JP7593315B2 - Method for manufacturing a transmissive optical element - Google Patents

Description

The present invention relates to a method for manufacturing a transmissive optical element. More specifically, the present invention relates to a method for manufacturing a transmissive optical element using a resin film.

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 installed in these electronic and electrical devices. There is also a need for even higher image quality in such camera units, and there is a demand for high performance in the transmissive optical elements such as lenses and prisms that are installed in these optical devices.

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 forming in the resulting lenses. In addition, lenses obtained by injection molding are prone to birefringence. For this reason, it is difficult to sufficiently increase the proportion of areas capable of exhibiting sufficiently high optical performance in the resulting lenses, and even if small-diameter lenses with diameters of less than 1 cm are formed by injection molding, it is difficult to make them function adequately as lenses.

Therefore, in recent years, 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 for manufacturing optical lenses in which a resin sheet is vacuum compression molded in a mold. In Patent Document 1, optical lenses with low birefringence and high shape accuracy can be efficiently manufactured by molding under conditions where a specific relationship is satisfied among the thickness of the resin sheet, the depth of the deepest part of the mold, the glass transition temperature of the resin sheet, and the surface temperature of the mold during molding.

International Publication No. 2017/126599

As mentioned above, there is a demand for even higher image quality in camera units and the like that are equipped in electronic and electrical devices. In addition, when manufacturing electronic and electrical devices, it is naturally required to manufacture them with high manufacturing efficiency. However, the manufacturing method for optical lenses described in Patent Document 1 leaves room for improvement in terms of efficiently manufacturing optical lenses with high shape accuracy. Also, as mentioned above, there is also room for improvement in the conventional injection molding method in terms of suppressing the occurrence of birefringence in the obtained optical lenses.

Therefore, the present invention aims to provide a method for manufacturing transmissive optical elements that is capable of efficiently producing transmissive optical elements that have low birefringence and high shape accuracy.

The present inventors have conducted extensive research to achieve the above object. As a result, the present inventors have newly discovered that when forming a resin film by press molding using a mold, it is possible to efficiently manufacture a transmissive optical element that has low birefringence and high shape accuracy by using a flat mold as the mold and applying tension to the resin film at a specific timing in the manufacturing process, and have completed the present invention.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the manufacturing method of the transmissive optical element of the present invention is a manufacturing method for manufacturing a transmissive optical element using a thermoplastic resin film, and is characterized by including a heat pressing step of heat pressing the thermoplastic resin film with at least a pair of flat molds to obtain a heat pressed film, a mold cooling step of cooling the pair of flat molds to a temperature equal to or lower than the glass transition temperature (Tg _r ) ° C. of the thermoplastic resin film to cool the heat pressed film, and a mold releasing step of releasing the heat pressed film from the pair of flat molds after the mold cooling step while applying tension to the heat pressed film to obtain a molded film including a plurality of transmissive optical elements. When releasing the thermoplastic resin film heat pressed using the pair of flat molds after cooling, releasing it while applying tension makes it possible to efficiently manufacture a transmissive optical element having low birefringence and high shape accuracy.
The "glass transition temperature (Tg _r ) ° C. of the thermoplastic resin film" can be measured based on JIS K7121.

In addition, it is preferable that the method for producing a transmissive optical element of the present invention further includes a transport step of transporting the thermoplastic resin film along a predetermined transport direction prior to the heat pressing step, and that the thermoplastic resin film is released in the demolding step while being subjected to tension along the transport direction, and the magnitude of the tension is 1 N or more and 2000 N or less per meter of the width of the thermoplastic resin film in a direction perpendicular to the transport direction. By setting the magnitude of the tension within the above range, a plurality of transmissive optical elements with less variation in shape accuracy can be produced more efficiently.
The "magnitude of tension" can be controlled by the method described in the Examples.

In addition, in the manufacturing method of the transmissive optical element of the present invention, it is preferable that at least one of the pair of flat molds includes a plurality of optical surface forming regions having a diameter of 1 mm or more and 15 mm or less, and an outer periphery forming region which is an area adjacent to each outer periphery of the plurality of optical surface forming regions, and that the sum of the shallowest parts of the optical surface forming regions and the outer periphery forming region of the pair of flat molds is 500 μm or less. By using a flat mold that satisfies the above conditions, a transmissive optical element having excellent strength can be efficiently manufactured.

In addition, in the manufacturing method of the transmissive optical element of the present invention, it is preferable that at least one of the pair of flat molds includes a plurality of optical surface forming regions that are discretely arranged in the planar direction of the flat mold, and the minimum distance between the plurality of optical surface forming regions is 1.0 mm or more. By using a flat mold that satisfies the above conditions, the manufacturing efficiency of the transmissive optical element can be further improved. Note that the "minimum distance between optical surface forming regions" means the shortest distance between the contours of adjacent optical surface forming regions in the planar direction of the flat mold. Note that the "planar direction of the flat mold" means the direction along the plane that includes the opening of the optical surface forming region, which is a recess provided in the flat mold.

In the method for producing a transmission optical element of the present invention, the thermoplastic resin film preferably has a glass transition temperature (Tg _r ) of 100° C. or more and 200° C. or less. When the glass transition temperature of the thermoplastic resin film is within the above range, the heat resistance and shape accuracy of the obtained transmission optical element can be improved.

In the method for producing a transmissive optical element of the present invention, it is preferable that the temperature of the pair of flat dies in the heat pressing step is not less than (Tg _r + 30)° C. and not more than (Tg _r + 70)° C. By setting the temperature of the pair of flat dies in the heat pressing step within the above range, a transmissive optical element with low birefringence can be produced more efficiently.

In the method for producing a transmissive optical element of the present invention, it is preferable that in the die cooling step, the pair of flat dies are cooled to a temperature equal to or lower than (Tg _r -15)° C. By setting the temperature of the pair of flat dies in the die cooling step to the above upper limit value or lower, a plurality of transmissive optical elements with less variation in shape accuracy can be produced more efficiently.

In addition, in the method for producing a transmissive optical element of the present invention, it is preferable that the thermoplastic resin film contains an alicyclic structure-containing resin. If the thermoplastic resin film contains an alicyclic structure-containing resin, a transmissive optical element having excellent transparency can be produced.

In the method for producing a transmissive optical element of the present invention, it is preferable that at least one of the pair of flat molds has optical surface forming regions at a number density of 0.16 pieces/ ^cm2 or more. By using a flat mold having 100 or more optical surface forming regions, transmissive optical elements can be produced more efficiently.

In addition, in the method for manufacturing a transmissive optical element of the present invention, it is preferable that both of the pair of flat molds have a plurality of optical surface forming regions. By molding using a pair of flat molds each having an optical surface forming region, a transmissive optical element having a shape on both sides can be efficiently manufactured.

It is also preferable that the method for producing a transmissive optical element of the present invention includes a transmissive optical element separation step of separating the plurality of transmissive optical elements from the molded film obtained through the demolding step. By carrying out the transmissive optical element separation step of separating the plurality of transmissive optical elements from the molded film, the transmissive optical elements can be produced more efficiently.

