JP2010256480A - Reflection film for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection film for liquid crystal displays which is not colored though including an inorganic phosphor superior in UV resistance in a coating layer and has high light diffusivity exceeding that due to lens effect and shows higher brightness. <P>SOLUTION: The reflection film for the liquid crystal displays includes a white film and a coating layer provided on the film, and the coating layer includes an inorganic phosphor which is excited in a wavelength region of 400 to 450 nm and has an emission peak at a wavelength of 500 to 600 nm, transparent particles, and a binder, wherein a total content of the inorganic phosphor and transparent particles in the coating layer is 50 to 90 wt.% per 100 wt.% of the total weight of the coating layer, a content of the inorganic phosphor is ≥1 wt.%, and the content of the inorganic phosphor is smaller than or equal to the content of transparent particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a reflective film used as a reflective plate in a backlight unit of a liquid crystal display device.

  The backlight unit of the liquid crystal display device includes an edge light type and a direct type depending on the arrangement of light sources (Japanese Patent Laid-Open No. 63-62104). In LCD TVs that have become larger, direct type is the mainstream. In the direct type, the cold cathode ray tubes of the light source are arranged in parallel on the reflecting plate at a predetermined interval.

  Increasing the luminance of the backlight has been a conventional problem, but as a method for solving this problem, a method of applying a transparent particle to the surface of a film to impart a lens effect has been proposed (Japanese Patent Laid-Open No. 2006-2006). -137046). However, a significant improvement in luminance cannot be expected with the lens effect alone.

  In order to improve the luminance of the backlight unit, a method of converting light energy having a wavelength not used for display on a liquid crystal screen into visible light has been proposed. However, even if a phosphor is simply used to convert it into visible light, the film may be colored depending on the light absorption characteristics and light emission characteristics of the phosphor, and accurate color reproduction when used in a backlight unit as a reflective film. Becomes difficult.

  The method of coating the surface of the reflective film with a fluorescent brightening agent (Japanese Patent Laid-Open No. 2002-40214) can provide a reflective film with relatively little coloration, but the effect of improving the brightness is insufficient, and the fluorescent film is fluorescent. The brightening agent itself is deteriorated by ultraviolet rays contained in the light emitted from the cold cathode ray tube, and the reflective film is yellowed with time.

  The development trend of direct type backlights is to reduce the number of cold cathode ray tubes as light sources while maintaining the brightness of the display surface. If the number is reduced, the distance between the cold cathode ray tubes becomes wider, and the difference in luminance between the position just above the cold cathode ray tube and a position slightly away from directly above becomes large, and the luminance unevenness becomes conspicuous. This unevenness in brightness can be eliminated to some extent by imparting light diffusivity to the reflective film by a lens effect that reflects light not only in the front direction but also in a direction deviating from the front side.

JP 63-62104 A JP 2002-40214 A JP 2006-137046 A

  The present invention provides a reflective film for a liquid crystal display device that contains an inorganic phosphor excellent in ultraviolet resistance in a coating layer, has no coloration, has a high light diffusibility exceeding the light diffusibility due to the lens effect, and exhibits higher brightness. It is an issue to provide.

  That is, the present invention comprises a white film and a coating layer provided on the film, the coating layer being excited in a wavelength region of 400 to 450 nm and having an emission peak wavelength of 500 to 600 nm, transparent particles And the total content of the inorganic phosphor and the transparent particles in the coating layer is 50 to 90% by weight per 100% by weight of the coating layer, and the content of the inorganic phosphor is 1% by weight or more. A reflective film for a liquid crystal display device, characterized in that the content of the inorganic phosphor is less than or equal to the content of the transparent particles.

  According to the present invention, an inorganic phosphor excellent in ultraviolet resistance is contained in a coating layer, and there is no coloring, it has high light diffusibility exceeding the light diffusibility due to the lens effect, and exhibits higher luminance. A reflective film can be provided.

