JP2007140542A - Light reflection film and surface light source using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light reflection film which is excellent in a reflection characteristic and a hiding property. <P>SOLUTION: The light reflection film has a hole in the film and is characterized in that the number of interfaces formed by the hole in the film thickness direction is 65 or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement in a light reflecting film used for a reflecting member, and more particularly, a light reflecting film suitable as a reflecting plate and a reflector for a surface light source, which is brighter and has excellent illumination efficiency. It is related with the light reflection film which can be obtained.

  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 a side light type or a direct type in order to meet the requirement that the entire screen should be irradiated uniformly, not just light. In particular, for the thin liquid crystal display applications used in notebook PCs, etc., where thinness and miniaturization are desired, a sidelight type, that is, a backlight that emits light from the side of the screen is applied. (Kaisho 63-62104).

  In general, this sidelight type backlight 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. It has been adopted. In this illumination method, in order to use light more efficiently, a 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, Is provided with a reflector. Thereby, the loss of light from the cold cathode ray tube is reduced, and the function of brightening the liquid crystal screen is provided.

  On the other hand, for large screens such as liquid crystal televisions, the edge-light method has been adopted because it is not possible to increase the screen brightness. 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.

  Reflectors and reflectors used in such surface light sources for liquid crystal screens (collectively referred to as surface light source reflecting members) are required to have a high reflection function as well as a thin film. A single film containing fine bubbles inside, or a laminate of these films and a metal plate, a plastic plate or the like has been used. In particular, when a film containing fine bubbles is used, it is widely used because of its excellent brightness improvement effect and uniformity (Japanese Patent Laid-Open Nos. 6-322153 and 7-118433). Such).

By the way, the application of the liquid crystal screen has been widely used in various devices such as a stationary personal computer, a television, and a mobile phone display in recent years in addition to a conventional notebook personal computer. With the demand for higher-definition images on LCD screens, improvements have been made to increase the brightness of LCD screens to make the images clearer and easier to see. Lighting sources (for example, cold cathode ray tubes) Has become higher brightness and higher output.
JP 63-62104 A JP-A-6-322153 JP-A-7-118433

However, when the above-described conventional film is used as a reflector or reflector that is a surface light source reflecting member, since the concealability is inferior, a part of the light of the illumination light source is transmitted to the opposite surface, resulting in liquid crystal It has been pointed out that the brightness (brightness) of the screen is insufficient, and that the efficiency of illumination decreases due to light transmission loss from the illumination light source. It has been demanded.

  In order to solve the above problems, the present invention has the following configuration. That is, the present invention is a light reflecting film having pores inside the film, and when a straight line is drawn perpendicularly to the film surface from one point on the film surface to the other film surface in the film cross section, The number of interfaces existing on the line (measured as one interface both from the gas phase to the solid phase and from the solid phase to the gas phase) is 65 or more per 100 μm of film thickness. The essential feature is a light reflecting film characterized by the above.

  The light reflecting film of the present invention is lightweight, excellent in reflection characteristics, concealment properties, etc., and when used as a reflector or reflector in a surface light source, the liquid crystal screen can be illuminated brightly to make the liquid crystal image clearer and easier to see. Can be useful.

  The light reflecting film of the present invention is a light reflecting film containing pores in the film, and the number of interfaces in the film thickness direction needs to be 65 or more. By setting the number of interfaces to 65 or more, it becomes possible to dramatically improve the reflectivity and concealment of the light reflecting film.

  As a result of intensive studies, the inventors of the present invention should not simply define the light reflectivity by the bubble volume or the amount of incompatible components as described above, but mainly exist inside the film. The inventors have found that it is governed by the number of interfaces formed by the holes, and have completed the present invention.

  In the conventional reflection film, the detailed reason why the simple increase of incompatible components did not greatly contribute to the improvement of light reflectivity is unknown, but the number of interfaces does not increase effectively due to the connection of bubbles. It is thought that

  In the present invention, the component of the pore (hereinafter sometimes referred to as the gas phase) is generally air, but it may be vacuum or other gas components may be filled, for example, as a gas component Examples include oxygen, 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, and ethyl ether. It is done. One kind or two or more kinds of these gas components may be mixed. Further, the pressure in the holes may be less than or equal to atmospheric pressure.

