EP1480802A1

EP1480802A1 - Light-curing device and process for producing hearing aid shells using light-curable resins

Info

Publication number: EP1480802A1
Application number: EP03709285A
Authority: EP
Inventors: Patrick J. Courtney; Karl E. Gabrielson; Donald L. Tew
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 2002-02-28
Filing date: 2003-02-24
Publication date: 2004-12-01
Also published as: CN1638932A; WO2003074248A1; KR20040088558A; JP2005518959A; WO2003074248A9; AU2003213239A1

Abstract

An apparatus (10) is provided having a radiation curing chamber (16) and at least one tubular gas diffuser for (20) introducing an inert gas (e.g., argon) into the curing chamber (16) at a plurality of locations. The introduction of the inert gas limits the exposure to oxygen of any resin curing within the chamber (16) due to radiation curing, such as UV light-curing. Advantageously, the introduction at multiple locations provides for a more thorough blanket of inert gas in the curing chamber (16) than previously provided for in the prior art, and, thus, less oxygen inhibition. The apparatus(10) of the subject invention is particularly well-suited for the process of preparing hearing aid shells, but may be used in other light-curing applications.

Description

LIGHT-CURING DEVICE AND PROCESS FOR PRODUCING HEARING AID SHELLS USING LIGHT-CURABLE RESINS

FIELD OF THE INVENTION;

[0001] This invention relates to apparatuses and methods for curing light-curable resins, and more particularly, curing light-curable resins in the formation of hearing aid shells.

BACKGROUND AND RELATED TECHNOLOGY;

[0002] Custom-fit hearing aids have been developed with shells formed to match a person's ear canal. Techniques are known in the prior art to produce an investment (a mold) which defines a cavity matching the shape of the person's ear canal. To form a corresponding hearing aid shell, one method in the prior art calls for preparing a two-part mixture and then pouring the mixture into the investment. The filled investment is placed into a warm water bath with the heat from the warm water curing the mixture to a limited depth, thus forming a shell. After a predetermined period, a shell of desired thickness is formed, and the uncured mixture is poured from the shell. This technique, however, is time-consuming.

[0003] It is also known to use radiation, such as ultraviolet (UV) light, to cure certain resins. A technique has been developed, wherein a resin-filled investment is placed within a closed chamber and exposed to UN light for a limited duration, thereby curing a limited depth of the resin and forming a shell. Upon pouring out the uncured resin from the shell, a solution, such as a water/glycol solution, is poured into the emptied shell, and the shell is placed again into the UN chamber for further UN light exposure and full curing. Certain light-curing compounds (e.g., light-curing acrylic molding compounds) are prone to "oxygen inhibition" - poor and/or incomplete curing resulting from the material being cured while exposed to oxygen. The solution within the shell limits the exposure of the shell's interior to oxygen and allows for more thorough curing. [0004] In an alternative approach to avoid oxygen inhibition, the chambers of certain light-curing devices have been equipped with a limited supply of inert gas. By introducing inert gas, the amount of oxygen in a curing chamber may be reduced. After shell formation and removal of uncured resin, an empty shell may be placed into the curing chamber, inert gas introduced, and full curing completed. This technique obviates the need to introduce a solution into the shell's cavity prior to full curing.

[0005] The known light-curing devices provide a limited dispersion of inert gas, since the gas is introduced into the chamber via limited points. For example, a curing device sold under the trade name 'TOLYLUX-2000" by Dreve-Otoplastic GmbH of Unna, Germany includes a single hose supply which is split and connected to side-by-side nozzles on one wall of the curing chamber for ejecting carbon dioxide into the curing chamber in the same direction. As such, the detrimental effects of oxygen inhibition are somewhat remediated, but not eliminated.

SUMMARY OF THE INVENTION;

[0006] In one aspect of the subject invention, an apparatus is provided having a radiation curing chamber and at least one tubular gas diffuser for introducing an inert gas (e.g., argon) into the curing chamber at a plurality of locations. The introduction of the inert gas limits the exposure to oxygen of any resin curing within the chamber due to radiation curing, such as UN Ught-curing. Advantageously, the introduction at multiple locations provides for a more thorough blanket of inert gas in the curing chamber than previously provided for in the prior art, and, thus, less oxygen inhibition. Additionally, less inert gas than provided with known devices may be provided to avoid oxygen inhibition. The apparatus of the subject invention is particularly well-suited for the process of preparing hearing aid shells, but may be used in other Ught-curing applications.