Hereinafter, the present invention will be described in detail.
The reflective film for a liquid crystal display device of the present invention comprises a white film and a coating layer provided on the film.

[White film]
In the present invention, a white thermoplastic resin film is used as the white film. As the thermoplastic resin, a thermoplastic aromatic polyester is preferable from the viewpoint of mechanical properties.
Examples of the thermoplastic aromatic polyester include polyethylene terephthalate, polyethylene naphthalene dicarboxylate, and polybutylene terephthalate. The thermoplastic aromatic polyester may be copolymerized with a copolymer component. The ratio of the copolymerization component is, for example, 20 mol% or less.

  When a thermoplastic aromatic polyester film is used as the white film, inorganic particles, organic particles or an incompatible resin is contained in the thermoplastic aromatic polyester and stretched to form a void at the interface with the thermoplastic aromatic polyester. A white film is used. The film may be a single layer, but is preferably a white laminated film comprising a reflective layer and a support layer that supports the reflective layer. This white laminated film will be described below. In addition, when using this white laminated film, in order to suppress yellowing of a reflective layer, it is preferable that an application layer is provided on a reflective layer.

[Reflective layer]
The reflective layer is composed of a thermoplastic aromatic polyester composition having a void volume ratio of preferably 30 to 80%, more preferably 35 to 75%, and particularly preferably 38 to 70%. This void volume fraction is obtained by peeling off the interface between the thermoplastic aromatic polyester, the inorganic particles, the organic particles, and the incompatible resin, and generating voids.

  When inorganic particles or organic particles are used as the substance forming the void of the reflective layer, these particles are preferably 0.3 to 3.0 μm, more preferably 0.4 to 2.5 μm, and particularly preferably 0.8. Particles having an average particle diameter of 5 to 2.0 μm are used. It is preferable to use inorganic particles or organic particles having an average particle diameter in this range to prevent aggregation of the particles and to stretch without breaking.

  When inorganic particles or organic particles are used, the amount is preferably 31 to 60 parts by weight, more preferably 35 to 55 parts by weight, and particularly preferably 37 to 50 parts by weight per 100 parts by weight of the polyester composition of the reflective layer. By using in this range, the reflectance can be kept high, deterioration due to ultraviolet rays can be prevented, and at the same time, breakage during stretching of the film can be prevented.

  When inorganic particles are used as the substance forming the void, it is preferable to use a white pigment from the viewpoint of obtaining high reflection performance. As the white pigment, for example, titanium oxide, barium sulfate, calcium carbonate, silicon dioxide particles, preferably barium sulfate particles are used. The barium sulfate particles may be either plate-like or spherical. A particularly good reflectance can be obtained by using barium sulfate particles.

  When organic particles are used as the substance for forming voids, organic polymer particles such as crosslinked polystyrene and acrylic particles can be used, and particles made of an incompatible resin described below can be used.

When using an incompatible resin as a substance that forms voids, examples of the incompatible resin include a polyolefin resin and a polystyrene resin, specifically, for example, poly-3-methylbutene-1,
Poly-4-methylpentene-1, polyethylene, polypropylene, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polyfluorostyrene, cellulose acetate cellulose propionate, Polychlorotrifluoroethylene can be used, and polypropylene and polymethylpentene are particularly preferably used. Since these polypropylenes and polymethylpentenes are highly transparent, they are optimal because they can suppress light absorption and improve reflectance.

  When an incompatible resin is used, the ratio is preferably 5 to 30 parts by weight, more preferably 8 to 25 parts by weight, and particularly preferably 10 to 20 parts by weight per 100 parts by weight of the thermoplastic aromatic polyester composition of the reflective layer. Used in. By using in this range, it is possible to prevent breakage during stretching of the film while forming the necessary voids.

