JPH0924633A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device for a thermal transfer type serial printing system which can conduct reciprocating printing in the main scanning direction with high economy. SOLUTION: A printing cartridge 4 moves in the direction of the arrow B by driving a carriage shaft 3 in this image forming device 1, and a toner carrying film 6 moves in the direction of the arrow E by driving a take-up hub 8a. Toner (t) stored in a toner adhesion device 7b is attracted to the toner supporting film 6. The toner carrying film 6 is clamped between a printing head 5 and a platen 2 with paper P at an image transfer part, and the toner (t) melts according to heat generation of a heater of the printing head 5, thus being transferred onto the paper P. When the printing cartridge 4 moves back in the direction of the arrow A by driving the cartridge shaft 3 in the opposite direction, the toner supporting film 6 moves in the direction of the arrow F by driving a take-up hub 8b, the toner (t) stored in the toner adhesion device 7a is attracted to the toner carrying film 6, the toner (t) melted by heat generation of the heater is transferred on the paper P.

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 serially transferring an image forming medium such as ink or toner by a thermal transfer method in the main scanning direction of a sheet.

[0002]

2. Description of the Related Art Conventionally, a thermal transfer type image forming apparatus has been put into practical use. In such an image forming apparatus, an ink ribbon is interposed between the print head and the paper, and the ink of the ink ribbon is thermally transferred onto the paper to perform printing. The above print head includes a heating element that selectively generates heat according to print information, and the ink ribbon is formed by applying ink to the film surface. The print head melts the ink on the ink ribbon by the heat generated by the heating element, and transfers the ink onto the paper at a position corresponding to the melted ink for printing. Such a thermal transfer type image forming apparatus has an advantage that it is inexpensive and can be downsized as compared with other types of image forming apparatuses. In particular, a serial printer that prints by running a print head and an ink ribbon in the main scanning direction of the paper (width direction of the paper) is widely used by being incorporated in a word processor or the like.

Such a thermal transfer type serial printer is provided with a carriage that reciprocates in the width direction of the paper, and the above-mentioned print head is arranged on the carriage. Further, a ribbon cassette accommodating an ink ribbon is detachably attached to the carriage. When the carriage travels in a predetermined direction (usually from left to right) to move the print head and the ribbon cassette in the main scanning direction of the paper, the print head presses the ink ribbon of the ribbon cassette against the paper and prints as described above. I do. After printing, the film surface of the ink ribbon is transferred by printing, and the ink is missing only at the printed area. Therefore, the ink ribbon used once cannot be used again. The above ink ribbon is wrapped around a reel and stored in a ribbon cassette. The used ink ribbon used for printing is sequentially wound up by the take-up reel, and by this winding, new unused ink ribbon is drawn out from the delivery reel and sequentially fed to the print head.

[0004]

By the way, the ink ribbon must be stationary relative to the paper so that the ink can be transferred. Therefore, on the moving carriage, the ribbon cassette moves the unused portion of the ink ribbon in synchronization with the moving speed of the carriage so that the ink ribbon can be relatively stationary with respect to the paper. The print head is sequentially fed from the delivery reel. However, the direction in which the unused ink ribbon is sent out in the ribbon cassette is necessarily fixed from the sending reel side to the take-up reel side. For this reason, printing is possible only when the print head moves in a certain direction (usually the above-mentioned left-to-right direction), and when the print head moves in the opposite direction, the unused ink ribbon is fed. Printing cannot be performed because it does not correspond to the direction, that is, one way (outward) in the main scanning direction.
Only can print. For this reason, the return path of the print head becomes a play, and time is wasted, so that the thermal transfer type serial printer has a complaint that the printing operation takes too much time.

Further, as described above, the ink ribbon cannot be reused once it has been used, and therefore it becomes disposable. Therefore, there is a problem that the use cost increases. Generally, the printing area ratio of a document is about 5%, so the ink remaining as a non-printing portion on the film surface of the used ink ribbon that is disposable as described above is
It is 95% of the entire ink that has been applied. Since this is discarded as it is, the problem of the above-mentioned use cost is not only expensive, but also has the problem that the cost is not economical.

