JPH07304197A - Thermal transfer image forming device - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a thermal transfer image forming apparatus, in which a toner is carried on a recyclable film without using a photoconductor, and an image is printed on a sheet by heating with a thermal head. Therefore, the object is to be compact and to reduce the cost of the device. [Structure] A thermal head 2 having a large number of heating elements arranged in the direction perpendicular to the plane of the paper and a platen roller 3 are arranged opposite to each other, and a sheet P is superposed on a toner carrying film 4 and conveyed between them.
The toner t adheres to the peripheral surface of the toner-carrying film 4 by electrostatic force, and during this time, the heating element formed on the thermal head 2 is selectively energized, so that the heating element 2 is energized.
Generates heat, melts the toner t at the corresponding position on the toner carrying film 4, and transfers it to the paper P. By continuing this transfer process, a toner image according to the print information is formed 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 a thermal transfer image forming apparatus for transferring toner onto paper by a thermal transfer system to form an image.

[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, (a) an electrophotographic printer device has a charger (exposure head), a developing device, a transfer device, etc. arranged around a photoconductor (photosensitive drum), and a predetermined charge is held in advance by the charger. The exposure head performs optical writing according to the print information on the formed photoconductor to form an electrostatic latent image on the photoconductor. The electrostatic latent image is visualized by a developing device containing toner. After being imaged (formed into a toner image) and transferred to a sheet by a transfer device, it is thermally fixed by a fixing device and discharged to the outside of the device.

On the other hand, (b) a conventional thermal transfer type printer apparatus, an ink ribbon coated with ink is interposed between a thermal head that generates heat according to print information and a sheet, and the thermal head is selectively selected according to print information. It is a device that generates heat, melts the ink on the ink ribbon, and prints on the paper at the corresponding position.

[0004]

The above-mentioned conventional image forming apparatus has the following problems. First, in the case of (a) the electrophotographic method, an expensive photoconductor must be used,
This will increase the cost of the device. Further, since a fixing device is also required, the device becomes large.

On the other hand, in the case of the conventional thermal transfer system (b),
Although an ink ribbon is used, since the ink ribbon cannot be reused, running costs increase, and this method also causes an increase in the cost of the apparatus.

The present invention has been made in view of the above-mentioned problems of the prior art, and is a compact thermal transfer apparatus capable of reducing the cost of the apparatus by heating a thermal head to print a toner image on a sheet. An object is to provide an image forming apparatus.

[0007]

The structure of a thermal transfer image forming apparatus of the present invention comprises a toner carrying means for carrying a toner on the surface, in which a heating head having a plurality of heating elements in the main scanning direction and a platen are arranged to face each other. A sheet of paper is superposed and conveyed to a portion where the heating head and the platen are opposed to each other, and the heating element is selectively energized to melt the toner on the toner carrying means and selectively transfer the sheet to the sheet to form a dot image. This is the configuration.

Further, the thermal transfer image forming apparatus of the present invention has a structure in which an adhesive member is provided on the toner carrying surface of the toner carrying means, for example. Alternatively, for example, an elastic body may be arranged on the toner carrying surface of the toner carrying means.

Further, the thermal transfer image forming apparatus of the present invention may be provided with a heating means such as a heater for heating the platen, and the heating means is controlled to be below the melting temperature of the toner. As a means, a temperature control circuit including a thermistor or the like may be provided and configured.

[0010]

According to the present invention, a toner is used, and the toner is carried by a toner carrying means such as a film, and is sent to a transfer portion in which a thermal head is arranged to selectively heat a heating element constituting the thermal head. This melts the toner and transfers the toner to the paper. With this configuration, the cost of the device can be reduced.

Further, the platen is heated by the heating means,
By preheating the toner to a predetermined temperature equal to or lower than the toner melting temperature, the toner can be heated to the melting temperature in a short time during the above-mentioned toner transfer. In particular, if a low melting point toner is used, the transfer time can be further shortened and high-speed printing processing can be performed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of the thermal transfer image forming apparatus of the first embodiment. In the figure, the thermal transfer image forming apparatus 1 is composed of a thermal head 2, a platen roller 3, a toner carrying film 4, a toner container 5, and a sheet conveying mechanism 6. The thermal head 2 contains a large number of heating elements, and the individual heating elements are arranged in a line in the direction perpendicular to the paper surface of the figure. For example, the thermal transfer image forming apparatus 1 according to the present exemplary embodiment has a print density of 240 DPI and A in the vertical direction.
In the case of an apparatus capable of printing 4 size sheets, the thermal head 2 is provided with about 2000 heating elements. Further, for example, when the print density is 300 DPI, the thermal head 2 is provided with about 2500 heating elements.
A pulse voltage according to the print information output from the host device is applied to each heating element, and each heating element is selectively heat-controlled.

