JP2001080100A - Thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal printer in which variation of manufacture has minimum effect on the print quality and no adjustment is required during manufacture. SOLUTION: A heating resistor 1c is formed at a position shifted by a distance Y upstream in the carrying direction of recording sheet from the top position of a partial glaze and positional relation between a thermal head 1 and a platen is shifted by a distance X downstream in the carrying direction of recording sheet. A region exhibiting good print quality against variation can be widened by setting a following relationship, X : Y = radius of platen roller 2 : radius of curvature of partial glaze.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an improvement in a thermal printer for performing thermal recording on a recording medium using a thermal head.

[0002]

2. Description of the Related Art A thermal head used in a thermal printer is roughly classified into a thick film type and a thin film type according to a method of manufacturing a heating resistor. The thin-film type has a heating resistor formed by photo-etching for each element, and has the advantage that the reproducibility of the dot shape printed on the recording paper is high and that high printing quality is easily obtained as compared with the thick-film type. However, since the shape of the heat generating portion is concave, the positional relationship between the platen roller and the thermal head affects the image quality.
Therefore, as described in Japanese Patent Application Laid-Open No. 2-136249, actual printing is performed by a printer at a design stage or a manufacturing stage to set or adjust an area having good image quality.

[0003]

However, in the prior art described in the above-mentioned publication, even if the heating element is designed to be located at the center of the partial glaze, that is, at the top of the convex portion, it is difficult to manufacture the head. Since deviations occur due to process variations, the head is inspected and sorted, and the positional relationship between the platen roller and the thermal head is adjusted in three regions according to the deviation. Including such inspection and adjustment steps in the manufacture of the printer imposes a burden on the factory and increases the cost of the product. SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal printer which minimizes the influence on printing quality even if there is a variation in manufacturing and does not require adjustment during manufacturing.

[0004]

In order to solve the above-mentioned problems, the present invention provides a thermal head in which a heating resistor is arranged on a partial glaze forming a substantially arc-shaped projection having a radius R2, and a predetermined pressing force. Radius R1 pressed by the thermal head
A thermal printer that includes a platen roller and prints while nipping the recording medium between the thermal head and the platen roller while transporting the recording medium. On the other hand, a heating resistor is formed at a position shifted by a predetermined distance Y to the upstream side, and the thermal head is shifted from the platen roller by a predetermined distance X to the downstream side in the transport direction of the recording medium in parallel with the substrate. And X: Y = R1: R2.

[0005] When transporting the recording medium, the platen roller
It deforms asymmetrically with respect to the contact position with the thermal head, and contacts with a stronger force on the upstream side in the transport direction. That is, the pressure distribution moves upstream from the contact position between the platen roller and the thermal head. In the case of a thermal printer, a partial glaze is arranged at the contact position between the platen roller and the thermal head.At this time, the heating resistor is located at a position shifted from the center of the partial glaze to the upstream side in the recording medium conveyance direction. Is arranged, the adhesion between the heating resistor and the recording medium is improved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermal printer according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a pressure contact portion between a thermal head 1 and a rubber platen roller 2 used in a thermal printer according to the present invention.
Is pressed between the thermal head 1 and the platen roller 2 and is pressed from the back surface of the thermal head 1 in the direction of the platen roller 2 by a force P. When the rubber portion of the platen roller 2 is compressed and the platen roller 2 rotates in the direction of arrow A, the thermal paper 3 is fed in the direction of arrow B by the frictional force. This embodiment shows an example of a thin film type thermal head.

The thermal head 1 includes an insulating substrate 1a formed of an electrically insulating material such as ceramic, a partial glaze layer 1b having an arc-shaped cross section, a heating resistor 1c, and a pair of resistors connected to both ends of the heating resistor 1c. And a protective film 1e that covers the surface of the thermal head 1. The partial glaze layer 1b is for accumulating heat generated by the heating resistor 1c attached to a predetermined position near the top so as to have an appropriate temperature, and has a low thermal conductivity and excellent heat resistance. , For example, glass.

