JPH09193432A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal transfer image forming apparatus regenerating a uniform toner particle layer on the surface of a toner carrier by an inexpensive device. SOLUTION: The toner coating device 14 of an apparatus main body is equipped with a housing 8, the elastic roller 17 arranged to the opening part thereof and a blade 19 and toner T is housed in an internal space. A toner carrying film 13 comes into slide contact with the rear surface of a thermal head at an upper central part and the right end thereof is supported from its rear surface by a feed roller and the left end thereof is pressed to an elastic roller 17 by a feed roller 15. The elastic roller 17 receives toner T prescribed to constant thickness by a blade 19 on its surface to be rotated and fed. The peripheral surface of the elastic roller 17 is flexibly formed and the hardness thereof is higher than that of the toner carrying surface of a toner carrier. By this constitution, the elastic roller 17 transfers the toner T to the toner carrying film 13 by the difference of Van der Waals force to uniformly coat the film.

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 selectively melting toner applied on a toner carrier and transferring it to a sheet to form an image.

[0002]

2. Description of the Related Art Conventionally, 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 printer using an electrophotographic system has a charging device, an exposure head, a developing device, a transfer device, etc. arranged around the photosensitive drum, and a peripheral portion of the photosensitive drum in which a predetermined charge is held by the charging device. Optical writing according to print information is performed on the surface by an exposure head to form an electrostatic latent image on the peripheral surface of 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 toner image on the transferred sheet is heat-fixed by a fixing device, and the sheet is ejected to the outside of the apparatus. However, this electrophotographic printer device requires the use of an expensive photosensitive drum, which increases the cost of the device. Further, since a fixing device is also required, there is a drawback that the device becomes large.

Further, in the thermal transfer type printer device, an ink ribbon coated with ink is run between a thermal head and paper which generate heat according to print information, and the thermal head selectively generates heat according to print information to print on the ink ribbon. The one that melts the above ink and prints on the paper at the corresponding position has been put into practical use. This thermal transfer type printer device has advantages that it is inexpensive and can be downsized because it does not use an expensive photosensitive drum and does not require a fixing device. However, since the ink ribbon used once cannot be reused and is thrown away, there is a problem that running cost increases. Generally, the print area ratio of a document is about 5%, and therefore, the unprinted residual portion of the ink applied on the film after use is 9% of the whole.
It will be 5%. Since this is thrown away as it is, it cannot be said that the economical efficiency is good even in the case of this method, and on the contrary, there is a drawback that the use cost becomes expensive.

On the other hand, although the printer device of the thermal transfer system is also similar, the toner supply system is different and toner particles (hereinafter also simply referred to as toner) are used as the ink, and this toner can be recycled. There is a toner-melting type thermal transfer type image forming apparatus in which an endless film is applied, the toner is selectively melted by a thermal transfer head according to print data, and the molten toner is transferred to a sheet to form an image. In this system, since the film carrying the toner is an endless circulation system, it can be used semipermanently, and the unmelted toner is collected by the toner coating device, so that there is extremely no waste. Therefore, as compared with the above-mentioned ink ribbon disposable thermal transfer system, it is advantageous in that the number of consumables is small.

[0006]

By the way, in the thermal transfer type image forming apparatus having such a structure, the toner applying means for applying the toner to the above-mentioned film electrostatically applies the toner by frictional charging between the toner and the film. The toner was applied dielectrically by applying or by applying a charge to the film upstream of the toner applying means. Applying a charge to the film has the disadvantage that the device is very expensive. Further, in any of the above cases, after the thermal transfer, it is necessary to newly attach the toner to the portion where the toner is transferred to the paper due to the thermal transfer and disappeared from the film surface to regenerate a uniform toner particle layer. In reproducing the toner particle layer, in the above method, a uniform toner particle layer cannot be formed on the film surface due to the influence of the cohesive force between the toner particles, etc., and the toner particle layer is unevenly formed. Therefore, the amount of toner particles corresponding to the image information is not thermally transferred, and thus a problem that a high-quality image cannot be obtained occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional circumstances,
It is an object of the present invention to provide a thermal transfer type image forming apparatus which reproduces a uniform toner particle layer on the surface of a toner carrier by an inexpensive device.

