JP3969245B2 - Light reflection film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a light reflecting film used for a reflecting member, and more specifically, a light reflecting film suitable as a reflector for a surface light source and a lamp reflector, which is brighter and has excellent illumination efficiency. The present invention relates to a light reflecting film from which a light source can be obtained.
[0002]
[Prior art]
In recent years, many displays using liquid crystals have been used as display devices for personal computers, televisions, mobile phones, and the like. Since these liquid crystal displays themselves are not light emitters, they can be displayed by installing a surface light source called a backlight from the back side and irradiating light. Further, the backlight has a structure of a surface light source called an edge type or a direct type in order to meet the requirement that the entire screen should be irradiated uniformly, not just irradiating light. In particular, for use in a thin liquid crystal display used in a notebook personal computer or the like for which a thin and small size is desired, an edge type, that is, a backlight of a type that irradiates light from the side of the screen is applied (Japanese Patent Application Laid-Open (JP-A)). Sho 63-62104).
[0003]
In general, this edge type backlight employs a light guide plate method that uses a cold cathode ray tube as an 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. Has been. In this illumination method, in order to use light more efficiently, a lamp reflector is provided around the cold cathode ray tube, and in order to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side, A reflector is provided below. Thereby, the loss of light from the cold cathode ray tube is reduced, and the function of brightening the liquid crystal screen is provided.
[0004]
On the other hand, for large screens such as liquid crystal televisions, the direct backlight type has been adopted because it is not possible to increase the screen brightness with an edge type backlight. In this system, a cold cathode ray tube is provided in parallel at the lower part of the 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 part formed into a semicircular concave shape is used.
[0005]
Lamp reflectors and reflectors (generally referred to as surface light source reflectors) used in such surface light sources for liquid crystal screens have excellent brightness improvement effects and uniformity, and therefore contain fine bubbles inside. Films such as JP-A-6-322153 and JP-A-7-118433 are generally used. Among them, a film containing flat bubbles inside by a method such as stretching a resin sheet in which an incompatible component is dispersed has been particularly widely used as a reflecting member because it has particularly high reflectivity. Further, as such a reflecting member, it has been proposed to adjust the glossiness (Japanese Patent Laid-Open No. 63-62104).
[0006]
[Problems to be solved by the invention]
By the way, in addition to conventional notebook computers, LCD screens have been increasingly used in various devices such as stationary computers, televisions, and mobile phone displays. Yes. The liquid crystal screen image is required to have a higher definition, and there is a demand for increasing the brightness of the liquid crystal screen to make the image clearer and easier to see. For this reason, as a light reflection film, a film excellent in reflection characteristics and luminance characteristics, more specifically, a film capable of obtaining a high-brightness backlight is desired.
[0007]
[Means for Solving the Problems]
The present invention has the following configuration in order to solve the above problems. That is, in the present invention, the layer (A layer) having a gas phase flatness of 0.7 or more and the gas phase flatness are 0.2 It is composed of at least two layers (layer B) that are: And the reflectivity is 97.9% or more The essential feature is a light reflecting film characterized in that.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The material of the film of the present invention is not particularly limited, but preferably a thermoplastic resin is the main material. Here, the main means that it is 40% by weight or more. Examples of the thermoplastic resin include polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate, and the like. Polyolefins such as polyester, polyethylene, polypropylene, polycarbonate, polystyrene, polyamide, polyether, polyurethane, polyphenylene sulfide, polyesteramide, polyetherester, polyvinyl chloride, polymethacrylic acid ester, acrylonitrile-styrene copolymer, acrylonitrile-butadiene- Styrene copolymer, modified polyphenylene ether, polyarylate, polysulfone, polyetherimide, poly Midoimido, such as polyimide and the like. Of these, polyester is preferably used. These resins may be homopolymers or copolymers, but are preferably homopolymers.
[0009]
The light reflecting film of the present invention has a layer (A layer) having a gas phase flatness of 0.7 or more and a gas phase flatness of 0.2 It is necessary to comprise at least two layers of the following layers (B layer).
