Molding sheet, method for producing molding sheet, and method for producing optical element

Abstract

The present invention relates to a method for manufacturing a molded sheet, comprising: a hot pressing step, using a pair of molds having a plurality of optical surface forming areas separated from each other, hot pressing and molding a single-piece sheet formed by a thermoplastic resin film under normal pressure to obtain a molded sheet.

Description

Technical Field

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

[0002] In recent years, electronic and electrical equipment has been moving towards lighter weight, smaller size, and thinner profiles, and there is a growing demand for thinner and smaller-diameter camera units, etc., which are installed in these electronic and electrical equipment. In addition, such camera units, etc., are required to have higher image quality, and the transmissive optical elements such as lenses and prisms that these optical devices have are also required to have high performance.

[0003] Transmissive optical elements such as lenses used in camera units and the like have been generally manufactured by injection molding. However, when a lens is formed by injection molding, it is difficult to completely suppress the weld line formed in the obtained lens. In addition, the lens obtained by injection molding is prone to birefringence. Therefore, in the obtained lens, it is difficult to fully increase the proportion of the area that can fully exert high optical performance. Even if a small diameter lens such as a lens with a diameter of less than 1 cm is formed by injection molding, it is difficult to fully function as a lens.

[0004] Therefore, in recent years, people have begun to study methods for manufacturing small-diameter lenses and other transmissive optical elements by methods other than injection molding. For example, Patent Document 1 discloses the following method: a plurality of molds are arranged in the plane direction of a resin sheet, and a plurality of lens portions are molded simultaneously. More specifically, the method disclosed in Patent Document 1 is: a resin is placed in a positioned state on a plurality of lower molds of negative molds formed of metal or the like, and a plurality of upper molds of positive molds formed of metal or the like are pressed to cause plastic deformation of the resin sheet to mold a plurality of lens portions simultaneously.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent document 1: International Publication No. 2000 / 012291. Summary of the invention

[0008] Problem that the invention aims to solve

[0009] However, in the above-mentioned prior art characterized by arranging a plurality of molds in the planar direction of a resin sheet and simultaneously performing mold molding on a plurality of lens portions, when manufacturing a molded sheet having a plurality of optical planar portions that can be used as a lens, etc., it is not possible to efficiently manufacture a molded sheet having a plurality of optical planar portions with sufficiently high shape accuracy, small deviation in thickness accuracy, and low birefringence.

[0010] Therefore, an object of the present invention is to provide a molded sheet having a plurality of optical planar portions having sufficiently high shape accuracy, small variations in thickness accuracy, and low birefringence.

[0011] Another object of the present invention is to provide a method for producing a molded sheet capable of efficiently producing the above-mentioned molded sheet.

[0012] Furthermore, an object of the present invention is to provide a method for producing an optical element using the above-mentioned molding sheet.

[0013] Solutions for solving problems

[0014] The present inventors have conducted intensive research to achieve the above-mentioned purpose. Then, the present inventors have found that by heat-pressing a single-piece sheet formed of a thermoplastic resin film under specified conditions, a molded sheet having a plurality of optical planar portions with sufficiently high shape accuracy, small deviation in thickness accuracy, and low birefringence can be provided, thereby completing the present invention.

[0015] That is, the purpose of the present invention is to advantageously solve the above-mentioned problem. The manufacturing method of the molding sheet of the present invention is characterized in that a molding sheet having a plurality of optical surface portions is manufactured by hot pressing a thermoplastic resin film formed using a thermoplastic resin, and the manufacturing method comprises: a hot pressing step, using a pair of molds having a plurality of optical surface forming regions separated from each other, hot pressing a monolithic sheet formed by the thermoplastic resin film under normal pressure to obtain a molding sheet. In this way, by hot pressing a monolithic sheet under normal pressure using a pair of molds having a plurality of optical surface forming regions separated from each other, it is possible to easily manufacture a molding sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small deviation in thickness accuracy, and low birefringence.

[0016] In addition, in this specification, the sheet being "in a single sheet form" means that the sheet is cut into a predetermined size and is in an unwound state.

[0017] In addition, in this specification, "normal pressure" refers to the air pressure at a certain location when no pressure is applied or reduced, and is generally the same as the atmospheric pressure at that location. More specifically, "normal pressure" refers to the pressure range under standard conditions specified in JIS Z8703:1983, that is, the air pressure is within the range of 86 kPa or more and 106 kPa or less.

[0018] Here, the method for producing a molded sheet of the present invention preferably includes: a demolding step, wherein the glass transition temperature of the thermoplastic resin is set to Tg (°C), and when the molded sheet obtained in the hot pressing step is demolded 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. By performing the demolding step within the prescribed temperature range, the shape accuracy of the plurality of optical planar portions contained in the obtained molded sheet can be made higher, the deviation of the thickness accuracy can be made smaller, and the birefringence can be made smaller.

[0019] In the present invention, “glass transition temperature of a thermoplastic resin” can be measured based on JIS K7121:2012.

[0020] The method for manufacturing a molded sheet of the present invention is preferably such that, in the hot pressing step, the single-piece sheet is not extruded from the pair of dies while the single-piece sheet is being pressed by the pair of dies. By preventing the single-piece sheet from being extruded from the pair of dies during the pressing state, the shape accuracy of the plurality of optical planar portions contained in the obtained molded sheet can be made higher, the deviation of the thickness accuracy can be made smaller, and the birefringence can be made smaller, thereby improving the production efficiency of the molded sheet.

[0021] Furthermore, in the method for manufacturing a molded sheet of the present invention, the thermoplastic resin is preferably a resin containing an alicyclic structure. If the thermoplastic resin is a resin containing an alicyclic structure, the shape accuracy of the plurality of optical planar portions contained in the obtained molded sheet can be higher, the deviation of the thickness accuracy can be smaller, and the production efficiency of the molded sheet can be improved.

