JPS61252192A - Thermal transfer recording method - Google Patents

Abstract

PURPOSE:To solve the problem of defective transfer arising from the surface condition of a recording paper, by a method wherein a conductive ink is changed from solid phase to liquid phase in accordance with picture information, and the ink in the liquid phase is moved in the direction of a recording paper in an electric field. CONSTITUTION:An ink donor film 11 comprising a conductive base 11A coated with a heat-fusible conductive ink 11B is used. A counter electrode 12 is disposed on the opposite side of the recording paper 4 which is laminated on the film 11 on one side thereof. A voltage is impressed between the electrode 12 and the base 11A of the film 11 from a DC power source 13, thereby generating an electrostatic field. When a thermal head 1 is driven under this condition to selectively operate a heating element 1R to generate heat, the ink 11B at a part corresponding to the heating part is melted. Induced electric charges are generated at the free surface of the ink, and at the part where the paper 4 and the ink 11B do not make contact with each other, a Coulomb force given as the product of the electric charge and the intensity of the electrostatic field causes the molten ink to fly toward the counter electrode 12, whereby the ink is transferred onto the recording paper 4.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a recording method used in printers, facsimile machines, etc., and more specifically, the present invention relates to a recording method used in printers, facsimile machines, etc. The present invention relates to a thermal transfer recording method for recording.

``Prior Art'' With the spread of office equipment such as computers and facsimile machines, recording of various types of information has become more and more commonplace. There are various recording methods for recording such various information. Among these, the recording method in which recording or display is performed using thermal energy has the advantage of being able to manufacture inexpensive and compact devices, and is widely used.

As a recording method using thermal energy, a method using thermal paper and a method using a thermal transfer recording medium are known as representative methods. Among these, the thermal transfer recording method using a thermal transfer recording medium has an excellent feature of being able to perform recording on plain paper.

FIG. 7 shows the main parts of an example of a recording apparatus that performs recording using this thermal transfer recording method. An ink donor film 3 as a thermal recording medium and a recording paper (plain paper) 4 for recording on this are superimposed between a line type thermal head 1 and a platen roll 2 arranged in parallel thereto. As supplied in condition.

As shown in the figure, the platen roll 2 is in contact with the recording paper 4,
It plays the role of pressing this onto the thermal head 1 via the ink donor film 3.

FIG. 8 shows the general structure of an ink donor film, in which an ink layer 3B made of thermally transferable ink is formed on one surface of a base material 3A made of a polyethylene film or the like. The thermal head 1 is adapted to come into sliding contact with the other surface of the ink donor film 3. The heat pulse output from the thermal head 1 is transmitted from the base material 3A to the ink layer 3B, and the ink in the corresponding portion is melted and transferred to the recording paper 4. The platen roll 2 is rotated by one minute angle in the direction of the arrow in the figure each time one line is recorded, thereby performing sub-scanning. After recording is completed, the ink donor film 3 and the recording paper 4 are separated by, for example, a separation roll 5, and the recording paper 4 is discharged to a discharge tray (not shown).

FIG. 9 is an enlarged view of the contact portion between the ink donor film and the recording paper in such an apparatus. In this example, the recording paper used is high-quality paper with a smoothness of 205 eC. Although the surface of this recording paper is quite smooth, there are many unevenness from a macroscopic perspective, and the ink i! 3B also has a certain amount of "undulation". Therefore, the recording paper 4 and the ink layer 3B
There are parts of the surface that are in contact and parts that are not. For example, in this example, there are gaps of about 5 μm at maximum. In the areas where the ink layer 3B and the recording paper 4 are not in contact, even if the ink layer 3B is liquefied by heating, it cannot be transferred to the recording paper 4.

Therefore, the presence of such a portion causes density unevenness and "fading" of printed characters, and insufficient ink transfer causes a decrease in image density.

``Problems to be solved by the invention'' For these reasons, although the recording paper used for thermal transfer recording is plain paper, it actually has a very high surface smoothness.
Satisfactory image quality could not be achieved unless specially selected paper with a so-called "shiny" gloss was used. For example, even if you try to record using bond paper, which is often used as writing paper in offices, the recording will not be good, and even in solid black printing areas, the optical density will be 1 on average.
There was a problem that it remained at around 60.

In view of these circumstances, it is an object of the present invention to provide a thermal transfer recording method that can perform recording satisfactorily regardless of the surface condition of recording paper.

"Means for Solving the Problem" In the present invention, conductive ink is changed from the same phase to a liquid phase according to image information, and the ink that has changed to the liquid phase is moved in the direction of the recording paper in an electric field. Aim to improve transfer. According to the present invention, ink that has not been in contact with the recording paper in a solid state also adheres to the paper surface in a liquefied state by flying or the like, so it is possible to solve transfer defects caused by the surface condition of the recording paper. Ru.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 1 is for explaining the recording principle of an embodiment of the present invention. This thermal transfer recording method uses an ink donor film 11 in which a heat-melting and electrically conductive ink IIB is coated on an electrically conductive base material 11A. A counter electrode 12 is disposed on the opposite surface of the recording paper 4 that is overlapped with the ink donor film 11 . A voltage is applied between the counter electrode 12 and the base material 11A of the ink donor film by the DC power supply 13, and an electrostatic field is generated.

