Characterization and integrity testing utilizing corona beam technology.

There have been decades of non-destructive testing development in the rubber and synthetic rubber industries. This article proposes a new and unique technology that has the capability to surpass some of the standard methods of NDT. This article deals with the characterization of porosity, permeability and integrity of conductive and non-conductive rubber and synthetic rubber materials that can be determined by utilizing a novel electron beam technology and electronic instrumentation in an open atmosphere for 100% testing in a non-destrucfive, real-time, on-line testing system. An electron beam developed in an open atmosphere maintains a prescribed and applied frequency through the use of a nitrogen cover gas, ionizing the gas to create a corona beam. The corona beam discharge, maintained at a high positive voltage, forms from the holes or anomalies in the flexible rubber material. The anomaly 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. The process can also utilize an established range of acceptability to certify materials that require a well defined level of permeability. This process can be performed by the flexible rubber film manufacturer to certify a specific quality level. It can be performed by the material fabricator to ensure quality standards for preformed materials. It can also be performed by product packaging manufacturers that use the rubber material to wrap their products and confirm the integrity of the final sealed rubber by measuring the atmosphere inside the finished package. There are many other packaging applications that can utilize this technology for rubber film characterization, validation and integrity testing within the pharmaceutical, medical device and food processing industries, as well as other industrial applications.

This technology relates to a method and apparatus for the on-line, real-time, non-destructive, 100% testing and measuring of the integrity and location of anomalies in thin flexible rubber and synthetic rubber materials and products made from these types of materials. The terms rubber and synthetic rubber are used in this text synonymously as "rubber," since the corona beam's testing process applies equally to both natural and synthetic types of material. These products include many different products made with various molding and extrusion processes. This also includes laminated composites and adhesive backed materials coated on metal foil, paper and plastic film. This discussion also includes composite materials with strengthening fillers and structured engineering materials that have combinations of conductive and non-conductive elements.

The detection of viral and sub-viral sized apertures, voids, holes, blisters, contaminants, stress fractures, overlapped material, formulation defects and other anomalies is critical to the product's structural and performance function. In other instances where a degree of permeability is required, this technology can characterize and certify the degree of permeability and porosity. More particularly, this technology relates to an electronic measuring method and apparatus which utilizes electron beams in an open atmosphere (i.e., corona beams) and electronic instrumentation to measure the constructive and destructive harmonics of the frequency loaded electronic corona discharge from the holes or anomalies in order to characterize, qualify and quantify their integrity for their prescribed performance criteria on a 100% basis.

Background

For many decades, experts in the rubber molding and forming field have been actively engaged in the technology of non-destructive testing. During this period, they have covered a wide range of industries and applications. As a result, many technical societies have developed to form a valuable resource network. This network is well versed in many different industries that include metalworking, shipbuilding, aerospace, power plants and numerous advanced non-destructive technology techniques. These non-destructive techniques cover a wide range of scientific disciplines. These disciplines could range from the series of different gas leak detection methods to vacuum valuation methods for hermetic seal validation. They include but are not limited to the following: X-ray, magnetic particle, radiography, ultrasound, eddy current and visual flaw detection. Visual testing (VT), the world's oldest NDT method, is becoming more sophisticated by the incorporation of other conventional methods such as advances in fiber optic boroscopes, miniature television cameras, imaging chips and others. These technical methods all serve their purpose and work well for the type of product that they are designed to test. However, there is always room for another method that has its own inherent limits and still has other inherent capabilities that are not proficient or possible by the more conventional approaches.

Things like holes or voids may be formed during the manufacturing of the rubber products in the forming process, in a coating process or in a sealing process. Accordingly, the present technology has been developed for the testing, measuring and characterization of the porosity and detection of anomalies in materials to certify materials to a desired performance level. In particular, the present technology has been developed for the on-line, real-time, non-destructive, non-contact, non-abrasive, 100% dry testing and measuring of rubber and rubber-like performance materials. These materials include thin film protective barrier materials; for voids, holes or anomalies having a diameter as large as a millimeter to as small as one nanometer. Moreover, the present corona beam technology can detect anomalies in the material, such as contamination, blisters, bubbles, un-catalyzed or unblended resin, low density material (e.g., weak molecular crosslinking strength areas), high density material, overlapping material, measured thickness, stress fractures, formulation defects and other structural and non-void anomalies. In the meantime, this technology can be calibrated to certify a very narrow or very high range of acceptability for products that are designed to have a degree of porosity and permeability, such as spun bonded materials, filtration media, filtration membranes, protective clothing, evaporation breatheable weather barriers and medical devices.