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 a thermal transfer type serial printing type image forming apparatus capable of reciprocating printing in the main scanning direction and having good economical efficiency.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a print head and a platen are opposed to each other with a ribbon carrying an image forming medium for forming an image on a sheet and the sheet sandwiched therebetween, and the print head and the ribbon are arranged in the main scanning direction. It is premised on an image forming apparatus that forms an image on a sheet by driving the print head while moving the sheet to transfer the image forming medium to the sheet.

In the image forming apparatus of the present invention, the driving means selectively drives the ribbon to travel in a predetermined direction and in a direction opposite to the predetermined direction. This means is, for example, two winding hubs that fasten both ends of the ribbon.

Then, the first and second applying means apply the image forming medium to the ribbon on the upstream side and the downstream side of the print head in the ribbon running direction. The means is, for example, a toner adhering member or an ink adhering foam member impregnated with ink.

The image forming medium is toner, for example. In addition, for example, as described in claim 3, the ink is impregnated in a foam. Further, the image forming apparatus of the present invention can be configured, for example, by further providing a heating unit facing the first and second coating units with the ribbon sandwiched therebetween. Also,
For example, as described in claim 5, a heating means for heating the platen may be further provided. In this case, for example, as described in claim 6, it can be configured to further include control means for heating and controlling the heating means to a temperature not higher than the melting temperature of the image forming medium.

The toner carrying means is constructed, for example, by providing an adhesive member on the toner carrying surface. Further, for example, as described in claim 8, the toner carrying surface may be an elastic member.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a schematic plan view of the image forming apparatus of the first embodiment, and FIG.
FIG. 3 is an enlarged cross-sectional view of the vicinity of the ribbon cartridge. As shown in FIG. 1A, the image forming apparatus (main body apparatus) 1 is
A platen 2 extending in the longitudinal direction of the main body device and movable in a direction perpendicular to the longitudinal direction, a carriage guide shaft 3 arranged in parallel with the platen 2, and a carriage driven by the carriage guide shaft 3. The print cartridge 4 is detachably mounted.

The carriage guide shaft 3 is composed of, for example, a ball screw or the like, and is engaged with a drive mechanism (not shown) of the main body device. When printing (image transfer), the drive mechanism rotates in both forward and reverse directions. Then, the carriage, that is, the print cartridge 4 is driven in the left or right direction indicated by arrows A and B in the figure. By this drive, the print cartridge 4 horizontally reciprocates parallel to the platen 2, and at this time, the platen 2 advances toward the print cartridge 4 and prints as shown by an arrow C in FIG. The paper P is sandwiched between it and the cartridge 4.

In the print cartridge 4, as shown in FIG. 1B, the print head 5 disposed on the carriage is moved upward from below (the side facing the plane of the drawing) to face the platen 2. are doing. In the print cartridge 4,
Toner-carrying film 6 and toner adhering devices 7a and 7b for adhering toner to the toner-carrying film 6.
Are arranged. Further, winding hubs 8a and 8b for fastening both ends of the toner carrying film 6 are disposed below both sides of the print cartridge 4. When one of the take-up hubs 8a and 8b is driven and rotated, the other is driven, and when the other is driven and rotated, one is driven. Further, guide rollers 9a and 9b are disposed on the upper left and right sides of the print cartridge 4. The toner carrying film 6 is stretched between the guide rollers 9a and 9b, and the print head 5 presses the stretched toner carrying film 6 against the paper P. As a result, the toner carrying film 6 and the paper P are pressed and nipped by the platen 2 and the print head 5. An image transfer portion D is formed by the pressure contact nip portion formed by the platen 2 and the print head 5.

The print head 5 has a large number of built-in heating elements, and the individual heating elements are arranged in a line in the direction perpendicular to the paper surface of FIG. A pulse voltage according to print information output from a host device (not shown) is applied to each of the heat generating elements, whereby heat generation of the individual heat generating elements is selectively controlled. These heating elements are configured to perform serial printing in the width direction (main scanning direction) of the paper P as the print cartridge 4 moves.

