Method of forming a transparent one piece timepiece component

Abstract

Method for forming a transparent timepiece component including top and bottom surfaces: a transparent polymerizable material is chosen; there is applied to a plate a flexible female mold including a capillary network and having a contact surface which is the negative of the bottom surface, bordered by an edge; a cavity is delimited by the sealed juxtaposition of the edge with a plate having a contact surface which is the negative of the top surface; the material is injected through the capillary network to fill the cavity; the material is polymerized to obtain a rigid component; the component is removed from the plates by the deformation of this flexible mold. Hardness is improved by the UV exposition of this component.

Claims

1. A method for forming a timepiece component, the method comprising: making a plate comprising a contact surface which is negative of a top surface of the timepiece component; making a flexible female mould from polymethylsiloxane as a second moulding material, wherein the female mould comprises: a first contact surface forming a female mould of a bottom surface of the timepiece component, an edge comprising a first bearing surface arranged to cooperate in a complementary manner with the contact surface of the plate around the first contact surface, and a second bearing surface opposite to the first contact surface; creating an injection and degassing capillary network in the female mould; applying the second bearing surface of the female mould to a support plate; positioning the plate with the contact surface of the plate facing the first contact surface of the female mould and with the first bearing surface in sealed contact with the contact surface of the plate at a distance from the first contact surface corresponding to a thickness required for the timepiece component and exactly positioned relative to the first contact surface of the female mould; injecting a first moulding material through the injection capillary network so as to completely fill with the first moulding material a cavity delimited by the contact surface of the plate, the first contact surface of the female mould and the edge in sealed abutment via the first bearing surface thereof on the contact surface of the plate; polymerizing the first moulding material injected into the cavity to obtain a rigid timepiece component; removing the plate and the support plate; and removing the timepiece component from the female mould by deforming the female mould, wherein: the timepiece component is a transparent, one-piece, and single layer component and comprises the top surface and the bottom surface connected by an edge extending in a thickness direction of the timepiece component, and the first moulding material is a transparent material and comprises, based on a total amount of the first moulding material: 50-97.5% of a mixture of trimethylolpropane tri(methacrylate) and pentaerythrityl tetraacrylate, 0.5-1.5% of bis (4-tert-butylcyclohexyl) peroxydicarbonate, 0.7-2.3% of 1-benzoylcyclohexanol, and 0-50% of at least one additive.

2. The method according to claim 1, wherein the at least one additive is selected from the group consisting of: 10-15% of polyamide-polyether copolymer, 10-30% of an ethylenic ionomer resin, 10-30% of trineoalkoxy zirconate, 10-30% of at least one conductive nanoparticle selected from the group consisting of gold, a carbon nanotube, silver, an antimony tin oxide alloy, a zinc aluminium oxide alloy, an indium tin oxide alloy, and a zinc gallium oxide alloy, 5-30% of magnetic nanoparticles or magnetite, 10-30% of silver ions, 0.05-0.2% of benzotriazole, 0.05-0.2 of of hindered amine light stabilizers, 0-1.5% of an additive comprising phenolic phosphite; ethylene bis [3,3-bis (3-tert-butyl-4-hydroxyphenyl) butyrate]; pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), 0-15% of triphenyl phosphate, 0-15% of exfoliated montmorillonite, 0-15% of clay nanotubes, 0.5-2% of silicone acrylate, 0-50% of anthraquinones, 0-50% of azoics, 0-50% of pigments, 0-50% of adjuvants for controlled delivery, wherein the adjuvants are gradually released into an operating environment, and 0-50% of microcapsules of repair agent, wherein the microcapsules are formed of polymerisable liquid of the same nature as the microcapsules.

3. The method according to claim 1, wherein the first moulding material comprises: 78.0% of trimethylolpropane tri(methacrylate), 19.5% of pentaerythrityl tetraacrylate, 0.5% of bis (4-tert-butylcyclohexyl) peroxydicarbonate, and 2.0% of 1-benzoylcyclohexanol.

