Injection molding apparatus and method for manufacturing an ophthalmic lens mold through injection molding

Abstract

An injection molding apparatus for manufacturing an ophthalmic lens mold having a front surface comprising a lens forming portion and a rear surface, comprises a first molding tool and a second molding tool. The first and second molding tools are movable towards and away from each other between a closed position and an open position. In the closed position the first mold forming portion of the first molding tool and the second mold forming portion of the second molding tool define a cavity between them corresponding in shape to the shape of the ophthalmic lens mold. The surface of the second mold forming portion, at least in a central zone thereof, has a surface roughness S.sub.a in the range of 0.3 μm to 2 μm, and a surface roughness S.sub.z in the range of 10 μm to 50 μm.

Claims

1. Injection molding apparatus for manufacturing an ophthalmic lens mold (5) from an injection-moldable plastic material, the ophthalmic lens mold having a front surface (500) comprising a lens forming portion (502) and a rear surface, the injection molding apparatus comprising a first molding tool comprising at least one first mold forming portion for forming the front surface of the ophthalmic lens mold, a second molding tool comprising at least one second mold forming portion (4, 40, 41) for forming the rear surface (501) of the ophthalmic lens mold (5), wherein the first and second molding tools are movable towards and away from each other between a closed position, in which the ophthalmic lens mold (5) can be manufactured by injection molding, and an open position, in which the manufactured ophthalmic lens mold (5) can be removed from the second molding tool, and wherein in the closed position the at least one first mold forming portion of the first molding tool and the at least one second mold forming portion of the second molding tool define a cavity between them corresponding in shape to the shape of the ophthalmic lens mold (5) to be manufactured, wherein the surface (400) of the second mold forming portion (4, 40, 41), at least in a central zone (401) that corresponds to a portion (501) on the rear surface of the ophthalmic lens mold opposite to the lens forming portion (502) on the front surface (500), has a surface roughness S.sub.a in the range of 0.3 μm to 2 μm, and a surface roughness S.sub.z in the range of 10 μm to 50 μm.

2. Injection molding apparatus according to claim 1, wherein the surface roughness S.sub.a is about 1 μm.

3. Injection molding apparatus according to claim 1, wherein the surface roughness S.sub.z is about 25 μm.

4. Injection molding apparatus according to claim 1, wherein at least the first mold forming portion and second mold forming portion are made from aluminum.

5. Injection molding apparatus according to claim 1, wherein the surface roughness of the second mold forming portion has been created using one or more techniques selected from the group consisting of laser roughening, sand blasting, grinding, and lapping.

6. Injection molding apparatus according to claim 1, wherein the first mold forming portion of the first molding tool and the second mold forming portion of the second molding tool correspond to each other in shape so that in the closed position the cavity formed between them has a uniform thickness.

7. Injection molding apparatus according to claim 1, wherein the second molding tool comprises an ejector which is arranged outside of the central zone of the second mold forming portion.

8. Method of manufacturing a plastic ophthalmic lens mold (5), through injection-molding, the ophthalmic lens mold (5) having a front surface (500) comprising a lens forming portion (502) and a rear surface, the method comprising the steps of: providing a first molding tool comprising at least one first lens mold forming portion for forming the front surface of the ophthalmic lens mold; providing a second molding tool comprising at least one second lens mold forming portion (4, 40, 41) for forming the rear surface of the ophthalmic lens mold, wherein the first and second molding tools are movable towards and away from each other between a closed position and an open position; moving the first and second molding tools to the closed position, wherein in the closed position the at least one first lens mold forming portion of the first molding tool and the at least one second lens mold forming portion of the second molding tool define a cavity between them, the cavity corresponding in shape to the shape of the ophthalmic lens mold to be manufactured; injecting an injection-moldable plastic material into the cavity to manufacture the ophthalmic lens mold (5) through injection-molding; moving the first and second molding tools to the open position; removing the ophthalmic lens mold (5) from the second molding tool; wherein the step of providing a second molding tool comprises providing a second molding tool having a surface (400) of the second mold forming portion (4, 40, 41) which, at least in a central zone (401) corresponding to a portion (501) on the rear surface of the ophthalmic lens mold (5) opposite to the lens forming portion (502) on the front surface, has a surface roughness S.sub.a in the range of 0.3 μm to 2 μm, and a surface roughness S.sub.z in the range of 10 μm to 50 μm.

