TWI461747B - A light diffusion sheet, a backlight unit using it, and a light diffusion sheet manufacturing method - Google Patents

Description

Light diffusing sheet, backlight unit using the same, and method of manufacturing light diffusing sheet

The present invention relates to a light diffusing sheet, a backlight unit using the same, and a method of manufacturing a light diffusing sheet.

The liquid crystal display device is widely used as a screen display device such as a television or a computer. The liquid crystal display device is mainly classified into a direct view type in which a display screen is directly viewed and a projection type in which an image projected onto a screen is viewed. The direct-view type liquid crystal display device has a transmissive type that transmits light from a backlight, a reflection type that uses natural light and an indoor light without a backlight, and a transflective type that is transmissive in a dark place and a transmissive type in a dark place. . On the other hand, the projection type liquid crystal display device has a front projection type that projects an image onto the front of the screen, and a rear projection type that projects the image onto the back of the screen.

A backlight system that illuminates the liquid crystal layer from the back surface of the transmissive liquid crystal display device is widely used, and a backlight unit such as an edge light type (side light type) or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 7, the edge light type backlight unit 40 generally includes a lamp 41 as a light source, a square plate-shaped light guide plate 42 disposed at an end portion along the lamp 41, and is disposed on the surface of the light guide plate 42 in an overlapping manner. A plurality of optical sheets 43 on one side. LEDs (light-emitting diodes), cold cathode tubes, and the like are used as the light source 41, and LEDs are now popularized from the viewpoints of miniaturization and energy saving. The optical sheet 43 has an optical function of diffusing and refracting transmitted light, and uses (1) a light diffusion sheet 44 mainly provided on the surface side of the light guide plate 42 and having a light diffusion function; and (2) disposed on the light diffusion sheet. On the surface side of 44, a cymbal sheet 45 or the like which refracts light toward one side in the normal direction is provided.

In addition, it is not shown in the figure, considering the light guiding of the light guide plate 42 The optical function of the optical and optical sheet 43 and the like also include a backlight unit in which a plurality of optical sheets 43 such as a light diffusion sheet and a cymbal sheet are disposed.

The function of the backlight unit 40 will be described. First, the light incident from the lamp 41 to the light guide plate 42 is reflected by the reflection point or the reflection sheet (not shown) on the back surface of the light guide plate 42 and the respective side surfaces, from the surface of the light guide plate 42. Shoot out. The light emitted from the light guide plate 42 is incident on the light diffusion sheet 44, and the light is diffused and emitted from the surface. Thereafter, the light emitted from the surface of the light-diffusing sheet 44 is incident on the cymbal sheet 45, and the light is refracted toward the normal side by the crotch portion in which a plurality of ridges are formed on the surface, and is emitted from the surface, thereby being upwardly The entire liquid crystal layer not shown in the figure is illuminated.

As shown in FIG. 7(b), the light diffusion sheet 44 which is superposed on the surface of the light guide plate 42 generally includes a transparent synthetic resin base material layer 46, an optical layer 47 laminated on the surface of the base material layer 46, and a laminate layer. The adhesion preventing layer 48 on the back side of the base material layer 46. The optical layer 47 generally has a structure in which the resin beads 50 are dispersed in the binder 49, and has a light diffusion function of diffusing transmitted light or the like. Further, the adhesion preventing layer 48 has a structure in which a small number of beads 52 are separated and dispersed in the bonding agent 51, and a lower portion of the beads 52 protrudes from the back surface of the bonding agent 51. The adhesion preventing layer 48 serves to prevent the occurrence of interference fringes due to the adhesion of the back surface of the light diffusion sheet 44 to the surface of other optical sheets or the like (light guide plate 42), or to be wound up in the manufacturing step. When it is stored in a cylindrical shape, lumps (attachments) and the like are generated.

As the beads 52 dispersed in the adhesion preventing layer 48 of the light diffusion sheet 44, acrylic beads or the like are generally used, and since the acrylic beads are relatively hard, the beads 52 protruding on the back surface may be damaged and overlapped and disposed on the light diffusion sheet. 44 The surface of the light guide plate 42 or the like on the back side. The damage of the light diffusion sheet causes uneven brightness of the liquid crystal display device.

Therefore, an optical sheet having a damage preventing layer on the back surface has been developed in order to prevent damage to other components such as a light guide plate and a gusset which are disposed on the back side of the back surface (refer to Japanese Laid-Open Patent Publication No. 2004-85626, etc.).

However, even in the optical sheet provided with the damage preventing layer, since fine beads for preventing adhesion still exist, damage to other optical sheets and the like cannot be sufficiently prevented.

[Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-85626

In view of the above problems, an object of the present invention is to provide a light diffusing sheet which can prevent damage to other components which are overlapped and adhere to other components which are overlapped, and can prevent occurrence of brightness without using the light diffusing sheet. A high-quality backlight unit that is uniform with interference fringes.

