Method for manufacturing luminous pointers by replication of microstructures

Abstract

One aspect of the invention relates to a method for producing luminous timepiece hands (80), according to which at least one light guide (30) or light guide strip (35) is separately produced on the one hand and at least one hand body (50) or hand body strip (55) on the other hand, the at least one light guide (30) or the light guide strip (35) is manufactured by a first set of operations (1000) by replication of a microstructure initially made on a master mask (1), and the at least one pointer body (50) or the pointer body strip (55) is manufactured by a second set of operations (2000), the at least one pointer body (50) or the pointer body strip (55) is assembled with the at least one light guide (30) or the light guide strip (35) by an engagement operation (600) and an assembly operation (700) before the illuminated pointer (80) is finished trimmed by a final cutting operation (800).

Description

Technical Field

[0001] The invention relates to a method for producing a luminous horological hand.

[0002] The invention also relates to a pointer manufactured according to this method.

[0003] The invention relates to the production of timepiece hands, and in particular luminous hands. Background Art

[0004] Documents EP3845974 A1 and WO 2022 / 122199 A1 describe the operating principle of a fluorescent illuminated pointer and a method for manufacturing such a pointer, the main components of which are composed of a metal sheet, a low refractive index layer, a medium refractive index layer and a deposition of fluorescent pigments, wherein the function of the low refractive index layer is to optically isolate the metal surface, the function of the medium refractive index layer is to guide the fluorescent light toward the edge of the pointer, and the fluorescent pigment is excited by a remote primary light source (such as an LED, etc.).

[0005] Document WO 2022 / 122199 A1 describes more particularly a manufacturing method based on the deposition of different resins on a pre-cut metal foil. This method is difficult to implement because it proves difficult to keep the liquid resin in the opening, in this case the metal foil is difficult to pre-cut. The use of a sacrificial film to close the opening around the pointer is also particularly delicate. In addition, with this method, the attachment at the tip of the pointer should be cut outside the resin forming the light guide to achieve light extraction all around the pointer. The attachment therefore remains visible. Summary of the invention

[0006] The present invention aims at developing an industrializable method for producing luminous hands.

[0007] To this end, the invention relates to a method for producing a luminous timepiece hand according to claim 1 .

[0008] The invention also relates to a pointer produced according to this method.

[0009] The present invention relates to the field of watch displays and in particular to the field of watch hands, more particularly luminous hands. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Objects, advantages and features will be better understood after reading the following detailed description and by referring to the accompanying drawings, in which: - Figures 1 to 5The steps of the method according to the invention are schematically illustrated in several alternative sequences, in which a first set of operations for manufacturing the light guide and a second set of operations for manufacturing the pointer body are performed in parallel before a third set of assembly operations and then followed by a fourth set of finishing operations: o Figure 1 Involving unitary manufacturing of the light guide and unitary manufacturing of the pointer body, and joining of the pointer body during a third set of assembly operations; o Figure 2 involving a single manufacture of a light guide and a single manufacture of a pointer body, and joining of the light guide during a third set of assembly operations; o Figure 3 Concerning the manufacture of light guides in strips and the unitary manufacture of the pointer body, and the joining of the pointer body during a third set of assembly operations; o Figure 4 involving strip-type manufacturing of the light guide and unitary manufacturing of the pointer body, and joining of the pointer body during a third set of assembly operations; o Figure 5 involving strip-wise manufacturing of the light guide and strip-wise manufacturing of the pointer body, and joining of the pointer body during a third set of assembly operations; - Figure 6 and Figure 7 Two examples of luminous pointers made according to the invention, coupled to groups of three LEDs each, are shown in schematic form and in plan view. DETAILED DESCRIPTION

[0011] The method according to the invention is intended to produce a timepiece hand, in particular a watch hand, the edge of which can be illuminated by optically coupling light into a light guide, so that the hand can emit light.

[0012] In particular, such a method intends to achieve a monolithic assembly of a pointer body, in particular a metallic pointer body, a light guide system, means for coupling light into the light guide and means for diffusing light outside the light guide.

[0013] In particular, the present invention uses the technology described in EP3845974A1 (incorporated herein by reference).