According to the manufacturing method of the transmissive optical element of the present invention, it is possible to efficiently manufacture transmissive optical elements having low birefringence and high shape accuracy.

FIG. 1 is a diagram showing a schematic structure of a transmissive optical element manufacturing apparatus that can be used to implement a transmissive optical element manufacturing method according to an embodiment of the present invention. 1A to 1C are schematic diagrams for explaining one example of the production of an optical lens that is a transmissive optical element according to one embodiment of the present invention. 3 is a schematic diagram for explaining a case where an optical lens having a shape different from the shape shown in FIG. 2 is manufactured. FIG.

The following describes in detail the embodiments of the present invention. According to the manufacturing method of the transmissive optical element of the present invention, transmissive optical elements such as optical lenses and prisms can be suitably manufactured. Here, "optical lens" means a transparent body that exhibits the refraction action of light. Also, "prism" means a transparent polyhedron that exhibits the dispersion action, refraction action, total reflection action, and/or birefringence action of light. According to the manufacturing method of the transmissive optical element of the present invention, transmissive optical elements having high shape accuracy and low birefringence can be efficiently manufactured. More specifically, according to the manufacturing method of the transmissive optical element of the present invention, lenses of various shapes such as plano-convex lenses, biconvex lenses, convex meniscus lenses, plano-concave lenses, biconcave lenses, concave meniscus lenses, aspheric lenses with inflection points on one side and/or both sides can be suitably manufactured. Furthermore, according to the manufacturing method of the transmissive optical element of the present invention, various transmissive optical elements having a relatively small diameter can be manufactured with high shape accuracy, and therefore, for example, optical lenses that can be suitably used as lenses for camera units of small electronic and electrical devices can be efficiently manufactured.

(Method of manufacturing a transmissive optical element)
The manufacturing method of the transmissive optical element of the present invention is a manufacturing method for manufacturing a transmissive optical element using a thermoplastic resin film. The manufacturing method of the transmissive optical element of the present invention is characterized by including a "heat pressing step" in which a thermoplastic resin film is heat-pressed with at least a pair of flat molds to obtain a heat-pressed film, a "mold cooling step" in which the pair of flat molds are cooled to a temperature equal to or lower than the glass transition temperature (Tg _r ) ° C. of the thermoplastic resin film to cool the heat-pressed film, and a "mold releasing step" in which, after the mold cooling step, the heat-pressed film is released from the pair of flat molds while applying tension to the heat-pressed film to obtain a molded film including a plurality of transmissive optical elements. When the thermoplastic resin film heat-pressed using the flat molds is released after cooling, it is possible to efficiently manufacture a transmissive optical element having low birefringence and high shape accuracy by releasing the film while applying tension. Furthermore, the manufacturing method of the transmissive optical element of the present invention may include a conveying step in which the thermoplastic resin film is conveyed along a predetermined conveying direction prior to the heat pressing step. Furthermore, the method for producing a transmission type optical element of the present invention may include a transmission type optical element separating step of separating a plurality of transmission type optical elements from the molded film after the demolding step.
Each step will be described in detail below. The atmospheric pressure of the environment in which each step is performed is not particularly limited and may be within the range of standard conditions defined in JIS Z 8703. Each step below can be performed by any means without particular limitation, but is preferably performed using a so-called roll-to-roll manufacturing means. This is because the manufacturing efficiency of the transmissive optical element can be improved by performing each step described below using a roll-to-roll manufacturing means.

<Transportation process>
In the conveying step, prior to the heat pressing step, the thermoplastic resin film is conveyed along a predetermined conveying direction to a position where the heat pressing is performed. The conveying direction is preferably a direction along the longitudinal direction perpendicular to the width direction of the thermoplastic film.

<Heat pressing process>
In the heat pressing step, the thermoplastic resin film is heat pressed by at least a pair of flat molds to obtain a heat pressed film. Note that, in the heat pressing step, there is no particular limitation as long as at least a pair of flat molds is used, and the thermoplastic resin film may be heat pressed by a pair of flat molds, or different parts of one thermoplastic resin film may be heat pressed simultaneously or at different times by a plurality of pairs of flat molds. In the manufacturing method of the transmission type optical element of the present invention, the occurrence of birefringence in the obtained transmission type optical element can be suppressed by subjecting the thermoplastic resin film to heat pressing using a flat mold without using an injection molding method.

<<Thermoplastic resin film>>
The thermoplastic resin film is not particularly limited as long as it is thermoplastic, and any film formed using any known thermoplastic resin can be used. Here, the term "film" refers to an object having a shape in which the front and back surfaces (i.e., the main surfaces) face each other at a distance equal to the thickness. Examples of thermoplastic resins that can constitute the thermoplastic resin film include (meth)acrylic resins, alicyclic structure-containing resins, styrene-based resins, polycarbonate resins, polyester resins, polyether resins, urethane resins, and thiourethane resins. 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 types.
Among these, it is preferable that the thermoplastic resin film contains an alicyclic structure-containing resin, since a transmission type optical element having excellent transparency can be obtained.

An 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 they are more likely to produce a transmissive optical element with excellent mechanical strength and heat resistance. The proportion of repeating units having an alicyclic structure in the polymer (hereinafter also referred to as an "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 in which the proportion of repeating units having an alicyclic structure is 50% by mass or more, it is easier to produce a transmissive optical element with excellent transparency and heat resistance.

Specific examples of polymers containing an alicyclic structure include norbornene-based polymers, monocyclic olefin-based polymers, cyclic conjugated diene-based polymers, and vinyl alicyclic hydrocarbon-based polymers. Among these, norbornene-based polymers are preferred from the viewpoint of improving the transparency, heat resistance, and mechanical strength of the resulting transmissive optical element. In this specification, these polymers refer not only to polymerization reaction products but also to their hydrogenated products.

Norbornene-based polymers are polymers of norbornene-based monomers or their hydrogenated products. Examples of norbornene-based polymers include ring-opening polymers of norbornene-based monomers, ring-opening polymers of norbornene-based monomers and other monomers that can be copolymerized with norbornene-based monomers, addition polymers of norbornene-based monomers, addition polymers of norbornene-based monomers and other monomers that can be copolymerized with norbornene-based monomers, and hydrogenated products of these polymers. Among these, hydrogenated ring-opening polymers of norbornene-based monomers (i.e., hydrogenated norbornene-based ring-opening polymers) are preferred. By using a thermoplastic resin film formed using a hydrogenated norbornene-based ring-opening polymer, the transparency, heat resistance, and mechanical strength of the resulting transmissive optical element can be further improved, and the releasability and transferability during the manufacture of the transmissive optical element can be improved.

Examples of norbornene monomers include bicyclo[2.2.1]hept-2-ene (common name: norbornene) and its derivatives, tricyclo[4.3.0 ^{1,6 .} 1 ^2,5 ]deca-3,7-diene (common name: dicyclopentadiene) and its derivatives, 7,8-benzotricyclo[4.3.0.1 ^2,5 ]deca-3-ene (common name: methanotetrahydrofluorene, also called 1,4-methano-1,4,4a,9a-tetrahydrofluorene) and its derivatives, and tetracyclo[4.4.0.1 ^{2,5 .} 1 ^7,10 ]dodec-3-ene (common name: tetracyclododecene) and its derivatives. Substituents that may be included in the derivatives include alkyl groups, alkylene groups, vinyl groups, alkoxycarbonyl groups, and alkylidene groups. For example, derivatives of 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 can be used alone or in combination of two or more.

