JP4314080B2 - Reflector film and reflector using the same - Google Patents

Description

  The present invention relates to a reflector film used for a reflector of a light source such as a liquid crystal display device, and a reflector using the same.

  As a lighting method using a backlight of a liquid crystal display device used in a color television or a personal computer, a sidelight method in which light from a light source is irradiated onto a liquid crystal display panel through a light guide plate such as a transparent resin, and The direct type that directly irradiates the liquid crystal display panel with the light from the light source is used, and the sidelight method is used for general-purpose relatively small-screen liquid crystal screens such as notebook computers, and the color of the large screen A liquid crystal screen such as a television uses a direct type because high brightness is required.

  A schematic cross-sectional view of an example of a backlight unit using a sidelight system is shown in FIG. In the backlight unit 1, the light beam emitted from the light source 2 disposed on one side of the transparent light guide plate 5 is directly incident on the light guide plate 5, reflected by the reflector 3, and incident on the light guide plate 5. The incident light is reflected by the reflecting plate 4 disposed on the lower side of the light guide plate 5, passes through the light guide plate 5 again, and is diffused by the light diffuser 6 disposed on the upper side of the light guide plate 5. The liquid crystal display body 7 disposed on the upper side of the diffuser 6 is uniformly irradiated.

  A schematic cross-sectional view of an example of a backlight unit using a direct type is shown in FIG. In the backlight unit 1, the light emitted from the light source 2 disposed between the reflector 4 and the light diffuser 6 is directly or directly reflected by the reflector 4 and diffused by the light diffuser 6. The liquid crystal display body 7 disposed on the upper side of the body 6 is uniformly irradiated.

  As an example of the reflector used in the backlight unit configured as described above, Patent Document 1 discloses melting a resin composition containing a polyolefin resin or a polyester resin and containing an inorganic filler such as calcium carbonate or titanium oxide. A light reflecting plate for a porous backlight unit is disclosed in which an unstretched sheet is formed by extrusion or the like, and then the obtained unstretched sheet is uniaxially or biaxially stretched. According to this publication, an unstretched sheet containing an inorganic filler is uniaxially or biaxially stretched to form an opening between particles of the inorganic filler, thereby forming a porous sheet. The light reflectance of 95% or more at the wavelength of the light is obtained. And this porous sheet is integrally formed with the light guide plate in the backlight unit using the sidelight system shown in FIG. 1 and used as a light reflecting sheet.

  Patent Document 2 also discloses a white laminated polyester film for a surface light source reflecting member used in a backlight unit using a sidelight system. This white laminated polyester film is a white laminated polyester film in which white polyester layers containing inorganic fine particles are laminated on both sides of a white polyester layer having fine bubbles. The white polyester layer having fine bubbles generates fine bubbles by adding a thermoplastic resin such as polyolefin resin that is incompatible with polyester and stretching it uniaxially or biaxially. Therefore, this three-layer white laminated polyester film is a non-stretched laminated sheet formed by coextrusion molding a white resin layer containing inorganic fine particles / incompatible resin layer / white resin layer containing inorganic fine particles into a sheet shape. Then, the unstretched laminated sheet is biaxially stretched in the longitudinal direction and the transverse direction to obtain a target white laminated polyester film for a surface light source reflecting member. The white laminated polyester film obtained in this way is laminated on a substrate, and used as a reflector in a backlight unit using the sidelight system shown in FIG. As shown in these prior arts, the light reflecting sheet and the white laminated polyester film used for the backlight unit using the sidelight method are both uniaxial or biaxially stretched films used as flat sheets. Yes.

  On the other hand, Patent Document 3 is disclosed as a reflector used in a backlight unit using a direct type. This reflecting plate is obtained by laminating three stretched films having the same structure as the white laminated polyester film disclosed in Patent Document 2 on a metal plate such as aluminum or copper. As shown in FIG. 2, a flat plate made of a stretched film-coated metal plate is pressed at two locations on both sides and bent into a substantially U-shape to form a reflector.