In order to solve the problems, the present invention provides a light diffusing sheet comprising: a sheet main body having an optical function; and a plurality of fibers protrudingly disposed on a back side of the sheet main body.

Since a plurality of fibers are protruded from the back side of the sheet main body, the light diffusion sheet is brought into contact with other members such as a light guide plate or a gusset which are disposed on the back side by overlapping the plurality of fibers. Since a plurality of fibers that are in such contact are soft, even if they are in contact with other members, the possibility of damage is small.

Further, since the light-diffusing sheet is in contact with other members such as a light guide plate disposed on the back side by overlapping the plurality of fibers, it has high adhesion preventing performance and can prevent interference fringes due to adhesion.

The sheet body and the plurality of fibers may be joined by an adhesive portion. A plurality of fibers can be more firmly bonded to the sheet body by the adhesive portion On the top, it can prevent the fibers from falling off.

The adhesive portion may be laminated on the entire surface of the back surface of the sheet main body. By laminating the adhesive portion on the entire surface of the back surface of the sheet main body in this manner, a plurality of fibers can be protruded along the entire surface of the back surface of the sheet main body, and the above-described damage prevention performance, adhesion prevention performance, and the like can be improved.

The adhesive portion may be attached to the back surface of the sheet main body in a dispersed manner. By attaching the adhesive portion to the back surface of the sheet main body in such a manner as to be dispersed, it is possible to reduce the amount of the applied adhesive and to reduce the layer laminated on the back surface of the sheet main body, and it is possible to maintain the above-described damage prevention performance, adhesion prevention performance, and the like. While increasing the transmittance of light.

The adhesive portion may be formed of an acrylic emulsion adhesive. The acrylic emulsion adhesive can be easily applied to the sheet body, and the risk of ignition is small. Therefore, the processability of the light diffusing sheet can be improved. The plurality of fibers may be protruded from the back side of the sheet main body by electrostatic flocking. The electrostatic flocking method can plant a plurality of fibers on the back side of the sheet main body at a desired angle, and it is also easy to adjust the density of the planted fibers. Therefore, according to the electrostatic working method, the damage prevention performance, the adhesion prevention performance, and the like can be improved.

The fibers can be transparent chemical fibers. By making the fiber a transparent chemical fiber, the light transmittance of the sheet main body can be maintained, and the light transmission property of the light diffusion sheet can be prevented from being lowered.

Preferably the fiber density per unit area of the back sheet body is 40 / cm ² or more 5000 / cm ² or less. By setting the fiber density per unit area of the back surface of the sheet main body within the above range, the above-described damage prevention performance, adhesion prevention performance, and the like can be improved, and light transmittance can be prevented from being lowered.

It is preferred that the fibers have an average diameter of 5 μm or more and 50 μm or less. Further, the average length is preferably 20 μm or more and 2 mm or less. By making the average diameter and the average length of the fibers within the above range, the above-described damage prevention performance, adhesion prevention performance, and the like can be effectively obtained, and the film property of the light diffusion sheet can be improved.

The sheet body may include a base material layer and an optical layer formed on a surface of the base material layer. By dividing the sheet body into the base material layer and the optical layer, the influence on the optical function can be reduced, and a plurality of fibers can be easily and reliably protruded from the base material layer.

In addition, in order to solve the above problems, the present invention also provides a backlight unit for a liquid crystal display device, wherein the liquid crystal display device uses a backlight unit to disperse light emitted from the lamp and direct the dispersed light to the surface side. The backlight unit includes the light diffusion sheet described.

The backlight unit can prevent the unevenness of brightness caused by damage of other components by using the high damage prevention performance of the light diffusion sheet, and can improve the quality of the liquid crystal display screen, and can be manufactured, Handling during transportation, storage, etc. is easy. Further, the backlight unit can prevent adhesion to other members that are disposed on the back side by overlapping by the adhesion preventing performance of the light diffusion sheet, and it is possible to prevent interference fringes or the like from occurring due to adhesion.

In addition, in order to solve the above problems, the present invention also provides a method of manufacturing a light diffusion sheet, comprising: an optical layer forming step of laminating an optical layer on a surface of a base material layer; and a binder coating step in the base material layer a back coating adhesive; a fiber spreading step of planting a plurality of fibers on the surface coated with the adhesive; a curing step of the adhesive to cure the adhesive after the hair is implanted; and a residual fiber removal step from the body after the adhesive is cured Remove excess fiber.

According to the method for producing a light-diffusing sheet, a plurality of fibers can be implanted on a desired surface of the light-diffusing sheet by the above-described steps, and in addition, a plurality of fibers can be firmly bonded and fixed to the light by the adhesive. The desired face of the diffuser. Therefore, the light-diffusing sheet obtained by this manufacturing method can exhibit high damage prevention performance and adhesion prevention performance against other members.

Here, the "adhesive portion" means a portion formed by curing the adhesive applied to the sheet main body. The "optical layer" refers to a layer that has a predetermined optical function for transmitted light.

