TWI425251B - A film for surface light source peflecting member - Google Patents

Description

Surface light source reflective material film

The present invention relates to a film for reflecting a light-reflecting member of a surface light source which is easy to recognize one side and the other side. In particular, it relates to a film for a surface light source reflecting member having less time-dependent brightness reduction. Further, the present invention relates to a direct-lit type liquid crystal backlight for a liquid crystal display using a thin film for reflecting a material for a surface light source, a liquid crystal backlight of a reverse mode, and a lamp reflector for backlight.

In the liquid crystal display, a backlight that illuminates a liquid crystal cell (hereinafter referred to as a liquid crystal backlight) is used. In the liquid crystal monitor, a liquid crystal backlight with an edge light method is used; in the liquid crystal television, a liquid crystal backlight of a direct type is used. A film for a surface light source reflective member for a liquid crystal backlight (hereinafter referred to as a reflective film) is generally a porous white film formed by bubbles (Patent Document 1). Further, a white film in which an ultraviolet absorbing layer is laminated in order to prevent yellowing of a film caused by ultraviolet rays emitted from a cold cathode tube has been proposed (Patent Documents 2 and 3). Further, a white film which controls the glossiness of both sides of a film in order to have adhesiveness has been proposed (Patent Document 4).

(Patent Document 1) Japanese Patent Laid-Open No. Hei. No. 2001-166295 (Patent Document 3) Japanese Patent Laid-Open Publication No. 2002-90515 (Patent Document 4) Open 2005-125700

Most of the reflective film is used in a liquid crystal backlight process, and is used in combination with an aluminum plate or a stainless steel plate. In addition, metal plates are sometimes not used in light reflectors, but are used as reflective film monomers. In these processes, since the reflective film provided with the layer imparted with a single surface is white on both sides, it is difficult to visually recognize the surface on the opposite side to the surface on which the functional layer is provided. Since it is difficult to recognize such faces, there is also a problem that extra time is consumed in the backlight process, and productivity is lowered.

In particular, in a reflective film having a resin layer containing a light stabilizer and/or an ultraviolet absorber on one side, a resin layer containing a light stabilizer and/or an ultraviolet absorber may be mistakenly disposed due to such problems. The surface is attached to an aluminum or stainless steel plate. When mislabeled, the surface of the resin layer not containing the light stabilizer and/or the ultraviolet absorber is deteriorated by the light exposure of the cold cathode tube. As a result, there is a serious problem that the brightness of a product such as a liquid crystal television using the reflective film is lowered in use over time.

Further, in a liquid crystal backlight of a reverse type which is an end-illuminated type backlight, since a reflective film having a large amount of regular reflection components is suitable for enhancing brightness, a reflective film having a high glossiness is required. On the other hand, when the liquid crystal backlight is assembled, the frame of the liquid crystal backlight may be damaged by contact with the reflective film as shown in Fig. 2 . A notebook computer with an end-illuminated backlight is very important for lightweighting, and a hollow is also provided in the frame of the liquid crystal backlight to reduce the weight. In the end-illuminated backlight, damage to the reflective film can be seen through the cavity. Since the liquid crystal backlight which is damaged is seen to lower the quality of the finished product, there is a problem that the yield is lowered. Especially in the liquid crystal backlight of the ruthenium type, a reflective film having a high glossiness is used, and when it is damaged, it is easy to be conspicuous, and thus the problem is apparent.

In order to solve the above problems, the present invention employs the following means. That is, the film for a surface light source reflecting member of the present invention is characterized in that it is composed of a white film, and the difference ΔG between the glossiness (60°) of one surface and the other surface is ΔG > 80%.

Further, in the preferred embodiment of the film for reflecting light of a surface light source of the present invention, (1) a resin layer is provided on one side of the white film, and the gloss (60°) of the other side of the white film is 90% or more. .

(2) The resin layer is a resin layer containing an ultraviolet absorber and/or a photostabilizer.

(3) The heat shrinkage ratio in the longitudinal direction of the film and the film width direction after heat treatment at 90 ° C for 30 minutes is -0.1% or more and 0.2% or less.

(4) The white film is formed of three layers of A layer/B layer/A layer, B layer is a layer containing fine bubbles, and layer A is a layer containing inorganic particles and/or organic particles in polyester. The content of the particles is 0.5% by weight or less based on the total weight of each of the A layers.

(5) The white film is formed of three layers of A layer/B layer/C layer, B layer is a layer containing fine bubbles, and layer A and/or C layer contains inorganic particles and/or organic in polyester. The layer of the particles has a particle content of 0.5% by weight or less based on the total weight of the respective layers containing the particles.

Further, the liquid crystal backlight of the direct type, the light reflector for liquid crystal backlight, and the liquid crystal backlight of the reverse type of the present invention use the above-described film for a light source reflective member of the present invention.

