JP2004219437A - Light-reflecting film and surface light source using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-reflecting film having superior reflection characteristics and luminance characteristics. <P>SOLUTION: In the light-reflecting film, in which the average reflectance is 80 % or higher and glossiness is different according to the direction of the film surface. When glossiness is G1 in a direction (direction of minimum glossiness) where the glossiness is minimized and glossiness is in a direction orthogonal to the direction is G2, any one of at least equations (1): G2-G1≥20 or equation (2): G2/G1≥1.2 is satisfied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light-reflective film capable of obtaining a high luminance particularly suitable as a backlight for a liquid crystal display, and a surface light source using the same.
[0002]
[Prior art]
In recent years, many displays using liquid crystal have been used as display devices for personal computers, televisions, mobile phones, and the like.
[0003]
Since a liquid crystal display itself is not a light-emitting body, it is generally practiced to irradiate light by installing a surface light source called a backlight on the back side.
As a light source of the backlight, a fluorescent tube or a light emitting diode is often used in order to take advantage of the characteristics of a liquid crystal display such as thinness, light weight, and low power consumption.
[0004]
Since these light emitting sources generally have a point shape or a linear shape, a light beam emitted from the light emitting source is diffused on a surface in order to form a surface light source. Further, in order to prevent the loss of the light beam, inside the surface light source, the surface facing the emission surface is a light reflection surface, and the light beam emitted from the light emitter is introduced between the light reflection surface and the emission surface. In this case, as many light beams as possible are emitted from one surface, that is, the emission surface.
[0005]
As means for introducing a light beam emitted from the luminous body between the reflecting surface and the emitting surface, the following two means are generally employed.
[0006]
One is that the light flux emitted from the light emitting source is once introduced into a substantially flat transparent resin formed body (light guide plate), so that the light flux is emitted from the light emitting body between the light reflecting film and the light emitting surface. The luminous flux is introduced. Such a backlight is generally called a sidelight type or an edgelight type because a light emitting source is often arranged at a position around the screen when the screen is viewed from the front (see Patent Document 1).
[0007]
The other is to introduce a light flux emitted from the luminous body between the light reflecting film and the light emitting surface by disposing a light emitting source between the light emitting surface and the reflecting surface. The light is often called a direct type because the light source is located directly below the screen.
[0008]
Above all, an edge type, that is, a type of backlight that irradiates light from a side surface to a screen, is applied to a thin liquid crystal display used for a notebook personal computer or the like where a thin and small size is desired.
Generally, this edge-type backlight employs a light guide plate system that uses a cold cathode ray tube as the illumination light source from the edge of the light guide plate and uses a light guide plate that uniformly propagates and diffuses light to uniformly illuminate the entire liquid crystal display. Have been. In this illumination method, a lamp reflector is provided around the cold cathode ray tube in order to utilize light more efficiently, and a light guide plate is provided in order to efficiently reflect light diffused from the light guide plate toward the liquid crystal screen. A reflection plate is provided below. This reduces the loss of light from the cold cathode ray tube and provides a function of brightening the liquid crystal screen.
[0009]
On the other hand, for large screens such as liquid crystal televisions, a direct-type backlight system has been employed because edge-type backlights cannot provide high screen brightness. In this method, cold cathode ray tubes are provided in parallel at the lower part of a liquid crystal screen, and the cold cathode ray tubes are arranged in parallel on a reflector. As the reflector, a flat plate or a cold cathode ray tube formed into a semicircular concave shape is used.
[0010]
Such lamp reflectors and reflectors (collectively referred to as surface light source reflection members) used for surface light sources for liquid crystal screens contain fine bubbles inside because of their excellent brightness improving effect and excellent uniformity. A film (for example, see Patent Document 2) is generally used. Above all, a film containing flat bubbles inside by a method such as stretching a resin sheet in which an incompatible component is dispersed is widely used as a white reflecting member because it has particularly high whiteness and reflectivity. (See Patent Document 3). Furthermore, in recent years, there has been an example in which the surface gloss of such a white film is adjusted to achieve high functionality (see Patent Document 4).