[Support layer]
The support layer is made of a polyester composition and contains, for example, 0.5 to 30% by weight, preferably 1 to 27% by weight, and more preferably 2 to 25% by weight of inorganic particles per 100 parts by weight of the polyester composition. If it is less than 0.5% by weight, it is not preferable because sufficient slipperiness cannot be obtained, and if it exceeds 30% by weight, the strength as a support layer for supporting the reflective layer cannot be maintained, which may lead to film breakage. Not preferable. The average particle diameter of the inorganic particles is preferably 0.1 to 5 μm, preferably 0.5 to 3 μm, and more preferably 0.6 to 2 μm. If the thickness is less than 0.1 μm, the particles are likely to be aggregated, and if it exceeds 5 μm, coarse protrusions are formed and the film may be broken.

[Coating layer]
The coating layer is composed of an inorganic phosphor that is excited in a wavelength region of 400 to 450 nm and has an emission peak wavelength of 500 to 600 nm, transparent particles, and a binder composition. In the present invention, it is necessary that inorganic phosphors and transparent particles are mixed in the coating layer. When transparent particles are applied to the surface of a white film without using an inorganic phosphor together, the brightness is improved by the lens effect of the transparent particles, but the reflected light cannot be sufficiently diffused. On the other hand, when an inorganic phosphor is applied to the surface of a white film without using transparent particles, the brightness is greatly improved because the inorganic phosphor converts part of the light emitted from the backlight into a wavelength component with high relative visibility. However, the inorganic phosphor is buried in the binder, and the light diffusing effect of the inorganic phosphor is not exhibited.

  In the reflective film of the present invention, the inorganic phosphor and the transparent particles are mixed in the coating layer, whereby the inorganic phosphor is dispersed in the coating layer without being buried or aggregated in the binder. And since the light component converted into visible light by light excitation light emission in inorganic fluorescent substance is light-emitted toward all directions, the reflective film which has high light diffusibility and shows high brightness | luminance can be obtained.

  The total content of the inorganic phosphor and the transparent particles in the coating layer is 50 to 90% by weight, preferably 60 to 80% by weight, per 100% by weight of the total weight of the coating layer. If it is less than 50% by weight, a sufficient brightness enhancement effect cannot be obtained, and if it exceeds 90 parts by weight, the inorganic phosphor and the transparent particles may peel off from the surface of the white film.

  The content of the inorganic phosphor in the coating layer is 1% by weight or more, and the content of the inorganic phosphor is less than or the same as the content of the transparent particles. When the inorganic phosphor is contained in a larger amount than the transparent particles, the lens effect of the transparent particles is hardly exhibited. On the other hand, if the content of the inorganic phosphor is less than 1% by weight, the effect of improving luminance is small. The content of the inorganic phosphor is particularly preferably 5 to 30% by weight. When the content is within this range, the inorganic phosphor and the transparent particles tend to be more uniformly dispersed in the coating layer, and the higher light Diffusivity and brightness can be obtained.

[Inorganic phosphor]
In the present invention, it is important to use an inorganic phosphor as the phosphor to be contained in the coating layer. By using an inorganic phosphor, a reflective film for a liquid crystal display device having excellent ultraviolet resistance can be obtained. On the other hand, when an organic substance is used as the phosphor, the phosphor is decomposed by ultraviolet rays, and the film is yellowed by ultraviolet rays after long-term use.

  In the present invention, an inorganic phosphor that is excited in the wavelength region of 400 to 450 nm and has an emission peak wavelength of 500 to 600 nm is used. By using an inorganic phosphor that satisfies the conditions of the excitation wavelength and the emission peak, high luminance can be obtained without greatly biasing the color. Since the light from the cold cathode ray tube hardly contains light having a wavelength shorter than 400 nm, the excitation wavelength of the inorganic phosphor may extend over a region having a wavelength shorter than 400 nm. As an inorganic phosphor that satisfies this condition, an inorganic phosphor containing an activator is formed based on an alkaline earth metal sulfide having a rock salt type crystal structure, an alkaline earth metal composite oxide, or a lanthanum phosphate compound. Can be used.

