JPS60242059A - Heat sensitive printer - Google Patents

Abstract

PURPOSE:To lessen the omission of printing, by a method wherein in the printer which carries out halftone printing by changing the density of color development by the change of the temperature of heat generation, the rubber layer of the platen roller for the purpose of forcing a printing paper onto a printer head is thinned and hardened. CONSTITUTION:In the printer which carries out halftone printing by changing the density of color development by the change of the temperature of the surface rubber layer of the platen roller 2 for the purpose of forcing a printing paper 3 onto the printer head 1 equipped with the heating element is made to be of 2mm. max. Then, the rubber hardness of the rubber layer should preferably be made to be of 60 deg. min.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printing device, and more particularly to halftone printing in a thermal printing device.

In halftone recording using thermal paper, the color density of the thermal paper is changed by changing the printing energy of the thermal head, that is, by changing the applied power or its pulse width. However, in reality, random missing prints remain as white dots on the image, giving the impression that the image quality is rough. One way to solve this problem is to
It has been proposed to use thermal paper suitable for intermediate tones, for example, to use thermal paper in which a thermal agent is evenly dispersed and the surface of the thermal paper is smooth. Therefore, random printing omissions in thermal intermediate printing have a print density of tJ)
Occurs in small gradations. In other words, places with high concentration are
Since the applied energy of the thermal head is increased, the heat spreads widely, and even if there is slight unevenness in the dispersion state of the thermal agent or irregularities on the surface of the thermal paper, the thermal agent develops color almost uniformly. However, where the density is low, the applied energy is low, so non-uniformities on the thermal paper are not covered and appear as missing prints.

The present invention was made in view of the above-mentioned circumstances.
In particular, this technique was developed with the aim of improving the image quality of heat-sensitive halftones depending on platen conditions.

Configuration The configuration of the present invention will be described below based on examples.

FIG. 1 is a side view of the head of a thermal printing device to which the present invention is applied. In the figure, 1 is a thermal head, 2 is a platen roller, and 3 is thermal paper. 2 presses against the thermal head 1 to print. At this time, if the contact between the thermal paper 3 and the thermal head 1 is improved, the number of missing prints due to surface irregularities will be reduced. In order to improve the contact state, the hardness of the rubber 4 on the platen 2 may be increased so that the platen load can be effectively applied to the thermal head.

Figure 2 is a diagram showing the relationship between the rubber thickness of the platen and the rubber hardness. As shown in the figure, the rubber hardness increases as the rubber thickness becomes thinner (however, when the base is metal), I investigated what kind of printing results depending on the rubber hardness as follows.

Printing was performed while changing the rubber hardness from 30° to 80°. Density evaluation was carried out at a density of around 0.3, which is the gradation level where printing omissions are most noticeable.6 Figure 3 shows the density measurement values for rubber hardness.
As is clear from the figure, when the rubber hardness is low, there are many missing prints and the density is low. As the rubber hardness increases 1, the density increases and becomes almost saturated at a hardness of 60''.Next, halftone printing is performed using a platen roller with different rubber hardness and rubber thickness, and visual inspection of 1 image quality is performed. A subjective evaluation was conducted.

The density of the evaluated gradation is around 0.3.

The results are shown in Table ■. According to Table 1, it can be said that the image quality is good if the rubber thickness is 2 thick or less.

Table 1 (0 mark: Good, △ mark: Slightly poor, × mark: Unsatisfactory) Based on the above results, 8-gradation halftone printing was performed.

The platen conditions were a rubber hardness of 30° and a rubber thickness of lllll11 and 4 mm. Halftone expression is achieved using a pulse number modulation method, and the power applied to the thermal head is 0.35W.
The pulse period is 300 μsec, the pulse width is 150 μs,
A thermal head of 8 dot/mo+ was used.

FIG. 4 shows density measurement values for each gradation, where curve A shows the case where the rubber thickness is one stroke, and curve B shows the case where the rubber thickness is four strokes. As is clear from the figure, when the density is 1.0 or less, the density is higher when the rubber thickness is 1 m, and there are fewer missing characters.

Therefore, if the above-mentioned platen conditions are followed, halftones with stable image quality can be obtained even in low density areas.

(1) By using a platen roller with a rubber thickness of 2 mm or less, there were fewer omissions in halftone printing, and the image quality was improved.

(2) The same advantage as (1) was obtained by using a platen roller with a rubber hardness of 60° or more.

(3) Just change the platen roller (conventionally, the rubber thickness was 5
m or more and hardness of 30 to 50°), good image quality can be obtained at low cost.

There are advantages such as

[Brief explanation of the drawing]

FIG. 1 is a side view of the head of a thermal printing device to which the present invention is applied, FIG. 2 is a relationship between the rubber thickness of the platen and rubber hardness, and FIG. 3 is a relationship between rubber hardness and print density. FIG. 4 is a diagram showing the relationship between each gradation and density. l...Thermal head, 2...Platen roller, 3...
Thermal paper, 4...Rubber.

Claims (2)

[Claims] (1) It has a thermal head for heating thermal paper and a platen roller that presses the thermal paper against the thermal head, and the heat generation temperature of the thermal head can be controlled by changing the electric energy applied to the thermal head. In a thermal printing device that prints thermal halftones that express intermediate densities by controlling and changing the color density of thermal paper, the thickness of the rubber of the platen roller that brings the thermal paper and thermal head into close contact is set to 2 m or less. A thermal printing device characterized by: (2) The thermal printing device according to claim (1), wherein the platen roller has a rubber hardness of 60' or more.