[0022] In addition, the present invention aims to solve the above-mentioned problems advantageously, and the manufacturing method of the optical element of the present invention is characterized in that the molded sheet obtained by the manufacturing method of any of the above-mentioned molded sheets is separated at the positions corresponding to the plurality of optical planar portions to obtain a plurality of optical elements. According to the manufacturing method of the present invention, an optical element with sufficiently high shape accuracy, small deviation in thickness accuracy, and sufficiently small birefringence can be easily manufactured.

[0023] Furthermore, the present invention aims to advantageously solve the above-mentioned problems. The molded sheet of the present invention is characterized in that it is a single-piece molded sheet formed of a thermoplastic resin and having a plurality of optical planar portions, wherein the optical planar portions are arranged at a density of 0.16 pieces / cm 2Above, the minimum spacing between adjacent optical planar portions is more than 1.0 mm, the diameter of the optical planar portion is more than 1 mm and less than 15 mm when viewed from above, the phase difference of the optical planar portion is less than 50 nm, and the deviation of the thickness accuracy of the optical planar portion is less than 0.2 μm. Like this, if the setting density, minimum spacing, diameter, phase difference, and thickness accuracy deviation of the optical planar portion of the molding sheet are within the specified range, the shape accuracy of the optical planar portion of the molding sheet is excellent. And then, by using this molding sheet, an optical element with excellent optical performance can be efficiently manufactured.

[0024] In addition, the "phase difference" and the "variation in thickness accuracy" can be evaluated or measured using the methods described in the Examples.

[0025] Here, in the molded sheet of the present invention, it is preferred that at least one surface of the optical surface portion is an aspherical surface having an inflection point in the cross-sectional shape 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.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide a molded sheet having a plurality of optical planar portions having sufficiently high shape accuracy, small variations in thickness accuracy, and low birefringence.

[0028] Furthermore, according to the present invention, it is possible to provide a method for producing a molded sheet capable of efficiently producing the above-mentioned molded sheet.

[0029] Furthermore, according to the present invention, a method for manufacturing an optical element using the above-mentioned molding sheet can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic cross-sectional view showing a cross section of a molded sheet along the thickness direction according to an example of the present invention.

[0031] Figure 2 This is a schematic diagram for explaining a hot pressing step in a method for producing a molded sheet according to an example of the present invention. DETAILED DESCRIPTION

[0032] Hereinafter, the embodiments of the present invention will be described in detail. The method for manufacturing the molding sheet of the present invention can be used, for example, when manufacturing the molding sheet of the present invention. In addition, the method for manufacturing the optical element of the present invention can be preferably applied when manufacturing an optical element using the molding sheet obtained by the method for manufacturing the molding sheet of the present invention. Moreover, the molding sheet of the present invention can be preferably used for the manufacture of optical elements having optical surfaces of various shapes, without particular limitation. Here, "optical surface" means an interface that can produce optical effects such as reflection, refraction and transmission of light, and as its shape, plane, spherical surface, aspherical surface, free-form surface, lenticular lens and Fresnel lens can be cited. In addition, as an "optical element" that can be preferably manufactured using the molding sheet of the present invention, a transmission type optical element such as an optical lens and a prism can be cited. Here, "optical lens" means a transparent body that exhibits the refraction of light. In addition, "prism" means a transparent polyhedron that exhibits the dispersion, refraction, total reflection and / or birefringence of light other than an optical lens. If the molding sheet of the present invention is used, a transmission type optical element with high shape accuracy and low birefringence (i.e., small phase difference) can be efficiently obtained. In particular, among optical elements of various shapes, the molding sheet of the present invention can be used to manufacture an aspheric lens having a bending point on one side and / or both sides. Moreover, the aspheric lens can be preferably used as a lens of a camera unit of a small electronic and electrical device, for example.

[0033] (Molding piece)

[0034] The molded sheet of the present invention is formed into a cross-sectional shape in the thickness direction, for example Figure 1 The single-piece molded sheet 10 formed of a thermoplastic resin as shown in the figure has a plurality of optical planar portions 11. The molded sheet 10 of the present invention needs to have a density of 0.16 pieces / cm 2 The above, the minimum interval P between the adjacent optical planar portions 11 is more than 1.0mm, the diameter D of the optical planar portion 11 is more than 1mm and less than 15mm when viewed from above, the phase difference of the optical planar portion 11 is less than 50nm, and the deviation of the thickness accuracy of the optical planar portion 11 is less than 0.2μm. If the setting density, minimum interval, diameter, phase difference, and thickness accuracy of the optical planar portion are within the above range, the shape accuracy can be improved. And then, by using this molding sheet, an optical element with excellent optical performance can be efficiently manufactured.

[0035] In addition, the shape of the optical surface portion of the molded sheet is not limited to Figure 1The shape shown can be any shape such as a plano-convex lens, a biconvex lens, a meniscus convex lens, a plano-concave lens, a biconcave lens, and a meniscus concave lens. Moreover, the optical planar portion of the molded sheet is not particularly limited, and can be used as a lens cut out from the molded sheet, for example. Here, from the viewpoint of being able to be advantageously used as a transmission optical element such as a lens, it is preferred that at least one surface of the optical planar portion has a cross-sectional shape with an inflection point in the thickness direction.

[0036] <Thermoplastic resin>

[0037] Examples of the thermoplastic resin include (meth) acrylic resin, resins containing an alicyclic structure, styrene resins, polycarbonate resins, polyester resins, polyether resins, polyurethane resins, and polythiourethane resins. In addition, "(meth) acrylic acid" refers to acrylic acid and / or methacrylic acid. Moreover, the above-mentioned thermoplastic resins may be used alone or in combination of two or more.