As the alkaline earth metal sulfide, for example, zinc sulfide (ZnS), strontium sulfide (SrS), or yttrium oxide (Y ₂ O ₂ ) can be used.
As the alkaline earth metal composite oxide may be used such as barium, magnesium, aluminum composite oxide _(BaMgAl 10 _{O 17).}

  As the activator, for example, Eu, Cu, Mn, Al, Ce, Tb, Ba, Sr, Ag can be used, and further, for example, a combination of Eu, Cu and Al, or a combination of Ce and Tb. Combinations, combinations of Ba and Eu, and combinations of Ba, Sr, and Eu can be used.

Particularly preferred inorganic phosphors are strontium sulfide (SrS) or yttrium oxide (Y ₂ O ₂ ) as a base material, inorganic phosphors containing europium (Eu) and / or copper (Cu) as activators, barium magnesium -An aluminum composite oxide (BaMgAl ₁₀ O ₁₇ ) is used as a base, an inorganic phosphor containing europium (Eu) and / or manganese (Mn) as an activator, and a lanthanum phosphate (LaPO ₄ ) is used as a base for activation. An inorganic phosphor containing Ce and / or Tb as a substance.

When the activator is Eu, for example, Eu ₂ O ₃ can be used as the activator. In this case, the content of the activator _Eu 2 _{O 3} in the inorganic phosphors, based on the total weight of the inorganic phosphors, such as 0.01 to 10% by weight.

  When the activator is Mn, for example, MnO can be used as the activator. In this case, the content of the activator MnO in the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

When the activator is Ce, for example, CePO ₄ can be used as the activator. In this case, the content of the activator CePO _{4 in} the inorganic phosphor is, for example, 0.01 to 35% by weight based on the total weight of the inorganic phosphor.

When the activator is Tb, for example, Tb ₄ O ₇ can be used as the activator. In this case, the content of the activator Tb ₄ O _{7 in} the inorganic phosphor is, for example, 0.01 to 25% by weight based on the total weight of the inorganic phosphor.

If activator is Cu, it can be used as an activator e.g. Cu 2 _S. In this case, the content of the activator Cu ₂ S in the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

When the activator is Al, for example, Al ₂ S ₃ can be used as the activator. In this case, the content of the activator Al ₂ S _{3 in} the inorganic phosphor is, for example, 0.01 to 1% by weight based on the total weight of the inorganic phosphor.

  The inorganic phosphor is, for example, in the form of particles and the shape of the particles is not limited, but for example, a spherical one can be used. The average particle diameter of the particles is, for example, 2 to 10 μm, preferably 3 to 7 μm. By using a particulate inorganic phosphor having an average particle diameter in this range, it is possible to uniformly disperse in the coating liquid, and to obtain a coating layer in which the phosphor is uniformly distributed.

Inorganic phosphors are commercially available. For example, the following can be used.
As green light emitting inorganic phosphors, 2210 (ZenS manufactured by Kasei Optronics Co., Ltd. is used as a base material, Cu is used as an activator), E7031-2 (La ₂ O ₂ S manufactured by Nemoto Special Chemical Co., Ltd. is used as a base material, and Eu is used as an activator material. ), E4011-1 (SrAl ₂ O ₄ manufactured by Nemoto Special Chemical Co., Ltd. and Eu as an activator) can be used.

As a red inorganic phosphor, D1110 (Nemoto _Co., as a host of Y 2 _{O 3,} consisting of Eu as activator) can be used.

As a blue inorganic phosphor, D1230 (SrS manufactured by Nemoto Special Chemical Co., Ltd. is used as a base material and Eu is used as an activator), E2031-2 (BaMgAl ₁₀ O ₁₇ manufactured by Nemoto Special Chemical Co., Ltd. is used as a base material, and Eu is used as an active material) Can be used.