According to the film for a reflective material for a surface light source of the present invention, it is possible to easily visually recognize the surface on the opposite side to the surface on which the functional layer is provided, and to improve the productivity of the liquid crystal backlight process. Further, when a resin layer containing an ultraviolet absorber and/or a photostabilizer is provided as a function-imparting layer, it is easy to visually recognize the surface of the resin layer containing the ultraviolet absorber and/or the light stabilizer. On the opposite side of the surface, when the liquid crystal backlight is assembled, the resin layer containing the ultraviolet absorber and/or the light stabilizer can be surely disposed toward the cold cathode tube side, so that the deterioration of the temporal brightness can be reduced. In addition, when used in a liquid crystal backlight of a ruthenium type, the damage of the film is hard to be conspicuous due to the contact between the backlight frame and the film for reflecting the reflective material of the surface light source during assembly, and the production of the liquid crystal backlight can be improved. rate.

According to the present invention, since the reflective film having a layer imparting a function on one side is white on both sides, it is difficult to visually recognize the surface on which the surface to which the function is provided and the surface on the opposite side are carefully examined. As a result, when the difference ΔG between the glossiness (60°) of one surface and the other surface of the film for reflecting the surface light source (hereinafter referred to as a reflective film) is ΔG>80%, it is easy to recognize that the function is provided. The surface of the layer and the surface on the opposite side thereof solve the above problems in one fell swoop.

In the present invention, the gloss (60°) is a value measured by setting the incident angle and the light receiving angle to 60° in accordance with JIS K7105 (1981 edition). A digital variable angle gloss meter (UGV-4D) manufactured by Suga Test Instruments Co., Ltd. can be used for the measurement.

The difference ΔG between the glossiness (60°) of one side and the other side of the reflective film of the present invention must be greater than 80% so that one side and the other side can be identified. ΔG is preferably 85% or more, and more preferably 90% or more. When ΔG is 80% or less, it is difficult to recognize the face. Among the methods of making ΔG greater than 80%, there are the following methods.

(1) One side of the white film constituting the reflective film differs from the gloss of the other side.

(2) One side of the white film constituting the reflective film is provided with a resin layer, and the gloss of the surface is lowered.

The specific content of these methods will be described in detail later.

The white film which is a polymer used for the reflective film of the present invention preferably has a higher visible light reflectance. In order to increase the visible light reflectance, it is preferred to use a white film containing bubbles inside. The white film containing bubbles inside is not particularly limited, but is preferably, for example, a porous film which is not stretched, or a polypropylene film or a polyester film. Among these, the polyester film is particularly suitable as the white film of the present invention because it is excellent in heat resistance and rigidity.

The polyester constituting the white film of the present invention means a polymer obtained by polycondensation of a diol and a dicarboxylic acid. Representative of dicarboxylic acids are: terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, and the like. Representative of the diol is ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, and the like. Specifically, for example, polytrimethylene terephthalate, polytetramethylene terephthalate, polyethylidene-p-oxybenzoate, poly-1, 4 - cyclohexyl dimethylene terephthalate, polyethylidene-2,6-naphthalenedicarboxylate, and the like. In the present invention, in particular, polyethylene terephthalate or polyethylene naphthalate is preferred.

Of course, the polyesters may be homopolyesters or copolyesters. Examples of the copolymerization component include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol; adipic acid, sebacic acid, phthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylate; A dicarboxylic acid component such as an acid or 5-sodium sulfoisophthalic acid.

Further, various additives known in the art may be added to the polyester. The additives are exemplified by an antioxidant, an antistatic agent, and the like.

The polyester used in the white film of the present invention is preferably a polyethylene terephthalate. The polyethylene terephthalate film is excellent in water resistance, durability, chemical resistance, and the like.

In the reflective film of the present invention, the average reflectance in a wavelength region of light of preferably 400 to 700 nm is 90% or more on at least one side of the reflective film. In the present invention, the average reflectance refers to the installation of an integrating sphere by a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies Co., Ltd., which will be a standard white plate (alumina). The reflectance at 100% was measured at 400 to 700 nm, and the reflectance was read at intervals of 5 nm by the obtained graph, and the average value was obtained.

In order to set the average reflectance to 90% or more, it is very important to contain fine bubbles inside the film and whiten it. Since the fine bubbles exert a light scattering effect, the reflectance can be improved. The average reflectance is preferably 95% or more, more preferably 98% or more. Although there is no upper limit on the average reflectance, it is preferably 108% or less. In order to increase the average reflectance, it is necessary to increase the amount of the nucleating agent added, which is based on the sometimes unstable film forming property.

The white film of the present invention is preferably whitened by containing fine bubbles inside the film. The formation of fine bubbles is, for example, a fine dispersion of a polymer which is incompatible with a polyester having a high melting point in a film base material of a polyester, and this is achieved by stretching (for example, biaxial stretching). At the time of stretching, voids (bubbles) are formed around the incompatible polymer particles, and since the holes exert a scattering effect on the light, they can be whitened to obtain a high reflectance. The non-compatible polymer is, for example, selected from the group consisting of poly-3-methylbut-1-ene, poly-4methylpent-1-ene, polyvinyl-third-butane, 1,4-trans-poly- 2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluoro A polymer having a melting point of 200 ° C or higher, such as styrene, polyethylene-tert-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride or polychlorotrifluoroethylene. Among them, as the base material of the polyester, polyolefin is preferred, and polymethylpentene is more preferred.

