JP4525055B2 - Light reflecting film and surface light source using the same - Google Patents

Description

  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 reflecting plate for a surface light source, and to obtain a surface light source that is brighter and excellent in illumination efficiency. The present invention relates to a light reflecting film and a surface light source using the same.

  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, display is possible by installing a surface light source called a backlight from the back side and irradiating light using the surface light source. 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 thin LCD displays used in notebook PCs, where thinness and miniaturization are desired, there is a sidelight type, that is, a backlight that illuminates the screen from the side. Applied (Patent Document 1).

  Generally, in this sidelight type backlight, a cold cathode ray tube is used as an illumination light source from the edge of a plate called a light guide plate made of a transparent plate provided on one side even if there are at least one irregular reflection surface, and light is uniformly propagated and diffused. A light guide plate system that uniformly irradiates the entire liquid crystal display using a light guide plate is adopted. In this illumination method, in order to use light more efficiently, a reflector made of a white film or white tape is provided around the cold cathode ray tube and on the side surface of the light guide plate that does not have the cold cathode tube. Further, in order to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side, a reflection layer called a reflection plate is provided under the irregular reflection surface of the light guide plate. 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 film containing fine bubbles inside is used alone, or a film in which these films are bonded to a metal plate, a plastic plate or the like has been used. In particular, when a film containing fine bubbles inside is used, it is widely used because of its excellent brightness improvement effect and uniformity. Such fine bubbles can be obtained by causing a resin to contain an incompatible component (void nucleating agent) and stretching it in one or more directions. Such a film containing fine bubbles inside is disclosed in a patent publication (Patent Document 2).

  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 LCD screens, improvements have been made to increase the brightness of LCD screens to make the images clearer and easier to see. Tubes) are also becoming brighter and more powerful.

  However, when the film is used as a reflector or reflector that is a surface light source reflector, the front luminance is not improved as expected. A reflection film in which the amount of void nucleating agent is simply increased and a reflection film using two or more kinds of void nucleating agents (Patent Document 3) have also been proposed, but this has not led to a dramatic improvement in backlight front luminance.

  In addition, the direct-type backlight has a problem that due to its structure, a large luminance difference is likely to occur between a position directly on the light source on the screen and a position not so, and it is easily recognized as luminance unevenness. Therefore, generally, a semi-transparent milky white plate (so-called light diffusing plate) having a very strong light diffusibility is used on the light emitting surface, and luminance unevenness is reduced as much as possible. As this light diffusion plate, a resin plate made of acrylic or polycarbonate having a thickness of several millimeters mixed with a light scattering material such as organic or inorganic fine particles is used.

  However, since the total light transmittance of such a light diffusing plate is at most about 60%, the luminance (brightness) of the liquid crystal screen is insufficient due to the use of the light diffusing plate, and further illumination is caused by light transmission loss from the illumination light source. There were problems such as a decrease in efficiency.

In order to solve such a problem, there has been proposed a film that aims to reduce luminance unevenness by deforming the light reflecting film in accordance with the arrangement of the light sources and controlling the light emitting direction of the light (for example, Patent Documents 4 and 5). However, since a very large-scale apparatus is required for these processes, at the same time, it is necessary to process each piece one by one, there is a problem in terms of productivity, resulting in high costs. In addition, there are problems in that the deformable reflector is not easy to handle, does not contribute to thinning of the entire backlight, and that the effect of improving luminance unevenness is low in cost.
JP-A-63-62104 (Claims) JP-A-6-322153 (column 0010, Example 1) JP-A-2001-288291 (Claim 5, No. 0007, No. 0027, No. 0031, Examples 1 to 3) JP-A-2001-318614 (Claim 1, No. 0012, No. 0013, No. 0037, FIG. 1) JP-A-2002-82624 (Claim 1, No. 0009, No. 0023, No. 0025, FIGS. 1 and 2)

  The present invention does not require large-scale processing in view of the above-mentioned problems of the prior art, and is a low-cost reflector plate having an effect of improving front luminance and an effect of improving luminance unevenness while maintaining high reflectivity. It is an object of the present invention to provide a clear liquid crystal image that is brighter and has no luminance unevenness.

In order to solve the above problems, the present invention contains low-gloss particles that are agglomerated particles having an average particle size of 5 μm to 10 μm and a pore volume of 1 ml / g to 1.5 ml / g. A low-gloss layer and a light-reflecting layer having fine bubbles, the content of low-gloss particles in the low-gloss layer being 40% by weight or more, an 85 ° specular gloss of 10 or less, and light The essential feature is a light reflecting film having a reflectance of 80% or more and a surface light source using the light reflecting film.

