HK1099815B - A lens blank, and a method and a mold for fabricating it - Google Patents

Abstract

English abstract will be submitted.

Description

Lens blank and method and mold for manufacturing same

Technical Field

The present invention relates to a lens blank manufactured by injecting a thermoplastic material into a mould prepared with an insert, typically a piece of polarized, photochromic or tinted material which has been cut to shape and finished, and to a method of manufacturing such a blank.

Background

Components of this type are known. It is used in particular for the manufacture of corrective lenses for ophthalmic spectacles or comfort lenses (of sunglasses, goggles … …).

For this type of component, several manufacturing techniques are known. One of which is described, for example, in U.S. patent No. 2004/0217495. In this patent document, a mould is used comprising two parts open to each other, one of the two parts defining a complex cavity in which is provided a type of aperture plane for an insert in sheet form containing a portion, such as a polarizing film, the aperture plane being defined by a plurality of mould parts adjustable relative to each other.

The molds disclosed therein appear to consume large quantities of injected material, most of which constitute waste when forming a lens from a molded blank.

Furthermore, the blank in this mould is not suitable for automatic operation, or even for constituting a stack, since the surface presenting the polarizing film as a whole protrudes from the blank and is then exposed to external attack that could scratch the film.

Industrialization of the process disclosed in this document appears to require complex equipment that is constantly precisely adjusted, thereby adversely affecting the cost of manufacturing the blank.

The present invention proposes a novel design for such a lens blank: it allows a simpler manufacturing process to be implemented and used to produce a part at competitive price.

Disclosure of Invention

To this end, in a first aspect, the invention provides an ophthalmic lens blank from a mold having a piece of insert placed therein prior to injection, the blank comprising a peripheral top imprint, said imprint being located outside the insert. This feature is an indication of the present invention. As will be described below, the portions of the insert that are free of any expensive components are used in those portions of a blank that are designed to be damaged when manufacturing a lens for eyeglasses or eyepieces.

Preferably, each trace is realized by a tab having an additional thickness on the same side of the insert and a recess in the other side thereof, the recess forming an element for centering a spacer adjacent to the blank. By means of these tabs, it is possible to stack the blanks on each other without the surface of an insert coming into contact with the blank immediately below it in the stack, said surface then being protected from the external environment.

In a second aspect, the invention provides a method for manufacturing the above specified blank by moulding, using a mould divided into two parts, one of the two parts being provided with an ejector movable perpendicularly to the closing plane of the mould, starting from the opening of the mould, the method comprising:

placing a mold stripper at the ejection position;

engaging the sheet insert between the ejector and holding it therebetween by resilient wedging;

closing the mold while retracting the ejector into the corresponding part;

injecting a thermoplastic material into the mold;

opening the mold after the thermoplastic material has hardened;

the mold stripping device is placed back to the ejection position; and

the synthetic blank obtained in this way is ejected.

Naturally, in the manufacturing process, the open mould will have a plurality of cavities, each provided with at least three ejectors, so that the insert can be kept fixed in each cavity by wedging.

Other features and advantages of the present invention will appear from the description given below of an embodiment of the invention.

Brief description of the drawings

Reference is made to the accompanying drawings, wherein:

FIG. 1 is a generally plan view of a lens blank according to the present invention;

figure 2 is a cross-sectional view through a stack of blanks according to the invention, on one of the lines II-II of figure 1;

figures 3, 4 and 5 show three stages in the process of manufacturing such a blank.

Detailed Description

With reference to figures 1 and 2, it can be seen that a lens blank according to the invention is synthetic, comprising a film 1 of polarizing material and a base 2 of transparent resin, which may optionally be coloured, or may even comprise photochromic pigments.

The film 1 is cut to present two rectilinear sides 3 and 4 and two curvilinear sides 5 and 6. Beyond the edges 3 and 4, the blank has ejection tracks 7, 8, 9 and 10, which are the sites of the ejector action to eject the blank from the cavity of the production tool, as will be described in more detail below.

In the particular example shown in the figures, these top traces are in fact cylindrical tabs defined by a bottom surface 11 and a top surface 12 parallel to the bottom surface, and the bottom surface 11 is provided with an additional thickness 13, while the top surface presents a recess 14. The distance between the bottom of the recess 14 and the top of the additional thickness 13 is such that: when two blanks are superimposed, as shown in fig. 2, a clearance 15 is maintained between the polarizing film 1 of an upper blank and the base 2 of a lower blank on which the upper blank is placed. The additional thickness 13 thus constitutes a spacer which penetrates into the interior of the recess 14 and also constitutes means for centering the two superimposed blanks with respect to one another.