The entire projection formed by the partial glaze layer 1b, including the protective film portion, is generally called partial glaze.
In the case of a thin film head, the upper portion of the heating resistor 1c is formed as a concave portion by the electrode 1d. Since the concave portion has a peak of the heat distribution, it is referred to as a heating portion 1f.

A line perpendicular to the insulating substrate 1a and passing through the center of the platen roller 2 is defined as a platen center line 4, and a distance between the platen center line 4 and the center of the heat generating portion 1f is defined as a distance X. A line passing through the center of the arc of the partial glaze layer 1b perpendicular to the insulating substrate 1a is defined as the glaze center line 5, and the glaze center line 5
And the distance to the center of the heat generating portion 1f is defined as a distance Y. The distance X and the distance Y are set so that the heat generating portion 1f is in close contact with the thermal paper 3.

By the way, the position of the heating resistor 1c with respect to the partial glaze layer 1b varies to some extent due to manufacturing variations. However, when the partial glaze layer has a substantially circular arc shape, the heating section 1f and the platen roller The state of contact with 2 changes slightly. As a result, even if predetermined power is applied to the heating resistor 1c to generate predetermined Joule heat, the color development state of the thermal paper 3 changes.
This example will be described based on the print density measurement result of the thermal printer when the distance Y = 0 mm.

FIG. 2 shows a thermal head having a distance Y = 0 mm, that is, a thermal head in which a heating element is formed at the center of a partial glaze, by applying a predetermined applied energy to the heating resistor 1c to cause the thermal paper 3 to move. FIG. 4 is a density distribution diagram in which the density at which color is developed is measured. The horizontal axis indicates the distance X, and the vertical axis indicates the OD value in a predetermined checkered print pattern. The OD value of 0.6 or more indicates that the heat generating portion 1f and the thermal paper 3
Is good, and if the OD value is less than 0.6, the colored portion 1f
This indicates that the adhesion between the heat-sensitive paper 3 and the thermal paper 3 is poor. X +
On the side, the heat generating portion 1f is shifted to the sheet discharge side. In other words, this indicates that the heat generating portion 1f is located downstream of the platen center line 4 with respect to the paper transport direction. The good printing range is indicated by C1. In the range of C1, the value of X is -0.
0.9 mm from 5 mm to +0.4 mm. Here, the better printing range on the-(minus) side is
Since the platen roller 2 rotates in the direction of arrow A, the rubber portion of the platen roller 2 is deformed in the direction opposite to the direction of arrow A, and the pressure distribution between the platen roller 2 and the thermal head 1 is different from the paper transport direction. This is because it shifts to the upstream side. That is, the degree of adhesion is higher when the value of X is on the-(minus) side,
As a result, when X is on the negative side, the OD value is high for printing. The center value of the good printing range C1 is X
= −0.05 mm, and when designing a printer using a thermal head of Y = 0 mm, the design center is X = −0.05 mm.

Next, an example will be described in which the position of the heating element is specially shifted from the center of the glaze in the thermal head. In FIG. 1 already described, the center of the glaze and the position of the heating element are shifted by the distance Y. Thus, the case where the position of the heating element is shifted in the direction opposite to the paper discharge direction is-(minus).
FIG. 3 shows a density distribution diagram obtained by performing the same OD value measurement as in FIG. 2 for a thermal head having a distance Y = −0.06 mm, which is expressed as being shifted in the direction. The good printing range is indicated by C2, and the central value of C2 is X = + 0.25 mm. This is because when the position of the heating element is shifted by 0.06 mm from the case of Y = 0 mm in FIG. 2, the manner of contact between the platen roller 2 and the heating element 1c changes, and the distance at which the optimal contact state is obtained X will be shifted by 0.3 mm. This is explained next using a simple model.

FIG. 4 shows a rigid platen having a radius R1 and a radius R.
2 is a model diagram in which a rigid glaze thermal head of No. 2 contacts at a point P. FIG. When a heating element is formed at the position of the point P, an optimal contact state is established. The triangle T1 and the triangle T2 are similar. The relationship of X: Y = R1: R2 is established. In the thermal printer shown in this example, the platen radius is 6 mm
And the glaze radius is 1.2 mm, so that X: Y is 5: 1.
become. In the experimental results of FIG. 3, if the value of Y is changed by 0.06 mm, the value of X at the optimum printing position is changed by 0.3 mm, which is consistent with the concept shown in the model of FIG.

