Etching

Hie invention relates to an improved method for producing an object through photochemical etching. Hie object is preferably a frame for eyeglasses or parts of such frame like e.g. a frame front adapted to support lenses and/or lateral temples articulable to the frame front.

In photo-etching (or photo-shearing) technology, a metal or epoxy- glass sheet is coated with a photosensitive film of which the some parts are removed away to obtain a processing mask. Then with a corrosive acid the unprotected areas are removed from the film. Thus, under the residual film the piece remains unchanged, while the thickness of the zones without film is being eroded by the acid in programmable amount. As an example of this process in FIG. 1 there is shown a frame front 10, for eyeglasses, which has two opposite plane faces 16, 14. By eroding a compact foil, the mask 10 was obtained with two central openings 20 in which to mount the lens.

Almost always, photo-etching involves the two sides 16, 14 of the starting blank foil, so that the acid digs the foil starting from the two faces 16, 14 and heading towards the center of the thickness. There results an undesirable burr 12 which in cross-section has the form of a cusp (Fig. 2) which completely runs the edges of the mask 10, both on the outer perimeter and on the edges of the openings 20.

The burr 12 is a problem because not only it is less than aesthetic, relatively large and such as to hamper the next processing steps, but it can be quite sharp and therefore dangerous. To eliminate it, usually the mask 10 (or each object produced in the same way) undergoes several hours of tumbling, which, however, is expensive and often does not reach the goal.

Another more recent solution to prevent the burr 12 is to completely abandon the photo-etching technology and use a laser beam for the cutting of the foil. But this technology however has disadvantages. For instance, according to the type of laser employed the cut is not perfect but leaves a roughness on the edges of the cut object; or the foil suffers deformation during cutting because of the local heating or the outburst of internal tensions, and manufacturing tolerances grow conspicuously.

To improve this state of the art is the main object of the invention.

Another object is to obtain a method for producing an object by photochemical etching that gets rid of the burr 12.

Another object is to obtain a method to produce without the burr 12 a frame for eyeglasses or parts of such frame like e.g. a frame front adapted to support lenses and/or lateral temples to be articulated to the frame front. By frame it is meant here the support that supports a transparent medium fixed thereto to hold it in suitable position before the eyes. Eyeglasses are the optical instrument consisting of the frame and the associated transparent medium.

A first aspect of the invention relates to a method for producing a flat object through photochemical etching, wherein a material or film is deposited on a (e.g. metallic) foil, the material or film masking certain areas of the foil by covering them, the so-coated foil is subjected to the action of a chemical agent for removing, from the object's thickness, portions external to said areas, and after the chemical agent's aggression the margins of the resulting object are subjected to milling for removing a burr present thereat. By flat object it is meant here preferably an object extending with level development or substantially along a plane. In particular it is meant an object substantially devoid of in- relief parts and/or devoid of convexities or concavities.

The main application of the method is that wherein both the opposite flat faces of the foil 10 are subjected to the action of the chemical agent. Preferably, then, the eliminated burr is the one described above, and indicated with 12 in Fig. 2. However, the method also lends itself to the elimination of other forms or types of burrs arising from photochemical etching, e.g. the burrs derived from the etching of only one side of the foil. Hie milling step not only eliminates the burr 12 thereby improving production, but increases the dimensional accuracy of the final produced object. Note in fact that the burr 12 has variable and unpredictable projection, therefore as the total tolerance of the piece you must consider - unfortunately - that of the point with the most protruding burr. By removing the burr 12 through milling, which inherently has higher machining precision, the object is corrected while giving it the precision of milling.

A merit of the invention has been to overcome the prejudice of said random tolerance, which led to exclude milling as subsequent processing since milling is ordinarily considered to request pieces with small tolerances and, above all, having negligible variance.

By the method the final shape of the object after the milling step is more precise. The tolerance of the photo-etching, and also the size of the burr 12, amounts to a percentage of the thickness of the foil. The thicker the foil, the greater the tolerance (and the burr 12) in photo-etching. By the milling action, however, not only the final tolerance on the object is essentially that of milling, but the tolerance of the photochemically- etched products is disconnected from the thickness thereof.

Preferably, multiple objects are milled at a time. In particular, objects resulting from the chemical agent's aggression are preferably stacked one on another aligning the respective edges, and the milling operation takes place on the aligned edges of the stack so obtained. Therefore one can increase the hourly production efficiency and exploit the stack of objects to lock them to one another and/or to place them on the milling machine, especially if all the objects are equal. In particular the centering step can be simplified if the objects have the same shape and/or have central pass-through openings, and are stacked by inserting into these openings a complementary centering means, e.g. a template or an arrangement of pins or marks that touches the perimeter of a pass-through opening. The locking thus takes place at the center of the objects and milling can proceed quickly on their outer perimeter. Or an object resulting from the chemical agent's aggression may comprise an end, preferably an elongated end, and the object is clamped at said end to stabilize the object during milling. The clamped objects too may be stacked on one another.

In particular, in the objects or in the method said margins refer to the resulting object's outermost perimeter. Still more in particular, said margins constitute only the outermost perimeter (i.e. the edge) of the resulting object, which inter alia simplifies and shortens the milling operations.

A second aspect of the invention relates to an object obtained via the method. In particular, the object is a pair of eyeglasses or a part thereof (e.g. a frame, a frame front or a lateral temple). The object is in particular characterized by the absence of the burr 12, i.e. the surface orthogonal to the two opposite faces (indicated with 14, 16 in the example of Fig. 2) is smooth and exhibits no cusps in cross-section.

The advantages of the invention will be more apparent from the following description of a preferred embodiment of eyeglasses frame, making reference to the attached drawing wherein:

Fig. 1 shows a three dimensional view of a known front piece for eyeglasses;

Fig. 2 shows the piece of Fig. 1 in side view with a detail magnified;

Fig. 3 shows a three dimensional view of a front portion for eyeglasses obtained by the method; Fig. 4 shows the portion of Fig. 3 in a side view with a detail magnified.

The processing method aims to produce a frame mask having shape similar to that of Fig. 1.

In Fig. 3 there is shown a front mask 50 of a pair of eyeglasses that has two opposite flat faces 52, 54. The mask 50 is obtained by eroding a compact foil, like the mask 10 of Fig. 1, and comprises an outer perimeter or edge P and two central openings 60 in which to mount lenses. To remove the burr present along the perimeter P, after the chemical photo- etching a milling cutter or grinding wheel 30 runs the perimeter P along a closed path or circuit Q, so as to mechanically remove the burr.

As seen in Fig. 4, the action of the milling makes the edge and the thickness 90 of the mask 50 smooth and orthogonal to the faces 52, 54 with continuity (see fig. 4). That is to say that the thickness 90 lies on a plane substantially orthogonal to the (parallel) lying planes of the faces 52, 54.

Optionally also the edges of the openings 60 may be milled.

The objects produced by the method preferably have a thickness of 0.5 to 2 mm.