WO2013079939A2

WO2013079939A2 - Oscillator spring composition and method for fabricating an oscillator spring

Info

Publication number: WO2013079939A2
Application number: PCT/GB2012/052941
Authority: WO
Inventors: Gideon Levingston
Original assignee: Carbontime Limited
Priority date: 2011-11-30
Filing date: 2012-11-29
Publication date: 2013-06-06
Also published as: WO2013079939A3; GB201120588D0

Abstract

An oscillator spring made of a spring material consisting of any of carbon, ceramic, polymer, polymer precursor, composite and any combination of these materials, and a barrier material for altering the number of bonding sites which are available at the surface of the spring material, wherein the barrier material consists of one or more hydrophobic silicone compounds or one or more hydrophobic silane compounds. The barrier material can provide a full or partial barrier to the adsorption of water vapour in the ambient atmosphere. The barrier may thus enable the elasticity of the spring to be regulated.

Description

OSCILLATOR SPRING COMPOSITION AND

METHOD FOR FABRICATING AN OSCILLATOR SPRING

FIELD OF THE INVENTION

The invention relates to oscillating spring elements of precision instruments, oscillators, micro electromechanical oscillators and sensors made of carbon, ceramic, polymer, polymer precursor, composite or combinations of these materials. The invention concerns a treatment of the material of the spring elements, which modifies its mechanical characteristics, and in particular its reactivity with the surrounding environment. BACKGROUND TO THE INVENTION

Oscillators require in part a spring material which operates in flexion mode whether the oscillator is a simple lamellar blade such as found in micro-oscillator or sensor applications or a shaped length of material such as in the spiral of a watch hairspring. In order to perform its function the varying signal captured from the oscillator indicates the change in the parameter being measured. Any interference with this signal must either be understood or compensated for, or eliminated.

In general, the formula for timekeeping changes (U ) consequent upon a rise in temperature of 1°C in a watch's mechanical oscillator system, where the thermal expansion coefficient of the balance wheel is represented by the term _x , the thermal expansion coefficient of the balance spring by c₂ , the elastic modulus (Young's modulus) by the term E, and the change in E over the 1°C temperature rise by SE , is: U can be made to tend to zero when suitable values of a_x

, a₂ and E are selected by careful choice of appropriate materials. It can be expedient to derive the solution to this equation in the material of the balance spring if possible by

SE

focusing on the terms and . In other words, if the

² IE

dimensional changes and elastic modulus can be controlled and equated with a given (i.e. fixed or otherwise predetermined) balance wheel thermal expansion rate, the total number of industrial processes and parts required to produce the oscillator can be reduced.

The inventor's previous applications and granted patents include the use of carbon materials, preferably but not exclusively amorphous carbon, known also as vitreous carbon or glassy carbon.

For example, in WO 2004/008259, the contents of which are hereby incorporated by reference, the present inventor disclosed using the anisotropy of certain balance spring materials such that the length of the spring did not increase with a rise in temperature whilst the width and height of the spring did increase with the same temperature rise. Such balance springs were disclosed for use in mechanical

oscillator systems for horological instruments, e.g.

mechanical watches. The thermal evolution of the balance spring material disclosed in this application can allow a very close rate in watches to be obtained and maintained using nonmagnetic materials.

In WO 2011/095780, the contents of which are hereby incorporated by reference, the inventor disclosed an

oscillator spring made from a material comprising a mixture of phase-transformed host material having a normal thermal evolution of elastic modulus and a non-phase-transformed additive having an abnormal thermal evolution of elastic modulus, wherein the proportion of additive in the mixture is selected to control the thermal evolution of the spring's elastic modulus in an ambient temperature range to provide thermal stability to the spring's oscillation. The host material, which can resemble a matrix in which the additive is dispersed, or a body to which the additive is applied may comprise carbon material, e.g. derived from any polymeric, or pitch or polyacrylonitrile (PAN) precursors. The additive has a crystalline structure that exhibits abnormal (i.e. positive) thermal evolution of its elastic modulus in the ambient range. Such an additive material may, for example, be silicon dioxide .

