Manufacturing method of transmission type optical element

Abstract

To provide a manufacturing method of a transmission type optical element capable of manufacturing a circular transmission type optical element having a sufficient degree of concentricity.SOLUTION: A manufacturing method of a transmission type optical element of the present invention is a method for manufacturing a transmission type optical element by using a thermoplastic resin sheet. The method includes: preparing a thermoplastic resin sheet including an optical region having a circle shape in plan view and a recess extending so as to surround an outer peripheral part of the optical region; and obtaining the transmission type optical element by cutting the thermoplastic resin sheet into a circle shape by emitting laser light such that a side surface of the optical region side of the recess remains. The recess is formed so as to have an annular shape being substantially concentric with the optical region in plan view. A cross section of the thermoplastic resin sheet by the laser light is formed on the same surface as a virtual surface passing an outermost end edge of the transmission type optical element, or is formed further in the optical region side than the virtual surface, the virtual surface extending perpendicularly to the thermoplastic resin sheet.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a transmissive optical element.

Background Art

[0002] Against the backdrop of the increasing demand for cost reduction and performance improvement of electronic and electrical equipment, as well as the improvement in the quality of resin materials, attempts have been made to manufacture components of transmissive optical elements mounted on electronic and electrical equipment using resin sheets.

[0003] In recent years, even higher image quality has been demanded for small camera units and the like provided in electronic and electrical equipment. Therefore, from the perspective of enabling the construction of a high-precision optical system, circular transmissive optical elements such as small lenses, which are components of camera units, are required to have excellent shape accuracy.

[0004] For example, Patent Document 1 discloses a method for manufacturing a transmissive optical element using a thermoplastic resin sheet in which an optical region is formed, the method comprising circularly cutting the thermoplastic resin sheet using laser light having a wavelength of 350 nm or more and 550 nm or less to obtain a transmissive optical element having a diameter of 10 mm or less. Patent Document 1 describes that a transmissive optical element having sufficiently high shape accuracy can be obtained by the above manufacturing method.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, there was room for improvement in the method for manufacturing a transmissive optical element of the above prior art in terms of improving the shape accuracy of the obtained transmissive optical element. More specifically, there was room for improvement in terms of improving the concentricity (hereinafter simply referred to as "concentricity") between the outer shape of the transmissive optical element in plan view and the shape of the optical region in plan view.

[0007] Therefore, an object of the present invention is to provide a method for manufacturing a transmissive optical element capable of manufacturing a circular transmissive optical element having sufficiently high concentricity.

Means for Solving the Problems

[0008] The present inventor conducted intensive studies for the purpose of solving the above problems. Then, the present inventor found that the concentricity decreases due to displacement of the position when scanning the laser beam in cutting using the laser beam. Therefore, the present inventor further repeated studies, and when manufacturing a transmissive optical element by cutting a thermoplastic resin sheet in which an optical region is formed with a laser beam, a predetermined recess surrounding the outer peripheral portion of the optical region is formed, and when circularly cutting the thermoplastic resin sheet by laser cutting, while leaving the side surface (wall surface) on the optical region side of the recess, if the laser cutting surface is formed at a predetermined position, it was newly found that a circular transmissive optical element having sufficiently high concentricity can be obtained, and the present invention was completed.

[0009] That is, the object of the present invention is to advantageously solve the above problems. The present invention provides a method for manufacturing a transmissive optical element using a thermoplastic resin sheet, the method including: preparing a thermoplastic resin sheet having a circular optical region in plan view and a recess extending around the outer peripheral portion of the optical region; and circularly cutting the thermoplastic resin sheet by irradiating it with laser light so that the side surface of the recess on the optical region side remains, thereby obtaining a transmissive optical element. The recess is formed to be an annular shape substantially concentric with the optical region in plan view, and the cutting surface of the thermoplastic resin sheet by the laser light is formed on the same plane as a virtual plane passing through the outermost edge of the transmissive optical element and extending perpendicular to the thermoplastic resin sheet, or on the optical region side of the virtual plane. By forming a predetermined recess in the outer peripheral portion of the optical region and circularly cutting the thermoplastic resin sheet by irradiating it with laser light, while leaving the side surface of the recess on the optical region side, and forming the cutting surface of the thermoplastic resin sheet by the laser light on the same plane as a virtual plane passing through the outermost edge of the transmissive optical element and extending perpendicular to the thermoplastic resin sheet, or on the optical region side of the virtual plane, a circular transmissive optical element with a sufficiently high concentricity can be obtained.

[0010] [2] In the method for manufacturing a transmissive optical element according to [1] above, it is preferable to form the recess only on one surface of the thermoplastic resin sheet. By forming the recess only on one surface of the thermoplastic resin sheet, the concentricity of the obtained transmissive optical element can be further improved. Also, by forming the recess only on one surface of the thermoplastic resin sheet, the roundness (hereinafter simply referred to as "roundness") of the outer shape of the obtained transmissive optical element in plan view can be increased.

[0011] [3] In the method for manufacturing the transmissive optical element of [2] above, it is preferable to irradiate the laser light from the side of the thermoplastic resin sheet where the concave portion is not formed. If the laser light is irradiated from the side of the thermoplastic resin sheet where the concave portion is not formed, a transmissive optical element with a sufficiently high concentricity can be easily obtained. Further, if the laser light is irradiated from the side of the thermoplastic resin sheet where the concave portion is not formed, the roundness of the obtained transmissive optical element can be increased.

[0012] "4" In the method for manufacturing the transmissive optical element according to any one of [1] to [3] above, the thickness of the portion of the thermoplastic resin sheet where the concave portion is formed is preferably 10 μm or more and 200 μm or less. If the thickness of the portion of the thermoplastic resin sheet where the concave portion is formed is equal to or greater than the above lower limit value, the occurrence of sheet breakage when removing the molding die used for forming the optical region or the concave portion can be suppressed. Further, if the thickness of the portion of the thermoplastic resin sheet where the concave portion is formed is equal to or less than the above upper limit value, laser cutting can be easily performed.