  On the other hand, the components other than the pores constituting the light reflecting film of the present invention, that is, the matrix component (hereinafter abbreviated as solid phase) may be any of various resins, organic substances, inorganic substances and the like as long as they are in a solid state. It may be the body.

  The light reflecting film of the present invention exhibits its light reflecting effect by reflecting light at the interface formed by the holes present in the film. For this reason, it is preferable that the refractive index of the solid component forming the solid phase has a large difference from the refractive index of the gas phase. If the refractive index difference is small, reflection at the interface does not occur so much, and as a result, a desired light reflection effect may not be obtained. Since the refractive index of various gases and vacuum is substantially 1.0, in order to obtain effective light reflectivity, the refractive index of the solid phase is preferably 1.4 or more, more preferably 1.5. That's it.

  In the present invention, the number of interfaces in the film thickness direction needs to be 65 or more, more preferably 70 or more and 3000 or less. By increasing the number of interfaces, high light reflectivity and concealment can be obtained, and by controlling the number of interfaces, the productivity in producing the light reflecting film of the present invention can be improved.

  The average thickness of the holes in the film thickness direction is preferably 0.1 μm to 10 μm, more preferably 0.4 μm to 8 μm, in terms of light reflectivity and light diffusibility. If the thickness is less than 0.1 μm, the reflectance varies depending on the wavelength due to an optical interference effect or the like, and the reflected light may be colored. In addition, if it exceeds 10 μm, the film thickness must be very large in order to allow a certain number of interfaces, the mechanical strength of the film becomes weak, or it is too thick than the desired film thickness, etc. It may be difficult to put to practical use. As described above, liquid crystal display members are becoming thinner and lighter, and an increase in film thickness is not welcomed.

  It is preferable to have 65 or more interfaces per 100 μm of film thickness. More preferably, it is 70 or more and 3000 or less. By providing 65 or more interfaces per 100 μm of film thickness, it is possible to obtain a light reflecting film having a high reflectivity and a high concealing property while being a thin film. When the number of interfaces per film thickness of 100 μm exceeds 3000, the effect of improving the reflectivity and concealment tends to be saturated, and the film thickness tends to increase.

  In the present invention, the shape of the hole is not particularly limited. It may be an independent bubble or a two-dimensional or three-dimensional continuous hole.

  Also, the cross-sectional shape of the hole in the film thickness direction is not particularly limited, but the cross-sectional shape of the hole is circular or an ellipse that is elongated with respect to the film surface direction in order to form a large number of interfaces in the film thickness direction. It is preferable that it is a shape.

  As a method for forming the interface, a method known in this technical field can be used. For example, (I) a mixture containing the main resin component (a) constituting the light reflecting film and the incompatible component (b) with respect to the resin component (a) is melt extruded and then stretched in at least one direction. (II) Method of forming pores by adding foamable particles and foaming inside the film by melt extrusion (III) Carbon dioxide gas Method of forming pores in the film by injecting and foaming a gas such as (IV) Mixing two or more polymers, organic substances, or inorganic substances, melt-extruding, and then extracting at least one component by solvent extraction (V) A method of forming pores by adding hollow particles and melt-extruding by adding hollow particles (VI) Examples include a method of forming a dry porous layer by coating a urethane resin for wet processing and the like, but in the present invention, it is finer because it contains 65 or more interfaces in the film thickness direction. Since it is important to generate flat bubbles, it is preferable to use the method (I), in which the particle diameter and the dispersion diameter of the incompatible component (b) have a certain distribution or more. It is more preferable to use

  The method (I) is a method of generating flat holes by utilizing the fact that peeling occurs at the interface between the main resin component (a) and the incompatible component (b) constituting the light reflecting film during stretching. is there. Therefore, when the method (I) is used, biaxial stretching is more preferably used than uniaxial stretching in order to increase the hole occupied volume and increase the number of interfaces per thickness.

  Hereinafter, the method (I) will be described in detail as a preferred example of the present invention.

  The main resin component (a) constituting the light reflecting film 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 Polyester such as -2,6-naphthalenedicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, etc. Styrene resin, polyolefin such as polyethylene and polypropylene, polycarbonate, polyamide, polyether, polyurethane, polyphenylene sulfide, polyesteramide, polyester Examples thereof include tellurester, polyvinyl chloride, polymethacrylic acid ester, modified polyphenylene ether, polyarylate, polysulfone, polyetherimide, polyamideimide, polyimide, a copolymer containing these as main components, or a mixture of these resins. it can. 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.

