JP5787493B2 - Backlight device - Google Patents

Description

  The present invention relates to a backlight device in which a light diffusion film having specific diffusion characteristics is installed between a light guide plate and an LED light source unit, thereby reducing light emission spots at an edge portion and improving luminance uniformity.

  In recent years, liquid crystal display devices (LCDs) have been widely used as flat panel displays taking advantage of thin, lightweight, low power consumption, etc., and their applications are information on mobile phones, personal digital assistants (PDAs), personal computers, televisions, etc. It is expanding year after year as a display device.

  The liquid crystal display device is equipped with a backlight unit on the lower surface side of the liquid crystal layer in order to suppress loss in the light transmission path from the light source to the panel and improve the luminance on the panel. Among them, those that emit light by illuminating a liquid crystal layer from the back are widespread, but are roughly classified into a side type and a direct type depending on the arrangement of light sources.

  In recent years, LEDs (light-emitting diodes) having features such as low energy consumption and long life are attracting attention as light sources for backlights from the viewpoint of energy saving. Interior lighting, interior lighting, outdoor lighting, advertising lights, and display devices It has been widely used as a light source for illumination.

  Since the light emitted from the LED light source has high straightness (directivity), it is possible to efficiently illuminate a spot-like narrow area, but the light diffusibility is insufficient. Therefore, in order to illuminate a wide area using a large number of light sources, the individual light sources are arranged in a spot shape, and to obtain uniform brightness, increase the number of light sources and install in a dense state. There is a need to. For example, when illuminating the display using the edge light method, it is necessary to increase the number of LED light sources in order to obtain uniform brightness, and thus the feature of energy saving cannot be effectively utilized.

  Therefore, in order to obtain a uniform light amount distribution over a wide area, various devices are required even in an edge light type backlight device.

  For example, a plate having at least one primary light source, a light incident end surface on which light emitted from the primary light source is incident and on which light emitted from the primary light source is incident, and a light emitting surface on which the guided light is emitted The light guide body includes a light emitting mechanism on both or one of the light emitting surface and the opposite back surface, and both or one of the light emitting surface and the back surface. At least one local lens array forming portion, and each of the local lens array forming portions includes at least one local lens array, and the local lens array is emitted from the primary light source and formed on the light incident end surface. A method is disclosed in which unevenness of luminance is eliminated by forming the incident light in a direction different from the direction of the peak light in the luminance distribution at the incident position of the maximum intensity light (Patent Document). Reference).

  In addition, a lamp housing having a light source housing portion whose opening is formed at one end and whose inner wall is a light reflecting surface, a light emitting diode provided in the light source housing portion, and a display plate provided in front of the opening portion And a technology for making the light from the light-emitting diode uniform by diffuse reflection (see Patent Document 2).

  Furthermore, a light source that emits light, an optically transparent light guide that propagates light from the light source and has a radiation surface at a predetermined position in the radiation direction, and a surface other than the radiation surface of the light guide A non-covered casing that closes the light source, inner reflection means provided between the casing and the light guide, and radiation-side reflection that is provided on the radiation surface and reflects light from the light source at a predetermined ratio And a surface illumination light source including the means (see Patent Document 3).

  The methods disclosed in Patent Documents 1 to 3 have a problem that the structure of the light source is complicated and the cost is inferior.

  On the other hand, for example, in order to improve the uniformity of the luminance of the display, there is disclosed one in which various anisotropic light diffusion films are provided on the light exit side of the light guide plate of an edge light type backlight device (Patent Documents 4 and 4). (See 5). And as an anisotropic light-diffusion film, the film which consists of 2 types of incompatible thermoplastic resins, such as cyclic polyolefin resin and polystyrene resin, crystalline polypropylene, and polypropylene resin, is used, for example.

  However, the backlight device also has a problem that the light amount (also referred to as the total light amount) of the entire illumination device is reduced and the spot disappearance property is inferior.

JP 2002-343124 A JP 2003-186427 A JP 2008-027886 A Japanese Patent Laid-Open No. 2004-101641 JP 2008-21527 A

  The present invention was devised in view of the problems of the prior art, and the object thereof is to interpose the light diffusion film having a specific characteristic between the LED light source unit and the light guide plate so that the edge portion of the light guide plate is provided. An object of the present invention is to provide a backlight device suitable for a liquid crystal display device in which light emission spots are reduced and luminance uniformity is increased.

  As a result of intensive studies to achieve this object, the present inventor has installed a light diffusion film in which the diffusivity (A) and diffusivity (B) in the main diffusion direction are controlled in a specific range in front of the LED light source unit. As a result, it was found that the edge light emission spots of the light guide plate can be reduced, and the present invention has been completed.

That is, the present invention comprises the following (i) to (v).
(I) a light guide plate having a light entrance surface, a light exit surface substantially perpendicular to the light entrance surface, and a reflective surface facing the light exit surface; and a light guide plate arranged substantially linearly in a longitudinal direction of the light entrance surface of the light guide plate In a side-edge type backlight device including an LED light source unit having a plurality of LED light sources, the following characteristics (1) to (4) are provided between the light incident surface of the light guide plate and the LED light source unit. Backlight device characterized by having a light diffusion film having:
(1) The diffusion degree (A) in the main diffusion direction is 50 to 95 degrees;
(2) The diffusivity (B) in the main diffusion direction is 155 to 180 degrees;
(3) The total light transmittance is 80% or more;
(4) diffusivity ratio is from 2.7 to 20.
(Ii) The backlight device according to (i), wherein the light diffusion film is installed so that a main diffusion direction thereof is substantially parallel to an arrangement direction of the LED light sources of the LED light source units.
(Iii) The backlight according to (i) or (ii), wherein the light diffusion film is obtained by melt extrusion molding a mixture of at least two incompatible thermoplastic resins. apparatus.
(Iv) The backlight device according to (iii), wherein at least one of the at least two incompatible thermoplastic resins is made of a polyolefin resin.
(V) The backlight device according to (iii), wherein both of the at least two incompatible thermoplastic resins are polyolefin resins.