Other monomers capable of ring-opening copolymerization with norbornene-based monomers include monocyclic olefin-based 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.

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. Furthermore, these hydrogenated products can be obtained by hydrogenation reactions using known hydrogenation catalysts.

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

In addition, commercially available products can be used as the alicyclic structure-containing polymer. Examples of commercially available products include 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.

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

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 the thermoplastic resin film can be obtained by melt extrusion molding, melt casting molding, injection molding, or the like.

[Glass transition temperature of thermoplastic resin film]
The glass transition temperature ( _Tgr ) of the thermoplastic resin film 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 ( _Tgr ) of the thermoplastic resin film is equal to or higher than the lower limit, the shape precision of the resulting transmission type optical element can be further improved. If the glass transition temperature ( _Tgr ) of the thermoplastic resin film is equal to or lower than the upper limit, the production efficiency of the transmission type optical element can be increased and the shape precision can be further improved.

[Thickness of thermoplastic resin film]
Here, the thickness of the thermoplastic resin film may vary even within a single film. From the viewpoint of effectively suppressing the variation in the shape precision of the resulting transmission type optical element, the thickness variation of the thermoplastic resin film is preferably within 10 μm, more preferably within 5 μm. Of course, in a film with a completely uniform thickness, the thickness variation is 0 μm, but generally, the thickness variation can be 0.5 μm or more. The thickness variation of the thermoplastic resin film is the difference between the maximum thickness and the minimum thickness of the thermoplastic resin film, and can be measured according to the method described in the examples.

The thickness of the thermoplastic resin film can be appropriately selected depending on the diameter of the transmission optical element to be manufactured. 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 thermoplastic resin film has a thickness variation, the thickness of the thermoplastic resin film corresponds to the simple arithmetic average value of the thickness at multiple randomly selected measurement points, as described in the examples.

<<Flat plate mold>>
[shape]
The pair of flat molds used in the manufacturing method of the transmissive optical element of the present invention is not particularly limited and may have any shape as long as at least one of them has a plurality of recesses that are optical surface forming regions. The optical surface forming regions are discretely arranged in the planar direction of the flat mold. It is preferable that the optical surface forming regions are arranged at equal intervals in the planar direction of the flat mold.

Here, the transmissive optical element formed according to the manufacturing method of the transmissive optical element of the present invention may have at least one optical surface, such as a concave surface, a convex surface, or an aspheric surface with an inflection point, and an outer periphery (flange portion) which is a region adjacent to the optical surface and can function as an attachment region for a holding member for holding the transmissive optical element. The outer periphery may be perpendicular or approximately perpendicular to the optical axis of the transmissive optical element. The "optical axis of the transmissive optical element" corresponds to an axis that passes through the center of the transmissive optical element and is perpendicular to the optical surface. For example, when one rotational symmetry axis can be defined for the shape of the transmissive optical element, the rotational symmetry axis coincides with the optical axis. The flat mold for forming the transmissive optical element having an optical surface and an outer periphery includes a plurality of optical surface forming regions and an outer periphery forming region which is a region adjacent to each of the outer peripheries of the plurality of optical surface forming regions. At least a part of the outer periphery forming region may be a horizontal region parallel to the planar direction of the flat mold. Furthermore, the flat mold may optionally have a peripheral portion (margin portion) for forming an area adjacent to the outer periphery, which is not included in the transmissive optical element obtained by separation in the transmissive optical element separation process described below.

Both of the pair of flat molds may have multiple optical surface forming regions. This is because by using a pair of flat molds each having an optical surface forming region for molding, it is possible to efficiently manufacture transmissive optical elements having shapes on both sides. Naturally, the shapes of the pair of flat molds may be the same or different depending on the shape of the transmissive optical element to be manufactured.

From the viewpoint of improving the manufacturing efficiency of the transmissive optical element, the number density of the optical surface forming region in at least one of the pair of flat molds is preferably 0.16 pieces/cm2 or more, and more preferably 0.32 pieces/ ^cm2 or ^more . When the number density is 0.16 pieces/ ^cm2 , there are about 100 optical surface forming regions in an area of 210 mm x 297 mm (A4 size), and when the number density is 0.32 pieces/ ^cm2 , there are about 200 optical surface forming regions in an area of A4 size. Therefore, for example, when a transmissive optical element is manufactured using a flat mold of about A4 size in which the number density of the optical surface forming region is equal to or more than the above lower limit, 100 or more transmissive optical elements can be obtained by performing one cycle of processing including one heat pressing process, so that the manufacturing efficiency of the transmissive optical element can be further improved. The upper limit value of the number density of the optical surface forming region in at least one of the pair of flat molds is not particularly limited. For example, the number density may be such that the number of transmissive optical elements that can be manufactured per cycle is 2000 or less.

[Diameter of optical surface forming area]
The diameter of the plurality of optical surface forming regions provided on at least one of the pair of flat molds is preferably 1 mm or more and 15 mm or less. If the diameter is 1 mm or more, the resulting transmission type optical element can transmit a sufficient amount of light. Therefore, for example, when an optical lens is manufactured as the transmission type optical element, the lens diameter of the obtained optical lens is sufficiently large, and a sufficient amount of light can reach a light receiving element such as a sensor provided on the rear side of the optical system including the optical lens. In addition, a transmission type optical element having a diameter of 15 mm or less is not too large and has an appropriate size for mounting on a camera unit or the like. The diameter of the optical surface forming region is the diameter of the opening of the optical surface forming region, which is a recess provided on the flat mold. That is, the diameter of the optical surface forming region corresponds to the largest diameter when the recess is viewed in the depth direction.
According to the manufacturing method of the present invention for a transmissive optical element, it is possible to mold a transmissive optical element with high shape accuracy, so that the diameter of the optical surface forming region of the flat mold can substantially correspond to the diameter of the optical surface of the obtained transmissive optical element.

[Minimum spacing between optical surface forming regions]
Furthermore, the minimum interval between the multiple optical surface forming regions provided on at least one of the pair of flat molds is preferably 1.0 mm or more, more preferably 3.0 mm or more, and preferably 50 mm or less. If the minimum interval between the multiple optical surface forming regions is equal to or more than the above lower limit, the transmission type optical elements can be efficiently separated from the molded film in the transmission type optical element separation step described later, and the manufacturing efficiency of the transmission type optical elements can be improved. Furthermore, if the minimum interval between the multiple optical surface forming regions is equal to or less than the above upper limit, the number density of the transmission type optical elements in the molded film obtained through one heat pressing step can be sufficiently increased, and the manufacturing efficiency of the transmission type optical elements can be further improved.
As described above, it is preferable that the multiple optical surface forming regions are spaced apart at equal intervals in the planar direction of the flat die.

