Apparatus for forming an image with a reversible thermosensitive medium

Abstract: In image formation, a reversible thermosensitive medium, preferably in the form of an endless belt, is selectively heated in accordance with an electrical image signal, so that the areas of the thermosensitive belt will have different transmittances corresponding to the respective pixels of the image signal. A photosensitive member, preferably in the form of a drum, widely employed in electrophotography, is uniformly charged, and the thermosensitive belt is then superimposed on the photosensitive drum, and the photosensitive drum is exposed to light of a uniform intensity through the thermosensitive belt. The intensity of light which each area of the photosensitive drum receives depends on the transmittance of the corresponding area of the thermosensitive belt. An electrostatic image that is formed on the photosensitive drum as a result of the exposure is therefore a conversion from the transmittance image on the thermosensitive belt. A toner image may then be developed and transferred and fixed on recording paper.

Description: This invention relates to an apparatus for forming an image using a reversible thermosensitive medium in combination with a photosensitive member, according to the preamble of claim 1. Conventionally, recording methods using heat-emitting recording elements have been widely used in telecopiers and printers because the heat-emitting recording elements were low cost and the process was simple. In such devices, the image was written directly on thermosensitive paper. The recording paper used in this method however is a special paper which changes its color due to the action of heat, and it therefore has poor conservation properties. To improve this situation, a thermal transfer method has been proposed wherein an ink-coated film is used as an intermediate medium, the ink on the film is melted by the heat-emitting elements, and then transferred to paper. This method has been widely used in printers (see Japanese Patent Application Publication No. 61-030791, and "Proceedings of the 4th NIP Technical Symposium", Electrophotography Institute (July 23, 1987)). In the above arrangement, however, if the recording paper does not have a smooth surface, the ink cannot be completely transferred. Consequently, ordinary paper cannot be used to record images using heat-emitting recording elements. An electrophotographic method has been proposed in order to record on ordinary paper. If this is applied to printers, however, a laser and image-forming optical system, or an LED (light-emitting diode) array and image-forming system must be used as the exposure means, and the cost of the equipment is thereby increased. EP-A-0 322 903 shows an image-forming apparatus according to the preamble of claim 1. SUMMARY OF THE INVENTION Accordingly, an object of the invention as defined in claim 1 is to provide a low-cost image-forming device which solves the problems inherent in conventional equipment, and permits the recording to be made on ordinary paper. The reversible thermosensitive medium may have such a hysteresis characteristics between temperature and transmittance that it assumes a first state when it is cooled to a first temperature after being heated to a second temperature higher than said first temperature, and assumes a second state when it is cooled to said first temperature after being heated to a third temperature higher than said first temperature and lower than said second temperature. In this case, it is preferable that areas of the thermosensitive medium are selectively heated to said third temperature, and after the exposure the thermosensitive medium is heated to said second temperature to erase the transmittance image. When the development of the toner image is made on the thermosensitive medium, the transfer of the toner image to the recording paper, the fixing of the toner image on the recording paper and the erasure of the transmittance image on the thermosenstive medium may be achieved at the same location, by a combination of a heating roller and a pressure roller holding the thermosensitive medium and the recording paper between them. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the relation between temperature and density of a reversible thermosensitive medium of a first type, Type A. Fig. 2 is a diagram showing the relation between temperature and transmittance of a reversible thermosensitive medium of a second type, Type B. Fig. 3 is a shematic diagram of the image-forming apparatus of a first embodiment. Fig. 4A to Fig. 4F show the image-forming process of the first embodiment. Fig. 5 shows the sequence of operations for each component in the first embodiment. Fig. 6A to Fig 6G show the image-forming process of a second embodiment. Fig. 7 shows the sequence of operations for each component in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is featured by the combination of use of a reversible thermosensitive medium for conversion of electrical signals into a transmittance image on the thermosensitive medium, and