JPS61185461A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain a low-cost thermal head capable of giving half-tone recording by pulse width applied to heating elements by using a melt-type ink sheet and a heating element consisting of plural dots of different resistance values. CONSTITUTION:A thermal head of a resolution of 4/mm is made up by using a set of three heating resistors 24a, 24b, and 24c having different resistance value resulted from varying the lengths of the resistor 24 whose width W1 is kept constant. Using the thermal head, a transfer recording using melt-type ink sheet is made. As shown by the curved line 1, the printing density is gradually increased with the pulse width, and the density of print picture element is controlled by the modulation of pulse width, thereby permitting half-tone recording to be performed. Even when the length of width of the heating element are varied concurrently, the same effect is obtained. The resistance values may be changed by varying the thickness or specific resistance of each heating resistor while keeping its shape unchanged. When the same power is applied and the printing density is varied with pulse width applied by using the conventional thermal head having the same resolution, abrupt rising of density takes place, as shown by the broken line 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use Thermal transfer recording is a recording method that is expected to develop in the future because it allows easy-to-maintain color printers.

The present invention relates to a thermal head used for this thermal transfer recording.

Conventional technology To perform color recording using thermal transfer recording, it is necessary to print three colors, cyan, magenta, and yellow, in an overlapping manner. There are various types of device configurations for such an overlapping printing reservoir. l@
FIG. 6 shows the configuration of a color recording device in which image-receiving paper is wound around a drum.

In FIG. 6, 1a is an image receiving paper, 2 is a drum, 1b is a transfer ink sheet, and on this sheet 1b is a cyan ink 11b.
, magenta 12b1 yellow 13b and black 14b
The dyes or pigments of each color are applied to a length approximately equal to the length of one revolution of the drum 2. 6 is a thermal head.

Color recording is performed in the following manner using the apparatus configuration shown in FIG. The image receiving paper 1a wound around the drum 2 is pressed against the thermal head 5 via the transfer ink sheet 1b'i).

The transfer ink is applied onto the notebook 1b by applying electricity to a predetermined heating element of the thermal head 5 while moving it in the direction shown by the arrow in FIG. The transferred dye or pigment is recorded on the image receiving paper 1a.In this case, the drum 2
By rotating once, printing for one color is completed, the image receiving paper 1a returns to the initial state, and the transfer ink sheet 1b becomes the initial state for the next color. This is cyan 11b and magenta 12b.

A color image can be obtained by performing four recordings of yellow o-13b and black 14b. In addition, black is /An,
It can also be obtained by mixing magenta and yellow, so it may not be used in some cases.

In order to obtain a full-color image like a photograph using thermal transfer recording, it is necessary not only to perform the above-mentioned overlapping printing recording but also to be able to record halftones for each color.

As a method for recording all halftones, there is thermal transfer recording using a sublimation ink sheet. In this recording method, dye ink is sublimated in accordance with the heating amount of the thermal head and transferred and recorded onto the image receiving paper, and the heating amount is controlled by the pulse width applied to the heating element. This method can obtain good halftone recording with a simple control method, but as shown in C in Figure 7, it has problems such as the large amount of energy required for recording and the poor preservation of recorded images. have.

Since the melting type ink sheet shown in A in FIG. 7 requires less energy for recording and has good storage stability of recorded images, there is also a method of recording full-color images using such an ink sheeter.

As can be seen from the person in FIG. 7, with a melt-type ink sheet, it is not possible to record all halftones by changing the applied pulse width with a conventional thermal head. For this reason, this recording method uses a high-density thermal head to perform area gradation recording by combining a plurality of dots.

FIG. 8 shows the configuration of a heating element substrate of a thermal head used for these thermal transfer recordings. In Figure 8, 4o
is a glazed alumina substrate, 41a is a common electrode, 41b
43 is an individual electrode, 43 is a heating resistor, and 42 is a wear-resistant protective film. In order to perform full color recording using a melt-type ink sheet using the thermal head shown in FIG. 8, a head having a resolution of 16 dots/rIrIn or more is required.

Problems to be solved by the invention Thermal transfer recording using a melt-type ink sheet has low recording energy and good image preservation, but halftone recording requires complex image processing using a high-density thermal head. Therefore, it was not possible to provide a low-cost device. Furthermore, compound'l! 1. There is also a problem in that the resolution of the image is lowered because area gradation recording is performed using a fixed number of dots.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and to provide a thermal head that enables halftone recording by changing the pulse width applied to a heating element using a melting type ink sheet roller.

Means to Solve the Problems The present invention develops a heating element shape that prints as a set of multiple dots with different resistance values, thereby making it possible to print using a melt-type ink sheet, which was not possible with conventional heads. This enables halftone recording through pulse width control.

By configuring the action heating element with multiple dots with different resistance values, each coloring pixel can be controlled by controlling the pulse width applied to the heating element! ! It is now possible to record halftones by controlling the intensity, eliminating the need for complex image processing for area gradation, and eliminating the need for a high-density thermal head, which significantly reduces equipment costs. Can be lowered.

