JPH11115233A - Thermal head and printer equipped therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal head that is capable of performing printing at high speed in multiple gradation by a method wherein a plurality of lines each constructed with a plurality of heating elements being arranged are provided with resistance values of the heating elements made different respectively for each of the lines, and each of pixels is constructed by the combination of the heating elements belonging to the lines in the plural number. SOLUTION: In an ink transfer printer, a film 2 having through holes 25 is stuck to a thermal head 3 with a spacer 8 interposed in between and a platen roller 4 is provided at a position above the film 2. Heating elements 30 are arranged in two lines along the direction in which the through holes 25 are arranged, and the heating elements 31 and 32 belonging to the first and the second lines are of such that are different respectively in resistance value. Ink is thrust into the through holes 25 of the film 2 with vapor pressure generated on vaporization and expansion of the ink heated by the heating elements 30 and made to pass through the through holes 25 for transferring onto a recording paper P. On transferring, the density of pixels is made variable by the combination of the heating elements 31 and 32 belonging to each of the lines, thereby forming images in multiple gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head for heating a recording medium such as thermal paper according to image information in a printer or the like.

[0002]

2. Description of the Related Art In a thermal printer, a thermal transfer printer or the like, a thermal head is used to heat a recording medium in accordance with image information. Generally, a thermal head has a plurality of heating elements, and pixels (dots) formed on a recording paper are formed by one heating element. 2. Description of the Related Art Conventionally, a so-called gradation process for varying the density of one pixel has been performed. In the prior art, gradation is applied by changing the heat generation time (voltage application time) of the heating element of the thermal head. That is, if the heating time of the heating element is long, the area to be heated (such as recording paper) increases, so that the area of the pixel increases and the image becomes dark. Conversely, if the heating time of the heating element is short, the area of the pixel becomes small, and the image becomes thin.

[0003]

However, if the heating time of the thermal head is varied as described above, there is a problem that the printing speed is reduced. In addition, there is another problem that if a print control is performed while changing the heat generation time of each heating element, the control system becomes complicated.

[0004] The present invention has been made in view of the above problems, and has as its object to provide a thermal head capable of obtaining multiple gradations and capable of printing at high speed.

[0005]

In order to solve the above problems, a thermal head according to the present invention is provided with a plurality of lines in which a plurality of heating elements are arranged, and the resistance value of the heating elements is different for each line. And each pixel is constituted by a combination of heating elements belonging to a plurality of lines.

With this configuration, it is possible to easily obtain multiple gradations (that is, vary the density of pixels in multiple steps) by combining which heating element is turned on and which heating element is turned off. it can. Further, since it is not necessary to change the heating time of the heating element, the control is simplified and the printing speed can be increased.

It is to be noted that a configuration is possible in which one pixel further corresponds to a plurality of heating elements belonging to each line. With this configuration, the number of combinations of the heating elements that are turned on and off is further increased, and more gray levels can be obtained.

The above-mentioned thermal head can be applied to an ink transfer printer. In this ink transfer printer, a film having a predetermined through hole and the thermal head are arranged to face each other, an ink space for holding ink is provided between the film and the thermal head, and a side opposite to the thermal head across the film. The recording paper can be configured by bringing the recording paper into close contact with the recording paper. In this case, when the thermal head is heated according to the image information, the heated ink passes through the through holes of the film and is transferred to the recording paper.
Note that the heating elements belonging to the plurality of lines correspond to the respective through-holes, and the amount of ink passing through the through-holes can be varied by applying a combination of the heating elements to perform gradation.

The thermal head may be a thermal printer that forms an image by heating a thermosensitive recording paper with the thermal head, or forms an image by overlapping the recording paper with the thermal head with a heat-fusible ribbon interposed therebetween. The present invention can also be applied to a thermal transfer printer.

[0010]

FIG. 1 is a side sectional view showing an ink transfer printer using a thermal head 3 according to an embodiment. In the ink transfer printer, the film 2 having the through-hole 25 and the thermal head 3 are bonded via the spacer 8. A gap of about 0.1 mm is provided between the thermal head 3 and the film 2.

