WO1994020876A1

WO1994020876A1 - An eyeglass frame with polymeric encapsulated shape-memory alloy components

Info

Publication number: WO1994020876A1
Application number: PCT/US1994/001932
Authority: WO
Inventors: John F. Krumme; Robert B. Zider
Original assignee: Cvi/Beta Ventures, Inc.
Priority date: 1993-03-05
Filing date: 1994-02-24
Publication date: 1994-09-15

Abstract

An eyeglass frame (12) includes at least one component, such as the temples (20, 22), the bridge (18) or the nosepad wires (23, 25), which is formed from a shape memory alloy existing in the pseudoelastic metallurgical state. The component has a coating of a thermally insulating polymeric material, which allows the alloy to be exposed to temperatures greater than its Md temperature, at least for a short period of time, while continuing to exhibit pseudoelastic behavior.

Description

AN EYEGLASS FRAME WITH POLYMERIC ENCAPSULATED SHAPE-MEMORY ALLOY COMPONENTS

FIELD OF THE INVENTION

This invention relates to an eyeglass frame, and to a method of making an eyeglass frame.

BACKGROUND TO THE INVENTION

U.S. Patent 4,896,955 ("the '955 patent"), the subject matter of which is hereby incorporated by reference, discloses an eyeglass frame, of which components are formed from nickel- titanium based shape memory alloys. Components of the frame can be formed from such alloys treated in a variety of ways, to confer desired properties on the component. For example, fastening elements used in the frame can exhibit conventional shaped memory properties of the alloy. Other components of the frame can exhibit the enhanced elastic properties exhibited by shape memory alloys.

A shape memory alloy can exhibit "super elastic" behavior at a temperature below the M, of the alloy as a result of a significant degree of work-hardening, for example to about 30% or more plastic deformation. By selection of an alloy with an appropriate M, temperature, with appropriate work-hardening, such behavior can be obtained in a temperature range of -20°C to 40°C.

A shape memory alloy can exhibit "pseudo-elastic" properties. Such properties are exhibited in a narrow temperature range, between the M, and M_d temperatures of the alloy. They involve transformation of an alloy in its austenite phase to its martensite phase by the application of stress. Application of stress in these conditions can give rise to high strain values. Provided that the temperature is between the M, and the M_d temperatures of the alloy, virtually all of the strain is recovered. The deformation and recovery are marked by significant deviations from linear elastic behavior.

A shape memory alloy which has been work-hardened, perhaps to 30% or more plastic deformation, and at a temperature between its M, and M_d temperature, exhibits a combination of superelastic and pseudoelastic behavior. The optimized elastic behavior is referred to in the '955 patent as "work-hardened pseudoelastic" behavior.

It is advantageous to use shape memory alloys which exhibit enhanced elastic behavior in the manufacture of eyeglass frames, for their kink resistance. Pseudoelastic properties are particularly preferred, because of the large amount of strain which can be recovered. However, a disadvantage of relying on pseudoelastic properties is that they are available only over a narrow temperature range.

This problem was addressed in the '955 patent by subjecting shape memory alloy eyeglass frame components to work-hardening. In this way, the advantages of superelastic behavior, and some of the advantages of pseudoelastic behavior can be obtained from temperatures below the M, temperature up to the M_d temperature of the selected alloy.

SUMMARY OF THE INVENTION

The invention provides an eyeglass frame which has at least a portion thereof formed from a shape memory alloy existing in the pseudoelastic metallurgical state, the portion having a coating of a thermally insulated polymeric material. The portion can be a bridge, nosepad wires, eyewires and/or a pair of temples of the eyeglass frame.

According to the invention, the shape memory alloy can be any suitable material such as a nickel-titanium based alloy or a copper based alloy. The coating can be applied in a variety of ways. For instance, the coating can be provided as a tube of polymeric material which engages and conforms to the shape memory alloy portion elastically. Alternatively, the coating can be provided by dipping the shape memory alloy portion in a liquid, which has solidified in ≤itji on the portion. The coating can have any suitable thickness such as 0.2-2.0 mm. However, the minimum thickness of the coating of polymeric material can be less than about 0.2mm and the maximum thickness of the coating of polymeric material can be greater than about 2.0mm. The material of the coating can comprise a silicone based polymer or a polyurethane based polymer as an example. Also, the coating can comprise a plurality of layers of polymeric material and each layer can be of a different polymeric material. In addition, the coating can contain additives to enhance various properties and features of the eyeglass frames and/or of the coating itself.