[0008]

The construction of the image forming apparatus according to the present invention will be described below. The image forming apparatus of the present invention includes a recording unit that selectively melts toner according to recording information, a platen that is arranged to face the recording unit, and a toner particle layer that faces the platen and the recording unit. An endless belt-shaped toner carrier for carrying and carrying, and a carrying means for carrying the paper so that the toner particle layer of the toner carrying body and the paper are overlapped at the facing portion of the platen and the recording means, The toner particles on the toner carrier are melted according to the recording information, and selectively transferred to the paper to form a dot image, and after the image is formed, the toner particle layer is pressed against the surface of the toner carrier to form a toner particle layer. In an image forming apparatus having a toner applying unit for reproducing, when the hardness of the toner applying unit is x and the hardness of the toner carrying surface of the toner carrying body is y, the relationship between x and y is “x> y”. Configured to set.

The hardness x of the surface of the toner applying means is 6 in JIS-A hardness as described in claim 2, for example.
It is configured to be 5 ° or less.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged side view showing a configuration of a toner application unit of a thermal transfer image forming apparatus according to an embodiment, and FIG. 2 is a schematic side sectional view of the thermal transfer image forming apparatus. First, the overall configuration will be described with reference to FIG.

As shown in FIG. 2, a thermal transfer image forming apparatus (apparatus main body) 1 includes a recording section 2 disposed substantially in the center of the apparatus main body, and an upstream side of the recording section 2 in the sheet conveying direction (left side in the figure). A guide plate 3, a pair of transport rolls 4, and a paper feed roller 5 that are provided are provided. Below the paper feed roller 5, a paper feed cassette 6 loaded with paper P is detachably attached from one side surface of the apparatus main body 1. A paper transport belt 7 is provided downstream of the recording unit 2 in the paper transport direction (on the right side in the drawing).
A paper discharge port 8 is formed on the other side surface of the apparatus main body 1 further downstream of the paper transport belt 7, and a paper discharge tray 9 is disposed outside the discharge port 8.

The above-mentioned paper feed roller 5 is composed of a half-moon roller and rotates once counterclockwise as indicated by arrow A in the drawing to take out the paper P in the paper feed cassette 6 one by one. , The sheet P is fed to the pair of transport rollers 4.

The transport roll pair 4 is composed of a transport roll that is rotationally driven by a drive mechanism (not shown) and a transport roller that is driven by the transport roll. The transport roll pair 4 rotates in a direction indicated by an arrow at a predetermined timing to transport the transport roll. The sheet P is conveyed to the recording unit 2 via the guide plate 3.

The conveying belt 7 is an air suction type conveying belt, which adsorbs and holds the sheet P on which the toner image is transferred in the recording section 2 from above, and onto the sheet ejection tray 9 through the ejection port 8. To discharge.

The recording section 2 for transferring the toner image onto the paper P is composed of a thermal head 11, a platen roller 12, a toner carrying film 13, and a toner applying device 14.

The thermal head 11 contains a large number of heating elements, and the individual heating elements are arranged in a line in the direction perpendicular to the plane of the drawing. For example, the thermal transfer image forming apparatus 1 of this embodiment
However, assuming that the print density is 240 dpi (dots / inch) and it is possible to print using A4 size paper in the vertical direction, the thermal head 11 is provided with about 2000 heating elements. Also, for example, the print density is 300 dpi.
In this case, the thermal head 11 is provided with about 2500 heating elements. A pulse voltage according to the print information output from the host device is applied to each of these heating elements, and the heating of each heating element is selectively controlled.

The platen roller 12 is composed of a hard cylindrical member and is arranged so as to face the above-mentioned heating element disposing portion at the tip of the thermal head 11, and is moved at the same peripheral surface moving speed as that of the toner carrying film 13. It rotates in the counterclockwise direction indicated by arrow B.

