Molded sheet, manufacturing method thereof, and manufacturing method of optical element

Abstract

A method for manufacturing a molded sheet, the method including a hot-pressing step for obtaining a molded sheet by hot-press molding a sheet-form sheet material comprising a thermoplastic resin film at normal pressure using a pair of dies having a plurality of optical surface formation regions separated from each other.

Description

[Technical field]

[0001] The present invention relates to a molded sheet, a method for manufacturing a molded sheet, and a method for manufacturing an optical element. The molded sheet, the method for manufacturing a molded sheet, and the method for manufacturing an optical element are useful for manufacturing a transmission type optical element. [Background technology]

[0002] In recent years, electronic and electrical devices have become lighter, smaller, and thinner, and there is an increasing need for thinner and smaller diameter camera units and the like mounted on these electronic and electrical devices. In addition, there is a need for even higher image quality in such camera units and the like, and the lenses, prisms, and other transmissive optical elements mounted on these optical devices are also required to have high performance.

[0003] Conventionally, transmissive optical elements such as lenses used in camera units and the like have generally been manufactured by injection molding. However, when lenses are formed by injection molding, it is difficult to completely prevent weld lines from being formed in the obtained lenses. In addition, lenses obtained by injection molding are prone to birefringence. For this reason, it is difficult to sufficiently increase the ratio of the area capable of exhibiting sufficiently high optical performance in the obtained lenses, and even if a small-diameter lens with a diameter of less than 1 cm is formed by injection molding, it is difficult to make it function sufficiently as a lens.

[0004] In recent years, therefore, methods for manufacturing transmission type optical elements such as small-diameter lenses by methods other than injection molding have been considered. For example, Patent Document 1 discloses a method in which a plurality of dies are arranged in the planar direction of a resin sheet, and a plurality of lens portions are molded simultaneously. More specifically, Patent Document 1 discloses a method in which a resin sheet is placed in a positioned state on a plurality of female lower dies made of metal or the like, and a plurality of male upper dies made of metal or the like are pressed against the resin sheet to plastically deform the resin sheet and mold a plurality of lens portions simultaneously. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2000 / 012291 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned conventional technology, which is characterized by arranging multiple molds in the planar direction of a resin sheet and simultaneously molding multiple lens portions, it was not possible to efficiently manufacture a molded sheet having multiple optical surface portions that can be used as, for example, lenses, with sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence.

[0007] Therefore, an object of the present invention is to provide a molded sheet having a plurality of optical surface portions that has sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence. Another object of the present invention is to provide a method for producing a molded sheet that can efficiently produce the above molded sheet. A further object of the present invention is to provide a method for producing an optical element using the above molded sheet. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to achieve the above object, and have found that a molded sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence can be provided by hot press molding a discrete sheet material made of a thermoplastic resin film under specified conditions, thereby completing the present invention.

[0009] That is, the present invention aims to advantageously solve the above problems, and the manufacturing method of the molded sheet of the present invention is a manufacturing method of a molded sheet in which a thermoplastic resin film formed using a thermoplastic resin is hot-press molded to produce a molded sheet having a plurality of optical surface portions, and is characterized in that it includes a hot-pressing step in which a sheet material made of the thermoplastic resin film is hot-press molded under normal pressure using a pair of dies having a plurality of optical surface forming regions spaced apart from each other to obtain a molded sheet. In this way, by hot-press molding a sheet material in the form of a sheet using a pair of dies having a plurality of optical surface forming regions spaced apart from each other under normal pressure, a molded sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence can be easily manufactured. In this specification, the term "sheet-like" sheet material means that the sheet material is cut to a predetermined size and is not in a rolled-up state. In this specification, "normal pressure" refers to the air pressure at a certain point when no pressure increase or decrease is performed, and is usually equal to the atmospheric pressure at that point. More specifically, "normal pressure" refers to the pressure range under standard conditions specified in JIS Z8703:1983, which is within the range of 86 kPa to 106 kPa.

[0010] Here, the method for producing a molded sheet of the present invention preferably includes a demolding step in which, when releasing the molded sheet obtained in the heat pressing step from the pair of molds, the pair of molds are released at a temperature of (Tg-80)° C. or more and (Tg-15)° C. or less, where Tg (° C.) is the glass transition temperature of the thermoplastic resin. By carrying out the demolding step in such a predetermined temperature range, it is possible to further increase the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet, further reduce the variation in thickness accuracy, and further reduce birefringence. In the present invention, the "glass transition temperature of the thermoplastic resin" can be measured based on JIS K7121:2012.

[0011] Furthermore, in the method for producing a molded sheet of the present invention, it is preferable that in the heat pressing step, when the sheet material is pressed by the pair of dies, the sheet material does not protrude from the pair of dies. By preventing the sheet material from protruding from the pair of dies in the pressed state, the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet can be further improved, the variation in thickness accuracy can be further reduced, birefringence can be further reduced, and the production efficiency of the molded sheet can be further improved.

[0012] In the method for producing a molded sheet of the present invention, the thermoplastic resin is preferably an alicyclic structure-containing resin. If the thermoplastic resin is an alicyclic structure-containing resin, the shape precision of the optical surface portions contained in the obtained molded sheet can be further improved, the variation in thickness precision can be further reduced, and the production efficiency of the molded sheet can be further improved.

