JP2002100227A - Surface light source apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight with excellent reflectance and durability using a reflection sheet having a metal layer, which can prevent partial decrease in brightness due to deflection of the reflection sheet without changing the existing structure of the backlight. SOLUTION: The reflection sheet 70 is positioned on the bottom face of a light guide plate 60. A backlight is manufactured by using the reflection sheet obtained by applying particles having particle sizes of 1 μm or more and 15 μm or less together with a binder onto a base material to form an irregular face and forming a metal layer on the irregular face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflector having excellent reflectance and a surface light source device using the same. Further, the present invention relates to a liquid crystal display device using a surface light source device.

[0002]

2. Description of the Related Art Compared to conventional CRT displays, liquid crystal display devices are thinner and can save space, operate at low voltage, consume less power, and can save energy. Widely used mainly for displays.

[0003] Among them, a liquid crystal display device widely used at present is a transmission type liquid crystal display device using a backlight as a light source. The visibility of the display on this liquid crystal display device is
In addition to the performance of the liquid crystal itself, the performance of the backlight is also increasing. In recent years, liquid crystal display devices are required to be even lighter and thinner, and because of the uniformity of brightness and the difficulty in transferring heat from the light source to the liquid crystal panel, the backlight system is not suitable for the light source. Edge light type backlights that use a light guide plate instead of a direct type with a reflection plate behind the light source and make a light source disposed at one end of the light guide plate into a surface light source by multiple reflection are often used. In the light guide plate of the backlight, diffusion dots are printed on the lower surface, and the size (area) changes according to the position. As the size of the dot increases, the probability that light will strike the dot Will be higher. As a result, more light is emitted from the position where the dot is located.Thus, by optimizing the size and distribution of the diffusion dot, the unevenness in luminance on the light emitting surface is reduced, and High brightness can be obtained. A reflection plate is provided on the lower surface of the light guide plate, and the reflection plate here is generally a white plate. on the other hand,
Recently, in order to further reduce the absorption loss due to the polarizing plate and further improve the brightness in the liquid crystal display device, instead of the light guide plate with the diffusion dot printed on the lower surface, the lower surface has an uneven shape, or the diffusion particles in the light guide plate There is what blended. In these light guide plates, it is said that the reflector disposed on the lower surface is not a white plate but a metal reflector can obtain higher luminance. This reflector is used for the purpose of reflecting the light other than the panel surface direction of the edge light toward the panel side to increase the light use efficiency. However, as the liquid crystal display device becomes lighter and thinner, it becomes lighter and thinner. It is necessary to use a metal plate, and a material having a metal layer formed on a resin surface is generally used. In the backlight,
This reflector is provided on the lower surface of the light guide plate, but is not bonded to the light guide plate. This is because, due to the material of the light source, the light guide plate easily expands and the reflector plate easily contracts due to the heat of the light source. For this reason, the reflection sheet may move slightly on the lower surface of the light guide plate, and if the sheet bends due to the movement, sufficient reflected light at that portion cannot be obtained, and the brightness of the liquid crystal display device becomes lower. There was a problem that it appeared as an unobtainable black part.

[0004]

An object of the present invention is to provide a backlight using a reflection sheet having a metal layer without causing a reduction in luminance due to the deflection of the reflection sheet without changing the current backlight structure. It is an object of the present invention to provide a backlight using a reflective sheet having excellent reflectance and durability.

[0005]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, surprisingly,
By forming a metal layer on an uneven layer surface obtained by applying a binder having a mean particle size of 1 μm or more and 15 μm or less together with a binder on a base material to a reflection sheet used on the lower surface of a light guide plate in a backlight. It has been found that the above problem can be solved by using the obtained reflection sheet.