As a green inorganic phosphor, KX732A (Kasei Optronics Co., barium, magnesium, aluminum composite oxide _(BaMgAl 10 _{O 17)} as a matrix, consisting of Eu and Mn as an activator) can be used.

As a yellow-green inorganic phosphor, P22-GN4 (a Kasei Optonix Ltd. ZnS as a host, Cu, comprising Al as activator), LP-G2 of (Kasei Optonix Ltd. LaPO ₄ as a matrix, Ce, and Tb As an activator).

  The inorganic phosphor is preferably particles having an average particle diameter of 1 to 15 μm. By using a particulate inorganic phosphor having a particle size in this range, the light reflected by the reflective film can be diffused and uniformly dispersed with the transparent particles in the coating layer.

[Transparent particles]
As the transparent particles, either inorganic transparent particles or organic transparent particles can be used. These may use a plurality of particles in combination. The transparent particles are particles made of a transparent material, and the light transmittance of the material itself constituting the transparent particles is 50% or more, preferably 60% or more, and more preferably 70% or more. The light transmittance is a value at 550 nm, but preferably has no light absorption in the visible light region.

  As the organic transparent particles, for example, acrylic particles, silicone particles, and styrene particles can be used. Acrylic particles and styrene particles are preferred because they hardly absorb light in the visible light region. As the inorganic transparent particles, for example, glass particles can be used.

  The transparent particles are composed of a curved surface or a shape composed of a curved surface and a plane in order to collect light. As this shape, for example, a spherical shape, a rugby ball shape, or a convex lens shape can be used. In order to effectively improve the luminance, an aspect ratio of 3 or less is preferable, and an aspect ratio of 1.2 or less is more preferable. A preferable shape is a spherical particle. The aspect ratio is major axis / minor axis. The particle diameter of the transparent particles is a value obtained by taking the average of the major axis and the minor axis when the transparent particles are not spherical.

  The particle size of the transparent particles is preferably 1 to 100 μm, more preferably 5 μm to 50 μm. If the average particle size is too small or too large, it is not preferable because it is difficult to uniformly disperse with the inorganic phosphor.

[binder]
The transparent particles are supported on the white film with a binder coating. As the binder for the coating layer, for example, acrylic, polyester, polyurethane, polyesteramide, polyolefin, copolymers or blends thereof can be used.

The binder may further contain a crosslinking agent in addition to the above polymer, and for example, an isocyanate compound, a melamine compound, or an epoxy compound can be used as the crosslinking agent. It is preferable to use a crosslinking agent as the binder in addition to the polymer because the adhesiveness to the film tends to be improved.
In the coating layer, the binder accounts for 10 to 50% by weight per 100% by weight of the total weight of the coating layer.

[Ratio of reflection intensity]
In this invention, the relative intensity | strength in the reflection direction 0 degree and 13 degree of reflected light was used as a parameter | index which evaluates the diffusion degree of the reflected light by a reflective film. The greater the reflection intensity in the reflection direction 13 ° (angle of 13 ° from the normal direction) relative to the reflection intensity in the reflection direction 0 ° (film normal direction) when light is incident from the film normal direction, When the reflected light has a strong tendency to diffuse and (reflecting intensity at 13 °) / (reflecting intensity at 0 °) is 0.7 or more, it can be said that the reflected light has sufficient light diffusibility.

  The reflective film of the present invention can obtain a light diffusibility in which (reflecting intensity at 13 °) / (reflecting intensity at 0 °) is 0.7 or more. In a reflective film having a (reflected intensity at 13 °) / (reflected intensity at 0 °) of less than 0.7, the irradiation light from the cold cathode ray tube is more likely to be specularly reflected on the surface of the reflective film. Luminance unevenness at a position slightly shifted from directly above the cold cathode ray tube in the light becomes noticeable.

