JP2001272501A - Plastic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic lens excellent in transferability even in a thin part and capable of ensuring good optical performance even when used in a short-wavelength laser optical system. SOLUTION: The convex plastic lens having <=0.7 minimum thickness for an optical pickup device for recording and/or reproducing information in an/or from an optical information recording medium with laser beam in the wavelength range of 350-450 nm is obtained by injection molding using a vinyl alicyclic hydrocarbon resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical lens for an optical pickup device, and more particularly, to an optical recording medium for recording and / or reproducing information on an optical information recording medium such as an optical disk or a magneto-optical disk. The present invention relates to an optical lens for a pickup device of a reproducing apparatus, and more particularly to a thin convex plastic lens manufactured by injection molding.

[0002]

2. Description of the Related Art Optical components such as an objective lens for a pickup device used for recording information on an optical information recording medium such as a compact disk (CD) or a digital video disk (DVD) or reproducing the recorded information are known. Recently, plastic lenses have been widely used because the development of molding technology has made it easy to form lenses having special shapes such as aspherical surfaces and fine patterns at low cost.

[0003] In recent years, since the speed of the optical pickup device has been demanded, it has become important to reduce the weight of the actuator used therein. For this reason, there is an increasing demand for smaller and thinner lenses for use in optical pickup devices for the purpose of weight reduction. Therefore, the present inventor tried to form a thin and convex plastic lens having positive power by injection molding using acrylic resin which has been conventionally used as a material of a pickup lens or the like. Inferior transferability deteriorates optical performance, and if the method of raising the resin temperature and injection pressure and increasing the mold temperature is used to improve the transferability, the resin will deteriorate and the mechanical strength of the lens will decrease. Various problems have arisen, such as inferior quality and time required for molding to increase product cost.

Further, in order to improve the recording density of the optical information recording medium, studies have been made to shorten the laser beam used for recording information or reproducing the recorded information. The shift to a blue laser having a wavelength of 350 to 450 nm has been attempted, and a lens that can cope with this is required. However, a conventional plastic lens has not been able to exhibit sufficient performance such as transmittance for short-wavelength light.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic lens which is excellent in transferability even in a thin portion and which can obtain good optical performance even when used in a short wavelength laser optical system. is there.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a thin film having a minimum thickness of 0.7 mm or less can be obtained by using a vinyl alicyclic hydrocarbon resin. When a convex lens is molded, a plastic lens having good transferability can be obtained even in the thin portion, and good optical performance can be obtained even for a short wavelength light having a wavelength of 350 to 450 nm such as a blue laser. Heading,
The present invention has been completed.

Thus, according to the present invention, optical information is obtained by laser light having a minimum thickness of 0.7 mm or less and a wavelength range of 350 to 450 nm, which is obtained by injection molding a vinyl alicyclic hydrocarbon resin. Provided is a convex plastic lens for an optical pickup device that records and / or reproduces information on a recording medium.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

Vinyl alicyclic hydrocarbon resin The vinyl alicyclic hydrocarbon resin used in the present invention is a resin having a repeating unit having an alicyclic structure in its side chain, usually 50% of the total repeating units of the resin. Or more, preferably 70% or more,
More preferably, the main component is a vinyl alicyclic hydrocarbon-based polymer containing 90% or more (hereinafter, may be simply referred to as a polymer). It is used as a composition containing an agent. In the present invention, each case is referred to as a vinyl alicyclic hydrocarbon-based resin (hereinafter, sometimes simply referred to as a resin).