  In the backlight device of the present invention, since the light diffusion film in which the diffusivity (A) and the diffusivity (B) in the main diffusion direction are controlled in a specific range is installed between the LED light source unit and the light guide plate, the edge portion The brightness uniformity is extremely high. Furthermore, if the light diffusion film is installed so that the main diffusion direction is substantially parallel to the LED light source arrangement direction of the LED light source unit, the dotted light can be diffused in the length of the edge light, greatly increasing the number of LED light sources. Can be reduced.

The schematic of the structure of the backlight apparatus of this invention is shown. An example of the preferable light distribution pattern of the light-diffusion film of this invention is shown.

  The backlight device of the present invention is for irradiating a liquid crystal display device such as a mobile phone, a personal digital assistant (PDA), a personal computer, and a television from the back side, and the light incident on the light incident surface from the LED light source. A side edge type having a light guide plate that emits light from a light exit surface substantially perpendicular to the light entrance surface is employed.

  FIG. 1 schematically shows an example of the configuration of the backlight device of the present invention. In FIG. 1, reference numeral 10 denotes a light guide plate, which is made of a transparent material such as polymethyl methacrylate or polycarbonate. One side surface of the light guide plate 10 has a light incident surface 11 on which light is incident. An upper surface substantially perpendicular to the light incident surface 11 has a light output surface 12, and a lower surface facing the light output surface 12 has a light output surface 12. There is a reflective surface 13. The reflection surface 13 is formed with a deflection pattern that reflects the light incident from the light incident surface 11 toward the light exit surface 12.

  An LED light source unit 20 is disposed in the vicinity of the light incident surface 11 of the light guide plate 10, and a plurality of LED light sources are arranged in a substantially straight line parallel to the longitudinal direction of the light incident surface 11. A light diffusion film 30 is installed between the light incident surface 11 of the light guide plate 10 and the LED light source unit 20. The light diffusion film 30 is preferably installed so that the main diffusion direction is substantially parallel to the arrangement direction of the LED light sources 21 of the LED light source unit 20.

  In the backlight device of the present invention, when light is emitted from the LED light source 21, the light enters the light incident surface 11 of the light guide plate 10 through the light diffusion film 30, and then in various places on the reflective surface 13. The light is reflected and emitted from the light exit surface 12 to irradiate the liquid crystal display device from the side opposite to the viewer side.

The light diffusion film used in the backlight device of the present invention is characterized by having the following properties (1) to (4).
(1) The diffusion degree (A) in the main diffusion direction is 50 to 95 degrees;
(2) The diffusivity (B) in the main diffusion direction is 155 to 180 degrees;
(3) The total light transmittance is 80% or more;
(4) diffusivity ratio is from 2.7 to 20.

The diffusivity (A) in the main diffusion direction is an angle range in the light amount half of the maximum light amount in the light amount change profile obtained by measuring the light amount change by changing the light receiving angle. a degree called index, is from 50 to 95 degrees. The diffusivity (A) is an evaluation value that is widely adopted in general, and is obtained by measurement by the method described in the examples described later. When the diffusivity (A) is less than 50 degrees, it is difficult to reduce light emission spots, which is not preferable. Conversely, when the angle exceeds 95 degrees, the amount of emitted light may decrease, which is not preferable.

Above the main diffusion direction of the diffusion degree (B) is from 155 to 180 degrees, 160-180 degrees good preferable. The diffusivity (B) is an index of how much light can be diffused to the end, and is an evaluation value that is not generally used, and is obtained by measurement by the method described in the examples described later. When the diffusivity (B) is less than 155 degrees, it is difficult to reduce light emission spots, which is not preferable. Since it is impossible to exceed 180 degrees, the upper limit is 180 degrees.

In the present invention, it is preferable that the diffusivity is a so-called anisotropic light diffusion film in which the diffusivity varies depending on the direction of the film. The degree of anisotropy can be obtained by the method described in the examples. Diffusivity ratio of the film is 2.7 or more. By satisfying these characteristics, the degree of light collection in a specific direction can be controlled, so that a light diffusion effect that cannot be achieved with an isotropic diffusion film can be imparted. For example, when the LED light source is arranged in a line and used so that the main diffusion direction of the anisotropic light diffusing film is substantially parallel to the arrangement direction of the LED light sources, the LED is a dot shape. The light of the light source can be converted into a linear uniform light band in the arrangement direction of the LED light sources. With these measures, it is possible to reduce the amount of light emitted and reduce the light emission spots at the edges. When the diffusivity ratio is less than 1.5, the above effect becomes small. Although an upper limit is not limited, it can be said that 20 or less is preferable from the point of technical possibility.

Total light transmittance of the light diffusion film is 80% or more. Note that 100% is the upper limit because there is no principle that it exceeds 100%. Since it is preferable that the total light transmittance is higher, it is more preferably 90% or more, and most preferably 100%. However, a loss may occur due to reflection at the interface, and the upper limit is practically 98%. Furthermore, it may be about 95% and about 93% when there is a lot of loss. If the light transmittance is less than 80 %, for example, the transmittance of light emitted from the LED light source decreases, the light amount decreases, and the luminance decreases, which is not preferable.

