JPH11174204A - Laser pickup lens and optical element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser pickup lens having excellent non-double refractiveness, heat resistance and low hygroscopicity and an optical element using the same. SOLUTION: This lens is constituted by using a resin obtd. by polymerizing a monomer mixture consisting of the following monomer components, (A) to (E) at such a monomer compounding ratio at which the absolute value of the orientation double refraction of the resulted resin attains <1×10<-6> . (A) 5 to 40 wt.% methacrylate or acrylate having 5-22C alicyclic hydrocarbon group in an ester moiety, (B) 50 to 80 wt.% methyl acrylate, (C) 5 to 40 wt.% N-substd. maleimide, (D) 0 to 30 wt.% benzyl methacrylate and 0 to 10 wt.% monomer copolymerizable therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser pickup lens using a resin obtained by polymerizing a specific monomer at a specific monomer blend ratio such that the absolute value of the orientation birefringence is less than 1.times.10.sup.- ^6. And an optical element using the same.

[0002]

2. Description of the Related Art Conventionally, lenses, prisms, optical disks,
Glass has been used for optical elements such as LCD substrates. However, in recent years, plastics have been used for weight reduction and miniaturization. Polystyrene, polycarbonate, polymethyl methacrylate, styrene-methyl methacrylate copolymer, and the like are generally known as plastics used for optical elements. But,
Since polystyrene and polycarbonate have an aromatic ring in the molecule, birefringence is likely to occur due to orientation distortion, and it is necessary to devise a molding die as shown in JP-A-61-14617. So far,
Polymethyl methacrylate has been mainly used as an optical element material.

Polymethyl methacrylate has a small photoelastic coefficient and is relatively unlikely to cause birefringence due to orientation distortion, and is therefore used for optical elements that do not require relatively high precision, such as finder lenses and CD pickup lenses. It has been.

However, in recent years, there has been a demand for optical elements that require higher precision. In particular, a laser pickup lens for a write-once optical disc or a laser pickup lens for a magneto-optical disc using a laser beam is required to have not only a small birefringence but also a birefringence near zero near the gate.

On the other hand, polymethyl methacrylate can reduce the birefringence to some extent depending on the molding conditions, but the birefringence in the vicinity of the gate does not become zero and cannot be used for a laser pickup lens requiring high precision.

For the purpose of reducing birefringence, a monomer capable of obtaining a resin having a positive photoelastic coefficient and a monomer capable of obtaining a resin having a negative photoelastic coefficient are used as essential raw materials. Elastic modulus is -1 × 10 ^-13 cm ² / dyne or more, + 1 ×
A method of copolymerizing so as to be 10 ^-13 cm ² / dyne or less (JP-A-60-185236), copolymerization of methyl methacrylate, alkyl methacrylate having an alkyl group having 3 to 8 carbon atoms, and styrene (Japanese Unexamined Patent Publication No.
0-250010 and JP 61-76509 JP), methyl methacrylate, tricyclo [5.2.1.0 ^{2, 6]} dec-8-yl and a method of copolymerizing styrene (JP JP-A-62-246914), a monomer capable of forming a homopolymer having a positive birefringence (trifluoroethyl methacrylate, benzyl methacrylate, etc.) and a monomer capable of forming a homopolymer having a negative birefringence (methyl methacrylate, etc.) ) (JP-A-2-129211),
A method of copolymerizing methyl methacrylate with a compound having an unsaturated double bond whose photoelastic coefficient is opposite to that of polymethyl methacrylate when it is a homopolymer (JP-A-4-76013) is proposed. Have been.

[0007]

These conventional methods are:
Although each has achieved results, there are still many inadequate aspects. For example, the above, and methods, when injection molding, it is impossible to completely eliminate birefringence, birefringence due to stress strain remains near the gate, is insufficient as a non-birefringent material. is there.

[0008] The above-mentioned methods include combinations thereof, in which methyl methacrylate (MMA) and trifluoromethacrylate (3FMA) are included.
In the method using the monomer mixture of (2), the latter material (3F
MA) is a very expensive material.

Further, a method of copolymerizing a monomer mixture of methyl methacrylate (MMA) and trifluoroethyl methacrylate (3FMA) and a method of copolymerizing a monomer mixture of methyl methacrylate (MMA) and benzyl methacrylate (BZMA) can be used. ,
Unless the mixing ratio of trifluoroethyl methacrylate (3FMA) or benzyl methacrylate to methyl methacrylate is considerably increased, the development of orientation birefringence cannot be suppressed. That is, the mixing ratio necessary to cancel the orientation birefringence is MMA / 3FMA = 50 in the former case.
/ 50 (wt% / wt%), in the latter case MMA / BZ
MA = 80/20 (wt% / wt%). For this reason, the obtained material cannot have the same properties as PMMA, and is inferior in heat resistance and transparency as compared with PMMA. The present invention solves these problems with a specific resin.