SUMMARY OF THE INVENTION The inventor has noticed a degree of interference with the regular oscillation of an oscillator using spring material of the type discussed above in specific test bench conditions wherein an increased stability of elastic modulus was obtained in anhydrous conditions of the spring material where the spring material was previously thought to be inert to changes in the ambient atmosphere. In particular, it has been noticed by the inventor in the course of the development of a carbon- based spring material that enhanced characteristics can be obtained from the material by modifying the adsorption of water vapour in the ambient atmosphere.

Whereas it is known that water vapour can affect certain allotropes of carbon such as the graphites or turbostratic carbon fibre allotropes, diamond-like carbon has been thought to be generally exempt from reactivity to water vapour in the ambient environment. For example, WO 2009/043391 and CN

102032302 disclose quartz springs which have diamond-like carbon coatings to provide water repellent properties.

Diamond-like carbon is also known to be so inert as to be non-reactive to nitric acid at ambient temperature, and allegedly has a very small permeability (~10^-9 nm) . However, it has now been observed that the elastic modulus of this material is not the same at small scale as it is in bulk, and that the adsorption of atmospheric borne species may cause changes to its elastic modulus. The changes observed occur at a molecular level and are therefore difficult to detect.

At its most general, the present invention provides a modification of the spring material with a full or partial barrier to control this activity. The barrier may thus enable the elasticity of the spring to be regulated. Thus, in the case of an oscillator comprising the spring element made from the modified material, frequency can be regulated as a result.

In one aspect, the barrier may be used to prevent or restrict the reactivity to allow for a fixed elastic modulus to be established.

In another aspect, the barrier may be used to harness the discrete nature of the activity in a micro-sensing device. Here the variables of frequency and H₂0 uptake and temperature can be exploited as variables for a sensing device which operates by detection using these separate or combined parameters .

According to the invention, there may thus be provided an oscillator spring made of a spring material consisting of any of carbon, ceramic, polymer, polymer precursor, composite and any combination of these materials, and a barrier material for altering the number of bonding sites which are available at the surface of the spring material, wherein the barrier material consists of one or more hydrophobic silicone

compounds or one or more hydrophobic silane compounds.

Herein, silane means saturated hydrosilicon compound. The one or more silicone compounds may comprise any suitable

hydrophobic polysiloxane, e.g. polydimethylsiloxane . The one or more hydrophobic silicone compounds or one or more

hydrophobic silane compounds may include one or more fluorinated silicone compounds or one or more fluorinated silane compounds.

The barrier material may consist of one or more

hydrophobic dipodal silane compounds. For example, the barrier material may be any one or more of: bis [2- (chlorodimethylsilyl) -ethyl] benzene;

bis (cholorodimethylsilyl ) ethane;

bis (cholorodimethylsilyl ) hexane;

bis (cholorodimethylsilyl) propane;

bis (methyldicholorosilyl) octane;

bis (methyldicholorosilyl) ethane;

bis (methyldiethoxysilyl) ethane;

bis (methyldifluorosilyl) ethane; bis (tricholorosilyl ) decane; bis (tricholorosilylethyl) hexa-decafluorooctane;

bis (tricholorosilyl ) hexane; bis (tricholorosilyl ) methane ;

bis (tricholorosilyl) octane; bis (tricholorosilyl) propane;

bis (tricholorosilylundecyl) ether; bis (triethoxysilyl ) benzene; bis (triethoxysilyl) ethane; bis (triethoxysilyl) methane;

bis (triethoxysilyl ) octane; bis (trimethoxysilyl) decane;

bis (trimethoxysilyl) ethane; bis (trimethoxysilylethyl ) benzene; bis (trimethoxysilyl) hexane; bis-1, 3- (trimethoxysilylpropyl ) - benzene; (chlorodimethylsilyl) -6- [2- (cholorodimethylsilyl) ethyl] bicycloheptane; and 1- (triethoxysilyl) -2- (diethoxymethylsilyl) ethane.

