EP0632763A1 - Printing method and apparatus - Google Patents

Abstract

The present invention relates to a method and apparatus for printing in which the fountain solution (37) for a lithographic printing device is treated by the direct injection of electromagnetic radiation. Most preferably, the electromagnetic radiation is within the radio frequency range and is injected through a conductor (30) directly in contact with the fountain solution (37). Such treatment eliminates or substantially reduces the need for chemical treatment of the fountain solution (37), especially the need for isopropyl alcohol or alcohol substitutes.

Description

PRINTING METHOD AMD APPARATUS

Cross-Reference to Related Applications. If Any; None.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to the art of printing and more specifically to a lithographic printing method and apparatus in which the fountain solution is treated by the injection of electromagnetic radiation. In the most preferred form of the invention, the electromagnetic radiation is in the radio freguency range and injection occurs through a conductor in direct contact with the fountain solution.

Description of the Prior Art

Numerous systems have been proposed over the years for treating various aqueous solutions to obtain improvements in certain methods or to achieve certain properties for the treated solution. Several examples of the types of treatment include those involving the use of electromagnets, permanent magnets, ultrasound, electrostatic fields and the like. While some within the scientific community are convinced of the effectiveness of such treatment metaods, considerable skepticism remains, and the devices which have been marketed have not received a high degree of commercial success. The types of applications with which such treatment methods have been employed are also widely varied. Some will be described below in connection with the description of certain specific prior art, but generally, they have included the treatment of aqueous solutions to prevent scaling in boilers, cooling towers and the like; the treatment of emulsions; the treatment of certain non- aqueous materials such as fuels for increasing the fuel burning efficiency thereof; the treatment of automobile radiator fluid; and other diverse applications.

Several representative samples of such prior art treatment systems will now be disclosed briefly, but particular attention should be direct to the Morse patents, the backgrounds provided therein, and the references cited against same.

One such treatment device, called the Ion Stick, utilizes the application of an electrostatic field, as illustrated in a brochure entitled "The Ion Stick", copies of which are provided with this specification. This device is a non-chemical, non-polluting electrostatic water treater energized by its own power pack. Another electrostatic treatment method and device is disclosed in U.S. Patent 4,545,887 issued October 8, 1985 to Arnesan, et al.

Other devices employ fixed magnets for water treatment. Examples include U.S. Patent No. 4,808,306, issued February 28, 1989 to Mitchell and entitled "Apparatus for Magnetically Treating Fluids", and U.S. Patent No. 4,367,143, issued to Carpenter on January 4, 1983 for "Apparatus for Magnetically Treating Liquid Flowing Through a Pipe and Clamping Means Therefor".

A different magnet arrangement for water treatment is disclosed in U.S. Patent No. 4,888,113, issued to Holcomb on December 19, 1989 for "Magnetic Water Treatment Device". In this patent, Holcomb discusses the use of a plurality of rectangular magnets attached to the exterior of a pipe. The magnets are arranged in pairs adjacent the pipe such that the positive pole of one pair is oriented to one end of the support housing and the negative pole is oriented toward the other end of the housing. Another similarly constructed housing is secured to the opposite side of the pipe, but reversed with respect to magnet polarity. Thus, the positive pole of the first set faces the negative pole of the second set to cause an "attractive" mode of magnetic flux treatment. Applications such as scale prevention, as well as use in washing machines, swimming pools, ice rinks, livestock watering, and coffee brewing are suggested. The patent also suggests that the taste of treated water is superior to that of untreated water. The patent further mentions that the magnetic force fields can be generated through wound iron coils coupled to a DC generator.

The assignee of the present invention is the owner of several patents relating to electro-magnetic water treatment devices, including Stickler et al., U.S. Patent No. 4,746,425, issued May 24, 1988 for "Cooling System for Magnetic Water Treating Device" and Stickler et al., U.S. Patent No. 4,659,479, issued April 21, 1987 for "Electromagnetic Water Treating Device". Both use a pipe core of alternating magnetic and non-magnetic sections with an electromagnet surrounding the pipe through which the fluid to be treated passes.