The number of carbon atoms constituting the alicyclic structure of the vinyl alicyclic hydrocarbon polymer is usually 4 to 30, preferably 5 to 20, from the viewpoint of mechanical strength, heat resistance and moldability.
, More preferably in the range of 5 to 15, most preferably 6. Examples of such a vinyl alicyclic hydrocarbon-based polymer include a hydrogenated product of a vinylcyclopentene-based polymer, a hydrogenated product of a vinylcyclopentane-based polymer, a hydrogenated product of a vinylcyclohexene-based polymer, and a vinylcyclohexane-based polymer Hydrogenated products of vinylcycloheptene-based polymers or vinylcycloheptane-based polymers, hydrogenated products of vinylcyclooctene-based polymers or hydrogenated products of vinylcyclooctane-based polymers and aromatic vinyl-based polymers, etc. No. Among these, a hydrogenated product of a vinylcyclohexene-based polymer or a hydrogenated product of a vinylcyclohexane-based polymer and an aromatic vinyl-based polymer is preferable, and the hydrogenation rate of the carbon-carbon unsaturated bond in the ring is higher. Is preferred from the viewpoint of low birefringence.

The vinyl alicyclic hydrocarbon-based monomer used for obtaining the above-mentioned vinyl alicyclic hydrocarbon-based polymer includes, for example, styrene, α-methylstyrene, α-ethylstyrene, α-propyl Styrene, α-isopropylstyrene, α-t-butylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,
Styrene-based monomers such as 4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, and 4-phenylstyrene Isomers; vinylcyclohexane monomers such as vinylcyclohexane and 3-methylisopropenylcyclohexane; 4-vinylcyclohexene, 4-isopropenylcyclohexene, 1-methyl-4-vinylcyclohexene, 1-methyl-4-isopropenylcyclohexene; 2-methyl-4-vinylcyclohexene, 2
Vinylcyclohexene-based monomers such as -methyl-4-isopropenylcyclohexene; vinylated 6-membered hydrocarbon-based monomers such as terpene monomers such as d-terpene, 1-terpene and diterpene, or substituted products thereof And the like. When a styrene monomer containing an aromatic ring is used, the hydrogenation rate is preferably adjusted to 80% or more by a hydrogenation reaction. These monomers can be used alone or
More than one type may be used in combination.

In the present invention, a monomer other than the above-mentioned monomers may be copolymerized within a range where the repeating unit in the polymer is less than 50% by weight. The copolymerizable monomer is not particularly limited as long as it can be copolymerized in a polymerization method such as radical polymerization, anionic polymerization, or cationic polymerization, and the copolymer may be a random copolymer or a pseudo-random copolymer. Any of a polymer, a gradient block copolymer and the like may be used. Specific examples of the copolymerizable monomer include α-olefin monomers such as ethylene, propylene, isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, and 4-methyl-1-pentene. Cyclopentadiene-based monomers such as cyclopentadiene, 1-methylcyclopentadiene, 2-methylcyclopentadiene, 2-ethylcyclopentadiene, 5-methylcyclopentadiene, and 5,5-dimethylcyclopentadiene; cyclobutene, cyclopentene, cyclohexene , Cyclic olefin monomers such as dicyclopentadiene; butadiene,
Conjugated diene-based monomers such as isoprene, 1,3-pentadiene, furan, thiophene, and 1,3-cyclohexene; nitrile-based monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile; methyl methacrylate, methacrylic acid (Meth) acrylate-based monomers such as ethyl acid ester, propyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc .; acrylic acid, Unsaturated fatty acid monomers such as methacrylic acid and maleic anhydride; phenylmaleimide; ethylene oxide, propylene oxide, trimethylene oxide, trioxane, dioxane, cyclohexene oxide, styrene Kisaido, epichlorohydrin,
Cyclic ether monomers such as tetrahydrofuran; heterocyclic-containing vinyl compound monomers such as methyl vinyl ether, N-vinylcarbazole and N-vinyl-2-pyrrolidone; Generally, when the content of the repeating unit derived from a monomer other than the cyclic hydrocarbon monomer increases, the strength and heat resistance of the polymer decrease.

The method for producing the polymer having a vinyl alicyclic structure comprises homopolymerizing the above-mentioned monomer using a known polymerization method such as radical polymerization, anion polymerization, anion living polymerization, cation polymerization, or cation living polymerization. Alternatively, it can be obtained by copolymerization. The method of hydrogenating the polymer is not particularly limited and may be in accordance with a conventional method. The hydrogenation ratio of all unsaturated bonds including an aromatic ring is usually 80% or more, preferably 85%. Above, more preferably 90% or more, in many cases 90 to 100%.

