Apparatus And Process For Printing

Abstract

A printed paper including permanent mechanically lodged pulverized magnetic particles held between the fibers of ordinary paper. The particles are embedded between the fibers by a magnetic field of a strength which is several times the value required for simple transfer deposit of magnetic particles. The field is concentrated by use of an edged field plate to facilitate providing the desired field strength.

Parent Case Text

This application is a continuation of my copending application, Ser. No. 67,810 now abandoned which was filed on Aug. 28, 1970 as a continuation of my previous application, Ser. No. 506,960, filed Nov. 9, 1965, and granted as U.S. Pat. No. 3,526,708 dated Sept. 1, 1970. The entire disclosure of said applications are specifically incorporated herein by this reference.

Description

This invention relates to apparatuses and processes for magnetic printing, impregnation, coating, duplication and so forth.

Technical progress of recent years has seen the development of many printing and reproduction techniques that have considerably broadened the original work of Gutenberg. Methods finding modern favor offer processes that are dry, fast, and economical.

The formation of marks and written characters has received considerable attention in recent decades and some processes have been developed to relatively advanced points. Among the handicaps to any printing or impregnating process is that if the process is wet, a drying stage must be incorporated. If dry, a means must be found for melting by heat, hammering, softening by vapors, or otherwise causing the powders to become fixed to the paper, plastic, etc. These treatments normally must be carried out after forming the mark, and therefore special care is required not to smudge or disturb the pattern. This requirement can call for appreciable consumed time and/or space in the process. Disadvantages of time and cost are also involved if it is necessary to apply heat to the otherwise finished material to accomplish fixing.

It is apparent that wet or dry printing or impregnating processes of the past have met with considerable disadvantage. One process that has been used for certain printing or coating tasks to overcome some of the disadvantages of the prior art is the electrostatic process.

Several problems arise in the area of electrostatic processes. Large black areas are not alwasy amenable to reproduction capable of distinguishing these black areas from the background. The electrical insulation characteristics of paper and plastics permits such things as latent images in electrostatics but also cause distortion of the electric field to produce distorted copy. Handling of the materials, or operation of the machinery, also can produce electric charges by "friction" at unndesired places possibly resulting in background problems. Atmospheric humidity may have an adverse effect on the operation of electrostatic methods. Some electrostatic methods require sensitive image plates and other fragile devices that can become scratched and worn with direct adverse effects on results. In addition, electrostatic equipment requires higher voltages than that available from ordinary transmission lines.

It is an object of this invention to provide a printed paper wherein magnetizable particles printing or impregnating is done instantly without need for a subsequent fixing stage.

It is another object of this invention to provide methods for printing or impregnating wherein printin or impregnation is done instantly to firmly hold the print in a receiving material in a permanent manner.

It is still another object of this invention to provide a process for reproduction of printed matter wherein the detail of the light and dark areas of the original is defined accurately on the copy.

It is yet another object of this invention to provide a printed paper which is not dependent on electrostatic or magnetic image plates or other fragile elements for its formation.

These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and claims taken in connection with the accompanying drawings, wherein like components in the several views are generally identified by like reference marks, in which:

FIG. 1 is a schematic diagram partially in cross section showing an apparatus for magnetic printing and impregnating;

FIG. 2 is a top plan view of indicia, design, pattern and the like used to form magnetic printing;

FIG. 3 is a top plan view of a piece of paper printed by the present method;

FIG. 4 is a view of a portion of the device of FIG. 1 showing the magnetic lines of force and distribution of magnetic particles;

FIG. 5 is a top plan view of a tape bearing ferro-magnetic indicia or intelligence;

FIG. 6 is a side view of the tape of FIG. 5;

FIG. 7 is a side view of a modified form of tape in which the ferromagnetic members have an outer surface in the same plane as the matrix of the tape;

FIG. 8 is a tape in which the indicia have been embossed or raised;

FIG. 9 is a vertical diagrammatic view of magnetic printing apparatus in which the magnetic particles are contained in a holder in the air gap;

FIG. 10 is a perspective view of a pole piece bearing indicia on one restricted end;

FIG. 11 is a view similar to FIG. 9 in which a capacitor is used to provide a damped oscillatory discharge current flow in the coil of the magnet; and

FIG. 12 is a top plan view of a magnetically printed piece of paper using the apparatus of FIG. 11.

