JP3118282B2 - Method for producing methacrylic resin for optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a methacrylic resin molding material, and more particularly to a method for producing a methacrylic resin for an optical element having thermal stability and excellent mold release properties.

[0002]

BACKGROUND ART Methacrylic resins, excellent optical properties, since the by Awa have excellent weather resistance and high mechanical properties, a tail lamp, automobile parts such as a back panel, lighting equipment, such as lamp covers and louvers , Are widely used for indicators such as tuners. recent years,
In particular, optical elements such as lenses for video camera lenses and VTRs, optical information recording carriers for laser disks, etc. are being developed for optical applications such as lenses in terms of weight reduction, mass production, asphericalization, etc. , The advance to laser optical equipment is remarkable. As a method for producing these optical elements and optical information recording carriers, an injection molding method is generally used in many cases. Injection molding of these optical elements and optical information recording media requires a high cylinder temperature, high mold temperature, and high cylinder temperature in order to improve the low birefringence, dimensional stability, or transferability from the required performance of the molded product. In many cases, the resin is molded under severe conditions such as a long stay in the inside, and thermal decomposition of the resin is likely to occur. Therefore, when the molded product is taken out, a number of defects such as cleavage delamination due to poor mold release and poor transfer due to gas occur, which causes a reduction in yield.

[0003] As means for solving the releasability, for example, a method using an alkyl alcohol having 22 carbon atoms or an ester of a polyhydric alcohol and a fatty acid (JP-A-61-737).
No. 54) Further, a method of using a fatty acid ester of glycerin and a higher alcohol in combination (Japanese Patent Application Laid-Open No. 1-294763) has been proposed. Also, a technique for producing a methacrylic resin using lauroyl peroxide is known,
The thermal stability of a polymer obtained by polymerization of lauroyl peroxide alone is low. As a method for improving these, for example, a peroxide or azo compound having a 10-hour half-life temperature of lauroyl peroxide and a polymerization initiator of 90 ° C. or more is used. Method using a compound (JP-A-59-1984)
No. 15410).

[0004] However, in the above-mentioned prior art in which a lubricant or a releasing agent having low volatility is simply added or in the above-mentioned art which merely improves thermal stability, defects such as mold blemishes and surface contamination of molded articles occur. It is likely to cause defects such as poor adhesion of the film when depositing an anti-reflection film on the lens surface or depositing an aluminum film on the disk signal. At present, there are drawbacks such as frequent peeling, damage to the lens surface and the signal of the laser disk, and no satisfactory product can be obtained.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to overcome the drawbacks of these conventional methacrylic resins for optical applications, to retain excellent thermal stability, to have excellent mold releasability, and to improve the metal release. It is an object of the present invention to provide a method for producing a methacrylic resin for an optical element which is excellent in mold fog and stains on a molded product surface.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by using two or more specific polymerization initiators in a specific amount, the releasability has been improved. It has been found that a methacrylic resin excellent in mold and molded product surface free of stains can be obtained, and the present invention has been completed.

[0007] That is, the above object is to polymerize a methyl methacrylate alone or a monomer mixture containing methyl methacrylate as a main component with respect to 100 parts by weight of the monomer .
As a polymerization initiator , lauroyl peroxide 0.02-0.3
Parts by weight and 1,1,3,3-tetramethylbutyl par
Oxy-2-ethylhexanoate, tert-hexyl
Peroxy 2-ethylhexanoate, tert-butyl
Luperoxy 2-ethylhexanoate and 2,2 '
At least one of azobisisobutyronitrile
(Hereinafter, it may be referred to as “other polymerization initiator”.)
It can be achieved by a method for producing a methacrylic resin for an optical element, characterized by adding 02 to 0.2 parts by weight and polymerizing. Hereinafter, the present invention will be described in detail.

As the polymerizable monomer of the present invention, methyl methacrylate alone or a monomer mixture containing methyl methacrylate as a main component and a copolymerizable monomer is used. .