That is, the present invention provides [1] a surface light source device comprising a light guide plate and a reflection sheet disposed on the lower surface thereof, wherein the reflection sheet has an average particle diameter of 1 μm on a substrate. A surface light source device, characterized in that a reflection sheet obtained by forming a metal layer on the uneven layer surface obtained by applying particles having a size of 15 μm or less together with a binder is used; When forming the uneven surface, the ratio of particles and binder,
The volume of the particles is 5 to 52 with respect to the volume of the uneven layer to be formed.
The surface light source device according to claim 1, wherein the surface light source device is a reflection sheet that is blended so as to have a volume% ratio and the dry weight (g / cm ² ) of the uneven layer satisfies the condition of the following formula (1). Formula (1): 0.6 × 2r × 10 ² / (p / a + (100
-P) / b) ≦ weight (g / cm ² ) ≦ 2.5 × 2r × 1
0 ² / (p / a + (100−p) / b) [However, p = 100 / (1+ (100 / v−1) × b /
a)], r: average value of the radius of the fine particles used (cm) p: ratio of fine particles in the uneven layer (% by weight) v: ratio of fine particles in the uneven layer (% by volume) a: Density of used fine particles (g / cm ³ ) b: Density of used binder (g / cm ³ ) [3] 550 nm measured from the metal layer side of the reflection sheet
The surface light source device according to [1] or [2], wherein the reflection sheet has a reflectance of 85 to 99%. [5] The surface light source device according to any one of [1] to [3], [5] wherein the configuration of the reflective layer of the reflective sheet includes a base layer (A), a silver layer (B), and silver. The surface light source device according to any one of [1] to [4], wherein the surface light source device has a metal layer (C) and a silicon oxide layer (D) of an alloy mainly composed of The surface light source device according to any one of [1] to [5], wherein the particles forming the uneven layer of the reflection sheet are acrylic particles.
The surface light source device according to any one of [1] to [6], wherein the binder forming the uneven layer of the reflection sheet is an acrylic resin. The underlayer (A) is made of gold, copper, nickel, iron,
A metal layer of cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium, or palladium having a thickness of 5 to 50 nm, or zinc oxide or indium doped with aluminum oxide of 0 to 5% by weight; The surface light source device according to any one of [1] to [7], wherein the surface light source device is a transparent oxide layer having a thickness of 1 to 20 nm made of tin oxide (ITO).
[9] The surface light source device according to any one of [1] to [8], wherein the thickness of the silver layer (B) in the reflection layer of the reflection sheet is 70 to 400 nm. [1
0] The metal layer (C) of an alloy mainly composed of silver in the reflection layer of the reflection sheet is a layer made of an alloy containing 0.001 to 2% by weight of silver and copper and palladium in total, The surface light source device according to any one of [1] to [9], wherein the metal layer has a thickness of 5 to 40 nm, [11] a silicon oxide layer in the reflection layer of the reflection sheet. The thickness of (F) is 1-50 nm, The surface light source device [1] in any one of Claims 1-10 characterized by the above-mentioned.
2] The ratio of the diffuse reflectance to the total reflectance at a wavelength of 550 nm (haze value of reflection) of the reflection sheet is 5 to 50.
%, Wherein the surface light source device according to any one of claims 1 to 11, wherein
The present invention relates to the surface light source device according to any one of [11].

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The surface light source device of the present invention is an edge light type surface light source device in which an uneven metal reflection sheet is disposed on a reflector used on a lower surface of a light guide plate.

As the light guide plate in the present invention, for example,
Acrylic resins such as polymethyl methacrylate, polycarbonate resins such as polycarbonate and polycarbonate / polystyrene polymers, transparent resins such as epoxy resins and glass, etc., which exhibit transparency in a wavelength range of about 400 to 700 nm are preferably used. However, the material is not limited to this as long as it is a material showing transparency according to the wavelength region of the light source.

As a method of manufacturing the light guide plate, for example, a method of filling or casting a liquid resin polymerized by heat, ultraviolet rays, radiation or the like into a mold capable of obtaining a predetermined lower surface shape, and performing a polymerizing process, A method in which a resin is pressed against a mold having a predetermined lower surface shape under heating and molded, and a thermoplastic resin melted by heating or a resin fluidized through heat or a solvent is formed into a mold having a predetermined shape. And the like. However, the method is not limited to this as long as the method has a good mass productivity to some extent.

[0010] The thickness of the light guide plate can be appropriately determined depending on the size of the light guide plate to be used, the size of the light source, and the like. The general thickness of the light guide plate when used in a liquid crystal display device or the like is preferably 0.1 to 20 mm or less, more preferably 0.3 to 12 mm, and still more preferably 0.6 to 12 mm.
8 mm. The general area ratio between the incident surface and the upper surface is preferably from 1: 5 to 100, more preferably from 1:10 to 80, and still more preferably 1:15.
~ 50.

The light source used in the surface light source device of the present invention includes, for example, an incandescent light bulb, a light emitting diode (LED), an electroluminescence (EL), a fluorescent lamp, a metal hydride lamp, and the like. Used. Fluorescent lamps are roughly classified into hot cathode type and cold cathode type according to their electrode structure and lighting method.
Hot cathode type inverters also tend to be larger. The hot-cathode type has a small illumination loss near the electrode that does not contribute to light emission, has good efficiency, exhibits luminous efficiency several times better than the cold-cathode type, emits light more strongly, but has a longer life than the cold-cathode type. Therefore, the cold cathode type is more preferably used from the viewpoint of low power consumption and durability. In order to guide the divergent light from the light source to the side surface of the light guide plate, the light source is usually surrounded by a reflector. As the reflector, a resin sheet or a metal foil provided with a high-reflectance metal thin film is generally used.

The reflecting sheet used on the lower surface of the light guide plate in the surface light source device of the present invention is obtained by mixing fine particles (hereinafter, also referred to as filler) having a specific average particle size with a binder in a specific weight ratio, After applying so that the dry weight becomes a specific weight, and forming a layer having a concavo-convex structure on the polymer film, an oxide or a single metal layer, a silver layer, and silver are mainly formed on the concavo-convex layer. This is a reflection sheet in which a metal layer and a silicon oxide layer are sequentially formed.