[0010]

According to the present invention, a monomer mixture comprising the following monomer components (A) to (E) is prepared by adjusting the absolute value of the orientation birefringence of the obtained resin to 1 × 10 ^-6. The present invention relates to a laser pickup lens using a resin obtained by polymerization at a monomer compounding ratio of less than. (A) 5 to 40% by weight of a methacrylate or acrylate having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion, (B) 50 to 50% of methyl methacrylate
80% by weight, (C) 5 to 40% by weight of N-substituted maleimide, (D) 0 to 30% by weight of benzyl methacrylate, and (E) 0 to 10% by weight of a monomer copolymerizable therewith.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Monomer component (A) used in the present invention: As a methacrylic acid ester or an acrylic acid ester having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion, for example, acrylic acid Cyclopentyl,
Cyclohexyl acrylate, methylcyclohexyl acrylate, trimethylcyclohexyl acrylate, norbornyl acrylate, norbornyl methyl acrylate, cyanonorbornyl acrylate, isobornyl acrylate, bornyl acrylate, menthyl acrylate, fentyl acrylate, acrylic acid Adamantyl, dimethyl adamantyl acrylate, tricycloacrylate [5.
2.1.0 ^2,6 ] dec-8-yl, tricyclo [5.2.1.0 ^2,6 ] dec-4-methyl acrylate, cyclodecyl acrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, methacrylic acid Methylcyclohexyl, trimethylcyclohexyl methacrylate, norbornyl methacrylate, norbornylmethyl methacrylate, cyanonorbornyl methacrylate, phenylnorbornyl methacrylate, isobornyl methacrylate, bornyl methacrylate, menthyl methacrylate, fentyl methacrylate, methacrylic acid Adamantyl acrylate, dimethyl adamantyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] dec-8-yl methacrylate, tricyclo [5.2.1.0 ^2,6 ] deca-4-methyl methacrylate,
And cyclodecyl methacrylate. Among these, in terms of low hygroscopicity, cyclopentyl methacrylate, cyclohexyl methacrylate, methylcyclohexyl methacrylate, trimethylcyclohexyl methacrylate, norbornyl methacrylate, norbornyl methyl methacrylate,
Isobornyl methacrylate, bornyl methacrylate, menthyl methacrylate, fentyl methacrylate, adamantyl methacrylate, dimethyl adamantyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] deca-8-yl, tricyclomethacrylate [ 5.2.1.
0 ^2,6 ] dec-4-methyl, cyclodecyl methacrylate and the like are preferred. Further, heat resistance, particularly preferable in terms of low moisture absorption, cyclohexyl methacrylate, isobornyl methacrylate, norbornyl methacrylate,
Norbornylmethyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] dec-8-yl methacrylate and tricyclo [5.2.1.0 ^2,6 ] deca-4-methyl methacrylate are mentioned. Can be

The monomer component (C) used in the present invention:
Examples of the N-substituted maleimide include N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, Ni-propylmaleimide, N-butylmaleimide, Ni-butylmaleimide, Nt-butylmaleimide, N-laurylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, N-phenylmaleimide, N- (2-chlorophenyl) maleimide, N
-(4-chlorophenyl) maleimide, N- (4-bromophenyl) phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenylmaleimide, N- (2-methoxyphenyl) maleimide, N-
(2,4,6-trimethylphenyl) maleimide, N-
(4-benzylphenyl) maleimide, N- (2,4,
6-tribromophenyl) maleimide and the like.
Preferred from the viewpoint of non-birefringence and heat resistance are N
-Methylmaleimide, N-ethylmaleimide, N-propylmaleimide, Ni-propylmaleimide, N-butylmaleimide, Ni-butylmaleimide, Nt-
Butyl maleimide, N-cyclohexyl maleimide, N
-Laurylmaleimide and N-phenylmaleimide.