Since the light reflection film of the present invention has an 85 ° specular gloss of 10 or less and a light reflectance of 80% or more, it is excellent in front luminance improvement and luminance unevenness improvement, and the liquid crystal screen is lightened. Illuminates and makes the liquid crystal image clearer and easier to see.

  The light reflecting film of the present invention needs to have an 85 ° specular gloss of 10 or less and a light reflectance of 80% or more.

  The 85 ° specular gloss needs to be 10 or less. More preferably, it is 7 or less, More preferably, it is 5 or less. The lower limit is not particularly set, but 0 is the lower limit in measurement.

  By using the light reflecting film of the present invention in which the 85 ° specular gloss is in such a range, the front luminance is significantly improved in the sidelight type backlight and the luminance unevenness is greatly improved in the direct type backlight. Although the detailed reason for this effect is still unclear, the present inventors consider as follows.

  First, the side light type will be described. In the side light type, as described above, light is emitted from the surface of the light guide plate toward the viewer. However, light is not emitted only from the front surface of the light guide plate, but also from the back surface. For this reason, in the sidelight type, light emitted from the back surface is reflected toward the observer by a reflector, and the light is effectively used.

  However, according to the measurement by the present inventor, the emission angle of the light beam emitted from the rear surface of the light guide plate to the light reflection film is extremely biased in the non-normal direction. Specifically, the amount of light emitted in the direction perpendicular to the light guide plate is small, and most of the light is emitted at a considerably large angle (60 to 85 °) with respect to the direction perpendicular to the light guide plate. Therefore, if the light reflecting film reflects these rays specularly, the reflected light is considered to have a considerably large angle with respect to the vertical direction (observer direction) of the light guide plate. That is, no matter how high the light reflection performance is, it does not contribute to the improvement of the front luminance. On the other hand, when the light reflecting film reflects the incident light beam in a non-specular reflection manner, that is, in a diffuse reflection manner, it is considered that a part of the diffusely reflected light beam is emitted in the front direction, and the front luminance is improved. It is done.

  Here, as described above, most of the light incident on the light reflecting film from the back surface of the light guide plate is incident on the light reflecting film in a state inclined by about 60 ° to 85 ° with respect to the normal direction of the light reflecting film. The Therefore, it is presumed that the lower the 85 ° specular gloss of the light reflecting film, the higher the light diffusibility with respect to the light near the incident angle of 85 °, and the effect of improving the front luminance.

  Next, the direct type will be described. First, luminance unevenness is a phenomenon caused by the difference between the luminance directly above the fluorescent tubes and the luminance between the fluorescent tubes. When the backlight is observed from the front (when viewed from the normal direction with respect to the backlight back plate), the fluorescent tube itself is a light emitter, so that the luminance is very high. On the other hand, as a matter of course, there is no illuminant between the fluorescent tubes, only a light reflecting film is present, and the luminance is remarkably lower than that immediately above the fluorescent tube. Here, the luminance between the fluorescent tubes (that is, the luminance of the light reflecting film located between the fluorescent tubes) is mainly reflected (diffuse reflected) in the direction of the observer from the light entering the light reflecting film from the adjacent fluorescent tubes It is inferred that it will be decided.

  Here, as to what angle the light enters from the fluorescent tube to the light reflecting film positioned between the fluorescent tubes, various backlights were investigated. As a result, 60 ° with respect to the normal direction of the light reflecting film. It was found that there were many backlights incident at an angle of about 85 °.

  Therefore, it is considered that the lower the 85 ° specular gloss of the light reflecting film, the higher the diffuse reflectance with respect to light incident at an angle near 85 °, and the effect of improving the front luminance and the luminance unevenness is expressed. Inferred.

  In the case of the side light type, as the emission angle of the emitted light from the back surface of the light guide plate is greatly inclined from the normal direction of the light guide plate, a higher front luminance improvement is expected. As the emission angle of the emitted light to the light reflecting film located between the fluorescent tubes is greatly inclined from the normal direction of the light reflecting film, higher luminance unevenness improvement can be expected. Specifically, a higher effect is exhibited when the above-described emission angle is 60 ° or more, and a particularly high effect is exhibited when the output angle is 85 ° or more.

