US3598993A

US3598993A - Imaging apparatus using a magnetizable printing ink with a temperature dependent magnetic permeability

Info

Publication number: US3598993A
Application number: US804777A
Authority: US
Inventors: Helmut Kaufer; Erich Burger; Hans-Peter Huber
Original assignee: Agfa AG
Current assignee: Agfa Gevaert NV
Priority date: 1969-03-06
Filing date: 1969-03-06
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10

Abstract

An image is formed by utilizing the temperature dependency of the magnetic permeability of a magnetizable material, in a device which comprises an image carrier carrying an image to be reproduced, a composite sheet including a layer comprising magnetizable material the magnetic permeability of which depends upon the extent of heating of such magnetizable material, a transporting arrangement for concurrently moving the image carrier and the composite sheet in superposed relationship adjacent to each other, a source of heat for selectively heating the composite sheet, while in such superposed relationship, corresponding to the image on the image carrier so that on the composite sheet a selective pattern of portions of the magnetizable material having a predetermined magnetic permeability range will be formed, which portions will correspond to the image on the image carrier, and a source of magnetic force located downstream of the heat source in the direction of movement of the composite sheet so that magnetic force will be exerted on the portions of the magnetizable material forming the selective pattern of predetermined permeability range.

Description

United States Patent [54] IMAGING APPARATUS USING A MAGNETIZABLE PRINTING INK WITH A TEMPERATURE DEPENDENT MAGNETIC PERMEABILITY [56] References Cited UNITED STATES PATENTS 2,793,135 5/1957 Sims, Jr. et al 117/175 2,909,118 10/1959 Wellcome, .lr.... 101/470 3,056,904 10/1962 Kotz et a1 250/65 X 3,202,093 8/1965 Childress 1 17/175 X 3,250,636 5/1966 Wilferth 1 17/17.5

Primary Examiner-William F. Lindquist Attorney-Michael S. Striker ABSTRACT: An image is formed by utilizing the temperature dependency of the magnetic permeability of a magnetizable material, in a device which comprises an image carrier carrying an image to be reproduced, a composite sheet including a layer comprising magnetizable material the magnetic permeability of which depends upon the extent of heating of such magnetizable material, a transporting arrangement for concurrently moving the image carrier and the composite sheet in superposed relationship adjacent to each other, a source of heat for selectively heating the composite sheet, while in such superposed relationship, corresponding to the image on the image carrier so that on the composite sheet a selective pattern of portions of the magnetizable material having a schims 10 Drawing Figs predetermined magnetic permeability range will be formed, [52] U.S. Cl 250/65 T which portions will correspond to the image on the image car- [51] Int. Cl. B05b 5/02, rier, and a source of magnetic force located downstream of 603g 15/14 the heat source in the direction of movement of the composite [50] Field of Search 101/470; sheet so that magnetic force will be exerted on the portions of 117/175, 238; 1 18/639; 250/65.1, 65.2; 346/74 the magnetizable material forming the selective pattern of M, 74 T predetermined permeability range.

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SHEET B 0F 4 Y PIIIEIIIEIIIIIIIIIIIQII TII %I Elli 77W I INVENTORS HELMUT KAUFER E BURGER H -PETER HUBER PATENTED AUB I 0 nan "SHEET '4 OF 4 v lml l IN V EN TORS HEL MUT KAUFE R E H BURGER By -PETER HUBER f n 46h? II! IMAGING APPARATUS USING A MAGNETIZABLE PRINTING INK WITH A TEMPERATURE DEPENDENT MAGNETIC PERMEABILITY CROSS-REFERENCES TO RELATED APPLICATIONS The present application is a division of our copending application, Ser. No. 428,964, filed Jan. 29, 1965 and entitled Method and Apparatus For Forming an Image, and now U.S. Pat. No. 3,472,695, issued on Oct. 14, 1969.

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for forming an image and, more particularly, the present invention is concerned with forming a visible image with the help of a magnetizable material, by heating the magnetizable material in a pattern corresponding to the image to be formed and by utilizing the variation of a magnetic property of the magnetizable material as a function of the temperature for producing a latent magnet image.

Several methods have been proposed for making latent magnet images visible and for magnetically transferring the same onto a suitable image carrier. Such magnet-printing processes are easy to carry out because the printing process itself as well as the possibly required cleaning steps can be carried out with the help of suitable magnetic fields without direct contact, whereby the intensity of the magnet fields can be easily controlled. When a graduated latent magnetic image has been produced or is available, it is even possible to produce halftone prints thereof.

However, up to now, these advantages were connected with the disadvantage that the latent magnet image could be produced only in a relatively involved and difficult manner. According to the known methods, for instance, the latent magnetic image is produced by pointwise magnetizing a remanently magnetizable layer, whereby the energizing current of the electromagnet is controlled through a photocell amplifier which scans an image which is to be reproduced. In another device which may be used for rapid printout in connection with electronic data processing apparatus, a matrix which is formed of small magnet coils is activated corresponding to the image so as to form a magnetic replica thereof. Another method of the prior art proposes the forming of a magnetic printing form by application of a highly permeable material in accordance with the pattern of the image to be produced.

Whenever in the present specification and claims reference is made to permeability, this is to denote magnetic permeability.

