Thermal head

Abstract

 A thermal head characterized by comprising: a heating resistor layer (4) formed on a glaze layer (3) formed on an insulating substrate (2) so as to rise therefrom; electrodes (14, 15) connected to inclined surface portions of the heating resistor layer (4) which is raised by the glaze layer (3) for passing a current to the heating resistor layer (4) so as to energize the heating resistor layer; and step portions (13) formed on surface ends of the electrodes (14, 15) on the inclined surface portions, the surface ends being not in contact with the heating resistor layer (4), so that projection of edges of the electrodes (14, 15) due to the rising of the glaze layer (3) and the thickness of the electrodes are suppressed by the step portions (13).

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a thermal head, more particularly, to a structure for improving the contact property between heating elements of the thermal head and a material to be heated.

[0002] Fig. 3 is a sectional view showing a conventional thermal head disclosed, for example, in Japanese Patent Unexamined Publication No. 62-173266, and Fig. 4 is a sectional view showing a state of printing by means of the thermal head.

[0003] In the drawings, reference numeral 1 designates a thermal head; 2, an insulating substrate of ceramics or the like; 3, a glaze layer formed so as to rise on the insulating substrate 2; 4, a heating resistor layer formed on the glaze layer 3; 5, a common electrode connected to the heating resistor layer 4; and 6, an independent electrode, the heating resistor layer 4 being connected in series between the independent electrode and the common electrode 5 so that a predetermined heating resistor layer 4 is energized at predetermined timing by a pulse current supplied from a printing control circuit (not shown). Reference numeral 7 designates a protection layer formed over the heating resistor layer 4, the common electrode 5, and the independent electrode 6.

[0004] Generally, a portion between the comnon and independent electrodes 5 and 6 is carved by etching to expose the heating resistor layer 4, and the protection layer 7 of glass or the like is provided by sputtering over the electrodes 5 and 6 and the exposed heating resistor layer 4 so that a recess portion 8 is formed.

[0005] The state of printing by means of the foregoing conventional thermal head 1 will be described with reference to Fig. 4. In the drawing, reference numeral 16 designates an ink sheet composed of a base film 16a and ink 16b. Reference numeral 17 designates a printing paper; and 18, a platen. The thermal head 1 is pressed against the platen 18 through the ink sheet 16 and the printing paper 17, and the heating resistor layer 4 is energized by the pulse current supplied from the printing control circuit so that the ink 16b of the ink sheet 16 is fused by the heat and thermo-transferred onto the printing paper 17.

[0006] In the conventional thermal head as described above, however, an air gap 20 is formed because of the recess portion 8 at the thermo-transfer printing, although the thermal head 1 is urged against the platen 18. Therefore, there has been a problem in that the air gap 20 prevents conduction of heat from the heating resistor layer 4 so that fusing of the ink 16b is not sufficiently performed and thermo-transfer of the ink 16b onto the printing paper 17 is made insufficient, and in that pressing of the ink 16b against a fusing point is made insufficient because of existence of projections on opposite sides of the recess portion 8.

[0007] As means for eliminating such an air gap 20, there have been proposed such a double partial glaze thermal head as shown in Fig. 5, and another thermal head as disclosed in Japanese Patent Unexamined Publication No. 62-173266 in which a protection layer 7 is cut so as to be flat. It is difficult, however, to produce those thermal heads of the types as described above so that those thermal heads are expensive.

SUMMARY OF THE INVENTION

[0008] The present invention has been accomplished to solve the foregoing problems, and an object thereof is to provide an inexpensive thermal head in which a recess portion is made small so that no gap due to the recess portion is formed and heat conduction from the heating resistor layer to the ink is not prevented to make it possible to surely perform thermo-­transfer.

[0009] In the thermal head according to the present invention, stepped portions are formed on surface ends of electrodes in which the electrodes are connected to the inclined surface portions of a heating resistor layer raised by the existence of a glaze layer and the surface ends do not contact with the heating resistor layer.