[0013] The present invention also aims to advantageously solve the above problems, and the method for manufacturing an optical element of the present invention is characterized in that a molded sheet obtained according to any one of the above-mentioned methods for manufacturing a molded sheet is separated at positions corresponding to each of the plurality of optical surface portions to obtain a plurality of optical elements. According to the manufacturing method of the present invention, an optical element having sufficiently high shape accuracy, small variation in thickness accuracy, and sufficiently small birefringence can be easily manufactured.

[0014] The present invention also aims to advantageously solve the above problems, and the molded sheet of the present invention is a disc-shaped molded sheet formed of a thermoplastic resin and having a plurality of optical surface portions, the optical surface portions being arranged at a density of 0.16 pieces / cm. 2The optical surface portion has a minimum distance of 1.0 mm or more between adjacent optical surface portions, a diameter of 1 mm or more and 15 mm or less in plan view, a phase difference of 50 nm or less, and a variation in thickness accuracy of 0.2 μm or less. Thus, if the variations in the arrangement density, minimum distance, diameter, phase difference, and thickness accuracy of the optical surface portions in the molded sheet are within a predetermined range, the optical surface portions of the molded sheet have excellent shape accuracy. Furthermore, by using such a molded sheet, an optical element with excellent optical performance can be efficiently manufactured. The "phase difference" and "variation in thickness accuracy" can be evaluated or measured using the method described in the examples.

[0015] Here, in the molded sheet of the present invention, at least one surface of the optical surface portion is preferably an aspheric surface having an inflection point in the cross section in the thickness direction. An optical surface portion having such a shape can be advantageously used as a transmission optical element such as a lens. Effect of the Invention

[0016] According to the present invention, it is possible to provide a molded sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence. Furthermore, according to the present invention, it is possible to provide a method for producing a molded sheet, which can efficiently produce the above molded sheet. Furthermore, according to the present invention, it is possible to provide a method for producing an optical element using the above molded sheet. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a cross section along the thickness direction of a molded sheet according to an example of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining a heat pressing step in a method for producing a molded sheet according to an example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the embodiment of the present invention will be described in detail. The manufacturing method of the molded sheet of the present invention can be used, for example, when manufacturing the molded sheet of the present invention. In addition, the manufacturing method of the optical element of the present invention can be suitably applied when manufacturing an optical element using a molded sheet obtained according to the manufacturing method of the molded sheet of the present invention. And, the molded sheet according to the present invention can be suitably used for manufacturing an optical element having an optical surface of various shapes without being particularly limited. Here, the "optical surface" means an interface that can exert optical actions such as reflection, refraction, and transmission on light, and its shape can be a plane, a spherical surface, an aspheric surface, a free curved surface, a lenticular surface, a Fresnel surface, and the like. In addition, examples of "optical elements" that can be suitably manufactured using the molded sheet according to the present invention include transmission type optical elements such as optical lenses and prisms. Here, the "optical lens" means a transparent body that exhibits a refraction action of light. In addition, the "prism" means a transparent polyhedron that exhibits a dispersion action, a refraction action, a total reflection action, and / or a birefringence action of light other than an optical lens. By using the molded sheet according to the present invention, a transmission type optical element having high shape accuracy and low birefringence (i.e., a small phase difference) can be efficiently obtained. In particular, the molded sheet according to the present invention can be suitably used in the manufacture of aspherical lenses having inflection points on one and / or both sides, among various shapes of optical elements, and the aspherical lenses can be suitably used, for example, as lenses for camera units of small electronic and electrical devices.

[0019] (Molded sheet) The molded sheet of the present invention is a disc-shaped molded sheet 10 having a cross-sectional shape along the thickness direction, for example as shown in Fig. 1, formed of a thermoplastic resin, and has a plurality of optical surface portions 11. The molded sheet 10 of the present invention has an arrangement density of the optical surface portions 11 of 0.16 pieces / cm 2It is required that the minimum interval P between adjacent optical surface portions 11 is 1.0 mm or more, the diameter D of the optical surface portion 11 in a plan view is 1 mm or more and 15 mm or less, the phase difference of the optical surface portion 11 is 50 nm or less, and the variation in thickness accuracy of the optical surface portion 11 is 0.2 μm or less. If the arrangement density, minimum interval, diameter, phase difference, and thickness accuracy variation of the optical surface portions are within the above ranges, the shape accuracy can be improved. Furthermore, by using such a molded sheet, optical elements with excellent optical performance can be efficiently manufactured. The shape of the optical surface portion of the molded sheet is not limited to the shape shown in Fig. 1, and can be any shape, such as a plano-convex lens, a biconvex lens, a convex meniscus lens, a plano-concave lens, a biconcave lens, and a concave meniscus lens. The optical surface portion of the molded sheet is not particularly limited, and can be suitably used as a lens, for example, by cutting it out from the molded sheet. Here, from the viewpoint of advantageous use as a transmission optical element such as a lens, it is preferable that at least one surface of the optical surface portion has a cross-sectional shape in the thickness direction that has an inflection point.

[0020] <Thermoplastic resin> Examples of the thermoplastic resin include (meth)acrylic resin, alicyclic structure-containing resin, styrene resin, polycarbonate resin, polyester resin, polyether resin, urethane resin, and thiourethane resin. Note that "(meth)acrylic" refers to acrylic and / or methacrylic. The above-mentioned thermoplastic resins may be used alone or in combination of two or more. Among these, it is preferable that the thermoplastic resin contains an alicyclic structure-containing resin, because it can further increase the shape precision of the multiple optical surface portions contained in the obtained molded sheet, further reduce the variation in thickness precision, and further increase the production efficiency of the molded sheet. It is also preferable that the thermoplastic resin contains an alicyclic structure-containing resin, because the obtained molded sheet has excellent transparency.