The toner-carrying film 6 is made of a heat-resistant material such as polyimide, and is guided by the above-mentioned guide rollers 9a and 9b by the rotational driving of the take-up hub 7a or 7b, slidingly contacting the print head 5. Arrow E or F in the figure
As shown in, the reciprocating movement is performed between the winding hubs 8a and 8b. At this time, the surface of the toner carrying film 6 that should come into contact with the paper P slides on the toner adhering device 7a or 7b between the guide roller 9a and the take-up hub 8a and between the guide roller 9b and the take-up hub 8b, respectively.

Non-magnetic toner t, which will be described later, is stored in the toner adhering devices 7a and 7b. Toner t is
The toner carrying film 6 is adsorbed to the toner carrying film 6 while passing through the toner adhering devices 7a and 7b.

The winding hub 8a and the winding hub 8b described above.
So that the toner carrying film 6 can be relatively stationary with respect to the paper P, the toner carrying film 6 is wound and driven in synchronization with the moving speed of the carriage. As a result, the toner carrying film 6 becomes
When the print cartridge 4 moves in the forward direction indicated by the arrow B in the drawing, the take-up hub 8 indicated by the arrow E in FIG.
The print cartridge 4 is wound in the direction a and the print cartridge 4 is indicated by an arrow A in the figure.
When it moves in the opposite direction shown by, it is wound in the direction of the winding hub 8b shown by the arrow F in the figure.

The toner t adsorbed on the above-described toner carrying film 6 is moved along with the movement of the toner carrying film 6 in the direction shown by the arrow E or F in the figure, and the position of the print head 5, that is, the image transfer portion D. Move up to. This allows
The surface of the toner carrying film 6 on which the new toner t is constantly adsorbed moves to the image transfer portion D that moves in the main scanning direction with respect to the paper P and comes into contact with the paper P.

The toner t is transferred to the paper P,
A toner image is formed. The paper P to which the toner image has been transferred is successively conveyed and discharged outside the machine. In the first embodiment configured as described above, the operation is performed again with reference to FIG.
An explanation will be given using (a) and (b).

First, when a switch or the like on an operation panel (not shown) of the image forming apparatus 1 is operated to turn on the power of the main body apparatus, a central processing is performed in a control unit (not shown) arranged in the main body apparatus. The processing device starts operation based on a predetermined program. Based on this control, the memory, head control circuit, IO port, etc. in the control unit are initialized. Then, in response to a print start instruction, a drive signal output from the control unit via the IO port drives the carriage guide shaft 3 on the one hand, which causes the print cartridge 4 to move in the direction of arrow B in the figure, while the other Then, the winding hub 8a is driven, and the toner carrying film 6 moves in the direction of arrow E in the figure.

At this time, the toner t accommodated in the toner adhering device 7b is adsorbed to the toner carrying film 6.
This is because the toner-carrying film 6 is the toner attaching device 74b.
This is because the toner carrying film 6 and the toner t in the toner adhering device 7b rub against each other during the movement to, and the toner t is electrostatically adsorbed to the toner carrying film 6.

The toner carrying film 6 on which the toner t is adsorbed in this manner is sent to the image transfer section D. Further, in accordance with the above-described print start instruction, the paper P is fed to the image transfer section D from a paper feed cassette (not shown).

FIGS. 2 (a) and 2 (b) are diagrams showing a state near the image recording portion D indicated by a circle H in FIG. 1 (b) at this time. At this time, in the image recording portion D, the paper P and the toner carrying film 6 are placed between the print head 5 and the platen 2 as shown in FIG. The platen 2 is sandwiched in a state of being overlapped with the surface, and the platen 2 presses the toner carrying film 6, the toner t, and the paper P against the print head 5.

In this state, the print head 5 is moved by the arrow J in the figure.
The toner-carrying film 6 moves to the right in the print cartridge 4 from the right to the left in synchronization with the moving speed of the print cartridge 4, as described above. Is stationary. During this time, the heating element 5-1 of the print head 5 is selectively energized according to the print information output from the head control circuit of the control unit. The heating element 5-1 generates heat in response to this energization, and due to this heat generation, the toner t adsorbed on the toner carrying film 6 melts and adheres to the paper P, that is, is transferred.

