JPH04148945A - Thermal head - Google Patents

Abstract

PURPOSE:To easily perform gradation printing by preventing the sudden change of printing density by partially changing the thickness of the resistor layer constituting the heater of a thermal head. CONSTITUTION:Thick film regions 40a, 40b and a thin film region 42 are provided to the region constituting the heater 38 of a resistor layer 34. These thick film regions 40a, 40b and the thin film region 42 are strip-like regions extending in the direction mutually connecting conductors 36, 36 opposed to each other and, in any region within the range from one conductor 36 to the other conductor, the cross section of the heater 38 within the plane vertical to the direction mutually connecting the conductors 36, 36 is constant. The power consumption of the thin region 42 becomes less than that of the thick regions 40a, 40b and the heat value thereof also becomes little. The change of the printing density of the heater 38 becomes gentle with respect to the change of applied pulse width and good gradation printing is obtained by the use of a thermal head 30.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of a heating element of a thermal head used in a thermal transfer type or thermal type recording device.

(Prior Art) For example, in a thermal transfer recording device, a thermal transfer film and a recording paper are stacked, a thermal head is placed on the side of the film, and a heating element is selectively heated to the thermal transfer film. It is configured to form a desired visible image by transferring ink to recording paper.

FIG. 2(a) and FIG. 2(b) show the schematic structure of a conventional thermal head, in which a resistor layer 4 is provided on an insulating substrate 2, and a conductor 6 is arranged on this resistor layer 4. and a heating element 8 that generates heat by supplying power from this conductor 6.
is formed in the resistor layer 4.

Figure 3 shows the printing characteristics when this conventional thermal head is driven, and by increasing the applied pulse width while keeping the applied power constant, the printing density is changed as shown in the printing characteristics curve 10. There is.

As is clear from this printing characteristic curve 10, the printing density changes rapidly due to minute increases or decreases in the applied pulse width, and in order to perform gradation printing, minute control of this applied pulse width is required, and in practice -1- There is a problem that this method cannot be applied to gradation printing.

Therefore, in order to solve such problems, various efforts have been made in the past. Figure 4(a) and Figure 4(
1)) shows a thermal head according to the conventional example, which includes an insulating substrate 12, a resistor layer 14, a conductor 16, and a heating element 18.
In addition, this heating element 18 is cut into a predetermined shape.

Therefore, a change in current density occurs in the heat generating current path -1-, a heat generation distribution having a heat generation peak at the narrow portions 20a to 20d on the heat generating element 18 is obtained, and a change in the print density of the heat generating element 18 is obtained. As shown by the printing characteristic curve 22 in FIG. 5, the curve becomes gentle with respect to changes in the applied pulse width.

This results in good gradation printing.

(Problem to be Solved by the Invention) However, in the above thermal head, the heating element 18
Since the current flowing through the heating element 18 is concentrated in the narrow portions 20a to 20d, deterioration is severe particularly in areas where the print density is high, that is, areas where the applied pulse width is long, and the life of the heating element 18 is shortened. This poses a problem in that it is not possible to provide a thermal head that has a long life and is highly reliable.

The present invention has been made in view of this type of problem, and an object of the present invention is to provide a thermal head that has a long life, is excellent in reliability, and is capable of easily performing gradation printing.

(First Step for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a heating element for a thermal head, in which the thickness of the resistor layer constituting the heating element is configured to partially change. This is what I did.

(Function) According to the present invention, when power is supplied to the heating element via the conductor,
The resistor layer that constitutes this heating element generates heat. At this time, since this resistor layer has partially different thicknesses, it is possible to obtain the desired heat generation distribution, thereby preventing sudden changes in print density. It becomes possible. In addition, there is no local concentration of current on the heating element, and a reduction in the life of the heating element can be effectively prevented.

(Embodiment) FIGS. 1(a) and 1(b) are plan views of a thermal head according to a first embodiment of the present invention, and FIG.
) is a sectional view taken along line Ib-1b in FIG. 1(a), and FIG. 6 is a sectional view taken along line vi-v'r in FIG. This thermal head 30 includes an insulating substrate 32 and the insulating substrate 32.
a resistor layer 34 provided on the second resistor layer 34; a conductor 36 disposed on the resistor layer 34; and a conductor 36 formed on the resistor layer 34;
A heating element 38 that generates heat by receiving power from the conductor 36 is provided.

A portion of the resistor layer 34 that constitutes the heating element 38 is provided with thick regions 40a and 40b and a thin region 42. The thick regions 40a, 40b and the thin region 42 are band-shaped that extend in a direction that connects the opposing conductors 36, 36 to each other, and therefore, any portion between one conductor 36 and the other conductor Also, the heating element 38 in the plane perpendicular to the direction connecting the conductors 36 and 36
The cross-sectional area of is constant.

In the illustrated example, thick regions 40a, 40b and thin region 42
have the same width W, and the film thickness and T
1 and the film thickness T2 (Tl>T2).