The prior art is replete with devices that employ electromagnetic energy for water treatment. Many such devices employ electromagnetic energy at a fixed frequency. Examples of such fixed frequency devices are U.S. Patent No. 4,407,719, issued October 4, 1983 to Van Gorp and entitled "Magnetic Water Treatment Apparatus and Method of Treating Water"; U.S. Patent No. 4,288,323, issued September 8, 1981 to Brigante and entitled "Free Flow Non-Corrosive Water Treatment Device"; and U.S. Patent No. 2,596,743, issued May 13, 1952 to Vermeiren and entitled "Electric Device". Several other United States patents disclose specific methods and/or devices which employ varied and/or mixed frequency electromagnetic energy. For example, U.S. Patent No. 3,511,776, issued to Avanpoto, discloses a method of using various wavelengths of electromagnetic energy, mostly within the ultraviolet and x-ray spectra, to cause ionic species within a flowing water system to become more susceptible to attraction by a subsequent magnetic field. U.S. Patent No. 3,625,884, issued to Waltrip, discloses a sewage treatment method which employs multiple signal generators to simultaneously provide audio frequency and/or radio frequency energy at a number of different frequencies. The frequency output of each separate signal generator may be selected on the basis of the mineral content of the untreated sewage.

U.S. Patent No. 4,365,975, issued to Williams et al. , discloses a method of recovering alkali metal constituents from coal gasification residues by subjecting the residues to electromagnetic energy in the radio frequency-microwave (0.1 to 10⁵ MHz) range. Such electromagnetic radiation is purported to facilitate extraction of the metal.

Another treatment system is disclosed in a patent owned by the assignee of the present invention, namely Larson et al., U.S. Patent No. 4,865,747, issued September 12, 1989 for "Electromagnetic Fluid Treating Device and Method". An electromagnetic field having a voltage which operates in the range of 1 KHz to 1,000 MHz is applied to a non-ferromagnetic conduit in which a ferromagnetic core is mounted. The core acts as a sacrificial anode and as a receiving antenna for the radio frequency radiation.

Also designed for use in fighting scale formation, a device known as the "Aquabel" has been sold and purportedly involves an electronic circuit producing electromagnetic signals which are transmitted into water through cables coiled in a spiral shape around the water line. A copy of a brochure relating to this device is included with this specification.

Electromagnetic radiation, in the form of microwave radiation, is discussed as a treatment mechanism for emulsions in U.S. Patent No. 4,582,629, issued to Wolf on April 15, 1986.

An electromagnetic process for altering the energy content of dipolar substances is disclosed in British Patent 417,501, issued Dec. 28,1934, to Johnson. According to Johnson, irradiating colloids with electromagnetic energy having a wavelength characteristic of the colloid will alter the mobility and viscosity of the colloid. Also, treatment of organic substances such as milk or meat will prevent aging of the substance.

Another use is the treatment of living organic matter, such as bean seeds, to increase their growth.

Other methods and devices which involve the treatment of water using electromagnetic energy having a variable frequency include German Patent 463,844 issued August 6, 1928 to Deutsch and British Patent 606,154, issued August 6, 1948, to Brake.

Yet another type of scale prevention is disclosed in U.S. Patent No. 1,773,275, issued August 19, 1930 to Neeley, which discloses supplying an electric current to the water by subjecting the water to electromagnetic fields or by having it come into contact with electrically charge surfaces. A hardness reducing treatment using electrical current is disclosed in Pierpoint, et al., U.S. Patent No. 2,161,933, issued June 13, 1939.

Another water treating technique is that disclosed in U.S. Patent No. 4,865,748, issued September 12, 1989 to D. Morse and entitled "Method and System for Variable Frequency Electromagnetic Water Treatment". In this patent, a conductor in direct contact with a fluid to be treated is coupled to a generator of electromagnetic radiation, preferably in the radio frequency range. According to the patent, the radiation is injected at a frequency which is related to the electromagnetic radiation absorption or emission profile of the particular system being treated. This patent focuses on the use of that device for the elimination and prevention of scale buildup in boiler systems and the like. The Morse patent is also owned by the assignee of the present invention. A continuation-in-part of the aforementioned Morse patent issued as Patent No. 4,963,268 on October 16, 1990.