[1 has also been attempted to produce a latent magnetic image by heating a portion of a premagnetized layer of magnetic material, which portion corresponds to the image which is to be reproduced, above the Curie point of the material. Thereby, however, the useful range of temperatures is extremely limited by the coercive forces. Even when using the most favorable magnet material which presently is available for this process, such as ferromagnetic chromium oxides, it will be found that for Curie points in the temperature range which is suitable for the forming of an image or an image copy by application of heat, the coercive force drops to the lower limit of the value which is suitable for magnetic image formation and copying. Even at the upper limit of the temperature range which is suitable for the heat copying method, the coercive forces which can be brought to play suffice only for the selective attraction of very easily movable pigment particles which are located at a very small distance from the magnetic layer.

It is therefore an object of the present invention to provide a device which will not be subject to the above-discussed difficulties and disadvantages.

It is a further object of the present invention to provide an improved apparatus for effecting magnetic printing by utiliz ing the temperature dependency of the permeability of a magnetizable printing ink.

SUMMARY OF THE INVENTION The present invention proposes a device for forming an image by utilizing the temperature dependency of the magnetic permeability of a magnetizable material, comprising, in combination, an image carrier carrying an image to be reproduced, sheet means including a layer comprising magnetizable material the magnetic permeability of which depends upon the extent of heating of the same, moving means for concurrently moving the image carrier and the sheet means in superposed relationship adjacent to each other, heating means for selectively heating the sheet means, while in said superposed relationship, corresponding to the image so as to form on the sheet means a selective pattern of portions of the magnetizable material having a predetermined magnetic permeability range which portions correspond to said image, and magnetic means located downstream of the heating means in the direction of movement of said sheet means for exertion of magnetic force on the portions of said magnetizable material forming said selective pattern of predetermined permeability range.

The moving means, according to one preferred embodiment, will serve to move the image carrier and the sheet means along a straight path.

The magnetic means may comprise an elongated magnetic bar including opposite magnetic poles arranged immediately adjacent each other, or the magnetic means may comprise an elongated arrangement of a plurality of magnetic coils wherein, preferably, the magnetic characteristics of the individual coils will be separately controllable.

The moving means may include a driven rotatable transport roller and driving means for rotating the transport roller about its axis, whereby the driving means preferably may comprise an adjustable motor so that the rotational speed of the transport roller, and thereby the forward speed of the superposed image carrier and sheet means, may be adjusted.

The sheet means preferably will comprise a composite sheet formed of two superposed sheets which removably adhere to each other, whereby one of the sheets may be formed at its face adjacent to the other of the sheets with indentations capable of holding a magnetizable material at the portions of the indentations which are closer to the other face of the one sheet than to the other of the sheets, and the other of the sheets will cover the indentations in the adjacent face of the one sheet. Preferably the other of the sheets will be opaque so that the magnetizable material in the indentations, as long as the magnetizable material will remain spaced from the other sheet, cannot be seen therethrough.

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 drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows the permeability of several materials which are suitable for producing a transitory, latent magnetic image, as a function of the temperature;

FIG. 2 shows a schematic arrangement for the forming of a transitory, latent magnetic image in an intermediate layer;

FIG. 3 shows an arrangement wherein the transitory, latent magnetic image is produced in a carrier layer for the imageforming magnetic material (ink);

FIG. 4 shows the forming of a transitory, latent image in a magnetizable ink layer;

FIG. 5 is a schematic showing of the forming of a latent magnetic image in a permanently magnetizable layer by means of an intermediate layer of temperature dependent permeability which is inserted as a variable, magnetic resistance into the magnetizing or demagnetizing field;

FIG. 6 shows a raster or screen of highly coercive and temperature-dependent permeable magnetizable material arranged in a magnetic field;

' FIG. 7 is a schematic illustration of the forming of a copy by using a permanently magnetizable magnetic ink;

FIG. 8 illustrates schematically the use of a magnetizable sieve for applying a soft magnetic ink;

FIG. 9 schematically illustrates the use of a permanently magnetizable ink carrier layer; and

FIG. 10 illustrates a simple magnetic copying device which utilizes an ink raster or screen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention encompasses in a device for forming a copy of an image by utilizing the temperature dependency of the magnetic permeability of a magnetizable material, in combination, means for forming a surface of magnetizable material, the permeability of which depends upon the heating of the material, means for selectively heating the surface according to a predetermined pattern so as to form within the surface a selective pattern of surface portions within a predetermined range of permeability corresponding to the selective pattern of heating of the surface, and means for forming from the selec tive pattern of surface portions within the predetermined permeability a permanent reproduction having the same pattern.

