JP4200715B2 - Light reflecting film and manufacturing method thereof - 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 a thin liquid crystal display used for a notebook personal computer or the like that is desired to be thin and small, an edge type, that is, a backlight of a type that irradiates light from the side of the screen is disclosed in, for example, Patent Document 1. Has been.
[0003]
[Patent Document 1]
JP-A 63-62104.
[0004]
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.
[0005]
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 method, 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 the reflector. The reflecting plate may be a flat plate or a cold cathode ray tube formed into a semicircular concave shape.
[0006]
Lamp reflectors and reflectors used in such surface light sources for liquid crystal screens (collectively referred to as surface light source reflecting members) have excellent brightness improvement effects and uniformity, and therefore contain fine bubbles inside. The use of a film is disclosed in Patent Document 2 and Patent Document 3, for example.
[0007]
[Patent Document 2]
JP-A-6-322153,
[0008]
[Patent Document 3]
JP-A-7-118433
Among them, 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 reflecting member because it has particularly high reflectivity.
[0009]
As a means for making the film surface porous, for example, Patent Document 4 discloses a method in which two or more kinds of resins having low mutual solubility are applied and the film surface is made porous by a wet desolvation method. Patent Document 5 discloses a method for making a film surface porous by mixing an appropriate water-dispersible polymer of different sizes and colloidal silica at an appropriate ratio, applying the coating liquid to a base film, and drying. , Respectively.
[0010]
[Patent Document 4]
JP-A-63-197183,
[0011]
[Patent Document 5]
JP-A-3-96332
However, they do not disclose any means for forming an opening hole on the surface of a film containing flat bubbles.
[0012]
[Problems to be solved by the invention]
By the way, in addition to conventional notebook PCs, LCD screens have been used in various devices such as stationary PCs, TVs, and mobile phone displays in recent years, and demand is rapidly increasing. . On the other hand, with the demand for higher-definition images on the liquid crystal screen, it is desired to increase the brightness of the liquid crystal screen to make the image clearer and easier to see. For this reason, the light reflection film is also desired to obtain a high-brightness backlight.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the light reflecting film of the present invention mainly has the following configuration. That is,
The film contains closed cells that are flat with respect to the film surface direction, and has an opening on at least one surface.In addition, the opening diameter of the opening holes is 0.1 to 50 μm, and the number of the opening holes is 1000 or more per square mm of the film surfaceIt is characterized byFor surface light source reflectorIt is a light reflecting film.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The light reflecting film of the present invention needs to contain closed cells that are flat in the film surface direction inside the film and have an opening hole on at least one surface.
[0016]
By forming an opening hole in at least one surface of the flat bubble-containing layer, the reflective film is maintained while maintaining excellent reflection characteristics.As a surface light source reflecting memberThe front luminance of the used surface light source can be dramatically improved.
[0017]
As a method for producing a light reflecting film, there is a technique in which light reflecting components such as bubbles and various inorganic / organic particles are included in the main resin component constituting the light reflecting film, but these light reflecting components are simply increased. Only the front luminance of the surface light source using the light reflecting film is hardly improved. As a result of intensive studies on such a phenomenon, the inventors of the present invention should not simply define the front luminance of the surface light source by the amount of the light reflection component of the light reflection film used for the surface light source. I found out that it is also controlled by diffusivity. Furthermore, in order to obtain light diffusibility that can achieve high brightness of the backlight, it is very effective to form an opening hole on at least one surface of the flat bubble-containing layer, and the front brightness is high. The inventors have found that it can be dramatically improved, and have reached the present invention.
[0018]
Here, the flat closed cell means a bubble flatness (L / S) which is a ratio of a length (L) in a direction parallel to the film surface of the bubble and a length (S) in a direction perpendicular to the film surface. A bubble that is 1.5 or more and that is not confirmed to be connected to other bubbles. Moreover, as shown in FIG. 1, particles may be present in the flat bubbles regardless of whether they are inorganic or organic.
[0019]
The bubble flatness is preferably 2 or more, more preferably 3 or more in terms of light reflectivity. High light reflectivity and concealment can be obtained by enclosing flat closed cells having a large cell flatness inside the film.
