JPH03190760A - Thermal head - Google Patents

Abstract

PURPOSE:To make the area of the part of a resistance heating element, with which an ink sheet comes in contact, uniform to eliminate the uneven concentration of printed letters by lengthening an interelectrode distance in the thick part of an electrode and by shortening the interelectrode distance in the thin part of the electrode. CONSTITUTION:The substrate 11, glaze layer 12, resistive layer 13, electrodes 14a, 14b, protective layer 15 and heating resistor 16 are completely the same as those of a thermal head known heretofore. In this case, when the thickness t1 of an electrode is thin, the part of an ink sheet 17 coming in contact with a heating resistor 16 is smaller than an interelectrode distance l1, and when an electrode thickness t2 being a contact length L is thick, the interelectrode distance l2 of the part of the ink sheet 17 coming in contact with the heating resistor 16 is made larger than l1 so as to be the contact length L. Thus, when the contact length L is made equal in each picture element, a printing area is also made equal so that uneven concentration is difficult to occur and a high picture quality is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used in a melt-type or sublimation-type thermal transfer printer.

[Summary of the invention]

In order to eliminate density unevenness during printing caused by variations in the thickness of the electrodes of the heating resistor part, the present invention increases the distance between the electrodes in the thicker portions of the electrodes, and increases the distance between the electrodes in the thinner portions of the electrodes. By shortening the distance between the electrodes, we aim to equalize the area of the part of the resistive heat generating part that is in contact with the ink sheet, thereby providing a thermal head for thermal transfer printers that has excellent image quality with less density unevenness.

[Conventional technology]

Thermal heads used in conventional thermal transfer printers include a full-glaze thermal head with a glaze layer on the entire surface, a partial glaze thermal head with a glaze layer only near the heat-generating resistor, or a heat-generating resistor layer on the edge of the substrate. End-face heads and the like are known and are widely varied in practice. The configurations of these thermal heads differ in that they are made of a thin film or a thick film, but they basically have the same structure.

A conventional thermal head will be explained with reference to FIG. 2, taking as an example the case of a flat glaze. A glassy glaze 712 is provided on the alumina group Fi,1, and a resistive layer 3 is placed on it.
and electrodes 4a and 4b are provided. Furthermore, a protective layer 5 is provided to protect these surfaces. With this configuration, by passing a current between the electrodes 4a+4b, the resistance layer 3
The heating resistor section 6 is heated.

[Problem to be solved by the invention]

In the conventional thermal conductor, since the electrodes 4a and 4b are configured higher than the resistance layer 3, the heat generating resistor portion 6 of the protective layer 5 also has a concave shape. Although this dent is slight, the ink sheet 7 does not touch the area near the electrode 4a4b of the heating resistor 6 and is not heated, so the area actually printed is shorter than the distance between the electrodes 4a and 4b.
The thicker the electrodes 4a and 4b, the narrower the printing area becomes, and thus the printing density decreases.

Therefore, if the thickness of the electrodes 4a, 4b differs from pixel to pixel, the print density also differs, resulting in a phenomenon called density unevenness.

In the actual manufacturing process of the thermal head, the electrode 4a,
When 4b is a thin film formed by vapor deposition or the like, there is a tendency for the electrode thickness to be thick at the center of the linear thermal head and thin at the edges, and this tendency differs depending on the vapor deposition method.

For example, if the electrode thickness is 1.5 μm,
Even a difference of about 0.2 μm causes significant density unevenness, and it cannot be used for gradation expression like dye-sublimation printers or for high-end products.In particular, the higher the pixel density, the less density unevenness will occur. Significant.

[Means to solve the problem]

In order to solve the above problems, in the present invention,
The distance between the electrodes was made long in the thick part of the heating resistor, and the distance between the electrodes was made short in the part where the electrode was thin.

[Effect]

With the above configuration, the contact area between the heating resistor and the ink sheet can be made almost equal even if the electrode thickness differs depending on the pixel position, so the 4 degree unevenness caused by variations in printing area can be eliminated. be done.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 tag and (bl) are schematic cross-sectional views of a thermal head according to an embodiment of the present invention, FIG. 1 fat is a pixel with a thin electrode, and FIG. 1 fb is a pixel with a thick electrode.

Substrate 11. Glaze layer 12. Resistance N13. Ti pole 14a
, 14b, the protective layer 158 heating resistor part I6 is exactly the same as the conventional thermal head, but the electrode thickness t1°L2
The distance between the electrodes +4a, ] and 4b, which are the heating resistor portion 16, is 1. ．． 142 is different from the conventional example. When the electrode thickness 1. is thin as shown in Fig. 1 (al), the part where the ink sheet 17 contacts the heating resistor 16 is smaller than the interelectrode path N a + and becomes the contact length. Fig. 1 [bl When the electrode thickness t is large as in Figure 1 (a), the step becomes large.
In order to obtain the same contact length as l, the interelectrode path M I! ! It is necessary to provide a large By making the contact length equal for each pixel in this way, the printing area becomes equal, so density unevenness is less likely to occur, and high image quality can be achieved.

Next, a method for setting the electrode thickness t and the interelectrode path #l will be explained. Generally, when forming a thin film, it is formed by placing a thermal layer in a vapor deposition or sputtering apparatus, and the electrode thickness t always shows the same tendency depending on the arrangement.

For example, if the electrode thickness t in the central part of the thermal head corresponding to the pixel is large, the tendency will always be the same, so if the difference in thickness is known in advance, it can be easily achieved by changing the shape of the mask. Ru.

Next, there is a problem that the distance l between the electrodes differs from pixel to pixel, and the resistance value changes, but if it is formed using the same method as forming the electrodes, the resistance layer in the pixel where the electrode thickness t is thick will be the same. Even if the electrodes are formed thickly and the distance between the electrodes differs, this is not a problem because it is canceled out to some extent, and when gradation is important, such as in a sublimation type thermal transfer printer, resistance value correction is generally performed, so there is no problem.

[Effects of the Invention] As described above, according to the present invention, the distance between the electrodes can be increased in the thicker portions of the electrodes by simply changing the mask shape.
By configuring the distance between the electrodes to be short in the thinner part of Nh, it is possible to equalize the contact area of the ink sheet with the heat generating resistor part in each pixel, and the printing area of each pixel is equal, which reduces density unevenness. It is possible to provide a thermal hand that performs high-quality printing without any blemishes, and the effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a thermal head according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a conventional thermal head.・Substrate ・Glaze layer resistance layer ・Electrode protection layer ・Heating resistance part ・Ink quantity or more

Claims (1)

[Claims] A thermal head in which heat-generating resistors are arranged in a line, and the distance between the electrodes is longer in the thicker electrodes of the heat-generating resistor, and the distance between the electrodes is shorter in the thinner electrodes. head.