4. The method according to claim 1, wherein said polymerizing occurs at a temperature of from 100 C. to 120 C. for 10 to 20 seconds.

5. The method according to claim 1, wherein after said injecting, the timepiece component is exposed to UV radiation, either through the plate made in a UV transparent plate or after the timepiece component is removed from the female mould, to obtain improved hardness of the timepiece component.

6. The method according to claim 5, wherein the female mould is UV transparent in that the second moulding material is UV transparent and the support plate is UV transparent so that the timepiece component is exposed to the UV radiation through the support plate and the female mould in addition to exposition through the UV transparent plate to further improve the hardness of the timepiece component.

7. The method according to claim 1, wherein a tightening force is applied to the plate and to the support plate during said injecting and during said polymerizing.

8. The method according to claim 1, wherein the top surface of the timepiece component is a plane surface, the contact surface of the plate is a plane surface, and the first bearing surface of the edge of the female mould is a plane surface.

9. The method according to claim 1, further comprising: inserting nodules into the cavity before, during or after said injecting, wherein the nodules each comprise an electrifiable and/or magnetisable and/or electrified and/or magnetised core, and electrification or magnetisation of the core occurs prior or subsequent to said injecting.

10. The method according to claim 1, wherein the timepiece component is a crystal, a crown, a middle part of a case, a plate, a bridge, an escape wheel, a pallet, an oscillating weight, a bearing housing, or a shock absorber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the invention will appear more clearly upon reading the following detailed description, with reference to the annexed drawings, in which:

(2) FIG. 1 shows a schematic flow chart of the series of operations for implementation of the method.

(3) FIG. 2 shows a schematic cross-section through the thickness of the component to be formed substantially perpendicular to its main surfaces, the moulding equipment in the configuration thereof during shaping of the component, in a first variant without exposition through said equipment.

(4) FIG. 3 shows, in a similar manner to FIG. 2, a second variant wherein the component is exposed through one piece of the equipment.

(5) FIG. 4 shows, in a similar manner to FIG. 2, a variant wherein the component is exposed through several pieces of equipment.

(6) FIG. 5 shows block diagrams of a timepiece including at least one component made according to the invention.

(7) FIG. 6 shows a cross-section in proximity to the top surface of a component made according to a particular variant of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) The invention concerns a method of forming a transparent timepiece component 1 including top 2 and bottom 3 surfaces connected by an edge 4, the edge 4 extending in the thickness of component 1.

(9) The first step of the method consists in selecting a first moulding material 5.

(10) Generally, this first material 5 includes at least acrylic monomers, at least one thermal initiator, at least one UV initiator and at least one cross-linking agent which may be formed by at least one of the acrylic monomers. It may also include one or more additives, which will be detailed below.

(11) More specifically, this first material 5 includes a mixture of acrylic monomers including at least one monomer having a functionality greater than or equal to 2, at least one thermal initiator, and and at least one photochemical initiator. Here too, the material may include one or more additives.

(12) Even more specifically, this first material 5 includes, as a proportion of the total: a mixture of acrylic monomers having a functionality greater than or equal to 2: 50-97.5% at least one thermal initiator: 0.5-3% at least one photochemical initiator: 0.5-3% at least one additive: 0-50%.

(13) In an even more specific composition, this first material 5 includes, as a proportion of the total: a mixture of trimethylolpropane tri (methacrylate) and pentaerythrityl tetraacrylate: 50-97.5% bis (4-tert-butylcyclohexyl) peroxydicarbonate: 0.5-1.5% 1-benzoylcyclohexanol: 0.7-2.3% at least one additive: 0-50%.
In a preferred composition, which will be referred to hereinafter as model composition CT of first material 5, this first material 5 includes, as a proportion of the total: trimethylolpropane tri (methacrylate): 78.0% pentaerythrityl tetraacrylate: 19.5%; bis (4-tert-butylcyclohexyl) peroxydicarbonate: 0.5% 1-benzoylcyclohexanol: 2.0%
As regards those compositions of first material 5 which include additives, which are within a range of 0-50% of the total of first material 5, these additives may include, as a percentage of the total of said first material:

(14) a. Antistatics: a. Copolymer polyamide-polyether: 0-15% preferably from 10-15% b. Ethylenic ionomer resin: 0-30% preferably from 10-30% c. Trineoalkoxy Zirconate: 0-30% preferably from 10-30%

(15) b. Conductors: a. Conductive nanoparticles: gold, carbon nanotubes, silver, antimony tin oxide alloy, zinc aluminium oxide alloy, indium tin oxide alloy, zinc gallium oxide alloy: 0-30% preferably from 10-30%

(16) c. Magnetics: a. Magnetic nanoparticles: magnetite: 0-30% preferably from 5-30%

(17) d. Antibacterials a. Silver ions: 0-30% preferably from 10-30%

(18) e. Anti-UV: a. Absorbers: benzotriazole: 0-0.2% preferably from 0.05-0.2% b. HALS (Hindered Amine Light Stabilizers): 0-0.02% preferably from 0.05-0.2%

(19) f. Antioxidants: a. Phenolic phosphite; ethylene bis [3,3-bis (3-tert-butyl-4-hydroxyphenyl) butyrate]; pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate): 0-1.5%

(20) g. Fire retardants: a. Phosphorus derivative: triphenyl phosphate 0-15% b. Exfoliated montmorillonite: 0-15% c. Clay nanotubes: 0-15%

(21) h. Lubricants: a. Silicone acrylate: 0-2% preferably from 0.5-2%

(22) i. Colorants: a. Anthraquinones: 0-50% b. Azoics: 0-50%

(23) j. Pigments: 0-50%

(24) k. Adjuvants withr controlled delivery: incorporated in the formulation, these adjuvants are gradually released into the operating environment: 0-50%

(25) l. Microcapsules of repair agent, formed of polymerisable liquid of the same nature as the composition concerned, in particular in a model composition CT, the content then being integrated in the total content: 0-50%

(26) To implement this method the following steps are carried out: A: A transparent, polymerisable material 5 is selected for forming component 1 preferably of the model composition CT or Cover Form material by Evonik; this first transparent, polymerisable, moulding material 5 may also be chosen for making component 1, from among the acrylic polymer family or Nanocryl by Hanse Chemie B: A flexible female mould 9 is made, a contact surface 10 of which is the negative of bottom surface 3, bordered by an edge 11, said mould 9 including a capillary network 14: C: Flexible female mould 9 having a contact surface 10 which is the negative of bottom surface 3, bordered by an edge 11 is applied to a support plate 15, said mould 9 including a capillary network 14; D: A cavity 17 is delimited by the sealed juxtaposition of edge 11 with a plate 6 having a contact surface 7 which is the negative of top surface 2; E: Material 5 is injected through capillary network 14 to fill cavity 17; F: Material 5 is polymerised to obtain a rigid component 1; G: Component 1 is detached from the plates and from flexible mould 9 by the deformation of said mould.

(27) Hardness is improved by the UV exposition of component 1. The preferred implementation of the invention includes this UV exposition allowing the photochemical initiator to be actuated in order to react, otherwise the mechanical properties of the finished component 1 are weaker.

(28) Preferably, for implementation of the invention, either first material 5 is chosen to be the model composition CT which includes, as a proportion of the total: trimethylolpropane tri (methacrylate): 78.0% pentaerythrityl tetraacrylate: 19.5% bis (4-tert-butylcyclohexyl) peroxydicarbonate: 0.5% 1-benzoylcyclohexanol: 2.0%; or the Cover Form material by Evonik Rhm is chosen as first polymerisable, moulding material 5 for making component 1. This material is derived from the combination of two components: a liquid reactive referenced 30A and a liquid initiator referenced 30B.

(29) This operating mode will be detailed below.

(30) Preferably, to make a very precise female mould 9, a precision model matching the male profile of bottom surface 3 is made in a material such as SU8 or similar, and a flexible female mould 9 is made with this precision model of the second moulding material 8. This second moulding material 8 for making a flexible mould to mould first moulding material 5 and to allow the removal thereof from the mould, is chosen from among PDMS or polymethylsiloxane.