Effect of the Invention

[0013] According to the present invention, it is possible to provide a method for manufacturing a transmissive optical element capable of manufacturing a circular transmissive optical element with a sufficiently high concentricity.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

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Figure 9

Figure 10

MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail. Here, according to the method for manufacturing a transmissive optical element of the present invention, a circular transmissive optical element such as a lens can be manufactured while achieving a sufficiently high concentricity. Therefore, the transmissive optical element obtained according to the manufacturing method of the present invention can be suitably used, for example, as a lens of a camera unit of a small electronic and electrical device.

[0016] (Method for manufacturing a transmissive optical element) The manufacturing method of the transmissive optical element of the present invention (hereinafter, may be abbreviated as "the manufacturing method of the present invention") is a method for manufacturing a transmissive optical element using a thermoplastic resin sheet. Specifically, the manufacturing method of the present invention includes a step of preparing a thermoplastic resin sheet having an optical region circular in plan view and a concave portion extending around the outer peripheral portion of the optical region (preparation step), and a step of circularly cutting the thermoplastic resin sheet by irradiating laser light so that the side surface on the optical region side of the concave portion remains, to obtain a transmissive optical element (laser cutting step). Further, the manufacturing method of the present invention is characterized in that the concave portion is formed in an annular shape substantially concentric with the optical region in plan view. Furthermore, the manufacturing method of the present invention is characterized in that the cutting surface of the thermoplastic resin sheet by laser light is on the same plane as or on the optical region side of a virtual plane passing through the outermost edge of the transmissive optical element and extending perpendicular to the thermoplastic resin sheet. Note that the manufacturing method of the present invention may optionally further include a step of cleaning the optical surface of the transmissive optical element obtained in the laser cutting step (cleaning step) and the like.

[0017] <Preparation step> In the preparation step, a thermoplastic resin sheet having an optical region circular in plan view and a concave portion extending around the outer peripheral portion of the optical region is prepared. The concave portion is formed in an annular shape (specifically, a circular ring shape) substantially concentric with the optical region in plan view (see FIG. 9). Here, concentric means that the center of the optical region and the center of the circular ring of the concave portion coincide. The concave portion and the optical region can be efficiently formed simultaneously, for example, by thermally pressing the thermoplastic resin sheet using a mold such as a pair of flat molding dies capable of forming the concave portion and the optical region. The optical region may be formed before or after the formation of the concave portion. However, from the viewpoints of manufacturing efficiency and improving the roundness and further improving the concentricity of the transmissive optical element, it is preferable that the optical region is formed simultaneously with the concave portion. Note that a thermoplastic resin sheet in which the concave portion and the optical region are formed in advance may be used.

[0018] [Optical region] The number of optical regions formed on the thermoplastic resin sheet is not limited and may be one or more. However, from the perspective of the manufacturing efficiency of the transmissive optical element, it is preferable to form a plurality of optical regions. The optical regions formed on the thermoplastic resin sheet are circular regions in plan view having a desired surface shape. More specifically, such optical regions may have a planar shape on both the front and back surfaces, or at least one of the front and back surfaces may have a spherical or aspherical shape. Note that examples of the optical element having an optical region in which at least one of the front and back surfaces has a spherical or aspherical shape include a plano-convex lens, a biconvex lens, a convex meniscus lens, a plano-concave lens, a biconcave lens, a concave meniscus lens, and an aspherical lens in which one or both surfaces have an aspherical shape with an inflection point. These optical regions can be efficiently formed, for example, by thermally pressing the thermoplastic sheet using a pair of flat molds.

[0019] [Concave portion] The concave portion is formed so as to surround the optical region at the outer peripheral portion of the optical region so as to be annular and substantially concentric with the optical region in plan view (see FIG. 9). Here, in FIG. 9, reference numeral 11 indicates the optical region, and reference numeral 20 indicates the concave portion. The concave portion may be formed on only one surface of the thermoplastic resin sheet or on both surfaces of the thermoplastic resin sheet. However, from the perspective of improving the roundness of the obtained transmissive optical element and further improving the concentricity of the transmissive optical element, it is preferable to form it on only one surface of the thermoplastic resin sheet. When the concave portion is formed on both surfaces of the thermoplastic resin sheet, the concave portions on both surfaces are usually formed so as to face each other in the thickness direction of the thermoplastic resin sheet (see FIG. 8(a)). Hereinafter, the properties and formation positions of the concave portion will be specifically described with reference to the drawings.

[0020] FIG. 1 is a partial cross-sectional view of a thermoplastic resin sheet that can be a cutting target in a method for manufacturing a transmissive optical element according to an example of the present invention, and FIG. 2 is an enlarged cross-sectional view of the vicinity of a recess in the thermoplastic resin sheet. Specifically, in FIG. 1, one transmissive optical element 10 in a state included in the thermoplastic resin sheet 100 is enlarged and shown, an optical region 11 that constitutes a part of the transmissive optical element 10, and a recess 20 having a rectangular cross-sectional shape provided in an outer peripheral portion adjacent to the optical region 11 are shown. In FIG. 2, the vicinity of the recess 20 in the thermoplastic resin sheet 100 is enlarged and shown, reference numeral 21 indicates the inner wall surface of the recess 20, and reference numeral 22 indicates the bottom of the recess. In FIGS. 1 and 2, EL indicates an end line of the optical region 11, L1 indicates a normal line to the thermoplastic resin sheet 100 at the starting point of the recess 20 (wall surface 21) as viewed from the optical region 11 side, and L2 indicates a normal line to the thermoplastic resin sheet 100 at the intersection of the wall surface 21 and the bottom 22 of the recess 20. Further, d indicates the distance between EL and L1, that is, the distance of the recess 20 from the end of the optical region 11.