When the total amount of the layer containing the incompatible polymer is 100% by weight, the amount of the non-compatible polymer (for example, polyolefin) is preferably 5% by weight or more and 25% by weight or less. If it is less than 5% by weight, the whitening effect is weak, and it is difficult to obtain high reflectance. When it exceeds 25% by weight, the mechanical properties such as the strength of the film itself may be too low.

The non-compatible polymer is preferably dispersed uniformly. By uniform dispersion of the incompatible polymer, bubbles are uniformly formed inside the film to make the degree of whitening and the reflectance uniform. In order to uniformly disperse the incompatible polymer, it is effective to add a low specific gravity agent as a dispersing aid. The low specific gravity agent refers to a compound having an effect of reducing the specific gravity, and has such an effect on a specific compound. For example, a representative of polyester such as: polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, polypropylene glycol and other polyalkylene glycol; ethylene oxide / propylene oxide copolymer; For example, sodium dodecylbenzenesulfonate; sodium alkylsulfonate; glyceryl monostearate; tetrabutylphosphonium p-aminobenzenesulfonate.

In the case of the white film of the present invention, the low specific gravity agent is preferably a polyalkylene glycol, and more preferably polyethylene glycol. Further, it is also suitable because the copolymer of polybutylene terephthalate and polytetramethylene glycol can also improve the dispersibility of the incompatible polymer. When the entire layer containing the incompatible polymer is 100% by weight, the amount of the low specific gravity agent added is preferably 10% by weight or more and 25% by weight or less. If it is less than 10% by weight, the addition effect is weak. If it exceeds 25% by weight, the original properties of the film base material are impaired. The above-mentioned low specific gravity agent can be previously added to the film base material polymer to be adjusted as a main polymer (main wafer).

As described above, since the white polyester film contains fine bubbles, the polyester film has a lower specific gravity than a general polyester film. If a low specific gravity agent is added, the specific gravity becomes lower. That is, a white and light film is obtained. The white polyester film is formed to be light in weight while maintaining the mechanical properties as a reflective film, and the specific gravity is preferably 0.5 or more and 1.2 or less. Further, since the apparent specific gravity is made 0.5 or more and 1.2 or less, a higher reflectance can be obtained, which is preferable. The apparent specific gravity is preferably 0.5 or more and 1.0 or less, and particularly preferably 0.5 or more and 0.8 or less.

In order to form the apparent specific gravity to 0.5 or more and 1.2 or less, when polymethylpentene having a specific gravity of 0.83 is used as the incompatible polymer as described above, first, it is made to contain polymethylpentene as a film mother. The polyester polymer of the material is 5% by weight or more and 25% by weight or less. Next, a polyester unstretched film is produced, which can be achieved by extending the stretch ratio by 2.5 to 4.5 times in both the machine direction and the transverse direction. When the apparent specific gravity is in the range of 0.5 or more and 1.2 or less, when used as a reflective film, the brightness is remarkably excellent in the brightness of the screen.

The glossiness of the white film of the present invention is not particularly limited as long as the difference ΔG between the one side of the reflective film using the white film and the other side (60°) is more than 80%, but it is preferably at least a white film. One side has a gloss (60°) of 90% or more. When the glossiness of one side of the white film is 90% or more, the glossiness of the other side of the white film can be reduced. Alternatively, a resin layer may be provided on the other side of the white film to reduce the gloss of the surface, whereby the ΔG of the reflective film can be easily formed to be more than 80%. The glossiness of one side of the white film is preferably 95% or more, more preferably 100% or more, more preferably 115% or more, and most preferably 120% or more. Although the upper limit of the gloss is not particularly limited, it is preferably less than 130%. When it exceeds 130%, sometimes the friction coefficient of the film becomes high, and it is difficult to remove air at the time of winding.

The white film of the present invention can be formed by forming various layers such as a single layer, two layers, and three layers. Among them, it is formed of three layers of A layer/B layer/A layer or A layer/B layer/C layer, and the B layer is formed into a layer containing the above fine bubbles to facilitate both high reflectance and film forming property. .

Further, various additives may be added to the respective layers of the aforementioned white film insofar as the effects of the present invention are not impaired. As the additive, for example, organic and/or inorganic fine particles, a fluorescent whitening agent, a heat-resistant stabilizer, an ultraviolet absorber, an antioxidant, or the like can be used, and the glossiness of one side and the other side of the reflective film can be recognized to have The layers of the functional additives are located on which side of the white film. Further, when it is composed of three layers of the A layer/B layer/A layer, the A layer corresponding to the surface of the film preferably contains inorganic particles and/or organic particles in the polyester as 0.5 of the total weight of each A layer. A layer of weight % or less. The content is preferably 0.1% by weight or less, particularly preferably 0.07% by weight or less. Further, when it is composed of three layers of the A layer/B layer/C layer, the A layer and/or the C layer corresponding to the surface of the film preferably contain inorganic particles and/or organic particles in the polyester as layers (including inorganic layers). A layer of 0.5% by weight or less based on the total weight of the microparticles and/or layers of the organic particles. The content is preferably 0.1% by weight or less, particularly preferably 0.07% by weight or less. The glossiness of the A layer (or the C layer) can be increased by reducing the content of the inorganic fine particles and/or the organic fine particles contained in the A layer (or the C layer).

