Method and apparatus for recording and/or displaying images utilizing thermomagnetically sensitive microscopic capsules

[57] ABSTRACT

A method of producing a record of original images wherein the images are converted to equivalent heat images, the heat images are then transferred to a heat and magnetic field sensitive medium, and the final image is made readable by the action of magnetic means. A method of providing an information display which is viewable by means of reflected light and adaptable to be sustained in memory or reusable by erasure of the displayed information. The heat and magnetic field sensitive medium incorporates a capsular coating wherein the capsules contain magnetic particles suspended in a heat-meltable material, so that, as the material is changed from a solid to a flowable state by heating thereof, the particles with the scope of the heat image have freedom of motion and are rearranged by the magnetic field to a pattern corresponding to that of the original image, whereby the image is reproduced on the medium upon cooling of the heat-meltable material.

Claims, 11 Drawing Figures

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26·

PATENTED JUN 2 71972

SHEET 1 OF 2

3,673,597

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FIG. 2

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FIG. 3

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INVENTORS WILLIAM R. HORST a LOWELL SCHLEICHER

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BY

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PATENTED JUM 2 71972

3,673,597

SHEET 2 OF 2

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FIG. 8

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FIG. 9

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INVENTORS WILLIAM R. HORST a LOWELL SCHLEICHER

BY z //

THEIR ATTORNEYS

3,673,597

METHOD AND APPARATUS FOR RECORDING AND/OR DISPLAYING IMAGES UTILIZING

THERMOMAGNETICALLY SENSITIVE MICROSCOPIC CAPSULES

BACKGROUND OF THE INVENTION

The use of photoconductive materials in thermography has heretofore been successful in the process and procedure of writing or printing wherein heat is utilized to produce a visual _ copy from optical images. Currently, a common method used to produce a hard copy from these optical images involves the use of standard photographic film or paper, or the use of one of the various forms of electrophotography. The methods commonly used cannot be criticized from the standpoint of quality, but they are costly in equipment and accessories, so that such methods are used only in those limited areas where the need exceeds the economic concern. Representative of one process is where an optical image is projected upon a layer of heat-sensitive material on a record-receiving sheet 20 wherein the sheet converts the incident light energy into heat energy, thereby producing a thermal image and a subsequent visual image.

A specific example of the prior art is shown and described in U.S. Pat. No. 2,798,959, issued July 9, 1957, on the applica- 25 tion of Alexander J. Moncrieff-Yeates, the apparatus including a pair of parallel adjacent electrodes, a layer of photoconductive material between the electrodes, connection means for a source of voltage for the electrodes, means directing a light image on the photoconductive layer, and a layer of a 30 material which changes in visual characteristics in accordance with changes in temperature. One arrangement has a heat-sensitive material distributed within the photoconductive layer, and, in a second arrangement, a heat-sensitive material comprises a separate layer in contact with the photoconductive 35 layer.

Another example of the prior art is U.S. Pat. No. 3,221,315, issued Nov. 30, 1965, on the application of George T. Brown, Jr., Joseph A. Bakan, and David J. Striley, which patent shows and describes a magnetic recording medium utilizing microscopic capsules containing magnetic material entrapped within the capsules and suspended in an oily liquid, wherein permanent but erasable visual recordings are produced as a result of subjecting the recording medium to a magnetic field. Selected areas of the microscopic capsular coating are responsive to the magnetic field and present a markedly different appearance to incident light from the magnetic field sensitive coating in the unselected areas. The difference or contrast in appearance between the selected and unselected areas is accomplished by orienting the magnetic material in a manner so as to be either more transmissive or less transmissive of the incident light.

U.S. Pat. No. 3,320,523, issued May 16, 1967, on the application of Lyne S. Trimble, shows and describes a method for 55 visually indicating and recording magnetic fields utilizing small water-phase droplets having a resin coating, the droplets containing tiny magnetic particles suspended in the fluid. A lesser magnetic field aligns the particles into a permanent image by virtue of the fluid droplet density or viscosity, and a go transverse field of greater magnetic strength causes realignment of the tiny particles to destroy, or erase, the visible pattern.