The method and apparatus described herein for printing on paper provide a dry magnetic printing process in which the printing and fixing stages preferably are carried out "instantly," dry, and without heat. The apparatus can be used simultaneously to establish the mark initially and to fixt the mark in place without need for special handling, time or space requirement.

The present process can eliminate blocking and offset problems, solvent, base, or chemical carrier and so forth.

Referring now to FIG. 1 of the drawings, a laminated iron magnetic core structure 1 is partially wound with a magnetizing winding 2 connected to a source of electric current 3. A "magnetically soft" (unretentive) alloy shaped in the form of a flat cutout arabic numeral "2," designated 4 in the drawing, and shown in FIG. 2, is mounted on the underside of pole piece 5 so as to be within the area defined by air gap 7. In air gap 7 of core 1, adjacent magnetic numeral 4, there is disposed paper, fabric or other nonmagnetic (paramagnetic or diamagnetic) particle-receiving fibrous material 8 having distinct openings defined by the fibers. Positioned also in air gap 7 is container 13 having opening 14 and containing magnetic particles. Container 13 serves as a reservoir of the supply system for introducing magnetic particles into air gap 7. Upon closing switch 15, the current in winding 2 establishes a magnetic field across air gap 7. The field thus formed acts to attract particles from container 13 so as to bring said particles into contact with the lower surface of particle-receiving material 8. The presence of magnetic numeral 4 within the space defined by air gap 7 causes a larger number of magnetic particles to be attracted against particle-receiving material 8 at those areas directly in line with and corresponding to the shape of magnetic numeral 4 than are attracted at other portions of particle-receiver material 8. Furthermore, the force of attraction is greater at said areas than elsewhere on particle-receiving material 8. Upon de-energizing core 1, and examining particle-receiving material 8, it is found, when the proper apparatus and process is used, that a permanent printed character 16 of FIG. 13 is formed on material 8 corresponding to the shape of magnetic numeral 4. The permanent nature of the printed character has been found to be a result of the acceptance of the magnetic particles into the interstices, or openings between fibers, of the particle-receiving material. Thus, the openings and the particles should be of such relative size as to permit the acceptance action to take place. The particles individually or as a comglomerate of such particles move between the paper fibers and are held within the fibers by the mechanical holding force and without the necessity for the use of a binder of any type such as widely used in present magnetic printing, including the offset type printing and carbon type transfer typing.

Thus, as employed herein a dry particle is defined sa one having an outer surface which is free of a material which creates a separate adherence to the fibers.

In the embodiment of the invention illustrated in FIG. 1, the release of particles 10 from supply chamber 13 is controlled by means of a shutter 9 positioned adjacent particle-receiving material 8 in air gap 7 of core 1. Shutter 9 contains one or more openings 9a to permit passage of the magnetic particles 10 to the surface of particle-receiving material 8. As shown, shutter 9 is mounted on shaft 11 for rotation by motor 12. Openings 9a of shutter 9 and openings 14 of container 13 should be about the same size so as to define the general area to be printed and of a size at least sufficient to cover the dimensions of magnetic numeral 4 of FIG. 1. The areas of shutte 9 intermediate openings 9a should be sufficient to seal off opening 14 to prevent escape or loss of particles 10 from container 13.

The source of electric current 3 may be a variable-current power source. By variable current power source, it is meant to include currents that are alternating, transient, impulse or oscillatory. When frequencies of 10 to 500,000 cycles per second are used, the magnetic particles are driven into the openings of the fibrous paper, fabric, etc., and are mechanically held within such openings by the fibers to remain permanently embedded therein.