As described above, the light-diffusing sheet of the present invention has excellent damage prevention performance, adhesion prevention performance, and the like for a surface such as a light diffusion sheet which is disposed on the back side. Further, the backlight unit of the present invention can prevent unevenness in brightness due to damage of a light diffusion sheet, a light guide plate, and the like, and generate interference fringes. Further, the backlight unit of the present invention can be easily handled in manufacturing, transportation, storage, and the like.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The optical sheet 1 of Fig. 1 is a so-called light diffusion sheet, and the optical sheet 1 includes a sheet main body 2, and a plurality of fibers 3 projecting from the back side of the sheet main body 2. The sheet main body 2 includes a base material layer 4 and an optical layer 5 laminated on the surface of the base material layer 4.

The base material layer 4 is made of a transparent synthetic resin or glass because of the need to transmit light. In addition to colorless transparency, the term "transparent" as used herein also includes colored transparent or translucent, and particularly preferred is colorless and transparent. The synthetic resin used for the base material layer 4 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, and propylene. Acid resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending properties is particularly preferable.

The base material layer 4 may contain an antistatic agent. By containing an antistatic agent, it is possible to prevent the optical sheet 1 from being charged by static electricity generated by the plurality of fibers 3 protruding from the sheet main body 2. The antistatic agent is not particularly limited, and a known antistatic agent can be used. For example, an anionic antistatic agent such as an alkyl sulfate or an alkyl phosphate; a cationic antibiotic such as a quaternary ammonium salt or an imidazoline compound can be used. An electrostatic agent; a nonionic antistatic agent such as polyethylene glycol, polyoxyethylene sorbitan monostearate or ethanol decylamine; a polymer-based antistatic agent such as polyacrylic acid. Among them, a cationic antistatic agent having a good antistatic effect is preferable, and an antistatic effect can be achieved by adding a small amount. Further, in the electrostatic flocking step of the fiber 3 described later, an appropriate amount of the antistatic agent is uniformly dispersed in the base material layer 4, so that the fibers 3 can be uniformly protruded.

The average thickness of the base material layer 4 is not particularly limited, and is, for example, 10 μm or more and 500 μm or less, preferably 35 μm or more and 250 μm or less, and particularly preferably 50 μm or more and 188 μm or less. If the thickness of the base material layer 4 is less than the lower limit of the range, when the resin composition for forming the optical layer 5 is applied, curling easily occurs, resulting in problems such as difficulty in handling. On the contrary, if the thickness of the base material layer 4 is larger than the upper limit of the range, the brightness of the liquid crystal display device tends to decrease, and in addition, the thickness of the backlight unit is increased, which is also a requirement for thinning the liquid crystal display device. Opposite.

The optical layer 5 includes a binder 7 and a plurality of light diffusing agents 8, and the light diffusing agent 8 is disposed substantially uniformly in the binder 7. Through a plurality of light diffusing agents 8 The light transmitted from the back side of the optical layer 5 to the surface side is uniformly diffused. Further, substantially uniform fine concavities and convexities are formed on the surface of the optical layer 5 by the light diffusing agent 8, and each of the concave portions and the convex portions of the minute concavities and convexities are formed in a lens shape. The optical sheet 1 can exhibit an excellent light diffusing function by the lens action of the minute unevenness, and has a refractive function and a macroscopic view of the light diffusing function for refracting the transmitted light toward the normal side. A concentrating function that transmits light to the normal direction.

The light diffusing agent 8 is a particle having a property of diffusing light, and is mainly classified into an inorganic filler and an organic filler. Specifically, as the inorganic filler, for example, cerium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfate, magnesium citrate or a mixture thereof can be used. As a specific material of the organic filler, for example, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyamine, polyacrylonitrile or the like can be used. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is particularly preferred.

The binder 7 is formed by curing (crosslinking, etc.) the polymer composition containing the polymer of the base material. The light diffusing agent 8 is disposed at substantially equal density on the entire surface of the base material layer 4 by the binder 7. Further, in addition to the above, the polymer composition for forming the binder 7 may be appropriately blended with a fine inorganic filler, a curing agent, a plasticizer, a dispersant, various leveling agents, and an antistatic agent. , UV absorbers, antioxidants, viscosity modifiers, lubricants and light stabilizers.

A plurality of fibers 3 are protruded by the adhesive portion 6 laminated on the back surface of the sheet main body 2. In detail, the plurality of fibers 3 are substantially uniformly implanted on the adhesive portion 6 laminated on the back surface of the sheet main body 2, and are protruded in a substantially vertical manner.

Adhesive formed by the adhesive coated on the entire surface of the back surface of the sheet main body 2 Mixing section 6. The plurality of fibers 3 can be protruded along the entire surface of the back surface of the sheet main body 2 by the adhesive portion 6. Further, the adhesive portion 6 can bond the root portion of the fiber 3 more firmly, and can prevent the fiber 3 from coming off.

