Patent Application
20170062172
The present disclosure is directed towards electron beam apparatuses, and more particularly, electron beam apparatuses having an adjustable air gap.
An electron beam processing apparatus is commonly used to expose a substrate or coating to highly accelerated electrons, for example, in the form of an electron beam (EB), to cause a chemical reaction on the substrate or coating.
An electron is a negatively charged particle found in all matter. Electrons revolve around the nucleus of an atom much like planets revolve around the sun. By sharing electrons, two or more atoms bind together to form molecules. In EB processing, electron beams are used to modify the molecular structure of a wide variety of products and materials. For example, electrons can be used to alter specially designed liquid coatings, inks, rubbers, and adhesives. During EB processing, electrons break bonds and form charged electrons and free radicals. These radicals then combine to form large molecules. By this process, the liquid is transformed into a solid. This process is known as polymerization.
Liquid coatings treated with EB processing may include printing inks, varnishes, silicone release coatings, primer coatings, pressure sensitive adhesives, barrier coatings, barrier layers, and laminating adhesives. EB processing may also be used to alter and enhance the physical characteristics of solid materials such as paper, plastic films, substrates (including, e.g., non-woven textile substrates), and polymeric materials (such as elastomers), all specially designed to react to EB treatment.
An electron beam processing apparatus may generally include three zones. A vacuum chamber zone where the electron beam may be generated, an electron accelerator zone, and a processing zone. In the vacuum chamber, a tungsten filament may be heated to about 2400 K, which is the electron emission temperature of tungsten, to create a cloud of electrons. A positive voltage differential may then be applied to the vacuum chamber to extract and simultaneously accelerate these electrons. Thereafter, the electrons may pass through a thin foil and enter the processing zone. The thin foil functions as a barrier between the vacuum chamber and the processing zone. Accelerated electrons exit the vacuum chamber through the thin foil and enter the processing zone at atmospheric conditions.
The accelerated electrons that enter the processing zone are directed to the substrate that is to be treated. Between the thin foil support assembly and the drum or other apparatus that supports the substrate is an air gap, which the electrons cross to reach the substrate. The distance of the air gap for an electron beam system is fixed based on the positioning of the electron beam apparatus and the processing assembly (e.g., rollers or drums feeding the substrate). The air gap distance may be set based on several intended processing variables, for example, the operating voltage, product, processing speed, etc.
More recently, electron beam processing apparatuses have been developed that operate at both lower voltage (e.g., 110 kV or less) and higher voltage (e.g., 110 kV or greater) at increased efficiency. Some examples of these systems are described in U.S. Pat. Nos. 6,426,507; 6,610,376; 7,026,635; and 7,348,580, which are incorporated herein by reference in their entireties.
Despite the advances and improvements in electron beam processing apparatuses, a need exists for more versatile electron beam processing apparatuses capable of maintaining efficiency when operating at both high and low voltage and capable of maintaining efficiency processing a variety of products. The present disclosure is directed to improved electron beam processing apparatuses and method of operation.
In one embodiment, the present disclosure is directed to an electron beam processing apparatus for treating a substrate. The apparatus may include an electron beam generating assembly housed in a chamber that includes a filament for generating a plurality of electrons upon heating. The apparatus may also include a foil support assembly that is configured to direct the plurality of electrons through a thin foil out of the chamber. The apparatus may further include a processing assembly that is configured to pass the substrate by the thin foil so that the plurality of electrons penetrates the substrate and causes a chemical reaction. A distance of an air gap between the thin foil and the substrate is adjustable.
In another embodiment, the present disclosure is directed to a method of treating a substrate with an electron beam processing apparatus. The method may include generating a plurality of electrons using an electron beam generating assembly by heating a filament within a chamber of the assembly. The method may also include directing the plurality of electrons out of the chamber and through a thin foil located within a foil support assembly. The method may further include feeding the substrate into a processing assembly and passing the substrate in front of the thin foil so that the plurality of electrons penetrates the substrate and causes a chemical reaction. The method is also to include adjusting a distance of an air gap between the thin foil and the substrate.