  These polyesters may be homopolymers or copolymers, but are preferably homopolymers. The copolymer component in the case of a copolymer is not particularly limited, and examples thereof include aromatic dicarboxylic acid, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, diol component having 2 to 15 carbon atoms, and the like. As isophthalic acid, adipic acid, sebacic acid, terephthalic 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, etc. Can be mentioned.

  In these polyesters, 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, an inorganic, and the like within a range not impairing the effects 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.

  The main resin component (a) constituting the light reflecting film of the present invention is preferably substantially colorless in the visible light region. Here, “substantially colorless” means colorless and transparent or white. The a * value and the b * value defined in JIS Z-8729 are obtained, and both the a * value and the b * value are ± 10. Say that it is within.

  Next, the incompatible component (b) added to form the pores will be described. The incompatible component (b) is not particularly limited as long as it is incompatible with the main resin component (a) constituting the light reflecting film and can be dispersed in the form of particles in the resin component (a). 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.

  Among these, as the inorganic fine particles, those capable of forming pores with themselves as nuclei 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 which have little absorption in the visible light range of 400 to 700 nm. If there is absorption in the visible light region, there may be a problem that the luminance is lowered.

  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 organic fine particles may be hollow.

  The above inorganic fine particles and organic fine particles may be used alone or in combination of two or more.

  In the case of a biaxially stretched film, the total content of the fine particles in the light reflecting film is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, and even more preferably 3 to 20% by weight. When the content is less than 1% by weight, the effect of pore formation is reduced. Conversely, when the content exceeds 30% by weight, film breakage may occur during film formation.

  In the case of a uniaxially stretched film, the total content of the fine particles in the light reflecting film is preferably 2 to 80% by weight, more preferably 5 to 70% by weight, and even more preferably 10 to 65% by weight. If the content is less than 2% by weight, the effect of forming pores is reduced. Conversely, if the content exceeds 80% by weight, the film may be broken during stretching.

  Next, as an example of using a resin as the incompatible component (b), when the resin component (a) is a polyester resin, (b) is a polyolefin resin such as polyethylene, polypropylene, polybutene, or polymethylpentene, polystyrene Resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, fluororesins, 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 critical surface tension difference with polyester and being difficult to be deformed by heat treatment after stretching is preferred, and a polyolefin-based resin, particularly polymethylpentene is particularly preferred.

  The content of the incompatible resin (b) in the light reflecting film is not particularly limited, and can be selected in consideration of breakage during film formation and reflection effect due to hole formation with the incompatible resin (b) as a core. Usually, it is preferably 3 to 35% by weight, more preferably 4 to 30% by weight, even more preferably 5 to 25% by weight. If it is less than 3% by weight, the effect of improving the brightness is reduced, and if it exceeds 35% by weight, the film may be broken during film formation.

  The equivalent sphere diameter of the incompatible component (b) in the film is not particularly limited, but is preferably 0.05 to 15 μm, more preferably 0.1 to 10 μm, and still more preferably 0.3 to 5 μm. If the thickness is less than 0.05 μm, the hole forming property may be insufficient. Conversely, if the thickness exceeds 15 μm, the number of interfaces tends to decrease.

  It is a preferred embodiment that a thermoplastic resin layer is laminated on at least one surface of a film having an interface formed inside the film by a method such as coextrusion. By laminating such a thermoplastic resin layer, surface smoothness and high mechanical strength can be imparted to the film.

  At this time, the laminated thermoplastic resin layer can also contain organic or inorganic fine particles or incompatible resin. In this case, bubbles can be contained in the laminated thermoplastic resin layer by stretching in at least one direction during the production of the film.

  The thickness of the holes present in the laminated thermoplastic resin layer is preferably smaller than the thickness of the holes present in the laminated base film from the viewpoint of luminance. The ratio (thickness of holes present in the laminated thermoplastic resin / thickness of holes present in the laminated base film) is not particularly limited, but is preferably 0.05 to 0.8, more preferably 0.07. It is -0.7, Most preferably, it is 0.1-0.6. The size of the pores can be controlled by, for example, the size of the particles to be added.

  The content of fine particles in the laminated thermoplastic resin is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, even more preferably 3 to 20% by weight. When the content is less than 1% by weight, the effect of pore formation is reduced. Conversely, when the content exceeds 30% by weight, film breakage may occur during film formation.