Additionally, U.S. Pat. No. 3,472,695, issued Oct. 14, 1969, on the application of Helmut Kaufer, Erich Burger, and Hans- 65 Peter Huber, shows and describes a method for forming a visible image in a magnetizable ink layer by selectively heating the surface layer and subjecting the layer to an external magnetic force, the permeability of the magnetizable material depending upon the heating of the material in a predetermined 70 pattern, and then forming a permanent reproduction of the pattern. The magnetic image is produced with the help of variations of the permeability as a function of the temperature, in that relatively small heat differences have a reversible effect as a variable magnetic resistance in the magnetizing or 75 de-magnetizing field. Depending on whether a permanent field or an alternating field with decreasing amplitude is present (that is, whether, the increase or decrease of the permeability is used with the changes in temperature), it is possible to obtain either a positive copy or a negative copy of the original image.

SUMMARY OF THE INVENTION

The present invention relates to recording and/or display of images and, more particularly, to a method and apparatus for producing and obtaining permanent but erasable images of optical patterns. This invention brings together several technologies which enable the production of a hard copy at low cost but further provide economies by permitting the copy medium to be reused. Basically, the invention shows ways and means to convert an original image to an equivalent heat image, to transfer by conduction the heat image to a heat-andmagnetism-sensitive medium, and to produce the final image by subjecting the heated medium to a magnetic field. In one embodiment, optical images are projected onto and are admitted into a photoconductive transducer which converts or transforms these images into thermal or heat images. Immediately adjacent the photoconductive transducer element is the thermally sensitive medium, which includes a coating of capsules thereon, the capsules containing heat-meltable material in which are suspended a plurality of magnetic particles along with a dispersed non-magnetic material in the nature of a light pigment or like colored matter. The micro-encapsulated magnetic particles are generally “set” in the capsular non-magnetic material at room temperature, but they have freedom of motion in the material at elevated temperatures, the magnetic particles being of the order of one to ten microns in dimension, so as to employ a multitude of them within the capsule body. The capsule and the capsular coated medium are the subject matter of a separate patent application and will not be shown and described in detail in this application, but will be incorporated by reference in so far as to teach the importance of the capsular construction in relation to the present invention. The capsular coated medium or substrate may be paper, tape, film-like material, or glass, or it may be associated with a surface of any material which is in sheet form, provided that the surface is compatible to accept the capsular coating and that the proper magnetic field may be applied thereto. The capsules may be coated on an endless tape or on a drum or a disc to be used as the subject of a temporary recording operation of write, erase, and write, in which the information is temporarily stored as the supporting material is moving. Suffice it to say that the heat-meltable characteristic of the capsular coated medium plays an important part in the working of the present method and apparatus.

Two arrangements utilizing the concept of the transducer element and the coated medium may be accomplished, wherein one is termed a “through” conductor arrangement and the other is termed a “surface” conductor arrangement. In the through arrangement, the assembly includes two parallel electrically conductive surfaces separated by a photoconductive material, so that, when an optical image strikes the photoconductive material, an electric current flows from one conductive surface through the photoconductive material to the other conductive surface. This action locally generates heat in the area struck by the light image, and the heat passes through one of the conductive surfaces to the heat or thermal sensitive material — for example, capsular coated paper — which paper is adjacent one conductive surface. In this respect, the thermal sensitive material can be pressed against the outside of the conductor-photoconductive-material package, so the material may be in the form of a sheet, a roll, or a tape, and also be accessible to a preferred magnetic field. In the surface arrangement, the photoconductive material is in the form of a plate having the conductors laced or interwoven in a grid pattern, so that, as the optical image strikes the photoconductive material, the circuit is energized, and the