  On the other hand, about commercially available white films (E60L, E20 (above, Toray Industries, Inc.), WS-100, WS-180 (Mitsui Chemicals), MC-PET (Furukawa Electric Co., Ltd.), etc.) 85 ° mirror surface When the glossiness was measured, it was a value much higher than 10. Further, when these films were actually incorporated into a backlight by the method described later and the front luminance and luminance unevenness were observed, sufficient front luminance improvement and luminance unevenness improvement were not observed. Although the details of the reason are unclear, it is thought that these films focus only on the development of high light reflectivity.

  In addition, there is an example in which the glossiness is defined by paying attention to the above-described light diffusibility (Patent Publication No. 3018539), but when the 85 ° specular glossiness is 10 or less even if the requirements shown in the patent are satisfied. However, the films shown in Examples and the like were prepared again, and the 85 ° specular gloss was measured. This can be achieved by simply delustering the surface to reduce the specular glossiness of about 60 °, but the specular reflected light intensity becomes abnormally high when the incident angle exceeds 80 °. Therefore, it is considered that the specular gloss of 85 ° or more does not decrease by simply performing a matting process such as roughening the surface. Therefore, the above film must be said to be inadequate for the light reflector application aimed at in the present invention.

The 85 ° specular gloss to 10 or less can be achieved by laminating a low gloss layer having a low gloss particles on one surface of the film. By providing such a low gloss layer, the light incident on the light reflecting film is efficiently diffused and reflected, and the 85 ° specular gloss can be effectively reduced.

  As a method for forming the low gloss layer, for example, a method of coating at least one surface of a film with a coating material in which low gloss particles are added to a binder resin can be suitably used. Hereinafter, the binder component and the low glossy particles that are preferably used in the method will be described.

  The binder component is not particularly limited, but a resin mainly composed of an organic component is preferable. For example, polyester resin, polyurethane resin, acrylic resin, methacrylic resin, polyamide resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, Examples thereof include vinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, and fluorine resin. These resins may be used alone or in the form of two or more copolymers or a mixture. Of these, polyester resin, acrylic resin, and methacrylic resin are preferably used from the viewpoint of heat resistance and transparency.

  On the other hand, as the low gloss particles, for example, silica, alumina, magnesium oxide and the like can be suitably used. Here, when silica or alumina is used as the low-gloss particles, it is preferable to use an aggregate. By using the agglomerate, it is possible to achieve low gloss because a specific shape is not formed on the surface of the coating layer. Among these, agglomerated silica is particularly preferable from the viewpoint of excellent dispersibility and stability in the coating liquid.

Hereinafter, agglomerated silica will be described as a particularly preferred example.
The average particle diameter (laser method) of the agglomerated silica is not particularly limited, but is preferably 0.1 to 50 μm from the viewpoint of low gloss expression, more preferably 2 to 20 μm, and still more preferably 5 to 15 μm. If the particle size is smaller than 0.1 μm, the glossiness is significantly smaller than the wavelength of light, so that sufficient low glossiness may not be exhibited. Moreover, when larger than 50 micrometers, the increase in the layer thickness of a low gloss layer may be caused, and as a result, it leads to thickness increase of the whole light reflection film, and may be unpreferable. The pore volume is preferably 0.2 to 4 ml / g, more preferably 0.4 to 3 ml / g, still more preferably 0.8 to 2 ml / g. On the other hand, the average pore diameter is preferably 1 to 50 nm, more preferably 3 to 35 nm, and still more preferably 5 to 25 nm. By setting the pore volume and the average pore diameter within such a range, even in the pores, light is further scattered, so that higher low gloss can be expressed. On the other hand, when it is out of the above range, there may be inconveniences such as insufficient low glossiness or insufficient viscosity due to excessively high viscosity.

  The low gloss particles may be a single component or a combination of two or more components.

The content of the low gloss particles in low gloss layer is required to be 40 wt% or more, more preferably 50 wt% or more, more preferably 70 wt% or more. When it is 40% by weight or less, low glossiness may not be sufficiently exhibited. Moreover, although the upper limit of content is not specifically limited, When it is 300 weight% or more, it may be inferior to applicability | paintability.

  As a means for coating, for example, gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife coating, dipping, and the like can be used. Further, when the low gloss layer is cured after coating, the curing method may be a 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. In addition, the timing of providing the low gloss layer may be applied during the production of the light reflecting layer (in-line coating) or may be applied on the light reflecting layer after completion of crystal orientation (off-line coating).

