JP2015116788A - Method for molding optical lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a thin and small lens having a low birefringence, high surface accuracy and an excellent appearance.SOLUTION: A method for molding an optical lens is provided, which includes vacuum compression molding of a resin sheet having a projection in a lens mold. A thickness T of the resin sheet, a radius of curvature r of the projection, a projection height h, a radius of curvature R of the lens mold, and a lens height H1 in a thickest part and a lens height H2 in a thinnest part of the lens satisfy R>r, h≥(H1-H2), and T>H2.

Description

  The present invention relates to a molding method suitable for a thin and small optical lens.

Along with recent developments in electronic technology, electronic and electrical devices are becoming lighter, smaller, and thinner. In particular, in mobile phones, the mounted camera unit is required to have a thin shape and a small diameter, and to have good F-number characteristics (aperture value) and MTF characteristics (contrast reproduction ratio) in terms of image quality. It has been. In addition, a lens employed in a camera unit is required to be manufactured by an injection molding method that is low in manufacturing cost and suitable for mass production.
By the way, a small-diameter lens whose diameter is less than 1 cm has a wide optically effective surface. However, when a lens is formed by injection molding, it is difficult to widen the optical effective surface because weld lines and birefringence are made non-uniform.

As a method for injection molding a small and thin lens, Patent Document 1 proposes using a composition comprising a norbornene polymer and a wax. However, when a wax is blended, the wax may bleed on the surface of the molded body, causing problems such as mold contamination.
Further, Patent Document 2 discloses that a polymer having a specific monomer composition is excellent in thin-wall moldability, and provides a small and thin lens in which optical characteristics and heat resistance are highly balanced. .
By the way, in Patent Document 3, as a method of forming a microlens array having irregularities of different sizes on both surfaces, a resin pellet is filled in a mold for forming a large convex portion, this is covered with a resin sheet, and a small concave portion is formed. A method of heat pressing with a mold having

JP 2009-138111 A JP 2010-150443 A JP 2012-181515 A

When trying to obtain a thin and small lens by injection molding, the resin fills the fine gaps in the mold, so birefringence appears in the lens and it is difficult to ensure high surface accuracy. As a result of the study by the present inventors, it has been found that these problems cannot be solved even if the polymer of Patent Document 2 is used.
As a result of further studies, the present inventors have found that this problem can be solved by compression molding using a specific resin member instead of injection molding, and the present invention has been completed.

Thus, according to the present invention, there is provided an optical lens molding method in which a resin sheet having protrusions is vacuum compression molded in a lens mold, wherein the thickness of the resin sheet is T, the radius of curvature of the protrusions is r, the protrusion height is When the thickness is h, the radius of curvature of the lens mold is R, the lens thickest part height is H1, and the lens thinnest part height is H2.
R> r and h ≧ (H1−H2) and T> H2
An optical lens molding method is provided.
A remarkable effect is obtained when the resin sheet is made of an alicyclic structure-containing resin.
Further, when the optical lens is an imaging system convex lens, a significant effect is obtained.

It is a figure for demonstrating the relationship between a resin sheet and a lens metal mold | die.

  The resin constituting the resin sheet used in the present invention is a (meth) acrylic resin, an alicyclic structure-containing resin, a styrene resin, a polycarbonate resin, a polyester resin, a polyether resin, or a urethane resin that is generally used for plastic lenses. And thiourethane resin. In particular, in the present invention, an alicyclic structure-containing resin is preferably used.

  The alicyclic structure-containing resin is a resin having an alicyclic structure in the main chain and / or side chain. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance, etc., a cycloalkane structure or a cycloalkene structure is preferable, and among them, a cycloalkane structure is most preferable. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The heat resistance and the moldability characteristics of the imaging element are highly balanced and suitable.