9. Method according to claim 8, wherein the surface roughness S.sub.a is about 1 μm.

10. Method according to claim 8, wherein the surface roughness S.sub.z is about 25 μm.

11. Method according to claim 8, wherein at least the lens mold forming portions of the first and second molding tools are made from aluminum.

12. Method according to claim 9, wherein the moldable plastic material is a polyolefin.

13. Method according to claim 9, wherein removing the ophthalmic lens mold from the second molding tool is performed by pressing an ejector against a portion of the rear surface of the ophthalmic lens mold outside of the portion opposite to the lens forming portion on the front surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantageous aspects of the injection molding apparatus and method for manufacturing an ophthalmic lens mold will become apparent from the following description of an embodiment with the aid of schematic drawings in which:

(2) FIG. 1 shows the mold forming portion of a molding tool of a conventional injection molding apparatus and an ophthalmic lens mold arranged thereon, with removal forces being applied to the rear surface of the ophthalmic lens mold;

(3) FIG. 2 shows the mold forming portion of FIG. 1 and the deformation of the ophthalmic lens mold as well as the sticking of the ophthalmic lens mold to the central zone of the surface of the mold forming portion of the molding tool;

(4) FIG. 3 shows a mold forming portion of the molding tool of an embodiment of the injection molding apparatus according to the invention, having the particular surface roughness in a central zone of the surface of the mold forming portion of the molding tool and the ophthalmic lens mold arranged thereon, with removal forces being applied to the rear surface of the ophthalmic lens mold; and

(5) FIG. 4 shows the mold forming portion of the molding tool of the embodiment of the injection molding apparatus of FIG. 3 with the ophthalmic lens mold during removal from the molding tool without deformation and sticking of the ophthalmic lens mold to the central zone of the surface of the mold forming portion of the molding tool.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) In FIG. 1 the mold forming portion 1 of a fixedly arranged molding tool of a conventional injection molding apparatus is shown in a schematic representation. In the embodiment shown in FIG. 1 the injection molding apparatus comprises molding tools having mold forming portions configured to manufacture male ophthalmic lens molds. However, the following description similarly applies to an injection molding apparatus that comprises molding tools having mold forming portions configured to manufacture female ophthalmic lens molds. The essential difference then is that the mold forming portions of the molding tools are configured to manufacture female ophthalmic lens molds.

(7) Turning back to FIG. 1, mold forming portion 1 of the fixedly arranged molding tool comprises a central mold forming portion 10 and a peripheral mold forming portion 11. Central mold forming portion 10 and peripheral mold forming portion 11 together have a front surface 100 that has a central zone 101 (corresponding to the portion of the front surface 100 of the central mold forming portion 10). The injection molding apparatus further comprises a further molding tool (not shown) that comprises a further mold forming portion. This further molding tool with the further mold forming portion is movable towards and away from the fixedly arranged molding tool to a closed an open position of the molding tools, respectively.

(8) For the manufacture of an ophthalmic lens mold, the movable molding tool is first moved to the closed position. In this closed position, a cavity is formed between the mold forming portion of the movable molding tool (not shown) and the mold forming portion 1 of the fixedly arranged molding tool. This cavity corresponds in shape to the ophthalmic lens mold to be manufactured. A moldable plastic material, for example molten polypropylene, is then injected under high pressure into the cavity through a so-called runner that is connected to the cavity. The moldable plastic material injected into the cavity is then allowed to cure to form an ophthalmic lens mold 2 that corresponds in shape to the cavity formed between the mold forming portion of the movable molding tool (not shown) and the mold forming portion 1 of the fixedly arranged molding tool. During curing, the plastic material shrinks onto the mold forming portion 1 of the fixedly arranged molding tool, and in particular in the area of the central mold forming portion 10 the plastic material may stick to the central zone 101 of the surface 100 of the mold forming portion 1 of the molding tool.