[0014] The method is based on the replication of microstructures.

[0015] The method according to the invention is based on the assembly, in particular by joining, of a pointer body with a pre-cut light guide. More particularly, the pointer body is superimposed on the light guide.

[0016] The light guide may be in sheet form or in strip form and may be used as a transport substrate.

[0017] Similarly, the strip of the pointer body can be used as a transport substrate.

[0018] The pointer body may be manufactured in a conventional manner known to those skilled in the art and is similar to a standard pointer.

[0019] More particularly, and without limitation, the light guide comprises a thin, transparent plastic substrate that is as non-diffusing as possible, on which the resin is deposited and structured. The plastic substrate can be made of different materials such as, but not limited to, PET, TAC, PMMA, and PC. PET and TAC offer very good optical / mechanical tradeoffs.

[0020] The method of depositing and structuring the resin on the plastic substrate involves selecting a resin whose index is close to that of the plastic sheet. More specifically, and without limitation, the resin is structured by UV embossing (which can be translated as ultraviolet embossing) to create coupling and light extraction areas.

[0021] The adhesive used to assemble the plastic substrate and the pointer body should be transparent, non-diffusing, and have an optical index lower than that of the substrate.

[0022] The method comprises different operations, which may be in different chronological order, as described below.

[0023] Parallel operations involve the manufacture of the light guide on the one hand and the manufacture of the pointer body on the other hand.

[0024] The first set of operations 1000 concerns the fabrication of light guides: either for fabricating a single light guide 30 or for fabricating a light guide strip 35 .

[0025] In either case, a first operation 100 involves making a master 1 which is a positive model of the micro-reliefs to be transferred onto the light guide. More particularly, and without limitation, this master 1 is made of a material such as PMMA, which is processed using an etching device 110 which may consist of a laser etching device, in particular a CO2 laser, a picosecond laser or a femtosecond laser, a micro-milling device or a thermal etching device, etc. Reliefs of coupling and light extraction microstructures are created on this master 1, which reliefs are then reproduced during the replication process. Thus, different microstructures are made, some intended to couple / extract light and others as alignment marks for subsequent manufacturing steps.

[0026] The second operation 200 consists of making a negative tool 2 (such as a stamp) based on the master 1 in order to print the microstructure; this negative tool 2 can be made in particular of nickel or silicon or any suitable material. A plastic substrate 20 is provided on which a suitable resin is deposited. In particular, but without limitation, the substrate 20 can be made of PET or TAC, for example, having a thickness of 50 to 100 microns. The replication of the microstructure is achieved by reproducing on the plastic substrate 20 the microstructure created on the master 1 by means of this resin under the action of a buffer 2, which allows the microstructure to be printed in the resin previously deposited on the plastic substrate 20, and thus making at least one original light guide 30. This replication can be done by UV embossing or by hot embossing, i.e. hot stamping, or any similar method that achieves an accurate reproduction of the details of the microstructure. The replication method can be implemented in a single way, in sheets (sheet to sheet or roll to sheet depending on the manufacturing method) or in strips. The UV embossing method is particularly effective because it offers mechanical possibilities, in particular the possibility of replicating structures 30 microns deep. The output of this second operation is either an original light guide 30 in the case of a single fabrication or a light guide strip 35 comprising a plurality of original light guides 30 in the case of a strip fabrication.

[0027] The third operation 300 concerns the pre-cutting of the light guide: in order to be able to join the light guide and the pointer together, the original light guide 30 should be cut at the location where the pipe of the pointer will be placed. Without this, assembly would not be possible, since the pointer pipe would prevent the entire surface of the pointer from being in contact. This cutting is carried out using a cutting device 310 (including but not limited to a CO2 laser) and should be aligned with the different microstructures present on the original light guide 30. Preferably, the alignment marks have been previously placed on the master 1 and are reproduced on the original light guide 30 for this purpose.

[0028] In the case of strip production of the light guide strip 35 , it is possible to separate each original light guide by cutting before, during or after this third cutting operation 300 .