The spring material may be a diamond-like allotrope of carbon. For example, the spring material may be predominantly vitreous carbon, also known as glassy carbon. The spring material may include an additive comprising a crystalline material having a lower phase transformation temperature than the phase-trans formed host material, wherein the proportion of additive in the mixture is selected to control the thermal evolution of the spring' s elastic modulus in an ambient temperature range to provide thermal stability to the spring's oscillation, as disclosed in WO 2011/095780. The additive may be silicon dioxide. The spring material may include further additives in addition to the barrier material. For example, the spring material may include an outer coating e.g. of ceramic or the like, on which the barrier material may be applied.

The spring material, optional additive, and barrier may be non-magnetically sensitive.

The barrier material may be arranged to generate a hydrophobic outer layer on the spring material. The barrier material may function to reduce or eliminate the number of available hydrophilic bonding sites on the surface of or within the spring material. Herein, a hydrophilic bonding site may mean a site having a moiety (e.g. H, 0, OH) with a propensity to bond e.g. covalently or via van der Waal's force to water molecules or the functional groups (e.g. H, 0, OH) of water molecules. The hydrophilic bonding sites may be created during the fabrication of the spring itself. For example, where a carbon-based spring is formed by heat treating a polymer precursor material to cause a phase transformation to vitreous carbon, the hydrophilic bonding sites may be provided by residual precursor material remaining on or within the spring material after heat treatment. The hydrophilic bonding sites may thus be residual surface OH groups or the like.

The hydrophobic outer layer may be monomolecular or multi-layered. It may be arranged to provide complete coverage of the hydrophilic bonding sites, or it may provide partial coverage, whereby a number of reactive sites remain, thus modifying in a quantified manner the way in which the spring material reacts with its environment. The hydrophobic outer layer may also act to shield any polar regions on the surface of the spring material.

The hydrophobic outer layer may be composed of several layers or applications wherein the first layer or application serves to provide an intermediate interface which has specific characteristics providing key bonding to the spring material upon which a successive layer or application, e.g. of the same or a different material, may bond to further complete, control, modify or augment the desired barrier layer.

In one embodiment, the barrier material is included as a hydrophobic additive in a pre-phase-transformed precursor material of the spring material, whereby the hydrophobic additive renders the finished (i.e. phase-transformed) spring material inert to environmental reactivity with H₂0.

According to another aspect of the invention, there is provided a method of manufacturing an oscillator spring for a mechanical oscillator mechanism in a horological or other precision instrument, the method comprising: heating a phase- transformable precursor material to a temperature that causes the precursor material to exhibit a phase transformation into a spring material consisting of any one or more of carbon, ceramic, polymer, polymer precursor and composite materials; and applying a barrier material to the spring material to alter the number of bonding sites which are available at the surface of the spring material, wherein the barrier material consists of one or more hydrophobic silicone compounds or one or more hydrophobic silane compounds. Any conventional coating method may be used to apply the barrier material.

Chemical, electrochemical or electropolymerisation techniques, e.g. chemical vapour deposition (CVD) , or molecular vapour deposition (MVD) or physical vapour deposition (PVD) may be used.

Alternatively, the barrier material may be mixed with the precursor between phase transformation to form the spring material. In this aspect, the invention may provide a method of manufacturing an oscillator spring for a mechanical oscillator mechanism in a horological or other precision instrument, the method comprising: mixing a phase- transformable precursor material with a hydrophobic additive; heating the mixture to a temperature that causes the precursor material to exhibit a phase transformation into a spring material consisting of any one or more of carbon, ceramic, polymer, polymer precursor and composite materials; wherein following heat treatment, the hydrophobic additive functions as a barrier material to alter the number of bonding sites which are available at the surface of the spring material, and wherein the barrier material consists of one or more

hydrophobic silicone compounds or one or more hydrophobic silane compounds.

