JP5248634B2 - Method for determining uneven shape of optical member - Google Patents

Description

  The present invention relates to a method for determining an uneven shape of an optical member. Moreover, this invention relates to the manufacturing method of the optical member using the method which concerns.

  An optical sheet such as a light guide plate or a light diffusing plate may have a concavo-convex shape designed on the surface so as to exhibit desired optical characteristics. As a method of manufacturing an optical sheet having an uneven shape, a method of transferring a transfer mold shape onto the surface of a continuous resin sheet is known (for example, Patent Document 1).

JP 2009-220555 A

  The uneven shape of an optical member such as an optical sheet is generally optimized by designing the uneven shape by simulation, producing a prototype having the designed uneven shape, and evaluating the prototype. In order to achieve the desired optical characteristics, it is necessary to precisely adjust the concavo-convex shape. Therefore, in order to optimize the concavo-convex shape, production of a prototype and its evaluation are often repeated by trial and error.

  However, according to the conventional method, it is necessary to newly prepare a transfer mold every time a prototype is manufactured, and therefore it is actually necessary to spend a great deal of money and time for optimizing the uneven shape.

  Therefore, a main object of the present invention is to provide a method for more easily determining the uneven shape of an optical member.

  The present invention provides a step of forming a plurality of optical member prototypes having different uneven shapes by transferring the shape of a prototype transfer mold at different transfer rates, and the optical characteristics of each of the plurality of optical member prototypes. The present invention relates to a method for determining a concavo-convex shape of an optical member, comprising: an evaluating step;

  According to the above method of the present invention, a plurality of prototypes having different concavo-convex shapes are prepared by changing the transfer rate at the time of molding, and thus a prototype transfer mold is newly prepared to prepare a prototype. There is no need to do. Therefore, the uneven shape of the optical member can be determined more easily than in the past.

  In another aspect, the present invention relates to a method for manufacturing an optical member. The manufacturing method according to the present invention includes a step of forming an optical member by transfer from a transfer mold for manufacturing an optical member having an inverted shape corresponding to the uneven shape determined by the above method.

  According to the production method of the present invention, an optical member production transfer mold can be easily prepared, so that an optical member having excellent optical characteristics can be produced more efficiently.

  In order to stably manufacture the optical member, it is preferable that the transfer mold for manufacturing the optical member has an inverted shape in which the uneven shape of the optical member is formed when transferred at a transfer rate of 90% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the method for determining the uneven | corrugated shape of an optical member more simply is provided.

It is a perspective view which shows one Embodiment of an optical sheet. It is a schematic diagram which shows one Embodiment of the manufacturing method of an optical sheet. It is an expansion schematic diagram which shows one Embodiment of the step which shape | molds an optical member prototype.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a perspective view showing an embodiment of an optical sheet that is an optical member. The optical sheet 30 shown in FIG. 1 has a pair of main surfaces having a rectangular shape in plan view, and one main surface S1 forms an uneven shape having a plurality of convex portions 35. The convex portion 35 extends in a direction along one side of the main surface of the optical sheet 30, and the shape of the cross section orthogonal to the extending direction of the convex portion 35 is a mountain shape. The plurality of convex portions 35 are arranged in parallel in a direction perpendicular to the extending direction. The concavo-convex shape having the convex portion 35 is formed by transfer from a transfer mold.

  The optical sheet 30 can be used as, for example, a light guide plate of a surface light source device (backlight) mounted on a transmissive image device or a light diffusion plate for uniformly diffusing light from the light source. When the optical sheet 30 is used as a light guide plate, for example, light from a light source enters the optical sheet 30 from the side surface 33, and planar light is emitted from the main surface S1 having an uneven shape. When the optical sheet 30 is used as a light diffusing plate, for example, a light source is disposed on the back surface S2 side behind the main surface S1.

  The optical sheet 30 is a translucent sheet mainly composed of a transparent material. The refractive index of the transparent material is usually 1.48 or more and 1.62 or less or 1.56 or more and 1.62 or less. Examples of the transparent material include transparent resin and transparent glass.

  In the case of the light diffusion plate, the transparent resin is preferably a polycarbonate resin (refractive index: 1.59), MS resin (methyl methacrylate-styrene copolymer resin) (refractive index: 1.56 to 1.59), AS resin (acrylonitrile-styrene copolymer resin) (refractive index: 1.56-1.59), polystyrene resin (refractive index: 1.59), and cycloolefin resin (refractive index: 1.51-1.55) Selected from. In the case of the light guide plate, the transparent resin is preferably a polymethyl methacrylate (PMMA) resin.

  When a transparent resin is used as the transparent material, the optical sheet 30 may contain additives such as an ultraviolet absorber, an antistatic agent, an antioxidant, a processing stabilizer, a flame retardant, and a lubricant. These additives are used alone or in combination of two or more.