  The parallel light transmittance of the light diffusion film is preferably 10% or less, more preferably 5% or less, and still more preferably 2% or less. In addition, since it is not theoretically less than 0%, 0% is a lower limit. When the parallel light transmittance exceeds 10%, for example, the spot extinction property of the LED light source is improved, the light amount of the spot due to the strong light of the light source is increased, and the light emission spot is likely to increase, which is not preferable.

  The haze of the light diffusion film is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 97% or more. Note that 100% is the upper limit because there is no principle that it exceeds 100%. By setting the haze to 80% or more, it becomes possible to improve the light diffusibility and reduce the light emission spots, and as a result, the number of LED light sources can be reduced, which is economically advantageous. In addition, the distance between the light source and the light diffusing film can be shortened, and the lighting device can be miniaturized and power consumption can be saved.

  In the present invention, the total light transmittance, parallel light transmittance, and haze value of the light diffusing film are obtained by measuring the film winding direction on the sample stage of the haze measuring device in the vertical direction and the horizontal direction, respectively. The average value of the measured values is displayed. The reason why the film winding direction is measured in the vertical direction and the horizontal direction is that the optical characteristics greatly change in the directions.

  Next, a method for manufacturing the backlight device of the present invention will be described. There are a large number of conventionally known light guide plates and LED light source units constituting the backlight device, and the present invention is not particularly limited. Therefore, the description thereof is omitted here, and only the method for producing the light diffusion film is described in detail below. To do.

  The light diffusion film of the present invention can be obtained by melt extrusion molding a mixture of at least two incompatible thermoplastic resins. The presence form of the mixture of at least two incompatible thermoplastic resins is not particularly limited as long as the above optical characteristics are satisfied, and a so-called sea / island structure in which each resin exists independently as a continuous phase and a dispersed phase. It may be a structure in which both resins form a co-continuous phase. The above characteristics can be controlled by light refraction and scattering at the interface between the two resins.

  Examples of the thermoplastic resin used include polyethylene resins, polypropylene resins, polybutene resins, polyolefin resins such as cyclic polyolefin resins and polymethylpentene resins, polyester resins, acrylic resins, polystyrene resins, and polycarbonate resins. Examples thereof include resins and copolymers thereof. The at least two incompatible thermoplastic resins may be blended in the film forming step, or may be used in a form blended in advance by a kneading method or the like.

  In the present invention, three or more kinds of thermoplastic resins may be blended, and additives such as a compatibilizing agent and a dispersion diameter adjusting agent for improving the conformability of each resin may be used in combination. Moreover, you may mix | blend additives, such as stabilizers, such as antioxidant and a ultraviolet absorber, and antistatic agent. Further, fine particles such as inorganic particles and polymer beads may be added as long as the above optical characteristics are not impaired.

  What is necessary is just to select at least two types of incompatible (incompatible with each other) resins from these thermoplastic resins. The blending ratio of the at least two incompatible thermoplastic resins is preferably 10/90 to 90/10, more preferably 20/80 to 80/20, and more preferably 30/70 to 30/70, respectively. Although it can be said that the ratio of 70/30 is more preferable, it largely varies depending on the kind of the resin component and the layer configuration described later, the thickness of the light diffusion layer, the manufacturing method, and the like. Generally speaking, the more the mass ratio is away from 50/50, the more the number of interfaces between the two incompatible thermoplastic resins decreases, so the total light transmittance decreases, the haze decreases, and the parallel light transmittance increases. is there.

  In addition, when the melt flow rate of the island component is low, it becomes difficult to apply a force to thin the island component due to the share or draft in the die and the anisotropy may be reduced, but the mass ratio is 50/50. This tendency becomes stronger as you move away from. Each characteristic can be adjusted in consideration of these tendencies. Of the two types of incompatible thermoplastic resins, the one with a higher blending ratio tends to be a continuous phase. In particular, when the melt flow rate is close, it is necessary to take into account that the components of the sea-island structure are reversed depending on the ratio.

  The resin may be selected from commercially available resins having high versatility. However, a custom-made product may be used for measures such as more stable production. Polyester resins are easy to achieve the above-mentioned optical characteristics, and are excellent in mechanical and thermal characteristics other than optical characteristics, so that a single layer of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate is used. Preference is given to using copolymers and / or copolymers. It is also economically advantageous. As the resin combined with the polyester, a polyolefin resin described later is preferable.

  Also, the fluororesin is not limited as long as it satisfies the above characteristics, but from the viewpoint that the above optical characteristics are easily achieved and economically advantageous, a vinylidene fluoride resin and a fluorine-containing monomer such as perfluoroethylene It is preferable to use a copolymer with an olefin monomer such as ethylene or propylene. The fluorine-based resin is excellent in light resistance. For example, by combining with a polyolefin-based resin, an anisotropic light diffusion film excellent in light resistance can be obtained. As the resin combined with the fluorine resin, a polyolefin resin described later is preferable.

  It is preferable that at least one of the thermoplastic resins to be used is made of a polyolefin resin from the viewpoint that the above characteristics can be stably expressed. Examples of the polyolefin resin include polyethylene, polypropylene, polybutene, potipentene, polyhexene, polymethylpentene and the like, copolymers thereof, cyclic polyolefin and the like.

  From the viewpoint of light resistance and economy, it is preferable to use a polyolefin-based resin for both types of thermoplastic resins. When both types use polyolefin resin, the combination is not particularly limited, but the difference in refractive index between the two types of polyolefin resin is preferably in the range of 0.003 to 0.07. The range of 0.005-0.05 is more preferable, and 0.01-0.02 is more preferable. By setting the difference in refractive index within this range, it is possible to obtain a light diffusing film having the above optical characteristics more stably. For example, when the difference in refractive index exceeds 0.07, it is advantageous to make the haze and parallel light transmittance within the above range, but it becomes difficult to balance the total light transmittance. On the other hand, when it is less than 0.003, the total light transmittance is easily achieved, but it is difficult to balance haze and parallel light transmittance. The greater the difference in refractive index, the greater the angle change at the interface between the two incompatible thermoplastic resins, which favors diffusion, while the reflection at the interface increases exponentially. It is done. Therefore, it becomes easy to satisfy the above-described various optical characteristics at the same time in the above range.