[0010]
As a result of intensive studies on the above-described problems of the light reflecting film, the present inventors have found that the light reflectivity and luminance characteristics of the light reflecting plate are simply determined by the volume of bubbles and the amount of incompatible components added as described above. It is governed by the flatness of the gas phase part existing inside the film, and the layer (A layer) having a large gas phase flatness and the layer having a small level (B layer) are different. It has been found that by providing two layers independently, light reflectivity, concealment, and luminance characteristics can be dramatically improved. That is, the layer (A layer) having a gas phase flatness of 0.7 or more and the gas phase flatness are 0.2 By forming a light reflecting film composed of at least two layers (B layers) as described below, the front luminance of the surface light source using the light reflecting film is dramatically increased while maintaining excellent reflection characteristics. It can be improved.
[0011]
In the conventional reflective film, the detailed reason why the amount of incompatible components and the simple increase of flat bubbles did not greatly contribute to the improvement of light reflectivity and luminance characteristics is unknown. This is probably because the number of interfaces and the shape of the gas phase portion were not appropriate.
[0012]
In the present invention, the gas phase flatness can be determined by the following method. A) First, a layer for determining the flatness of the gas phase is determined, and the thickness of the layer is measured. Let M be the measured thickness.
B) A straight line having a length M is drawn in parallel to the film surface at an arbitrary position inside the layer for obtaining the gas phase flatness, and the number of gas-solid interfaces existing on the line is counted.
C) The number of gas-solid interfaces obtained in (a) is converted into the number of gas-solid interfaces per 1 mm length to obtain the surface-direction gas-solid interface density P.
D) Next, when a straight line having a length M is drawn from one end of the layer to the other end in the film thickness direction at an arbitrary position inside the layer for determining the flatness of the gas phase portion, it exists on the line. Count the number of gas-solid interfaces.
E) The number of gas-solid interfaces obtained in step d) is converted into the number of gas-solid interfaces per 1 mm length to obtain the gas-solid interface density V in the thickness direction.
F) P / V obtained by dividing P by V is defined as gas phase flatness.
[0013]
Here, the measurement frequency of P and V is not particularly limited, but is preferably 10 times or more, more preferably 100 times or more.
[0014]
Note that V and P in the A layer are AV and AP, and V and P in the B layer are BV and BP.
[0015]
The vapor phase flatness AV / AP of the A layer needs to be 0.7 or more in terms of light reflectivity and concealment property, preferably 0.8 or more, more preferably 0.9 or more. The upper limit of AV / AP is not particularly limited, but it is usually preferably 10.0 or less from the viewpoint of luminance characteristics and film productivity.
[0016]
The vapor phase flatness ratio BV / BP of layer B is in terms of light reflectivity and luminance characteristics. 0.2 Must be Ah The The lower limit of BV / BP is not particularly limited, but is usually preferably 0.05 or more from the viewpoint of film productivity.
[0017]
In addition, when three or more layers exist in a film, the layer applicable to A layer and B layer should just be 1 layer or more respectively.
[0018]
The gas-solid interface density AV in the direction perpendicular to the film surface of the A layer, that is, the thickness direction is preferably 50 or more per mm. More preferably, it is 100-10000, More preferably, it is 200-5000. By setting AV within such a range, it is possible to improve the reflection luminance characteristic and the luminance characteristic more efficiently. If the number of gas-solid interfaces per 1 mm exceeds 10,000, the scattering / reflection phenomenon may depend on the wavelength, so that the reflected light may be colored.
[0019]
Similarly, the thickness direction gas-solid interface density BV of the B layer is preferably 50 or more per mm. More preferably, it is 100-10000, More preferably, it is 200-5000. By setting BV within such a range, it is possible to improve the reflection luminance characteristic and the luminance characteristic more efficiently. If the number of gas-solid interfaces per 1 mm exceeds 10,000, the scattering / reflection phenomenon may depend on the wavelength, so that the reflected light may be colored.
