|Publication number||US3613100 A|
|Publication date||Oct 12, 1971|
|Filing date||Apr 1, 1965|
|Priority date||Apr 4, 1964|
|Also published as||DE1300145B|
|Publication number||US 3613100 A, US 3613100A, US-A-3613100, US3613100 A, US3613100A|
|Inventors||Berger Erich, Huber Hans Peter, Kaufer Helmut|
|Original Assignee||Agfa Ag|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (14), Classifications (19)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Inventors Appl. No.
Filed Patented Assignee Priority Helmut Kauter Metzkausen ueber Mettmann; Y Erich Berger, Unterhaching Munich; Hans- Peter Huber, Munich, all of Germany 444,875
Apr. 1, 1965 Oct. 12, 1971 Agfa Aktiengesellschaft Leverkusen, Germany Apr. 4, 1964 Germany A 45665 IXG/Zl A METHOD AND DEVICE FOR MAGNETIC IMAGE FORMATION 29 Claims, 20 Drawing Figs.
................................................ G1 lb 5/02  Field of Search 346/1, 74 M, 74 MD; 179/1002 A; 274/41.4; 117/235; 101/D1G. 13; 310/4; 178/6.6 A; 340/174.1
 References Cited UNITED STATES PATENTS 2,643,130 6/1953 Kornel 274/41.4 2,793,135 5/1957 Sims et a1. ll7/l7.5 3,176,278 3/1965 Mayer 340/1741 3,364,496 l/ 1968 Greiner et a1 346/74 Primary Examiner-Joseph W. Hartary Attorney-Michael S. Striker ABSTRACT: Recording means for magnetic data recording which include at least two magnetic materials of different temperature dependency with respect to at ieast one magnetic characteristic of the same, and a method of operating a device of such type for storing magnetic recording which includes subjecting the recording means, particularly the two magnetic materials of different temperature dependency to the influence of a magnetizing or demagnetizing field.
PATENTEUnm 12 I97! sum on HF 11 lNVjENTOR, ur KAUFER BURGER HANS PETER HUBER HELM ERICH Fig.7
PATENTEDncr 12|97| 3, 13,100
SHEET 05 0F 1 1 22 9 73 I0 14 II 15 l2 76 PI .9 27 20 27B 9 77 IIIaIE w 4 A J! an? INKENTORe HELM KAUFER ERICH URGER BY HANS PETER HUBER PATENTEDUCT 1 2 I971 sum 0s 0F 11 Sinimax INVENTORg HELMUT KAuFER BY ERICH BURGER HANS PETER HUBER PATENTEUUCTIZISTI 3,513,100
. sum U'IUF 11 INVENTORQ HELMUT "UFER ERICH 6 BY HANS PETE UBER PATENTEDnm 12 197i SHEET 08 0F 11 e WO y 5 I4 0 %%N R L l4 WW N B H5 0 o m0 IN VI-.N TORI) HELMUT KAUFER ERICH BURGER 613,100 SHEET OSUF 11 PATENTEDBCT 12 Ian 2 v H Q H 2. 0 83 H Fw: W 6 2 n 3 A n m- I Pl 8/ 82 E w 9 n m a I l I l I l I I I I I ll l l ll 1|. D m CM 5, 0/3 W H mm 3 "mm \S INKENTORS HELMUT KAUFER ERICH BURGER BY HANS PETER HUBER M, [,Z 9/ (r METHOD AND DEVICE FOR MAGNETIC IMAGE FORMATION The present invention relates to a method and device for magnetic image formation. More particularly, the present invention is concerned with a magnetic storage means or device for magnetic recording wherein the recording is produced with the help of the temperature dependency of a magnetic characteristic of a magnetic material contained in the storage device.
It has already been proposed to carry out magnetic data recording by heating selective portions of a conventionally premagnetized recording layer above their Curie point. It has also been proposed to form a magnetic image under utilization of the temperature dependency of the permeability of a magnetizable material.
It is an object of the present invention to provide a method and device for preparing latent magnetic images corresponding to an original image, and for forming from such latent magnetic image a reproduction of the original image, which device can be easily produced and which method can be carried out in a relatively simple manner, while lending itself to a great variety of practical usages, including, for instance, the forming of multicolor copies of multicolor original images, as
well as for halftone copying of images comprising a variety of shades of gray.
Other objects of the present invention, as well as various further practical applications of the same will become apparent from a further reading of the description and of the appended claims.
With the above and other objects in view, the present invention broadly includes recording means for magnetic data recording, the recording means including at least two magnetic materials of different temperature dependency with respect to at least one magnetic characteristic of the same.
The present invention also contemplates in a device for storing magnetic recordings wherein the temperature dependency of a magnetic characteristic of a magnetic material is utilized for magnetic data recording, recording means for magnetic data recording including at least two magnetic materials of different temperature dependency of their magnetic permeability.
The present invention also provides in a method of preparing a latent image steps of forming a layer including portions of different magnetizable materials in the region of the face of the layer, the magnetic characteristics of each of the materials being adapted to be changed by heating the materials to at least a predetermined different temperature, respectively, and heating the face of the layer selectively to different ones of the predetermined different temperatures in such a manner that each of the different ones of the predetermined different temperatures corresponds to a selected characteristic of an image to be reproduced, so as to change the magnetic characteristics of the materials of those particles which are heated to at least their respective predetermined temperatures, whereby the distribution in the layer of different magnetizable materials the magnetic characteristics of which have been changed corresponds to the distribution of the selected characteristics of the image to be reproduced.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:
FIGS. 1 and 2 are graphic illustrations of the temperature dependency of the permeability and of the coercive force of various materials, mixtures of which may be incorporated in the magnetic recording layer;
FIGS. 3-5 schematically illustrate the structure of mixed layers formed of hard magnetic constituents and of soft magnetic constituents, the permeability of the latter being temperature dependent;
FIG. 6 is a schematic illustration of the manner in which a latent magnetic image corresponding to a colored original image appears in a magnetic recording layer according to the present invention;
FIG. 7 is a graphic representation of the temperature dependency of the individual components of the layer of FIG. 6;
FIG. 8 is a schematic illustration of the forming of a colored image on a recording layer carrying or holding a corresponding latent magnetic image;
FIG. 9 illustrates the selective application of various colors after stepwise heating of the carrier of the latent magnetic color image;
FIGS. 10-12 serve to schematically illustrate the structure and manner of operation of inking arrangements which respond to selected magnetic field strengths;
FIG. 13 is a schematic illustration of a segment of a magnetically produced halftone block;
FIGS. 14-17 are schematic and graphic representations of the manner in which the latent magnetic image may be produced under utilization of external magnetic fields of different strength;
FIG. 18 is a schematic illustration of a magnetic recording layer according to the present invention wherein each of the particles of magnetic material comprises a core with two su perposed cover layers around the same;
FIG. 19 is a graphic illustration of the correlation between the color separations of an original colored image and the temperature stages of a layer containing magnetic particles comprising a core portion and a covering layer; and
FIG. 20 is a schematic illustration of an arrangement for multiple form printing with changes in the printed matter of different forms of each set.