Thus, according to the present invention, the magnetic image is produced with the help of variations of the permeability as a function of the temperature. A transitory, latent magnetic image is formed which is suitable for use in magnetic duplication processes as well as for carrying out a very effective printing process. For this purpose magnetizable materials are available in all temperature ranges including also the range of elevated temperatures directly adjacent to ambient or normal room temperature. Thereby the permeability may drop within a range of a few degrees centigrade from a four-digit value to that of a completely nonmagnetic material. Consequently, by utilizing relatively small heat differences, it is possible to selectively use external magnetic fields of any desired strength. Since the temperature dependent change of the permeability is reversible, it is possible to store the materials which are used for a certain specific manner of carrying out the method of the present invention even at temperatures which are above the working temperature of the respective method. I

A permanent latent magnetic image with, for practical purposes, any desired strength of permanent magnetic force can be produced many range of working temperature provided that, as further proposed according to the present invention, a layer of temperature dependent variable permeability is introduced as a variable magnetic resistance in a magnetizing or demagnetizing field which penetrates a permanently magnetizable layer. The magnetic record may then be fixed in a highly coercive magnetic material which may possess a Curie point which is considerably higher than the working temperature of the method, in other words, the magnetic record may then form a latent image in practically any presently known hard or permanently magnetic material. The layer of temperature-dependent variable permeability which controls the intensity of the recorded signal need not by itself possess any permanent magnetizability. Such materials are available in all desired temperature ranges.

Since the distribution laws which are valid for electric resistances arranged in parallel are also applicable for the magnetic resistance of two adjacent portions of a layer which is permeated by a magnetic field, the magnetic fluxes through two adjacent portions or points of a layer which is located in an initially homogeneous magnetic field will behave inversely to their local permeability number. Since further the materials which are available for this method possess four digit permeability values which upon heating to above the Curie temperature will drop to the value of l of a nonmagnetic material, it is possible in this manner to achieve very strong differences in the magnetization of the permanent magnetizable material which is located in the same or any identical magnetic flux. Depending on whether a permanent field or an alternating field with decreasing amplitude is present, it is also possible to produce either a positive or negative image.

Very thin and easily heatable layers and a particularly low influence of constant magnetic resistance portions are obtained by exposing a network formed of permanently magnetizable materials of low permeability and materials of high, temperature-dependent variable permeability to a magnetizing or demagnetizing field.

The method of the present invention may be carried out by utilizing the increase in the permeability which is connected with an increase in the temperature particularly of a ferrite or a mixed ferrite, or the steep drop of the permeability particularly of such'materials in the vicinity of the Curie point for producing variations of magnetization according to the image. Particularly the last-mentioned effect is suitable for carrying out a method which works very reliably and gives a great contrast, because in this area of the permeability curve, i.e., in the vicinity of the Curie point, a temperature rise of a few degrees centigrade will convert the magnetizable material from its condition of maximum permeability into a completely nonmagnetic condition.

According to a furthercharacteristic of the invention, it is possible to produce a graduated latent magnetic image by utilizing the progressive decrease of the permeability, particularly of a metallic magnetic alloy, for instance an iron-nickel alloy. When a graduated magnetic image which is obtained by means of a gradual increase or decrease of the permeability coacts, for instance with a powder dispersion or emulsion ink layer in which the magnetizable pigment particles are slowed down dependent on the printing speed, then a magnetic halftone print is obtained. Depending on whether the increase or the decrease 'of the permeability is used, either a negative or a positive copy of the original image is obtained.

Basically, the heat image which is required for producing the latent magnetic image can be applied in any desired manner, for instance by impressing for a short period of time a heated die. However, for quick conversion of an original image which, for instance, is drawn or imprinted on paper, into a latent magnetic image, preferably, the heat image which is required for producing the latent magnetic image is produced by an image controlled heat radiation. The known methods for producing a heat image provide the utilization of reflected as well as of transmitted radiation. With both methods, i.e. with reflected as well as with transmitted radiation, depending on the type of heat contact with the original image, and depending on the length of radiation, positive or negative heat images may be produced. Furthermore it is also possible to apply theheat image by an optical copying system which may be based on projection through a transparency, or also on projection of light reflection from an opaque image. In each of these reversible radiation methods, it is thus possible to adjust the entire copying method so as to obtain the most desirable positive or negative effect with respect to the prevailing magnetic or copying condition.

In connection with the present magnetic-copying method, particularly favorable conditions are achieved according to a further embodiment of the present invention by contacting an original image with-a layer of magnetizable material which is interrupted by a translucent screen or raster, whereby the image-forming portions of the original image possess an ability to absorb heat which differs from the ability to absorb heat of the image free portions. This is particularly advantageous when thereby a heat image is produced in a layer of magnetizable material which possesses in the vicinity of the Curie point steeply dropping permeability characteristics, which heat image comprises portions formed at a temperature closely below the temperature at which the permeability reaches its maximum, as well as portions formed at a temperature which is above the Curie point.

When using transitory, latent magnetic images, according to a further characteristic or embodiment of the present invention, an arrangement can be made thus that a transitory or temporary, latent magnetic image is produced in an intermediate layer which is arranged between an external magnetic pole and the backing for the image which is to be produced. The image-producing material will then be attracted under the influence of a homogeneous magnetic field only at the portions of the backing sheet at which the heat image which has been formed in the intermediate layer has left a sufficient degree of permeability. Since, as described above, the permeability can be changed by one to a thousand-or can be brought from a four-digit value to the value of a nonmagnetic material, it is possible with this arrangement to achieve without difficulties a clearly different actuation of the printing or image-forming and the nonprinting or nonimage-forming portions.