[0020]
The shape of the gas phase contained in the A layer and the B layer is not particularly limited, but the gas phase in the B layer is composed of substantially ellipsoidal (flat) bubbles, and the gas phase in the A layer is approximately A spherical gas phase is preferable in terms of light reflectivity and luminance characteristics. The A layer and the B layer may be formed into a film by coextrusion or the like, or may be separately produced and bonded using a known technique. Examples of the bonding include thermocompression bonding and techniques using various adhesives.
[0021]
Examples of the method for forming a layer (A layer) having a gas phase flatness of 0.7 or more include the following methods (I) to (VI).
(I) A method in which at least one selected from organic hollow particles, inorganic hollow particles, organic porous particles, and inorganic porous particles is added to a thermoplastic resin to form a melt.
(II) A method in which expandable particles are coated on a base film and foamed by heating or the like.
(III) A method in which foamable particles are added to a thermoplastic resin and melt-extruded to foam inside the film.
(IV) A method of bonding a nonwoven fabric to a base film.
(V) A method of forming a porous layer by dissolving an inert gas in a resin at a high pressure and then releasing the pressure.
(VI) A method in which at least one selected from organic hollow particles, inorganic hollow particles, organic porous particles and inorganic porous particles is coated on a substrate film and dried.
(VII) After the resin (a) is dissolved in the solvent (b) and applied to the base film, the film is solidified through the solvent (c) in which the solvent (b) is dissolved but the resin (a) is not dissolved. And let it dry. These methods may be used alone, or a plurality of methods may be used in combination.
[0022]
Hereinafter, the methods (I) and (II) will be described in detail as preferred examples of the present invention. First, the case of (I) will be described. Here, a hollow particle is a particle containing one or more closed cells inside the particle, and a porous particle is a particle having one or more open holes (including continuous holes, through holes, etc.) inside the particle. It is. Further, secondary particles substantially having a hollow portion and secondary particles having substantially one or more opening holes are also included. Specific examples of these secondary particles include “Godd Ball” (manufactured by Suzuki Yushi Kogyo Co., Ltd.), which consists of fine primary particles of silica, and the primary particles are aggregated in a hollow sphere shape to form secondary particles. Wanoshin Microcapsule "(manufactured by Washin Chemical Co., Ltd.). The secondary particles in which the primary particles are simply randomly aggregated are generally not included in the hollow particles, but can be included in the porous particles when the secondary particles have one or more open pores.
[0023]
Regardless of inorganic or organic, particles may exist in the hollow part of the hollow particle or the pore of the porous particle.
[0024]
As a component which forms a hollow particle and a porous particle, inorganic and organic are not ask | required. Examples of inorganic materials include calcium carbonate, barium carbonate, calcium silicate, magnesium silicate, cobalt carbonate, nickel carbonate, basic copper carbonate and other metal salts, iron oxide, silica (anhydrous silicic acid), alumina, copper oxide, cobalt oxide, A metal oxide such as nickel oxide, a hydroxide such as aluminum hydroxide, barium titanate, or the like can be preferably used. In organic, polystyrene resin, polyacrylate resin, polyphenol resin, cross-linked polystyrene-polyacrylate resin, etc. can be used suitably. For the addition of such particles to the thermoplastic resin, for example, a master chip prepared by melt-kneading uniformly in advance may be used, or it may be directly supplied to a kneading extruder.
[0025]
Next, (II) will be described. The expandable particles are particles whose foaming agent inside the particles is vaporized by heating. Expandable particles are generally composed of a core portion which is a foaming agent and a shell portion which wraps the core portion. The component that forms the core portion is not particularly limited as long as it is a component that is vaporized by heating, but liquid hydrocarbons are preferably used. The component forming the shell portion is not particularly limited, but is preferably a component excellent in stretchability and gas barrier properties, and specifically, an acrylonitrile-based copolymer resin or the like is preferably used. In addition, the form after foaming may be a form having closed cells inside the particles, or the particles may burst and become indefinite by foaming. That is, the form of the particles after foaming is not particularly limited as long as a gas-solid interface can be formed in the layer as a result.