The invention also provides a method of making an eyeglass frame, which includes the steps of (a) forming a component of the frame at least partially from a shape memory alloy, the alloy in the component being in the pseudoelastic metallurgical state, and (b) applying to the component a coating of a thermally insulating material. The coating can be applied as a tube of a polymeric material, and the method can include (a) positioning the shape memory alloy component inside the tube, and (b) allowing the tube to engage and to conform to the shape memory alloy component elastically. The tube can be conformed to the shape memory alloy by heating the tube and shrinking the tube onto the shape memory alloys. Alternatively, the method can include steps of (a) dipping the shape memory alloy component in a liquid, and (b) allowing the liquid to solidify in situ on the component to provide the coating. The dipping step can be carried out more than once. The coating can contain at least one additive such as a coloring additive. Preferably, the coating is provided in a thickness sufficient to enlarge a temperature range at which the component exhibits pseudoelastic behavior.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an isometric view of an eyeglass frame; Figures 2A to 2G illustrate strain-temperature and stress- strain behavior of a shape memory alloy; and Figures 3A to 3H illustrate various cross sections of coated eyeglass frame components in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a technique for making an eyeglass frame from a shape memory alloy such as a nickel- titanium based or copper based alloy exhibiting pseudoelastic behavior, by providing a coating of a thermally insulating polymeric material on a component made from such an alloy.

In one aspect, the invention provides an eyeglass frame of which at least a portion is formed from a shape memory alloy existing in the pseudoelastic metallurgical state, the portion having a coating of a thermally insulating polymeric material.

In another aspect, the invention provides a method of making an eyeglass frame, which includes the steps of:

(a) forming a component of the frame at least partially from a shape memory alloy, and (b) applying to the component a coating of a thermally insulating material,

the alloy in the component being in the pseudoelastic metallurgical state. The technique of the present invention of producing an eyeglass frame has the advantage of enhanced kink resistance, arising from the use of a shape memory alloy which exhibits pseudoelastic behavior.

The provision of a coating of a thermally insulating polymeric material on the shape memory alloy portion of the eyeglass frame allows the frame to be exposed to temperatures outside the narrow range in which pseudoelastic behavior is exhibited, at least for short periods of time. In this way, an eyeglass frame can be provided, having the advantages of pseudoelastic behavior, but with an ability to tolerate temperatures lower than the M, temperature and greater than the M_d temperature of the alloy. This is made possible without any requirement necessarily to subject the alloy to a specific, controlled work- hardening processing step.

The eyeglass frame of the invention can include any of a number of components, at least a portion of one of which is formed from a shape memory alloy. For example, the eyeglass frame might include a pair of temples, and/or eyewires, and/or a bridge, and/or a pair of nosepad wires (which connect a pair of nosepads through respective lens rims), a portion of any one or more of which can be formed from a shape memory alloy.

The material of the coating may include additives. Additives may be included, for example, to affect the appearance of the eyeglass frame. For example, colorant additives may be added to impart a desired color to the coated shape memory alloy component. Additives might also, or alternatively, be included to modify surface feel, wear texture, chemical resistance, UV resistance, durometer, flexibility, or to create specific zones of enhanced thermal conductivity in order to draw heat from the wearer while in use in cold ambients.

The coating can be provided as a tube of polymeric material which engages and conforms to the shape memory alloy portion el stically. It might be convenient in some circumstances for the tube to be closed at one end, for example when the tube is to be fitted to a temple for an eyeglass frame. The use of a tube of polymeric material to provide the coating on the shape memory alloy component has the advantage of allowing the coating to be provided in a reliable way, without a significant minimum skill level required of the operator of the coating process. It is envisaged, for example, that the coating tube might be allowed to shrink onto the shape memory alloy component, for example by the application of heat. In another arrangement, an elastically deformable tube might be rolled over a shape memory alloy eyeglass frame component. Other possibilities include simple molding of the coating by injection or transfer molding techniques and insertion of the metal parts in thermoplastic materials that are heated to the softening point. It is preferred for many applications that the coating of polymeric material be applied to the shape memory alloy component as a liquid, which solidifies in sifii on the surface of the component. For example, the component might be dipped in a quantity of the liquid. The coating might then solidify, for example, by evaporation of a solvent, or as a result of a curing reaction. This process is commonly referred to as "dipping".

The application of the coating as a liquid for solidification has the advantage that coatings can be built up on the shape memory alloy component in a number of layers. This allows coatings with different thickness or materials to be built up on components as required without a requirement for a large inventory of coating tubes. Furthermore, by use of different coating liquids in respective layers of the coating material, a variety of aesthetic and other effects can be created. For example, the inner layer might be a solid or vivid color with the outer layer being translucent, thereby giving an unusual aesthetic effect. It should be noted, however, that such multilayered coatings can also be obtained from layered sheet materials thus obviating the need to use a liquid for building up the layers on the shape memory alloy.