When the thermal head 1 is driven under such conditions and its heating element IR selectively generates heat corresponding to the pixel, the ink IIB corresponding to the heat generating portion is melted. An induced charge is generated on the free surface of the ink, and the recording paper 4 and the ink I
In the part where the IB is not in contact, the ink in the melted part is transferred to the counter electrode 12 by the Coulomb force given as the product of this charge and the electrostatic field.
It flies in the direction of and transfers onto the recording paper 4. Recording paper 4
In the area where ink IIB is in contact from the beginning, the molten ink adheres to the surface of the recording paper as in the conventional case, and then penetrates into the inside by capillary action in the fibrous area. At this time, the penetration of ink IIB is enhanced by Coulomb force. The ink that has flown onto the recording paper 4 also permeates into the inside of the paper well.

Based on the principle described above, the molten ink is transferred both in the areas where the recording paper and the ink donor film 11 are in contact and in the areas where they are not, and fixing is also ensured. In this way, it is possible to transfer the ink almost uniformly to the surface of the recording paper, which has an uneven surface, with a transfer rate of nearly 100%.

FIG. 2 schematically shows a recording section/installation to which the recording method of this embodiment is applied. The apparatus includes a supply roll 23 having an ink donor film 21 wound around a supply paper tube 22. The ink donor film 21 fed out from the supply roll 23 passes through the guide roll 24 and the ground roll 25 and reaches the recording section 26 . In the recording section 26, the ink donor film 21 passes between the thermal head 1 and a conductive platen roll 27. At this time, the recording paper 4 is conveyed from a supply tray (not shown) to the recording section 26, passes between a line type thermal head and a conductive platen roll 27 while being overlapped with the ink donor film 21, and thermal transfer recording is performed. be exposed. At this time, the thermal head driver 28 drives the thermal head 1 according to the image signal 29.

The recording paper 4 and the ink donor film 21 then pass between a drive roll 31 and a pinch roll 32, at which time they are separated. Ink donor film 21
is guided by a guide roll 33 and wound onto a winding paper tube 34. On the other hand, the recording paper 4 advances along a conveyance path indicated by a broken line 35 and is discharged to a paper discharge tray (not shown). This recording apparatus detects when the ink donor film 21 is no longer present on the supply roll 23, and can continue recording by setting a new supply roll and replacing the winding paper tube.

FIG. 3 shows the structure of the ink donor film used in this device. The ink donor film 21 is made by depositing an aluminum layer 21B with a thickness of 1 μm on a polyethylene film 21A with a thickness of 6 μm, and further applying an ink layer 21C with a thickness of 3 μm thereon by a hot melt method. . The ink layer 21C is 0.5 to ICr on each side of the ink donor film 21! The aluminum layer 21B is coated excluding a width i, and the surface of the aluminum layer 21B is exposed in these excluded areas. Ink layer 21
The ink constituting C has, for example, the following composition.

(Example 1) For black ink, paraffin/wax weight ratio: 30% ester/
Wax 〃 40% carbon black
〃 20% oilyv
〃10% (Example 2) For black ink Carnauba wax Weight ratio 10% Ester
Wax 〃 30% paraffin wax 〃 30% carbon black 〃
13% conductive carbon 〃 8%
Oil 〃 9% (Example 3) Ester wax for black ink or color ink Weight ratio 20% Paraffin wax
〃 40% pigment or dye 〃 20
% Conductive inorganic particles 〃 10% (tin oxide, alumina, etc.) Oil 〃 10% (Example 4) Ester wax for black ink or color ink Weight ratio 20% Paraffin wax
〃 40% pigment or dye 〃 20
% ionic impurities (surfactant)〃 10% oil
10% Such ink has, for example, the following characteristics.

Melting point 69°C Melt viscosity 40cp volume resistivity at 100°C
1. OXI O'~10"Ω' CmSurface tension
The aluminum layer 21B of the ink donor film 21, such as 2Qdyne cm-' or more, is maintained at ground potential by the ground roll 25 shown in FIG. FIG. 4 illustrates this principle. Ground roll 25
A silicon rubber cylinder 42 is fitted into a grounded metal core 41, and a metal ring 43 with a diameter slightly larger than the outer diameter of the cylinder 42 is fitted on both sides of the silicon rubber cylinder 42. It is always in electrical contact with layer 21B. Ground roll 2 like this
5 can apply an appropriate tension to the ink donor film 21 in its transport path from the guide roll 24 to the recording section 26, and also has the effect of preventing wrinkles from forming on the film surface.