The proportion of methyl methacrylate used as a main component in the present invention is at least 50% by weight, preferably at least 60% by weight. If the proportion of methyl methacrylate is less than 50% by weight, the optical characteristics and mechanical strength, which are the characteristics of the methacrylic resin, decrease, which is not preferable. The monomer copolymerizable with methyl methacrylate used in the present invention is not particularly limited, but preferred examples are methyl acrylate, ethyl acrylate, acrylates such as butyl acrylate, ethyl methacrylate, Propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, tricyclodecyl methacrylate, phenyl methacrylate, 2,4,6-methacrylic acid
Methacrylic esters such as tribromophenyl and isobornyl methacrylate; aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene; nitrile compounds such as acrylonitrile and methacrylonitrile; N-methylmaleimide; N-phenyl Maleimide,
N-substituted maleimide compounds such as No-chlorophenylmaleimide and N-cyclohexylmaleimide.

The most characteristic feature of the present invention is that
A specific amount of lauroyl peroxide is used as a polymerization initiator, and a specific amount of another polymerization initiator is used in combination. When polymerized by lauroyl peroxide alone, the thermal stability is poor, and it is difficult to mold under the aforementioned severe molding conditions. On the other hand, when the polymerization is carried out solely with another polymerization initiator, the releasing effect cannot be obtained, and the above-mentioned disadvantage occurs, which is not preferable.

The lauroyl peroxide used in the present invention is:
It is necessary to obtain good releasability due to the effect of by-products generated by decomposition in the polymerization step.
Since the by-product and methacrylic resin have appropriate compatibility, by forming a thin by-product film at the interface between the mold and the fluid resin, good mold releasability can be obtained without soiling the mold surface. You can get it. The amount of lauroyl peroxide used is 0.
02 to 0.3 parts by weight der Rukoto need der is, preferably in an amount of 0.05 to 0.25 parts by weight. If the used amount of lauroyl peroxide is less than 0.02, the releasability from the mold is insufficient, so that the lens surface and the disk surface are damaged by cleavage-like separation. When the amount of lauroyl peroxide exceeds 0.3 parts by weight, the releasability is good, but the thermal stability is lowered, so that molding defects such as silver streaks may occur or molded products may be produced. Undesirably, surface dirt and mold clouding occur, and the yield decreases in the subsequent steps such as deposition of an antireflection film on a lens and deposition of aluminum on a laser disk.

[0012] The present invention other polymerization initiator in the to complete the polymerization reaction, it is necessary to further maintain the thermal stability of the polymer, by using in combination with lauroyl peroxide, first the present invention Ru can be to achieve the objective
Monodea Ru. The other polymerization initiators in the present invention are 1 , 1
1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, tert- hexylperoxy 2-ethylhexanoate, tert -butylperoxy2-
Ethyl hexanoate and 2,2' Azobisuisobuchi b nits Li least one of Le. The used amount of the other polymerization initiator needs to be 0.02 to 0.2 parts by weight, and the preferable used amount is 0.05 to 0.15 parts by weight. Can be If the amount used is less than 0.02, unreacted monomers remain in the resin, so that strength and heat resistance are insufficient, and defects such as cleavage during molding tend to occur. If the amount used exceeds 0.2 parts by weight, the polymerization initiator or generated radicals remain in the resin in a large amount to promote thermal decomposition of the resin. It is not preferable because flash is easily generated.

[0013] The intrinsic viscosity of 20 ° C. in chloroform of polymerized methacrylic resin Ru 0.3~0.6dl / g Der
That it is preferable, 0.35~0.55dl / g
Is more preferred. When the intrinsic viscosity is less than 0.3 dl / g, the mechanical strength is low and the effect of the present invention cannot be obtained.
If it exceeds dl / g, the birefringence is so high that it is not suitable for optical element applications.

The polymerization in the present invention is usually carried out at 60 to 150 ° C.
The polymerization method is a known method for methacrylic resin, such as a suspension polymerization method, (continuous) bulk polymerization method,
A solution polymerization method or the like is applied, and a chain transfer agent for controlling the degree of polymerization can be used as necessary. There is no particular limitation on the type and amount of the chain transfer agent.

