Method for manufacturing optical sheet

Abstract

This method for manufacturing an optical sheet includes: a step for preparing a transparent sheet-like body having a plurality of protrusions and recesses on one surface thereof; a step for forming, on the one surface of the body, a photocurable resin composition having optical transmission characteristics and / or reflection characteristics different from those of the body; a step for projecting parallel light having a predetermined direction onto the photocurable resin composition, from the surface of the body on the opposite side to the one surface of the body; and a step for removing an uncured portion of the photocurable resin composition. The plurality of protrusions and recesses has a plurality of prisms each having a first inclined surface and a second inclined surface that face each other, and the predetermined direction may be a direction that is more nearly parallel to the second inclined surface than to the first inclined surface.

Description

Method for Manufacturing Optical Sheet

[0001] The present invention relates to a method for manufacturing an optical sheet.

[0002] Patent Document 1 describes "a step of forming a large number of fine parallel convex strips with a serrated cross-section on the surface of a transparent plate; a step of spray-coating a photosensitive coating for an anti-reflection light-shielding film on the surface of the transparent plate on which the convex strips are formed; a step of electrostatically coating the photosensitive coating for an anti-reflection light-shielding film on the surface of the transparent plate on which the convex strips are formed; and a step of irradiating light onto the surfaces of the convex strips to expose and cure the photosensitive coating on the vertical surfaces of the convex strips, removing the unexposed coating portions on the inclined surfaces by washing, and forming the anti-reflection light-shielding film of the photosensitive coating on the vertical surfaces". [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Unexamined Patent Publication No. 10-318797 [General Disclosure]

[0003] According to a first aspect of the present invention, there is provided a method for manufacturing an optical sheet, comprising the steps of: preparing a transparent sheet-like main body having a plurality of concavities and convexities on one surface thereof; forming a photocurable resin composition having optical transmission characteristics and / or reflection characteristics different from those of the main body on the one surface of the main body; irradiating parallel light in a predetermined direction onto the photocurable resin composition from a surface opposite to the one surface of the main body; and removing an uncured portion of the photocurable resin composition.

[0004] The plurality of concavities and convexities have a plurality of prisms each including opposing first inclined surfaces and second inclined surfaces, and the predetermined direction may be a direction closer to being parallel to the second inclined surfaces than to the first inclined surfaces. The predetermined direction may be a direction substantially parallel to the second inclined surfaces.

[0005] The photocurable resin composition may include a material that absorbs visible light. Examples of the material that absorbs visible light include carbon black, graphite, pigments, and dyes.

[0006] In the step of forming the photocurable resin composition, the photocurable resin composition may be formed such that an exposed side surface of the photocurable resin composition is flat.

[0007] The opposite surface of the main body may be flat.

[0008] The process may further include a step of forming a photocuring member on the opposite side of the main body that converts the optical path of the parallel light, at least before the step of irradiating with parallel light. The process may further include a step of removing the photocuring member from the opposite side of the main body, at least after the step of irradiating with parallel light.

[0009] The step of preparing the main body may include the step of forming multiple indentations and protrusions on one surface of the main body.

[0010] The optical sheet may be used for head-up display applications, reflective screen applications, street lighting applications, or aerial levitation display applications.

[0011] It should be noted that the above summary of the invention does not enumerate all of its features. Furthermore, subcombinations of these features may also constitute an invention.

[0012] Figure 4 is a schematic cross-sectional view of an example of an optical sheet 10 manufactured in this embodiment. Figure 6 is a schematic cross-sectional view illustrating the step of preparing the main body 100 in the manufacturing method according to this embodiment. Following Figure 2, this is a schematic cross-sectional view illustrating the step of forming an uncured photocurable resin composition 130 on the main body 100. Following Figure 3, this is a schematic cross-sectional view illustrating the step of irradiating the photocurable resin composition 130 with parallel light 230 from the flat surface 104 of the main body 100. This is a schematic diagram illustrating a predetermined angle for irradiating with parallel light 230. Following Figure 4, this is a schematic cross-sectional view showing the state in which the light-shielding film 134 has hardened. Following Figure 6, this is a schematic cross-sectional view illustrating the step of removing the uncured photocurable resin composition 130. This is a schematic cross-sectional view illustrating a modified example using a photocuring member 150. An example is shown in which an optical path conversion member is used as the photocuring member 160.