As a specific example of the alicyclic structure-containing resin,
(1) Ring-opening polymer of norbornene-based monomer, ring-opening copolymer of norbornene-based monomer and other monomer capable of ring-opening copolymerization, and hydrogenated products thereof, norbornene-based Norbornene polymers such as addition polymers of monomers and addition copolymers of norbornene monomers and other monomers copolymerizable therewith,
(2) a monocyclic olefin polymer and a hydrogenated product thereof,
(3) a cyclic conjugated diene polymer and a hydrogenated product thereof,
(4) Polymers of vinyl alicyclic hydrocarbon monomers, copolymers of vinyl alicyclic hydrocarbon monomers and other monomers copolymerizable therewith, and hydrogenation thereof , Aromatic aromatic hydrogenated products of vinyl aromatic monomers, and aromatic aromatic hydrogenated copolymers of vinyl aromatic monomers and other monomers copolymerizable therewith And vinyl alicyclic hydrocarbon-based polymers. Among these, an alicyclic structure-containing polymer is particularly preferable from the viewpoints of heat resistance, mechanical strength, and the like.
Specific examples of such alicyclic structure-containing polymers include ring-opening polymers described in JP-A-5-279554 and hydrogenated products thereof, and methacrylic groups described in JP-A-2004-0697985. And a polymer obtained by subjecting a norbornene derivative having a side chain to ring-opening polymerization with a metallocene catalyst or the like and then hydrogenation, and a copolymer of ethylene and a cyclic olefin described in JP-A No. 2001-26693.

  Specific examples of commercially available alicyclic structure-containing resins include ZEONEX (registered trademark), ZEONOR (registered trademark) manufactured by Nippon Zeon, APEL (registered trademark) manufactured by Mitsui Chemicals, ARTON (registered trademark) manufactured by JSR, and polyplastics. TOPAS (registered trademark) manufactured by SU

In the present invention, arbitrary additives such as a rubbery polymer, an antioxidant, a light stabilizer, a heat stabilizer, an antistatic agent, and a lubricant can be added to the resin.
There is no particular limitation on the method of adding the additive to the resin, for example, a method of mixing the resin and the additive while kneading in a kneader such as a roll, kneader, extrusion kneader, Banbury mixer, feeder ruder, etc .; A method of dissolving in an appropriate solvent, adding an additive to the solvent, mixing the mixture, and then removing the solvent; and the like.
A resin containing additives as required is usually formed into a sheet after being pelletized. There are no particular restrictions on the pellet manufacturing method, but the resin and additives blended as needed are mixed using a mixer such as a twin-screw kneader and then extruded into a strand, which is then extruded with a pelletizer, etc. Pellets can be obtained by finely cutting.

There is no special restriction | limiting in the shaping | molding method of the resin sheet which has protrusion, Melt extrusion molding, solution casting molding, injection molding, etc. are mentioned. In particular, a melt extrusion method capable of forming protrusions simultaneously with sheet forming is preferred.
In order to form a resin sheet having protrusions by the melt extrusion method, for example, using a film extrusion molding machine, the molten resin extruded from the T die is guided between the embossing roll and the nip roll, and the molten resin is embossed by the nip roll. Examples include a method of pressing the roll and transferring the surface shape of the embossing roll. At this time, the molten resin temperature is usually Tg + 100 ° C. to Tg + 150 ° C., and the roll temperature is usually Tg−5 ° C. to Tg−30 ° C.

The thickness of the resin sheet having protrusions is T, the curvature radius of the protrusion is r, the protrusion height is h, the curvature radius of the lens mold is R, the lens thickest part height is H1, and the lens thinnest part height. Is H2,
R> r and h ≧ (H1−H2) and T> H2
It is preferable that
The radius of curvature r of the projection should be smaller than the radius of curvature R of the mold lens. However, from the viewpoint of lens shape transfer and surface accuracy, preferably R>r> 0.05R, more preferably R>r> 0.5R. It is.
The height h of the protrusion may be equal to or greater than the difference between the lens thickest part height H1 and the lens thinnest part height H2 of the lens mold, but from the viewpoint of lens surface accuracy near the thickest part of the molded product, 1.5H1 ≧ h ≧ (H1−0.5H2), more preferably 1.2H1 ≧ h ≧ (H1−0.8H2).
The thickness T of the resin sheet may be thicker than the lens thinnest part of the lens mold, but preferably 1.2H2>T> H2, more preferably 1 from the viewpoint of lens surface accuracy near the thinnest part of the molded product. .1H2>T> H2.

