JP5436655B2 - Light guide plate and light guide plate manufacturing method - Google Patents

Description

  The present invention relates to a surface light source device that emits light from the back surface of a liquid crystal display panel, a signboard, etc., a light guide plate for a so-called backlight device, and a method for manufacturing the light guide plate, and in particular, a diffusion portion is formed on at least the front surface or the back surface of the light guide plate. The present invention relates to a light guide plate and a method for manufacturing the light guide plate.

  A backlight device that emits light from the back of a liquid crystal display panel, a signboard, etc. has a light source arranged in a plane and a direct type that forms a uniform light emission by a diffuser plate, etc., and a linear light source arranged on the end face of the light guide plate A light guide plate system called edge light or side light is known.

  In recent years, a thinner, lighter, energy-saving type has been desired. As such a backlight device, a light guide plate method has attracted attention. In particular, instead of conventional fluorescent lamps and cold cathode fluorescent lamps, LEDs (Light Emitting Diodes) have attracted attention from the viewpoint of high brightness, long life, and energy saving.

  In a light guide plate for a backlight device, a diffusion material is dispersed inside the light guide plate, or a light diffusion layer or a diffusion pattern is provided on at least one of the front surface and the back surface. This light guide plate allows light to enter the light guide plate from a cold cathode tube or LED array light source provided on the end face, and emit light to the output side to form a surface light source device.

  As a light guide plate type backlight device used for such a transmissive liquid crystal display panel or a signboard, a technique for providing a gradation distribution is known (see Patent Document 1). The gradation distribution increases the light diffusion capability of the diffusion layer as the distance from the light source increases so that the brightness of the exit surface of the backlight device becomes uniform.

  As a method of providing gradation distribution by a diffusion layer or a diffusion pattern, a method of transferring an uneven pattern by injection molding using a mold or press molding is known. A desired gradation pattern is formed in advance on the mold. Also known is a method of dot-printing light diffusing ink by screen printing (see Patent Document 2).

JP-A-57-128383 Japanese Patent No. 3734547

  In the diffusion layer formed on the light guide plate substrate, it is necessary to make the individual diffusion portions finer and smaller in pitch so that the pattern of the diffusion layer is not noticeable. In recent years, display devices are required to be thin. However, when the light guide plate is thinned, the pattern of the diffusion layer is easily noticeable. Therefore, it is necessary to further refine the pattern of the diffusion layer and reduce the pitch.

  However, in the injection molding, press molding, and screen printing methods using a plate or a mold, it is difficult to sufficiently miniaturize the pattern of the diffusion layer. If the design pattern is inadequate, not only redesign, but also expensive plates, molds, and screen plates are recreated, leading to increased costs.

  An object of this invention is to provide the manufacturing method of the light-guide plate which can form the fine pattern of a diffused layer easily and cheaply, and a light-guide plate.

  The light guide plate manufacturing method according to the present invention is a light guide plate manufacturing method in which a light source is disposed on an end face to constitute a surface light source device, and the light diffusing fine particles are formed on the back surface or front surface or both surfaces of the light guide plate substrate. And a coating liquid containing a light-transmitting binder is applied in the form of fine droplets to coat the diffusion layer, the light diffusing fine particles are aggregated, and the aggregate occupied by the aggregate on the coated surface of the light guide plate base material. The ratio between the area and the application area of the coating solution is set to 0.1% to 70%. Thereby, even if it does not produce a plate and a metal mold | die conventionally, when a coating liquid is apply | coated to a light-guide plate base material, the diffusion layer excellent in the light-diffusion capability of a fine pattern can be formed easily and cheaply.

  When coating the diffusion layer, it is preferable that the portion near the light source has a low coating density of the light diffusing fine particles, and the portion far from the light source has a high coating density of the light diffusing fine particles. Thereby, even if it does not produce a plate and a metal mold | die conventionally, when a coating liquid is apply | coated to a light-guide plate base material, the diffusion layer excellent in the light-diffusion capability of a fine pattern can be formed easily and cheaply.

  The coating liquid is preferably applied to the back surface, the front surface, or both surfaces of the light guide plate base material by a spray coating method in which the coating liquid is sprayed from a nozzle. Since the spray coating method only scans light and small nozzles in the XY directions, the object can be achieved with inexpensive equipment. That is, the spray coating method is applied to a large light guide plate with inexpensive equipment.

  It is preferable that the coating density of the light diffusing fine particles is changed one-dimensionally or two-dimensionally by arranging a plurality of nozzles in parallel and scanning the plurality of nozzles substantially in parallel.

  The distance from the nozzle to the coating surface of the light guide plate substrate is preferably 70 mm or more and 300 mm or less.

  In the spray coating method, the nozzle is moved in a direction substantially parallel to the first side of the light guide plate base material on the coating surface of the light guide plate base material while ejecting the coating liquid from the nozzle. It is preferable that the coating liquid is applied to the entire surface or a part of the coating surface by repeating at a predetermined feed pitch in a direction orthogonal to the first side.

  The step of repeating the scanning for moving the nozzle in a direction substantially parallel to the first side of the light guide plate base material at a predetermined feed pitch in a direction orthogonal to the first side is applied to the light guide plate base material. It is preferable to change the coating density of the light diffusing fine particles one-dimensionally by partially repeating on the work surface.

  It is preferable to change the coating density of the light diffusing fine particles in a one-dimensional manner by changing the feed pitch of the nozzles and applying the coating liquid to the whole or part of the coating surface of the light guide plate substrate. .

  By changing the scanning speed of the nozzle for each scanning of the nozzle and applying the coating liquid to the whole or a part of the coating surface of the light guide plate base material, the coating density of the light diffusing fine particles is one-dimensionally changed. It is preferable to change.

  The amount of coating liquid applied from the nozzle per unit time is changed for each scanning of the nozzle, and the light-diffusing fine particles are applied by coating the coating liquid on the whole or part of the coating surface of the light guide plate substrate. It is preferable to change the coating density in a one-dimensional manner.

  A light guide plate according to the present invention is a light guide plate in which a light source is disposed on an end surface to constitute a surface light source device, and a light diffusion fine particle and a light-transmitting binder are provided on the back surface, the front surface, or both surfaces of the light guide plate substrate. A diffusion layer is applied by applying a coating solution containing the light diffusion fine particles as aggregates, and a plane area occupied by the aggregates on a coating surface of the light guide plate substrate and a coating area of the coating solution The ratio is between 0.1% and 70%. Thereby, even if it does not produce a plate and a metal mold | die conventionally, when a coating liquid is apply | coated to a light-guide plate base material, the diffusion layer excellent in the light-diffusion capability of a fine pattern can be formed easily and cheaply.

  The coating liquid is preferably applied to the back surface, the front surface, or both surfaces of the light guide plate base material by a spray coating method in which the coating liquid is sprayed from a nozzle. Since the spray coating method only scans light and small nozzles in the XY directions, the object can be achieved with inexpensive equipment. That is, the spray coating method is applied to a large light guide plate with inexpensive equipment.

  The number of light diffusing fine particles contained in one aggregate is preferably 10 or more and 10,000 or less.

  As the distance from the light source increases, the ratio of the flat area occupied by the aggregates on the coated surface of the light guide plate substrate and the coated area of the coating solution or the coated area of the coating solution and the coated surface area of the light guide plate substrate It is preferable that the coating area ratio is high.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the light-guide plate and light-guide plate which can form the fine pattern of a diffused layer easily and cheaply can be provided.

