JPH0924634A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is of low cost and can attain high processing speed by fitting a plurality of toner adhesion means for making toner adhere to a toner carrying means on the upstream side of a recording means, and changing toner adhesion by a plurality of toner adhesion means for each toner adhesion means. SOLUTION: An image forming device is provided with a thermal head 1, a platen roll 2, toner adhesion devices 4 (4a-4d), a toner carrying film 5 and film cartridges 6 and 7. The top end of the thermal head 1 where a plurality of heaters are fitted in a single line faces the platen roll 2 to form an image transfer part D. The toner adhesion device 4 makes non-magnetic toner stored in it attract to the underside of the film 5 while the toner carrying film 5 is passing through the toner adhesion device 4. At this time, CPU discriminates printing data of black, yellow, M(magenta) and C(cyan) according to a printing sequence to control the respective toner adhesion devices 4 as necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by transferring toner onto a sheet by a thermal transfer system.

[0002]

2. Description of the Related Art Today, as an image forming apparatus that prints on paper according to print information output from a host device such as a host computer, a printer apparatus using an electrophotographic method or a thermal transfer method is known.

For example, in a printer apparatus using an electrophotographic system, a charging device, an exposure head, a developing device, a transfer device, etc. are arranged around a photosensitive drum, and a charging device holds a predetermined charge in advance with respect to the photosensitive drum. Then, the exposure head performs optical writing according to the print information to form an electrostatic latent image on the photosensitive drum. This electrostatic latent image is visualized (formed into a toner image) by a developing device that contains toner, and is transferred onto a sheet by a transfer device. The transferred paper is heat-fixed with a toner image by a fixing device,
Emitted outside the machine.

In a thermal transfer type printer, an ink ribbon coated with ink on a base film surface is interposed between a thermal head that generates heat according to print information and a sheet, and the thermal head selectively generates heat according to print information. However, a method has been put into practical use in which the ink on the ink ribbon is melted and printing is performed at a position on the paper corresponding to the melted ink. The ink ribbon used for this is in the form of a long strip having almost the same width as the paper. Ink planes having a size substantially corresponding to the area of one sheet are formed in the longitudinal direction in a frame-sequential manner. The ink surface after the printing is transferred by the printing, and the ink is removed only at the printed portion. Therefore, the ink ribbon used once cannot be used again.

[0005]

By the way, as described above, the electrophotographic printer apparatus must use an expensive photosensitive drum. Therefore, it has the drawback of increasing the price of the device. Further, this system also has a drawback that the apparatus becomes large in size because a fixing device is also required.

On the other hand, the thermal transfer type printer device has the advantages that it does not use an expensive photosensitive drum and the fixing device is unnecessary, so that it is inexpensive and the device can be downsized. By the way, generally, the printing area ratio of a document is about 5%, and the non-printing residual portion after the use of the ink coated on the film of the ink ribbon is 9% of the whole.
It will be 5%. As described above, since the ink ribbon used once cannot be reused, the ink ribbon in which 95% of the ink remains will be discarded as it is. Therefore, as a result, this method has a drawback that it is uneconomical and its use cost is high. Further, if the surface of the paper is not smooth, the ink is transferred only to the convex portions of the paper, and the concave portions are likely to be blank, so that it is difficult to use plain paper and it is recommended to use special paper. Therefore, there is a problem that the use cost becomes higher. Not only that,
When performing color printing, an ink ribbon to which three or four colors of ink are applied in a frame-sequential manner must be used even if one-color printing is sufficient. Therefore, there is also a problem that the use cost becomes more expensive because all the inks of unused colors are wasted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional circumstances,
An object of the present invention is to provide an image forming apparatus that can be used at low cost and can be processed at high speed.