  The reason why the reflection intensity at an angle of 13 ° was selected as the evaluation target was that the reflected light with a narrower angle than that of the direct type backlight of many liquid crystal televisions returned to the cold cathode ray tube emitted from the backlight again. On the other hand, the reflected light having a wider angle than that is less than 13 ° has a relatively weak intensity when it reaches the display surface and has less influence on luminance unevenness.

[Coating layer]
The components constituting the coating layer are dissolved or dispersed in an organic solvent to form a coating solution, and the coating solution is applied to a white film to form the coating layer.

  In the present invention, the coating layer may be provided directly on the white film. However, if the adhesiveness is insufficient, the white film is previously provided with a corona discharge treatment or a subbing treatment to improve the adhesiveness. Good. The subbing treatment may be a method (in-line coating method) provided in the film manufacturing process, or may be applied separately after the film is manufactured. The material to be applied to the subbing treatment is not particularly limited and may be appropriately selected. As suitable materials, copolymerized polyester, polyurethane, acrylic, various coupling agents and the like can be applied.

The coating layer can be applied by any method. For example, methods such as gravure, roll, spin, reverse, bar, screen, and dipping can be used. A known method can be used as a curing method after coating. For example, a method using active rays such as thermosetting, ultraviolet rays, electron beams, and radiation can be applied. The application may be performed before the completion of the crystal orientation of the film during the production of the base film, or may be performed after the completion of the crystal orientation of the film.
In addition, you may add components other than said inorganic fluorescent substance, transparent particle | grains, and a binder to an application layer as needed.

Hereinafter, the present invention will be described in detail by way of examples.
Measurement and evaluation were performed by the following methods.

(1) Thickness of film A film sample was measured for 10-point thickness with an electric micrometer (K-402B, manufactured by Anritsu), and an average value was obtained to obtain a film thickness.

(2) Thickness of coating layer Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., an arbitrary 10 points in the film cross section were measured at a magnification of 3000 times, and the average value was defined as the thickness of the coating layer.

(3) Average particle diameter of transparent particles Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., 100 particles were arbitrarily measured at a magnification of 1000 times (in the case of other than spherical (long diameter + short diameter) ) / 2), and the average particle size was determined.

(4) Aspect ratio of transparent particles Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., arbitrarily observing 30 exposed particles at a magnification of 500 times, and calculating from the values of major axis and minor axis according to the following formula: The average value was calculated.
Aspect ratio = major axis / minor axis

(5) Luminance improvement rate by coating (5-1) Creation of evaluation backlight unit Take out a direct type backlight unit (32 inches) from a liquid crystal television (BRAVIA KDL-32F1 manufactured by SONY) prepared for evaluation, The reflection sheet originally incorporated in the backlight unit was replaced with a reflection film to be measured, and an evaluation backlight unit was created.
(5-2) Measurement of luminance Using a luminance meter (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-7700), the light receiving portion of the optical fiber for light reception is perpendicular to the optical sheet surface of the backlight unit (0 °). And the distance from the optical sheet surface of the backlight unit for evaluation was fixed at a position of 50 cm, the viewing angle was 2 °, and the luminance was measured 1 hour after the backlight was turned on.
(5-3) Luminance improvement rate The luminance improvement rate is a relative value calculated on the basis of the luminance of the reflective film not provided with the coat layer.
Brightness improvement rate = (luminance of the reflective film provided with the coat layer) / (luminance of the reflective film not provided with the coat layer) × 100 (%)