[0038] Among these, from the viewpoint that the shape accuracy of the multiple optical planar portions contained in the obtained molded sheet can be higher, the deviation of the thickness accuracy can be smaller, and then the production efficiency of the molded sheet can be improved, it is preferred that the thermoplastic resin contains a resin containing an alicyclic structure. In addition, from the viewpoint that the transparency of the obtained molded sheet is excellent, it is preferred that the thermoplastic resin contains a resin containing an alicyclic structure.

[0039] The resin containing an alicyclic structure refers to 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 the side chain. Among them, from the viewpoint of easily obtaining a molded sheet with excellent mechanical strength and heat resistance, a polymer having a cycloalkane structure in the main chain is preferred. The proportion of repeating units having an alicyclic structure in the polymer constituting the resin containing an alicyclic structure (hereinafter also referred to as "polymer containing an alicyclic structure") is not particularly limited, and is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more relative to all repeating units contained in the polymer. By using a polymer containing an alicyclic structure having a ratio of more than 50% by mass of repeating units having an alicyclic structure, the obtained molded sheet contains a plurality of optical planar portions with higher shape accuracy, smaller deviation in thickness accuracy, and thus can improve the production efficiency of the molded sheet. In addition, by using a polymer containing an alicyclic structure having a ratio of more than 50% by mass of repeating units having an alicyclic structure, it is easy to obtain a molded sheet with excellent transparency and heat resistance.

[0040] As a specific example of a polymer containing an alicyclic structure, norbornene-based polymers, monocyclic cyclic olefin-based polymers, cyclic conjugated diene-based polymers, vinyl alicyclic hydrocarbon-based polymers, etc. can be cited. Among these, from the viewpoint of improving the transparency, heat resistance, and mechanical strength of the obtained molding sheet and making the shape accuracy of the multiple optical planar parts contained in the obtained molding sheet higher, the deviation of the thickness accuracy is smaller, and then the viewpoint of improving the production efficiency of the molding sheet, the preferred norbornene-based polymer. In addition, from the viewpoint that the shape accuracy of the multiple optical planar parts contained in the obtained molding sheet is higher, the deviation of the thickness accuracy is smaller, and then the production efficiency of the molding sheet can be improved, the preferred norbornene-based polymer. In addition, in this specification, the meaning of these polymers is not only a polymerization reaction product, but also refers to its hydride.

[0041] Norbornene polymers are polymers of norbornene monomers or their hydrides. As norbornene polymers, ring-opening polymers of norbornene monomers, ring-opening polymers of norbornene monomers and other monomers capable of being ring-opened copolymerized therewith, addition polymers of norbornene monomers, addition polymers of norbornene monomers and other monomers capable of being copolymerized therewith, and hydrides of these polymers, etc., can be cited. Among them, ring-opening polymer hydrides of norbornene monomers are preferred (i.e., norbornene ring-opening polymer hydrides). By using norbornene ring-opening polymer hydrides, the transparency, heat resistance and mechanical strength of the molded sheet can be further improved, and the demoulding property and transferability when the molded sheet is manufactured by hot pressing molding can be improved.

[0042] Examples of the 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-benzenetricyclo[4.3.0.1 2,5 ]Deca-3-ene (common name: tetrahydrofluorene, also known as 1,4-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 can be contained in the derivatives include: alkyl, alkylene, vinyl, alkoxycarbonyl, alkylidene, etc. For example, as derivatives of norbornene monomers, there can be mentioned: 8-methoxycarbonyl-tetracyclo[4.4.0.1 2,5 .1 7,10 ] dodec-3-ene, 8-methyl-8-methoxycarbonyl-tetracyclo[4.4.0.12,5 .1 7,10 ] dodec-3-ene, 8-ethylene-tetracyclo[4.4.0.1 2,5 .1 7,10 ] dodec-3-ene, etc. These norbornene-based monomers can be used alone or in combination of two or more.

[0043] Other monomers capable of ring-opening copolymerization with norbornene monomers include monocyclic cyclic olefin monomers such as cyclohexene, cycloheptene and cyclooctene. Other monomers capable of addition copolymerization 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-tetrahydroxy-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.

[0044] The ring-opening polymer and addition polymer containing the above-mentioned norbornene-based monomer can be synthesized by polymerization in the presence of a known catalyst. In addition, their hydrogenated products can be obtained by hydrogenation reaction using a known hydrogenation catalyst.

[0045] Examples of monocyclic cyclic olefin polymers, cyclic conjugated diene polymers, and vinyl alicyclic hydrocarbon polymers include polymers described in International Publication No. 2017 / 126599.

[0046] In addition, commercial products can also be used as polymers containing an alicyclic structure, such as ZEONEX (registered trademark) manufactured by Zeon Co., Ltd., APEL (registered trademark) manufactured by Mitsui Chemicals, Inc., ARTON (registered trademark) manufactured by JSR Corporation, and TOPAS (registered trademark) manufactured by Polyplastics Co., Ltd.

[0047] Moreover, the glass transition temperature (Tg) of the thermoplastic resin is not particularly limited, and is preferably 100°C or more, more preferably 120°C or more, preferably 200°C or less, and more preferably 160°C or less. If the glass transition temperature (Tg) of the thermoplastic resin is above the above lower limit, the shape accuracy of the optical planar portion of the molded sheet can be made higher, and the deviation of the thickness accuracy of the optical planar portion can be reduced, thereby improving the manufacturing efficiency of the molded sheet. In addition, if the glass transition temperature (Tg) of the thermoplastic resin film is below the above upper limit, the production efficiency of the molded sheet can be improved, and the shape accuracy of the optical planar portion can be made higher.