[0008]

The construction of the image forming apparatus according to the present invention will be described below. The present invention relates to a recording unit that selectively melts toner according to recording information, a platen that is arranged to face the recording unit, a belt-shaped toner carrier that carries toner particles on the surface thereof, and conveys the toner particles. The recording means has a conveying means for superposing the toner carrier and the paper and conveying the recording medium and the platen to the opposing portion, and the recording means selectively selects the toner on the toner carrier according to the recording information. It is premised on an image forming apparatus that melts and transfers the melted toner onto the paper to form a dot image on the paper.

In the image forming apparatus of the present invention, a plurality of toner adhering means for adhering toner to the toner carrying member upstream of the recording means, and the toner adhering by the plurality of toner adhering means are provided for each of the toner adhering means. And an adhesion control means for changing the adhesion control means.

The conveying means conveys the sheet back and forth at the portion where the recording means and the platen face each other, as described in claim 2, for example. The toner carrier has an adhesive member on the toner carrier surface, for example, as described in claim 3. Further, for example, as described in claim 4, the toner carrying surface is an elastic member.

Further, the image forming apparatus further comprises heating means for heating the platen, as described in claim 5, for example. Further, for example, as described in claim 6, it further comprises control means for heating and controlling the heating means to a temperature not higher than the melting temperature of the toner.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view schematically showing a configuration of a main part of an image forming apparatus as an embodiment. As shown in the figure, this image forming apparatus includes a thermal head 1, a platen roll 2, a recording paper conveyance path 3, a toner adhering device 4 (4a, 4b, 4c, 4d), a toner carrying film 5, a film cartridge 6 and It is composed of 7.

The thermal head 1 has an image transfer portion D formed with its tip end facing the platen roll 2. A large number of heating elements are built in the tip of the thermal head 1 and arranged in a line in the direction perpendicular to the paper surface of the drawing. The number of heat generating elements provided in the image forming apparatus is, for example, 300 dpi (dots / inch) for the printing density.
Therefore, when line-sequential printing is possible while A4 size paper is conveyed in the vertical direction, about 2,500 sheets are arranged. A pulse voltage according to the print information output from the host device is applied to each of these heating elements, whereby the heating of each heating element is selectively controlled.

On the other hand, the platen roller 2 is composed of a cylindrical member and is rotatable in the clockwise direction indicated by arrow A in the figure. The recording paper conveyance path 3 is formed of guide rolls, guide plates, etc., and reciprocally conveys a recording paper (paper) P sent from a paper feed mechanism (not shown) such as a paper feed cassette to the image transfer section D.

The toner-carrying film 5, which is a toner-carrying means, is made of a heat-resistant material such as polyimide, and moves between the film cartridge 6 and the film cartridge 7 by winding by a driving means (not shown).

The non-magnetic toner t is accommodated in the toner adhering device 4, and the toner t in the toner adhering device 4 carries the toner while the toner carrying film 5 passes through the toner adhering device 4 by the above movement. Adsorb to the lower surface of the film 5.

The toner t adsorbed on the toner carrying film 5 moves to the position of the image transfer portion D together with the toner carrying film 5 as the toner carrying film 5 moves to the right as shown by the arrow B in the figure.

The above-mentioned paper P is brought into contact with the toner-bearing surface of the toner-bearing film 5 conveyed to the image transfer section D so as to be superposed on the toner-bearing film 5, and together with the toner-bearing film 5, the right side shown by an arrow B in the figure. Move in the direction. While moving together with the toner carrying film 5, a toner image is transferred as described later. The paper P on which the toner image has been transferred is discharged out of the apparatus along with the paper transport path 3 so that the transferred toner image is not affected.

Next, FIG. 2 shows the configuration of the main circuit of the control unit of the image forming apparatus. As shown in the figure, the CPU
(Central processing unit) 11 has an I / F (interface)
Print data is input from an external host device via the controller 12. The CPU 11 includes a memory for a program and a page buffer for print data, which are not shown in the figure. It also has various I / O port functions. The CPU 11 follows the above program
Based on the print data input from the host device, processing for inputting / outputting control signals to / from each unit via the input / output port is performed.