In the reflection sheet, the polymer film used as a base material includes, for example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polycarbonates such as bisphenol A-based polycarbonate, and polyolefins such as polyethylene and polypropylene. , Cellulose derivatives such as cellulose triacetate, vinyl resins such as polyvinylidene chloride, polyimides, polyamides, polyethersulfone, polysulfone resins, polyarylate resins, and films made of various plastics such as fluororesins. However, the material is not limited to these, and any material having a high glass transition point and a smooth surface can be used. Among them, polyethylene terephthalate is preferred.

The thickness of the polymer film to be used is not particularly limited as long as a certain degree of stiffness can be obtained in the sheet, but it is usually about 10 to 400 μm, preferably 1 to 400 μm.
About 0 to 200 μm, more preferably 25 to 100 μm.
It is about μm.

The uneven layer formed on the polymer film is
It is formed by fine particles serving as a filler and a binder. Examples of the fine particles serving as fillers include polymer (organic) particles such as acryl, polystyrene, vinylbenzene, polymethyl methacrylate, styrene methacrylate, styrene acrylate, styrene butadiene, silica, alumina, titania, zirconia, and oxidized particles. Inorganic fine particles composed of lead (lead white), zinc oxide (zinc white), calcium carbonate, barium carbonate, barium sulfate, potassium titanate, sodium silicate, and conductive materials such as tin oxide, indium oxide, cadmium oxide, and antimony oxide Transparent fine particles can also be used, but are not necessarily limited thereto. Among them, acrylic resin is preferable.

The method for preparing fine particles composed of a polymer includes an emulsion polymerization method, a suspension polymerization method and a dispersion polymerization method. Among them, the emulsion polymerization method is the most common, but in recent years, dispersion polymerization has been actively performed. In any polymerization method, the produced polymer is hardly soluble in the dispersion medium, and is formed into particles by the surface tension between the dispersion medium and the polymer. Polymer particles are
It is stabilized by a protective colloid bonded or adsorbed to the particle surface, and further stabilized by intra-particle crosslinking. Among these methods, in particular, when a dispersion polymerization method is used, there is a feature that particles in a wide range from submicron to several tens of microns can be obtained.

The average particle size of the fine particles serving as a filler for obtaining a desired roughness on the surface of the polymer film is 1 to 1
It is 5 μm, preferably 2 to 10 μm, and more preferably 3 to 8 μm. If the average particle diameter is less than 1 μm, it becomes difficult to form the surface of the concavo-convex structure due to the burial of the particles, and if it exceeds 15 μm, the unevenness of the concavo-convex structure becomes large, resulting in a rough textured reflection sheet. It is preferable that the particle size distribution of the fine particles is small. The ratio of the standard deviation of the particle size to the average particle size is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less. If the particle size distribution greatly exceeds the above ratio, it is difficult to obtain a controlled uneven structure.

The binder used to disperse the fine particles may be, for example, an acrylic resin such as polymethyl methacrylate, a polyacrylonitrile resin, a polymethacrylonitrile resin, a silicon resin such as a polymer obtained from ethyl silicate, a fluorine resin, or a polyester. Resin, polystyrene resin, acetate resin, polyethersulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, polyurethane resin, urea resin, melamine resin, epoxy resin, and mixtures thereof And the like, but are not necessarily limited to these. These are selected in consideration of the adhesion to the polymer film and the particles, and among them, acrylic resins are preferable.

As the method for forming the uneven layer, the fine particles and the binder as the filler are formed by coating on a polymer film. When applying, as a solvent for dispersing the fine particles as a filler in the binder,
Toluene, methyl ethyl ketone, ethyl acetate, isopropyl alcohol and the like are preferably used. These are solvents generally used at the time of the coating operation, and any other solvent that does not affect the base polymer film or the filler fine particles can be used without any problem. Further, additives such as a wetting agent, a thickener, a dispersant, and an antifoaming agent may be added to the coating solution as needed.

The mixing ratio of the fine particles serving as the filler is determined by the solid content (filler + binder) in the coating solution.
It is expressed by the volume% of the filler in the medium, and is preferably 5% by volume or more and 52% by volume or less based on 100% by volume of the solid content.
More preferably, the content is 10% by volume or more and 45% by volume or less, and still more preferably 20% by volume or more and 40% by volume or less.
When the used amount of the filler is 5% by volume or less, desired light diffusibility cannot be obtained. When the used amount exceeds 52% by volume, sufficient reflected light cannot be obtained due to birefringence.

