JPH02241755A - Thermal head - Google Patents

Abstract

PURPOSE:To prevent unevenness in density from taking place by providing a means for effecting uniform heat transfer so that heat transfer from an insulated substrate to a radiation plate is effected uniformly along the line of a resistance-heating element. CONSTITUTION:A head substrate 14 comprising an insulated substrate 13 etc., provided with a resistance-heating element 12 placed thereon in rows is superposed on a radiation plate 16 through a rubber sheet 15 having high heat conductivity, while the rear edge of the head substrate 14 is secured to the radiation plate 16 by means of a substrate holding member 17. By inserting, in this manner, the rubber sheet 15 of high heat conductivity between the head substrate 14 and radiation plate 16, the rubber sheet 15 is caused to come fully into contact with the rear side of the head substrate 14, wherein the sheet 15 is deformed by the undulation on the substrate 14, so that heat is transferred relatively uniformly from the substrate 14 to the plate 16 through the sheet 15. In this manner, even in the case of an image, wherein unevenness in density becomes conspicuous, e.g. solid printed letters and the like, such unevenness can be restrained effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used in a thermal dye sublimation printer or the like.

[Conventional technology]

One of the image forming methods is thermal dye sublimation recording method.
As shown in FIG. 6, the principle of this recording is that an ink sheet 101 coated with a heat-sublimable dye and an image receiving paper 102 are placed one on top of the other, and a platen roller 103 is used to align heating resistor elements in a line perpendicular to the cross section of the head. By pressing and heating the ink sheet from the back side of the thermal heads 104 arranged side by side, the sublimable dye of the ink sheet 101 is transferred to the surface of the image receiving paper 102 to form a visible image.

A feature of the thermal sublimation recording method is that by controlling the amount of heat generated by the thermal head, the amount of dye transferred to the ink sheet can be changed, making it possible to easily record gradations with shading. In addition, there are three colors of Inksey + yellow, magenta, and cyan.
Use -, * L, te, receive f! By finely transferring each color onto the 1flJ surface, any color can be recorded on the receiving paper7.For this reason, thermal dye sublimation printers can be used with various video equipment/! : Close-up 4) 廿、Photo-like full color・
- It is being seen as a promising terminal device for outputting prints in a timely manner.

As mentioned above, thermal dye sublimation printers have excellent features that make them suitable for full-color recording, but on the other hand, uneven density occurs due to variations in the resistance value of the heating resistor element in +f-maru rad.・It has some drawbacks. Regarding this point ζ, for example, JP-A-51-128
The problem disclosed in Japanese Patent No. 539 can be easily solved by correcting the power supplied to each heating resistor element.

However, in the case of such a full head, there are actually still larger unresolved problems.

In other words, the actual Sir-Full 1-F104 has the seventh
Schematically shown in the figure (1), as shown in
4 along the line direction, on the order of several tens of micrometers.”
There is 4 degree of waviness. This is due to the degree of curvature of the ceramic plate used as the insulating substrate 10G of 104. This is due to this problem and cannot be avoided due to the manufacturing process.

Therefore, when the paper sheet 101 coated with the phlegm dye and the image receiving paper 102 are pressed between the thermal head 104 and the platen roller 103, the head substrate 105 will undulate as shown in FIG. Therefore, it is not possible to bring the ink sheet ~i·lOl and the image receiving paper 102 into even and close contact with each other.In addition, in FIGS. 7 and 8,
Reference numeral 107 denotes a line-shaped heating resistor stack formed on an insulating substrate 106, 108 a protective film for protecting the heating resistor element 107, and 109 a heat dissipation plate supporting the Bahe-rad substrate 105. In order to accurately transfer the sublimation agent on the ink sheet 101 to the surface of the image receiving paper 1020, the dye R1 coated surface of the ink sheet 101 must be brought into close contact with the image receiving paper 1102 for 1 minute. , (Therefore, when recording is actually performed in the state shown in Fig. 8 using a wavy surf-full head), recorded dots may be chipped or transfer may occur in areas with weak adhesion. is not performed, the image receiving paper 102
As shown in FIG. 9, a striped shading pattern occurs parallel to the sub-scanning direction of the screen.

In extreme cases, no records may be made at all.1. It's not white, it's off-white, and it's even real.