Water sterilization using current injection is discussed in U.S. Patent No. 3,965,008, issued June 22, 1976 to Dawson and in U.S. Patent No. 3,753,886, issued August 21, 1973 to Myers. The assignee of the present invention has three pending applications relating to use of devices, generally similar to the devices described in the Morse patents. These include application Serial No. 07/621,619, filed December 3, 1990 and entitled "Ice Making Water Treatment", Serial No. 07/531,021, filed May 31, 1990 and entitled "Beverage Brewing System", and Serial No. 07/564,790, filed August 8, 1990 and entitled "Filtration Cleaning System".

Lithographic printing is a well known printing technique used for a broad range of applications, including books, magazines, business forms, advertising materials, etc. Lithography is a planographic method, wherein the printing and non-printing areas are located in the same plane on a metal plate. The distinction between the two areas is made chemically, with the image area water repellant and the non-image area water receptive.

One type of lithographic printing is offset lithography, wherein the image is transferred from the image plate to an intermediate or blanket cylinder, and then to the substrate. In many cases, the substrate is printed on opposite sides at the same time using techniques which, in and of themselves, are old to the art. A typical printing press may comprise anywhere from 1 to as many as 12 printing units.

It is common in lithographic printing to use a "fountain solution" to make the non-image areas unreceptive to the ink. Since printing inks are typically oil-based, the fountain solution is usually water-based and various additives are employed, the most common of which is isopropyl alcohol. Isopropyl alcohol is a volatile organic compound (VOC) and has been a problem for the printing industry in terms of air contamination and in terms of cost. Most fountain solutions have up to 35% by volume isopropyl alcohol, with the most typical compositions falling in the 5-20% range. Many plants have attempted to reduce the amount of alcohol by employing magnetic devices, one of which is called a "Superior Water Conditioner." This device magnetizes the fountain solution and claims to reduce its surface tension so that less alcohol is needed.

Non-alcohol substitutes have been developed as a replacement for isopropyl alcohol, but while such compositions reduce the volatile emissions from printing presses, the use thereof is typically offset by higher costs and chemical disposal problems.

To give some idea as to the magnitude of the isopropyl alcohol problem in the printing industry, it has been estimated that a typical facility can use between 1-800 tons of alcohol per year, depending upon the type of facility. A review of offset lithographic printing, especially as it relates to VOC problems, is contained in a publication entitled Draft for NAPCTAC

Meeting - Offset Lithographic Printing Control Techniques Guideline, prepared for the U.S. Environmental Protection Agency and dated September 6, 1991. A copy of Sections 1-5 of this publication is included with this specification for reference purposes. The remainder of the publication appears to relate to cost impact analyses and techniques for estimating emissions which are less relevant to the subject matter of this specification. SUMMARY OF THE INVENTION

The present invention features a method and apparatus for lithographic printing in which substantial reductions in the amount of isopropyl alcohol are obtained. Another feature of the invention is the elimination in some cases of the amount of alcohol required for fountain solutions, while maintaining the printing quality previously obtained when the alcohol was used.

A different feature of the invention is the elimination of alcohols and other VOC materials from fountain solutions and offset lithographic printing equipment, which can be achieved in an easy manner without substantial modifications to existing equipment. How these and other features of the invention are achieved will be described in detail in the following description of the preferred embodiment, taken in conjunction with the drawings. Generally, however, they are accomplished using conventional printing equipment with the addition of a device for injecting into the fountain solution, before and/or during application thereof to the printing plate, of electromagnetic radiation, preferably within the radio frequency range. The injection system features a generator of electromagnetic radiation, a cable for conducting the radiation from the generator to an injector, or in the case of the most preferred embodiment to a splitter, and subsequently to a conductor in direct contact with the liquid used in the fountain solution. Other ways in which the features of the invention are accomplished will become apparent to those skilled in the art after the present specification has been read and understood. Such ways are also deemed to fall within the scope of the present invention, and the invention is not to be limited by the single illustrated embodiment, but it is to be limited by the scope of the claims which follow. DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a schematic illustration of a portion of a typical lithographic printing unit; FIGURE 2 is a schematic illustration of the water treatment of the fountain solution according to the present invention in a modified form of printing unit which includes additional rollers than those employed in FIGURE 1; FIGURE 3 is a front view of a frequency generator used in the FIGURE 2 embodiment; and

FIGURE 4 is a schematic diagram of the PC board of the frequency generator of FIGURE 3.