Products and materials used as barriers against viruses and bacteria must and should have their porosity and anomaly presence determined in order to insure that no imperfections are present or may be formed by processing, which would permit the passage of a virus or bacteria. These bacteria and viruses may be as small as twenty nanometers in diameter. These disease causing elements can be transmitted by external environmental moistures and internal body fluids, since it is the open atmosphere moisture and body fluids that transport the infecting agent. It is therefore most beneficial to test all barriers down to a single digit micron level for maximum protection.

It is also critical for manufactured materials that will be used as structural components or sub-components of larger assembled items. Testing with this process is not limited to thin materials. However, the most economical application will be achieved on coatings and thin materials where production processing speeds play a major part in the cost of production.

The U.S. NIH funded the original proof of concept model that was presented to a group of NIH and FDA scientists for comments on practical applications. The U.S. FDA purchased the first prototype that was used in a study that conclusively (100%) discovered holes and anomalies in latex and polyurethane condoms and also with other types of synthetic surgical glove material. The test was performed from one micron and above in an approximate time of one second per item. This accuracy assures the barrier will prevent atmosphere and body fluid transmission, thus, viral transmission. In the year 2000, a major producer of latex and polyurethane condoms and surgical grade gloves licensed the technology for validation of their production products to a revolutionary and innovative industry protective level of 100% integrity testing level of one micron and above testing for their product lines.

The actual capable accuracy is to 0.5 nanometers. This puts real-time measured integrity testing on an atomic level.

Technology

In general terms, the integrity or presence of anomalies in or on a rubber material is determined by using an electronic sensor in an open atmosphere under a fluid cover gas, or a flow of a cover gas. The cover gas is directed at the material and, if there is a small aperture, hole or anomaly in the material, a change in the electronic charge or "corona beam" (also known as an electron beam, an electrostatic corona or a corona discharge) occurs, which is measured by an AM radio pick-up sensor. The corona beam gun comprises an electrode and a sensing mechanism which records electrons that are drawn through the hole or anomaly in the barrier material. The sensor also contains a series of focusing resistors for attenuating the beam. The occurrence of this change in discharge is due to the Griebel-Gormley aperture effect, (referred to herein as the "aperture effect") (figures 1 and 2).

[FIGURES 1-2 OMITTED]

It should be noted that testing for anomalies in the material include, but are not limited to, contamination, blisters, bubbles, un-catalyzed 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. In the characterization of materials, a prescribed range of acceptability can be calibrated. This means that a "window" of desirable sized permeable material can be measured to reject, mark or numerically value against a calibration standard. The items measured include porosity, permeability and the consistency of the material's signature. The corona beam carries an applied frequency that creates a consistent "noise" (i.e., signature) when it passes through normal material that has a solid or permeable designed structure. The electronic corona beam with its imposed frequency will always flow through the structure of the test material. It is the destructive interference of the frequency moving through the material with the electronic corona beam that is digitally compared to the calibration standard for valuation.

It should also be noted that the overall design of the system is based on the type of material being tested and the perceived or desired outcome required. The diameter of the anode needle's tip in the corona beam sensor gun, the quality of the needle material (e.g., barium, platinum, gold, silver), and the heating of the anode and cathode needle tips are factors that relate to the quality and length of the electronic corona discharge (i.e., the corona beam) that is detected and quantified.

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 for characterization, such as the frequency, the amplitude, the wave shape and the voltage. The proper combination of these factors leads to the ability to detect and monitor sub-micron sized permeability, porosity, apertures, holes or anomalies in the material being tested. All of these components can be tuned to a prescribed calibration standard.

Figures 3-6 illustrate the sizes and types of anomalies and that this technology can pinpoint their location on a sheet of PTFE filtration material. SEM photos could further identify the types of anomalies that are normally not detected. This creates the basis for a digital "look-up table" for identifying anomalies for process control.

