JPH0794170B2 - Driving method for sublimation thermal transfer printer - Google Patents

Description

The present invention relates to a driving method of a sublimation type thermal transfer printer for printing an image having gradation.

(B) Conventional Technology Various methods have been proposed for recording images and characters in accordance with external signals in communication devices, terminal output devices of electronic computers, and the like. Among them, as a method for recording a multi-tone image by the thermal transfer recording method, as shown in, for example, JP-A-55-69482, an ink sheet having a thermally sublimable ink layer is used, and an electric current corresponding to the print density is used. Time control that reads the required energization time from a read-only memory (ROM) in which time data is written in advance, heats the ink layer according to the energization time with a thermal head, and transfers the ink to the recording sheet surface. The gradation recording system of the formula is known.

This method is different from the so-called dither gradation method in which one pixel is composed of a plurality of dots and the number of transferred dots is changed to perform gradation expression. Since the gradation is expressed by controlling the temperature of, a good image having smooth gradation can be obtained by a relatively small and inexpensive device.

By the way, in a conventional printer, the voltage applied to the heating element of the thermal head is increased as much as possible to increase the applied power and the pulse application time is shortened to reduce the required printing time (TV. John Society Journal Vo1.39 No.1
2 (1985) pp. 115 to 1161 “Color hard copy device for electronic still camera by sublimation dye thermal transfer system”
Familiar with. (C) Problems to be Solved by the Invention However, in an ink sheet in which a cyan, magenta, or yellow sublimation dye is applied to a polyethylene terephthalate film whose back surface is currently heat-treated, the applied voltage should be increased. When abrupt energy is flown in, the ink sheet melts, hindering the running of the ink sheet. Further, the image receiving surface of the recording paper that adsorbs the sublimation dye is roughened in a matte shape, and there is a problem that the actual density changes.

(D) Means for Solving the Problems In the present invention, a recording sheet and an ink sheet coated with a sublimation dye are superposed, a predetermined applied voltage is applied to a thermal head to heat the ink sheet, and the sublimability of the ink sheet is increased. In a sublimation type thermal transfer printer that transfers dye to a recording sheet,
The ink sheet has a characteristic that the smaller the voltage applied to the thermal head, the higher the recording density at the same applied energy, and the maximum energization time to the thermal head for a preset single printing. The thermal head is energized with an applied voltage when the recording density of the ink sheet has a maximum value.

(E) Operation According to the present invention, the smaller the applied voltage applied to the head by the ink sheet, the higher the memory density at the same applied energy. The applied voltage can be reduced, the image receiving surface of the recording paper is not roughened, and the printing density can be increased with a glossy image, and the melting of the ink sheet can be prevented.

(F) Example Hereinafter, an example of the present invention will be described with reference to the drawings.

First, the basic principle of the sublimation thermal transfer printer will be described with reference to FIG. In FIG. 3, (31) is a thermal head, (32) is a platen roller, (33) is a base film for carrying a sublimation dye, and (34) is a thermal sublimation applied on the base film with an appropriate binder. Dye,
(35) is an image receiving paper which is an image receiving body. The base film (33) so that the sublimation dye application surface faces the recording paper (35).
On the back of the base film (33) (the surface not coated with dye) and the back of the recording paper (35) (the surface not in contact with the dye). Press with the platen roller (32) installed. next,
When power is applied to the heating element of the thermal head (31) according to the recording signal, the heat energy generated from the heating element is transmitted to the sublimable dye (34) through the base film (33). As the heated sublimable dye (34) sublimes,
Immediately, a visible image is formed by dyeing on the surface layer of the recording paper (35) facing and in contact with it. The feature of the thermal sublimation recording method is that the sublimation layer of the dye can be changed by controlling the heating layer of the thermal head (31) to perform gradation recording with light and shade.

Next, an embodiment of the drive circuit of the printer described above will be described with reference to FIGS. In Fig. 1, (1)
Is a comparator, (2) is a gradation counter, (3) is an energizing pulse generating circuit, (4) is a shift register, (5) is a thermal head, (20) is a switch, and (21) is a head assembly. .