[0021] Here, as shown in FIGS. 1 and 2, the recess 20 is usually formed in the outer peripheral portion of the optical region 11 at a distance from the end of the optical region 11. Specifically, the recess 20 is formed so as to surround the outer peripheral portion of the optical region 11 at a position separated from the end of the optical region 11 by a distance d. The distance d is usually 0.05 mm or more, preferably 0.1 mm or more, and preferably 10 mm or less, more preferably 5 mm or less. Note that the distance d can be appropriately set according to the "diameter of the transmissive optical element" described later.

[0022] The cross-sectional shape of the recess 20 (the shape of the cross-section in the width direction of the recess 20) is not particularly limited, and for example, it can be a quadrilateral such as a rectangle, a square, a trapezoid (with the bottom side of the recess as the upper base and the opening side of the recess as the lower base wider than the upper base). Here, among the wall surfaces of the concave portion 20, at least the wall surface 21 on the optical region 11 side preferably has an inclination angle θ (in FIG. 2, the angle θ formed by the wall surface 21 on the optical region 11 side of the concave portion 20 and L2) of 0° or more and 5° or less, more preferably 0° or more and 3° or less, and still more preferably 0°. If the inclination angle θ is within the above range, while increasing the roundness of the obtained transmissive optical element, the concentricity of the transmissive optical element can be further improved. When the inclination angle θ is 0° (that is, when the wall surface 21 is perpendicular), L1 and L2 coincide.

[0023] The width of the concave portion 20 (the length in the width direction of the upper base of the concave portion 20) is not particularly limited and can be 0.5 mm or more and 10 mm or less.

[0024] The depth of the concave portion 20 is not particularly limited, but the concave portion 20 preferably has a depth such that the thickness of the portion of the thermoplastic resin sheet 100 where the concave portion 20 is formed (hereinafter, also simply referred to as "remaining sheet thickness") is 10 μm or more, more preferably 30 μm or more, still more preferably 50 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, and still more preferably 100 μm or less. If the remaining sheet thickness of the thermoplastic resin sheet is equal to or greater than the above lower limit value, the occurrence of sheet breakage when removing the molding die used for forming the optical region or the concave portion (that is, during demolding) can be suppressed. Also, if the remaining sheet thickness of the thermoplastic resin sheet is equal to or less than the above upper limit value, laser cutting can be easily performed.

[0025] Also, the concentricity between the inner wall surface 21 of the concave portion 20 and the optical region 11 is preferably 1 μm or less. If the concentricity between the inner wall surface 21 of the concave portion 20 and the optical region 11 is equal to or less than the above upper limit value, a circular transmissive optical element with higher concentricity can be obtained. In the present invention, the concentricity between the inner wall surface 21 of the concave portion 20 and the optical region 11 can be measured, for example, in the same manner as the method described in the examples, with a reference wall surface concentric with the optical region 11 as the reference plane.

[0026] [Thermoplastic resin sheet] As the thermoplastic resin sheet used in the shaping process, as long as it is thermoplastic, it is not particularly limited, and a sheet formed using any known thermoplastic resin can be used. Here, the "sheet" means an object having a shape in which the front surface and the back surface (i.e., the main surfaces) face each other with a distance corresponding to the thickness therebetween. Examples of the thermoplastic resin that can constitute the thermoplastic resin sheet include (meth)acrylic resins, resins containing an alicyclic structure, styrenic resins, polycarbonate resins, polyester resins, polyether resins, urethane resins, and thiourethane resins. Note that "(meth)acrylic" refers to acrylic and / or methacrylic. Among these, since a transmissive optical element with excellent transparency can be obtained, it is preferable that the thermoplastic resin constituting the thermoplastic resin sheet contains a resin containing an alicyclic structure. Further, from the viewpoint of obtaining a transmissive optical element with even better shape accuracy, it is preferable that the thermoplastic resin constituting the thermoplastic resin sheet contains a resin having no polar group in the repeating unit. Resins having no polar group in the repeating unit are difficult to process because they are less likely to absorb laser light compared to resins having a polar group or the like. On the other hand, when resins having no polar group in the repeating unit are processed, the amount of energy that changes to heat during processing is also small, so the occurrence of deformation due to heat can be suppressed. As a result, by using a thermoplastic resin sheet containing a resin having no polar group in the repeating unit, a transmissive optical element with high concentricity can be obtained. Therefore, from the viewpoint of obtaining a transmissive optical element with even better transparency and concentricity, it is preferable that the thermoplastic resin sheet contains a resin containing an alicyclic structure and having no polar group in the repeating unit.

[0027] The alicyclic structure-containing resin is a polymer having an alicyclic structure such as a saturated cyclic hydrocarbon structure and an unsaturated cyclic hydrocarbon structure in the main chain and / or side chain. Among them, those having a cycloalkane structure in the main chain are preferred because it is easy to obtain a transmissive optical element excellent in mechanical strength and heat resistance. The ratio of the repeating unit having an alicyclic structure in the polymer (hereinafter also referred to as "alicyclic structure-containing polymer") constituting the alicyclic structure-containing resin is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 90% by mass or more based on all the repeating units contained in the polymer. By using an alicyclic structure-containing polymer having a ratio of the repeating unit having an alicyclic structure of 50% by mass or more, it is easy to obtain a transmissive optical element excellent in transparency and heat resistance.

[0028] Specific examples of the alicyclic structure-containing polymer include norbornene-based polymers, monocyclic cyclic olefin-based polymers, and cyclic conjugated diene-based polymers. Among these, norbornene-based polymers are preferred from the viewpoint of enhancing the transparency, heat resistance, and mechanical strength of the resulting transmissive optical element. In the present specification, these polymers mean not only the polymerization reaction products but also their hydrogenated products.

[0029] The norbornene-based polymer is a polymer of a norbornene-based monomer or its hydrogenated product. Examples of the norbornene-based polymer include ring-opening polymers of norbornene-based monomers, ring-opening polymers of norbornene-based monomers and other monomers capable of ring-opening copolymerization therewith, addition polymers of norbornene-based monomers, addition polymers of norbornene-based monomers and other monomers capable of copolymerization therewith, and hydrogenated products of these polymers. Among them, hydrogenated ring-opening polymers of norbornene-based monomers (i.e., hydrogenated norbornene-based ring-opening polymers) are preferred. By using a thermoplastic resin sheet formed using a hydrogenated norbornene-based ring-opening polymer, the transparency, heat resistance, mechanical strength, etc. of the resulting transmissive optical element can be further enhanced.