  As shown in FIG. 2, in the conventional backlight unit using the direct type, one slightly large light source is arranged between the reflector and the light diffuser, and the light emitted from one light source is irradiated. The liquid crystal display body disposed on the upper side of the light diffusing body is uniformly irradiated by being directly or directly reflected by a reflector and diffused by a light diffusing body. However, the backlight unit is thick due to the large light source, which is slightly poor in size reduction, and the brightness of the liquid crystal display body is slightly poor because only one light source is used. In order to remedy these drawbacks, a backlight unit using a direct type using a plurality of small light sources has been proposed as shown in a schematic cross section in FIG. In the backlight unit using a plurality of small light sources, as shown in FIG. 3, the reflector 4 is bent into a substantially U shape so as to surround each of a plurality (five in the figure) of the small light sources 2. By arranging a plurality of the small reflection spaces 9 in parallel, the light rays emitted from the individual light sources 2 are reflected directly or by the reflection plate 4 of each reflection space 9 and diffused by the light diffuser 6. The liquid crystal display body 7 disposed on the upper side of the diffuser 6 is uniformly irradiated. In this case, the light beam emitted from the light source 2 disposed in each reflection space 9 is irradiated and diffused only to the light diffuser 6 portion directly above each reflection space 9, so that the liquid crystal display 7 is As a whole, the liquid crystal screen is very bright because it is irradiated with the sum of the light rays diffused from the individual reflection spaces 9. Further, since a small light source is used, the thickness of the reflection space 9 can be reduced, and the backlight unit can be configured to be thin and compact.

  However, the individual reflective spaces shown in FIG. 3 are formed by bending a reflector formed by laminating a uniaxial or biaxially stretched film used on the conventional sidelight type backlight unit or direct type backlight unit. When a plurality of 9 are arranged side by side, the uniaxial or biaxially stretched film having a small curvature radius of the bent portion 8 where the adjacent reflecting spaces 9 are connected to each other and having poor workability is bent during or after the bending process. The film peels off in the vicinity of the portion 8 and floats from the substrate, causing wrinkles on the film, resulting in non-uniform reflection of light at that portion.

Prior art document information relating to the present application includes the following.
Japanese Patent Application Laid-Open No. 07-230004 JP 2002-09881 A JP-A-10-177805

  The present invention is a film for a reflector used for a reflector of a light source such as a liquid crystal display device excellent in processability, in which a film does not peel when a film laminate formed by laminating a film on a substrate is bent, And it aims at providing the reflecting plate using the same.

According to the present invention, a film for a reflecting plate made of an unstretched white polyolefin film containing a polyolefin resin containing titanium oxide having a particle size of 0.2 to 0.5 μm is laminated and bonded to a metal plate. A reflector is provided .

In the reflector of the present invention ,
1. The polyolefin resin of the reflector film is an ethylene / propylene copolymer,
2. The reflector film contains 20 to 80% by weight of titanium oxide,
3. The elongation at break of the reflector film is 150 to 1500%,
4). The average reflectance of light having a wavelength of 550 nm of the reflector film is 85% or more;
5). The metal plate is an aluminum alloy plate, a copper alloy plate, a stainless steel plate, a plated steel plate, or a surface-treated steel plate ,
Is preferred.

  The film for a reflector according to the present invention is composed of an unstretched film obtained by adding a white pigment such as titanium oxide to a polyolefin resin such as an ethylene / propylene copolymer, and has a breaking elongation of 150 to 1500% and an amount of 85% or more. It has a reflectivity of 550 nm, and the reflectivity hardly decreases even when irradiated for 100 hours, and can be suitably applied as a film for a reflector. In addition, the reflector of the present invention is formed by laminating and bonding the above-described film for the reflector of the present invention to a metal plate, and is excellent in processing adhesion and bending workability. It does not peel off or crack in the film.

  In the present invention, a non-stretched film obtained by adding a white pigment to a polyolefin resin having a large elongation at break and extremely excellent processability as a resin film is used as a film for a reflector of a backlight unit. It has been found that it is possible to manufacture a backlight unit that does not peel off the film even when subjected to severe bending with a small radius of curvature, and can obtain uniform light reflection. The present invention will be described below.

  The film for a reflector of the present invention uses an unstretched film obtained by adding a white pigment to a polyolefin resin. Examples of the polyolefin resin include low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, ethylene / propylene copolymer, polymethylpentene, and norbornene. In the present invention, as shown in FIG. It is preferable to use an ethylene / propylene copolymer having a large elongation at break and excellent workability so as not to cause peeling by severe bending on the reflector.

  As the white pigment to be contained in the polyolefin resin, inorganic pigments such as calcium carbonate, silicon oxide, titanium oxide, zinc oxide and boron nitride, white organic pigments and the like can be used. Moreover, micro hollow bodies, such as a silica balloon and a glass microballoon, can also be used as a white pigment. Furthermore, it is possible to use a fluorescent whitening agent in combination. These white pigments are preferably contained in the polyolefin resin in an amount of 20 to 80% by weight. When the content in the resin is less than 20% by weight, sufficient light reflectance cannot be obtained when a reflector is used. If the content in the resin exceeds 80% by weight, the film will crack. As the white pigment, it is preferable to use titanium oxide which is inexpensive and can be contained in a large amount in the resin.