The platen roller 3 is composed of a tubular member and is rotatable in the direction of arrow a. The toner carrying film 4 as a toner carrying means is made of a heat-resistant material such as polyimide and has an endless belt shape. By driving the film carrying rolls 7a and 7b, the above-mentioned thermal head 2 and toner container 5 are connected. Rotate between. The non-magnetic toner t is stored in the toner container 5, and the toner t in the toner container 5 is adsorbed to the toner carrying film 4 while the toner carrying film 4 moves inside the toner container 5. Further, the toner t adsorbed on the toner carrying film 4 moves to the position of the thermal head 2 as the toner carrying film 4 rotates in the arrow B direction.

On the other hand, the paper transport mechanism 6 is composed of a paper feed cassette 8, a transport roll 9, a paper transport guide plate 10, a transport belt 11 and the like. Paper (plain paper) P is stored in the paper feed cassette 8, and the thermal transfer image forming apparatus 1 of the present embodiment is used.
It is detachably attached to the side of the machine. The paper P stored in the paper feed cassette 8 is carried into the machine as the paper feed roller 8'rotates. The transport roll 9 is a roll that transports the paper P carried in by the paper feed roller 8 ′ to the image transfer portion D along the paper transport guide plate 10.

The image transfer section D is the thermal head 2 described above.
And the platen roller 3 are opposed to each other, and while the paper P moves while being overlapped with the toner carrying film 4 described above,
The toner image is transferred as described later. The paper P on which the toner image has been transferred is guided to the air suction type transport belt 11 so as not to affect the transferred toner image, and is discharged to the paper discharge tray 12 via the discharge port 12 ′.

The operation of the thermal transfer image forming apparatus 1 having the above structure will be described. First, after the power supply to the thermal transfer image forming apparatus 1 of the present embodiment is turned on, initialization processing is performed, and when a print start is instructed, the film transport rolls 7a, 7
b rotates, and the toner carrying film 4 rotates in the arrow B direction. At this time, the toner container 5 is attached to the toner carrying film 4.
The toner t stored in is adsorbed. This is because the toner carrying film 4 and the toner t in the toner container 5 rub against each other while the toner carrying film 4 moves in the toner container 5, and the toner t is electrostatically adsorbed to the toner carrying film 4. . The toner carrying film 4 on which the toner t has been adsorbed in this manner is sent to the image transfer portion D.

Further, according to the above-mentioned print start instruction,
The paper P is carried in from the paper feed cassette 8 and is sent to the image transfer portion D by the rotation of the carrying roll 9. FIG. 2 is a diagram showing a state near the image transfer portion D at this time. As shown in the figure, at this time, in the image transfer portion D, the paper P and the toner carrying film 4 are sandwiched between the thermal head 2 and the platen roller 3 in an overlapping state, and the platen roller 3 rotates in the direction of arrow a. Then, the toner carrying film 4 moves in the arrow B direction, and the paper P moves in the arrow C direction. Further, at this time, FIG. 3 is an enlarged view of a portion A indicated by a circle in FIG. still,
Reference numeral 2'shown in the figure denotes a heating element formed in the thermal head 2.