[0030] Examples of norbornene monomers include bicyclo[2.2.1]hept-2-ene (common name: norbornene) and its derivatives, tricyclo[4.3.0 1,6 .1 2,5 deca-3,7-diene (common name dicyclopentadiene) and its derivatives, 7,8-benzotricyclo[4.3.0.1 2,5 deca-3-ene (common name methanotetrahydrofluorene: also referred to as 1,4-methano-1,4,4a,9a-tetrahydrofluorene) and its derivatives, tetracyclo[4.4.0.1 2,5 .1 7,10 dodeca-3-ene (common name: tetracyclododecene) and its derivatives, and the like. Examples of substituents that may be included in the derivatives include alkyl groups, alkylene groups, vinyl groups, alkylidene groups, and the like. These norbornene monomers can be used alone or in combination of two or more.

[0031] Examples of other monomers that are ring-opening copolymerizable with norbornene monomers include monocyclic cyclic olefin monomers such as cyclohexene, cycloheptene, and cyclooctene. Examples of other monomers that are addition copolymerizable with norbornene monomers include α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 1-pentene, and 1-hexene and their derivatives; cycloolefins such as cyclobutene, cyclopentene, cyclohexene, cyclooctene, and 3a,5,6,7a-tetrahydro-4,7-methano-1H-indene and their derivatives; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, and 1,7-octadiene; and the like.

[0032] The ring-opening polymers and addition polymers containing the norbornene monomers as described above can be synthesized by polymerization in the presence of known catalysts. Further, these hydrides can be obtained by a hydrogenation reaction using a known hydrogenation catalyst.

[0033] Examples of the monocyclic cyclic olefin polymer and the cyclic conjugated diene polymer include those described in JP-A-2016-57403.

[0034] In addition, commercially available products can also be used as the alicyclic structure-containing polymer. Examples of commercially available products include ZEONOR (registered trademark) and ZEONEX (registered trademark) manufactured by Zeon Corporation, APEL (registered trademark) manufactured by Mitsui Chemicals, Inc., ARTON (registered trademark) manufactured by JSR Corporation, and TOPAS (registered trademark) manufactured by Polyplastics Co., Ltd.

[0035] The thermoplastic resin sheet may contain components other than the resin components described above. Examples of components other than the resin components include additives such as light stabilizers, ultraviolet absorbers, antioxidants, mold release agents, antistatic agents, carbon materials (such as carbon), pigments, and dyes. The blending amounts of these components are not particularly limited and can be appropriately determined. For example, the total amount of these additives can be, for example, 20% by mass or less, preferably 10% by mass or less, based on 100% by mass of the resin components.

[0036] The method for producing the thermoplastic resin sheet is not particularly limited, and a conventionally known appropriate method can be adopted. For example, a molding material for producing a thermoplastic resin sheet can be obtained by mixing predetermined components, and using this, a thermoplastic resin sheet can be obtained by a melt extrusion molding method, a melt casting molding method, an injection molding method, or the like. Alternatively, a commercially available product may be used as the thermoplastic resin sheet.

[0037] The thickness of the thermoplastic resin sheet to be subjected to the shaping step is preferably 100 μm or more, more preferably 200 μm or more, preferably 800 μm or less, and more preferably 500 μm or less.

[0038] <Laser cutting step> In the laser cutting process, a thermoplastic resin sheet having an optical region and recesses is circularly cut by irradiating it with laser light to obtain a transmissive optical element. Here, the laser cutting needs to be performed while leaving the side surface (wall surface) on the optical region side of the recesses. Further, in the laser cutting, the cutting surface of the thermoplastic resin sheet by the laser light needs to be formed on the same plane as a virtual plane passing through the outermost edge of the obtained transmissive optical element and extending perpendicular to the thermoplastic resin sheet or on the optical region side of the virtual plane. As a result, the side surface (wall surface) on the optical region side of the recesses remaining after cutting becomes a part of the side circumferential surface of the obtained transmissive optical element, and as a result, a transmissive optical element with excellent concentricity can be obtained. If the laser cutting is performed so that the side surface on the optical region side of the recesses does not remain, or if the cutting surface of the thermoplastic resin sheet is formed on the side opposite to the optical region from the virtual plane, the concentricity of the transmissive optical element cannot be sufficiently increased.

[0039] Here, with reference to the drawings, the positional relationship between the cut surface of the thermoplastic resin sheet and the outermost edge of the transmissive optical element will be specifically described. FIG. 3 is a partially enlarged cross-sectional view of a thermoplastic resin sheet cut in a laser cutting process according to an example of the present invention. FIG. 3(a) is a partially enlarged cross-sectional view when the wall surface 21 has a concave portion inclined with respect to the normal of the thermoplastic resin sheet 100 (that is, when the inclination angle θ from L2 in FIG. 2 is greater than 0°), and FIG. 3(b) is a partially enlarged cross-sectional view when the wall surface 21 has a concave portion parallel to the normal of the thermoplastic resin sheet 100 (that is, when the inclination angle θ from L2 in FIG. 2 is 0°). In FIGS. 3(a) and 3(b), reference numeral 12 indicates the outermost edge of the transmissive optical element obtained by cutting the thermoplastic resin sheet, reference numeral 13 indicates the cut surface, and reference numeral P indicates a virtual plane passing through the outermost edge 12 and extending perpendicular to the thermoplastic resin sheet 100. Referring to FIG. 3(a), the cut surface 13 of the thermoplastic resin sheet 100 is formed on the optical region 11 side of the virtual plane P. Further, in FIG. 3(a), the wall surface 21 on the optical region side of the concave portion is located on the optical region 11 side of the virtual plane P. Referring to FIG. 3(b), the cut surface 13 of the thermoplastic resin sheet 100 is formed on the same plane as the virtual plane P, and the wall surface 21 is also formed on the same plane as the virtual plane P. Thus, in the manufacturing method of the present invention, the thermoplastic resin sheet 100 is cut with a laser so that the cut surface 13 of the thermoplastic resin sheet 100 by the laser light is formed on the same plane as the virtual plane P or on the optical region 11 side of the virtual plane P. Thereby, even when the position of the laser irradiation is deviated, the outermost edge 12 of the obtained transmissive optical element can maintain the same distance from the optical center of the optical region 11, and a transmissive optical element with a sufficiently high concentricity can be obtained. Note that the cut surface 13 is preferably formed on the optical region 11 side of the virtual plane P. In particular, as shown in FIG. 3(a), when the wall surface 21 is inclined with respect to the normal of the thermoplastic resin sheet 100 (when the inclination angle θ is greater than 0°), the cut surface 13 is preferably formed on the optical region 11 side of the virtual plane P as shown in FIG. 3(a).