An optical lens can be obtained by vacuum compression molding the above-described resin sheet in a lens mold and punching a lens molded product in the mold. The shape of the optical lens is a convex lens, and may be a plano-convex lens, a biconvex lens, or a convex meniscus lens. The curvature R shape of the convex lens may be a spherical lens or an aspheric lens. In vacuum compression molding, for example, using a vacuum heat press, mold heating compression temperature: Tg + 40 ° C. to Tg + 80 ° C., degree of vacuum: 10000 Pa or less, mold clamping pressure: 1 to 5 ton, mold compression time: 30 to Vacuum compression molding was performed under molding conditions of 120 seconds. A molded article that has been vacuum-compressed may be punched out in a mold, cooled at a mold temperature of Tg-3 ° C. to Tg-30 ° C., and then removed from the mold.
In the molding method described above, a plurality of lenses can be obtained in one step.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, the part and% in each example are a basis of weight unless there is particular notice.
Moreover, the measurement and evaluation in each example were performed by the following methods.
-Appearance evaluation The lens was visually observed, and the case where any one of outgassing failure, weld failure, or bubble failure occurred was evaluated as x, and the case without any defect was evaluated as ◯.
-Surface accuracy PV value was measured using the three-dimensional shape measuring instrument "UA3P" (made by Panasonic Corporation). A PV value of 0.5 or more was evaluated as x, 0.3 or more and less than 0.5 was evaluated as ◯, and less than 0.3 was evaluated as ◎.
-Birefringence Wide range The phase difference was evaluated using a birefringence evaluation system "WPA-100" (manufactured by Photonic Lattice). A sample having a phase difference of less than 80 nm was evaluated as ◯, and a sample having a phase difference of 80 nm or more was evaluated as ×.

(Manufacture of resin sheets)
A resin sheet was obtained by melt molding according to the following procedure.
Resin materials include norbornene-based ring-opening polymer hydride (product name “ZEONEX (registered trademark) F52R”, Tg: 156 ° C., manufactured by Nippon Zeon Co., Ltd.), and norbornene-ethylene addition copolymer (product name “APEL ( Registered trademark) 5514ML ”, Tg: 130 ° C., manufactured by Mitsui Chemicals, Inc.). The glass transition temperature is a value measured using a differential scanning calorimeter (manufactured by Nanotechnology, product name “DSC6220SII”) based on JIS K 6911 under a temperature increase rate of 10 ° C./min.
The resin material is put into a film extrusion molding machine (single screw extruder, φ = 20 mm: manufactured by GSI Kraos Co., Ltd.), the resin is melted at a temperature of Tg + 100 ° C., and the molten resin extruded from the T die is put between an embossing roll and a nip roll. The molten resin was pressed against the embossing roll with a nip roll to transfer the surface shape of the embossing roll to produce a resin sheet having a spherical protrusion shape. The roll temperature was Tg-10 ° C.
Table 1 shows the curvature radius r, projection height h, and film thickness T of the obtained resin sheet.
Examples 1-2 and Comparative Examples 1-5
The resin sheet obtained above is arranged so that the protrusions face the lens surface of the mold, and using a vacuum heat press (product name “VACUUM STAR (registered trademark), manufactured by Mikado Technos)”, the following Vacuum compression molding was performed under the conditions to obtain a lens, and various evaluations were performed on the obtained lens, and the results are shown in Table 1.
Compression molding conditions-Mold heating compression temperature: Tg + 40 ° C
・ Vacuum degree: 1000Pa
・ Clamping pressure: 5ton
・ Clamp compression time: 60 seconds ・ Mold cooling temperature: Tg-5 ° C.
Mold: 1 and 2 in FIG. 1 (R = 7.58 mm, H1 = 0.3 mm, H2 = 0.15 mm, H3 = 0.2 mm)

  From this result, when the curvature radius of the projection of the resin film is larger than the curvature radius of the mold (Comparative Examples 1 and 2), when compression molding is performed without applying a vacuum (Comparative Example 3), or when the thickness of the resin film is insufficient It can be seen that (Comparative Example 4) and when the height of the projection of the resin film is insufficient (Comparative Example 5), the appearance is poor and the surface accuracy is poor.

1: Lens side mold 2: Holding side mold 3: Resin sheet with protrusion h: Projection height of resin sheet T: Resin sheet thickness H1: Thickest part height of mold H2: Thinnest part of mold height

Claims (3)

An optical lens molding method in which a resin sheet having protrusions is vacuum compression molded in a lens mold, wherein the thickness of the resin sheet is T, the radius of curvature of the protrusions is r, and the protrusion height is h. When the radius of curvature of the mold is R, the lens thickest part height is H1, and the lens thinnest part height is H2,
R> r and h ≧ (H1−H2) and T> H2
An optical lens molding method. The molding method according to claim 1, wherein the resin sheet is made of an alicyclic structure-containing resin. The molding method according to claim 1, wherein the optical lens is an imaging system convex lens.