WO1999022668A1

WO1999022668A1 - Apparatus for inert gas lamp cure

Info

Publication number: WO1999022668A1
Application number: PCT/US1998/022848
Authority: WO
Inventors: Arun Prasad; Martin Schulman; George Zychek
Original assignee: Jeneric/Pentron Incorporated
Priority date: 1997-10-31
Filing date: 1998-10-28
Publication date: 1999-05-14
Also published as: AU1204199A

Abstract

An apparatus is presented for the rapid curing of resinous materials by application of energy from an external source to excite polymerization in a polymerizable system under controlled temperature and pressure. The apparatus comprises a chamber and at least one inert gas flash lamp light source arranged at a predetermined distance from the chamber to irradiate an object positioned on the sample holder. Preferably, the inert gas light source is at least one inert gas linear flash lamp positioned to effectively irradiate an object positioned in the chamber. In accordance with the present invention, the inert gas flash lamp emits pulse radiation of very high energy and power peaks. Preferably, the spectral output of the inert gas flash lamp is in the range between about 350 nm and about 550 nm. The radiant energy emitted by the present apparatus is diffused or flooded to produce an even distribution of light intensity over the entire base of a chamber. The apparatus of the present invention achieves very fast cure rates, high degrees of cure, greater depths of penetration, low heat buildup and instant on-off capability and is particularly suitable for the curing of dental materials comprising filled or unfilled resin(s) having at least one ethylenically unsaturated group, in particular acrylate, methacrylate or vinyl groups.

Description

APPARATUS FOR TNFRT GAS LAMP CIJRR

Background of the Invention

1. Field of the Invention:

This invention relates generally to an apparatus for the rapid curing of resinous materials by application of energy from an external source to excite polymerization in a polymerizable system. More specifically, this invention relates to an apparatus for the rapid curing of dental materials by using an inert gas strobe system.

2. Brief Description of the Related Art

Curing, as used herein, is the processing of a plastic or resinous material from a fluid or soft and compliant state to a permanent hard, durable and solid state. Conventionally, this is accomplished both by the elimination of solvents and by chemical changes involving interlinking of molecules commonly known as polymerization of the material. Of the two, polvmerization is the more advantageous since it does not commonly involve dimensional changes and usually produces a substantial increase in the strength of the material. Polymerization is usually caused by the addition of activating chemicals (activators), by irradiation with some form of wave energy either electric or electromagnetic in nature or by applying heat or by a combination thereof. One of the associated problems with the polymerization of a material is the time involved. For example, when polymerization is caused by the application of heat, the rate of the polymerization is largely determined by the intensity of the heat applied. However, it has been found that the application of high heat usually results either in the formation of inferior polymers having less complex molecules, lower density and being weak and relatively fragile, or in the complete destruction of the material. Polymerization by the application of low heat and different forms of wave energy results in a delayed curing process. While the use of chemical activators can increase the polymerization rate, it is extremely inconvenient under some conditions. For the rapid polymerization of a resinous material, the material generally contains passive activators which are then activated by the application of outside energy. Critical factors which affect the optimum properties and the production costs are the amount of energy required and the time over which it must be applied, and these factors must be accounted for to implement an effective system. Consequently, there is a need for an apparatus that effectively and efficiently can cure a polymerizable resinous material, such as a dental material. The present invention is directed to a novel apparatus for the rapid curing of a polymerizable resinous material, preferably a dental material.

Summary of the Invention The above-described and other problems and deficiencies of the prior art are overcome or alleviated by the curing apparatus of the present invention, wherein a filled or unfilled resin(s) having at least one ethylenically unsaturated group is cured in accordance with the present invention.