The spring shape may be obtained before or after phase transformation. Thus, before final phase transformation of the precursor material, the method may include forming the mixture into a shape for subsequent use. Alternatively, after phase transformation of the precursor material, the method may include cutting one or more components from the spring material. The cutting may be performed using a precision laser on the like. In one embodiment, the cutting step may comprise performing deep reactive ion etching (DRIE) to obtain a plurality of components from the spring material in a single cutting operation. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are discussed in detail below with reference to the accompanying drawings, in which:

Fig. 1 is a graph showing the frequency response of a vitreous carbon spring to a change in humidity;

Fig. 2 is a graph showing the frequency response of a vitreous carbon spring having a hydrophobic barrier layer that is an embodiment of the invention;

Fig. 3 is a graph showing the frequency response of a vitreous carbon spring having a hydrophobic barrier layer that is another embodiment of the invention;

Fig. 4 is a photograph comparing water droplets on vitreous carbon in an untreated state and in a state treated with a silane compound in the manner of the present invention; and Fig. 5 shows the equilibrium contact angle of the water droplets shown in Fig. 4

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES Demonstration of reactivity

Fig. 1 is a graph showing the effect of a change in relative humidity on the oscillation frequency of a

chronometer having a vitreous carbon oscillator spring. The oscillator spring was obtained by cutting a spiral spring from a piece of vitreous carbon, in the manner disclosed in the inventor's earlier publication WO 2006/123095, e.g. with through the use of a precision laser beam. The vitreous carbon itself may be prepared by heat treating a suitable polymer precursor in the manner disclosed in WO 2006/123095 or WO 2011/095780. The oscillator spring is cut with appropriate dimensions for the chronometer. The spring is mounted as normal to the balance staff of a conventional chronometer balance wheel to form the oscillating mechanism.

The chronometer was set to run in an hermetic test chamber containing temperature and humidity sensors and a microphone. These sensors were connected to a computer, which was arranged to record the frequency of the watch, the temperature and humidity. Fig. 1 shows the recorded relative humidity as line 12, the recorded temperature as line 14 and the recorded frequency of the oscillator as solid bars 16. The left hand axis 18 represents frequency units in vibrations per hour (where 18000 vibrations per hour is equivalent to 2.5 Hz, as two vibrations equals one oscillation) . An increase in the height of the bar represents a speeding up of oscillation. The right hand axis 20 represents % relative humidity. The origin of this axis is shifted up for clarity. The horizontal axis is the elapsed time of the experiment. As indicated on the graph, the duration shown is 4.9 hours. In the experiment, the test chamber was opened at time A and a bowl of water at ambient temperature placed within the chamber and the chamber closed. The introduction of the water causes an immediate rise in relative humidity, which is instantly matched by a corresponding change (increase) in frequency of the oscillator. Thus, the adsorption and desorption of water vapour causes the elastic modulus of the spring to increase and decrease. This is understood to be due to reactivity between the free reactive sites on the spring material surface and the availability of H₂ and 0 in the environment. Furthermore the rate of increase of modulus appears proportional to the change in relative humidity at a constant (ambient) temperature.

In itself, this instant reaction to a change in humidity may be used in various ways. In taking the principle of elastic modulus change as an example, the frequency change resulting from the elastic modulus change from adsorption of water vapour can be detected or recorded in the change of frequency of an oscillator where the vibrating spring element is made of a water vapour sensitive material. The signal provided via the oscillator alters according to the presence of the reactive species H₂ and 0₂ in the environment. The present disclosure contemplates a sensor incorporating such a sensitive oscillator.

Demonstration of blocking effect

Fig. 2 is a graph showing similar information to Fig. 1. The same reference numbers are used to label the same information. However, in Fig. 2 the chronometer used an oscillator spring in which the vitreous carbon has a barrier material comprising polydimethylsiloxane (also known as dimethicone) applied to it. The vitreous carbon spring was prepared in the same way as for the experiment in Fig. 1, before the polydimethylsiloxane barrier material was applied by submerging the spring in a liquid solution of

polydimethylsiloxane . Other techniques for applying the barrier material could be used. For example, known treatments to bulk material by chemical, electrochemical or

electropolymerisation means including e.g. CVD and MVD processes can be used. The result of applying the barrier material was to change the number of reactive sites on the surface of the spring material (vitreous carbon) . The chemical deposition therefore alters the material reactivity. In the case of a spring component displaying large surface area in relation to volume, this can alter the reactivity of the elastic modulus of the treated material with the

environment in which it is used.