Particularly advantageous structural conditions are met when the latent magnetic image is formed in a magnetizable carrier layer for the copy of the image which is to be formed or in a magnetically controlled sieve for the image-forming material. The image-forming material or magnetic ink will then be retained at the portions of the carrier layer in which the homogeneous magnetic field which acts on the magnetic ink and on the carrier layer can produce large'induced magnetic forces due to the still high permeability at these portions. This is preferably the case when the permeability of the carrier layer is considerably greater than the permeability of the magnetic ink and when the induction causing magnetic pole does not directly contact the magnetic ink. The printing magnetic ink is particularly firmly retained when it has to pass a regionally strongly magnetically controllable sieve, somewhat comparable with the silk screen process.

The simplest arrangement and at the same time the most immediate control of the attraction of the magnetic ink by the heat image, without any conversion loss is obtained when the latent magnetic image is produced in the image-forming or copy-forming material, for instance in a layer of magnetizable powder or in a magnetic ink layer. Here again in the homogeneous magnetic field only those particles of magnetic material will be attracted which still possess a sufficiently high degree of permeability. Thereby, negative or positive images may be produced by having the image formed either by the ink or magnetic powder portion which is thus transferred from the original layer thereof, or by the ink or magnetic powder portion of lesser permeability which has not been removed from the layer and which may subsequently be fixed to its original support in suitable manner known in the art.

The term homogeneous magnetic field as used hereinabove is not meant to denote a field which shows no gradation but is to denote primarily a field which is homogeneous at its origin, in other words, which at its origin does not include portions of varying strength, for instance corresponding to an image. it is entirely possible to produce a magnetic field which originates from two immediately adjacent magnetic poles and which is of diminishing strength in the direction towards the image-forming layer, in other words, a magnetic field which in the strict sense of the word would have to be considered an inhomogeneous magnetic field, and to shift the same by means of an intermediate or carrier layer of variable permeability in parts into the image'forming layer.

The effect of the arrangement according to the present invention can be further increased if the latent magnetic image isproduced in a plurality of adjacent layers of magnetizable material which possess complementary magnetic properties. Thus, for instance, a magnetic image may be produced in a carrier for the magnetic ink as well as in the magnetic ink itself. lf in such case the permeability of the magnetic ink has characteristics opposite to that of the carrier, then, at the heated portions, an intensified transfer of the magnetic ink onto the carrier sheet for the copy which is to be produced, or by reversal of the characteristics an increased adherence of the notor less-heated portions of the magnetic ink at their original support will be accomplished. The same holds also true for the combination of magnetic ink and intermediate layer with identical characteristics, and intermediate layer and support also with identical characteristics, as well as basicallyalso for the combination of three layers, although in the latter case the exact application of the heat image becomes somewhat more difficult.

By utilizing the permanent latent magnetic image, it is possible to produce the same according to a further embodiment in the present invention also in the image-forming material. For instance, it is possible in a very simple manner by using an intermediate layer of variable permeability to accomplish a permanent magnetization of the magnetic ink corresponding to the image which is to be reproduced. The transfer of a thusprepared ink onto a carrier sheet can be achieved by the simple expedient of placing underneath a highly permeable material, for instance a soft iron plate.

A particularly effective separation of the printing and the nonprinting portions of the magnetic ink, i.e. of the imageforming portions of the magnetic ink from the remainder of the layer of magnetic ink can be achieved under utilization of the permanent latent magnetic image by using a permanently magnetizable sieve for the image-forming material such as a magnetic ink or magnetizable powder, which, for instance under interposition of a variably permeable intermediate layer which has been magnetized or demagnetized in a pattern corresponding to the image which is to be reproduced.

According to a further embodiment of the present invention, the image-forming material may be applied onto a permanently magnetizable carrier layer which contains the latent magnetic image, which carrier layer has been premagnetized or demagnetized under interposition of a variably permeable intermediate layer. It is possible to operate with the smooth surface of a thus produced printing form in a manner somewhat similar to the conventional lithoprinting. Due to'the fact that the inking in, as well as the printing and the cleaning is carried out without direct contact, this method can be carried out in a much simpler manner than lithoprinting and the useful lifespan of the printing form is considerably prolonged.

Such permanently magnetizable carrier layer containing the latent magnetic image is particularly suitable for attaching to a printing cylinder, whereby the printing form may be applied and extinguished in the printing machine. This possibility may be utilized in a particularly advantageous manner in connection with the partial printing according to the so-called system printing which is described for instance in U.S. Pat. No. 2,925,032.

It is also possible to form on a foil a layer which may be magnetized corresponding to an image and to attach the foil with the magnetizable layer thereon onto a printing machine which may be provided with special magnetic ink supply and cleaning devices. Furthermore, such foil of synthetic material or paper on which an image has been formed by application of a magnetic pigment or magnetic ink may serve not only as printing form but also as a copy of the original image by suitably fixing the image-forming magnetic pigment or ink thereon.

Several methods are known for making the latent magnetic image visible. Preferably, according to a further embodiment of the present invention, the latent magnetic image is made visible by means of a magnetizable powder with the individual particles thereof coated with a material which will melt at a temperature above the working temperature required for the forming of the magnetic image. In this case, the fixing of the image formed of the magnetizable powder on a carrier sheet can be carried out in a very simple manner by heating above the working temperature to the melting temperature of the coating, whereby this melting temperature may be sufficiently high so that the magnetizable powder having such coating may be stored in the vicinity of room heating devices such as radiators or the like without endangering the storability of the coated powder. This method is particularly suitable for magnetic duplication processes.