[0040] Here, when forming the concave portion only on one surface of the thermoplastic resin sheet as described above, the laser light may be irradiated from the side of the surface of the thermoplastic resin sheet where the concave portion is not formed, as shown in FIGS. 4 to 6, or may be irradiated from the side of the surface where the concave portion is formed, as shown in FIG. 7. However, from the viewpoint of easily obtaining a transmissive optical element with high roundness and sufficiently high concentricity, it is preferable to irradiate from the side of the surface of the thermoplastic resin sheet where the concave portion is not formed.

[0041] In addition, the irradiation of the laser light is not particularly limited as long as the side surface on the optical region side of the concave portion remains and the cut surface of the thermoplastic resin sheet is on the same plane as the virtual plane passing through the outermost edge of the obtained transmissive optical element and extending perpendicular to the thermoplastic resin sheet or on the optical region side of the virtual plane, and can be performed using the desired laser light and conditions.

[0042] [Laser light] As the laser light used in the laser cutting process, it is preferable to use laser light with a wavelength of 350 nm or more and 550 nm or less. By using laser light with a wavelength of 350 nm or more and 550 nm or less as the laser light, the thermoplastic resin sheet can be cut well. Furthermore, as the laser light, it is preferable to use laser light that satisfies the following conditions. By appropriately controlling the conditions of the laser light used in the laser cutting process, the bulge at the cut end of the thermoplastic resin sheet can be suppressed, and the linearity of the cut surface can be improved.

[0043] - Wavelength - The wavelength of the laser light used in the laser cutting process is preferably 350 nm or more and 550 nm or less, more preferably 500 nm or less, as described above. If the wavelength of the laser light is 500 nm or less, the cutting efficiency in the laser cutting process can be increased.

[0044] - Pulse width (P)- The pulse width (P) of the laser beam used in the laser cutting process is preferably 0.01 ps or more, more preferably 1.0 ps or more, and preferably 20 ps or less. If the pulse width (P) of the laser beam is 1.0 ps or more, the cutting efficiency in the laser cutting process can be increased. Also, if the pulse width (P) of the laser beam is 20 ps or less, it is possible to suppress an increase in the bulge width of the cut end of the thermoplastic resin sheet and to enhance the linearity of the cut surface.

[0045] - Output (O)- The output of the laser beam used in the laser cutting process is preferably 0.4 W or more, more preferably 1.0 W or more, still more preferably 2.0 W or more, and preferably 20 W or less. If the output of the laser beam is 1.0 W or more, the processing time in the laser cutting process can be shortened and the cutting efficiency in the process can be increased. Also, if the output of the laser beam is 20 W or less, it is possible to effectively suppress contamination of the optical surface of the transmissive optical element obtained by the gas resulting from the thermoplastic resin sheet in the laser cutting process. As a result, the quality of the obtained transmissive optical element can be enhanced. Also, if the output of the laser beam is 20 W or less, it is possible to suppress an increase in the bulge width of the cut end of the thermoplastic resin sheet and to enhance the linearity of the cut surface.

[0046] - Output (O) [W] / Pulse width (P) [ps]- Regarding the laser beam used in the laser cutting process, the value obtained by dividing the output (O) [W] of the laser beam by the pulse width (P) [ps] of the laser beam (O [W] / P [ps]) is preferably 0.025 [W / ps] or more, more preferably 0.10 [W / ps] or more, preferably 1.5 [W / ps] or less, and more preferably 0.8 [W / ps] or less. If the value of (O [W] / P [ps]) is 0.10 [W / ps] or more, the processing time in the laser cutting process can be shortened and the cutting efficiency in the process can be increased. Further, if the value of (O [W] / P [ps]) is 0.8 [W / ps] or less, it is possible to suppress the expansion of the bulge width at the cutting end of the thermoplastic resin sheet, and to increase the linearity of the cut surface. Furthermore, if the value of (O [W] / P [ps]) is 0.8 [W / ps] or less, it is possible to effectively suppress the contamination of the optical surface of the transmissive optical element obtained by the gas generated from the thermoplastic resin sheet in the laser cutting process. As a result, the quality of the obtained transmissive optical element can be improved.

[0047] - Frequency - The frequency of the laser beam used in the laser cutting process is preferably 50 kHz or more, more preferably 100 kHz or more, still more preferably 200 kHz or more, preferably 1800 kHz or less, and more preferably 500 kHz or less. If the frequency of the laser beam is 100 kHz or more, the processing time in the laser cutting process can be shortened and the cutting efficiency in the process can be increased. If the frequency of the laser beam is 1800 kHz or less, it is possible to suppress the expansion of the bulge width at the cutting end of the thermoplastic resin sheet, and to increase the linearity of the cut surface.