[0011]
[Patent Document 1]
JP-A-63-62104
[0012]
[Patent Document 2]
JP-A-7-118433
[0013]
[Patent Document 3]
JP-A-6-322153
[0014]
[Patent Document 4]
JP 2000-348450 A
[0015]
[Problems to be solved by the invention]
By the way, the use of the liquid crystal screen is adopted in various devices such as a stationary personal computer, a television, and a display of a mobile phone in recent years in addition to a conventional notebook personal computer, and the demand is rapidly increasing. . On the other hand, as the image on the liquid crystal screen is required to have higher definition, it is required to increase the brightness of the liquid crystal screen to make the image clearer and easier to see. For this reason, a light reflection film that can provide a high-luminance backlight is also desired. However, simply increasing the light reflection component in the film using a conventional method of manufacturing a reflection film (particularly a method of including a light reflection component such as a gas or a solid in the film) can be incorporated into a backlight or the like. In fact, when actually used as a surface light source, there is almost no effect in terms of front luminance.
[0016]
[Means for Solving the Problems]
The present invention relates to a light reflection film having an average reflectance of 80% or more and having anisotropy in glossiness, wherein the glossiness in the direction in which the glossiness is smallest is G1 and the direction orthogonal to the direction is G1. Is a light reflecting film that satisfies at least one of the following formulas (1) and (2), where G2 is the glossiness.
G2-G1 ≧ 20 (1)
G2 / G1 ≧ 1.2 (2)
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Conventionally, as a method of manufacturing a reflective film, there are many methods in which a light reflecting component such as a gas or a solid is included in the film, but simply increasing the light reflecting component simply incorporates it into a backlight or the like to actually incorporate a surface light source. When used as, almost no effect is seen in terms of front luminance.
[0018]
The present inventors have conducted intensive studies on the problem of the light reflection film described above, and as a result, the backlight luminance should not be simply defined by the volume of bubbles or the amount of addition of an incompatible component as described above. In other words, if the reflectance has a certain level or more, the gloss (incident angle 60 ° -light receiving angle 60 °) G1 in the direction in which the film surface has the smallest gloss (minimum gloss direction), and It has been found that it is governed by the magnitude relationship of the gloss G2 in the direction perpendicular to the direction.
[0019]
That is, by forming a light reflecting film having an average reflectance of 80% or more and having gloss anisotropy such that G1 and G2 satisfy at least the expression (1) or (2), excellent reflection can be obtained. It is possible to drastically increase the front luminance of the surface light source using the light reflection film while maintaining the characteristics.
G2-G1 ≧ 20 (1)
G2 / G1 ≧ 1.2 (2)
Although the detailed reason why the front luminance of the surface light source using such a light reflecting film is improved is not yet clear, it can be considered as follows.
In the edge type backlight, the emission angle of the light emitted from the light guide plate to the reflection film is not substantially uniform, and in most cases, it is largely deviated (has anisotropy) depending on the angle and direction. Also in a direct type backlight, when a linear light source such as a cold cathode tube is used as a light source, the emission angle of light emitted from the light source to the reflection film very often shows anisotropy. Even if such emitted light is reflected using a reflective film having an isotropic gloss, the reflected light angle also reflects the original emission angle anisotropy. And the front luminance is not always high. By covering the reflective film and imparting gloss anisotropy to the reflective film, the exit angle anisotropy of the light emitted from the backlight is negated, and the reflected light with little anisotropy in the exit angle is directed toward the front of the surface light source. It is considered that the light can be emitted, and the front luminance of the surface light source can be improved by such an action.
[0020]
In the conventional light reflecting film, the detailed reason why the simple increase in the number of incompatible components or the number of interfaces did not significantly contribute to the improvement in the backlight luminance is unknown, but even if the light reflecting component was increased. It is considered that the gloss did not change in anisotropy.
[0021]
Here, the reflectivity is such that, with respect to a normal to the film surface showing light reflection characteristics, one ray bundle in which the angle formed by the optical axis is 10 degrees or less is applied to the film at an incident angle of 10 °. It is determined by collecting and receiving light reflected at an angle. However, when using an integrating sphere, the sum of the areas of all the openings must not exceed 10%.
[0022]
The average reflectance can be determined by measuring the reflectance at intervals of 10 nm from 400 nm to 700 nm and calculating a simple average thereof. The average reflectance is required to be 80% or more, preferably 85% or more, and more preferably 90% or more, in terms of light reflectivity and backlight luminance characteristics. When the light reflectance is less than 80%, the film has poor concealing properties, and when used as a light reflection film in a liquid crystal display or the like, sufficient luminance may not be obtained. In the case where the film contains a wavelength conversion agent such as a fluorescent whitening agent, the average reflectance may exceed 100%. The upper limit of the average reflectance in such a case is not particularly limited, but is preferably 200% or less from the viewpoint of the lightness and color of the light reflecting film.