In various drawings, like reference numerals are used to describe like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Before proceeding to the detailed description of the preferred embodiment, several comments are appropriate with regard to the applicability of the invention. While the invention is shown in the FIGURES to involve the treatment of a fountain solution in a tank in a particular printing apparatus, the invention has much wider applicability, including the treatment of the liquid in the fountain solution pan, rather than in the storage tank, or the treatment of the liquid within a conduit.

It should also be stated prior to the description of FIGURES 1 and 2 that the printing equipment shown is in very schematic form, and that the direct injection of electromagnetic radiation into the fountain solution could be accomplished in any other type of lithographic system, including offset lithographic systems, to achieve the desired features of the invention. Furthermore, in FIGURES 1 and 2 , a single injector is shown, but the invention does not require the use of a single injector, as plural injectors can be used for a system. Furthermore, as will be described later, it is sometimes desirable to use a single generator leading to a splitter, with the splitter carrying the ultimate signal to numerous injectors. Again by way of introduction, it will be helpful at this point to generally describe the effect of the direct injection system, as it is currently understood by the present inventors. This description is without prejudice to other explanations and other mechanisms which might result from the direct injection of electromagnetic radiation into the aqueous solution of the fountain formula.

Testing conducted by the assignee of the present invention has indicated that such direct injection causes certain fundamental changes in the physical constants of water which have a beneficial effect on electroplating. Clustering properties of the water molecules are believed to be altered. In fact, it has been determined that numerous physical properties associated with water are modified, including such properties as boiling point, freezing point, surface tension, dielectric constant, evaporation rate and the like. The following Table A lists certain characteristics of water which are well documented in recognized sources and the comparable figures determined for a distilled water sample after treatment by a system for directly injecting into the water electromagnetic radiation in the radio frequency range ("Treated Water") . All testing was done using well-known testing procedures and were done at least three times to verify the accuracy of the numbers reported. It should be kept in mind in examining Table A that the tests were performed on divided samples of a particular water solution. The injector system used for the testing will be described in detail in connection with FIGURES 3-4, and the treatment of the water prior to the testing for the results shown in Table A was carried out for 60 minutes using radio frequency injection having a frequency of 43.9 MHz and a current of 425 milliamps at 50 volts p/p.

It is also believed that the frequency of the injected radiation plays a part in the alteration of the physical properties of the solution, and this belief is verified by the fact that the NMR frequency associated with the hydrogen atom is 42.5759 MHz, a number very near that used for testing. It is also believed that other frequencies determined from textbooks for other atomic species present in a solution could be beneficially injected into the solution. Injection of plural frequencies using separate injectors, frequency scanning or multiplexing could result in even greater improvements than those noted below. Current testing would seem to indicate that the water molecules themselves are most strongly influenced.

With regard to the present invention, it is believed that the alteration of the characteristics of surface tension and the ability of ions to move through the aqueous solution resulting from such changes are predominantly responsible for the dramatic results which will be shown in comparative plating data below. Testing conducted on ionic solutions of various commonly encountered compounds, including calcium, magnesium, and silica compounds has produced numerous surprising results which may involve the clustering phenomenon mentioned above or which may involve the effects of the energetics of the ionic or colloidal species present in the solution. For example, significant changes have been noted in the rate of evaporation of such solutions when compared to untreated solutions. Changes in freezing and melting points, changes in ion mobility, changes in dissolved oxygen properties, changes in solubility characteristics, and changes in the antimicrobial properties of the water have all been noted. Moreover, changes in the density of water before and after treatment at various temperatures have also been documented.