[0026]
The expandable particles are preferably well dispersed in the coating liquid. By making such a dispersed state, a uniform coating state can be obtained, and good light diffusibility and luminance characteristics can be obtained.
[0027]
The particle coating method can be performed by any means. For example, methods such as gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife coating, and dipping can be used.
[0028]
The timing for providing the coating layer containing the expandable particles is not particularly limited, and it may be applied during production of the base film (in-line coating), or may be applied onto the base film after crystal orientation (off-line coating). good. It should be noted that other resins, organic materials, and inorganic materials may be included in order to improve the stability of the coating liquid and improve various properties within the range where the effects of the present invention are not lost.
[0029]
Next, the gas phase flatness is 0.2 It describes about the formation method of the layer (B layer) which is the following. Examples of the method for forming the B layer include the following methods.
1) A resin composition in which particles (e) incompatible with the thermoplastic resin (d) are dispersed in the thermoplastic resin (d) is formed into a sheet shape, and then the sheet is stretched to stretch the interior of the film. A method of forming fine flat bubbles.
2) A method in which flat bubbles are formed by adding foamable particles having a flat shape to a thermoplastic resin, and foaming inside the film by melt extrusion.
3) A method of forming flat bubbles by adding hollow particles having a flat shape to a thermoplastic resin and melt-extruding them.
[0030]
In the present invention, a film containing a large amount of fine flat bubbles in the film is preferable. Particularly, the method 1) is preferable because the reflectance is further improved and the front luminance is improved in a surface light source. The method 1) is a method for generating fine flat bubbles by utilizing the fact that peeling occurs at the interface between the thermoplastic resin (d) and the incompatible particles (e) during stretching.
[0031]
Hereinafter, the method 1) will be described in detail as a preferred example of the present invention.
[0032]
The thermoplastic resin (d) is not particularly limited as long as it is a thermoplastic resin capable of forming a film by melt extrusion. Preferred examples include polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalene. Polyester such as carboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polyolefin such as polyethylene and polypropylene, polycarbonate, polystyrene, polyamide, polyether, polyurethane, polyphenylene sulfide, polyesteramide, poly Ether ester, polyvinyl chloride, polymethacrylic acid ester, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer Modified polyphenylene ether, polyarylate, polysulfone, polyetherimide, polyamideimide, polyimide, etc., and the like, and mixtures of copolymers or these resins to them as a main component.
[0033]
In particular, in the present invention, polyolefin or polyester is preferable from the viewpoint that there is almost no absorption in the visible light region, and among them, polyester is particularly preferable from the viewpoint of good dimensional stability and mechanical properties. The polyester may be a homopolymer or a copolymer, but is preferably a homopolymer. Examples of the copolymer component in the case of a copolymer include aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, diol component having 2 to 15 carbon atoms, and specific examples thereof include isophthalic acid. Examples include acids, adipic acid, sebacic acid, phthalic acid, sulfonate group-containing isophthalic acid, and ester-forming compounds thereof, diethylene glycol, triethylene glycol, neopentyl glycol, polyalkylene glycol having a molecular weight of 400 to 20,000, and the like. it can.
[0034]
In these polyesters, various additives such as a fluorescent brightening agent, a crosslinking agent, a heat resistance stabilizer, an oxidation resistance stabilizer, an ultraviolet absorber, an organic lubricant, an organic and an inorganic substance are used within the range not inhibiting the effect of the present invention. Fine particles, fillers, light-proofing agents, antistatic agents, nucleating agents, dyes, dispersing agents, coupling agents, and the like may be added.
[0035]
Next, incompatible particles (e) added to form fine flat bubbles will be described. The incompatible particles (e) are not particularly limited as long as they can be dispersed in the thermoplastic resin (d), and examples thereof include inorganic fine particles, organic fine particles, and various thermoplastic resins. The above components may be used alone or in combination of two or more.