The spacer 8 and the support substrate 33 of the thermal head 3 are formed of a material that does not allow ink to pass therethrough.
An area surrounded by the spacer 8, the support substrate 33, and the film 2 becomes an ink space 1 for holding ink. The heating element 30 of the thermal head 3 is the ink space 1
Located within. An ink container 6 for replenishing the ink space 1 with ink is provided on the left side of the spacer 8 in the drawing. The ink in the ink container 6 is drawn into the ink space 1 by a capillary phenomenon through a communication hole 85 formed in the spacer 8.

Above the film 2, there is provided a platen roller 4 for bringing the recording paper P into close contact with the upper surface of the film 2. The platen roller 4 is a so-called rubber roller, and is disposed so that its axial direction is orthogonal to the paper surface.
When the platen roller 4 rotates, traction acts between the platen roller 4 and the recording paper P, and the recording paper P is transported in the direction of the arrow in the figure.

FIG. 2 is a plan view showing the positional relationship between the film 2 and the thermal head 3. In FIG. 2, the direction of conveyance of the recording paper P is indicated by an arrow X. A large number of through holes 25 are arranged in the film 2 in one row. The heating elements 30 are arranged in two rows along the arrangement direction of the through holes 25. The heating element belonging to the upstream line (referred to as the first line) is indicated by 31, and the heating element belonging to the downstream line (referred to as the second line) is indicated by 32. For the sake of simplicity, in FIG. 2, the heating element 30 is shown as a rectangular block, and a lead pattern for energizing the heating element is omitted. The arrangement direction of the through holes 25 and the heating elements 30 is
It is parallel to the axial direction of FIG.

The heating element 31 belonging to the first line and the second heating element 31
The heating elements 32 belonging to the line have different resistance values, and generate different amounts of heat when energized. In this embodiment,
The heating value when one heating element 31 in the first line is heated is 0.3 mJ / dot, and the heating value when one heating element 32 in the second line is heated is 0.1 mJ / dot. is there. Note that the heat generation time (voltage application time) of the heating element 31 in the first line is the same as the heat generation time (voltage application time) of the heating element 32 in the second line. One through hole 25 corresponds to two heating elements 31 belonging to the first line and two heating elements 32 belonging to the second line, that is, a total of four.
Each heating element is individually driven and controlled by a control unit (not shown).

FIG. 3 is a schematic diagram showing the principle of image formation by the ink transfer printer of the embodiment. In the normal state of FIG. 3A, the inner diameter of the through hole 25 of the film 2 is a size that does not allow ink to pass through. Here, when the heating element 30 generates heat, the ink near the heating element 30 and the film 2 that is almost in contact with the heating element 30 are heated. And FIG.
As shown in (b), the ink heated by the heating element 30 is vaporized and expanded, and a local pressure is generated in the ink by the vapor pressure. At the same time, the heated portion of the film 2 has a reduced elastic modulus and is easily deformed.

Thus, the ink is pushed into the through hole 25 of the film 2 by the above pressure, and the ink is pushed into the through hole 2 of the film 2.
5 is spread. Then, the ink passes through the through hole 25 of the film 2 and is transferred to the recording paper P which is in close contact with the upper surface of the film 2. After the transfer, with the local heating stopped by the heating element 30, the heated portion of the ink and the film 2 is cooled by the surrounding ink, and the through-hole 25 of the film 2 returns to the original size (a size that does not allow the ink to pass through). Return. Therefore, the heat generation of the thermal head 3 is controlled in accordance with the image information, and the rotation of the platen roller 4 is controlled to control the recording paper P.
Are sequentially conveyed to form a two-dimensional ink image on the recording paper P.

Here, as shown in FIG. 2, the amount of ink passing through one through-hole 25 can be varied by a combination of the on / off of the four heating elements corresponding to one through-hole 25. That is, the density of the pixels (dots) formed by the ink that has passed through one through hole 25 can be varied (that is, gradation can be provided). This gradation will be described by taking the leftmost through hole 25 in FIG. 2 as an example. Of the heating elements 31 in the first line corresponding to the through hole 25 on the leftmost side in the figure, the heating element on the left side in the figure is 31a and the heating element on the right side is 31b. Similarly,
Of the heating elements 32 on the second line, the heating element on the left side in the figure is 3
2a, and the heating element on the right side is 32b.