In the manufacturing method of the light-guide plate which concerns on this invention, it is the schematic which shows a mode that a coating liquid is spray-coated on the coating surface of a light-guide plate base material. It is a side view which shows the state by which the coating liquid was apply | coated to the light-guide plate base material with the spray coating method. It is a top view which shows the state by which the coating liquid was apply | coated to the light-guide plate base material with the spray coating method. It is a side view which shows the state by which the coating liquid was apply | coated to the light-guide plate base material with the spray coating method. It is a top view which shows the state by which the coating liquid was apply | coated to the light-guide plate base material with the spray coating method. It is a side view which shows the state in which the light-diffusion fine particle was arranged in a line. It is a top view which shows the state in which the light-diffusion fine particle was located in a line. It is the schematic which shows a mode that the luminance distribution of a surface light source device is measured. It is a figure which shows distribution of the X direction of the relative luminance of the light-guide plate which apply | coated the coating liquid uniformly by changing a feed pitch. It is a figure which shows roughly the locus | trajectory of the nozzle at the time of apply | coating a coating liquid with a spray coating method. It is a figure which shows distribution of the X direction of the coating density of the applied light-diffusion fine particle with the locus | trajectory of the nozzle shown to FIG. 7A. It is the figure which prescribed | regulated the scanning direction and feed direction of a nozzle at the time of apply | coating a coating liquid with a spray coating method. It is a figure which shows the conditions of the coating method used for the manufacturing method of the light-guide plate of this invention in detail. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows the locus | trajectory of the nozzle by the coating method shown to FIG. 8B, and the distribution of the X direction of the coating density of light-diffusion fine particle. It is a figure which shows distribution of the X direction of the coating density of the light-diffusion fine particle at the time of apply | coating a coating liquid uniformly to a light-guide plate base material. It is a figure which shows distribution of the X direction of the brightness | luminance which installed the light source in the left end of the light-guide plate base material of FIG. 10A, and was measured. It is a figure which shows distribution of the X direction of the target application density of light-diffusion fine particles. It is a figure which shows distribution of the X direction of the target application density of a different light-diffusion fine particle. It is a figure which shows typically the two-dimensional gradation distribution assumed that a line light source is installed in 4 sides of a light-guide plate. It is the schematic which shows a mode that a coating liquid is spray-coated on the coating surface of a light-guide plate base material with a some nozzle. It is the schematic which shows each process order of the manufacturing method of the light-guide plate which concerns on this invention. It is a side view which shows roughly the light-guide plate with which the coating liquid was apply | coated to the polka dot shape. It is a top view which shows roughly the light-guide plate with which the coating liquid was apply | coated to the shape of a polka dot. It is a side view which shows roughly the light-guide plate with which the coating liquid was apply | coated to the whole surface of the coating surface. It is a top view which shows roughly the light-guide plate with which the coating liquid was apply | coated to the whole surface of the coating surface. It is a microscope picture of the coating surface of a light-guide plate base material. It is a microscope picture of the coating surface of a light-guide plate base material.

  First, the background of the technical idea of the present invention will be described, and then the details of each embodiment will be described.

  Examples of the technique for forming the diffusion layer on the light guide plate substrate include a screen printing method and an offset printing method. In either case, it is necessary to create a master pattern such as a printing plate or a mold first. For example, a screen printing plate draws a pattern that is precisely optically designed by laser drawing or an ink jet printer. Next, the pattern image formed on the silk coated with the photosensitive emulsion is selectively exposed and washed. Thereby, a diffusion layer is formed on the light guide plate.

  In these processes, there is a limit to miniaturization. For example, problems such as laser drawing line width and emulsion sensitivity, and stickiness during cleaning must be cleared. Even if the plate is produced, it causes printing process and performance problems such as printing defects accompanying miniaturization and product performance fluctuations due to fluctuations in transfer rate. Therefore, it is necessary to improve the printing technology at the same time. Furthermore, if the design pattern or the created version is defective, an expensive master version is recreated. In order to avoid these problems, a diffusion layer forming method that does not require a master plate is essentially suitable.

  On the other hand, in a large-sized light guide plate, a gradation pattern may be formed in the diffusion layer in order to make the luminance of the light exit surface uniform. That is, a pattern with a low light diffusion capability is formed near the light source, and a pattern with a high light diffusion capability is formed as the distance from the light source increases. In order to reduce the light diffusion capacity, for example, the geometrical patterning method that reduces the pitch and area of the pattern and the light diffusion capacity itself of the diffusion layer, such as reducing the concentration of the diffusion material and the reflection material, are physically used. The method of reducing to is mentioned. However, changing the concentration of the diffusing material or reflecting material significantly reduces productivity. Therefore, it is common to adjust by the area density, pitch, and height of the application part. However, for the reasons described above, precision patterning printing becomes a barrier, and it is difficult to increase the size of the light guide plate.

Therefore, in view of these problems, the present invention has sought to provide a light guide plate and a method for manufacturing the light guide plate that can form a diffusion layer having a fine pattern easily and inexpensively without creating a plate or a mold.
That is, the light guide plate and the method for manufacturing the light guide plate according to the present invention have the following configurations and processes.

<Embodiment 1>
Embodiment 1 of the present invention will be described below. The light guide plate according to the present invention is one of constituent members of a backlight device that emits light from the back surface of a liquid crystal display panel, a signboard, and the like. A light source is disposed on the end face of the light guide plate.

  As shown in FIGS. 1 and 2, this light guide plate applies a coating liquid 2 containing light diffusing fine particles 21 and a light-transmitting binder 22 on the back surface, front surface, or both surfaces of the light guide plate substrate 1 in a fine droplet state. Thus, the diffusion layer 3 is applied. The light diffusing fine particles 21 become aggregates 210.

Specifically, first, the light guide plate substrate 1 is prepared. As the light guide plate substrate 1, a general transparent resin substrate such as polymethyl methacrylate (PMMA) resin, polystyrene resin, polycarbonate resin, or the like is preferably used. In particular, as the large light guide plate substrate, a polymethyl methacrylate resin substrate having the most excellent transparency is more preferable. The warp of the light guide plate substrate 1 is preferably within a range of ± 1.61 × 10 ⁻⁴ (1 / mm) in curvature (curvature of the most curved portion).

  Next, the coating liquid 2 containing the light diffusing fine particles 21 and the translucent binder 22 is applied to the back surface or the front surface of the light guide plate substrate 1 or both surfaces (however, in this embodiment, only the front surface is referred to as a coating surface). To do. Incidentally, as shown in FIGS. 2A and 2B, the diffusion layer 3 of the present embodiment was coated with the coating solution 2 so that the coated portion and the uncoated portion were randomly arranged. However, in the illustrated example of FIGS. 2A and 2B, island-shaped application portions are randomly arranged, but as shown in FIGS. 3A and 3B, island-shaped uncoated portions may be randomly arranged.

  Here, the light guide plate used in the surface light source device means that light incident at an angle less than the critical angle repeats total reflection at the interface between the gas phase and the individual phase (hereinafter sometimes referred to as a gas interface). However, the light is propagated to a place away from the light source by using the traveling in the light guide plate. Thus, light is extracted by inhibiting total reflection at the interface from which light is to be extracted. Accordingly, it is a matter of course that a diffusion layer is formed in a portion where light emission is desired, but a technique for leaving the interface as it is in a portion where light emission is not desired is required. That is, it is a matter of course that a diffusion layer is formed, but a technique for intentionally leaving a gas interface is necessary. As a diffusion layer forming method corresponding to this requirement, a spray coating method in which a coating liquid is sprayed together with gas ejection is preferable.

  In general, a coating apparatus that does not use a plate is intended to uniformly coat the entire surface. Therefore, it is difficult to intentionally make an uncoated part. Although the uncoated portion can be formed even when the coating liquid is deficient, the control of the dripping is extremely unstable. Moreover, although unapplied parts, such as a pinhole, may occasionally occur as an unforeseen situation, it is originally uncontrollable. On the other hand, since the spray coating method sprays a coating liquid in the form of fine droplets, it has an excellent feature that it essentially includes a coating unit and a non-coating unit in a very small unit.

  Therefore, in this embodiment, the coating liquid 2 is apply | coated to the light-guide plate base material 1 by the spray coat method. That is, as the coating apparatus, an apparatus that is excellent in flow rate stability and does not have a worry of nozzle clogging is preferable. Further, as the coating apparatus, a coating apparatus that can spray the coating liquid 2 in a uniform fine droplet state, hardly scatters the coating liquid 2 outside the planar area of the light guide plate base material 1, and has high coating efficiency is preferable. It is. Therefore, a spray coater 4 is used as a coating apparatus. However, the diffusion layer forming method is not limited to the spray coating method, and may be any spray coating method that can apply the coating liquid 2 to the light guide plate substrate 1 in a fine droplet state.

  The spray coater 4 pumps gas to the nozzle 5 to eject it. Then, the spray coater 4 sprays the gas to be ejected onto the light guide plate substrate 1 by bringing the coating liquid 2 pumped from the storage tank 6 to the nozzle 5 by a pump or the like. The flow rates of the gas fed to the nozzle 5 and the coating liquid 2 are controlled by the flow rate control units 7 and 8, respectively.

  The nozzle 5 is preferably of a swirl flow type. In the swirl flow nozzle, the spray fluid becomes spiral and the spray angle becomes narrow. Therefore, the light diffusing fine particles 21 are likely to aggregate. Further, since the flow velocity in the normal direction when the light diffusing fine particles 21 arrive at the light guide plate substrate 1 is low, the light diffusing fine particles 21 can be attached to the light guide plate substrate 1 without breaking the aggregation of the light diffusing fine particles 21.

  The nozzle 5 is configured to be movable in the X direction and the Y direction. The nozzle 5 is configured to be able to spray the coating liquid 2 on the entire planar area (but may be a part) of the light guide plate substrate 1. The nozzle 5 is configured to be further movable in the vertical direction. Thus, it is preferable that the nozzle 5 is configured to be able to change the interval between the nozzle 5 and the light guide plate substrate 1. Incidentally, the drive mechanism of the nozzle 5 in the X and Y directions and the drive mechanism in the vertical direction are not particularly limited. However, in this embodiment, the nozzle 5 is configured to be movable in the X / Y direction and the vertical direction, but the stage (not shown) that supports the light guide plate substrate 1 is moved in the X / Y direction and the vertical direction. A possible configuration is also possible.