[0036]
Among these, the inorganic fine particles are preferably those capable of forming fine flat bubbles with themselves as nuclei. For example, calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide (anatase type, rutile type), zinc oxide, barium sulfate. 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 these, it is particularly preferable to use calcium carbonate and barium sulfate which have little absorption in the visible light range of 400 to 700 nm. This is because if the absorption is in the visible light range, problems such as a decrease in luminance may occur.
[0037]
In the case of organic fine particles, those that do not melt by melt extrusion are preferred, and crosslinked fine particles such as crosslinked styrene and crosslinked acrylic are particularly preferred. The above fine particles may be used alone or in combination of two or more.
[0038]
Next, as an example of using a resin as the incompatible particles (e), when using a polyester resin for the thermoplastic resin (d), a polyolefin resin such as polyethylene, polypropylene, polybutene, 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 homopolymers or copolymers, or two or more of them may be used in combination. In particular, a resin having a large difference in critical surface tension from polyester and not easily deformed by heat treatment after stretching is preferred, and a polyolefin resin, particularly polymethylpentene is particularly preferred.
[0039]
The thickness of the layer having a vapor phase flatness of 0.7 or more (A layer) is not particularly limited, but is preferably 0.3 μm to 50 μm, more preferably 0.3 to 30 μm. . If the function of the present invention is exhibited, it is preferable that the thickness is small.
[0040]
Moreover, 30-1000 micrometers is preferable and, as for the total thickness of the light reflection film of this invention, 50-500 micrometers is more preferable. When the thickness is less than 30 μm, it becomes difficult to ensure the flatness of the film, and unevenness in brightness tends to occur when used as a surface light source. On the other hand, if it is thicker than 1000 μm, the thickness may be too large for use as a light reflecting film in a liquid crystal display or the like.
[0041]
The light reflecting film of the present invention may be a film composed of two layers of an A layer and a B layer, but other layers are formed by coextrusion of a thermoplastic resin layer on at least one surface of the A layer or the B layer. May be laminated. By laminating such a thermoplastic resin layer, surface smoothness and mechanical strength can be imparted to the film.
[0042]
Furthermore, for the purpose of improving the reflectivity and imparting electromagnetic wave shielding properties and bending workability, a metal such as aluminum or silver may be added to the light non-incident surface by vapor deposition or bonding.
[0043]
The light reflectance of the light reflecting film of the present invention is preferably 80% or more, more preferably 90% or more. When the light reflectance is less than 80%, the film is inferior in concealability, and when used as a light reflecting film in a liquid crystal display or the like, sufficient luminance may not be obtained.
[0044]
Next, although an example is demonstrated about the manufacturing method of the light reflection film of this invention, this invention is not limited to this example.
[0045]
In a composite film-forming apparatus having a main extruder and a sub-extruder, a mixture of a thermoplastic resin (d) chip and an incompatible component (e) constituting the B layer that has been vacuum-dried as necessary. Feed to heated main extruder. Here, adding a third component having compatibility with both the thermoplastic resin (d) and the incompatible component (e) as the third component is also effective in forming more flat bubbles. Subsequently, in order to laminate the A layer, a mixture of the thermoplastic resin chips and the hollow particles constituting the A layer which has been vacuum-dried as necessary is supplied to a heated sub-extruder. Here, the addition of the incompatible component (e) and the addition of the hollow particles may be performed by using a master chip prepared by melt-kneading and kneading in advance, or directly supplied to the extruder. Etc.
[0046]
In this way, the raw materials are supplied to each extruder and 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. Co-extruded into a sheet shape to obtain a melt-laminated sheet.
[0047]
The melt-laminated sheet is tightly 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 make it adhere to the drum. Thereafter, if necessary, a desired light reflecting film is obtained through a stretching step, a heat treatment step, and the like.
[0048]
The stretching method is not particularly limited, but a sequential biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are separated or a simultaneous biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are simultaneously used are preferably used. Is done.