In this state, when the thermal head 2 (heating element 2 ') generates heat according to the print information output from the host device, the toner t adsorbed on the toner carrying film 4 melts and adheres to the paper P. FIG. 4 is a diagram showing this state, and is a diagram showing a transfer state of the toner t onto the sheet P when the heating element 2'is selectively energized and the heating element 2'heats.
When the heating element 2'generates heat based on the print information, this heat is transferred to the toner t through the toner carrying film 4, and when the temperature of the glass transition point (for example, about 150 ° C) is reached, the toner t is melted and the paper is melted. Transcribed to P. The melted toner t ′ is transferred to the sheet P and does not adhere to the toner carrying film 4 side because the toner carrying film 4 and the toner t are not originally attached.
This is because the electrostatic attraction force between and is weak, and the melted toner t ′ is easily transferred onto the paper P due to its viscosity. In this way, the heating element 2 ′ that has generated heat according to the print information on the paper P is used.
The toner t ′ is transferred corresponding to the position of, and a dot image (toner image) according to the print information is formed on the paper P. Then, the paper P on which the toner image is formed is sent in the direction of arrow C by the air suction type conveyor belt 11 as described above, and is output to the paper discharge tray 12.

As described above, in the thermal transfer image forming apparatus 1 of this embodiment, the toner t is electrostatically adsorbed on the toner carrying film 4, and the toner is generated in the image transfer portion D according to the heat generated by the heating element 2 '(thermal head 2). The toner image is created by transferring t onto the paper P. Therefore, it is possible to form a toner image without using an expensive device such as a photoconductor or an expendable item such as an ink ribbon that increases running costs.
The cost of the device can be reduced.

Next, a second embodiment of the present invention will be described.
This embodiment has the same basic configuration as the above embodiment,
The difference is that an adhesive layer is formed on a toner carrying film as a toner carrying means. FIG. 5 shows a cross-sectional view in the vicinity of the image transfer portion D in the thermal transfer image forming apparatus 13 having a structure in which the adhesive layer is formed on the toner carrying film 4 (however, the drawing shows
A sheet P is fed to the image transfer portion D, and the toner carrying film 14 having the toner t adhered thereto is moving in the image transfer portion D. In the figure, the same members as those shown in FIG. 3 will be designated by the same reference numerals.

The toner carrying film 14 is composed of a base film 14a and an adhesive layer 14b, and the adhesive layer 14b is attached to the peripheral surface of the base film 14a. The base film 14a is made of a heat-resistant film such as polyimide, as described above. In addition, the adhesive force of the adhesive layer 14b is not so strong and holds the toner t,
The adhesive force is such that the held toner t can be conveyed to the image transfer portion D without dropping. The other configurations of this embodiment, for example, the thermal head 2, the heating element 2 ', the platen roller 3, the sheet conveying mechanism 6, and the like are the same as those shown in FIG.

In the thermal transfer image forming apparatus 13 having such a structure, the initial setting process is performed after the power is turned on as described above.
When printing is instructed, the film transport roll 7
a and 7b rotate, and the toner carrying film 14 rotates. Then, while the toner carrying film 14 moves in the toner container 5, the adhesive layer 14b of the toner carrying film 14
The toner t adheres to the. As described above, this adhesive layer 14
Since the adhesive force of b is such that the toner t can be reliably conveyed to the image transfer portion D without dropping the toner t, the toner t attached to the toner carrying film 14 (adhesive layer 14b) is conveyed to the image transfer portion D. It

FIG. 5 described above also shows the state of the image transfer portion D at this time. As shown in the figure, at this time, in the image transfer portion D, between the thermal head 2 and the platen roller 3,
In the state where the paper P and the toner carrying film 14 are overlapped and sandwiched, the platen roller 3 rotates in the arrow A direction, the toner carrying film 14 moves in the arrow B direction, and the paper P draws the arrow as in the above-described embodiment. Move in the direction of c. In this state, when the heating element 2'heats according to the print information output from the host device, the toner t attached to the toner carrying film 14 is melted and transferred to the paper P.

FIG. 6 is a diagram showing this state. When the heating element 2'heats based on the print information, this heat is transferred to the toner t through the toner carrying film 14, and when the melting temperature is reached, the melted toner t'is transferred to the paper P. In the case of this embodiment, the force for holding the toner t on the toner carrying film 14 is the adhesive force of the adhesive layer 14b. Therefore,
At first glance, the melted toner t ′ is not transferred to the paper P, but is likely to adhere to the toner carrying film 14 (adhesive layer 14b) side. However, it does not adhere to the adhesive layer 14b. The reason is considered as follows.