The present invention refers to an apparatus having an enclosed chamber with an entrance door; of size capable of storing a typical replicate model of a human jaw or hand; to cure filled or unfilled resins in the formation of dental materials. The resins typically include at least one ethylenically unsaturated group, in particular an acrylate, methacrylate or vinyl group. The resin may further include appropriate photo and heat initiators and accelerators known in the dental arts. The curing operation is performed under the pulsed radiation of an inert gas lamp. The pulses are bursts of very high energy and power peaks and the spectral output of the inert gas lamp utilized for the present invention is in the range of about 380 nanometers to 550 nanometers. The radiant energy is diffused or flooded to produce an even distribution of light intensity over the entire base of the chamber. The walls of the chamber preferably have reflective surfaces and may include airways for cooling and for pressurizing the chamber. The apparatus of the present invention provides very fast cure rates, high degrees of cure, greater depths of penetration, low heat buildup and instant on-off capability. The curing chamber can have an aerobic or anaerobic atmosphere. The curing apparatus may additionally include a power supply, a timer, a rotating table and cooling devices.

Brief Description of the Drawing

For the purpose of illustrating the invention, there are shown in the drawing forms which are presently preferred; it being understood, however that this invention is not limited to the precise arrangements and instrumentalities shown. Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:

FIGURE 1 is a perspective view of the apparatus of the present invention;

FIGURE 2 is a perspective view of an alternate embodiment of the apparatus of the present invention; FIGURE 3 a sectional view of the apparatus of FIGURE 2 at line 2-2; and

FIGURE 4 is an exploded view of the apparatus of FIGURE 2.

Detailed Description of the Invention

The present invention is directed to a new and improved method for curing a polymerizable resinous material, such as a dental material. U.S. Patent Nos. 4,873,446, 4,839,521, 4,167,669, 5,040, 964, and 4,309,617 are directed to polymerization and/or curing of materials and are hereby incorporated by reference. The present invention utilizes an inert gas flash lamp source comprising one or more gas flash lamps for providing the additional energy for rapid polymerization. A particularly desirable feature of such a flash lamp is the ability to provide energy pulses with high rise and decay rates. Inert gas flash lamps operate with short, high energy pulses. The source in the flash lamp may be any inert gas, preferably argon, xenon or krypton and most preferably xenon. The pulses are bursts of very high energy and power peaks. They can be operated either in strobe or what appears to be a continuous mode (based on very high frequency) by varying the frequency.

Thus, the apparatus of the present invention polymerizes thermally sensitive polymerizable resins by exposing the resins to pulsed or continuous radiation in a predetermined wavelength range. The polymerization of dental materials is preferably effectuated by irradiation of a selective wave length range which falls between about

350 nm and 550 nm. Consequently, the spectral output of the inert gas flash lamp utilized in the present invention is in the range of between about 380 nm to about 550 nm. Preferably, energy is applied in pulses at a rate of 3 to 120 pulses per second and more prefereably at a rate of about 20 pulses per second and the pulses have a pulse width of lx 10^"3 to 1 x 10^"6 seconds, more preferably in the range of about 70 x 10^'6 to about 75 x 10^"6. The energy delivered from each pulse is in the range of about 7.5 to about 100 joules and preferably is about 15 joules per pulse at a repetition rate of 20 hertz or 300 watts. These operating conditions may require very effective cooling for the lamps. Referring now to the FIGURE 1 a curing apparatus 10 is shown having a door

12 which can be opened automatically. FIGURE 2 shows an alternate embodiment of a curing apparatus 20 having a door 22 and a handle 24 attached thereto for opening door 22. Curing units 10 and 20 include panels 14 and 26, respectively, which include buttons or the like for selecting program options and for operating the apparatus and a display window for displaying the function numbers and time of operation. FIGURES 3 and 4 depict the internal components of curing units 10 and 20. Units 10 and 20 include a sample holder 30 for placement of a sample thereon. An inert gas flash lamp source 32 is positioned in the upper section of the curing unit such that energy is radiated onto a sample in sample holder 30. It should be mentioned that the lamp source is not limited to the position shown in FIGURES 3 and 4 but may be positioned any where in the unit which allows energy to be radiated to the sample. The lamp source may be a single inert gas flash lamp or a plurality of individually based inert gas flash lamps. The lamp source may be a linear lamp (also known as wall-stablized) or a bulb lamp (also known as probe-stabilized unconfined arc lamp). Preferably, a linear stabilized flash lamp is used available from EG&G

Electro-Optics, Salem, MA.