According to the present invention it is proposed to form a magnetic recording layer which contains at least two different magnetic materials which differ with respect to the temperature dependency of their magnetic properties. Thereby a storage device for magnetic recordings is provided which may be used in many different ways and achieve a variety of results which cannot be achieved with a recording layer containing only a single magnetic material.
The storage means or device for magnetic recordings will contain, in accordance with the present invention, for instance, at least one soft magnetic material the permeability of which is temperature dependent within the operating temperature of the recording means, and at least one hard magnetic material which has a Curie point above the range of operating temperatures of the storage means for magnetic recordings.
It is possible to produce in such layer by very small temperature differentials very great differences in the permanent magnetization of the individual portions of the layer when the layer is subjected to a uniform external magnetic field. The permeable portions of the layer, the permeability of which may change within a few degrees Centigrade by three powers of 10 are capable of nearly completely shielding the hard magnetic constituents of the layer against the effect of external magnetizing or demagnetizing fields, at such portions of the layer where permeable constituents are interposed between the source of the magnetic field and the hard magnetic constituents, or where the hard magnetic constituents are covered by permeable constituents. In addition, by means of this blocking or bypass effect disturbing effects of the reading means or scanning arrangement on the recording are largely repressed. For instance, for effectively erasing a magnetic printing form, an opposing magnetic field of about twice the strength of the latent magnetic image would be required. When, however, a permanently magnetic particle is blocked with a factor of by surrounding material of temperature dependent permeability, then the retroaction of an opposing magnetic field of double the strength of the field formed by the permanently magnetic or hard magnetic particle, will equal only one five-thousandth of the magnetization of the particle carrying the magnetic recording.
This means that the normal effect of the magnetization of the hard magnetic portions of the recording layer will be reduced only by the blocking ratio, while the reactive disturbance of an external field is reduced by about the square of the blocking ratio. Thus, a true increase in the stability or resistance to unwanted erasion is obtained which may be utilized in connection with all magnetic storage means which cooperate with a reading or scanning device, for instance in computers, sound recording devices and the like. It is also possible to subject such a magnetic storage device also in stationary condition to scanning with a strong external alternating field, for instance a filed probe according to Brankotf. Such storage devices for magnetic recordings, when in cold condition are thus also effectively protected against unwanted external fields.
'When a signal field is available for magnetizing the magnetic storage layer, which field is stronger than the blocking factor, heating during recording will not be necessary.
When, however, primarily the thermal control effect of the mixed magnetic layer and its increased resistance to magnetic fields is to be utilized, then, during recording, the layer may be heated corresponding to the image to be recorded, and during reading, the layer may be evenly heated, in both cases to a temperature above the Curie point of the soft magnetic constituents of the layer.
These soft magnetic constituents act then only as simple magnetic resistance and, due to their small cross-sectional dimension, will permit external and internal magnetic fields to exert a nearly full strength effect.
The present invention further proposes that the storage device for magnetic recordings includes at least one soft magnetic material the permeability of which is temperature dependent within the range of operating temperatures of the recording device, and at least one hard magnetic material having a Curie point within the range of operating temperatures of the device or method. In this case, the recording layer will have several operating temperatures of which, for instance, one may be utilized for controlling the magnetic recording, while another operating temperature may serve for complete or par tial erasure of the recording. This system may be used, for instance, for multiple form printing with changes in the printed matter of different forms of each set.
According to a further embodiment of the present invention,-the magnetic storage device or recording layer may contain at least two hard magnetic materials of different coercive force, or at least one of the soft magnetic materials may possess within the range of operating temperatures of the recording layer an essentially linear increase or decrease of its permeability. Such layers permit to correlate to each temperature range a certain recording magnetic field strength, and this may be utilized, for instance, for superposed copying of several halftone separations on one printing form or copy sheet. Similar effects can be achieved when the recording layer contains at least two hard magnetic materials of different Curie point and different coercive force, provided that the layers have been premagnetized.
According to a preferred embodiment of the present invention, the hard magnetic particles are embedded in a soft magnetic layer. This arrangement, whereby preferably the hard magnetic particles are completely surrounded by the soft magnetic material, will result in an excellent blocking effect. In this manner a spatial or three-dimensional lattice is formed having a total resistance which remains substantially the same for each direction of an external magnetic field, due to the parallel connection of the individual magnetic resistances and due to the bending of the lines of flux or magnetic force at the separating surfaces between the two constituents of different permeability. This is of significant importance, particularly in connection with the magnetizing arrangement which is frequently utilized for magnetic data storage, for instance for sound recording tape, wherein two magnetic poles are arranged at one and the same side of the layer closely adjacent to each other, and the lines of flux of these magnetic poles penetrate the individual elements of the layer under a variety of angles ranging from perpendicular to the layer surface to parallel thereto.
The recording layer may suitably consist of a pulverulent mixture of hard magnetic and soft magnetic particles or grains, whereby the hard magnetic and the soft magnetic components may be adjusted with respect to their relative volumes so as to obtain the desired shielding effect. Preferably, the total volume of the soft magnetic particles will be greater than that of the hard magnetic particles so that the hard magnetic particles may be substantially completely covered by the soft magnetic particles. The two types of magnetic particles may be embedded in or bound together by means of a thermoplastic or thermosetting synthetic resin which melts or decomposes at a temperature above the range of working temperatures of the recording layer, or the magnetic particles may be attached to each other by sintering.
When a synthetic resin binder is used, it is desirable to have the highest possible filling ratio, in other words, the proportion of synthetic resin in the recording layer should be relatively small, because the total permeability drops significantly when the filling ratio is low. By forming the recording layer on rigid plates or, for instance, on printing cylinders which remain in the printing equipment, so that the recording layer need not possess a particularly high degree of resiliency, it is possible without difficulties to obtain a filling ratio of up to percent which results in a total permeability which is sufficient for many purposes.
