JPH07324138A - Method of molding optical component - Google Patents

Abstract

PURPOSE:To provide an optical component-molding method whereby the formation of a silver streak on an optical component can be prevented, and the percentage of rejects can be markedly lowered. CONSTITUTION:An optical component reduced in the formation of silver streak is molded from pellets made of a polycarbonate of a molecular weight of 10000-18000 and having a content of a powdery polymer of a mean particle diameter of 0.5mm or below of 2.0-wt.% or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of molding an optical component such as an optical disk which rarely produces silver.

[0002]

2. Description of the Related Art Polycarbonate resins are excellent in transparency, heat resistance, and low water absorption, and have been used as molding materials for optical applications, especially optical discs recently. Since it is necessary to read and write signals of micron order with a laser beam in an optical disk, if there is a defect of micron order or more in the substrate of the optical disk, reading and writing cannot be performed and the error rate deteriorates. Black spots due to heat deterioration of the resin are well known as such defects, but there are other linear defects called silver. Regarding the black spots, countermeasures have been taken by incorporating an organic phosphite into a polycarbonate resin (see JP-A-58-126119).

[0003]

On the other hand, silver has been regarded as a problem because it generally has a large shape, but the cause is that the moisture content of the pellets immediately before molding is 0.
Various measures have been taken in consideration of insufficient drying of 01% or more, or inadequate molding conditions. However, the current situation is that it has not been possible to reduce the defective rate due to silver to 1% or less.

[0004]

Means for Solving the Problems The inventors of the present invention have investigated the cause in order to suppress the generation of silver in the molding of an optical disk substrate which is an optical component. The inventors have found that the cause is the presence of fine powder having a size of 1 mm or less, and have reached the present invention. That is, the gist of the present invention is that the average particle diameter in a polycarbonate pellet having a molecular weight of 10,000 to 18,000 is 0.5 mm.
The present invention resides in a method for molding an optical component with less silver generation, which comprises using a polycarbonate pellet having a powdery polymer content of 2.0% by weight or less.

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below.
The polycarbonate resin in the present invention is a polymer or copolymer obtained by a phosgene method of reacting various dihydroxydiaryl compounds with phosgene, or a transesterification method of reacting a dihydroxydiaryl compound with a carbonic acid ester such as diphenyl carbonate. A typical example thereof is a polycarbonate resin produced from 2,2-bis (4-hydroxyphenyl) propane (bisphenol A).

Examples of the dihydroxydiaryl compound include bisphenol A, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, and 2,2-bis (4-hydroxyphenyl).
Butane, 2,2-bis (4-hydroxyphenyl) octane, bis (4-hydroxyphenyl) phenylmethane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 1,1-bis (4- Hydroxy-3-tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3-bromophenyl) propane, 2,2-bis (4-hydroxy-3,5dibromophenyl) propane, 2,2- Bis (hydroxyaryl) such as bis (4-hydroxy-3,5dichlorophenyl) propane
Alkanes, 1,1-bis (4-hydroxyphenyl)
Cyclopentane, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxy-3,3′-dimethyldiphenyl ether, Dihydroxy diaryl ethers such as 4,4'-dihydroxy diphenyl sulfide, dihydroxy diaryl sulfides such as 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide, 4,4'-dihydroxy diphenyl sulfoxide, , 4'-Dihydroxy-3,3'-dimethyldiphenyl sulfoxide, such as dihydroxydiaryl sulfoxides, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxy-3,3'-
Examples thereof include dihydroxydiaryl sulfones such as dimethyldiphenyl sulfone.

These may be used alone or in admixture of two or more, but in addition to these, piperazine, dipiperidyl,
Hydroquinone, resorcin, 4,4'-dihydroxydiphenyl and the like may be mixed and used. Since optical components such as optical disks are required to have no optical distortion, the molecular weight is 10,000 to 18,000, preferably 1
It should be in the range of 1000 to 17000. In addition,
The molecular weight (M) as used herein is determined by using an Ostwald viscometer to obtain the intrinsic viscosity [η] of a solution containing methylene chloride as a solvent
Schnell's viscosity formula

[0008]

[Equation 1] [η] = 1.23 × 10 ⁻⁵ M ^0.83

[0009] Polycarbonate molding materials used for optical parts such as optical discs have low viscosity, so there is little shear heat generation by the screw of the molding machine, and it is usually 1 mm in granules (pellets) with a particle size of 2 to 4 mm. A finely divided polymer having a diameter not larger than that can be melted only by heat from the cylinder. However, since a polymer such as polycarbonate has a low thermal conductivity, a finely divided polymer is injection-molded in an unmelted state and is observed as a silver-like defect in a molded product. Therefore, the content of the powdery polymer is 2.
If it is more than 0% by weight, unmelted powder is likely to occur and silver is often generated. If it is 2.0% by weight or less, preferably 1.0% by weight or less, the defective rate due to silver is 1-2.
%, And the target required for optical applications is achieved.