[0048] In addition, the molded sheet may also contain ingredients other than the above-mentioned resin component. As ingredients other than the resin component, additives such as light stabilizers, ultraviolet absorbers, infrared absorbers, antioxidants, mold release agents, antistatic agents, carbon materials (carbon, etc.), pigments and dyes can be cited. The amount of these ingredients is not particularly limited and can be appropriately determined. For example, when the resin component is 100% by mass, the total amount of these additives can be, for example, less than 20% by mass, preferably less than 10% by mass.

[0049] <Optical Surface Section>

[0050] Optical surface part ( Figure 1 The setting density of 11) in the above example needs to be 0.16 pieces / cm 2 The optical planar portions are preferably provided at a density of 0.30 pieces / cm 2 More preferably, 0.40 pieces / cm 2 More than, preferably 3.0 / cm 2 Below, more preferably 2.0 pieces / cm 2 Below, more preferably 1.0 pieces / cm 2 Below, particularly preferably 0.60 pieces / cm 2 If the density of the optical surface portion is 0.16 pieces / cm 2 In addition, if the density of the optical planar portion is below the upper limit, the shape accuracy can be improved and the birefringence can be reduced, and the deviation of the thickness accuracy can be further reduced.

[0051] In addition, the minimum interval between adjacent optical planar portions ( Figure 1 The minimum interval between the optical planar portion is more than 1.0mm, more preferably more than 3.0mm, more preferably more than 5.0mm, more preferably more than 7.0mm. If the minimum interval between the optical planar portion is more than 1.0mm, then the deviation of the thickness precision of the optical planar portion can be reduced and the shape accuracy can be improved, and then birefringence can be reduced. In addition, if the minimum interval between the optical planar portion is more than 1.0mm, then even when using molding methods such as compression molding to make, also can suppress the accumulation of bubbles and air in the molded sheet. In addition, the minimum interval between the optical planar portion is generally below 20mm.

[0052] Furthermore, the diameter of the optical planar portion when viewed from above ( Figure 1 D) in needs to be more than 1mm and less than 15mm, and the diameter of the optical planar portion is preferably more than 3mm, preferably less than 9mm. If the diameter of the optical planar portion is within the above range, the deviation of the thickness accuracy of the optical planar portion can be reduced and the shape accuracy can be improved.

[0053] In addition, the thickness at the center of the optical surface portion ( Figure 1 H mid ) is preferably 50 μm or more, more preferably 100 μm or more, preferably 1500 μm or less, more preferably 1000 μm or less. If the thickness at the center of the optical planar portion is within the above range, it can be advantageously used as a transmission optical element such as a lens.

[0054] Furthermore, the variation in thickness accuracy of the optical planar portion needs to be 0.2 μm or less, and preferably 0.1 μm or less. If the variation in thickness accuracy is equal to or less than the upper limit value, the birefringence of the optical planar portion can be reduced.

[0055] And the phase difference of optical planar portion need be below 50nm, is preferably below 20nm.If the phase difference is below the above-mentioned upper limit, the birefringence of optical planar portion is enough little.And then, when the phase difference is made as below the above-mentioned upper limit, the deviation of the thickness precision of optical planar portion can be reduced and shape accuracy can be improved.

[0056] Here, the thinnest part of the molded sheet ( Figure 1 H min ) is preferably 50 μm or more, more preferably 100 μm or more, preferably 500 μm or less, more preferably 300 μm or less, and further preferably 200 μm or less. If the thickness of the thinnest portion is below the above upper limit, the deviation of the thickness accuracy of the optical planar portion can be reduced and the shape accuracy can be improved. In addition, if the thickness of the thinnest portion is above the above lower limit, the strength of the molded sheet can be fully improved.

[0057] (Method for producing molded sheet)

[0058] The method for manufacturing a molding sheet of the present invention is a method for manufacturing a molding sheet having a plurality of optical surface portions by hot pressing a thermoplastic resin film formed using a thermoplastic resin. The method is not particularly limited and can be used, for example, when manufacturing the molding sheet of the present invention. Moreover, the method for manufacturing a molding sheet of the present invention is characterized in that it includes a "hot pressing step" in which a pair of molds having a plurality of optical surface forming regions separated from each other are used to hot press a monolithic sheet formed by a thermoplastic resin film under normal pressure to obtain a molding sheet. Furthermore, the method for manufacturing a molding sheet of the present invention preferably includes a "demolding step" in which the molding sheet obtained by the hot pressing step is demolded from a pair of molds. In the method for manufacturing a molding sheet of the present invention, a pair of molds having a plurality of optical surface forming regions separated from each other are used to hot press a monolithic sheet under normal pressure, so that a molding sheet having a plurality of optical surface portions with sufficiently high shape accuracy, small deviation in thickness accuracy, and sufficiently small birefringence can be easily manufactured.

[0059] <Molding sheet>

[0060] The molded sheet produced by the method for producing a molded sheet of the present invention is not particularly limited as long as it is a single sheet having a plurality of optical planar portions separated from each other. The molded sheet preferably has the same properties as the molded sheet of the present invention described above.

[0061] <Thermoplastic resin film>

[0062] The thermoplastic resin used as the thermoplastic resin film is not particularly limited, and for example, the same resin as the thermoplastic resin of the molding sheet of the present invention can be cited. In addition, the meaning of "film" is an object having a shape in which the front and back surfaces (i.e., the main surfaces) face each other across a thickness.

[0063] Moreover, the manufacturing method of the thermoplastic resin film is not particularly limited, and any known suitable method can be used. For example, after mixing the prescribed components to obtain a molding material for the manufacture of the thermoplastic resin film, the material can be used to obtain the thermoplastic resin film by melt extrusion molding, melt casting molding, injection molding, etc.