According to another embodiment of the present invention, in a magnetic printing method, the latent magnetic image is to be made visible by means of a magnetic printing ink wherein in a known manner a proportion of magnetic pigment-which is as high as possible is bound in a binder which will be taken up by paper. The large magnetic forces which can be controlled according to the present invention permit application of the magnetic dye onto a carrier sheet without direct contact between the magnetic dye layer and the carrier sheet. Due to the absorbability of the binder in the carrier sheet, the printed sheets may be immediately stacked so'that the magnetic-printing process can be carried out with the same speed as conventional printing processes.

According to the present invention, a device for carrying out the method of the invention preferably should include at least a motor-driven transporting roller, a source of heat radiation and an elongated magnetic bar such as is used for instance for extinguishing recordings on magnetic tapes. A particularly simple duplicating device is obtained by providing a hollow cylinder which preferably carries at its outer surface a translucent screen or a plurality of closely adjacent grooves and which is contacted by a sheet carrying the original image, as well as by a backing sheet for the copy which is to be produced. The cylinder serves as carrier for the image-forming magnetizable material, which is deposited in the grooves. Furthermore, a permanent magnet is provided which holds the portions of the magnetic powder, which serve for forming the image, in the grooves while the cylinder surface rotates downwardly, so that the not image-forming portions of the 'pulverulent material will fall off the cylinder surface.- The magnet is arranged so as to act on the magnetizable powder between a heating area in which the same is heated corresponding to the image which is to be copied, and a transfer area or printing line in which the cylinder surface is preferably located directly above the backing sheet for the copy which is to be produced. 1

Furthermore, in a simple device according to the present invention for producing undistorted, authentic copies, an endless resilient carrier band is provided'which on its outer surface is formed with translucent grooves and which passes through a bath of magnetic ink and a heating zone, whereby the outer surface of the band serves as carrier for the magnetic ink which represents the image-forming material. Immediately following the heating zone, in the direction of movement of the endless band, a permanent magnet isprovided which will draw the image-forming portions of the magnetic ink onto a carrier sheet which passes in the vicinity but out of contact with the endless band.

A device which permits the printing of a large number of copies as well as the printing of single copies or system copies ineludes, according to a further embodiment of the present invention, a cylinder which carries a permanently magnetizable carrier layer for the image-forming material and around which a device for applying the heat image, a magnetizing or demagnetizing device, a supply device for magnetic ink, a paper transporting device, a counter roller and a cleaning device are arranged. Preferably, there are also provided a pattern carriage for carrying the original image which is to be copied or printed and which carriage will move with a speed corresponding to the circumferential speed of the cylinder, furthermore, a mirror which can be interposed intothe path of the heat rays which form the heat image, as well as a thermostatically controlled heating device for maintaining a cylinder temperature which is slightly below the working temperature of the method. The ink supplying device, preferably, will include an ink container having a permanently magnetized outlet opening or screen opening, the magnetic forces of which will permit the flowing out of the magnetizable ink only under the combined influence of the gravity acting on the magnetic ink and the magnetic force of the ink carrier layer.

The strong permanent magnetic image which can be produced according to the present inventioncan be used in a particularly advantageous manner for carrying out magnetic printing by applying to a carrier layer'which is permanently magnetized in accordance with the image to be reproduced, a magnetizable material forming on the carrier layer a relief corresponding to the magnetic image, and the raised portions of which can be inked with conventional relief printing ink. Preferably, the surface of the carrier layer is provided with grooves or the like, in order to prevent a dislocation of the relief image during the printing process.

Referring now to the drawing, and particularly to FIG. 1, the mixed ferrites Ni Zn Fe,O Ni,,,,zn,,,,F,o, and Ml'10 5Zn0 5FzO4 are taken from the treatise Ferrite by Dr. -wijmtih l p q 1qi9h92i 2li9$hs5l22- The first two mentioned materials belong to a system of materials within which the temperature-dependent properties of the materials can be continuously changed as a function of the proportion of Ni or Zn. 1500 N 4 is the tradename ofa ferrite which is obtainable from the firm Siemens and Salske AG for use in high-frequency cores. Thermoperm" is the trade name of an iron-nickel alloy which is available for temperature compensation in magnetic loops and produced by the firm Krupp.

If the ambient room temperature is indicated by A, the temperature at which the permeability reaches its maximum by D and the temperature at which the permeability of the material drops to the value of l of a nonmagnetic material, which temperature is substantially identical with the Curie temperature, is indicated by C, it will be seen that heating of the materials from A to 31-84 will cause an approximately linear rise of the permeability by a factor of about 1.5 in each case, which upon suitable arrangement of the magnetic field and the retarding forces in the binder containing the magnetic pigments may be used for producing a magnetic image. ln the case of heating Thermoperms from A to C5, a permeability curve is found which drops by the factor with substantially linear gradation, which, for instance, is suitable for producing magnetic halftone prints.