Structure and product of vinyl alicyclic hydrocarbon polymer
The configuration of the vinyl alicyclic hydrocarbon-based polymer used in the present invention may be any of atactic, isotactic, and syndiotactic.
Any of 100% can be used. The glass transition temperature (Tg) of the polymer is not particularly limited, but is usually in the range of 80 to 250 ° C, preferably 90 to 220 ° C, more preferably 100 to 200 ° C. When Tg is in the above range, the balance between the strength characteristics and the moldability is excellent. The weight average molecular weight (Mw) of the polymer is generally 10,000 to 1,000, as a value in terms of polystyrene measured by gel permeation chromatography (GPC).
0000, preferably 50,000 to 500,000
0, more preferably in the range of 100,000 to 300,000. If Mw is too small, the strength properties will be poor, and if it is too large, the moldability will be poor, and the birefringence of the molded product will be large.
The molecular weight distribution of the polymer is similar to that of Mw described above,
Number average molecular weight in terms of polystyrene (M
n), it is usually 5.0 or less,
It is preferably at most 4.0, more preferably at most 3.0, particularly preferably at most 2.0. If this Mw / Mn is too large, the strength properties and heat resistance are reduced. In particular, in order to highly balance mechanical strength, heat resistance and moldability, Mw
/ Mn is preferably 2.0 or less, more preferably 1.7 or less, and particularly preferably 1.3 or less.

[0015] The difference contained in the vinyl alicyclic hydrocarbon resin
The vinyl alicyclic hydrocarbon resin used in the present invention preferably contains as few foreign substances as possible.
Foreign matter here refers to impurities mixed in from the outside,
It is not compatible with the resin, such as a catalyst residue, a gelled product, a by-product, and the like mixed in the polymer production process. The shape is usually granular, but is not limited thereto. If the number of foreign objects is large,
The transmitted light is scattered, and the power loss of the transmitted light is increased. The light scattering increases as the wavelength of the light used is shorter.
The effect is great when it is used for a pickup device of a short wavelength laser optical system of m to 450 nm. The resin used in the present invention has a content of foreign substances having a particle diameter of 0.5 μm or more of 3 × 10 ⁴ particles / g or less, preferably 2 × 10 ⁴ particles / g.
It is as follows. In particular, when a high degree of transparency (low haze value) is required, the content of foreign matter having a particle size of 0.5 μm or more is preferably 1 × 10 ⁴ particles / g or less, more preferably 7 × 10 ⁴ particles / g or less.
^It is reduced to ³ / g or less, particularly preferably 5 × 10 ³ / g or less. In the present invention, since the foreign matter in the resin falls within the above range, it is particularly suitable for use in a pickup device of a short wavelength laser optical system having a wavelength of 350 to 450 nm.

The method for reducing foreign matter is not particularly limited. In the polymer production process, the solution containing the polymer is mixed with (a) having a pore size of 0.5 μm or less, preferably 0.3 μm or less.
m, at least once, preferably twice or more, with a mechanical filter, and (b) a method of filtering with a filter having a charge trapping function.

The content of foreign matter in the resin can be measured using a light scattering type fine particle detector.

Volatile Component The vinyl alicyclic hydrocarbon resin used in the present invention has a volatile component content of usually 0.3% by weight (3000 pp).
m) or less, preferably 0.1% by weight (1000 ppm)
Or less, more preferably 500 ppm or less. In particular, in order to obtain a high-quality plastic lens, the content of the volatile component is preferably reduced to 500 ppm or less, more preferably to 300 ppm or less, and particularly preferably to 200 ppm or less. Examples of the volatile component include an organic solvent, an unreacted monomer or a modified product thereof. If the volatile component is too large, voids and concave defects on the surface are likely to occur during molding, and the homogeneity of the molded plastic lens is impaired.
Light scattering is likely to occur when used in a pickup device of a short wavelength laser optical system of up to 450 nm.