  For example, dry air or dry nitrogen can be used as the gas. When a flammable solvent is used, dry nitrogen is preferably used to prevent ignition due to static electricity. As will be described later, in order to promote the aggregation of the light diffusing fine particles 21, the carrier gas may be heated to, for example, 30 ° C. or higher and 120 ° C. or lower before spraying.

  The coating liquid 2 is a mixture containing the light diffusing fine particles 21 and the light transmissive binder 22 as described above. The light diffusing fine particles 21 are members that transmit and diffuse light. As the light diffusion fine particles 21, inorganic fine particles such as silica, calcium carbonate, barium sulfate, titanium oxide, and aluminum oxide, and organic fine particles such as silicone beads, PMMA beads, MS beads, and styrene beads can be used.

  When the coating liquid 2 is applied to the surface (light emitting surface) of the light guide plate substrate 1, it is preferable to use transparent glass fine particles and transparent resin fine particles that are transmitted and scattered as the light diffusing fine particles 21. When the coating liquid 2 is applied to the back surface (light reflecting surface) of the light guide plate substrate 1, it is preferable to use white particles and pigment that are reflected and scattered as the light diffusing fine particles 21.

The shape of the light diffusing fine particles 21 may be a true spherical shape, a spherical shape, a scale shape, an indefinite shape, or the like, and is not particularly limited.
The average particle diameter of the light diffusing fine particles 21 is preferably 1 μm or more and 50 μm or less. If the average particle size is smaller than the lower limit value described above, the ability to diffuse light may be insufficient, or diffused light may be colored. If the average particle size is larger than the above-described upper limit, clogging may easily occur when the nozzle is used, or light diffused by the light diffusing fine particles 21 may become conspicuous as a bright spot at a portion where the coating density is low. . In particular, the average particle diameter is preferably 1 μm or more and 20 μm or less.

  The ratio of the light diffusing fine particles 21 to the coating liquid 2 is preferably 1 wt% or more and 20 wt% or less. When the ratio is out of the above-described range, the aggregate of the light diffusing fine particles 21 may not easily be generated. If the ratio is lower than the lower limit value described above, it may be difficult to obtain a high aspect ratio and the light diffusion capability may be insufficient.

  The light transmissive binder 22 is a member that adheres the light diffusing fine particles 21 to the light guide plate substrate 1. As the translucent binder 22, for example, a solvent-type adhesive, a thermosetting resin, an ultraviolet curable resin, or the like can be used. As the light-transmitting binder 22, as described later, a resin component such as an acrylic pressure-sensitive adhesive that does not adhere during solvent dilution but develops adhesion after solvent drying may be used. However, it is also within the scope of the present invention to cause the light diffusing fine particles to function as an adhesive by dissolving a non-reactive polymer in a solvent and spray-coating and drying the solvent on the light guide plate substrate.

  When the length of the light guide plate in the light guide direction is 600 mm or less, the difference between the refractive index of the light transmissive binder 22 and the refractive index of the light diffusing fine particles 21 may be −0.1 or less or 0.1 or more. preferable. This is because the light diffusing effect is exhibited by both the unevenness of the surface and the refractive index difference, and light can be efficiently extracted in the surface direction at a relatively short light guide distance. When the length of the light guide plate in the light guide direction is 300 mm or more, the difference between the refractive index of the light transmissive binder 22 and the refractive index of the light diffusing fine particles 21 is preferably −0.1 or more and 0.1 or less. . The light diffusing effect is mainly exhibited only by the unevenness of the surface, and light can be gradually extracted, which is suitable for a relatively long light guide distance. The light diffusing fine particles 21 having a small refractive index difference may be mainly used near the light source, and the light diffusing fine particles 21 having a large refractive index difference may be mainly used at a position away from the light source. The light diffusion effect can be changed more dynamically in the light guide direction, and a high light extraction efficiency can be achieved at a long light guide distance.

The translucent binder 22 preferably has a viscosity of 1 mPa · s to 100 mPa · s. If the viscosity is smaller than the lower limit value described above, leveling is likely to occur in the light guide plate substrate 1, and the light diffusion capability is reduced. If the viscosity is larger than the above-described upper limit, uneven coating tends to occur. Particularly preferably, it is 1 mPa · s or more and 20 mPa · s or less.
The difference between the refractive index of the translucent binder 22 and the refractive index of the light guide plate substrate 1 is preferably within ± 0.1. Since it is not necessary to consider refractive reflection at the interface between the translucent binder 22 and the light guide plate substrate 1, the optical design is simple.

  By the way, when only a translucent binder is applied using a spray coater, the translucent binder applied to the light guide plate base material causes a leveling phenomenon. It is difficult to form a surface unevenness sufficient to cause light diffusion by the leveling phenomenon, that is, a surface unevenness sufficient to inhibit total reflection, particularly an unevenness height / an average pitch of unevenness (hereinafter sometimes referred to as an aspect ratio). , There is a possibility of flattening. Further, if the light-transmitting binder is repeatedly applied, the coating liquid in the form of fine droplets may be brought into close contact with each other due to the surface tension, and may be flattened.

  In order to improve these, a method of applying a high-viscosity light-transmitting binder and a method of forming irregularities by adding (mixing) light diffusing fine particles to the light-transmitting binder can be considered. However, increasing the viscosity of the translucent binder tends to cause uneven coating during spraying. In addition, when a coating liquid in which light diffusing fine particles having a large diameter are added to a light transmissive binder is applied, there is a possibility that the nozzle of the spray coater is clogged or the light diffusing fine particles are settled in the light transmissive binder.

  Therefore, in this embodiment, the translucent binder is diluted by about 1.1 to 10 times with a solvent. For example, a light-diffusing fine particle having a small particle diameter of 1 μm or more and 20 μm or less is added to a low-viscosity light-transmitting binder diluted to 1 mPa · s to 20 mPa · s and sprayed between the nozzle and the light guide plate substrate. By reaggregating the light diffusing fine particles 21 of the liquid 2, the diffusion layer 3 having a high light diffusing ability is obtained (see FIGS. 2A and 2B and FIGS. 3A and 3B).

  That is, the coating liquid 2 sprayed from the nozzle 5 is in a dispersed state while the content of the solvent is large. When the solvent dries, it reaggregates with one light diffusing fine particle 21 as a nucleus due to surface tension. At this time, the light diffusing fine particles 21 become cocoon-like aggregates 210. Aggregate 210 adheres to light guide plate substrate 1. By the way, if a large amount of solvent remains, leveling will occur after adhesion, which is not good. Therefore, aggregation may be promoted using hot air.

  If the speed at which the light guide plate base material 1 is reached is high, as shown in FIGS. 4A and 4B, the wings of the ridges are crushed and the light diffusing fine particles 21 are individually arranged, leading to a reduction in light diffusing ability. These can be eliminated by adjusting the interval T (FIG. 1) from the nozzle 5 to the light guide plate substrate 1. For example, the interval T from the nozzle 5 to the light guide plate substrate 1 is preferably 70 mm or more and 300 mm or less. When the interval T is shorter than the lower limit value described above, the solvent is not sufficiently dried. Therefore, the formation of aggregates of the light diffusing fine particles 21 hardly occurs, and the light diffusing fine particles 21 may settle in the light transmissive binder 22 and the light diffusing ability may be significantly reduced. Moreover, since the coating speed to the coating surface of the light-guide plate base material 1 is quick, an aggregate is easy to break. When the interval T is longer than the above-described upper limit value, the flow rate is remarkably reduced until the coating liquid 2 reaches the coating surface of the light guide plate substrate 1. Therefore, the coating liquid 2 is not applied to the coated surface of the light guide plate substrate 1 and the amount of the coating liquid 2 scattered outward increases.

  There is no restriction | limiting, such as a ketone type | system | group, alcohol type | system | group, and ester type, as a solvent. However, the solvent preferably has a boiling point of 60 ° C. or higher and 200 ° C. or lower in order to stabilize reaggregation of the light diffusing fine particles 21. Further, the solvent preferably has a specific gravity of 0.8 or more and 1.3 or less from the viewpoint of preventing sedimentation. When the boiling point and specific gravity are higher than the upper limit values described above, the solvent is not sufficiently dried. For this reason, the formation of aggregates of the light diffusing fine particles 21 may hardly occur. When the boiling point or specific gravity is lower than the lower limit value described above, many have relatively low viscosities. Therefore, there may be a problem that the light diffusing fine particles 21 are likely to settle. The boiling point is preferably 120 ° C. or higher and 170 ° C. or lower. Further, the boiling point is more preferably 130 ° C. or higher and 160 ° C. or lower.