The output ports are connected to the toner adhering device 4
A signal for applying (adhering) Bk (black, black) toner to the toner carrying film 5 is output to a, and Y (yellow, yellow) toner is applied to the toner carrying film 5 to the toner adhering device 4b. A signal is output, a signal for applying M (magenta, red dye name) toner to the toner carrying film 5 is output to the toner adhering device 4c, and C (cyan, greenish blue) is output to the toner adhering device 4d. The signal for applying the toner of 4) to the toner carrying film 5 is output. In this image forming apparatus, printing is performed in the order of Bk (black), Y (yellow), M (magenta), and C (cyan).

Further, the above-mentioned output port further outputs a signal for rotating the tip of the thermal head 1 in a direction in which the tip of the thermal head 1 is pressed against the platen roll 2 to the head crimping drive mechanism 14 so that the heating element of the thermal head 1 can be selectively heated. In addition, a print signal corresponding to the print data is output to the head drive mechanism 15 that applies a pulse voltage according to the heat history. Then, a drive pulse signal corresponding to the paper transport distance is output to the paper transport motor 16 that reciprocally transports the paper P to the image transfer portion D.

Next, the operation of the image forming apparatus having the above structure will be described again with reference to FIG. First, the CPU 11 has an I / F
Print data input from the controller 12 for each color 4
Colors are expanded in the page buffer at the same time. In this case, 4
Colors may be expanded in the page buffer one by one, and the next color may be expanded in the page buffer each time printing of one color is completed. By doing so, the memory capacity can be reduced.

The CPU 11 first determines the Bk (black) print data according to the above-described printing order, and determines the area (toner carrying) of the print data in the sub-scanning direction (the vertical direction of the paper P, that is, the conveying direction). (Length of film 5 side)
The toner adhering device 4a is controlled so that the Bk (black) toner is applied to the toner. Next, it is determined whether or not there is Y (yellow) print data, and if there is print data, the toner adhering device is configured to apply Y (yellow) toner to the area corresponding to the print data in the sub-scanning direction. 4b is controlled.
Subsequently, the M (magenta) print data is judged, and if there is print data in this case as well, toner is attached so that M (magenta) toner is applied to the area corresponding to the print data in the sub-scanning direction. Control the device 4c. Then, the C (cyan) print data is further determined, and if there is print data, the toner adhering device 4d is controlled so as to apply the C (cyan) toner to the area corresponding to the print data in the sub-scanning direction. . In any of the above cases, when there is no print data, the print data of the next color is immediately determined.

FIGS. 3 (b) and 3 (c) are views showing an example of a state in which the toner is selectively applied to the toner carrying film 5 according to the print data judged as described above. Also, the same figure
For comparison, (a) shows an example of the ink arrangement of a normal four-color ink ribbon. The ink ribbon 21 shown in FIG. 9A and the toner carrying film 5 shown in FIGS. 8B and 8C are both shown as being conveyed in the right direction shown by arrow B in the figure. There is.

As shown in FIG. 1A, the normal ink ribbon 21 includes Bk (black) ink 21a, Y (yellow) ink 21b, M (magenta) ink 21c and C.
The (cyan) ink 21d is applied in the same area in the longitudinal direction of the ink ribbon 21 in a frame-sequential manner. Since these are used as a set of four colors, the ink ribbon of a constant length is always consumed even if the amount of ink used for each color changes depending on the printing content.
For example, even when printing only Bk (black) and Y (yellow) print data, the ink surface of one set of the above four colors is used, and therefore Bk (black) and Y (yellow) other than those actually used are used. The two colors, M (magenta) and C (cyan), are discarded without being used.