  In order to impart easy adhesion and antistatic properties to the light reflecting film of the present invention, various coating liquids are applied using a well-known technique, and a hard coat layer is provided to improve impact resistance. May be.

  Here, as a means for coating, 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. Moreover, when hardening an application layer after application | coating, the hardening method can use a well-known method. For example, thermosetting, a method using active rays such as ultraviolet rays, electron beams, radiation, or a combination of these methods can be applied. At this time, it is preferable to use a curing agent such as a crosslinking agent in combination. Moreover, as a method of providing the coating layer, it may be applied (inline coating) at the time of manufacturing the base film, or may be applied (offline coating) on the light reflecting film after completion of crystal orientation.

  In the light reflecting film of the present invention, it is not impeded to add various particles that do not form pores in order to further improve surface slippage and running durability during film formation.

  In general, the light reflecting film of the present invention preferably has a higher whiteness, and more preferably has a bluish color than yellow. Considering this point, it is preferable to add a fluorescent brightening agent to the light reflecting film.

  Commercially available fluorescent whitening agents may be used as appropriate, for example, “Ubitech” (manufactured by Ciba-Gaigi), OB-1 (manufactured by Eastman), TBO (manufactured by Sumitomo Seika Co., Ltd.), “Kecoal” (Manufactured by Nippon Soda Co., Ltd.), “Kayalite” (manufactured by Nippon Kayaku Co., Ltd.), “Lyukopua” EGM (manufactured by Client Japan) and the like can be used. The content of the optical brightener in the film is preferably 0.005 to 1% by weight, more preferably 0.007 to 0.7% by weight, and even more preferably 0.01 to 0.5% by weight. It is particularly preferred. If it is less than 0.005% by weight, the effect is small, and if it exceeds 1% by weight, it may turn yellowish. When the light reflecting film is a laminated film, it is more effective to add the fluorescent whitening agent to the surface layer portion.

  The apparent specific gravity, which is a measure of the vapor phase occupancy of the light reflecting film of the present invention, is preferably from 0.1 to 1.5. More preferably, it is 0.3 or more and 1.3 or less. When the specific gravity is less than 0.1, the mechanical strength as a film may be insufficient, or problems such as easy breakage and poor handleability may occur. On the other hand, when it exceeds 1.5, the occupation ratio of the gas phase is too low, the reflectance is lowered, and the luminance tends to be insufficient.

  When polyester is used as the main resin component (a) constituting the film, the lower limit of the specific gravity is preferably 0.4. If the specific gravity is less than 0.4, the occupation ratio of the gas phase may be too high, and problems such as frequent breaks in the film-forming stretching process may occur.

  10-500 micrometers is preferable and, as for the thickness of the light reflection film of this invention, 20-300 micrometers is more preferable. When the thickness is less than 10 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, when it is thicker than 500 μm, when it is used as a light reflecting film in a liquid crystal display or the like, the thickness may be too large. Moreover, when the film is a laminated film, the ratio of the surface layer portion / inner layer portion is preferably 1/200 to 1/3, and more preferably 1/50 to 1/4. In the case of a three-layer laminated film of surface layer portion / inner layer portion / surface layer portion, the ratio is expressed as the sum of both surface layer portions / inner layer portion.

  Next, although the preferable example is demonstrated about the manufacturing method of the light reflection film of this invention, it is not limited to this example.

  In a composite film-forming apparatus having a main extruder and a sub-extruder, a mixture of a resin component (a) chip and an incompatible component (b), which has been sufficiently vacuum-dried as necessary, is heated. Supply to the extruder. The incompatible component (b) may be added using a master chip prepared by uniformly melting and kneading in advance, or may be directly supplied to a kneading extruder. In order to obtain a laminated film, a thermoplastic resin chip, inorganic particles and fluorescent brightening agent that have been sufficiently vacuum-dried as necessary are supplied to a heated sub-extruder to be co-extruded and laminated.

Here, as the incompatible component (b), it is desirable to use a component having a certain distribution in the dispersion diameter (or the equivalent sphere diameter if not completely spherical). The constant distribution refers to a distribution in which the simple average value d of the dispersion diameter of the incompatible component (b) contained in the reflective film and the standard deviation σ satisfy the relationship represented by the formula (1).
σ ≧ d / 2 Formula (1)
In this case, the incompatible component (b) may be a single type or two or more types. When two or more types of incompatible components (b) are used, it is desirable that they are not compatible with each other and have different compatibility with the resin component (a).