  Examples of the cyclic polyolefin-based resin include those having a cyclic polyolefin structure such as norbornene and tetracyclododecene. For example, (1) a ring-opening (co) polymer of a norbornene monomer is subjected to polymer modification such as maleic acid addition or cyclopentadiene addition as necessary, and then a hydrogenated resin, (2) a norbornene monomer Examples include addition-polymerized resins, and (3) addition-copolymerized resins with norbornene monomers and olefin monomers such as ethylene and α-olefin. The polymerization method and the hydrogenation method can be performed by conventional methods.

  These can increase the glass transition temperature, and it is considered that the island components thinned by the shear and draft in the die are solidified quickly during cooling, and stable characteristics are easily obtained. The glass transition temperature is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and particularly preferably 120 ° C. or higher. The upper limit is naturally determined by the monomer type (Tg of 100% cyclic monomer), but is preferably 230 ° C. or lower, more preferably 200 ° C. or lower, and particularly preferably 190 ° C. or lower. When the upper limit is exceeded, a high temperature is required at the time of melt extrusion, and coloring may occur or undissolved matter may be generated. In addition, a value is a value measured by the temperature increase rate of 10 degrees C / min based on ISO11357-1, -2, -3.

  The content of the cyclic component of the cyclic polyolefin resin is preferably 70 to 90% by mass, more preferably 73 to 85% by mass. This range is preferable particularly in the case of norbornene. In particular, a cyclic polyolefin resin copolymerized with ethylene has a high affinity with a polyethylene resin and is preferable for achieving the characteristics. As content of ethylene, Preferably it is 30-10 mass%, More preferably, it is 27-15 mass%.

  The polyethylene resin may be a single polymer or a copolymer. In the case of a copolymer, it is preferable that 50 mol% or more is an ethylene component. The density of the polyethylene resin and the polymerization method are not limited, but it is preferable to use a copolymer having a density of 0.909 or less. For example, a copolymer with octene is mentioned. The polymerization method may be either a metallocene catalyst method or a nonmetallocene catalyst method. In particular, the use of a block copolymer of ethylene and octene is preferred in that high diffusibility can be stably imparted. An example of such a copolymer is INFUSE (trademark) manufactured by Dow Chemical Company. Since this resin has a crystalline part because of the block structure, it has a feature that it has a low melting point and a high melting point, and has the advantage that the heat resistance and the like of the obtained anisotropic light diffusion film can be improved. is there.

  The polypropylene resin may be a single polymer or a copolymer. In the case of a copolymer, it is preferable that 50 mol% or more is a propylene component. The production method, molecular weight and the like of the resin are not particularly limited, but those having high crystallinity are preferable from the viewpoint of heat resistance. Specifically, the crystallinity is determined by the heat of fusion measured by a differential scanning calorimeter (DSC), and preferably has a heat of fusion of 65 J / g or more.

  Examples of polyolefin resins containing ethylene and / or butene include homopolyethylene resins, homopolybutene resins, copolymers of these resins with other olefinic monomers, acrylic acid, methacrylic acid, and ester derivatives thereof. And the like. In the case of a copolymer with other olefinic monomers, any of random, block and graft copolymers may be used. Further, a dispersion such as EP rubber may be used. There are no particular limitations on the production method and molecular weight of the resin. For example, use of the above-described polyethylene resin or a copolymer of ethylene and butene is preferable.

  The nano-crystal structure control type polyolefin elastomer resin is a thermoplastic polyolefin-based elastomer in which the crystal / amorphous structure of the polymer is controlled in the nano order and the crystal has a network structure in the nano order. For example, manufactured by Mitsui Chemicals, Inc. Notio (registered trademark). The conventional polyolefin-based elastomer resin has a crystal size on the order of microns, whereas the nanocrystal structure control-type polyolefin-based elastomer resin has a feature that the crystal size is controlled on the order of nanometers. For this reason, it is often superior in transparency, heat resistance, flexibility, rubber elasticity and the like as compared with conventional polyolefin-based elastomer resins. Therefore, there are cases where the appearance of the resulting film can be improved by blending the nanocrystalline structure control polyolefin elastomer resin.

  The melt flow rate of the at least two incompatible thermoplastic resins is not particularly limited as long as the above optical characteristics are satisfied. Each thermoplastic resin is appropriately selected in the range of a melt flow rate measured at 230 ° C. of 0.1 to 100, preferably 0.2 to 50.

  In the present invention, as described above, it is preferable to impart anisotropy to the diffusivity. In order to impart this characteristic, it is preferable to give anisotropy to the island structure. In order to form an island structure having such a shape, it is preferable to make a difference in melt viscosity between the sea component resin and the island component resin. In particular, it is preferable to lower the melt viscosity of the island component than the sea component. For this purpose, for example, it is preferable to make a difference in the melt flow rate, and it is preferable to lower the melt flow rate of the island component than the sea component. It is also preferable to make a difference between the rigidity of the sea component resin and the island component resin. In particular, it is preferable to lower the rigidity of the island component than the sea component.

  The melt flow rate of the resin is appropriately selected in consideration of the resin composition, composition ratio, which resin is used as the sea phase, desired optical characteristics, and the like. The guideline is a sea phase when the composition ratio is high and the melt flow rate is high. In the case of the same amount, a higher melt flow rate tends to be a sea phase. When the melt flow rate is higher at a lower composition ratio, a simple sea / island structure may be formed instead of a co-continuous phase, for example.