Proceeding now to a description of FIGURE 1, a schematic printing system 10 is shown to include a plate cylinder with a fountain solution application system and an inking system. Not shown in this FIGURE are the additional inking systems which would be used for additional colors in multi-color presses or the blanket cylinder or substrate which typically are used in such operations. For further information concerning the construction of typical printing press, reference should be had to the aforementioned study about the printing industry as identified in the background section of this specification. Illustrated printing system 10 includes the plate cylinder 12, an inking system designated generally at 13, and a dampening system indicated generally at 15. The dampening system includes a plurality of rollers 16-18, including roller 18 immersed in a fountain solution 20 contained in pan 22. Solution may be of typical composition, except that in the present invention it need contain little, if any, isopropyl alcohol or isopropyl alcohol substitute. Proceeding next to FIGURE 2, a generator 25 is shown coupled to a wall outlet by cable 27 and coupled to an injector 30 by a cable 32. The injector 30 is schematically illustrated as being placed into a fountain solution tank 35 containing a quantity of fountain solution 37. In the illustration, conduits 39 and 40 convey fountain solution 37 from tank 35 to a pan 42 which contains sufficient fountain solution 45 to be applied to a pan roller 46. One typical application technique involves the use of a doctor roller 47, vibrator roller 48 and form rollers 49 for application of the fountain solution to the plate cylinder 50.

As previously mentioned, the injection could be made directly into the fountain solution pan 42 or into the conduits 39 and/or 40 as deemed appropriate for a particular printing facility. Moreover, as is the case with many printing applications, a number of fountain solution applications may be involved in the printing of a single substrate, and one variation of the invention would be to couple cable 32 to a signal splitter 51, shown schematically in dotted form in FIGURE 2, with additional cables 52 extending therefrom to the additional fountain solution baths.

Dramatic improvements have been noted in printing quality as illustrated by one system which was installed for the purpose of eliminating or reducing as much alcohol or alcohol substitute as possible. The printing press was a 26 inch, 6-color press with a Komori-Matic dampening system using a Royce circulating system with six 5-gallon tanks. The generator used a single transmitter which was sent to a splitter box where six individual outputs were fed by RG-59 coaxial cable through stainless steel injectors immersed in the 5- gallon tanks. In this test, the alcohol substitute (Alkaless Plus Two, manufactured by Printers' Service, Newark, New Jersey) was 100% eliminated from the system before the generator was turned on. A baseline printing quality had been established before any changes were made, and there was a 4% DOT gain over the baseline. Since DOT gain is undesirable, 1 ounce of alcohol substitute per gallon was added to the solution, and at that point, the print quality matched the baseline exactly. The alcohol substitute was reduced from 15 ounces to 5 ounces, which was a reduction of 67%.

Additional units have been installed in other presses, resulting in the elimination of 100% of the alcohol. These presses have continued to operate with outstanding results without any alcohol or alcohol substitutes.

In our testing to date, 60% of the test applications were able to eliminate 100% of all alcohol or alcohol substitutes. Additional benefits have been achieved at test locations, including cleaner tanks, reduced conductivity and extended roller life, as compared to the results obtained when alcohol or alcohol substitutes are used.

Referring now to FIGURE 3, radio frequency generators 25 is shown in detail. Radio frequency generator 25 includes a casing 53 comprised of galvanized steel or 11 gauge sheet aluminum. A PC board 54, a fuse 56, a transformer 58, and a terminal block 60 are mounted within casing 53. A power supply cord 27 is connected to terminal block 60 and extends through a hole 64 in one side of case 53. Power cord 27 terminates in a conventional three-prong plug 66 for insertion into a common 120 volt AC outlet. Cable 32 is connected to PC board 54 and passes through an opening 70 in case 53. As stated above, cable 32 is coaxial, and preferably an RG59/U type coaxial cable. Cable 32 terminates in a platinum tipped spark plug 72 whose casing is removed. Other materials may be used to terminate cable 32 such as, stainless steel injector electrodes which are milled to be approximately 1" long and V in diameter. The length of coaxial cable 32 is selected such that it is approximately either one wave length, one quarter wave length, or one-half wave length of the RF signal injected into the bath. For example, for an RF signal having a frequency of 42.7 MHz the cable should preferably have a length of approximately 23-24 feet to be one wave length long. For other treatment frequencies, the cable length would preferably change to the approximate length dictated by the wave length or a harmonic thereof. When we use a splitter, the cables 32 have been 12 feet long or about 1/2 wave length.

In operation radio frequency generator 25 is connected to an AC 120 volt power source, such as a common household electrical outlet through power cord 27. Power cord 27 terminates at terminal block 60 and the 120 volt AC power is provided to transformer 58 through fuse 56. Fuse 56 is rated at 0.5 amps and protects the circuit on PC board 54 in the event of a short circuit by open circuiting with a momentary short at either the primary or the secondary of transformer 58. Transformer 58 transforms the 120 volt AC, 60 hertz power to 20 volts AC, 60 hertz. Transformer 58 provides power to PC board 54, which generates an RF signal having a typical peak- to-peak voltage of 45 volts. The 45 volt peak-to-peak RF signal is provided on coaxial cable 32 to spark plug 72, where it is injected into the solution.