On the other hand, in this example, as shown in FIG. 2B, for example, the toner ta of Bk (black) and the toner tc of M (magenta) are almost the same according to the actual usage amount. The size is applied over a wide range α and a range γ, respectively. Then, the toner tb of Y (yellow) and the toner td of C (cyan) are respectively applied in the narrow range β and the range δ according to the actual usage amount. In this example, Y
The application range β of the (yellow) toner tb is narrower than the application range δ of the C (cyan) toner td, and is the least applied among the four colors.

In this way, the color tone data (spectral data) is examined in the sub-scanning direction, and in the range in which there are colors to be used, such as the above ranges α, β, γ, and δ, the colors to be printed are The toner is applied in the sub-scanning direction. Therefore, neither the toner used nor the toner carrying film 5 has an unused portion, and there is no waste, so that the consumable member is economical.

Further, in FIG. 3C, only the toner ta of Bk (black) and the toner tb of Y (yellow) are repeatedly applied to areas of the same size. This is an image in which the print image in this case is composed of only black and yellow, and represents the state of the toner carrying film 5 when at least two such images are continuously printed on a sheet. Also in this case, since toner is not applied from the beginning for M (magenta) and C (cyan) which are unused among the four colors, neither the toner nor the toner carrying film 5 is wastefully consumed.

As is apparent from the examples shown in FIGS. 3 (b) and 3 (c), even if printing is performed with one color or two colors, there is no unused toner application surface, and therefore, a normal toner application surface is not used. It is not necessary to idle feed the toner carrying film 5 like an ink ribbon,
Therefore, the printing speed is increased.

On the one hand, the CPU 11 shown in FIG. 2 controls the toner adhering device 4 to apply the toner to the toner carrying film 5 as described above, and on the other hand, the head pressing drive mechanism 14 is provided with the tip of the thermal head 1. A signal for rotating in the direction of the platen 2 is output to press the thermal head 1 in the direction of the platen 2 so that the toner carrying film 5 and the paper P are sandwiched by the image transfer portion D, and the paper transport motor 16 is moved to the arrow in FIG. The paper P is conveyed in the printing direction together with the toner carrying film 5 by driving in the forward direction indicated by E (rightward in the drawing).
Then, on the image transfer portion D, B of the toner carrying film 5 is
When the area (adhesion surface) of the k (black) toner ta is present, the thermal head 1 is driven via the head drive mechanism 15 according to the print data of Bk (black). Further, in the case of other colors, the same procedure is performed in sequence. For example, when the area of Y (yellow) toner tb is present, Y (yellow)
The thermal head 1 is driven via the head drive mechanism 15 in accordance with the print data. The same applies to the case of M (magenta) or C (cyan). As a result, the toner of a predetermined color is transferred from the toner carrying film 5 to the paper P as described later.

When the printing process is performed as described above and the printing of one color is completed, the thermal head 1 is released from the pressure contact, and the paper transport motor 16 is moved in the reverse direction (leftward in the drawing) shown by the arrow F in FIG. It is rotationally driven, the paper P is fed back, and the initial print position is set. Then, the printing in the next color is performed again by the procedure described above. By repeating this, a desired plurality of colors are applied and overlapped on one sheet of paper P, and a full-color image or a desired hue image is printed.

FIG. 4 is a schematic enlarged view of the image transfer portion D for executing the above printing. Since each member shown in the same drawing is the same as each member shown in FIG. 1 described above, the same reference numerals as those in FIG. 1 are used in FIG. It is shown with the same symbols. As shown in FIG. 4, in the image recording unit D, the paper P and the toner carrying film 5 are overlapped between the thermal head 1 and the platen roll 2 with the film surface having the toner t attached to the paper surface. It is clamped in the closed state. Then, the thermal head 1 presses the toner carrying film 5, the toner t, and the paper P against the platen roll 2. In this state, the toner carrying film 5, the toner t, and the paper P move in the right direction shown by the arrow B or the arrow E in the figure with the rotation of the platen roll 2.