[FIGURES 3-6 OMITTED]

The aperture effect is based on the point-to-point effect, a well known effect in physics. The point-to-point effect, in practical terms, is the passage of a static electrical charge from a cathode electrode to an anode electrode in an open atmosphere, i.e., static electricity from a carpet in a dry room and collected by your body and then discharged when you get near a grounded item is an example. The aperture effect is shown by the use of a smooth, grounded cylindrical cathode electrode (i.e., approximately cylindrical) in proximity to a needle tip anode electrode (a needle point). Very few electrons (or corona discharge) are discharged if the voltage is too low. But when the cathode is masked with a thin film material containing a very small void of material (a hole or anomaly), an electrical cathode electrode point is masked out on the grounded cathode. A point-to-point effect is created on a microscopic level, and electrons flow from the cathodic roller through the hole or anomaly in the thin film material to the anodic tip of the corona beam gun without increasing the applied voltage. This flow of electrons (the corona beam) carries a prescribed frequency that is measured to determine the amount of constructive and destructive changes that occur in the frequency. Most important to understand is that the corona electrons are always flowing through the material. The electrons of the corona beam do not crash or are like lightning or as a static electric discharge. The corona electrons that flow through the material at the location that is pre-defined as "good material" creates the material's baseline signature. It is from this baseline signature that the range of acceptability is established. The amount of change can then be compared to a library of calibration readings contained in the digital controller system for comparative identification and analysis. The system can also be set to a range of acceptability for a pass-fail response. It is important to note that a tremendous amount of data is produced and is easily digitally filtered and processed in a presentable format (figures 7 and 8).

[FIGURES 7-8 OMITTED]

A cover gas is also important in achieving the aperture effect. Typical cover gases include nitrogen, non-combustible gases, noble gases and dehydrated air. The results vary with the particular cover gases used. It makes a dramatic difference whether nitrogen is used as opposed to dry air, neon or other noble gases and other attractive sources. The flow rate and gas pressure are also important factors; at higher gas pressure there is more gas flow and the beam lengthens. As the pressure increases, the gas becomes denser and the electrons flowing from the cathode to the anode move slower. It should be noted that the beam may move or wander in the cover gas environment. The beam is self-seeking within the material's focal area. The focal area is the circular area of the test material being hit by the fluid cover gas. Thus, the beam moves in the area of the material bounded by the fluid cover gas in order to locate a properly sized aperture or anomaly. The pressure of the gas creates a focal area on the surface of the test material that can vary based on the required parameters.

Other important factors in the creation of the aperture effect are the power supply's voltage, the frequency of the pulsed D.C. signal and the distance from the cathode to the anode electrodes. 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, i.e., the cylindrical roller, the aperture effect will be lost. However, this can be alleviated when a conductive noble gas or other energy source is grounded and used to supplement the difference in the conformal space required between the material and the cylindrical mandrel.

Figure 9 is a simplified comparison of a corona beam and a laser beam. The laser beam uses a series of glass focusing lenses to draw the photon light energy to a point so that it can be effectively used to perform much different types of operations. The beam is projected to the work piece so, in a mechanical sense, it can cut, weld, etc. In the case of the corona beam, the electrons are drawn from the cylindrical cathode electrode side of the material to the anode electrode side with test material between the two electrodes. To create the corona beam's aperture effect through the material, it is the relative dielectric weakness of the test point in the material in the focal area relative to the more dielectric strength of good solid material that induces the flow of electrons of the corona beam. The raw energy from the power supply is drawn through a series of resistors to develop a very high density attenuated negative field at the end of the anodic needle tip inside the corona beam gun.

[FIGURE 9 OMITTED]

Current state of rubber testing

In the ideal universe of in-line process packaging, packages would be "100% non-destructively tested and 100% validated." This would include in-line packaging materials, formed containers, receptacles and blisters, the confirmation that the delivery process has correctly delivered a suitable product, and that the overall integrity of the outside of the package and the inside atmosphere is validated. The validation of the atmosphere inside a package provides a sure indication that the thermal seals on the package are correct.

Very little in-line testing and validation of materials and packages is being performed. Manufacturers rely on a series of destructive and non-destructive off-line statistical based tests. These statistically based methods are time consuming, are often a costly destructive process and are a gray measurement in comparison to 100% in-line process validation.

Statistical testing has many downfalls, other than some of it is destructive. The positive side of the argument is that it is popular because it has been the standard method and is relatively easy to do, with written ASTM standards to follow. However, some of these tests are very subjective and heavily rely on the skills of the tester, and are not always easy to confirm.

There have been many new innovative testing products introduced in the last several years that save time and are non-destructive. However, they are still off-line and statistically based. Some of the technology instruments are near-infrared light sensors that cover a range of inspection aspics. There is automated strain gauge technology. There is a vacuum decay system. There are pressure test systems. There are mass-flow sensing systems. There are tension, compression and flexural test methods and systems. There are digital force gauge systems that can pull, compress, peel, burst and crush. There are camera systems that can identify the presence of a pill in a blister package. There are systems that can count pills. There are systems that can measure gross over-fill and under-fill. However, there is only one technology that can be applied to perform all the above listed tasks 100% of the time, non-destructively, in-line and in real-time.