[0021] 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 molded sheet having excellent mechanical strength and heat resistance. The proportion of repeating units 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 even more preferably 90% by mass or more, based on the total repeating units contained in the polymer. By using an alicyclic structure-containing polymer having a proportion of repeating units having an alicyclic structure of 50% by mass or more, the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet can be further improved, the variation in thickness accuracy can be further reduced, and the production efficiency of the molded sheet can be further improved. In addition, by using an alicyclic structure-containing polymer having a proportion of repeating units having an alicyclic structure of 50% by mass or more, it is easy to obtain a molded sheet having excellent transparency and heat resistance.

[0022] Specific examples of the alicyclic structure-containing polymer include norbornene-based polymers, monocyclic cyclic olefin-based polymers, cyclic conjugated diene-based polymers, vinyl alicyclic hydrocarbon-based polymers, etc. Among these, norbornene-based polymers are preferred from the viewpoint of improving the transparency, heat resistance, and mechanical strength of the obtained molded sheet, and from the viewpoint of further improving the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet, further reducing the variation in thickness accuracy, and further improving the production efficiency of the molded sheet. Norbornene-based polymers are also preferred because they can further improve the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet, further reduce the variation in thickness accuracy, and further improve the production efficiency of the molded sheet. In this specification, these polymers refer not only to polymerization reaction products but also to their hydrogenated products.

[0023] The norbornene polymer is a polymer of a norbornene monomer or a hydrogenated product thereof. Examples of the norbornene polymer include a ring-opening polymer of a norbornene monomer, a ring-opening polymer of a norbornene monomer and another monomer capable of ring-opening copolymerization with the norbornene monomer, an addition polymer of a norbornene monomer, an addition polymer of a norbornene monomer and another monomer capable of copolymerization with the norbornene monomer, and a hydrogenated product of these polymers. Among these, a hydrogenated ring-opening polymer of a norbornene monomer (i.e., a hydrogenated ring-opening polymer of a norbornene monomer) is preferred. By using a hydrogenated ring-opening polymer of a norbornene, the transparency, heat resistance, and mechanical strength of the molded sheet can be further improved, and the mold releasability and transferability can be improved when the molded sheet is manufactured using hot press molding.

[0024] 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 (commonly known as dicyclopentadiene) and its derivatives, 7,8-benzotricyclo[4.3.0.1 2,5 ]dec-3-ene (commonly known as methanotetrahydrofluorene: 1,4-methano-1,4,4a,9a-tetrahydrofluorene) and its derivatives, tetracyclo[4.4.0.1 2,5 .1 7,10 ]dodec-3-ene (common name: tetracyclododecene) and its derivatives. Substituents that may be contained in the derivatives include alkyl groups, alkylene groups, vinyl groups, alkoxycarbonyl groups, and alkylidene groups. For example, derivatives as norbornene-based monomers include 8-methoxycarbonyl-tetracyclo[4.4.0.1 2,5 .1 7,10 ]dodec-3-ene, 8-methyl-8-methoxycarbonyl-tetracyclo[4.4.0.1 2,5 .1 7,10 ]dodec-3-ene, 8-ethylidene-tetracyclo[4.4.0.1 2,5 .1 7,10]dodec-3-ene, etc. These norbornene-based monomers may be used alone or in combination of two or more.

[0025] Other monomers capable of ring-opening copolymerization with norbornene-based monomers include monocyclic olefin monomers such as cyclohexene, cycloheptene, and cyclooctene. Other monomers capable of addition copolymerization with norbornene-based monomers include α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 1-pentene, and 1-hexene, and derivatives thereof; cycloolefins such as cyclobutene, cyclopentene, cyclohexene, cyclooctene, and 3a,5,6,7a-tetrahydro-4,7-methano-1H-indene, and derivatives thereof; 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.

[0026] The ring-opening polymers and addition polymers containing norbornene-based monomers as described above can be synthesized by polymerization in the presence of a known catalyst, and their hydrogenated products can be obtained by hydrogenation using a known hydrogenation catalyst.

[0027] Examples of the monocyclic olefin polymer, cyclic conjugated diene polymer, and vinyl alicyclic hydrocarbon polymer include those described in WO 2017 / 126599.

[0028] In addition, commercially available products may be used as the alicyclic structure-containing polymer, such as 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.

[0029] The glass transition temperature (Tg) of the thermoplastic resin is not particularly limited, but is preferably 100°C or higher, more preferably 120°C or higher, and preferably 200°C or lower, more preferably 160°C or lower. If the glass transition temperature (Tg) of the thermoplastic resin is equal to or higher than the lower limit, the shape precision of the optical surface portion of the molded sheet can be further improved, the variation in thickness precision of the optical surface portion can be reduced, and the manufacturing efficiency of the molded sheet can be improved. If the glass transition temperature (Tg) of the thermoplastic resin film is equal to or lower than the upper limit, the manufacturing efficiency of the molded sheet can be improved, and the shape precision of the optical surface portion can be further improved.

[0030] The molded 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, infrared absorbers, antioxidants, release agents, antistatic agents, carbon materials (carbon, etc.), 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.