In another embodiment, the present disclosure is directed to an electron beam processing apparatus for treating a substrate having an adjustable air gap.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the present disclosure and together with the description, serve to explain the principles of the present disclosure.
The term “about” or “approximately” as used herein means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, e.g., the limitations of the measurements system. For example, “about” can mean within one or more than one standard deviation per the practice in the art. Alternatively, “about” can mean a range of up to 20%, such as up to 10%, up to 5%, and up to 1% of a given value.
Electron beam generating assembly 110 may be kept in a vessel or chamber 114 that is a vacuum environment. Chamber 114 may be constructed of a tightly sealed vessel. A vacuum pump 212 (shown in
When heated, filament 112 may glow white hot and generate a cloud of electrons. Because the electrons are negatively charged, the electrons may be drawn from filament 112 to areas of higher voltage and accelerated to extremely high speeds. In some embodiments, filament 112 may be constructed of one or more wires, which may be made, for example, of tungsten.
As shown in
Extractor grid 116 may operate at a slightly different voltage, for example, higher than that of filament 112. Extractor grid 116 may attract electrons away from filament 112 and guide them toward terminal grid 118. Extractor grid 116 may be configured to control the quantity of electrons being drawn from the cloud, which determines the intensity of the electron beam.
Terminal grid 118 may operate generally at the same voltage as extractor grid 116, and terminal grid 118 may be configured to act as the final gateway for electrons before they accelerate to extremely high speeds for passage through foil support assembly 140.
As shown in
High-speed electrons may pass freely between the copper ribs, through thin foil 142, and into substrate 10 being treated. To minimize undue energy loss, thin foil 142 may be made as thin as possible while at the same time providing sufficient mechanical strength to withstand the pressure differential between the vacuum state inside chamber 114 and ambient conditions for processing assembly 170. In some embodiments, thin foil 142 of the foil support assembly may be made of, for example, titanium or alloys thereof and may have a thickness of about 12 micrometers or less (e.g., 10 micrometers, 9, micrometers, or 8 micrometers). In some embodiments, thin foil 142 may be constructed of aluminum or alloys thereof and may have a thickness of about 15 micrometers or less.
Processing assembly 170 may include a plurality of components and mechanisms configured to direct substrate 10 past thin foil 142. A protective lining may surround the periphery of processing device 100, such as evacuated chamber 114 and processing assembly 170. The protective lining may be configured to absorb substantially all X-rays created when electrons decelerate in matter. The thickness and material selected for the protective lining may be determined, at least in part, by the desired absorption rate of the X-rays.
Dose is the energy absorbed per unit mass and is measured in terms of megarads (Mrad), which is equivalent to 2.4 calories per gram. A higher number of electrons absorbed reflect a higher dose value. In application, the desired dose is commonly determined by the material of the coating and the depth of the substrate to be cured. For example, a dose of 5 Mrad may be required to cure a coating on a substrate that is made of rice paper and has a mass density of 20 gram/m2. Alternatively, a dose of 7 or 10 Mrad may be required to cure a substrate that is made of rubber and has a mass density of about 1000 gram/m2 or about 2000 gram/m2, respectively. Dose is directly proportional to the operating beam current, which is the number of electrons extracted, and inversely proportional to the feed speed of the substrate, as expressed by the following formula:
Dose=K·(I/S)
whereby I is the current measured in mAmp, S is the feed speed of the substrate measured in feet/min, and K is a proportionality constant, which represents a machine yield of the processing device, or the output efficiency of that particular processing device.
The amount of dose delivered and the location of dose delivery may be manipulated by adjusting a variety of variables, for example, the thickness of the thin foil, the size of the air gap, and the voltage at which the electron beam processing apparatus is operated. The desired dose amount and location may be calculated based on the substrate and use of the assembly. For example, a low operation voltage is usually used in conjunction with thinner foils to cure the surface of thinner substrates. With a lower voltage, the electrons move at slower speeds, and with a smaller air gap and thinner foil, less electron energy losses in air will occur in the foil and the air gap. This will result in a higher deposition of dose and thus yield efficiency at the surface and shallower dose penetration in the substrate. By contrast, higher operation voltages are usually used for thicker substrates to achieve a lower surface dose and deeper dose penetration. With higher voltages, energy loss is less of a concern, so a larger air gap and thicker foil can be used to decrease the surface dose and increase the dose delivered at a deeper substrate depth.