Looking at the good printing range C2 in FIG.
2 is 1.1 mm. This is 0.2 mm wider than the good printing range C1 in FIG. This means that the degree of adhesion between the platen and the heating element is better when the heating element is shifted to the upstream side in the paper transport direction than when the heating element is located at the center of the partial glaze. Is shown. This is because the platen roller is not a rigid cylinder, but is deformed to the upstream side in the paper transport direction by rotation.

Next, a case where a heating element is formed in a direction opposite to the case shown in FIG. 3 will be described. In FIG. 5, the distance Y = +
It is a density distribution figure in the case of 0.06 mm. The good printing range C3 is 0.7 mm, which is 0.2 mm narrower than the case of FIG. 2, 3, and 5 that the print density distribution changes when the position of the heating element formed in the partial glaze varies. As a design center, even a thermal head that sets a heating element in the center of the partial glaze,
In the manufacturing process of the thermal head, it is not possible to eliminate all variations, so that the position of the heating element may be shifted to the downstream side in the paper transport direction as shown in FIG. Becomes narrower than the range set by.

Therefore, in the present invention, the heating element is not formed at the center of the partial glaze, but is specially shifted to the upstream side in the paper transport direction. When the distance for shifting the heating element from the center of the partial glaze is Y and the distance for shifting the heating element from the center of the platen is X, X: Y
= Platen radius: partial glaze radius. As a result, there is an advantage that the printing good range is wider than that of the conventional printer, and even if there is a component tolerance, the printing does not become thin, and the printing inspection and adjustment steps which have been required conventionally become unnecessary. This is effective for securing the printing quality of the printer and reducing the cost.

Although the present invention has been described with reference to a thin film type thermal head, the present invention is not limited to a thin film head, but can be applied to a thick film head. However, in the thin-film type thermal head, the heating element is a concave portion, and when the position of the platen and the head position change slightly, the print density greatly changes. Therefore, the present invention is more effective for the thin film head than for the thick film head. It acts on.

[0019]

As described above, according to the present invention, the heating resistor is formed at a position shifted upstream by a distance Y from the vertex position of the partial glaze in the recording paper conveying direction, and the positional relationship between the thermal head and the platen is formed. Is shifted to the downstream side in the recording paper conveyance direction by the distance X, and the relationship X: Y = platen roller radius: partial glaze radius of curvature is applied. The influence on quality can be reduced. This eliminates the need for inspection and adjustment conventionally required, and makes it possible to obtain a thermal printer that is inexpensive and has good printing quality.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a contact portion between a thermal head and a platen roller of a thermal printer according to the present invention.

FIG. 2 is a density distribution diagram when a heating element is formed at the center of a partial glaze.

FIG. 3 is a density distribution diagram when a heating element is formed on the upstream side of the center of the partial glaze in the recording paper conveyance direction.

FIG. 4 is a model diagram for supplementary explanation of the present invention.

FIG. 5 is a density distribution diagram when a heating element is formed downstream of the center of the partial glaze in the recording paper conveyance direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal head 1b Partial glaze layer 1c Heating resistor 1f Heating part 2 Platen roller 3 Thermal paper 4 Center line of platen roller 5 Center line of radius of curvature of partial glaze

Claims (1)

[Claims] 1. A thermal head in which a heating resistor is disposed on a partial glaze formed on a substrate and forming a substantially arc-shaped projection having a radius R2, and a radius R1 pressed by the thermal head with a predetermined pressing force. A thermal printer that includes a platen roller and prints the recording medium while transporting the recording medium while nipping the recording medium between the thermal head and the platen roller. The heating resistor is formed at a position shifted by a predetermined distance Y to the upstream side with respect to the transport direction of the recording medium, and the thermal head is moved from the platen roller to the transport direction of the recording medium in parallel with the substrate. It is set to be shifted by a predetermined distance X to the downstream side, and X: Y = R1: R
A thermal printer, characterized in that the relationship is two.