Further, the copolymerizable monomer (E) used in the present invention: The other copolymerizable monomer described above is basically composed of a polymer having transparency, non-birefringence, heat resistance and the like. There is no particular limitation as long as the low hygroscopicity is not impaired. Specific examples include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, i-butyl acrylate, and t-butyl acrylate. , Pentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate,
Acrylic esters such as n-octyl acrylate, dodecyl acrylate, octadecyl acrylate, butoxyethyl acrylate, phenyl acrylate, benzyl acrylate, naphthyl acrylate, glycidyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid Ethyl, propyl methacrylate, n-butyl methacrylate,
I-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, butoxyethyl methacrylate, phenyl methacrylate , Naphthyl methacrylate, glycidyl methacrylate,
Methacrylic esters such as 2-hydroxyethyl methacrylate, α-methylstyrene, α-ethylstyrene,
aromatic vinyl compounds such as α-fluorostyrene, α-chlorostyrene, α-bromostyrene, fluorostyrene, chlorostyrene, bromostyrene, methylstyrene, methoxystyrene, acrylamide, methacrylamide, N-dimethylacrylamide, N-diethylacrylamide (Meth) acrylamides such as N-dimethylmethacrylamide, N-diethylmethacrylamide, calcium acrylate, barium acrylate, lead acrylate, tin acrylate acrylate, zinc acrylate, calcium methacrylate, barium methacrylate, Metallic (meth) acrylates such as lead methacrylate, tin methacrylate, zinc methacrylate, etc .; unsaturated fatty acids such as acrylic acid and methacrylic acid; vinyl cyanide such as acrylonitrile and methacrylonitrile Thing, and the like. These may be used alone or in combination of two or more.

In the present invention, the ester moiety has 5 carbon atoms.
Methacrylate or acrylate having from 5 to 22 alicyclic hydrocarbon groups, from 5 to 40% by weight of methyl methacrylate; from 50 to 80% by weight of methyl methacrylate;
40% by weight, 0 to 30% by weight of benzyl methacrylate and 0 to 10% by weight of monomers copolymerizable therewith,
A resin obtained by copolymerizing a monomer mixture is used.

The monomer component (A) used in the present invention: the content of the methacrylate or acrylate having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion is 5 to 40% by weight. It is preferably from 10 to 40% by weight in terms of hygroscopicity. If the content of the alicyclic (meth) acrylate is less than 5% by weight, the birefringence tends to be large, and the hygroscopicity tends to be high. If it exceeds 40% by weight, the mechanical strength decreases. Occurs.

Also, the monomer component (B) used in the present invention:
The compounding amount of methyl methacrylate is 50 to 80% by weight, and preferably 60 to 75% by weight. If the amount of methyl methacrylate is less than 50% by weight, the mechanical strength is reduced, and if it exceeds 80% by weight, problems arise in non-birefringence, heat resistance and low moisture absorption.

Further, the compounding amount of the monomer component (C): N-substituted maleimide used in the present invention is from 5 to 40% by weight, and preferably from 10 to 30% by weight. It is preferred in that respect. If the amount of N-substituted maleimide is less than 5% by weight, birefringence tends to be large and the glass transition temperature tends to be low. If it exceeds 40% by weight, the reactivity tends to decrease and the residual monomer tends to increase. The birefringence also increases.

Further, the monomer component (D) used in the present invention:
The blending amount of benzyl methacrylate is 0 to 30% by weight, and preferably 4 to 20% by weight in terms of heat resistance and birefringence. If the amount of benzyl methacrylate exceeds 30% by weight, the glass transition temperature tends to decrease.

Also, the monomer component (E) used in the present invention:
The amount of the monomer copolymerizable therewith is 0 to 10% by weight.
And preferably 0 to 5% by weight. If the amount of the monomer component (E) is more than 10% by weight, the heat resistance decreases and the non-refractive property deteriorates.

The resin of the present invention preferably has an absolute value of the orientation birefringence of less than 1 × 10 ⁻⁶ .
From the polymer of each mixing ratio obtained by suspension polymerization, about 5
This is carried out by a method in which a film having a thickness of 0 μm is prepared and stretched twice (stretching temperature: 90 ° C.) to find a compounding ratio at which the absolute value of birefringence becomes less than 1 × 10 ⁻⁶ .

As the polymerization method for producing the resin for a laser pickup lens of the present invention, existing methods such as bulk polymerization, suspension polymerization, emulsion polymerization and solution polymerization can be applied.
In order to manufacture a laser pickup lens, a suspension polymerization method is preferred from the viewpoint of handling as a product.

In carrying out the polymerization of the present invention, a polymerization initiator can be used. As the polymerization initiator, benzoyl peroxide, lauroyl peroxide, di-t-butylperoxyhexahydroterephthalate, t-butylperoxy-
Organic peroxides such as 2-ethylhexanoate, 1,1-t-butylperoxy-3,3,5-trimethylcyclohexane, azobisisobutyronitrile, azobis-4
Azo compounds such as -methoxy-2,4-dimethylvaleronitrile, azobiscyclohexanone-1-carbonitrile and azodibenzoyl; water-soluble catalysts such as potassium persulfate and ammonium persulfate; and peroxides or persulfates and reducing agents Any of those that can be used for ordinary radical polymerization, such as a redox catalyst by a combination of the above, can be used. The polymerization initiator is 0.01% based on the total amount of the monomers.
It is preferably used in the range of 10 to 10% by weight.