Next, the operation of this embodiment will be described with reference to FIGS. Image data for one line is input to the comparator (1) from the line memory. On the other hand, gradation data is input from the gradation counter. Here, both data are compared, and 1 or 0
The data determined to be transferred is transferred to the shift register (4). Next, the data input to the shift register (4) is transferred to the thermal head (5). Next, the gradation data from the gradation counter is sent to the energizing pulse generating circuit (3), and the energizing pulse for controlling ON / OFF of the thermal head (5) is generated here. The energizing pulse controls a switch (20) provided between the shift register (4) and the thermal head (5), thereby controlling energization. Depending on the data contents in the shift register (4) and ON / OFF of the switch, the thermal head (5) generates heat and is printed.
Transfer and print the data of the gradation. Similarly, the second gradation,
3rd gradation, ... Prints the data of m gradation. FIG. 2 is a timing chart showing the operation of FIG. In this embodiment, as shown in FIG. 2, the data of the first gradation and the data of the second gradation are sequentially transferred, and printing is performed after each transfer. By this method, printing up to m gradations is performed.

By the way, the above-mentioned energization time is determined by the applied voltage printed on the thermal head. That is, the applied energy required to obtain one gradation is expressed by applied energy = (V ² / R) × t V: applied voltage, R: resistance value, t: energization time.

From the above equation, the smaller the applied voltage is, the longer the energization time is required.

Now, as a result of various studies on the relationship between the driving voltage applied to the thermal head and the density of the sublimation dye transferred to the recording paper, the present inventor has found that the smaller the driving voltage is, the higher the maximum density is for the same applied energy. I found it. FIG. 4 and Table 1 show the results of measuring the density value by changing the driving voltage. FIG. 4 shows the relationship between the applied energy and the density value, and Table 1 shows the maximum density value at each applied voltage.

Here, the density value is the reflection density.

The resistance value of the used head is 1000Ω ± 15%.

Although the amount of ink transferred onto the recording paper increases in proportion to the applied energy, the density reaches a peak in the middle as shown in FIG.

This is because the amount of transferred ink itself has increased, but when energy above a certain level is applied, the image receiving surface of the recording paper becomes rough and the gloss is lost, so that the density decreases.

However, as is apparent from FIG. 4, even if the same applied energy is applied, the lower the applied voltage is, the less likely the image receiving surface of the recording paper is roughened, and the more it reaches a peak, and the higher the maximum density is correspondingly. .

Next, the maximum density is set to 63, which is the maximum gradation, and a pulse train is generated by the energizing pulse generation circuit (3) shown in FIG. 1 so that the density changes linearly with respect to the gradation. The gradation-density characteristics at that time are shown in FIG. 5, taking cyan in Table 1 as an example.

As is clear from FIG. 5, the lower the voltage applied to the thermal head (15 V), the higher the density of the image can be printed, and a clear image with good contrast can be obtained. Also,
When the head temperature becomes high, the ink sheet is melted to cause defective running, resulting in defective printing. Table 2 shows the relationship between the substrate temperature and the applied voltage, which causes the traveling failure.

It can be seen from Table 2 that when the applied voltage is lowered, the running defect of the ink sheet does not occur up to a higher temperature even if the head temperature rises.

As described above, the smaller the applied voltage applied to the thermal head, the higher the density, and the poor running of the ink sheet can be prevented. However, if the applied voltage is reduced, the energization time becomes longer in proportion to it. Therefore, the applied voltage may be reduced within a possible range in relation to the printing time.

(G) Effect of the Invention As described above, according to the present invention, high-density printing is possible, a clear image with good contrast is obtained, and the ink sheet does not melt to cause a running defect.

[Brief description of drawings]

1 is a block diagram showing a printer device to which the present invention is applied, FIG. 2 is a timing chart showing the operation of FIG. 1, FIG. 3 is a perspective view showing the principle of a sublimation thermal transfer printer, and FIG. FIG. 5 is a characteristic diagram showing the relationship between applied energy and density value, and FIG. 5 is a characteristic diagram showing the relationship between gradation and density. (1) ... comparator, (2) ... gradation counter, (3) ...
... energizing pulse generator, (4) ... shift register,
(5) ... Thermal head.

Claims (1)

[Claims] 1. A sublimation type in which a recording sheet and an ink sheet coated with a sublimable dye are superposed, a predetermined voltage is applied to a thermal head to heat the same, and the sublimable dye of the ink sheet is transferred to the recording sheet. In the thermal transfer printer, the ink sheet has a characteristic that the smaller the voltage applied to the thermal head is, the higher the recording density at the same applied energy is. A driving method for a sublimation type thermal transfer printer, characterized in that an applied voltage is applied to the thermal head when the recording density of the ink sheet has a maximum value during the maximum energization time.