Glass manufacturing – Product or parison centering means – or mold and/or core...
Reexamination Certificate
2001-05-31
2004-12-21
Walls, Dionne A. (Department: 1731)
Glass manufacturing
Product or parison centering means, or mold and/or core...
C065S305000, C425S405100, C425S406000, C425S408000
Reexamination Certificate
active
06832495
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a molding die having the die structure capable of producing molded parts such as highly accurate optical parts in a stable manner, a molding device equipped with the molding die, a molding method employing the molding die or the molding device, an injection molding machine, an injection compression molding machine, a compression molding machine and a glass molding machine.
Up to now, the die structure composed of a pair of dies
1
a
and
1
b
, molding cavity
1
c
formed between the paired dies, and barrel die
2
holding the paired dies to be in contact therewith as shown in
FIG. 8
has been popular, in a molding die that molds a highly accurate form such as an optical surface.
In the case of a die structure having a plurality of molding cavities for a multi-cavity mold, the die structure has had construction wherein barrel dies are united solidly to be a thick plate called a mold plate, and holes each fitting or sliding on a die in quantity equivalent to the number of cavities are formed on the thick plate and a die is embedded in each hole. For example, an injection molding metallic mold for plastic optical elements is composed of fixed side mold plate
5
that is fixed on a molding device and movable side mold plate
4
that is fixed on movable platen
7
and is moved for open and close, as shown in
FIG. 9
, and plural dies
5
a
and plural dies
4
a
are embedded and held to form plural cavities respectively in the fixed side mold plate and the movable side mold plate. In the construction, when the movable side mold plate
4
is closed, parting surface
6
of the mold plate
4
and parting surface
6
of the mold plate
5
are brought into close contact with each other so that dies
5
a
and dies
4
a
face each other to form molding cavities to which resins are injected. The foregoing also applies to a metallic mold for injection compression molding wherein after the fixed side mold plate and the movable side mold plate are closed each other and optical materials such as resins are injected in a cavity, a die on one side moves in the direction of an optical axis of an optical surface to reduce a cavity volume and thereby to apply pressure of 10 kN/cm or more on resins in the cavity to enhance transferability of a molded form.
In particular, in the case of a molding die for a lens, it is important, for forming a highly accurate lens, that each die has a pair of highly accurate optical surface forms, and the optical surface form on one side does not have eccentricity such as tilting or shifting for the optical surface on the other side when the die is closed and coaxiality can be kept accurately.
Until now, in the case of a multi-cavity mold, it has been a common method that holes are formed on a mold plate and dies are fitted in the holes, when fixing a die on a mold as stated above, and therefore, when enhancing coaxiality for a pair of dies, it has been common to make fitting tolerance small, by making tolerance for hole position accuracy and a hole diameter on a mold plate and for perpendicularity for the parting plane and tolerance for an outside diameter dimension of a die and for cylindricity to be small. However, molded products have been required to be highly accurate, and thereby an eccentricity tolerance has been narrowed to be more strict, and narrowing of the tolerance of fitting for dies and mold plates is approaching to its limit in the conventional technology for parts processing. For example, in the case of an injection molding metallic mold, a plurality of dies are arranged in a form of concentric circles around an injection outlet (a sprue) for resins at the central portion on the mold plate because molded products are usually produced on a multi-cavity mold basis for enhancing molding efficiency. A diameter of this pitch circle is 100 mm or more even for a relatively small molded product, and when there is a temperature difference of 1° C. between a fixed die and a movable die in the course of molding operation, there is caused a deviation of 1 &mgr;m between diameters of pitch circles. Further, with regard to processing accuracy for making holes on a mold plate, about 3 &mgr;m for a hole diameter and about 5 &mgr;m for a hole position are the limit, even when the holes are processed accurately by using a jig grinding machine. Furthermore, with regard to accuracy for processing an outside diameter of a die to be fitted in a hole, about 3 &mgr;m is a limit again, and if these limit tolerances for parts processing are accumulated, coaxiality of about 8 &mgr;m of the die can be caused when dies are closed. Thus, it is generally difficult to make the coaxiality between optical surfaces of dies to be 8 &mgr;m or less, even at the cost of enormous labors and expenses. Further, even if the coaxiality between dies can be restrained to 8 &mgr;m or less, an increase of friction, galling and seizing are brought about and troubles in operations tend to be caused because of a small fitting clearance, when a die is slid in the direction of an optical axis of an optical surface for taking out of a molded optical element or for pressurization. Therefore, it is impossible, after all, to keep a thickness of a molded optical element to be highly accurate and constant with excellent reproducibility. From the foregoing, in the case of a pickup objective lens for an optical disk with high NA such as NA of 0.85, for example, allowable eccentricity of an optical surface and allowable dispersion of axial thickness are not more than about 1 &mgr;m, and therefore, in the case of the structure of a multi-cavity metallic mold that is dependent on conventional accuracy of parts processing, each of the eccentricity of the optical surface and the dispersion of the axial thickness results in several times that of the aforesaid allowable eccentricity and the allowable dispersion, even when the production is tried at the highest accuracy possible, which causes serious spherical aberration and coma on molding lens power to make it impossible to obtain sufficient optical efficiency.
In glass molding technology for molding a glass lens, there are a single-cavity mold type and a multi-cavity mold type, and in the case of the multi-cavity mold type, its structure is exactly the same as that of the injection molding metallic mold for plastic lenses, and the limit of accuracy for processing each part makes it difficult equally to lower the eccentricity tolerance to 8 &mgr;m or less. In the case of a single-cavity mold type, it employs a mold structure wherein three parts including a pair of dies each having an optical surface and a barrel die that holds the paired dies are bases. With regard to this, tapered portions
8
a
are provided on barrel die
8
as shown in
FIG. 10
, and these tapered portions
8
a
are fitted respectively with tapered portions provided on a pair of dies
9
a
and
9
b
so that a molding cavity is formed between the dies
9
a
and
9
b
. Coaxiality between both dies is determined by accuracy for processing parts such as coaxiality between both tapered portions on the barrel die
8
and coaxiality between optical surfaces of tapered portions respectively on the dies
9
a
and
9
b
. Coaxiality of about 1 &mgr;m for tapered portions is a conventional ordinary limit for processing, and if parts processing accuracy is accumulated, therefore, shifted eccentricity of optical surfaces of about 3 &mgr;m is a limit. Because of taper fitting between barrel die
8
and dies
9
a
and
9
b
, fitting surfaces tend to be worn away, which is different from non-tapered fitting, thus, the barrel die is made of hard-machining materials having high hardness such as ceramics.
From the foregoing, even in the case of glass molding, accuracy of eccentricity of molded optical elements is also dependent greatly on processing accuracy for parts of a mold and is limited, and how the eccentricity is dispersed is less reproducible and its control is difficult, which makes ensuring of molding power and stable manufacturing both for ad
Konica Corporation
Walls Dionne A.
LandOfFree
Molding die does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Molding die, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molding die will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3284287