A particularly preferred material for the coating comprises the family of dippable and/or sprayable silicone polymers as produced by Dow Corning. Preferably, the minimum thickness of the coating of polymeric material is at least about 0.2mm. More preferably, the minimum thickness is at least about 0.5mm. Preferably, the maximum thickness of the coating of polymeric material is less than about 2.0mm. More preferably, the maximum thickness is less than about 1.0mm. However, the preferred coating can have a thickness ranging from less than 0.2 to more than 2.0 mm.

The shape memory alloy component of the eyeglass frame of the invention can be work-hardened, and the method of the invention can include a work-hardening step applied to the shape memory alloy component. Examples of suitable work-hardening conditions are disclosed in the '955 patent referred to above.

The application of a coating of a thermally insulating polymeric material to a shape memory alloy component of an eyeglass frame which has been work-hardened has the advantage that pseudoelastic behavior, or work-hardened pseudoelastic behavior, is exhibited for some period of time by the component at ambient temperatures greater than the M,, temperature of the alloy from which the component is formed.

Alloys will be selected for use in the eyeglass frame of the invention, with a M,, temperature which is greater than the temperature which can be expected to be encountered in use by a user of the frame. Such a temperature might be, for example, 35°C, preferably 40°C, for example about 45 °C. Suitable shape memory alloys are generally based on a nickel-titanium system. Some of the nickel or the titanium can be replaced by one or more other elements, such as iron, chromium, copper, cobalt or vanadium. Suitable alloys are disclosed in U.S. Patent Nos. 3,174,851; 3,351,463; 3,558,369; 3,672,879;

4,505,767; 4,894,100; and 4,983,029. However, other shape memory alloys can be used. For example, copper based shape memory alloys can be used. Examples of copper based shape memory alloys can be found in U.S. Patent No. 4,490,112.

Figure 1 shows an eyeglass frame 12. The frame 12 includes two rims 14, 16, a nose bridge 18, nosepads 19, 21, and temples 20, 22. The temples are connected to the rims by means of hinges. The temples extend rearwardly from the rims, over the ears of a wearer when in use. The bridge 18 connects the two lenses. Tne ncsepads 19, 21 rest on the nose of a wearer, and are attached to the eyewires or rims by means of wires 23, 25.

Each of the nose bridge 18, the temples 20, 22 and the nosepad wires 23, 25 is formed from a nickel-titanium based shape memory alloy, which exhibits pseudoelastic behavior at ambient temperature. Each is provided with a coating of a thermally insulating polymeric material. The coating is provided by dipping each of the components in liquid silicone polymer, which solidified in situ. Figure 2A illustrates conventional shape memory effect behavior of the shape memory alloy. It provides an illustration of the strain-temperature behavior of an alloy, as it is cycled from low temperature to high temperature and back again, at constant stress. It can be seen that a component made from an alloy, on cooling or heating in the temperature range M_f to A_f can be made to change configuration. As shown in the drawings, the change in configuration results in a reduction of strain. On subsequent cooling from the temperature above A, the configuration of the article in question reverts to the original configuration, the revision taking from a place between M, and M_d of the alloy. Generally, A, is higher than M,.

The alloy is stable in the martensite phase at a temperature below M_f and is stable in the austenite phase at a temperature above A_f. When an article formed from a shape memory alloy in this configuration as is subjected to a change in temperature, its phase changes between martensite and austenite phases.

Figures 2B to 2G illustrate the behavior of a shape memory alloy which exhibits pseudoelastic, superelastic and work-hardened pseudoelastic behavior, depending on the temperature at which the behavior is observed, and the method by which a component is formed from the alloy.

Transformation of a shape memory alloy from its austenite phase to its martensite phase can be induced by the application of stress. This is possible provided that the temperature does not exceed M,, the characteristic temperature of a shape memory alloy above which the stress induced transformation can no longer take place. The M_d temperature is generally greater than the A, temperature. This behavior of a shape memory alloy at a temperature less than its M,, temperature when under stress is referred to generally as pseudoelastic behavior, and is illustrated in Figures 2B to 2E.

In Figure 2B, the temperature T_! is less than the M₈ temperature of the alloy. In Figure 2C, the temperature T₂ is between the M, and M_d temperatures of the alloy. The behavior illustrated in Figure 2C is classical pseudoelastic behavior of a shape memory alloy in which all (or virtually all) of the strain resulting from the application of stress is recovered. In Figure 2D, the temperature T₃ is between the M, and M_d temperatures of the alloy, and is greater than the temperature T₂ of which the behavior shown in Figure 2C takes place. In Figure 2E, the temperature T₄ is greater than both the Mj and A_f temperatures of the alloy being observed.