  Here, the compatibility can be determined by the following method. That is, the ratio (L / R) of the cavity length (L) of the hole in the cross section in the lateral direction (plane direction) of the film and the equivalent diameter (R) of the sphere generating the hole is taken. This ratio (L / R) is determined for each incompatible component (b), and this ratio (L / R) is determined by comparing large particles with small particles. It is preferable that the (L / R) of the larger particles and the smaller particles have a difference of 1.5 times or more. Particularly preferably, it is twice or more. When two or more kinds of incompatible components (b) having different particle sizes and compatibility are used, the number of interfaces can be increased efficiently.

  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.

  Here, it is preferable that the screw speed of the extruder is large and the extrusion time is long. By increasing the screw speed and the extrusion time, the dispersibility of the incompatible component (b) in the resin component (a) is improved, and when the incompatible component (b) is a resin component, The dispersion diameter tends to be small. With such an effect, fine holes can be efficiently formed.

  The obtained molten 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 bring the film into close contact with the drum. Then, the target light reflecting film is obtained through a stretching process, a heat treatment process, and the like as necessary.

  In the stretching step, the stretching speed is preferably 5000% / min or more. Particularly preferred is 10000% / min or more. By setting it as this extending | stretching speed, formation of a hole can be promoted efficiently in an extending process, and the number of interfaces can be increased.

  The stretching method is not particularly limited, but a sequential biaxial stretching method in which the stretching in the longitudinal direction and the stretching in the width direction are separately performed, a simultaneous biaxial stretching method in which the stretching in the longitudinal direction and the stretching in the width direction are performed simultaneously are preferably used. It is done.

  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, it is possible to use a method in which both ends of the film stretched in the longitudinal direction are guided to a heated tenter while being held by clips and stretched in a direction perpendicular to the longitudinal direction (lateral direction or width direction).

  In sequential biaxial stretching, it is preferable that the stretching temperature during longitudinal stretching is lower by 15 ° C. or more than the stretching temperature during transverse stretching, and the surface magnification is 15 times or less. By providing a difference in the stretching temperature, it is possible to efficiently generate uniform holes in the surface, and by further reducing the surface magnification to 15 times or less, it is possible to prevent connection of holes due to overstretching. As a result, a large amount and fine holes can be formed efficiently.

  In addition, as a method of simultaneous biaxial stretching, for example, the both ends of the unstretched laminated film are guided to a heated tenter while being gripped by clips, and stretched in the width direction and simultaneously accelerated the clip traveling speed. Thus, there is a method of simultaneously stretching in the longitudinal direction. This simultaneous biaxial stretching method has an advantage that the film surface does not come into contact with a heated roll, so that the film surface is not damaged as an optical defect.

  Here, in the case of the simultaneous biaxial stretching method, it is preferable that the transverse stretching ratio is 0.2 times or more lower than the longitudinal stretching ratio and the surface magnification is 15 times or less. By providing a difference in the vertical and horizontal stretch ratios, it is possible to efficiently generate well-balanced holes in the surface, and further by reducing the surface ratio to 15 times or less, it is possible to prevent connection of holes due to excessive stretching. As a result, a large amount of fine holes can be efficiently formed.

  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, winding is performed. By taking, the light reflective film of the present invention can be obtained.

  Here, the heat treatment is 20 ° C. or more lower than the lowest melting point of the resin component (a) and the incompatible component (b) (softening point for amorphous materials and decomposition point for degradable materials). Heat treatment at a temperature is desirable. By performing the heat treatment at such a temperature, it is possible to impart planar stability and dimensional stability to the film while maintaining high reflectivity without eliminating the generated holes.

  Thus, the light reflecting film of the present invention can be obtained by a method of subsequent stretching and heat treatment after melt extrusion. Therefore, it is possible to obtain a light reflecting film that is excellent in line with high reflectivity, surface flatness, mechanical properties, heat resistance, and productivity.

  To the light reflecting film of the present invention, aluminum, silver, or the like may be added to the film surface by a method such as metal vapor deposition or bonding for the purpose of providing electromagnetic shielding properties or bending workability.

  The light reflecting film of the present invention is preferably used as a plate material incorporated in a surface light source for light reflection. Specifically, it is preferably used for a reflection plate of an edge light for a liquid crystal screen, a reflection plate of a surface light source of a direct type light, a reflector around a cold cathode ray tube, and the like.