FIGS. 5A and 5B are enlarged views showing the state in the vicinity of the image recording section D at this time. Figure (a),
The heating element 1a arranged in the thermal head 1 is also shown in (b). It should be noted that the arrows A, B and C shown as the moving directions in FIG. 1A are the same as the arrows A, B and C shown as the moving directions in FIGS. 1 and 2, respectively.
As shown in FIG. 3A, while the toner carrying film 5, the toner t and the paper P move to the right together with the platen roll 2, the heating element 1a of the thermal head 1 is selectively controlled by the CPU 11. The toner t adsorbed on the toner carrying film 5 is melted and adheres to the paper P, that is, is transferred.

FIG. 3B is a diagram showing a transfer state of the toner t onto the paper P. As shown in FIG. As shown in the figure, when the heating element 1a generates heat based on the print data, this heat is transferred to the toner t through the toner carrying film 5, and the transferred heat is the temperature at the glass transition point (for example, about 150). (° C), the toner t melts to become toner t'and the paper P
Is transferred to The melted toner t ′ is transferred onto the sheet P and does not adhere to the toner carrying film 5 side because the electrostatic attraction between the toner carrying film 5 and the toner t is originally weak, and the melted toner t ′ is Paper P due to its viscosity
This is because it is easy to transfer to. In this way, the toner t'is transferred onto the paper P on the paper surface corresponding to the position of the heating element 1a which has generated heat according to the print data.

In this manner, when the above-mentioned printing (transfer of the toner t) by the thermal head 1 is line-sequentially performed in the sub-scanning direction of the paper P and printing of one color corresponding to one page is completed, as described above. Then, the paper P is conveyed in the reverse direction to print (transfer) the toner of the next color.

By repeating the printing operation as described above, a dot image (toner image) according to the print data is formed on the paper P. Then, the paper P on which the toner image is formed is discharged onto, for example, a discharge tray outside the machine.

As shown in FIGS. 5 (a) and 5 (b), the toner t
Are independently adsorbed on the toner carrying film 5. Therefore, when the toner t is transferred to the paper P, the individual toner t can flexibly contact the unevenness of the paper P.
Therefore, the toner t is completely transferred to both the convex and concave portions of the paper P. Therefore, unlike the case of a recording method using a thermal transfer type ink ribbon, the problem that printing on plain paper is difficult does not occur.

As described above, the image forming apparatus 1 of this embodiment
Is a device for electrostatically adsorbing the toner t on the toner carrying film 5 and line-sequentially transferring the toner t onto the paper P in accordance with the heat generation of the heating element 1a (thermal head 1) in the image transfer portion D to form a toner image. Is.

Next, FIGS. 6 (a) and 6 (b) are cross-sectional views of the vicinity of the image transfer portion when the adhesive layer is formed on the toner carrying film in the above embodiment. Figures (a), (b)
6A is a cross-sectional view when the toner carrying film 15 (15a, 15b) having the toner t attached to the image transfer portion D and the paper P are moving to the right in the image transfer portion D as the platen 2 rotates. . 5 (a) and 5 (b), the same members as those shown in FIGS. 5 (a) and 5 (b) are shown in FIG.
The numbers are the same as in (b).

In the example shown in FIGS. 6 (a) and 6 (b), the toner carrying film 15 is composed of a base film 15a and an adhesive layer 15b. The adhesive layer 15b is formed on the outer surface of the base film 15a, that is, the surface in contact with the toner adhering device 4 and the paper P. Base film 1
5a is made of a heat resistant film such as polyimide, like the toner carrying film 5 described above. Also,
The adhesive force of the adhesive layer 15b is not so strong, and is such that the toner t is held and the held toner t can be conveyed to the image transfer portion D without dropping.

Also in this constitution of the toner carrying film 15, while the toner carrying film 15 is moving in the toner adhering device 4, the CPU 11 controls the toner adhering device 4 to cause the toner on the adhesive layer 15b of the toner carrying film 15. t is attached. As described above, the adhesive force of the adhesive layer 15b is such that the toner t can be reliably conveyed to the image transfer portion D without dropping the toner t, and thus the adhesive layer 15b adheres to the adhesive layer 15b. The toner t is carried to the image transfer section D along with the toner carrying film 15.