  In the case of a combination of a cyclic polyolefin resin and a polyethylene resin, the polyethylene resin is used as the sea phase, and the melt flow rate of the polyethylene resin of the sea phase is set higher than the melt flow rate of the cyclic polyolefin resin of the island phase. Is preferred.

  In the case of a combination of a cyclic polyolefin resin and a polyethylene resin, it is preferable that 10 to 60% by mass of the cyclic polyolefin resin is blended in the total resin amount, and more preferably 10 to 50% by mass. The said range is preferable with respect to implementation | achievement of the preferable embodiment which makes the below-mentioned polyethylene-type resin sea phase. When the cyclic polyolefin resin, which is the reverse of the above configuration, is used as the sea phase, the desired optical properties, particularly the diffusivity ratio, are related to the share in the die, the flexibility and fluidity of the sea phase. It is difficult to obtain a high anisotropic light diffusion film.

  According to the above embodiment, even when the film forming apparatus is changed, it is possible to stably obtain a light diffusion film having desired optical characteristics. The reason for this is not clear, but even if there is a change in share etc. due to differences in extrusion conditions and die shapes that occur when the film forming apparatus is changed, the sea phase resin is made softer than the island phase resin, and It is presumed that the effect is mitigated by increasing the liquidity.

  Although the manufacturing method of the light-diffusion film of this invention will not be specifically limited if said optical characteristic is satisfy | filled, The method of forming into a film by melt extrusion molding is preferable at the point of economical efficiency. In the present invention, since it is not necessary to contain non-meltable fine particles in order to impart light diffusibility, clogging of the filtration filter of the molten resin in the film forming process is reduced even when the melt extrusion method is used. It has the characteristics that it is excellent in productivity and the clarity of the film obtained is high.

  The film forming method by the melt extrusion method is not particularly limited, and may be, for example, either a T-die method or an inflation method. Moreover, the film may be an unstretched film or may be subjected to a stretching process.

  In the melt extrusion molding method, generally, a resin melted by an extruder is extruded from a die into a sheet shape, and the sheet is adhered to a cooling roll to be cooled and solidified to form a film. The close contact with the cooling roll may be performed by pressing with a generally used pressure roll. However, in the point of imparting anisotropy, the close contact portion may It is preferable that no liquid pool zone (sometimes referred to as a bank) is formed at the entrance. Since the liquid pool zone is formed when pressed against the cooling roll, that is, when pressed with a strong pressure, it is preferable to reduce the contact pressure at the time of the close contact. For example, it is better to avoid the method of being brought into close contact by pressing with a generally used pressure roll. Although it will not be limited if it is the method of making it adhere by a weak pressure, For example, it extrudes the resin fuse | melted with the extruder to the sheet form from die | dye, and it adheres by the pressing method by a gas pressure, and / or the suction method, and / or the electrostatic contact method It is preferably formed by cooling and solidifying. By this method, a light diffusion film having anisotropy can be obtained stably.

  There is no limitation on the method of pressing by the gas pressure and / or the method of adhering and cooling and solidifying by the suction method and / or the electrostatic adhesion method. For example, as a pressing method by gas pressure, for example, a method such as a so-called air knife method in which pressing is performed with a gas pressure such as air, a vacuum chamber method in which suction is performed by a vacuum nozzle, a static contact method in which contact is performed by electrostatic force, etc. Is mentioned. This method may be used alone or a plurality of methods may be used in combination. The latter is preferable because the thickness accuracy of the obtained film can be increased.

  The light diffusing film of the present invention may be produced by either a non-stretching method or a stretching method. For example, when a polyester resin is used for the light diffusion layer, it is preferable to perform uniaxial stretching. The draw ratio is preferably 2 times or more. The upper limit is not particularly limited, but is preferably less than 10 times. As a result, the island phase is stretched in the stretching direction to form an elongated structure, the light diffusibility in the direction orthogonal to the orientation direction of the island phase is remarkably improved, and an anisotropic and high diffusibility can be secured.

  When manufacturing by a non-stretching method, you may manufacture by the method of extending | stretching before melt-extruding the sheet | seat extruded by extrusion, ie, the method of raising a draft rate.

  In addition, the light diffusion film of the present invention may be a single layer or a multilayer structure of two or more layers. In the case of a multilayer structure, as long as at least one layer is a layer made of a light diffusion film having the above structure, the other layer may be a simple transparent layer having no light diffusibility. Moreover, the structure of the light-diffusion layer may be sufficient as all the layers. In the case of the multilayer structure, it may be produced by a multilayer coextrusion method, or may be carried out by an extrusion lamination method or a dry lamination method.

  The mixture of the at least two incompatible thermoplastic resins may be blended with each of the thermoplastic resins by an extruder in the film forming process, or in a form that has been previously mixed by a kneading method or the like. It may be used.

  Although the thickness of the light-diffusion film of this invention is not specifically limited, Generally 10-1000 micrometers is preferable, 30-500 micrometers is more preferable, 50-500 micrometers is further more preferable. Generally speaking, the thicker the film, the greater the diffusivity, the lower the total light transmittance, the lower the haze, and the lower the parallel light transmittance. Can do. In the conventional technique, it is difficult to satisfy the optical characteristics of the present application in the above thickness range. The thickness can be adjusted by changing the draft ratio, the extrusion flow rate, the lip width, and the like.

