Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
2001-11-26
2003-09-02
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
Reexamination Certificate
active
06614460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thermal head comprising a protection layer having a printing surface which is brought into contact with a heat sensitive record medium, a heat generating section which includes heat generating resistors and electrodes connected to the heat generating resistors and generates a heat to be transferred to said heat sensitive record medium through said protection layer, and a driving circuit connected to said electrodes for supplying a heating electric power to the electrodes.
The present invention also relates to a method of manufacturing the thermal head of the kind mentioned above.
2. Related Art Statement
The thermal head of the kind described in the preamble has been used in simple and low cost printers using heat sensitive papers and heat transfer papers which do not require a supply of inks. In a printer using such a thermal head, a high image quality and high printing speed have been required. For instance, in a heat transfer type color printer or an index printer installed in an automatic mini-laboratory, a thermal head having a very high resolution such as 600 dpi to 1200 dpi has been required.
However, in such a thermal head, an excellent heating up and cooling down property is required in order to raise a temperature of the heat generating section within a very short time and to dissipate a generated heat at a high rate. Such a high speed heating up and cooling down property is particularly required for avoiding undesired blur in an printed image. In order to attain a prompt heating up, it is required that a generated heat does not escape from the heat generating section, and in order to effect the rapid heat dissipation, a generated heat has to be dissipated as soon as possible. For attaining a desired heating up and cooling down property, these two contradictory problems have to be solved simultaneously.
Various requirements generally required for the thermal head may be summarized as follows.
1) small size, light weight, simple structure
2) low price
3) large image size covering A3 size
4) low power consumption
5) high printing speed
6) high density and high resolution
7) uniform image quality without irregular color
8) maintenance free faculty
FIG. 1
is a cross sectional view showing a known typical thermal head. This known thermal head comprises an alumina substrate
1
serving as a heat sink, a heat storage layer
2
formed by depositing a glass having a high melting point of about 1000° C. on the alumina substrate
1
, a heat generating resistors
3
formed on the heat storage layer
2
, a common electrode
4
a
connected commonly to one ends of the resistors
3
, separate electrodes
4
b
connected to the other ends of respective resistors
3
, and a protection layer
5
formed on the resistors
3
and electrodes
4
a
,
4
b
. The protection layer
5
operates as an abrasion resistance layer and includes a printing surface against which a heat sensitive record paper
7
is urged by a press roller
6
.
Upon manufacturing the heat storage layer
2
, a paste prepared by adding glass powders to a binder is applied on the surface of the substrate
1
, and then an assembly is heated to sinter the glass. In the known thermal head, the glass having a high melting point is used for the heat storage layer
2
due to the following reasons. When the electrodes
3
is made of a metal having a low electric resistance such as aluminum and copper, the glass of the heat storage layer
2
has to be sintered at a high temperature in order to prevent the electrodes from being oxidized or altered by the heat storage layer. Furthermore, in order to improve a resistance/temperature coefficient (TCR) of the heat generating resistors, the resistors have to be subjected to a relatively high heating treatment, and thus the glass of the heat storage layer should have a melting point higher that a temperature of said heating treatment. The heat storage layer
2
has also a function to compensate a roughness of the surface of the substrate
1
.
As shown in
FIG. 1
, on the substrate
1
, there is further secured a driving IC
8
by means of an adhesive layer
9
, and the separate electrodes
4
b
are connected to the IC
8
by means of connecting wires
10
.
In the conventional thermal head illustrated in
FIG. 1
, a shallow groove
5
a
is formed in the printing surface of the protection layer
5
, and therefore the heat sensitive record paper
7
could not be effectively brought into contact with the printing surface. Therefore, a heat generated by the heat generating resistors
3
could not be efficiently transferred to the heat sensitive record paper
7
through the printing surface.
In order to mitigate the above mentioned problem of the known thermal head shown in
FIG. 1
, in Japanese Patent Kokai Hei 5-64905, there is proposed another known thermal head as shown in FIG.
2
. In this known thermal head, a printing surface is formed to be flat, and therefore a space is hardly formed between the printing surface and a heat sensitive record medium and a thermal efficiency is improved. As shown in
FIG. 2
, on a flat surface of a preliminary substrate
11
, a pealing-off layer
12
, a wear and abrasion resistance layer
13
, a protection layer
14
, a heat generating resistance layer
15
, an electrode layer
16
and a heat storage layer
17
made of a synthetic resin are successively applied. After cementing the assembly to a substrate
18
by means of an adhesive layer
19
, the preliminary substrate
11
is removed by means of the pealing-off layer
12
. In this manner, a flat printing surface
13
a
can be obtained.
However, in the known thermal head illustrated in
FIG. 2
, in which the heat storage layer
17
is made of a synthetic resin and the printing surface
13
a
constituted by a portion of the wear and abrasion resistance layer
13
is formed to be flat, has the following problem.
Since the heat storage layer
17
is subjected to a high temperature process and is liable to be softened. Therefore, the heat storage layer
17
is preferably made of a heat resistant synthetic resin such as epoxy resin and polyimide resin. However, it has been experimentally confirmed that although the heat storage layer
17
is made of a heat resistant synthetic resin, it is softened during the operation. When the heat resistant layer
17
is softened, it might be deformed to a certain extent. For instance, if a hard particle is introduced between the printing surface of the thermal head and the press roller or heat sensitive paper, the heat storage layer
17
might be locally deformed. Moreover, when the heat storage layer
17
is softened, its mechanical strength is decreased, and thus the thermal head might be deformed and a quality of a printed image might be deteriorated.
In the known thermal head illustrated in
FIG. 2
, since the heat storage layer
17
is formed after the heat generating resistor layer
15
and electrode layer
16
have been formed, the heat storage layer
17
could never be made of a glass having a high melting point like as the thermal head shown in FIG.
1
. Therefore, the above mentioned problem of softening could not be avoided.
Moreover, in the known thermal head shown in
FIG. 2
, the heat sensitive record paper is urged against the thermal head with a very strong force by means of a press roller
6
, but since the printing surface is flat, the roller is brought into contact with the thermal head over a larger area and thus the pressing force per unit area is decreased. This results in that an influence of the roller deformation and abrasion might occur.
In order to mitigate the above problems, the inventors have proposed a thermal head, in which a printing surface is curved outwardly or is protruded from one surface of a protection layer and a driving IC is provided on the other surface of the protection layer. In this thermal head having the protruded printing surface, the heat sensitive record paper is urged against the printing surface with an extremely large force. However, thi
Hagiwara Jun
Hirabayashi Jun
Nagano Katsuto
Saita Yoshio
Susukida Masato
TDK Corporation
Tran Huan
LandOfFree
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