[0064] The thickness of the thermoplastic resin film can be appropriately selected according to the diameter of the optical planar portion of the molded sheet to be manufactured. For example, the thickness of the thermoplastic resin film is usually 50 μm or more, preferably 70 μm or more, usually 500 μm or less, preferably 400 μm or less. In addition, when there is a deviation in the thickness of the thermoplastic resin film, the thickness of the thermoplastic resin film is equivalent to the simple arithmetic average value of the thickness of a plurality of randomly selected measurement points.

[0065] Then, the thermoplastic resin film can be cut into a desired size such as A4 size to 50 cm×50 cm size to form a single sheet.

[0066] <Hot Pressing Process>

[0067] In the hot pressing process, a pair of molds having a plurality of optical surface forming areas separated from each other are used to hot press mold a single sheet formed of a thermoplastic resin film under normal pressure. In addition, when the hot pressing process is started, a configuration operation of configuring the single sheet on the hot pressing device can be implemented. Figure 2 A schematic diagram showing a hot pressing process for explaining a method for producing a molded sheet according to an example of the present invention is shown. Figure 2 As shown, in the hot pressing step of this example, a pair of molds 1 consisting of an upper mold 1A and a lower mold 1B are used to hot press a single sheet 10'. Figure 2 As shown in the figure below, it is preferred that the single-piece sheet 10' is not extruded from the pair of dies 1 when the single-piece sheet 10' is pressed by the pair of dies 1. By preventing the single-piece sheet 10' from being extruded from the pair of dies 1 under the pressed state, the shape accuracy of the multiple optical planar portions contained in the obtained molded sheet can be made higher, the deviation of the thickness accuracy can be made smaller, and the birefringence can be made smaller, thereby improving the production efficiency of the molded sheet. In addition, in the manufacturing method of the molded sheet of the present invention, the optical planar portion of the obtained molded sheet can be suppressed from birefringence by hot pressing the thermoplastic resin film using a mold instead of an injection molding method.

[0068] [Mold]

[0069] The pair of molds 1 is not particularly limited as long as at least one of them has a plurality of cavities serving as optical planar portion forming regions, and a mold of any shape such as a flat mold can be used.

[0070] In addition, as the material used for the mold, known materials can be used. For example, carbon steel, stainless steel, and alloys based on these can be cited. From the viewpoint of processability and hardness, stainless steel such as STAVAX (registered trademark) material (manufactured by Uddeholm) is preferred. In addition, from the viewpoint of demoulding properties, it is preferred to use a mold formed by plating metals such as chrome, titanium and nickel on the mold surface, and it is more preferred to use a mold formed by chemically plating nickel-phosphorus on the mold surface.

[0071] Furthermore, in at least one of the molds used in the manufacturing method of the present invention, the plurality of cavities are discretely arranged in the plane direction of the mold. The plurality of cavities are preferably separated and arranged at equal intervals in the plane direction of the mold.

[0072] Here, a pair of molds may have multiple cavities. This is because by using a pair of molds each having a cavity to perform molding, a molded sheet with two sides shaped can be efficiently manufactured. In addition, depending on the shape of the molded sheet to be manufactured, the shapes of the pair of molds can naturally be the same or different.

[0073] The density of the cavities is preferably 0.16 cavities / cm 2 More preferably, 0.30 pieces / cm 2 More preferably, 0.40 pieces / cm 2 More than, preferably 3.0 / cm 2 Below, more preferably 2.0 pieces / cm 2 Below, more preferably 1.0 pieces / cm 2 Below, particularly preferably 0.60 pieces / cm 2 If the cavity density is 0.16 / cm 2 More than, then can reduce the deviation of the thickness accuracy of the optical planar portion of the obtained molding sheet and can improve shape accuracy. In addition, if the arrangement density of the cavity portion is below the above-mentioned upper limit value, then can improve the shape accuracy of the obtained molding sheet and reduce birefringence and can further reduce the deviation of thickness accuracy.

[0074] In addition, the minimum spacing between adjacent cavities (equivalent to Figure 1 The minimum interval (P) between the cavity portion is preferably more than 1.0mm, more preferably more than 3.0mm, further preferably more than 5.0mm, and particularly preferably more than 7.0mm. If the minimum interval (P) between the cavity portion is more than 1.0mm, the deviation of the thickness accuracy of the optical planar portion of the obtained molding sheet can be reduced and the shape accuracy can be improved, and then birefringence can be reduced. In addition, if the minimum interval of the cavity portion is more than 1.0mm, the accumulation of bubbles and air in the molding sheet can be suppressed. In addition, the minimum interval between the cavity portion is generally less than 20mm.

[0075] Furthermore, the diameter of the cavity when viewed from above (equivalent to Figure 1 D) is preferably 1 mm or more and 15 mm or less, more preferably 3 mm or more, preferably 9 mm or less. If the diameter of the cavity is within the above range, the deviation of the thickness accuracy of the optical planar portion of the obtained molding sheet can be reduced and the shape accuracy can be improved.

[0076] In addition, in the state of closing the mold (closed mold state), the depth of the center of the cavity (the distance in the direction corresponding to the thickness direction at the center of the formed optical planar portion; H mid) is preferably 50 μm or more, more preferably 100 μm or more, preferably 1500 μm or less, more preferably 1000 μm or less. If the depth of the center of the cavity is within the above range, the optical planar portion of the obtained molded sheet can be advantageously used as a transmissive optical element such as a lens.

[0077] Furthermore, the minimum distance between the molding sheet forming surfaces when the mold is in the closed state (H min ) is preferably 50 μm or more, more preferably 100 μm or more, preferably 500 μm or less, more preferably 300 μm or less, and further preferably 200 μm or less. If the minimum interval is below the above upper limit, the deviation of the thickness accuracy of the optical planar portion of the obtained molding piece can be reduced, and the shape accuracy can be improved. In addition, if the minimum interval is above the above lower limit, the strength of the obtained molding piece can be fully ensured.

