AGS Annual Conference 2000
Hotel Inter-Continental
New Orleans, Louisiana
TESTING THE INTEGRITY OF GLOVEBOX GLOVES FOR
SUB-VIRAL SIZE DEFECTS UTILIZING ELECTRON BEAMS
ABSTRACT: The porosity and integrity of a nonconductive glovebox
gloves is determined utilizing a novel electron beam technology and electronic
instrumentation in an open atmosphere. The electric corona discharge, maintained
at high positive voltage, from holes and anomalies in the nonconductive
material is detected and analyzed in order to determine the presence of
viral and sub-viral sized voids or holes, as well as other anomalies such
as blisters and bubbles. This process can be performed by the glove manufacturer
as a certified quality level, in-line within the glovebox or in-line with
the glove turned inside out of the glovebox by a hand held device.
INTRODUCTION
This technology relates to a method and apparatus for the on-line, real-time, non-destructive porosity and anomaly testing and measuring of nonconductive materials and products made from these types of materials. These products include glovebox gloves, surgical grade gloves, protective barrier gowns, condoms, encapsulation devices, packaging, and filtration media. The detection of viral and sub-viral sized apertures, voids, holes, blisters, contaminants, stress fractures, overlapped material, formulation defects and other anomalies are critical to the product’s function. More particularly, this technology relates to an electronic measuring method and apparatus which utilizes electron beams and electronic instrumentation to measure electronic corona discharge from the holes and anomalies in order to qualify their integrity.
BACKGROUND
There is much concern among world health organizations and regulatory agencies regarding the quality of nonconductive materials, including protective barrier materials or products, such as glovebox gloves. The concern is due to the fact that disease-causing viruses such as the AIDS virus and the hepatitis B virus can pass through small holes or voids present in these materials or goods, thus infecting the user with the virus or contaminating the glovebox with a hazardous and contagious material. These holes or voids may be formed during the manufacturing of the nonconductive products or pursuant to anomalies present in the nonconductive materials. Accordingly, the present technology has been developed for the testing and measuring of the porosity and anomalies of these nonconductive materials. In particular, the present technology has been developed for the on-line, real-time, non-destructive, non-contact, non-abrasive, dry testing and measuring of nonconductive materials, including thin film protective barrier materials, for voids, holes or anomalies having a diameter as little as one nanometer. Moreover, the present electron beam technology can detect anomalies in the material such as contamination, blisters, bubbles, uncatalyzed or unblended resin, low density material (e.g. weak molecular crosslinking strength), high density material, overlapping material, stress fractures, formulation defects and other structural and non-void anomalies in the material.
Products and materials used to screen viral-size viruses must have their porosity and anomaly presence determined in order to insure that no imperfections are present or may be formed by anomalies which would permit the passage of a virus. These viruses may be as small as twenty nanometers in diameter. Goods and materials that may act as viral barriers include glovebox gloves, condoms, medical grade gloves, thin film membranes, filtration media, materials used in electronic applications, gowns and aprons used in the medical field and operating room environments. Goods and materials that may act as filter media include medical and scientific membranes, fiber and cloth-like filled devices, and microporous analytical and diagnostic membranes, as well as various polymer combinations. (See Fig.-1)
One primary test for determining the porosity of nonconductive thin film materials is the water or electrical hydraulic test. Using this test, the product or material to be tested, such as a glove, is placed on a conformal shaped electrode or mandrel and is submersed in a water bath or electrolyte solution. An electrical potential is applied between the mandrel and the water solution. If there is a void of material in the condom, the water will pass from the charged container water bath to the electrode, causing a short circuit. A current reading will be displayed on a connected ammeter indicating that a defective void exists in the material, and the material is rejected. However, this test can only determine if there is a sizable hole in the material. It cannot reveal the presence of an anomaly, such as a blister or a bubble, in the material because the blister or the bubble will not break in the water test, thus not permitting the water to pass from the water bath to the ground. However, a blister or bubble could very easily break in the use of a glove and thus the glove would fail during use. Therefore, this test would not find the defect in the glove. Another drawback of the water test is that only holes of about fifty microns or greater will be detected, due to the surface tension of the water. It has been proposed to add soap or alcohol to the water in order to decrease the surface tension. However, even with a lower surface tension, this test will not detect viral size holes.