[0049]
As a method of sequential biaxial stretching, for example, the unstretched laminated film is guided to a heated roll group, stretched in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and then cooled by a cooling roll group. Subsequently, both ends of the film stretched in the longitudinal direction are guided to a heated tenter while being held by clips, and can be stretched in a direction perpendicular to the longitudinal direction (lateral direction or width direction).
[0050]
As a method of simultaneous biaxial stretching, for example, by guiding the both ends of the unstretched laminated film with a clip to a heated tenter, stretching in the width direction and simultaneously accelerating the clip traveling speed There is a method of performing stretching in the longitudinal direction simultaneously. This simultaneous biaxial stretching method has an advantage that the film surface does not come into contact with the heated roll, so that scratches that are optical defects are less likely to enter the film surface.
[0051]
In order to impart planar stability and dimensional stability to the biaxially stretched laminated film thus obtained, heat treatment (heat setting) is subsequently performed in the tenter, and after uniform cooling, cooling to near room temperature and winding up Thus, a film in which a layer having a hollow particle (low gas phase flatness; A layer) is laminated on a layer having flat bubbles extending in the film surface direction (high gas phase flatness; B layer) is obtained. Can do.
[0052]
Although the use of the light reflecting film of the present invention is not particularly limited, it is preferably used as a plate-like material incorporated in a surface light source for light reflection. Specifically, it is preferably used for a reflection plate of an edge type backlight for a liquid crystal screen, a reflection plate of a surface light source of a direct type backlight, a lamp reflector around a cold cathode tube, and the like.
[0053]
Next, the measurement method and evaluation method used in the present invention will be described.
[0054]
[Measurement and evaluation method of characteristics]
(1) Measurement of thickness-direction gas-solid interface density V and gas phase flatness in the direction perpendicular to the film surface of each layer
Using a microtome, the film is cut without being crushed in the thickness direction. Next, the layer to be measured is determined using a scanning electron microscope, and the cut section is enlarged and observed at an appropriate magnification (100 to 10,000 times) so that the gas phase part and the solid phase part can be clearly observed. . A straight line is drawn at an arbitrary position of the magnified observation image in a direction parallel to the film surface (film surface direction) and a direction perpendicular to the film surface (thickness direction), and the gas phase portion and the solid phase portion existing on each straight line are drawn. Count the number of interfaces, ie gas-solid interfaces. The number of gas-phase interfaces obtained in this way is converted into the number of gas-solid interfaces per unit length to determine the gas-solid interface density P in the surface direction and the gas-solid interface density V in the thickness direction. A value P / V divided by V is defined as a gas phase flatness. In addition, in an Example, the same operation | work (from cutting of a film to measurement of P and V) is performed 100 times about arbitrary places in the layer to be measured, and a simple average value of P, V, and P / V is obtained. Calculated.
[0055]
(2) Reflectance
With a spectrophotometric diameter U-3410 (manufactured by Hitachi, Ltd.) and a φ60 integrating sphere 130-063 (manufactured by Hitachi, Ltd.) and a 10 ° inclined spacer attached, a reflectance of 560 nm is obtained on both surfaces of the film. The maximum value is taken as the reflectance of the film. As the standard white plate, the one attached to U-3410 (manufactured by Hitachi, Ltd.) was used.
[0056]
(3) Luminance as a surface light source
The film was incorporated into the backlight and measured. The backlight used was a straight tube type edge type backlight (14.1 inches) used for notebook computers prepared for evaluation, and instead of the light reflection sheet originally incorporated, Built-in light reflection film. The measurement was performed by dividing the backlight surface into 4 × 2 × 2 sections and determining the luminance after 1 hour of lighting. The luminance was measured using BM-7 manufactured by Topcon Corporation. A simple average of the luminances at the four intersections of the diagonal lines of each surface obtained by dividing the light reflecting film into four equal parts vertically and horizontally was obtained and used as the average luminance. This operation is performed on both sides of the film, and a higher value is adopted as the luminance. The backlight does not incorporate other optical films such as a diffusion film and a prism sheet.