As described above, the white film of the present invention preferably has a gloss of at least 90% on one side thereof, and the content of the inorganic fine particles and/or inorganic fine particles contained in one of the outermost layers of the white film is set to 0.5. Since the weight is %, the glossiness of the surface can be made 90% or more. Further, by increasing the content of the inorganic fine particles and/or the inorganic fine particles contained in the other outermost layer of the white film, the gloss of the surface can be lowered, so that the glossiness of one side and the other side of the white film can be improved. Make a difference. The content of the inorganic fine particles and/or inorganic fine particles contained in each layer can be appropriately adjusted in accordance with a desired difference in gloss.

Next, the method for producing the white film of the present invention will be described, but it is not limited to this example.

Polymethylpentene as a non-compatible polymer, polyethylene glycol as a low specific gravity agent, polybutylene terephthalate and polytetramethylene glycol copolymer are added to the polyethylene terephthalate In the diformate. This is thoroughly mixed, dried and supplied to the extruder B which has been heated to a temperature of 270 to 300 °C. If necessary, the polyethylene terephthalate containing an inorganic additive such as SiO ₂ may be supplied to the extruder A in a usual manner. Then, the polymer of the extruder B can be used as the inner layer (layer B) in the T die 3-layer joint, and the polymer of the extruder A can be laminated as the two skin layers (layer A). It is a 3-layer structure of the A layer/B layer/A layer.

The molten flakes are cooled on a reel which has been cooled to a surface temperature of the drum of 10 to 60 ° C by electrostatic bonding to obtain an unstretched film. The unstretched film is guided to a roller group heated to 80 to 120 ° C, longitudinally extending 2.0 to 5.0 times in the longitudinal direction, and cooled by a roller group of 20 to 50 ° C. Next, the both ends of the longitudinally stretched film are gripped by a clip, and guided to the tenter, and laterally extended in a direction perpendicular to the long side in an environment heated to 90 to 140 °C. The stretching ratio is extended from 2.5 to 4.5 times in the vertical and horizontal directions, respectively, but the area magnification (longitudinal stretching ratio × lateral stretching ratio) is preferably 9 to 16 times. When the area ratio is less than 9 times, the whiteness of the resulting film may be poor. When the area magnification exceeds 16 times, breakage easily occurs during stretching, and the film forming property tends to be poor. In order to impart planarity and dimensional stability to the thus biaxially stretched film, heat setting is carried out in a tenter at 150 to 230 ° C, and after uniform slow cooling, it is cooled to room temperature. Next, it was wound up in a winder to obtain a white film of the present invention.

In order to form the difference ΔG of the gloss (60°) of one side of the reflective film of the present invention to be more than 80%, a resin layer may be provided on one side of the white film. By providing the resin layer, the glossiness of one side of the white film can be lowered, and the ΔG of the reflective film can be easily formed to be more than 80%.

The resin layer of the present invention is not particularly limited, and a resin having an organic component as a main component is preferable, and examples thereof include a polyester resin, a polyurethane resin, an acrylic resin, a methacrylic resin, a polyamide resin, and a polyethylene resin. Polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, fluorine resin, and the like. These resins may be used singly or in combination of two or more kinds of copolymers or mixtures. Among them, a polyester resin, an acrylic resin or a methacrylic resin is preferably used from the viewpoint of heat resistance, particle dispersibility, coatability, and gloss.

The white film of the present invention may be deteriorated by light emitted from a lamp such as a cold cathode tube during use, in particular, ultraviolet rays (for example, deterioration of optical properties such as yellowing, deterioration of decomposition due to low molecular weight, etc.) A resin layer containing an ultraviolet absorber and/or a light stabilizer may also be used as the resin layer.

The resin constituting the resin layer containing the ultraviolet absorber is not particularly limited, and a resin containing an inorganic ultraviolet absorber such as titanium oxide or zinc oxide, or a resin containing an organic ultraviolet absorber such as benzotriazole or benzoquinone; or A resin in which a benzotriazole-based or benzoquinone-based reactive monomer is copolymerized.

The resin constituting the resin layer containing the light stabilizer is preferably an organic ultraviolet absorbing resin containing a resin copolymerized with a hindered amine (HALS)-based reactive monomer.

The inorganic ultraviolet absorber is generally zinc oxide, titanium oxide, cerium oxide, zirconium oxide or the like. Among these, at least one selected from the group consisting of zinc oxide, titanium oxide, and cerium oxide does not flow out, and also has excellent light resistance and the like, and is suitable for use. Related UV absorbers can sometimes be used in combination with several types as needed. Among them, zinc oxide is most desirable in terms of economy, ultraviolet absorption, and photocatalytic activity. As the zinc oxide, FINEX-25LP, FINEX-50LP (manufactured by Nippon Chemical Industry Co., Ltd.), or the like can be used.

