Patent Application
20240411270
This application claims priority to European Patent Application No. 23178673.2 filed Jun. 12, 2023, the entire contents of which are incorporated herein by reference.
The invention relates to a method for manufacturing luminous horological hands.
The invention also relates to hands manufactured according to this method.
The invention relates to the manufacture of horological hands, and in particular luminous hands.
The documents EP3845974 A1 and WO 2022/122199 A1 describe the principle of operation of fluorescently illuminated hands and methods for manufacturing such hands, the main components of which consist of a sheet metal, a low refractive index layer, the function of which is to optically isolate the metal surface, a medium index layer, the function of which is to guide the fluorescent light towards the edges of the hand, and the deposition of fluorescent pigments which are excited by a remote primary source, for example a LED or the like.
The document WO 2022/122199 A1 describes more particularly a manufacturing method based on the deposition of different resins over a pre-cut sheet metal. This method is difficult to implement, as it proves difficult to hold a liquid resin in an opening, in this case the pre-cut of the metal sheet. The use of a sacrificial film to close the opening around the hand is also particularly delicate. In addition, with such a method, the attachment at the tip of the hand should be cut beyond the resin that forms the light guide, to enable light extraction all around the hand. Hence, the attachment remains visible.
The invention aims to develop an industrialisable method for manufacturing luminous hands.
To this end, the invention relates to a method for manufacturing luminous horological hands according to claim 1.
The invention also relates to hands made according to this method.
The invention relates to the field of watch displays, and in particular watch hands, more specifically luminous hands.
The aims, advantages and features will be better understood upon reading the following detailed description and from the appended drawings wherein:
The method according to the invention aims to manufacture horological hands, in particular watch hands, the edge of which could be illuminated by optically coupling light into a light guide, so that the hand could be luminous.
In particular, this method is intended to enable monolithic assembly of a hand body, in particular a metal hand body, an optical guide system, means for coupling light into the optical guide and means for diffusing light outside the guide.
In particular, the invention uses the techniques described in EP3845974A1, incorporated herein by reference.
This method is based on the replication of micro-structures.
The method according to the invention is based on the assembly, in particular by bonding, of hand bodies with a light guide cut beforehand. More particularly, the hand bodies are superimposed on this light guide.
The light guide may be in sheet or strip form, and may be used as a transport substrate.
Similarly, a strip of hand bodies may be used as a transport substrate.
The hand bodies may be manufactured in a conventional manner, well-known to a person skilled in the art, and are similar to standard hands.
More particularly, and without limitation, the light guide includes a thin, transparent plastic substrate that is as non-diffusing as possible, over which a resin is deposited and structured. The plastic substrate may be made from different materials, for example and without limitation PET, TAC, PMMA and PC. PET and TAC offer very good optical/mechanical trade-offs.
The method of depositing and structuring the resin over the plastic substrate involves selecting a resin with an index close to that of the plastic sheet. More particularly, and without limitation, the resin is structured by UV-embossing, which could be translated as ultraviolet embossing, to create coupling and light extraction areas.
The adhesive used to assemble the plastic substrate and the hand body should be transparent, non-diffusing and have an optical index lower than that of the substrate.
The method includes different operations, which may differ in chronological order, as described below.
Parallel operations relate to the manufacture of the light guides on the one hand, and the hand bodies on the other hand.
A first group of operations 1000 relates to the manufacture of a light guide: either for the manufacture of unitary light guides 30, or for the manufacture of strips 35 of light guides.
In either case, a first operation 100 involves making a master 1, which is a positive model of a micro-relief to be transferred onto the light guides. More particularly and without limitation, this master 1 is made from a material such as PMMA or the like, which is machined using etching means 110, which may consist of laser etching means, in particular CO2 laser, picolaser or femtolaser, micro-milling means, or thermal etching means, or the like. The relief of coupling and light extraction micro-structures are created on this master 1, which are then reproduced during a replication process. Thus, different micro-structures are made, some intended to couple/extract light, and others as alignment marks for subsequent manufacturing steps.
A second operation 200 consists in making a negative tool 2, such as a stamp, based on the master 1, in order to print micro-structures; this negative tool 2 may in particular be made of nickel, or silicone, or any suitable material. A plastic substrate 20 is provided, over which a suitable resin is deposited. In particular, yet without limitation, the substrate 20 may be made of PET or TAC, for example, with a thickness of 50 to 100 micrometres. The replication of the micro-structures is achieved by reproducing the micro-structures created on the master 1 on the plastic substrate 20, by means of this resin, under the action of the buffer 2 which allows printing the micro-structures in the resin deposited beforehand over the plastic substrate 20, and thus making at least one raw light guide 30. This replication may be done by UV-embossing, or by hot-embossing, i.e. hot stamping, or any similar method enabling an accurate reproduction of the details of the micro-structures. This replication method may be carried out in a unitary way, in sheets (plate-to-plate or roll-to-plate depending on the manufacturing method), or in strips. The UV-embossing method is particularly effective because of the mechanical possibilities it offers, in particular the possibility of replicating 30 micrometre deep structures. The output of this second operation is either a raw light guide 30 in the case of unitary manufacture, or a strip of light guides 35, including a plurality of raw light guides 30, in the case of strip manufacture.