The binder that forms the binder portion 6 is not particularly limited, and a water-soluble binder, a solvent-based binder, an ultraviolet-curable binder, or the like can be used. Among them, it is preferred to use a water-soluble binder which is easy to apply to the sheet and which is less likely to catch fire. Specifically, as the water-soluble binder, an adhesive such as an acrylic emulsion, a polyurethane emulsion, an epoxy emulsion, or a vinyl acetate emulsion can be exemplified, and an acrylic emulsion adhesive is particularly preferable in terms of sprayability and abrasion properties. Further, as the solvent-based binder, specifically, an adhesive such as an epoxy resin, an acrylic resin, a polyurethane resin, a polyester resin, a vinyl acetate resin, a vinyl chloride resin, or a phenol resin can be exemplified, and in terms of heat resistance, it is particularly preferable. It is epoxy resin. Further, from the viewpoint of improving the transmittance of light, a transparent adhesive is preferred, and a colorless transparent adhesive is particularly preferred. Further, if environmental considerations are taken into consideration, it is preferred that a volatile organic compound (VOC) binder (low VOC binder) is not easily released. Further, the thickness of the adhesive portion 6 is not particularly limited, but is, for example, 0.1 μm or more and 10 μm or less after curing.

The method of planting the plurality of fibers 3 is not particularly limited as long as the plurality of fibers 3 can be protruded from the back side of the sheet main body 2. However, it is preferable to use an electrostatic flocking method. If the electrostatic flocking method is used, a plurality of fibers 3 can be planted and fixed on the back surface of the sheet main body 2 at a desired angle, and in addition, the density of the planted fibers 3 can be easily adjusted. In particular, a plurality of fibers 3 can be planted substantially vertically and fixed to the back side of the sheet body 2. By planting a plurality of fibers 3 substantially vertically, it is possible to suppress the fibers 3 from falling down before the adhesive of the roots of the bonded fibers 3 is solidified. In addition, As the electrostatic flocking processing method, there may be exemplified a method in which a sheet having an uncured adhesive portion is placed as an opposite electrode with respect to one electrode, a DC high voltage is applied to the electrode, and the electrode is supplied to the electrode by Coulomb force. A plurality of fibers fly along the power line, and the roots of the fibers are plucked into the surface of the sheet for flocking, and the like. The electrostatic flocking method is not particularly limited as long as it is a known electrostatic flocking method.

The fiber 3 is not particularly limited, and natural fibers and chemical fibers can be used. As the natural fiber, cotton fiber, hemp fiber, or the like can be exemplified. Examples of the chemical fiber include rayon, polyester fiber, polyolefin fiber (polyethylene fiber, polypropylene fiber, etc.), and polyamide fiber (aliphatic polyamide fiber, aromatic polyamide fiber). Etc.), acrylic fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polyimide fibers, carbon fibers, lanthanoid fibers, and fluorine fibers. Among them, the chemical fiber can be formed into a shape without curl, and can be suitably used for an electrostatic flocking process. From the viewpoint of improving the transmittance of light, a transparent chemical fiber is preferable, and a colorless and transparent chemical fiber is more preferable.

As a unit area of the back surface of the sheet body 2 a fiber density lower limit of 3, preferably is 40 / cm ^2, more preferably it is 60 / cm ^2, and particularly preferably is 80 / cm ^2. On the other hand, the upper limit of the density of the fibers 3 is preferably 5,000 / cm ² , more preferably 4,000 / cm ² , and particularly preferably 3,000 / cm ² . When the density of the fibers 3 on the back surface of the sheet main body 2 is less than the lower limit, there is a problem that the damage prevention function and the adhesion prevention function for other members cannot be sufficiently exhibited. Further, when the density of the fibers 3 is equal to or greater than a certain value, the foreign matter mixed in the back side of the sheet main body 2 can be caught by the fiber layer formed of the plurality of fibers 3, and sealed in the fiber layer. Therefore, it is difficult for other components superposed on the surface to be in contact with foreign matter, whereby damage of other components can be further reduced. On the contrary, if the density is larger than the upper limit, there is a problem that light transmittance is lowered.

The lower limit of the average diameter of the fibers 3 is preferably 5 μm, more preferably 10 μm, and particularly preferably 20 μm. On the other hand, the upper limit of the average diameter of the fibers 3 is preferably 50 μm, more preferably 40 μm, and particularly preferably 30 μm. If the average diameter of the fibers 3 is less than the lower limit, there is a problem that the above-described damage prevention function and adhesion prevention function cannot be sufficiently exhibited. On the contrary, if the average diameter is larger than the upper limit, there is a problem that light transmittance is lowered.