[0057]
【Example】
The present invention will be described using the following examples and comparative examples, but the present invention is not limited thereto.
[0058]
[Example 1]
Pellets mixed with 89% by weight of polyethylene terephthalate (hereinafter abbreviated as PET), 10% by weight of polymethylpentene and 1% by weight of polyethylene glycol are fed to the main extruder, and PET is fed to another sub-extruder. A pellet containing 15% by weight of highly crosslinked styrene-acrylic hollow particles (“SX-782 (B) -02”, manufactured by JSR Corporation) with 85% by weight and an average particle size of 1 μm is supplied, and one side surface layer is formed by a known method. Then, melt extrusion was performed so that the components supplied to the sub-extruder were laminated, and the mixture was cooled on a mirror-casting drum by an electrostatic application method to produce a laminated sheet. This laminated sheet was stretched 3.1 times in the longitudinal direction at a temperature of 92 ° C., then passed through a preheating zone of 100 ° C. with a tenter, and then stretched 3.1 times in the width direction at 120 ° C. Furthermore, it heat-processed at 230 degreeC for 30 second, and obtained the extending | stretching heat processing sheet | seat with a film thickness of 200 micrometers.
[0059]
The obtained light reflection film consists of two layers. The layer extruded from the main extruder had a gas phase flatness of 0.2, corresponding to the B layer. On the other hand, the gas phase portion flatness of the layer extruded from the sub-extruder was 0.9, corresponding to the A layer. Also, the thickness direction gas-solid interface densities AV and BV per mm in the direction perpendicular to the film surface in the A layer and the B layer were 530 and 670, respectively. The reflectance of the film obtained by this method is 98.3%, and the luminance when incorporated in a backlight is 3370 cd / m. ² And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film were highly reflective and high luminance characteristics, and were very excellent in practical use.
[0060]
[Example 2]
Example 1 except that pellets mixed with 88% by weight of PET, 10% by weight of polymethylpentene and 2% by weight of polyethylene glycol were fed to the main extruder without using a sub-extruder and melt-extruded. Thus, a single-layer sheet was produced to obtain a stretch heat-treated sheet. The following coating material was applied to one side of the sheet so that the average thickness after heating was 30 μm. The coating material has an average particle size (after foaming) of 17 μm foamed particles (“HTR-001”, manufactured by Sekisui Chemical Co., Ltd., shell composition: acrylonitrile copolymer, core composition (foaming agent): liquid hydrocarbons) 1 part (parts by weight, hereinafter the same) was used by stirring and adding 6 parts of an aqueous binder pigment solution (solid content concentration 50%) made of modified styrene-butadiene. After the coating agent was applied by a known method, it was heated at 160 ° C. for 2 minutes to dry the solvent and foam the expanded particles.
[0061]
The obtained light reflecting film was composed of two layers, and the total film thickness was 220 μm. The flatness of the gas phase of the layer extruded from the main extruder was 0.2, corresponding to the B layer. On the other hand, the flatness of the gas phase of the layer provided by the coating agent was 0.8, corresponding to the A layer. Further, the thickness-direction gas-solid interface densities AV and BV per mm in the direction perpendicular to the film surface in the A layer and the B layer were 60 and 680, respectively. The reflectance of the film obtained by this method is 98.4%, and the luminance when incorporated in a backlight is 3330 cd / m. ² And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film were highly reflective and high luminance characteristics, and were very excellent in practical use.
[0062]
[Example 3]
Using a rectangular die with a hole diameter of 0.4 mm and a hole number of 75, a PET raw material is spun by a melt blow method, an average fiber diameter of 8 μm, and a basis weight of 100 g / m. ² A non-woven fabric was prepared. Next, using the same raw material as in Example 2, it was cast on a cast drum to produce an unstretched single layer film. The non-woven fabric was layered on the unstretched single layer film, supplied to a heating roll, and thermocompression bonded at a roll temperature of 80 ° C. to prepare a two-layer laminated sheet. The laminated sheet was stretched 3.3 times in the longitudinal direction between 90 ° C. heated rolls, and then stretched 4 times in the width direction at 120 ° C. through a 110 ° C. preheating zone. Furthermore, it heat-processed at 210 degreeC for 30 second, and obtained the light reflection film with a total film thickness of 250 micrometers.