The toner carrying film 13 is formed by forming an elastic layer of silicon rubber or the like on the surface of a base film made of a heat-resistant hard resin such as polyimide, and the surface thereof has an appropriate elasticity as will be described later. Have The toner-carrying film 13 is formed in an endless belt shape, and slidably contacts the tip of the thermal head 11 (the portion where the heating element is arranged) inside the upper center of the endless belt, and inside the upstream and downstream ends. Are supported and driven by the transport rollers 15 and 16, respectively, and cyclically move in the clockwise direction indicated by arrows C and C ′ in the figure.

An elastic roller 17 as a toner applying means of the toner applying device 14 is pressed against the upstream conveying roller 15 via the toner carrying film 13. As shown in FIG. 1, the toner applying device 14 includes an enclosure 18, and an elastic roller 17 and a doctor blade 19 are provided in a lower opening of the enclosure 18. The doctor blade 19 has one end fixed to the opening edge of the casing 18 and the other end fixed to the elastic roller 17
Sliding contact with the peripheral surface of. The elastic roller 17 and the doctor blade 19 close the opening of the casing 18, and the casing 1
The toner T is accommodated in a cavity formed in the upper part of the inside of the container 8.

The elastic roller 17 is coated with silicon rubber on its surface, and its surface hardness is set to be higher than that of the surface of the toner carrying film 13. This elastic roller 17 rotates counterclockwise,
The rotating surface speed is configured to rotate at the same speed in the same direction as the circulating movement direction of the toner carrying film 13 on the pressing surface with the toner carrying film 13.

In such a structure, the elastic roller 17
Rotates to cause triboelectric charging with the toner T, and the toner T is adsorbed by the electric charge and the physical adhesion of the surface. The adhering layer of the adsorbed toner T is applied to the doctor blade 1
It is suppressed to a constant thickness by 9. The elastic roller 17 is
This toner layer is shown by the elastic roller 1 indicated by the dotted circle D in the figure.
7, the toner carrying film 13 and the carrying roller 15 are carried to a pressure contact portion. The toner T is uniformly applied to the surface of the toner carrying film 13 at this pressure contact portion.

FIG. 3 is a schematic enlarged view of the pressure contact portion indicated by the above-mentioned dotted circle D. As shown in the figure, on the surface of the elastic roller 17, the toner T whose thickness is regulated to be constant by the doctor blade 19 of FIG. The toner T adheres due to an adhesion force f1 of a relatively large force, and the toner T is conveyed by the rotation of the elastic roller 17 and pressed against the surface of the toner carrying film 13.

Due to the flexibility and flexibility of the elastic layer on the surface of the toner carrying film 13, the toner carrying film 13 is pressed against the toner T so as to enclose the contact portion with the toner T, as shown in FIG. The contact surface S2 of the spherical contact surface of the toner particle (toner T) becomes geometrically larger as it sinks into the elastic layer of the toner carrying film 13. As described above, the surface hardness of the elastic roller 17 is better than that of the toner carrying film 13.
Of the toner carrying film 13 is softer than that of the elastic roller 17. Therefore, the contact area S2 between the toner carrying film 13 and the toner T is more in contact with the toner T and the elastic roller 17. It becomes larger than the area S1. Since the force of Van der Waals is proportional to the size of the contact area, the toner T has an adhesion force f2 with the toner carrying film 13 due to the larger contact area S2 and an adhesion force f1 with the elastic roller 17 having a smaller contact area S1. Separated from the toner carrying film 13
Is transferred (applied) to.

As a result, after the thermal transfer, which will be described later, the toner carrying film 13 has the surface 1 where the toner T has been transferred to the paper by the thermal transfer and lost as shown by the arrow C'in FIG.
3-1 is exposed and moved to the pressure contact portion, and the toner T is newly applied on the surface thereof to form a uniform toner particle layer T-1.
Is played. The toner particle layer T-1 is conveyed to the recording unit 2 as the toner carrying film 13 moves downstream as shown by an arrow C in the drawing.