The method for reducing the volatile component is not particularly limited, but in the polymer production process, the polymerization conversion is improved during polymerization, the unreacted monomer is reduced, and in the process using an organic solvent, the solvent is removed. (For example, a method of optimizing the conditions (for example, temperature, degree of reduced pressure, etc.)).

Additives Various additives can be added to the vinyl alicyclic hydrocarbon resin used in the present invention as long as the properties of the plastic lens are not impaired. As additives,
For example, phenolic antioxidants, phosphorus antioxidants,
Antioxidants such as thioether-based antioxidants; UV absorbers such as benzophenone-based UV absorbers, salicylic acid-based UV absorbers, benzotriazole-based UV absorbers, acrylate-based UV absorbers, and metal complex salt-based UV absorbers; Light stabilizers such as light stabilizers; phosphoric acid triester compounds, phthalic ester compounds,
Fatty acid monobasic acid ester compounds, dihydric alcohol ester compounds, oxyacid ester compounds, paraffin compounds, liquid polymer compounds, etc .; plasticizers or softeners; alkyl sulfonates, glycerin esters of stearic acid, etc. Antistatic agents; aliphatic alcohols, aliphatic esters, aromatic esters, triglycerides,
Release agents such as fluorine surfactants and metal salts of higher fatty acids; lubricants; heavy metal deactivators and the like. Also,
As a modifier for preventing white turbidity in a long-time high-temperature and high-humidity environment, a soft polymer or an alcoholic compound having a Tg of 30 ° C. or less may be added. These additives are
Each of them may be used alone or in combination of two or more.

The amount of the additive is not particularly limited. For example, if it is an antioxidant, an ultraviolet absorber or a light stabilizer, it is usually 0.0001 to 5.0.
0 parts by weight, preferably 0.001 to 1.0 parts by weight, more preferably 0.01 to 0.5 parts by weight, and other additives may be appropriately selected according to the purpose. The method of adding the additive is not particularly limited, for example, during the production process of the polymer using an organic solvent, the additive is added to a solution in which the polymer is dissolved in the organic solvent and blended,
Thereafter, a method of removing the solvent, a method of kneading an additive to the polymer from which the solvent has been removed by using a twin-screw kneader or the like can be used.

Plastic Lens (Molding of Plastic Lens) The plastic lens of the present invention can be obtained by injection molding the above molding material. As a condition for injection molding, the cylinder temperature is usually 2
The temperature is 20 to 350 ° C, preferably 250 to 300 ° C.
Mold temperature is usually 50 to 180 ° C, preferably 80 to 15 ° C.
0 ° C. The injection pressure is usually 30 to 200 MPa, preferably 60 to 150 MPa. The pressure holding time is usually 1 to 300 seconds, preferably 5 to 150 seconds. The cooling time is usually 5 to 300 seconds, preferably 10 to 15 seconds.
0 seconds. If the cylinder temperature is too high, the resin will decompose,
Deterioration or the like may occur, resulting in a decrease in strength characteristics or coloring. If the temperature is too low, residual stress is generated in the plastic lens, thereby increasing birefringence or deteriorating transferability. If the mold temperature is too high, mold release failure occurs, and if the mold temperature is too low, birefringence increases and transferability deteriorates. If the pressure-holding time is too long, the resin is decomposed or deteriorated, and if it is too short, the molding shrinkage becomes large. If the cooling time is too long, the productivity decreases, and if it is too short, the birefringence increases or the transferability deteriorates. Therefore, when these molding conditions are in the above range, the mechanical strength, the birefringence, the releasability, the transferability, the productivity, etc. of the molded plastic lens are highly balanced, which is preferable.

The plastic lens of the present invention can be used not only for injection molding but also for (1) pressing a molten resin mass formed by heating and melting a resin while the temperature of the resin mass is equal to or higher than the glass transition temperature. Press molding using a mold,
It is also possible to mold using a molding method such as (2) a method of press-molding a preformed body formed by injection molding, and (3) a method of directly supplying a resin pellet to a mold and press-molding. .