The electrons accelerated through thin foil 142 may cross air gap 150 before penetrating substrate 10. As the electrons travel across air gap 150, the air present may become heated due to electrons being stopped in the air and energy transfer taking place resulting in heat increase from the slowing and stopping of electrons. The temperature of the air within air gap 150, which is adjacent thin foil 142, may affect the life of thin foil 142. For example, if the air temperature in air gap 150 becomes extremely hot, it may reduce the life of thin foil 142, leading to premature failure. The air temperature in air gap 150 may depend on a variety of parameters, including for example, the speed of the electrons and the distance of air gap 150. For example, the greater the distance of air gap 150, the hotter the air temperature due to the increased heat created by low energy electrons being stopped and slowed down as they pass over the distance of air gap 150. Additionally, as the electrons travel through air, they may stop and/or slow down and lose energy due to momentum transfer. Therefore, a larger air gap will increase the distance the electrons must travel through air, resulting in a greater loss of electron energy over that distance, whereas a smaller air gap will reduce the distance travelled by the electrons, resulting in a smaller loss of energy.
Other factors may also be considered in determining a suitable air gap 150 distance for an electron beam processing apparatus 100. For example, a minimum air gap 150 may be established based on substrate 10. For example, the minimum air gap 150 distance between foil 142 and substrate 10 may be such that substrate 10 may pass by thin foil 142 without interfering or contacting thin foil 142 and/or foil support assembly 140. The minimum air gap 150 may vary based on the type of substrate 10 and/or the thickness of substrate 10. The operating voltage (chosen because of certain penetration depth requirements in the substrate for some applications) of particle beam generating assembly 110 may also be another factor considered in determining the air gap 150 for an electron beam processing apparatus 100. For example, at lower voltages (e.g., 110 kV to 125 kV), it may be preferable to have a reduced air gap 150 to minimize energy losses in air of electrons. At lower voltages, because of shallow electron energy depth requirement, energy loss due to air gap distance may be of greater concern. In contrast, at high voltages (e.g., 125 kV to 300 kV) energy losses in air of electrons may be less of a concern, and thus the distance of air gap 150 may be increased. In some embodiments, for higher voltages, increased air gap may be desired to maximize efficiency (K-value) resulting in higher product speed at fixed dose.
Traditional electron beam processing apparatuses have an air gap 150 of a fixed, pre-determined distance. The distance of air gap 150 may be calculated at time of system design based on the intended use of that particular apparatus. For example, the ideal air gap may be calculated based on intended substrate product which fixes the operating voltage, to maximize efficiency (K-value) to allow desired commercial speed of process, and the apparatus is built to reflect the air gap calculated for those specific criteria. As a result, if any of the parameters are later changed, for example, the substrate and the depth to cure the substrate and thus the desired operating voltage change, the distance of air gap 150 may no longer be optimal for the new product or operating voltage, thereby causing a loss in efficiency.
In the example shown in
Electron beam processing apparatus 100, according to an exemplary embodiment, resolves this issue by being configured such that the distance of air gap 150 is adjustable. The ability to adjust air gap 150 broadens the penetration ranges that may be achieved using a single apparatus 100 and does so while optimizing production speeds and machine uptime. Using electron beam processing apparatus 100 may allow a user to easily adjust air gap 150 to meet the new product requirements. For example, using processing apparatus 100, the air gap may be adjusted to 19 mm and the apparatus may then operate 300 kV with a thin foil 142 thickness of 12 microns, which may obtain 100% dose at a depth of 275 gram/m2, as shown in
In
For some applications, a product substrate may require a very shallow electron penetration requiring less than 100 kV, e.g., because the product requires just surface dose and very limited penetration in the substrate. For some electron beam processing systems, if the minimum operating range is 100 kV this could create a challenge. However, process apparatus 100 as described herein may increase the air gap, thereby one may effectively limit electron penetrate to less than 100 kV, even though the minimum machine capability is 100 KV.