FIGURES 3 and 4 depict the inert gas flash lamp source 32 as a plurality of linear flash tubes 34 located in a flash head chassis 36. Flash tubes 34 are attached to a mounting board 38. As shown in FIGURE 3, located atop mounting board 38 is a trigger generator 40 for providing pulses to the inert gas flash lamp source 32.

Trigger generator 40 may be attached to the mounting board 38 as depicted in FIGURE 3 or it may be a separate unit. The trigger generator 40 has a trigger rate, which may be fixed or it may be a variable rate in a range sufficient to provide triggering pulses effective to cure the polymerizable resinous material. The range of the trigger rate may be empirically determined and should be such that the time for polymerization begins to approach the same time that would be required if the energy used was averaged over and applied continuously at an average rate. The shape of each pulse and the amount of energy in each pulse are determined by the parameters of the inert gas flash lamp system. Trigger generator 40 is powered by power supply 41 which is further connected to a pulse control/timing circuit board such that the apparatus of the present invention has instant on-off capability. The energy in the form of pulses used to irradiate the polymerizable resinous material may be controlled by the power supply 41 in combination with power/discharge board 43 and trigger generator 40 so that radiation in a desired wavelength sufficient to effectively cure a sample in sample holder 30 is directed at the object for a predetermined period of time with a predetermined pulse rate.

Reflectors 42 may also be included in the lamp source 32 to assist in directing the energy toward a sample in holder 30. Chassis 36 is positioned in the upper section of the curing unit. Located below lamp source 32 is a chamber 44 for receiving sample holder 30. During the curing operation, sample holder 30 is arranged in chamber 44 with its work tray holder 46 and work tray 48 located within the radiation path of lamp source 32. Chamber 44 consists of an enclosed chamber with an entrance door 50. The dimensions of the chamber and more particularly of sample holder 30 are such that a typical replicate model of a human jaw or hand may be placed on sample holder 30 in a manner that allows curing of the material in accordance with the present invention. Work tray 48 is preferably in the form of a bowl- or cup-like container having reflective lining therein. Additionally, or alternatively, the walls of chamber 44 preferably have reflective surfaces 52 thereon. Chamber 44 may further include airways 45 for controlling pressure and cooling of the inside of chamber 44 and are of suitable size for carrying out the aforementioned function. Chamber 44 may be rectangular in shape as illustrated in FIGURES 3 and 4 or it may be in the form of another shape, such as circular. Chamber 44 may be pressurized and include a high pressure glass disc 54 as the ceiling of the chamber and as a transparent barrier between lamp source 32 and sample holder 30. The sample holder 30 can be slid in and out easily from chamber 44 and may also be in the form of a plate rotatably mounted within chamber 44. The curing unit may also contain a sensing device 47 such as a one or more photocells or photovoltaic cells for sensing the amount of energy output of flash lamps 34. The radiant energy produced by inert gas light source 32 is diffused or flooded to produce an even distribution of light intensity over the entire base 56 of chamber 44. The inert gas light source 14 may be internal or external to chamber 44. When the inert gas light source 32 is external to chamber 44, then the walls of chamber 44 comprise a transparent material allowing for radiation from the inert gas light source 32 to freely pass through the walls and irradiate an object on sample holder 30. The inert gas light source 32 is connected to a power supply 41 and power/discharge board which are capable of providing the desired energy pulses to the inert gas linear lamps. The trigger generator 40 provides trigger pulses to control the discharge of power supplied to the inert gas lamps. The discharges are conventionally triggered by high voltage triggering from a separate source. Discharge is provided by high voltage triggering from the output of a pulse transformer or other low current high voltage source used to initiate ionization in the inert gas flash lamp. A central processing unit (cpu) board/operator panel 58 controls the various functions and modes of the curing unit.

The door on the unit may be manually operational, semi-automatic or fully automatic. In the manual form, the door is opened and closed by means of a handle designed in conjunction with a cam lock or center crossing locking mechanism. The force of the cam is used to seal the chamber. The closed position can be detected by either a mechanical switch or a non-contact proximity detector. Door weight is compensated for by means of either a balance spring, a gas filled counterbalance cylinder or other similar device so as to allow easy and repeated opening and closing. During operation while the chamber is pressurized, the door is prevented from opening accidentally by means of an electrical or pressurized device such as a solenoid or shot pin or the like.