[0023]
Also, the glossiness G1 (incident angle 60 ° -light receiving angle 60 °) in the direction in which the film surface has the smallest glossiness (hereinafter sometimes referred to as “minimum glossiness direction”), and a direction orthogonal to the direction. G2 (incident angle 60 ° -receiving angle 60 °) and their relationship can be determined by the following method.
A) An arbitrary direction is determined on the film surface, and the glossiness is measured under the conditions of an incident angle of 60 ° and a light receiving angle of 60 ° according to JIS-Z8741. The measurement is performed three times or more, and a simple average value is obtained.
B) The same operation is performed from 0 ° to 165 ° by changing the direction determined in a) by 15 ° with respect to the film surface, and the minimum values thereof are defined as G1 and the direction of G1 as the minimum gloss direction. .
C) Measure the gloss in the direction orthogonal to the minimum gloss direction in the same manner as in a). The measurement is performed three times or more, and the simple average value is defined as G2.
D) With respect to the obtained G1 and G2, a value obtained by subtracting G1 from G2 (G2-G1) and a value obtained by dividing G2 by G1 (G2 / G1) are obtained.
[0024]
(G2-G1) or (G2 / G1) needs to satisfy at least the above formula (1) or (2) in terms of backlight luminance characteristics. In terms of productivity and backlight luminance, (G2-G1) is more preferably 25 or more and 150 or less, particularly preferably 30 or more and 100 or less, and (G2 / G1) is 1.3 or more and 200 or less. More preferably, it is particularly preferably from 1.4 to 100.
[0025]
In the present invention, the method for forming the light reflection film having an average reflectance of 80% or more is not particularly limited, but for example, (i) the thermoplastic resin (a) is incompatible with the thermoplastic resin (a) in (a). A method of forming a resin composition in which the particles (b) are dispersed into a sheet, and then stretching the sheet to form fine flat cells inside the film; (ii) a resin (c) in the resin (c). )) And a method of dispersing incompatible particles (d) having different refractive indices.
[0026]
Hereinafter, the methods (i) and (ii) will be described in detail as preferred examples of the present invention.
First, the method (i) will be described. The method (i) is a method of generating fine flat bubbles by utilizing the fact that peeling occurs at the interface (b) between the thermoplastic resin (a) and the immiscible particles during stretching. It is considered that light is reflected at the gas-solid interface.
[0027]
The thermoplastic resin (a) is not particularly limited as long as it is a thermoplastic resin capable of forming a film by melt extrusion. Preferred examples thereof include polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalenedicarboxy. Polyester such as acrylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyolefin such as polycarbonate, polystyrene, polyethylene, polypropylene, polyamide, polyether, polyurethane, polyphenylene sulfide, polyester amide, polyether Ester, polyvinyl chloride, polymethacrylate, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer Modified polyphenylene ether, polyarylate, polysulfone, polyetherimide, polyamideimide, copolymers to polyimides and those composed mainly or can be exemplified mixtures thereof such as a resin. In particular, in the present invention, polyolefin or polyester is preferred from the viewpoint that there is almost no absorption in the visible light region, and among them, polyester is particularly preferred from the viewpoint of good dimensional stability and mechanical properties.
[0028]
Of course, these polyesters may be homopolymers or copolymers, but are preferably homopolymers. Examples of the copolymer component in the case of a copolymer include an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, and a diol component having 2 to 15 carbon atoms. Examples of these are, for example, isophthalic acid. , Adipic acid, sebacic acid, phthalic acid, isophthalic acid containing a sulfonate group, and ester-forming compounds thereof, diethylene glycol, triethylene glycol, neopentyl glycol, and polyalkylene glycol having a molecular weight of 400 to 20,000. .
[0029]
Next, the immiscible particles (b) added to form fine flat bubbles will be described. The immiscible particles (b) are not the same as the thermoplastic resin (a) and may be any particles that can be dispersed in the thermoplastic resin (a) in the form of particles. And a plastic resin. The above components may be used alone or in combination of two or more.