FIG. 2B is a diagram showing the transfer state of the toner t onto the paper P. As shown in FIG. As shown in the figure, when the heating element 5-1 generates heat based on the print information, this heat is transferred to the toner t through the toner carrying film 6, and the transferred heat (eg, the temperature at the glass transition point). When the temperature reaches about 150 ° C., the toner t is melted and becomes the toner t ′, and the paper P
Is transferred to The melted toner t ′ is transferred to the sheet P and does not adhere to the toner carrying film 6 side because the electrostatic attraction between the toner carrying film 6 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 5-1 which has generated heat according to the print information.

In this way, the print heads 5 come to the right end of the main body while performing the above-mentioned printing (transfer of the toner t), so that the print heads 5 are first arranged in one vertical line (vertical direction to the paper surface of the figure). The serial printing of one line of the paper P in the main scanning direction by the plurality of heating elements 5-1 is completed.

Incidentally, the toner carrying film 6 is again moved from the toner adhering device 7a by the operation of moving the toner t consumed by the recording operation of the print head 5 in the direction of arrow E in FIG. 1 (b). You will get it. This makes it possible to prepare for the next recording operation. Further, when the printing of one line in the main scanning direction is completed, the toner carrying film 6 is attached to the take-up hub 6a until the toe t is attracted to all the portions used for recording by the supply from the toner adhering device 7a. It is wound up and moves in the direction of the arrow E.

When printing of one line in the main scanning direction is completed in this way, the paper P moves one line of the print head 5 in the sub scanning direction (vertical direction of paper) in order to print the next line.
Then, the carriage guide shaft 3 is rotationally driven in the opposite direction. As a result, the print cartridge 4, that is, the print head 5 starts moving in the direction of arrow A in FIG. At the same time, the winding hub 8b is driven, whereby the toner carrying film 6 starts moving in the direction of arrow F in FIG. 1 (b). Then, the toner t accommodated in the toner adhering device 7a is adsorbed to the toner carrying film 6. That is, as described above, the toner t that has been consumed by the printing of the preceding one line is replenished at the time of winding, and then the toner t is replenished. As a result, the previously consumed toner t is replenished to the surface of the toner-carrying film 6 without omission, and when the toner-carrying film 6 passes over the print head 5, the same toner as in the initial state is used as described above. The surface of the film on which t is sufficiently adhered is pressed against the paper P and is stationary relative to the paper P, and the heating element that has generated heat in accordance with the print information 5-
The toner t ′ is transferred onto the paper surface corresponding to the position of 1.
As a result, as in the case shown in FIG. 2B, serial printing of the next one line in the main scanning direction of the paper P by the plurality of heating elements 5-1 is performed from right to left. The transfer state in this case is the same as that of the case where the front and back sides of FIG. In this case also, the print head 5
The toner adhering device 7b replenishes the toner carrying film 6 which has consumed the toner t due to printing by passing through the toner t.

As described above, by repeating the printing operation in the arrow B direction and the arrow A direction in FIG. 1 (b), the dot image (toner image) according to the print information is printed in the forward direction in the main scanning direction. The paper P is sequentially formed by reciprocating one line in the line and the return path. 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. 2 (a) and 2 (b), the toner t
Are independently adsorbed on the toner carrying film 6. Therefore, when the toner t is transferred to the sheet P, the individual toner t can flexibly contact the unevenness of the sheet P.
Therefore, the toner t is completely transferred to both the convex and concave portions of the paper P. Therefore, for example, the problem that printing on plain paper by thermal transfer recording using an ink ribbon is difficult does not occur. Further, when printing is performed in either of the reciprocating directions, since the toner t is sufficiently replenished in the toner carrying film 6, good printing can always be achieved in both reciprocating directions.

As described above, the image forming apparatus 1 of this embodiment
Electrostatically adsorbs the toner t on the toner carrying film 6, transfers the toner t while reciprocating in the main scanning direction of the paper P according to the heat generation of the heating element 5-1 (print head 5) in the image transfer portion D, A toner image is created.