In the semi-automatic mode, the door operates by means of a front panel button or the like that controls an electrical solenoid. Closing the chamber door with light pressure will cause the "door in closed" position to be detected by a sensor. The sensor will control electrical devices such as a soleniod or valve that will energize devices to secure the chamber door to provide a seal and prevent opening during operation. To open the door, a "door open" button is pressed. This will cause locking devices to be released providing the chamber pressure has been released first. The door will open under light spring pressure for ease of operation.

In the fully automatic mode, the door is controlled by a motorized drive device that will open the door under light pressure and close the door under light pressure. It will use sensors to detect the open or closed position as well as have a means of detecting a "door jammed" condition in the event of jamming or the like (similar to a CD ROM in a computer). Door operation can be integrated into the automatic curing cycle and can also be opened or closed by a button or like means.

The curing operation may operate under three variations. The first variation involves only the use of strobe lighting to cure the material. This involves the emission of pulsed radiation to the material to effect curing. The second variation involves the combination of pulsed radiation with a pressurized atmosphere. Preferably the chamber is pressurized in the range of about 30 to about 95 psi and more preferably to about 85 psi prior to the irradiation process. The pulsed radiation thereafter is initiated and the curing process is performed. U.S. Patent No. 5,000,687 teaches a light curing process performed under pressure and is incorporated by reference herein. In the third variation, the combination of radiation, pressure .and a pressure purge are performed. The chamber is pressurized to a pressure in the range of about 30 to about 95 psi and more preferably to about 85 psi. Pressure is released to allow the chamber to equalize. Pressure is again applied at a rate in the range of about 30 to about 95 psi and more preferably to about 85 psi. Pressure is released. Pressure is again applied at a rate in the range of about 30 to about 95 psi and more preferably to about 85 psi and the light pulsing begins for a preset time to effect curing. The application of pressure is beneficial to the curing process in a variety of ways. It helps to reduce the amount of voids in the sample. The final product provides a better fit due to the compaction on the die. The material is cured without an oxygen ihhibited layer due to the presence of the inert gas. Higher mechanical properties are realized and obtained due to the application of pressure.

The curing cycle may be set at any desired time necessary to cure the material. Preferably, the curing unit provides cylce time options in increments of .1 minute intervals or in 10 second intervals so that for example, a cycle may be programmed for 4 x 10 seconds or 40 seconds to cure the material. The apparatus according to the present invention provides rapid curing of a polymerizable resinous material. The present invention is particularly suited for curing unfilled or filled polymerizable dental resins having at least one ethlenically unsaturated group. Generally, dental materials contain a polymeric matrix and may contain a filler component. Preferred polymerizable dental resins are unsaturated resins containing acrylate, methacrylate or vinyl groups. Particularly preferred dental resins include those based on acrylic and methacrylic monomers, for example those disclosed in U.S. Patent No. 3,066,112, No. 3,179,623, and No. 3,194,784 to Bowen; U.S. Patent No. 3,751,399 and No. 3,926,906 to Lee et al.; and commonly assigned U.S. Patent No. 5,276,068 to Waknine, all of which are herein incorporated by reference in their entirety. Filled dental resins can, in general, include any suitable filler which is capable of being covalently bonded to the polymeric matrix itself. Example of suitable filling materials include but are not limited to, silica, silicate glass, quartz, barium silicate, strontium silicate, barium borosilicate, strontium borosilicate, borosilicate, lithium silicate, amorphous silica, ammoniated or deammoniated calcium phosphate and alumina zirconia, tin oxide and titania. The polymerizable dental resin may further include photo .and heat initiators and accelerators which are known in the dental arts.