[0078] [Pressing temperature]

[0079] In the hot pressing process, the pressing temperature (mold temperature) when a pair of molds are used to hot press the thermoplastic resin film is preferably a temperature 40°C higher than the glass transition temperature (Tg) of the thermoplastic resin (Tg+40°C) or higher, and the pressing temperature is more preferably a temperature 50°C higher than the glass transition temperature (Tg+50°C) or higher, and further preferably a temperature 55°C higher than the glass transition temperature (Tg+55°C) or higher. If the pressing temperature is above the above lower limit, the deviation in the thickness accuracy of the optical planar portion of the obtained molded sheet can be reduced, and the shape accuracy can be improved. In addition, from the viewpoint of efficiently manufacturing the molded sheet, the pressing temperature is preferably below a temperature 80°C higher than the glass transition temperature (Tg+80°C).

[0080] The pressing temperature is not particularly limited and can be appropriately adjusted by controlling the temperature of the mold by a known general method (for example, a temperature control method using a known heater and cooler).

[0081] [Pressure of repression]

[0082] In the hot pressing step, it is preferred that the pressing pressure when hot pressing the thermoplastic resin film with the die is increased to a final pressing pressure at a predetermined pressure increasing rate and then maintained at the final pressing pressure for a predetermined time as desired.

[0083] -Boost speed-

[0084] Here, the average pressure rise rate of pressing pressure is preferably below 0.1MPa / second, more preferably below 0.07MPa / second, further preferably below 0.05MPa / second.If the average pressure rise rate is below the above-mentioned upper limit, then the birefringence of the optical planar portion of the obtained molding sheet can be reduced and shape accuracy can be improved.In addition, from the viewpoint of efficiently manufacturing molding sheet, the average pressure rise rate is preferably more than 0.04MPa / second.

[0085] - Final suppression pressure -

[0086] 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 accuracy of the optical planar portion of the obtained molded sheet can be further improved, and the variation in thickness accuracy and birefringence can be further reduced.

[0087] [Other suppression conditions]

[0088] In addition, the pressing time of the hot pressing step is not particularly limited, and can be appropriately determined according to the type and size of the thermoplastic resin film used, the shape and size of the target molded piece, 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 maintaining the pressing pressure at the final pressing pressure can be 0 seconds or more and 180 seconds or less.

[0089] <Mold release process>

[0090] In the demolding process, when the molded sheet obtained by the hot pressing process is demolded from a pair of molds, the pair of molds are demolded at a temperature of more than (Tg-80)°C and less than (Tg-15)°C (hereinafter sometimes referred to as "demolding temperature"). By implementing this process, the shape accuracy of the multiple optical planar portions contained in the obtained molded sheet can be higher, the deviation of the thickness accuracy can be smaller, and the birefringence can be smaller. In addition, the demolding process can be started at the following time point: for example, after a specified time has passed from the time point when the hot pressing process starts, the time point when the temperature control starts in order to cool the mold, or after a specified time has passed from the time point when the hot pressing process starts, the time point when the heat input to the mold is stopped.

[0091] [Demolding temperature]

[0092] The demolding temperature needs to be below the glass transition temperature (Tg) of the thermoplastic resin, preferably below a temperature (Tg-15°C) 15°C lower than the glass transition temperature, more preferably below a temperature (Tg-20°C) 20°C lower than the glass transition temperature, and further preferably below a temperature (Tg-30°C) 30°C lower than the glass transition temperature. In addition, the demolding temperature is preferably above a temperature (Tg-80°C) 80°C lower than the glass transition temperature, and more preferably above a temperature (Tg-75°C) 75°C lower than the glass transition temperature. If the demolding temperature is below the above upper limit, demolding is easy, and the shape accuracy of the optical planar portion of the obtained molding piece can be effectively improved. Furthermore, if the demolding temperature is below the above upper limit, the deviation of the thickness accuracy of the optical planar portion of the obtained molding piece can be reduced, and birefringence can be reduced. In addition, if the demolding temperature is below the above upper limit, failures can be suppressed during demolding, and the manufacturing efficiency of the molding piece can be further improved. Furthermore, when the demolding temperature is equal to or higher than the lower limit, the temperature adjustment time required for cooling the pair of molds and raising the temperature in the subsequent hot pressing step can be shortened, and the production efficiency of the molded sheet can be further improved.

[0093] [Other demoulding conditions]

[0094] 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 according to the type and size of the single-piece sheet, the shape and size of the optical surface portion of the target molded sheet, etc. For example, the mold cooling time can be more than 10 seconds and less than 100 seconds, and the mold cooling rate can be more than 50°C / min and less than 300°C / min.

[0095] Then, in the demolding step, after the mold is cooled to the demolding temperature, the hot pressed film is demolded from the mold to obtain a molded sheet.

[0096] (Method for manufacturing optical element)

[0097] The manufacturing method of the optical element of the present invention is characterized in that it includes: an optical element separation step, in which a molded sheet obtained by the manufacturing method of the present invention is separated at positions corresponding to a plurality of optical planar portions to obtain a plurality of optical elements. According to the manufacturing method of the present invention, an optical element with sufficiently high shape accuracy, small deviation in thickness accuracy, and sufficiently small birefringence can be easily manufactured.

[0098] <Optical element separation process>

[0099] In the optical element separation step, a plurality of optical elements are separated from the molded sheet obtained by the manufacturing method of the present invention. The separation method is not particularly limited, and the optical elements can be separated from the molded sheet by any known method such as punching with a stamping die or laser cutting.