[0030]
Among them, the inorganic fine particles are preferably capable of forming fine flat bubbles by themselves as nuclei, such as calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide (anatase type, rutile type), zinc oxide, barium sulfate, and the like. Zinc sulfide, basic lead carbonate, mica titanium, antimony oxide, magnesium oxide, calcium phosphate, silica, alumina, mica, talc, kaolin and the like can be used. Among them, it is particularly preferable to use calcium carbonate and barium sulfate, which have low absorption in the visible light region of 400 to 700 nm. If absorption occurs in the visible light range, problems such as a decrease in luminance may occur. In the case of organic fine particles, those which are not melted by melt extrusion are preferable, and cross-linked fine particles such as cross-linked styrene and cross-linked acryl are particularly preferable. These fine particles may be used alone or in combination of two or more.
[0031]
Next, as an example of using a resin as the incompatible particles (b), when a polyester resin is used as the thermoplastic resin (a), polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene; Cyclic polyolefin, polystyrene resin, polyacrylate resin, polycarbonate resin, polyacrylonitrile resin, polyphenylene sulfide resin, fluorine resin and the like are preferably used. These may be a homopolymer or a copolymer, and two or more of them may be used in combination. Particularly, a resin having a large difference in critical surface tension from polyester and hardly deformed by heat treatment after stretching is preferable, and a polyolefin resin, particularly, polymethylpentene is particularly preferable.
[0032]
Next, the method (ii) will be described. The method (ii) is a method of dispersing incompatible particles (d) having a different refractive index from the resin (c) to reflect light at an interface between the resin (c) and the particles (d). is there.
The resin (c) is not particularly limited as long as it is a resin capable of forming a film. However, as long as it is a thermoplastic resin, the resins listed as preferred examples of the thermoplastic resin (a) of (i) can be suitably used. . Next, the incompatible particles (d) will be described. The immiscible particles (d) are not the same as the resin (c) and may be any particles that can be dispersed in the thermoplastic resin (a) in the form of particles. For example, inorganic fine particles, organic fine particles, various thermoplastic resins , And the like. Examples of suitable particles include organic / inorganic hollow particles and porous particles in addition to the particles mentioned as preferable examples of the incompatible particles (b) of (i). The above components may be used alone or in combination of two or more.
[0033]
Among these, it is preferable to select particles whose refractive index difference from the resin (c) is as large as possible. The difference in the refractive index between the resin (c) and the particles (d) is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more from the light-reflecting surface.
[0034]
When polyester (refractive index = 1.5 to 1.65) is selected as the resin (c), titanium oxide (refractive index = 2.5 to 2.7), zinc oxide (refractive index = 2.1), It is particularly preferable to use zirconium oxide (refractive index = 2.1), hollow particles (hollow refractive index = 1.0), and the like.
[0035]
In addition, various additives such as a fluorescent whitening agent, a crosslinking agent, a heat-resistant stabilizer, an oxidation-resistant stabilizer, and the like are included in the thermoplastic resin (a) and the resin (c) as long as the effects of the present invention are not impaired. UV absorbers, organic lubricants, organic and inorganic fine particles, fillers, light stabilizers, antistatic agents, nucleating agents, dyes, dispersants, coupling agents, and the like may be added.
[0036]
Further, another layer may be laminated on at least one surface of the resin layer formed by such a method by a method such as co-extrusion of a thermoplastic resin. By laminating such a thermoplastic resin layer, surface smoothness and mechanical strength can be imparted to the film. In addition, adding particles to such a thermoplastic resin layer or enclosing fine flat bubbles are also effective for improving light reflectivity.
[0037]
In the present invention, for example, the following method can be used as a method for forming a light reflecting film in which the relationship between G1 and G2 satisfies the expression (1) or (2). That is, (I) a method by forming a hairline, (II) a method by arranging fibrous substances substantially uniformly, and (III) a method by coating using a wire bar.
[0038]
Hereinafter, specific methods (I) to (III) will be described in detail as preferred examples of the present invention. First, the method (I) will be described. Here, the hairline refers to unevenness oriented in a substantially constant direction on the film surface. The hairline can be formed, for example, by (A) polishing the film surface only in a certain direction using a sandpaper, and (B) rubbing the film surface only in one direction by passing through a brush roll. It is particularly preferable to use the method (B) from the viewpoint of productivity.