The organic ultraviolet absorber may be, for example, a resin containing an organic ultraviolet absorber such as benzotriazole or benzoquinone; or a resin obtained by copolymerizing a benzotriazole-based or benzoquinone-based reactive monomer; A resin which is copolymerized with a light stabilizer such as a hindered amine (HALS)-reactive monomer. In particular, a resin containing a benzotriazole-based or benzoquinone-based reactive monomer copolymerized; and an organic ultraviolet absorbing resin such as a resin copolymerized with a hindered amine (HALS)-based reactive monomer is thin. The ultraviolet absorption effect in the layer is higher, so it is more desirable.

Such a manufacturing method and the like are disclosed in detail in paragraphs [0019] to [0039] of JP-A-2002-90515. In addition, HALS-hybrid (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.) containing a copolymer of an acrylic monomer and an ultraviolet absorber as an active ingredient can also be used.

In the present invention, various additives may be added to the resin layer within a range that does not impair the effects of the present invention. As the additive, for example, organic and/or inorganic fine particles, a fluorescent whitening agent, a crosslinking agent, a heat-resistant stabilizer, an antioxidant stabilizer, an organic slip agent, a nucleating agent, a coupling agent and the like can be used.

The resin layer of the present invention can be provided by a coating method. When set by a coating method, the coating liquid system can be applied by any method. For example, a gravure coat, a roller coat, a spin coat, a reverse coat, a bar coat, or a screen coat can be used. Screen coat), blade coat, air knife coat, dipping, and the like. Further, the coating liquid for forming the resin layer can be applied (in-line coating) when the white film of the substrate is produced, or can be coated on the white film after the crystal alignment is completed. (off-line coating).

The reflective film of the present invention preferably has a heat shrinkage ratio in the longitudinal direction of the film and the film width direction after the heat treatment at 90 ° C for 30 minutes as a reflective film of -0.1% or more and 0.2% or less. It is preferably -0.05 to 0.15% or less. When the heat shrinkage ratio in the longitudinal direction of the film or the width direction of the film is not in the range of -0.1% or more and 0.2% or less, when the temperature is high, the film is bent, and unevenness in brightness is likely to occur in the liquid crystal backlight. In particular, in the reflective film for retanning use, when the 导-shaped light guide plate is in contact with the mirror-shaped reflecting surface, the liquid crystal panel is liable to cause unevenness in the screen and is apparently exhibited.

Here, the heat shrinkage rate in the longitudinal direction of the film after heat treatment at 90 ° C for 30 minutes is measured by the following procedure. First, a film sample of a certain size is prepared, and a certain length (L ₀ ) is measured in the longitudinal direction (extrusion direction at the time of production) at room temperature. The sample was placed in a thermostat kept at 90 ° C for 30 minutes, and then slowly cooled to room temperature in the same manner, and then the length (L) corresponding to the portion of L _{0 was} measured. Next, the value calculated by the following formula based on the length (L) and the initial length (L ₀ ) is defined as the heat shrinkage ratio in the longitudinal direction of the film.

. Heat shrinkage rate (%) = {(L _{0 -} L) / L ₀ } × 100

Among them, a negative value indicates that the film has been extended.

In addition, the heat shrinkage ratio in the film width direction after heat treatment at 90 ° C for 30 minutes is measured in the same manner as the longitudinal direction of the film in the width direction of the film (the direction perpendicular to the extrusion direction at the time of production). value.

The reflective film of the present invention preferably has an average reflectance of 85% or more in a wavelength of from 400 to 700 nm as measured by the surface on which the resin layer is provided. More preferably 87% or more, and 90% or more is particularly good. When the average reflectance is less than 85%, there is a case where the brightness is insufficient depending on the liquid crystal display to be applied. However, when a resin layer containing an ultraviolet absorber and/or a photostabilizer is provided on both surfaces of a white film, the average reflectance measured by any resin layer may be 85% or more.

The reflective film of the present invention can be applied to a liquid crystal backlight of a direct type of liquid crystal TV and a large monitor. In the liquid crystal backlight of the direct type, as shown in Fig. 1, a reflective film is provided in the vicinity of the cold cathode tube. At this time, when the surface of the reflective film provided with the resin layer (preferably the resin layer containing the ultraviolet absorbing material and/or the light stabilizer) is not disposed toward the cold cathode tube side, ultraviolet rays emitted from the cold cathode tube may be formed. And the case where the white film of the substrate turns yellow. Therefore, when assembling the backlight, it is necessary to identify the surface of the reflective film on the side opposite to the side on which the resin layer is provided. The reflective film of the present invention is easy to recognize the surface on the opposite side to the surface on which the resin layer is provided, and the work efficiency of the assembly process of the backlight is improved, and the productivity is also improved.