3,673,597 resulting heat image raises the temperature of the capsular material to that degree where the magnetic particles are free to move within the capsules and produce a copy of the optical image. The active element consists of a photoconductive layer on which the conductive strips are deposited, alternate strips being connected to one terminal of a power supply and the remaining strips being connected to the other terminal. An optical image striking the photoconductive material causes an electric current to flow from one strip (or more) to adjacent strips in that area illuminated by the image. This again produces heat which reacts with the thermal sensitive material to allow freedom of the magnetic particles within the capsules. In both arrangements, the optical image is converted to an equivalent heat image which, in turn, melts the material within the capsule, so that an electromagnet or a moving permanent magnet displaces or moves the magnetic particles in a manner to effect an image on the coated paper. When the capsular material sets or is allowed to return to its original, or unheated, condition, the magnetic particles also are set, and the image is therein produced for recording or display. If it is desired to erase the image, the area is subjected to a thermal element which melts the capsular material, and the particles are then free to move into a distorted field with the aid of the magnet. The above-mentioned recording operation makes the system suitable for storage for whatever length of time the data is required to be stored, and, in addition, it permits movement of the stored data from one place to another while the data is in existence. It also provides a delay of the existence of evanescing data such as is commonly used in operations of computers where a factor is required for a short time and then is erased. This is a magnetic delay line of relatively long time period characteristics as compared to electromagnetic delay lines which depend upon the flow of electricity and the induction effect thereof. This data can be recirculated as often as desired, as might be used in multiplication problems and calculations, until erased and replaced by another factor. The continuing exciting magnetic field for either writing or erasing is not required after the data is fixed, and it is intended to be reused in the fixed condition until an erasure thereof is desired.

In view of the above discussion, the principal object of the present invention is to provide a method and apparatus for recording and/or displaying original images by converting these images into heat images for effecting the record or the display.

Another object of the present invention is to provide a method for producing reusable copy from original images wherein the method utilizes a meltable material capsular coated medium.

An additional object of the present invention is to provide a printing and/or display device with characteristics whereby the printing and/or display may be retained or may be erased for reuse.

A further object of the present invention is to provide an information display which is viewable by reflected light and which utilizes both magnetic and non-magnetic particles in the meltable material capsular coating.

Additional advantages and features of the present invention will become apparent and fully understood from a reading of the following description taken together with the annexed drawings, in which:

FIG. 1 is a diagrammatic cross-sectional view of a coated medium responsive to heat and magnetism for producing a record of an original image;

FIG. 2 is a diagrammatic view of the position of the parts in a negative working medium;

FIG. 3 is a diagrammatic view of the position of the parts in a positive working medium;

FIG. 4 is a view of the capsular coating showing the effect of the action of a permanent magnet on the particles within the capsule;

FIG. 4a is a view of a modified capsular coating showing the effect of the action of a permanent magnet on the magnetic particles within the capsule;

FIG. 5 is a sectional view of a coated medium with the particles displaced and viewable by reflective light in the direction of the arrows;

FIG. 6 is a sectional view of a coated medium responsive to heat and magnetism and carried on an endless member for recording and display of printed matter;

FIG. 7 is a sectional view of a coated medium responsive to heat and magnetism for producing a display with memory;

FIG. 8 is a detailed view of the capsule showing a writing condition;

FIG. 9 is a similar view of the capsule showing an erasing condition; and

FIG. 10 is a diagrammatic view of the grid pattern portion of a typical transducer.

Referring to FIG. 1 of the drawings, there is shown a recording medium 12 in the form of coated paper which is responsive to heat and to a magnetic field. The structure and the composition of the coated paper are shown and described in a United States patent application of Robert G. Bayless, John J. Spiwak, Robert W. Brown, and Thurman J. Mattingly Ser. No. 25,223, entitled “Articles of Manufacture”, which application is co-pending with the instant application, and commonly assigned.

In accordance with the Bayless et al. application, the coating on the paper is composed of a plurality of minute capsules or tiny containers with transparent walls, which contain a heat-meltable material suspending tiny magnetic particles therein along with a dispersed non-magnetic light-reflecting material or pigment, the non-magnetic material being of white or other colored pigment; for example, in one composition of the capsule, the pigment is in the form of titanium dioxide. The capsules, containing the magnetic particles suspended in the heat-meltable material, can have sizes ranging from about 10 to 200 microns, usually average diameters ranging from about 15 to about 100 microns, and more usually from about 20 to 50 microns. The capsules are composed of a polymeric cell wall material which passes light, the wall enclosing a core containing a mixture of the heat-meltable material and the magnetic particles, and preferably additionally containing the particulate light-reflecting material, which serves to enhance the visual contrast in reflectivity observable upon magnetic alignment of the magnetic particles in a given region within the capsules. The heat-meltable material is a material which does not flow at moderate ambient temperatures yet accommodates movement of the magnetic particles responsive to the magnetic field at slightly elevated temperatures in response to heating. Such a material is usually a solid at the ambient temperature but is changed to a liquid at the elevated temperature to allow the magnetic particles to move freely within the capsules. Suitable materials which fall within this category include the various waxes such as tristearin wax, paraffin wax, beeswax, spermaceti wax, carnauba wax, hydrocarbon wax, polyethylene wax, silicone wax, grease, vegetable fat, petrolatum, margarine, or the like, which materials have a melting range of from about 60° C. to about 75° C.