For example, using electron beam processing apparatus 100 with a 12.5 micron foil at an air gap of 19 mm and a voltage of 121 kV would produce a yield of 1 normalized, as measured by dosimetry. On the other hand, using a 12.5 micron foil with an adjusted air gap of 22 mm and a voltage of 121 kV would produce a yield dose of 0.9 normalized, as measured by dosimetry. Accordingly, in this example, reducing the air gap would increase the machine efficiency increased by 10% when operating at 121 kV.
In another example, to optimize the machine efficiency at 100 grams/m2 at 200 kV on the same machine, the air gap could be increased. In one example, machine efficiency, as measured by dosimetry results, would be 1.07, normalized, using a 12.5 micron foil with an air gap of 22 mm and a voltage of 200 kV. Using a 12.5 micron foil with an air gap of 19 mm and a voltage of 200 kV on the same machine would result in an efficiency of 1.0, normalized. In this example, the electrons may have more energy when approaching the product substrate using a reduced air gap than the electrons would otherwise have with a higher air gap. With a reduced air gap, the electrons would have less of a propensity to slow or stop and instead would deposit the dose when meeting the substrate rather than continue to move through the substrate. As a result, the machine yield would be higher at 200 kV with a higher air gap than with a lower air gap. The opposite would be seen with a low voltage, in which the electrons would slow when moving across the larger air gap and would deposit when meeting the substrate surface. Thus requiring adjustable air gap on these versatile EB machines varying from low voltages 70 kV to higher voltages 300 kV as determined by various product requirements and its electron penetration depths.
In some situations, a manufacturer using an electron beam processing apparatus may know from the start they are going to process a variety of different substrates requiring different depths of electron penetration and thus requiring operating at a variety of different voltages. In these situations, the distance of the air gap has traditionally been calculated based on one substrate type its electron depth requirement and thus the voltage, or the distance of the air gap may be calculated based on an average of the substrate types and average depth requirements and thus the voltages. However, regardless of the method in used to calculate the distance of the air gap, at times the apparatus will be operating at a less-than-optimal air gap, which reduces efficiency.
As described herein, an electron beam processing apparatus with a permanently set gap can broaden the depth of penetration ranges by changing the voltage applied, but simply changing the voltage to attain different depth of penetration ranges will also affect production speed and foil life, which ultimately shortens yield. One may operate at lower depths of penetration and thus lower voltages, for example with a 12.5 micron foil, but as taught in earlier patents, the energy absorbed by the foil at these lower voltages will increase substantially. This will result in premature foil failure unless one restricts the mA resulting and in combination with lower yields will result in lower product speeds making this technology not commercially viable. As described herein, another option is to change the thin foil thickness by changing the window foils as various substrates are processed, but as described herein, changing the window foil is time consuming.
Electron beam processing apparatus 100, according to an exemplary embodiment, resolves this issue by being configured such that the distance of air gap 150 is adjustable. The ability to adjust air gap 150 broadens the penetration ranges that may be achieved using a single apparatus 100 and does so while optimizing production speeds and machine uptime. Being able to vary the distances between thin foil 142 and substrate 10, along with changing the voltage applied, makes apparatus 100 able to more closely control the dose of energy delivered and the dose penetration depth with a single apparatus, while also allowing for differences in heat loads, production speed, and up-time yield. By doing so, apparatus 100 may efficiently accommodate a variety of substrate types and uses. Apparatus 100 may enable broader processing capabilities for multitudes of products that each requires different depths of dose penetration and energy in a manner that cannot be achieved using current technology.