Particularly favorable conditions are obtained when the temperature difference between B and C is used for forming the magnetic image. Thereby heating by less than 5 C. will cause a sudden change in the degree of permeability by a factor of 1,000. With devices operating in this range of permeability change, it is not necessary to take particular care with respect to the adjustment between the magnetic fields and the retarding forces of the magnetic pigment. If the pigment itself consists of a material which within the working temperature range of the method possesses a suddenly changing permeability, then the pigment will be attracted at the temperature B by'very weak magnetic fields, while upon exceeding temperature C, the pigment cannot be moved even by the strongest magnetic fields because it has become completely nonmagnetic.

In this manner, it is possible with the help of relatively low degrees of heating to control magnetic fields which are capable of achieving the desired effect with a very high degree of certainty. Therefore, the required heating can be carried out in such a manner that the temperature-dependent layer is generally heated by a thermostatically controlled heat source to the temperature B which preferably is slightly above the maximum possible temperature of the surrounding area. For producing the latent magnetic image it is then only necessary to carry out an additional heating of the image-forming portion by less than 5 C. These small temperature differences can be applied even with the help of copying systems for transparencies as well as those which project light reflected from an opaque image, although particularly the latter are of relatively low efficiency.

When a strong heat source is available, it is not necessary to carefully control the same, since for producing a difference in the permeability by the factor 1,000, it suffices if part of the layer is heated to any temperature between A and B while other portions of the layer are heated to a temperature above C which may be higher than temperature C to any desired extent, provided that the temperature does not reach the point at which the originalimage or for instance the paper backing thereof will be yellowed.

It is known from the pertinent literature that in addition to the materials illustrated in FIG. 1 there exist a great number of other materials which are suitable for carrying out the process of the present invention. Thus, cobalt mixed ferrites are known with a steeper rise and a shallower drop of the permeability curve, as well as magnetic metal alloys with Curie points which may be chosen as desired. Furthermore, it was found experimentally that the temperature curves of materials which were not produced for the purpose of having specific Curie points, very frequently represent the average values of a mixture from which by means of magnetic separation after heating to specific temperatures, groups of material with a correspondingly smaller variation of the temperature dependency can be obtained.

According to FIG. 2 a temperature dependent, permeable layer 1 is arranged as a magnetic resistance in the field of a magnet pole 4 which attracts the magnetic ink particles 2 onto a backing sheet 3 which may consist, for instance, of paper. In this case, the backing sheet or support 5 for the ink is formed of a magnetically neutral material.

In order to stress what is to be essentially shown in this and the following schematic representations, the details of the application of the heat image and of the fixing of the copy are not illustrated therein. In FIGS. 29, heating is shown by wavy arrows, inducted magnetism by small arrows and permanent magnetism by N or S, whereby the opposite pole or magnetic conductor which is generally required for producing the magnetic field, has not been illustrated. A small minus sign indicates that at this point either the permeability has disappeared or, in the case of the permanent magnetic image, no magnetization has been produced. In accordance with these symbols, FIG. 2 shows that at the portions of the intermediate layer which are not touched by the heat rays, due to the there still present permeability, magnetism is induced which is transmitted to the permeable magnetic ink particles which thereby, at these portions, are attracted to the carrier layer.

According to FIG. 3, the permeable ink particles 2 are firmly held at such portions of highly permeable support which possess within the working range of the method a strongly varying permeability, at which the high permeability and the magnetism which is induced in this layer by magnetic pole 4 has not disappeared due to heating, or at least has not dropped below the value presented by the ink.

According to FIG. 4, magnetic ink 2 possesses a preferably high permeability and in any event a permeability which within the working temperature range of the method is clearly temperature dependent. By means of an external magnetic pole 4 a sufficient magnetism is induced into the dye particles which have not been heated above a predetermined temperature, which magnetism suffices for attraction of these dye particles onto carrying sheet 3.

According to FIG. 5, a layer 1 having a temperature-dependent variable permeability is located in the magnetizing or demagnetizing field of external magnetic pole 4 which affects a permanently magnetizable layer 7. For the purpose of magnetization, pole N may be formed either by a strong permanent magnet or by a direct current coil. For demagnetization, the same coil is fed with alternating current. The carrier layer 7 is then moved jointly with intermediate layer 1 past pole 4. Intermediate layer 1, previous thereto has been heated in accordance with the image which is to be printed or copied, whereby each portion of permanent magnetic layer 7 passes through the tapered or decreasing alternating field which is required for demagnetization.

FIG. 6 shows a thin screen or raster 9 which may be formed on a magnetically neutral or generally constant permeable support 8 by a conventional printing process. Raster 9 consists of highly coercive portions 90 and temperature-dependent permeable portions 9b. If this raster consists for instance of magnetic pigments such as the one known as Bayer 81 l" which is used for producing magnetic recording tape and which has a coercive force of 800 Oerstedt and a permeability of the magnitude of 10, and of the mixed ferrite Mn Zn Fe, 0 which has a maximum permeability of about 2,000, then at temperature B according to FIG. 1, the by far largest portion of the lines of magnetic force 4a will pass through ferrite 9b. However, at temperature C2 at which the permeability of the ferrite has dropped to the value 1, the lines of magnetic force 4b will be passed to a large extent through the raster portions 9a which consist of Bayer S11 and which now possess the higher permeability and will give to these raster portions a permanent magnetization or, when an alternating field with decreasing amplitude is applied, will extinguish the previously present premagnetization.