The magnetic particles contained within the capsule core can be iron oxides (both red and black), iron flake, nickel flake or powder, stainless steel flake, barium-ferrite, iron carbonyl, or suitable ferro-magnetic alloys. Additionally, it is within the purview of the invention to utilize generally spherical magnetic particles which are themselves capsules in a range of diameter of from about 1 to about 10 microns and composed of finely divided magnetic pigment, such as red or black iron oxide particles having a particle size ranging from about 0.2 .to about 1 micron.

The capsular cell wall material can be any of the polymeric materials conventionally employed to form capsules for other purposes, such materials as gelatin-gum arabic, polyvinyl alcohol, starch or the like material which is a water-soluble polymer prior to the formation of the cell wall, yet upon cell wall formation can maintain wall integrity and resistance to breakdown over repeated thermomagnetic cycles to allow reasonable longevity for the magnetic record capsules.

3,673,597

The light-reflecting pigment material can be suitable particulate type such as titanium dioxide, zinc oxide, magnesium oxide, zinc sulfide-cadmium sulfide fluorescent pigments, nacreous pigments, aluminum flakes, or red or other colored dyes mixed or in solution with one or more components of the heat-meltable or immobilizing material.

Additionally, it is sometimes advisable to employ dispersing or wetting agents such as oleic acid, sorbitan monooleate, sorbiton trioleate, or the like to assist in uniformly dispersing the particulate light-reflecting material within the immobilizing or heat-meltable material at the time of encapsulation.

A typical capsule can contain as core material the following components in the indicated concentrations by weight: magnetic particles 5 percent to 35 percent, heat-meltable or immobilizing material 80 percent to 60 percent, particulate lightreflecting material 0 percent to 15 percent, and dispersing or wetting agents 0 percent to 5 percent. The total of the maximum percentages may be seen to be larger than 100 percent; however, the light-reflecting material and a wetting agent are not utilized under certain conditions.

Now, referring back to the drawings, FIG. 1 shows the structural elements of the invention in diagrammatic form, wherein a low-intensity image 14 is provided, a source of this image being one generated on the face of a cathode ray tube 15, which image is transferred and focused onto a selected surface. The image can also be obtained from an optical arrangement such as that used in a microform viewer or the like, and the image can be made up of any color or combination of color light, the only restriction being that the receiving surface or device must exhibit a sensitivity to that part of the electromagnetic spectrum.

In the present embodiment, the second element is a receiving surface or device in the nature of an opaque transducer 16, which converts the optical image into a corresponding or equivalent heat image. The transducer is prepared and constructed by depositing a thin layer of gold 18 onto the surface of a glass plate 20, after which a fine “interdigital electrode” or grid pattern is formed by well known photo-resist methods. A layer 22 of a photoconductive material such as cadmium sulfide or other like material is then deposited over the electrode pattern. The electrodes are connected to a source of electrical energy to provide heat by means of the flow of current across the electrode pattern, the resistance of the gold conductors being sufficiently small so that heat is generated only in the light-struck areas of the activated photoconductive materials.

With the basic configuration, as shown in FIG. 1, it is seen that, if the optical image is projected onto the above-described transducer, the areas where the light falls will become photoconductive, and the flow of the resistive current will produce heat in these selected areas. The amount of the heat produced is a function of the intensity of the light directed at the particular areas, and the optical image is therefore converted into a corresponding or equivalent heat image which is relatively high in temperature as compared to those areas where no light is directed or allowed to project. The electrical current passing through the electrode grid is, in effect, an amplification of the light energy in producing the required heating for the next step in the process of producing a copy of the optical image.

