Thermal printhead and method of making the same

Details Thermal printhead and method of making the same Thermal printhead and method of making the same

2001-02-13

2002-08-06

Tran, Huan (Department: 2861)

Incremental printing of symbolic information

Thermal marking apparatus or processes

Specific resistance recording element type

Reexamination Certificate

active

06429887

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal printhead for recording on a recording medium such as a paper thermosensitively or by thermal transfer. The present invention also relates to a method of making such a thermal printhead.
2. Description of the Related Art
FIGS. 9 through 11
illustrate a conventionally used thick film type thermal printhead. The thermal printhead X′ includes a substrate
1
′ and a heat sink plate
2
′ each of which is in the form of an elongated rectangle
The substrate
1
′ is provided with a glaze layer
3
′ formed thereon. The glaze layer
3
′ serves as a heat-retaining layer. The glaze layer
3
′ is formed with a common electrode
4
′, a plurality of individual electrodes
5
′ and a heating resistor
6
′. Further, a plurality of drive ICs
8
′ are mounted on the glaze layer
3
′.
The common electrode
4
′ comprises a plurality of comb-teeth
41
′ and a common line
40
′ connected to one end of each comb-tooth
41
′. Each of the individual electrodes
5
′ has one end
5
a
′ extending between two adjacent comb-teeth
41
′.
The heating resistor
6
′ extends across the comb-teeth
41
′ and the respective ends
5
a
′ of the individual electrodes
5
′.
The common electrode
4
′, the individual electrodes
5
′ and the heating resistor
6
′ are protected by an insulating protective layer
60
′. The insulating protective layer
60
′ may be made of glass for example and is transparent. Therefore, it is possible to view the common electrode
4
′, the individual electrodes
5
′ and the heating resistor
6
′ through the insulating protective layer
60
′.
The other end
5
b
′ of each individual electrode
5
′ is connected to the corresponding drive IC
8
′ via a wire W
1
′. The drive ICs
8
′ are protected by a hard coating layer
81
′.
The substrate
1
′ is bonded to the heat sink plate
2
′. As clearly shown in
FIG. 12
, the bonding is performed by forming an adhesive layer
20
′ on the heat sink plate
2
′ and pressing the substrate
1
′ onto the adhesive layer.
In bonding, it is necessary to precisely position the substrate
1
′ relative to the heat sink plate
2
′ so that the heating resistor
6
′ is positioned in accordance with the customer's specifications. For positioning the substrate
1
′ relative to the heat sink plate
2
′, use is made of a positioning apparatus (not shown) for example. The positioning apparatus comprises a fixing base for fixing the heat sink plate
2
′, an image pick-up device
91
for detecting the absolute position of the heat sink plate on the fixing base, and a monitor
93
for displaying the image taken by the image pick-up device.
The monitor has a display provided with an X-reference line X
0
′ extending longitudinally of the heat sink plate
2
′ and a Y-reference line Y
0
′ extending widthwise of the heat sink plate
2
′. The operator positions the substrate
1
′ while watching, via the display of the monitor, the image taken by the image pick-up device. For example, the operator moves the substrate
1
′ manually so that the heating resistor
6
′ overlaps the X-reference line X
0
′, whereas the end
5
a
′ of a selected individual electrode
5
′ (or a selected comb tooth
41
′) overlaps the Y-reference line Y
0
′.
As shown in
FIG. 14
, the thermal printhead X′ may be formed with a conductive protective layer
61
′. The conductive protective layer
61
′ covers the heating resistor
6
′ via the insulating protective layer
60
′. The conductive protective layer
61
′ is provided to prevent electrostatic breakdown of the heating resistor
6
′. The conductive protective layer
61
′ may be formed of a material containing carbon black for example to provide conductivity. In this case, the conductive protective layer
61
′ is black and opaque for example.
Thus, in the thermal printhead X as shown in
FIG. 14
, the common electrode
4
′, the ends
5
a
′ of the individual electrodes
5
′ and the heating resistor
6
′ cannot be viewed because they are covered with the conductive protective layer
61
′ which is opaque. Therefore, as shown in
FIG. 15
, the common electrode
4
′, the individual electrodes
5
′ and the heating resistor
6
′ cannot be viewed on the display of the monitor of the positioning apparatus. As a result, with the above-described positioning apparatus, it is not possible to position the substrate
1
′ relative to the heat sink plate
2
′ by referring to the positions of the heating resistor
6
′ for example.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to precisely position a substrate relative to a heat sink plate in making a thermal printhead having a heating resistor provided on the substrate and covered with an opaque conductive protective layer.
In accordance with a first aspect of the prevent invention, there is provided a thermal printhead comprising an elongated rectangular substrate including an attaching surface and a non-attaching surface, and a heat sink plate attached to the attaching surface of the substrate, the non-attaching surface of the substrate being provided with a common electrode, a plurality of individual electrodes, a heating resistor extending longitudinally of the substrate in conduction with the common electrode and the individual electrodes, an insulating protective layer and an opaque conductive protective layer for covering the heating resistor. The thermal printhead further includes a positioning indicia which serves as a reference for positioning the substrate relative to the heat sink plate.
Preferably, the positioning indicia may be provided on the non-attaching surface of the substrate at a portion avoiding the conductive protective layer.
Preferably, the positioning indicia may include a first positioning reference portion extending longitudinally of the substrate and a second positioning reference portion extending widthwise of the substrate. The positioning indicia may comprise a cross for example.
Preferably, one of the first and the second positioning reference portions may be formed of the same material as that of the heating resistor, whereas the other one of the first and the second positioning reference portions may be formed of the same material as that of the common electrode and the individual electrodes.
Preferably, the positioning indicia may comprise a plurality of positioning marks. One of the positioning marks may be arranged at one end of the substrate, whereas another of the positioning marks may be arranged at the other end of the substrate.
In accordance with a second aspect of the present invention, there is provided a method of making a thermal printhead comprising an elongated rectangular substrate including an attaching surface and a non-attaching surface, and a heat sink plate attached to the attaching surface of the substrate, the non-attaching surface of the substrate being provided with a common electrode, a plurality of individual electrodes, a heating resistor in conduction with the common electrode and the individual electrodes, an insulating protective layer and an opaque conductive protective layer for covering the heating resistor, and a positioning indicia including a first positioning reference portion having a first positioning reference line and a second positioning reference portion having a second positioning reference line. The method comprises the steps of forming the common electrode and the plurality of individual electrodes, forming the heating resistor, positioning the substrate relative to the heat sink plate, and attaching the substrate onto the heat sink plate

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