In the production of the reflection sheet, when applying a solution in which fine particles made of a polymer are dispersed in a binder using a solvent, 4 hours, preferably 12 hours, after preparing the dispersion solution, It is preferable to apply the coating after 24 hours. Since the fine particles made of polymer are affected by the solvent and swell over time for several hours,
Immediately after the preparation of the dispersion solution, if the coating is performed, the particle size of the fine particles changes with time, the uneven structure becomes uneven, and the viscosity of the dispersion solution also changes with time, making it difficult to adjust the coating conditions. It may be.

The weight of the concavo-convex layer formed on the polymer is expressed by the following equation (1): 0.6 × 2r × 10 ² / (p / a + (100
-P) / b) ≦ weight (g / cm ² ) ≦ 2.5 × 2r × 1
It is preferably 0 ² / (p / a + (100−p) / b). More preferably, the formula (3): 0.6 × 2r × 10 ² / (p / a + (100
-P) / b) ≦ weight (g / cm ² ) ≦ 2.0 × 2r × 1
O ² / (p / a + (100−p) / b) More preferably, the formula (4): 0.6 × 2r × 10 ² / (p / a + (100
-P) / b) ≦ weight (g / cm ² ) ≦ 1.5 × 2r × 1
0 ² / (p / a + (100−p) / b). When the weight of the uneven layer is smaller than the value on the left side of the formula (1), the number of particles for forming the uneven layer is too small, and a desired uneven structure cannot be obtained on the polymer film. If the weight of the uneven layer is smaller than the value on the right side of the expression (1), the number of particles becomes too large, and it becomes difficult to form a controlled uneven structure. Here, the weight refers to the weight after drying (dry). Before drying (wet)
Although the weight (application amount) is useful for selecting the number of the gravure plate or the Meyer bar used for coating, the actual measurement is often difficult. Therefore, in practice, the film thickness after drying and the coating weight after drying are often measured and evaluated. However, because the particle layer is an uneven layer,
The coating amount and the film thickness do not always match. Therefore, it is considered preferable to carry out the evaluation based on the weight after drying (dry).

As a method of measuring the dry weight, for example, the fine particles on the surface of the uneven layer and the solvent that dissolves the binder are carefully wiped off, the peeled uneven layer and the solvent are dried, and the solvent is easily measured by evaporating the solvent. Can do things. As a method for forming a concavo-convex layer with fine particles on a base polymer film, various solution coating methods are considered, and the amount of coating at that time is controlled by wet weight. If the weight percent of solids in the coating solution shown in N, substantially between the wet weight and dry weight and wet weight (g / cm ²⁾ = Dry Weight (g / cm ²⁾
/ N × 100 N: There is a relationship of the solid content ratio (% by weight) in the wet coating solution. Therefore, equation (1) can be expressed as equation (5). Formula (5): 0.6 × 2r / N × 10 ⁴ / (p / a + (1
00-p) / b) ≦ coating amount (g / cm ² ) ≦ 2.5 × 2
r / N × 10 ⁴ / (p / a + (100−p) / b) However, as described above, the wet weight often cannot be consistent with the final dry weight depending on the application method and drying conditions. Because of this, it is only a guideline value during coating,
The evaluation is performed by dry weight.

Hereinafter, a method for forming the uneven layer of the reflection sheet will be described. First, the roll coater will be described. The roll coater is composed of three, a metering roll, an applicator roll, and a backup roll, and is divided into a forward rotation roll coater and a reverse roll coater according to the position where the metalling roll is arranged. The role of the metering roll is to maintain a precise and constant amount of coating agent on the applicator roll, and the amount of coating agent present on the applicator roll depends on the nip between the applicator roll and the metering roll. The width and the relative surface speed are adjusted. In actual operation, the applicator roll and the metering roll each control the speed independently. This is especially important when dealing with a wide range of coatings, and for most coatings, by properly adjusting the relative velocity relationship at the metalling nip,
A coating film having a very smooth appearance can be obtained. In the case of a forward rotation roll coater, if the peripheral speed of the metering roll and the applicator roll is made equal, when the coating liquid splits at the exit of the nip between the rolls, the liquid is pulled up and down, causing a split pattern. Rotate the tallon faster. In general, the spacing between the metering roll and the applicator roll is slightly spaced to take part of the metering. If this gap is too far, there is a disadvantage that a ring-shaped pattern is generated.

In a roll coater, a reverse roll coater performs coating while the applicator roll rotates in the reverse direction. In a reverse roll coater, the coating thickness is determined by the size of the gap between the rolls in contact with each other, the peripheral speed ratio of each roll,
It is determined by the viscosity of the coating solution, the solid content concentration, and the like. The advantages of this coater are (1) coating is possible over a wide viscosity range, (2) coating thickness can be adjusted during running,
(3) The thickness of the coating film can be greatly changed. (4) The coating film surface is formed along the surface of the support, and the coating film thickness is uniform microscopically. A small loss of solvent due to sharing. However, on the other hand, (1) if the speed of the metering roll is too high, a rough wavy pattern is formed on the coating material measured on the applicator roll, and this pattern appears as the same pattern when moved to the film surface. (2) When the metering roll is made slower than the ideal speed, concentric bulges occur in the coating agent weighed on the applicator roll. (3) Strong stirring effect in the coating agent tank generates bubbles (4) The homing effect of the application roll is increased, and the coating agent reservoir needs to be deepened to prevent overflow. (5) It is difficult to attach the edge doctor, and it is necessary to step the backup roll. (6) There is also a drawback that the coating speed is limited due to the problem of scattering of the coating agent due to the pumping action.