  The mixing ratio of the mixture of the light diffusing fine particles 21 and the light transmissive binder 22 with respect to the solvent is preferably 2 wt% or more and 50 wt% or less. When the mixing ratio is larger than the above-described upper limit, the formation of the aggregate 210 of the light diffusing fine particles 21 may hardly occur or the coatability may be poor. Even when the mixing ratio is less than the above-described lower limit, the formation of aggregates of the light diffusing fine particles 21 is not particularly noticeable, and an increase in cost due to an increase in the amount of solvent used may be a problem. The mixing ratio is more preferably 3 wt% or more and 30 wt% or less.

  Next, the light guide plate substrate 1 on which the coating liquid 2 is spray-dried is dried by natural air drying, hot air, or the like. When the translucent binder 22 is made of an ultraviolet curable resin, the translucent binder 22 is cured by irradiating ultraviolet rays in the subsequent steps. As a result, as shown in FIGS. 2A and 2B and FIGS. 3A and 3B, the plurality of light diffusing fine particles 21 form a cocoon-shaped aggregate 210 with one light diffusing fine particle 21 as a nucleus. The aggregate 210 adheres to the coated surface of the light guide plate substrate 1. The aggregate 210 has a high aspect ratio and forms the diffusion layer 3 having a fine pattern. Therefore, when the coating liquid 2 is applied to the light guide plate base material 1 without creating a plate or a mold as in the prior art, the diffusion layer 3 having excellent light diffusing ability of a fine pattern can be easily and inexpensively formed. it can. Moreover, even if the coating liquid 2 is applied over the light guide plate substrate 1 by spray coating, the light diffusing fine particles 21 adhere in an agglomerated state and are difficult to flatten. Therefore, the coating liquid 2 can be satisfactorily applied to the light guide plate substrate 1 by a spray coating method.

  Here, the ratio R between the flat area occupied by the aggregates on the coated surface of the light guide plate substrate 1 and the coating area of the coating liquid 2 is 0.1% or more and 70% or less. If the ratio R is less than the lower limit value described above, the light diffusion capability of the light guide plate 100 may be insufficient. If the ratio R is larger than the above-described upper limit value, the light diffusing ability of the light guide plate 100 becomes too large, and when the light guide length L (FIG. 5) is long, the amount of emitted light at a position away from the light source may be insufficient. is there.

  In the light guide plate 100 manufactured as described above, the diffusion layer 3 is applied by applying the coating liquid 2 including the light diffusion fine particles 21 and the light transmissive binder 22 to the surface of the light guide plate substrate 1. The light diffusing fine particles 21 are aggregates 210. The ratio R between the flat area occupied by the aggregates 210 on the coated surface of the light guide plate substrate 1 and the coating area of the coating liquid 2 is 0.1% or more and 70% or less. For example, as shown in FIG. 5, the light guide plate 100 includes a line light source 9 such as an LED array installed at one end, a diffuse reflection film 10 installed on the back side, and a diffusion film installed on the front side. 11 constitutes a surface light source device. The aggregate 210 of the plurality of light diffusing fine particles 21 has a high aspect ratio and forms the diffusion layer 3 having a fine pattern. Therefore, when the coating liquid 2 is applied to the light guide plate base material 1 without creating a plate or a mold as in the prior art, the diffusion layer 3 having excellent light diffusing ability of a fine pattern can be easily and inexpensively formed. it can. Incidentally, a light-transmitting binder that does not contain the light diffusing fine particles 21 may be applied between the light guide plate substrate 1 and the diffusion layer 3 to the entire upper surface region of the light guide plate substrate 1 with a uniform thickness. The translucent binder functions as an antistatic layer, a hard coat layer, or the like.

  It is preferable that the coating area ratio S between the coating area of the coating liquid 2 (the planar area of the diffusion layer) and the area of the coating surface of the light guide plate substrate 1 is 5% or more and 95% or less. If the coating area ratio S is less than the lower limit value described above, the light diffusion ability of the light guide plate 100 may be insufficient. If the coating area ratio S is larger than the above-described upper limit value, light absorption by the translucent binder 22 cannot be ignored and the brightness may be insufficient.

  The number of the light diffusing fine particles 21 contained in one aggregate 210 is preferably 10 or more and 10,000 or less. If the number is less than the lower limit value described above, the light diffusion capability of the light guide plate 100 may be insufficient. When the number is larger than the above-described upper limit value, appearance defects such as unevenness, rough feeling, and bright spots are likely to occur.

  However, the coated surface of the light guide plate substrate 1 is composed of monodispersed light diffusing fine particles 21 and less than 10 light diffusing fine particles 21 in addition to the aggregates in which the number of light diffusing fine particles 21 is 10 or more and 10,000 or less. Aggregates 210 may be present. In this case, it is preferable that the monodispersed light diffusing fine particles 21 and the aggregate 210 composed of less than 10 light diffusing fine particles 21 are less than 20% of the total number of light diffusing fine particles.

  Incidentally, the number of the light diffusing fine particles 21 contained in the aggregate 210 can be counted by observation with an optical microscope or a laser microscope of about 300 to 1000 times. Moreover, after collecting the aggregate 210 and removing the translucent binder 22, it can be counted by observation with an optical microscope or the like.

  If the light diffusing ability is insufficient after a single application, it may be overcoated. The high aspect ratio of the aggregate 210 is maintained even if the aggregates of the light diffusing fine particles 21 are adhered and integrated by recoating. Therefore, there is an advantage that the light diffusion ability is high and it is difficult to cause the appearance defect.

  The difference between the refractive index of the aggregate and the refractive index of the translucent binder is preferably 0.001 or more and 0.5 or less. The light diffusing capacity is based on the difference in refractive index of a substance that has a refractive index different from that of a substantially transparent material, the volume of the substance, the volume concentration of the substance, the shape of the substance (a regular or irregular shape such as a true sphere), and fine irregularities on the surface It changes by etc. When the difference in refractive index is smaller than the lower limit value described above, it is difficult to obtain an effect of uniforming illuminance due to low refractive scattering properties. When the difference in refractive index is larger than the above-described upper limit, reflection at the interface (gas interface) increases, and it is difficult to obtain an effect of uniforming illuminance when the light guide length is relatively long, for example, 300 mm or more.

  The arithmetic average surface roughness of the fine irregularities in the aggregate 210 is preferably 0.01 μm or more and 10 μm or less. When the arithmetic average surface roughness is smaller than the above-described lower limit, the reflection / scattering property is small and the entire surface tends to be dark. When the arithmetic average surface roughness is larger than the above-described upper limit value, it is difficult to obtain an effect of uniform illuminance such that the reflection / scattering element is physically large and the vicinity of the light source is locally bright.

<Embodiment 2>
Embodiment 2 of the present invention will be described below. The light guide plate and the light guide plate manufacturing method of the present embodiment are substantially the same as the light guide plate and light guide plate manufacturing method of the first embodiment, but as the brightness of the light guide plate becomes substantially uniform, The ratio R between the flat area occupied by the aggregates on the coated surface of the light guide plate substrate and the coated area of the coating solution, or the coating area ratio S between the coated area of the coating solution and the coated surface area of the light guide plate substrate was increased. . That is, as the distance from the light source increased, the coating density of the light diffusing fine particles was increased.

  With the recent increase in size of display devices, the backlight is also required to increase in size. That is, the light guide length L (FIG. 5) needs to be increased. In order to make the brightness of the light exit surface of the light guide plate uniform, it is necessary to reduce the light diffusion capability of the diffusion layer in the vicinity of the light source in the light guide plate, while increasing the light diffusion capability as the distance from the light source in the light guide plate increases. is there. Therefore, it is necessary to remarkably increase the light diffusion capability of the diffusion layer at the position farthest from the light source in the light guide plate. If the patterning of the diffusion layer is inappropriate, or if the printing accuracy is inferior even if the pattern can be designed, only the edge near the light source in the light guide plate is bright and the central portion is dark, that is, essential as a light guide plate There is a problem that the performance is not satisfied and a problem that luminance unevenness occurs on the light exit surface. From these viewpoints, it is necessary to refine the pattern of the diffusion layer and to accurately form a pattern arrangement that is rougher as the diffusion portion is closer to the light source and becomes denser as the distance from the light source is increased. “Near the light source” refers to a portion located closest to the light source in the effective light emitting portion of the light guide plate. That is, “in the vicinity of the light source” means an end portion on the side where the light source is installed. The “position farthest from the light source” refers to a part of the effective light emitting portion of the light guide plate that is farthest from the light source. That is, the “position farthest from the light source” means an end on the side facing the end on the side where the light source 9 is installed in the case of the light guide plate shown in FIG.