use of a photosensitive member for conversion of the transmittance image into an electrostatic image on the photosensitive member. The photosensitive member may be in the form of a drum which is widely employed in the Carlson's electrophotography, which is well known, but is briefly described below. The Carlson's electrophotography uses a drum having a photosensitive surface which passes a charging section where the photosensitive surface is uniformly charged, an exposure section where the photosensitive surface is exposed to light image or pattern of light to form an electrostatic latent image consisting of charged areas and discharged areas, a developing section where toner is attracted to the charged areas of the latent image so that a toner image is developed, a transfer section where the toner image is transferred to a recording paper which has been brought into contact with the photosensitive drum, and a cleaning section which removes any residual toner on the photosensitive surface. The toner image that has been transferred to the recording paper is fixed by application of heat, for example, and the recording paper is then discharged from the apparatus. Examples of conventional electrophotography arrangements are shown in U. S. Patent No. 2,297,691, and "Fundamentals and Applications of Electrophotography, " page 28, and pages 303 to 304, Edited by The Society of Electrophotography of Japan, Published by Corona K. K., June 15, 1988. A reversible thermosensitive medium which also forms the crux of the invention will now be described. The reversible thermosensitive medium consists of a substrate coated with a thermochromic material. Recording on a thermochromic material can be made by utilizing its capacity to change transmittance depending on temperature variation. Fig. 1 is a diagram of the relation between temperature and color density of a reversible thermosensitive medium of a first type, which is hereinafter called Type A. The reversible thermosensitive medium of Type A shows a change of color density depending on temperature, and this change is reversible. There is hysteresis in the variation of temperature and color density, and the state of the material varies in the order A1, A2, A3 and A4 with rise and fall of temperature. When writing an image, the areas of the thermosensitive medium on which dots or pixels of one color (e.g., black) should be formed are heated from an initial state A1 to temperature above Tc. Thereafter, until the temperature is lowered to Tb, the thermosensitive medium maintains the state A4, and a color density is maintained to be different from the areas where pixels of another color (white, or background) are to be formed. If the reversible thermosensitive medium is then cooled below a temperature Ta, the image is erased. An example of thermosensitive material of the type A is shown in Proceedings of SID, Vol. 22/1, 1981, pp. 223 to 27, "Display System Using Reversible Heat-Sensitive Material" by Nakaya, et al. With this material, the temperatures Ta, Tb, and Tc are respectively, 20°C, 40°C, and 55°C. Another publication showing an example of such thermosensitive material is Technical Paper of the Institute of Electronics and Communication Engineers of Japan, Vol. 80, No. 123, IE 80-61 to 62 (September 24, 1980), pp. 1 to 8, "Display Device Using Thermotropically Reversible Material, "Saito et al. Fig. 2 is a diagram showing the relation between temperature and transmittance for a reversible thermosensitive medium of a second type, which is hereinafter called Type B. The thermosensitive medium of Type B is characterized by the fact that they change between a transparent state and a translucent state, and these two states can be maintained even at room temperature. Assume that this thermosensitive medium is first in the translucent state C at room temperature Te. When the thermosensitive medium is heated, the transmittance begins to increase at temperature Tf, and reaches its maximum at a temperature Tg. When the thermosensitive medium is then cooled to room temperature, it follows along the solid line and reaches the state D where it maintains the transparent state D. Next, If this transparent reversible thermosensitive medium is heated to a temperature above Th, it reaches an intermediate state between transparent state D and translucent state C. if the thermosensitive medium is then cooled to room temperature Te, it follows along the chain line, and reaches the original translucent state C. Let image-writing begin at state C. The areas of the thermosensitive medium on which pixels of one color (e.g., black) of the image are to be formed are heated to the temperature Tg. When the thermosensitive medium returns to room temperature, the areas heated to Tg assume the state D, and a difference of transmittance is thus produced between the heated areas and the non-heated areas. Further, if the thermosensitive medium is heated to a temperature above Th, it can be returned to the original translucent state C. An example of thermosensitive material of the type B is shown in Proceedings of 4 th Japanese