[0013] The present invention will be described below through embodiments, but these embodiments are not intended to limit the scope of the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0014] Figure 1 is a cross-sectional view of an example of an optical sheet 10 manufactured in this embodiment. The optical sheet 10 has a substantially sheet-shaped main body 100 having any size from a few millimeters square to a few meters square, and a light-shielding film 134 arranged on a part of the main body 100.

[0015] One of the opposing main surfaces of the main body 100 is a textured surface 102, and the other (i.e., the surface opposite to the textured surface 102) is a flat surface 104. Multiple sawtooth-shaped prisms 120 are periodically provided on the textured surface 102. Each of the prisms 120 extends in a direction perpendicular to the paper plane. The portion of the main body 100 other than the prisms 120 may be referred to as the flat plate portion 101.

[0016] Each of the prisms 120 has an opposing first inclined surface 122 and a second inclined surface 124. Furthermore, the first inclined surface 122 and the second inclined surface 124 are non-parallel and connected by a common vertex in cross-sectional view. The inclination angles θ1 and θ2 of the first inclined surface 122 and the second inclined surface 124 are expressed as angles with respect to the direction parallel to the flat surface 104, as shown in Figure 1. Also, for convenience, when the inclination angles θ1 and θ2 are 0 degrees and 90 degrees, they are referred to as "inclination angles" and "inclination surfaces," respectively.

[0017] The main body 100 is transparent to the wavelengths at which the optical sheet 10 is used, such as visible light. On the other hand, the light-shielding film 134 is opaque to the same wavelength, and is, for example, black. The light-shielding film 134 is arranged to cover the first inclined surface 122 of the prism 120, but not the second inclined surface 124.

[0018] The optical sheet 10 is used, for example, in a head-up display. In this case, the optical sheet 10 emits image light incident from the flat surface 104 side to the uneven surface 102 side from the second inclined surface 124, and blocks ambient light incident from the uneven surface 102 side by absorbing it with the light-shielding film 134. This prevents reflection of ambient light and allows the user to see image light with high visibility.

[0019] Figure 2 is a schematic cross-sectional view illustrating the step of preparing the main body 100 in the manufacturing method according to this embodiment. In each of the figures from Figure 2 onward, the same reference numerals are used for components that are the same as those in the previously shown figures, and explanations are omitted as appropriate.

[0020] As shown in Figure 2, a main body 100 having an uneven surface 102 on which a prism 120 is arranged is prepared. As described above, it is preferable that the main body 100 is transparent to the wavelength used and also highly transparent to the wavelength at which the photocurable resin composition described later is cured. Examples of materials for the main body 100 include acrylic resin, urethane, polycarbonate, and glass.

[0021] The size of the prism 120, for example, the repeating pitch, may be, for example, several tens of micrometers to several hundred micrometers, preferably 20 micrometers to 500 micrometers. In the example shown in Figure 2, θ1 < θ2.

[0022] Figure 3 is a schematic cross-sectional view illustrating the step of forming an uncured photocurable resin composition 130 on the main body 100, following Figure 2. The photocurable resin composition 130 is a photosensitive resin composition that hardens when irradiated with light of a predetermined wavelength, such as ultraviolet light. An example of such a photocurable resin composition 130 is a resin composition comprising an ionic group-containing photosensitive resin and a photoinitiator. This ionic group-containing photosensitive resin is not particularly limited, but examples include an anionic group-containing photosensitive resin containing anionic groups such as carboxyl groups, sulfonic acid groups, or phosphate groups, and a cationic group-containing photosensitive resin containing cationic groups such as amino groups. The photoinitiator is not particularly limited, but examples include carbonyl compounds such as acetophenone, benzophenone, benzyl, benzoin, acylphosphine oxide, benzoin benzoate, and α-acyloxime esters; sulfur compounds such as tetramethylthiuram monosulfide and thioxanthones; and phosphorus compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. Furthermore, in order to provide light-shielding properties when using the optical sheet 10, the photocurable resin composition 130 is black at least after curing. The following description will use a photocurable resin composition 130 that is cured by ultraviolet light as an example.