  In addition, various additives such as a crosslinking agent, a heat stabilizer, an oxidation stabilizer, an ultraviolet absorber, an organic lubricant, an organic or inorganic fine particle, and a filler are added to the coating liquid within the range not impairing the effects of the present invention. Further, a light resistance agent, an antistatic agent, a nucleating agent, a dye, a dispersing agent, a coupling agent and the like may be added.

  Further, the light reflecting film of the present invention needs to have a light reflectance of 80% or more. More preferably, it is 85% or more, More preferably, it is 90% or more. This is because the higher the light reflectance, the higher the front luminance of the backlight. When the light reflectance is less than 80%, the luminance characteristics may be poor when incorporated in a surface light source. The upper limit is not particularly defined, but is preferably 150% or less from the viewpoint of color tone.

Although the light reflectance can be increased to 80% or more by providing the above-described low gloss layer, in order to achieve a higher light reflectance, the light reflecting film of the present invention is as described below. It is necessary to have a light reflecting layer. By providing such a light reflecting layer, a light reflectance of 85% or more can be achieved. Further, by providing the above-described low gloss layer on at least one side of the light reflection layer, the 85 ° specular gloss can be set to 7 or less. The clear reason that the presence of the light reflecting layer contributes to the low glossiness is unclear, but (i) the light reflecting layer also has a certain light diffusibility, and this light diffusibility contributes to the low glossiness. (Ii) Since the light reflecting layer is often composed of a thermoplastic resin as will be described later, the low-gloss layer described above can be provided uniformly and with good adhesion, and the low-gloss performance of the low-gloss layer is sufficient. The present inventors consider that the main reason is that it is expressed in the above.

As the light reflecting layer, it is necessary to use (a) a layer having a large amount of fine bubbles.

The light reflective film of the present invention, it is necessary to take a method of (b). Since fine bubbles are excellent in light reflectivity, by providing a layer having fine bubbles, the light reflectivity of the light reflection film can be dramatically improved, and the luminance characteristics of the backlight are further increased. be able to.

As a method for forming a light reflecting layer having a large amount of fine bubbles, for example,
(1) A method in which a void nucleating agent is contained in the light reflecting layer and fine bubbles are generated inside by stretching it in at least one direction;
(2) A method of forming bubbles inside by injecting a gas such as carbon dioxide and extruding it,
(3) A method of forming bubbles inside by mixing at least two components of polymer, organic substance, or inorganic substance, melt extrusion, and then dissolving at least one component by solvent extraction,
(4) A method of forming air bubbles by adding hollow particles and melt extrusion,
Etc.

  Here, it is desirable from the viewpoint of light reflectivity that the shape of the bubbles inside the film is an elliptical shape that is elongated in the film surface direction, that is, a flat shape. This is because by making the shape of the bubbles flat, a large number of bubbles can be formed in the film thickness direction, and the light reflectivity can be dramatically improved. Furthermore, it is preferable that the bubbles in the film are independent from the viewpoint of light reflectivity and backlight luminance characteristics.

  Therefore, in the present invention, it is particularly preferable to use the method (1) capable of forming a large number of fine closed flat bubbles. The technique (1) is a technique for generating flat bubbles (voids) by utilizing the fact that peeling occurs at the interface between the resin component constituting the light reflecting film and the void nucleating agent during stretching.

  Furthermore, in this method, (i) by increasing the bubble occupying volume by biaxial stretching and increasing the number of bubbles per thickness (ii) increasing the film thickness (iii) The light reflectance can be increased to 90% or more by taking at least one treatment of increasing the addition amount. Here, the specific film thickness and the added amount of void nucleating agent in the measures (ii) and (iii) necessary for achieving a light reflectance of 90% or more are the types of matrix resin and void nucleating agent, and stretching. Since it differs depending on conditions and the like, it cannot be clearly indicated, but in general, it can be achieved by setting the film thickness to 100 μm or more, and to adding 10% by weight or more if the added amount of the void nucleating agent.