The apparatus according to the present invention achieves very fast cure rates, high degree of cure, greater depth of penetration, low heat buildup and instant on-off capability. In addition to delivering more energy faster, the high peak pulses and broad wavelengths have advantage in penetrating and speeding up the cure of thick and opaque dental materials. The apparatus of the present invention also has low heat buildup. The lower heat associated with pulsed inert gas flash lamps is an important advantage in curing heat sensitive dental devices. The lower heat associated with this apparatus is attributed to four characteristics of the present apparatus: (1) narrow pulses, (2) a cooling zone between the pulses, (3) conversion to useful radiation without heating to vapor levels, as required with mercury lamps, (4) and minimum infrared generation. As previously mentioned, chamber 20 may include cooling devices to cool the air around the inert gas flash lamp to a lower temperature without affecting radiation efficiency.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is understood that the present invention has been described by way of illustration and not limitation.

Claims

What is claimed is:

1. An apparatus for curing a polymerizable dental material comprising: an air-tight chamber for placing the dental material therein; a pulsed radiation source for irradiating the dental material, wherein the pulsed radiation source is an inert gas flash lamp source.

2. The apparatus of claim 1 wherein the chamber is pressurized.

3. The apparatus of claim 2 wherein the chamber is pressurized in an inert atmosphere.

4. The apparatus of claim 1, 2, or 3 wherein the radiation is pulsed at a rate of about 3 to about 120 pulses per second.

5. The apparatus of claims 1-4 wherein the radiation is pulsed at a rate of about 20 pulses per second.

6. The apparatus of claim 5 wherein the pulses have a width of about 1 x 10³ to 1 x 10^"6 seconds.

7. The apparatus of claim 6 wherein the pulses have a width of about 70 x 10^"6 seconds.

8. The apparatus of claims 1-7 wherein the radiation has a wavelength spectrum of from about 380 to about 550 nanometers.

9. The apparatus of claims 1-8 wherein each pulse emits about 7.5 to about 50 joules.

10. The apparatus of claims 2-9 wherein the inert gas is selected from the group consisting of argon, xenon, krypton and mixtures thereof.

11. The apparatus of claims 1-10 wherein the inert gas flash lamp source comprises a plurality of linear flash lamps.

12. The apparatus of claims 1-11 wherein the polymerizable dental material is a replicate model of a human jaw.

13. The apparatus of claims 2-12 wherein the inert gas irradiates in a diffused or and flooded manner.

14. The apparatus of claims 1-13 further comprising a photocell detecting intensity of radiation from at least one inert gas light source.

15. The apparatus of claims 1-14 further comprising a reflector arranged adj acent the chamber for reflecting light to the chamber.

16. A method for curing a polymerizable dental material comprising: placing the polymerizable dental material in an apparatus comprising a chamber; sealing the chamber to make it airtight; emitting pulsed radiation into the chamber from an inert gas flash lamp source to cure the dental material.

17. The method of claim 16 further comprising pressurizing the chamber prior to emitting pulsed radiation.

18. The method of claim 17 wherein the pressurizing step is performed in an inert atmosphere.

19. The method of claims 16-18 wherein the radiation is pulsed at a rate of about 3 to about 120 pulses per second.

20. The method of claims 16-19 wherein the radiation is pulsed at a rate of about 20 pulses per second.

21. The method of claims 16-20 wherein the pulses have a width of about 1 x 10^"3 to 1 x 10^"6 seconds.

22. The method of claim 21 wherein the pulses have a width in the range of about 70 x 10^"6to about 75 x 10^"6 seconds.

23. The method of claims 16-22 wherein the radiation has a wavelength spectrum of from about 380 to about 550 nanometers.

24. The method of claims 16-23 wherein each pulse emits about 7.5 to about 100 joules.

25. The method of claims 18-24 wherein the inert gas is selected from the group consisting of argon, xenon, krypton and mixtures thereof.

26. The method of claims 16-25 wherein the inert gas flash lamp source comprises a plurality of linear flash lamps.

27. The method of claims 16-26 wherein the polymerizable dental material is a replicate model of a human jaw.

28. The method of claims 18-27 wherein the inert gas irradiates in a diffused or and flooded manner.

29. The method of claims 16-28 further comprising detecting intensity of radiation from at least one inert gas light source with a photocell or photovoltaic cell.

30. The method of claims 16-29 further comprising reflecting light to the chamber with a reflector located adjacent the chamber.