Ultraviolet Curing System and Process
Stephen B. Siegel President U. V. Process Supply, Inc. Chicago, Illinois |
| Ultraviolet light is commonly used for the cross-linking or polymerization of inks, coatings, and adhesives for any manufacturing applications requiring fast drying techniques, or methods of coating which contain little or no solvents and are non-polluting. Ultraviolet lamps which emit ultraviolet light are very useful but gradually lose a significant portion of their energy Output because of wear or accumulated dust, dirt, or other debris, causing varying, uneven and progressively longer curing and drying times which creates non-uniform products and many problems. High energy ultraviolet lamps typically lose their effective output ofenergyover time, because of degradation of the quartz envelop such as from wear or foreign materials acting on the surface of the quartz, causing it to vitrify or degrade, which blocks the transmission of the ultraviolet light. Lamps cleaning and maintenance can be very costly because of the inaccessibility of the lamps, loss of production time due to maintenance, and labor costs associated with the maintenance. The reflectors used to focus the light energy from the ultraviolet lamps to the product being exposed will also lose their reflecting properties over time due to various factors, such as the high operating temperatures from the lamps, wear, the presence, exposure and accumulation of large amounts of ultraviolet light or ozone, and/or the exposure to vapors, hydrocarbons and volatile gases from the coatings, inks or adhesives, and substraits being processed. In an effort to overcome these problems, it has been suggested to decrease production Tate and conveyor speed in proportion to the rate of loss of energy, efficiency, and effectiveness of the ultraviolet lamps and reflectors. This solution, however, decreases the production output and cannot be effectively used in high speed applications and multi-station production lines. Problems with a single lamp station often effect the entire production line. It is, therefore, desirable to provide an improved process and system for curing and drying printing inks, coatings, adhesives and the like which overcome most if not all of the above problems. An improved ultraviolet process and system are provided for polymerizing, curing and drying printing inks, coatings, adhesives and the like which are effective, efficient, economical and safe. The ultraviolet process can also be used to sterilize bottles, jars, and other products. Desirably, the novel process and system increases product quality, and output. The process and system are also convenient, simple to use and easy to operate. To this end, the novel process and system has at least one sensor for sensing the ultraviolet light intensity or radiant energy output of one or more ultraviolet lamps and a control circuit and logic board operatively connected to the sensor to automatically activate an auxiliary booster lamp or increase the power and intensity of the existing (primary) ultraviolet lamps, in proportion to the measured (sensed) loss of light intensity light intensity or radiant energy output of the sensed lamps. The control circuit and logic board can include a variable controller, such as a rheostat or transformer, to increase and control the power (wattage) and the ultraviolet intensity of the booster lamp and/or primary lamps. The control circuit and logic board can also include a speed detector, such as a tachometer, to sense the speed of the conveyor belt, or an interval timer to measure the exposure time the product (ink coatings, adhesive etc.) is under the lamps or to time the sequence of operations of the product or components of the system, and/or an integrator to compare the sensed input and determine the needed makeup ultraviolet light intensity and radiant energy output of the lamps in accordance with pre-selected desired values. This system can be installed new or used to replace unreliable obsolete equipment. Advantageously, existing equipment can also be retrofitted or revamped with components of the inventive system to achieve this process without substantial replacement costs. The ultraviolet drying process and printing system utilizes ultraviolet drying and processing equipment to dry, polymerize, and or cure ultraviolet sensitive or ultraviolet reactive printing ink on sheets or a continuous web of paper, plastic or metal. The printing system has a printing press, a horizontal conveyor, and a loading platform and station. The printing press can be one of the many types of printing presses and coating equipment used in publishing newspapers or magazines or in printing labels for cartons, packaging or products. More than one printing press can be used for multi-color printing. Spaced down stream of each printing press is an associated ultraviolet drying unit. The ultraviolet drying unit and equipment includes one or more primary ultraviolet lamps, and at least one auxiliary booster, variable intensity ultraviolet lamp, a power supply, an ultraviolet sensor or meter, a tachometer or interval timer, and a controller assembly. The