Referring now to FIGURE 4, a circuit diagram of the components on PC board 54 is shown. There are three different circuits on PC board 54: a power supply circuit 73, a turn off circuit 74, and an oscillator circuit 75. Power supply circuit 73 provides power to turn off circuit 74 and oscillator circuit 75. Turn off circuit 74 is used to disable the output of oscillator circuit 75 and may be omitted in alternative embodiments. Oscillator circuit 75 generates the RF signal which is injected into the solution. Power supply circuit 73 includes terminals INI and IN2, diodes D1-D4, capacitor Cl, resistors R2 and R3, variable resistor VR1, and voltage, regulator REG1. A 20 volt RMS AC signal is applied by transformer 108 to terminals INI and IN2. Diodes D1-D4 rectify the 20 volt RMS AC signal and the AC ripple is filtered by capacitor C9. The rectified and filtered 20 volts DC is provided to input terminal II of voltage regulator REG1. The output terminal 0UT1 and adjust terminal Al of voltage regulator REG1 are connected to a voltage divider resistor network comprised of R2, R3 and VRl to provide +20 volts at terminal OUTl of voltage regulator REG1. The voltage of OUTl is adjusted by adjusting the resistance of VRl. The +20 volt supply is then provided to turn off circuit 74 and oscillation circuit 75.

Turn off circuit 74 is comprised of an input 77, a resistor R4, a relay RLY1, a diode D5 and a transistor Ql. Turn off circuit 74 is coupled to power supply circuit 73 and receives the +20 volt power supply. Resistor R4 is applied to the base of Ql and the emitter of Ql is connected to ground. The collector of Ql is connected to the parallel combination of the coil of relay RLY1 and diode D5. The opposite ends of relay RLY1 and diode D5 are connected to the positive +20 volt supply. When a positive voltage, relative to ground, sufficient to turn on transistor Ql, is applied to the base of Ql through resistor R4 and input 77, transistor Ql begins conducting and causes relay RLY1 to trip. As will be explained later, this causes the output of oscillator circuit 75 to be grounded, in effect turning off oscillator circuit 75.

Oscillator circuit 75 is coupled to power supply circuit 73 and is powered by the +20 volt power supply. Output OUT2, for lighting an LED, and outputs TP1, TP2 which carry the 45 volt peak-to-peak RF signal are provided. Generally, oscillator 75 includes tank circuit 78 and amplifier circuit 80. Tank circuit 78 provides a RF signal at a frequency of about 42.9 MHz, and an amplitude of about 10 volts peak-to-peak. The amplitude is controlled by the magnitude of the supply signal, and thus selected by adjusting the resistance of VRl, in power supply circuit 73. The RF signal is provided to amplifying circuit 80, where it is amplified to about 45 volts peak-to-peak. Tank circuit 78 includes resistors R5, R6, R7, R8, R9, capacitors C2, C3, and C4, variable capacitor C5, inductors LI, L2 and L3, and a high frequency transistor Tl. Inductor LI is provided to further filter the AC ripple in the +20 volt supply. Resistors R5, R6 and R7 are provided to DC bias the base of transistor Tl, which has resistor R8 and capacitor C2 tied between the emitter and ground. Capacitors C3 and C4, variable capacitor C5, resistor R15 and inductors L2 and L3 complete a tank circuit which oscillates at a frequency selected by adjusting the capacitance of variable capacitor C5. It has been determined that using components having the values listed below provides a tank circuit that operates at a frequency of about 42.9 MHz. Of course, as those skilled in the art will recognize, other component values, as well as different oscillating circuits, may be used to obtain this frequency. If treatment frequencies other than 42.9 MHz are desired, one skilled in this art will recognize that changing the values of the tank circuit components just identified would result in a new output frequency. Moreover, as previously mentioned, different frequencies could be applied in the treating step by using multiple generators, crystal systems, frequency scanning or by multiplexing tank circuit 78. The output of tank circuit 78 is provided to amplifier circuit 80. Amplifier circuit 80 includes capacitors C6, C8 and C9, variable capacitor C7, resistors R9, R10, Rll, R12, R13 and transistors T2 and Q2. The approximately 10 volt peak-to-peak AC signal is provided through capacitor C6 and variable capacitor C7 to the base of transistor T2. The DC bias set for the base of transistor T2 is provided by a voltage divider network comprised of R9, R10 and Rll. Variable capacitor C7 couples with tank circuit 54 and is used to fine tune the frequency of its output, in cooperation with variable capacitor C3. Transistor T2 amplifies the RF signal, which is then provided to output TP2 through capacitor C9. Output TP1 is connected to ground so that the 45 volt peak-to-peak AC signal is seen across outputs TP2 and TP1. Relay RLY1 is connected across TP2 and TP1 so that when the coil of RLY1 is set, a short circuit is provided between TP1 and TP2, grounding the output provided by oscillator circuit 80. As described above, the RF signal across TP1 and TP2 is provided to coaxial cable 18 for treating the bath.