[0031] <Optical surface section> The optical surface portion (11 in FIG. 1) has an arrangement density of 0.16 pieces / cm 2 The optical surface portion must be arranged at a density of 0.30 pieces / cm or more. 2 It is preferable that the number of particles is 0.40 / cm or more. 2 More preferably, it is 3.0 particles / cm or more. 2 It is preferable that the number of particles is 2.0 or less per cm. 2 More preferably, it is 1.0 particles / cm or less. 2 More preferably, the number is 0.60 / cm or less. 2 It is particularly preferable that the density of the optical surface portions is 0.16 pieces / cm or less. 2If the density of the optical surface portions is equal to or less than the upper limit, the shape precision can be improved, birefringence can be reduced, and the thickness precision can be further reduced.

[0032] In addition, the minimum distance between adjacent optical surface portions (P in FIG. 1) must be 1.0 mm or more, preferably 3.0 mm or more, more preferably 5.0 mm or more, and even more preferably 7.0 mm or more. If the minimum distance between the optical surface portions is 1.0 mm or more, the variation in thickness accuracy of the optical surface portions can be reduced, the shape accuracy can be increased, and birefringence can be reduced. In addition, if the minimum distance between the optical surface portions is 1.0 mm or more, the occurrence of air bubbles and air pockets in the molded sheet can be suppressed even when the sheet is produced using a molding method such as press molding. The minimum distance between the optical surface portions is usually 20 mm or less.

[0033] Furthermore, the diameter of the optical surface portion in plan view (D in FIG. 1) must be 1 mm or more and 15 mm or less, and the diameter of the optical surface portion is preferably 3 mm or more and 9 mm or less. If the diameter of the optical surface portion is within the above range, the variation in thickness accuracy of the optical surface portion can be reduced, and the shape accuracy can be increased.

[0034] In addition, the thickness of the center of the optical surface (H in Fig. 1) mid ) is preferably 50 μm or more, more preferably 100 μm or more, and is preferably 1500 μm or less, and more preferably 1000 μm or less. If the thickness of the center of the optical surface portion is within the above range, it can be advantageously used as a transmission type optical element such as a lens.

[0035] Furthermore, the variation in thickness precision of the optical surface portion must be 0.2 μm or less, and is preferably 0.1 μm or less. If the variation in thickness precision is equal to or less than the upper limit mentioned above, the birefringence in the optical surface portion can be reduced.

[0036] The phase difference of the optical surface portion must be 50 nm or less, and is preferably 20 nm or less. If the phase difference is equal to or less than the upper limit, the birefringence in the optical surface portion is sufficiently small. Furthermore, if the phase difference is equal to or less than the upper limit, the variation in thickness accuracy of the optical surface portion can be reduced, and the shape accuracy can be improved.

[0037] Here, the molded sheet is thinnest part (H in FIG. 1). min ) is preferably 50 μm or more, more preferably 100 μm or more, and preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. If the thickness of the thinnest part is equal to or less than the upper limit, the variation in thickness precision of the optical surface portion can be reduced and the shape precision can be improved. Furthermore, if the thickness of the thinnest part is equal to or more than the lower limit, the strength of the molded sheet can be sufficiently increased.

[0038] (Method of manufacturing molded sheet) The method for producing a molded sheet of the present invention is a method for producing a molded sheet having a plurality of optical surface portions by hot press molding a thermoplastic resin film formed using a thermoplastic resin, and can be used, for example, when producing the molded sheet of the present invention described above, without being particularly limited. The method for producing a molded sheet of the present invention is characterized in that it includes a "heat press step" in which a sheet-like sheet material made of a thermoplastic resin film is hot press molded under normal pressure using a pair of dies having a plurality of optical surface forming regions separated from each other to obtain a molded sheet. Furthermore, the method for producing a molded sheet of the present invention preferably includes a "mold release step" in which the molded sheet obtained in the heat press step is released from the pair of dies. In the method for producing a molded sheet of the present invention, in the "heat press step", a sheet-like sheet material is hot press molded under normal pressure using a pair of dies having a plurality of optical surface forming regions separated from each other, so that a molded sheet having sufficiently high shape accuracy, small variation in thickness accuracy, and sufficiently small birefringence and having a plurality of optical surface portions can be easily produced.

[0039] <Molded sheet> The molded sheet produced by the molded sheet production method of the present invention is not particularly limited as long as it is a sheet having a plurality of optical surface portions spaced apart from each other. In particular, it is preferable that the molded sheet has the same properties as the molded sheet of the present invention described above.

[0040] <Thermoplastic resin film> The thermoplastic resin used for the thermoplastic resin film is not particularly limited, and examples thereof include the same thermoplastic resin as that of the molded sheet of the present invention described above. Note that the term "film" refers to an object having a shape in which the front and back surfaces (i.e., main surfaces) face each other at a distance equal to the thickness of the object.

[0041] The method for producing the thermoplastic resin film is not particularly limited, and any suitable method known in the art can be used. For example, a molding material for producing a thermoplastic resin film can be obtained by mixing predetermined components, and then the thermoplastic resin film can be obtained by melt extrusion molding, melt casting molding, injection molding, or the like.

[0042] The thickness of the thermoplastic resin film can be appropriately selected according to the diameter of the optical surface portion of the molded sheet to be produced.For example, the thickness of the thermoplastic resin film is usually 50 μm or more, preferably 70 μm or more, and usually 500 μm or less, preferably 400 μm or less.In addition, when the thickness of the thermoplastic resin film varies, the thickness of the thermoplastic resin film corresponds to the simple arithmetic average value of the thickness at multiple randomly selected measurement points.

