JPH0533349Y2 - - Google Patents

Description

[Detailed Description of the Invention] -Field of Industrial Application- The present invention relates to a thermal printing device, and particularly to an improvement of a printing head including a heat sink.

-Prior art- A thermal printing device is equipped with a print head including a head board on which at least one row of heating elements is arranged and a heat sink supporting the head board, and the print head is aligned with respect to the printing paper feeding direction. A type of printer is known in which printing is performed while scanning in a direction orthogonal to the printer. In such a thermal printing device, the temperature of the heating elements located at both ends tends to be lower than the temperature of the heating elements located inside, so printing at both widthwise ends of one printing line may be incomplete. It will be enough. Therefore, for example, when printing enlarged characters by scanning the print head over two lines while feeding the printing paper,
There was a drawback in that blank spaces where no printing was done occurred along the scanning direction between the lines. To deal with this drawback, in order to prevent the temperature of the heating elements located at both ends from decreasing, for example,
As described in Japanese Patent No. 228171, a thermal printing device has been considered in which the area of heating elements located at both ends is increased to increase the amount of heat generated.

-Problem that the invention attempts to solve- However, if the area of the heating elements located at both ends is increased, the resistance values of those heating elements and those located inside will differ, so The current flow becomes uneven at
This causes uneven density in printing as a whole. In order to solve this problem, a method can be considered in which the current flowing through the heat generating element is divided into two parts: one at both ends and the other at the inside. However, this creates a new problem in that the heat generating mechanism becomes complicated.

- Means for Solving the Problems - The present invention was made to solve the conventional problems without causing such problems, and includes the head board and heat sink as described above. In a thermal printing device equipped with a printing head, a portion of the head substrate and/or the heat sink, which corresponds to at least one of the heating elements located at both ends, includes:
A heat transfer suppressing portion having a lower thermal conductivity than the surrounding portion is formed.

-Operations and Effects- With this arrangement, the heat generated in the head board by the heating element located inside is dissipated via the heat sink as in the conventional case. In addition, the heating elements located at both ends, which tend to lose heat, are prevented from excessive temperature drop by the heat transfer suppressor, so the temperature difference with the heating elements located inside is reduced, resulting in uneven density. This makes it possible to perform printing without printing. Further, forming such a heat transfer suppressing portion has the advantage that the heat generation mechanism is not complicated compared to changing the size of the heat generating element, and is also advantageous in terms of manufacturing.

-Example- Hereinafter, an example of the present invention will be described in detail based on the drawings.

Figure 3 shows an electronic typewriter 1.
It is 00. This electronic typewriter 100 has an integral structure including a keyboard 2 and a thermal printer 4, and a part of the keyboard 2 is provided with a liquid crystal display 6 having a predetermined number of digits. keyboard 2
is provided with various keys necessary for creating sentences, including an alphanumeric key 8.

The thermal printer 4 includes a paper feed roller 10, a platen 12, and a carriage 14. A platen support member 16 is horizontally suspended from the left and right above the printer 4, and the keyboard 2
A platen 12 is supported on the side surface. The paper feed roller 10 is rotatably supported by a frame 15 below the platen support member 16 and parallel to the platen 12, and is rotationally driven by a paper feed motor (not shown). Furthermore, the paper feed roller 10 and the platen 1
A guide rod 18 extends parallel to the guide rod 18, and the carriage 14 is slidably supported in the axial direction of the guide rod 18, and is moved by a drive motor (not shown). A ribbon cassette 22 is removably attached to the carriage 14, and a thermal ribbon 24 is housed within the ribbon cassette 22. Also,
A printing head 26 is attached to the carriage 14 and is movable together with the carriage 14, and the thermal ribbon 24 is drawn out through the printing surface side of the printing head 26. Then, by a head drive mechanism such as a cam mechanism (not shown), the printing head 26 is pressed against the printing paper 28 via the thermal ribbon 24 to perform printing. That is, printing is performed by scanning the printing head 26 in a direction perpendicular to the feeding direction of the printing paper 28 supplied between the thermal ribbon 24 and the platen 12.

The print head 26 includes a head substrate 30 and a heat sink 32, as shown in FIGS. 1 and 2. On the surface 31 of the head substrate 30, heating elements 34 are arranged in a straight line in the width direction of the thermal ribbon 24. These heating elements 34 are arranged for a predetermined number of dots (for example, if there are 24 dots, 24
printed wiring 36 is arranged so that current is sent to each one. This printed wiring 36 includes a conducting wire 38 commonly connected to all the heating elements 34 and a conducting wire 40 individually connected to each heating element 34, and is connected to a power source (not shown) at the conducting wire 38. When a heating element necessary for printing, for example, the heating element 34a located at the uppermost end, is energized, the ink layer of the thermal ribbon 24 corresponding to the heating element 34a is heated onto the printing paper 28 by the resistance heat generated at that time. transcribed into.
By performing such transfer with the movement of the carriage 14 and the paper feeding action of the paper feeding roller 10, desired printing can be performed.

The head board 30 has a second
As shown in the figure, it is fixed to a heat sink 32. The heat radiating plate 32 releases the heat generated in the head board 30 by the heating element 34 mainly by radiation, and also serves to support the head board 30. Cavities opening toward the back surface 42 of the head board 30 are formed in portions of the heat sink 32 corresponding to the heating elements 34a and 34b located at both ends of the heating elements 34 described above. The heat sinks 44 and 46 are closed by the back surface 42 of the heat sinks 44 and 46.

