JPH0560847U - Thermal head - Google Patents

Abstract

(57) [Abstract] [Purpose] To miniaturize the heat source and spread the heat by diffusion of the protective layer to facilitate area gradation display by the pulse width. [Structure] The shape of electrodes arranged relatively at both ends of the heating resistor is formed so as to become narrower toward the tip, and aluminum nitride having a thermal conductivity of 10 W / (m · K) or more is used for the protective layer. The area of the print dot can be controlled by changing the pulse width of the electric power applied to the electrode wiring or the number of applied pulses. [Effect] In melt transfer printing, gradation display can be easily controlled by controlling the applied pulse width.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a thermal head used for a facsimile, a video printer, etc.

[0002]

[Prior Art]

 Conventionally, a thin film type thermal head is formed by forming a glaze layer 2 on the surface of an insulating substrate 1 and sputtering a heating resistor 3 on the glaze layer 2 as shown in FIGS. In this case, the heating dots having the same shape and size as the printing dot density in this case are formed, and the conductive layer as the pair of electrodes 4 is formed thereon, and the surface thereof is covered with the protective layer 5. Then, when a voltage is applied to the electrodes, a current flows through the heating dots existing between them and the heating resistor 3 generates heat. The heat is transferred to the thermal transfer ink 7 held between the platen 6 and the protective layer 5 and the ink is melted and adheres to the paper 8. At this time, the heat flowing in the protective layer 5 hardly spreads in the surface direction, and retains the patterned shape of the heating resistor 3 and is conducted to the thermal transfer ink 7. Therefore, the thermal transfer ink 7 having the same area is always melted without depending on the applied pulse. Then, the thermal transfer ink 7 and the paper 8 move from the position of the heating dot, the ink sheet portion is peeled off by the paper-ink separating mechanism, and only the melted portion of the ink is transferred to the paper. Furthermore, the mechanism is such that drawing is performed on paper by continuously repeating such operations.

[0003]

[Problems to be solved by the device]

 However, when thermal transfer printing is performed using a thermal head with a conventional structure, even if the applied power is varied and the heating resistor is energized, heat is hardly diffused in the protective layer in the surface direction, so printing dots are printed. The shape hardly changes. As a result, even if the transfer area is varied by the applied power for the purpose of gradation printing, the transfer area cannot be changed and the same gradation is obtained. Therefore, if a thermal head is manufactured using a protective layer material with high thermal conductivity so that the heat generation temperature diffuses and moves on the surface of the protective layer, this time the heat diffuses more than the size of the shape of the heating dot. Therefore, in the conventional heating element shape, the print dots expand beyond the print density, causing bleeding or tailing of the print. Therefore, there has been a problem in that the printing area changes due to the surface heat diffusion of the protective layer by varying the applied power, and the printing area is kept below the printing density even if the heat diffuses on the surface.

[0004]

[Means for Solving the Problems]

 In order to solve the above problems, this invention uses aluminum nitride, which is a material with high thermal conductivity, for the protective layer so that the heat generated from the heating resistor diffuses over the surface of the protective layer over time. In order to prevent the printed dots from spreading more than the density, the heating resistor current-carrying part between the pair of electrodes is patterned so that it becomes narrower toward the tip, and the area of the heating part is made smaller than the printing density. With such a structure, gradation printing can be controlled by controlling the pulse application amount.

[0005]

[Action]

 When gradation printing is performed using the thermal head with the above characteristics, when a short-time pulse is applied, the area equal to the size of the heat generating part reaches above the melting point of the molten ink, and Print dots of the same area are required. Further, when the pulse application is continued for a long time, heat diffuses on the surface of the protective layer, so that the portion above the melting point of the molten ink increases on the head surface, and the amount of melt transfer ink increases. As a result, by varying the applied pulse amount, print dots having different areas can be obtained, and gradation printing can be performed by changing the dot area.

[0006]

【Example】

An embodiment of the present invention will be described below with reference to the drawings. 1A and 1B, a glass paste is printed on an insulating substrate 1 made of alumina and baked to form a glaze layer 2 of about 70 μm. Next, a Ta-SiO ₂ heating resistor 3 was deposited to a thickness of about 0.1 μm by sputtering, and a dot-patterned substrate was prepared by using a photoetching process. Aluminum is sputtered on this to a thickness of 1 μm and exposed using a photomask to pattern the electrode 4 so that it becomes narrower toward the tip, and a protective layer 5 of aluminum nitride is sputtered thereon to a thickness of 5 μm. The thermal head of the present invention was prototyped. Incidentally, the resistance value of 1 dot was set to 2500Ω / dot so as to be the same as that of the conventional thermal head.