Further, as a molecular weight modifier, a mercaptan compound, thioglycol, carbon tetrachloride, α-methylstyrene dimer and the like can be added as required.

In the case of thermal polymerization, the polymerization temperature is from 0 to 20.
It can be appropriately selected between 0 ° C., and preferably 50 to 120 ° C.

The suspension polymerization is carried out in an aqueous medium, and is carried out by adding a suspending agent and, if necessary, a suspending aid. As a suspending agent, polyvinyl alcohol, methyl cellulose, water-soluble polymers such as polyacrylamide, calcium phosphate,
There are poorly soluble inorganic substances such as magnesium pyrophosphate,
The water-soluble polymer is preferably used in an amount of 0.03 to 1% by weight based on the total amount of the monomers, and the hardly soluble inorganic substance is used in an amount of 0.05 to 0.5% by weight based on the total amount of the monomers. It is preferred to use.

As the suspending aid, there is an anionic surfactant such as sodium dodecylbenzenesulfonate. When a poorly soluble inorganic substance is used as the suspending agent, it is preferable to use the suspending aid. . The suspension aid is preferably used in an amount of 0.001 to 0.02% by weight based on the total amount of the monomers.

The molecular weight of the resin for a pickup lens of the present invention is not particularly limited, but preferably has a weight average molecular weight (in terms of polystyrene) of 10,000 to 1,000,000, and is 100% in terms of heat resistance and moldability.
Those in the range of 000 to 300,000 are particularly preferred.

When the resin for a pickup lens of the present invention is used, from the viewpoints of prevention of deterioration, thermal stability, moldability and processability, antioxidants such as phenolic, phosphite, thioether, etc. Release agents such as aliphatic alcohols, fatty acid esters, phthalic esters, triglycerides, fluorine-based surfactants, higher fatty acid metal salts, and other lubricants, plasticizers, antistatic agents, ultraviolet absorbers, flame retardants, and heavy metal deactivators An agent may be added for use.

The pickup lens of the present invention can be manufactured by using a known molding method such as an injection molding method, a compression molding method, a micro-molding method, a floating molding method, and a low-links method.

Further, the pickup lens of the present invention has M
gF ₂ , coating an inorganic compound such as SiO ₂ by a vacuum evaporation method, a sputtering method, an ion plating method, etc .; an organosilicon compound such as a silane coupling agent on a molded product surface; a vinyl monomer; a melamine resin; an epoxy resin; Moisture resistance, optical properties, chemical resistance, abrasion resistance, anti-fog, and the like can be improved by hard coating a fluorine-based resin, a silicone resin, or the like.

[0031]

EXAMPLES The present invention will now be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

The water-soluble polymer (A) (polymethacrylate) used as a suspending agent in the following examples was synthesized by the following method.

Synthesis of Water-Soluble Polymer (A) 5 g of methyl methacrylate, 12 g of 2-hydroxyethyl methacrylate, 23 g of potassium methacrylate and 360 g of deionized water were placed in a separable flask having an internal volume of 500 ml, and N 2 gas was supplied for 30 minutes. After blowing air to remove air in the system, the temperature in the system was raised to 65 ° C while heating and stirring in a water bath.
And 0.06 g of potassium persulfate was added. Polymerization was carried out at the same temperature for 5 hours, followed by heating to 90 ° C. and stirring for 2 hours to obtain a jelly-like water-soluble polymer (A).

Example 1 Tricyclo [5.2.1.0 ^2,6 ] deca-8 methacrylate
-Yl 100 g, methyl methacrylate 1500 g, N-
400 g of cyclohexylmaleimide, 8 g of lauroyl peroxide and 4 g of n-octylmercaptan were dissolved to obtain a monomer mixture.