In the gravure coater method, a gravure roll,
The gravure roll, which is composed of a backup roll and an adjustment roll, and is immersed in the liquid tank, has its surface engraved with irregularities.The coating liquid adhering to the projections is scraped off with a doctor blade, This is a method in which a coating solution is measured and transferred to a support, and the amount of coating is adjusted according to the shape, depth, mesh, and solid content concentration of the gravure cell. Factors affecting the transfer of the coating agent from the gravure cell to the substrate are viscosity and surface tension. The cell shape is a pyramid type, a lattice type, or a diagonal line type, and the coating amount increases in the order of pyramid type <lattice type <diagonal line type. The advantage of this method is that the coating thickness is uniform even when it is wide, and a thin film coating can be performed without any operation technique. On the other hand, (1) the transfer rate of the coating agent is extremely small in a shallow cell, and is about 50% at the maximum. (2) Transfer mechanism of the coating agent In cells deeper than the cell, the coating of Mesnicus has a shape in which the center of the cell is recessed and the coating agent adheres along the cell wall. There are also disadvantages such as that the coated film after removal has a center and appears as a donut-shaped ring.

In the rod coater method, the coating liquid is transferred to the support with a forward rotating applicator roll, and then the outer diameter is 6 to 1 mm.
It is a system in which a piano wire or stainless steel wire of about 0.1 to 0.8 mm thickness is densely wound around a rod of about 0 mm, and the excess coating liquid is shaved off and weighed.
In this method, it is important to keep the tension of the support on the rod constant to obtain a stable coating amount. Therefore, if there is a difference in tension in the width direction of the support, there is a difference between the left and right coating amounts. If the distance between the pressing rollers before and after the rod is as short as possible in order to prevent wrinkles and sagging of the support at this portion, there is a drawback that a streak occurs in the running direction.

In the blade coater method, a coating agent is measured by a blade and flattened, as when butter is applied to bread. Factors that affect the coating amount include blade thickness, blade pressure, angle with blade cutting line, length of blade crimping section, blade bevel,
The viscoelasticity of the coating agent, the coating speed, and the like.

In a knife coater in which a knife is installed vertically above a backup roll and the coating thickness is measured by the gap between the knife edge and the support conveyed by the roll, the factors determining the coating amount are as follows. Examples include the gap between the support and the knife edge, the coating speed, the viscosity of the coating agent, the pressure of the coating liquid reservoir on the support, the shape of the knife edge, and the like.

The die coating (extrusion) method is a method in which a solution stored in a hopper or the like is extruded from a die by a pump pressure and applied to a film surface. In the die coating method, all of the supplied coating liquid is usually coated on the film without recirculation. Therefore, the application amount is determined by the pump delivery amount and the line speed. In addition, when a coating liquid having a very low viscosity is used, a sufficient die internal pressure cannot be obtained in the width direction, and the coating amount may be non-uniform. This is addressed by making the internal pressure of the die uniform by making it narrower. The tip of the die is used as a measuring blade to increase the uniformity of the coating amount in the width method. For example, the die coating method in which the tip is rounded in the shape of a lip is also called the lip coating method, but in order to obtain a good coating surface as well as uniformity of the coating amount, devising the tip of the die in this way Are preferably used. The advantages of the die coating (extrusion) method include high-speed coating, high productivity, uniform coating thickness, and the ability to apply a wide range of coatings. Loss when changing the width may be slightly increased.

Various coating methods other than those described above are conceivable. As a coating method that satisfies the requirements of the present invention, the die coating method is considered in consideration of occurrence of bumps due to gelation during coating.
Among them, the use of the lip coating method is preferred.

The reflection layer of the reflection sheet is composed of four layers formed on the uneven layer. The first layer from the uneven layer side is a base layer (A), the second layer is a silver layer (B), the third layer is a metal layer (C) of an alloy mainly composed of silver, and the fourth layer is a silicon oxide layer. (D).

The first underlayer (A) is made of a single metal such as gold, copper, nickel, iron, cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium, palladium, or aluminum oxide. 0 to
A transparent oxide such as zinc oxide or an oxide of indium and tin (ITO) doped with 5% by weight is preferably used.