The lower limit of the average length of the fibers 3 is preferably 20 μm, more preferably 40 μm, and particularly preferably 80 μm. Further, as the upper limit of the average length of the fibers 3, it is preferably 2 mm, more preferably 1 mm, and particularly preferably 0.5 mm. If the average length of the fibers 3 is less than the lower limit, there is a problem that the above-described damage prevention function and adhesion prevention function cannot be sufficiently exhibited. On the other hand, if the average length is larger than the upper limit, the thickness of the backlight unit using the optical sheet is increased depending on the material of the fiber 3, the average diameter, and the like, which is in violation of the requirement for thinning of the liquid crystal display device or the fiber. 3 bending does not obtain an adhesion preventing function, and there is a problem that the transmittance of light is lowered.

The long diameter of the fiber 3 is preferably 2 or more and 40 or less. If the aspect ratio of the fiber 3 is less than the lower limit, there is a problem that the electrostatic flocking method cannot be performed well. On the contrary, if the aspect ratio of the fiber 3 is larger than the upper limit, the fiber 3 is bent to obtain an adhesion preventing function, and there is a problem that the transmittance of light is lowered. Further, the aspect ratio is the ratio of the average length of the fibers to the average diameter.

As the total light transmittance of the optical sheet 1, it is preferably 20% on. If the total light transmittance is less than the above range, there is a problem that the brightness is lowered.

The haze of the optical sheet 1 is preferably 50% or more. If the haze is less than the above range, there is a problem that the diffusion performance becomes insufficient and unevenness in brightness occurs.

Further, "total light transmittance" is a value measured in accordance with JIS K7361. "Haze" is a value measured in accordance with JIS K7105.

Since the optical sheet 1 has a plurality of fibers 3 projecting from the back surface of the sheet main body 2, when the liquid crystal display device is stacked and stored, the plurality of fibers 3 are in contact with other members. Since the plurality of fibers 3 are soft and have a predetermined elasticity, even if a force is applied to the back surface of the optical sheet 1, the plurality of fibers 3 are deformed by bending or the like, and the force is absorbed, so that it can be prevented. Damage is caused to other components that are placed on the back side of the overlap. Further, when the fiber 3 comes off from the adhesive portion 6 and comes into contact with other members, the possibility of damaging other members is also small. As a result, the cause of damage to other components can be significantly reduced. Further, adhesion of the optical sheet 1 and other members can be prevented by the contact of the plurality of fibers 3, and unevenness in brightness of the screen of the liquid crystal display device can be suppressed.

Further, the optical sheet 1 may be a sheet body having a light diffusing function by forming minute irregularities on the surface of the base material layer 4 by embossing, instead of dispersing the light diffusing agent 8 in the binder 7. The formed optical layer 5 is laminated on the sheet main body 2 on the base material layer 4.

Optical sheet manufacturing method

The method for producing the optical sheet 1 is not particularly limited. For example, as shown in (a) of FIG. 6, a method may be exemplified which comprises: (A) a step of forming a base material sheet to form a layer constituting the base material. Piece a base material sheet 40); (B) an optical layer forming step of laminating the optical layer 5 on the surface of the base material sheet 40; (C) a binder coating step of applying a binder to the back surface of the base material sheet 40; In the fiber flocking step, a plurality of fibers 3 are planted on the back surface of the base material sheet 40 coated with the adhesive; (E) a curing step of the adhesive, which cures the adhesive to form the adhesive portion 6 after the flocking; (F) residual fiber The removal step removes residual fibers from the sheet of base material 40 after the adhesive has cured.

The step (A) is a step of extruding a molten thermoplastic resin from a T die, and then stretching the extruded article in the longitudinal direction of the layer and the width direction of the layer to form the base material sheet 40 into a long piece. As a known extrusion molding method using a T die, a polishing roll method and a chill roll method can be exemplified. Further, the base material sheet 40 may be subjected to drawing processing, and a known film stretching method may, for example, be a tubular film biaxial stretching method or a flat film biaxial stretching method.

In the step (B), the coating liquid for the optical layer is prepared by mixing the light diffusing agent 8 in the polymer composition constituting the binder 7, and the coating liquid for the optical layer is applied onto the surface of the base material sheet 40, thereby laminating. The step of the optical layer 5. As a known method of laminating an optical layer, a coating method using a roll coater, a bar coater, a knife coater, a spin coater, a gravure coater, a flow coater, spray coating, screen printing, or the like can be exemplified.

The step (C) is a step of applying a binder to the back surface of the base material sheet 40. The adhesive in this step is in an uncured state. As a method of applying the binder, a known method can be used, and a method of spraying by a spray gun, a method of coating by a roll coater, or the like can be exemplified.

As shown in (b) of FIG. 6, step (D) is a step of arranging the electrode 32 in a flat state in a manner opposite to the base material sheet 40. On the side of the surface of the material sheet 40 (the surface on which the optical layer is laminated), a DC high voltage is applied between the base material sheet 40 and the electrode 32, and the plurality of fibers 3 are supplied from the fiber supply device to the base material by the Coulomb force generated therebetween. The sheet 40 is dropped, the root of the fiber 3 is inserted into the uncured adhesive, and the plurality of fibers 3 are planted on the base material sheet 40 in a protruding manner. The method of planting used in this step is not particularly limited as long as it is a known method of electrostatic flocking, except for the drop method in which a plurality of fibers 3 are dropped from above the base material sheet 40 as shown in (b) of FIG. Any method such as a rising method of raising a plurality of fibers from below, a side method of flying a plurality of fibers from a lateral direction, or the like may be used. Further, in the electrostatic flocking method, since the flocking direction of the plurality of fibers can be adjusted by operating the direction of the electric power line, it is also possible to perform the flocking in a state in which the long base material sheet 40 is bent, for example, the base material sheet 40 can be wound. The hair is placed in a state of being placed on a roll.