That is, when the toner t is not melted,
The adhesion force (electrostatic force due to friction) between the paper P and the toner t is F1.
When the adhesive force between the adhesive layer 14b and the toner t is F2, the adhesive force of the adhesive layer 14b is strong when the toner t is not melted, F2> F1, and the toner t is the adhesive layer 14b.
It remains adhered to the (toner carrying film 14) side.
Therefore, the paper P corresponding to the heating element 2'which is not energized
The toner t is not transferred to the position of
It is possible to prevent the background stain. On the other hand, the energized heating element 2 '
Then, the toner t at the corresponding position melts, the surface energy of the melted toner t ′ (surface tension of the toner t ′) decreases, and the melted toner t ′ and the adhesive layer 14b (toner carrying film 14) adhere to each other. Power is reduced. Also, the toner t
When is melted, the adhesive force between the toner t ′ and the paper P increases due to the viscosity of the toner t ′. Therefore, the adhesive force between the toner t ′ and the adhesive layer 14b when the toner t is melted is F
2 ′ and the adhesive force between the toner t ′ and the paper P is F1 ′, F1 ′> F2 ′, and the melted toner t ′ is transferred to the paper P. Therefore, when the heating element 2'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.

[0027]

[Equation 1]

However, γs: solid surface tension γL: liquid surface tension Since the molten toner is regarded as a liquid with high viscosity, the above equation can be applied to the interface between the adhesive layer and the molten toner and the interface between the paper P and the molten toner. . Therefore, F1 'and F2' are

[0029]

[Equation 2]

Where γp is the surface tension of the paper P and γt is the surface tension of the molten toner.

[0031]

[Equation 3]

However, γa: surface tension of adhesive layer Here, 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]. When a natural rubber material is used for the adhesive layer, the surface tension of the adhesive layer is about 24 [dyn / cm]. When F1 ′ and F2 ′ are calculated using these numerical values, F1 ′ = 61 [erg / cm ² ] F2 ′ = 47 [erg / cm ² ] is obtained. Therefore, the molten toner can be reliably transferred to the paper P.

Therefore, according to the present embodiment as well, a toner image is formed by the thermal transfer image forming apparatus 13, which does not use an expensive device such as a photoconductor or an expendable product such as an ink ribbon which causes a high running cost. Paper P
Can be created.

Further, according to the present embodiment, since the toner carrying film 14 is provided with the adhesive layer 14b, the toner t is not transferred to the position on the paper P where the transfer is not performed, and the background stain is surely caused. Can be prevented.

Next, a third embodiment of the present invention will be described.
This embodiment also has the same basic configuration as the first embodiment, but differs in that an elastic member is formed on the toner carrying film as the toner carrying member. Also in this embodiment, the toner carrying film is composed of a base film and an elastic layer, the base film is composed of a heat resistant film such as polyimide, and the elastic layer is composed of silicon rubber having a predetermined hardness. Note that other configurations of this embodiment, such as the thermal head 2, the heating element 2 ', the platen roller 3,
The configurations of the sheet transport mechanism 6 and the like are the same as the configurations shown in FIG.

In the thermal transfer image forming apparatus having such a structure, when the print start is instructed, the film transport rolls 7a and 7b are rotated and the toner t is attached to the toner carrying film, as described above. This adhesive force is, as shown in FIG. 7, an elastic layer 16b formed on the base film 16a.
This is because the toner t sinks into the elastic layer 16b due to the flexibility and flexibility of the toner, the contact area between the toner t and the elastic layer 16b increases, and the Vandel-Walls force increases. In this way
The toner t adhering to the elastic layer 16b is reliably sent to the image transfer portion D without dropping. The elastic layer 16
In order for b to have sufficient toner holding power, the hardness is JIS
It is preferably 30 degrees or less at -A.

FIG. 8 is a diagram showing the state of the image transfer portion D at this time. In this state, when the heating element 2'heats according to the print information output from the host device, the toner t attached to the toner carrying film 16 (elastic layer 16b) is melted and attached to the paper P (see FIG. 9). That is, when the heating element 2 ′ generates heat according to the print information, this heat is transferred to the toner t via the toner carrying film 16, the toner t is melted and transferred to the paper P. Also in this case, the toner t is transferred to the paper P without being transferred to the toner carrying film 16 side. The reason is the same as above.

Therefore, also in this embodiment, the toner image can be formed by the thermal transfer image forming apparatus which is intended to reduce the cost, and the background stain can be surely prevented. Next, a fourth embodiment of the present invention will be described.