Of course, it is possible to ground the aluminum layer 21B or maintain it at a predetermined potential using other methods without using such a conductive roll. FIG. 5 shows an example of this, in which the aluminum layer 21B exposed on the surface of the ink donor film 21 is grounded by a copper electrode 45 in sliding contact therewith. Copper electrodes 45 are provided at two locations to ensure electrical contact with aluminum layer 21B. These copper electrodes 45 can be placed near the heating element of the thermal head 1.

On the other hand, the conductive platen roll 27 is a metal core made of stainless steel or the like with a diameter of 1 g+nm and an electrically conductive rubber roll with an outer diameter of 25 mm is fitted, and its hardness is 35 degrees. A high voltage is applied to the metal core of the platen roll 27 from a DC power supply 46 . The applied voltage has an electric field strength of 300 μm.
The voltage is set to 2 to 3 kV for the distance.

Experimental Example Recording was carried out under the conditions described above using an A3 size head with a recording density of 16 dots/mm as thermal head 1. Printing repetition time 1.4mS (milliseconds)/
line, and the energy applied to the heating element is 0, 24 W.
/dat, and printing was performed with a pulse width of 0.5 ms. As the recording paper 4, bond paper with a surface smoothness of 20 SeC was used.

As a result, a high-density transferred image with an average optical density of 1.4 was obtained in the area where solid black recording was to be performed.

When the density unevenness in this area was examined using a microphotometer, the difference between the maximum and minimum values was 0.2.

Next, the voltage application from the DC power supply 46 was turned off, and a similar experiment was conducted. In this case, the average optical density of the solid black area with respect to the bond paper was 1.0, and the difference between the maximum and minimum density values measured by a microphotometer was 0.7.

The above experiments confirmed that the ink transfer efficiency and transfer uniformity were improved by the present invention.

"Variation" FIG. 6 shows a modification of the invention.

In this modification, the recording signal electrode 52 formed on the substrate 51 of the thermal head 10 is kept at ground potential.

In a thick film type thermal head, a rod-shaped heating element 53 is arranged on a recording signal electrode 52 arranged in a comb-like shape, etc.
A wear-resistant layer 54 is typically formed over these. Therefore, when a high voltage is applied from the DC power supply 55 to the platen roll 56 while the recording signal electrode 52 is kept at ground potential, an electric field is generated between the thermal head 1 and the platen roll 56. Therefore, for example, even if the conventionally used ink donor film 3 as shown in FIG.
If the ink layer 3B is conductive, the liquefied portion will be moved by the electric field, resulting in good transfer.

Although the description has been made regarding a line type thermal head, it goes without saying that the present invention can also be applied to a serial type thermal head. Furthermore, the thermal transfer recording method of the present invention can be applied not only to single-color recording but also to two-color or multi-color recording. In particular, in multi-color recording, it is possible to create a recording surface with good color balance by improving the image quality for each color. I can do it.

Furthermore, in the embodiments of the present invention, a long ink donor film with the same width as the recording paper was used as the thermal recording medium, but a narrow ribbon-shaped thermal recording medium may also be used, or a thermal recording medium cut into a predetermined size may be used. It is also possible to use a thermal recording medium for recording.

"Effects of the Invention" As described above, according to the present invention, the ink is transferred well by the action of the electric field, so that the fixing properties of the recording paper are improved. In addition, since images can be recorded well even if the amount of ink applied to the ink donor film is reduced, the energy applied to the thermal head can be relatively reduced, and the driving power supply can be downsized. The life of the head can be extended without any problems.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing the principle of a thermal transfer recording method in an embodiment of the present invention, Fig. 2 is a schematic diagram of the recording device used in this embodiment, and Fig. 3 is an ink donor used in this embodiment. FIG. 4 is a side view showing the structure of the film, FIG. 4 is a perspective view showing the conductive roll and the ink donor film in contact with it, FIG. 5 is a principle diagram showing another example of grounding the ink donor film, and FIG. 6 7 is an enlarged view of the recording section for explaining a modified example of the present invention, FIG. 7 is an explanatory view showing the main parts of the recording device in the conventional thermal transfer recording method, and FIG. A sectional view showing the structure, and FIG. 9 is an enlarged view showing the contact portion between the ink donor film and the recording paper. 3.11.21... Ink donor film (thermal recording medium), 3B... Ink layer, 4... Recording paper, 11B1 2IC... Ink, 13.46.55...DC power supply. Applicant: Fuji Xerox Co., Ltd. Agent

Claims (1)

[Claims] Conductive ink, which is solid at room temperature and changes to liquid phase when heated, is selectively heated in an electric field according to image information, and the part of the ink that has changed to liquid phase is moved by the electric field and transferred to recording paper. Thermal transfer recording method.