[0007] In a second aspect of the subject invention, inert gas is introduced at locations disposed along at least two sides of the curing chamber. As such, a more thorough introduction of inert gas than with known devices is possible because the gas is introduced from different directions within the chamber.

[0008] These and other features of the subject invention will be better understood through a study of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0009] Figure 1 is a perspective view of an apparatus for curing resins utilizing principles of the subject invention;

[0010] Figure 2 is a top perspective view of the apparatus with its curing chamber exposed;

[0011] Figures 3 and 4 show a tubular diffuser of the subject invention disposed along a wall of the curing chamber;

[0012] Figure 5 is a cross-sectional view of the tubular diffuser;

[0013] Figure 6 shows a plurality of tubular diffusers disposed within the curing chamber;

[0014] Figure 7 shows ports located directly on the walls of the curing chamber;

[0015] Figure 8 is a schematic of a source of radiation and base of the curing chamber; and

[0016] Figures 9A-9F show a process of forming hearing aid shells using an apparatus formed in accordance with the subject invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] With reference to Figure 1, an apparatus 10 is shown for curing light-curable resins. The apparatus 10 is particularly well-suited to cure light-curable resins in the formation of hearing aid shells.

[0018] The apparatus 10 includes a cabinet housing 12, a control panel 14 and a light- curing chamber 16, which may be selectively isolated by movable cover 18. Light-curing apparatuses are known are in the prior art, and the structure and operation of the cabinet housing 12, the control 14, the curing chamber 16, and the cover 18 may be of any such construction known to those skilled in the art.

[0019] The cabinet housing 12 includes a supply of inert gas (e.g., argon) internally, or a fitting (not shown) for connecting to a supply of an inert gas. The inert gas may be of any type that is stable and that will not adversely react with resin that is being cured in the curing chamber 16. It is desired that the inert gas be selected to n- mmize oxygen inhibition effects during curing, thus, the inert gas should not include excessive amounts of oxygen and, ideally, no oxygen. Conventional valving (not shown) may be used to regulate the flow of the inert gas with the valving being controlled from the control panel 14 and/or external from the cabinet 12 using known controls and instrumentation.

[0020] With specific references to Figures 2-5, in a first aspect of the subject invention, a tubular gas diffuser 20 is disposed within the curing chamber 16 for introducing the inert gas into the curing chamber 16. The tubular diffuser 20 beneficially may be coextensive with a side wall 22 of the curing chamber 16.

[0021] The tubular diffuser 20 includes a tubular body 24 which defines a lumen 26 that extends the length of the tubular diffuser 20 (Figure 5). The tubular diffuser 20 may be connected to the supply of inert gas at one or more mid-points and/or at one or both ends via connections within the cabinet housing 12. Alternatively, the inert gas may be supplied at one or more mid-points or at one end of the tubular diffuser 20 with the open end(s) being capped, or open and connected to a return system or vent. A plurality of ports 28 are formed along the length of the tubular diffuser 20 at spaced locations to communicate the lumen 26 with the curing chamber 16. The tubular diffuser 20 may be configured in any manner to allow passage of inert gas to the ports 28. The ports 28 may be orifices (as shown in Figure 5), nozzles, diffusers, or a combination thereof. In a particularly desirable arrangement, the ports 28 are spaced (desirably, evenly spaced) along the full length of the tubular diffuser 20 so as to allow a blanket of inert gas to be formed which is generally coextensive with the side wall 22 of the curing chamber 16. The inert gas should be sufficiently pressurized in being supplied to the tubular diffuser 20 such that a relatively equal amount of inert gas is passed through each of the ports 28.

[0022] The body .24 of the tubular diffuser 20 is shown with a cylindrical shape in

Figure 5, but may be of other cross-sectional shapes, such as polygonal, elliptical or irregular.