The +20 volt power supply is provided to output OUT2 through a resistor R14 for illuminating an external LED. The external LED is illuminated when power is applied to oscillator circuit 75.

The generator 25 of the most preferred embodiment thus provides a 45 volt peak-to-peak RF signal having a frequency of about 42.9 MHz for injection into the fountain solution. The device is powered by conventional house current and delivers the signal using coaxial cable 32 terminated with a platinum tipped spark plug 72. For maximum power transfer, certain applications may require impedance matching of the coaxial cable, thus reducing standing waves to the minimum.

IDENTIFICATION OF CIRCUIT COMPONENTS

While the present invention has been described in connection with certain schematic and illustrative components of lithographic printing devices, the invention has applicability for other printing systems wherein it is desirable to change the ink receptive nature of a printing surface which includes an aqueous based material. While the invention has been described in connection with lithography, it is not to be limited thereto but is to be limited solely by the claims which follow.

Claims

WHAT IS CLAIMED IS :

1. A printing apparatus of the type including a printing surface, a portion of which is to be rendered ink receptive and a portion of which is to be rendered ink repellant, and wherein an aqueous solution is used for the treatment of the ink receptive area, the improvement comprising: means for injecting electromagnetic radiation into the solution, said injecting means including a generator for generating electromagnetic radiation at a preselected frequency and an injector in direct contact with the solution, the generator and injector being coupled by a cable.

2. The article of Claim 1, wherein the solution is contained in a tank and the injector includes a conductor in contact with the solution within the tank.

3. The article of Claim 2, wherein the solution is a fountain solution.

4. The article of Claim 1, wherein the electromagnetic radiation is generated within the range of 1 KHz to 1,000 MHz.

5. The article of Claim 1, wherein the length of the cable is selected depending upon the radiation frequency.

6. The article of Claim 1, wherein the surface is a printing cylinder and wherein the solution is applied to the cylinder from a roller pan.

7. A method for printing an image on a surface using a printing unit, wherein a portion of the surface is rendered ink receptive and another portion of the surface is rendered ink repellant, comprising the steps of: applying an aqueous solution to the area to be rendered ink receptive and applying an ink to the ink- receptive areas; and treating the solution by injecting therein electromagnetic radiation from a signal generator capable of generating electromagnetic radiation through a cable into a conductor in direct contact with the solution.

8. The method of Claim 7, wherein the electromagnetic radiation has a frequency in the range of 1 KHz to 1,000 MHz.

9. The method of Claim 7, wherein the surface is a printing plate and wherein the solution is a fountain solution applied to the plate by a roller, and wherein the treating step comprises treating the liquid in a reservoir and conveying the treated liquid to a roller pan.

10. The method of Claim 7, wherein a plurality of units are used in a printing operation and wherein the aqueous solution for each printing unit is treated by the treating step.

11. A system for eliminating alcohol-type additives in fountain solutions in lithographic printing operations, comprising: providing a printing plate, a fountain solution and a roller system for applying the solution to the plate having no alcohol added thereto; injecting into the solution electromagnetic radiation from a generator capable of generating electromagnetic radiation through a cable and to an injector in contact with the solution; and means for conveying the treated solution to the roller system.