[0020]
Further, from the point of light reflectivity, the ratio of the number of flat closed cells occupied by the flat closed cells (flat bubble content) in all the bubbles in the layer containing flat bubbles (A layer) is 40% or more, and further 60%. In particular, 80% or more is preferable. When the flat bubble content is within such a preferable range, sufficient light reflection characteristics and luminance characteristics can be easily obtained with a desired film thickness.
[0021]
In addition, when a several layer exists in a film, the said measurement is performed about each layer and inner layer or more should just achieve flat bubble content rate 40% or more.
[0022]
As a method for forming the flat bubbles in the light reflecting film of the present invention, a method known in the art can be used. For example, (1) by forming a resin composition in which the thermoplastic resin (a) and incompatible particles (b) are dispersed in a thermoplastic resin (a) into a sheet, and then stretching the sheet Forming fine flat bubbles inside the film, (2) Adding foamable particles whose shape is flat, and foaming inside the film by melt extrusion to form flat bubbles, (3) Shape For example, flat bubbles are formed by adding hollow particles having a flat shape and melt extrusion.
[0023]
In the present invention, it is preferable to contain a large amount of fine flat bubbles inside the film, especially in the application of the present invention, the light reflectance is further improved, and in the surface light source, the front luminance is improved, The method (1) is preferable. The method (1) is a method for generating fine flat bubbles by utilizing the fact that peeling occurs at the interface (b) between the thermoplastic resin (a) and incompatible particles during stretching.
[0024]
Hereinafter, the method (1) will be described in detail as a preferred example of the present invention.
[0025]
The main thermoplastic resin constituting the light reflecting film (a) is not particularly limited as long as it is a thermoplastic resin capable of forming a film by melt extrusion, but as a preferred example, polyethylene terephthalate (hereinafter abbreviated as PET), Polyester such as polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate, polyolefin such as polycarbonate, polystyrene, polyethylene, polypropylene, polyamide, polyether, polyurethane , Polyphenylene sulfide, polyester amide, polyether ester, polyvinyl chloride, polymethacrylic acid ester, acrylonitrile-styrene copolymer, acrylonite Le - 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 preferable from the viewpoint that there is almost no absorption in the visible light region, and polyester is particularly preferable from the viewpoint of good dimensional stability and mechanical properties.
[0026]
Of course, these polyesters may be homopolymers or copolymers, but are preferably homopolymers. Examples of copolymer components in the case of a copolymer include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and diol components having 2 to 15 carbon atoms. Examples of these components include isophthalic acid. , 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. .
[0027]
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.
[0028]
Next, the thermoplastic resin (a) and the particles (b) incompatible with the thermoplastic resin (a) added to form fine flat bubbles will be described. The particles (b) incompatible with the thermoplastic resin (a) are not the same as the thermoplastic resin (a) constituting the A layer and can be dispersed in the thermoplastic resin (a) in the form of particles. Examples thereof include inorganic fine particles, organic fine particles, and various thermoplastic resins. These thermoplastic resin (a) and incompatible particles (b) may be used alone or in combination of two or more.
[0029]
Among these, as the inorganic fine particles, those capable of forming fine flat bubbles with themselves as the core are preferable. 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 that have low absorption in the visible light region of 400 to 700 nm from the viewpoint of maintaining high luminance. 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.
[0030]
Next, as an example of using a resin as the incompatible particles (b), when using a polyester resin for the thermoplastic resin (a), 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 being difficult to be deformed by heat treatment after stretching is preferred, and a polyolefin resin, particularly polymethylpentene is particularly preferred.
[0031]
Further, a surface layer may be laminated by a method such as coextrusion of a thermoplastic resin layer on at least one surface of a film in which flat bubbles are formed. By laminating such a thermoplastic resin layer, surface smoothness and mechanical strength can be imparted to the film.
[0032]
At this time, the surface layer can contain organic or inorganic fine particles or incompatible resin. In this case, flat bubbles can be contained in the surface layer by co-extrusion during production of the film and stretching in at least one direction.
[0033]
In the present invention, the components in the flat bubbles are generally components present in the air, but may be in a reduced pressure state or may be filled with other gas components. , Nitrogen, hydrogen, chlorine, carbon monoxide, carbon dioxide, water vapor, ammonia, nitrogen monoxide, hydrogen sulfide, sulfurous acid, methane, ethylene, benzene, methyl alcohol, ethyl alcohol, methyl ether, ethyl ether, and the like. One kind or two or more kinds of these gas components may be mixed. Furthermore, the pressure in the holes may be greater than or less than atmospheric pressure.