In figures 3, 4 and 5 there is shown generally a die 20 for making the blank of the invention, comprising two parts 21 and 22, the two parts 21 and 22 being movable relative to each other between an open position shown in figure 3 and a closed position shown in figure 4. When the mould is closed, it defines an engagement plane 23 and a cavity 24.

The lower part 21 presents a generally concave bottom surface 25 of the cavity, while the upper part 22 presents a generally concave top surface 26 of the cavity. The lower part 21 is provided with four ejector dies through the bottom surface 25. Two ejectors 27 and 28 are shown in the figure.

The method of the invention includes initially removing the part 22 while the mould is open, thereby providing free access to the mould cavity in the lower part 21. The ejectors 27 and 28 are in their position in which they project above the surface 25 so as to constitute two posts between which a polarising film 1 can be placed, which polarising film 1 has been pre-shaped to have substantially the same surface as one or other of the surfaces 25 or 26, but the transverse dimension, i.e. the distance maintained between the longitudinal edges 3 and 4 of the polarising film 1, is slightly greater than the distance between two ejectors such as those referenced 27 and 28. It will therefore be appreciated that the polarized film may be held stationary by being resiliently wedged (secured) between the ejectors prior to contacting surface 25. Three ejector can meet the requirement.

With the film 1 placed in position in this way using any suitable robotic arm or mechanism, the mould is closed by bringing the mould parts 22 over the parts 21 and by bringing their surfaces 23 into register so as to constitute the joining plane of the mould. At the same time, the ejectors 27, 28 retract below the surface 25 as shown in figure 4. It can be seen that the top surfaces of the ejectors 27, 28 have a depression, while the bottom surface 26 of the upper part 22 of the mould exhibits a substantially circular portion facing each ejector and exhibiting a protrusion. The cavity 24 is then shaped in such a way that: in alignment with the ejectors 27, 28, the shape of the tabs 7, 8, 9 and 10 as described above is obtained.

Thereafter, the thermoplastic material used to construct the base 2 of the blank is injected. This injection takes place substantially parallel to the joining plane 23 and in a direction perpendicular to the plane of fig. 3-5, i.e. in the longitudinal direction of the insert 1. The shape of the cavity 24 is such that: the curved edges 5 and 6 of the insert fit tightly to the corresponding edges of the cavity 24. In the example shown, the cavity 24 has a curved side identical to the side 6 and a straight side tangent to the side 5. Under such conditions, the injected flow of thermoplastic material causes the position of the insert 1 to be practically unchanged, even if the ejectors 27 and 28 are retracted.

Once the material has hardened, the mold may be opened and the ejectors 27 and 28 extended, as shown in fig. 5. The blanks of the present invention may then be processed by any suitable robotic means.

It will be appreciated that the design of the lens blank and the method of manufacturing the same of the invention, simplifies the shape of the mould cavity and thus the design of the mould, in order to save polarizing material by ensuring that it does not extend out of the ejector, but without cutting away the film of polarizing material in a complicated manner, and finally, the invention makes it easier to store the blank made by the manufacturing method of the invention, in particular to protect the sensitive outer surface of the polarizing film 1 from any environmental attack.

Claims (3)

1. A method for manufacturing a synthetic lens blank with an insert (1) by injection molding, using a mold divided into two parts (21, 22), the two parts (21, 22) defining at least one cavity (24) therebetween, one of the two parts (21) being provided with a plurality of ejectors (27, 28) movable perpendicularly to the closing plane (23) of said mold (20), said method being characterized in that, starting from the opening of the mold, it comprises:

-placing the ejector (27, 28) in an ejection position;

engaging said patch insert (1) between said ejectors (28) and holding it therebetween by resilient wedging;

-closing the mould (20) while retracting the ejector (27, 28) into the respective part (21);

-injecting a thermoplastic material (2) into said mould (20);

opening the mold after the thermoplastic material has hardened;

-replacing the ejector (27, 28) in the ejection position; and

the synthetic blank obtained in this way is ejected.

2. A lens blank manufactured by the method according to claim 1, comprising a peripheral ejection track (7, 8, 9, 10), characterized in that said track is located outside said insert (1).

3. Lens blank according to claim 2, characterized in that each imprint is realized by a tab (7, 8, 9, 10) having an additional thickness (13) on the same side of the insert (1) and a recess (14) in its other side, the recess (14) forming an element for centering a spacer (13) adjacent to the blank.