According to FIG. 7, a magnetizable ink layer 10 is applied to a magnetically neutral support 5. Ink layer 10 has been magnetized according to one of the methods described further above in conformance with an image so as to form a magnetic image. The permanently magnetic ink portions caused by induction magnetization of a highly permeable layer 11 located behind the support for the image copy to be produced, and the magnetized image-forming ink portions are attracted in this manner to the support 3.

According to FIG. 8, a magnetic ink 2 is applied to a support 3 with interposition of a magnetic sieve which carries a latent magnetic image. At the magnetized portions of the sieve, the preferably highly permeable ink particles cannot pass the sieve and thus -a magnetic screen print is produced. This effect can also be obtained with magnetically controlled sieve which is formed of a material of temperature-dependent permeability.

FIG. 9 shows a foil 13 to which ink has been applied by conventional means, for instance an applicator roller which does not contact foil 13, by applying magnetic whiskers or the like so that the dye is applied only at the image-forming magnetized portions of foil 3. The magnetization has been carried out in a known manner with varying polarity in order to achieve a better contrast or a sharper delineation of the magnetic fields. The printing from a thus inked foil can be carried out in an offset manner, if desired also with interposition of a transfer cylinder.

According to FIG. 10, a paper 14 carrying prints on both sides is passed by means of a motor-driven transport roller 15 together with a translucent ink raster or screen foil l6, 17 along a source of heat radiation 18 and an elongated magnetic bar 19. Printed paper 14 and ink screen foil l6, 17 move at the same speed. The elongated magnetic bar 19 may consist, for instance like the permanent elongated magnets which are used for extinguishing tape recordings, of two immediately adjacent poles, or it may also consist of an elongated, possibly controllable arrangement of magnetic coils. Any desired source of red and infrared light may serve as source for heat radiation, however, in order to obtain a sharply defined heat image, the radiation should be as intensive as possible. For rotating roller 15, preferably a geared or adjustable motor is used so that the length of the radiation period may be adjusted to the heat absorbtivity and starting temperature of sheet 14 or of

foil

16, 17.

Foil

16, 17 consists of two

layers

16 and 17 which are preferably adhered to each other with a conventional pressure sensitive adhesive. Carrier layer 16 may consist, for instance, of a translucent paper or polycarbonate foil and is formed at its surface with groove or cup-shaped indentations 16a which may have been embossed into carrier 16 or formed together with the same in a casting or extrusion mold. lndentations 16a are filled at their bottom portion with a preferably highly viscous, nondrying, magnetizable printing ink 16b. Printing ink 16b fills the indentations 16a only partly and does not reach the surface plane of foil 16. This can be achieved, for instance, by removing excess printing ink with a rubber rake in a manner known, for instance, in intablio printing processes.

Cover foil 17 which is preferably dulled at its inner face and which consists of transparent paper of synthetic material will make printing ink 16b, when located at the base of the indentations 16a, practically invisible. Only portions of the printing ink which by the action of elongated magnet 19 have been brought in immediate contact with cover foil 17 will be visible through the same.

If the magnetizable constituents of the printing ink consist of a magnetic material possessing the temperature-dependent permeability required according to the present invention, then only those portions of the printing ink will become visible, whose permeability, corresponding to the heat image will permit attraction by external magnet pole 19.

In this one-sheet method, the heating in correspondence with the image which is to be copied can be carried out by a reflex method without interposition of a further layer. However, also by means of transmitted radiation positive right side right image are formed. This method will give authentic copies only if the cover foil 17 is torn off after the copying process and if a printing ink is used which contains an oil or binder which is absorbable in the material of the cover foil 17.

It is also possible to write on the unused foil 16-17 or on the foil on which a copy has been produced by means of a magnetic stylus or the like. The material, i.e., the composite foil 16-17 can be stored prior or after the copying process for any desired length of time, even at high temperatures.

The heat image is formed by the direct general radiation 18a in combination with the additional radiation 18b which corresponds to the image-forming portion and which is achieved by the reflecting portions 140 of the sheet 14. The absorption heat which is formed by the radiation 180 in the dark portions 14b of sheet 14 will be effective only upon very prolonged radiation and very close heat contact between sheet 14 and carrier 16. This translucentraster or screen arrangement which, as will be described below, is used according to several embodiments of the present invention permits to heat the ink even above yellowing temperature of sheet 14 or the like, provided that the absorption of

heat rays

18a and 18b by the ink is stronger than the absorption of heat rays 18b and. 180 by sheet 14. The absorption of heat rays by sheet 14 can also be controlled by pretreatment of sheet 14 with a more strongly reflecting protective lacquer. 'ln cases where the magnetic powder is to serve directly and without admixtures as the image-forming material, for instancein accordance with FIGS. 4 and 10, the powder which possesses the magnetic properties according to FIG. 1 should be ground as fine as possible in order to have a good adherence to the carrier sheet, for instance a paper surface on which the image is to be printed. Very fine grain sizes of the magnetic powder are obtained by'wet grinding for between about 20 and 40 hours of precominuted ferrite particles. It may be pointed out that the term "mixed ferrite as used herein does not denote a mixture of several ferrites, but a ferrite which contrary to a simple ferrite contains in addition to iron not only one metal oxide but several metal oxides, for instance like the nickel-zinc and manganese-zinc ferrite according to FIG. 1.