Next, a second embodiment of the present invention will be described.
3A and 3B are cross-sectional views of the vicinity of the image transfer portion in the image forming apparatus of the second embodiment in which the adhesive layer is formed on the toner carrying film as the toner carrying means. In this embodiment,
The basic configuration is the same as that of the above-mentioned first embodiment, and FIG.
As shown in (b), the difference is that an adhesive layer is formed on the toner carrying film. 1A and 1B, the paper P is fed to the image transfer portion D, and the toner carrying film 6 (6-1, 6-2) to which the toner t is attached is shown in FIG. It is sectional drawing when moving. In FIGS. 2 (a) and 2 (b), the same members as those shown in FIGS. 2 (a) and 2 (b) are given the same numbers as in FIGS. 2 (a) and 2 (b). Is shown.

In the image forming apparatus 1b in which the adhesive layer is formed on the toner carrying film 6, as shown in FIGS. 3 (a) and 3 (b), the toner carrying film 6 includes a base film 6-1 and an adhesive layer. It is composed of 6-2. Adhesive layer 6-2
Is affixed to the outer surface of the base film 6-1, that is, the surface in contact with the toner adhering devices 7a and 7b and the paper P. The base film 6-1 is composed of a heat-resistant film such as polyimide, like the toner carrying film of the first embodiment described above. Further, the adhesive force of the adhesive layer 6-2 is not so strong, and is an adhesive force that can hold the toner t and convey the held toner t to the image transfer portion D without dropping. It should be noted that other configurations of this embodiment, such as the print head 5, the heating element 5-1, the platen 2, the carriage guide shaft 3, and the print cartridge 4 are provided.
The configuration such as is the same as that shown in FIGS. 1 (a) and 1 (b).

In the image forming apparatus 1b having such a structure, also in this case, as in the first embodiment, the initialization process is performed after the power is turned on, and the print start is instructed.
The paper P is fed to the image transfer portion D from a paper feed cassette (not shown). As the carriage guide shaft 3 is driven and the print cartridge 4, that is, the print head 5 moves to the right as indicated by the arrow K in the drawing, the toner carrying film 6 moves in the left direction as indicated by the arrow L in the print cartridge 4. To the platen 2 and the paper P, and then stands still. Then, while the toner carrying film 6 moves on the toner adhering devices 7a, 7b, the toner t adheres to the adhesive layer 6-2 of the toner carrying film 6. As described above, the adhesive force of the adhesive layer 6-2 has an adhesive force capable of surely transporting the toner t to the image transfer portion D without dropping the toner t, so that the toner carrying film 6 (adhesive layer 6-2) does not. The adhered toner t is conveyed to the image transfer portion D.

Also in this case, as shown in FIG. 3 (b), in the image transfer portion D, between the print head 5 and the platen 2,
In the state where the paper P and the toner carrying film 6 are overlapped and sandwiched, the toner carrying film 6 stands still with respect to the paper P, and only the print head 5 moves to the right. In this state,
When the heating element 5-1 generates heat according to the print information, this heat is transferred to the toner t through the base film 6-1 and the adhesive layer 6-2 of the toner carrying film 6, and the transferred heat is the melting temperature of the toner t. When the toner reaches t, the toner t is melted to become toner t ′, which is transferred to the paper P.

The force for holding the toner t on the toner carrying film 6 is the adhesive force of the adhesive layer 6-2. 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 6 (adhesive layer 6-2) side.
However, actually, it does not adhere to the adhesive layer 6-2. 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 6-2 and the toner t is F2, the toner t Is not melted, the adhesive force of the adhesive layer 6-2 is strong, F2> F1, and the toner t is the adhesive layer 6
-2 (toner carrying film 6) side is still adhered. Therefore, the toner t is not transferred to the position of the paper P corresponding to the heating element 5-1 that is not energized, and so-called background stain of the paper P can be prevented.

On the other hand, in the energized heating element 5-1, 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 melted toner t ' The adhesive force between the adhesive layer 6-2 and the adhesive layer 6-2 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, when the adhesive force between the toner t ′ and the adhesive layer 6-2 when the toner t is melted is F2 ′ and the adhesive force between the toner t ′ and the paper P is F1 ′, F1 ′> F2 ′, The melted toner t ′ is transferred to the paper P. Therefore, when the heating element 5-1 generates heat, the melted toner t ′ only on the paper P is reliably 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 this embodiment, the molten toner t'can be reliably transferred to the paper P, and
Since the adhesive layer 6-2 is provided on the toner-carrying film 6, the toner t is not transferred to the position on the paper P where transfer is not performed.
(T ') is not transferred, and the background stain can be reliably prevented.

