of forming acrylic film]
The acrylic film of the present invention can be formed using a melt extrusion method using a T die or the like, or a solution casting method. Among these, the melt extrusion method is preferable because it can be produced efficiently and inexpensively.

  The molded acrylic film can be wound on a roll such as a paper tube or a plastic core, or cut or punched into a predetermined size one by one. When producing a light guide plate having a concavo-convex structure using a transfer mold, it is preferable that the light guide plate is wound in a roll shape because it can be produced continuously and efficiently at low cost.

〔Light guide plate〕
The light guide plate of the present invention can take the form of a thin light guide plate in which irregularities are provided on both sides or one side of the acrylic film of the present invention.

  Examples of the method for imparting the concavo-convex shape include a method of hot pressing using a transfer mold member having a concavo-convex shape on the surface, a photocurable resin composition applied to the acrylic film surface, and a photocurable resin composition applied. There is a method of transferring the uneven shape of the transfer surface of the transfer mold member to the layer. Moreover, you may give a dot shape by printing. These concavo-convex shape and the method of imparting the concavo-convex shape may be used alone or in combination.

  Specific examples of the uneven shape of the light guide plate include a mat structure, a dot shape, and a prism array arrangement structure. Since the acrylic film of this invention can give these shapes continuously, a light-guide plate can be manufactured with sufficient productivity.

  The light guide plate of the present invention is particularly suitable as a light guide plate for use in thin liquid crystal display devices, thin personal computer keyboard lighting, thin mobile phone keypad lighting, etc., because it has excellent light transmission characteristics and satisfies the demand for thinning. Can be used.

[Backlight unit]
The backlight unit of the present invention is characterized by incorporating the light guide plate of the present invention, and the other configurations can be the same as those of the conventional backlight unit. For example, the light guide plate of the present invention is incorporated by arranging a light source (such as a plurality of LEDs) on the side surface (incident surface) of the light guide plate and laminating a reflection sheet on the lower surface side of the light guide plate as necessary. A backlight unit may be manufactured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these.

  The measurement methods in the examples are shown below.

[Total light transmittance of acrylic film]
The obtained acrylic film having an average thickness of 350 μm was cut into a 5 cm square and measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K7361-1.

[Acrylic film haze]
The obtained acrylic film having an average thickness of 350 μm was cut into a 5 cm square and measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K7136.

[Brightness of acrylic film]
As a light source, a reflective sheet made by Reiko Co., Ltd. was placed on a base on which 20 LED lamps (NSC 335 made by Nichia Chemical Co., Ltd.) having a thickness of 450 μm were placed, and an acrylic film was placed thereon. One reflective sheet was installed on top (see FIG. 1). The acrylic film had a square planar shape and a size of 20 cm in length, 5 cm in width, and a film thickness of 350 μm. The distance from the end face (I) to the end face (O) is 20 cm. In addition, the end surface (I) and the end surface (O) were polished using a rotary polishing machine (AP-120 manufactured by Kasai Shoko Co., Ltd.) and using # 1200 polishing paper.

  A luminance meter CS-100A manufactured by Konica Minolta was installed at a position 1 m from the end face (O), light was transmitted from the end face (I), and the brightness of the light emitted from the end face (O) was measured.

[Elongation at break of acrylic film]
The obtained acrylic film having an average thickness of 350 μm was punched into a dumbbell No. 1 type using a dumbbell super dumbbell cutter (trade name: SDK-100D), and a tensile test was conducted at a room temperature of 50 mm / min at room temperature. It was. At that time, the average elongation at the time when the sheet broke was defined as the breaking elongation.

  Below, the raw material preparation method of an acrylic film and the Example and comparative example of an acrylic film are demonstrated.

[Acrylic polymer (A)]
As the acrylic polymer (A), an acrylic polymer (trade name: Dianal BR80) manufactured by Mitsubishi Rayon Co., Ltd. was used.

[Fluorine resin (B)]
As the fluorine-based resin (B-1), a vinylidene fluoride homopolymer (trade name: KYNER720) manufactured by Arkema Inc. is used, and as the fluorine-based resin (B-2), vinylidene fluoride single-polymer manufactured by Kureha Co., Ltd. is used. Combined product (trade name: Kureha KF Polymer T # 1000) was used.

[Example 1]
Vent type twin screw extruder (Toshiba Machine) in which 95 parts by mass of the acrylic polymer (A) and 5 parts by mass of the fluororesin (B-1) were mixed with a Henschel mixer, and the resulting mixture was heated to 200 to 240 ° C. (TEM Co., Ltd. TEM-35B) was supplied and kneaded to obtain pellets.