Symposium on Non-Impact Printing Technologies Symposium, on July 23 and 24, 1987, pp. 57 to 60, "Reversible Thermosensitive Material and Printing Characteristics, Hotta, et al. With this material, the temperatures Te, Tf, Tg and Th are respectively 20°C, 50°C, 60°C and 72°C. Embodiments of the invention will now be described. First embodiment A first embodiment of this invention will now be described with reference to Fig. 3 to Fig. 5. The illustrated image-forming apparatus shown in Fig. 3 comprises a photosensitive member in the form of a photosensitive drum 11 rotatably mounted on a frame, not shown. The photosensitive drum 11 has a photosensitive layer on an electrically conducting support. Suitable materials for the photosensitive layer are selenium photosensitive material, and an organic photosensitive material. The image-forming apparatus also comprises a heating roller 12 and a pressure roller 13 which are pressed against each other by a means not shown. The heating roller 12 may be of a hollow metal member enclosing a halogen lamp, or one having a heat-emitting body disposed directly on a metal surface. An endless thermosensitive medium of Type B, in the form of a belt 14 is passed around the photosensitive drum 11 and the pressure roller 13. More particularly, the thermosensitive belt 14 is in contact, on a first or inner surface thereof, with the peripheral surface of the photosensitive drum 11 over a portion of the photosensitive drum arc, and as the photosensitive drum 11 rotates, the thermosensitive belt 14 moves together with the photosensitive drum 11. Where the thermosensitive belt 14 passes around the pressure roller 13, it passes between the heating roller 12 and the pressure roller 13. The location where the heating roller 12 confronts the pressure roller 13 forms an integrated transfer-fixing-erasure section (TFE section) 28. As the photosensitive drum 11 rotates its surface sequentially passes various processing sections or devices, namely a charging device 15, an exposure device 16, a developing device 17, and a discharge lamp 26. The exposure device 16 and the developing device 17 are provided to face the photosensitive drum, not directly, but through the thermosensitive belt 14. Between the location where the charging device 15 confronts the photosensitive drum 11 and tire location where the exposing device 16 confronts the photosensitive drum 11, the thermosensitive belt 14 is brought into contact with the photosensitive drum 11. Between the location where the developing device 17 confronts the photosensitive drum 11 anti the location where the discharging lamp 26 confronts the photosensitive drum 11, the thermosensitive belt 14 is separated from the photosensitive drum 11. Before being brought into contact with the photosensitive drum 11, the thermosensitive belt 14 passes through a thermal writing section 4, which comprises a thermal head 5 and a platen roller 6. The thermosensitive belt 14 is held between the thermal head 5 and the platen roller 6. After being separated from the photosensitive drum 11, the thermosensitive belt 14 passes the TFE section 28, a cleaning device 23, and a discharge brush 27. The thermal head 5 comprises a row of heat-emitting elements which are disposed to produce pixels of a transmittance image on the thermosensitive medium, and are driven selectively in accordance with electrical signals representing the image to be formed. When the heat-emitting elements are driven, they heat the areas for the corresponding pixels to the temperature Tg. When the heat-emitting elements are not driven, the areas corresponding to the respective pixels are kept at a temperature below Tf. The electrical signals representing the image are supplied from a controller 30 which also performs the overall control of the apparatus. The areas or dots of the thermosensitive belt 14 that have been heated to the temperature Tg have a high transmittance, while the areas or dots of the thermosensitive belt 14 that are kept below Tf have a low transmittance. This does not mean that each area can assume either of the two distinct states: a transparent state or a translucent state with a certain fixed transmittance: there can be intermediate states and the transmittance of each area is dependent on the density of the corresponding area of the image. However, the following description will be made assuming that the image consists of the two states, for simplicity of explanation and illustration. The charging device 15 is a corona discharge device for providing an electrostatic charge uniformly over the entire width of the photosensitive surface of the photosensitive drum 11. The charging device 15 may alternatively be formed of a brush charging device. The exposure device 16 exposes the photosensitive drum 11 through the thermosensitive belt, while the transmittance image on the thermosensitive medium is still maintained either because of the hysteresis characteristics or because the erasure takes place before the heated parts of the thermosensitive medium have not cooled substantially. The exposure device 