[Mold depth]
Furthermore, the sum of the depths of the shallowest parts in the optical surface forming region and the outer peripheral portion forming region of the pair of flat molds is preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and preferably 50 μm or more. Here, the sum of the depths of the shallowest parts in the optical surface forming region and the outer peripheral portion forming region of the pair of flat molds (D _min in Figs. 2 and 3 described later) corresponds to the thickness of the thinnest part of the obtained transmission type optical element. Note that in Figs. 2 and 3, D _min is illustrated as being located within the outer peripheral portion forming region of the pair of flat molds. However, for example, when the target transmission type optical element is a biconcave lens and has a shape in which the thickness of the thinnest part of the optical surface forming region is thinner than the thickness of the outer peripheral portion forming region, D _min will be located within the optical surface forming region of the pair of flat molds. And, if the sum of the depths of the shallowest parts in the optical surface forming region and the outer peripheral portion forming region is equal to or less than the upper limit, the obtained transmission type optical element can be made compact. For example, when an optical lens is manufactured as a transmissive optical element, the thickness of a lens unit including such an optical lens can be reduced. In addition, if the sum of the depths of the shallowest parts in the optical surface forming region and the outer peripheral portion forming region is equal to or greater than the above-mentioned lower limit, the mechanical strength of the transmissive optical element can be improved by suppressing localized stress concentration when an external force is applied to the resulting transmissive optical element. Furthermore, if the sum of the depths of the shallowest parts in the outer peripheral portion forming region is equal to or greater than the above-mentioned lower limit, the strength of the molded film can be ensured, and cracks or the like can be suppressed from occurring in the molded film at unexpected times such as during transportation, thereby improving the manufacturing efficiency of the transmissive optical element.
In addition, the "sum of the depths of the shallowest parts in the outer periphery forming region of the flat mold" corresponds to the shortest distance between a pair of flat molds in the outer periphery forming region when the molds are placed opposite each other or in contact with each other during molding.

Furthermore, the sum of the depths of the deepest parts in the optical surface forming regions of the pair of flat molds (D _max ) corresponds to the thickness of the thickest part in the resulting transmissive optical element. Note that the "sum of the depths of the deepest parts in the optical surface forming regions of the flat molds" corresponds to the maximum distance between the molds in the optical surface forming regions when the pair of flat molds are placed or contacted against each other in a facing relationship for molding. The sum of the depths of the deepest parts in the optical surface forming regions of the pair of flat molds is greater than the sum of the depths of the shallowest parts, and may be, for example, more than 50 μm and not more than 1000 μm.

[Relationship between thickness of thermoplastic resin film and shape of flat plate mold]
In the manufacturing method of the transmission type optical element of the present invention, it is preferable that the thickness _Tf of the thermoplastic resin film (simple arithmetic average value of thickness at 100 or more randomly selected measurement points) is equal to or more than the sum ( _Dmin ) of the depth of the shallowest part in the peripheral part forming region of the pair of flat molds and equal to or less than the sum ( _Dmax ) of the depth of the deepest part in the optical surface forming region. More preferably, it is preferable that the thickness _Tf of the thermoplastic resin film satisfies ( _Dmin x 1.1) ≦ _Tf ≦ ( _Dmax x 0.9). If the thickness _Tf of the thermoplastic resin film is equal to or less than the upper limit, the thickness of the thinnest part of the transmission type optical element can be efficiently thinned to a desired thickness. In addition, if the thickness _Tf of the thermoplastic resin film is equal to or more than the lower limit, the thermoplastic resin can be filled well in the optical surface forming region in the pair of flat molds, and the shape precision of the obtained transmission type optical element can be further improved.

[Mold temperature]
The temperature of the pair of flat dies in the heat pressing step is preferably at least ( _Tgr + 30)°C, more preferably at least ( _Tgr + 40)°C, and is preferably at most ( _Tgr + 70)°C, and more preferably at most ( _Tgr + 60)°C. If the temperature of the pair of flat dies in the heat pressing step is at least the above lower limit, the occurrence of birefringence in the resulting transmissive optical element can be more effectively suppressed. If the temperature of the pair of flat dies in the heat pressing step is at most the above upper limit, the transmissive optical element can be more efficiently manufactured.
The heat pressing step refers to a period during which a predetermined press pressure is applied to the flat mold to heat-press the thermoplastic resin film in the operation process for pressing the thermoplastic resin film with a pair of flat molds while heating it. Here, it is preferable to further include a mold heating step between the heat pressing step and the above-mentioned conveying step, which includes heating the thermoplastic resin film while sandwiched between the flat molds. The press pressure in the mold heating step is preferably lower than the press pressure in the heat pressing step. More specifically, for example, when the press pressure in the heat pressing step is set to 1 MPa or more and 10 MPa or less, the press pressure in the mold heating step can be less than 1 MPa. The mold heating step starts when the thermoplastic resin film comes into contact with one of the pair of flat molds, and ends when the press pressure is switched to the press pressure in the heat pressing step. Heat input to the flat mold is started at a desired timing in the mold heating step, and the temperature is gradually increased to the above-mentioned "temperature of the pair of flat molds in the heat pressing step". The temperature increase may be completed at a timing prior to the end of the mold heating step (for example, 50 seconds prior to the end of the mold heating step).
The mold temperature is not particularly limited and can be appropriately adjusted according to a known general method (for example, a temperature control method using a known heater, cooler, etc.).

[Mold material]
Known materials can be used as the material for the mold. For example, carbon steel, stainless steel, and alloys based on these can be mentioned. Among them, from the viewpoint of workability and hardness, stainless steel such as STAVAX (registered trademark) material (manufactured by Woodholm) is preferable. In addition, 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 among them, it is more preferable to use a mold whose surface is plated with electroless nickel-phosphorus plating.

<<Other heat press conditions>>
The pressing pressure and pressing time in the heat pressing step are 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 intended transmission optical element, etc. For example, the pressing pressure can be 1 MPa or more and 10 MPa or less, and the pressing time can be 10 seconds or more and 100 seconds or less. The pressing pressure in the mold heating step can be, for example, less than 1 MPa. The time required from the start point to the end point of the mold heating step can be 10 seconds or more and 100 seconds or less.

<Mold cooling process>
In the mold cooling step, the pair of flat molds are cooled to a temperature equal to or lower than the glass transition temperature (Tg _r ) ° C. of the thermoplastic resin film to cool the heat-pressed film. By carrying out such a step, the shape precision of the resulting transmission optical element can be improved. The start point of the mold cooling step can be, for example, the time when the temperature control for cooling the flat mold is started after a predetermined time has elapsed from the start of the heat pressing step, or the time when the heat input to the flat mold is stopped after a predetermined time has elapsed from the start of the heat pressing step. The end point of the mold cooling step can be the time when the mold temperature has dropped to the mold cooling temperature described later, or the time when a predetermined time (for example, 50 seconds) has elapsed from such a time.