  The light diffusion film can be bonded to the light guide plate of the backlight device using an adhesive, an adhesive, or the like. Examples of the pressure-sensitive adhesive include a rubber-based pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive, a silicon-based pressure-sensitive adhesive, and a vinyl-based pressure-sensitive adhesive. Since the light diffusing film of the present invention may be used at a high temperature, an adhesive that is stable even at room temperature to 120 ° C. is preferable. Among them, acrylic pressure-sensitive adhesives are widely used because they are inexpensive. Whichever adhesive is used, the thickness is preferably 0.5 to 50 μm.

  Adhesives include adhesives that are bonded with the aid of heat or a catalyst. Specifically, a silicon-based adhesive, a polyurethane-based adhesive, a polyester-based adhesive, an epoxy-based adhesive, a cyanoacrylate-based adhesive, an acrylic-based adhesive, or the like can be used. These adhesives are roughly classified into a thermosetting type, a hot melt type, and a two-component mixed type depending on the bonding method, and a thermosetting type or a hot melt type is preferably used. Whichever adhesive is used, the thickness is preferably 0.5 to 50 μm.

  When pasting together with an adhesive, a double-sided adhesive sheet may be used. In the case of this method, it is preferable to use a highly transparent optical pressure-sensitive adhesive, but it is not particularly limited. For example, an adhesive sheet having light diffusibility may be used. The pressure-sensitive adhesive sheet may be given light diffusibility to the pressure-sensitive adhesive layer. Moreover, you may superimpose and use, without using an adhesive agent or an adhesive.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. It is also possible. The measurement / evaluation methods employed in the examples are as follows. In the examples, “parts” means “parts by mass” unless otherwise specified, and “%” means “% by mass” unless otherwise specified.

<Total light transmittance, parallel light transmittance, and haze>
It measured based on JISK7136 using the Nippon Denshoku Industries Co., Ltd. haze measuring device "NDH-2000". This measurement used the measured value obtained by fixing and measuring to a sample fixing part so that the winding direction of a light-diffusion film might become a perpendicular direction. Moreover, when there was a difference in the surface roughness of the light diffusion film, the surface with the rougher surface roughness was fixed to the light receiving side. For example, in the case of a light diffusing film roughened only on one side, the measurement was performed by fixing in the direction in which light passes when actually used.

<Diffusion degree B>
The measurement was performed using an automatic variable angle photometer (GP-200: manufactured by Murakami Color Research Co., Ltd.).
Transmission measurement mode, light incident angle: 0 ° (angle that is perpendicular to the sample surface, both right and left, right and left), light receiving angle: -90 ° to 90 ° (angle on the equator plane), filter: ND10 used, luminous flux Aperture: 10.5 mm (VS-1 3.0), light receiving aperture: 9.1 mm (VS-3 4.0), SENSITIVITY: 950, HIGH VOLTON: 600, and variable angle interval 0.1 degree, The frequency of the angle between the peak rising angle and the peak ending angle of the variable light curve of the transmitted light obtained by moving the light receiver from 90 degrees to +90 degrees was obtained (see FIG. 2). ). With respect to the rising and ending angles of the peak, the portion was observed with a magnifying glass 10 times, and the most advanced angle where the line of the peak disappeared was defined as each angle. A clear determination can be made if this is done.
The surface on which the light receiver is moved is defined as the equator plane.
The above measurement was performed by fixing the film so that the film winding direction was parallel to the vertical direction of the sample fixing base and the horizontal direction, and the value with the larger angle was defined as the diffusivity B.
In addition, when there was a difference in the surface roughness of both surfaces of the film, it was measured by fixing in the direction in which light passes in the same direction as when the viewing angle improvement performance was actually evaluated.
The larger diffusion degree (B) was defined as the main diffusion direction.
In the measurement, before the measurement of the sample, the light-up film (product registration) 100DX2 film, which is a light diffusion film manufactured by Kimoto Co., Ltd., the film winding direction is parallel to the vertical direction of the sample fixing table, and The sample was fixed to the sample fixing base so that the diffusion layer side was the light output side, and the variable angle photometric measurement was performed under the same conditions as described above. In the measurement, when the height of the peak top of the variable angle light curve exceeds 80% or less than 70% with respect to the full scale, the value becomes 70 to 80% with respect to the full scale. The numerical value of the SENSITIVITY or HIGH VOLTON dial was finely adjusted.

<Diffusion degree A>
Similarly to the diffusivity B, the measurement was performed using an automatic variable angle photometer (GP-200: manufactured by Murakami Color Research Co., Ltd.).
The sample was fixed in the main diffusion direction obtained by the measurement of the diffusivity B, and the measurement was performed under the same conditions as the diffusivity B except for SENSITIVITY and HIGH VOLTON.
The SENSITIVITY and HIGH VOLTON settings are adjusted so that the peak top value of the transmitted light angle curve is 20 to 80% of the full scale. A light curve was determined.
The angle of the angle width (half-value width) at the half height of the peak height of the obtained variable-angle luminous intensity curve of the transmitted light was defined as diffusivity A (see FIG. 2).
In the case of a sample having a high parallel light transmittance, even if the measurement sensitivity is lowered, the peak top of the variable angle luminous intensity curve may be traded off, and the peak at the top of the head may not appear. In this case, the diffusivity A was defined as a peak width of 50% of the full scale as measured at SENSITIVITY: 150 and HIGH VOLTON: 500.
In addition, when the value of the diffusivity A was small, the half value width was calculated | required using the 10 times magnifier.

<Diffusion ratio>
The above-mentioned diffusivity A was measured by fixing the winding direction of the light diffusion film in the vertical direction and the horizontal direction, and by dividing the value having the larger half-value width by the smaller value.

<Melt flow rate of thermoplastic resin>
Based on JIS K 7210 A method, it measured on condition of 230 degreeC and 2.16kgf. Some resins were measured under the conditions described in the examples.