[0048] [Laser beam irradiation pattern] Furthermore, in the laser cutting process, in order to cut out a certain transmissive optical element in a circular shape, it is preferable to perform trepanning processing in which laser light is irradiated along a circular cutting line. Furthermore, in the trepanning processing, rather than completing the cutting of a certain transmissive optical element in one round of scanning, it is preferable to complete the cutting by scanning over multiple rounds. Completing the cutting by irradiating laser light over multiple rounds, in other words, the amount of energy required for cutting is not imparted to the thermoplastic resin film by a single irradiation, but is imparted in multiple portions.

[0049] Also, the laser irradiation is preferably performed while blowing a charged gas onto at least the cutting portion of the thermoplastic resin sheet to be cut. By performing the laser irradiation while blowing the charged gas, it is possible to suppress the adhesion of debris when cutting out the transmissive optical element. As the charged gas, for example, air, nitrogen gas, argon gas, etc. can be used.

[0050] Furthermore, the laser irradiation is preferably performed while blowing an inert gas onto at least the cutting portion of the thermoplastic resin sheet to be cut. By performing the laser irradiation while blowing the inert gas, it is possible to suppress the oxidative degradation of the cut end portion of the thermoplastic resin sheet. As the inert gas, for example, nitrogen gas, argon gas, etc. can be used.

[0051] The laser processing thickness (that is, the thickness of the thermoplastic resin sheet removed by the irradiation of the laser light) is preferably within the residual sheet thickness + 30 μm, and more preferably within the residual sheet thickness + 10 μm. If the laser processing thickness is within the above-mentioned predetermined range, it is possible to suppress the decrease in the diameter accuracy of the obtained transmissive optical element.

[0052] [Shape of Transmissive Optical Element] In the manufacturing method of the present invention, the diameter of the transmissive optical element obtained by circular cutting in the laser cutting step is not particularly limited, but is preferably 10 mm or less. The diameter of the transmissive optical element may be 1 mm or more and 8 mm or less. When manufacturing such a small-diameter transmissive optical element, by applying the manufacturing method of the present invention, a small-sized transmissive optical element with high concentricity can be efficiently obtained. In this specification, the "diameter of the transmissive optical element" means the diameter of the entire transmissive optical element. The transmissive optical element manufactured according to the manufacturing method of the present invention may include an optical region and an outer peripheral portion adjacent to the optical region. The width of such an outer peripheral portion can be, for example, 0.05 mm or more and 3 mm or less in the total value in the radial direction. Therefore, the "diameter of the transmissive optical element" corresponds to the value obtained by adding the value of the width of the outer peripheral portion (total value in the radial direction) to the diameter of the "optical region" of the transmissive optical element.

[0053] Hereinafter, embodiments of laser cutting will be described with reference to the drawings.

[0054] <First Embodiment> FIG. 4 is a schematic cross-sectional view (a) and (b) for explaining the laser cutting step according to the first embodiment of the present invention. In FIG. 4(a), a concave portion 20 (the inclination angle θ from L2 = 0°) is formed only on one surface of the thermoplastic resin sheet 100. Further, in FIG. 4(a), the laser beam 40 is irradiated perpendicularly (in the vertical direction in FIG. 4) to the thermoplastic resin sheet 100 at the position of L2 on the thermoplastic resin sheet 100 from the side opposite to the side where the concave portion 20 is formed.

[0055] In this embodiment, the laser beam 40 is irradiated perpendicularly to the thermoplastic resin sheet 100 at the position of L2 on the thermoplastic resin sheet 100. Specifically, the laser beam 40 is irradiated perpendicularly to the thermoplastic resin sheet 100 such that the laser spot straddles the position of L2 on the thermoplastic resin sheet 100. By irradiating the laser beam 40 in this manner, while leaving the inner side surface (wall surface) of the recess 20, the cut surface is formed inside the transmissive optical element 10 (on the optical region side) rather than on the virtual plane P (shown by the dashed line) that extends perpendicularly in the sheet thickness direction through the outermost edge of the transmissive optical element 10, and the transmissive optical element 10 can be cut out from the thermoplastic resin sheet 100 (FIG. 4(b)). That is, in the transmissive optical element 10 thus obtained, as shown in FIG. 4(b), the inner side surface (wall surface) of the recess 20 remaining after cutting becomes the outermost edge of the transmissive optical element 10, and the cut surface is inside the transmissive optical element 10 (on the optical region side) rather than on the virtual plane P that extends perpendicularly in the sheet thickness direction through the outermost edge.

[0056] In this embodiment, the laser beam 40 is irradiated perpendicularly such that the laser spot straddles the position of L2. However, as long as the laser beam 40 is irradiated such that while leaving the inner side surface of the recess 20, the cut surface is formed on the same plane as the virtual plane P or on the optical region side of the virtual plane P, the irradiation position and irradiation angle of the laser beam 40 are not limited. For example, the laser beam 40 may be irradiated such that the laser spot does not straddle the position of L2 on the thermoplastic resin sheet 100 and the end portion of the laser spot on the side opposite to the transmissive optical element 10 is located at the position of L2 on the transmissive optical element 10, or the laser beam 40 may be irradiated such that the laser spot does not straddle the position of L2 on the thermoplastic resin sheet 100 and the end portion of the laser spot on the transmissive optical element 10 side is located at the position of L2 on the transmissive optical element 10, and / or the laser beam 40 may be irradiated while being inclined with respect to the main surface of the thermoplastic resin sheet 100. Specific description will be given below with reference to FIGS. 5 and 6.

[0057] FIG. 5 is a schematic cross-sectional view (a) and (b) for explaining a laser cutting process according to a first modification of the first embodiment of the present invention. In the first modification of the first embodiment of the present invention, as shown in FIG. 5(a), the laser beam 40 is irradiated perpendicularly to the thermoplastic resin sheet 100 such that the laser spot does not straddle the position of L2 on the thermoplastic resin sheet 100 and the end on the side opposite to the transmissive optical element 10 of the laser spot is located at (in contact with) L2 on the transmissive optical element 10. Even for the transmissive optical element 10 obtained in this way, as shown in FIG. 5(b), the inner side surface (wall surface) of the recess 20 remaining after cutting becomes the outermost edge of the transmissive optical element 10, and the cutting surface is located inside (on the optical region side) of the transmissive optical element 10 with respect to a virtual plane P (shown by a broken line) that extends perpendicularly in the thickness direction of the sheet through the outermost edge.