[0023] The photocurable resin composition 130 is applied to the uneven surface 102 of the main body 100, for example, by a roll coater 200. Preferably, the photocurable resin composition 130 is applied so that the prism 120 is embedded. In Figure 3, the applied photocurable resin composition 130 is applied so that the exposed surface 132 (i.e., the top surface in Figure 3) is flat. Here, flatness includes intentionally not forming any irregularities, and may include irregularities that are several orders of magnitude smaller than the irregularities of the prism 120.

[0024] Figure 4 is a schematic cross-sectional view illustrating the step of irradiating the photocurable resin composition 130 with parallel light from the flat surface 104 of the main body 100, following Figure 3. Note that the hatching of the main body 100 has been omitted to make the direction of the light rays easier to see.

[0025] The light source 210 emits ultraviolet light. The optical system 220 converts the ultraviolet light emitted by the light source 210 into parallel light 230 and irradiates the flat surface 104 at a predetermined angle. Here, "parallel light" may include light whose "central ray parallelism (declination angle)" and "viewing angle (collimation half-angle)" are 0° to 1° and 0° to 2.5°, respectively. The combination of the light source 210 and the optical system 220 may irradiate the entire flat surface 104 with parallel light 230, but for the sake of simplifying the diagram, parallel light 230 is depicted only for a portion of the area.

[0026] Figure 5 is a schematic diagram illustrating a predetermined angle for irradiating with parallel light 230. In this embodiment, it is preferable that parallel light 230 is irradiated onto the first inclined surface 122 to form a light-shielding film 134, while parallel light 230 is not irradiated onto the second inclined surface 124 and therefore no light-shielding film 134 is formed.

[0027] Therefore, it is preferable that the direction of the parallel light 230 is substantially parallel to the second inclined surface 124 on which the light-shielding film 134 is not formed. That is, in Figure 5, it is preferable that the angle β2 between the second inclined surface 124 and the parallel light 230 is close to 0°. For example, it is preferable that the angle β2 is within the range of 0° or more and 1° or less.

[0028] Since the refractive index n1 of the main body 100 with respect to ultraviolet light is greater than the refractive index n0 of air, refraction occurs on the flat surface 104. Therefore, it is preferable to determine the incident angle α0 for irradiating the flat surface 104 with parallel light 230 to be the angle β2 described above, taking into account the refraction angle α1 when incident on the main body 100.

[0029] Since the first inclined surface 122 faces the second inclined surface 124, the parallel light 230, which is substantially parallel to the second inclined surface 124, is non-parallel to the first inclined surface 122. Geometrically, this means that β1 = 180° - (θ1 + (θ2 + β2)), and β2 is within the range of 0° to 1°. Furthermore, the predetermined direction mentioned above can be said to be closer to parallel to the second inclined surface 124 than to the first inclined surface 122. As a result, the first inclined surface 122 can be irradiated with parallel light 230 sufficient for curing.

[0030] Figure 6 is a schematic cross-sectional view showing the state in which the light-shielding film 134 has hardened, following Figure 4. As described above, the parallel light 230 is substantially parallel to the second inclined surface 124, but not parallel to the first inclined surface 122. Therefore, the photocurable resin composition 130 on the first inclined surface 122 hardens and the light-shielding film 134 is formed. On the other hand, the photocurable resin composition 130 on the second inclined surface 124 does not harden, and the light-shielding film 134 is not formed.

[0031] The thickness of the light-shielding film 134 is, for example, 100 μm or less, preferably 0.5 μm to 50 μm, and more preferably 0.5 μm to 20 μm. The thickness can be controlled by the time integral value of the intensity of the parallel light 230 irradiated onto the first inclined surface 122.