In some embodiments, the distance of air gap 150 may be adjustable by changing the positioning of one or more components of processing assembly 170. In some embodiments, the distance of air gap 150 may be adjustable by changing the positioning of substrate 10 relative to thin foil 142 such that the position of substrate 10 changes while the positioning of thin foil 142 stays the same. In some embodiments, the distance of air gap 150 may be adjustable by changing the position of thin foil 142 such that the position of thin foil 142 changes, while the positioning of substrate 10 remains the same. In some embodiments, the distance of air gap 150 may be adjustable by changing the position of both thin foil 142 and one or more other components of processing assembly 170.
In some embodiments, when apparatus 100 is curing a product that is about 50 gram/m2 thick, it may be desirable to reduce the voltage to, for example, 150 kV, to reduce the velocity and kinetic energy of the electrons. Correspondingly, apparatus 100 may be configured to also reduce the distance of air gap 150 so that the energy loss in the air is less, thereby increasing the surface dose and enabling optimization of the dose on the surface. This optimization may allow for increased production speed, which is typically desired. In some embodiments, apparatus 100 operating at even lower voltages (e.g., about 110 kV and 60-70 kV) with a 10 micron and 5 micron thin foil 142 thickness, the efficiency and dose may be increased by 20-30%. This may be attributed to changing of the scattering angle of the electrons. Scattering angle is described in detail in U.S. Pat. No. 4,952,814, which is incorporated herein by reference in its entirety.
In some embodiments, apparatus 100 having a thin foil 142 thickness of 10 microns may be configured to have an air gap 150 of about 9.5 mm when operating at a voltage of between about 100 kV to about 125 kV and may have an air gap 150 of about 7.5 mm when operating at a voltage between about 60 kV to about 100 KV. In some embodiments, apparatus 100 having a thin foil 142 thickness of 12.5 microns may be configured to have an air gap 150 of about 9.5 mm when operating at a voltage of between about 100 kV to about 150 kV and an air gap 150 of about 19 mm when operating at a voltage between about 150 kV to about 200 kV. In some embodiments, apparatus 100 having a thin foil 142 thickness of 12.5 microns may be configured to have an air gap 150 of about 9.5 mm when operating at a voltage between about 125 kV and 150 kV and an air gap 150 of about 19 mm when operating at a voltage between about 150 kV and 300 kV. It is contemplated that other air gap 150 distances and ranges of operation (e.g., voltages, and thin foil thickness) may be utilized depending on a number of variables (e.g., substrate type, substrate thickness, desired speed of operation, etc.).
Electron beam processing apparatus 100, as shown in
First roller 181 and second roller 182 may include a first adjustment mechanism 191 and a second adjustment mechanism 192 attached to first roller 181 and second roller 182. First adjustment mechanism 191 and second adjustment mechanism 192 may be configured to adjust the position of first roller 181 and second roller 182, respectively. For example, first adjustment mechanism 191 and second adjustment mechanism 192 may be actuators configured to adjust the positioning of first roller 181 and second roller 182 along an axis Y. First adjustment mechanism 191 and second adjustment mechanism 192 may be, for example, hydraulic actuators, pneumatic actuators, electrical actuators, or any other suitable type of actuator. When pneumatic actuators are used, the compressed air may be supplied by a pneumatic system within the processing or manufacturing facility.
Electron beam processing apparatus 100, 1100 may further include a controller 200, such as a computerized microprocessor, to control operation of apparatus 100, 1100. Controller 200 may be configured to control several processes including but not limited to maintaining the required vacuum environment within chamber 114, receiving inputs from an operator, initiating system operation with predetermined voltages and filament power, synchronizing electron generation with process speed to maintain constant treatment level, monitoring functions and interlocks, controlling adjustment mechanisms (e.g., 191, 192, 180) to set the distance of air gap 150, and providing warnings and/or alarms whenever the system functions exceed set limits or an interlock problem is detected. Adjustment mechanisms may be manual or automated. For example, a user may input substrate parameters, and apparatus 100, 1100 may automatically be adjusted. Some embodiments may include one or more sensors that are configured to detect one or more characteristics substrate 10 or apparatus 100, 1100 and may automatically make adjustments based on those characteristics. Even if automatic, however, apparatus 100, 1100 may include a manual override.