In this embodiment, the platen roller 3 is provided with a heating device such as a heater. With this heater, for example, the temperature of the heating device is preheated to A1. The temperature A1 is the glass transition temperature A2 at which the toner t melts.
The temperature is lower than (for example, 150 ° C.) and, of course, higher than normal temperature (for example, 20 ° C.).

The toner t is preheated by disposing such a heating device in the platen roller 3 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 2 '.

FIG. 10 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 not heated, the heating element 2'must be heated from room temperature A0 to temperature A2.
It costs 2. On the other hand, in the case of preheating, since the toner t is preheated to the temperature A1 as described above, it can be heated to the melting temperature A2 in a short time T1.
Therefore, the printing time for each line can be shortened, and the printing process can be performed at high speed.

The temperature control circuit as a 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 roller 3 or the temperature detected by the thermistor. It is composed of a control circuit based on.

[0043]

As described in detail above, according to the present invention, it is not necessary to use an expensive photoconductor or an ink ribbon which increases running cost, so that the cost of the apparatus can be reduced.

Further, by using an adhesive layer or an elastic layer on the toner carrying film, it is possible to surely prevent the background stain,
A thermal transfer image forming apparatus having excellent print quality can be provided.

Further, by incorporating a heating device in the platen roller or the like and preheating the toner in advance, it is possible to set the melting temperature of the toner in a short time when the transfer processing is performed according to the print information, thereby improving the print processing speed. You can

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a thermal transfer image forming apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating a configuration of main parts of the thermal transfer image forming apparatus according to the first embodiment.

FIG. 3 is a diagram illustrating a cross-sectional configuration of an image transfer portion D of the thermal transfer image forming apparatus according to the first embodiment.

FIG. 4 is a diagram illustrating a transfer state onto a sheet when the thermal transfer image forming apparatus according to the first embodiment is used.

FIG. 5 is a diagram illustrating a cross-sectional configuration of an image transfer portion D of the thermal transfer image forming apparatus according to the second embodiment.

FIG. 6 is a diagram showing a transfer state onto a sheet when the thermal transfer image forming apparatus according to the second embodiment is used.

FIG. 7 is a diagram illustrating a state in which toner t is held on an elastic layer when the thermal transfer image forming apparatus according to the third embodiment is used.

FIG. 8 is a diagram illustrating a cross-sectional configuration of an image transfer portion D of a thermal transfer image forming apparatus according to a third embodiment.

FIG. 9 is a diagram showing a transfer state onto a sheet when the thermal transfer image forming apparatus according to the third embodiment is used.

FIG. 10 is a temperature characteristic diagram illustrating a fourth embodiment.

[Explanation of symbols]

 1, 13 Thermal transfer image forming apparatus 2 Thermal head 2'Heating element 3 Platen roller 4, 14, 16 Toner-carrying film 6 Paper transport mechanism 7a, 7b Film transport roll 8 Paper feed cassette 8'Feeding roll 9 Transport roll 10 Paper transport Guide 11 Conveyor belt 12 'Paper discharge port 12 Paper discharge tray 14a Base film 14b Toner container 16a Base film 16b Elastic layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Oda 3-2-1 Sakaemachi, Hamura-shi, Tokyo Casio Computer Co., Ltd. Hamura Technical Center

Claims (5)

[Claims] 1. A heating head having a plurality of heating elements in a main scanning direction and a platen are arranged so as to face each other, and a toner carrying means for carrying toner on the surface and a sheet of paper are superposed on each other so that the heating head and the platen face each other. A thermal transfer image forming apparatus characterized in that a toner image on the toner carrying means is melted by selectively energizing the heating element and is selectively transferred to a sheet to form a dot image. 2. The thermal transfer image forming apparatus according to claim 1, wherein an adhesive member is provided on the toner carrying surface of the toner carrying means. 3. The thermal transfer image forming apparatus according to claim 1, wherein the toner carrying surface of the toner carrying means is an elastic body. 4. The thermal transfer image forming apparatus according to claim 1, 2 or 3, further comprising heating means for heating the platen. 5. The thermal transfer image forming apparatus according to claim 4, further comprising control means for heating the heating means to a temperature below the melting temperature of the toner.