    Hereinafter, the resin component and the void nucleating agent that can be suitably used in the method (1) will be described in detail. First, the main resin constituting the light reflecting layer is not particularly limited, but a resin that does not absorb in the visible light region is preferable. In addition, in this method, light is reflected at the gas-solid interface between the bubbles inside the film and the resin, so that light reflectivity is expressed. Therefore, the refractive index of the resin component forming the solid phase is the refractive index of the gas phase. It is preferable that the difference between is large. When the refractive index difference is small, reflection at the gas-solid interface does not occur so much, and as a result, a desired light reflection effect cannot be obtained. Since the refractive index of gas and vacuum is substantially 1.0, in order to obtain substantially effective light reflectivity, the refractive index of the resin component is preferably 1.4 or more, more preferably 1 .5 or more. Examples of resins that satisfy such conditions include polyolefins and polyesters. Among them, an aromatic polyester is preferably used as a resin having good dimensional stability, mechanical properties, handling properties (handleability) and a high refractive index.

  Among aromatic polyesters, polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalenedicarboxylate, polypropylene terephthalate, polybutylene terephthalate, and poly-1,4-cyclohexylenedi have good film forming properties. More preferably, methylene terephthalate or the like is used. Further, among these, PET resin can be most preferably used because it is inexpensive and easily available.

  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. .

  In these polyester resins, various additives within the range not inhibiting the effect of the present invention, such as fluorescent brightener, crosslinking agent, heat stabilizer, oxidation stabilizer, ultraviolet absorber, organic lubricant, organic, inorganic Fine particles, fillers, light-proofing agents, antistatic agents, nucleating agents, dyes, dispersing agents, coupling agents and the like may be added.

  Next, the void nucleating agent added to form bubbles will be described. The void nucleating agent is not the same as the main resin constituting the light reflecting layer, and may be any material that can be dispersed in the resin component in the form of particles, such as inorganic fine particles, organic fine particles, and various thermoplastic resins. It is done.

  The void nucleating agent is preferably one that can form bubbles with itself as a nucleus, such as 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, polyolefin resin such as polyethylene, polypropylene, polybutene, polymethylpentene, polystyrene resin, polyacrylate resin, polycarbonate resin, polyacrylonitrile Resins, polyphenylene sulfide resins, fluororesins and the like are preferably used.

  In particular, when aromatic polyester is used as the main resin constituting the light reflection layer, it is preferable from the viewpoint of bubble generation ability to use calcium carbonate, barium sulfate, polypropylene, polystyrene, polymethylpentene, etc. as the void nucleating agent. Furthermore, when PET is used for the resin, barium sulfate, polymethylpentene, or the like can be suitably used.

  The void nucleating agent may be a single component, but two or more types of components may be used.

  Further, another resin layer may be laminated on at least one surface of the light reflection layer formed by such a method by a method such as coextrusion. By laminating such resin layers, surface smoothness and mechanical strength can be imparted to the film. In addition, particles and various components may be added to the thermoplastic resin layer, or fine flat bubbles may be included.

  Furthermore, in order not to lose the effects of the present invention, various coating liquids are applied to the surface of the light reflecting layer to impart easy adhesion, antistatic properties, etc. A coat layer or the like may be provided.

  Further, for the purpose of imparting electromagnetic wave shielding properties or folding workability, various papers, various plastics, aluminum, silver, or the like may be added to one surface of the film by a technique such as bonding or metal vapor deposition.

  As described above, the light reflecting film is a plate-like material that is incorporated into a surface light source for light reflection. It is used for reflectors around plates and cold cathode ray tubes. When used for the light reflection film of the present invention for such applications, the reflector is preferably higher in whiteness in terms of the color tone of the screen, and more preferably has a bluish color than yellow. In consideration of this point, it is also a preferred embodiment 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 apparent specific gravity of the light reflecting film of the present invention is preferably 0.1 or more and less than 1.5. More preferably, it is 0.3 or more and less than 1.3. 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 in the light reflecting layer is too low, the light reflectance is lowered, and the luminance may be insufficient.

  10-2000 micrometers is preferable, as for the thickness of the light reflection film in this invention, 20-1000 micrometers is more preferable, More preferably, it is 30-500 micrometers. 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 2000 μm, when it is used as a light reflecting film in a liquid crystal display or the like, the thickness may be too large.

  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.

  In a composite film-forming apparatus having a main extruder and a sub-extrusion machine, a mixture of a chip of a main resin component and a void nucleating agent constituting a light reflecting layer that has been sufficiently vacuum-dried as necessary is heated. Supply to the extruder. The addition of the void nucleating agent may be performed using a master chip prepared by uniformly melting and kneading in advance, or may be directly supplied to a kneading extruder. Also, to laminate a thermoplastic resin layer that gives film strength, supply thermoplastic resin chips, inorganic particles, and fluorescent whitening agent that have been sufficiently vacuum-dried as necessary to a heated sub-extruder. To do.