The third element of one embodiment of this invention is the recording medium 12, in the form of a coated paper or the like, as mentioned above, which is best termed a reusable copy medium. The coating on the paper generally comprises a plurality of capsules 24 having magnetic particles 25 and nonmagnetic pigment particles 27 suspended in heat-meltable material 26. The medium is reusable in that a series of optical images may be projected onto and through the transducer, which converts these optical images into heat images which, in turn, melt the material within the capsules 24, so that the magnetic particles 25 are free to move in the heat-meltable material 26 and around and about the pigment particles 27 when subjected to the influence of a permanent magnet or an elec6 tromagnet 30. After passage of the magnet, in one or the other direction as indicated by the arrows in FIG. 1, across the heated areas, the material in the capsules cools sufficiently so that the print or image is set and therefore readily observable. This is shown by the position of the magnetic particles 25 within the three central capsules, wherein the particles are substantially aligned in an image pattern of the optics, when they are displaced by the moving magnet. As will be later shown, the movement and grouping into position of the magnetic particles 25 when acted upon by the electromagnet 30 may take different shapes and forms; however, generally the particles will be displaced in a pattern readily observable when viewed from a certain direction. It should also be here stated that the size of the electromagnet 30 may be sufficiently large to cover an entire sheet of paper or the like, the magnet being fixed rather than movable, and actuated or pulsed in timely manner with the formation of the heat image to effectively displace the particles within the capsules 24. If it is desired to erase or delete the image thus presented, it is only necessary to reheat the entire area of matter on the coated paper, and again subject the area to the action of the magnet. This effectively changes the direction and alignment of the magnetic particles within the capsules, so that they are no longer aligned in a pattern corresponding to the original optical image.

When an optical image is projected onto the surface of the transducer 16 and electrical energy is pulsed therethrough, a corresponding heat image is produced on the surface 22 of the transducer opposite the optical image striking surface, and by conduction the heat image is transferred to the coated paper 12, thereby melting the capsular material 26 in those areas subjected to the heat image. The properly placed magnetic field is then moved in the direction shown, and the magnetic particles 25 are displaced nearer to the surface only in those capsules affected by the heat. Subsequent allowance of the capsules to cool to a lower temperature or to room temperature fixes the image on the paper.

It should be stated that the capsular material as described above would be white pigmented, as shown in FIG. 2 at the left side thereof, prior to the above sequence of operations, thus producing a black image on a white background when the magnet 30 is moved across the field of view and, observing in the direction of the arrows, the image being portrayed is represented by the three central capsules. When the original state of the coated paper is in its white reflective form, as seen by the position of the pigment particles 27 in the lower portion of the capsules, it is called a negative working medium in that, wherever light was projected in the initial image, a black permanent record is made, as shown by the displacement of the magnetic particles 25 in the lower portion of these three capsules. Thus, if the image was generated from negative microfilm, the final image would be a positive. If, oh the other hand, the recording medium has fixed an initial black form, as shown at the left side in FIG. 3, it would be a positive working system in that, where the light struck the surface of the transducer and was converted for the purpose of heating the corresponding areas of the coated paper, the final image would be white, as observed from the location of the pigment particles 27 within the three central capsules. Thus, if the optical image was again generated from negative microfilm, the final permanent copy would now also be a negative. This ability of the same recording medium to be either positive or negative working provides great flexibility in producing the choice of hard copy (positive or negative) regardless of the state of the optical information. In the positive working scheme, the position of the magnetic field must of course be different from that of the negative working system, as seen from the position of the magnets in FIGS. 2 and 3.

Once the image has been stabilized by bringing the temperature of the medium to ambient conditions, the contents of the capsules 24 are solidified, and the recording medium 12 can be removed from the apparatus and used indefinitely. To reuse the medium, the entire paper can be heated, and, by subjecting the paper to the magnetic field in proper position,

3,673,597 the coating can be reset in either condition (positive or negative working). Information can be recorded on the medium as described and removed from the apparatus for filing, and, at a later date, additional information can be added to the medium in an area not heretofore used without erasing the original data. Thus localized “add on” or “erasure” and also positive or negative working are possible with the meltable material feature of the coated paper.

The magnetic particles 25 in the two capsules or containers located adjacent the pole pieces of the magnet are shown displaced toward the bottom of the capsules, thereby exposing the non-magnetic suspension material 26 when viewed in a direction shown by the arrows. Although the magnetic material is in the form of ferric oxide, which is dark in color, in the area adjacent the pole pieces the material 26 effectively masks out the dark or black particles to show a white area on a black background. The pigment particles 27 are not shown in FIG. 4, it being known that the heat-meltable suspension material 26 may have characteristics which are similar to those of the pigmented particles. Various shades and colors of the waxes, etc., used for the meltable material are available; however, one of the best results is obtained from a material having a milk-like appearance. Therefore it is not always necessary to include the additional pigment for effective contrast with the magnetic particles.

