JPH05193168A - Structure of heating part of thermal printing head - Google Patents

Abstract

PURPOSE:To enhance printing quality by suppressing the heat interference between adjacent heating resistors and enhancing heat separability. CONSTITUTION:Insulating heat distributing layers 9 having heat conductivity higher than that of a glaze layer 2 and that of a protective layer are formed between the glaze layer 2 and the layers of heating resistors 3 so as to extend to the lower layers of a common electrode 4 and individual lead electrodes 5 and separated between the heating parts 7 of the adjacent heating resistors 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a heat generating portion of a thermal print head used in a thermal recording apparatus such as thermal recording and thermal transfer recording.

[0002]

2. Description of the Related Art The structure of a conventional thermal print head heat generating portion will be described with reference to the drawings. FIG. 4 is a schematic cross-sectional view showing the structure of a conventional thin film type thermal print head heat generating portion. By pulse-energizing the heating resistor 3 formed on the glaze layer 2 through the common electrode 4 and the individual lead electrode 5, Joule heat generated in the heating portion 7 of the heating resistor 3 is passed through the protective layer 6. Thermal recording is performed by transmitting the medium to a thermal paper, an ink sheet or the like.

However, in thermal recording, thermal interference between adjacent heating resistors causes a problem in print quality. A structure as shown in FIG. 5 has also been devised in order to suppress this thermal interference and enhance the thermal isolation between the heating resistors. That is, the structure is such that the glaze layer 2 acting as a heat storage layer is removed by etching or the like in the gap portion 8 of the array of the heating resistors 3.

[0004]

However, in the conventional structure as shown in FIG. 4, since the heat interference between the adjacent heating resistors is significant and the heat separation property is poor, the continuous 2 dots, 3 dots, ... However, there is a problem in that the print density becomes higher than the standard when both of them generate heat at the same time. The causal relationship of this point will be described below.

From the viewpoint of heat generation characteristics of the heat generation portion of the thermal print head, two characteristics, heat generation temperature and heat generation temperature distribution, must be considered. That is, when the heating resistor is pulse-energized, the heating temperature and the heating temperature distribution of the heating portion are as shown in FIG. 6, for example. In order to obtain good print quality without print density unevenness, it is ideal that this heat generation temperature and heat generation temperature distribution be uniform for all heat generating resistors in any print pattern. However, in the conventional thermal print head heating section structure, the heat conduction characteristics are two-dimensionally isotropic, so when adjacent heating resistors generate heat at the same time, Joule heat also leaks in the direction in which the heating resistors are arrayed. As shown in (4), the gap portion 8 of the heating resistor array also has a sufficient heating temperature to contribute to printing. As a result, the print dots have a shape as shown in FIG. 8, and the print quality is deteriorated such that the print shape is distorted and the print density is uneven.

In order to solve this drawback, a heat generating structure as shown in FIG. 5 has been devised. That is, the heat-separating resistor array gap portion of the glaze layer having a heat storage function is removed to prevent heat conduction in this portion, thereby enhancing the heat separation performance. However, since the glaze layer is generally made of a glass material and has a thickness of about 50 μm, it is extremely difficult to deeply remove the glaze layer while sufficiently improving the heat separation property while ensuring the shape accuracy by etching or the like. Further, even in this case, the heat leak through the protective layer cannot be prevented, so that the print quality is not essentially improved.

As described above, the conventional thermal print head heat generating structure cannot suppress the thermal interference between the heat generating resistors. Therefore, when a plurality of continuous dots are printed, the print dot shape is broken. This caused problems such as uneven print density. Further, the heating portion structure devised to solve this problem also has the drawback that it is difficult to maintain the processing accuracy and the degree of improvement is extremely low.

[0008]

In order to solve the above problems, in the present invention, as a structure of a heat generating portion of a thermal print head, a layer between a glaze layer and a heating resistor is used rather than a glaze layer material and a protective layer material. An insulating heat rectifying layer made of a material having high thermal conductivity is provided, and the heat rectifying layer is separated by a gap portion of the heating resistor array.

[0009]

[Function] By forming the above-mentioned thermal rectifying layer having a higher thermal conductivity than the glaze layer and the protective layer between the glaze layer and the heating resistor, heat generation is compared with the thermal conductance in the heating resistor array direction. The thermal conductance in the direction perpendicular to the resistor array direction can be increased, and the excess heat that leaks in the heating resistor array direction and causes thermal interference with the adjacent heat generating part can be quickly generated in the direction perpendicular to the heating resistor array direction. Therefore, it is possible to obtain good print quality without the print dot shape being distorted. This action will be quantitatively described with reference to the drawings.

In FIG. 9, the thermal conductivity and layer thickness of the glaze layer, the protective layer and the heat rectifying layer are defined as shown in Table 1.

[0011]

[Table 1]

The length of the heating resistor is L and the width of the heat rectifying layer is W. At this time, the heat conductance C _S thermal conductance C _M, the heating resistor array direction perpendicular to the direction of the heating resistor array direction (M direction) (S direction) can be represented approximately by each equation. C _M = L (λ _G · t _G + λ _P · t _P ) (1) C _S = W (λ _G · t _G + λ _P · t _P + λ _C · t _C ) (2) Therefore, the S-direction thermal conductance is the ratio ρ of the M direction thermal _{conductance, ρ≡C S / C M = (} W / L) = 1 + t C / {t G (λ G / λ C) + t P (λ P / λ C)} (3) Can be written. Here, it is assumed that each parameter has the following values.