The step (E) is a step of curing the adhesive which penetrates the root portion of the plurality of fibers 3 to form the adhesive portion 6. In the case of using a water-soluble binder or a solvent-based binder, it is cured by a drying treatment. As the method of the drying treatment, a known method can be used, and a method using a hot air dryer can be exemplified. In the case of using an ultraviolet curable adhesive, it is cured by irradiation with ultraviolet rays. As a method of irradiating ultraviolet rays, a known method can be used, and a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, an ultraviolet laser, or the like can be exemplified as an ultraviolet irradiation method.

The step (F) is a step of removing the remaining fibers which are not fixed to the back surface of the base material sheet 40 and adhered to the surface. As a method of removing the remaining fibers, a known method can be used, and examples thereof include a method of blowing air, applying vibration, and brushing. After implementing this step (F), the long base is The body material sheet 40 is cut, thereby forming an optical sheet.

According to the manufacturing method described above, the plurality of fibers 3 can be planted on the back surface of the base material sheet 40, and the plurality of fibers 3 can be firmly adhered and fixed by the adhesive portion 6. Therefore, the optical sheet obtained by this manufacturing method can exhibit high damage prevention performance and adhesion prevention performance against other components. Further, after the plurality of fibers 3 are protruded from the back surface of the base material sheet 40, the optical layer 5 may be laminated on the surface of the base material sheet 40. That is, after the step (A) is carried out, the step (C) may be carried out to the step (F), and thereafter the step (B) may be carried out. Further, instead of the carrying out step (B), a manufacturing method in which the base material sheet 40 itself contains an optical function may be employed. Specifically, a method of forming the fine unevenness on the base material sheet 40 by embossing in the step (A) to impart an optical function to the base material sheet 40 can be exemplified.

A backlight unit for a liquid crystal display device of the present invention includes: a square light guide plate; a lamp disposed along a long side end edge of the light guide plate; and a square of a light diffusion sheet, a cymbal sheet, a lenticular sheet, and the like which are disposed on the surface of the light guide plate Optical sheet. The optical sheet described above is used as the light guide plate, light diffusion sheet, cymbal sheet, lenticular sheet or the like. As described above, since the optical sheet has high damage prevention performance against other components, adhesion prevention performance, uniformity of total light transmittance, brightness, etc., economy, and film properties, the backlight unit can significantly improve the backlight. The utilization efficiency of the emitted light can promote the high brightness, high quality, energy saving, and thin weight reduction required by the current society.

Other implementations

The optical sheet of the present invention is not limited to the above-described embodiment, and may be the following embodiments.

The optical sheet 11 of FIG. 2 is a so-called light diffusion sheet, and the optical sheet 11 includes a sheet main body 2 and a plurality of fibers 3 which are protruded from the back surface of the sheet main body 2. The sheet main body 2 includes a base material layer 4 and an optical layer 5 laminated on the surface of the base material layer 4. The base material layer 4, the optical layer 5, the binder 7, the light diffusing agent 8, the manufacturing method, the material of the adhesive and the fiber 3, and the like are the same as those of the optical sheet 1 of Fig. 1, and therefore the same reference numerals are used. The description is omitted.

The plurality of fibers 3 are protruded from the back surface of the sheet main body 2 by a plurality of adhesive portions 16 attached in a dispersed manner. The adhesive portion 16 is a portion in which the adhesive is attached to the back surface of the base material layer 4 such that the adhesive is dispersed (island).

As shown in FIG. 2(b), since the adhesive portion 16 is applied to the back surface of the base material layer 4 in a dispersed manner, it is applied to the entire base material layer 4 as shown by the adhesive portion 6 of FIG. Compared to the case of the back side, the amount of the applied adhesive can be reduced. As a result, the transmittance of the optical sheet 11 can be improved as compared with the optical sheet 1 of the above-described embodiment. A plurality of adhesive portions 16 are formed substantially uniformly on the back surface of the base material layer 4. Preferably, the number and area of the plurality of adhesive portions 16 and the number of the plurality of fibers 3 in each of the adhesive portions are determined such that the density of the fibers 3 per unit area of the back surface of the base material layer 4 is within the above range. Thereby, the damage prevention function and the adhesion prevention function for the other components described above can be exerted. Further, in (a) of FIG. 2 and (b) of FIG. 2, a plurality of fibers 3 are bonded and fixed to one adhesive portion 16, but one fiber 3 may be used. Further, the method of implanting the plurality of fibers 3 is the same as that of the optical sheet 1 of Fig. 1, and an electrostatic flocking method can be used.