A second primary test which is used to determine the porosity of materials is called a dry test or a spark test. This method involves an electrically charged brush, charged with 1300 to 1500 volts A.C., 60Hz. The brush is conductive and it brushes against the mandrel, which the material (e.g. the glove) is placed on. Both the brush and the mandrel rotate. When there is a large void, about 50 to100 microns, the voltage from the brush will spark through as a straight forward, very thick spark. Because it is a strong discharge, it creates large holes, This method is destructive because the brush touches and breaks the glove. Furthermore, a very strong current flows which can destroy the glove.
A third test is disclosed in U.S. Pat. No.5,196,799 entitled METHOD AND APPARATUS FOR TESTING A PROTECTIVE BARRIER MATERIAL FOR PINHOLES AND TEAR STRENGTH and issued to Beard et al. This test is basically a water test that is conducted at different frequencies, not just D.C. or 60 Hz. This method permits the discovery of holes, bubbles and blisters in the material being tested. This is a capacitive test in which distance, environment and thickness of the product are critical to the repeatability and calibration of the test. It is an integral measurement meaning it measures relatively large areas as one "gray" measurement. It is also a wet tester. One of the inherent problems with wet testing is that after the material has been wet then it must be dried, and usually dried with hot air. The hot air, containing ozone, can weaken the nonconductive material and thus increases or enhances the number of voids that might be present in the final product.
In addition, the above tests are used in conjunction with more extensive destructive test methods to statistically sample lots of finished product. Laboratory testing has shown that a given finished production lot, there may be a few, if any, defective product. Thus more accurate and reliable process testing of each manufactured product is needed.
The foregoing illustrates the limitations known to exist in present porosity testing methods and apparatuses. Thus, it is apparent that it would be advantageous to provide an alternative porosity testing method and apparatus which will non-destructively detect viral size voids, blisters, bubbles, and other anomalies on the production line in fluctuating environments and in real-time for nonconductive materials.
TECHNOLOGY
In general terms, the porosity or presence of anomalies of a nonconductive material is determined by using an electron sensor in an open atmosphere under a fluid cover gas, or a flow of a cover gas. The cover gas is directed on the material and, if there is a small aperture, hole or anomaly in the material, a change in the electric discharge or "corona" (also known as an electron beam, an electrostatic corona or a corona discharge) occurs, which is measured by a sensor. The electron sensor comprises an electrode and a sensing mechanism which records electrons that are sent through the hole or anomaly in the nonconductive material. The occurrence of this change in discharge is due to the below-described Griebel-Gormley Aperture Effect (sometimes referred to herein as "the Aperture Effect").
It should be noted that anomalies in the material include, but are not limited to, contamination, blisters, bubbles, uncatalyzed or unblended resin, low density material (e.g. weak molecular crosslinking strength), high density material, overlapping material, stress fractures, formulation defects, and other structural and non-void anomalies in the material.
It should also be noted that the diameter of the anode tip in the electron sensor, the quality of the plating material (e.g., barium, platinum, gold, silver), and the heating of the anode and cathode tips are factors that relate to the quality and length of the electric discharge (i.e., the corona beam) that is detected. Other important factors are the dielectric quality of the material being tested, the type of defect that is being tested, and the operating parameters of the testing equipment, such as the frequency, the amplitude, the waveshape and the voltage. The proper combination of these factors leads to the ability to detect subnanometer size apertures, holes or anomalies in the material being tested.
The Griebel-Gormley Aperture Effect is based on the point-to-point effect, a known effect, which is described in a text by Moore, "Electrostatics" (Doubleday & Company, Inc.1968), which is incorporated herein by reference. The Griebel-Gormley Aperture Effect is shown by the use of a smooth, rounded grounded cathode (i.e., approximately cylindrical) in proximity to a tip of an anode (a point). Very few electrons (or corona) are discharged if the voltage is low enough. But when the cathode is masked with a dielectric material containing a very small void of material (or hole or anomaly), an electrical point is masked out on the grounded cathode. A point-to-point effect would be created and electrons would flow from the cathode through the hole or anomaly in the dielectric material to the anode tip without increasing the applied voltage. This flow of electrons is detected as a change in the electric discharge. (See Fig.-2.)
A cover gas is also important in achieving the Aperture Effect. Typical cover gases include nitrogen, noncombustible gases, noble gases, and dehydrated air. The results vary with the particular cover gases used. It makes a dramatic difference whether nitrogen is used opposed to air or neon or other noble gases. The flow rate and gas pressure are also important factors; the higher the gas pressure, the more gas flows and the beam lengthens. As the pressure increases, the gas becomes more dense, and the electrons flowing from the cathode to the anode become slower moving. For example, with a pressure of about 1 atmosphere in a cover gas of air, the electrons will move at about 1/10 the speed of light. If the pressure is increased, the speed will decrease.