[Measurement and evaluation method of characteristics]
(1) Number of interfaces inside the film Using a microtome, cut the film cross-section without crushing it in the thickness direction. Next, from the image obtained by magnifying the cut section at an appropriate magnification (500 to 10,000 times) using a scanning electron microscope S-2100A type (Hitachi Ltd.), any one of the film surface This is obtained by measuring the number of interfaces existing on a line when a straight line is drawn perpendicularly to the film surface from the point toward the other film surface. The number of interfaces is measured as one interface both in the interface from the gas phase to the solid phase and in the interface from the solid phase to the gas phase. In determining the number of interfaces, the number of interfaces at any 100 points is determined and the average is obtained. The same operation is performed from 0 to 315 ° by changing the cut surface by 45 ° with respect to the film surface direction. The maximum value of the obtained 8 data is defined as the number of interfaces.

(2) Particle size distribution of incompatible component (b) A cross-sectional image is obtained using the same method as in (1). 200 points of the incompatible component (b) are randomly selected from the obtained cross-sectional image, and the length in the film surface direction is measured. Let d be the simple average of these values, and σ be the standard deviation. Here, the incompatible component (b) satisfying the relationship of σ ≧ d / 2 was set to a large particle size distribution, and the incompatible component (b) not satisfying the relationship was set to a small particle size distribution.

(3) Reflectance Reflectance of 560 nm was measured on both sides of the film with a spectrophotometer U-3410 (Hitachi Ltd.) attached with a φ60 integrating sphere 130-0632 (Hitachi Ltd.) and a 10 ° C. inclined spacer. The higher value was taken as the reflectance.

(4) Chromaticity of resin component (a) Fill a colorless and transparent 31φ × 15 (mm) round cell with a resin chip of 80% or more, and use SE-2000 (Nippon Denshoku Industries Co., Ltd.) spectroscopic colorimeter. In accordance with the n-45 method described in JIS Z-8722, the reflected light was dispersed by post-spectrometry, and a * value and b * value defined in JIS Z-8729 were obtained.

(5) Heat resistance A film was incorporated into the backlight, and the lamp was lit continuously for 200 hours in an environment maintained at 40 ° C. Thereafter, the film was removed from the backlight, and the change in flatness was visually observed by placing it on a horizontal base. . The backlight used is a straight single-light sidelight type backlight (14.1 inches) used for a notebook computer prepared for evaluation. A film having a part that is bent by 3 mm or more from the horizontal stage and a film having a part that is floating by 5 mm or more is indicated as x, and a film that is not changed is indicated as ◯. ○ is a pass.

(6) Luminance Using a backlight similar to the backlight used in (5), a film was incorporated. Here, no sheet such as a diffusion sheet or a prism sheet is placed on the backlight. 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 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, PET (melting point 260 ° C., a * value −2.80, b * value 5.64) is 84% by weight as the resin component (a), and polymethylpentene (melting point 235 ° C.) is 15% as the incompatible component (b). Pellets mixed with 1% by weight of polyethylene glycol as a dispersant and 1% by weight were supplied and cooled on a mirror-casting drum by a predetermined method to produce a single layer sheet. The rotational speed of the extruder was 100 rpm, and the average time that the pellets stayed in the extruder was about 20 minutes. Here, the screw diameter of the extruder is 200 mm. This single-layer sheet was stretched 3.14 times in the longitudinal direction at a temperature of 84 ° C. and a stretching speed of 10000% / min, and then stretched by a tenter through a 96 ° C. preheating zone to 3.28 times in the width direction at 101 ° C. did. Furthermore, it heat-processed at 212 degreeC for 28 second, and obtained the single layer light reflection film with a film thickness of 100 micrometers and a surface magnification of 10.3 times. The number of interfaces of the obtained light reflecting film was 72, and the particle size distribution of the incompatible component (b) was small. The reflectivity was as high as 96% and was good. The result of heat deflection observation showing heat resistance was also good and good. Furthermore, the luminance when incorporated in the backlight was as high as 2370 cd / m ² . Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent heat resistance and practicality was obtained.