(9) The so formed ophthalmic lens mold 2 comprises a central portion 20 and a peripheral portion 21. The central portion 20 and the peripheral portion 21 of ophthalmic lens mold 2 together have a front surface 200 that comprises a lens forming portion 202 for determining the shape of the rear surface of an ophthalmic lens to be formed using ophthalmic lens mold 2. Opposite to that lens forming portion 202 on the front surface 200 there is a corresponding portion 201 of the rear surface of the ophthalmic lens mold 2. Peripheral portion 21 of ophthalmic lens molds 2 is not involved in determining the shape of an ophthalmic lens that is formed when using ophthalmic lens mold 2.

(10) Turning back to the manufacturing of the ophthalmic lens mold through injection molding, once injection and ophthalmic lens mold formation is completed the movable molding tool is moved away from the fixedly arranged molding tool. Ophthalmic lens mold 2 must then be removed from the fixedly arranged molding tool comprising mold forming portion 1. This is typically performed by applying removal forces 3 (indicated by the arrows in FIG. 1) to the rear surface of the ophthalmic lens mold 2 in the peripheral portion 21, i.e. outside of the portion 201 of the rear surface that corresponds to the lens forming portion 202 on the front surface 200. Application of the removal forces 3 outside of the portion 201 is performed since the (central) lens forming portion 202 of the ophthalmic lens mold must not be deformed as lens forming portion 202 is responsible for the shape of the ophthalmic lens (e.g. contact lens) to be molded using ophthalmic lens mold 2.

(11) So far injection molding of an ophthalmic lens mold is conventional and well-known in the art.

(12) However, when attempting to remove ophthalmic lens mold 2 from mold forming portion 1 through the application of removal forces 3 (see FIG. 2) it may occur that, due to the portion 201 of ophthalmic lens mold 2 sticking to the central zone 101 of the front surface 100, the ophthalmic lens mold 2 deforms to an extent such that after its removal it is outside the geometric specifications for the ophthalmic lens mold 2 so that it cannot be used anymore for the manufacture of an ophthalmic lens (e.g. contact lens). Also, stress-whitening (small tears or cracks in the plastic material) may occur during removal which also results in that the ophthalmic lens mold 2 cannot be used for the manufacture of an ophthalmic lens (e.g. contact lens).

(13) In FIG. 3, the mold forming portion 4 of a fixedly arranged molding tool of an injection molding apparatus according to the invention is shown in a schematic representation. Mold forming portion 4 comprises a central mold forming portion 40 and a peripheral mold forming portion 41. Central mold forming portion 40 and peripheral mold forming portion 41 together have a front surface 400 that has a central zone 401 (corresponding to the portion of the front surface 400 of the central mold forming portion 40). The injection molding apparatus according to the invention further comprises a further molding tool (not shown) comprising a further mold forming portion. This further molding tool is movable towards and away from the fixedly arranged molding tool to a closed an open position of the molding tools, respectively.

(14) Unlike the embodiment shown in FIG. 1, at least the central zone 401 of the front surface 400 of mold forming portion 4 of the fixedly arranged molding tool has a surface roughness S.sub.a in the range of 0.3 μm to 2 μm, and a surface roughness S.sub.z in the range of 10 μm to 50 μm. In particular, the surface roughness S.sub.a may be about 1 μm and the surface roughness S.sub.z may be about 25 μm. It is also possible that S.sub.a be about 1 μm and S.sub.z be selected from the range of 10 μm to 50 μm. Alternatively, S.sub.a may be selected from the range of 0.3 μm to 2 μm while S.sub.z is about 25 μm. This surface roughness of central zone 401 of the front surface 400 is indicated in FIG. 3 by the thickened line 402.