[0010] According to the present invention, the stepped portions formed on the surface ends of the electrodes which do not contact with the heating resistor layer suppress projection of the electrode edges due to rising of the glaze layer to thereby make the recess portion small so as to eliminate an air gap which prevents heat conduction between the heating resistor layer and ink.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Fig. 1 is a sectional view showing an embodiment of the thermal head according to the present invention;

Fig. 2 is a sectional view showing a printing state by the thermal head;

Fig. 3 is a sectional view showing an example of a conventional thermal head;

Fig. 4 is a sectional view showing a printing state by the conventional thermal head; and

Fig. 5 is a sectional view showing another example of a conventional thermal head.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Fig. 1 is a sectional view showing an embodiment of a thermal head according to the present invention, and Fig. 2 is a sectional view showing a state of printing by means of the thermal head.

[0013] In the drawings, reference numerals 2 - 5, 7, and 16 - 18 designate the same portions as those described in the foregoing conventional examples. Reference numeral 10 designates a thermal head; and 14, a comnon electrode connected to the heating resistor layer 4 and formed by a lamination of conductors 14a - 14c. Reference numeral 15 designates an independent electrode. The heating resistor layer 4 is connected in series between the independent electrode and the common electrode 14 so that a predetermined heating resistor layer 4 is energized at predetermined timing by a pulse current supplied from a printing control circuit (not shown). The independent electrode 15 is formed by a lamination of conductors 15a - 15c.

[0014] Generally, the common and independent electrodes 14 and 15 are formed by etching. At this time, the respective second layer conductors 14b and 15b are formed to be shorter by the length of a stepped portion 13 in the right/left direction with respect to the drawing than the first layer conductors 15a and 14a contacting with the respective inclined surface of the heating resistor layer 4 due to rising of the glaze layer 3, and the respective third layer conductors 14c and 15c are formed to be shorter than the conductors 14b and 15b by the length of the stepped portion 13.

[0015] Therefore, projection of electrode edges of the common and independent electrodes 14 and 15 at the portion in the vicinity of the top of the rising of the glaze layer 3 can be suppressed, and even if the protection layer 7 is formed over the electrodes 14 and 15, the recess portion can be exceedingly reduced in comparison with that of the conventional thermal head 1.

[0016] A state of printing by means of the thermal head 10 according to this embodiment will be described with reference to Fig. 2.

[0017] Heat conduction from the heating resistor layer 4 to the ink sheet 16 is improved because no gap is generated between the protection layer 7 formed just over the heating resistor layer 4 and the base film 16a, and thermo-transfer of.the ink 16b onto the printing paper 17 is surely performed because the urging force exerted to the platen 18 is directly transmitted onto a fusing point of the ink 16b.

[0018] As described above, according to the present invention, stepped portions are formed on the surface ends of the electrodes connected to the inclined surface portions of the heating resistor layer raised by the rising of the glaze layer, the surface ends being not in contact with the heating resistor layer. Accordingly, projection of the electrode edges due to rising of the glaze layer can be suppressed. It is therefore possible to obtain an inexpensive thermal head in which the recess portion is made small so that no air gap due to the recess portion is produced and the heat conduction from the heating resistor layer to ink can be improved so as to perform thermo-transfer surely.

Claims

1. A thermal head, comprising:
an insulating substrate;
a glaze layer formed on said insulating substrate;
a heating resistor layer formed on said glaze layer so as to rise therefrom;
electrodes connected to inclined surface portions of said heating resistor layer which is raised by said glaze layer, said electrodes passing a current to said heating resistor layer so as to energize said heating resistor layer; and
step portions formed on surface ends of said electrodes on said inclined surface portions, said surface ends being not in contact with said heating resistor layer, so that projection of edges of said electrodes due to the rising of said glaze layer and the thickness of said electrodes are suppressed by said step portions.

Drawing