[0023] In a second aspect of the subject invention, a plurality of the tubular diffusers

20 are provided to at least partially bound the curing chamber 16, and most desirably, wholly bound the curing chamber 16. With this arrangement, ports 28 are located along at least two of the side walls 22 and 30 of the curing chamber 16, and, thus, inert gas may be introduced into the curing chamber 16 in at least two different directions via the ports 28 located along the side walls 22, 30. For example, with reference to Figure 6, inert gas is introduced in a direction perpendicular to the side wall 22, and inert gas is introduced in a direction pe endicular to the side wall 30. Most desirably, the tubular diffusers 20 are located along each of the side walls of the curing chamber 16. With inert gas being introduced from locations along a multiple of the side walls 22, 30, multiple blankets of inert gas can be simultaneously introduced into the curing chamber 16. Although turbulent effects may be present, the inert gas will more thoroughly reach all points of the curing chamber 16 than with the prior art.

[0024] As an additional variation, one or more of the tubular diffusers 20 may be in fluid communication, with inert gas being passed directly from one of the tubular diffusers 20 to the next. As indicated above, sufficient pressure should be provided to force the inert gas 26 in equal amounts through all of the ports 28 of the connected tubular diffusers 20. In this second aspect of the subject invention, the ports 28 may be mounted relative to the curing chamber 16 using any technique known to those skilled in the art, and need not be supported by the tubular diffusers 20. For example, with reference to Figure 7, the ports 28 may be nozzles or orifices located directly on the side walls 22, 30 of the curing chamber which are in communication with a supply of inert gas. The ports 28 may be mounted in any manner allowing for inert gas to be introduced into the curing chamber 16 in at least two different directions. For example, the ports 28 maybe located along a single wall, but oriented in different directions.

[0025] With reference to Figure 8, the curing chamber 16 includes a base 32 which permits radiation to pass therethrough, and a source of radiation 34 located therebelow positioned to emit radiation into the curing chamber 16 through the base 32. As a non- limiting example, the base 32 may be glass and the source of radiation 34 may be a UN lamp which is directed to emit UN energy through the base 32 and into the curing chamber 16. The structure of the base 32 and the source of radiation 34 may be of any type known to those skilled in the art. As is readily evident, the volume of the curing chamber 16 is a direct function of the size of the base 32. It has been found that the base 32 should not be excessively large to maximize the effect of the inert gas. By way of non-hmiting example, the base 32 maybe 8 inches by 8 inches.

[0026] The apparatus 10 may be used to cure various Hght-curable resins, but is particularly well-suited in the preparation of hearing-aid shells. Figures 9A-9F depict an exemplary manner of utilizing the apparatus 10.

[0027] With respect to Figure 9A, a light-curable resin 100 is prepared and poured into an investment 102 which is formed using known techniques. The light-curable resin 100 maybe any of suitable type known to those skilled in the art, desirably an acrylic molding compound. The resin 100 may be selected from a variety of materials such as silicone, polyvinyl, polyurethane, polyester, polyether, acrylic- and methacryhc-type polymers, or combination thereof. These compositions are typically combined with various colorants, photoinitiator and reactive diluents to adjust viscosity of the composition. According to a common practice in this art, the curable composition can contain a curable prepolymer or oligomer having at least one unsaturated site which is a derivative of acrylic or alkylacrylic acid, and, if desired, a monofunctional or polyfunctional monomer derived from acrylic or methacrylic acid.

[0028] Once filled, with reference to Figure 9B, the investment 102 is placed into the curing chamber 16 and isolated by the cover 18. Radiation, such as ultraviolet light, is emitted into the curing chamber 16 for a limited period of time to allow for a shell 104 of limited depth to be at least partially cured. With reference to Figure 9C, the shell 104 conforms to a cavity 106 of the investment 102 and typically will have a thickness T of approximately 0.030 inches. Since uncured resin seals the shell 104 from the surrounding atmosphere, oxygen inhibition is not a critical issue in the first dose of radiation, and the inert gas need not be introduced. With a 400-watt metal halide ultraviolet lamp (50 mw/cm² @ 365 ran), ultraviolet energy is emitted for approximately 5-20 seconds (depending on the color of the resin 100) to form the shell 104. After this initial exposure, the investment 102 is removed from the curing chamber 16 and the uncured resin is poured therefrom, so that the internal volume 108 of the shell 104 is open and exposed within the investment 102.