Also in this case, as shown in FIG. 6B, the paper P, the toner t and the toner carrying film 5 are overlapped and sandwiched between the thermal head 1 and the platen roll 2 in the image transfer portion D, While moving to the right, the heating element 1a generates heat according to the print data. This heat is transferred to the toner t through the base film 15a and the adhesive layer 15b of the toner carrying film 15, and when the transferred heat reaches the melting temperature of the toner t, the toner t is melted to become the toner t'and the paper P is formed. Transcribed.

In this case, the force for holding the toner t on the toner carrying film 15 is the adhesive force of the adhesive layer 15b. Therefore, at first glance, the melted toner t ′ is not transferred to the paper P, and is likely to adhere to the toner carrying film 15 (adhesive layer 15b) side. However, in practice, the adhesive layer 15b
Does not adhere to. The reason will be described below.

That is, when the toner t is not melted and the adhesive force (electrostatic force due to friction) between the paper P and the toner t is F1 and the adhesive force between the adhesive layer 15b and the toner t is F2, the toner t is melted. When not, the adhesive force of the adhesive layer 15b is strong, F2> F1, and the toner t is the adhesive layer 1
5b (toner carrying film 15) side is still adhered. Therefore, the toner t is not transferred to the position of the sheet P corresponding to the heating element 1a that is not energized, and so-called background stain of the sheet P can be prevented.

On the other hand, in the energized heating element 1a, the toner t at the corresponding position is melted, the surface energy of the melted toner t '(the surface tension of the toner t') is lowered, and the toner t'is adhered to the melted toner t '. The adhesive strength with the layer 15b is reduced. Further, when the toner t is melted to become the toner t ′, the adhesive force between the toner t ′ and the paper P increases due to its viscosity. Therefore, the adhesive force between the toner t ′ and the adhesive layer 15b when the toner t is melted is F2 ′, and the toner t ′ and the paper P are
If the adhesive force with is F1 ', then F1'> F2 ',
The melted toner t ′ is transferred to the paper P. Therefore, when the heating element 1a generates heat, the toner t melted only on the paper P is discharged.
′ Is surely transferred.

The above mechanism will be described in more detail below. According to the adhesion theory, the adhesion energy (Wa) when a liquid comes into contact with the surface of a solid, that is, the above F1 ′ and F2 ′ is expressed by the following formula.

Wa = γs + γL- (√γs-√γL) ²
/(1-0.015 √γs · √γL) where γs: surface tension of solid γL: surface tension of liquid Since the molten toner is regarded as a liquid with high viscosity, the above formula represents the interface between the adhesive layer and the molten toner and the paper P. And can be applied to the interface of molten toner. Therefore, F1 ′ and F2 ′ are as follows: F1 ′ = γp + γt− (√rp−√rt) ² / (1-0.
Γrp: √rt) where γp: surface tension of the paper P γt: surface tension of the molten toner F2 ′ = γa + γt− (√γa−√γt) ² / (1-0.
Where γa: surface tension of the adhesive layer, the surface tension of the molten toner is about 23 [dyn / cm], and the surface tension of the paper P is about 45 [dyn / cm]. In addition, the adhesive layer 6 when a natural rubber material is used for the adhesive layer
The surface tension of -2 is about 24 [dyn / cm]. When F1 ′ and F2 ′ are obtained using these numerical values, F1 ′ = 61 [erg / cm ² ] and F2 ′ = 47 [erg / cm ² ] are obtained. Therefore, the molten toner t ′ can be reliably transferred to the paper P.

As described above, according to the embodiment, the molten toner t ′ can be reliably transferred onto the paper P, and the toner carrying film 15 is provided with the adhesive layer 15b. The toner t (t ′) is not transferred to a position where the transfer is not performed, and the background stain can be reliably prevented.