  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.

  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.

  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. 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).

  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, and therefore there is no scratch that becomes an optical defect on the film surface.

  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 (light reflecting layer) having fine bubbles can be obtained.

The agglomerated silica and a suitable binder component are then dispersed in a suitable solvent. Here, as a first method for producing the light reflecting film of the present invention, the average particle size of the agglomerated silica needs to be about 5 to 10 μm. If particles in such a range are used, the 85 ° specular glossiness can be further lowered because visible light can be efficiently scattered.

Further, as a second method for forming the light reflecting film of the present invention, the aggregated silica needs to have a pore volume of 1 to 1.5 ml / g and an average pore diameter of 10 to 25 μm. Is preferred. If the pore volume and the average pore diameter are in such ranges, the 85 ° specular glossiness can be further lowered because visible light is further scattered even in the pores.

  Furthermore, as a third method for producing the light reflecting film of the present invention, the amount of the aggregated silica added is preferably 80 to 120% with respect to the solid content of the binder. By setting the addition amount in such a range, low glossiness can be exhibited while maintaining good coating properties.

  This solvent is applied onto the film wound up earlier. When the coating liquid is dried, a light reflecting film having a light reflectance of 80% or more and an 85 ° specular gloss of 10 or less can be obtained.

  In particular, by providing a light reflecting layer by the above method and further providing a low gloss layer employing the above-described “first, second, and third methods for forming the light reflecting film of the present invention”, the 85 ° specular glossiness is obtained. It is possible to obtain a light reflecting film having a thickness of 5 or less.

[Measurement and evaluation method of characteristics]
The following measurements are performed at room temperature (20 ° C. to 30 ° C.), under high humidity conditions (relative humidity of 80% or more), at atmospheric pressure, and in the atmosphere.
(1) 85 ° specular glossiness Handy glossiness meter No. 1 manufactured by Suga Test Instruments Co., Ltd. Using CG1450, the 85 ° specular gloss was measured. The measurement was performed on both surfaces of the light reflecting film after standard matching with the attached standard plate, and the lower value was defined as the 85 ° specular gloss of the light reflecting film. The measurement is performed on a flat desk, and no gap is generated between the measuring film and the measuring machine. In addition, Kenran black paper is laid on the non-measurement surface side, that is, on the lower side of the measurement film.

(2) Light reflectivity The light reflectivity of 560 nm is obtained with a spectrophotometer U-3410 (Hitachi Ltd.) attached with a φ60 integrating sphere 130-0632 (Hitachi Ltd.) and a 10 ° inclined spacer. It was. In addition, a light reflectance is calculated | required about both surfaces of a light reflection film, and a higher numerical value is made into the light reflectance of the said light reflection film. Part number 210-0740 manufactured by Hitachi Instrument Service Co., Ltd. was used for the standard white plate.

(3) Backlight brightness Using a straight tube sidelight type backlight (diagonal 35.8 cm (14.1 inch type)) prepared for evaluation, light so that the low gloss surface is in the direction of the viewer. A reflective 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 determining the front luminance after 1 hour of lighting. As for the luminance, front luminance was measured using BM-7 manufactured by Topcon Corporation. Moreover, the measurement point was determined as follows. One side of the long side of the backlight surface is divided into three equal parts in the side direction, and a straight line is drawn from each equally divided point to the other long side facing the long side. Next, a straight line is similarly drawn for the short side. Then, there are four intersections of a straight line drawn from the long side and a straight line drawn from the short side. The measurement was performed on the four intersections, and a simple average of the luminance was obtained and used as the backlight front luminance.

(4) Brightness unevenness The brightness unevenness was measured as follows.
First, a light reflecting film is incorporated in the backlight so that the low gloss surface faces the viewer. The backlight used was a direct backlight with a diagonal of 50.8 cm (20 inches) prepared for evaluation. The backlight has twelve fluorescent tubes having a diameter of 2 mm arranged at equal intervals parallel to the long side. The average distance between the fluorescent tube and the adjacent fluorescent tube is 26 mm, and the average distance between the fluorescent tube and the light reflecting film is 3 mm. A light diffusing plate was mounted on the backlight, and luminance unevenness was visually determined after 1 hour had elapsed since the backlight was turned on. Judgment criteria were “A” when no luminance unevenness was observed, “A” when slightly observed, “A” when slightly observed, and “C” when clearly observed.