  Furthermore, the film made of polyolefin resin containing the above white pigment preferably has a reflectance of 85% or more of light having a wavelength of 440 to 700 nm, typically, light having a wavelength of 550 nm. If a white film having a reflectance of light having a wavelength of 550 nm is less than 85%, a liquid crystal display device having sufficient brightness cannot be obtained.

  When a white film is irradiated with light, the reflected light is reflected and interferes with the particle interface of the white pigment in the film. However, if the particle diameter of the white pigment is one-half of the wavelength of the light, the interference becomes stronger and the reflected light is reflected. Become stronger. Therefore, it is preferable that the particle diameter of the white pigment is about 0.2 to 0.5 μm which is strengthened by interference with light having a wavelength in the above range.

  The film made of polyolefin resin containing a white pigment as described above preferably has a breaking elongation of 150 to 1500%. When the elongation at break is less than 150%, the processability is lowered when a white pigment is contained, and when the film is severely bent, the film is cracked. When the elongation at break exceeds 1500%, the film surface is softened, and the surface is easily wrinkled during handling.

  The reflector film of the present invention having the above characteristics can be produced as follows. That is, a polyolefin resin pellet and a white polyolefin resin masterbatch pellet containing 100% by weight or more of a white pigment in the same polyolefin resin are weighed so that the mixed white pigment is 20 to 80% by weight. Then, they are heated and melted using an extruder, extruded from a T die at a thickness of 50 to 300 μm, and formed into an unstretched film.

  The reflector film of the present invention thus obtained is laminated and bonded to a metal plate to obtain the reflector of the present invention. As the metal plate, aluminum alloy plate, copper alloy plate such as brass, bronze, white copper, stainless steel plate, galvanized steel plate, aluminum plated steel plate, zinc alloy plated steel plate such as zinc-nickel, zinc-aluminum, nickel plated steel plate, nickel- A nickel alloy plated steel plate such as tin, a surface-treated steel plate formed by non-chromium chemical conversion treatment, or the like can be used. The above-mentioned film for a reflector according to the present invention is laminated and adhered to the metal plate via an adhesive to these metal plates to obtain a reflector. As the adhesive, any adhesive that can bond a polyolefin and a metal plate can be used. However, an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and anhydrides thereof can be used for the polyolefin resin. It is preferable to use a so-called acid-modified polyolefin resin-based adhesive obtained by graft polymerization of a product of 2% or less.

  The reflection plate of the present invention obtained as described above is a backlight unit using a sidelight system as shown in FIG. 1, or a slightly larger size between the reflection plate and the light diffuser as shown in FIG. A single light source is provided, and the light emitted from the single light source is directly or directly reflected by a reflector and diffused by a light diffuser, so that the liquid crystal display disposed above the light diffuser is uniform. However, it is preferable to apply a reflector plate so as to surround each of a plurality of small light sources as shown in FIG. The present invention can be particularly preferably applied to a backlight unit using a direct type system configured by arranging a plurality of small reflective spaces that are bent in a U-shape.

  In the reflector of the present invention, by using a non-stretched film obtained by adding a white pigment to a polyolefin resin having a large elongation at break and excellent workability as a film for a reflector, as a film for a reflector of a backlight unit. Since the film does not peel off even when severe bending processing is performed with a small curvature radius of the bent portion, a bent portion having a small partial curvature radius that connects individual small reflective spaces as shown in FIG. Even if it is molded, it is peeled off in the vicinity of the bent portion and lifted off from the substrate, so that the reflection of the light does not become uneven at that portion, and it can be manufactured as a backlight unit capable of obtaining uniform light reflection.

  In the direct type backlight unit using a plurality of small light sources manufactured in this way, the light emitted from each light source is reflected directly or by the reflecting plate of each reflecting space and is a light diffuser. And the liquid crystal display disposed on the upper side of the light diffuser is uniformly irradiated with the sum of the light rays diffused from the individual reflection spaces, so that the liquid crystal screen becomes very bright. In addition, since a small light source is used, the thickness of the reflection space can be reduced, and the backlight unit can be configured to be thin and compact.