Such mixed magnetic layer may consist, for instance, of 30 percent by volume of Leguval a pourable polyester resin made by Bayer, 5 percent by volume of hardener, 45 percent by volume of Siemens 1500 N4 and 20 percent of volume of Bayer S 12. The mean permeability of this mixture, in cold condition, will be about p.=15. The grain size of the highly coercive S 12 constituents preferably will be between 0.0l and 0.03 mm. in order to achieve the desired high resolution. The particle size of the highly permeable 1500' N4 constituent should be smaller by about one power of IO, i.e., between 1 and 3 microns. Due to the fact that the proportions by volume of the two components will be such that there will be between two and three parts by volume of highly permeable material for each part by volume of highly coercive material, it will be achieved that the highly coercive particles will be completely surrounded by the highly permeable particles.
A mixture such as described above will form a relatively rigid layer which may be cast on a printing cylinder or the like and the mean permeability of which and thus also the maximum shielding effect will be considerably reduced, due to the relatively high proportion of synthetic material having a permeability of p.=l
To increase the strength of the thus formed layer, it may be covered by a protective layer consisting exclusively of binder material. When a sintered layer is formed, the total permeability of the layer corresponds substantially to the total permeability of the magnetic starting materials since the organic binders, which are conventionally used for sintering, burn during the sintering process practically without leaving any residue.
Thus, a permeability of the layer which is close to the permeability of the highly permeable constituent can be obtained by adhering the magnetic particles by sintering. For in stance, 60 percent by volume of 1500 N4 and 30 percent by volume of Bayer S 12 are mixed with l0 percent by volume of an aqueous solution of polyvinyl alcohol and the thus formed doughy mass is then pressed, for instance, by calendering into the desired shape, dried and heated throughout to between about l000 and 1,200 C. The magnetic pigment S 12 produced by Farbenfabriken Bayer is a highly coercive, cobalt-containing cubical gamma--Fe O It is thus possible to encase the hard magnetic particles in layers of soft magnetic material, preferably by sintering the soft magnetic particles. For this purpose, for instance, the permeable constituents may be finely comminuted by wet grinding and mixed with the hard magnetic constituents which have a particle size which is preferably about times greater than that of the permeable constituents and ranges between 0.01 and 0.03 mm. The thus formed mixture of hard and soft magnetic powders with a greater proportion by volume of soft magnetic material is then transformed into a deformable doughy mass or a liquid slurry by mixing with an organic solvent which is soluble in liquid solvents and which will burn below the sintering temperature of the magnetic particles, practically without leaving any residue. Polyvinyl alcohol, methyl cellulose, wax and the like are suitable for this purpose, lf a doughy mass is formed in this manner, the same may be extruded and subsequently granulated. Preferably, the thus formed individual granules would have a diameter which is about twice the diameter of the hard magnetic particles since in this manner it is achieved that to the largest extent each granule contains only one hard magnetic particle. If a slurry has been formed, the same may be worked up by spray drying to form a mass of dried granules, whereby it is possible in conventional manner to control the size of the individual granules by suitably adjusting the conditions under which the spray drying is carried out.
It is then possible according to the present invention to form of the mass of individual composite granules, each consisting of a hard magnetic core and a soft magnetic covering, a coherent sintered layer. The temperatures required for forming by such sintered layer are considerably lower than those required for forming by sintering dense pressed bodies of the same material. In order to obtain a magnetic shielding effect, it will sufiice if there is only a slight welding together of the contacting surface portions of the individual granules. This, for instance, may be achieved at l,000 C., while for obtaining dense compressed sintered bodies of the same material a temperature of l,350 C. would be required. At these temperatures and by choosing a suitable sintering atmosphere, the magnetic properties of the starting materials will not be affected.
If is furthermore proposed according to the present invention to embed the particles of magnetic materials in a resilient film of synthetic resin or in a fibrous layer, for instance a paper layer, or to apply the magnetic materials, particularly granules consisting of a hard magnetic core and a permeable cover layer, to an adhesive support. In this manner highly resilient storage means for magnetic recordings are produced which may be used, for instance as sound recording tape or as a magnetic direct copy of paperlike feel.
For embedding the magnetic granules in a fibrous material, methods may be used which are conventional in producing pigmented filter papers. For instance, the aluminum oxide paper No. 288 which is used for chromatographic purposes and produced by the firm of Carl Schleicher & Schuell may contain up to 40 percent of the inorganic pigment, whereby the pigment is incorporated into the paper pulp prior to forming ofthe paper web.
The magnetic recording carrier of the present invention can be produced in a particularly simple manner by sheathing or covering a hard magnetic wire which may form for instance a screen or a sieve, with a soft magnetic material.
Apart from the advantages in the production and mechanical properties of the carrier of magnetic recordings which consist essentially of covered particles or wires, i.e., particles or wires of hard magnetic material which are covered with soft magnetic material, there are also considerable advantages achieved in the use of the magnetic storage or recording devices of the present invention. For instance, it is possible to form raster layers of several types of covered granules or wires, whereby the different types will possess different specific magnetic properties. For instance, the magnetic recording carrier may consist of an even mixture of granules or wires the temperature. dependency of the permeability of the covering layers of which may vary. Such storage means for magnetic recordings may also be used as a halftone raster since exposure to an infrared heat image will actuate all particles or wire portions only at the most intensively irradiated points.
Furthermore, if the hard magnetic core portions of the composite magnetic particles possess coercive forces of different strength, then a correlation between the intensity of radiation of the heat image and the magnetic field strength will be created which, as mentioned further above, may be used for producing colored halftone copies. A variation of the strength of the magnetization which is proportional to the intensity of the heat irradiation applied to the magnetic layer will also be achieved by surrounding the hard magnetic cores of the composite magnetic particles with a sheathing the permeability of which shows a linear dependency with respect to the temperature to which the storage device for magnetic recordings is ex posed. This linear dependency may be such that the permeability is either increased or decreased upon exposure to rising temperatures.
lf, according to a further embodiment of the present invention, the individual hard magnetic particles are covered with two different layers or sheathings the permeability of which shows a different temperature dependency, then it will be possible, for instance, upon forming a color copy from the latent magnetic image to achieve color selections which are independent from the temperatures selected for forming the magnetic image. This will be further described in connection with FIGS. 9 and 18.
According to another feature of the present invention, the
coercive grains, with or without a sheathing of soft magnetic material, may be embedded in a layer of a material the permeability of which increases or decreases in a substantially linear manner with changes in the temperature to which the layer is exposed. This is particularly important when it is intended to achieve, in addition to a shielding of the hard magnetic grains, within certain temperature ranges a continuously changing effect of the external magnetic field within its effective range.