[0032] Figure 7 is a schematic cross-sectional view showing the step of removing the uncured photocurable resin composition 130, following Figure 6. Once the uncured photocurable resin composition 130 is removed by washing or the like, the light-shielding film 134 that has hardened on the first inclined surface 122 remains. This forms the optical sheet 10.

[0033] As described above, according to this embodiment, by irradiating the first inclined surface 122 with parallel light 230, a light-shielding film 134 of uniform thickness can be formed over the entire surface of the first inclined surface 122. Furthermore, even if the uncured photocurable resin composition 130 is not uniformly applied to the first inclined surface 122, a light-shielding film 134 of uniform thickness can be formed over the entire surface of the first inclined surface 122 by the parallel light 230 from the flat surface 104. In addition, since the parallel light 230 is irradiated onto the first inclined surface 122 from the flat surface 104 side, the photocurable resin composition 130 hardens from the first inclined surface 122 side, preventing problems such as the hardened portion flowing out from the slope.

[0034] Furthermore, since parallel light 230 is incident substantially parallel to the second inclined surface 124, curing of the photocurable resin composition 130 on the second inclined surface 124 can be prevented. As a result, the coating rate of the light-shielding film 134 on the first inclined surface 122 can be set to approximately 100%, and the coating rate on the second inclined surface 124 can be set to approximately 0%.

[0035] In the above embodiment, θ1 < θ2 was set. Here, if the refractive index n1 of the main body 100 is greater than the refractive index n0 of air, light cannot be incident on the main body 100 at an angle α1 greater than the critical angle determined by the ratio of their refractive indices. Therefore, if the inclination angle θ2 of the second inclined surface 124 is smaller than "90° - critical angle", light parallel to the second inclined surface 124 cannot be incident from the flat surface 104. For example, if the refractive index n1 of the main body 100 is about 1.5 and the refractive index n0 of air is 1, light cannot be incident parallel to the second inclined surface 124 if the inclination angle θ2 is about 50° or less.

[0036] Figure 8 is a schematic cross-sectional view illustrating a modified example using the photocuring member 150. The photocuring member 150 is a member that contributes to accelerating photocuring. Examples of photocuring members include optical path conversion members that convert the optical path of parallel light, and anti-reflective films that increase the transmittance of light having a predetermined wavelength. From the viewpoint of efficiently curing the photohardening resin composition, it is preferable that the surface of the photocuring member 150 that comes into contact with light is smooth and has low haze. An example of the material of the photocuring member 150 is not particularly limited as long as it is transparent, and examples of preferred materials include acrylic, urethane, polycarbonate, glass, and quartz.

[0037] Figure 9 shows an example in which an optical path conversion member is used as the photocuring member 160. The photocuring member 160 is provided on the flat surface 104. The photocuring member 160 is, for example, made of a resin with a refractive index of n2 and transparent to ultraviolet light, and has a triangular or sawtooth shape in which the first inclined surface 162 and the second inclined surface 164 are connected. By providing such a photocuring member 160 on the flat surface 104, even when the inclination angle θ2 is smaller than "90° - critical angle", parallel light 230 substantially parallel to the second inclined surface 124 can be incident. From this viewpoint, the photocuring member 160 can be said to be an example of an optical path conversion member that converts the optical path of parallel light 230. If the angle between the first inclined surface 162 and the direction parallel to the flat surface 104 is θ3, the triangular shape is designed so that the inclination angle θ3 and the incident angle α0 of the parallel light 230 satisfy a specific relational expression. In Figure 9, the triangular pitch of the light-curing member 160 and the pitch of the prism 120 are depicted as being approximately the same. However, these pitches can be set independently of each other, and therefore, the number of triangles and the number of prisms 120 can be different. Also, for clarity, hatching has not been applied to the light-curing member 160.