[0029] The investment 102 is then returned to the curing chamber 16, as shown in

Figure 9E. Ultraviolet energy is once again applied, to fully cure the shell 104. In addition, with this second exposure of radiation, inert gas is introduced into the curing chamber 16 in any manner as described above, and, desirably is introduced at least partially simultaneously during the second radiation dose. The inert gas can be introduced for a shorter period of time than the period of time during which radiation is emitted into the curing chamber 16. With the aforementioned 400-watt metal halide UN lamp, the UN radiation will be typically emitted for a period of 60 seconds to fully or substantially fully cure the shell 104. The inert gas can be introduced for a period of 25 seconds or more during the second dose of UN radiation. As an alternative, the introduction of the inert gas into the curing chamber 16 can be initiated prior to the second exposure of radiation. To ensure a proper supply of inert gas is provided, as indicated above, sufficient pressure should be applied. With argon, a pressure in the range of 50-100 psi @ 150 SCFH maybe utilized, with a desired operating range of 60-100 psi @ 150 SCFH. Once the second radiation exposure step is completed, the shell 104 is cured or substantially cured without the detrimental effects of oxygen inhibition. As shown in Figure 9F, the shell 104 is used in the formation of a complete hearing aid assembly 110 as known in the prior art.

[0030] As is readily apparent, numerous modifications and changes may readily occur to those skilled in the art, and hence it is not desired to limit the invention to the exact construction operation as shown and described, and accordingly, all suitable modification equivalents may be resorted to falling within the scope of the invention as claimed.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for curing resins, said apparatus comprising: a curing chamber; a radiation source positioned to emit radiation into said curing chamber; and at least one tubular diffuser having a plurality of ports, said ports being in communication with said curing chamber, said tubular diffuser configured to pass inert gas to said ports, said ports for introducing inert gas into said curing chamber.

2. An apparatus as in claim 1, wherein a plurality of tubular diffusers are in communication with said curing chamber, said tubular dif-users being positioned to at least partially bound said curing chamber.

3. An apparatus as in claim 2, wherein said tubular diffusers bound said curing chamber.

4. An apparatus as in claim 1, wherein said radiation source is an ultraviolet lamp.

5. An apparatus as in claim 1, wherein said curing chamber is isolatable with a movable cover.

6. An apparatus as in claim 1 , wherein said tubular diffuser includes a tubular body defining a lumen, said ports extending through said cylindrical body into communication with' said lumen.

7. An apparatus as in claim 1, wherein at least one port is a nozzle.

8. An apparatus as in claim 1, wherein at least one port is an orifice.

9. An apparatus as in claim 1, wherein said ports are located along multiple locations on said tubular diffuser.

10. An apparatus for curing resins, said apparatus comprising: a curing chamber; a radiation source positioned to emit radiation into said curing chamber; and at least first and second ports in communication with said curing chamber for introducing inert gas into said curing chamber, said first and second ports being configured to introduce inert gas into said curing chamber in different directions.

11. An apparatus as in claim 10, wherein said curing chamber is defined by a plurality of walls, said first port being located along a first wall, and said second port being located along a second wall.

12. An apparatus as in claim 10, wherein at least one port is located along each of said walls of said curing chamber.

13. An apparatus as in claim 10, wherein said curing chamber is defined by a plurality of walls, said first and second ports being located on the same of said walls, said first and second ports being oriented to introduce inert gas into said curing chamber in different directions.

14. A process for curing resins, said process comprising: pouring a resin into an investment; partially curing said resin in the investment so as to form a shell of limited thickness; removing uncured resin from said shell;

.placing said shell into a curing chamber; curing said shell within said curing chamber; and introducing inert gas into said curing chamber from multiple locations.

15. A process as in claim 14, wherein said introducing inert gas occurs at least partially during said curing of said shell.

16. A process as in claim 15, wherein said introducing inert gas occurs both during said curing of said shell and for a shorter period than said curing of said shell.

17. A process as in claim 14, wherein said resin is an acrylic molding compound.

18. A process as in claim 14, wherein said curing includes exposing to radiation.

19. A hearing aid shell formed by the process of claim 14.

20. A process as in claim 14, wherein said multiple locations for said introducing inert gas are ports located along at least one tubular diffuser.

21. A process as in claim 14, wherein said multiple locations for said introducing inert gas are located to introduce inert gas in different directions in said curing chamber.