JPH06210889A - Thermal transfer printing method - Google Patents

Abstract

PURPOSE: To obtain a thermal transfer printing method in which a constant high print speed is attained at very low cost without overheating the heating dot elements. CONSTITUTION: A heating current pulse is applied to N print lines at a specified heating cycle using a printhead comprising heating dot elements arranged linearly and the heating cycle is inverted every N lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer printing method. The invention applies to the field of thermal printing of any medium, in particular plastics media such as electronic cards.

[0002]

BACKGROUND OF THE INVENTION As is well known, thermal transfer printing machines utilize a printhead having heating dot elements arranged in a line formed by electrical resistors. The current flow in the resistor heats the dot element. When the heated dot elements come into contact with the thermal medium or ink ribbon, several lines of parallel dots are printed in succession to obtain the final printed pattern. An electronic device with a current pulse generator and a program for controlling the current pulse generator is adapted to provide the required level of current pulses according to a programmed heating cycle.

However, a phenomenon of residual heat occurs between the two printed dot lines. In fact, the energy required to produce a high quality print is such that the temperature of the heated dot element rises even after the line has been printed, thus leading to faster head wear and (print blurring, Moreover, the ribbon may be cut off, which leads to deterioration of print quality. FIG. 1 (a) shows the change in heating current obtained by standard electronic control, and FIG. 1 (b) shows the change in energy corresponding to it.

Several methods have been proposed to solve this problem. The first method is to allow a sufficiently long time between the two pulses (longer than the manufacturer's instructions) to allow the heated dot elements to cool during the printing of the two lines. The change in current by this method is shown in Fig. 2 (a). Figure 2 (b) shows the corresponding energy changes. However, this method has a drawback that the printing time becomes extremely slow, and it is understood that this method is not preferable from the viewpoint of machine performance characteristics. The second method is to use several heating pulses as shown in FIG. This pulse has a shorter duration and thus no increase in temperature, but at the same time it has the disadvantage of a slower printing speed and a shorter head life set for the maximum number of pulses.

A third method is to use a thermistor that measures the temperature of the entire head and adjusts the duration of the heating pulse. For mechanical reasons, due to the thermal inertia of the thermistor, which is placed at a suitable distance from the heating dot element, it is not possible to make a quick enough adjustment to prevent overheating of the heating dot element, There is insufficient energy required to print the isolated dots. Yet another method is to use a head with a record that stores the already heated dot elements. While this method gives good results, it requires a highly sophisticated and expensive control system.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems, except for the drawbacks found in previously known methods.

[0007]

According to the present invention, there is provided a thermal transfer printing method of heating a dot element by applying a heating pulse using a print head having a heating dot element arranged in a line. Mainly the first N
A method is provided which comprises applying a heating pulse to the individual print lines in a predetermined heating cycle to invert the heating cycle regularly. This cycle is preferably reversed every N lines. Other features and advantages of the present invention will become more apparent by the following description with reference to the drawings. However, the following examples do not limit the present invention in any way. Figures 1 (a) and (b)
2 (a) and (b) and FIG. 3 relate to the prior art and have already been described.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The method of the present invention, as shown in the example of FIG. 4, applies a current pulse to a predetermined number of lines according to a heating cycle, and then performs the heating cycle on the next predetermined number of lines. It is to invert. That is, the heating cycle as shown in the first example is performed for each of the predetermined number N of printing lines. Number N
Is determined experimentally for each printhead,
Choose a number that gives the best printed results. In the method, the heating cycle is regularly reversed. That is, the heating cycle is reversed for the subsequent N lines or a number close to N. In FIG. 4, the cycle is newly started from line N + 1. In the example given here, the newly started cycle begins with a cooling time first, followed by a heating pulse.

In the present invention, the heating pulse recommended by the manufacturer is used, and the application method is the above-described method. By interchanging the heating period and the cooling period, it becomes possible to cool the heating dot element at intervals of N lines (N varies depending on the characteristics of the head). This makes it possible to prevent overheating very quickly and at the same time maintain the same level for all printed dots (even isolated dots).

By the method proposed here, without overheating the heating dot element, at a very low cost,
A constant high printing speed is achieved. This improves print quality without resorting to expensive print heads and sophisticated electronic systems as in the prior art. For example, for the ROHM KT2002CI type head, the selected pulse is 0.5
Energy of W is applied, and the total duration T2 = 3 ms, and the duration T1 = 500 μs. A heating cycle is applied to N = 4 lines, the heating cycle is reversed for the following 4 lines, and so on.

In practice, this method is implemented by an electronic controller for the head. For that purpose, as known to those skilled in the art, the pilot program of the existing pulse generator was changed so that the predetermined heating cycle was reversed every N lines. Of course, this method is applicable to any heating cycle. In particular, it is applicable to the heating cycle as shown in FIG. In fact, when it is necessary to use the cycle as shown in FIG. 3, this method is applied as shown in FIG. For example, when using the same printing as the above-described embodiment, the following values are set. t ₁ = 400 μs t ₂ = 400 μs t ₃ = 100 μs t ₄ = 300 μs t = 1 time per line

[Brief description of drawings]

FIG. 1 (a) shows a heating cycle for performing line printing based on the first conventional example, and FIG. 1 (b) shows
The energy change corresponding to Fig. 1 (a) is shown.

FIG. 2 (a) shows a heating cycle for performing line printing based on a second conventional example, and FIG. 2 (b) shows
Figure 2 (a) shows the corresponding energy changes.

FIG. 3 shows a heating cycle for performing line printing based on a third conventional example.

FIG. 4 shows an example of a heating cycle applied to a series of print lines according to the method which is the subject of the present invention.

FIG. 5 shows an example of a heating cycle applied to a series of print lines according to the method of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 8305-2H B41M 5/26 A

Claims (2)

[Claims] 1. A thermal transfer printing method for heating a dot element by applying a heating pulse using a print head having a heating dot element arranged in a line.
A thermal transfer printing method comprising applying a heating pulse to a first N printing lines in a predetermined heating cycle to regularly invert the heating cycle. 2. The method of claim 1, wherein the cycle is reversed every N lines.