[0043] The thermoplastic resin film can then be cut into a desired size, for example, A4 size to 50 cm×50 cm, to form a sheet material in the form of a single sheet.

[0044] <Heat pressing process> In the heat pressing step, a sheet material made of a thermoplastic resin film is heat-pressed under normal pressure using a pair of dies having a plurality of optical surface forming regions spaced apart from each other. In addition, when starting the heat pressing step, an arrangement operation of setting the sheet material in a heat pressing device may be performed. FIG. 2 shows a schematic diagram for explaining the heat pressing step in the manufacturing method of a molded sheet according to one example of the present invention. As shown in FIG. 2, in the heat pressing step according to this example, a sheet material 10' is heat-pressed using a pair of dies 1 consisting of an upper die 1A and a lower die 1B. Then, as shown in the lower diagram of FIG. 2, in a state in which the sheet material 10' is pressed by the pair of dies 1, it is preferable that the sheet material 10' does not protrude from the pair of dies 1. By preventing the sheet material 10' from protruding from the pair of dies 1 in the pressed state, the shape accuracy of the plurality of optical surface portions contained in the obtained molded sheet can be further improved, the variation in thickness accuracy can be further reduced, and further birefringence can be further reduced, and the production efficiency of the molded sheet can be further improved. In addition, in the manufacturing method of the molded sheet of the present invention, the occurrence of birefringence in the optical surface portion of the obtained molded sheet can be suppressed by subjecting the thermoplastic resin film to hot pressing using a mold, without using an injection molding method.

[0045] [Mold] The pair of molds 1 is not particularly limited as long as at least one of them has a plurality of cavities that are the optical surface portion forming regions, and molds of any shape, such as flat molds, can be used. The material used for the mold can be any known material. For example, carbon steel, stainless steel, or alloys based on these can be used. Among them, from the viewpoint of workability and hardness, stainless steel such as STAVAX (registered trademark) material (manufactured by Woodholm) is preferred. From the viewpoint of mold releasability, it is preferable to use a mold whose surface is plated with metals such as chromium, titanium, and nickel, and it is more preferable to use a mold whose surface is plated with electroless nickel-phosphorus plating.

[0046] At least one of the molds used in the manufacturing method of the present invention has a plurality of cavities arranged discretely in a planar direction of the mold. The plurality of cavities are preferably arranged at equal intervals in the planar direction of the mold. Here, both of the pair of dies may have multiple cavities. This is because by using a pair of dies each having a cavity, a molded sheet having a shape on both sides can be efficiently manufactured. Note that the shapes of the pair of dies may be the same or different depending on the shape of the molded sheet to be manufactured.

[0047] The cavity has a density of 0.16 pieces / cm 2 It is preferable that the number of particles is 0.30 / cm or more. 2 More preferably, it is 0.40 particles / cm or more. 2 More preferably, it is 3.0 particles / cm or more. 2 It is preferable that the number of particles is 2.0 or less per cm. 2 More preferably, it is 1.0 particles / cm or less. 2 More preferably, the number is 0.60 / cm or less. 2 It is particularly preferable that the cavity density is 0.16 / cm or less. 2 If the density of the cavities is equal to or less than the upper limit, the shape precision of the obtained molded sheet can be improved, birefringence can be reduced, and the thickness precision can be further reduced.

[0048] In addition, the minimum distance between adjacent cavity portions (corresponding to P in FIG. 1) is preferably 1.0 mm or more, more preferably 3.0 mm or more, even more preferably 5.0 mm or more, and particularly preferably 7.0 mm or more. If the minimum distance (P) between the cavity portions is 1.0 mm or more, the variation in thickness accuracy of the optical surface portion of the obtained molded sheet can be reduced, the shape accuracy can be increased, and further, birefringence can be reduced. In addition, if the minimum distance between the cavity portions is 1.0 mm or more, the occurrence of air bubbles and air pockets in the molded sheet can be suppressed. The minimum distance between the cavity portions is usually 20 mm or less.

[0049] Furthermore, the diameter of the cavity in plan view (corresponding to D in Fig. 1) is preferably 1 mm or more and 15 mm or less, more preferably 3 mm or more, and preferably 9 mm or less. If the diameter of the cavity is within the above range, it is possible to reduce the variation in thickness accuracy of the optical surface portion of the obtained molded sheet, and to increase the shape accuracy.

[0050] In addition, the depth of the center of the cavity when the mold is closed (closed mold state) (the distance in the direction corresponding to the thickness direction at the center of the optical surface portion to be formed; H mid ) is preferably 50 μm or more, more preferably 100 μm or more, and is preferably 1500 μm or less, and more preferably 1000 μm or less. If the depth of the center of the cavity is within the above range, the optical surface portion of the obtained molded sheet can be advantageously used as a transmission type optical element such as a lens.

[0051] Furthermore, the mold must have a minimum distance (H min) is preferably 50 μm or more, more preferably 100 μm or more, and preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. If the minimum interval is equal to or less than the upper limit, the variation in thickness accuracy of the optical surface portion of the obtained molded sheet can be reduced and the shape accuracy can be improved. Also, if the minimum interval is equal to or more than the lower limit, the strength of the obtained molded sheet can be sufficiently ensured.