In some embodiments, apparatus 100, 1100, may further include a temperature sensor 300 that generates a signal indicative of an air temperature within air gap 150, and temperature sensor 300 may be configured to transmit the signal to controller 200. In some embodiments, controller 200 may be configured to adjust the distance of air gap 150 based on the signal from sensor 300. Apparatus 100, 1100 may also include other sensors, e.g., those configured to detect a weight or thickness of a substrate or an actual operating voltage of the apparatus.
In some embodiments, electron beam processing apparatus 100, 1100 may operate as follows. Vacuum pump 212 may evacuate air from chamber 114 to achieve a vacuum level of approximately 10−6 Torr, at which point processing apparatus 100 may be fully operational. Electron generating assembly 110, including repeller plate 120, extractor grid 116, and terminal grid 118, may be set at three independently controlled voltages that initiate the emission of electrons and guide their passage through foil support 144 and thin foil 142. Controller 200 may be configured to control the voltages of repeller plate 120, extractor grid 116, and/or terminal grid 118. In some embodiments, an operator may manually input the voltages, or in some embodiments, an operator may input just one operating voltage and controller 200 may automatically determine the independent operation voltages of the different components. In some embodiments, an operator may just input a substrate type and/or operating speed and controller 200 may determine the operating voltages based on that input.
Operation of apparatus 100, 1100 may also include adjusting the distance of the air gap between thin foil 142 and substrate 10, as discussed herein. The distance of air gap 150 may be adjusted, for example, prior to the start of operation. In some embodiments, the distance of air gap 150 may be adjusted during operation. In some embodiments, controller 200 may be configured such that a set point for the distance of air gap 150 may be determined based on at least one of an operating voltage for the electron beam generating assembly, the type of substrate 10, the thickness of substrate 10, and/or the desired speed of production (i.e., speed of substrate 10). In some embodiments, an operator may input or set the distance of air gap 150 using controller 200. In some embodiments, an operator may input the type of substrate 10 into controller 200, and controller 200 may be configured to automatically determine an optimal operating voltage and an optimal distance of air gap 150. In some embodiments, controller 200 may also regulate the quantity of electrons generated so the electron beam output is proportional to the feeding speed of substrate 10. Electron beam processing apparatus 100, 1100 may be calibrated to achieve high-precision specification, because controller may provide the exact depth level of cure desired on substrate 10. Controller 200 may calculate the dose and the depth of electron penetration into substrate 10. The higher the voltage, the greater the electron speed and resultant penetration.
During the electron beam processing, a combination of electric fields inside evacuated chamber 114 may create a “push/pull” effect that guides and accelerates the electrons toward thin foil 142 of foil support 144, which is at ground (0) potential. The quantity of electrons generated may be directly related to the voltage of extractor grid 116. At slow production speeds, extractor grid 116 may be set at a lower voltage (e.g., by controller 200) than at high speeds, when greater voltage may be applied. As the voltage of extractor grid 116 increases, the quantity of electrons being drawn from filament 112 may also increase.
The coatings to be cured, for example, inks, adhesives, and other coatings, generally require a low-oxygen environment to cause the chemical conversion from a liquid state into a solid state. Therefore, in some embodiments, electron beam processing apparatus 100, 1100 may also include a plurality of nozzles (not shown) distributed in processing assembly 170 to inject gas (other than oxygen) to displace the oxygen therein. In some embodiments, nitrogen gas may be pumped into processing assembly 170 through the plurality of nozzles to displace the oxygen that would otherwise prevent or inhibit complete curing.
In each of the embodiments described herein, apparatus 100, 1100 may be adjustable along discrete, pre-determined intervals, or may be adjustable along a continuous range of distances. In some embodiments, apparatus 100, 1100 may have a maximum and/or minimum air gap distance beyond which the apparatus cannot be adjusted. For embodiments incorporating a controller, apparatus 100, 1100 may be adjustable by a user on-site and/or a user may be able to adjust the apparatus from a remote locations.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims and their equivalents.
| Number | Date | Country | |
|---|---|---|---|
| 62209951 | Aug 2015 | US |