<<Mold cooling temperature>>
The mold cooling temperature must be equal to or lower than the glass transition temperature (Tg _r )° C. of the thermoplastic resin film, and is preferably equal to or lower than (Tg _r -15)° C., more preferably equal to or lower than (Tg _r -30)° C., and even more preferably equal to or lower than (Tg _r -40)° C. In addition, the mold cooling temperature is preferably equal to or higher than (Tg _r -80)° C., and more preferably equal to or higher than (Tg _r -75)° C. If the mold cooling temperature is equal to or lower than the upper limit, the mold is easily released in the demolding step described below, and the shape precision of the resulting transmission optical element can be effectively improved. If the mold cooling temperature is equal to or higher than the lower limit, the production efficiency of the transmission optical element can be further improved.

<<Other mold cooling conditions>>
The mold cooling time and mold cooling rate are not particularly limited and can be appropriately determined depending on the type and size of the thermoplastic resin film, the shape and size of the intended transmission type optical element, 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.

<Mold release process>
In the demolding step, after the die cooling step, the heat-pressed film is released from the pair of flat die molds while applying tension to the heat-pressed film to obtain a molded film including a plurality of transmissive optical elements. "When releasing from the pair of flat die molds" means the time when the die cooling step is completed and the pair of flat die molds start to open. By applying tension to the heat-pressed film at this time, it is possible to suppress the distortion of the transmissive optical element during demolding and improve the shape accuracy of the resulting transmissive optical element. Here, it is preferable that the tension is applied as a force in the direction along the conveying direction. In addition, the method of controlling the tension in the demolding step is not particularly limited, and can be controlled by a known method. For example, it can be controlled by a roll for unwinding the heat-pressed film, a roll for winding the heat-pressed film, or a nip roll separately provided for tension control. An exemplary configuration of a roll-to-roll manufacturing device equipped with an unwinding roll and a winding roll will be described later with reference to FIG. 1.
Furthermore, it is preferable that tension is applied continuously or intermittently to the thermoplastic resin film not only in the demolding process but also in each stage from the mold heating process in which the thermoplastic resin film contacts one of the pair of flat molds in the above-mentioned heat pressing process until the demolding process is started. This is because the shape precision of the obtained transmission type optical element can be further improved. Of course, tension may also be applied to the thermoplastic resin film in other processes performed outside the above period. That is, tension may also be applied to the thermoplastic resin film through all processes from the conveying process to the processes that can be performed after the demolding process.

<<Tension>>
The magnitude of tension applied to the heat press film in the transport direction is preferably 1N or more, more preferably 10N or more, and preferably 2000N or less, more preferably 1000N or less per 1m of the width of the thermoplastic resin film. The "width of the thermoplastic resin film" refers to the direction perpendicular to the transport direction. If the magnitude of the tension is equal to or greater than the lower limit, the shape precision of the resulting transmission optical element can be further improved. If the magnitude of the tension is equal to or less than the upper limit, the heat press film is prevented from breaking, and the manufacturing efficiency of the transmission optical element can be further improved.

<Transmission Optical Element Separation Process>
In the transmissive optical element separation step, a plurality of transmissive optical elements are separated from the molded film obtained through the demolding step. By carrying out the transmissive optical element separation step of separating a plurality of transmissive optical elements from the molded film, the transmissive optical elements can be manufactured more efficiently. The separation method is not particularly limited, and the transmissive optical elements can be separated one by one from the molded film by any known method such as punching with a punching die. The transmissive optical element separation step may be carried out on the same manufacturing line as the previous steps, i.e., in-line. Alternatively, the transmissive optical element separation step may be carried out on a manufacturing line different from the previous steps, i.e., offline.

(Transmissive optical element manufacturing equipment)
FIG. 1 is a diagram showing a schematic structure of a transmissive optical element manufacturing apparatus that can be used to implement a method for manufacturing a transmissive optical element according to an embodiment of the present invention. The transmissive optical element manufacturing apparatus 100 includes an upper mold 1A and a lower mold 1B that constitute a pair of flat molds, an upper temperature controller 2A that supports the upper mold 1A and heats and cools it, a z-axis moving table 3 that supports the upper temperature controller 2A and is configured to be movable in the z-axis direction, a lower temperature controller 2B that supports the lower mold 1B and heats and cools it, and a lower table 4 that supports the lower temperature controller 2B. Furthermore, the transmissive optical element manufacturing apparatus 100 may include an unwinding roll 5A that is a component for sending out the thermoplastic resin film 7 and a winding roll 5B that is a component for winding up the molded film. Furthermore, the transmissive optical element manufacturing apparatus 100 may include a feed roll 6 as a component for controlling the sending mode of the thermoplastic resin film 7. Note that these various components are not limited to the illustrated embodiment, and can be replaced by any existing concrete means as long as they can perform the functions described above. 1, the vertical direction of the transmissive optical element manufacturing apparatus 100 is the z-axis, and the press surface of the transmissive optical element manufacturing apparatus 100 is the xy plane. The transmissive optical element manufacturing apparatus 100 shown in FIG. 1 is an apparatus for molding transmissive optical elements from a resin film by a so-called "roll-to-roll" method.

Hereinafter, among the steps that may be included in the above-mentioned manufacturing method of the transmissive optical element of the present invention, the conveying step (S01), the mold heating step (S02), the heat pressing step (S03), and the demolding step (S04) will be described as being performed using the transmissive optical element manufacturing apparatus 100 shown in FIG. 1.
The above-mentioned <Transmissive optical element separation step> can be performed by providing a punching unit (not shown) or the like in the transmissive optical element manufacturing apparatus 100 .

First, in preparation for carrying out the manufacturing method of the transmissive optical element of the present invention, a thermoplastic resin film 7 is set on the unwinding roll 5A, the winding roll 5B, and the feed roll 6 of the transmissive optical element manufacturing apparatus 100. Then, in the conveying step (S01), prior to the mold heating step and the heat pressing step (S02), the thermoplastic resin film 7 is conveyed along a predetermined conveying direction. In FIG. 1, the conveying direction is the direction indicated by the arrow 10.

When performing the mold heating step and the heat pressing step (S02), the thermoplastic resin film 7 is heat pressed by the upper mold 1A and the lower mold 1B. In addition, during the heat pressing step, the position of the thermoplastic resin film 7 in the z-axis direction can also be adjusted as appropriate. In the mold heating step that can be performed between the conveying step (S01) and the heat pressing step (S02), the temperature of the upper mold 1A and the lower mold 1B is set to the above-mentioned predetermined temperature range by the upper temperature adjustment device 2A and the lower temperature adjustment device 2B after the start of the mold heating step, that is, the time when at least one of the upper mold 1A and the lower mold 1B contacts the thermoplastic resin film 7, until the start of the heat pressing step (S02) (the time when the application of a predetermined press pressure starts).

In the mold cooling step (S03), it is preferable to adjust the temperatures of the upper mold 1A and the lower mold 1B to a temperature equal to or lower than the glass transition temperature (Tg _r ) °C of the thermoplastic resin film 7 by the upper temperature adjustment device 2A and the lower temperature adjustment device 2B.

Then, in the demolding step (S04), the thermoplastic resin film 7 as the heat-pressed film is released from the flat mold while tension is applied to the thermoplastic resin film 7. At this time, the tension can be applied and adjusted, for example, using the unwinding roll 5A, the winding roll 5B, and the feed roll 6.