[0052] [Press temperature] In the heat pressing step, the pressing temperature (mold temperature) when the thermoplastic resin film is heat pressed with a pair of molds is preferably 40°C higher than the glass transition temperature (Tg) of the thermoplastic resin (Tg+40°C) or higher, more preferably 50°C higher than the glass transition temperature (Tg+50°C) or higher, and even more preferably 55°C higher than the glass transition temperature (Tg+55°C) or higher. If the pressing temperature is equal to or higher than the lower limit, the variation in thickness accuracy of the optical surface portion of the obtained molded sheet can be reduced and the shape accuracy can be increased. From the viewpoint of efficiently producing the molded sheet, the pressing temperature is preferably equal to or lower than 80°C higher than the glass transition temperature (Tg+80°C). The pressing temperature is not particularly limited, and can be appropriately adjusted by controlling the temperature of the mold according to a known general method (for example, a temperature control method using a known heater, cooler, etc.).

[0053] [Press pressure] In the heat pressing step, it is preferable that the pressing pressure when the thermoplastic resin film is heat pressed with a mold is increased to a final pressing pressure at a predetermined pressure increase rate and then optionally maintained at the final pressing pressure for a predetermined period of time.

[0054] -Boost speed- Here, the average pressure increase rate of the press pressure is preferably 0.1 MPa / sec or less, more preferably 0.07 MPa / sec or less, and even more preferably 0.05 MPa / sec or less. If the average pressure increase rate is equal to or less than the upper limit, the birefringence of the optical surface portion of the obtained molded sheet can be reduced and the shape precision can be improved. From the viewpoint of efficiently producing the molded sheet, the average pressure increase rate is preferably 0.04 MPa / sec or more.

[0055] -Final press pressure- The final pressing pressure is not particularly limited and can be, for example, 1 MPa to 10 MPa. If the final pressing pressure is within the above range, the shape precision of the optical surface portion of the obtained molded sheet can be further improved, and the variation in thickness precision and birefringence can be further reduced.

[0056] [Other press conditions] The pressing time in the heat pressing step is not particularly limited and can be appropriately determined depending on the type and size of the thermoplastic resin film used, the shape and size of the target molded sheet, etc. For example, the time for increasing the pressing pressure to the final pressing pressure can be 20 seconds or more and 300 seconds or less, and the time for holding the pressing pressure at the final pressing pressure can be 0 seconds or more and 180 seconds or less.

[0057] <Mold release process> In the demolding process, when the molded sheet obtained in the heat pressing process is released from the pair of molds, the pair of molds are demolded at a temperature of (Tg-80)°C or higher and (Tg-15)°C or lower (hereinafter, sometimes referred to as the "mold releasing temperature"). By carrying out such a process, the shape accuracy of the multiple optical surface portions contained in the obtained molded sheet can be further improved, the variation in thickness accuracy can be further reduced, and birefringence can be further reduced. The start point of the demolding process can be, for example, the time when temperature control for cooling the mold is started after a predetermined time has elapsed from the start of the heat pressing process, or the time when heat input to the mold is stopped after a predetermined time has elapsed from the start of the heat pressing process.

[0058] [Release temperature] The demolding temperature must be equal to or lower than the glass transition temperature (Tg) of the thermoplastic resin, and is preferably equal to or lower than 15°C lower than the glass transition temperature (Tg-15°C), more preferably equal to or lower than 20°C lower than the glass transition temperature (Tg-20°C), and even more preferably equal to or lower than 30°C lower than the glass transition temperature (Tg-30°C). The demolding temperature is preferably equal to or higher than 80°C lower than the glass transition temperature (Tg-80°C), and more preferably equal to or higher than 75°C lower than the glass transition temperature (Tg-75°C). If the demolding temperature is equal to or lower than the upper limit, the mold is easily demolded, and the shape accuracy of the optical surface portion of the obtained molded sheet can be effectively improved. Furthermore, if the demolding temperature is equal to or lower than the upper limit, the variation in the thickness accuracy of the optical surface portion of the obtained molded sheet can be reduced, and birefringence can be reduced. Furthermore, if the demolding temperature is equal to or lower than the upper limit, the occurrence of problems during demolding can be suppressed, and the manufacturing efficiency of the molded sheet can be further improved. Furthermore, if the demolding temperature is equal to or higher than the lower limit, the time required for cooling the pair of molds and for adjusting the temperature during heating in the subsequent hot pressing process can be shortened, thereby further improving the production efficiency of the molded sheet.

[0059] [Other release conditions] The time required to cool the mold to the demolding temperature (mold cooling time) and the mold cooling rate are not particularly limited and can be appropriately determined depending on the type and size of the disc-shaped sheet material, the shape and size of the optical surface portion of the desired molded sheet, etc. For example, the mold cooling time can be 10 seconds or more and 100 seconds or less, and the mold cooling rate can be 50° C. / min or more and 300° C. / min or less.

[0060] In the demolding step, the mold is cooled to a demolding temperature, and then the hot-pressed film is demolded from the mold to obtain a molded sheet.

[0061] (Method of manufacturing optical elements) The method for producing an optical element of the present invention is characterized by including an optical element separation step of separating a molded sheet obtained according to the production method of the present invention at positions corresponding to each of a plurality of optical surface portions to obtain a plurality of optical elements. According to the production method of the present invention, it is possible to easily produce optical elements having sufficiently high shape accuracy, small variation in thickness accuracy, and sufficiently small birefringence.