The thermal conductivity of the air in the spaces serving as such heat reservoirs 44 and 46 is lower than that of the heat sink 32 (for example, made of aluminum). Therefore, while the heat of the head board 30 caused by the heating elements 34 on the inside is dissipated by radiation from the heat sink 32 as in the conventional case, the heating elements 34a, 34 on both ends
Due to the presence of the heat reservoirs 44 and 46, heat conduction from the head substrate 30 to the heat sink 32 is suppressed, and the temperature of the heating elements 34a and 34b is prevented from dropping excessively. In this embodiment, the heat reservoirs 44 and 46 serve as heat transfer suppressing parts.

Now, assuming that all the heating elements 34 are energized and generate heat, in the conventional print head 47 in which no heat pool is formed, as shown in FIG. The temperature of the objects 34a and 34b that are located inside is reduced compared to the temperature of the objects located inside. On the other hand, the fourth
In the print head 26 of this embodiment shown in the figure,
Since the heat retaining effect of the heat reservoirs 44 and 46 prevents the temperature of the heating elements 34a and 34b at both ends from decreasing, the temperature distribution becomes almost uniform over all the heating elements 34, and enlarged characters can be printed satisfactorily.

Normally, enlarged characters whose size exceeds the width dimension of the thermal ribbon 24 are, for example, as shown in FIG.
First, a printed portion 50 corresponding to half of the enlarged character 48 is formed by all the heating elements 34 for the first time. Thereafter, the paper is fed by an amount corresponding to the printing section 50 (one line), and following the printing section 52 printed by the heating element 34b located at the bottom end of the printing section 50, It is set so that the heating element 34a is positioned, and the second printing is performed to form the remaining half of the printed portion 54. As a result, one enlarged character 48 is obtained from these printing sections 50 and 54.

When the enlarged characters 48 are printed by the conventional print head 47, for the reasons mentioned above,
Between the printed part 52 by the heating element 34b located at the lowermost end of the first printing part 50 and the printed part 56 by the heating element 34a located at the uppermost end of the second printing part 54, there is a mark in the scanning direction. A gap 58 was created due to poor transfer. On the other hand, in this embodiment, heat pools 44 and 46 are formed in the heat dissipation plate 32, which prevents the temperature of the heat generating elements 34a and 34b from decreasing, thereby avoiding transfer defects. Enlarged characters can be printed without creating any gaps 58.

Yet another embodiment will be described based on FIG. 5, in which the same members and portions as in the first embodiment are given the same reference numerals to indicate correspondence, and their explanation will be omitted.

In the embodiment shown in FIG. 5, the portions corresponding to the heat reservoirs 44, 46 (vacancies) in the previous embodiment are made into heat insulating parts 60, 62 filled with a heat insulating material. Examples of the material for the heat insulating parts 60 and 62 include materials whose thermal conductivity is sufficiently lower than that of the heat sink 32 (for example, aluminum), such as polyurethane, NBR (acrylonitrile butadiene rubber), and silicone rubber. This embodiment also provides substantially the same effects as the first embodiment.

In the above embodiment, the heat reservoirs 44, 46 and the heat insulating parts 60, 62 were formed corresponding to the heating elements 34a and 34b at both ends, but the heat sinks 44, 46 and the heat insulating parts 60, 62 were formed corresponding to the heating elements 34a and 34b at either end. Even if it is formed, it has a corresponding effect. This is because when printing the above-mentioned enlarged characters, the printed portions formed by the heating elements that cause a temperature drop will not be adjacent to each other.

Further, in the above embodiment, the heat transfer suppressing portions such as the heat reservoirs 44 and 46 and the heat insulating portions 60 and 62 were formed on the heat sink 32, but the heat transfer suppressing portions were formed on the heat sink 32.
Alternatively, it may be formed on the head substrate 30. Furthermore, it is possible to form the head board 30 and the heat sink 32 independently and in correspondence with each other, or it is also possible to form the head board 30 and the heat sink 32 so as to extend over the head board 30 and the heat sink 32.

Further, the present invention is not limited to a case where the heating elements 34 are arranged in a single row, but can also be applied to a case where the heating elements 34 are arranged in two rows in a staggered manner, for example. Furthermore, the present invention is not limited to the type that uses the thermal ribbon 24, but is also applicable to, for example, the type that uses thermal paper.

Furthermore, if the temperature decrease occurs not only in the heating elements at both ends but also in the heating elements on the inside, heat transfer suppressing parts may be provided corresponding to the heating elements on the inside depending on the degree of the drop. .

In addition, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a front view of a print head of a thermal printing device which is an embodiment of the present invention, and FIG.
It is a - sectional view in the figure. FIG. 3 is a perspective view showing the appearance of an electronic typewriter including a thermal printing device according to an embodiment of the present invention. FIG. 4 is a diagram showing the temperature distribution of the heating element array in the print head of FIGS. 1 and 2, and FIG. 5 is a sectional view of the print head in another embodiment of the present invention. FIG. 6 is a diagram showing the temperature distribution of the heating element array in a conventional print head, and FIG. 7 is a diagram showing an example of printing when enlarged characters are printed by the conventional print head. 12...Platen, 14...Carriage, 24
...Thermal ribbon, 26...Print head, 28
... Printing paper, 30 ... Head board, 32 ... Heat sink, 34, 34a, 34b ... Heat generating element, 36
...Printed wiring, 44, 46... Heat accumulation (heat transfer suppressing section), 60, 62... Heat insulation section (heat transfer suppressing section).

Claims (1)

[Claims for Utility Model Registration] A printing head including a head board on which at least one row of heating elements is arranged and a heat sink supporting the head board is scanned in a direction perpendicular to the feeding direction of printing paper. In a thermal printing device that performs printing while printing, a part of the head substrate and/or the heat sink, which corresponds to at least one of the heating elements located at both ends, has a thermal conductivity lower than that of the surrounding part. A thermal printing device characterized by forming a heat transfer suppressing portion.