(31) Female mould 9 preferably includes: a first contact surface 10 forming a female mould of bottom surface 3; around first contact surface 10, an edge 11 including a first bearing surface 12 arranged to cooperate in a complementary manner with contact surface 7 of plate 6; and a second bearing surface 13 opposite first surface 10.

(32) An injection and degassing capillary network 14 is made in female mould 9;

(33) The second bearing surface 13 of female mould 9 is preferably applied to a support plate 15. To facilitate automation, this support plate 15 is preferably rigid. When the plate is chosen to be transparent in an advantageous variant of the invention, it may be made of glass or similar.

(34) A plate 6 is made having a contact surface 7 which is the negative of top surface 2; this plate 6 is formed of a material facilitating the separation of component 1 once polymerised. To facilitate automation of the method, plate 6 is advantageously rigid. When the plate is chosen to be transparent in an advantageous variant of the invention, it may be made of glass or similar. Naturally, it may also be made of the same second moulding material 8 and then be added to a support plate which is not shown in the Figures.

(35) At a distance from first surface 10 corresponding to the thickness required for component 1, and exactly positioned in relation to first surface 10, plate 6 is positioned using centring, locating or similar agents, with its contact surface 7 facing first contact surface 10 of female mould 9, with the first bearing surface 12 in sealed contact with contact surface 7 of plate 6.

(36) The first moulding material 5 is injected through injection capillary network 14, so as to completely fill with first moulding material 5 a cavity 17 delimited by contact surface 7 of plate 6, first contact surface 10 of female mould 9 and edge 11 in sealed abutment via its first bearing surface 12 on contact surface 7. Care is taken to completely degas cavity 17 so that no air bubbles remain.

(37) The first material 5 injected into cavity 17 is left to polymerise until a rigid component 1 is obtained. This natural polymerisation may be accompanied by heating H, and/or ultraviolet ray (hereinafter UV) exposition J, which each have the effect of increasing the surface hardness of the component 1 obtained, by permanently cross-linking the system. Exposition provides significant additional hardness, of around 10% compared to the same component polymerised at ambient temperature, or polymerised with heating, and in this latter case, for a surface hardness that is already higher than that of the same component polymerised at ambient temperature.

(38) After polymerisation, plate 6 and support plate 15 are moved away. It is clear that it is possible to carry out a complementary heating and/or exposition both when component 1 is confined inside cavity 17 defined by the moulding equipment, or when it is removed therefrom. The duration of an injection and polymerisation cycle with heating is brief, around 30 to 40 seconds. The exposition cycle has a duration of 10 to 20 seconds.

(39) In a preferred embodiment, polymerisation heating is performed when component 1 is still in the mould, the choice of exposition in or out of the moulding equipment essentially depends on the constraints of the production cycle: in one case the moulding equipment is immobilised slightly longer prior to shaping the following component, in the other case additional handling is required. In this case, first material 5 injected into cavity 17 is subjected during polymerisation to a temperature of less than 150 C., close to 110 C., particularly comprised between 100 C. and 120 C. for 10 to 20 seconds.

(40) In an advantageous variant, cooling to ambient temperature is carried out at least as abruptly as heating, for a duration of less than 20 seconds.

(41) Component 1 is easily detached from flexible female mould 9 simply by deforming the latter.

(42) Advantageously, to further improve the surface hardness of component 1 obtained by implementing the method, the component is exposed to UV radiation.

(43) For this purpose, in a second variant, as seen in FIG. 3: plate 6 is made transparent to UV radiation; after injection of first moulding material 5, component 1 is exposed to UV radiation, either through transparent plate 6, or after the removal of component 1 polymerised in cavity 17, to obtain improved hardness of rigid component 1.

(44) In a similar and advantageous manner, to further improve the surface hardness of component 1 obtained by implementing the method, all the surfaces of the component are exposed to UV radiation.