[0062] <Optical element separation process> In the optical element separation step, a plurality of optical elements are separated from the molded sheet obtained according to the manufacturing method of the present invention. The separation method is not particularly limited, and the optical elements can be separated one by one from the molded sheet by any known method such as punching with a punching die or laser cutting. EXAMPLES

[0063] The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is not limited to these examples. In the examples and comparative examples, the glass transition temperature of the thermoplastic resin was measured as follows. In the examples and comparative examples, the shape accuracy of the optical surface portion of the molded sheet, the variation in thickness accuracy and retardation, and the productivity of the molded sheet were evaluated as follows. In the examples and comparative examples, all of the operations from placement to demolding were performed at normal pressure, i.e., under conditions where the inside of the mold was not pressurized or reduced pressure.

[0064] <Glass transition temperature of thermoplastic resin> The glass transition temperature (Tg) of the thermoplastic resin was measured using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation, "DSC6220") at a temperature rise rate of 10°C / min in accordance with JIS K7121:2012.

[0065] <Shape accuracy> The optical surface portion of the molded sheet was punched out to obtain an optical lens as a measurement sample. The optical lenses obtained according to the examples and comparative examples were aspheric lenses in which the front and back surfaces each had an aspheric shape with an inflection point in the cross section along the thickness direction of the optical lens. Next, for 300 measurement samples of the punched optical surface portions, a shape measuring instrument (Panasonic, "UA-3P") was used to measure the PV value (the maximum error in the shape of the surface of the measurement sample relative to the reference surface, i.e., the difference between the highest point (Peak) and the lowest point (Valley) within the measurement range) based on the design value of the optical surface. The simple average of the measured PV values ​​was then evaluated as shape accuracy according to the following criteria. A: Simple average value of PV value is 0.5μm or less B: Simple average value of PV value is more than 0.5 μm and less than 1.0 μm C: Simple average value of PV value is more than 1.0μm and less than 2.0μm D: Simple average value of PV value is more than 2.0μm <Variation in thickness accuracy> The optical surface portion of the molded sheet was punched out to obtain an optical lens as a measurement sample. Next, the thickness of the center of 300 measurement samples of the obtained optical lenses was measured using a shape measuring instrument (manufactured by Panasonic, "UA-3P"), and the standard deviation of the measured thickness was evaluated as the variation in thickness precision according to the following criteria. A: Standard deviation is 0.1 μm or less B: Standard deviation is more than 0.1μm and less than 0.2μm C: Standard deviation is over 0.2μm <Phase difference> The optical surface portion of the molded sheet was punched out to obtain an optical lens as a measurement sample. Next, the phase difference of 300 measurement samples out of the obtained optical lenses was measured using a resin molded lens inspection system ("WPA-100" manufactured by Photonics Lattice, Inc.). The retardation values ​​were normalized to the measurement wavelength (543 nm) and the simple average value was used to evaluate the film according to the following criteria: A smaller retardation value means a smaller birefringence. A: Simple average phase difference is 20 nm or less B: Simple average phase difference is more than 20 nm and less than 50 nm C: Simple average phase difference is more than 50 nm

[0066] <Continuous productivity> The total downtime of the equipment due to problems that occurred when processing 100 pieces of sheet material into formed sheets was evaluated according to the following criteria. A: Downtime less than 30 minutes B: Downtime: 30 minutes or more but less than 120 minutes C: Stop time 120 minutes or more

[0067] Example 1 Thermoplastic resin containing a norbornene-based ring-opening polymer hydride (ZEONEX E48R (manufactured by Zeon Corporation), glass transition temperature: 139°C) was placed in a film extrusion molding machine (single-screw extruder, φ=20mm, manufactured by GSI Creos Corporation), melted at 260°C, extruded from a T-die, and cooled to obtain a thermoplastic resin film with a thickness of 500μm and a width of 295mm, with a length of 100m or more. The thermoplastic resin film thus obtained was cut into 250mm squares and used as a sheet material in the form of a leaf. The sheet material obtained as described above was set in a heat press molding machine equipped with a pair of 300 mm square dies with a temperature control device (placement operation). The pair of dies used had the properties shown in Table 1. Then, the temperature of the mold was raised to the pressing temperature shown in Table 1, and the sheet material in the form of a disc was then heat-pressed under the conditions shown in Table 1 while increasing the pressure to 9.5 MPa at a pressure increase rate of 0.045 MPa / sec (heat pressing process). Furthermore, while the sheet material was still pressed, the pair of dies were cooled to 100°C to cool the molded sheet sandwiched between the dies. Thereafter, the pair of dies were opened and the molded sheet having the properties shown in Table 1 was peeled off from the pair of dies (mold releasing process). Note that the diameter of the optical surface portion in the molded sheet corresponds to the diameter D of the cavity portion in the die, the minimum interval between the optical surface portions corresponds to the minimum interval P of the cavity portion in the die, the arrangement density of the optical surface portions corresponds to the arrangement density of the cavity portion in the die, and the thickness of the center of the optical surface portion corresponds to the depth H of the center of the cavity portion in a closed mold state. mid The thickness of the thinnest part of the molded sheet corresponds to the minimum distance H between the molded sheet forming surfaces in the closed mold. min corresponds to. The obtained molded sheet was subjected to various evaluations as described above. The results are shown in Table 1 together with the time (cycle time) from placement of the sheet material to release of the molded sheet.