[0039]
Next, the method (II) will be described. This method is a method of laminating a fibrous substance on a base film. As a forming method, for example, (A) a method in which fibers are arranged on a base film so that the fiber directions are substantially uniform and laminated by thermocompression bonding or the like; (B) a melt blow method or a spun bond method is used on the base film; And a method of spinning and laminating a resin into a fibrous form so that the fiber direction becomes substantially uniform. Although the material of the fibrous substance is not particularly limited, a polyester resin such as PET or a polyolefin resin such as polypropylene is preferably used in terms of productivity.
[0040]
Finally, the method (III) will be described. This is a method of coating a coating liquid on a base film using a wire bar. The kind of the binder and the solvent of the coating liquid used in this method is not particularly limited, but the binder is a polyester resin, an acrylic resin, polyvinyl chloride, a polyurethane, a silicone resin, etc. from the viewpoint of transparency, and the solvent is toluene, xylene, Methyl ethyl ketone, cyclohexane, ethyl acetate, water, and various alcohols can be suitably used. Also, dispersing fine particles in the coating liquid is more effective in improving the backlight luminance. Although the particle type is not particularly limited, styrene resin, silicone resin, acrylic resin, polyamide resin, polyurethane resin, polyethylene resin, polyester resin, silica, titanium oxide, calcium carbonate, zirconium oxide and the like can be preferably used. The shape and particle size of these particles are not particularly limited. Further, various hardeners, thickeners, dispersants, and the like may be added to the coating liquid within a range in which the effects of the present invention are not lost. A light reflecting film having gloss anisotropy can be obtained by applying such a coating solution to a base film using a wire bar. In addition, since the number of the wire bar is appropriately selected depending on the composition, viscosity and the like of the coating liquid, a preferable range cannot be determined in a straightforward manner. Is often obtained.
[0041]
The timing of performing the methods (I) to (III) is not particularly limited, and may be performed in-line at the time of manufacturing the base film, or may be performed offline using the base film after the oriented crystal. . Further, other resins, organic materials, and inorganic materials may be contained in order to improve the stability of the coating liquid and various characteristics as long as the effects of the present invention are not lost.
[0042]
The total thickness of the light reflecting film of the present invention is preferably from 30 to 1000 μm, more preferably from 50 to 500 μm. When the thickness is less than 30 μm, it becomes difficult to secure the flatness of the film, and when used as a surface light source, unevenness in brightness is likely to occur. On the other hand, when the thickness is more than 1000 μm, the thickness may be too large to be used as a light reflection film in a liquid crystal display or the like.
[0043]
In the present invention, the surface light source used is a surface light source that emits a light beam substantially uniformly from a plane serving as an emission surface, and the surface light source emits a light beam emitted from one or a plurality of point-like or linear light-emitting sources. After diffusing into a plane, the light flux is emitted from the emission surface substantially uniformly, and inside the surface light source, the surface facing the emission surface is a light reflection surface, and the light reflection surface and the light reflection surface A means for introducing a light beam emitted from the luminous body between the light emitting surfaces; a surface of the light reflecting surface facing the light emitting surface having an average reflectance of 80% or more; Assuming that the glossiness in any direction of the surface (incident angle 60 ° -receiving angle 60 °) is G1 and the glossiness in a direction orthogonal to the direction is G2, the above equation (1) or (2) It is preferable to satisfy either of them.
[0044]
The surface light source used in the present invention may take any form as long as it emits light at a substantially uniform speed from a substantially flat surface serving as an emission surface, but a surface light source generally called a backlight is preferable.
[0045]
There are various methods for introducing a light beam emitted from the light source between the reflection surface and the emission surface. There are various methods. (A) At least a substantially rectangular light guide plate, a point-like or linear light-emitting source, (B) a surface light source (edge type backlight) using means for introducing a light beam emitted from the light emitting source from one light incident side of the light guide plate or two light incident sides having a relationship opposite to each other. It is particularly preferable to use at least a plurality of linear fluorescent tubes arranged in parallel and a surface light source (direct backlight) having a structure in which a light reflecting plate is arranged on the back side of the fluorescent tubes. Hereinafter, the surface light source (A), which is one of preferred examples, will be described in detail.