Fig. 2 shows that the application of the

polydimethylsiloxane barrier material in this embodiment has the effect of partially blocking, i.e. effectively retarding, the adsorption of water vapour, which is observed through the corresponding effect on the mechanical characteristics of the oscillator. Similarly to the experiment shown in Fig. 1, the test chamber was opened at time B and a bowl of water at ambient temperature placed within the chamber and the chamber closed. An immediate rise in the relative humidity is seen in line 12, but instead of the instant corresponding change in frequency seen in Fig. 1, the frequency increases very slowly of the next few hours. Hence, the barrier layer is effective in block the adsorption of water.

Fig. 3 is a graph showing similar information to Fig. 2, but where the spring is provided with a barrier layer made of a mixture of bis (triethoxysilyl) octane and

bis (trimethoxysilyl) decane . Again, similarly to the

experiments shown in Figs. 1 and 2, the test chamber was opened at time C and a bowl of water at ambient temperature placed within the chamber and the chamber closed. An immediate rise in the relative humidity is again seen in line 12, but in this case there is substantially no change in the oscillator frequency over the next few hours of the

experiment. Thus the effectiveness of the barrier in blocking the effect of a change in humidity can be controlled through suitable selection of the barrier material and/or structure.

Figs. 1 to 3 shown that a water vapour barrier may be provided that can exclude or reduce the effect of water vapour upon the oscillator and therefore any other change in elastic modulus which would manifest via the oscillator, would result from a change in another parameter affecting modulus, such as temperature. Where an oscillator spring material has been engineered to compensate for both temperature changes, e.g. as discussed in the inventors earlier publications WO 2004/008259 and WO 2011/095780, and also has a water vapour barrier, and is inert to other external influences then constant frequency will result such as is desired in a time keeper. The

oscillator neither gaining or losing in frequency but remaining in an intended equilibrium state of oscillation.

In the same way an oscillating sensor, oscillating in such a stable equilibrium state may provide an interference signal of another external influence upon this equilibrium when altered by the influence of gyroscopic forces,

acceleration, electromagnetism etc.

Hydrophobic property

Figs. 4 and 5 illustrate the effect of a barrier layer comprising a mixture of bis (triethoxysilyl ) octane and bis (trimethoxysilyl) decane on a vitreous carbon substrate. Fig. 4 shows a photograph of two water droplets on respective substrates. The water droplet 24 on the left is on a vitreous carbon substrate 20 treated with a silane component. The water droplet 26 on the right is on an untreated vitreous carbon substrate 22. As shown in Fig. 5, the contact angle at the liquid-solid interface of the treated substrate 20 is 86°, whereas the contact angle at the liquid-solid interface of the untreated substrate is 50°. This illustrates the hydrophobic nature of the treated material.

The barrier layer may be a single material that bonds effectively with the spring material. However, in other embodiments an intermediate material, e.g. to facilitate binding, may be used. For example, electrochemical and electropolymerisation methods may be used to enable covalent bonding of phenyls on the surface of diamond-like or glassy carbon. The phenyls may themselves alter the adsorption characteristics of the spring material. Thus, these methods may be used either to create the desired modifying barrier or a linking layer between the material and the final barrier layer .

Alternatively a single requirement may be needed such as that of hydrophobicity in the bulk material from the point of manufacture of the material. In this case, and in the example of materials made from precursors, the required chemical additive may be included in the process of manufacture to.

The higher temperature required for the processing of such precursor material into their final form, or allotrope in the case of the carbon family materials, requires that the resultant chemical structure of the surface of the material is one which is either hydrophobe or provides for hydrophobicity to be achieved by a further compatible preferably but not exclusively low temperature application.

Claims

1. An oscillator spring for a mechanical oscillator mechanism in a horological or other precision instrument,

wherein the oscillator spring is made of:

a spring material consisting of any one or more of carbon, ceramic, polymer, polymer precursor and composite materials; and

a barrier material for altering the number of bonding sites which are available at the surface of the spring material, and

wherein the barrier material consists of one or more hydrophobic silicone compounds or one or more hydrophobic silane compounds.