Example 1 When recording is performed with a melt-type ink sheet using a thermal head with a resolution of 16 dots/wn, pixels corresponding to each dot are transferred, and the current ink sheet has a resolution of 16 dots/wn or more. It has a resolution of

On the other hand, when the same electric power is applied, the heating element surface temperature is proportional to the applied power density (applied power per unit area of the heating element) applied to the heating resistor. As shown in Figure 2, the heating element l
FIG. 3 shows the surface temperature when the same power is applied to three types of heating elements whose lengths are changed in the l@total representation. In FIG. 3, 4b is a case where the heating resistor is the smallest and a low resistance dot, and 4a is a case where the heating resistor is the largest and a high resistance dot. T in the figure is the surface texture required to transfer the meltable ink. Third
From the figure, the dot 4b, which has a small heating element and low resistance, is transferred with a pulse width of t, the intermediate dot 4c has a pulse width of T, and the dot 4a, which is the largest and has a high resistance, is transferred with a pulse width of T. The image is transferred with a pulse width of . From these results, it was found that the drum l-'! shown in FIG. If the same amount of power is applied at the same time as t1a, then t
During the application of a pulse width of n, transfer printing is performed sequentially starting from the small heating element dots, making it possible to record halftones using the pulse width. .

As shown in FIG. 2, it is not always necessary to keep the width of the heating element constant; the same effect can be obtained even if the heating element is entirely changed to reduce the dot area and resistance value.

FIG. 1 shows a partial configuration of a heating element substrate of a thermal head produced according to the present invention. In FIG. 1, 21a is a common electrode as one power supply conductor, 21b is an individual electrode as the other power supply conductor, 22 is a glazed alumina substrate,
23 is a wear-resistant protective film, 24 is a heating resistor, 24a,
24b.

24c are unit heating resistors each having a different resistance value. The thermal head of this example was created as described below.

A 5i-TB film is formed as a heating resistor film by electron beam evaporation, and then a Cr-Au film is formed as an electrode by vacuum evaporation. Thereafter, photolithography and etching were performed using a mask pattern to form a pattern as shown in FIG. Furthermore, after that, a wear-resistant protective film made of SiC was formed on the heating element portion to produce the thermal head of this example. In this example, an enlarged view of the heating element part is shown in Fig. 4, and three heating elements were constructed with different resistance values by changing the length of the heating element while keeping the width (Wl) of the heating element constant. One set of resistors, 4 heads
A head with a resolution of 1/rtrm was created.

FIG. 5 shows the results of transfer recording using a melt-type ink notebook using the thermal head of this example. Same + W
is the result of applying the same power and determining the print density change depending on the applied pulse width. 3 in the figure uses a conventional thermal head having the same resolution, and a sharp rise in density occurs.

In contrast to C, ■ is the case when the thermal head according to this example is used, and the print density gradually increases depending on the pulse width, and the print pixel density can be controlled by pulse width modulation, making it possible to record halftones. I understand something.

As a result of actual color recording using this thermal head, 16 or more gradations were obtained for each color, and the images were also good.

In this embodiment, only the length of the heating element was changed to change the resistance value of each dot, but the same effect can be obtained by changing the length of the heating element and the heating element II at the same time.

In addition, the resistance value may be changed by changing the film thickness or specific resistance of each heating resistor, assuming that all the heating elements have the same shape1.Furthermore, the number of heating resistors in one set is limited to three. Needless to say, the higher the transfer ink resolution, the easier it is to obtain halftone recording.

Effects of the Invention As described above, the present invention prints the heating resistor of a thermal head as a set of a plurality of dots having different resistance values. The density can be controlled, an inexpensive device is possible, and it has a great effect on creating a full-color printer with good image storage stability.

Furthermore, since the thermal head of the present invention has a high-density pattern only in the heat-generating resistor portion, compared to the high-density thermal head of 16 dots/rrrM used in melt-type ink sheets, the thermal head can be easily fabricated. It also has the effect of significantly reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the configuration of a heating element substrate of a thermal head according to the present invention, FIG. 2 is an explanatory diagram showing the shape of a heating element pattern prototyped to confirm the effects of the invention, and FIG. A diagram showing the surface temperature measurement results depending on the pattern shape,
FIG. 4 is an enlarged view showing the details of the heating element of the embodiment of the present invention shown in FIG. 1, and FIG. 5 is the result of transfer recording using a meltable ink sheet using the thermal head of the present invention. 6 is a perspective view showing the configuration of a drum-type recording unit for color recording by thermal transfer recording, and FIG. 7 is a characteristic diagram showing the configuration of a drum-type recording unit for color recording by thermal transfer recording. FIG. 8 is a plan view showing the configuration of a heating element substrate of a conventionally produced thermal head. 21a... Common electrode, 21b... Individual electrode, 22... Glazed alumina substrate, 23
...Wear-resistant protective film, 24.24a, 24b
, 24cm - heating resistor. Name of agent: Patent attorney Satoshi Nakao and one other person? l
a...5P, lotus/ll Yuzu21b...individual/grab 21b 22 Fig. 2 4α 4c, B Fig. 3 #l Rono\°le 2 輻-1-U- Fig. 4 Fig. 5 Elevation η Donkey 0 Luz 1 Singing Figure 6 Figure 7

Claims (2)

[Claims] (1) Consisting of a row of heating resistors formed on an insulating substrate, a conductor for feeding power to the resistor, and an abrasion-resistant protective film, two or more heating resistors formed in the row are considered as one set. A thermal head characterized in that the heating resistors in the same group are connected in parallel to the same power supply conductor and each has a different resistance value. (2) The thermal head according to claim 1, wherein the plurality of heat generating resistors connected to the same power supply conductor are made to have different resistance values by changing the lengths of the heat generating elements.