It should be noted that the beam may move and wander in the cover gas environment. The beam is self-seeking within the focus of the fluid cover gas. Thus, the beam moves in the area of the material bounded by the fluid cover gas in order to locate properly sized aperture or anomaly and creates a focal area on the surface of the test material that can vary based on the setting’s parameters.
It should also be noted that the sensor might be positioned using an automatic positioning device such as a servomotor, a stepper motor or a programmable positioning robot. (See Fig.-3)
Other important factors in the creation of the Griebel-Gormley Aperture Effect are the power supply voltage, the frequency of the pulsed D.C., and the distance from the cathode to the anode. Moreover, the distance between the cathode and the material being tested is an important factor in obtaining the Aperture Effect. If the material being tested is too far from the cathode, the Aperture Effect will be lost. However, this can be alleviated when a conductive noble gas is grounded and used to supplement the difference in the conformal space required between the material and the mandrel.
The U.S. FDA purchased the first prototype that was used in a study that conclusively (100%) discovered holes and anomalies in condoms from 1 micron and above (Reference: Journal of Testing and Evaluation, ASTM Publisher, January 1999). (See Fig.-4) This accuracy assures the barrier against body fluid transmission, thus, viral transmission. The actual capable accuracy is to 0.5 nanometers. This puts measured integrity testing on an atomic level. The beam is drawn and not projected. The truly unique aspect is that the beam will follow a tortuous path through the material and can curve to follow it’s potential in an open atmosphere.
The application of this technology as it relates to the glovebox industry can be applied in three different formats. The first format would be to test and certify the gloves at the manufacturing facility by the approach that has been mentioned in the previous text. This would be a conformal mandrel such as what the product is formed on in the dipping process. The mandrel would be made from a conductive material. The test could be performed as a secondary operation if the material has to be cured in a secondary process. However, if the material is fully cured at the end of the dipping process line, the product could be tested with a series of sensors that would account for the entire area of the product’s surface by rotating the mandrel one full revolution before glove removal. The method of removal from the mandrel is critical. The removal process has to assure that damage does not occur. Some removal methods are too harsh and may potentially relegate testing online useless. The basic idea is to eliminate the labor factors of re-handling the product to keep the cost as low as possible and test on-line.
The second method of testing is to test the deployed product in the glovebox. This could be accomplished by having a small series of sensors in the glovebox accessible to the operators reach so that the critical wear areas of the glove could be tested on a regular basis. This type of test is limited to the fingertips, finger shafts, and nest areas between the fingers. A light signal could indicate the acceptability of the integrity of the glove and an area that is flawed. The beam for this application would be very forgiving in that the beam would articulate from the flaw, since the C-Beam will follow it’s potential, by bending to eliminate line of sight problems associated with the complex geometry of the glove.
The third method would be to test a deployed glove from out side the glovebox. This would be accomplished by turning the glove inside out so that it would hang out. Then the test procedure would be to place a tourniquet type of device on the upper portion of the arm section of the glove above the location of a valve that would be built into the glove. The glove would be filled with a conductive gas, such as a neon or xenon, through the valve with a conductive needle to a prescribed level to extend the test area of the fingers, hand and arm. The needle for the valve would be left in place during the test and provide the necessary ground. Then a hand held device could scan the test area to determine the integrity of the glove prior to use. This may be a more favorable method because a single device is relatively inexpensive compared to building a series of sensors over every portal of the glovebox. In the second method multiple sensors would be required for each portal access location if total integrity were to be achieved.
Conclusion
The glove within the glovebox has been labeled the "Achilles’ heal" for many different reasons, "since they are often the weakest link in the containment barrier" as described in the article by Rodney B. Smith, A Glovebox-The Ultimate Cleanroom ? What the corona beam technology proposes is an alternative to the current status quo. Integrity can now be assured at every step of the glove’s life cycle all the way to its retirement. The manufacturers of the gloveboxes and gloves will have to make very minor changes if they intend to implement this technology. Manufactures of gloveboxes, "will" have to want to offer these features as an option and as a retro-fit patch to their current and future customers. Manufactures of gloves "will" have to want to make changes to provide a glove with the highest integrity and with additional on-line testing features. However, the real "will", will have to be driven by the needs of customers who pride themselves on making the glovebox the cleanest and safest of all cleanrooms for the protection of their customers and their employees.