controller assembly is positioned below the lamp housing (protective covering) and includes a controller housing containing a variable saturated reactor, rheostat or transformer, a control knob connected to the reactor for varying and setting the initial power (wattage) and intensity of the variable intensity lamp(s), an on-off timer control switch or button connected to the interval timer for activating the timer, an on-off tachometer-control switch or button connected to the tachometer for activating the tachometer, and an on-off ultraviolet sensor control switch or button for activating the ultraviolet sensor. The controller assembly also has a controller logic Circuit board or integrator for receiving, assembling, processing and integrating the intensity, voltage, power (wattage) and status of the sensor, interval timer, tachometer, and other components of the system. The controller logic Circuit board or integrator relay and transmit that information to the other components of the system. Advantageously, the controller logic circuit board or integrator also automatically controls (increases or decreases) the power input to the reactor in response to such information, and controller logic board's or integrator's integration, and processing of the sensor, timer, tachometer, and other system components, in order to control and regulate the overall intensity of ultraviolet light being emitted from the lamps. The tachometer measures the speed (rpm) of the conveyor. The interval timer can comprise a photoelectric cell and receiver unit to detect the frequency of travel and/or the speed of the sheets or products on the conveyor. The ultraviolet light sensor faces the lamps and measures the total ultraviolet light intensity and/or energy emitted from the ultraviolet lamps and. The sensor can be a fluorescent active optical fiber sensor, filtered photodiode sensor. Sensors which sense a particular wavelength can be used. Other types of sensors can be used, if desired. A ballast, such as a mercury vapor ballast, has an input line and is connected to the lamps via electrical wires and a bank of parallel capacitors. The saturated reactor is connected the capacitor bank by electrical wires. The controller or controller logic board is connected to the reactor via electrical wires and a variable current voltage unit. The light sensor and the interval timer and/or tachometer can be connected to the controller via electrical wires. If desired, mercury vapor lamps or quartz lamps can be used for the ultraviolet lamps. The ultraviolet unit may also include an integrator in lieu of a controller and/or a magnitron comprising a microwave reactor mounted adjacent the lamps. In use, a web or sheets of paper for a magazine or shiny labels, or glossy paperback book covers, are printed with ultraviolet sensitive printing ink by the printing press. The sheets of paper containing the wet ink are conveyed through the special ultraviolet drying and processing unit of this invention. The ultraviolet drying unit will dry, polymerize, and/or cure the ink or all sheets of paper evenly, and uniformly to produce identical high quality products. The ultraviolet processing unit accomplished this by: (1) sensing the total light, intensity, and/or energy emitted by the lamps with the ultraviolet light sensor; (2) detecting the exposure time and how fast the paper or other product moves on the conveyor through the ultraviolet processing unit with the tachometer or interval timer; (3) integrating and correlating the sensed and detected valves with the controller and/or integrator (4) adjusting the DC voltage and power of the reactor and/or magnitron and lamps so that rate of total light energy and intensity emitted by the lamps per rate of travel of the product will remain substantially constant and uniform. Uniform drying is particularly important in multi-color printing where each color needs to be completely and uniformly dried before the next color is printed in order to attain excellent uniform products. The ultraviolet drying, bottling, and filling process and system has: an input feed conveyor; a rotary bottle feeder on a shaft driven by a motor ; a filling, bottling and labeling unit and station; an ultraviolet drying and processing unit; and a loading station with a carton or crate on a discharge conveyor. The rotary bottle feeder sequentially moves the bottles to the filling station. At the filling station the bottles are filled with the liquid product, the bottle is capped, and a label is glued and/or identifying indicia, information, an/or logos are printed or coated on the bottles. The ultraviolet drying and processing unit is structurally and functionally similar to the ultraviolet drying and processing unit, except that the ultraviolet lamps are on the side rather than top of the lamp housing to face the coated, printed, labeled, and/or glued side of the bottle and the light sensor or light meter faces downwardly from the top of the lamp housing rather than transversely from the side of the lamp housing to face the lamps. The ultraviolet drying and processing unit dries, cures, and/or polymerizes the coating, printing and/or