  Hereinafter, the present invention will be described with reference to the following examples and comparative examples, but is not particularly limited thereto.

( Comparative Example 5 )
Only PET was supplied to the extruder and cooled on a mirror-casting drum by a predetermined method to produce a single-layer sheet. The single layer sheet was stretched 3.2 times in the longitudinal direction at a temperature of 85 ° C., and then stretched 3.3 times in the width direction at 105 ° C. through a preheating zone of 95 ° C. with a tenter. Furthermore, it heat-processed for 30 seconds at 225 degreeC, and obtained the transparent film with a film thickness of 200 micrometers. The following coating agent was apply | coated to one surface of this single layer transparent film so that the thickness after drying might be set to 5 micrometers. After application, the light reflecting film having a low gloss layer formed on the single-layer transparent layer was obtained by drying at 120 ° C. for 2 minutes.
(Low gloss layer forming coating)
Binder; Udouble UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Silo Hovic 4004 (manufactured by Fuji Silysia Co., Ltd., average particle size 8 μm, pore volume 1.25 ml / g, average pore size 17 nm): 10 parts by weight solvent; toluene: 12 parts by weight of the obtained light reflecting film The 85 ° specular gloss was 8.3, the light reflectance was 85%, the front luminance was 1020 cd / m 2, and the luminance unevenness was o .

( Comparative Example 6 )
A stainless steel plate having a thickness of 0.5 mm was used as the light reflecting layer, and the following coating agent was applied on one surface so that the thickness after drying was 5 μm. After application, the film was dried at 120 ° C. for 2 minutes to form a low-gloss layer on the light reflecting layer to obtain a light reflecting film.
(Low gloss layer forming coating)
Binder; U-double UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight low diffusion particles (aggregated silica) Silo Hovic 4004 (manufactured by Fuji Silysia Co., Ltd., average particle size 8 μm, pore volume 1.25 ml / g, average pore size 17 nm): 10 parts by weight solvent; toluene: 12 parts by weight of the obtained light reflecting film The 85 ° specular gloss was 8.9, the light reflectance was 96%, the front luminance was 1120 cd / m 2, and the luminance unevenness was o .

( Comparative Example 7 )
The main extruder is supplied with pellets in which 89% by weight of PET as a main resin component constituting the light reflecting layer, 10% by weight of polymethylpentene as a void nucleating agent, and 1% by weight of polyethylene glycol as a dispersing agent are mixed. In addition to the main extruder, a sub-extruder was used. To this sub-extruder, pellets mixed with 86% by weight of polyethylene terephthalate (PET) and 14% by weight of calcium carbonate were supplied. 3 layer lamination co-extrusion is carried out to have the component layer supplied to the sub-extruder on both surface layers of the component layer supplied to the machine, and cooled on a mirror-casting drum by electrostatic application method to create a 3 layer laminated sheet did. This laminated sheet was stretched 3.2 times in the longitudinal direction at a temperature of 87 ° C., and then stretched 3.2 times in the width direction at 110 ° C. through a preheating zone of 95 ° C. with a tenter. Furthermore, it heat-processed for 30 second at 225 degreeC, and obtained the light reflection layer which contains a lot of fine bubbles which consist of a laminated film with a film thickness of 200 micrometers. The following coating agent was apply | coated to one surface of this light reflection layer so that the thickness after drying might be set to 5 micrometers. After application, the film was dried at 120 ° C. for 2 minutes to obtain a light reflecting film in which a low gloss layer was formed on the light reflecting layer.
(Low gloss layer forming coating)
Binder; U-double UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight low diffusion particles (aggregated silica) Silo Hovic 100 (manufactured by Fuji Silysia Co., Ltd., average particle size 2.5 μm, pore volume 1.60 ml / g, average pore size 21 nm): 5 parts by weight solvent; toluene: 11 parts by weight of obtained light reflection The 85 ° specular gloss of the film was 6.9, the light reflectance was 97%, the front luminance was 1160 cd / m 2, and the luminance unevenness was ◎ .