The total amount of heat generated per pixel changes as shown in Table 1 below, depending on the on / off combination of the four heating elements 31a, 31b, 32a, 32b corresponding to one through hole 25. In Table 1, ○ indicates ON, and X indicates OFF.

[0020]

Table 1 31a 31b 32a 32b Heat value per pixel (mJ / dot) (1) ○ ○ ○ ○ 0.8 (2) ○ ○ ○ × 0.7 (3) ○ ○ × × 0.6 (4) ○ × ○ ○ 0.5 (5) ○ × ○ × 0.4 (6) ○ × × × 0.3 (7) × × ○ ○ 0.2 (8) × × ○ × 0.1 (9 ) × × × × 0.0

As shown in Table 1, four heating elements 31a,
The amount of heat generated by one pixel changes in nine levels depending on the combination of ON / OFF of 31b, 32a, and 32b. That is, the amount of ink passing through one through-hole 25 can be changed in nine steps, whereby the density of one pixel can be changed stepwise.

As described above, according to the printer using the thermal head of this embodiment, the combination of the four heating elements corresponding to one through-hole 25 makes the through-hole 25
By varying the amount of ink that passes through, the pixel (dot) area can be changed, and multiple gradations can be obtained. still,
In the present embodiment, the heating elements 31a belonging to the first line,
Although the heating elements 31b and the heating elements 32a and 32b belonging to the second line correspond to one through-hole 25, the present invention is not limited to this, and three or more lines can be used. .

The thermal head of the present invention is a thermal printer that forms an image by heating a thermosensitive recording paper with a thermal head, or a recording paper and a thermal head are superimposed on each other with a heat-fusible ribbon interposed therebetween to form an image. The present invention can be applied to a thermal transfer printer to be formed. In the case of a thermal printer and a thermal transfer printer as well, if one pixel is constituted by a total of four heating elements, two heating elements belonging to the first line and two heating elements belonging to the second line,
Nine levels of gradation as shown in Table 1 can be provided.

[0024]

As described above, according to the thermal head of the present invention, the resistance of the heating element is configured to be different for each line, and one pixel is configured by a combination of the heating elements belonging to the plurality of lines. Multi-gradation can be easily obtained by combining which heating element is turned on and which heating element is turned off. Further, since it is not necessary to change the heating time of the heating element, the control is simplified and the printing speed can be increased.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating a basic configuration of an ink transfer printer using a thermal head according to an embodiment.

FIG. 2 is a plan view showing a relationship between a film and a thermal head in the ink transfer printer of FIG.

FIG. 3 is a schematic diagram illustrating a printing principle of the ink transfer printer of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink space 2 Film 3 Thermal head 4 Platen roller 25 Through-hole 30 Heating element 31 Heating element of 1st line 32 Heating element of 1st line 33 Support substrate

Claims (6)

[Claims] A plurality of lines in which a plurality of heating elements are arranged are provided so that resistance values of the heating elements are different for each line, and one pixel is formed by a combination of heating elements belonging to the plurality of lines. A thermal head in an ink transfer printer, comprising: 2. The method according to claim 1, wherein one pixel further corresponds to a plurality of heating elements belonging to each line.
The thermal head according to 1. 3. A film having a predetermined through-hole and the thermal head are disposed to face each other, an ink space for holding ink is provided between the film and the thermal head, and the thermal head is interposed between the film and the thermal head. The recording paper is adhered to the opposite side, and the thermal ink is heated according to image information, so that the heated ink is transmitted to the recording paper through the through hole of the film. 1 or 2
A printer using the thermal head according to 1. 4. The heating element belonging to the plurality of lines corresponds to each through-hole, and the amount of ink passing through the through-hole changes according to the combination of the heating elements. Printer. 5. An image is formed on the heat-sensitive recording paper by bringing the heat-sensitive recording paper which is colored by heat into close contact with a thermal head and heating the heat-sensitive recording paper with the thermal head according to image information. A printer using the thermal head according to claim 1. 6. A recording paper and a thermal head are overlapped with a thermally fusible ribbon interposed therebetween, and the thermal head heats the ribbon in accordance with image information to form an image on the recording paper. Forming,
A printer using the thermal head according to claim 1 or 2.