[0038] As shown in Figure 9, if the angle of refraction of parallel light 230 at the first inclined plane 162 is α2' and the angle of incidence to the flat surface 104 is α2, then using geometrical optics, the specific relationship is, for example, the following (1) and (2): (1) n1・sin(α1) = n2・sin(α2) (2) sin(α0) = n2 / n0・sin(α2-θ3)

[0039] Furthermore, when a material satisfying n1=n2 is used, Expression (2) becomes the following Expression (3). (3) sin(α0)=n2 / n0·cos(θ2+θ3)

[0040] Furthermore, in order to reduce reflected light on the first inclined surface 162, when α0=0°, Expression (3) becomes the following Expression (4). (4) θ3=90°−θ2

[0041] The photo-curing members 150 and 160 are formed before the step of irradiating the parallel light 230. For example, they may be formed before forming the photo-curable resin composition 130, or may be formed after forming the photo-curable resin composition 130 and before irradiating the parallel light 230.

[0042] The photo-curing members 150 and 160 may be removed after the step of irradiating the parallel light 230. In this case, they may be removed either after the step of irradiating the parallel light 230 and before removing the uncured photo-curable resin composition 130, or after removing the uncured photo-curable resin composition 130. Alternatively, the photo-curing members 150 and 160 may be used as they are without being removed.

[0043] As the photo-curing member 150 in FIG. 8, a transmissive anti-reflection film that prevents reflection of the parallel light 230 on the flat surface 104 may be used. The anti-reflection film may, for example, have a fine structure such as a multilayer film or a moth-eye structure. The use of the transmissive anti-reflection film can increase the transmittance of the parallel light 230 transmitting through the inside of the main body 100.

[0044] In the above embodiment, a plurality of saw-tooth shaped prisms 120 are provided on the uneven surface 102. Instead of this, the uneven surface 102 may have other uneven shapes. For example, it may be a rectangular uneven shape in which first inclined surfaces parallel to the flat surface 104 (that is, θ1=0°) and second inclined surfaces perpendicular to the flat surface 104 (that is, θ1=90°) are alternately arranged. Also in this case, by making the parallel light enter from the flat surface 104 at an angle at which the parallel light is substantially parallel incident on the second inclined surface where the light shielding film 134 is not provided, it is possible to obtain a structure in which the light shielding film 134 is provided on the first inclined surface and the light shielding film 134 is not provided on the second inclined surface. In addition, the uneven shape does not need to be a periodic structure. Furthermore, each surface of the uneven surface 102 is not limited to a flat surface, and may be a curved surface. In particular, the surface on which the light shielding film is provided may be a concave curved surface.

[0045] In the above embodiment, the step of preparing the main body 100 may include a step of forming a concavo-convex shape on the main body 100 to obtain a concavo-convex surface 102. In this case, for example, a concavo-convex shape may be bonded to the flat plate portion 101. Also, the flat plate portion 101 and the concavo-convex shape may be made of different materials. In this case, if there is a refractive index difference between the flat plate portion 101 and the concavo-convex shaped portion, it is preferable to determine the angle α0 in consideration of refraction at the boundary therebetween so that the parallel light 230 is substantially parallel to the second inclined surface 124.

[0046] In the above embodiment, the photocurable resin composition 130 forms a black light-shielding film 134 that absorbs visible light. Alternatively, the photocurable resin composition 130 may form a film having optical transmission characteristics and / or reflection characteristics different from those of the main body 100. For example, the photocurable resin composition 130 may form a film that has a color other than black and absorbs all of visible light or a specific wavelength range of visible light. As still another example, the photocurable resin composition 130 may contain a pearl pigment, a white pigment, or the like, and form a film that actively reflects visible light.

[0047] In the above embodiment, the uncured photocurable resin composition 130 is applied by a roll coater 200. The photocurable resin composition 130 may be formed by any other method. For example, it may be applied by spraying or the like other than using the roll coater 200. Further, instead of applying, a sheet obtained by forming the uncured photocurable resin composition 130 on a base material may be bonded to the main body 100.

[0048] In the above embodiment, the uncured photocurable resin composition 130 is applied such that an exposed-side surface 132 is flat. Alternatively, the surface 132 may not be flat. More specifically, it is only required that the photocurable resin composition 130 is sufficiently placed on the first inclined surface 122 to be cured, so as to fill the concavo-convex surface 102.