[0058] FIG. 6 is a schematic cross-sectional view (a) and (b) for explaining a laser cutting process according to a second modification of the first embodiment of the present invention. In the second modification of the first embodiment of the present invention, as shown in FIG. 6(a), the laser beam 40 is irradiated perpendicularly to the thermoplastic resin sheet 100 such that the laser spot does not straddle the position of L2 on the thermoplastic resin sheet 100 and the end on the side of the transmissive optical element 10 of the laser spot is located at (in contact with) L2 on the transmissive optical element 10. In the transmissive optical element 10 obtained in this way, as shown in FIG. 6(b), the inner side surface (wall surface) of the recess 20 remaining after cutting and the cutting surface become the outermost edge of the transmissive optical element 10, and the cutting surface is located on the same plane as a virtual plane P (shown by a broken line) that extends perpendicularly in the thickness direction of the sheet through the outermost edge.

[0059] <Second Embodiment> The second embodiment is different from the first embodiment in that the laser beam 40 is irradiated from the side where the recess 20 is formed on the thermoplastic resin sheet 100. FIG. 7 is a schematic cross-sectional view (a) and (b) for explaining the laser cutting process according to the second embodiment of the present invention. In Fig. 7(a), the laser beam 40 is irradiated onto the bottom near the inner side surface of the recess 20 while being inclined with respect to the main surface of the thermoplastic resin sheet 100 on the side opposite to the optical region. When the laser beam 40 is irradiated from the side where the recess 20 of the thermoplastic resin sheet 100 is formed, by irradiating the laser beam 40 in this way, while leaving the inner side surface of the recess 20, the cut surface is formed inside the transmissive optical element 10 (on the optical region side) rather than the virtual plane P that extends perpendicularly in the sheet thickness direction through the outermost edge of the transmissive optical element 10, and the transmissive optical element 10 can be cut out from the thermoplastic resin sheet 100 (Fig. 7(b)). That is, in the obtained transmissive optical element 10, as shown in Fig. 7(b), the inner side surface (wall surface) of the recess 20 remaining after cutting becomes the outermost edge of the transmissive optical element 10, and the cut surface is located inside the transmissive optical element 10 (on the optical region side) rather than the virtual plane P (shown by the broken line) that extends perpendicularly in the sheet thickness direction through the outermost edge.

[0060] <Third Embodiment> The third embodiment is different from the second embodiment in that the recess 20 is also formed on the surface of the thermoplastic resin sheet 100 on the side where the laser beam 40 is not irradiated. Fig. 8 is schematic cross-sectional views (a) and (b) for explaining the laser cutting process according to the third embodiment of the present invention. In Fig. 8(a), the laser beam 40 is irradiated while being inclined with respect to the main surface of the thermoplastic resin sheet 100 at the bottom near the inner side surface of the recess 20, similarly to the second embodiment. When the recess 20 is formed on both surfaces of the thermoplastic resin sheet 100, by irradiating the laser beam 40 in this way, while leaving the inner side surfaces of both recesses 20, the cut surface is formed inside the transmissive optical element 10 (on the optical region side) rather than the virtual plane P that extends in the sheet thickness direction through the outermost edge of the transmissive optical element 10, and the transmissive optical element 10 can be cut out from the thermoplastic resin sheet 100 (Fig. 8(b)). That is, in the obtained transmissive optical element 10, as shown in FIG. 8(b), the inner side surface (wall surface) of the recess 20 remaining after cutting becomes the outermost edge of the transmissive optical element 10, and the cut surface is located inside the transmissive optical element 10 (on the optical region side) with respect to a virtual plane P (shown by a broken line) that extends perpendicularly in the sheet thickness direction through the outermost edge.

Example

[0061] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, the measurements and evaluations were carried out as follows.

[0062] <Roundness> Using Surtronic R-150 of TAYLOR HOBSON, for the outermost periphery of the transmissive optical elements produced in the examples and comparative examples, according to the content described in "JIS B 7451 Appendix 1(1) LSC Least Squares Center", with the cut-off value of the filter being 50, the roundness (μm) was measured. The roundness was measured for 10 transmissive optical elements, and the average value was obtained and evaluated according to the following criteria. A: Roundness is 1 μm or less B: Roundness is more than 1 μm and 2 μm or less C: Roundness is more than 2 μm and 5 μm or less D: Roundness is more than 5 μm <Concentricity> Similar to the roundness, using Surtronic R-150 of TAYLOR HOBSON, the outermost periphery of the transmissive optical elements produced in the examples and comparative examples was measured, and with a reference wall surface (reference numeral 30 in FIG. 10) provided at the end of the optical region of the transmissive optical element and concentric with the optical region as the reference circle, the concentricity of the transmissive optical element was measured. The concentricity (μm) was measured for 10 transmissive optical elements, and the average value was obtained and evaluated according to the following criteria. A: Concentricity is 1 μm or less B: Concentricity is more than 1 μm and 2 μm or less C: Concentricity is more than 2 μm and 5 μm or less D: Concentricity is more than 5 μm <Tearing during release> In the same manner as the method for manufacturing the transmissive optical element of the example, the thermoplastic resin sheet was press-molded 10 times, and a total of 10 thermoplastic resin sheets having an optical region and a concave portion were manufactured (9 transmissive optical elements / 1 thermoplastic resin sheet). When the thermoplastic resin sheet was removed from the molding die, the number of transmissive optical elements that were partially or completely torn from the sheet was visually confirmed as (n), and based on the following formula, the occurrence rate (A) [%] of tearing in all the optical elements was calculated. A = [n / (9 × 10)] × 100 A: The occurrence rate of tearing is 0% B: The occurrence rate of tearing is more than 0% and 2% or less C: The occurrence rate of tearing is more than 2% and 5% or less D: The occurrence rate of tearing is more than 5%