It is desirable that the second silver layer (B) is basically silver alone, but gold, copper, nickel, iron, cobalt, tungsten, molybdenum which does not impair the performance of the silver layer (B). And metal impurities such as tantalum, chromium, indium, manganese, titanium, and palladium.

In the third layer (C), the metal layer of an alloy mainly composed of silver contains 2% by weight of copper and palladium in total with respect to silver.
An alloy containing the following range is preferably used.

The fourth silicon oxide layer (D) usually has
Although it is preferable to use silicon dioxide which is a general silicon oxide, the number of oxygen does not necessarily have to be 2, and there is no problem even when the number is, for example, 1.8.

The metal thin film layer can be formed by a wet method or a dry method. The wet method is a general term for the plating method, and is a method of depositing a metal from a solution to form a film. A specific example is a silver mirror reaction. On the other hand, the dry method is a general term for a vacuum film forming method, and specific examples thereof include a resistance heating type vacuum deposition method, an electron beam heating type vacuum deposition method, an ion plating method, and an ion beam assisted vacuum deposition method. And a sputtering method. In particular, in the present invention, a vacuum film forming method capable of a roll-to-roll method for continuously forming a film is preferably used.

In the vacuum deposition method, a raw material of a metal is melted by electron beam, resistance heating, induction heating, or the like, and the vapor pressure is increased, preferably 13.3 mPa (0.1 mTorr).
It is evaporated on the substrate surface below. At this time, a gas such as argon may be introduced at 13.3 mPa or more to cause high frequency or direct current glow discharge.

As the sputtering method, a DC magnetron sputtering method, an RF magnetron sputtering method, an ion beam sputtering method, an ECR sputtering method, a conventional RF sputtering method, a conventional DC sputtering method, or the like can be used. In the sputtering method, a metal plate-shaped target may be used as a raw material, and helium,
Neon, argon, krypton, xenon and the like may be used, but preferably argon is used. The purity of the gas is preferably 99% or more, more preferably 99.5%.
That is all. In addition, a vacuum film formation method is preferably used for forming the transparent oxide film. Mainly, the sputtering method is used,
Helium, neon, argon, krypton, xenon, or the like is used as a sputtering gas, and in some cases, oxygen gas may be used.

The thickness of the thin film formed on the base polymer film is determined in consideration of a light transmittance of less than 1% when the reflection sheet is used.

In the case where a metal layer is used as the first underlayer, the thickness is preferably 5 to 50 nm, more preferably 5 to 30 nm. When the thickness of the layer is smaller than 5 nm, the desired barrier effect cannot be obtained, and the silver layer of the second layer causes aggregation. Further, even if the thickness is more than 50 nm, not only the effect is not changed but also it is not preferable from the viewpoint of effective use of resources. When a transparent oxide is used, the thickness of the layer is preferably 1 to 20 nm, more preferably 5 to 10 nm. When the thickness of such a layer is smaller than 1 nm, a desired barrier effect cannot be obtained, and aggregation occurs in the silver layer of the second layer.

The silver layer as the second layer has a thickness of 70 to 400.
nm, more preferably 100 to 300 nm,
More preferably, it is 150 to 250 nm. When the thickness of such a layer is smaller than 70 nm, a sufficient reflectance cannot be obtained because a sufficient metal layer cannot be formed. Further, even if the thickness is more than 400 nm, not only the effect does not change but also it is not preferable from the viewpoint of effective use of resources.

The thickness of the third layer of the metal layer mainly composed of silver is preferably 5 to 40 nm. If the thickness of such a layer is smaller than 5 nm, the desired barrier effect cannot be obtained, and if it is larger than 40 nm, the characteristics of the silver layer as the second layer are undesirably lost.

The thickness of the fourth silicon oxide layer is 1 to
It is preferably 10 nm, more preferably 1 to 7 nm, and still more preferably 1 to 5 nm. The thickness of such a layer is 1n
When the thickness is smaller than m, a desired barrier effect cannot be obtained, and aggregation occurs in the second silver layer. Further, even if the thickness is more than 10 nm, the effect is not changed, and it is not preferable from the viewpoint of effective use of resources.

As a method of measuring the film thickness of each layer, there are a method using a stylus roughness meter, a repetitive reflection interferometer, a microbalance, a quartz oscillator method, and the like. Since the thickness can be measured, it is suitable for obtaining a desired film thickness. There is also a method in which the conditions for film formation are determined in advance, a film is formed on a sample substrate, the relationship between the film formation time and the film thickness is examined, and the film thickness is controlled by the film formation time.

The reflecting sheet formed as described above is
When the reflectance is measured from the layer side, it is usually 85 to 99% at a wavelength of 550 nm. More preferably 90 to 9
9%. If the reflectivity is lower than 85%, the resulting luminance is undesirably low when incorporated in a backlight unit. On the other hand, here, the upper limit of the reflectivity is set to 99%, but the higher the reflectivity is, the more preferable it is. Achieving a reflectance higher than that has a trade-off with cost, but can be said to be very preferable in terms of performance.