It is clear that considerable variety is possible in the practice of the invention. For instance, the opacity of the mark can be varied by using magnetic fields of various intensities. The positioning of numeral 4 in the air gap can assume many forms such as loose, or attached to pole 5 by means of an adhesive layer 6 of FIG. 1, clipped in place, brazed, soldered, or welded to pole piece 5.

The material of numeral 4 of FIGS. 1 and 2 is not restricted. Magnetic or magnetizable materials, ferromagnetic alloys, and the like, can be used. Numeral 4 can be replaced by a collection of inserts of iron or other magnetic material defining a message, word, sentence, and so forth, which it is desired to print or reproduce. Also, it is believed that under suitable circumstances, numeral 4 can be paper, cloth, or plastic and the like which has been printed with a magnetic ink (an ink containing magnetic particles and a binder such as an air-drying or heat-drying oil, resin, or plastic).

Core 1 of FIG. 1 has been discussed as being magnetically energized by means of winding 2. Another form that core 1 could take is that of a permanent magnet outfitted with a shunt magnetic circuit the reluctance of which could be varied so as to achieve a variable magnetic field in air gap 7 when desired. An example of such practice is found in focussing devices used for television picture tubes. In the application being discussed here, the variable reluctance would probably be motor-driven, instead of manually adjustable as in television practice, so as to achieve higher frequencies of variation.

The paper, fabric, or other fibrous particle-receiving material 8 in air gap 7 can, instead of a single piece, be in the form of a web which is withdrawn from a supply roll, passed through the air gap, and rewound on a take-up roll after being marked, printed, or impregnated. The supply and takeup rolls are not shown since means for delivering and removing paper or other webs from processing means are well known.

Magnetic particles of barium ferrite or carbonyl iron have been used. The use of other finely divided magnetic or ferro-magnetic materials such as iron oxide, powdered cast iron, etc., will be apparent to those skilled in the art.

The structure materials which comprise shutter 9, container 14, or other devices which can be employed in air gap 7 to control particles 10 are preferably constructed of nonmagnetic (paramagnetic or diamagnetic) materials to avoid adversely affecting the configuration of the magnetic field. Examples of materials suitable for these structures are rigid polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, a ployester-glass or epoxide-glass fiber composition, ceramic, wood, and in some cases aluminum or brass, and so forth.

It will be appreciated that air gap 7 between pole piece 5 and pole piece 17 of FIG. 1 should be of small vertical dimension but gaps of various dimensions will be satisfactory depending on the apparatus disposed in the air gap and the results to be desired. Moreover, excessive amounts of current or power are not required to obtain printing or impregnation, and when a lesser degree of penetration is desired, the output of the electrical supply can easily be reduced in intensity by means well known to the art.

The present invention provides means for controlling the degree of penetration or impregnation of the particles into the openings with respect to the particle-receiving material to provide an inherently indelible impregnated mark in a dry process without heat and without special binders for adhering of the particles to the fibers of the receiving material 8. Further, means are discussed to control and select the general areas to which the particles are applied and received. If the particle-receiving material is pulled through the magnetic field developed while the current remains on, the magnetic force will continue to vibrate the magnetic particles, and further pull or drive them into the openings of particle-receiving material so that the present process is not only useful for printing but also for impregnating and treating various materials with finely divided magnetic particles or particle mixtures. When it is desired to make abrasive papers containing iron oxide particles, for example, element 4 may be a simple solid square or bar to treat a wide area or complete width of particle-receiving material by scanning, or element 4 can be eliminated. Or, it a design is to be printed, element 4 may be of other shape than shown in FIG. 2. Moreover, the action of the magnetic field in the air gap tends to collect loose magnetic particles into an organized pattern corresponding to the shape of element 4 or the shape of the field, so that special apparatus and operations to blow, brush, shake, or dust off excess powder from the paper after the marking operations are reduced or eliminated.