Next, a third embodiment of the present invention will be described.
4A and 4C are cross-sectional views of the vicinity of the image transfer portion in the image forming apparatus of the third embodiment in which the elastic layer is formed on the toner carrying film as the toner carrying means. In this embodiment,
The basic structure is the same as that of the first embodiment described above, except that an elastic layer is formed on the toner carrying film. Figure (a),
In (c), the paper P is fed to the image transfer portion D and the toner carrying film 6 (6-3, 6-
FIG. 4) is a cross-sectional view when moving the image transfer portion D. In FIGS. 2 (a) and 2 (c), the same members as those shown in FIGS. 2 (a) and 2 (b) are given the same numbers as in FIGS. 2 (a) and 2 (b). Is shown.

In the image forming apparatus 1c having the structure in which the elastic layer is formed on the toner carrying film 6, as shown in FIG. 4 (a), the toner carrying film 6 is the base film 6-.
3 and the elastic layer 6-4. The elastic layer 6-4 is provided on the outer surface of the base film 6-3 (toner adhesion device 7a,
7b and the surface which contacts the paper P). This base film 6-3 is also made of a heat resistant film such as polyimide. The elastic layer 6-4 is made of silicon rubber having a predetermined hardness. Incidentally, other configurations of this embodiment, for example, the print head 5, the heating element 5-1,
The configurations of the platen 2, the carriage guide shaft 3, the print cartridge 4, etc. are the same as those shown in FIGS. 1 (a) and 1 (b).

In the image forming apparatus 1c having such a configuration, also in this case, similarly to the first embodiment, the initialization process is performed after the power is turned on, and the print start is instructed.
The paper P is fed to the image transfer portion D from a paper feed cassette (not shown). On the other hand, the toner carrying film 6 moves on the toner adhering devices 7a and 7b, and the toner t adheres to the elastic layer 6-4 of the toner carrying film 6.

In this embodiment, the force for holding the toner t on the toner carrying film 6 is as shown in FIG.
The elastic layer 6-4 has a toner t due to its flexibility and flexibility.
Emphasized Van der Waals that come from contacting toner t in a way that wraps around the bottom of the
Force (the force that appears in the adhesion phenomenon between solid surfaces).

If the toner carrying film 6 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 6 and is sufficient. There is a possibility that the adhesive force cannot be obtained. On the other hand, when the toner bearing surface is the elastic layer 6-4 as described above, the toner t comes into surface contact with the toner t in a form of wrapping the toner t as described above. That is, the lower surface of the toner t is embedded in the elastic layer 6-4. The diameter of the contact surface becomes larger as it is buried, and the size of the contact surface expands in proportion to the square of the diameter of the contact surface. Therefore, as compared with the case of point contact, the toner t and the toner carrying film 6 (the elastic layer 6). -4) The mutual contact area increases geometrically.
Therefore, the power of Van der Waals will dramatically increase. As a result, the toner-carrying film 6 can be provided with a sufficient function for holding and carrying the toner t in the above-described print processing operation. still,
In order for the elastic layer 6-4 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. 4C, in the image transfer portion D, between the print head 5 and the platen 2,
In the state where the paper P and the toner carrying film 6 are overlapped and sandwiched, the toner carrying film 6 stands still with respect to the paper P,
Only the print head 5 moves to the right. In this state, when the heating element 5-1 generates heat according to the print information, this heat is generated by the base film 6-3 and the elastic layer 6 of the toner carrying film 6.
When the transferred heat reaches the melting temperature of the toner t, the toner t is melted and becomes the toner t ′ and is transferred to the paper P. Also in this case, the toner t
′ Is transferred to the paper P without staying on the toner carrying film 6 side. The reason is the same as above.

Therefore, according to the present embodiment, a toner image can be formed on both sides of the print head by an image forming apparatus having a simple structure for serial transfer, and the background stain can be surely prevented.