FIG. 4A is a schematic enlarged view showing a state near the recording unit 2. As shown in FIG. 4A, in the recording unit 2, the paper P and the toner carrying film 13 are provided between the thermal head 11 and the platen roller 12.
It is sandwiched in a state where the toner adhesion surface is attached to the paper surface and overlapped. The thermal head 11 and the platen roller 12 are arranged at positions where the toner carrying film 13, the toner T and the paper P are brought into pressure contact with each other. In this state, platen roller 1
2 rotates counterclockwise as indicated by arrow G in FIG. 2 (see arrow B in FIG. 2), and the toner-carrying film 13 moves from the diagonally left downward direction indicated by arrow H in FIG. 2 (see arrow C in FIG. 2) to the thermal head. While slidably contacting with 11, slanting downward to the right (arrow C ′ in FIG. 2
Reference sheet), and the sheet P moves to the right as shown by arrow J in the figure.

FIG. 4B shows the recording unit at this time (FIG. 4A).
2 is a schematic enlarged view of a portion indicated by a circle K). Figure (b)
As shown in, the toner carrying film 13 has an elastic layer 13-3 formed on the surface of the base film 13-2,
The toner T is evenly applied to the elastic layer 13-3. The toner layer is attached to the heating element 11 of the thermal head 11.
-1 selectively generates heat in accordance with the print information output from the host device and transfers it to the paper P.

FIG. 5 is a diagram showing a state of thermal transfer in the recording section. Now, in the figure, the platen roller 12, the paper P, the toner carrying film 13 and the toner T attached to the surface thereof move rightward as indicated by an arrow L in the recording portion where the heating element 11-1 is located. ing.

When the heating element 11-1 generates heat according to the print information, the toner T corresponding to the position of the heating element 11-1 is generated.
The thermal energy is transferred to 1 via the toner carrying film 13, and the toner T1 adsorbed on the toner carrying film 13 is melted and adhered to the paper P, that is, transferred. Toners T2 and T3 that have already been transferred to the paper P in FIG.
Are transferred to the sheet P by being melted by the thermal energy of the heating element 11-1 at that time at the printing timing before the toner T1. Further, the granular toners T4 and T5 do not have a print command in the print information when passing through the recording portion, so that the heating element 11-1 does not generate heat and the toner T
Is not melted and is directly attached to the toner carrying film 13 and carried out from the recording section. It should be noted that the melted toner adheres to the paper P and does not adhere to the toner carrying film 13 side because the adsorbing force between the toner carrying film 13 and the toner is originally weak, and the melted toner adheres to the paper P due to its viscosity. This is because it becomes easy to adhere.

In this way, the toner T transferred to the paper P is
Moves the recording sheet 2 from the recording unit 2 by moving the recording sheet P.
Are discharged and placed on the discharge tray 9. Further, the toner carrying film 13 returns to the pressure contact portion with the toner applying device 14, re-adheres the toner T evenly on the elastic layer 13-3, reproduces the toner layer T-1, and goes to the recording portion 2. Repeat that.

As described above, by using the endless heat-resistant elastic film that can be recycled and the thermal head, a complicated processing step such as the electrophotographic method is not used, and as much as 95% as in the thermal thermal transfer method. It is possible to obtain a small-sized image forming apparatus which does not generate waste and has a low cost of use, without disposing of an ink ribbon in which ink remains.

In this embodiment, as the elastic layer 13-3 of the toner carrying film 13, silicone rubber having a JIS-A hardness of 20 ° is used, and the toner applying device 14 is used.
The elastic roller 17 has a JIS-A hardness of 65 °.
The following silicone rubber is attached. In the experiment, when the above-mentioned printing processes were performed by the elastic rollers 17 coated with silicone rubber having different hardness, the uniformity of the applied toner layer, the transfer of the toner to the toner carrying film, and the recording portion It was observed that there was a difference in the obtained print quality and the like.