<Edge Idemitsu Spot>
A white reflective film is placed at the bottom of a 5-inch acrylic plate having a thickness of 7 mm, a light diffusion film is superimposed on the top of the acrylic plate, and an interval of 2 mm is provided at the edge in the longitudinal direction of the acrylic plate, A linear LED light source unit in which Top View type white LED light sources are arranged at intervals of 10 mm is fixed in parallel with the edge part of the acrylic plate, and the LED light source unit of the side edge type backlight device shown in FIG. A light diffusing film was attached to the surface of the edge portion of the acrylic plate with an optical adhesive.
On the lower surface side of the acrylic plate, a gradation pattern was printed by screen printing so that light was uniformly emitted over the entire acrylic plate.
Turn on the backlight device in a dark room, and observe the light emission spots of the light emitted from the LED light source at the edge part at a height of about 50 cm from the surface of the acrylic plate. went.
The light diffusion film was attached in such a direction that the main diffusion direction was parallel to the LED light source array direction of the LED light source substrate. The light diffusion film superimposed on the top of the acrylic plate was also superimposed in the same direction as the light diffusion film attached to the edge portion.
A: The spot of the LED light source cannot be seen, and light is emitted uniformly over the entire edge portion.
X: The spot of an LED light source can be observed, and the light emission spot resulting from the spot of an LED light source is observed in the whole edge part.

[Example 1]
Block copolymer resin (INFUSE (trademark) manufactured by Dow Chemical Co., Ltd.) consisting of 35 parts by mass of cyclic polyolefin resin (TOPAS (trademark) 6013 Topas Advanced Polymers, melt flow rate: 2.0 (230 ° C)), ethylene and octene D9817.15 Melt flow rate: 26 (230 ° C)) 65 parts by mass using a PCM45 extruder manufactured by Ikekai Tekko Co., Ltd., melt-mixed at a resin temperature of 250 ° C, extruded with a T-die, and cooled with a mirror surface cooling roll Thus, a light diffusion film having a thickness of 400 μm was obtained. The film was adhered to the cooling roll at the time of cooling using a vacuum chamber.
Table 1 shows the characteristics of the obtained light diffusion film.
The obtained light diffusing film is used for optics in which an adhesive layer is laminated on both sides of a polyester film on the edge part surface of an acrylic plate facing the LED light source substrate of the backlight device used for the above-mentioned edge part light emission spot evaluation. A backlight device of this example was produced by pasting using a double-sided pressure-sensitive adhesive film (Kureha Elastomer Prototype).
The backlight device obtained in this example had small edge light emission spots and high luminance uniformity.

[Example 2]
In the method of Example 1, the resin was mixed with a cyclic polyolefin resin (TOPAS ™ 6015 Topas Advanced Polymers, melt flow rate: 0.41 (230 ° C.)) 50 parts by mass, a block copolymer composed of ethylene and octene. Resin (INFUSE (trademark) D91011.15 melt flow rate: 2.1 (230 ° C.) manufactured by Dow Chemical Company) was changed to 50 parts by mass and the film thickness was changed to 200 μm. A light diffusion film was obtained by this method.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

[ Reference Example 5 ]
In the method of Example 1, the resin compounding was a random polyolefin resin composed of 50 parts by mass of cyclic polyolefin resin (TOPAS (trademark) 6015 Topas Advanced Polymers, melt flow rate: 0.41 (230 ° C.)), ethylene and octene. (ENGAGE (trademark) 8137 manufactured by Dow Chemical Co., Ltd., melt flow rate: 30 (190 ° C.)) The light diffusing film was prepared in the same manner as in Example 1 except that the content was changed to 50 parts by mass and the film thickness was changed to 200 μm. Got.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

[Reference Example 1]
85 parts by mass of a substantially non-lubricating polyethylene terephthalate resin from which moisture has been sufficiently removed by drying at 180 ° C. for 3 hours in a vacuum dryer and 15 parts by mass of a low density polyethylene resin (SP1540) manufactured by Prime Polymer Co., Ltd. The mixture is fed to a single screw extruder, melted at 280 ° C, passed through a filter and gear pump, removed foreign matter, and the amount of extrusion is leveled, and then the sheet is placed on a cooling drum whose temperature is controlled to 25 ° C by a T-die. It discharged in the shape. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched film. Next, the film was stretched 5.0 times in the longitudinal direction at a temperature of 103 ° C. in the longitudinal direction to obtain a light diffusion film having a thickness of 150 μm.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

[Reference Example 2]
In Reference Example 1 , the low density polyethylene resin was changed to a modified polypropylene resin (CAP350 manufactured by Dainichi Seika Co., Ltd.), and the obtained film thickness was changed to 200 μm. A light diffusing film was obtained.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

Example 6
50 parts by mass of fluorine-based resin (Kynar 720 (PVDF), Arkema Corporation, melt flow rate: 10 (230 ° C., 5 kgf)) and polymethylpentene resin (TPX ™ DX820, Mitsui Chemicals, melt flow rate: 110 ( 260 ° C., 5 kgf)) 50 parts by mass is melt-mixed at a resin temperature of 250 ° C. using a PCM45 extruder manufactured by Ikekai Tekko Co., Ltd., extruded with a T-die, and cooled with a mirror-surface cooling roll to thereby diffuse a light of 225 μm thickness. A film was obtained. The film was adhered to the cooling roll during the cooling using an air knife. Moreover, the corona treatment was given to one side.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

[Reference Example 3]
50 parts by mass of fluororesin (Kynar 720 (PVDF) Arkema, Inc., melt flow rate: 10 (230 ° C., 5 kgf)) and cyclic polyolefin resin (TOPAS ™ 6013, Topas Advanced Polymers) Melt flow rate: 2.1 (230 ° C., 2.16 kgf)) 50 parts by mass was melt-mixed at a resin temperature of 0 ° C. using a PCM45 extruder manufactured by Ikekai Tekko Co., Ltd., extruded with a T-die, and cooled with a mirror surface cooling roll to a thickness of 70 μm. A light diffusion film was obtained. The film was adhered to the cooling roll at the time of cooling using a vacuum chamber. Moreover, the corona treatment was given to one side.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small brightness at the edge portion and high luminance uniformity.