[0034]
The light reflecting film of the present invention needs to contain such flat closed cells and have an opening on at least one surface. An opening hole is a hole opened to the surface. The aperture diameter and aperture shape of the hole are not particularly limited, but the aperture (equivalent to a circle) diameter is 0.1 to 50 μm in terms of light diffusibility and light reflectivity.is necessary.More preferably, it is 0.2-20 micrometers, More preferably, it is 0.4-10 micrometers. When the aperture diameter is less than 0.1 μm, the light diffusibility and the light reflectivity change depending on the wavelength due to the light interference effect, and the diffused light and the reflected light may be colored. Further, the number of opening holes is not particularly limited, but may be 1000 or more per square mm.is necessary.More preferably, it is 10,000 or more. When the opening diameter is in such a preferable range, the effect of improving luminance is excellent.
[0035]
Moreover, the state of a hole is not specifically limited. Fine holes may be laminated to form continuous holes. Further, the fine holes may form a two-dimensional network structure in the film surface direction or thickness direction, or may form a three-dimensional network structure and form a through hole from one surface to the other surface. .
[0036]
The thickness of the layer having an opening is not particularly limited, but is preferably 0.3 μm to 30 μm, and more preferably 0.3 to 10 μm because the thickness is not unnecessarily increased.
[0037]
Examples of the method for forming the opening hole include the following. (I) After an appropriate resin is dissolved in an appropriate solvent and applied to the base film, the solvent is dissolved, but the resin is not dissolved but is allowed to solidify and dry to form an opening. Method, (II) A method of forming an aperture by mixing an appropriate water-dispersible polymer of different sizes and colloidal silica in an appropriate ratio, applying the coating liquid to a base film, and drying. (III ) Coating the base film with urethane resin for moisture permeation processing, etc., and drying to form openings, etc. (IV) After mixing and extruding two or more polymers, organics or inorganics , By extracting at least one component by solvent extraction, forming a hole in the surface layer of the film, (V) adding foamable particles, and melt-extruding the film inside A method of forming an opening hole by foaming and rupturing bubbles (VI), a method of forming an opening hole by injecting a gas such as carbon dioxide and extrusion-foaming (VII), and a non-woven fabric on a base film For example, a method of forming an opening hole by bonding. Of these, the coating method (I) is preferable in that high performance can be achieved with a thin film.
[0038]
Hereinafter, the technique (I) will be described in detail as one preferred example of the present invention. The resin is not particularly limited, and a single resin may be used. However, by using two or more resins having low miscibility with each other as a resin material, a surface having a large amount and fine opening holes can be formed. . Examples of the combination of resins having low miscibility with each other include polyester and polyurethane, acrylonitrile-styrene copolymer resin and cellulose acetate, etc., but the best effect of the present invention can be achieved with (A) vinyl chloride alone or Among the copolymers, (B) acrylonitrile homopolymer or copolymer, and (C) butyral resin (A) and (B) and (A) and (C). As the copolymerization partner of (A) vinyl chloride in the above, vinyl acetate, maleic acid and the like are good, and as the copolymerization partner of (B) acrylonitrile, acrylic acid esters and vinyl acetates can be mentioned, It may contain a small amount of sodium acrylic sulfonate. The reason why these combinations are easily made porous is considered to be because the solubility parameters are greatly different from each other. Moreover, the combination of a vinyl chloride-vinyl acetate copolymer and a butyral resin is particularly preferable in terms of ease of dissolution in a solvent and stability of the coating liquid. Furthermore, other resins, organic materials, and inorganic materials may be included mainly for the above combination in order to improve the stability of the coating liquid and various properties. Although the details of the mechanism of micropore formation by such a method are unknown, since the two resins are poorly miscible with each other in the coating liquid state, a small amount of resin is dispersed in a spherical shape in a large amount of resin. However, it is presumed that with the solidification in the solvent, the above-mentioned two kinds of resins are concentrated, and therefore the distance between the two becomes large and a gap is formed.