[0029] In parallel with the first set of operations 1000 involving light guide fabrication, the second set of operations 2000 includes operations for fabricating the pointer body 400 in strip form, either in a single manner for fabricating the pointer body 50, or according to standard methods with final cutting by punching. In the case of strip fabrication, the pointer body 50 may be separated immediately after the pointer body fabrication operation 400 in a separation operation 500 using a separation device 510, such as a punching device or other suitable cutting device. In one variant, the pointer body strip 55 may be retained until separation later in the process.

[0030] The third group of assembly operations 3000 includes a bonding operation 600 for bonding the original light guide 30 or light guide strip 35 and / or the pointer body 50 or pointer body strip 55 before assembly between the light guide and the pointer body. To this end, an adhesive 6 having an optical index lower than that of the light guide is selected, and the adhesive 6 is usually deposited on the pointer body and / or the light guide by a dispensing device 610.

[0031] Figure 1 , Figures 3 to 5 The following is illustrated: where the engagement is performed on the pointer body, Figure 1 and Figure 3 is implemented on a single pointer body 50, or in Figure 4 and Figure 5 In the embodiment, the pointer body strip 55 is implemented, and the joining product is then a joined pointer body 68 or a joined pointer body strip 685, respectively. Figure 2 A situation is illustrated in which a light guide is joined, in which figure it consists of a single light guide 30 which after the joining operation 600 becomes a joined light guide 38 .

[0032] After this joining operation 600, within the time allowed by the properties of the chosen adhesive, an assembly operation 700 is carried out, during which the pointer body is optically aligned and placed against the light guide, followed by joining by polymerization. More particularly, and without limitation, a UV optical adhesive is chosen because of its rapid polymerization. Advantageously, a robotic handling device 70 is used, such as a robot coupled to an optical recognition device to ensure proper alignment and positioning. At the end of this assembly operation 700, an assembled raw pointer 70 is obtained, which is yet to be finished.

[0033] In the case of strip manufacturing, whether the light guide strip 35 and / or the pointer body strip 55, the third set of operations 3000 can be implemented in a similar manner. However, when assembling the light guide strip 35 with the pointer body strip 55, the assembly operation 700 is more delicate to implement.

[0034] The fourth set of operations 4000 comprises a final cutting operation 800, the purpose of which is to complete and release each luminous pointer 80. In particular, this final cutting operation 800 is implemented by the aforementioned laser cutting device, in particular by a femtosecond laser giving good results on PET or cutting by a CO2 laser or the like.

[0035] In the case of a single manufacture, the light guide may finally be cut to release the hands during this final cutting operation 800. Preferably, the cut is about 0.1 mm wider than the nominal width of the hands, so as to let the light escape from around the hands and towards the wearer of the watch, thanks to the extraction microstructures provided for this purpose.

[0036] The above method details the manufacture of a pointer that will be illuminated on its periphery. In the case of a skeletonized pointer, it is also possible to have the illumination done through an opening in the pointer, or both. The lighting design is not limited to the entire periphery and, depending on the position of the extractor and the final cut, could be, for example, only on one side or only on the tip of the pointer.

[0037] An alternative method can be implemented, comprising similar steps, but in a different order. In particular, the method may include pre-cutting the pointer into strips. Advantageously, the cut is approximately 0.1 mm narrower than the nominal width of the assembled original pointer 70, so as to allow light to escape from around the pointer and towards the wearer of the watch, thanks to the extraction microstructure provided for this purpose. At the same time, the light guide can be manufactured in strips in the form of a light guide strip 35, and the light guide can be cut / fixed. During the operation of assembling the pointer body and the light guide, an adhesive whose optical index is lower than the optical index of the light guide is typically deposited on the light guide (alternatively on the pointer body) by dispensing. Thereafter, the light guide is optically aligned and placed against the pointer body to cure the adhesive. During the final cutting operation, the pointer is finally cut into strips to release the assembled pointer. Advantageously, the cutting is done by a laser or stamping.