[0046]
First, the edge type backlight (A) will be described. The light guide plate used in the edge type backlight has a generally rectangular shape, although the shape differs depending on the shape of the light emitting source to be introduced and the method of introduction. In any case, it is preferable to use a material having high transparency because a light beam propagates inside. Further, a resin having excellent moldability is more preferable, and an acrylic resin, a cyclic polyolefin resin or the like is particularly preferably used. In the case of introducing a light beam only from one side direction of the light guide plate, a light guide plate having a wedge-shaped or rectangular cross-sectional shape is preferably used. Can be Generally, in order to extract a light beam from the light guide plate, processing is performed on the back side (reflection plate side). For example, a light diffusion paint is printed in a dot shape by a method such as screen printing.
[0047]
Further, a point-like or linear light source is preferable as the light-emitting source. LEDs, fluorescent tubes, organic or inorganic electroluminescence, and the like are preferably used. The light source color is preferably close to an achromatic color. The number of these light sources may be one or more, and different types of light sources may be mixed. Depending on the application, the light source may be introduced from one side direction or from two sides that are in opposite sides.
[0048]
When the edge-type backlight of (A) is used, the light-reflecting film of the present invention may be arranged such that the minimum gloss direction of the light-reflecting film is perpendicular to the light incident side on the light guide plate surface. In the case of using the direct type backlight of B), it is preferable to arrange the minimum gloss direction of the light reflecting film perpendicular to the long axis direction of the parallel fluorescent tubes as the light emitting source from the viewpoint of luminance characteristics. . The light reflection film of the present invention has different light reflection characteristics (gloss) in the minimum gloss direction and the direction perpendicular thereto in the film plane. In other words, it is a film having a biased anisotropic reflectivity. The orientation characteristics of the light emitted from the surface light source of the present invention to the reflector exhibit a very uneven distribution. For the light incident on the reflector having such a biased distribution, by employing the arrangement of the light reflection film in each surface light source of the present invention, it is possible to efficiently emit light while maintaining excellent light reflectivity. The backlight can be directed in the front direction, and higher luminance can be realized.
[0049]
Next, an example of the method for manufacturing the light reflection film of the present invention will be described, but the present invention is not limited to this example.
In a composite film forming apparatus having a main extruder and a sub-extruder, the chips of the thermoplastic resin (a) constituting the layer A and the immiscible component (b) were vacuum-dried as needed. The material is fed to a heated main extruder. Here, adding a component having a compatibilizing action to the thermoplastic resin (a) and the incompatible component (b) as the third component is also effective for forming more flat bubbles. The immiscible component may be added by using a master chip prepared by uniformly melt-kneading and mixing in advance, or may be directly supplied to a kneading extruder. In addition, in order to laminate the layer B, the chips of the thermoplastic resin (a ′) and the incompatible component (b ′), which have been sufficiently vacuum-dried if necessary, are supplied to a heated sub-extruder.
In this way, the raw material is supplied to each extruder, and the extruder is laminated (A / B or A / B / A) so that the polymer of the sub-extruder comes to one side of the polymer of the main extruder in the T-die composite die. It is co-extruded and formed into a sheet to obtain a molten laminated sheet.
[0050]
The molten laminated sheet is fixed and cooled and fixed on a cooled drum to produce an unstretched laminated film. At this time, in order to obtain a uniform film, it is desirable to apply static electricity to bring the film into close contact with the drum. Thereafter, a desired light reflection film is obtained through a stretching step, a heat treatment step, and the like, if necessary.
[0051]
Although the stretching method is not particularly limited, a sequential biaxial stretching method in which stretching in the longitudinal direction and a stretching in the width direction are separately performed, and a simultaneous biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are performed simultaneously are used.
[0052]
As a method of sequential biaxial stretching, for example, the unstretched laminated film is guided to a heated roll group, stretched in a longitudinal direction (longitudinal direction, that is, a film traveling direction), and then cooled by a cooling roll group.
[0053]
Subsequently, the film stretched in the longitudinal direction is guided to a heated tenter while gripping both ends of the film with clips, and can be stretched in a direction perpendicular to the longitudinal direction (lateral direction or width direction).
[0054]
As a method of simultaneous biaxial stretching, for example, by grasping both ends of the unstretched laminated film with a clip and guiding it to a heated tenter, stretching in the width direction and simultaneously accelerating the clip traveling speed. In addition, there is a method of simultaneously performing stretching in the longitudinal direction. This simultaneous biaxial stretching method has an advantage that the film does not come into contact with the heated roll, so that scratches, which are optical defects, do not occur on the film surface.
