Optical element molding die and optical element

Details Optical element molding die and optical element Optical element molding die and optical element

2002-02-22

2004-07-27

Mackey, James P. (Department: 1722)

Static molds

Container-type molding device

Of named component

C425S808000

Reexamination Certificate

active

06766999

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical element molding die and optical element, and particularly to a molding die for the optical element by which a desired optical surface can be easily formed, and can be used for a long period of time, and to an optical element molded by using the molding die.
A technology by which, by using an amorphous alloy having a super-cooled liquid phase (called also amorphous alloy or metallic glass), a metallic glass-made optical element molding die is formed by the heat press molding, is well known (for example, refer to Japanese Patent Application Nos. 2001-054182 and 2001-054183 which are a base of the claim of priority of the present invention by the present inventor and the patent application accompanied by the claim of priority based on them). Because such the amorphous alloy has a characteristic which is softened within the temperature range of about 300° C.-500° C., a desired shape can be comparatively easily molded by pressing, and particularly as the optical element molding material for the optical element such as a plastic lens, it can be said that it is a material having such various excellent characteristics that the hardness at the time of optical element molding is sufficiently high, and the optical surface and the dimension reference surface such as the outer periphery to be high accurately engaged with a die set can be very finely formed by the diamond cutting, or the like.
Because the ordinary metal has large crystallizing energy, when it is heated and cooled, it is crystallized, and normally, it is cooled and solidified in the polycrystal condition. In contrast to this, in the case of amorphous alloy, by quick cooling from the melt condition, the time for the crystallization is not given, and as in the atomic arrangement in the melt liquid condition, it is solidified and becomes the amorphous condition. Specifically, the composition is a polycrystal system by which many kinds of crystals are easily formed, and when it is heated and melted, the growth of the crystal nucleus is prevented by depriving each other the composition atom for its crystallization, and the critical state in which the crystal is generated, is increased, and the condition having the super-cooled liquid phase is maintained. In this condition, because each of constituent atoms is not strongly combined, it has the glass transition point, and when it is heated again, it is softened at a low temperature. However, as described above, when the crystallizing energy is not enough large, at about the temperature to be heated and softened, crystallization begins at once and it is solidified, therefore, the molding processing can not be conducted. It can be said that the amorphous alloy is made into such the composition that, by devising the composition, the crystallizing energy is increased, and the crystallization when heated and softened, is delayed as later as possible, and the super cooling liquid condition can be maintained for a long period of time.
However, even the amorphous alloy in which the crystallization is suppressed, when it is heated and softened, the higher the temperature is, or the longer the softening time is, there is the characteristic that the crystallization is easily started. Accordingly, when the processing such as press molding is conducted after the heating and softening, because the processing time is limited by the heating temperature, the longer the time to start the crystallization is, it can be said that it is the easier processable amorphous alloy.
In this connection, when the amorphous alloy is used for the optical element molding die as described in the above-described patent application, a study will be made into an amorphous alloy, the characteristic of which is more appropriate for that purpose, as follows.
The most important point in the optical element molding die is how the optical molding surface which is used for molding the optical surface of the optical element, is treated. This optical molding surface is used for the purpose that the optical material such as plastic or glass is formed into the product optical element by the injection molding or press molding. Accordingly, when considering the deterioration of the optical performance due to the disadvantages such as a shrunk deformation at the molding time of the optical element, double refraction due to the internal stress of the optical material, or eccentricity of each of molding dies, the optical molding surface of the optical element molding die is required that the allowable error is smaller than the optical surface shape of the optical element as the product, and it is nearer the ideal shape. For the shape error of the optical molding surface of the optical element molding die, in a camera-use image pick-up lens, when, generally, it is about 100-300 nm, it is enough for the purpose, however, in a pickup-use objective lens of a device such as the optical information recording and/or reproducing device, the high accuracy, which is lower than 50 nm, is required.
Further, it is preferable that the surface roughness of the optical molding surface of the optical element molding die is, at least, lower than {fraction (1/10)} of the wavelength, when possible, lower than {fraction (1/200)}, so that the light does not scatter. Specifically, for the general surface roughness of the optical molding surface, in a case of a camera-use image pick-up lens for which the visible light entire range is used, it is lower than Rz 30 nm, and also in a case of a DVD-use pickup objective lens whose using wavelength is 650 nm, it is required to be lower than Rz 50 nm. Further, in a case of the optical pickup device for which a HD-DVD currently studied extensively as the optical information recording and/or reproducing device of the next generation is made the optical information recording medium, because the using wavelength &lgr; is 405 nm, it is preferable that the surface roughness is lower than Rz 8 nm. This is for the reason that, because R∞1/&lgr;
4
(1) when the scattering of the light on the optical surface is expressed by Rayleigh scattering R, when compared with the case where a common DVD is made the optical information recording medium, equivalently the 6-7 times surface roughness is necessary. Because the scattering condition of the light depends also on the shape of the optical molding surface, these surface roughness are standard values, however, when the surface roughness of the optical molding surface of the optical element molding die exceeds these values, the stray light due to the scattering is generated, and actual damages in which the contrast of the image is lowered and the image becomes unclear, or the effective light amount for the signal processing is lowered, and the SN becomes poor, are generated.
As described above, because the optical molding surface of the optical element molding die is necessary for the vary high shape accuracy and very high flatness depending on the cases, although the forming method is by the cutting processing or molding processing, the very high easiness for being cut and fine and accurate composition structure are preferable for the metal material, and for the purpose that the condition of the optical. molding surface is maintained for a long period of time, it is preferable to have the high resistance to oxidation or hardness.
Conventionally, for example, when, by the cutting processing such as diamond machining, the optical molding surface of the optical element molding die is formed, as the molding die material by which the diffusion wear of the diamond can be suppressed, aluminum alloy or soft metal such as copper, or electroless nickel galvanizing is used. Because the optical element molding die by the soft metal has disadvantages in which, because the harness is low, the optical molding surface is easily scared, and because the resistance to oxidation is low, after cutting processing, the surface of the optical molding surface is oxidized and hazed in several weeks, it can be said that this moldi

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