[Reference Example 4]
Block copolymer resin (made by Dow Chemical Co., Ltd.) consisting of 50 parts by mass of cyclic polyolefin resin (TOPAS ™ 6015 Topas Advanced Polymers, melt flow rate: 0.41 (230 ° C., 2.16 kgf)), ethylene and octene INFUSE (trademark) D9817.15 Melt flow rate: 26 (230 ° C., 2.16 kgf)) 50 parts by mass was melt-mixed at a resin temperature of 250 ° C. using a PCM45 extruder manufactured by Ikekai Tekko Co., Ltd. and extruded with a T-die. A light diffusion film having a thickness of 400 μm was obtained by cooling with a chilled roll (Ra = 0.55). The opposite surface of the cooling roll was a mirror holding roll.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this example.
The backlight device of this example had small edge light emission spots and high luminance uniformity as in Example 1. However, since the amount of light introduced into the light guide plate was greatly reduced compared to Example 1, The brightness on the surface of the light plate was slightly reduced.

[Comparative Example 1]
In a 60 mmφ single screw extruder (L / D; 22), polypropylene resin (Sumitomo Chemical Co., Ltd., Sumitomo Nobrene FS2011DG3) 53 parts by mass of ethylene / butene copolymer (Mitsui Chemicals Co., Ltd., Toughmer A1085S) was added. After melt mixing at a resin temperature of 240 ° C. and extrusion with a T-die, the unstretched sheet was obtained by cooling with a 20 ° C. casting roll. Subsequently, this unstretched sheet was stretched 4.5 times at a stretching temperature of 118 ° C. using the difference in roll peripheral speed of a longitudinal stretching machine, and then a corona treatment was performed on one side to obtain a light diffusion film having a thickness of 200 μm.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this comparative example.
The backlight device of this comparative example had large light emission spots at the edge portions, and the brightness uniformity at the edge portions was inferior.

[Comparative Example 2]
On one side of a highly transparent polyester film having a thickness of 250 μm (Cosmo Shine A4300 manufactured by Toyobo Co., Ltd.), 50 parts by mass of spherical acrylic resin particles having a mean particle diameter of 3 μm (Toughtick ™ FH-S300 manufactured by Toyobo Co., Ltd.) A light diffusion film was obtained by coating and drying using a coating machine so that a mixed part of 50 parts by mass of the polyurethane resin had a thickness of 25 μm after drying.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this comparative example.
The backlight device of this comparative example had large light emission spots at the edge portions, and the brightness uniformity at the edge portions was inferior.

[Comparative Example 3]
A light diffusion film made of a polycarbonate resin embossed on the surface was obtained.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film of this comparative example.
The backlight device of this comparative example had large light emission spots at the edge portions, and the brightness uniformity at the edge portions was inferior.

[Comparative Example 4]
In Reference Example 2 , a light diffusion film was obtained in the same manner as Reference Example 2 , except that the draw ratio was changed to 1.5 and the obtained film thickness was changed to 25 μm.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this comparative example.
The backlight device of this comparative example had large light emission spots at the edge portions, and the brightness uniformity at the edge portions was inferior.

[Comparative Example 5]
In Example 6, the light-diffusion film was obtained like Example 6 except having changed the draw ratio into 1.5 time and having changed the film thickness obtained into 25 micrometers.
Table 1 shows the characteristics of the obtained light diffusion film.
A backlight device was produced in the same manner as in Example 1 using the light diffusion film obtained in this comparative example.
The backlight device of this comparative example had large light emission spots at the edge portions, and the brightness uniformity at the edge portions was inferior.

  The backlight device of the present invention is extremely useful for improving the function of the liquid crystal display device because it has almost no light emission spots at the edge of the light guide plate and is excellent in luminance uniformity.

Claims (5)

A light guide plate having a light entrance surface, a light exit surface substantially perpendicular to the light entrance surface, and a reflective surface facing the light exit surface, and a plurality of light guide plates arranged substantially linearly in the longitudinal direction of the light entrance surface of the light guide plate In a side-edge type backlight device including an LED light source unit having a plurality of LED light sources, light diffusion having the following characteristics (1) to (4) is provided between the light incident surface of the light guide plate and the LED light source unit. Backlight device characterized in that a film is installed:
(1) The diffusion degree (A) in the main diffusion direction is 50 to 95 degrees;
(2) The diffusivity (B) in the main diffusion direction is 155 to 180 degrees;
(3) The total light transmittance is 80% or more;
(4) diffusivity ratio is from 2.7 to 20.   The backlight device according to claim 1, wherein the light diffusion film is installed so that a main diffusion direction thereof is substantially parallel to an arrangement direction of the LED light sources of the LED light source units.   The backlight device according to claim 1, wherein the light diffusion film is obtained by melt extrusion molding a mixture of at least two incompatible thermoplastic resins.   The backlight device according to claim 3, wherein at least one of the at least two incompatible thermoplastic resins is made of a polyolefin resin.   4. The backlight device according to claim 3, wherein both of the at least two incompatible thermoplastic resins are polyolefin resins.

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