The selective effect of external field strengths of different values can be increased in a particularly advantageous manner by providing hard magnetic core grains which possess a different steepness of the slope of their respective initial magnetization curves of the well-known hysteresis loop. The selective effect of the sheathing can be increased by providing hard magnetic core grains which possess different Curie points, however, so that all of the different Curie points are within the range of working temperatures of the magnetic storage layer. In this case, there will be an upper and a lower limit of the actuating temperature for the individual composite magnetic particles.
According to another embodiment of the present invention, the magnetic materials, the magnetic characteristics of which differ in their temperature dependency, may be applied as a very thin layer, for instance, as a printed raster on the surface of a hard magnetic recording layer. In this manner a very thin composite recording layer or magnetic storage device can be easily produced. Composite layers of this type can be made so as to be highly heat sensitive particularly if, according to a further embodiment of the present invention, the surface layer is formed as a raster of altematingly adjacently arranged highly coercive hard magnetic materials of relatively low permeability and of materials possessing a relatively high permeability which within the range of working temperatures of the magnetic storage layer is highly temperature dependent. Due to the parallel arrangement of the low, constant, magnetic resistance particles with particles of high and temperature variable magnetic resistance, the degree of magnetization in a homogeneous magnetic field will vary proportional to the magnitude of the variation of permeability which are of the magnitude of about 3 Powers of 10.
Another advantageous arrangement according to the present invention provides that the surface of the magnetic storage device is to be formed of a raster arrangement of several permanently magnetizable materials possessing, respectively, different Curie points all of which are within the range of operating temperatures of the magnetic storage means and, furthermore, preferably also having different coercive forces. In this manner a very simple magnetic storage arrangement can be provided which may be used for producing magnetic raster or screen prints or halftone copies.
The method of the present invention for using the magnetic storage means or layer provides, according to one embodiment, that a network formed of permanently magnetizable materials of low permeability and of materials of high, temperature dependent, variable permeability is exposed to a magnetizing or demagnetizing field.
According to another embodiment of the method of the present invention, the magnetic recording layer is to be magnetized or demagnetized at a temperature which is within the vicinity of the Curie point of the permeable portions of the recording layer, and is then to be read or scanned at the same or a higher temperature. In this manner the strength of the stored magnetic field of the data storage device of the present invention is fully utilized. If the magnetic storage layer includes several different permeable materials with different Curie points, then this method will permit by heating the data storage layer to different temperatures to obtain a selective scanning or radiation of the various groups of data or information which were incorporated in the data storage device at different temperatures.
Another embodiment of the method of the present invention provides that the storage device for magnetic recordings is magnetized or demagnetized at a temperature within the vicinity of the Curie points of the permeable portions of the storage layer, and is then scanned or read at a lower temperature. While thereby the outward effect of the initially applied magnetization will be of reduced strength, it will be achieved that the magnetic recording cannot be erased during reading or scanning of the same even if exposed to opposing magnetic fields of a strength which is a multiple of the strength of the magnetic'field created by the recording.
A further embodiment of the method of the present invention provides that a heat image is formed of an original halftone image, which ranges over the operating temperatures of several permeable portions of the recording layer so that depending on the gray value or darkness of a respective portion of the original image, at the corresponding portions of the magnetic recording layer a different number of composite magnetic bodies (i.e., hard magnetic cores with a sheathing of a soft magnetic material of temperature dependent permeability) will be activated.
In this manner, it is possible without interposition of auxiliary means, particularly without interposition of an optical or chemical process, to covert a halftone image into a screen or halftone dot image wherein the variations in the color density of portions of the original image will be reproduced by the variations in the numbers of dots of uniform color density which will be formed per unit area. The fineness of the gradation as well as the steepness of the layer gradation can be controlled by suitably choosing the type and number of different components of the recording layer.
A raster which operates in a continuous manner like a photographic tone print raster or a halftone block, is formed by applying the heat image of an original image which shows a continuous gradation of gray values onto a layer of magnetic composite particles, the sheathing of which possesses a linear temperature dependency of its permeability, so that depending on the gray value of the respective portions of the original image, a rasterlike magnetic field of different densities will be formed at the corresponding portions of the magnetic recording layer. Since the dye or ink which is to be attracted by the latent magnetic image always possesses a certain threshold value, the magnetic field which extends from the individual composite magnetic grains will require a certain strength in order to be effective at a sufficient distance from the magnetic grain from which it emanates in order to achieve that no gap in ink or dye attraction appears between adjacent composite magnetic grains. Thus, upon a low degree of magnetization, the individual magnetic raster grains will either attract no ink at all or will attract ink only over a very limited area which may be less than the surface area occupied by the respective composite magnetic grain. If the field strength of the permanent magnetization is low, a gap will be formed in this manner which is or relatively light color or color intensity and which will consist of fine ink points spaced from each other, while at portions of the magnetic image from which a greater magnetic force or field strength emanates, the individual areas of attraction will grow together and thus a continuously inked copy portion will be formed.
The method of the present invention also provides that the magnetic storage layer is exposed to the heat images of several color separations of a colored original image, which heat images contact the magnetic storage layer with different intensities. in this case, the sheathings of the individual composite magnetic grains will be of different temperature dependency of their permeability and, in addition, the permanently magnetizable core portions of the composite magnetic grains may possess different Curie points. Differently colored dyes or printing inks are then exposed to and attracted by the thus formed latent magnetic image at different temperatures of the magnetic recording layer, whereby, in the case of this magnetic image carrier one has to start with the lowest temperature range.
According to this method at a given temperature only those composite or sheathed magnetic grains will be magnetized for which the temperature range between the Curie point of the sheathing material and the preferably higher Curie point of the core material corresponds to the intensity of the respective color separation. Composite magnetic grains with a higher Curie point of the sheathing are still blocked, while grains with a lower Curie point will respond but will not be able to maintain their magnetization. The application of the color separations to the recording layer, i.e. the exposure of the recording layer to the heat images of the color separations must start with the color separation of highest intensity since uponexposure of the recording layer to a higher temperature range latent magnetic images which are formed previously thereto within lower temperature ranges will be extinguished. Since the conventional original colored images such as images on a paper support or transparencies do not possess complete coverage even at the darkest image portions and since furthermore, the blocking effect of the corresponding radiating energy does not depend directly on the color of the respective image portions, it is always possible to transpose each color separation by suitable choice of the radiant energy such as a source of infrared radiation, into a heat image within a temperature range which does not or only slightly overlaps the temperature ranges of the heat images formed of the other color separations.