Superelastic behavior of a shape memory alloy is exhibited once it has been subjected to a work-hardening step. A suitable work-hardening step can be plastic deformation of at least 25%, for example at least about 35%. Figures 2F and 2G illustrate the stress-strain behavior of a shape memory alloy component which has been subjected to such a work-hardening step. Figure 2F shows the behavior of a shape memory alloy at a temperature which is less than the M, temperature of the alloy. The behavior illustrated in Figure 2F is classical superelastic behavior of a shape memory alloy. Figure 2G illustrates the behavior of a component formed from a shape memory alloy which has been work-hardened, at a temperature between M, and M_d temperatures of the alloy.

It will be seen that the advantages respectively of the superelastic and pseudoelastic behaviors of a shape memory alloy are made available as a result of work-hardening, provided that the temperature is kept below the M_d temperature of the alloy.

Figures 3A to 3H show various cross sections of coated eyeglass frame components in accordance with the invention. For instance, the cross sections of the component and coating can be circular (Fig. 3A), rectangular (Fig. 3B), irregular (Fig. 3C), elliptical (Fig. 3D), or C-shaped (Fig. 3H). In Figure 3E, a portion of the T-shaped component is not coated. In Figure 3F, the component is covered with multiple coatings. In Figure 3G, the elliptical component is coated with air or gaseous spaces between the coating and the component (e.g., four air spaces can be created between four radially extending polymeric standoffs 30).

The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. An eyeglass frame, of which at least a portion is formed from a shape memory alloy existing in the pseudoelastic metallurgical state, the portion having a coating of a thermally insulating polymeric material.

2. An eyeglass frame as claimed in claim 1, wherein the portion comprises a pair of temples.

3. An eyeglass frame as claimed in claim 1, wherein the portion comprises a bridge.

4. An eyeglass frame as claimed in claim 1, which includes a pair of lens rims, a pair of nosepad wires and a pair of nosepads, each nosepad being connected to a respective rim by a nosepad wire, the at least one portion comprising the nosepad wires.

5. An eyeglass frame as claimed in claim 1, in which the coating is provided as a tube of polymeric material which engages and conforms to the shape memory alloy portion elastically.

6. An eyeglass frame as claimed in claim 1, in which the coating is provided by dipping the shape memory alloy portion in a liquid, which then solidifies in situ on the portion.

7. An eyeglass frame as claimed in claim 1, in which the coating of polymeric material has a thickness ranging from about 0.2mm to about 2.0mm.

8. An eyeglass frame as claimed in claim 1, in which the shape memory alloy comprises a nickel-titanium based alloy or a copper based alloy.

9. An eyeglass frame as claimed in claim 1, in which the material of the coating comprises a silicone based polymer.

10. An eyeglass frame as claimed in claim 1, wherein the coating comprises a plurality of layers of polymeric material.

11. An eyeglass frame as claimed in claim 10, wherein each layer is of a different polymeric material.

12. An eyeglass frame as claimed in claim 1, wherein the coating contains at least one additive in an amount sufficient to impart coloring or improve a physical property of the coating.

13. A method of making an eyeglass frame, which includes the steps of:

(a) forming a component of the frame at least partially from a shape memory alloy, the alloy in the component being in the pseudoelastic metallurgical state, and (b) applying to the component a coating of a thermally insulating material.

14. A method as claimed in claim 13, in which the coating is applied as a tube of a polymeric material, and which includes the steps of (a) positioning the shape memory alloy component inside the tube, and (b) allowing the tube to engage and to conform to the shape memory alloy component elastically.

15. A method of claimed in claim 13, which includes the steps of (a) dipping the shape memory alloy component in a liquid, and (b) allowing the liquid to solidify in sϋϋ on the component to provide the coating.

16. A method as claimed in claim 13, wherein the shape memory alloy comprises a nickel-titanium based alloy or a copper based alloy.

17. A method as claimed in claim 14, wherein the tube is conformed to the shape memory alloy by heating the tube and shrinking the tube onto the shape memory alloys.

18. A method as claimed in claim 13, wherein the coating contains at least one additive in an amount sufficient to impart coloring or improve a physical property of the coating.

19. A method as claimed in claim 18, wherein the additive is a coloring additive.

20. A method as claimed in claim 14, wherein the coating is provided in a thickness sufficient to enlarge a temperature range at which the component exhibits pseudoelastic behavior.