Next, two types of pulse widths of 0.8 msec and 1.5 msec were applied to the conventional thermal head and the thermal head of the present invention under the condition of applied voltage of 25 w / m m ² , and the thermal head at that time was applied. The maximum surface temperature distribution was measured. FIG. 3 shows the surface temperature distribution of the heating resistor of the conventional thermal head and the protective layer on the electrode. The solid line temperature distribution shows the distribution when a pulse of 1.5 msec is applied, and the dotted line temperature distribution is the distribution when a pulse of 0.8 ms ec is applied. Since the conventional protective layer has a very small thermal conductivity of about 5 W / (m · K), the heat generated by the heating resistor causes a temperature rise concentrated toward the surface of the thermal head regardless of the pulse width. The shape and size of the heating resistor, that is, the dot density during printing, is almost the same.

FIG. 4 shows a heating resistor of the thermal head of the present invention and a surface temperature distribution of the protective layer on the electrode. Similar to FIG. 3, the solid line shows the distribution when a pulse with a temperature distribution of 1.5 msec is applied, and the dotted line temperature distribution is the distribution with a pulse of 0.8 msec. In the graph of the solid line, the temperature when the temperature rises to the shape and size of the heating resistor in the conventional thermal head is about 230 ° C. Looking at the 0.8 msec distribution of the dotted line in the region exceeding this temperature, it is seen that the heating resistor is patterned to have a tapered shape and the size of the heating resistor increases. Based on this result, the pulse width and the thermal diffusion area were calculated, and the result of area gradation printing was shown in FIG. It is a graph in which the applied pulse width is plotted on the horizontal axis and the print density (OD value) at that time is plotted on the vertical axis. A smooth gradation was obtained from white to black depending on the pulse width.

[0009]

[Effect of the device]

 As described above, according to the present invention, in order to make the dimension of the heating resistor smaller than the print dot density, the opposing tips of the pair of electrodes that conduct electricity to the heating resistor are tapered, and as a result, Heat is generated in a small spot. Furthermore, by increasing the thermal diffusivity of the surface of the protective layer using aluminum nitride, which has a high thermal conductivity, and making it possible to control the thermal diffusion area with respect to the application time, it is easy to print dark and light using area gradation in thermal transfer printing. You will be able to.

[Brief description of drawings]

FIG. 1A is a top view of a thermal head of the present invention. (B) is a sectional view of the thermal head of the present invention.

FIG. 2A is a top view of a conventional thermal head.
(B) is a cross-sectional view of a conventional thermal head.

FIG. 3 is a surface temperature distribution of a conventional thermal head.

FIG. 4 is a surface temperature distribution of the thermal head of the present invention.

FIG. 5 is a relationship between applied pulse width and print density.

[Explanation of symbols]

 1 Insulating Substrate 2 Glaze Layer 3 Heating Resistor 4 Electrode 5 Protective Layer 6 Platen 7 Thermal Transfer Ink 8 Paper

Claims (3)

[Scope of utility model registration request] 1. A glaze layer for storing heat when heat is generated on an insulating substrate, a heat generating resistor for generating heat during printing, electrode wiring for supplying electric power to the heat generating resistor,
And a thermal head comprising a protective layer sequentially laminated for abrasion resistance and insulation of a heating head portion during printing, wherein a heating resistor conducting portion between a pair of electrodes supplying electric energy from both ends of the heating resistor. A thermal head characterized in that the heating resistor is patterned so that the shape becomes thinner from the electrode toward the tip to cover a part of the heating resistor, and the heating portion area of the heating resistor is smaller than the printing density in thermal printing. .. 2. The thermal head according to claim 1, wherein aluminum nitride having a thermal conductivity of 10 W / (m · K) or more is used for the protective layer covering the heating resistor and the electrode wiring. 3. Gradation printing is performed by controlling the area of print dots by changing the pulse width of the electric power applied to the electrode wiring for supplying electric power to the heating resistor or by changing the number of applied pulses. The thermal head according to claim 2, wherein