JPS60250970A - Thermal head - Google Patents

Abstract

PURPOSE:To enable to heat a printing head and, particularly, a paper just before printing and to print at high speed with high quality, by providing cells of heating elements for preheating in the vicinity of cells of heating elements for printing, respectively. CONSTITUTION:In the same printing head, the cells r1-r7 of heating elements for preheating are provided at the side of the cells R1-R7 of heating elements for printing, respectively, and the thermal head and the paper just before printing are heated by the heating elements for preheating, thereby improving the color forming and transferring characteristics. When the resistance R of the heating element 8 (R1-R7) and the resistance (r) of the heating element 9 (r1- r7) are so set as to satisfy the relationship R<(r) by adjusting the areas of the heating elements, it is possible to use a power source voltage in common. In this case, the resistance (r) is so selected that color development due to generation of heat at the time of preheating is prevented from occurring. Accordingly, printing can be conducted at high speed, and high printing quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermal printer or a thermal transfer type thermal printer, and particularly to a copying type thermal printer having a preheating function.

(Background technology) As a conventional method for preheating a thermal printer when the power is turned on or at a low temperature, the print head is preheated by passing a current with a minute pulse width to the printing heating element of the print head even when no printing is being performed. something is known. However, when preheating only the print head, for example, when printing on copy thermal paper or high-speed printing, sufficient heat transfer may not occur until the second sheet of paper, resulting in blurred prints or poor print quality. There was a drawback.

Thermal transfer printers also have similar drawbacks.

The coloring principle of a copying thermal printer is as shown in Fig. 1. When an applied pulse is applied to the heating element 2 of the print head 1, it generates heat, first coloring the first sheet of paper (thermal paper) 3, and then coloring the first sheet of paper (thermal paper). Thermal transfer ink 4 applied to the back side of the first sheet of paper is melted and transferred to plain paper 5. In a copying thermal printer, the relationship between the applied energy (El) and the ambient temperature ('I'') for the first sheet of paper (thermal paper) and the second sheet of paper (thermal transfer) is as shown in Figure 2. 6 is 1
The energy E0,7 that causes the second sheet of paper to develop color indicates the energy E2 that causes the second sheet of paper to develop color. In order to achieve sufficient color development and transfer to the first and second sheets of paper, it is necessary to apply more than the required energy (E2) for the second sheet of paper to the print head. In order to provide the same voltage, it is necessary to consider detecting the ambient temperature using a thermistor or the like and adjusting the applied pulse width.

The cycle of applied pulses when printing at an additive character/second is approximately 2
ms (as a result, sufficient heat transfer did not occur, particularly at low temperatures and when printing the first character, resulting in insufficient color development and transfer.

Electrical energy (El is V2 as shown in the formula below.

E = Wt - πt (joule) E - Electrical energy W - Power t = Application time ■ - Applied voltage R - Heating element resistance value By increasing the applied voltage, the electrical energy of the heating element (E)
However, increasing the applied voltage will significantly reduce the life of the print head.

(Problem to be solved by the invention) The purpose of this invention is to improve the printing quality and obtain high-speed printing by improving the preheating method of thermal printers (including thermal transfer methods). This is because the heating element cell for preheating is arranged near the heating element cell for printing.

(Structure and operation of the invention) As shown in FIG. 3, the present invention provides heating element cells for preheating (r, to r7) and heats the print head and the paper immediately before printing using a heating element for preheating, thereby improving color development and transfer characteristics, thereby increasing printing quality.

The relationship Epr>EH holds between the electrical energy required for printing (Epr) and the electrical energy required for preheating (,EH), and as a method to satisfy this relationship,
By adjusting the areas of the printing heating element 8 (he ~ horse) and the preheating heating element 9 (r1~r7) shown in Fig. 3, the resistance value is set to R<r.
If so, it is possible to use a common power supply voltage.

However, in order to prevent color development (or transfer) due to heat generation during preheating, it is necessary to select the resistance value (r) of the heating element for preheating so as not to develop color (or transfer) using the following formula.

■2 r ) B, t max E3 - Electrical energy required for color development ■ - Applied voltage r = Resistance value of heating element for preheating trmx = Maximum application time Figure 4 is a part of the thermal head drive circuit of the present invention. . In the figure, 10 indicates a thermal head, and SLI~
SL7 is a selection signal for selecting a heating element for printing, 110R1
-R7 are heating elements for printing, and r1 to r7 of 12 are heating elements for preheating. When one or more of the printing heating elements 11 (for printing) is driven by the selection signals SL1 to SL7, the preheating heating elements r, to r are activated through 13 OR gate circuits.
By heating all of 7, it is possible to preheat the paper just before printing.

(Effects of the Invention) As explained above, this invention provides a heating element for printing and a heating element for preheating in the same helix, and can heat the print head and especially the paper just before printing, thereby achieving high-speed printing and high-quality printing. It has the advantage of providing quality.

In this embodiment, the heating element for preheating shown in Fig. 3 is placed opposite the heating element for printing, but the same effect can be obtained even if there is only one heating element corresponding to the total height of the heating element for printing. be able to. Furthermore, although the driving voltages for the preheating heating element and the printing heating element are the same, the same effect can be obtained even if the driving voltages are different.

Furthermore, by controlling a thermistor, etc. that detects the ambient temperature installed inside the thermal head or inside the device, which is a conventional preheating method, the heating element for printing (in the present invention, the heating element for printing + the heating element for preheating) can be used. It is even more effective when combined with a method of passing current with a minute pulse width to the body) at low temperatures.

The same effect can be achieved by applying the same method to the print head of a thermal transfer printer that uses a thin film ribbon instead of the first sheet of paper (thermal paper) in a decoding thermal printer.

In this example, a serial thermal print head in which heating elements are arranged in a vertical line is explained, but a line thermal printer device with a fixed printing throat can also be used by arranging heating elements for preheating in parallel in the paper feeding direction. , can be used similarly.

[Brief explanation of drawings]

Figure 1 is a diagram showing the printing principle of decoding type thermal printing, Figure 2
3 is a diagram showing the relationship between applied energy and ambient temperature, FIG. 3 is a structural example of a print head according to the present invention, and FIG. 4 is a circuit diagram of an embodiment of the present invention. 1: Print head 2: Heating element 3: First sheet of paper (thermal paper) 4: Thermal transfer ink 5: Second sheet of paper (plain paper) 6: Required energy to color the first sheet of paper to a certain density or higher (E,) 7: Necessary energy to transfer the image to the second sheet of paper at a certain density or higher (E2) 8: Heating element for printing (he ~ koshi) 9: Heating element for preheating (r, ~ r7) 10: Thermal head 11: Driver section 12: Driver section 13 Niogate circuit Patent applicant Oki Electric Industry Co., Ltd. Patent application agent Megumi Yamamoto - Figure\1\N- 0 1 Town (3 X5 gong tit <' C)

Claims (2)

[Claims] (1) A thermal printer having a thermal print head having an arrangement of cells of heating elements for printing, characterized in that cells of heating elements for preheating are provided in the vicinity of the cells of the heating elements for printing. head. (2) The thermal head according to claim 1, wherein the resistance value of the heating element for preheating is larger than the resistance value of the heating element for printing.