In the polymerization of the present invention, commonly used additives such as a lubricant, an ultraviolet absorber, a dye, a pigment, an antioxidant, and the like can be used. Either a method of polymerizing, or a method of mixing with the obtained polymer and then pelletizing may be used.

[0016]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited by these examples. In Examples, “%” and “parts” are all “% by weight”,
Represents "parts by weight". The evaluation in the examples was performed based on the following method.

1. 1. Amount of residual monomer (%) Determination by gas chromatography Intrinsic viscosity (dl / g) After dissolving a certain concentration of resin in chloroform, it was measured at 20 ° C with an automatic viscometer.

3. Releasability and mold blemishes 1) 300 mm diameter with a nickel stamper with a groove width of 0.8 μm, a groove depth of 0.07 μm, and a pitch between grooves of 1.6 μm attached to an injection molding machine M-200DM (manufactured by Meiki Seisakusho). A disk mold of (mm) is mounted, and a disk is injection-molded for 50 shots under the conditions of a cylinder temperature of 270 ° C. and a mold temperature of 70 ° C. and a cooling time of 15 seconds. The number of shots in which defects such as the cleavage-like damage and adhesion between the groove and the stamper surface of the disk at the time of release were measured was measured and expressed as a percentage.

2) A uniconvex lens 2 having a diameter of 40 mm and a curvature of 60 R (mm) was injected into an injection molding machine J75SAV (manufactured by Nippon Steel Works).
A single die was attached, the lens was molded at 50 shots under the conditions of a cylinder temperature of 240 ° C., a mold temperature of 80 ° C., and a cooling time of 90 seconds, and the number of shots at which a cleavage phenomenon occurred during mold release was measured. expressed. Example 1 To 100 parts by weight of a monomer mixture of 93% by weight of methyl methacrylate and 7% by weight of ethyl acrylate, 0.15 part by weight of lauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy 2- Ethyl hexanoate 0.06
15 parts by weight of a monomer mixture in which 0.27 parts by weight of n-octyl mercaptan and 0.1 part by weight of stearyl alcohol are dissolved; 300 g of a 1% by weight aqueous solution of potassium polymethacrylate; 7 g of sodium dihydrogen phosphate; 2
See charged previously dissolved purified water 30kg sodium 22g in 50 liters pressure reaction vessel equipped with a stirrer, perform N ₂ substitutions, and polymerized at 80 ° C., and further polymerized for 1 hour at 120 ° C. after the exothermic peak. After cooling, a beaded copolymer was obtained through the steps of washing, filtration and drying. The residual monomer content of the beads was 0.05%, and the intrinsic viscosity was 0.420 dl / g. After pelletizing the beads with an extruder (manufactured by Nakatani Machinery) having a cylinder diameter of 40 mm, the pellets were evaluated by the above-described evaluation method. As a result, in the 300φ disk mold, the beads were uniformly separated without any cleavage phenomenon and no adhesion of the disk to the stamper. The mold was good and had no mold fogging. In the evaluation of the convex lens mold, no cleavage phenomenon occurred, and the releasability was good. Comparative Example 1 The polymerization initiator was tert. -Butyl peroxy 2-ethylhexanoate 0.1 part by weight, and the intrinsic viscosity was as in Example 1.
When to be substantially equal, except for changing the n- octyl mercaptan to give exactly the same polymerized copolymer beads as in Example 1. The residual monomer content of the beads was 0.06
%, And the intrinsic viscosity was 0.423 dl / g. The beads were evaluated after pelletization in the same manner as in Example 1. In the evaluation of the disk, no cleavage occurred, but adhesion to the stamper occurred, and the incidence of defective molding was 26%. In the convex lens mold, cleavage occurs at the flow end,
The mold releasability was insufficient, and the incidence of molding failure was 34%. The composition ratio of Examples 2-6 monomer, type and amount of polymerization initiator, and except that the polymerization temperature was changed polymerizes in the same manner as in Example 1, was evaluated after pelletization. Table 1 shows the results. Since all of the resins are within the scope of the claims of the present invention and the obtained resin is excellent in mold releasability, there is no cleavage or mold fogging in the molding of the disc, the mold releasability with the stamper is good, and the convex lens Cleavage was not observed in the molding of, and a good lens was obtained.