(Example 4)
The following coating agent was apply | coated to the light reflection layer which consists of a laminated | multilayer film obtained by the comparative example 7 so that the thickness after drying might be set to 5 micrometers. After application, the film was dried at 120 ° C. for 2 minutes to form a low-gloss layer on the light reflecting layer to obtain a light reflecting film.
(Low gloss layer forming coating)
Binder; U-double UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight low diffusion particles (aggregated silica) Silo Hovic 4004 (manufactured by Fuji Silysia Co., Ltd., average particle size 8 μm, pore volume 1.25 ml / g, average pore size 17 nm): 10 parts by weight solvent; toluene: 12 parts by weight of the obtained light reflecting film The 85 ° specular gloss was 4.8, the light reflectance was 96%, the front luminance was 1200 cd / m 2, and the luminance unevenness was ◎. Thus, the light reflecting film of the present invention showed high front luminance characteristics and improved luminance unevenness, and a light reflecting film excellent in practicality was obtained.

(Example 5)
The following coating agent was apply | coated to the light reflection layer which consists of a laminated | multilayer film obtained by the comparative example 7 so that the thickness after drying might be set to 5 micrometers. After application, the film was dried at 120 ° C. for 2 minutes to form a low-gloss layer on the light reflecting layer to obtain a light reflecting film.
(Low gloss layer forming coating)
Binder; U-double UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight low diffusion particles (aggregated silica) Silo Hovic 4004 (manufactured by Fuji Silysia Co., Ltd., average particle diameter 8 μm, pore volume 1.25 ml / g, average pore diameter 17 nm): 12 parts by weight solvent; toluene: 15 parts by weight of the obtained light reflecting film The 85 ° specular gloss was 3.7, the light reflectance was 96%, the front luminance was 1230 cd / m 2, and the luminance unevenness was ◎. Thus, the light reflecting film of the present invention exhibited high front luminance characteristics and improved luminance unevenness, and a light reflecting film excellent in practicality was obtained.

(Comparative Example 1)
A light reflecting film was formed without applying any coating agent to the light reflecting layer composed of the laminated film obtained in Comparative Example 7 .
The obtained light reflecting film had a light reflectance of 97%, but had an 85 ° specular gloss of 72.3, a front luminance of 880 cd / m 2 and a luminance unevenness of Δ.

(Comparative Example 2)
The following coating agent was apply | coated to the light reflection layer which consists of a laminated | multilayer film obtained by the comparative example 7 so that the thickness after drying might be set to 5 micrometers. After application, the light reflecting film was obtained by drying at 120 ° C. for 2 minutes.
(Coating)
Binder; Udouble UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight solvent; Toluene: 10 parts by weight The obtained light reflection film had an 85 ° specular gloss of 110.2, a light reflectance of 98%, a front luminance of 750 cd / m 2, and luminance unevenness of x.

(Comparative Example 3)
The following coating agent was apply | coated to one surface of the light reflection layer which consists of a laminated | multilayer film obtained by the comparative example 7 so that the thickness after drying might be set to 5 micrometers. After application, the light reflecting film was obtained by drying at 120 ° C. for 2 minutes.
(Coating)
Binder; U-double UVG13 (solid content 40%, manufactured by Nippon Shokubai Co., Ltd.): 10 parts by weight curing agent; Sumidur N3200 (manufactured by Sumika Bayer Urethane Co., Ltd.): 0.5 parts by weight low diffusion particles (aggregated silica) Silophobic 603 (manufactured by Fuji Silysia Co., Ltd., average particle size 6.5 μm, pore volume 0.44 ml / g, average pore size 2.5 nm): 5 parts by weight solvent; toluene: 11 parts by weight was obtained. The 85 ° specular gloss of the light reflecting film was 21.1, the light reflectance was 96%, the front luminance was 960 cd / m 2, and the luminance unevenness was Δ.

(Comparative Example 4)
The surface of the Kendan black cardboard was rubbed 20 times with # 240 sandpaper to obtain a light reflecting sheet.
The 85 ° specular glossiness of the obtained sheet was 1.7, the light reflectance was 1.3%, the front luminance was 240 cd / m ² , and the luminance unevenness was x.

  The light reflecting film of the present invention can be applied not only to a surface light source but also to a printing member such as a receiving paper or a cushioning material that requires cushioning properties, but its application range is limited to these. It is not something that can be done.

Claims (2)

A low-gloss layer containing low-gloss particles which are agglomerated particles having an average particle diameter of 5 μm to 10 μm and a pore volume of 1 ml / g to 1.5 ml / g, and a light reflecting layer having fine bubbles The content of the low gloss particles in the low gloss layer is 40% by weight or more, the 85 ° specular gloss is 10 or less, and the light reflectance is 80% or more. Light reflection film. A surface light source using the light reflecting film according to claim 1.