In the polycarbonate molding material of the present invention, in order to reduce the content of the polycarbonate powder having an average particle diameter of 0.5 mm or less to 2% or less, the cutting conditions in the cutting step of cooling and pelletizing the molten polymer are set. It is necessary to optimize the generation amount of the powder to the minimum and to suppress the mechanical shearing force applied to the pellet as much as possible in the whole process even after the pelletization to suppress the generation of the powder as much as possible. In particular, minimizes collision between pellets, pellets and equipment walls in each process such as drying process, compounding process, packaging process, and pellet transport process such as empty transportation that connects these processes, and rotates in all unit operations. It is important not to use means such as a mechanical stirrer to provide a strong shear history. 10, as used in the present invention,
Since a polycarbonate having a relatively low molecular weight of 000 to 18,000 has low strength, powder is likely to be generated in the pelletizing cutting process. Therefore, the abrasion of the cutter blade during pelletization, the temperature of the strand, etc. are major factors in the generation of powder. Further, regarding the polycarbonate powder which is inevitably generated in the manufacturing process, it is possible to reduce the powder at the final stage of the manufacturing process. A mechanical method such as a vibrating screen is well known as a method for removing powder. However, it is difficult to satisfactorily remove the fine powder adhering to the pellet surface by a mechanical method, and when performing special powder removal such as washing with water, the process becomes complicated and the production efficiency is lowered. Therefore, it is more preferable to minimize the amount of powder generated in the manufacturing process and further reduce the amount of powder in the final process.

The total amount of powder in the polycarbonate pellets of the present invention is measured by the following method. After weighing 100 to 200 g of polycarbonate pellets, 3
Put in 0 mesh stainless wire mesh container, 300-40
The pellet is washed by shaking well in 0 cc of methanol and the powder is separated in methanol. The powder separated here usually has a particle size of 1 mm or less.

The washing solution is filtered with a G4 glass filter. This operation is repeated until no suspended substance is observed in methanol. Usually, the weight of the residue collected by filtration after 4 to 5 times reaches a constant weight. The weight of this residue is the weight of the powder. The above is the case where the additive is not attached to the surface of the pellet, but usually the additive is usually mixed in polycarbonate, and the cleanliness of the molding chamber is maintained below class 1000, especially for optical discs. To this end, it is preferable that all the additives are kneaded. When the additive is surface-attached, the additive also migrates into methanol, so the additive must be qualitatively and quantitatively determined. Since the specific method of analysis differs depending on the type of additive, it is only necessary to select the optimum quantification method for each additive.

Polycarbonate pellets are usually 2.0-
3.5 mm diameter spherical or diameter and length 2.0-4.
It is a cylindrical granular body of 0 mm, and if the diameter or the length is 2.0 mm or more, the shape does not matter. The average particle size of the powder is measured by the particle size of 1 mm collected as described above.
Using an optical microscope, the following powders were used in a field of view of 200 to 10
It is assumed that the maximum width of the particles (the maximum distance between the projected images of the particles when they are sandwiched by the two parallel lines in the surface) is measured for 00 powder particles, and the arithmetic mean is taken. The molding material in the present invention is effective in a molding machine that plasticizes by shearing force such as a screw, that is, an injection molding machine, an injection compression molding machine, and an extrusion molding machine, and can be used for various materials such as disks, lenses, mirrors, nameplates, sheets and plates. Processed into a thing.

[0014]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Examples 1, 2 and Comparative Example 1 Bisphenol A and phosgene were polymerized by an interfacial polymerization method by a conventional method to obtain a polycarbonate powder having a molecular weight of 15,000, and organic phosphite (trisnonylphenyl phosphite, manufactured by ADEKA ARGUS CORPORATION) was added. Made Mark 1
178) was blended with 0.05%, extruded in a strand shape at 250 ° C. with a 40 mmφ vent extruder, and cut for pelletization to obtain a cylindrical pellet having a diameter of 2.5 mm and a length of 3.0 mm. The average particle size and content of the powdery polymer of this granular material were measured by the method described above. The results were 0.41 mm and 2.8% by weight, respectively. The pellets containing the powder as shown in Table 1 were obtained by further subjecting the pellets to vibration sieving or washing with water.

These pellets were dried by the Karl Fischer method until the water content became 50 ppm, and the diameter was 120 mm with an injection molding machine (M-100DM manufactured by Meiki).
A 1.2 mm thick compact disc was molded. The conditions were a resin temperature of 340 ° C., a mold temperature of 95 ° C., and an injection speed of an injection rate of 105 cc / sec. 200 compact disks were continuously molded, the disks with silver were visually observed, and the number was measured.
The ratio of the silver-generated disc was measured as a defective rate. The results are shown in Table-1. From this, it is shown that the generation of silver is not abrupt when the amount of fine powder decreases.

[0016]

[Table 1]

[0017]

According to the molding method of the present invention, the occurrence of silver in optical parts can be prevented and the defective rate can be remarkably reduced, so that it has a very high commercial utility value.

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Claims (3)

[Claims] 1. A polycarbonate pellet having a molecular weight of 10,000 to 18,000, wherein a polycarbonate pellet having an average particle diameter of 0.5 mm or less and a powdery polymer content of 2.0% by weight or less is used. Molding method for few optical parts. 2. The molding method according to claim 1, wherein the polycarbonate pellets are substantially granular particles having a particle diameter of 2 mm or more. 3. The molding method according to claim 1, wherein the powdery polymer has a particle diameter of 1 mm or less.