16 is a light source, such as a fluorescent lamp, a halogen lamp, a row of LEDs (light-emitting diodes), for illuminating the thermosensitive belt 14 with a uniform intensity over the entire width of the thermosensitive belt 14. Because the transmittance of the thermosensitive belt 14 has been modulated according to the image the amount of light reaching the surface of the photosensitive drum 11 is modulated and hence an electrostatic latent image is formed on the photosensitive surface of the photosensitive drum 11. The areas or dots of the photosensitive surface which have been irradiated by light are discharged, while the areas or dots of the photosensitive drum which have not been irradiated is kept charged. Although there can be intermediate states and each area is discharged to the degree which is dependent on the transmittance of the corresponding area of the transmittance image, the following description will be made assuming that the latent image consists of charged areas and discharged areas, for simplicity of explanation and illustration. The developing device 17 is installed facing the outer surface of the thermosensitive belt 14 which is moving in intimate contact with the photosensitive drum 11, as described above. The developing device is provided with a developing agent support in the form of a roller 17a, to which toner 18 is attached. The toner 18 is transported so as to develop a toner image on the outer surface of the thermosensitive belt 14. The developing device may be a two-component magnetic brush developer, a one-component magnetic brush developer, or a one-component non-magnetic developer. The TFE section 28 applies heat and pressure on the thermosensitive belt 14 and recording paper 20 which is supplied in a manner described later to perform the transfer of the toner image onto the recording paper 20, the fixing of the toner image on tire recording paper 20, and the erasure of the transmittance image on the thermosensitive belt 14. The discharge lamp 26 is provided so as to face the part of the photosensitive drum 11 which has just separated from the thermosensitive belt 14 after developing. The function of the discharge lamp 26 is to irradiate the photosensitive drum through its entire width to dissipate all the charges on it thereby making it ready for next cycle of operations. As described earlier, after passing through the TFE section 28, the thermosensitive belt 14 also passes the cleaning device 23 and then the discharge brush 27. The cleaning device 23 is provided in apposition to the pressure roller 13, but after the TFE section 28. The function of the cleaning device 23 is to remove any residual toner from the thermosensitive belt 14. The discharge brush 27 is provided in contact with the thermosensitive belt 14. The function of the discharge brush 27 is to remove any residual electrostatic charge from the thermosensitive belt 14. The paper feed system for the recording paper 20 is comprised of a paper feed cassette 19, a paper pick-up roller 22, a paper advance roller 24, and a paper eject roller 25. Their operation Is controlled by the controller 30. The photosensitive drum 11 and the heating roller 12 are rotated at a constant peripheral speed in the direction shown by the arrow in the figure by a drive mechanism not shown. As a result, due to the friction of the photosensitive drum 11 and the pressure roller 12, the thermosensitive belt 14 is moved in the direction shown by the arrow. The image-forming process will now be described with reference to Fig. 4A to Fig. 4F. Fig. 4A shows the thermal writing step, Fig. 4B shows the charging step, Fig. 4C shows tire exposure step, Fig. 4D shows the development step, and Fig. 4E shows the transfer and fixing step. The reversible thermosensitive belt 14 is initially at the translucent state C (Fig. 2). In the thermal writing step shown in Fig. 4A, transmittance image is written on the thermosensitive belt 14 by selective heating in accordance with electrical image signals. The resultant transmittance image has transmittances for the respective pixels corresponding to the electrical image signals. The areas or dots heated to a high temperature to have become transparent are shown unhatched in Fig. 4A, whereas the areas or dots that have not been heated and remain translucent are shown hatched in Fig. 4A. In the charging step shown in Fig. 4B, the surface of the photosensitive drum 11 is directly charged uniformly by the corona discharge device 15. The photosensitive drum 11 is formed of a photosensitive layer 11a coated on an electrically conductive support 11b. In the illustrated example, a positive type photosensitive member is used, and positive charges are shown to be accumulated on the surface, as a high voltage is applied to the corona discharge device 15. In the exposure process shown in Fig. 4C, light from the exposure device 16 passes through thermosensitive belt 14 and is irradiated onto the photosensitive drum 11 to form an electrostatic latent image on the photosensitive layer 11a of the photosensitive drum 11. The amount of light irradiating