adhesive (glue) on the bottles evenly and uniformly to produce identical high quality labeled and/or printed bottles. Glass and plastic bottles, as well as metal cans, plastic and paper cups, and other products can be dried, cured, and/or polymerized in this manner and/or with the unique ultraviolet drying and processing unit of this invention. The ultraviolet drying and processing unit can also be used to sterilize bottles, jars, and other ultraviolet reactive (sensitive) products. The controller or integrator can maintain a level of energy imputed into device, by increasing the voltage or power going to the lamp. The regulation of the voltage can be maintained at the desired energy level by the controller in conjunction with the light sensor. The regulated lamp and controller can be mounted over a conveyor or on printing or other processing equipment. The energy specification of the variable intensity, controlled lamp can be 25% to 200% over the initial desired energy levels, such as from t).n7 to 4.7 watts/cm2. This will allow the regulated lamp to increase its energy output over time as the efficiency of the lamps decreases. The range would also allow the speed of the equipment to be adjusted over a wide range. A single sensor and controller can sum the energy of all the lamps used and then control the energy delivered to the coatings. In one test unit, the light energy and intensity emitted by the ultraviolet lamps was varied from 100 to 600 NM (nanometers). Multiple ultraviolet light sensors can be connected to one or more controllers or integrator. The multi-lamp ultraviolet curing system need only have one variable intensity regulated lamp. For example, two fixed intensity standard lamps might be used with a variable intensity controlled lamp. This is advantageous in "retro-fitting" existing curing systems and offers great flexibility. The variable intensity controlled lamp would add the lost or needed energy for higher production rates. This would allow the standard lamps to operate either at needed light intensity. With the regular lamps operating at lower power levels, overall lamp life would increase since it would not be operating at its full power or at a high temperature level. In most curing applications, the total amount of energy which the ink, coating, or adhesive receives, will determine the degree of polymerization. Therefore it is possible to have each station or lamp operating at different levels depending on the specific energy requirements. In the case of a plastic cup decorator, the lamp controller may be used to regulate the energy used for each color printed. A pigmented ink will require more energy than a clear coating, due to the light adsorptiveness of the pigments. In these type of applications, the controller can be used to regulate and control the appropriate amount of energy for each color printed on the container. In use, the operator establishes an energy level to which he wishes the process to operate under. This value is set into the controller board and/or initially set with the control knob. The lamps are then turned on and allowed to warm up to achieve a stable operating temperature. This warm up period can be set manually or controlled by the logic board, such as ten to twenty minutes. During the warm-up time the operator is able to set up the printing or coating machinery. The controller system would then be switched into action. The intensity and energy of the ultraviolet light being emitted by the lamps are monitored by a light sensor(s), each sensor sending a signal to the controller board. The signals value, are summed by the controller. The light value is linear with respect to the ultraviolet energy which the product receives. The lamps sensor can sense all of the lamps at once, such as by using quartz fiber optics or quartz rods to deliver the sight to a single sensor, or a ultraviolet fluorescing fiber, which would fluoresce a visible light in the fiber as a result of the ultraviolet light. The florescent fiber would allow a single sensor to read many lamps within a curing system. The electronics which "drive" the sensor can be a part of the controller board or a signal from a radiometer. The interval timer transmits to the controller board the speed and exposure time of the products being conveyed through the ultraviolet curing unit. The logic board processes and integrates this information and calculates the relationship of the speed of the product and sensed light energy. The logic board determines the differential power or voltage needed to achieve the desired ultraviolet light intensity and energy, based upon the conveyed speed of the product and the sensed light intensity and transmits this value into voltage or power signal which is transmitted by the logic board to the saturated reactor. This DC voltage to the saturated reactor is set to a minimum amount so that the lamps do not prematurely shutoff. The logic board can have a trimming pot which would allow the setting of the maximum voltage sent to the saturated reactor. This setting can be part of the logic board input and could be switched on and off during the initial start-up of the