  The pellets produced by the above method were dried at 80 ° C. for a whole day and night. The dried pellets were supplied to a 30 mmφ non-vent screw type extruder equipped with a 15-cm wide T die, and the extruder temperature was 200 to 240 ° C., T Film formation was performed at a die temperature of 240 ° C. and a cooling roll temperature of 95 ° C. to produce an acrylic film having a thickness of 350 μm. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

[Example 2]
90 parts by mass of the acrylic polymer (A), the fluororesin (B-2) was used instead of the fluororesin (B-1), and the amount was changed to 10 parts by mass. An acrylic film having a thickness of 350 μm was prepared. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

Example 3
85 parts by mass of the acrylic polymer (A), the fluororesin (B-2) is used instead of the fluororesin (B-1), and the amount is 15 parts by mass. An acrylic film having a thickness of 350 μm was prepared. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

Example 4
Example 1 except that 80 parts by mass of the acrylic polymer (A), fluorine resin (B-2) was used instead of the fluorine resin (B-1), and the amount thereof was 20 parts by mass. An acrylic film having a thickness of 350 μm was prepared. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

Example 5
70 parts by mass of the acrylic polymer (A), the fluororesin (B-2) was used instead of the fluororesin (B-1), and the amount was 30 parts by mass in the same manner as in Example 1, An acrylic film having a thickness of 350 μm was produced. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

[Comparative Example 1]
20 parts by mass of the acrylic polymer (A), the fluororesin (B-2) is used instead of the fluororesin (B-1), and the amount is 80 parts by mass. An acrylic film having a thickness of 350 μm was prepared. The brightness could not be evaluated because the film became cloudy.

[Comparative Example 2]
Using only the acrylic polymer (A), an acrylic film having a thickness of 350 μm was produced in the same manner as in Example 1. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

[Comparative Example 3]
The acrylic polymer (A) is replaced by 90 parts by mass, and a polylactic acid resin (Mitsui Chemicals, trade name: Lacia H-100) is used instead of the fluorine resin (B-1). An acrylic film having a thickness of 350 μm was produced in the same manner as in Example 1 except that the part was made a part. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

  When comparing the results of Examples 1 to 5 with the results of the acrylic film consisting only of the acrylic polymer (A) of Comparative Example 2, the light transmission loss is suppressed by adding the fluororesin (B). It can be seen that a film with improved luminance at the end face (O) and improved elongation at break can be obtained. In Comparative Example 1, light could not pass through to the end face (O) due to crystallization of the fluororesin (B). In the acrylic film of Comparative Example 3 in which polylactic acid was added instead of the fluororesin, the luminance of the end face (O) was greatly reduced.

  The acrylic film provided by the present invention can be applied to a light guide plate used for thin liquid crystal displays, flat panel displays, plasma displays, mobile phone displays, mobile phone keypad lighting, personal computer keyboard lighting, and other signs.

  In addition to light guide plate applications, various types of housings that require transparency, such as electrical and electronic parts, optical filters, automobile parts, mechanical mechanism parts, housings for OA equipment and home appliances, and their parts, general goods, etc. Applicable to the field. Specifically, Fresnel lens, polarizing film, polarizer protective film, retardation film, light diffusion film, viewing angle widening film, reflective film, antireflection film, antiglare film, brightness enhancement film, prism sheet, microlens array It can be applied to conductive materials for touch panels, reflective materials used for road signs and the like.

It is a figure explaining the measuring method of the brightness | luminance of an acrylic film.

Explanation of symbols

1 Acrylic film 2 Reflective sheet 3 Light source 4 End face (I)
5 End face (O)

Claims (3)

An acrylic film comprising a resin composition (C) containing an acrylic polymer (A) and a fluororesin (B),
The mass ratio (A / B) of the acrylic polymer (A) to the fluororesin (B) is in the range of 30/70 to 99.9 / 0.1,
For optical use, light is incident from the end face of the acrylic film, and the brightness of the light emitted from the opposite end face facing the end face is greater than the brightness of the film made of only the acrylic polymer (A) measured under the same conditions. Acrylic film.   The light-guide plate formed by providing uneven | corrugated shape to both surfaces or one side of the acrylic film of Claim 1.   A backlight unit in which the light guide plate according to claim 2 is incorporated.

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