[0063] (Example 1) [Manufacture of Transmissive Optical Element] [Press Molding] A thermoplastic resin sheet (manufactured by Nippon Zeon Co., Ltd., Zeonoa Film ZF14, thickness: 400 μm) made of a resin containing a norbornene-based ring-opening polymer hydride was pressed by a pair of flat molding dies to form an optical region (diameter 5 mm) and an annular concave portion on one surface that is concentric with the optical region (inner diameter of the concave portion bottom surface 7 mm, outer diameter of the concave portion bottom surface 9 mm, depth 345 μm (remaining sheet thickness 55 μm), annular concave portion (tilt angle of the inner and outer side wall surfaces 2°)), and a resin sheet with an optical region shown in FIGS. 9 and 10 was obtained. The above press molding was performed 10 times in total, and a total of 10 resin sheets with an optical region were manufactured. [Laser Cutting] Align the position so that the optical region at the center of the obtained resin sheet with an optical region is centered, irradiate laser light from the surface where the annular recess is not formed, and scan the laser light in a circle with a diameter of 7 mm centered on the optical region (that is, the cut surface of the resin sheet by the laser light is a virtual surface passing through the outermost edge of the obtained transmissive optical element and is formed on the optical region side (inside the transmissive optical element) of the virtual surface extending perpendicular to the thermoplastic resin sheet). Set the pattern and perform trepanning processing for 20 passes. When it is visually confirmed that it has not been cut, repeat the additional 20 - pass trepanning processing until the resin sheet is cut. The conditions of the laser light at this time are as follows. Wavelength: 355 nm, Pulse width (P): 15 ps, Output (O): 1 W, O / P: 0.07, Frequency: 200 [kHz], Scanning speed: 100 mm / s) During laser light irradiation, nitrogen gas was blown as an inert gas by an antistatic blower. Then, the above various measurements and evaluations were performed on the obtained transmissive optical element. The results are shown in Table 1.

[0064] (Examples 2 - 5) In press molding, various operations and evaluations were carried out in the same manner as in Example 1, except that the remaining sheet thickness of the recess was changed as shown in Table 1. The results are shown in Table 1.

[0065] (Comparative Example 1) In press molding, no recess was formed in the thermoplastic resin sheet, and punching blade cutting was performed as follows instead of laser cutting. Various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. <Punching blade cutting> Align the position so that the optical region at the center of the thermoplastic resin sheet with an optical region is centered, and use a circular Thomson blade with a diameter of 7 mm to punch out the thermoplastic resin sheet to obtain a transmissive optical element.

[0066] (Comparative Example 2) Except for performing laser cutting of the thermoplastic resin sheet without forming recesses in the thermoplastic resin sheet during press molding, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0067] (Comparative Example 3) Except for performing punching blade cutting as described below instead of laser cutting, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. <Punching blade cutting> The position was adjusted so that the optical region at the center of the thermoplastic resin sheet with an optical region was centered, and using a circular Thomson blade with a diameter of 7 mm, the thermoplastic resin sheet was punched from the surface where no recess was formed to obtain a transmissive optical element.

[0068] (Comparative Example 4) Except for performing laser cutting in a circular shape with a diameter of 8 mm centered on the optical region so that the cutting surface of the thermoplastic resin sheet by the laser light is formed outside the transmissive optical element with respect to a virtual surface passing through the outermost edge of the obtained transmissive optical element and extending perpendicular to the thermoplastic resin sheet, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

Table 1

[0069] From Table 1, when a thermoplastic resin sheet having a circular optical region in plan view and a predetermined recess extending around the outer peripheral portion of the optical region is circularly cut by irradiating laser light so that the side surface on the optical region side of the recess remains, the cutting surface of the thermoplastic resin sheet by the laser light is a virtual surface passing through the outermost edge of the transmissive optical element and is on the same plane as or on the optical region side of the virtual surface extending perpendicular to the thermoplastic resin sheet. It can be seen that the transmissive optical elements of Examples 1 to 5 obtained in this way have high concentricity.

Industrial Applicability

[0070] According to the present invention, it is possible to provide a method for manufacturing a transmissive optical element capable of manufacturing a circular transmissive optical element with a sufficiently high concentricity.

Explanation of Signs

[0071] 10 Transmissive optical element 11 Optical region 12 Outermost edge 13 Cutting surface 100 Thermoplastic resin sheet 20 Recess 21 Wall surface 22 Bottom 30 Reference wall surface End line of EL optical region L1 Normal to the thermoplastic resin sheet at the starting point of the recess L2 Normal to the thermoplastic resin sheet at the intersection of the wall surface and the bottom P Virtual plane passing through the outermost edge and perpendicular to the thermoplastic resin sheet d Distance between EL and L1

Claims

1. A method for manufacturing a transmissive optical element using a thermoplastic resin sheet, comprising: preparing a thermoplastic resin sheet having a circular optical region in plan view and a recess extending around the outer peripheral portion of the optical region; circularly cutting the thermoplastic resin sheet by irradiating it with laser light so that the side surface of the recess on the optical region side remains, to obtain a transmissive optical element; the recess is formed in an annular shape substantially concentric with the optical region in plan view; the cutting surface of the thermoplastic resin sheet by the laser light is a virtual surface passing through the outermost edge of the transmissive optical element and is formed on the same plane as or on the optical region side of a virtual surface extending perpendicular to the thermoplastic resin sheet.

2. The method for manufacturing a transmissive optical element according to claim 1, wherein the recess is formed only on one surface of the thermoplastic resin sheet.

3. The method for manufacturing a transmissive optical element according to claim 2, wherein the laser light is irradiated from the side of the thermoplastic resin sheet where the recess is not formed.

4. The method for manufacturing a transmissive optical element according to any one of claims 1 to 3, wherein the thickness of the portion of the thermoplastic resin sheet where the recess is formed is 10 μm or more and 200 μm or less.

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