Hereinafter, the present invention will be described in more detail with reference to examples.
Mixing pellets of ethylene / propylene copolymer (ethylene: 40 mol%) and white pellets of a masterbatch containing 150% by weight of titanium oxide with an average particle size of 0.4 μm in this ethylene / propylene copolymer Then, it was melted by heating at 230 ° C. using an extruder, extruded from a T-die, and formed as an unstretched film indicated by sample numbers: 1 to 7 having the titanium oxide content and thickness shown in Table 1, and a reflecting plate It was set as the test material of the film for a camera.

  The reflectance of light having a wavelength of 550 nm of these unstretched films of sample numbers 1 to 7 was measured using a spectrophotometer (trade name: U-3400, manufactured by Hitachi, Ltd.). The elongation at break was measured using Tensilon. The results are shown in Table 2. For comparison, a commercially available biaxially stretched white laminated polyester film having a thickness of 188 μm (trade name: Product name: a white polyester layer containing inorganic fine particles is laminated on both sides of a white polyester layer having fine bubbles. The elongation at break of E-60 (manufactured by Toray Industries, Inc.) was also measured with Tensilon (sample number: 8).

These film samples Nos. 1 to 8 were laminated and bonded to an aluminum alloy plate (JIS 5052) using an acid-modified polyolefin resin adhesive (trade name: SC-481, manufactured by Sony Chemical Corporation) for a reflector. It was set as the processing test material. A polyester film for comparison (sample number: 8) was laminated and bonded using a polyester-based adhesive (trade name: Olivevine-GX, manufactured by Toyo Ink Co., Ltd.) to obtain a processed specimen for a reflector. On the film surface of these processed specimens, using a cutter knife, put a wrinkle with a depth that reaches the metal plate in the form of a grid at intervals of 5 mm, and then apply Erichsen overhanging with an overhang of 2 mm. The film peeling state after the processing was observed with the naked eye, and the processing adhesion was evaluated according to the following criteria.
○: No peeling is observed.
X: Peeling is recognized.
The results are shown in Table 2.

Moreover, 0T bend | folding was performed to the test material for a process, the generation | occurrence | production condition of the crack of the film of the bending process part after a process was observed visually, and the bending workability was evaluated on the following reference | standard.
○: No cracks are observed.
X: Generation | occurrence | production of a crack is recognized.
The results are shown in Table 2.

  As shown in Table 2, the film for a reflector of the present invention has a large elongation at break, a large reflectance of a light beam of 550 nm, and the reflectance is hardly lowered even when irradiated for a long time. Moreover, even if it is laminated and adhered to a metal plate and subjected to a severe bending process, the film does not peel off or a film crack does not occur.

  The film for a reflector according to the present invention is composed of an unstretched film obtained by adding a white pigment such as titanium oxide to a polyolefin resin such as an ethylene / propylene copolymer, and has a breaking elongation of 150 to 1500% and an amount of 85% or more. It has a reflectivity of 550 nm, and the reflectivity hardly decreases even when irradiated for 100 hours, and can be suitably applied as a film for a reflector. In addition, the reflector of the present invention is formed by laminating and bonding the above-described film for the reflector of the present invention to a metal plate, and is excellent in processing adhesion and bending workability. It does not peel off or crack in the film. Therefore, the present invention can be particularly preferably applied to a direct type backlight unit using a plurality of small light sources.

FIG. 3 is a schematic cross-sectional view showing an example of a backlight unit using a sidelight system. The schematic sectional drawing which shows an example of the backlight unit by a direct type. FIG. 5 is a schematic cross-sectional view showing an example of a direct-type backlight unit using a plurality of small light sources.

Explanation of symbols

1: Backlight unit 2: Light source 3: Reflector 4: Reflector 5: Light guide plate 6: Light diffuser 7: Liquid crystal display 8: Bending part 9: Reflection space

Claims (6)

A reflector obtained by laminating and bonding a film for a reflector made of an unstretched white polyolefin film obtained by adding a titanium resin having a particle size of 0.2 to 0.5 μm to a polyolefin resin to a metal plate . The polyolefin resin of the reflector film is an ethylene-propylene copolymer, a reflector according to claim 1. The reflector film is formed by incorporating 20 to 80 wt% of titanium oxide, the reflection plate according to claim 1 or 2. The breaking elongation of the reflector film is 150 to 1,500 percent, a reflection plate according to claim 1. The average reflectance of light having a wavelength 550nm of the reflector film is 85% or more, the reflection plate according to claim 1. The reflecting plate according to claim 1, wherein the metal plate is any one of an aluminum alloy plate, a copper alloy plate, a stainless steel plate, a plated steel plate, and a surface-treated steel plate.

Images