In the molding of the plastic lens of the present invention, it is preferable to reduce foreign substances in the environment at the time of molding in order to prevent the aforementioned foreign substances from being mixed. The above steps are preferably performed in a clean room, and more preferably all steps are performed in a clean room. In this case, the cleanliness in the clean room is usually 10,000 (the number of particles having a particle diameter of 0.5 μm or less in 1 m ^{3 of} air is 10,10).
000 or less), preferably class 6,000 or less (6,000 or less).

(Plastic Lens) The plastic lens of the present invention has a positive power and is particularly a biconvex lens. As shown in FIG. It is injected into the flange 13 and formed. The flange 13 may be omitted for positioning when the plastic lens 1 is incorporated into the device. As described above, in order to actually incorporate the injection-molded plastic lens 1 into the apparatus, an unnecessary gate portion 11 is removed by cutting a position indicated by a broken line in FIG. The plastic lens of the present invention is not limited to the shape as shown in FIG. 1, but has a blazed grating type by forming a sawtooth-shaped step in a ring shape on the lens surface in order to suppress a change in the focal position due to a temperature change. It may be a shape having a diffraction surface or a step for forming astigmatism.

In the present invention, the above-mentioned vinyl alicyclic hydrocarbon resin is injection-molded so that the minimum thickness T is 0.7.
It is now possible to mold plastic lenses having a size of less than 1 mm.
(Here, the “minimum thickness T (mm)” refers to a thickness (length) in a direction parallel to the optical axis when the plastic lens is viewed in a cross section substantially passing the center of the gate section 11 including the optical axis. Of which
Refers to the shortest thickness. If the exact position of the gate portion 11 is not known because the gate portion 11 is removed by being cut as described above, the cross section including the substantially center of the cut portion and the optical axis is used. . Alternatively, when there are many cut portions and the position of the gate portion 11 is not known at all, the cross section is viewed at an arbitrary cross section including the optical axis, and is the shortest of the thicknesses (lengths) in the direction parallel to the optical axis. The thickness is defined as a minimum thickness T (mm). In general, as the minimum thickness T decreases, T and the thickness D (m on the optical axis (indicated by a dashed line in FIG. 1A)).
m), the flowability of the molten resin during injection molding decreases, and it becomes difficult to mold a plastic lens having good transferability. However, in the present invention, the minimum thickness T is 0.7 m.
m or less, and when the difference between T and D is large, specifically, when the ratio of T to D (T / D) is 0.4 or less, good plastic lens molding can be achieved. It is possible.

In addition, a residual stress generally occurs in a plastic lens manufactured by injection molding, which causes birefringence in the plastic lens. When a plastic lens having a large birefringence is used for an optical pickup device, the spot shape is deformed into an elliptical shape, and recording / reproducing of an optical information recording medium (an optical disc such as a CD or DVD) cannot be performed well. Therefore, since the magnitude of the birefringence can be considered as equivalent to the phase difference, the phase difference distribution of the plastic lens measured from the direction parallel to the optical axis is δ <δ when the maximum phase difference in the lens is δ. | 50 ° | is preferable, and δ <|
It is more preferable to satisfy 20 ° |. By satisfying this condition, a good spot shape can be obtained. The phase difference can be measured by a method generally known as the Senarmont method.

When this plastic lens is used for an optical element (objective lens, collimator lens, etc.) used in an optical pickup device for recording / reproducing an optical information recording medium, the radii of curvature near the optical axis are R1, R2. (However, R
When 1> R2), it is preferable to satisfy R1 / R2 <−0.26. If the value of R1 / R2 is 0.26 or more, the absolute value of the magnification of the plastic lens becomes small, and the distance between the object and the image becomes long, which makes it possible to achieve miniaturization of the optical pickup device. Disappears. The radius of curvature near the optical axis was measured using a three-dimensional measuring device “UA3P” manufactured by Matsushita Electric Industrial Co., Ltd.
It can be measured by the R measurement function attached to this “UA3P”. The measurement conditions are near the optical axis (φ0.6
mm) at a pitch of 10 μm.

