Thermal head and method of manufacturing the same

Details Thermal head and method of manufacturing the same Thermal head and method of manufacturing the same

1998-08-18

2002-06-18

Tran, Huan (Department: 2861)

Incremental printing of symbolic information

Thermal marking apparatus or processes

Specific resistance recording element type

C347S200000, C029S611000

Reexamination Certificate

active

06407764

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a thermal head for use in a thermo-recording machine such as printer and facsimile and a method of manufacturing the same, and more particularly to a thermal head comprising a printing section including a wear-resistant layer having a printing surface to be brought into contact with a thermal record medium, a heat generating layer for generating heat to be transmitted to the thermal record medium through the wear-resistant layer and an electrically conductive layer connected to the heat generating layer, a driving circuit section connected to the electrically conductive layer of the printing section to control a heating electric power to be supplied to the printing section, and a wiring section for connecting the driving circuit section to an external circuit and a method of manufacturing such a thermal head.
BACKGROUND OF THE INVENTION
A thermal head is an equipment, in which heat generated in accordance with a supplied electric signal is transmitted to a thermal record medium, for instance a thermal paper to record characters and figures of desired shapes. A conventional thermal head is composed of the following basic components:
(Component I) Printing Section
A printing section includes a printing surface to be brought into contact with a thermal paper and generates and transmits heat for coloring the thermal paper.
(Component II) Driving Circuit Section
A driving circuit section supplies an electric power according to an electric signal bearing information to be printed. Here, the information is to be understood to mean image data representing characters and figures. Since normal semiconductor integrated circuit chips are used as the driving circuit, the driving circuit is denoted as a driving IC for the sake of simplicity in the present specification.
(Component III) Wiring Section to External Circuit
A wiring section is provided for connecting the thermal head to a connector of a cable to be connected to an external circuit. The printing information and electric power are supplied to the thermal head from the external circuit via the wiring section. A connection to the external circuit is performed by a lead wire such as a flexible FPC (Flexible Print Circuit), and in this case, the wiring section includes pin-like conductors to be connected to the connector of the lead wire, a part of said pin-like conductors being exposed from the thermal head.
[Construction of Conventional Thermal Head]
Several examples of conventional thermal heads will be explained hereinbelow.
FIG. 1
is a cross sectional view showing a structure of an example of the conventional thermal head, in which a driving IC is connected to a printing section and a wiring section by means of wire-bonding. The thermal head shown in
FIG. 1
has been used in a usual type thermo-recording printer. In
FIG. 1
, a reference numeral
10
denotes a wear-resistant layer having anti-physical and anti-chemical characters, a reference numeral
11
a heat generating layer, reference numerals
12
a
and
12
b
an electrically conductive layer constituting electrodes for the heat generating layer, a reference numeral
13
an electrically conductive layer constituting a wiring section for connecting the thermal head to an external circuit, a reference numeral
14
solders constituting connecting portions for connecting the wiring section and a wiring cable with each other, a reference numeral
15
a
driving IC, a reference numeral
16
a
wiring for connecting the driving to the external circuit, a reference numeral
17
a
heat storage layer, a reference numeral
18
a resin layer for isolating and protecting the driving IC and bonding wires, a reference numeral
19
an electrically insulating substrate, a reference numeral
20
bonding wires connecting terminals of the driving IC to the electrically conductive layer
12
b
and wiring section, a reference numeral
21
a thermal paper, and a reference numeral
22
represents a rubber roller for urging the thermal paper against the thermal head. A reference character P shows a printing section which is composed of a part of the wear-resistant layer
10
, the heat generating layer
11
and parts of the electrically conductive layers
12
a
and
12
b.
A reference character S denotes the printing surface of the printing section P, that is a part of the surface of the wear-resistant layer
10
which is brought into contact with the thermal paper
21
. A reference character L expresses a distance between the printing section P and the resin layer
18
protecting the driving IC
15
.
In the known thermal head shown in
FIG. 1
, the heat storage layer
17
is formed on the substrate
19
, on which the heat generating layer
11
, electrically conductive layers
12
a
and
12
b
and wear-resistant layer
10
constituting the printing section P are successively stacked. The thermal head shown in
FIG. 1
will be further explained by dividing it into several components.
(Component I) Printing Section
(Component II) Driving IC
(Component III) Wiring Section to External Circuit
(Component IV) Heat storage Layer
(Component V) Substrate
And particularly the printing section is constructed by stacking the following layers:
(I-
1
) Wear-resistant Layer
(I-
2
) Heat Generating Layer
(I-
3
) Electrically Conductive Layer
Therefore, the conventional thermal head illustrated in
FIG. 1
is composed not only of the basic components (Component I), (Component II), and (Component III), but also by the heat storage layer of (Component IV). These components are arranged on the substrate
19
of (Component V). In other words, the (Component I)-(Component IV) are supported as a unit body by means of the (Component V).
The heat storage layer
17
, however, is an additional component for attaining a power save. There are also proposed thermal heads, in which a heat radiating or other components for increasing a printing speed. By providing such a component, a performance of the thermal head can be improved. The heat generating layer II constituting the printing section P is divided into many heat generating elements in a direction normal to a plane of the drawing of FIG.
1
. The electrically conductive layer
12
a
form a common electrodes to these heat generating elements and the electrically conductive layer
12
b
constitutes divided electrodes each being connected to respective heat generating elements in order to flow an electric current only through one or more desired heat generating elements according to the print information. The common electrode and divided electrodes are called the electrically conductive layer in a general term in this specification.
[Functions and Required Characteristics of Respective Components of Thermal Head]
Subsequently, functions of respective components will be explained.
At first, respective layers constituting the printing section P of (Component I) will be discussed.
(I-
1
) Wear-resistant Layer
The wear-resistant layer
10
is brought into contact with the thermal paper
21
to transmit the heat generated by the heat generating layer
11
to the thermal paper. Therefore the printing surface S is composed of the surface of the wear-resistant layer
10
situating in the printing section P. The wear-resistant layer
10
is required to have a basic characteristic that the layer does not chemically react to components contained in the thermal paper. Moreover good wear-resistant and heat-resistant characteristics, a lower coefficient of friction and a proper hardness are required for the wear-resistant layer. Furthermore, the wear-resistant layer preferably has a suitable electrical conductivity. This is due to a reason that dusts and charged particles might adhered to the printing surface S by an electrostatic charge caused by a friction between the printing surface and the thermal paper, said dust and particles causing a degradation in a print quality and undesired wear. Therefore, in order to prevent the charging, the wear-resistant layer preferably has a proper electric conductivity. However sinc

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