2. An oscillator spring according to claim 1, wherein the barrier material consists of one or more hydrophobic dipodal silane compounds .

3. An oscillator spring according to claim 2, wherein the barrier material consists of any one or more of:

bis [2- (chlorodimethylsilyl) -ethyl] benzene;

bis (cholorodimethylsilyl) ethane;

bis (cholorodimethylsilyl) hexane;

bis (cholorodimethylsilyl) propane;

bis (methyldicholorosilyl) octane;

bis (methyldicholorosilyl) ethane;

bis (methyldiethoxysilyl) ethane;

bis (methyldifluorosilyl) ethane;

bis (tricholorosilyl) decane;

bis (tricholorosilylethyl) hexa-decafluorooctane;

bis (tricholorosilyl) hexane;

bis (tricholorosilyl) methane;

bis (tricholorosilyl) octane;

bis (tricholorosilyl) ropane; bis (tricholorosilylundecyl) ether;

bis (triethoxysilyl) benzene;

bis (triethoxysilyl) ethane;

bis (triethoxysilyl) methane;

bis (triethoxysilyl) octane;

bis (trimethoxysilyl) decane;

bis (trimethoxysilyl) ethane;

bis (trimethoxysilylethyl) enzene;

bis (trimethoxysilyl) hexane;

bis-1, 3- (trimethoxysilylpropyl ) -benzene;

(chlorodimethylsilyl) -6- [2- (cholorodimethylsilyl) ethyl] bicycloheptane; and

1- (triethoxysilyl) -2- (diethoxymethylsilyl ) ethane .

4. An oscillator spring according to any preceding claim, wherein the spring material consists substantially of vitreous carbon.

5. An oscillator spring according to claim 4, wherein the spring material includes an additive comprising a crystalline material having a lower phase transformation temperature than the vitreous carbon, wherein the proportion of additive in the mixture is selected to control the thermal evolution of the spring' s elastic modulus in an ambient temperature range to provide thermal stability to the spring' s oscillation .

6. An oscillator spring according to claim 5, wherein the additive is silicon dioxide.

7. An oscillator spring according to any preceding claim, wherein the barrier material forms a hydrophobic outer layer on the spring material.

8. An oscillator spring according to claim 7, wherein the hydrophobic outer layer is monomolecular .

9. An oscillator spring according to claim 7, wherein the hydrophobic outer layer is composed of a plurality of layers .

10. An oscillator spring according to claim 9, wherein the plurality of layers includes an intermediate interface layer providing key bonding to the spring material.

11. A method of manufacturing an oscillator spring for a mechanical oscillator mechanism in a horological or other precision instrument, the method comprising:

heating a phase-transformable precursor material to a temperature that causes the precursor material to exhibit a phase transformation into a spring material consisting of any one or more of carbon, ceramic, polymer, polymer precursor and composite materials; and

applying a barrier material to the spring material to alter the number of bonding sites which are available at the surface of the spring material,

wherein the barrier material consists of one or more hydrophobic silicone compounds or one or more hydrophobic si1ane compounds .

12. A method of manufacturing an oscillator spring for a mechanical oscillator mechanism in a horological or other precision instrument, the method comprising:

mixing a phase-transformable precursor material with a hydrophobic additive;

heating the mixture to a temperature that causes the precursor material to exhibit a phase transformation into a spring material consisting of any one or more of carbon, ceramic, polymer, polymer precursor and composite materials; wherein following heat treatment, the hydrophobic additive functions as a barrier material to alter the number of bonding sites which are available at the surface of the spring material, and

13. A method according to claim 11 or 12 including, before final phase transformation of the precursor material, forming the mixture into a shape for subsequent use.

14. A method according to any one of claims 11 to 13 including, after phase transformation of the precursor material, cutting one or more components from the spring material .

15. A method according to claim 14, wherein the cutting step comprises performing deep reactive ion etching (DRIE) to obtain a plurality of components from the mixture of host material and additive in a single cutting operation.