(Outline of a manufacturing example of a transmissive optical element)
With reference to Figures 2 and 3, a case where an optical lens as a transmissive optical element is manufactured by the manufacturing method of a transmissive optical element of the present invention will be described. The components having the same reference symbols as in Figure 1 are as described in relation to Figure 1. In Figures 2 and 3, optical lenses of different shapes are manufactured, and therefore the shapes of the flat molds are different. For this reason, in Figure 2, they are shown as upper mold 1A' and lower mold 1B', and in Figure 3, they are shown as upper mold 1A" and lower mold 1B". In addition, since the shapes of the obtained optical lenses are different, in Figure 2, the obtained optical lens is shown as optical lens 8', and in Figure 3, the obtained optical lens is shown as optical lens 8".
2 and 3 are cross-sectional views seen from the conveying direction, and only a portion of the thermoplastic resin film 7, upper mold 1A' and lower mold 1B', upper mold 1A" and lower mold 1B", and optical lenses 8' and 8" are shown.

As shown in FIG. 2, the thermoplastic resin film 7 conveyed through the conveying step (S01) (not shown) is heat-pressed by a pair of flat molds, an upper mold 1A' and a lower mold 1B', in the heat pressing step (S02), to melt or deform the thermoplastic resin film 7 by heat, and fill the flat mold with the thermoplastic resin. The upper mold 1A' and the lower mold 1B' are in contact with each other at a portion not shown in the mold heating step and the heat pressing step (S02). In the heat pressing step (S02), the thickness of the thinnest part of the thermoplastic resin film 7 becomes D _min . Then, in the mold cooling step (S03), the upper mold 1A' and the lower mold 1B' are cooled. Furthermore, in the mold releasing step (S04), the thermoplastic resin film 7 as the molded film is released from the upper mold 1A' and the lower mold 1B'. Then, in the transmission optical element separating step (S05), the thermoplastic resin film 7 as the molded film is cut along the cutting lines shown by the dashed lines to obtain a plurality of optical lenses 8'.

Figure 3 is the same as Figure 2, except that the shapes of the upper mold 1A" and the lower mold 1B" are different, and multiple optical lenses 8" having a shape different from the example described with reference to Figure 2 are obtained.

(Transmissive Optical Element)
The optical lens as a transmissive optical element obtained by the manufacturing method of the transmissive optical element of the present invention has low birefringence and high shape accuracy. For example, the optical lens as a transmissive optical element obtained by the manufacturing method of the transmissive optical element of the present invention has a phase difference within the optical effective diameter of preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. An optical lens with a phase difference of 100 nm within the optical effective system is an optical lens with sufficiently low birefringence. In the present invention, the value of the phase difference can be obtained according to the method described in the examples.
The maximum error of the optical surface shape of the manufactured transmissive optical element obtained by the manufacturing method of the present invention, i.e., the PV (Peak to Valley) value, when the designed optical surface shape is used as a reference, is preferably 1.0 μm or less, more preferably 0.6 μm or less, and even more preferably 0.4 μm or less. A transmissive optical element having a PV value of 1.0 μm or less is a transmissive optical element having sufficiently high shape precision.

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 thickness, thickness variation, and glass transition temperature of the thermoplastic resin film were measured as follows. In the examples and comparative examples, the manufacturing efficiency considering the average shape accuracy, the shape accuracy variation, the retardation, and the shape quality rate, as well as the manufacturing efficiency considering the shape and low birefringence, were calculated and evaluated as follows.
In Examples 1 to 14 and Comparative Examples 2 to 3, when adjusting the tension during demolding to a desired value, a tension controller was used to control the unwinding roll and the take-up roll, etc., provided in a manufacturing apparatus having the schematic configuration shown in Fig. 1. The control values are shown in Table 1. The tension values shown in Table 1 are values per meter of the width of the thermoplastic resin film. The direction of the tension was set along the transport direction.
In the examples and comparative examples, optical lenses (biconvex lenses or convex meniscus lenses) were manufactured as the transmissive optical elements.

<Thickness of Thermoplastic Resin Film>
Three pieces of 250 mm length were cut out from the thermoplastic resin film at arbitrary positions, and the thickness was measured at 11 x 11 positions at 20 mm intervals in the center of each cut-out sample in the longitudinal direction and the width direction, to obtain the maximum thickness and minimum thickness of the thermoplastic resin film. The thickness of the thermoplastic resin film was the average value of these values. The thickness variation of the thermoplastic resin film was the difference between the maximum thickness and the minimum thickness.

<Glass Transition Temperature of Thermoplastic Resin Film>
The glass transition temperature (Tg) of the thermoplastic resin films used in the examples and comparative examples was measured using a differential scanning calorimeter (manufactured by SII Nano Technology, Inc., "DSC6220") at a temperature rise rate of 10°C/min in accordance with JIS K7121.

<Average shape accuracy and shape accuracy variation>
The shape accuracy of the optical lenses, which were the measurement samples obtained in the examples and comparative examples, was measured as a PV value with the designed optical surface as the reference surface using a shape measuring instrument ("NH-3SP" manufactured by Mitaka Optical Works, Ltd.) The simple average of the measured PV values was taken as the average shape accuracy, and the standard deviation was taken as the shape accuracy variation.
In Examples 1 to 14 and Comparative Examples 1 and 2, the PV value was measured for each of 396 optical lenses obtained in the same heat press process as the optical lenses serving as the measurement samples. In Comparative Example 3, the PV value was measured for each of 414 optical lenses, which were molded products from one revolution of the embossing roll. Furthermore, in Comparative Example 4, the PV value was measured for each of 160 optical lenses obtained by performing ten manufacturing steps using a 16-cavity mold.
[Evaluation criteria for average shape accuracy]
The obtained average value of shape accuracy was evaluated according to the following criteria.
A: 0.4 μm or less B: More than 0.4 μm and less than 0.6 μm C: More than 0.6 μm and less than 1.0 μm D: More than 1.0 μm [Evaluation criteria for shape accuracy variation]
The obtained values of variation in shape accuracy were evaluated according to the following criteria.
A: Within 0.1 μm B: Over 0.1 μm and within 0.2 μm C: Over 0.2 μm and within 0.3 μm D: Over 0.3 μm

<Phase difference>
The phase difference within the effective diameter of the optical lens, which is the measurement sample, was measured using a resin molded lens inspection system ("WPA-100", manufactured by Photonics Lattice). The phase difference value was obtained as a value normalized by the measurement wavelength (543 nm). The phase difference value was the simple average value of the values obtained by measuring multiple measurement samples.
The measurement samples used in each of the examples and comparative examples were the same as those described in the section <Average value of shape accuracy and variation in shape accuracy>.
The obtained retardation values were evaluated according to the following criteria: A smaller retardation value means a smaller birefringence.
A: 20 nm or less B: More than 20 nm and less than 50 nm C: More than 50 nm and less than 100 nm D: More than 100 nm

<Manufacturing efficiency taking into account shape and low birefringence>
The PV value and phase difference were measured for each measurement sample in the same manner as described in the items <Average shape accuracy and variation in shape accuracy> and <Retardation>, and a measurement sample having a PV value of 1.0 μm or less, a phase difference of 100 nm or less, and no cracks in the outer periphery was determined as "optical lens A with high shape accuracy and low birefringence." The number of such optical lenses A was divided by the time (cycle time; minutes) required to manufacture all the measurement samples used in each example and comparative example to calculate the number of optical lenses A per minute.
Furthermore, the ratio of the optical lens A to all the measurement samples was calculated.