[0039]
In addition, the layer having an aperture has various additives such as a fluorescent brightening agent, a crosslinking agent, a heat stabilizer, an oxidation stabilizer, an ultraviolet absorber, an organic lubricant, an organic lubricant within the range not inhibiting the effect of the present invention. Further, inorganic fine particles, fillers, light resistance agents, antistatic agents, nucleating agents, dyes, dispersing agents, coupling agents, and the like may be added.
[0040]
In addition, for the purpose of improving light reflectivity and imparting electromagnetic wave shielding property or bending workability, a metal such as aluminum or silver may be added to the light non-incident surface by vapor deposition or bonding.
[0041]
10-1000 micrometers is preferable and, as for the thickness of the light reflection film of this invention, 20-500 micrometers is more preferable. When the thickness of the light reflecting film is within a preferable range, it is easy to ensure the flatness of the film, and when used as a surface light source, unevenness in brightness is less likely to occur. On the other hand, when it is used for a liquid crystal display or the like as a light reflecting film, the thickness does not become too large.
[0042]
Further, 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 in such a preferable range, the film has excellent concealing properties, and when used as a light reflecting film in a liquid crystal display or the like, sufficient luminance can be obtained.
[0043]
Next, although an example is demonstrated about the manufacturing method of the light reflection film of this invention, it is not limited to this example.
[0044]
In a composite film-forming apparatus having a main extruder and a sub-extruder, the chips of the thermoplastic resin (a) constituting the A layer which was sufficiently vacuum-dried as necessary were mixed with the incompatible component (b). Feed things to a heated main extruder. Here, adding a third component having a compatibilizing action to the thermoplastic resin (a) and the incompatible component (b) as the third component is also effective in forming more flat bubbles. In addition, the incompatible component may be added using a master chip prepared by uniformly melting and kneading in advance, or may be directly supplied to a kneading extruder. Moreover, in order to laminate | stack another thermoplastic resin layer, the chip | tip and incompatible component of the thermoplastic resin which performed vacuum drying enough as needed are supplied to the heated subextruder.
[0045]
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.
[0046]
This melt-laminated sheet is closely 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.
[0047]
The stretching method is not particularly limited, and there are a sequential biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are separated and a simultaneous biaxial stretching method in which stretching in the longitudinal direction and stretching in the width direction are performed simultaneously.
[0048]
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.
[0049]
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 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, and therefore there is no scratch that becomes an optical defect on 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 .
[0052]
Next, two kinds of resins having low miscibility are dissolved in a suitable solvent. This solvent is applied by a known application means on the film wound up earlier. The above-mentioned coating is solidified in a solvent that dissolves the solvent contained therein but does not dissolve the resin. Here, adding a substance soluble in the coagulation liquid as the third component is also effective for making the pores. Further, by passing the coating film again through a liquid of the same system as the coagulation liquid heated to 60 ° C. or higher, preferably 80 ° C. or higher, further detachment of the solvent and shrinkage of the resin are promoted, and the porosity is further advanced. To do. When the coagulation liquid is drained and dried, a sheet in which opening holes are formed on a film containing flat closed cells can be obtained.
[0053]
The light reflecting film of the present invention is a plate-like material incorporated in a surface light source for light reflection.Used.Specifically, light reflectors for edge type backlights for LCD screens, light reflectors for surface light sources of direct type backlights, lamp reflectors around cold cathode tubes, etc.Used as a surface light source reflecting member.
[Measurement and evaluation method of characteristics]
(1) Flat bubble content
Using a microtome, the film cross section is cut without being crushed in the thickness direction. Next, 1000 pieces of bubble components are randomly extracted from an image obtained by magnifying and observing the cut section at an appropriate magnification (100 to 10000 times) using a scanning electron microscope, and the bubble flatness (L / S). Here, L represents the long diameter of the bubble, and S represents the short diameter of the bubble. The bubbles having a bubble flatness of 1.5 or more were defined as flat bubbles, and the ratio of the number of flat bubbles in all the bubble components was determined to calculate the flat bubble content. The same operation is carried out by changing the film surface direction by 30 ° from 0 ° to 330 °. The maximum value of the flat bubble content determined by this method is defined as the flat bubble content of the film.
(2) Number of apertures
The film surface was determined from an image obtained by magnifying and observing the film surface at an appropriate magnification (100 to 10,000 times) using a scanning electron microscope. That is, the number of aperture holes having an aperture diameter of 0.1 to 50 μm per square mm of the film surface was measured.