(6) Reflection intensity in each reflection direction Using a variable angle photometer (GONIOPHOTOMETER GP-200, manufactured by Murakami Color Research Laboratory) to which SX-UI250HQ manufactured by USHIO ELECTRIC is connected as a light source device, it is true to the surface of the reflective film. Light was irradiated from above and the reflection intensity was measured every 0.1 ° in the reflection direction range of −45 ° to 45 ° to obtain a graph of the frequency distribution of the reflection intensity. In this graph, the horizontal axis represents the reflection direction, and the vertical axis represents the reflection intensity. The reflection intensity is measured in 0.1 ° increments from the reflection direction −45 ° to 45 °, and the reflection direction −45 ° to 45 °. The reflection intensity was normalized so that the integrated value of the reflection intensity at ° was 1.0000. The settings of the light source device and the goniophotometer are as follows.
・ Light source: Ultra high pressure mercury lamp 250W (USH-250SC manufactured by USHIO)
-Light beam stop: The diameter of the light stop was set to 2 mm.
-UV cut filter: 42 L (light having a wavelength shorter than 420 nm was cut from the light source) was used to irradiate the reflective film with light.
From the reflection intensity graph, the reflection intensity is read for the reflection direction of 0 ° (normal direction of the film) and the reflection direction of 13 ° (13 ° from the normal direction), and the reflection direction is 13 ° with respect to the reflection intensity at the reflection direction of 0 °. The reflection intensity ratio (reflection intensity at 13 ° / reflection intensity at 0 °) was calculated.

(7) Color change by coating The color change (dy) of the reflective film by coating is the same as the method for measuring the backlight unit produced in (5-1) above, and the coating layer is provided on the film by the measurement method in (5-2) above. The y value before (before coating) and the y value after coating (after coating) were measured and calculated by the following formula.
dy = (y value after coating) − (y value before coating)
The y value was evaluated by using a luminance meter (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-7700), with the light receiving portion of the optical fiber for light reception perpendicular (0 °) to the optical sheet surface of the backlight unit. The distance from the optical sheet surface of the backlight unit for use was fixed at a position of 50 cm, the viewing angle was 2 °, and the y value was measured 1 hour after the backlight was turned on.

[Example 1]
A white film having a total thickness of 225 μm (Teijin Tetron UX02-225 manufactured by Teijin DuPont Films) was prepared as a white film. This is a white laminated film having a two-layer structure comprising a reflective layer containing barium sulfate particles and a support layer in contact therewith.
On the reflective layer of this white laminated film, 70 parts by weight of MBX-15 (manufactured by Sekisui Chemical Co., Ltd., average particle diameter of 15 μm, particles of crosslinked polymethyl methacrylate) is used as transparent particles, and 2210 (chemical conversion Optronics) as inorganic phosphors. 10 parts by weight of ZnS as a base material and Cu as an activator), 30 parts by weight of Udouble S2740 (manufactured by Nippon Shokubai, acrylic binder) as an acrylic binder, and Coronate HL (manufactured by Nippon Polyurethane Industry Co., Ltd.) A coating solution obtained by mixing 7 parts by weight of an isocyanate-based crosslinking agent) and 135 parts by weight of butyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic solvent was applied at a wet coating amount of 25 g / m ² , and then in an oven Was dried at 100 ° C. for 2 minutes to obtain a reflective film. The evaluation results of this reflective film are shown in Table 2.

2210 (manufactured by Kasei Optronics) used as the inorganic phosphor has an excitation wavelength of 260 to 440 nm and an emission peak wavelength of 500 to 570 nm.
KX-732A (manufactured by Kasei Optronics) used as the inorganic phosphor has an excitation wavelength of 240 to 425 nm and an emission peak wavelength of 500 to 550 nm.
MBX-12 (manufactured by Sekisui Plastics Co., Ltd.) used as transparent particles is a crosslinked polymethyl methacrylate particle having an average particle diameter of 12 μm.
MBX-15 (manufactured by Sekisui Plastics Co., Ltd.) used as transparent particles is a crosslinked polymethyl methacrylate particle having an average particle size of 15 μm.
MBX-30 (manufactured by Sekisui Plastics Co., Ltd.) used as transparent particles is a crosslinked polymethyl methacrylate particle having an average particle size of 30 μm.
MBX-50 (manufactured by Sekisui Plastics Co., Ltd.) used as transparent particles is a crosslinked polymethyl methacrylate particle having an average particle diameter of 50 μm.