each area or dot of the photosensitive layer 11a of the photosensitive drum 11 corresponds to the transmittance of the corresponding area or dot of the transmittance image of the thermosensitive belt 14. Simply stated, the electrostatic image consists of charged areas which have not been irradiated, and discharged areas which have been irradiated. In the developing step shown in Fig. 4D, reversal development is used, and a means 32 of applying a bias potential is connected across the electrically conducting support 11b of photosensitive drum 11 and the toner support 17a, to apply the bias potential. As a result, the discharged areas of the latent image on the photosensitive drum 11 attract the positively charged toner 18, and the attracted toner 18 is attached to the outer surface of the thermosensitive belt 14 directly over the discharged areas. More specifically, electric lines of force are generated between the toner support 17a and the discharged areas of the latent image on the photosensitive drum 11, passing through the thermosensitive belt 14. The particles of the toner 18 travel along these electric lines of force and adhere to the outer surface of the thermosensitive belt 14, and are kept adhering there by a relatively weak electrostatic force. Finally, the toner image on the thermosensitive belt 14 is moved past the TFE section 28. In synchronism with the toner image on the thermosensitive belt 14, the recording paper 20 is fed to the TFE section 28. More specifically, the recording paper is the supplied from the paper supply cassette 19, being picked up by the pick-up roller 22, and is advanced by the paper advance roller 24, such that the leading edge of the recording paper (to be precise, the leading edge of the area in which the image is to be reproduced) arrives at the TFE section 28 simultaneously with, and hence comes into contact with the leading edge of the area of the thermosensitive belt 14 in which the toner image is formed. The thermosensitive belt 14 and the recording paper 20 are moved at the same speed. Simultaneously with the transfer and fixing, the thermosensitive belt 14 is heated to a temperature above Th so that they reach the state D and they then resume the original state C when they thereafter cool. In this way, all the pixels along the entire width of the thermosensitive belt 14 will resume the original translucent state C ready for the next cycle operations. During the transfer and fixing, the recording paper 20 and the thermosensitive belt 14 are held between the pressure roller 13 and the heating roller 12. The toner image on the thermosensitive belt 14 is therefore melted by the heat of the heating roller 13, whereupon the pressure causes melted toner 18 to permeate the fibers of the recording paper 20. This transfers and fixes the toner image so as to reproduce a toner image (printed image) on the recording paper 20. The recording paper 20 is thereafter discharged or ejected by means of the eject roller 25, out of the housing of the apparatus, onto a stacker, not shown, for example. After the transfer onto the recording paper 20 is completed, a small amount of toner 18 may remain on the thermosensitive belt 14, however this is wiped off by bringing the cleaning device 23 into pressure-contact with the thermosensitive belt 14 on the heating roller 12. Further, the discharge brush 27 is also arranged in contact with the thermosensitive belt 14 to remove static electricity which may be present on the thermosensitive belt 14. In this way, the thermosensitive belt 14 is cleaned and electrically discharged, and may thus be used again. The above described steps repeatedly take place in sequence. In addition, while some of the steps of the photosensitive drum 11 are taking place, other steps of the thermosensitive belt 14 are taking place. Some of the steps are common to the photosensitive drum 11 and thermosensitive belt 14. Such sequence of operations in regard to each component is illustrated in Fig. 5, in which the dotted line indicates the sequence of the steps followed by the photosensitive drum 11, the chain line indicates the sequence of the steps followed by the thermosensitive belt 14, and the phantom line indicates the sequence of the steps followed by the recording paper 20. In the above-described transfer and fixing step, the thermosensitive belt 14 is heated by the heating roller 12 to reach a temperature of about 160°C. It must therefore be heat resistant. The thermosensitive belt 14 must therefore comprise a substrate which is sufficiently heat-resistant. Suitable materials include polyester, polyimide, polyetherimide, polyethersulfone and polyetheretherketone. Further, from consideration of the electric lines of force generated in the developing process, it is desirable that the thickness of the thermosensitive belt 14 be no greater than 200 µm; while from considerations of tensile strength and ease of handling, it is desirable that its thickness be no less than 10 µm. The arrrangement in which toner images are formed on the thermosensitive belt 14 rather than on the photosensitive