  Examples of UV absorbers include benzotriazole UV absorbers, benzophenone UV absorbers, cyanoacrylate UV absorbers, malonic ester UV absorbers, oxalic anilide UV absorbers, and triazine UV absorbers. Can be mentioned. Of these, benzotriazole-based UV absorbers and triazine-based UV absorbers are preferred.

The optical sheet 30 may contain a light diffusing agent. As the light diffusing agent, particles having a refractive index different from that of the transparent material mainly constituting the optical sheet 30 are preferably used. Examples of the light diffusing agent include organic particles such as styrene resin particles and methacrylic resin particles, and inorganic particles such as potassium carbonate particles and silica particles. The particle size of the light diffusing agent is usually 0.8 μm to 50 μm.

  FIG. 2 is a schematic view showing an embodiment of a method for producing an optical sheet. According to the optical sheet manufacturing apparatus 50 shown in FIG. 2, the optical sheet 30 having a concavo-convex shape is formed by resin extrusion. The optical sheet manufacturing apparatus 50 discharges the resin extruded by the extruder 58, an extruder 58 for extruding the resin in a heated and melted state, a resin inlet 57 for charging the resin attached to the extruder 58, and the extruder 58. The die 51 that forms the continuous resin sheet 3 and the pre-loading roll 52D, the first pressing roll 52A, and the second pressing roll 52B that are sequentially spaced apart from each other on the downstream side of the die 51 are mainly configured. A transfer mold 53 corresponding to the uneven shape of the optical sheet 30 is formed on the peripheral surface of the second pressing roll 52B.

  The continuous resin sheet 3 discharged from the die 51 passes between the preload roll 52D and the first pressing roll 52A. The thickness of the continuous resin sheet 3 is controlled mainly by the distance between the preload roll 52D and the first pressing roll 52A. In many cases, a melt bank 4 in which molten resin stays is formed at a position where the continuous resin sheet 3 enters between these rolls.

  The continuous resin sheet 3 that has passed between the preloading roll 52D and the first pressing roll 52A is pressed between the first pressing roll 52A and the second pressing roll 52B on the peripheral surface of the first pressing roll 52A. It is transported to the position.

  The continuous resin sheet 3 is pressed from both sides in the thickness direction when passing between the first pressing roll 52A and the second pressing roll 52B, and the shape of the transfer mold 52 is transferred to the surface S1 of the continuous resin sheet 3. The The continuous resin sheet 3 to which the shape has been transferred is transported while being cooled on the peripheral surface of the second pressing roll 52 </ b> B, and then taken up as the optical sheet 30. On one main surface S <b> 1 of the optical sheet 30, an uneven shape transferred from the transfer mold 53 is formed.

  When the optical sheet 30 is molded as an optical member prototype, a plurality of prototypes having different concavo-convex shapes are produced by performing a plurality of moldings while changing the transfer rate using the prototype transfer mold 52. The

  FIG. 3 is a schematic diagram showing an embodiment of steps for forming an optical sheet 30 as a prototype optical member. As shown in FIG. 3A, the transfer mold 53 has an inverted shape in which a concave portion 53a, which is a groove having a depth h1, corresponding to the convex portion 35 of the concave and convex shape of the optical member 30 is formed. ing. As shown in FIG. 3B, the continuous resin sheet 3 is pressed and filled into the recess 53a. The height h2 of the convex portion 35 formed in the concave portion 35a in a state where the resin is in close contact with the transfer mold 53 is smaller than the maximum depth h1, and a gap is left between the resin and the transfer mold 53. . The resin may be completely filled in the convex portion 35a, and h1 = h2. After the resin temperature has dropped to some extent, the optical sheet 30 is removed from the transfer mold 53. Thereafter, since the resin shrinks due to thermoelastic deformation, the height h3 of the convex portion 35 of the optical sheet 30 in a state where the resin is solidified becomes smaller than the height h2. Even when the filling rate (h2 / h1) is small, the shape of the bottom of the final convex portion 35 often accurately reflects the shape of the transfer mold.

  The transfer rate (%) can be defined as a value calculated by the formula: (h3 / h1) × 100. By changing the transfer rate within a range of 30 to 100%, for example, a plurality of types of prototypes having various uneven shapes can be easily and quickly manufactured from one type of transfer mold.

  As understood by those skilled in the art, the transfer rate of the shape from the transfer mold can be controlled by appropriately adjusting the molding conditions of the optical sheet. For example, there is a method of setting conditions by paying attention to the filling rate (h2 / h1) of the resin into the transfer type concave portion 53a. In this method, for example, when the temperature of the resin discharged from the die is increased, when the line speed is increased, when the melt bank is reduced, or when the temperature of the pressure roll having the transfer mold is increased, the filling is performed. Since the fluidity of the resin during printing increases, the transfer rate tends to increase. Or you may set conditions, such as roll temperature and a line speed, paying attention to the extent (h3 / h2) of the thermoelastic deformation of resin after mold release.