Shutter 9, instead of being rotated as shown in FIG. 1, can by suitable mechanism not shown be oscillated or even reciprocated in the plane of the web or paper 8 by means of solenoids, etc. It may be preferred in some cases to control the appliation of the particles 10 by selectively energizing and de-energizing core 1 in intermittent fashion without the need for a shutter so as to effect control of the application of the particles 10. Thus, although shutter 9 of FIG. 1 can provide a convenient means for preventing unnecessary deposition of particles, it has been found in practice that satisfactory definition is obtained without the aforesaid shutter. For example, a core corresponding to core 1 of FIG. 1 annd comprising a bonded stack of laminations of a magnetic material such, for example, as is marketed under the trademark "Hipersil" (Trademark of Westinghouse Electric Corporation) and having a cross section of approximately 2 inches .times. 3 inches was wound with 100 turns of insulated copper strip. The winding was connected to a power supply comprising a 220-volt 60-cycle power line. A magnetic numeral corresponding to 4 of FIG. 1 was cut from a sheet of 0.004 inch thick, high-permeability heat-treated nickel alloy of about 18 fe, 75 Ni, 2 Cr, and 5Cu, and was about 1 inch in largest dimension. A folded paper sprinkled with ground barium ferrite magnetic particles was placed in the air gap of the core defining a space of about 0.040 inch along with the cutout numeral. Upon energizing the core, a few amperes of 60 cycle current were drawn from the power source. After a period of 30 seconds it was found that an indelible printed character corresponding to the shape of the magnetic numeral had been formed. Under the same conditions as herein above described for barrium ferrite, magnetic particles of carbonyl iron produced a permanent mark of lesser intensity.

In still another example of permanent shaped magnetic marking, according to this invention, core 1 of FIG. 1 consisted of bonded thin laminations and was about 1/2 inch by 11/2 inch in cross section. The winding 2 consisted of about 12 turns of water-cooled copper tubing. The power source consisted of an 85 kw induction heating motor generator set operating at a frequency of 10,000 cycles per second (10 kc), and operating at about 10 per cent of rated output current which would correspond to a power output less than about 1,000 watts. Folded paper covered with magnetic particles of barium ferrite was placed in the air gap of the core which define a space of about 0.030 inch. Application of power for only 1 second produces an image of the magnetic core which could not be erased and which even darkened the reverse side of the paper. On both sides of the paper, particularly the particle-receiving side, there was a sharp line of demarcation between the darkened (printed) and undarkened (unprinted) portions of the paper. The darkening of the reverse side of the paper was considered to illustrate the abilities of the method to serve in impregnation capacity, and the dark, sharply-defined marking obtained was considered to illustrate the printing capacities of a method of fast, dry, permanent marking without heat. Splitting of paper printed in this manner have shown that the significant portions of the particles of the order in excess of twenty-five percent move into ordinary fibrous paper beyond one-half the thickness of the paper and are physically held therein by the fibers so as to prevent dislodging of the particles from the paper.

The particle-receiving material, paper, fabric, (or carrier yet to be described), and the magnetic particles should be positioned in an asymetric portion of the magnetic field of the air gap so that said particles will be drawn toward the particle-receiving material. This arrangement is preferable because of the principles believed to be involved in the present invention as to be described with the air of FIG. 4. FIG. 4 represents a portion of the apparatus shown in FIG. 1 (and several subsequent figures) wherein some of the elements have been eliminated and others separated for purposes of simplicity. This principle involved in part the tendency for magnetic flux lines to choose the path of least reluctance in traversing the air gap of a magnet. As shown in FIG. 4, flux lines 18 which are normally distributed somewhat uniformly in core 1 through poles 5 and 17 flow in higher concentration through magnetic numeral 4, paper 8 and powder 10 near the numeral than they do elsewhere in air gap 7. This uneven, although organized, distribution causes power 10 to be drawn into position directly facing numeral 4, and the alternating or oscillating nature of the magnetic field then vibrates the magnetized powder particles on to the paper and into the openings in the paper selectively at the location of numeral 4.