Next, FIGS. 7A and 7C are sectional views in the vicinity of the image transfer portion in the example of the embodiment in which the elastic layer is formed on the toner carrying film. This example is also shown in FIGS.
The same members as those shown in FIG. 5 are shown with the same numbers as in FIGS. 5 (a) and 5 (b).

In the structure in which the elastic layer is formed on the toner carrying film, the toner carrying film 25 is composed of a base film 25a and an elastic layer 25b as shown in FIG. 7 (a). The elastic layer 25b is the base film 25a
Is formed on the outer surface (the surface in contact with the toner adhering device 4 and the paper P). This base film 25a also
It is composed of a heat resistant film such as polyimide. The elastic layer 25b is made of silicon rubber having a predetermined hardness.

Also in this case, the toner t adhering to the elastic layer 25b of the toner carrying film 25 is transferred to the paper P at the image transfer portion D by the printing process by the CPU 11 described above.

The force with which the toner carrying film 25 holds the toner t is such that the elastic layer 25b wraps the upper part of the toner t due to its flexibility and flexibility, as shown in FIG. It is the force of Van der Waals (the force that appears in the adhesion phenomenon between solid surfaces) that is effectively utilized by contacting with the toner t.

If the toner-carrying film 25 is made of only a heat-resistant film such as polyimide, and therefore is not flexible or soft, the toner t is in point contact with the surface of the toner-carrying film 25, which is sufficient. There is a possibility that the adhesive force cannot be obtained. On the other hand, when the toner carrying surface is the elastic layer 25b as described above, the toner t comes into surface contact with the toner t in such a manner as to enclose the toner t as described above. That is, the upper surface of the toner t is embedded in the elastic layer 25b. The diameter of the contact surface increases as the contact surface is buried, and the size of the contact surface increases in proportion to the square of the diameter of the contact surface.
The contact area between the (elastic layers 25b) increases geometrically. Therefore, the power of Van der Waals will dramatically increase. As a result, the toner carrying film 25 can be provided with a sufficient function of holding and carrying the toner t in the above-mentioned print processing operation. In order for the elastic layer 25b to have a sufficient toner holding force, the hardness is preferably 30 degrees or less according to JIS-A.

Also in this case, as shown in FIG. 7C, the paper P, the toner t and the toner carrying film 25 are overlapped and sandwiched between the thermal head 1 and the platen roll 2 at the image transfer portion D. In this state, the heating element 1a generates heat according to the print data in this state, and this heat is transferred to the toner t through the base film 25a of the toner carrying film 25 and the elastic layer 25b, and the transferred heat is transferred. When the temperature reaches the melting temperature of the toner t, the toner t is melted and becomes the toner t ′, which is transferred to the paper P. Again,
The toner t ′ is transferred to the paper P without staying on the toner carrying film 25 side. The reason is the same as the above case.

Therefore, according to the embodiment, the toner image can be formed on the paper P and the background stain can be surely prevented. Next, still another embodiment will be described.

In this example, a heating device such as a heater is arranged in the platen roll 2. With this heater, for example, the temperature of the heating device is preheated to A1. This temperature A1
Is a temperature lower than the glass transition temperature A2 (for example, 150 ° C.) at which the toner t melts, and of course is a temperature higher than room temperature (for example, 20 ° C.).

In this example, such a heating device is provided in the platen roll 2 and the toner t is preheated by controlling it to a predetermined temperature (the above-mentioned temperature A1). With this configuration, it is possible to heat to the temperature A2, which is the melting temperature of the toner, in a short time based on the heat generated by the heating element 1a.