In order to form a color copy from the latent magnetic image, the magnetic storage layer is evenly heated to the average or mean actuating temperature of one of the groups of composite magnetic particles, starting with the group which is actuated within the lowest temperature range, and the dye or ink of the color corresponding to this temperature range is then exposed to the magnetic storage layer so as to be attracted only by the thus activated composite magnetic grains. All groups of magnetic grains which will emanate magnetic force at higher temperature ranges are still blocked while all groups of composite magnetic grains which are activated at lower temperature ranges are already extinguished. Consequently, a magnetic ink which is evenly exposed to the thus heated magnetic storage layer will be attracted and attach itself only to the group of composite magnetic grains, the latent image of which corresponds to a single color separation.
in this manner, it is possible to make color copies of a colored transparency on paper layers in which the composite magnetic particles are sufficiently fine or of sufficiently small diameter, and it is possible to reproduce mixed colors in this manner.
According to a further embodiment of the present method, the heat images of several color separations of a colored original image are applied with different intensities to a magnetic recording layer which contains permeable constituents of linear temperature dependency of their permeability and/or permanently magnetizable constituents of different coercive force, and/or different temperature dependency of the permanently magnetizable constituents and/or their sheathings, so that each color will be correlated to a certain range of magnetic field strength.
This latent stored image of the color image to be stored, which is proportional to the field intensity, can now be used to produce thereon in different ways a color copy of the original color image. For instance, the individual magnetic printing inks may be exposed to the magnetic recording layer carrying the latent image at different distances therefrom, or the individual magnetic printing inks may be of different permeability and may be exposed to the magnetic storage layer at one and the same distance therefrom possibly in the form of a dispersion.
For instance, a recording layer carrying a latent magnetic image consisting of portions of different field intensity of strength may be passed successively along inking arrangements or rollers located at different distances or forming airgaps of different length with the magnetic recording layer, so that at first the magnetic ink located the shortest distance from the latent magnetic image is exposed to the same. In this manner, magnetic ink will be applied to the latent magnetic image successively from all ink rollers which are located at a distance from the magnetic recording which still can be overcome by the magnetic field strength of the respective portion of the latent magnetic image, If magnetic inks of high covering power are to be applied, whereby preferably the color with lowest covering power, for instance, yellow is correlated to the lowest magnetic field strength or intensity, and the color of highest covering power, for instance, black, is correlated to the highest magnetic field strength, the inking arrangement which is last actuated will determine the final color of the respective portion of the inked recording layer.
When it is desired to produce a copy of the latent magnetic color image which is to be transferred to another image carrier, for instance a paper sheet, then the application or attraction of colored magnetic ink must be started with the ink supplied by the inking arrangement which forms the largest airgap with the magnetic recording layer. This is necessary in order to achieve that the dyes which are actuated only by portions of the recording layer will form an outer or upper layer of the thus produced color print. Any desired number of color copies or prints can be thus produced since the latent magnetic image of the recording layer is not destroyed thereby.
When colored copies of the original image are to be produced with magnetic dyes or printing inks of different permeability, then the length of the airgap between each of the dye supplies or inking arrangements and the magnetic storage layer may be the same for all colors, or all of the dif ferent colored magnetic inks or dyes may be jointly offered in the form of a dispersion. The dye with the greatest magnetic permeability will then be attracted by the portions of the magnetic recording layer creating the lowest field intensity, while the dye of lowest permeability will be only attracted by the portions of the magnetic recording layer creating the highest field intensity. In both cases, the color characteristics of the visible color copy can be influenced by adjusting the minimum field intensity at which the individual magnetic inks are attracted. This can be done by changing the distance from which the magnetic ink is supplied or offered or exposed to the magnetic storage layer carrying the latent image.
Apart from these inking methods which operate depending on a minimum field intensity and according to which each portion or point of the magnetic storage layer will attract a number of different magnetic inks, which number depends on the final color of such point or portion, the present invention also proposes an inking method for producing colored copies according to which the individual inking arrangement for any given color will not dispense magnetic ink below or above a certain range of magnetic field intensity or strength. This is accomplished by exposing the individual magnetic inks to the magnetic recording layer either on a permeable support or through a permeable orifice, the magnetic saturation value of which is lower than that of the respective ink by at most the threshold value of the respective inking arrangement, and which support or orifice, prior to reaching the saturation value of the ink has a lower total permeability than the latter.
With inking devices of this kind, like those described further above, there exists a threshold value which depends on the permeability of the magnetic ink or dye and the distance of the magnetic dye from the magnetic recording layer carrying the latent image. Below this threshold value the magnetic dye will not be attracted. Since at the beginning the total permeability of the dye is higher than that of the support, the induced magnetization within the dye rises faster than the opposing field induced in the support. As soon as the difference between these two magnetizations become greater than the threshold value of the inking device, dye will be supplied to or attracted by the magnetic recording layer. When the inking arrangement is exposed to external magnetic fields of a greater strength than the saturation value of the magnetic ink, then with increase of the external field only the induction of the permeable support will be increased and the difference in the magnetization will be reduced so that at a certain strength of the external field this difference will fall below the threshold value of the inking arrangement.
Thus, every point or portion of the magnetic recording layer will be supplied by this inking arrangement only with the specific magnetic ink which is correlated to the intensity of the magnetic field created by such point or portion. It is possible thereby to shift the range of magnetic field strength or intensity at which the inking arrangement for the specific colored ink will be actuated, by applying a permanent magnetic field which is superposed upon the magnetic field of the magnetic printing fonn or layer carrying the latent magnetic image.
According to a further embodiment of the present invention, the individual colored inks are offered by means of inking arrangements having partially overlapping range responses.
In this manner a subtractive mixed color application can be carried out. Magnetic printing methods are particularly suitable in this respect because it is possible to carry out the ink transfer without contact between the inking arrangement and the support for the transferred ink such as a copy sheet and thus even in the case of the so-called wet-in-wet" printing process contamination of the not yet applied dye at the inking arrangement, which would severely interfere with the subtractive method, will not take place.
On the other hand, particularly when very weak latent magnetic images are used for forming the copy, it might be advantageous to apply the magnetic ink with contact between the ink supplying roller and the printing form and to wet the latter in the manner conventionally carried out in connection with a planographic or lithographic printing methods in order to avoid transfer of ink by adhesion at the nonmagnetic portions of the printing form, i.e. at the portions of the printing form which are not within a magnetic field of the required strength. For this purpose, preferably an ink is used which, like an offset oil, consists of a binder which will be absorbed by the printing form, for instance a paper sheet, and which binder contains a large proportion of magnetic particles and pigment particles and/or magnetic pigments.