  In the present embodiment, the coating liquid 2 is applied to the light guide plate substrate 1 by a spray coating method in substantially the same manner as in the first embodiment. At this time, a plurality of light diffusing fine particles 21 are aggregated in the shape of a hull with one light diffusing fine particle 21 as a nucleus. The gradation distribution pattern arrangement is such that the aggregates 210 thus aggregated become denser as they move away from the light source.

  Here, uniform coating was attempted on a PMMA substrate having a thickness of 5 mm and a light guide length of 600 mm by repeating nozzle scanning in the Y direction at a constant feed pitch in the X direction. And the LED array light source 9 was installed in the left end of the light-guide plate 100 which apply | coated the coating liquid 2 by changing the feed pitch on the conditions shown in FIG. The coated surface of the light guide plate substrate 1 was set as the exit surface side. The diffuse reflection film 10 was installed on the back side of the coated surface. A diffusion film 11 was installed on the front surface of the coating surface. Thus, a sidelight type backlight was produced. As shown in FIG. 5, the surface luminance measuring device 12 was used to measure from above the sidelight type backlight. In this case, the side arranged in the Y direction in the light guide plate substrate 1 is the first side referred to in the present invention.

  The coating width by one scan of the nozzle 5 in the Y direction is about 50 mm. The central portion has a distribution similar to the Gaussian distribution in which the coating density of the light diffusion fine particles 21 is high and gradually decreases toward the outside. In the case of a rough pitch such that the feed pitch in the X direction exceeds 10 mm, unevenness occurs in the coating density of the light diffusing fine particles 21, and unevenness in brightness is generated in the luminance distribution as shown in FIG. By setting the feed pitch to 10 mm, coating without unevenness due to the feed pitch is possible.

  Also, as shown in FIG. 6, the relative luminance decreases as the distance from the light source 9 increases. The light diffusion performance of the light guide plate 100 to which the coating liquid 2 is applied is proportional to the application density of the light diffusion fine particles 21 on the surface of the light guide plate substrate 1. Therefore, the coating liquid 2 may be spray-coated so that the coating density of the light diffusing fine particles 21 is low on the light source side and high on the far side of the light source. The method is described below.

  7A and 7B, scanning for moving the nozzle 5 in the Y direction is repeated at a predetermined feed pitch in the X direction, and the light diffusing fine particles 21 are applied one-dimensionally around the center of the coating surface of the light guide plate substrate 1. The figure shows a gradation distribution in which the density is high and the coating density of the light diffusing fine particles 21 is lowered on both sides (that is, the end faces A and B sides) of the central portion.

  This light guide plate base material 1 assumes a light guide plate base material in which line light sources such as LED arrays are installed on both end faces A and B. 7A and 7B, the coating amount of the coating liquid 2 is kept constant, and the nozzle 5 is scanned in the Y direction at a constant speed. From the end face A side, the feed pitch in the X direction of the nozzle 5 starts from 10 mm so as not to be uneven. The coating liquid 2 is applied around the central portion of the light guide plate substrate 1 so that the feed pitch is gradually changed in a narrow manner. As a result, a complete gradation distribution without discontinuities is realized.

  The spray coating method is extremely flexible in realizing the gradation distribution. 8A and 8B summarize the parameters and various coating methods when the coating liquid 2 is applied. Here, consider the case of manufacturing a light source plate of both ends light source type in which linear light sources such as LED arrays are installed on the left and right end faces A and B of the light guide plate substrate 1.

  In the case of the both-end light source type, in order to make the in-plane luminance distribution constant, the ratio R or the coating area ratio S is increased as the distance from the light source increases. That is, the coating density of the light diffusing fine particles 21 at both ends of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 is increased around the central portion. The other conditions are set so that the light diffusing fine particles 21 can be satisfactorily aggregated 210 and adhere to the light guide plate substrate 1. In the present embodiment, the X direction is the length direction of the light guide plate substrate 1, that is, the light guide direction, and the Y direction is the width dimension direction of the light guide plate substrate 1.

  In the table of FIG. 8B, the parameters may include the scanning direction of the nozzle 5, the scanning speed of the nozzle 5, the feed pitch of the nozzle 5, the coating amount of the coating liquid 2 per unit time, and the like. Any one or more of these parameters are controlled and the other parameters are kept constant.

  More specifically, in the coating method (1) shown in FIG. 8B, the coating liquid 2 is applied as follows. In the said coating method (1), the edge | side arrange | positioned in the Y direction in the light-guide plate base material 1 becomes a 1st edge | side said by this invention.

  First, the coating liquid 2 is uniformly applied to the whole or a part of the transparent light guide plate substrate 1 with all parameters being constant (FIG. 9A). Next, the coating solution 2 is applied uniformly and uniformly around the central portion. That is, the application of the coating liquid 2 is repeated around the central portion with all parameters being constant.

Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. This situation is shown in FIG. 9A, but it is inevitable that a finite step is always generated at the boundary of overpainting. Therefore, it is preferable that the coating amount of the coating liquid 2 is as small as possible and the scanning speed of the nozzle 5 is as fast as possible. That is, it is desirable to apply the coating liquid 2 so as to reduce the coating density of the light diffusing fine particles 21 in one uniform coating as much as possible and to increase the number of repeated coatings.
Note that such multi-layer overcoating may be performed while appropriately adjusting the coating amount of the coating liquid 2, the scanning speed of the nozzle 5, the feed pitch of the nozzle 5, and the like.

  The coating method (2) shown in FIG. 8B is a coating method in which only the feed pitch in the X direction is continuously changed and other parameters are constant. Also in the coating method (2), the side arranged in the Y direction in the light guide plate substrate 1 is the first side referred to in the present invention.

  The application density of the applied light diffusion fine particles 21 increases and decreases in inverse proportion to the feed pitch of the nozzles 5. Therefore, the feed pitch is continuously increased or decreased so as to have an inversely proportional relationship of the desired gradation distribution function (FIG. 9B). That is, the feed pitch of the nozzles 5 is widened at both ends of the light guide plate substrate 1, and the feed pitch of the nozzles 5 is narrowed around the center.

  Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. In this coating method (2), a desired gradation distribution can be obtained and the productivity is high even if the coating liquid 2 is not overcoated. Moreover, since it is a complete gradation distribution in which discontinuities do not occur, a high-quality surface light source device without luminance unevenness can be obtained.

  The coating method (3) shown in FIG. 8B is a coating method in which only the scanning speed is changed every time the nozzle 5 is scanned and other parameters are constant. Also in the coating method (3), the side arranged in the Y direction in the light guide plate substrate 1 is the first side referred to in the present invention.

  The coating density of the light diffusing fine particles 21 is inversely proportional to the scanning speed of the nozzle 5. For this reason, as shown in FIG. 9C, the scanning speed for each scanning of the nozzle 5 is continuously changed so as to have an inversely proportional relationship of a desired gradation distribution. That is, both ends of the light guide plate substrate 1 increase the scanning speed of the nozzle 5 and decrease it around the center.

  Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. This coating method (3) is also preferable in terms of both productivity and brightness unevenness.

The coating method (4) shown in FIG. 8B is a coating method in which only the coating flow rate of the coating liquid 2 is changed every time the nozzle 5 is scanned, and other parameters are constant. In the coating method (4), the side arranged in the Y direction in the light guide plate substrate 1 is the first side referred to in the present invention.
That is, as the nozzle 5 is sent at a predetermined pitch from the end surface A side to the central portion, the coating amount of the coating liquid 2 is increased, and as the nozzle 5 is fed from the central portion to the end surface B side where the light source is installed, the coating liquid 2 is applied. Reduce the amount (Figure 9D).

  Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. In the spray coating method in which the coating amount setting of the coating liquid 2 can be set quickly, easily, with high accuracy and with high reproducibility during coating, this coating method (4) is also of high productivity and uneven brightness. Preferred on both sides.

  However, the agglomerate 210 of the light diffusing fine particles 21 is allowed to settle in the translucent binder 22 by increasing the coating amount of the coating liquid 2 on the end surface A side. As the nozzle 5 is sent to the center, the coating amount of the coating liquid 2 is set to an appropriate amount. Further, as the nozzle 5 is sent from the central portion to the end face B side, the coating amount of the coating liquid 2 is excessively increased again to cause the aggregates 210 of the light diffusing fine particles 21 to settle in the translucent binder 22. By applying in this way, the same effect can be obtained.

  The coating method (5) shown in FIG. 8B is a coating method in which scanning for moving the nozzle 5 in the X direction is repeated at a predetermined feed pitch in the Y direction. More specifically, the scanning speed is continuously changed during the scanning of the nozzle 5, and other parameters are constant. In the coating method (5), the side arranged in the X direction in the light guide plate substrate 1 is the first side referred to in the present invention.