The reflective film of the present invention is applicable to a light reflector of a liquid crystal backlight. The light reflector is formed by bonding a stainless steel plate or the like to a reflective film so that the reflective film is molded into a curved shape on the inner side. As shown in Fig. 2, the light reflector is assembled in the backlight in such a manner as to cover the cold cathode tube. The light reflector is also provided with a reflective film in the vicinity of the cold cathode tube, similarly to the direct type backlight. At this time, the surface of the reflective film provided with the resin layer (preferably, the resin layer containing the ultraviolet absorbing material and/or the light stabilizer) faces the cold cathode tube side, and when the stainless steel plate or the like is not bonded to the reflective film, There is a case where the white film of the substrate turns yellow due to the ultraviolet rays emitted from the cold cathode tube. Therefore, when bonding, it is necessary to recognize the surface on the opposite side to the surface on which the resin layer is provided. In the film for a reflective material for a surface light source of the present invention, it is easy to recognize the surface on the opposite side to the surface on which the resin layer is provided, and the work efficiency of the bonding process is improved, and the productivity is also improved.

The reflective film of the present invention is suitable for use in a liquid crystal backlight of a ruthenium type. As described above, when the backlight is assembled, sometimes the frame of the backlight comes into contact with the reflective film to cause damage. In the end-illuminated backlight, in order to reduce the weight, a cavity is provided in the frame of the backlight, and the damage on the reflective film can be seen through the cavity. Since the damaged backlight is seen to lower the quality of the finished product, the yield is lowered. The lower the gloss of the reflective film, the less noticeable the damage on the surface, but on the other hand, especially in the liquid crystal backlight of the ruthenium type, in order to achieve high brightness, a reflection with high gloss is required. film. Therefore, the reflective film of the present invention is assembled such that the surface having a low glossiness faces the backlight casing side and the surface having a high glossiness faces the side of the light guide plate, whereby the damage required on the side of the backlight casing can be achieved. The degree of less noticeable and the reflection of more specular reflection components required on the side of the light guide plate. That is, the liquid crystal backlight of the ruthenium type using the reflective film of the present invention does not impair the quality of the finished product of the backlight, but can improve the yield and form a high brightness.

(Example)

The measurement method and evaluation method are as follows.

(1) Average Reflectance The average reflectance of the surface of the reflective film provided with the resin layer was measured by the following procedure. The integrating sphere was attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Tech Co., Ltd., and the reflectance at a standard white plate (alumina) of 100% was measured at 400 to 700 nm. The reflectance was read from the obtained graph at intervals of 5 nm, and the average of these reflectances was calculated to form an average reflectance. Three samples were measured for each of the reflective films, and the average value thereof was defined as the average reflectance of the reflective film. In the measurement of "(3) glossiness (60°)", the average reflectance of the surface which is regarded as "the surface on which the resin layer is provided" is measured.

(2) Thermal contraction rate (thermal shrinkage ratio in the longitudinal direction) A sample having a width of 10 mm (film width direction) × 230 mm long (longitudinal direction of the film) was cut out from the reflective film. A mark of 200 mm spacing was placed in the longitudinal direction of the sample, and the distance between marks (L ₀ mm) was correctly read with a metal ruler. The sample was placed in a hot air oven at 90 ° C for 30 minutes and then slowly cooled to room temperature. Next, the inter-marker distance (Lmm) of the sample was read in the above manner. The heat shrinkage ratio was calculated from the following formula based on the distance between the marks and expressed in %. Three samples were cut out from one reflective film, and the average value of the heat shrinkage values of the respective samples was defined as the heat shrinkage ratio of the reflective film.

. Heat shrinkage ratio (%) = (L _{0 -} L) / L ₀ × 100 wherein a negative value indicates that the film has been stretched.

(The heat shrinkage ratio in the width direction) A sample having a width of 10 mm (long film direction) × 230 mm long (film width direction) was cut out from the reflective film, and was measured in the same manner as the measurement method of the heat shrinkage ratio in the longitudinal direction. .

(3) Gloss (60°) The gloss (60°) on both sides of the surface of the reflective film provided with the resin layer on the opposite side was measured by the following procedure. The gloss was measured by using a digital variable angle gloss meter (UGV-4D) manufactured by Suga Test Instruments Co., Ltd. according to JIS K7105 (1981 edition), and the incident angle and the light receiving angle were both 60°. Three samples were measured for each of the reflective films, and the average value thereof was defined as the gloss (60°) of the reflective film. In the case where the resin film is not provided in the reflective film, the surface having a small gloss (any surface having the same gloss when both surfaces are the same) is regarded as "the surface on which the resin layer is provided".

(4) Average reflectance after the light resistance test The reflective film was placed in an ultraviolet light deterioration promoting tester EYE SUPER UV tester SUV-W131 (manufactured by Iwasaki Electric Co., Ltd.), and a forced ultraviolet irradiation test was performed under the following conditions.

"UV irradiation conditions" illumination: 100mW/cm ² , temperature: 60 ° C, relative humidity: 50% RH, irradiation time: 48 hours

Regarding the sample after the irradiation, the average reflectance was measured in accordance with the method of (1).

(5) Recognition of the surface of the reflective film The surface of the reflective film was visually observed by any of the 10 judges selected. If all of the 10 faces are recognized as the surface on the opposite side to the surface on which the resin layer is provided, it is judged as ○, and if it is unrecognizable, it is judged as ×. Each of the reflective films was evaluated in one sample.