The optical sheet 12 of Fig. 3 is a so-called light diffusing sheet, and the optical sheet 12 includes a sheet main body 2 and a plurality of fibers 3, and a plurality of fibers 3 are protrudedly disposed on the sheet main body 2 on the back. The sheet main body 2 includes a base material layer 4, an antistatic agent layer 17 laminated on the surface of the base material layer 4, and an optical layer 5. The fiber 3, the base material layer 4, the optical layer 5, the adhesive portion 6, the binder 7, the light diffusing agent 8, the manufacturing method, and the like are the same as those of the optical sheet 1 of Fig. 1, and therefore the same reference numerals are used and omitted. Description.

The antistatic agent layer 17 is formed of a synthetic resin to which an antistatic agent is incorporated. As described above, the antistatic agent is not particularly limited, and a known antistatic agent can be used.

The use of the antistatic agent layer 17 can better prevent the electrostatic charge of the optical sheet 12 due to static electricity generated by the plurality of fibers 3 protruding from the sheet main body 2, as compared with the case where the antistatic agent is contained in the base material layer 4.

The optical sheet 13 of FIG. 4 is a so-called cymbal sheet, and the optical sheet 13 includes a sheet main body 2 and a plurality of fibers 3, and a plurality of fibers 3 are protruded from the back surface of the sheet main body 2. The sheet main body 2 includes a base material layer 4 and a ruthenium layer 18 laminated on the surface of the base material layer 4. The fiber 3, the base material layer 4, the adhesive portion 6, the manufacturing method, and the like are the same as those of the optical sheet 1 of Fig. 1, and therefore, the same reference numerals are used, and the description thereof is omitted.

The ruthenium layer 18 includes a sheet portion 19 laminated on the surface of the base material layer 4, and a dam portion 20 formed of a plurality of triangular prisms, and the triangular prisms of the crotch portion 20 are arranged in parallel, at equal intervals, and closely. A synthetic resin can be used as the material forming the ruthenium layer 18. The manufacturing method is not particularly limited, and the base material layer 4 and the ruthenium layer 18 may be integrally formed, or may be formed by laminating the adhesive layer between the base material layer 4 and the ruthenium layer 18 after being separately formed. The layer 18 is laminated on the base material layer 4.

The optical sheet 13 has a strong effect of improving the front luminance by using the enamel layer 18, and can improve the light reuse effect in the backlight unit. The brightness unevenness of the emitted light is suppressed. Further, the optical sheet 13 utilizes a plurality of fibers 3 having high damage prevention performance and adhesion prevention performance against other members.

In addition, the ridge line of the crotch portion 20 of the optical sheet 13 may also adopt a serpentine manner, and the arrangement of the triangular prisms of the crotch portion 20 may also be adopted in an unequal interval manner, and the ridge line of the crotch portion 20 may also be used. The way of bending in the height direction, and the like.

The optical sheet 14 of FIG. 5 is a so-called microlens sheet, and the optical sheet 14 includes a sheet main body 2 and a plurality of fibers 3, and a plurality of fibers 3 are protruded from the back surface of the sheet main body 2. The sheet main body 2 includes a base material layer 4 and a microlens surface 21 laminated on the surface of the base material layer 4. The fiber 3, the base material layer 4, the adhesive portion 6, the manufacturing method, and the like are the same as those of the optical sheet 1 of Fig. 1, and therefore the same reference numerals are used, and the description thereof is omitted.

The microlens surface 21 includes a sheet portion 22 laminated on the surface of the base material layer 4, and a microlens array 23 formed on the surface of the sheet portion 22. Further, the lenticular surface 21 may be formed of only the microlens array 23 without the sheet portion 22, and in this case, the microlens array 23 may be directly formed on the surface of the base material layer 4. Further, the lenticular surface 21 and the base material layer 4 may be integrally formed.

The optical sheet 14 has a high optical function of condensing light, refracting light toward one side in the normal direction, and diffusing light by the microlens array 23, and can control the optical function easily and reliably. Therefore, the optical sheet 14 can control, for example, the peak direction of the incident light to the cymbal of the backlight unit to an optimum tilt angle refracted toward the normal side. Further, the optical sheet 14 utilizes a plurality of fibers 3 having high damage prevention performance and adhesion prevention performance against other members.

Further, the "microlens" refers to a microlens having a partial spherical shape, for example, a hemispherical convex lens, a hemispherical concave lens, or the like corresponding to the microlens.