Figure 7 shows the thermal conductor 30 configured in this way.
shows the equivalent circuit of In addition, in the figure, ■ represents the resistance value of the thick regions 4.0a and 40b.

Here, when the voltage V is applied between the terminals 50 and 52, the thick regions 40a and 40b consume power of VXV/R, while the thin region 42 consumes power of (VxV/R)xT2/
Tl power is consumed.

At this time, since Tl>T2 is selected, the power consumption of the thin region 42 is smaller than that of the thick regions 40a and 40b, and the amount of heat generated is also smaller.

As a result, a heat generation distribution having heat generation peaks in the thick regions 40a and 40b is obtained. Therefore, the printing characteristics of the thermal head 30 are almost the same as the printing characteristics curve 22 shown in FIG. 5, and the print density of the heating element 38 changes gradually with respect to the change in the applied pulse width. Therefore,
By using this thermal head 30, it is possible to easily perform good gradation printing.

Furthermore, in FIG. 7, when the voltage ■ is applied between the terminals 50 and 52, the thick regions 40a and 40b have a voltage of V/
A current of R flows in the thin region 42, (V/R)XT2
/TI- current flows. Therefore, the thick region 40a,
The current density at 40b is ■/(r<
W), and the current density in the thin region 42 is V/I
“l”2/TI Xi/ (T2XW)=V/ (R,
XTIXW), and from this, the thick region 40a
,4. It can be seen that the current densities in Ob and thin region 42 are the same.

Therefore, in this embodiment, even if the thickness of the heating element 38 differs partially, the current density becomes uniform over the entire heating element 38, and the current passing through the heating element 38 does not concentrate locally. . As a result, it is possible to effectively prevent a decrease in the life of the thermal head 30, and improve reliability.

Next, a thermal head according to a second embodiment will be explained.

FIG. 8(a) shows a thermal head 6 according to the second embodiment.
The plan view of FIG. 8(b) is VI II of FIG. 8(a).
It is a sectional view taken along the line b-VIIIb, and the same reference numerals as those of the thermal head 30 shown in FIGS. 1(a) and 1(b) indicate the same components, and detailed explanation thereof will be omitted.

This thermal head 60 is equipped with a heating element 62, and in a portion of the resistor layer 34 constituting the heating element 62, a band-shaped film is formed that extends diagonally, but not straight, in the direction connecting the conductors 36 and 36. Thick regions 63a and 63b are provided, and a diamond-shaped double thick region 64 is formed where these regions overlap. Also, thick region 6
3a, 63b, the portion other than the double thick portion 64 forms a thin region 66. Therefore, in this embodiment as well, the cross-sectional area of the heating element 38 in the plane perpendicular to the direction connecting the conductors 36 and 36 is constant at any location between one conductor 36 and the other conductor.

As a result of this configuration, the thermal head 60 according to the second embodiment can achieve substantially the same effects as the thermal head 30 according to the first embodiment described above.

In the first and second embodiments, the entire heating element 38, 62 is made of the same material, that is, the resistor layer 34, or a partial film is formed by combining resistor layers made of different materials. It is also possible to form heating elements with different thicknesses.

(Effects of the Invention) As described in detail below, in the thermal head according to the present invention, the resistor layer constituting the heating element is
Since the thickness is partially different, a desired heat generation distribution can be obtained, and rapid changes in print density can be prevented and good gradation printing can be easily achieved. Moreover, since the current does not concentrate locally on the heating element, it is possible to effectively prevent a decrease in the life of the heating element, making it possible to provide a thermal head with a long life and high reliability. Become.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view of a thermal head according to a first embodiment of the present invention, FIG. 1(b) is a sectional view taken along line Ib-Ib in FIG.
a) is a plan view of a conventional thermal head, FIG.
4(a) is a plan view of another conventional thermal head, and FIG. 4(b) is a diagram showing printing characteristics when the conventional thermal head is driven. ) IVb-IVb sectional view,
5 is a printing characteristic diagram of the other conventional thermal head, FIG. 6 is a sectional view taken along the line vi-Vl of FIG. 1, and FIG. 7 is a sectional view of the other conventional thermal head. FIG. 8(a) is a plan view of the thermal head according to the second embodiment of the present invention, and FIG. 8(b) is an equivalent circuit diagram of the thermal head according to the second embodiment of the present invention. FIG. 30... Thermal head 32... Insulating substrate 34... Resistor layer 36... Conductor 38... Heating element 40a, 4. Ob...Thick film thickness region 42...Thin film thickness region 50.52...Terminal 60...Thermal head 62...Heating elements 63a, 63b...Thick film thickness region 64...・Doubly thick film thickness area 66... thin film thickness area

Claims (1)

[Scope of Claims] An insulating substrate; a resistor layer provided on the insulating substrate; a conductor disposed on the resistor layer; and a conductor formed on the resistor layer that generates heat when supplied with power from the conductor. A thermal head comprising: a heating element, wherein a resistor layer constituting the heating element has partially different thicknesses.