The field strength method may be carried out in connection with all recording layers consisting of portions or particles on which different magnetic field strengths can be imposed dependent on the intensity of the radiant heat image to which such recording layer is exposed. Thus, for instance recording layers may be used which contain permanently magnetizable, premagnetized constituents of different coercive force and different Curie points, or permanently magnetizable con- Furthermore, it is also possible to use in a simple manner a combination layer comprising one material with linear temperature dependency of its magnetic characteristics having embedded therein magnetizable core portions which have a Curie point located above the operating temperature of the recording layer. The large ranges of magnetic field strengths corresponding to a color may then be adjusted by suitably chosing different initial magnetic field intensities during magnetization, while the smaller differences in the magnetic field strength within the range of a color which determine quantitatively the strength or amount of the respective color which will be attracted, can be adjusted by means of the linear temperature dependency of the permeability of the covering layer or sheathing of the individual core portions. The foregoing will be further described in. connection with FIGS. 14 and 15 of the drawing.
By using these layers, several color separations may be united with each other on a single printing form and may be supplied wit magnetic ink in one path along inking arrangements for different colors which will be activated depending on the respective magnetic field intensities, and then transferred from the printing form onto a copy sheet, and this process may be repeated as often as desired since the magnetic printing form or the latent magnetic image will not be affected thereby. Since with respect to these layers the selection of temperatures during formation of the magnetic image acts only in one direction so that recordings applied with varying intensities will partially be superposed upon each other, the methods which can be carried out therewith are predominantly suitable for the reproduction of screened or rastered colored original images or form multiple form printing with changes in the printed matter or information of different forms within each set, whereby each portion of the surface of the magnetic recording layer will serve only for the recording of a single pure or primary color.
For the halftone block reproduction of mixed colors of an original image which is not a screened or rastered image, and without interposition of optical or chemical screening processes, a preferred embodiment of the present invention provides that during application with different intensities of the heat images of the individual color separations of a multicolor original image external magnetic fields of different field strengths are to be applied.
Thereby, preferably, the strength or intensity of the external magnetic field should be inversely proportional to the intensity of the heat image of the respective color separation. Thereby a double selection can be achieved, on the one hand, biased on the release temperature and, on the other hand, based on the magnetic field strength. lf then the ranges of magnetic field strength or intensity of the individual groups of magnetic particles responding to the difierent colors are arranged without overlapping or if the composite magnetic particles contain cores of differently steep slope of their respective initial magnetizing curves, then the magnetic field strength which is correlated with the magnetic particles of low coercive force cannot effectively magnetize the particles of higher coercive force, while the particles of lower coercive force are protected by the blocking effect of the sheathing which blocking effect will terminate only at higher temperatures. In this manner it is possible to dissociate or divide even mixed colors into networks or rasters of magnetic particles which represent the individual color components.
According to another embodiment of the present invention, the above-described storage devices for magnetic recordings or carriers of latent magnetic images can be utilized in a simple manner for multiple form printing with changes in the printed matter or information within different formsof each set. This can be accomplished by forming a plurality of latent magnetic images each of which, however, does not represent the heat image of a color separation but a specific information or printing arrangement, and each of which is imposed upon the magnetic image carrier or storage device at a different temperature so that the latent image can be read or utilized with a temperature selective arrangement or an arrangement which is selective with respect to the magnetic field strength. It is possible in this manner, for instance by selecting different reproduction temperatures or magnetic field strengths to print a set of multiple forms consecutively, starting from printing minimum information, for instance for a delivery slip, up to the complete text, for instance a bill including address, price, discounts, etc. It is also possible with the help of selecting maximum-minimum ranges of magnetic field strength to print or delete individual lines or columns, for instance of a work ticket.
Furthermore, according to another embodiment of the method of the present invention it is also possible to selectively reproduce portions of information or of a latent magnetic image although the entire latent magnetic image has been formed in a uniform manner. This is possible by forming the latent magnetic image in a layer or the like which includes constituents the permeability of which is temperature dependent and by heating certain lines or other portions of the magnetic image carrier to a temperature at which the blocking effect of the particles of temperature dependent permeability is greatly reduced. An inking arrangement having a threshold value of about the magnetic field strength of the not released, i.e., still blocked particles will then cause only transfer of ink corresponding to the released particles or magnetic image portions. It is possible with this arrangement, independent of the number of different magnetic components in the recording layer, to reproduce any desired number of individual portions of an original image, including relatively very small portions of such image.
It is particularly advantageous to form the heat image to which the magnetic recording layer is to be exposed by heating the original image with a source of infrared rays and to shield portions of the original image which upon copying should be free of ink.
According to a further embodiment of the present invention, the arrangement for producing copies from a latent magnetic image will include for each differently colored magnetic ink or dye which is to be applied an ink supply roller or screen roller which consists essentially of a ferromagnetic material having a value of magnetic saturation which is lower than that of the magnetic ink by at most the threshold value of the dye or magnetic ink dispenser, and which prior to reaching the saturation value of the magnetic ink has a lesser total permeability than the latter. Preferably in such arrangement, the distance of each ink applying roller or screen from the carrier of the latent magnetic image should be individually adjustable.
Referring now to the drawing and particularly to FIG. 1, it is noted that the temperature dependency of the permeability of the mixed ferrites Ni Zn Fe Q Ni ln Fe Q, and Mn Zn e O are taken from the treatise Ferrite by Dr. J. Smit and Dr. H. P. J. Wijn, published in Philip technische Bibliothek, 1962. The first two mentioned materials belong to a series of materials within in which the temperature dependent properties can be continuously changed depending on the proportion of the nickel and zinc constituents. 1500 N4." is the trade name of a ferrite which is offered by Siemens & Halske AG for use in high-frequency cores. It is a nickelzinc ferrite of the approximate composition Ni ln Fe O, and has an initial permeability at room temperature of p.=l,500. Thermoperm is a trade name of an iron nickel alloy made by Krupp, containing about 30 percent nickel and used for temperature compensation in magnetic circuits.
Ambient room temperature is indicated by A and the temperature at which the respective material reaches its maximum permeability by B. The temperature at which the permeability has just dropped to the value 1 of a nonmagnetic material is indicated by C. This temperature is the approximate equivalent of the Curie point or temperature. lt can be seen that the heating of the ferrite materials from A to B,--B will cause an approximately linear rise of the permeability by about the factor 1.5.
In the case of Then-noperm, the penneability curve slopes downwardly in a linear manner at a factor of about 100, while further heating of the ferrites from the respective points B to the respective points C causes a drastic linear drop of the permeability by about the factor 1,000 down to the value 1 of a nonmagnetic material. When these ferrites form part of a mixed magnetic layer according to the present invention, then, as will be described in detail below, the shielding of the hard magnetic coercive constituents against an external magnetic field, as well as the weakening of the outwardly extending magnetic field emanating from these coercive constituents will change within the corresponding temperature ranges by about the same factor.