  Specifically, the scanning speed of the nozzle 5 in the X direction is continuously changed so as to have an inverse function relationship of a desired gradation distribution function. That is, in the scanning of the nozzle 5 in the X direction, the scanning speed of the nozzle 5 is increased at both ends of the light guide plate substrate 1 and is decreased around the center (FIG. 9E).

  Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. This coating method (5) is also preferable in terms of both productivity and luminance unevenness.

The coating method (6) shown in FIG. 8B is also a coating method in which the scanning for moving the nozzle 5 in the X direction is repeated at a predetermined feed pitch in the Y direction. More specifically, the application amount of the application liquid 2 is continuously changed during the scanning of the nozzle 5, and the other parameters are constant. Also in the coating method (6), the side arranged in the X direction in the light guide plate substrate 1 is the first side referred to in the present invention.
Specifically, in the scanning of the nozzle 5 in the X direction, the application amount of the coating liquid 2 is small at both ends of the light guide plate substrate 1, and a large amount is ejected around the center (FIG. 9F).

  Thereby, the said ratio R or the coating area ratio S is made high as it leaves | separates from a light source. That is, the coating density of the light diffusing fine particles 21 at both ends near the light source of the light guide plate substrate 1 is lowered, and the coating density of the light diffusing fine particles 21 around the central portion far from the light source is increased. This coating method (6) is also preferable in terms of both productivity and luminance unevenness. Further, when the coating amount of the coating liquid can be varied at high speed, a desired gradation distribution can be easily realized by this coating method (6).

  However, the application amount of the coating liquid 2 is excessive at both ends of the light guide plate substrate 1 to cause the aggregates 210 of the light diffusing fine particles 21 to settle in the translucent binder 22, and the coating amount of the coating liquid 2 is set at the central portion. Even if the amount is appropriate, the same effect can be obtained.

  More detailed and quantitative explanation will be given. First, the light-diffusing fine particles 21 and the light-transmitting binder 22 and, if necessary, the coating liquid 2 containing a solvent are uniformly applied to the light guide plate substrate 1 at a feed pitch that does not cause uneven brightness, for example, a feed pitch of 10 mm. To do. Several kinds (three types α to γ in the illustrated example) of the light guide plate coated uniformly as described above are manufactured by changing the coating amount of the coating liquid 2 and the scanning speed of the nozzle 5. FIG. 10A shows the coating density of the light diffusing fine particles 21 on the manufactured light guide plates α to γ. For each light guide plate α to γ, a line light source such as an LED array is installed at the left end, and the luminance distribution is measured as shown in FIG. Based on this, the coating density of the light diffusing fine particles 21 that gives in-plane uniform luminance is as shown in FIG. Moreover, in the case of the light guide plate of the left one end light source, it becomes as shown in FIG. 10D.

In order to realize such a coating density of the light diffusing fine particles 21, the six coating methods (1) to (6) shown in FIG. 8B are preferably used. The coating amount F (X, Y) of the coating liquid 2, the scanning speed V _Y (X) of the nozzle 5 in the _Y direction, the scanning speed V _X (X) of the nozzle 5 in the X direction, and the nozzle 5 in the X direction. The feed pitch ΔX (X) is the feed pitch ΔY (X) of the nozzle 5 in the Y direction. The coating methods (1) to (6) shown in FIG. 8B may be applied as follows. However, the X coordinate at the left end of FIG. 8A is X ₀ , the application amount of the coating liquid 2 at the left end is F ₀ , V _Y0 , ΔX ₀ , and the target application density of the light diffusion fine particles 21 at the left end is C ₀ . Then, the target application density C (X) of the light diffusing fine particles 21 at the position X in FIG. 10C or FIG. 10D may be applied while determining parameters as follows. At this time, in order to prevent uneven coating, it is necessary to set the feed pitch of the longest nozzle to be 10 mm as described above.
Coating method (1): F, V _Y , ΔX and the number of overcoating steps are appropriately selected and applied Coating method (2): ΔX (X) = ΔX ₀ × C ₀ / C (X ₀ + ΣΔX), F and V _Y is constant Coating method (3): V _Y (X) = V _Y0 × C ₀ / C (X ₀ + ΣΔX), F and ΔX are constant Coating method (4): F (X) = F ₀ × C (X ₀ + ΣΔX) / C ₀ , V _Y and ΔX are constant Coating method (5): V _X (X) = V _X0 × C ₀ / C (X), F and ΔY are constant Coating method (6): F (X ) = F ₀ × C (X) / C ₀ , V _X and ΔY are constant Note that, if necessary, the coating methods (1) to (6) may be used in combination.

  Using such coating methods (1) to (6), the diffusion layer is applied by applying a coating liquid containing light diffusing fine particles and a light-transmitting binder to the surface of the light guide plate substrate 1. The light diffusing fine particles are aggregated. The ratio of the flat area occupied by the aggregates on the coated surface of the light guide plate substrate 1 and the coating area of the coating liquid is 0.1% or more and 70% or less. Therefore, also in this embodiment, the aggregate of a plurality of light diffusing fine particles has a high aspect ratio and forms a fine pattern diffusion layer. Therefore, if a coating solution is applied to the light guide plate substrate 1 without creating a plate or a mold as in the prior art, a diffusion layer excellent in light diffusing ability of a fine pattern can be formed easily and inexpensively.

  Moreover, the spray coating method can be applied to the front and back surfaces of the light guide plate substrate 1 and also to both surfaces without any problem. For example, a one-dimensional gradation distribution in the X direction is realized for the front surface by the coating methods (1) to (6), and a one-dimensional gradation in the Y direction is performed for the back surface by the coating methods (1) to (6). It is also possible to realize gradation distribution and manufacture a three-sided light source type and a four-sided light source type light guide plate.

  In general, in order to realize a gradation distribution with high luminous efficiency, a wide diffuse reflection capability range, that is, a coating density range of the light diffusing fine particles 21 is required. It is generally difficult to increase or decrease the coating density of the light diffusion fine particles 21 to achieve a light diffusion performance of 5 to 10 times or more. In such a case, the gradation distribution is applied by the coating methods (1) to (6) so that the coating density of the light diffusing fine particles 21 is uniformly sprayed on the back surface, and the surface is supplemented with insufficient light diffusion performance. Realize. Thereby, it may be easy to manufacture a gradation light guide plate with high luminance efficiency and uniform brightness. The present invention can be effectively applied even in such a case.

  The spray coating method can be easily applied to a large light guide plate having a size of 50 inches or more, for example. Injection molding, press molding, dot printing, etc. all require large precision molds and screen plates, as well as large facilities and high investment costs. In addition, in the ink jet printing method, enormous investment is required to support a large format. With the spray coating method, it is only necessary to scan a light and small nozzle in the XY direction. Therefore, the purpose can be achieved with inexpensive equipment. That is, the spray coating method of the present invention is applied to a large light guide plate with inexpensive equipment. In particular, it is suitable for a light guide plate having a light guide length L of 900 mm or more. In this case, the ratio between the illuminance near the light source and the illuminance at the position farthest from the light source is preferably 0.8 or more and 1.2 or less.

  Furthermore, if the light guide plate base material itself contains a diffusing material, the coating density of the light diffusing fine particles applied to the surface can be lowered as a whole. Therefore, it is beneficial in some cases. For example, as described above, light diffusion performance is insufficient only by surface coating. Further, for example, in the case of a thick and short light guide plate, the light guide light incident from the light source may reach the opposite end surface before sufficiently colliding with the diffuse reflection surface, and the surface light emission may not be sufficiently performed. In that case, it is possible to emit light effectively by slightly dispersing the diffusion portion in the light guide plate. The present invention is also suitably used for such applications.

  Incidentally, the coating area ratio S1 in the vicinity of the light source is 5% or more and 50% or less, the coating area ratio S2 at the position farthest from the light source is 20% or more and 95% or less, and S2> S1. preferable.

  Further, the (2π / 360) × 60 rad gloss value GS1 of the coated surface of the light guide plate substrate in the vicinity of the light source is 40 or more and 90 or less, and (2π of the coated surface of the light guide plate substrate 1 at the position farthest from the light source. / 360) × 60 rad gloss value GS2 may be 10 or more and 60 or less, and GS2> GS1.

  Further, the haze value H1 in the surface direction in the vicinity of the light source is 5% or more and 30% or less, the haze value H2 at the position farthest from the light source is 10% or more and 40% or less, and H2> H1 may be satisfied. .

<Embodiment 3>
Embodiment 3 of the present invention will be described below. The light guide plate and the light guide plate manufacturing method of the present embodiment are substantially the same as the light guide plate and light guide plate manufacturing method of the second embodiment, except that the light diffusing fine particles have a two-dimensional gradation distribution. Therefore, only the differences will be described in detail.