In another simple form, as seen in FIG. 5, the substrate or paper 12 is coated with the capsules 24, and, by attracting the magnetic particles to one side of the capsule, the characters are displayed in a manner viewable by reflective light, wherein a portion of the paper 12 is coated with capsules and the capsules have been heated and subjected to a magnetic field. When the paper is viewed from the direction shown by the arrows, the two capsules at either end will appear black to the eye by reason of reflected light, while the two central capsules will appear white.

Referring to FIG. 6, there is shown a slightly different aspect of the recording medium, which is carried on an endless belt 40 to provide a reflector-type light display which is capable of displaying a number of lines of data but which is resettable. In this regard, the converted or displayed information is held permanently without the expenditure of energy beyond that used in establishing the initial information. In this display system, the important features are that multiple lines of data can be presented to the viewer, that the data is displayed without expenditure of energy such as is required with cathode ray tubes or other type devices, that the information can be changed as desired with energy expended only at the time of change, that the displayed information is viewed by reflected light, which provides for greater acceptability by the user as compared to cathode ray tube devices, and that it is possible to display more than one color.

The belt 40 has coated on its outside surface a multitude of the capsules 24 described above and described in detail in the above-referred-to copending U.S. Pat. application. The capsules contain the suspension material 26, the magnetic particles 25, and the non-magnetic dispersal particles 27, it being observed that the material 26 need not be of a meltable type but need only be sufficiently viscous at room temperature and highly fluidic at higher temperatures. In the rest condition, the dispersed material (magnetic 25 and non-magnetic 27) is held in place due to the solid nature of the dispersion or suspension material 26, whereas, in the working condition, the suspension material is melted and the particles of dispersed material are free to move about when attracted or displaced by the action of a magnetic field.

The capsules are heated to produce a viscous, or fluidic, state, which then permits the magnetic field to provide movement of the black magnetic particles in the desired direction. Once the magnetic particles are positioned properly, the liquid can be caused to solidify or to cool to ambient conditions, and the recorded information will be permanently held until one wishes to change it by repeating the proper sequence of steps.

The displayed data is held visible to the eye without the expenditure of additional energy once it has been set in the desired form. The capsules or containers 24 have transparent walls which are not affected by the heating of the material therein, and the size of the capsules can be varied, as mentioned earlier, but the most suitable size is in the range of 20 to 50 microns in diameter, the size depending upon the resolution requirements in the display or recordation of the final image. The meltable material can be viscous at room temperature but should have a significant drop in viscosity upon being heated and should be compatible with the material used for the capsule wall and with the dispersed particles. Mixtures of several capsules of different materials can be prepared, where each of the capsules uses a dispersion material that melts at a different temperature, and it is possible to combine the capsules so mixed and apply them to one belt, so as to thus provide the ability to record different information according to the temperature of the capsular area heated. If different colored non-magnetic pigments are used in the various capsules mixed, a multicolored display is possible where the actual color displayed would be determined by the temperature applied to the system.

Referring to FIG. 6 again, and looking at the left-hand side of the belt 40, it is seen that the particles 27 in the lower run have been so oriented that the coated belt appears white to reflected light, as viewed from the bottom of the belt. Moving counter-clockwise around the belt, a heating device in the form of a thermal printer 42 is positioned to input a thermal image on the belt, it being realized that a number of these printer elements can be arranged in a matrix from which any alpha-numeric character can be generated. By applying electrical energy from a cash register, a computer, or the like, the proper thermal element heats and, by conduction, produces a melted image in the capsules on the belt. A properly positioned magnetic field 44 attracts or displaces the black magnetic particles 25 and moves them to the lower side of the capsules on the surface of the belt, where they are held until the temperature is decreased and solidification of the capsule material 26 then fixes the information. Thus, as the belt 40 moves past the thermal printing elements, multiple lines of data or information are displayed in the form of black characters on a white background. Of course, it should be understood that not all the magnetic particles within the heated capsules are equally affected by the action of the magnetic field; however, for purposes of illustration in the several figures, the representation is much simpler than is the actual configuration of the particles.