Example 1
A 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=20 mm, manufactured by GSI Creos Corporation), melted at 260°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film having a maximum thickness of 202 μm, a minimum thickness of 198 μm, a thickness variation of 4 μm, and a width of 280 mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the film had a sufficient length for molding by a roll-to-roll molding method.

The thermoplastic resin film obtained as described above was set in a manufacturing apparatus having a schematic configuration shown in FIG. 1. The pair of flat molds used had 396 optical surface (i.e., lens surface) forming regions each having a diameter of 3.2 mm (number density: 0.63 pieces/cm ² ). The diameter of the optical surface forming portion included in the flat mold was 3.2 mm, the minimum distance between the optical surface forming regions was 10 mm, the total depth of the shallowest part (D _min ) was 150 μm, and the total depth of the deepest part in the optical surface forming region (D _max ) was 550 μm. The optical lens obtained by such a pair of flat molds is a biconvex lens. In this example, tension was applied to the heat press film in the conveying direction in all steps from the conveying step to the demolding step.

In the manufacture of the optical lens, a conveying step was carried out, and the thermoplastic resin film was conveyed in the conveying direction along the longitudinal direction of the film to a predetermined position. Then, the thermoplastic resin film was sandwiched between the pair of flat molds in an unheated state (80° C. or less) (press pressure: 0.5 MPa), and while maintaining that state, the flat molds were heated to 190° C. (press temperature, glass transition temperature Tg _r of the thermoplastic resin film +51° C.) (mold heating step). Then, the thermoplastic resin film was hot-pressed using a pair of flat molds at a press pressure of 6 MPa to obtain a hot-pressed film (hot-pressing step). Furthermore, while the hot-pressed film was pressed, the pair of flat molds were cooled to 80° C. (glass transition temperature Tg _r of the thermoplastic resin film −59° C.) over 40 seconds to cool the hot-pressed film sandwiched between the molds (mold cooling step). Then, the flat molds were opened to end the mold cooling step, and the demolding step was started. Then, the molded film containing the optical lenses obtained through the demolding process was subjected to a separation process by punching with a round blade having an inner diameter of 8 mm, to obtain 396 optical lenses. The magnitude of the tension applied to the heat press film in the demolding process was 100 N (100 N/m) per 1 m width of the thermoplastic resin film. The time required from the start of the conveying process to the completion of the demolding process (cycle time) was 180 seconds. The obtained optical lenses were subjected to various measurements and evaluations according to the above. The results are shown in Table 1.

Example 2
An optical lens was produced in the same manner as in Example 1, except that the tension applied to the thermoplastic resin film was changed as shown in Table 1. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

Example 3
An optical lens was manufactured in the same manner as in Example 2, except that no tension was applied to the thermoplastic resin film in the mold heating step, the heat pressing step, and the mold cooling step. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. Note that in steps other than the mold heating step, the heat pressing step, and the mold cooling step (i.e., the conveying step and the demolding step), the thermoplastic resin film was in a state of being under tension, as in Example 2.

(Examples 4 to 5)
The magnitude of tension applied to the hot-press film in the demolding process, the thickness of the thermoplastic resin film, and the sum of the shallowest depths (D _min ) and deepest depths (D _max ) of the flat metal mold used in the hot-pressing process were changed as shown in Table 1. Except for these points, optical lenses were manufactured in the same manner as in Example 1. Various measurements and evaluations were then performed in the same manner as in Example 1. The results are shown in Table 1. In Examples 4 and 5, slight breaks occurred in the thermoplastic resin film after the demolding process, reducing the manufacturing efficiency.

Example 6
Optical lenses were manufactured in the same manner as in Example 1, except that the temperature of the flat mold in the heat pressing step (pressing temperature) was changed as shown in Table 1. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.

(Examples 7 to 8)
An optical lens was manufactured in the same manner as in Example 1, except that the temperature (pressing temperature) of the flat die in the hot pressing step and the cooling temperature of the flat die in the die cooling step were changed as shown in Table 1. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Example 9)
An optical lens was produced in the same manner as in Example 1, except that a thermoplastic resin film prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of Thermoplastic Resin Film>
A thermoplastic resin 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 placed in a film extrusion molding machine (single-screw extruder, φ=20 mm, GSI Creos), melted at 260°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film having a maximum thickness of 202 μm, a minimum thickness of 198 μm, and a thickness variation of 4 μm and a width of 280 mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the film had a sufficient length for molding by a roll-to-roll molding method.

(Example 10)
An optical lens was produced in the same manner as in Example 1, except that a thermoplastic resin film prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of Thermoplastic Resin Film>
Polycarbonate resin (Wonderlite PC-115 (Asahi Kasei Corporation), glass transition temperature: 145°C) was placed in a film extrusion molding machine (single-screw extruder, φ=20 mm, GSI Creos Corporation), melted at 275°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film having a maximum thickness of 202 μm, a minimum thickness of 198 μm, a thickness variation of 4 μm, and a width of 280 mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the film had a sufficient length for molding by a roll-to-roll molding method.

Example 11
An optical lens was manufactured in the same manner as in Example 1, except that a thermoplastic resin film prepared as described below was used, and the temperature (pressing temperature) of the flat mold in the heat pressing step and the cooling temperature of the flat mold in the mold cooling step were changed as shown in Table 1. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of Thermoplastic Resin Film>
Polymethyl methacrylate resin (Delpet 80NH (Asahi Kasei Chemicals), glass transition temperature: 100°C) was placed in a film extrusion molding machine (single screw extruder, φ=20mm, GSI Creos), melted at 250°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film with a maximum thickness of 202μm, a minimum thickness of 198μm, and a thickness variation of 4μm and a width of 280mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the length was sufficient for molding by a roll-to-roll molding method.

Example 12
An optical lens was produced in the same manner as in Example 1, except that a thermoplastic resin film prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of Thermoplastic Resin Film>
Polyester resin (OKP-1 (Osaka Gas Chemicals), glass transition temperature: 132°C) was placed in a film extrusion molding machine (single screw extruder, φ=20 mm, GSI Creos), melted at 260°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film having a maximum thickness of 202 μm, a minimum thickness of 198 μm, a thickness variation of 4 μm, and a width of 280 mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the film had a sufficient length for molding by a roll-to-roll molding method.

Example 13
An optical lens was produced in the same manner as in Example 1, except that a thermoplastic resin film prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of Thermoplastic Resin Film>
A thermoplastic resin containing a norbornene-based ring-opening polymer hydride (ZEONEXE48R (manufactured by Zeon Corporation), glass transition temperature: 139°C) was placed in a film extrusion molding machine (single-screw extruder, φ=20 mm, manufactured by GSI Creos Corporation), melted at 260°C, and the molten resin was extruded from a T-die and cooled to obtain a thermoplastic resin film having a maximum thickness of 352 μm, a minimum thickness of 348 μm, a thickness variation of 4 μm, and a width of 280 mm. The direction perpendicular to the width direction of the thermoplastic film was the longitudinal direction, and the film had a sufficient length for molding by a roll-to-roll molding method.