In more advanced, mechanized applications of the apparatus of FIG. 1, particle-receiving material 8 can be fed in the form of a web, and the operation of shutter 9 can be synchronized with the formation of the magnetic field by means of a suitable control means used in place of switch 15. Container 13 can be part of a powder supply conduit provided with a storage hopper, air or gas supply, blowers, etc., to deliver the right amount of particle mixture to the operating area. Electrostatic charges may also be used to control the movement of, or to support, the particles in the conduit. Vibratory or sonic means may also be an aid in handling of particles. Likewise, the apparatus of FIG. 1 can be inverted and the magnetic particles 10 can be cascaded from a chute or other container over web 8 as the core 1 is operated.

Instead of fixably or removably securing numeral 4 to pole 5, numeral 4 can be replaced by a web or tape 19 carrying ferromagnetic indicia 20 as shown in FIGS. 5 and 6. Tape 19 can be fed across pole 5 and adjacent thereto in the position of numeral 4 and adhesive 6 as shown in FIG. 1, the indicia being next to paper web 8. The web can be supplied from a roll supported, and wound up on on a take-up roll in the same manner used for feeding the paper web through the magnetic field. In this manner a series of characters or messages can be printed on the paper web. Web 19 can be synchronized electronically, mechanically, or by other means with web 8 in the manner described above so that both travel at the same speed and web 8 is printed as each character 20 passes under the magnetic fluxing head. The travel of the webs can be intermittent or continuous. Also, one web can travel at different speeds or each can move intermittently at different times so that the indicia printed on web 8 will be closer or farther apart than shown on web 20, one character can be printed on web 8 several times before the next character, or a character can be omitted entirely. Also, means can be provided in the conveying system for handling webs 8 and 19 to reverse as well as stop their travel if desired.

In FIGS. 5 and 6, web 19 is made of a flexible nonmagnetic material to which the characters or indicia 20 made of iron or other magnetic material or alloy, are secured to web 19 by suitable adhesives, or, as in the case of some thermoplastics, the characters may be bees best pressed onto the web. FIG. 7 shows a modification in which the indicia 20 have been heat-pressed down into the web 19 so that the surface of the web is planar or smooth. Alternatively, the equipment can be used to make light characters on a dark background by substituting a magnetic metal strip, for web 19, in which the indicia or message is punched out of the strip and it is recognized that numeral 4 can be formed in this manner. Moreover, it is possible to use an embossed or stamped thin magnetic metal strip in which the characters or indicia are either raised or lowered. FIG. 8, magnified four times with respect to FIGS. 5, 6, and 7, shows a metal strip or tape 21 which has been stamped to give raised characters or indicia 22. In this case the magnetic field flux will concentrate at the raised portions, causing the magnetic particles to be attracted to the raised portions and deposit on the paper disposed between strip 21 and particles to form the required printed character.

In FIGS. 9, 10, 11, 12 and 13, modifications of the invention are shown which permit substantially larger air gap openings to be used than are preferred in connection with FIG. 1. Referring to FIG. 9, papge 43 (edge view) upon which printed characters are to be made is located close to or in contact with a magnetic type face 44 such as shown in perspective view in FIG. 10. Type-face 44 is arranged to serve as a part of magnetic core 46 which is provided with winding 47 energized by power supply 48. The power supply provides current flow to coil 47 so as to produce a corresponding magnetic field in air gap 49 and paper 43. To make a printed character, magnetic powder 51 is for convenience placed into reservoir or holder 52 near the type-face 44, but separated from it by paper 43. Upon energizing winding 47, a quantity of powder 51 is attracted toward type-face 44 because the magnetic flux line 55 are more concentrated at that area, particularly at the active surface of type-face 44 upon which the shaped type is present. The attraction and powder movement takes place very rapidly, beyond the ability of the eye to follow. The powders strike the paper and simultaneously form into the pattern determined by the type-face. Where a variable magnetic field is present, some of the power is immediately impregnated or embedded into paper 43 in the desired pattern by movement between the fibers.