The purpose of the plastic lens of the present invention is to provide a lens for an optical pickup device using a laser beam having a wavelength in the range of 350 to 450 nm, but in another wavelength range, for example, 450 to 830 n.
It may be used for an optical pickup device using laser light in the wavelength range of m.

[0030]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Production Examples, Examples, and Comparative Examples, but the scope of the present invention is not limited to these examples. In addition,
[Parts] and [%] are based on weight unless otherwise specified.

Various physical properties were measured according to the following methods. (1) The molecular weight was measured by GPC using toluene as a solvent, and the weight average molecular weight (Mw) in terms of standard polystyrene was determined. Similarly, the number average molecular weight (Mn) is determined, and Mw and M
The ratio of n (Mw / Mn) was calculated as the molecular weight distribution. (2) The hydrogenation rate was measured by the ¹ H-NMR method. (3) The light transmittance was measured using a visible spectrophotometer. (4) Haze value (haze value) was measured according to JIS K-7105. (5) The transfer rate was determined by observing the molded lens with an optical microscope, and the lens having no defects such as sink marks, dents on the surface, and roughness was evaluated as good. (6) Wavefront aberration was measured using a Mark IV xp interferometer system (manufactured by Zygo).

[0032] [Production Example 1] A stainless steel pressure vessel producing polymerized sufficiently dried and purged with nitrogen for molding material (vinyl alicyclic hydrocarbon resin),
76 parts of styrene (St) and 4 parts of isoprene (IP) are sealed and mixed and stirred, and the composition is (St / IP) =
A mixed monomer of (95/5) was prepared. Next, the dehydrated cyclohexane 320 was placed in a stainless steel autoclave equipped with a sufficiently dried and nitrogen-purged electromagnetic stirrer.
Parts, 4 parts of a mixed monomer and 0.1 part of dibutyl ether, and 0.18 part of an n-butyllithium solution (hexane solution containing 15%) was added with stirring at 50 ° C. to initiate polymerization. After conducting the polymerization reaction under the same conditions for 0.5 hour (the conversion at this point was 96%), 76% of the polymerization reaction solution in the autoclave was added while continuing the polymerization reaction under the same conditions. Parts of the mixed monomer were added continuously over 1 hour. After completion of addition (conversion at this point is 95%
), And the polymerization was carried out under the same conditions for 0.5 hour. Thereafter, 0.1 parts of isopropyl alcohol was added to stop the reaction, and a styrene-isoprene copolymer was synthesized.

Hydrogenation of Polymer Next, 400 parts of the above polymer-containing polymerization reaction solution was added to a stabilized nickel hydrogenation catalyst E22U (manufactured by Nikki Chemical Co., Ltd .;
8 parts of a 60% nickel-supported silica-alumina support) were added and mixed, and charged into a stainless steel autoclave equipped with an electric heating device and an electromagnetic stirrer for controlling the hydrogenation reaction temperature. After completion of the charging, the inside of the autoclave was replaced with hydrogen gas, and a hydrogenation reaction was performed at 160 ° C. for 6 hours while supplying hydrogen so as to keep the pressure inside the autoclave at 4.5 MPa while stirring. After the completion of the hydrogenation reaction, the mixture was subjected to pressure filtration at a pressure of 0.25 MPa using Radiolite # 800 as a filtration bed using a pressure filter (Funda Filter, manufactured by Ishikawajima-Harima Heavy Industries, Ltd.) to obtain a colorless and transparent solution. Was. Then, the resulting solution was added with a polymer solid content of 10%.
To 0 parts, 0.02 parts of pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] was added as an antioxidant and dissolved.

Removal of foreign substances The solution was filtered with a metal fiber filter (pore size 0.5 μm).
m, manufactured by Nichidai Co., Ltd.). Then, the filtrate was filtered through a Zetaplus filter 3OS (pore size: 0.5 to 1 μm, manufactured by Kuno), and further filtered through a metal fiber filter (pore size: 0.2 μm, manufactured by Nichidai) to remove foreign substances.