(3) Light reflectance
Obtain a light reflectance of 560 nm on both surfaces of the film with a spectrophotometric diameter U-3410 (Hitachi Ltd.) attached to a φ60 integrating sphere 130-063 (Hitachi Ltd.) and a 10 ° inclined spacer, The maximum value is taken as the light reflectance of the film. The standard white plate was the one attached to U-3410 (Hitachi, Ltd.).
(4) Luminance as a surface light source
A film was incorporated into the backlight, and the front brightness after 1 hour of lighting was measured. The backlight used was a straight tube single-light edge type backlight (14.1 inches) used for a notebook computer prepared for evaluation. 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 luminance at four locations in the plane was determined and used as the average luminance. The backlight does not incorporate other optical films such as a diffusion film and a prism sheet.
[0054]
【Example】
The present invention will be described with reference to the following examples and comparative examples, but is not particularly limited thereto.
[Example 1]
In the main extruder, polyethylene terephthalate (hereinafter referred to as PET) having an intrinsic viscosity of 0.63 dl / g, melting point of 256 ° C. is 89% by weight, polymethylpentene having a melting point of 235 ° C. is 10% by weight, and polyethylene glycol having a molecular weight of 4,000 is 1% by weight. In addition, pellets mixed with 85% by weight of PET and 15% by weight of calcium carbonate are fed to another sub-extruder, and the components supplied to the sub-extruder on both surface layers by a predetermined method. Were melt-extruded so as to be laminated and cooled on a mirror-cast cast drum by an electrostatic application method to prepare a three-layer laminated sheet. This laminated sheet was stretched 3.3 times in the longitudinal direction at a temperature of 90 ° C., and then stretched 3.5 times in the width direction at 120 ° C. through a 110 ° C. preheating zone. Furthermore, it heat-processed at 220 degreeC for 30 second, and obtained the extending | stretching heat processing sheet. The following coating material was applied to one side of the sheet so that the thickness after drying was 10 μm, immersed in water at 20 ° C. for 1 minute, then immersed in hot water at 85 ° C. for 10 seconds, taken out and air-dried, A light reflecting film having a total film thickness of 200 μm was obtained. For the coating material, 100 parts of vinyl chloride-vinyl acetate copolymer resin (VROH, manufactured by Dow Chemical Co., Ltd.) (hereinafter, “parts” represents parts by weight) are dissolved in 400 parts of dimethylformamide (hereinafter, “DMF”), and (B ) 100 parts of butyral resin “Eslac B” (registered trademark, manufactured by Sekisui Chemical Co., Ltd.) dissolved in 400 parts of DMF and mixed with (A) :( B) = 1: 1 were used. The obtained light reflection film had a flat bubble content of 98.3% and a number of apertures of 561,000. The light reflectance is 98.1%, and the luminance when incorporated in a backlight is 3060 cd / m when the surface provided with the coating layer is the reflective surface.²And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film showed high light reflectivity and high luminance characteristics, and a light reflecting film having excellent practicality was obtained.
[Example 2]
In the same manner as in Example 1, a three-layer laminated sheet was produced to obtain a stretch heat-treated sheet. The following coating material is applied to one side of the sheet so that the thickness after drying is 100 μm, air-dried at 80 ° C. for 1 minute, then air-dried at 130 for 1 minute, and a light reflecting film having a total film thickness of 290 μm Got. The coating material is 9 parts of 2.5% ammonia water in 100 parts of IMPRAPERM 43153 (aliphatic urethane resin solution, manufactured by BAYER), 5 parts of IMPRANIL AV Solution (polyacrylate, manufactured by BAYER) and 27 parts of toluene. 32 parts of the mixed solution, 1.2 parts of IMPRAFIX SK Solution (crosslinking agent, manufactured by BAYER) and 80 parts of water were added while stirring, and the mixture was stirred for 5 minutes after the addition was completed. The obtained light reflection film had a flat bubble content of 98.5% and an opening hole count of 98,500. The light reflectance is 97.9%, and the luminance when incorporated in the backlight is 3110 cd / m when the surface provided with the coating layer is the light reflecting surface.²And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film exhibited high reflectivity and high luminance characteristics, and a light reflecting film having excellent practicality was obtained.