[0100] Example

[0101] The present invention is further described in detail by citing the following embodiments and comparative examples. In addition, the present invention is not subject to any limitation of these examples. In the embodiments and comparative examples, the glass transition temperature of the thermoplastic resin is measured as follows. In addition, in the embodiments and comparative examples, the shape accuracy of the optical planar portion of the molded sheet, the deviation of the thickness accuracy and the phase difference and the productivity of the molded sheet are evaluated as follows. In the embodiments and comparative examples, the various operations from configuration to demoulding are all under normal pressure, that is, the mold interior is not set to the condition of pressurized or decompressed environment and implemented.

[0102] <Glass transition temperature of thermoplastic resin>

[0103] The glass transition temperature (Tg) of the thermoplastic resin was measured using a differential scanning calorimeter (“DSC6220” manufactured by Hitachi High-Tech Analytical Science Co., Ltd.) under the condition of a temperature increase rate of 10° C. / min in accordance with JIS K7121:2012.

[0104] <Shape accuracy>

[0105] The optical surface portion of the molded sheet is punched out to obtain an optical lens as a measurement sample. In addition, the optical lens obtained by the embodiment and the comparative example is an aspheric lens having an aspheric surface shape on the front and back sides, respectively, and the cross-sectional shape of the aspheric surface along the thickness direction of the optical lens has an inflection point.

[0106] Next, for 300 measurement samples of the punched optical planar portion, a shape measuring device (manufactured by Panasonic Corporation, "UA-3P") was used to measure the PV value (the maximum error of the shape of the surface of the measurement sample relative to the reference surface, that is, the difference between the highest point (Peak) and the lowest point (Valley) in the measurement range) based on the design value of the optical surface. Then, the simple average value of the measured PV values ​​was used as the shape accuracy, and evaluation was performed according to the following criteria.

[0107] A: The simple average value of PV value is less than 0.5μm

[0108] B: The simple average value of PV value is greater than 0.5μm and less than 1.0μm

[0109] C: The simple average value of PV value is greater than 1.0μm and less than 2.0μm

[0110] D: The simple average value of PV value is greater than 2.0μm

[0111] <Thickness Accuracy Deviation>

[0112] The optical surface portion of the molded sheet was punched out to obtain an optical lens as a measurement sample.

[0113] Next, the center thickness of 300 measurement samples of the obtained optical lens was measured using a shape measuring instrument (manufactured by Panasonic Corporation, "UA-3P"), and the standard deviation of the measured thickness was evaluated as the deviation of thickness accuracy according to the following criteria.

[0114] A: Standard deviation is less than 0.1μm

[0115] B: Standard deviation is greater than 0.1μm and less than 0.2μm

[0116] C: Standard deviation greater than 0.2μm

[0117] <Phase Difference>

[0118] The optical surface portion of the molded sheet was punched out to obtain an optical lens as a measurement sample.

[0119] Next, the phase difference of 300 measurement samples among the obtained optical lenses was measured using a resin molded lens inspection system (“WPA-100” manufactured by Photonic Lattice Corporation).

[0120] The simple average value of the obtained retardation values ​​was used as a value normalized by the measurement wavelength (543 nm) and evaluated according to the following criteria: The smaller the retardation value, the smaller the birefringence.

[0121] A: The simple average value of the phase difference is less than 20nm

[0122] B: The simple average value of the phase difference is greater than 20nm and less than 50nm

[0123] C: The simple average value of the phase difference is greater than 50nm

[0124] <Continuous productivity>

[0125] The total time that the apparatus was stopped due to a failure that occurred when processing 100 individual sheets into molded sheets was evaluated based on the following criteria.

[0126] A: Stop time is less than 30 minutes

[0127] B: The stop time is more than 30 minutes and less than 120 minutes

[0128] C: Stop time is more than 120 minutes

[0129] (Example 1)

[0130] A thermoplastic resin containing a hydrogenated norbornene-based ring-opening polymer (ZEONEX E48R (manufactured by Zeon Japan Co., Ltd.), glass transition temperature: 139°C) was added to a film extruder (single-screw extruder, Φ=20 mm, manufactured by GSI Corp.), melted at 260°C, extruded from a T-die, and cooled to obtain a thermoplastic resin film having a length of more than 100 m, a thickness of 500 μm, and a width of 295 mm. The thermoplastic resin film thus obtained was cut into 250 mm squares and used as a single sheet.

[0131] The single-piece sheet obtained by the above method was placed in a hot press molding machine having a temperature control device and a pair of 300 mm square molds (placement operation). In addition, as a pair of molds, molds having the properties shown in Table 1 were used.

[0132] Then, after the temperature of the mold was raised to the pressing temperature shown in Table 1, the single-piece sheet was hot pressed under the conditions shown in Table 1 while increasing the pressure at a pressure increase rate of 0.045 MPa / sec to 9.5 MPa (hot pressing step).

[0133] Furthermore, while the single-piece sheet is being pressed, the pair of molds is cooled to 100°C, and the molded sheet sandwiched between the molds is cooled. Thereafter, the pair of molds is opened, and the molded sheet having the properties shown in Table 1 is peeled off from the pair of molds (mold release process). In addition, the diameter of the optical surface portion of the molded sheet corresponds to the diameter D of the cavity portion of the mold, the minimum spacing between the optical surface portions corresponds to the minimum spacing P of the cavity portion of the mold, the setting density of the optical surface portions corresponds to the setting density of the cavity portion of the mold, and the thickness of the center of the optical surface portion corresponds to the depth H of the center of the cavity portion in the closed mold state. mid Correspondingly, the thickness of the thinnest part of the molded sheet and the minimum distance H between the molded sheet forming surfaces in the closed mold state min Corresponding.

[0134] The obtained molded sheets were subjected to various evaluations according to the above-mentioned methods, and the results are shown in Table 1 together with the time (cycle time) from the placement of the sheet to the demolding of the molded sheet.