Removal of Volatile Components and Pelletization The filtrate (polymer concentration = 20%) obtained above is heated to 250 ° C. by a preheating device, and a cylindrical concentration dryer (manufactured by Hitachi, Ltd.) at a pressure of 3 MPa. Continuously. The operating conditions of the concentration dryer were adjusted so that the pressure was 60 kPa and the temperature of the polymer solution concentrated inside was 260 ° C. The concentrated solution was continuously led out of the concentration dryer, and further supplied to the same concentration dryer at a pressure of 1.5 MPa while maintaining the temperature at 260 ° C. The operating conditions were a pressure of 1.5 kPa and a temperature of 270 ° C. The polymer in a molten state is continuously drawn out from a concentration dryer, extruded from a die in a class 100 clean room, cooled with water, cut with a pelletizer (OSP-2, manufactured by Nagata Seisakusho), and pelletized (vinyl alicyclic type). (Hydrocarbon resin). The pellets were filled and stored in a stainless steel closed container having a polished surface.

The pellet was dissolved in chlorobenzene and analyzed by gas chromatography (G-3000, manufactured by Hitachi, Ltd., detection limit: 10 ppm). The volatile component content was 150 ppm. The weight average molecular weight (Mw),
And the molecular weight distribution (Mw / Mn) was measured.
= 132,000, Mw / Mn = 1.19. The hydrogenation rate was almost 100%, and Tg was 125 ° C. Further, using toluene purified by filtration with a filter having a pore size of 0.2 μm, the pellet was dissolved and 1.5%
And a light scattering particle detector (KS-58,
As a result of measuring the number of foreign particles having a particle size of 0.5 μm or more using Rion Co., Ltd., it was 2.1 × 10 ³ particles / g.

Example (Molding of Lens) An injection molding machine (manufactured by FANUC, AUTOSHOTC MODEL 30 ) was used using the pellets obtained in Production Example 1.
According to A), at a mold clamping force of 30 t, a resin temperature of 260 ° C., a mold temperature of 100 ° C. and an injection pressure of 90 MPa, the optical effective diameter =
A biconvex lens having a thickness of 2.8 mm, a minimum thickness T of 0.45 mm, and a thickness D on the optical axis of D = 1.8 mm (T / D = 0.25) was formed. The molding was performed in a class 1000 clean room. The transferability of the obtained lens was good, and 430 n
The light transmittance at m was 91% and the haze value was 0.1%. The wavefront aberration was 0.012λ, which was sufficiently small.

[0038] Instead of the pellets obtained in Comparative Example Preparation Example 1, except for using the acrylic resin (OPTOREZ OZ-1000, manufactured by Hitachi Chemical Co., Ltd.) in the same manner as in Example, the same shape as in Example Lenses were molded. The obtained lens had sink marks in the thick part and had poor transferability. The light transmittance at 430 nm was 90%, and the haze value was 0.2%. The wavefront aberration was as large as 0.052λ.

[0039]

As described in detail above, according to the present invention,
To provide a plastic lens that does not require time for injection molding, can reduce product cost, is excellent in transferability, and can obtain good optical performance especially when used in a short wavelength laser optical system such as a blue laser. Can be.

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a plastic lens (a sectional view (a) and a front view (b)).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Plastic lens 11; Gate part 12; Lens part 13; Flange part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 11:00 B29L 11:00 F term (Reference) 4F206 AA49 AC01 AH38 AH73 JA07 JE21 4J100 AA02Q AA03Q AA04Q AA15Q AA17Q AA20P AB02P AB03P AB04P AB07P AB08P AB10P AE03Q AJ02Q AK32Q AL03Q AM02Q AM48Q AQ08Q AQ26Q AR03Q AR04Q AR05Q AR17Q AR22Q AR31Q AR32Q AS02Q AS03Q AS04Q AS15P BC43P CA01 CA04 CA31 HA03 HA04 HA05 JA33

Claims (1)

[Claims] 1. Recording information on an optical information recording medium by using a laser beam having a minimum thickness of 0.7 mm or less and a wavelength range of 350 to 450 nm obtained by injection molding a vinyl alicyclic hydrocarbon resin. And / or a convex plastic lens for an optical pickup device for performing reproduction.