In practice, it has been found that the type-face 44 of FIG. 9 can be a steel stamping die as shown in perspective in FIG. 10. The apparatus of FIG. 9 has been used employing the numeral "6" as shown in FIG. 10 since it illustrates a closed loop. Upon energization with a 60-cycle electric current, the numeral 6 has been found to be accurately reproduced.

In FIG. 11, there is shown an apparatus employing capacitor-discharge techniques. An oscillatory transient current flow is realized in winding 61 (and consequent oscillatory magnetic flux in core 62) by first opening switching device 63 and then closing switching device 64 so as to permit power supply 65 to deliver electrical energy to storage capacitor 66. A d-c power supply is used, but the type of electrical power supply is not restricted. When electrical energy of the desired level corresponding to the design of coil 61 has been stored in capacitor 66, switch 64 is opened and switch 63 is closed to cause the capacitor to deliver its energy to coil 61. As well known in the electrical art, easily realized design conditions then result in a damped oscillatory discharge current flow in the circuit of capacitor 66 and coil 61. It is apparent that the apparatus can be modified to deliver greater voltage to the capacitor and that electronic or other high speed switching can be used to decrease the time. Also, synchronizing means can be used to synchronize the magnetic pulses with the feed of the paper past type bar 44.

In the apparatus shown in FIG. 11, 3 magnetic type faces (44) having the numerals "8," "6," and "0" were mounted on pole 54. By charging capacitor 66 to about 300 volts, the resultant oscillation produced the printing on paper 43 as seen in FIG. 12.

The magnetic type faces 4 and 44 of FIGS. 1, 4, 9 and 11 need not be used in the larger magnetic circuit as shown but can be individually supplied with magnetizing windings if desired without the magnetic flux return structure shown. Also, as shown above, it is not necessary to use a complete stamping die or type face for each separate character.

The methods previously described show portions of apparatus located on both sides of the material to be printed upon. However, in the method of the present invention the printing operation can be accomplished from one side of the material. For example, printed information can be applied to closed packages, solid objects, containers with small necks, etc. Preferably, the apparatus is arranged to avoid contact between the magnetic character forming face and the magnetic particles to avoid the necessity for cleaning the magnet face and to insure the application of more uniform pressure to the body being printed.

In other embodiments of this invention, in which magnetized type-face units may be used, magnetic bodies nominally of corresponding facing areas could be used to concentrate and adjust the configuration of the magnetic fields.

The accumulation of excess magnetic particles (aggregation) on the object to be printed and/or dragging of particles from the desired area to be printed caused by movement of the paper or object or movement of the magnet still having some residual magnetic force can be reduced or eliminated by proper timing and current pulse control in energizing and de-energizing the magnetizing elements so as to remove magnetization prior to the possible collection of excess particles. Air jets or turbulent air currents directed near the pattern being formed can be used to dislodge the excess, more loosely held particles. Vibration can be used to dislodge excess particles such as can be achieved by sonic or mechanical vibration, or by ultrasonic waves. Vacuum action can also be used to remove excess magnetic particles. Build-up of particles in an electrostatic process does not occur to a great extent since the charged particles neutralize the electrostatic image as they collect on it. However, with magnetic particles a charge neutralization effect does not occur in this manner since each magnetizable particle in a magnetic field tends to become a magnet itself and to transmit flux to its neighbor. The particles should be magnetically hard so as to form magnets in the presence of the moving field. This results in the particles moving deeply into the paper and lodging between the fibers to effect the desired mechanical lodging of the particles within the paper or other carrier. In this manner, printing of greater opacity may be realized by magnetic methods.