drum 11 has the same advantages as the arrangement in which a belt is provided specifically for the development of toner images thereon as disclosed in earlier European patent applications No. 90101614.7 (EP-A-380.132) and No. 90101612.1 (EP-A-380.130) both filed January 26, 1990). Such advantages include reduction of the diameter of the photosensitive drum because of the reduction of the components that must be disposed around the drum, and the reduction of the friction and wear of the drum, and hence the possibility of using a less expensive photosensitive drum with a positive type organic photosensitive layer. In the above embodiment, the toner 18 is a heat fixing toner. Instead of the photosensitive drum 11, a photosensitive belt may be used. In this case, the thermosensitive belt 14 is made to pass by the photosensitive belt over a certain length, and the developing device is provided facing the thermosensitive belt passing 14 by the protosensitive belt. The positions of the heating roller 12 and the pressure roller 13 may be interchanged such that the thermosensitive belt 14 is passed around the heating roller 12, rather than the pressure roller 13. The recording paper 20 as used in the above embodiment may be replaced by any other form of recording medium. In the above embodiment, the thermosensitive belt of the type B was used. But the thermosensitive belt of the type A may alternatively be used. According to the embodiment described above, a transmittance image is first written on a reversible thermosensitive medium, which is then converted to an electrostatic image on a photosensitive drum. Low-cost heat-emitting elements can therefore be used for recording, and the apparatus can be offered at a low price. Further, printing can be made on ordinary paper, and there is no need for any special paper. Moreover, the efficiency of transfer from the thermosensitive belt to the recording paper is high. Furthermore, even if some toner remains on the thermosensitive medium after transfer, it can be wiped off easily. Still further, transfer and fixing can be carried out simultaneously by superimposing the developed thermosensitive belt and the recording paper, and the transfer does not take place electrostatically, and the transfer can thus be performed even if an electrically conducting toner which is easy to develop is used. Moreover, as the toner image transferred to the recording paper is simultaneously fixed, the handling of the recording paper within the apparatus is facilitated because there is no state in which the toner image has just been transferred but not been securely fixed. Furthermore, when the exposure step is combined with the transfer step and the fixing step, the device can be made more compact, and the cost can be reduced. In addition, as developing is carried out on the thermosensitive belt, the transfer efficiency is high, and even if some toner remains on the thermosensitive medium after transfer, it can be wiped off easily. There is therefore no need for the cleaning process used in conventional electrophotographic devices. Second embodiment Another embodiment of the invention will be described with reference to Fig. 6A to 6G. This embodiment is similar to the first embodiment, but the transfer of the toner image to the recording paper 20, the fixing of the toner image on the recording paper 20, and the erasure of the transmittance image on the thermosensitive belt 14 are carried out separately: the toner image on the thermosensitive belt 14 is transferred onto the recording paper 20 first, and thereafter the toner image on the recording paper 20 is fixed, at a location separate from the location of the transfer, and the erasure of the transmittance image on the thermosensitive belt 14 is conducted at a location separate from the location of the transfer. The operations at the respective steps are as shown in Fig. 6A to Fig. 6G, in which Fig. 6A to Fig. 6D respectively show the thermal writing step, the charging step, the exposure step, and the development step similar to those shown in Fig. 4A to Fig. 4D. Fig. 6E, Fig. 6F and Fig. 6G on the other hand show the transfer step, the fixing step and the erasure step, respectively, different from those in the first embodiment. Specifically, the transfer, the fixing and the erasure are carried out at separate steps. The erasure is achieved as the thermosensitive belt 14 is passed between a roller 64 and a whole-surface heating member 65, which uniformly heats the entire width of the thermosensitive belt 14 to a temperature above Th. The sequence of operations for each step is illustrated in Fig. 7, in which the dotted line indicates the sequence of the steps followed by the photosensitive drum 11, the chain line indicates the sequence of the steps followed by the thermosensitive belt 14, and the phantom line indicates the sequence of the steps followed by the recording paper 20. The advantages discussed in connection with the first embodiment except those derived from the simultaneous transfer, fixing and erasure are also obtained with this second embodiment.