[0049] In the above embodiment, one light source 210 and one optical system 220 are provided to illuminate the entire flat surface 104. Alternatively, multiple sets of light sources 210 and optical systems 220, each illuminating a portion of the flat surface 104, may be provided in parallel to illuminate the entire flat surface 104. Furthermore, either as an alternative or in addition, the set of light source 210 and optical system 220 may be moved in parallel along the plane of the flat surface 104 while maintaining the incident angle of the parallel light 230 to illuminate the entire flat surface 104.

[0050] In the above embodiment, an example was described in which the optical sheet 10 is used in a head-up display. The applications of the optical sheet 10 are not limited to this, and may also be used in applications such as reflective screens, streetlights, or aerial levitation displays.

[0051] In the above embodiment, the second inclined surface 124 of the optical sheet 10 is exposed. Alternatively, a film having different transmission and / or reflection properties than the light-shielding film 134 may be formed on the second inclined surface 124. In this case, the light-shielding film 134 may be formed on the first inclined surface 122 in the manner described in Figures 1 to 7, and then, in the same manner as in Figures 3 to 7, an uncured photocurable resin composition different from the photocurable resin composition 130 may be formed on the uneven surface 102 of the main body 100, and parallel light substantially parallel to the first inclined surface 122 may be irradiated from the flat surface 104. This makes it possible to obtain a structure in which the light-shielding film 134 is provided on the first inclined surface and a film different from the light-shielding film 134 is provided on the second inclined surface.

[0052] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0053] It should be noted that the execution order of operations, procedures, steps, and stages in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not explicitly stated as "before," "prior to," etc., and that these can be performed in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," "next," etc. for convenience, this does not mean that it is mandatory to perform the operations in that order.

[0054] 10 Optical sheet, 100 Main body, 101 Flat plate section, 102 Uneven surface, 104 Flat surface, 120 Prism, 122 First inclined surface, 124 Second inclined surface, 130 Photocurable resin composition, 132 Surface, 134 Light-shielding film, 150, 160 Photocuring component, 162 First inclined surface, 164 Second inclined surface, 200 Roll coater, 210 Light source, 220 Optical system, 230 Parallel light

Claims

1. A method for manufacturing an optical sheet, comprising the steps of: preparing a transparent sheet-like body having a plurality of irregularities on one surface; forming a photocurable resin composition having different optical transmission and / or reflection properties from the body on the one surface of the body; irradiating the photocurable resin composition with parallel light in a predetermined direction from the surface of the body opposite to the one surface; and removing the uncured portion of the photocurable resin composition.

2. The method for manufacturing an optical sheet according to claim 1, wherein the plurality of irregularities have a plurality of prisms having opposing first inclined surfaces and second inclined surfaces, and the predetermined direction is a direction that is closer to parallel with respect to the second inclined surface than with respect to the first inclined surface.

3. The method for manufacturing an optical sheet according to claim 2, wherein the predetermined direction is substantially parallel to the second inclined surface.

4. The method for manufacturing an optical sheet according to claim 1, wherein the photocurable resin composition comprises a material that absorbs visible light.

5. The method for manufacturing an optical sheet according to claim 1, wherein, in the step of forming the photocurable resin composition, the photocurable resin composition is formed such that the exposed surface of the photocurable resin composition is flat.

6. The method for manufacturing an optical sheet according to claim 1, wherein the opposite surface of the main body is flat.

7. The method for manufacturing an optical sheet according to claim 1, further comprising the step of forming a photocuring member on the opposite side of the main body at least before the step of irradiating with parallel light.

8. The method for manufacturing an optical sheet according to claim 7, further comprising the step of removing the photocuring member from the opposite side of the main body after at least the step of irradiating with parallel light.

9. The method for manufacturing an optical sheet according to claim 1, wherein the step of preparing the main body includes the step of forming the plurality of irregularities on one surface of the main body.

10. The method for manufacturing an optical sheet according to any one of claims 1 to 9, wherein the optical sheet is for use in head-up displays, reflective screens, streetlights, or aerial levitation displays.

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