system. It is desirable that during the startup of the system that full power be available to the lamp so that voltage is matched to the lamps and the lamps will arc and start. Once the system is started and the lamps are up to the correct operating power, the controller system further adjusts the power and voltage to the reactor and the lamp(s). In a conveyor system, as the lamps age or if the reflectors get dirty and less light energy is produced for the process, the light sensor, typically would sense a drop in energy and light intensity by the lamps. The logic board would react by maintaining a constant value (energy vs. time) and change the DC voltage sent to the saturated reactor, thus increasing the power going to the ballast and therefore to the lamp. As the lamp power increases so will the energy emitted from the lamp. The light sensor would send a higher value to the logic board and when the correct power level was achieved, the logic boards concurrent response would be to maintain the correct energy value. Therefore, the DC voltage to the saturable reactor would be maintained and to will the ballast and the lamp. The interval timer sends a signal to the logic board. The logic board can convert this data to a time value. Some interval timers may sense time by counting a cycle of the process, such as a rotating gear or drive shaft. if the interval timer is establishing the rate by counting parts (product) as they go by, the logic board can lower the lamp power if there are no parts present. This represents a savings of energy and lamp life. In production equipment, there are times when full power is not desired. This occurs during setup of the equipment, maintenance, or during ideal production stoppages such as when the equipment needs to be adjusted. The switching to a lower power setting therefore is desirable to conserve energy, conserve lamp life, reduce heat from the lamp within the process. The reduction of heat in the process is critical in web printing applications. If the web has to be slowed down or stopped ft)r any reason, the heat generated by the mercury vapor lamp will often, burn or ignite the web. In this invention, there is an ability to use the variable saturable reactor to select the lowest power level to maintain the arc of the lamp and at the same time have the greatest heat reduction possible during the idle periods. As the operator adjusts the production speed, the interval timer senses the increase or decrease in speed. The logic board integrates, processes the required energy value and adjusts the [)C voltage to the saturable reactor accordingly. If the system is on a multi-color press the controlled lamps can be at each curing station after the print station. The logic board would function in the same fashion as described previously. Each lamp can be controlled individually. This gives a lot of flexibility to the process. In many instances, the first color printed will receive more energy than the last color printed, since it will pass under subsequent lamps. The controlling of each lamp individually can allow each lamp to be set at its required energy value. The logic board can also receive separate light sensor values and add them together to control the process with a total energy value. The DC side of the saturable reactor is connected to the logic board. When the light level if the lamps is reduced, the logic board receives the information from the sensors and integrates the needed energy value. The result is an decreasing the DC voltage, increasing the AC voltage and the operating voltage to the lamp. At a higher operating voltage, the lamp produces more light energy. If desired, the controller system can drive a mechanical shutter rather than the power supply. This shutter operates in a manner similar to a venetian blind. As more or less light required the angle of the shutter (blind) would vary, physically blocking the light. If desired microwave electroless lamps and power supplies which use a choke rather than the capacitors can be used with this invention. Such lamps can use a magnatron or a variable microwave reactor to generate microwaves and excite the mercury in the lamp. Furthermore, if desired, pulsed xenon lamps, can be used with regulating the power to the lamps and/or the number of pulses per second to effect the amount of energy emitted. This ultraviolet process system can also be used for sterilization, water purification, coating shiny no wax tiles, exposing images in offset plates, etching and producing semi-conductor chips and printed circuit boards, treating plastics for adhesion promotion, polymerizing and curing plastic contact lenses and glasses, and coating glossy paper and paperboard, such as paperback book covers, annual reports, brochures, printed advertising and promotional material, labels, and decorative shiny boxes containing perfume, cologne, and other cosmetics. If desired, the process and system can be used with lamps of other wavelengths in lieu of or in addition to ultraviolet emitting lamps. Among the many advantages of this ultraviolet process and apparatus are that they:
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