FIG. 2 is a graphic illustration of the temperature dependency of the lowering of a saturation premagnetization of several chromium oxides which are known from the patent literature and which, for instance, are described in German published application 1,152,932. In this case it is also possible to distinguish a temperature range from room temperature A to temperatures 8 -8, wherein the premagnetization is slowly reduced by about the factor 1.5, as well as a further range up to the temperatures C -C wherein the premagnetization disappears completely.
If one of these magnetic materials is used as the coercive constituent of a mixed magnetic layer according to the present invention the permeable constituent of which looses its permeability below one of the temperatures C C, then a layer is formed which can be magnetized only within a closely limited temperature range.
On the other hand, if the mixed layer consists only of premagnetized coercive or hard magnetic constituents having different Curie points, for instance of two materials the Curie points of which are at C -C and if difierent colors, for in stance red and black are correlated to the different coercive forces of these materials, then heating from A to B will first cause a dropping of the premagnetization and consequently of the intensity of red inking by about the factor 1.5. Upon further heating, the premagnetization will drop suddenly to the magnetic field strength correlated to the black magnetic ink and will finally disappear completely at C after first dropping to B which would correspond to a white portion of the pattern or original image.
FIG. 3 is a schematic view of the structure of a mixed layer according to the present invention which is formed of soft magnetic constituents 1 and hard magnetic constituents 2. The soft magnetic constituents may consist for instance of the ferrite Mn Zn Fe O which has been shown in FIG. 1 and which at 120 C. has a permeability of about p.=2,000 while at 130 C. the permeability has dropped to the value I of a nonmagnetic material. As the hard magnetic constituents, for instance the magnetic pigment known under the trade name Bayer S 12" may be used, i.e., a highly coercive, cobalt-containing cubical gamma-R having a coercive force of about 800 Oerstedt and within the range of operating temperatures of the layer a nearly unchanging permeability of ,u=l0.
According to FIG. 4, hard magnetic wires or grains 3 which may consist for instance of Bayer S 12 are covered with a soft magnetic sheathing or covering 4 which may consist for instance of the above-described Mn ,,Zn Fe O The wires may be arranged in the form of a screen or sieve or, as illustrated, the wires or grains may be embedded in a nonmagnetic carrier layer consisting for instance of resilient synthetic material, which, as far as magnetic properties are concerned, will have the same effect as if the materials 3 and 4 were embedded in arr.
For instance, as described further above, 60 percent by volume of 1,500 N4 may be wet ground in a ball mill for between about 20 and 40 hours until the particle size has been reduced to between 1 and 3 microns. A doughlike mass is then formed by mixing with 30 percent by volume of Bayer S 12 having a particle size of between about 10 and 30 microns and 10 percent by volume of an aqueous solution containing about 12 percent polyvinyl alcohol. The thus formed dough is then pressed through a perforated plate the perforations of which have the diameter of the desired grain size so as to form strands of such diameter and these strands are then comminuted for instance with a chopping knife. The diameter and length of the thus formed cylindrical particles are so chosen that they are equal to somewhat less than twice the diameter of the hard magnetic Bayer S 12 particles. It is achieved in this manner that each of the thus formed composite grains contains only one highly coercive permanently magnetic particle.
A suspension which may be spray dried can be formed of 50 percent by volume of an aqueous solution containing about 3 percent polyvinyl alcohol, 30 percent by volume 1,500 N4 and 20 percent by volume Bayer S 12.
Spray drying is carried out in conventional manner substantially similar to that used for producing milk powder. The suspension is mixed with air and sprayed through fine nozzles under high pressure into a stream of hot air which, in countercurrent to the sprayed suspension, withdraws moisture from the latter. The grain size of the thus formed granular mass depends on the viscosity of the suspension, the diameter of the nozzle orifices and the applied air pressure.
The thus obtained granular mass is then sintered by heating at about l,000 as described further above. Since thereby, in contrast to the first-described method of forming strands of the material, the granular mass is not compressed, the individual grains will remain substantially separated. Should some of the grains bake together, they can be easily separated again by impact comminution for instance in an impact mill. The sintered bodies are now rolled into a thermoplastic synthetic material, for instance into soft polyvinyl chloride and then together rolled to form a thin foil such as illustrated in FIG. 4, wherein the soft polyvinyl chloride forms the carrier layer 5.
On the other hand, it is also possible to embed the composite grains 34 in finely subdivided iron-nickel powder, for instance Thermoperm and to sinter the thus formed mixture. In this case, carrier layer 5 of FIG. 4, consisting of Ther moperm, would be of a linear temperature dependency of its permeability with lower permeabilities at higher temperatures as illustrated in FIG. 1.
Furthermore, FIG. 4 may also be considered as a cross-sectional view through a sieve or screen of a hard magnetic wire 3 which is coated with a soft magnetic material 4, in which case the surrounding layer 5 would represent nothing but air.
A thus covered wire can be drawn in conventional manner from a cylindrical bar of soft magnetic material having a hard magnetic core and substantially the same ratio between the diameter of the hard magnetic core and the soft magnetic outer bar as the ratio between these diameters in the drawn wire.
A layer of individual composite magnetic grains can be produced by applying the sintered composite grains by means of an adjustable rake to an adhesive support, for instance the gum-arabic coated surface of a sheet of paper.
FIG. 5 shows a preferably magnetically neutral carrier layer 6 to which has been applied a screen or raster of hard magnetic particles 7 and soft magnetic particles 8 which may consist of the above-described magnetic materials.
The structure of FIG. 4 can be produced in conventional manner, for instance similar to the method by which magnetically readable checks are produced with printing inks containing magnetic inks. Instead of indicia such as numbers, in the present case a fine dot or dash raster or screen is imprinted whereby a highly permeable pigment for instance 1500 N4 is applied so as to fill the voids in a printed screen of highly coercive pigment, for instance Bayer S 12.
According to one embodiment of the present invention, permanently magnetizable chromium oxides of the type illustrated in FIG. 2 may be used as the magnetic pigments, for carrying out a method, as described further above, wherein the mixed magnetic layer consists only of premagnetized coercive constituents having different Curie points.
In the left half of each of FIGS. 3, 4 and 5, the approximate course of the lines of magnetic force of a homogeneous external magnetic field are shown which penetrate through the respective layer at a temperature which is below the Curie point of the soft magnetic portions 1, 4 and 8, respectively.