[0135] (Examples 2 to 4)

[0136] A molded sheet was produced in the same manner as in Example 1 except that the pair of molds were changed to molds having properties shown in Table 1, and various evaluations were performed. The results are shown in Table 1.

[0137] (Examples 5 to 7)

[0138] Except having changed the demolding temperature in the demolding process into the temperature shown in Table 1, it carried out similarly to Example 1, and produced the molded sheet, and performed various evaluations.

[0139] (Example 8)

[0140] A molded sheet was produced in the same manner as in Example 1 except that a sheet cut into 400 mm square was used, and various evaluations were performed. The results are shown in Table 1. In the hot pressing step according to this example, the end portions of a single sheet are extruded from a pair of dies.

[0141] (Example 9)

[0142] As a thermoplastic resin film, a thermoplastic resin (TOPAS6013 (manufactured by Polyplastics Co., Ltd.), glass transition temperature: 138° C.) containing a norbornene-ethylene random copolymer obtained by random addition polymerization of norbornene and ethylene as monomers was used, and a molded sheet was 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.

[0143] (Example 10)

[0144] A molded sheet was produced in the same manner as in Example 1 except that a polycarbonate resin (Wonderlight 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.

[0145] (Example 11)

[0146] A molded sheet was produced in the same manner as in Example 1 except that a polymethyl methacrylate resin (DELPET80NH (manufactured by Asahi Kasei Chemicals Co., Ltd.), 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. Various evaluations were performed. The results are shown in Table 1.

[0147] (Example 12)

[0148] A molded sheet was produced in the same manner as in Example 1 except that a polyester resin (OKP-1 (manufactured by Osaka Gas Chemical Co., Ltd.), glass transition temperature: 132° 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.

[0149] (Comparative Example 1)

[0150] A molded sheet was produced in the same manner as in Example 1 except that the pair of molds were changed to molds having properties shown in Table 1, and various evaluations were performed. The results are shown in Table 1.

[0151] (Comparative Example 2)

[0152] The hot press molding machine with a pair of 300 mm square molds was replaced with a hot press molding machine with the following configuration: four pairs of 100 mm square molds arranged in a 2×2 manner, with the interval between the molds set to 20 mm. Using this hot press molding machine, a single sheet was simultaneously molded with four pairs of molds. In addition, a molded sheet was attempted to be produced in the same manner as in Example 1. However, during molding, the sheet broke in the gap between the molds, and a molded sheet could not be produced.

[0153] [Table 1]

[0154]

[0155] It can be seen from Table 1 that the molded sheets of Examples 1 to 12 have multiple optical planar portions with sufficiently high shape accuracy, small deviation in thickness accuracy, and sufficiently small birefringence. It can also be seen that the molded sheets of Examples 1 to 12 have excellent continuous productivity. In addition, it can be seen that the shape accuracy of the optical planar portion of the molded sheet of Comparative Example 1 is low, the deviation in thickness accuracy is large, and the birefringence is large. In addition, it can be seen that the continuous productivity of the molded sheet of Comparative Example 1 is low.

[0156] Industrial Applicability

[0157] According to the present invention, it is possible to provide a molded sheet having a plurality of optical planar portions having sufficiently high shape accuracy, small variations in thickness accuracy, and low birefringence.

[0158] Furthermore, according to the present invention, it is possible to provide a method for producing a molded sheet capable of efficiently producing the above-mentioned molded sheet.

[0159] Furthermore, according to the present invention, it is possible to provide a method for producing an optical element using the above-mentioned molding sheet.

[0160] Description of Reference Numerals

[0161] 1: A pair of molds;

[0162] 1A: upper mold;

[0163] 1B: lower mold;

[0164] 10: Molding sheet;

[0165] 10': single sheet;

[0166] 11: Optical surface part.

Claims

1. A method for producing a molded sheet, comprising: performing heat press molding on a thermoplastic resin film formed using a thermoplastic resin to produce a molded sheet having a plurality of optical planar portions, The method for manufacturing the formed sheet comprises the following steps: A heat pressing step of heat-pressing a single sheet formed of the thermoplastic resin film under normal pressure using a pair of molds having a plurality of optical surface forming regions separated from each other to obtain a molded sheet. The cavity portions as the optical surface forming area are arranged at a density of 0.16 cavities / cm 2 More than and less than 1.0 / cm 2 , The minimum interval between the adjacent cavities is 7.0 mm or more.

2. The method for producing a molded sheet according to claim 1, comprising the following steps: In the demolding step, the glass transition temperature of the thermoplastic resin is set to Tg (°C), and when the molded sheet obtained in the hot pressing step is demolded 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.

3. The method for producing a molded sheet according to claim 1 or 2, wherein: In the hot pressing step, in a state where the single-piece sheet is pressed by the pair of dies, the single-piece sheet is not pushed out from the pair of dies.

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

5. A method for manufacturing an optical element, comprising the following steps: The optical element separation step is to separate the molded sheet obtained by the method for producing a molded sheet according to any one of claims 1 to 4 at positions corresponding to the plurality of optical planar portions, thereby obtaining a plurality of optical elements.

6. A molded sheet, which is a single-sheet molded sheet having a plurality of optical planar portions formed using a thermoplastic resin, The optical surface portion is arranged at a density of 0.16 pieces / cm 2 More than and less than 1.0 / cm 2 , The minimum interval between the adjacent optical planar portions is 7.0 mm or more. The diameter of the optical planar portion is greater than or equal to 1 mm and less than or equal to 15 mm when viewed from above. The phase difference of the optical surface portion is 50 nm or less, The optical planar portion has a thickness accuracy deviation of 0.2 μm or less.

7. The molded sheet according to claim 6, wherein: At least one surface of the optical surface portion is an aspherical surface having a cross-sectional shape in the thickness direction with an inflection point.

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