(15) For the manufacture of the ophthalmic lens mold 5, the movable molding tool (not shown) is moved to the closed position. In this closed position, a cavity is formed between the mold forming portion of the movable molding tool (not shown) and the mold forming portion 4 of the fixedly arranged molding tool. This cavity corresponds in shape to the ophthalmic lens mold to be manufactured. Preferably, the cavity has a uniform thickness so that the formed ophthalmic lens mold 5 also has a uniform wall thickness which is preferred as regards a homogeneous shrinkage of the moldable plastic material during injection molding. This in turn is advantageous with respect to the manufacturing of ophthalmic lens molds with high precision and accuracy as regards the geometric specifications of the ophthalmic lens mold 5 and as regards the optical quality of the lens forming surface of the ophthalmic lens mold 5. A moldable plastic material, for example molten polypropylene, is then injected under high pressure into the cavity through a so-called runner that is connected to the cavity. While after-pressure is applied, the moldable plastic material injected into the cavity is allowed to cure to form an ophthalmic lens mold 5 corresponding in shape to the cavity formed between the mold forming portion of the movable molding tool (not shown) and the mold forming portion 4 of the fixedly arranged molding tool. During curing the plastic material shrinks onto the mold forming portion 4 of the fixedly arranged molding tool. Optionally, small projections (not shown) or other suitable means may be provided on the lateral surfaces of the mold forming portion 4 of the fixedly arranged molding tool to ensure that the ophthalmic lens mold 5 is retained on the mold forming portion 4 of the fixedly arranged molding tool in any event. Due to the well-defined surface roughness in the central zone 401 of the front surface 400 of mold forming portion 4 of the molding tool, the plastic material of ophthalmic lens mold 5 does not stick anymore or only loosely sticks to the surface 400 in the central zone 401 thereof.

(16) The so formed ophthalmic lens mold 5 comprises a central portion 50 and a peripheral portion 51. The central portion 50 and the peripheral portion 51 of ophthalmic lens mold 5 together have a front surface 500 that comprises a lens forming portion 502 for determining the shape of the rear surface of an ophthalmic lens to be formed using ophthalmic lens mold 5. Opposite to that lens forming portion 502 on the front surface 500 there is a corresponding portion 501 of the rear surface of the ophthalmic lens mold 5. Peripheral portion 51 of the ophthalmic lens mold 5 is not involved in determining the shape of an ophthalmic lens that is formed when using ophthalmic lens mold 5.

(17) Injection molding is performed in the manner already described above. Once injection and ophthalmic lens mold formation are completed the movable molding tool is moved away from the fixedly arranged molding tool. Ophthalmic lens mold 5 must then be removed from the fixedly arranged molding tool comprising mold forming portion 4. This is typically performed by applying removal forces 6 (indicated by the arrows in FIG. 3) to the rear surface of the ophthalmic lens mold 5 in the peripheral portion 51, i.e. outside of the portion 501 opposite to the lens forming portion 502. Application of the removal forces 6 outside of the portion 501 can be performed with the aid of an ejector which may, for example, comprise a number of ejector pins arranged in circumferential direction, or may comprise a ring-shaped ejector, or may be any other suitable type of ejector.

(18) As can be seen best in FIG. 4, due to the portion 501 of the rear surface of the ophthalmic lens mold 5 no longer sticking to the central zone 401 of the front surface 400 of the mold forming portion 4 of the fixedly arranged molding tool, ophthalmic lens mold 5 can be easily removed from the mold forming portion 4 of the fixedly arranged molding tool without the occurrence of deformation or stress-whitening. This increases the yield and efficiency of the injection-molding process and in particular enables to manufacture single use plastic ophthalmic lens molds in very short overall cycle times, as has been described further above.

(19) The invention has been described with respect to an embodiment. However, the invention is not intended to be limited to this embodiment, but rather many variations are possible without departing from the teaching underlying the instant invention. For example, the molding tool of the injection molding apparatus may be configured for the manufacturing of a female ophthalmic lens mold, as has been mentioned already. Also, instead of the parameters S.sub.a and S.sub.z it is conceivable to use other standard roughness parameters such as R.sub.a and R.sub.z instead. Therefore, many additional variations are intended to be covered by the teaching of the invention, and therefore the scope of protection is defined by the appended claims.