The corona beam technology has the capability to perform one or several of the validation tests that are listed above in a single system. It is done very simply by defining what you want tested and what you want from the test. Those features can be custom built into a system that will take benchmark measurements from the ideal package and build a series of acceptance or calibration parameters into the test system. The selection of the operations that a customer would want to have performed with this technology is based on what they feel are the critical aspects to the final package being validated. It is these types of effective cost comparisons with the current methods that will cost-justify the on-line system and the enhanced characteristics of the technology.

Application

Once the corona beam system's foundation resources are in place, such as the power supply and digital controller, the system has modular add-on capability for additional test locations at a fraction of the initial components' cost. There can be multiple test stations for many different aspects of the package process, while performing unrelated tasks. These can range from the integrity of a glass vial to the presence of bubbles in liquid fills; and at the same time perform a packaging film validation process, a gross over-under fill validation, validation of the presence or absence of a tablet or pill, and even container atmosphere validation. Vials, ampoules and syringes can have their glass integrity validated, since the harmonic frequency resonance of a fractured, cracked, or chipped item will resonate out of a normal and acceptable range.

Simply stated, the truly unique aspect of this technology is that the corona beam is drawn and not projected. The beam will follow a tortuous path through materials and containers, and can curve to follow its anodic high voltage potential in milli-amps or micro-amps, which makes it non-destructive. The process is performed non-destructively in a corridor of cover gas while on-line in an open atmosphere for 100% inspection and validation for the customers' critical packaging needs (figure 10).

[FIGURE 10 OMITTED]

The application of this technology as it relates to flexible barrier material can be applied in numerous ways and at several process levels. Some of these approaches have been mentioned in the previous text. The first format would be to test and certify the raw or initial processed barrier film. The manufacturing facility has the opportunity to certify that the manufactured film meets a prescribed and now-certified quality barrier level. The manufacturer has an opportunity to analyze the quality right after the aggregate has been converted. 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 process line, the product could be tested with a series of sensors that would account for the entire area of the product's surface (100%) by a moving or stationary gantry, with an array of beams each averaging a focal area of an eighth of an inch to a full half inch diameter. The method of reject removal from the process is critical and many different options for handling are available. The basic idea is to eliminate the labor factors of re-handling the product in off-line statistical testing and keep the cost as low as possible by testing on-line (figure 11).

[FIGURE 11 OMITTED]

Another format is to test for the consistency of permeability. This would create a range requirement for air or gas permeability. This would accommodate the requirements for the different types of sterilization that are currently being used and would also have the ability to facilitate other newer sterilization methods. The permeability level could also be calibrated and certified so that consistency is maintained. This would prevent some material from sneaking through off-line statistically based tests on a gray level. The third integrity test of barrier applications for this technology is to certify a range of acceptability for filtration material. A sieve requirement or strainer level can be well defined on a very stringent level with a close level of tolerance. Porosity distribution can be measured and characterized to ensure the even allocations and distribution of pores throughout the area of the material.

The technology also has other unique applications that can be food for thought for this readership. Since we can test for blisters and bubbles in fiat material, a similar type of test, for validation, has evolved that provides for testing sealed material. After the product has been sealed in the pouch or blister, etc., if there has been an atmosphere change due to the addition of a head gas or a drawn vacuum, the atmosphere in the pouch, vial, syringe, etc., has been altered. The corona beam passing through the sealed container will provide a signal that validates that the gas has not escaped and that, at that point in time, there is a solid sealed package. Thus, not only do you have the chance to validate the integrity of several components, but also of the final package seal and atmosphere in the container.

Conclusion

This corona beam technology can be validated by the current standard mechanical tests that are used on a destructive or non-destructive statistical basis. So don't throw out the tried and true methods of validation. They will still be needed to calibrate the corona beam technology's validation systems. The fact of the matter is that you will need to use them much less.

The corona beam technology has the capability to address many different customer concerns. We rely on our present and future customers to challenge us with their unique requirements so that more applications can be developed, that on-line testing can be increased and that validation can be simplified. We also rely on these developments so that we can pass them along to other customers who may have similar needs and requirements.

Now the technology is available to validate the integrity of barrier and porous packaging films and test flexible barrier material 100% to an application standard that will be precise, certified and confirmed to an exact calibration level. At the same time you will have the opportunity to be saving money and time in each part of the manufacturing and packaging process chain. You will also have the opportunity to include other areas of the production process for validation that, by themselves, would have been too difficult to cost-justify.