[0055]
In order to impart planar stability and dimensional stability to the biaxially stretched laminated film thus obtained, a heat treatment (heat setting) is subsequently performed in a tenter, and after uniform slow cooling, the film is cooled to around room temperature.
[0056]
The film is passed through a brush roll to form a hairline on one side of the film.
[0057]
By winding the thus obtained film, a light reflection film having a reflectance of 80% or more and having gloss anisotropy satisfying at least the expression (1) or (2) is obtained. be able to.
[0058]
The light reflection film of the present invention is preferably used as a plate-like material incorporated in a surface light source for light reflection. Specifically, it is preferably used for a reflector of an edge type backlight for a liquid crystal screen, a reflector of a surface light source of a direct type backlight, a lamp reflector around a cold cathode tube, and the like.
[0059]
[Method of measuring and evaluating characteristics]
(1) Average reflectance
With a φ60 integrating sphere 130-063 (Hitachi, Ltd.) and a 10 ° inclined spacer attached to a spectrophotometer U-3410 (Hitachi, Ltd.), the reflectance at 380 to 780 nm was measured, and the average reflectance was measured. I asked. The standard white plate used was that attached to U-3410 (Hitachi, Ltd.).
(2) Gloss G1 and G2
Gloss G1 and G2 were determined using a digital goniogloss meter UGV-5V (Suga Test Instruments Co., Ltd.).
(3) Luminance as surface light source
The film was assembled in the backlight and measured. The backlight used was a straight-tube, single-light, edge-type backlight (14.1 inches) used in a notebook computer prepared for evaluation. The light reflecting sheet was assembled such that the minimum gloss direction was perpendicular to the major axis direction of the light emitting source (linear fluorescent tube). The measurement was performed by dividing the backlight surface into four sections of 2 × 2 and obtaining the front luminance one hour after lighting. The luminance was measured using BM-7 manufactured by Topcon Corporation. The measurement angle was 1 °, and the distance between the luminance meter and the backlight was 80 cm. A simple average of the luminance at four locations in the backlight plane was obtained and defined as the average luminance.
[0060]
【Example】
The present invention will be described with reference to the following Examples and Comparative Examples, but it should not be construed that the invention is limited thereto.
[0061]
[Example 1]
A pellet obtained by mixing 89% by weight of PET, 10% by weight of polymethylpentene and 1% by weight of polyethylene glycol is supplied to the main extruder, and 95% by weight of PET and an average particle diameter of 2 μm are supplied to another extruder. Of 5% by weight of calcium carbonate is melt-extruded by a predetermined method so that the components supplied to the sub-extruder are laminated on both surface layers, and cooled on a mirror-surface cast drum by an electrostatic application method. Thus, a three-layer laminated sheet was produced. This laminated sheet was stretched 3.3 times in the longitudinal direction at a temperature of 90 ° C., and then stretched 3.3 times in the width direction at 120 ° C. through a 100 ° C. preheating zone with a tenter. Further, it was heat-treated at 210 ° C. for 30 seconds, and after cooling, passed through a brush roll to form a hairline, thereby obtaining a stretched heat-treated sheet having a thickness of 200 μm. The reflectance of the obtained light reflecting film was 96.3%. G1 was 13, G2 was 35, G2-G1 was 22, and G2 / G1 was 2.69. The brightness when incorporated in the backlight is 3200 cd / m ² It showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the same exhibited high reflectivity and high luminance characteristics, and a light reflecting film having extremely excellent practicability was obtained.
[0062]
[Example 2]
A laminated sheet was prepared in the same manner as in Example 1 except that the sheet was not passed through a brush roll, and a stretched heat-treated sheet was obtained. The following coating agent was applied to one surface of the sheet using a No. 30 wire bar so that the thickness after drying was 4 μm, and dried at 120 ° C. for 2 minutes to obtain a light reflection film having a total film thickness of 204 μm. . As the coating agent, an acrylic resin coating agent to which 5% by weight of an agglomerated silica having an average particle diameter of 2 μm and subjected to hydrophobic treatment was added was used. The reflectance of the obtained light reflecting film was 96.9%. G1 was 31, G2 was 39, G2-G1 was 15, and G2 / G1 was 1.26. The brightness when incorporated in the backlight is 3250 cd / m ² It showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the same exhibited high reflectivity and high luminance characteristics, and a light reflecting film having extremely excellent practicability was obtained.