(Example 14)
An optical lens was manufactured in the same manner as in Example 1, except that the flat mold was changed to make the obtained optical lens a convex meniscus lens, the total depth of the shallowest parts of the flat mold (D _min ) was 150 μm, and the total depth of the deepest parts in the optical surface forming region (D _max ) was 300 μm. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
An optical lens was produced in the same manner as in Example 1, except that no tension was applied to the thermoplastic resin film in the mold heating step, the heat pressing step, the mold cooling step, and the demolding step. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 2)
An optical lens was produced in the same manner as in Example 1, except that the flat mold was not cooled to a temperature equal to or lower than the glass transition temperature (Tg _r ) °C of the thermoplastic resin film in the mold cooling step. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 3)
Instead of an apparatus having a schematic configuration according to Fig. 1 as used in the examples, an apparatus having a schematic configuration including an embossing roll instead of the upper mold 1A and lower mold 1B in the schematic configuration according to Fig. 1 was used. The embossed shape of the embossing roll was a shape that could produce an optical lens having the same shape as in Example 1. In addition, a cooling process was not performed. Except for these points, an optical lens was produced in the same manner as in Example 1. Then, various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

(Comparative Example 4)
An optical lens was manufactured by carrying out an injection molding method according to each condition shown in Table 2. The same thermoplastic resin containing a norbornene-based ring-opening polymer hydride as in Example 1 was used as the injection molding material. The "ROBOSHOT S2000i100A" manufactured by FANUC was used as the injection molding device. A 16-cavity mold capable of manufacturing an optical lens of the same shape as in Example 1 was used as the injection molding die. Using these, 10 manufacturing steps were carried out at an injection speed of 30 mm/sec and a holding pressure of 80 MPa to manufacture 160 optical lenses. Then, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

In Tables 1 and 2, "NB-RO" stands for thermoplastic resin containing a norbornene-based ring-opening polymer hydride, "NB/ET" stands for norbornene-ethylene random copolymer, "PC" stands for polycarbonate resin, "ACR" stands for polymethyl methacrylate resin, and "PEs" stands for polyester resin.

From Table 1, it can be seen that in Examples 1 to 14, which were carried out by the manufacturing method of the present invention including a hot pressing step of hot pressing a thermoplastic resin film with a pair of plate dies to obtain a hot pressed film, a die cooling step of cooling the plate dies to a temperature below the glass transition temperature (Tg _r ) ° C., and a demolding step of releasing the hot pressed film while applying tension to it, it was possible to efficiently manufacture a transmission type optical element (optical lens) having low birefringence and high shape accuracy. On the other hand, from Table 2, it can be seen that in Comparative Example 1, in which tension was not applied to the hot pressed film in the demolding step, Comparative Example 2, in which the plate dies were not cooled to a temperature below the glass transition temperature (Tg _r ) ° C. in the die cooling step, and Comparative Examples 3 and 4, in which a plate dies were not used, it was not possible to efficiently manufacture a transmission type optical element having low birefringence and high shape accuracy.

According to the manufacturing method of the transmissive optical element of the present invention, it is possible to efficiently manufacture transmissive optical elements having low birefringence and high shape accuracy.

1A, 1A', 1A" Upper mold 1B, 1B', 1B" Lower mold 2A Upper temperature adjustment device 2B Lower temperature adjustment device 3 Z-axis direction moving table 4 Lower table 5A Unwinding roll 5B Winding roll 6 Feed roll 7 Thermoplastic resin film 8', 8" Optical lens 100 Transmissive optical element manufacturing apparatus

Claims (11)

A method for producing a transmissive optical element using a thermoplastic resin film, comprising the steps of:
A mold heating step of heating the thermoplastic resin film while sandwiching it between at least a pair of flat molds;
a heat pressing step of heat pressing the thermoplastic resin film with at least one pair of flat molds to obtain a heat pressed film after the mold heating step ;
a die cooling step of cooling the pair of flat dies to a temperature equal to or lower than the glass transition temperature (Tg _r ) ° C. of the thermoplastic resin film to cool the hot-pressed film;
a mold releasing step in which, after the mold cooling step, the heat-pressed film is released from the pair of flat molds while applying tension to the heat-pressed film at the time when the pair of flat molds start to open, thereby obtaining a molded film including a plurality of transmission type optical elements;
Including,
The pressing pressure in the die heating step is lower than the pressing pressure in the heat pressing step,
In the die heating step, heat input to the at least one pair of flat dies is started to be increased to a temperature of the at least one pair of flat dies in the heat pressing step.
A method for manufacturing a transmissive optical element. The method further includes a conveying step of conveying the thermoplastic resin film along a predetermined conveying direction prior to the heat pressing step,
2. The method for producing a transmissive optical element according to claim 1, wherein in the demolding step, the demolding is performed while applying tension along the transport direction, and the magnitude of the tension is 1 N or more and 2000 N or less per meter of the width of the thermoplastic resin film in a direction perpendicular to the transport direction. 3. The method for manufacturing a transmissive optical element according to claim 1 or 2, wherein at least one of the pair of flat dies includes a plurality of optical surface forming regions having a diameter of 1 mm or more and 15 mm or less, and an outer periphery forming region which is a region adjacent to each outer periphery of the plurality of optical surface forming regions, and a sum of depths of shallowest parts in the optical surface forming regions and the outer periphery forming region of the pair of flat dies is 500 μm or less. At least one of the pair of flat molds includes a plurality of optical surface forming regions that are discretely arranged in a planar direction of the flat mold,
The minimum distance between the optical surface forming regions is 1.0 mm or more.
A method for producing the transmissive optical element according to any one of claims 1 to 3. 5. The method for producing a transmission optical element according to claim 1, wherein the thermoplastic resin film has a glass transition temperature (Tg _r ) of 100° C. or more and 200° C. or less. 6. The method for producing a transmissive optical element according to claim 1, wherein a temperature of the pair of plate dies in the heat pressing step is (Tg _r +30)° C. or higher and (Tg _r +70)° C. or lower. 7. The method for producing a transmissive optical element according to claim 1, wherein in the die cooling step, the pair of plate dies are cooled to a temperature of (Tg _r -15) °C or lower. The method for producing a transmissive optical element according to any one of claims 1 to 7, wherein the thermoplastic resin film contains an alicyclic structure-containing resin. 9. The method for producing a transmissive optical element according to claim 1, wherein at least one of the pair of flat molds has an optical surface forming region with a density of 0.16 pieces/ ^cm2 or more. The method for manufacturing a transmissive optical element according to any one of claims 1 to 9, wherein both of the pair of flat molds have multiple optical surface forming regions. The method for producing a transmissive optical element according to any one of claims 1 to 10, further comprising a transmissive optical element separation step of separating the plurality of transmissive optical elements from the molded film obtained through the demolding step.

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