  FIG. 11 schematically shows a two-dimensional gradation distribution assuming that line light sources are installed on the four sides of the light guide plate 100. That is, M in FIG. 11 indicates a portion where the coating density of the light diffusing fine particles is substantially equal by connecting with a line. N in FIG. 11 indicates the distribution in the X direction of the coating density of the light diffusing fine particles. P in FIG. 11 indicates the distribution in the Y direction of the coating density of the light diffusing fine particles. If the target gradation distribution can be expressed by C (X, Y), it can be manufactured by using coating methods (1) to (6) alone or in combination.

  As an application of the coating method (1), it is possible to sequentially perform overcoating along the line (a) in FIG. In order to prevent luminance unevenness and luminance steps at the boundary of overcoating, a sufficiently large number of overcoating operations are required.

The application method (3) can be applied by continuously changing the scanning speed during one scanning of the nozzle in the Y direction. That is, the nozzle scanning speed in the Y direction may be scanned according to the following formula.
V _Y (X, Y) = V _Y0 × C ₀ / C (X ₀ + ΣΔX, Y), F and ΔX are constant

As an application of the coating method (4), it is possible to change the coating amount of the coating solution continuously during one scanning of the nozzle in the Y direction. That is, during the scanning of the nozzle in the Y direction, the coating amount of the coating solution may be ejected according to the following formula.
F (X, Y) = F ₀ × C (X ₀ + ΣΔX, Y) / C ₀ , V _Y and ΔX are constant.

A two-dimensional gradation distribution can also be realized by combining the coating methods (5) and (6). That is, the nozzle may be scanned in the X direction according to the following formula.
V _X (X, Y) = V _X0 × C ₀ / C (X, Y), F and ΔY are constant F (X, Y) = F ₀ × C (X, Y) / C ₀ , V _X and ΔY Is constant

  Further, by applying the coating method (2), a two-dimensional gradation distribution can be realized by changing the nozzle scanning speed and the coating liquid application amount during one nozzle scanning in the Y direction.

  Here, the two-dimensional gradation distribution is not limited to a four-side light source, but may be an orthogonal two-light source or a three-side light source, and includes a case where the application density of the light diffusing fine particles is finely adjusted in the peripheral portion of the end face. . The same applies to the one-dimensional gradation distribution described above.

  In the manufacturing method of the light guide plate in the first and second embodiments described above, when productivity is considered, it takes time to apply on the coating surface of the light guide plate substrate having a large area with only one nozzle. Therefore, it is not always a good idea. In FIG. 12, for example, a plurality of nozzles 5 are arranged in parallel at equal intervals in the Y direction, that is, in a direction substantially orthogonal to the scanning direction. The plurality of nozzles 5 are scanned in the X direction. However, a configuration may be adopted in which a plurality of nozzles 5 are arranged in parallel at equal intervals in the X direction and the plurality of nozzles 5 are scanned in the Y direction. Thus, the application time can be significantly shortened by using a multi-nozzle. It is conceivable that the interval between the adjacent nozzles 5 and 5 needs to be sufficiently wide so as not to interfere with each other at the time of application. In some cases, the adjacent nozzles may be shifted in the X direction and arranged alternately.

  The plurality of nozzles 5 are individually or commonly controlled and spray-apply the coating liquid onto the light guide plate substrate 1.

  In the case of a one-dimensional gradation distribution, for example, the nozzles 5 arranged in parallel by applying the coating method (5) or (6) are scanned once in the X direction. At this time, each nozzle 5 has the same flow rate. Next, a sufficiently small Y-direction feed pitch that does not cause luminance unevenness, for example, 10 mm is shifted in the Y direction, and scanning is performed in the X direction by the coating method (5) or (6). By scanning this for the nozzle interval, it can be applied uniformly over the entire surface.

  In the case of the two-dimensional gradation distribution, it is possible to control the coating amount of the coating liquid 2 from each nozzle 5 independently for each scanning so as to correspond to the coating density distribution of the light diffusing fine particles in the Y direction. Become.

  FIG. 13 shows a prototype / manufacturing process when the light-transmitting binder is an ultraviolet curable type and spray coating is performed using a coating solution of light diffusing fine particles in combination with a solvent. First, after the coating liquid 2 is spray-coated on the light guide plate substrate 1, the solvent is dried by warm air or the like. Next, the light-transmitting fine particles are permanently adhered to the surface of the light guide plate substrate by irradiating ultraviolet rays to cure the light-transmitting binder.

  In many cases, it is rare that a light guide plate having a uniform luminance is obtained by a single gradation distribution design. However, according to the present invention, as shown in FIG. 13, the luminance distribution is immediately measured and evaluated. If the desired uniformity cannot be obtained, fine adjustment is made to each parameter and coating is performed again. If this is repeated as necessary, the gradation distribution of the light diffusing fine particles can be easily realized in a short time.

  As described above, according to the present invention, the one-dimensional gradation distribution and the two-dimensional gradation distribution of the light diffusing fine particles do not require a mold, a printing plate, or the like, and can be prototyped and produced immediately from the design. In particular, the gradation distribution of the optimal light diffusing fine particles with uniform brightness so that the light from the light source can be emitted efficiently and uniformly forwards varies depending on the size, shape, plate thickness, light source position, etc. of the light guide plate substrate. The method of the present invention is suitably applied to the production of such a variety and variety.

  In the first embodiment, the aggregates 210 of the light diffusing fine particles 21 are randomly attached to the light guide plate substrate 1. In the second embodiment, as the distance from the light source 9 increases, the ratio R of the flat area occupied by the aggregates 210 on the coated surface of the light guide plate substrate 1 and the coating area of the coating solution 2 or the coating area of the coating solution 2 and the light guide plate base The coating area ratio S to the area of the coating surface of the material 1 is increased. However, if the ratio of the flat area occupied by the aggregate 210 on the coated surface of the light guide plate substrate and the coating area of the coating liquid 2 satisfies the requirement of 0.1% or more and 70% or less, the aggregate 210 of the light diffusing fine particles 21. May be attached to the light guide plate substrate 1 substantially uniformly. That is, the ratio S2 / S1 between the coating area ratio S1 in the vicinity of the light source 9 and the coating area ratio S2 at the position farthest from the light source 9 is configured to be 80% or more and 120% or less.

  In the said Embodiment 2, although the ratio of the flat area which the aggregate 210 in the coating surface of the light-guide plate base material 1 and the application area of the coating liquid 2 is 0.1% or more and 70% or less, it is not this limitation. In short, the coating density of the light diffusing fine particles should be low at the part close to the light source, and the coating density of the light diffusing fine particles should be high at the part far from the light source.

  In Embodiments 1 to 3, the light diffusing fine particles 21 are aggregates, but this is not restrictive. That is, the light diffusing fine particles 21 may not be aggregated. At this time, in order to obtain a desired light diffusion performance, spray coating conditions such as light diffusion fine particles, a light-transmitting binder, a solvent, and a distance between the light guide plate substrate and the nozzle are appropriately controlled and selected. At this time, for example, the coating liquid 2 may be applied in a polka dot shape (FIG. 14). Further, in order to increase the light diffusion performance, the entire surface may be covered with the coating liquid 2 (FIG. 15). Incidentally, FIGS. 16A and 16B are photomicrographs of a state in which a coating liquid of MS fine particles, an ultraviolet curable translucent binder, and a solvent is spray-coated on a PMMA substrate and cured. In FIGS. 16A and 16B, the part represented as a bubble is a light diffusing fine particle. Since the light diffusing fine particles adhering to the coated surface of the light guide plate base material 1 each become a diffusing portion, a fine diffusing portion can be easily formed. Further, since the light diffusing fine particles are always applied randomly, the generation of moire can be suppressed.

<Example 1>
An acrylic resin sheet having a length (length in the light guiding direction) of 1200 mm, a width of 1000 mm, and a thickness of 8 mm is placed as a light guide plate base material on a regular board (stage), and applied from above the acrylic resin sheet by a nozzle of a spray coater. The liquid was sprayed. The coating liquid is resin fine particles (refractive index 1.56, average particle size 3 μmφ) as light diffusing fine particles, acrylic UV curable resin as a light transmissive binder, and a ketone solvent as a diluting solvent so that the solid content is 5 wt%. It is a diluted mixed solution. This coating solution was spouted with nitrogen gas.

  At this time, in order to apply the coating solution over the entire surface, the nozzle was sprayed while being moved in the plane direction of the light guide plate substrate (that is, in the X and Y directions). Specifically, the coating amount is changed according to the length direction (that is, the X direction) of the light guide plate base material, and is applied once at a nozzle feed pitch of 10 to 40 mm depending on the location so as to be applied most at the center in the X direction. -8 times of overcoating were performed. By the way, the distance between the light guide plate substrate 1 and the nozzle 5 is 100 to 200 mm, the coating amount of the coating liquid 2 is 0.5 to 4.0 gr / min, and the scanning speed of the nozzle 5 is 200 to 400 mm / sec. did.