Next, a fourth embodiment of the present invention will be described.
In this embodiment, a heating device such as a heater is arranged in the platen 2. With this heater, for example, the temperature of the heating device is preheated to A1. The temperature A1 is a glass transition temperature A2 at which the toner t melts (for example, 150 ° C.).
It is a lower temperature and, of course, a temperature higher than normal temperature (for example, 20 ° C.).

The toner t is preheated by disposing such a heating device in the platen 2 and controlling it to a predetermined temperature (the above-mentioned temperature A1). With such a 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 5-1.

FIG. 5 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. When the toner t is not preheated, the heating element 5-1 has to heat it 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 a control means for controlling a heating device such as a heater to the temperature A1 is not particularly shown, but for example, a thermistor provided near the platen 2 or a temperature detected by the thermistor is used. It is composed of a control circuit based on.

[0054]

As described above in detail, according to the present invention, since the toner carrying film which is movable in both directions and can replenish the toner in both directions is used in the thermal transfer type serial printer, it can be reciprocated in the main scanning direction. Printing is possible, and therefore the efficiency of printing work is improved. Further, since the toner-carrying film capable of replenishing the toner is used, it is not necessary to use an ink ribbon whose running cost is high, and therefore the economical efficiency in use is improved. Further, since the adhesive layer or the elastic layer is used for the toner-carrying film, it is possible to surely prevent the background stain of the paper, and therefore it is possible to realize the thermal transfer type image forming apparatus which is excellent in the printing quality by using the toner. Further, since the heating device is built in the platen or the like to preheat the toner in advance, the melting temperature of the toner can be set in a short time when the transfer process is performed according to the print information, and therefore the print process speed can be improved.

[Brief description of drawings]

FIG. 1A is a schematic plan view of an image forming apparatus according to a first embodiment, and FIG. 1B is an enlarged cross-sectional view near the ribbon cartridge.

FIG. 2A is a diagram showing a state in which a sheet of paper and a toner-carrying film are sandwiched between the print head and the platen in the image recording unit with the film surface having toner attached to the sheet surface being overlapped. FIG. 6B is a diagram showing a state in which toner is transferred to the paper.

3A and 3B are cross-sectional views of the vicinity of an image transfer portion in the image forming apparatus of the second embodiment having a structure in which an adhesive layer is formed on a toner carrying film.

4A and 4B are cross-sectional views of the vicinity of an image transfer portion in an image forming apparatus of a third embodiment having a structure in which an elastic layer is formed on a toner carrying film.

FIG. 5 is a temperature characteristic diagram illustrating a fourth embodiment.

[Explanation of symbols]

 1, 1b, 1c Image forming apparatus (main unit) 2 Platen 3 Carriage guide shaft 4 Print cartridge 5 Print head 5-1 Heating element 6 Toner carrying film 7a, 7b Toner adhering device 8a, 8b Winding hub 9a, 9b Guide roller P paper D image transfer part t, t'toner

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[Procedure amendment]

[Submission date] December 1, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

4A to 4C are cross-sectional views of the vicinity of an image transfer portion in an image forming apparatus of a third embodiment having a structure in which an elastic layer is formed on a toner carrying film.

Claims (8)

[Claims] 1. A printing head and a platen are opposed to each other with a ribbon carrying an image forming medium for forming an image on a sheet and the sheet sandwiched therebetween, and the printing is performed while moving the printing head and the ribbon in a main scanning direction. In an image forming apparatus for forming an image on a sheet by driving a head to transfer the image forming medium onto the sheet, a drive for selectively driving the ribbon to run in a predetermined direction and a direction opposite to the predetermined direction. First means for applying the image forming medium to the ribbon on the upstream side and the downstream side of the print head in the ribbon traveling direction;
An image forming apparatus comprising: a second coating unit; 2. The image forming apparatus according to claim 1, wherein the image forming medium is toner. 3. The image forming apparatus according to claim 1, wherein the image forming medium is ink impregnated in a foam. 4. The image forming apparatus according to claim 3, further comprising heating means facing the first and second coating means with the ribbon interposed therebetween. 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 a melting temperature of the image forming medium. 7. The image forming apparatus according to claim 2, wherein an adhesive member is provided on the toner carrying surface of the toner carrying means. 8. The image forming apparatus according to claim 2, wherein the toner carrying surface of the toner carrying means is an elastic member.