Around the right side of FIG. 6 is a reset station comprising a heating element 46 and a magnet 48 positioned in relation to each other and to the belt 40 to effectively erase any displayed information. The heating element may be energized in a manner to heat the contents of the capsules across the entire width of the belt, or selected areas may be heated and erased or reset with the magnetic field positioned to act on these areas so that corrections can be made or additional data can be stored in the system. It should be noted that the abovedescribed system produces black characters on a white background; however, it is possible that the elements could have been set in their black-appearing form initially, and thus white characters could be produced on a black background. Although a thermal printer has been mentioned to produce the heat required to melt the capsular material, other devices, such as heated type or infra-red images projected on the belt could equally serve this purpose.

Another feature of the present invention is shown in FIG. 7 and concerns the provision of an information display which is viewable by reflected light, wherein a transducer 50 converts a projected optical image 52 into a corresponding heat image, which activates a film or layer of capsular coated sensing material 54, and a magnetic field 56 is applied to the activated sensing material to develop the image. The optical image 52, such as that obtained from a photographic slide projector, is projected onto the transducer element 50, and the transducer,

3,673,597 by its operation, becomes hot in any area struck by the light image and converts the optical image into a corresponding heat image. The heated pattern on the transducer melts the suspension material 58 in the layer of capsular sensing material, which permits the magnetic particles 60, dispersed and suspended in the layer, to move in response to the action of the magnetic field, whereby the light absorption and/or reflection properties of the particles in the heated areas are changed into a different arrangement within the capsules. As illustrated, the sensing layer or film 54 consists of a number of the small containers or capsules, each of which holds a mixture of the black magnetic particles 60 and the white non-magnetic particles 62 suspended in the heat-meltable material 58. Depending upon the arrangement of the magnetic particles 60 and the non-magnetic particles 62, the incident light will be either reflected or absorbed. For example, if the black particles 60 are magnetically displaced toward the front of the capsules, or to the right in FIG. 7, by the magnet 56, they will absorb the incident light and will appear black to the eye 64. If the field 56 is so applied that the black particles 60 are displaced toward the back side, or to the left, the white material particles 62 are forced to the front, or to the right, and, since these particles reflect the incident light, the image will appear white to the eye 64. When the heat is removed, the meltable material 58 solidifies, and all the particles 60 and 62 are fixed in the final image state.

Referring to FIG. 4a, there is shown still another example of a suitable sensing layer, which consists of small capsules 24 containing meltable material 26 and needle- or plate-like particles 25, where the cross-sectional area of these particles is much greater when the long dimensions of the particles are oriented along a plane perpendicular to incident light rays as compared to their orientation in a direction parallel to the light rays. In the perpendicular direction, most of the light rays will strike the particles, as seen by the orientation of the magnetic particles in the two capsules between the pole pieces in FIG. 4α, and will be either absorbed or reflected, depending on the characteristics of the particle surface. When oriented in the parallel direction, as seen by the orientation of the magnetic particles in the capsules over the pole pieces in FIG. 4α, most of the incident light rays will miss the particles and will pass through the sensing layer to be respectively absorbed or reflected by a coating under the layer. Again, the pigment particles 27 may be omitted from these capsules, as in the case of FIG. 4, where the suspension material is adequate for proper contrast.

A further example of a capsular sensing layer is the use of magnetic capsules 70 (FIGS. 8 and 9) having approximately one-half thereof in the nature of an optical absorber and the other half as a reflector, thereby permitting the absorption or reflection of incident light by proper orientation. Depending upon the position and/or polarity of the applied magnetic field 76, the resulting image on the viewing surface may be a positive or a negative reproduction of the input optical image due to the fact that either the white particles 72 or the black particles 74 can be brought into view as soon as the material within the capsules has been melted by the thermal image of the transducer 78. FIG. 8 shows a capsule 70 containing white non-magnetic particles 72 and black magnetic particles 74, wherein incident light at the right side of the capsule is reflected by the location of the white particles. The magnet 76 attracts or displaces the black magnetic particles toward the left side of the capsule upon heating of the meltable material suspending the particles within the capsule. The broom or brush effect of the clustered magnetic particles 74 near the surface of the capsule is readily observable under a sufficiently strong lens. FIG. 9 similarly shows the particles after heating of the material and subjection of the particles to a magnetic field, wherein incident light at the right side of the capsule is absorbed by the location of the black particles.