Further, the optical sheet and the backlight unit of the present invention are not limited to the embodiments described. The optical sheet is not limited to the above-described light diffusion sheet, condensing sheet (such as a lenticular sheet, a microlens sheet, etc.). For example, the optical sheet may be used for other light guide sheets, polarizers, retardation sheets, and enlarged field sheets. An optical sheet such as a lenticular lens sheet or a Fresnel lens sheet. It is particularly suitable as an optical sheet for a backlight unit which is disposed between a light guide plate and a liquid crystal display element. It is required that the optical sheet disposed at the position is to prevent damage to other components and interference fringes due to adhesion. Therefore, the optical sheet which can exhibit a high damage prevention function and adhesion prevention function for other components can be preferably used.

Further, the optical sheet may have other layers such as an ultraviolet absorber layer, a top coat layer, and an easy-adhesion layer on the sheet main body in addition to the base material layer, the optical layer, and the antistatic agent layer.

Further, the method of bonding and fixing the plurality of fibers 3 may directly bond the roots of the fibers 3 to the base material layer 4 without using a binder. For example, a method may be employed in which a plurality of fibers 3 are planted on the base material layer 4, and the like, after the base material layer 4 is formed, before the base material layer 4 is completely cured.

As described above, the optical sheet of the present invention is useful as a constituent member of a backlight unit of a liquid crystal display device, and is particularly suitable for use in a transmissive liquid crystal display device.

1‧‧‧ optical film

2‧‧ ‧ subject

3‧‧‧ fiber

4‧‧‧ base material layer

5‧‧‧Optical layer

6‧‧‧Binder Department

7‧‧‧Adhesive

8‧‧‧Light diffusing agent

11‧‧‧Optical film

12‧‧‧ optical film

13‧‧‧ optical film

14‧‧‧ optical film

16‧‧‧Binder Department

17‧‧‧Antistatic agent layer

18‧‧‧稜鏡

19‧‧‧Face

20‧‧‧稜鏡

21‧‧‧Microlens

22‧‧‧Flakes

23‧‧‧Microlens array

31‧‧‧Fiber providing device

32‧‧‧ electrodes

40‧‧‧Base material sheet

1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention; Figure.

Fig. 2 is a schematic explanatory view showing an optical sheet different from the optical sheet of Fig. 1, wherein (a) is a schematic cross-sectional view, and (b) is a schematic plan view showing a state of application of the adhesive portion.

Fig. 3 is a schematic explanatory view showing an optical sheet different from the optical sheets of Figs. 1 and 2;

4 is a schematic explanatory view showing an optical sheet different from the optical sheets of FIGS. 1, 2, and 3.

Fig. 5 is a schematic explanatory view showing an optical sheet different from the optical sheet of Figs. 1 to 4;

Fig. 6(a) is a flowchart showing a method of manufacturing the optical sheet of Fig. 1, and Fig. 6(b) is a schematic explanatory view showing the step (D).

Fig. 7 (a) is a schematic perspective view showing a general edge light type backlight unit, and Fig. 7 (b) is a schematic cross-sectional view showing a general light diffusion sheet.

1‧‧‧ optical film

2‧‧ ‧ subject

3‧‧‧ fiber

4‧‧‧ base material layer

5‧‧‧Optical layer

6‧‧‧Binder Department

7‧‧‧Adhesive

8‧‧‧Light diffusing agent

Claims (7)

A light diffusing sheet comprising: a sheet main body having a light diffusing function; and a plurality of fibers protrudingly disposed on a back side of the sheet main body and having an adhesion preventing function; the sheet main body and the plurality of fibers The adhesive portion is attached to the back surface of the sheet main body by a bonding point; the fibers have an average diameter of 5 μm or more and 50 μm or less, and an average length of 20 μm or more and 2 mm or less. The fiber density per unit area of the back surface is 40 pieces/cm ² or more and 5,000 pieces/cm ² or less. The light-diffusing sheet of claim 1, wherein the adhesive portion is formed of an acrylic emulsion adhesive. The light-diffusing sheet of claim 1, wherein the fiber is protruded from the back side of the sheet body by electrostatic flocking. The light diffusing sheet of claim 1, wherein the fiber is a transparent chemical fiber. The light diffusion sheet of claim 1, wherein the sheet body comprises a base material layer and an optical layer, and the optical layer is formed on a surface of the base material layer. A backlight unit for a liquid crystal display device, characterized in that the liquid crystal display device uses a backlight unit to disperse light emitted from the lamp and direct the dispersed light to the surface side; the backlight unit for the liquid crystal display device includes the first item of the patent application scope The light diffusing sheet. A method of manufacturing a light diffusing sheet, comprising: an optical layer forming step of laminating an optical layer having a light diffusing function on a surface of a base material layer; and a binder coating step of dispersing dots on a back surface of the base material layer coating binder manner; fiber tufting step, the fiber density per unit area of the sheet body a plurality of fibers in the back of 5000 / cm ² or less of embodiment 40 / cm ² or more implanted onto the surface coated with adhesive; a binder curing step of curing the binder after the hair is implanted; and a residual fiber removal step of removing the remaining fibers from the sheet body after the binder is cured; the fibers have an average diameter of 5 μm or more and 50 μm or less, and an average length of 20 μm or more and 2 mm or less .