[Example 3]
In the same manner as in Example 1, a three-layer laminated 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 thickness after drying was 10 μm, and dried at 130 ° C. for 2 minutes to obtain a light reflecting film having a total film thickness of 200 μm. The coating material was an acrylic polymer emulsion (methyl methacrylate / ethyl alcohol / acrylic acid (60/35/5 wt%) copolymer 70 parts with an average particle size of 0.20 μm and spherical colloidal silica 30 with an average particle size of 0.01 μm. The resulting light-reflecting film had a flat bubble content of 98.2% and a number of apertures of 2700000. The light reflectance was 98. The brightness when incorporated in the backlight is 3040cd / m when the surface provided with the coating layer is a light reflecting surface.²And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the same showed high light reflectivity and high luminance characteristics, and a light reflecting film having excellent practicality was obtained.
[Example 4]
Using a rectangular die with a hole diameter of 0.4 mm and a hole number of 75, the PET raw material was spun by the melt blow method, the average fiber diameter was 8 μm, and the basis weight was 100 g / m.²A non-woven fabric was prepared. Then, using the same raw material as in Example 1, it was cast on a cast drum to produce an unstretched three-layer laminated film. The non-woven fabric was layered on the unstretched three-layer laminated film, supplied to a heated roll, and thermocompression bonded at a roll temperature of 80 ° C. to prepare a four-layer laminated sheet. The laminated sheet was stretched 3.3 times in the longitudinal direction between 90 ° C. heating 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. The obtained light reflection film had a flat bubble content of 98.1% and an opening hole count of 1290. Further, the light reflectance is 98.4%, and the luminance when incorporated in the backlight is 3010 cd / m when the surface on which the nonwoven fabric is laminated is the light reflecting surface.²And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the film showed high light reflectivity and high luminance characteristics, and a light reflecting film having excellent practicality was obtained.
[Example 5]
A light reflecting film having a total thickness of 210 μm was obtained in the same manner as in Example 1 except that the coating material was applied on both sides. The obtained light-reflecting film had a flat bubble content of 97.6% and an opening hole number of 567,000. The light reflectance is 97.8% and the luminance when incorporated in a backlight is 3010 cd / m.²And showed a high value. As described above, the light reflecting film of the present invention and the surface light source using the same showed high reflectivity and high luminance characteristics, and a light reflecting film having excellent practicality was obtained.
[Comparative Example 1]
A three-layer laminated sheet was produced in the same manner as in Example 1 except that the coating material was not applied, and subjected to stretching heat treatment to obtain a laminated film having a total film thickness of 190 μm. The resulting laminated film had a flat bubble content of 98.6% and an opening hole count of 620. The light reflectance was 97.6%, but the luminance when incorporated in a backlight was 2740cd / m.²And showed a low value.
[Comparative Example 2]
Except that only PET was supplied to both the main extruder and the sub-extruder, stretching heat treatment was performed in the same manner as in Example 1, and the resulting stretched heat-treated sheet was coated with a coating material, air-dried, etc. A 190 μm thick laminated film was obtained. The obtained film had a flat bubble content of 4.3% and an opening pore number of 559000. The light reflectance is 83.0%, and the brightness when incorporated in the backlight is 2230cd / m²And showed a low value.
[0055]
【The invention's effect】
The light reflection film of the present invention is excellent in light reflection characteristics, luminance characteristics, etc., and when used as a light reflector or lamp reflector in a surface light source that illuminates the liquid crystal screen, the liquid crystal screen is brightly illuminated and the liquid crystal image is more Clear and easy to see.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of a bubble shape inside a light reflecting film of the present invention including closed cells that are flat with respect to the film surface direction.
[Explanation of symbols]
1: Particle
2: Flat bubbles
L: Length of bubble in the direction parallel to the film surface
S: Length of the bubble in the direction perpendicular to the film surface

Claims (3)

The number of internal film encloses the flat closed cell to the film plane direction, and have a opening hole on at least one surface, and a opening diameter of the opening hole is 0.1 to 50 [mu] m, and the opening hole Is a light reflecting film for a surface light source reflecting member, wherein the film surface is 1000 or more per square mm of the film surface . 2. The light reflecting film for a surface light source reflecting member according to claim 1, wherein the main resin component (a) constituting the film is a polyester resin. 3. The light reflecting film for a surface light source reflecting member according to claim 1, wherein the light reflectance is 90% or more .

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