Claims: image-forming apparatus comprising: charging means (15); exposure means (16); a photosensitive drum (11) having a surface moving to pass by said charging means (15) and said exposure means (16); said charging means (15) uniformly charging the surface of said photosensitive drum (11) as it passes by said charging means (15); thermal writing means (5); a reversible thermosensitive member (14), said thermosensitive member (14) passing by said thermal writing means (5) and then said exposure means (16); means for superimposing said thermosensitive member (14) with said photosensitive drum (11) when said thermosensitive member (14) passes by said exposure means (16); said thermal writing means (5) selectively applying heat to said thermosensitive member (14) to form a transmittance image represented by different transmittances; and said exposure means (16) exposing the uniformly charged photosensitive drum (11) through said thermosensitive member (14) on which said transmittance image has been formed, to form an electrostatic image on said photosensitive drum (11), said electrostatic image corresponding to said transmittance image; developing means (17) for forming a toner image corresponding to said electrostatic image; transfer means (12, 13) for transferring said toner image onto recording medium (20); and fixing means (12, 13) for fixing the toner image on the recording medium; characterized in that said reversible thermosensitive member (14) is in the form of a belt passed around said photosensitive drum (11) and passed by said transfer means (12, 13) and said fixing means (12, 13); said developing means (17) is disposed to confront said thermosensitive member being passed around said photosensitive drum (11), to form said toner image on said thermosensitive member (14); the toner used in the developing means (17) is of a type which melts by application of heat; and said transfer means (12, 13) transfers said toner image from said thermosensitive member (14) onto the recording medium (20) by application of heat. The apparatus according to claim 1, wherein said transfer means (12, 13) and said fixing means (12, 13) are integrated with each other to perform said transfer and said fixing at the same location. The apparatus according to claim 2, wherein said transfer means and said fixing means (12, 13) comprise a first roller (13) and a second roller (12); at least one of said first and second rollers (13, 12) is a heating roller (12); and said thermosensitive member (14) on which said toner image has been formed and the recording paper (20) are heated by said heating roller (12) and brought into pressure contact with each other by said first and second rollers (13, 12). The apparatus according to claim 3, wherein said apparatus further comprises means (22, 24) for feeding said recording medium (20) between said first and second rollers (13,12) such that said recording medium (20) is superimposed with said thermosensitive member (14); and said first and second rollers (13, 12) presses said recording medium (20) and said thermosensitive member (14) when they pass between said first roller (13) and said second roller (12). The apparatus according to any of the preceding claims, wherein said thermosensitive member (14) has such hysteresis characteristics between temperature and transmittance that it assumes a first state when it is cooled to a first temperature after being heated to a second temperature higher than said first temperature, and assumes a second state when it is cooled to said first temperature after being heated to a third temperature higher than said first temperature and lower than said second temperature, said thermal writing means (5) selectively heats the areas of said thermosensitive member to said third temperature; said apparatus further comprises erasure means (12, 13) for heating the thermosensitive member having passed the exposure means (16) to said second temperature to erase the transmittance image. The apparatus according to claim 5, wherein said transfer means, said fixing means and said erasure means (12, 13) are integrated with each other to perform said transfer, said fixing, and said erasure simultaneously. The apparatus according to claim 6, wherein said transfer means, said fixing means and said erasure means (12, 13) comprise a combination of a heating roller (12) and a pressure roller (13). The apparatus according to any of the preceding claims, wherein said belt forming said reversible thermosensitive member (14) is an endless belt. The apparatus according to any of the preceding claims, wherein said exposure means (16) comprises a light source of a uniform intensity across the width of the area of said photosensitive drum in which said electrostatic image is to be formed.

Inventors: ITOH SHINICHI C O OKI ELEKTRIC, TSUJI KENZO C O OKI ELEKTRIC I, ITOH, SHINICHI, C/O OKI ELEKTRIC INDUSTRY CO., LTD, TSUJI, KENZO, C/O OKI ELEKTRIC INDUSTRY CO., LTD
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1990
Main classification: G03F1
IPC codes: B41M5, G03F1