Magnetic materials for use in making the magnet or cores the magnetizable or magnetic particles can be any magnetic material known to the art. Examples of some metals and alloys are iron, cobalt and nickel and their allows such as a 35 Co - 65 Fe alloy; silicon steel; low carbon (0.1-0.2 percent) cast steel; high carbon (above 3 percent) cast iron containing 3 percent Si and varying amounts of P, Mn and S; Ni and Fe alloys with small amounts of Mo and Cr; 50Ni--50 Fe alloys which can contain a small amount of copper; 54.7 Fe -- 45 Ni -- 0.3Mn; 17 Fe -- 81 Ni -- 2 Mo; sintered MnFe.sub.2 o.sub.4 + ZnFe.sub.2 o.sub.4 ; tungsten steel containing 5W, 0.3 Mn and 0.7 C; chromium steel containing 3.5 Cr, 0.9C, and 0.3 Mn; alloys of iron and various amounts of Al, Ni, Co and Cu etc. such as 12 Al -- 20 Ni -- 5 Co, 10 Al -- 17 Ni -- 2.5 Co -- 6 Cu, 8 Al -- 15 Ni -- 24 Co -- 3 Cu = 1 Ti; alloys of iron, 52 Co and 10 -- 14 V; an alloy of 50 Cu, 21 Ni and 29 Co; an alloy of 86.8 Ag, 8.8 Mn and 4.4 Al; an alloy of 77 Pt and 23 Co; 77.8 Pt and 22.2 Fe; and the ferrites such as barium ferrite, manganese zinc ferrite, manganese magnesium ferrite and so forth. Many of these materials have to be suitably treates such as by annealing, cold working, forging, etc., and sometimes in the electrical field, to produce their best magnetic properties. Of these materials it is preferred to use the iron, cobalt and nickel alloys and the ferrites. It, also, is preferred that the magnetic material used for the core have little or no retentivity and be highly permeable or have maximum permeability, so that sufficient magnetic intensity is directed onto the particles and so that the particles and core after de-energization of the coil will not cause smearing or shifting of the pattern due to the presence of residual magnetism. The cores can be solid or be laminated; they also can be made by powdered metallurgical methods. The magnetic or magnetizable particles should be magnetically hard and thus of the oppposite characteristic of the core and have high retentivity. The particles can be made by methods well known in the art such as by spraying, micropulverizing, etc., can be acicular in shape, irregular, or can have other shaped and can have an average particle size of from about 0.001 to 80 microns.

The pole face, cores or tips of the magnets can have many shapes as shown herein. They, also, can have dots on the pole pieces to increase the dot patterns on the material reproduced.

In addition to printing and copying as described supra, the process of the present invention can be used for coating and impregnating applications. For example, polishing cloth can be made by impregnating cloths with a substantial amount of magnetic particles. Also, a disinfectant, deodorant, fertilizer, pisticide, developing chemican can be mixed with the magnetic particles, preferably with a binder, such as a readily decomposable, hydrolyzable or water soluble, etc. compound such as gelatin, polyvinyl alcohol, polyethylene glycol and the like (for later release of the disinfectant etc. on use) and employed to impregnate cloth or paper to make a paper product which contains a disinfectant. Since the magnetic particles can be driven into and throughout the fibers of paper or cloth, increased loading and extended service life and potency are thereby provided and which represents a distinct improvement over conventional wet impregnating processes. The present process can be used to provide decorative patterns on paper napkins, bathroom tissue, cleaning tissue and so forth.