(45) For this purpose, in a third variant, as seen in FIG. 4: the second moulding material 8 is selected to be UV transparent so as to obtain a UV transparent flexible female mould 9, and support plate 15 is selected to be UV transparent, so as to expose component 1 to UV radiation, in addition to the exposition through transparent plate 6, first material 5 injected into cavity 17, through the support plate 15 and flexible female mould 9, to obtain improved hardness of rigid component 1.

(46) With the choice of materials proposed here, given the properties of great fluidity, in the non-polymerised state, of first material 5 formed of model composition CT or of the Cover Form product, it is unnecessary to perform high pressure injection, since the wetability of the material is sufficient to enable it to perfectly and precisely occupy the whole of cavity 17, provided of course that capillary network 14 is properly formed to ensure complete degassing and the absence of any air bubbles. The first moulding material 5 can therefore be injected at a pressure of less than 150 MPa, and in particular at low pressure, notably less than 10 MPa.

(47) In an advantageous variant implementation, a tightening force FS is applied to plate 6 and to support plate 15 during the injection of first moulding material 5 into cavity 17 and during polymerisation of first moulding material 15 to produce component 1.

(48) In a particular embodiment, when component 1 has a plane top surface 2, plate 6 is made with at least its contact surface 7 plane, and flexible female mould 9 is made with its edge 11 having a first plane bearing surface 12.

(49) FIG. 6 illustrates a particular embodiment, wherein there is inserted into cavity 17 forming the mould, either prior to the injection of first moulding material 5, or during or after said injection, nodules 18 each including a electrifiable and/or magnetisable and/or electrified and/or magnetised core, particularly of the electret, ferrite, neodymium magnet type or similar. Electrification or magnetisation may be pre or post injection. FIG. 6 illustrates, for example, particles magnetised after the complete polymerisation of first moulding material 5, particularly of first material 5 formed of model composition CT or Cover Form FIG. 6 also illustrates, in one area of top surface 2, cavities 19 arranged for lubrication. Contact surface 7 of plate 6 is then arranged accordingly.

(50) In another variant, a lubricant material is mixed with first moulding material 5, in a similar manner to nodules 18 above.

(51) The invention further concerns the application of this method to the making of a timepiece component 1 selected from among: a crystal, crown, middle part of the case, main plate, bridge, wheel, escape wheel, pallets, oscillating weight, bearing housing, shock absorber, although this list is not exhaustive.

(52) The choice of first material 5 is the deciding factor for the resistance of the component 1 concerned. Indeed, some materials are specifically devised for surface coatings, but with a thickness of less than 50 m, it is not always possible to apply these materials to the making of complete timepiece components. The preferred choice of first material 5 for use, formed of model composition CT or of Cover Form in a range of thickness which can be much greater, notably several millimeters for watch crystals, is not self-evident and results from a long series of tests. Naturally, shrinkage is significant with these thicknesses, and the associated moulds must be sized accordingly.

(53) The invention also concerns a timepiece movement 100 including at least one component 1 made according to this method.

(54) The invention also concerns a timepiece 1000 including at least one component 1 made according to this method, or at least one movement 100 according to any of claims 1 to 9.

(55) In a particular embodiment, timepiece 1000 is a so-called mystery timepiece including at least one plate made according to this method.

(56) In another particular embodiment, this timepiece 1000 includes a jewellery cut faceted bezel made according to this method.

(57) The invention makes it possible to obtain components of greater transparency, having greater a surface than that of ordinary moulded plastic materials, and with a durable hardness. Scratch resistance is very good. By using as first moulding material 5 the first material 5 formed of model composition CT or the Cover Form product, with heat treatment at less than 130 C. and UV hardening, a hardness is obtained which is rated 7H on the graphite pencil hardness scale, compared to a hardness of 2H for a standard PMMA treated with scratchproof coating, or to the HB hardness of a polyamide.

(58) The component thereby formed is resistant to scratching by glass wool.

(59) If high quality carefully implemented moulds are used, it is not necessary to polish the component after manufacture.