[Example 2]
In the main extruder, 79% by weight of PET as the resin component (a) and 10% by weight and 10% of the two components of polymethylpentene and calcium carbonate (decomposition point: 890 ° C.) as the incompatible component (b), respectively. %, A single-layer sheet was prepared and subjected to stretching heat treatment in the same manner as in Example 1 except that pellets mixed with 1% by weight of polyethylene glycol as a dispersant were supplied, and a single-layer light reflecting film having a thickness of 100 μm was obtained. It was. In the obtained light reflecting film, the average dispersion diameter of polyethylene glycol was 5 μm, the average particle diameter of calcium carbonate was 1.3 μm, and the particle diameter ratio was 3.33. The L / R values indicating compatibility are 4.5 for polyethylene glycol and 2.2 for calcium carbonate, and the ratio of both is 2.05. The number of interfaces of the obtained light reflecting film was 70, and the particle size distribution of the incompatible component (b) was large. The reflectivity was as high as 96%, and the result of heat deflection observation showing heat resistance was also good and good. Furthermore, the luminance when incorporated in the backlight was as high as 2520 cd / m ² . Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent heat resistance and practicality was obtained.

[Example 3]
Mixing 85% by weight of PET as the resin component (a), 10% by weight of polymethylpentene as the incompatible component (b), and 5% by weight of “Hytrel” 7277 (Toray Industries, Inc.) as the dispersant in the main extruder A single layer sheet was prepared in the same manner as in Example 1 except that the pellets were supplied, and subjected to stretching heat treatment to obtain a single layer light reflecting film having a thickness of 100 μm. The number of interfaces of the obtained light reflection film was 103, and the particle size distribution of the incompatible component (b) was small. The reflectivity was as high as 98%, and the result of heat deflection observation showing heat resistance was also good and good. The luminance when incorporated in the backlight was as high as 2460 cd / m ² . Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent heat resistance and practicality was obtained.

[Example 4]
The main extruder is supplied with pellets mixed with 89% by weight of PET as the resin component (a), 10% by weight of polymethylpentene as the incompatible component (b), and 1% by weight of polyethylene glycol as the dispersant, In addition to the main extruder, a sub-extruder was used, and pellets mixed with 86% by weight of PET and 14% by weight of calcium carbonate were supplied to this sub-extruder and supplied to the main extruder by a predetermined method. Three-layer lamination co-extrusion was carried out so as to have the component layer supplied to the sub-extruder on both surface layers of the component layer, and cooled on a mirror cast drum by an electrostatic application method to prepare a three-layer laminate sheet. The three-layer laminated sheet thus obtained was stretched and heat-treated under the same conditions as in Example 1 to obtain a laminated light reflecting film having a total film thickness of 100 μm. In the obtained laminated light reflecting film, the ratio of the thickness per gas phase of the surface layer to the thickness per gas phase of the inner layer (thickness per gas layer of the surface layer / gas phase of the inner layer). The thickness per layer) was 0.3. Moreover, the thickness of the surface layer was 5 μm, and the thickness of the inner layer was 90 μm. Moreover, the number of interfaces of the obtained light reflection film was 68, and the particle size distribution of the incompatible component (b) was small. The reflectivity was as high as 96%, and the result of heat deflection observation showing heat resistance was also good and good. Furthermore, the luminance when incorporated in the backlight was as high as 2780 cd / m ² . Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent heat resistance and practicality was obtained.

[Example 5]
The main extruder was supplied with pellets in which 89% by weight of PET as the resin component (a), 10% by weight of polymethylpentene as the incompatible component (b), and 1% by weight of polyethylene glycol as the dispersant were mixed. A single-layer sheet was produced in the same manner as in Example 1 except that the screw speed of the extruder was 250 rpm, and a heat treatment was performed to obtain a single-layer light reflecting film having a thickness of 100 μm. Moreover, the number of interfaces of the obtained light reflection film was 75, and the particle size distribution of the incompatible component (b) was small. The reflectivity was as high as 96%, and the result of heat deflection observation showing heat resistance was also good and good. The luminance when incorporated in the backlight was as high as 2380 cd / m ² . Thus, the light reflecting film of the present invention showed high reflectivity, and a light reflecting film having excellent heat resistance and practicality was obtained.