[0063]
[Example 3]
A three-layer laminated sheet was prepared in the same manner as in Example 1 except that the sheet was not passed through a brush roll, to obtain a stretched heat-treated sheet. A PET material was spun onto one surface of the sheet by a melt blow method using a rectangular die having a hole diameter of 0.4 mm and a number of holes of 75 so that the arrangement direction of the fibers was substantially uniform. The average fiber diameter is 10 μm and the basis weight is 100 g / m ² Met. The laminated film was supplied to a heating roll and thermocompression-bonded at a roll temperature of 80 ° C. to obtain a four-layer laminated sheet having a thickness of 210 μm. The reflectance of the obtained light reflecting film was 96.5%. G1 was 12, G2 was 20, G2-G1 was 8, and G2 / G1 was 1.67. Brightness when incorporated in the backlight is 3300 cd / m ² It showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the same exhibited high reflectivity and high luminance characteristics, and a light reflecting film having extremely excellent practicability was obtained.
[0064]
[Example 4]
Using a 18-inch direct-type backlight (12 linear fluorescent tubes) as a surface light source, replacing the originally built-in light reflection sheet with the film obtained in Example 1 (reflectance is 95.5%, G1 was 13, G2 was 35, G2-G1 was 22, G2 / G1 was 2.69), and the direction of minimum gloss was incorporated so as to be perpendicular to the long axis direction of the light-emitting source (linear fluorescent tube). . The diffuser attached to the surface light source was not removed. The brightness when incorporated in the backlight is 3420 cd / m ² Met.
[0065]
[Comparative Example 1]
A three-layer laminated sheet was prepared and subjected to stretching heat treatment in the same manner as in Example 1 except that the sheet was not passed through a brush roll, to obtain a stretched heat-treated sheet having a thickness of 200 μm. The reflectance of the obtained film was 95.5%. G1 was 31, G2 was 33, G2-G1 was 2, and G2 / G1 was 1.06. The luminance when incorporated in the backlight is 2900 cd / m ² Met.
[0066]
[Comparative Example 2]
A film having a thickness of 205 μm was obtained in the same manner as in Example 2 except that coating was not performed with a wire bar, but with a reverse coater. The reflectance of the obtained film was 95.5%. G1 was 41, G2 was 45, G2-G1 was 4, and G2 / G1 was 1.10. The brightness when incorporated in the backlight is 2950 cd / m ² Met.
[0067]
[Comparative Example 3]
Using a 18-inch direct-type backlight (12 linear fluorescent tubes) as a surface light source and replacing the originally built-in light reflection sheet with the film obtained in Comparative Example 1 (reflectance is 95.5%, G1 was 31, G2 was 33, G2-G1 was 2, and G2 / G1 was 1.06) so that the direction of minimum gloss was perpendicular to the long axis direction of the light-emitting source (linear fluorescent tube). . The diffuser attached to the surface light source was not removed. The brightness when incorporated in the backlight is 3250 cd / m ² Met.
[0068]
【The invention's effect】
The light reflection film of the present invention has excellent reflection characteristics, luminance characteristics, and the like. When used as a reflection plate in a surface light source for illuminating a liquid crystal screen, the light reflection film can illuminate the liquid crystal screen brightly and make the liquid crystal image clearer and easier to see.

Claims (4)

A light reflection film having an average reflectance of 80% or more and having anisotropy in glossiness of the film surface, wherein the glossiness in the direction in which the glossiness is smallest is G1, and the glossiness in the direction orthogonal to the direction is G1. A light reflecting film that satisfies at least the following expression (1) or (2) when the glossiness is G2.
G2-G1 ≧ 20 (1)
G2 / G1 ≧ 1.2 (2) A surface light source using the light reflection film according to claim 1. A surface light source using at least a light guide plate, a light emitting source, and a means for introducing a light beam emitted from the light emitting source from one light incoming side of the light guide plate or two light incoming sides having a relationship opposite to each other. 3. The surface light source according to claim 2, wherein a light reflection film is disposed on a back surface side of the light plate, and the light reflection film is disposed so that a minimum glossiness of the light reflection film is perpendicular to a light incident side. A plurality of side-by-side linear fluorescent tubes, and a surface light source in which a light reflecting film is arranged on the back side of the fluorescent tube, the direction in which the glossiness of the light reflecting film is the smallest, relative to the major axis direction of the fluorescent tube. The surface light source according to claim 2, wherein the surface light source is arranged to be vertical.