In a 5-liter separable flask equipped with a stirrer and a condenser, 0.1 g of the above jelly-like water-soluble polymer (A) as a suspending agent and 2500 g of deionized water
Was added, and then 100 g of disodium hydrogen phosphate-sodium dihydrogen phosphate buffer was added and stirred, and the pH was adjusted to 7.2 to obtain a suspension medium. The monomer mixture was added thereto with stirring, and the mixture was polymerized at 60 ° C. for 3 hours and then at 98 ° C. for 2 hours under a nitrogen atmosphere at a stirring rotation speed of 240 rpm to obtain resin particles. Was 99%). The resin particles are washed with water, dehydrated and dried, and using an injection molding machine IS-50EP manufactured by Toshiba Machine Co., Ltd., cylinder temperature 260 ° C., injection speed 50 cm ³ / sec, mold temperature 90
C. to form a test piece for property evaluation. Regarding the molding of the pickup lens, a mold for the pickup lens was separately prepared, a pickup lens for a signal reading test was molded using resin particles, and a test piece for property evaluation (50 × 40 × 3 mm) as shown in FIG. ). Here, FIG.
Is set to a point 5 mm from the lower end of the protruding gate 20 at the upper end.

Examples 2 to 5 and Comparative Examples 1 to 7 Using monomers having the composition ratios (% by weight) shown in Table 1,
In the same manner as described above, a test piece for characteristic evaluation was obtained.

With respect to the resin particles and test pieces obtained in Examples 1 to 5 and Comparative Examples 1 to 7, orientation birefringence, birefringence of a molded product, saturated water absorption and glass transition temperature (hereinafter abbreviated as Tg).
The results are shown in Table 1. The evaluation was performed by the following method. (1) Orientation birefringence 1 g of resin particles of each mixing ratio obtained by suspension polymerization were dissolved in 6 g of tetrahydrofuran, applied on a glass substrate, and the surface was made uniform using a knife coater. After drying this film, peel it off from the glass
Film was made. Next, this film was stretched twice (stretching temperature: 90 ° C.), and the birefringence was measured. (2) Birefringence of molded article An ellipsometer (AEP-Shimadzu Corporation) using a He-Ne laser was used for a test piece of 50 × 40 × 3 (mm).
100), the phase difference (single pass) was measured at the measurement point in FIG. 1, and the birefringence per mm in thickness was calculated based on the following equation.

(Equation 1) (3) Saturated water absorption A test piece of 20 × 15 × 5 (mm) was dried, its weight was measured, and then it was left in water at 70 ° C. to allow saturated water absorption.
The weight was measured, and the saturated water absorption was calculated by the following equation.

(Equation 2) (4) Glass Transition Temperature (Tg) The glass transition temperature (Tg) of the obtained resin particles was measured by a differential scanning calorimeter (DSC7 manufactured by PerkinElmer). (5) Signal reading test A pickup lens for signal reading test was set at 40 ° C. and 90 °.
It was mounted on an MD player in a% RH atmosphere, and a test was performed to determine whether or not a signal from the signal evaluation MD could be read. ：: Readable. ×: reading defect

[0038]

[Table 1]

In the following, MMA is methyl methacrylate, and TCDMA is tricyclo methacrylate [5.2.
1.0 ^2,6 ] dec-8-yl, CHMI indicates N-cyclohexylmaleimide, and BZMA indicates benzyl methacrylate.

[0040]

According to the present invention, a laser pickup lens excellent in non-birefringence, heat resistance and low moisture absorption is provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of a test piece for measuring birefringence of a molded product used in Examples.

[Explanation of symbols]

 20 gate

Claims (4)

[Claims] 1. A monomer mixture comprising a monomer mixture comprising the following monomer components (A) to (E) such that the absolute value of the orientation birefringence of the obtained resin is less than 1 × 10 ^−6. Laser pickup lens using resin obtained by polymerization. (A) 5 to 40% by weight of a methacrylate or acrylate having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in the ester portion, (B) 50 to 50% of methyl methacrylate
80% by weight, (C) 5 to 40% by weight of N-substituted maleimide, (D) 0 to 30% by weight of benzyl methacrylate, and (E) 0 to 10% by weight of a monomer copolymerizable therewith. 2. The monomer component (A): a methacrylate or an acrylate having an alicyclic hydrocarbon group having 5 to 22 carbon atoms in an ester portion, wherein the methacrylate or acrylate is cyclohexyl methacrylate, isobornyl methacrylate, or methacrylic acid. norbornyl methacrylate norbornylmethyl methacrylate tricyclo [5.2.1.0 ^{2, 6]} deca -8
-Yl and tricyclomethacrylate [5.2.1.0
^2. The laser pickup lens according to claim 1, which is at least one compound selected from the group consisting of ^2,6 ] dec-4-methyl. 3. The N-substituted maleimide is N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, Ni-propylmaleimide, N-butylmaleimide, Ni-butylmaleimide, Nt-butyl. The laser pickup lens according to claim 1, which is at least one compound selected from the group consisting of maleimide, N-cyclohexylmaleimide, N-laurylmaleimide, and N-phenylmaleimide. 4. An optical element using the laser pickup lens according to claim 1.