[0063]
The obtained light reflection film consists of two layers. The flatness of the gas phase of the layer extruded from the main extruder was 0.2, corresponding to the B layer. On the other hand, the flatness of the gas phase portion of the nonwoven fabric layer laminated on the B layer was 0.7, corresponding to the A layer. The thickness-direction gas-solid interface densities AV and BV per mm in the direction perpendicular to the film surface in the A layer and the B layer were 460 and 670, respectively. The reflectance of the film obtained by this method is 97.9%, and the luminance when incorporated in a backlight is 3300 cd / m. ² And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film were highly reflective and high luminance characteristics, and were very excellent in practical use.
[0064]
[Comparative Example 1]
Except that only PET was supplied to the main extruder, a stretching heat treatment was performed in the same manner as in Example 1 to obtain a laminated film having a thickness of 200 μm. The obtained light reflection film consists of two layers. The interfacial density of the gas phase of the layer extruded from the sub-extruder was 0.9, corresponding to the A layer, but the gas-solid interface was not confirmed in the layer extruded from the main extruder, and it corresponds to the B layer. There wasn't. The reflectance of the film obtained by this method is 62.3%, and the luminance when incorporated in a backlight is 2340 cd / m. ² And showed a low value.
[0065]
[Comparative Example 2]
Except that only PET was supplied to the sub-extruder, a stretching heat treatment was performed in the same manner as in Example 1 to obtain a laminated film having a thickness of 200 μm. The obtained light reflection film consists of two layers. The gas phase flatness of the layer extruded from the main extruder was 0.2 and corresponded to the B layer, but the gas-solid interface was not confirmed in the layer extruded from the sub-extruder and corresponds to the A layer. There wasn't. The reflectance of the film obtained by such a method was 96.5%, but the luminance when incorporated in a backlight was 2720 cd / m. ² And showed a low value.
[0066]
[Comparative Example 3]
The main extruder is supplied with pellets containing 94% PET, 5% polymethylpentene and 1% polyethylene glycol, and 5% calcium carbonate with an average particle diameter of 2μm is supplied to the sub-extruder. Pellets mixed by weight% were supplied and subjected to stretching heat treatment and the like in the same manner as in Example 1 to obtain a laminated film having a thickness of 200 μm. The obtained light reflection film consists of two layers. The gas phase flatness of the layer extruded from the main extruder was 0.2 and corresponds to the B layer, but the gas phase flatness of the layer extruded from the sub-extruder was 0.6 and the layer A was Was not applicable. The reflectance of the film obtained by this method is 92.1%, and the luminance when incorporated in a backlight is 2610 cd / m. ² And showed a low value.
[0067]
【The invention's effect】
The light reflecting film of the present invention is excellent in reflection characteristics, luminance characteristics, etc., and when used as a reflector or lamp reflector in a surface light source for illuminating the liquid crystal screen, the liquid crystal screen is brightly illuminated, and the liquid crystal image is more vivid and clear. Easy to see.

Claims (4)

It is composed of at least two layers of a layer having a gas phase flatness of 0.7 or more (A layer) and a layer having a gas phase flatness of 0.2 or less (B layer), and the reflectance is 97.9. light reflection film characterized in der Rukoto than%. The gas-solid interface density AV in the direction perpendicular to the film surface of the A layer is 60 or more per 1 mm in the film thickness direction, and the gas-solid interface density BV in the direction perpendicular to the film surface of the B layer is 670 per 1 mm in the film thickness direction. It is the above, The light reflection film of Claim 1 characterized by the above-mentioned. The light reflecting film according to claim 1, wherein the light reflecting film is used for a surface light source. A surface light source using the light reflecting film according to claim 1.