(6) Visibility of damage On the surface of the reflective film provided with the resin layer, a load of 100 g was applied to Steel wool of #0000, and rubbing was performed three times with a stroke width of 10 cm and a speed of 30 mm/sec. The surface provided with the resin layer was visually observed by 10 judges arbitrarily selected. If all 10 people can see the damage, it is judged as ○, and if it is one, the damage is judged as ×. In the measurement of "(3) glossiness (60°)", the surface which is regarded as "the surface on which the resin layer is provided" is damaged, and the surface is observed. Each of the reflective films was evaluated in one sample.

(Example 1)

First, a polypropylene terephthalate-based wafer (F20S manufactured by Toray Co., Ltd., Japan) and a polyethylene glycol having a molecular weight of 4000 are added during polymerization of polyethylene terephthalate. The main wafer obtained by copolymerizing a copolymer of butyl terephthalate and polytetramethylene glycol was vacuum dried at 180 ° C for 3 hours.

Next, it was mixed in the following manner: 65 parts by weight of polyethylene terephthalate; 10 parts by weight of isophthalic acid and 5 mol% of polyethylene glycol were copolymerized in polyethylene terephthalate. Parts by weight; 5 parts by weight of a copolymer of polybutylene terephthalate and polytetramethylene glycol; and 20 parts by weight of polymethylpentene. The mixture was supplied to an extruder B (layer B) which had been heated to 270 to 300 °C.

On the other hand, 97 parts by weight of a wafer of polyethylene terephthalate; and 1 part by weight of a main wafer containing 2% by weight of cerium oxide having an average particle diameter of 1.5 μm were mixed in the following manner. After the mixture was vacuum dried at 180 ° C for 3 hours, it was supplied to an extruder A (layer A) which had been heated to 280 °C.

The polymers are laminated by a lamination device in the form of an A layer/B layer/A layer (thickness ratio A layer: B layer: A layer = 1:8:1), and are formed into a thin sheet by a T mold. shape.

Further, the sheet was cooled and solidified by a cooling roll having a surface temperature of 25 ° C to form an unstretched film. Next, the unstretched film was guided to a roller group heated to 85 to 98 ° C, extended 3.4 times in the longitudinal direction of the film, and cooled by a roller group of 25 ° C. Next, the two ends of the film extending longitudinally in the longitudinal direction are gripped by a clip, and guided to the tenter, and in the film width direction (with the longitudinal direction of the film) in an environment heated to 130 ° C The vertical direction) extends by 3.6 times. Thereafter, heat setting was carried out at 230 ° C in a tenter, and after uniform slow cooling, it was cooled to room temperature. Finally, it was wound up by a winder to obtain a white film having a thickness of 188 μm. The gloss (60°) of the obtained white film was 121%.

HALS-hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% solution, manufactured by Nippon Shokubai Co., Ltd.): 41.4 g; Desmodule (registered trademark) N3200 (hardener, concentration: 100%) Manufactured by Sumika Bayer Urethane Co., Ltd.: 2.1 g; toluene: 54.5 g; cerium oxide powder as inorganic fine particles (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) : 1.8 g, the coating liquid prepared was added as a coating liquid for forming a resin layer, and the coating liquid was applied to one side of a white film so as to have a thickness of 3 μm after drying, and a resin layer was provided and dried. The drying of the coating liquid was carried out for 1 minute at a temperature of 130 ° C. Thereby, a reflective film was obtained, and the gloss (60°) of the surface of the reflective film provided with the resin layer was 25%.

(Example 2)

A white film was obtained in the same manner as in Example 1 except that the amount of the main wafer (cerium oxide content: 2% by weight) mixed in the A layer was 2 parts by weight. The gloss of the obtained film (60°) was 107%.

A resin layer was provided in the same manner as in Example 1 except that the amount of cerium oxide powder (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) in the coating liquid for forming the resin layer was 2.3 g. A reflective film is obtained. The gloss (60°) of the surface of the reflective film provided with the resin layer was 13%.

(Example 3)

A white film was obtained in the same manner as in Example 1 except that the amount of the main wafer (cerium oxide content: 2% by weight) mixed in the A layer was 3.5 parts by weight. The gloss of the obtained film (60°) was 95%.

A resin layer was provided in the same manner as in Example 1 except that the amount of cerium oxide powder (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) in the coating liquid for forming the resin layer was 2.3 g. A reflective film is obtained. The gloss (60°) of the surface of the reflective film provided with the resin layer was 12%.

(Example 4)

The polymer compositions of the A layer and the B layer, and the temperatures of the extruder A and the extruder B were the same as in the first embodiment.

It was mixed in the following manner: 97 parts by weight of a polypropylene terephthalate wafer; and 3.5 parts by weight of a main wafer containing 2% by weight of a ceria having an average particle diameter of 1.5 μm. The mixture was vacuum dried at 180 ° C for 3 hours, and then supplied to an extruder C (C layer) which had been heated to 280 ° C.