The shape of the magnetic particles shown in FIGS. 8 and 9 as being substantially long lines of particles, wherein each particle may include a north pole and a south pole, has also been observed in the position wherein the particle lines are rotated 90° from the effective forces of the magnet. Indeed, it is within the scope of the present invention to provide a single magnetic capsule within the sphere 70 and suspended in the heat-meltable material, wherein one-half of the magnetic capsule is coated with a light-reflecting and non-magnetic material. When the suspension material is heated and the magnetic action is imposed on the sphere 70, the single magnetic capsule will turn or rotate in response to the magnet.

Erasure of the viewing surface in some cases may be accomplished by introducing another optical image; however, for most applications, it is necessary to return the entire area of the sensing material to its original condition prior to re-use of the same areas. This is accomplished by causing the entire surface to be heated and then applying the proper magnetic field (normally the inverse of the field used in the initial cycle). The heating of the entire surface may be performed by uniformly flooding the transducer with light, by the use of a tin oxide layer between the transducer and the sensing material as an electrical heater, or by externally applied heat. The magnetic field required for input and erasure is performed with a permanent magnet or an electromagnet moved across the layer of sensing material at the proper time or by the influence of fixed-position magnets. The preferred choice of methods depends upon such factors as the size of the image area, the desired response time, space limitations, and the need for flexibility in shifting between the functions of input, erase, and positive or negative imaging.

The construction of the transducer element depends upon the wavelength of the energy constituting the input optical image and the intensity of the input image. An absorbing layer, such as a black pigmented coating applied on or against the input side of the layer of sensing material, serves as the transducer when the input image is of such intensity that its absorption will produce sufficient heating to activate the sensing layer. An intense laser beam, scanning across the transducer and modulated to produce the image, is an example of a form of input suitable for such a transducer, as is an infra-red pattern obtained through a stencil mask. As mentioned above, the photoconductive cell transducer of the surface or interdigital grid type goes through a change in resistance where light strikes the surface and the external power supply causes increased current flow through the photocell, thereby heating those selected areas in the creation of the desired thermal reproduction of the optical input image. The grid pattern of the transducer is shown in FIG. 10, wherein the gold electrodes 80 are connected to an electric source lead 84 and electrodes 82 are connected to a lead 86. As stated above, the grid is effected by depositing a layer of gold onto the glass plate and etched into the pattern as shown. The gold and cadmium sulfide layered glass plate is most satisfactory; however, other types which are capable of producing sufficient heat, such as semiconductor junction devices arranged as a matrix of photosensitive elements provided by integrated circuit techniques, are equally satisfactory. It is not necessary for the photocell to serve both as light detector and as heat element, as the heat can be provided by a matrix of individual electrical heater elements, each of the heater elements being suitably connected to a corresponding photo-detector of a detector matrix through direct connection or through an amplifier. Photothermographic transducers of the above types have been demonstrated capable of producing sufficient heat at input image light levels as low as 4 foot candles. Consequently, transducers of the above type are capable of providing a display from input images optically projected from picture projectors, microfilm viewers, television pictures, cathode ray tube computer terminal displays, or any other source of sufficiently intense optical images.

The transducer may also consist of a material capable of absorbing the energy of an electron beam and converting this energy to heat. For example, it is well known that many materials, including conventional cathode ray tube phosphors, become very hot when bombarded by an electron beam. This

3,673,597 provides the means for thermally activating the sensing layer when the input image is in the form of an electron beam rather than visible light, and, since an electron beam can provide high electrical current densities, the electric current flowing in the vicinity of the sensing material can provide the magnetic field to orient the particles as well as heat activation. A transducer constructed according to the last-described is capable of giving a reflected light image on a cathode ray tube screen and storing the image indefinitely after the beam is extinguished.

All the above discussion has considered the use of heat as the means of providing the image to the sensing material and a magnetic field to develop the image; however, the inverse may also be employed, whereby the entire area is heated for activation and the magnetic field is selectively applied to create the image.

It is thus seen that herein shown and described is a method and apparatus for recording and/or displaying images by converting an optical image into a heat image for melting the contents of capsules and then subjecting the capsules to a magnetic field. Certain variations on the above, other than those shown and described, may occur to those skilled in the art, so it is contemplated that all such variations having these features are within the scope of the invention.