it is of course also possible to produce a magnetic printing ink which is suitable for the method of the present invention from the conventional materials of an offset printing ink. Thereby, the magnetic pigment is bound generally in varnishlike binders containing resinous and oily constituents. Upon contacting the copy sheet, the constituents of the binder separate into their component parts. The mineral oil constituent of the printing ink is immediately absorbed by the fiber structure, the fillers or the coating of the thus printed paper. The resinous constituents are thereby transformed into an immediately nonsmearable gelatinous form and adhere well to the paper. Known varnish combinations which quickly penetrate the paper are polymerized linseed oil and a resinous oil produced from mineral oil, or mineral oil combined with synthetic resins or rubber.

Such a magnetic printing ink which contains about between 5075 percent by weight of highly permeable magnetic pigment particles can be transferred in an inhomogeneous magnetic field which has a maximum field strength of about 500 Oerstedt across an airgap of between about 0.5 and 1 mm. formed between two rollers. The field strength required for such transfer across an airgap will be reduced, in known manner, by about the square of any reduction of the width of the airgap. It is possible to operate with a minimum field strength when transfer roller and printing form are in direct contact with each other so that direct ink transfer, due to such contact, would also be possible at the nonmagnetic portions, if in the manner of offset or flat printing such transfer at the nonmagnetic portions is prevented by moistening of the printing form.

Since the highly permeable-magnetic pigments do not always possess sufficient color strength, it is frequently advantageous to add thereto a certain percentage of conventional inorganic or organic pigments, for instance, channel black. This has been done in the example above by the addition of the Multilith printing ink which contains such black pigments.

It is, of course, also possible to apply in conventional manner, lacquer to the pigments in order to prevent undesirable spreading in the paper, and the consistency of the inkcan be adjusted to the respective printing process in conventional manner by the addition of appropriate diluting or thickening agents.

A layer of variable magnetic resistance corresponding to layer 1 of FIG. 2 can be obtained by mixing 50 percent of a pourable polyester resin, such as Leguval made by Bayer, with 45 percent by volume of ferrite powder, such as 1500 N 4 made by Siemens, and 5 percent by volume of a hardener (peroxide), and by pouring the mixture onto a proper support, for instance cylinder 44 of FIG. 13. A hard layer is formed thereby having a mean permeability in cold condition of about 15 and in hot condition, i.e. above the Curie point of the ferrite powder, of about 1.

In the same manner, however by using 50 percent by volume of Bayer S 12 powder, it is possible to produce a permanently magnetizable layer corresponding to layer 7 of FIG. 5. The particle size of the powder depends in both cases on the desired degree of optical resolving powder of the copy layer. Generally, the particle size may average about 10 microns.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of magnetic image-forming devices, differing from the types described above.

While the invention has been illustrated and described as embodied in a magnetic image-forming device utilizing the temperature variable permeability of certain materials, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

We claim:

1. A device for forming an image by utilizing the temperature dependency of the magnetic permeability of a magnetizable printing ink, comprising, in combination, an image carrier carrying an image to be reproduced; sheet means including two superposed layers removably adhering to each other, one of said layers being formed at its face adjacent to the other of said layers with indentations holding magnetizable printing ink at the portions thereof which are spaced from the other of said layers, said magnetizable printing ink having a magnetic permeability which depends upon the extent of heating of the same and being capable of being dislocated by magnetic force, the other of said layers closing the indentations in said face of said one layer; moving means for concurrently moving said image carrier and said sheet means in superposed relationship adjacent to each other; heating means for selectively heating said sheet means, while in said superposed relationship, corresponding to said image so as to form on said sheet means a selective pattern of portions of said magnetizable ink having a predetermined magnetic permeability range which portions correspond to said image; and magnetic means located downstream of said heating means in the direction of movement of said sheet means and facing the other of said layers for exertion of magnetic force on the portions of said magnetizable ink forming said selective pattern of predetermined permeability range, whereby upon passage of said sheet means along said magnetic means the portions of said magnetic ink forming said selective pattern will be drawn towards said magnetic means and thereby deposited at the inwardly directed face of said other layer.

2. A device as defined in claim 1, wherein said moving means move said image carrier and said sheet means along a straight path.

3. A device as defined in claim 1, wherein said magnetic means comprise an elongated magnetic bar including opposite magnetic poles arranged immediately adjacent to each other.

4. A device as defined in claim 1, wherein said magnetic means comprise an elongated arrangement of a plurality of magnetic coils.

5. A device as defined in claim 4, wherein the magnetic characteristics of the coil of the plurality of magnetic coils are individually controllable.

6. A device as defined in claim 1, wherein said moving means include a driven rotatable transport roller.

7. A device as defined in claim 1, wherein said moving means include a driven rotatable transport roller, and driving means for rotating said transport roller about its axis, said driving means comprising an adjustable motor so that the rotational speed of said transport roller and thereby the forward speed of said superposed image carrier and sheet means may be adjusted.

8. A device as defined in claim 1, wherein said other of said sheets is opaque so that as long as said magnetizable material in said indentations is spaced from said other sheet it cannot be seen therethrough.