These polymers are laminated by a laminating apparatus so as to form an A layer/B layer/C layer (thickness ratio A layer: B layer: C layer = 1:8:1), and are formed into a sheet shape by a T mold. .

Further, the sheet was stretched under the same conditions as in Example 1 to obtain a white film. The gloss (60°) of the obtained white film was A layer side: 121%, and C layer side: 95%.

The resin was placed on the A layer in the same manner as in Example 1 except that the amount of the cerium oxide powder (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) in the coating liquid in which the resin layer was formed was 2.3 g. The layer is obtained to obtain a reflective film. The gloss (60°) of the surface of the reflective film provided with the resin layer was 14%.

(Comparative Example 1)

A reflective film was obtained in the same manner as in Example 1 except that the resin layer was not provided.

(Comparative Example 2)

A resin layer was provided in the same manner as in Example 1 except that the amount of cerium oxide powder (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) in the coating liquid forming the resin layer was 0.3 g. A reflective film is obtained. The gloss (60°) of the surface of the reflective film provided with the resin layer was 70%.

(Comparative Example 3)

A resin layer was provided in the same manner as in Example 1 except that the amount of cerium oxide powder (Sylophobic (registered trademark) 100 manufactured by Fuji Silysia Co., Ltd.) in the coating liquid for forming the resin layer was 0.9 g. A reflective film is obtained. The gloss (60°) of the surface of the reflective film provided with the resin layer was 50%.

(Comparative Example 4)

White film made of 188 μm porous biaxially stretched ethyl terephthalate (Lumirror (registered trademark) E60L, manufactured by Toray Co., Ltd., gloss (60°): 30% The resin layer described in Example 1 was provided on one side of the substrate to obtain a reflective film. The gloss (60°) of the surface of the reflective film provided with the resin layer was 25%.

In Examples 1 to 4, the difference in gloss was more than 80%, and the surface on the side opposite to the side on which the resin layer was provided was easily recognized. Further, in Examples 1 to 4, the glossiness of the surface having a small glossiness (the surface on which the resin layer was provided) was 25% or less, and it was difficult to see that the damage of the surface was also good.

On the other hand, in Comparative Examples 1 to 4, the difference in gloss was 80% or less, and it was difficult to recognize the surface on the opposite side to the surface on which the resin layer was provided. Further, in Comparative Examples 1 and 2, the glossiness of the surface having a small glossiness (the surface on which the resin layer was provided) was more than 50%, and the damage of the surface was also confirmed.

(industrial availability)

The film for a surface light source reflective member of the present invention can be applied to a liquid crystal backlight. In particular, it can be applied to a liquid crystal backlight of a direct type, a liquid crystal backlight of a reverse type, and a light reflector for a liquid crystal backlight.

1. . . Diffusion film

2. . .稜鏡 film

3. . . Diffuser

4. . . Surface light source reflective material film

5. . . Cold cathode tube

6. . . framework

7. . .稜鏡 light guide

8. . . Light reflector

Fig. 1 is a liquid crystal backlight of a direct type using a film for reflecting a material of a surface light source of the present invention.

Fig. 2 is a liquid crystal backlight in which a surface light source of the present invention is used to reflect a film for a member.

1. . . Diffusion film

2. . .稜鏡 film

3. . . Diffuser

4. . . Surface light source reflective material film

5. . . Cold cathode tube

6. . . framework

Claims (9)

A film for reflecting light of a surface light source, which is composed of a white polyester film, and a difference ΔG between one side and the other side (60°) is ΔG>80%, and at the same time, the glossiness of one side thereof (60°) is less than 130% above 100%. The film for a light source reflective member according to the first aspect of the invention, wherein the white polyester film has a resin layer on one side thereof and the other side of the white polyester film has a gloss (60°) of 90% or more . The film for a surface light source reflective member according to the second aspect of the invention, wherein the resin layer contains a resin layer of an ultraviolet absorber and/or a light stabilizer. The film for a surface light source reflective member according to the first aspect of the invention, wherein the heat shrinkage ratio in the longitudinal direction of the film and the film width direction after heat treatment at 90 ° C for 30 minutes is -0.1% or more and 0.2% or less. The film for a light source reflective member according to the first aspect of the invention, wherein the white polyester film is formed of three layers of A layer/B layer/A layer, and layer B is a layer containing fine bubbles, layer A. The layer containing inorganic particles and/or organic particles in the polyester has a particle content of 0.5% by weight or less based on the total weight of each A layer. The film for a light source reflective member according to the first aspect of the invention, wherein the white polyester film is formed of three layers of A layer/B layer/C layer, and layer B is a layer containing fine bubbles, layer A. And/or the C layer is a layer containing inorganic particles and/or organic particles in the polyester, and the particle content thereof is 0.5% by weight or less based on the total weight of the respective layers containing the particles. A liquid crystal backlight of a direct type, which is a film for a surface light source reflective member according to any one of claims 1 to 6. A light reflector for a liquid crystal backlight, which is a film for a surface light source reflective member according to any one of claims 1 to 6. A liquid crystal backlight of a ruthenium type, which is a film for a surface light source reflective member according to any one of claims 1 to 6.