[Examples 2 to 7]
A reflective film was obtained in the same manner as in Example 1 except that the composition of the coating liquid was changed as shown in Table 1. The evaluation results are shown in Table 2.

[Comparative Example 1]
On the reflective layer of the white laminated film used in Example 1, 80 parts by weight of MBX-15 (manufactured by Sekisui Plastics Co., Ltd., average particle diameter of 15 μm, particles of crosslinked polymethyl methacrylate) as an acrylic binder 15 parts by weight of Udouble S2740 (manufactured by Nippon Shokubai Co., Ltd., acrylic binder), 5 parts by weight of coronate HL (manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanate crosslinking agent) as a crosslinking agent, and butyl acetate as an organic solvent (manufactured by Wako Pure Chemical Industries, Ltd.) A coating solution obtained by mixing 135 parts by weight was applied in a wet coating amount of 25 g / m ² and then dried in an oven at 100 ° C. for 2 minutes to obtain a reflective film. The evaluation results are shown in Table 2. Almost no effect of improving the brightness could be obtained, and almost no effect of diffusing the reflected light could be obtained.

[Comparative Example 2]
In addition to the reflective layer of the white laminated film used in Example 1, 22 parts by weight of inorganic phosphor 2210 (made by Kasei Optronics, using ZnS as a base material and Cu as an activator) and Udouble S2740 as an acrylic binder (Japan) 15 parts by weight of catalyst (acrylic binder), 5 parts by weight of coronate HL (manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanate crosslinking agent) as a crosslinking agent, and 135 parts by weight of butyl acetate (manufactured by Wako Pure Chemical Industries) as an organic solvent The coating solution obtained by mixing was applied at a wet coating amount of 25 g / m ² , and then dried in an oven at 100 ° C. for 2 minutes to obtain a reflective film. The evaluation results are shown in Table 2. Although the effect of improving the brightness was obtained, the effect of diffusing the reflected light could hardly be obtained. The color of the film changed greatly by application, and the film was colored.

[Comparative Example 3]
On the white laminated film used in Example 1, 80 parts by weight of MBX-15 (manufactured by Sekisui Plastics, average particle size of 15 μm, particles of crosslinked polymethyl methacrylate) as transparent particles, yeast bright OB-1 ( 1 part by weight of Eastman, benzoxazole-based organic fluorescent agent), 32 parts by weight of Udouble S2740 (manufactured by Nippon Shokubai Co., Ltd., acrylic binder) as an acrylic binder, and Coronate HL (manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanate-based crosslinking) as a crosslinking agent 4 parts by weight, and a coating obtained by mixing 133 parts by weight of butyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic solvent is applied on the reflective layer side in a wet coating amount of 25 g / m ² , and then in the oven And dried at 100 ° C. for 2 minutes to obtain a reflective film. The evaluation results are shown in Table 2. Almost no effect of improving the brightness could be obtained, and almost no effect of diffusing the reflected light could be obtained. Since an organic phosphor was used, the film was inferior in UV resistance.

  The reflective film for a liquid crystal display device of the present invention can be suitably used as a reflective film in a backlight unit of a liquid crystal display device.

Claims (1)

  It consists of a white film and a coating layer provided on the film, and the coating layer is composed of an inorganic phosphor excited in the wavelength region of 400 to 450 nm and having an emission peak wavelength of 500 to 600 nm, transparent particles, and a binder. The total content of the inorganic phosphor and the transparent particles in the coating layer is 50 to 90 wt% per 100 wt% of the total weight of the coating layer, the content of the inorganic phosphor is 1 wt% or more, and the inorganic fluorescence A reflective film for a liquid crystal display device, characterized in that the content of the body is less than or equal to the content of the transparent particles.