[0038] In short, the microstructures are sufficient to utilize light from an external light source (such as, one or more LEDs 90), which light "enters" the input light guide 70 of the luminous pointer 80 below the pointer head and "exits" from the microstructures of the light guide 30 arranged along the length of the pointer. Figure 6 and Figure 7 An example of a light-emitting pointer is shown, each transmitting light emitted by three LEDs arranged in a triangle, and wherein the light coupling region involves an input light guide 70, which is either as Figure 6 is rotationally symmetric as in Figure 7 The peripheral area is the area where the microstructures of the light guide 30 extract light along the entire length of the pointer and protrude slightly at its end relative to the pointer body 50. This allows to ensure the continuity of light even if some of the light extraction structures are cut away or removed, depending on the accuracy of the cutting alignment.

[0039] Regarding materials, the light guide is advantageously a combination of a plastic substrate 20 (support) and a resin, into which different microstructures are printed, in particular by means of a preferred UV embossing method which gives very good results, although hot embossing of the microstructures directly into the substrate 20 can also be considered.

[0040] 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 at the desired thickness. In principle, colored materials (e.g. fluorescent materials) can be considered while maintaining transparency. However, the refractive indices of the two materials must be as close as possible. The refractive index of the adhesive assembling the lightguide to the pointer must be as low as possible compared to the refractive index of the substrate in order to optically isolate the lightguide. It is not necessary to insert particles of any kind into the lightguide.

Claims

1. A method for manufacturing a luminous clock hand (80), characterized in that: Separately manufacturing at least one light guide (30) or light guide strip (35) on the one hand and at least one pointer body (50) or pointer body strip (55) on the other hand, the at least one light guide (30) or light guide strip (35) being manufactured by a first set of operations (1000) by replicating a microstructure initially made on a master (1), the at least one pointer body (50) or pointer body strip (55) being manufactured by a second set of operations (2000), the at least one pointer body (50) or pointer body strip (55) being assembled with the at least one light guide (30) or light guide strip (35) by a joining operation (600) and an assembling operation (700) before the luminous pointer (80) is finished by a final cutting operation (800).

2. The method according to claim 1, characterized in that In the first set of operations (1000), in a first operation (100), the master (1) is made using an etching device (110), the master (1) being a positive model of the micro-relief to be transferred to the at least one light guide (30) or the light guide strip (35), the micro-relief comprising microstructures, some of which are provided for coupling and extraction of light and other microstructures serve as alignment marks for other manufacturing steps.

3. The method according to claim 2, characterized in that In the first set of operations (1000), in a second operation (200), a negative tool (2) is produced based on the master (1) in order to print a microstructure, a substrate (20) made of plastic is provided, a resin is deposited on the substrate (20), and the microstructure is replicated by reproducing the microstructure created on the master (1) on the plastic substrate (20) with the help of the resin under the action of the negative tool (2), the negative tool (2) allowing the microstructure to be printed in the resin previously deposited on the plastic substrate (20) in order to produce at least one primitive light guide (30) or light guide strip (35).

4. The method according to claim 3, characterized in that The substrate (20) is selected from PET or TAC having a thickness of 50 to 100 micrometers.

5. The method according to claim 3 or 4, characterized in that: The replication of the microstructure is performed by UV embossing or hot embossing.

6. The method according to one of claims 3 to 5, characterized in that After the second operation (200), in a third operation (300), the original light guide is pre-cut using a cutting device (310) or a CO2 laser at the position of the tube where the pointer should be placed and aligned with the alignment mark present on the original light guide.

7. The method according to one of claims 1 to 6, characterized in that During the final cutting operation (800), each of the luminous hands (80) is trimmed and released using a laser cutting device, and the cut is approximately 0.1 wider than the nominal width of the hand in order to allow light to escape from around the hand and towards the wearer of the watch, thanks to the extraction microstructure provided for this purpose.

8. The method according to one of claims 1 to 7, characterized in that The method is implemented for producing a pointer to be illuminated on its periphery, onto which the microstructure is replicated.

9. The method according to claim 1, characterized in that The method is implemented for producing a skeletonized hand that is to be illuminated at least throughout the opening of the hand.

10. The method according to one of claims 1 to 9, characterized in that The method is implemented for producing a pointer which is to be illuminated only on one side or only on the tip of the pointer.

Images