As a result, the surface state by coating became gloss 85 near the light source and gloss 15 at a position of 600 mm in the length direction.
Next, a light source in which white LEDs are linearly arranged at both ends of the light guide plate base material is installed, a white diffuse reflection sheet is laminated on the back side of the light guide plate base material, and a light diffusion film is laminated on the coating surface to be the front side, A sidelight type backlight was produced.

  When the sidelight-type backlight was observed visually from a position 2 m away from the front, the luminance was uniform over the entire surface, and luminance unevenness such as bright spots was not noticeable.

<Example 2>
On the surface plate (stage), a transparent PMMA light guide plate substrate having the same size as that of Example 1 was placed, and the coating solution was applied from above by a nozzle as shown in FIG. At this time, by the coating method (1) shown in FIG. 8B, uniform application was first performed with the scanning direction as the Y direction and the X direction feed pitch as 10 mm. The coating solution is MS resin cross-linked particles (average particle size 3 μm, solid reconstitution residual concentration excluding solvent 10 wt%) as light diffusing fine particles, urethane-based UV curable resin as translucent binder, and PGMAC (propylene glycol monomethyl as diluting solvent). It is a mixed solution diluted with ether acetate) to a solid content of 20 wt%. This coating solution was spouted with nitrogen gas.

  The distance between the light guide plate substrate and the nozzle was 150 mm, the coating amount of the coating liquid was 1 mL / min in terms of solution, and the nozzle scanning speed was 150 mm / min. In this case, the coating width was about 50 mm.

  Under this condition, the coating liquid was applied to the entire surface of the light guide plate substrate while scanning the nozzle in the Y direction at intervals of 10 mm in the X direction. However, at the beginning of coating on one end surface (the lower end surface in FIG. 5) arranged in the X direction, blank scanning was started 20 mm before the light guide plate substrate. In addition, the light guide plate base material was scanned to a point exceeding 20 mm even at the end of coating on the other end surface (upper end surface in FIG. 5) arranged in the X direction. On one end face (left end face in the paper surface of FIG. 5) arranged in the Y direction, coating was performed from 20 mm before the light guide plate substrate. In addition, the other end face arranged in the Y direction (the end face on the right side in the paper surface of FIG. 5) is coated over the light guide plate base material by 20 mm, and coating unevenness at the direction changing portion of the nozzle is applied to the base body. It was carried out not to enter.

  In order to manufacture a light source plate of both-ends light source type, as shown in FIG. A sidelight-type backlight was produced in the same manner as in Example 1 with the coated surface of the light guide plate as the emission side. When the appearance inspection and the luminance distribution of the sidelight type backlight were measured, an eight-level luminance step was visually recognized, but a uniform light guide plate that was sufficiently acceptable was obtained.

<Example 3>
Coating was started under the same conditions as in Example 2, but a method of changing the scanning speed in the Y direction semi-continuously by the X direction feed pitch in the coating method (3) was used. Under the coating conditions of Example 2, the coating distribution of the light diffusing fine particles on the uniformly coated light guide plate substrate 1 with an X direction feed pitch of 10 mm is C ₀ , and the scanning speed 150 mm / min of the nozzle 5 in the Y direction is V. _Assuming that _Y0 and the feed pitch ΔX in the X direction of the nozzle 5 are constant at 10 mm, the n-th scanning speed V _Y (X) on the light guide plate substrate 1 is sequentially changed as follows. All other variables were applied as constant.
V _Y (X) = V _Y0 × C ₀ / C (X ₀ + ΣΔX)

  When the coated product was subjected to appearance inspection and luminance distribution measurement using both-end light sources, luminance irregularities and luminance steps were not visually recognized at all, and a high-quality light guide plate with extremely high luminance uniformity was obtained.

  In addition, this invention is not limited to the said embodiment and Example, In the range which does not deviate from the meaning, it can change suitably.

  The light guide plate and the light guide plate manufacturing method of the present invention can be used as a surface light source device that emits light from the back surface of a liquid crystal display panel, a signboard, or the like, a light guide plate for a so-called backlight device, and a method for manufacturing the light guide plate.

DESCRIPTION OF SYMBOLS 1 Light guide plate base material 2 Coating liquid 3 Diffusion layer 4 Spray coater 5 Nozzle 6 Storage tank 7 Flow control part 9 Light source 10 Diffuse reflection film 11 Diffusion film 12 Surface luminance measuring device 21 Light diffusion fine particle 22 Translucent binder 100 Light guide plate 210 Agglomerates

Claims (14)

A method of manufacturing a light guide plate in which a light source is disposed on an end surface to constitute a surface light source device,
A diffusion layer is applied by applying a coating liquid containing light diffusing fine particles and a light-transmitting binder on the back surface or the front surface or both surfaces of the light guide plate substrate in the form of fine droplets, and the light diffusing fine particles are aggregated, A method of manufacturing a light guide plate, wherein a ratio of a flat area occupied by the aggregates to a coating surface of the light guide plate base material and a coating area of the coating liquid is 0.1% or more and 70% or less.   2. When applying the diffusion layer, a portion close to the light source has a low coating density of the light diffusing fine particles, and a portion far from the light source has a high coating density of the light diffusing fine particles. The manufacturing method of the light-guide plate of description.   The said coating liquid is apply | coated to the back surface or the surface of the said light-guide plate base material, or both surfaces by the spray coating method which sprays the said coating liquid from a nozzle, The manufacturing method of the light-guide plate of Claim 1 characterized by the above-mentioned.   4. The coating density of the light diffusing fine particles is changed one-dimensionally or two-dimensionally by arranging a plurality of nozzles in parallel and scanning the plurality of nozzles substantially in parallel. The manufacturing method of the light-guide plate of description.   5. The method for manufacturing a light guide plate according to claim 3, wherein an interval from the nozzle to the coating surface of the light guide plate base is 70 mm or more and 300 mm or less.   In the spray coating method, the nozzle is moved in a direction substantially parallel to the first side of the light guide plate base material on the coating surface of the light guide plate base material while ejecting the coating liquid from the nozzle. 5. The light guide plate according to claim 3, wherein the coating liquid is applied to the whole or a part of the coating surface by repeating at a predetermined feed pitch in a direction orthogonal to the first side. Method.   The step of repeating the scanning for moving the nozzle in a direction substantially parallel to the first side of the light guide plate base material at a predetermined feed pitch in a direction orthogonal to the first side is applied to the light guide plate base material. 5. The method for manufacturing a light guide plate according to claim 3, wherein the coating density of the light diffusing fine particles is changed one-dimensionally by being partially repeated on the work surface.   The coating density of the light diffusing fine particles is changed one-dimensionally by changing the feed pitch of the nozzles and applying the coating liquid to the whole or part of the coating surface of the light guide plate base material. The manufacturing method of the light-guide plate of Claim 3 or 4 to do.   By changing the scanning speed of the nozzle for each scanning of the nozzle and applying the coating liquid to the whole or a part of the coating surface of the light guide plate base material, the coating density of the light diffusing fine particles is one-dimensionally changed. The light guide plate manufacturing method according to claim 3, wherein the light guide plate is changed.   The amount of coating liquid applied from the nozzle per unit time is changed for each scanning of the nozzle, and the light-diffusing fine particles are applied by coating the coating liquid on the whole or part of the coating surface of the light guide plate substrate. The method of manufacturing a light guide plate according to claim 3, wherein the coating density of the light guide is changed one-dimensionally. In order to constitute the surface light source device, the light source is a light guide plate disposed on the end surface,
The diffusion layer is coated by applying a coating liquid containing light diffusing fine particles and a light-transmitting binder on the back surface or the surface of the light guide plate substrate, or both surfaces,
The light diffusing fine particles are aggregates, and a ratio of a plane area occupied by the aggregates to a coating surface of the light guide plate base material and a coating area of the coating liquid is 0.1% or more and 70% or less. A light guide plate.   The light guide plate according to claim 11, wherein the coating liquid is applied to a back surface, a front surface, or both surfaces of the light guide plate base material by a spray coating method in which the coating liquid is sprayed from a nozzle.   The light guide plate according to claim 11 or 12, wherein the number of light diffusing fine particles contained in one aggregate is 10 or more and 10,000 or less.   As the distance from the light source increases, the ratio of the flat area occupied by the aggregates on the coated surface of the light guide plate substrate and the coated area of the coating solution or the coated area of the coating solution and the coated surface area of the light guide plate substrate The light guide plate according to claim 11, wherein the coating area ratio is high.

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