The half-value angle of luminance of the reflection sheet formed as described above is 10 to 40 °. When the half-value angle is smaller than 10 °, the specularity of the reflection sheet becomes strong, the diffusion component becomes insufficient, the directivity of light becomes strong similarly to a normal silver reflection sheet, and a dark portion occurs at the time of bending. Also, 40 °
When the value is more than 1, the light is excessively dispersed and the luminance as a whole decreases, which is not preferable. When the reflection sheet is measured for the total reflectance and the diffuse reflectance from the reflective layer side to the reflective layer side using a spectrophotometer, the ratio of the diffuse reflectance to the total reflectance (reflection haze value) is: Usually, it becomes 5 to 50%. If this value is less than 5%, the amount of specular reflection with respect to incident light is too strong, and the problem in the present invention cannot be solved. On the other hand, if it is larger than 50%, it is not preferable because sufficient brightness cannot be obtained as a whole.

[0048]

The present invention will be described below in detail with reference to examples.

Example 1 Acrylic resin having an average particle size of 5 μm
(Made by Negami Industry Co., Ltd., product name: Art Pearl) and Vine
Acrylic resin (made by Mitsui Chemicals, Inc., product name:
Armatex E269) (both density 1.2g / c
m^Three) Is a solvent consisting of toluene and ethyl methyl ketone
, The solid content ratio was 35%, and the ratio of particles in the solid content was 3%.
A solution with a volume of 7.0% by volume was prepared. Viscosity is 38 cps
Met. Substituting these physical property values into equation (1)
As a result, the application weight range was calculated to be 3.6 (g /
m ^Two) ≦ coating amount (g / m^Two) ≦ 10.8 (g / m^Two) And
The dry coating amount was 8.5 g / m^TwoSo that
Adjust the pump pressure and line speed,
On polyethylene terephthalate (PET) film
Was applied by a lip coating method. At this time,
No streaks were observed, and a good coated surface was obtained. did it
2% Al on the sheet by DC magnetron sputtering
_TwoO_ThreeZinc oxide (purity 99.9%) doped with
Get 99.5% pure argon as sputtering gas
Was formed so as to have a thickness of 5 nm.
Next, do not remove this sheet from the sputtering device.
Similarly, a purity of 99.99% was obtained by DC magnetron sputtering.
99.5% pure algo targeting 9% silver
Silver to a film thickness of 200 nm using
Molded. Then, remove this sheet from the sputtering device.
Purity by DC magnetron sputtering method
99.9% APC 2% (Pd and Cu combined with Ag
2% by weight in total)
APC2 using 99.5% argon as a sputtering gas
% Was formed to a film thickness of 8 nm. Next, this
RF magnet without removing the sheet from the sputtering equipment
99.9% pure SiO by netron sputtering_TwoThe
And a sputter gas of 99.5% purity argon.
SiO2_TwoIs formed to a film thickness of 5 nm,
A desired reflection sheet as shown in FIG. 1 was obtained. Next
Mold into a metal mold that has been released
After heating for 2 hours, it is further heated at 150 ° C. for 3 hours to cure.
After processing, gradually cool and enter the 195 mm x 150 mm entrance surface
5 mm thick, the exit surface is flat, and the bottom surface has an average surface roughness
Conductor with a concave and convex surface with a depth of 200 μm and a concave depth of 20 μm
A light plate was obtained. Next, the reflection obtained on the metal cover
Arranged sheets cut to size suitable for light guide plate
Then, a light guide plate was set thereon. In addition, the light guide plate
Place a 3mm diameter cold cathode tube on the firing surface and deposit silver on it
Lamp reflector made of polished polyester film
To obtain a surface light source device as shown in FIG. This state
The light source is turned on, and the brightness obtained in the front direction at the center of the surface
Was measured, and the luminance unevenness of the surface was observed.
Next, with the top of the reflective sheet flexed intentionally,
The same observation was performed by setting the light source device. Table 1 shows the results
Show.

[Comparative Example 1] A reflective sheet was made of a PET film having a thickness of 50 µm, and silver was purified by DC magnetron sputtering to a purity of 9%.
A liquid crystal display device according to Example 1, except that 9.9% silver was used as a target, and silver was molded to a thickness of 200 nm using argon having a purity of 99.5% as a sputtering gas. It was created. Subsequently, the same observation as in Example 1 was performed. Table 1 shows the results.