[Comparative Example 1]
Except that the main extruder was fed with 96% by weight of PET as the resin component (a), 3% by weight of polymethylpentene as the incompatible component (b), and 1% by weight of polyethylene glycol as the dispersant. In the same manner as in Example 1, a single layer sheet was prepared and subjected to stretching heat treatment to obtain a single layer light reflecting film having a thickness of 100 μm. The number of interfaces of the obtained light reflecting film was 32, and the particle size distribution of the incompatible component (b) was small. The result of observation of heat deflection indicating heat resistance was good with ○, but the reflectivity was as low as 87%, and the luminance when incorporated in a backlight was very low as 1350 cd / m ^2, and the optical characteristics Film was inferior to.

[Comparative Example 2]
A single-layer light reflecting film having a thickness of 100 μm was obtained using the same method as in Example 5 except that the screw speed of the main extruder was 50 rpm and the extrusion time was 10 minutes. The number of interfaces of the obtained light reflection film was 40, and the particle size distribution of the incompatible component (b) was small. The result of heat deflection observation showing heat resistance was good and good, but the reflectivity was as low as 91%, and the luminance when incorporated in a backlight was also low at 1710 cd / m ^2, which was inferior in optical characteristics. It became a film.

[Comparative Example 3]
The main extruder was supplied with pellets in which 82% by weight of PET as the resin component (a), 15% by weight of polymethylpentene as the incompatible component (b), and 3% by weight of polyethylene glycol as the dispersant were mixed. A single layer sheet was prepared and subjected to stretching heat treatment in the same manner as in Example 1 except that the screw rotation speed of the extruder was 50 rpm, and the average time for the pellets to stay in the extruder was about 10 minutes. A single layer light reflecting film was obtained. The number of interfaces of the obtained light reflection film was 57, and the particle size distribution of the incompatible component (b) was small. The result of the heat deflection observation showing heat resistance was good and good, but it was easy to crease and was inferior in handling property. Further, the optical characteristics were such that the reflectivity was 92%, and the luminance when incorporated into a backlight was as low as 1860 cd / m ² , resulting in a film with poor practicality and optical characteristics.

[Comparative Example 4]
A single layer sheet was prepared in the same manner as in Example 5 except that the heat treatment temperature was 250 ° C., and a heat treatment was performed to obtain a single layer light reflecting film having a thickness of 100 μm. The number of interfaces of the obtained light reflection film was 43, and the particle size distribution of the incompatible component (b) was small. The result of the heat deflection observation showing heat resistance was good and good, but the reflectivity was 91%, and the luminance when incorporated in a backlight was as low as 1740 cd / m ^2, and the film was inferior in practicality. .

[Comparative Example 5]
A single layer sheet was prepared in the same manner as in Example 5 except that the rotation speed of the extruder was 100 rpm, the average time for the pellets to stay in the extruder was about 20 minutes, and the speed during stretching was 500% / min. A stretching heat treatment was performed to obtain a single-layer light reflecting film having a thickness of 100 μm. The number of interfaces of the obtained light reflection film was 55, and the particle size distribution of the incompatible component (b) was small. The result of the heat deflection observation showing heat resistance was good and good, but the reflectance was 92% and the luminance when incorporated in a backlight was as low as 1840 cd / m ² , resulting in a film with poor optical properties. .

[Comparative Example 6]
Polyester resin (hereinafter abbreviated as PEI, abbreviated as PEI, a copolymer of 89% by weight of PET as resin component (a) and 12 mol% of isophthalic acid component as PET as component (b) in the main extruder. 3.19, b * value 1.20) was prepared in the same manner as in Example 1 except that pellets mixed with 10% by weight of polyethylene glycol as a dispersant and 1% by weight of polyethylene glycol were supplied. A single-layer film having a thickness of 100 μm was obtained. PEI was dissolved in PET, and dispersed particles composed of the incompatible component (b) were not confirmed. The number of interfaces in the film was 0. The result of the heat deflection observation showing heat resistance was good and good, but the reflectivity was 12% and the luminance when incorporated in the backlight was extremely low at 890 cd / m ² , which was not practical at all. became.

Claims (4)

A light reflecting film having holes in the film, wherein the film has 65 or more interfaces formed by the holes in the film thickness direction. The light reflecting film according to claim 1, wherein the light reflecting film has 65 or more interfaces per 100 μm of film thickness. Melting and extruding a mixture containing the main resin component (a) constituting the light reflecting film and the component (b) that is incompatible with the resin component (a), and stretching in at least one direction The light reflecting film according to claim 1, wherein a hole is formed by the step. The main resin component (a) which comprises this light reflection film is a polyester resin, The light reflection film in any one of Claims 1-3 characterized by the above-mentioned.