Λ _G = 1 W / mk λ _P = 5 W / mk λ _C = 200 W / mk t _G = 60 um t _P = 6 um t _C = 2 um L = 150 um W = 70 um At this time, the thermal conductance ratio ρ is about 2. It becomes 5. That is, under the above parameters, the amount of heat diffused in the direction perpendicular to the heating resistor arrangement direction is about 2.5 times larger than the amount of heat diffused in the heating resistor arrangement direction. Therefore, even if the adjacent heating resistors generate heat at the same time, the extra heat amount that does not contribute to printing is quickly diffused in the direction perpendicular to the arrangement direction of the heating resistors, so that it is possible to prevent thermal interference with the adjacent heating resistors. Therefore, high quality printing quality can be obtained.

Further, this effect has a high ratio of the thermal conductivity of the thermal rectification layer to the thermal conductivity of the glaze layer and the thermal conductivity of the protective layer, and becomes larger as the thickness of the thermal rectification layer increases. In the actual parameter setting, the thermal conductivity of the heat rectifying layer and the value of the layer thickness are determined by experiments or heat conduction simulations in order to maximize the above heat diffusion effect within the range that does not impair the heat generation characteristics of the heat generating part. Is easy to determine.

[0015]

FIG. 1 shows the first embodiment of the present invention. In FIG. 1, the thermal rectification layer 9 is formed between the glaze layer and the heating resistor, and the common electrode 4 and the individual lead electrodes 5 are formed.
Is formed to extend in the direction of. In addition, it is separated from the heat rectifying layer in the lower layer portion of the adjacent heat generating portion 7. Therefore, most of the amount of heat generated in the heat generating portion 7 which does not contribute to printing is conducted through the heat rectifying layer 9 and diffused in the direction of the common electrode 4 and the individual lead electrode 5 as shown by the arrow. Therefore, it is possible to suppress the thermal interference between the adjacent heat generating resistors, and it is possible to achieve the heat generating characteristics with high heat separation properties as shown in FIG. 2 and obtain the print dot shape without breakage.

Increasing the heat-separability also makes it easier to control the heat. That is, when the heat separation property is low, printing energy smaller than the reference value is applied to the heating resistor to prevent the print dot shape from becoming excessive due to thermal interference when a plurality of continuous heating resistors generate heat. It is general that the control method is taken. However, with this method, the printing energy must be controlled according to the printing pattern, and it is extremely difficult to obtain a heat control table for accurate control. By increasing the heat separation property by the method of the present invention, it is possible to eliminate the above heat control.

The thermal rectification layer 9 is formed with high precision by photoetching technology after depositing an aluminum nitride material having a thermal conductivity of about 240 W / mk on the glaze layer by a thin film forming technology. It can be formed by fine patterning. Further, it is possible to adjust the required thermal conductance according to the specifications of the thermal print head by controlling the pattern formation width, the layer thickness and the like.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, the portion of the heat rectifying layer 9 located below the heat generating portion 7 is removed. With this structure, a heat spot can be formed in the central portion of the heat generating portion 7, and a sufficient heat generation temperature can be obtained by pulsed current application, and at the same time, heat generation characteristics with high heat separation can be achieved. Further, by changing the design of the position, size, and shape of the portion to be removed, it becomes possible to obtain the heat generation temperature and the heat generation temperature distribution according to the required specifications.

[0019]

As described above, according to the present invention, the thermal rectifying layer having a higher thermal conductivity than the glaze layer and the protective layer is provided between the glaze layer and the heating resistor in the heating portion of the thermal print head. In addition, since the heat rectifying layer between the heat generating portion of the adjacent heating resistor is removed, the thermal interference caused by the heat leak toward the adjacent heating resistor when the adjacent heating resistors generate heat at the same time. This makes it possible to improve the heat separation property between the heat generating portions and obtain good print quality without the print dot shape being distorted. The thermal control method of controlling the printing energy to be applied according to the printing pattern is unnecessary. It has the effect of.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment.

FIG. 2 is a diagram showing a print dot shape according to the first embodiment.

FIG. 3 is a diagram showing a second embodiment.

FIG. 4 is a diagram showing a structure of a conventional thermal print head heat generating portion.

FIG. 5 is a diagram showing a structure of another conventional thermal print head heat generating portion.

FIG. 6 is a diagram showing a heat generation temperature distribution.

FIG. 7 is a diagram showing a heat generation temperature distribution.

FIG. 8 is a diagram showing a print dot shape.

FIG. 9 is a diagram illustrating the operation of the present invention.

[Explanation of symbols]

 1 Insulating Substrate 2 Glaze Layer 3 Heating Resistor 4 Common Electrode 5 Individual Lead Electrode 6 Protective Layer 7 Heating Unit 8 Heating Resistor Gap 9 Thermal Rectifying Layer

Claims (1)

[Claims] 1. An insulating substrate, a glaze layer formed on the insulating substrate, an insulating thermal rectifying layer formed on the glaze layer, and a row formed on the thermal rectifying layer. A plurality of heating resistors arranged in a line, a common electrode and a lead electrode connected to each end of the upper surface of the heating resistor, and at least a portion including the heating portion of the heating resistor. In the structure of a thermal print head heat generating portion having a protective layer, the thermal rectifying layer is made of a material having a higher thermal conductivity than the glaze layer material and the protective layer material, and even under the common electrode and the lead electrode. It is characterized in that it extends and at least the portion of the thermal rectification layer located under the heating portion of the heating resistor is formed separately from the thermal rectification layer located under the heating portion of the adjacent heating resistor. When The structure of the heat generating part of the thermal print head.