By using one or more of the various binders discussed herein including polyethylene, polyvinyl chloride, polyvinyl chloride-vinyl acetate copolymers, polyacrylates, phenol or resorcinol-aldehyde resins, polyesters, acrylonitrile-butadiene-styrene copolymers, vinylidene chloride polymers, polypropylene, polystyrene, cellulosic polymers, polyurethane and other thermoplastic or thermosetting materials and a pigment, colored magnetic particles can be made. Still other thermoadhesive polymers or resins can be used as binders such as resin, gum, copal, "Vinsol," Egyptian asphalt, hydrocarbon resins and the like. The binder can be disolved in solvent, mixed with the pigment and magnetic particle and spray dried. In another method the ingredients are mixed, preferably hot, cooled and micropulverized. Where the binder, magnetic particles and pigment exhibit the triboelectric effect, simple mixing may be sufficient to properly coat the magnetic particles with pigment and binder particles. Conventional compounding ingredients can be mixed with the resins or during preparation of the colored particles as desired such as antidegradants, stabilizers, curing agents if necessary, and so forth. Only sufficient binder is used to combine the pigment and magnetic particles; greater amounts can be used if desired. Generally the binder can be used in an amount from about 10 to 75 parts per 100 parts by weight total of pigment and magnetic particles. The completed pigment-binder-magnetic particle can have an average particle size of from about 0.01 to 100 microns or larger. The color pigment is used in amounts sufficient to obtain the desired color and mask the color of the magnetic particles if dark or black. Large excess should not be used as such may interfere with cloud and magnetic pattern formation. The pigment particles can be of the same size as the magnetic particles but preferably are smaller in order to coat or substantially coat the magnetic particles. Various color pigments can be used including carbon black, ultramarine blue, chrome oxide, cadmium orange, molybdate orange, cadsmium reds, Cd-Hg sulfide reds, CoSi violets, calcium carbonate, titanium dioxide, zinc sulfide, phthalocyanine blues, phthalocyanine greens, Amaplast orange LF, the Monastral Reds, the Benzidine and Amaplast yellows and so forth. Still other pigments can be used as shown in "Materials and Compounding Ingredients for Rubber and Plastics," 1965, Rubber World, New York, N.Y.

The process of the present invention can be used to imprint a serial number of a label which has been printed by a different method. Thus, this process can be used to provide various indicia and decorations on different printed media. In the case where the magnetic particles do not stick too well to the object to be printed such as certain coated papers, cold plastic, glass, ceramic, etc., the magnetic pattern can be sprayed with lacquer or enamel, or it can be laminated or coated by using a doctor blade, or by extruding a coating material on it, covering with transparent or translucent film, glassine or other suitable coating and so forth.

In addition to some of the other advantages mentioned herein, the magnetic printing process of the present invention provides means for dry printing without special paper or plastics of any sort, holding to the apparent public preference for, and several technical advantages of, dry processing with ordinary paper. Magnetic fields are not distorted by the presence of paper or plastics and such fields cannot be generated by "friction" effects. Magnetic fields are not affected by humidity, and the need for sensitive image plates and other fragile devices is eliminated.

There would appear to be no need for any voltages higher than ordinary line voltages (110 or 220) in magnetic printing equipment, and all-transistor electronics can be used. In contrast to the need for high voltages in electrostatic equipment, this feature can reduce certain space requirements, improve safety considerations, and maintenance. By suitably controlling fringing and aggregation, as disclosed herein, the tendency for magnetic particles to transfer or even intensify the magnetic field could promote collection of thicker particle patterns than realized with electrostatics, thereby contributing to opacity. The processes and methods disclosed herein have applications in the fields of printing, publications, communication systems, computation and business machines, copying, impregnating, coating, packaging, textiles, special papers and so forth.

It will be understood that various changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

Claims

I claim:

1. An article of manufacture comprising a particle receiving sheet material having fibers defining a plurality of particle receiving openings extending through the sheet material, a plurality of dry magnetized particles mechanically lodged and firmly mechanically held by said fibers within said openings and defining an indelibly imprinted character in said material, said particles being essentially, solely mechanically held by the fibers within the sheet material as a result of said mechanical lodging of the particles within the openings between the fibers and said particles being mechanically lodged within said openings with sufficient mechanical holding force by said fibers to prevent erasing of the particles from the sheet material, said particles being formed of a magnetically hard material whereby such particles define magnets in the paper, said particles have an average particle size of approximately 0.001 to 80 microns.

2. An article of manufacture as defined in claim 1 wherein said particles consist of ground barium ferrite.

3. An article of manufacture as defined in claim 1 wherein said particles are of irregular shape.

4. An article of manufacture as defined in claim 1 wherein said particles are of magnetic ferrite.

5. An article of manufacture as defined in claim 1 wherein said particles comprise magnetic iron oxide particles.