1 The right half of each of FIGS. 3, 4 and shows the course or path of the lines of magnetic force at a temperature above the above-mentioned Curie point, such as in the case of the materials of FIGS. 3-5, a temperature above 130 C.
As long as the permeability of the soft magnetic constituents l, 4 and 8 which at most might have a value of 2,000 amounts to a multiple of the permeability of the hard magnetic constituents the permeability of which has a value of about 10, the hard magnetic constituents will remain nearly field free. However, as soon as the permeability of the soft magnetic constituents has dropped to the value l of nonmagnetic materials, the lines of magnetic force will favor passage through the hard magnetic constituents.
The distribution of the magnetic field in a substantially twodimensional screen or raster according to FIG. 5 can be computed in accordance with the laws applicable to an electrical network whereby the electric resistance is to be replaced by the magnetic resistance, the latter being proportional to the reciprocal value of the permeability. In the case of a threedimensional lattice, an increased shielding effect will be found due to the bending of the lines of magnetic, force at the separating planes between two media of different permeability. For instance, for a spherical shell such as a hard magnetic particle covered by soft magnetic material, the following equation according to R. Gans Einfuehrung in die Theorie des Magnetismus, published by Teubner, 1908, will apply:
wherein ri and r0 indicate the inner and outer radius of the spherical shell of soft magnetic material.
It is thus possible to calculate a shielding factor which connects the inner magnetic field H* unequivocably with the outer or external field H. The formula applies strictly only for a permeability l of the material located inside the shell. For a permeability of the highly coercive hard magnetic core portion which is equal to about 10, the formula must be appropriately adapted.
By choosing suitable proportions between core diameter and outer diameter of the composite magnetic particle, and/or between the permeabilities of the core and the covering layer, any desired shielding factor may be obtained which, furthermore, can be changed in a well-defined manner by adjusting the temperature of the layer, due to the temperature dependency of the respective permeabilities.
FIG. 6 illustrates four different core particles 9-12 which have different Curie points or temperatures indicated in core particle 12 as Tc, and different remanences of saturation. Each of the core portions 9-12, respectively is surrounded by covering or sheathing 13-16, respectively and the materials of coverings 13-16 have different temperature dependencies of their permeability. For instance, a chromium oxide according to FIG. 2 may serve as core, while the covering layer or sheathing may be formed of a material of the composition Ni ,Zn,,Feb-2O in accordance with FIG. 1. All of the composite magnetic particles are embedded in a soft magnetic layer 17 of linear temperature dependency of its permeability, similar to that of the Thermoperm of FIG. 1.
The composite magnetic particles of FIGS. 6, 14 and 18 may be produced in a manner substantially similar to that described in connection with FIG. 4, with suitable replacement of the specific magnetic materials.
FIG. 7 relates to FIG. 6 and shows on a uniform temperature scale the permeability curves m13 to m16 of the sheathings or core coverings 13 to 16, the magnetization curves k9 to M2 of the cores 9 to 12 and also the linear permeability curve 1 of the embedding material.
If a different color is correlated to each of the different types of composite magnetic grains, then it is only necessary to see to it (as will be described in more detail further below) that each color separation is applied to the recording layer as a heat image within a predetermined temperature range so that only the grains which are correlated to this color will be magnetized by an external homogeneous magnetic field the strength of which should be above the value of magnetic saturation of the grain type having the highest coercive force. For instance, within the temperature range of between and the blue and the "black" grains are still blocked due to the characteristics of the permeability curves m15 and m16. The blocking of the yellow grains has been terminated due to the drop of the curve m13 as well as the blocking of the red grains due to the drop of the curve m14. However, the yellow" composite grain can no longer be subjected to permanent magnetization since the material of the core of the yellow grain has already been heated beyond its Curie point, as indicated by curve k9. Thus, within the temperature range of between 80 and 90, only the red" grains are subjected to permanent magnetization, whereby due to the fact of the linear temperature dependency of the permeability of the embedding layer 17, a gradation of the intensity within the red range will be achieved. Similar considerations are applicable for all of the various types of composite magnetic grains whereby the grain type which is correlated to the highest temperature range, in the present case the black" composite grains may have any desired Curie point since it is to be actuated at all temperatures which are higher than the release temperature of the permeability curve m16 of its covering layer. Below the release temperature of the permeability curve m13 none of the composite grains of FIGS. 6 and 7 will be magnetized. At such portions no color will subsequently be applied to the latent magnetic image so that at such portions the color copy will be of the color of the supporting sheet, for instance white if the color copy is produced on a white paper sheet.
Referring now to FIG. 8, it is shown how the individual colors can be offered to the recording layer from different distances, provided that the various portions of the recording layer are of different magnetic strength in correlation to the individual colors, as described in connection with FIGS. 6 and 7. The field strength of the composite magnetic grains 12-16 which are correlated to the black color and which, according to the present example, amounts of 200 Oerstedt, will then be capable with respect to all color supply rollers 18 to 22 to overcome the adhesion of the ink film at the roller as well as any other retarding forces of the ink or dye. Since, however, black has been applied as the last ink, and assuming that opaque, covering inks have been applied, the outward appearance of the respective portion of the reproduced image or of a paper support interposed between the magnetic recording layer or printing form and the ink supply rollers on which the copy of the image is formed, will be black. If the visible image which is formed is to be further transferred from its original support to a final support, then the visible image must be formed by passing the magnetic recording layer or initial support along the ink supply rollers in a direction opposite to that of arrow D so that initially the color black will form the lowermost ink layer and only upon transfer onto the final support, the opaque black ink portions will appear on the visible surface. In carrying out this process care should be taken by suitably choosing the printing form surface, by wetting or by utilization of a separating agent, in a manner known per se in the art, that the ink, under the influence of the respective magnetic field will be transferred as a coherent film.
The blue" composite grain, due to its lower coercive force of only Oerstedt will only be capable to attract ink from ink rollers 19 to 21, the distances d1 to d3 between roller and magnetic recording layer being smaller than the distance d4 of ink roller 18. Blue will then be the topmost color or, by reversing the direction of passage of the recording layer relative to the ink rollers, blue will be the bottom color, and this will be desired if the color image formed in this manner for in-
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|U.S. Classification||346/74.6, 101/487, G9B/5.233, 430/39, G9B/5.243, 360/59|
|International Classification||G11B5/70, C09D5/23, G03G19/00, G03G5/16, G11B5/62|
|Cooperative Classification||G11B5/62, G11B5/70, G03G5/16, G03G19/00|
|European Classification||G03G5/16, G11B5/70, G11B5/62, G03G19/00|