FIG. 6 is a chart showing the results of performing the above-described printing process by applying silicone rubbers of various hardnesses to the elastic roller 17, respectively. In the figure, the product number of a silicon rubber of a certain chemical manufacturer is shown in the leftmost column, and the JIS-A hardness of the product with that product number is shown in the next column. Then, in the third to fifth row frames, the evaluation of the results observed when the above-described printing process is performed by the elastic roller 17 coated with the silicone rubber of each hardness is “X” is indicated by “Δ” when it is ok, and “◯” when it is good. As shown in the figure, the toner generally transfers well regardless of which hardness is used, but in view of the uniformity of the toner layer, the hardness is 90 ° and the hardness is 70.
At a temperature of .degree. Or the like, the toner particles are not evenly deposited on the surface of the elastic roller, so that even if the toner particles are transferred to the toner carrying film, a uniform layer distribution cannot be obtained, and therefore an image of good print quality cannot be obtained. It is considered that this is because when the hardness is 70 ° or more, the elastic roller does not have sufficient flexibility and flexibility to carry the toner particles. And hardness 65 °,
When silicone rubber having a hardness of 65 ° or less such as 55 °, 50 °, 30 °, 25 ° is used for the elastic roller, the uniformity of the toner layer, the toner transfer state, and the printing result The image quality was good.

When the JIS-A hardness of such an elastic roller is x and the JIS-A hardness of the toner carrying film is y, setting is made such that x> y (in the present embodiment, the JIS of the toner carrying film is set. -A hardness is 20 °),
High quality printing can be obtained.

[0034]

As described above, according to the present invention,
Since the elastic roll body for toner application is provided so that the peripheral surface has flexibility and the hardness of the peripheral surface is set to be harder than the hardness of the toner carrying surface of the toner carrier, the elastic roll body does not The toner is well adsorbed and conveyed, and at the same time, the toner is uniformly and well transferred to the toner carrier, so that a good transfer result in the recording portion can be obtained and a high quality image can be formed. In addition, since it depends only on the elastic characteristics of the elastic roller, it does not require a structure such as a voltage applying power source or a toner stirring member for frictional charging, and thus it is possible to realize a small and inexpensive image forming apparatus. Become.

[Brief description of the drawings]

FIG. 1 is an enlarged side view showing a configuration of a toner application unit of a thermal transfer image forming apparatus according to an embodiment.

FIG. 2 is a schematic side sectional view of a thermal transfer image forming apparatus according to an embodiment.

FIG. 3 is a schematic enlarged view of a pressure contact portion (a portion indicated by a dotted circle D in FIG. 1) with an elastic roller, a toner carrying film, and a conveying roller.

FIG. 4A is a diagram showing a state in the vicinity of a recording unit (portion indicated by a circle K), and FIG. 4B is a schematic enlarged view of the recording unit.

FIG. 5 is a diagram showing a thermal transfer state in a recording unit.

FIG. 6 is a chart showing the results of a study showing the optimum hardness of the elastic roller surface.

[Explanation of symbols]

 1 Thermal transfer image forming apparatus (apparatus main body) 2 Recording unit 3 Guide plate 4 Conveying roll pair 5 Paper feeding roller P Paper 6 Paper feeding cassette 7 Paper conveying belt 8 Paper discharging port 9 Paper discharging tray 11 Thermal head 11-1 Heating element 12 Platen roller 13 Toner carrying film 13-1 Exposed surface after toner transfer 13-2 Base film 13-3 Elastic layer T Standard toner 14 Toner application device 15, 16 Conveying roller 17 Elastic roller 18 Case 19 Doctor blade

Claims (2)

[Claims] 1. A recording unit that selectively melts toner according to recording information, a platen that is arranged to face the recording unit, and a toner particle layer that is supported on the facing portion between the platen and the recording unit. The recording medium includes an endless belt-shaped toner carrier for transporting, and a transporting device for transporting the paper so that the toner particle layer of the toner carrier and the paper are superposed on the facing portion of the platen and the recording device. In response, the toner particles on the toner carrier are melted and selectively transferred to the paper to form a dot image, and after the image is formed, the toner particles are pressed against the surface of the toner carrier to regenerate the toner particle layer. An image forming apparatus having a coating unit, wherein when the hardness of the toner coating unit is x and the hardness of the toner carrying surface of the toner carrier is y, the relationship between x and y is set to "x>y". An image forming apparatus comprising and. 2. The hardness x of the surface of the toner applying unit is
The image forming apparatus according to claim 1, wherein the JIS-A hardness is 65 ° or less.