[0020]

[Table 1] Abbreviations of other monomers in the table are as follows.

MA: methyl acrylate EA: ethyl acrylate ST: styrene TBP: 2,4,6-tribromophenyl methacrylate The abbreviations of the polymerization initiators in the table are as follows.

A: 2,2'-azobisisobutyronitrile B: 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate H: tert. -Hexylpa-oxy 2-ethylhexanoate T: tert. - the composition ratio of butyl peroxy 2-ethylhexanoate Comparative Example 2-6 monomer, type and amount of polymerization initiator, and except that the polymerization temperature was changed polymerizes in the same manner as in Example 1 And evaluated after pelletization. Table 2 shows the results.

Comparative Examples 2 to 4 are resins polymerized using different polymerization initiators, respectively. In the case of resins not used in combination with lauroyl peroxide, cleavage occurs in disk molding,
It is likely to adhere to the stamper and damage the groove and signal of the disk when releasing. In addition, at the time of lens molding, a cleavage phenomenon is likely to occur due to poor mold release, which impairs the function of the lens, which is not preferable.

Comparative Example 5 is a case where the amount of lauroyl peroxide added is out of the range of claims. There is no cleavage or adhesion to the stamper during disk molding or lens molding, however, the mold is severely clouded, and the adhesion of the dirt is severe. This is not preferable because the signal surface of the disc or the lens surface is damaged.

Comparative Example 6 is a resin polymerized with lauroyl peroxide alone. However, the amount of residual monomer in the beads is high, and silver streaks occur during molding of a laser disk. Disadvantageously occurs.

[0026]

[Table 2] Abbreviations of other monomers in the table are as follows.

MA: methyl acrylate EA: ethyl acrylate ST: styrene TBP: 2,4,6-tribromophenyl methacrylate The abbreviations of the polymerization initiators in the table are as follows.

A: 2,2'-azobisisobutyronitrile B: 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate H: tert. -Hexylpa-oxy 2-ethylhexanoate T: tert. -Butyl peroxy 2-ethylhexanoate

[0029]

The methacrylic resin of the present invention solves the problems of the mold and the molded product at the time of mold release , for example, the problems of delamination in the form of cleavage or poor mold release due to close contact with the mold. Useful for

Therefore, it is suitably used particularly in the field of ultra-precision molding, that is, in the field of optical elements such as lenses and optical information recording carriers.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08F 20/12-20/18 C08F 2/38 C08F 4/32-4/38 G02B 1/04

Claims (3)

(57) [Claims] When a monomer mixture containing methyl methacrylate alone or methyl methacrylate as a main component is polymerized, 100 parts by weight of the monomer is used as a polymerization initiator.
Te, lauroyl peroxide 0.02-0.3 parts by weight and
1,1,3,3-tetramethylbutylperoxy 2-d
Tyl hexanoate, tert-hexyl peroxy 2
-Ethylhexanoate, tert-butylperoxy
2-ethylhexanoate and 2,2'-azobisui
At least one of sobutyronitrile, 0.02 to 0.2.
A method for producing a methacrylic resin for an optical element, comprising adding 2 parts by weight and polymerizing. 2. A monomer mixture containing methyl methacrylate as a main component is a mixture of methyl methacrylate, acrylate, and methacrylate except methyl methacrylate.
The method for producing a methacrylic resin for an optical element according to claim 1, comprising at least one selected from an aromatic vinyl compound, (meth) acrylonitrile, and an N-substituted maleimide compound, and containing 50% by weight or more of methyl methacrylate. . Wherein the intrinsic viscosity of the polymer, method for producing the methacrylic resin for an optical element according to claim 1 or 2, polymerized so that 0.3~0.6dl / g at 20 ° C. in chloroform.