Example 2 A solution was prepared according to Example 1, except that the ratio of the particles in the solid content was 10%. When the coating amount range was calculated by the equation (1), 3.6 (g / m2)
≦ coating amount (g / m2) ≦ 10.8 (g / m2), but the dry coating amount was set to 5.0 g / m2.
The coating of the particle layer and the formation of the reflection layer were performed according to the method described in Example 1.
The obtained reflector was used as a Hitachi automatic recording spectrophotometer (model U-34).
At 00), an integrating sphere of 150φ was installed, and the total reflectance and diffuse reflectance at a wavelength of 550 nm were measured. As a result, a reflectance of 93.5% and a diffuse reflectance of 15.6% were obtained. The reflection haze calculated from this value was 16.7%. The obtained reflection sheet was incorporated in a surface light source device in the same manner as in Example 1, and the reflection luminance was measured. Table 1 shows the results.

[0049]

[Table 1]

[0050]

According to the surface light source device of the present invention, when incorporated in a liquid crystal display device, the excellent reflectivity of the reflection sheet enables
Since a very high luminance can be obtained in the liquid crystal screen and the occurrence of a black portion with reduced luminance caused by the bending of the reflection sheet does not occur, the display capability of the liquid crystal can be improved, and the industrial The significance is great.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a reflection sheet according to the present invention.

FIG. 2 shows an example of the surface light source device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Reflective layer 20 Concavo-convex layer 30 Polymer film 40 Cold cathode tube 50 Lamp reflector 60 Light guide plate 70 Reflection sheet

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13357 G02F 1/13357 // F21Y 103: 00 F21Y 103: 00 F-term (Reference) 2H042 BA02 BA04 BA20 DA03 DA05 DA06 DA07 DA08 DA11 DC02 DC03 DC08 DE00 2H091 FA14Z FA23Z FA41Z FA42Z FB02 FB08 FC22 FC25 KA10 LA16

Claims (12)

[Claims] 1. A surface light source device having a light source on a side surface and comprising a light guide plate and a reflection sheet disposed on a lower surface thereof.
The reflective sheet has an average particle size of 1 μm or more and 15 μm on a substrate.
m. A surface light source device characterized by using a reflective sheet obtained by forming a metal layer on the uneven layer surface obtained by applying particles having a particle size of m or less together with a binder. 2. When forming the uneven surface of the reflection sheet, the ratio of the particles and the binder is blended so that the volume of the particles is 5 to 52% by volume with respect to the volume of the formed uneven layer. ^2. The surface light source device according to claim 1, wherein the reflection sheet satisfies the condition of the following expression (1), and the dry weight (g / cm ² ) of the uneven layer is: Formula (1): 0.6 × 2r × 10 ² / (p / a + (100
-P) / b) ≦ weight (g / cm ² ) ≦ 2.5 × 2r × 1
0 ² / (p / a + (100−p) / b) [However, p = 100 / (1+ (100 / v−1) × b /
a)], r: average value of the radius of the fine particles used (cm) p: ratio of fine particles in the uneven layer (% by weight) v: ratio of fine particles in the uneven layer (% by volume) a: Density of used fine particles (g / cm ³ ) b: Density of used binder (g / cm ³ ) 3. The reflection sheet measured from the metal layer side of the reflection sheet.
3. The surface light source device according to claim 1, wherein the reflectance at 50 nm is 85 to 99%. 4. A half-value angle of reflection luminance of the reflection sheet is:
The surface light source device according to any one of claims 1 to 3, wherein the angle is 10 ° to 40 °. 5. The reflection layer of the reflection sheet is composed of an underlayer (A), a silver layer (B), a metal layer (C) of an alloy mainly composed of silver and a silicon oxide layer (D) of ABCD. The surface light source device according to claim 1, wherein the surface light source device is provided in order. 6. The particles forming the uneven layer of the reflection sheet are acrylic particles.
5. The surface light source device according to any one of 5. 7. The surface light source device according to claim 1, wherein the binder forming the uneven layer of the reflection sheet is an acrylic resin. 8. A thickness in which a base layer (A) in the reflection layer of the reflection sheet is made of gold, copper, nickel, iron, cobalt, tungsten, molybdenum, tantalum, chromium, indium, manganese, titanium, or palladium. 5
0 to 50 nm metal layer or aluminum oxide
8. A transparent oxide layer having a thickness of 1 to 20 nm made of zinc oxide doped with 5% by weight or an oxide of indium and tin (ITO). Surface light source device. 9. The surface light source device according to claim 1, wherein the thickness of the silver layer (B) in the reflection layer of the reflection sheet is 70 to 400 nm. 10. The reflective layer of the reflective sheet, wherein the metal layer (C) of an alloy mainly composed of silver is a layer made of an alloy containing 0.001 to 2% by weight of silver and copper and palladium in total. 10. The surface light source device according to claim 1, wherein the metal layer has a thickness of 5 to 40 nm. 11. The surface light source device according to claim 1, wherein the thickness of the silicon oxide layer (F) in the reflection layer of the reflection sheet is 1 to 50 nm. 12. The reflection sheet according to claim 1, wherein the ratio of the diffuse reflectance to the total reflectance at a wavelength of 550 nm (haze value of reflection) is 5 to 50%.
2. The surface light source device according to claim 1.