FIG. 8 is a diagram for explaining this, and is a diagram for comparing the case where the toner t is preheated to the temperature A1 by a heating device (not shown) and the case where it is not preheated. Toner t
If the preheating is not performed, the heating element 1a must heat from the normal temperature A0 to the temperature A2.
It costs 2. On the other hand, when preheating, the toner t is preheated to the temperature A1 as described above, and therefore T1
It can be heated to the melting temperature A2 in a short time. Therefore, the printing time for each line can be shortened, and the printing process can be performed at high speed.

A temperature control circuit as control means for controlling the heating device such as a heater to the temperature A1 is not particularly shown, but for example, a thermistor provided near the platen roll 2 or a temperature detected by the thermistor. It is composed of a control circuit based on.

[0060]

As described above in detail, according to the present invention, a toner carrying film and a plurality of toner adhering devices are used, and toners of a plurality of colors are used in a range where the toner carrying film should be used according to print data. Since it is applied and transferred to paper, only the required toner and the toner carrying film coated with that toner are used. Therefore, it is economical because the usage cost is reduced. Further, similarly, since there is no part that is wastefully discarded without being used, no wasteful time for idling the toner carrying film is generated, and therefore the printing speed is increased and the efficiency of the printing operation is improved.

[Brief description of drawings]

FIG. 1 is a side sectional view schematically showing a configuration of an image forming apparatus as an embodiment.

FIG. 2 is a diagram showing a configuration of a main circuit of a control unit of the image forming apparatus.

3A, 3B, and 3C are diagrams showing an example of a state in which toner is selectively applied to a toner-carrying film in accordance with judged print data.

FIG. 4 is a schematic enlarged view of an image transfer unit that executes printing.

5 (a) and 5 (b) are enlarged views showing a state near the image recording unit.

6A and 6B are cross-sectional views in the vicinity of an image transfer portion in a form in which an adhesive layer is formed on a toner carrying film.

7 (a) and 7 (c) are cross-sectional views of the vicinity of an image transfer portion in a form in which an elastic layer is formed on a toner carrying film, and FIG.

FIG. 8 is a diagram comparing a case where toner is preheated by a heating device according to another embodiment and a case where toner is not preheated.

[Explanation of symbols]

 1 Thermal Head 1a, 15a, 25a Heating Element 2 Platen Roll 3 Recording Paper Conveying Path 4 (4a, 4b, 4c, 4d) Toner Adhering Device 5 Toner-carrying Film 6, 7 Film Cartridge 11 CPU (Central Processing Unit) 12 I / F (interface) controller 14 head pressure contact drive mechanism 15 head drive mechanism 16 paper transport motor D image transfer portion t toner t'fused toner ta black toner tb yellow toner tc magenta toner td cyan toner α, β, γ , Δ Application range 21 Normal ink ribbon

Claims (6)

[Claims] 1. A recording unit that selectively melts toner according to recording information, a platen disposed opposite to the recording unit, and a belt-shaped toner carrier that carries toner particles on the surface thereof and conveys the toner particles. The recording means selectively conveys the toner on the toner carrier according to the record information, and has a conveying means for superposing the toner carrier and a sheet on the sheet and conveying the sheet to the facing portion of the recording means and the platen. An image forming apparatus that melts the toner into a sheet and transfers the molten toner onto the sheet to form a dot image on the sheet; and a plurality of toner adhering means for adhering the toner to the toner carrier upstream of the recording means, An image forming apparatus comprising: an adhesion control unit that changes the adhesion of toner by the plurality of toner adhesion units for each of the toner adhesion units. 2. The image forming apparatus according to claim 1, wherein the conveying unit conveys the sheet reciprocally at a portion where the recording unit and the platen face each other. 3. The image forming apparatus according to claim 1, wherein the toner carrying member is provided with an adhesive member on a toner carrying surface. 4. The image forming apparatus according to claim 1, wherein the toner bearing surface of the toner bearing member is an elastic member. 5. The image forming apparatus according to claim 1, further comprising heating means for heating the platen. 6. The image forming apparatus according to claim 5, further comprising control means for heating and controlling the heating means to a temperature not higher than the melting temperature of the toner.