  In the embodiment shown in FIG. 3, the cross-sectional shape of the recess of the transfer mold is a mountain shape, but the shape of the transfer mold is not limited to this. For example, a transfer mold having a recess whose cross-sectional shape is a triangular prism shape can be suitably used. By using a plurality of types of transfer molds having different triangular prism-shaped low angles, various prototypes having different optical characteristics can be easily produced in a short period of time.

  It is also possible to prepare a plurality of transfer molds having different concavo-convex shapes and mold prototypes at different transfer rates for each transfer mold. A transfer mold composed of a plurality of regions having different concavo-convex shapes can also be used. By preparing multiple types of transfer molds with different concavo-convex shapes in advance, when designing a new optical sheet, prototypes with various concavo-convex shapes can be manufactured in a short period of time without having to prepare transfer dies again. .

  Furthermore, when producing a prototype, the optical sheet can be more efficiently optimized by changing the material constituting the optical sheet. For example, the refractive index, particle size and concentration of the light diffusing agent, as well as the embossing characteristics of the optical sheet surface can be adjusted.

  When manufacturing the optical member of the product by evaluating the optical characteristics of each prototype, comparing the optical characteristics of each prototype with the target optical characteristics, and producing a concavo-convex shape that achieves the desired optical characteristics satisfactorily It is possible to determine the uneven shape set as a target. If necessary, repeat the steps of forming prototypes and evaluating the optical characteristics of each prototype while changing the shape of the transfer mold and the transfer rate, etc. Is optimized.

  The optical characteristic as an index for selecting a non-defective product from the prototype and determining the uneven shape is selected from, for example, unevenness of emitted light, luminance, total light transmittance, and haze. In general, it is desirable that the in-plane unevenness of the emitted light is small (high uniformity), and it is desirable that the luminance is high as long as the uniformity of the emitted light is not significantly impaired. The evaluation of the optical characteristics may be performed in a state of being incorporated in a surface light source device or the like that is assumed to be used. If necessary, the optical sheet is optimized by using cross-sectional shape observation, simulation, and the like.

  After the design of the optical sheet that achieves the target optical characteristics is completed by the method as described above, an optical member manufacturing transfer mold having an inverted shape corresponding to the uneven shape is prepared. For example, the cross-sectional shape of a prototype as a standard product that has been determined to have a target concavo-convex shape is observed with an optical microscope or the like, and the concavo-convex shape having the observed cross-sectional shape is formed by transfer. In addition, a transfer mold is produced. Alternatively, a replica of a prototype as a standard product may be produced, a replica of this replica may be produced, and the electroforming mold may be further produced. An optical sheet as a product is manufactured by transfer from a transfer mold for manufacturing an optical member.

  In order to stably manufacture the optical member, the transfer mold for manufacturing the optical member is preferably formed with a target uneven shape when transferred at a transfer rate of 90% or more, more preferably 95% or more. Has an inverted shape. When molding is performed under a condition where the transfer rate is low, the variation of products tends to increase. Although this is not a problem at the prototype stage, it is strongly desired that the product variation be as small as possible for mass production.

  The present invention is not limited to the embodiment described above, and can be modified as appropriate without departing from the spirit of the present invention. For example, the optical sheet product or prototype molding method is not limited to extrusion molding, and may be other molding methods such as injection molding. The uneven shape determined by the present invention is not limited to a one-dimensional lenticular lens such as the optical sheet of FIG. 1, and for example, a two-dimensional uneven shape such as a microlens or a pyramid prism is used in the present invention. Can be determined. In addition, the optical sheet for which the concavo-convex shape is determined according to the present invention is not limited to the light guide plate and the light diffusing plate. A protective film may be used. Examples of the optical sheet for the surface light source device include a microlens film, a lenticular lens film, and a prism sheet with a rounded tip. Examples of the protective film provided with diffusibility include a protective film for a reflective polarizing film and a protective film for a polarizing plate.

Claims (3)

Forming a plurality of prototype optical members having different concavo-convex shapes by transferring the shape of the prototype transfer mold at different transfer rates;
Evaluating the optical properties of each of the plurality of optical member prototypes;
Determining the concavo-convex shape of the optical member based on the optical characteristics;
A method for determining an uneven shape of an optical member.   A method for manufacturing an optical member, comprising the step of forming an optical member by transfer from a transfer mold for manufacturing an optical member having an inverted shape corresponding to the uneven shape determined by the method according to claim 1.   The manufacturing method according to claim 2, wherein the transfer mold for manufacturing the optical member has an inverted shape in which an uneven shape of the optical member is formed when transferred at a transfer rate of 90% or more.

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