[0068] (Examples 2 to 4) A molded sheet was produced and various evaluations were carried out in the same manner as in Example 1, except that the pair of dies was changed to dies having the properties shown in Table 1. The results are shown in Table 1.

[0069] (Examples 5 to 7) Molded sheets were produced and various evaluations were carried out in the same manner as in Example 1, except that the demolding temperature in the demolding step was changed to the temperature shown in Table 1. The results are shown in Table 1.

[0070] Example 8 A molded sheet was produced in the same manner as in Example 1, except that a sheet material cut into a 400 mm square was used, and various evaluations were performed. The results are shown in Table 1. In the heat pressing process according to this example, the edge of the sheet material in the form of a sheet protruded from the pair of dies.

[0071] Example 9 A thermoplastic resin film containing a norbornene-ethylene random copolymer obtained by random addition polymerization using norbornene and ethylene as monomers (TOPAS6013 (Polyplastics), glass transition temperature: 138°C) was used, and molded sheets were produced in the same manner as in Example 1, except that the pressing temperature was changed to the temperature shown in Table 1, and various evaluations were performed. The results are shown in Table 1.

[0072] Example 10 A molded sheet was produced in the same manner as in Example 1, except that a polycarbonate resin (Wonderlite PC-115 (manufactured by Asahi Kasei Corporation), glass transition temperature: 145°C) was used as the thermoplastic resin film and the pressing temperature was changed to the temperature shown in Table 1, and various evaluations were performed. The results are shown in Table 1.

[0073] Example 11 A molded sheet was produced in the same manner as in Example 1, except that a polymethyl methacrylate resin (Delpet 80NH (manufactured by Asahi Kasei Chemicals Corporation), glass transition temperature: 100°C) was used as the thermoplastic resin film and the pressing temperature was changed to the temperature shown in Table 1, and various evaluations were performed. The results are shown in Table 1.

[0074] Example 12 A polyester resin (OKP-1 (Osaka Gas Chemicals), glass transition temperature: 132°C) was used as the thermoplastic resin film, and molded sheets were produced in the same manner as in Example 1, except that the pressing temperature was changed to the temperatures shown in Table 1, and various evaluations were carried out. The results are shown in Table 1.

[0075] Comparative Example 1 A molded sheet was produced and various evaluations were carried out in the same manner as in Example 1, except that the pair of dies was changed to dies having the properties shown in Table 1. The results are shown in Table 1.

[0076] Comparative Example 2 The heat press molding machine equipped with a pair of 300 mm square dies was changed to a heat press molding machine equipped with four pairs of 100 mm square dies arranged in a 2 x 2 configuration with the distance between the dies set to 20 mm. Using this heat press molding machine, an attempt was made to produce a molded sheet in the same manner as in Example 1, except that a sheet-like sheet material was simultaneously molded with four pairs of dies. However, the sheet material broke in the gap between the dies during molding, and a molded sheet could not be produced.

[0077] [Table 1]

[0078] From Table 1, it can be seen that the molded sheets of Examples 1 to 12 have multiple optical surface portions with sufficiently high shape accuracy, small variation in thickness accuracy, and sufficiently small birefringence. Furthermore, it can be seen that the molded sheets of Examples 1 to 12 were excellent in continuous productivity. Moreover, it can be seen that the molded sheet of Comparative Example 1 had low shape accuracy of the optical surface portions, large variation in thickness accuracy, and large birefringence. Furthermore, it can be seen that the molded sheet of Comparative Example 1 had poor continuous productivity. [Industrial Applicability]

[0079] According to the present invention, it is possible to provide a molded sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small variation in thickness accuracy, and low birefringence. Furthermore, according to the present invention, it is possible to provide a method for producing a molded sheet, which can efficiently produce the above molded sheet. Furthermore, according to the present invention, it is possible to provide a method for producing an optical element using the above molded sheet. [Explanation of symbols]

[0080] 1 pair of molds 1A Upper mold 1B Lower mold 10 Molded Sheet 10' Single Sheet Material 11 Optical surface section

Claims

1. A method for producing a molded sheet, comprising the steps of: hot press molding a thermoplastic resin film formed using a thermoplastic resin to produce a molded sheet having a plurality of optical surface portions, a heat pressing step of heat-pressing the sheet material made of the thermoplastic resin film under normal pressure using a pair of dies having a plurality of optical surface forming regions spaced apart from each other to obtain a molded sheet, The arrangement density of the cavity portion, which is the optical surface forming region, is 0.16 pieces / cm ２ 2.0 pieces / cm or more ２ is as follows: The glass transition temperature of the thermoplastic resin is Tg (°C), A mold releasing step is included in which, when releasing the molded sheet obtained in the heat pressing step from the pair of molds, the pair of molds are released at a temperature of (Tg-80) ° C. or more and (Tg-20) ° C. or less, In the heat pressing step, when the sheet material is pressed by the pair of dies, the sheet material does not protrude from the pair of dies. A method for producing a molded sheet.

2. The method for producing a molded sheet according to claim 1 , wherein the thermoplastic resin is a resin containing an alicyclic structure.

3. A method for manufacturing an optical element, comprising an optical element separation step of separating the molded sheet obtained according to the method for manufacturing a molded sheet according to claim 1 or 2 at positions corresponding to each of the optical surface portions to obtain a plurality of optical elements.

Images