A third operation 300 relates to the pre-cutting of the light guide: in order to be able to bond a light guide and a hand together, the raw light guide 30 should be cut at the location where the pipe of the hand will be placed. Without this, assembly would not be possible, as the hand pipe would prevent the entire surface of the hand from being brought into contact. This cut is made using cutting means 310, including but not limited to a CO2 laser, and should be aligned with the different micro-structures present on the raw light guide 30. Preferably, alignment marks have been placed beforehand over the master 1, and reproduced on the raw light guide 30 for this purpose.
In the case of strip manufacture of a strip of light guides 35, it is possible to separate each raw light guide by cutting before, during or after this third cutting operation 300.
In parallel with this first group of operations 1000 relating to the manufacture of a light guide, a second group of operations 2000 includes an operation of manufacturing hand bodies 400, either in a unitary way for the manufacture of a hand body 50, or in strip form according to a standard method with final cutting by stamping. In the case of strip manufacture, the hand bodies 50 may be separated immediately after the hand body manufacturing operation 400, in a separation operation 500 using separation means 510, such as stamping means or other suitable cutting means. In one variant, a strip of hand bodies 55 can be kept until later separation in the process.
A third group of assembly operations 3000 includes a bonding operation 600 for bonding the raw light guide 30, or the strip of light guides 35, and/or the hand body 50, or the strip of hand bodies 55, prior to assembly between the light guide and the hand body. To this end, an adhesive 6 with an optical index lower than that of the light guide is selected, which is deposited over the hand body and/or over the light guide, typically by dispensing means 610.
This bonding operation 600 is followed, within the time allowed by the properties of the selected adhesive, by an assembly operation 700, during which the hand body is then optically aligned and placed against the light guide, before proceeding with bonding by polymerisation. More particularly, and without limitation, a UV optical adhesive is selected because of its rapid polymerisation. Advantageously, robotic handling means 710 are used, such as a robot coupled to optical recognition means to ensure proper alignment and positioning. At the end of this assembly operation 700, an assembled raw hand 70 is obtained, which remains to be finished.
In the case of strip manufacture, whether a strip of light guides 35 and/or a strip of hand bodies 55, the third group of operations 3000 may be carried out in a similar manner. Nonetheless, the assembly operation 700 is more delicate to implement when assembling a strip of light guides 35 with a strip of hand bodies 55.
A fourth group of operations 4000 includes a final cutting operation 800, the purpose of which is to complete and release each luminous hand 80. In particular, this final cutting operation 800 is carried out by laser cutting means as already mentioned, in particular by femtolaser which gives good results on PET, or cutting by a CO2 laser, or others.
In the case of unitary manufacture, during this final cutting operation 800, the light guide may finally be cut to release the hand. Preferably, cutting is done approximately 0.1 mm wider than the nominal width of the hand, in order to let the light escape around the hand and towards the wearer of the watch, thanks to the extraction micro-structures provided for this purpose.
The above-described method details the manufacture of hands that will be illuminated over their periphery. It is also possible, in the case of skeleton hands, for the illumination to take place throughout the openings in the hand, or both. The illumination design is not limited to the entire perimeter and, depending on the position of the extractors and the final cut-out, may be only on one side, or only on the tip of the hand, for example.
An alternative method may be implemented, including similar steps, but in a different order. In particular, the method may include pre-cutting the hands into strips. Advantageously, the cut is approximately 0.1 mm narrower than the nominal width of the assembled raw hand 70 in order to let the light escape around the hand towards the wearer of the watch thanks to the extraction micro-structures provided for this purpose. At the same time, the light guide may be manufactured into a strip, in the form of a strip of light guides 35, and the light guide may be cut out/secured. During the operation of assembly of the hand body and the light guide, adhesive with an optical index lower than that of the light guide is deposited over the light guide (alternatively over the hand body), typically by dispensing. Afterwards, the light guide is optically aligned and placed against the hand body to cure the adhesive. During the final cutting operation, the hands are finally cut into strips to release the assembled hand. Advantageously, cutting is done by laser or by stamping.
In short, the micro-structures are sufficient to exploit the luminescence which originates from an external light source such as a LED 90, or LEDs 90, whose light “enters” an input light guide 70 of the luminous hand 80 under the hand head and “comes out” at the micro-structures of the light guide 30 which are arranged along the length of the hand.
With regards to materials, the light guide is advantageously a combination of a plastic substrate 20 (support) with a resin in which the different micro-structures are printed, in particular by the preferred UV-embossing method, which gives very good results, although hot-embossing of the micro-structures directly into the substrate 20 may also be considered.
Both the substrate and the resin must be as transparent as possible to avoid light losses. The choice of using “clear” materials is advantageous because they are accessible in the desired thicknesses. In principle, coloured materials (for example fluorescent) could be considered while remaining transparent. However, it is essential that the refractive indices of the two materials are as close as possible. The refractive index of the adhesive that assembles the guide to the hand must be as low as possible compared to that of the substrate, to optically isolate the guide. It is not necessary to insert particles of any kind into the light guide.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23178673.2 | Jun 2023 | EP | regional |