Conventionally, in order to solve this deficiency, the hardness of the rubber of the platen roller was softened, and the pressing force of the thermal head was increased, so that the variation in the adhesion between the ink sheet and the receiver paper was absorbed by the deformation of the platen rubber. (3rd edition): / Impact Printing Technology Symposium 12 Proceedings, 1980, pp. 33-36) Another solution is the "
In order to obtain uniform adhesion regardless of the undulation,
It is also possible to use a special platen roller manufactured by adjusting the diameter of the platen roller to correspond to the thermal waviness.

[Problems to be Solved by the Invention] By the way, each time the rubber hardness of the platen roller and the thermal rad pressing force described above are adjusted, it is possible to Although the method for preventing 7 is certainly simple, it has the following problems and is not a fundamental solution. The hardness of the platen rubber must be softened in order to absorb it with its elasticity.If the platen rubber is made softer, the width of the joint between the thermal head and the platen will be expanded, resulting in a lower pressure contact force per unit area. The sharpness of the recorded dots decreases.In other words, if the platen rubber is gently broken, the density will become less noticeable, but it will result in a so-called "sharp, blurred" printed image. Shima).

In order to further increase the pressure contact force, press the thermal head,
When attaching, the pressure must be increased, but the pressure must be increased)
If E is increased, the line-shaped heating resistor element of the full head will dig into the platen, causing trouble in the running performance of the ink sheet.

On the other hand, if the platen rubber is made harder, the contact force per unit area will be thicker (this will result in a sharper image output, but
:1 Due to the elasticity of the rubber pad, the number of pressure welds cannot be completed, resulting in uneven density.

Therefore, this method of preventing density unevenness by adjusting the rubber hardness of the platen roller and the pressing force of the thermal head cannot provide a fundamental solution, and the density unevenness is relatively inconspicuous and the image quality is improved.・In reality, 11 combinations of rubber hardness and pressing force that do not impair firmness have been selected through experiments and are used. Although it is possible to obtain a certain effect by making experimental selections in this way, it has not yet reached the level of completely eliminating density unevenness. was still insufficient.

The present invention is aimed at solving the above-mentioned problems in conventional thermal dye sublimation printers.6. The object of the present invention is to provide a thermal head that can fundamentally and easily solve density unevenness caused by uneven adhesion due to undulations of a head substrate.

[Means and effects for solving the problem] In order to solve the above-mentioned problems, the present invention includes forming a large number of heating resistor elements in a row on an insulating substrate 1, 2, and forming a plurality of heating resistor elements on the insulating substrate. A heat sink is brought into contact with the surface opposite to the surface provided with the heat dissipating plate, and the heat transfer action from the insulating substrate to the heat sink is in the column direction ζ of the heating resistor elements. It is equipped with a uniform heat transfer means to ensure uniform heat transfer along the length.

With this configuration, the heat transfer action from the insulating substrate to the heat sink is performed uniformly along the row direction of the heat generating resistor elements, so that the heat dissipation of the insulating substrate after forming the heat generating resistor elements is improved. This is done uniformly, eliminating the difference in heat radiation that causes density unevenness, and effectively preventing the density unevenness from occurring.

〔Example〕

Prior to describing embodiments, the principle of preventing density unevenness in a thermal head according to the present invention will be explained first. As shown in FIG. 1), the head substrate 2 of the thermal head 1 is pressed between the platen roller 3 and the heat sink 4 during printing press contact. At this time, is the platen roller 3 set at a certain internal position? "The thermal head is in pressure contact with the head 1, but because the ceramic plate that is the insulating substrate of the thermal head board 2 is highly rigid, the waviness deformation of the head board 2 is not necessarily completely corrected by the pressure contact force F. When we look at the forces acting on the platen row 3 and heat sink 4 of the thermal head substrate 2 in a state where the undulation deformation of the head substrate 2 remains, regarding the peaks and troughs of the undulations of the thermal head substrate 2, we find: The following can be said.In other words, at the peak of the undulation, the reaction force R3 on the platen roller 3 opposing the pressure contact force F of the head substrate 2 is large (and conversely, the contact pressure P with the heat sink 4 is small). In the troughs of the undulations, the reaction force R2 to the platen roller 3 is small and the contact pressure P! with the heat sink 4 is large, contrary to the former.

Conventionally, it has been considered to suppress the occurrence of density unevenness by reducing the pressure distribution between the platen roller 3 and the head substrate 2, that is, the difference between the reaction forces R and R2. As a result of a detailed study of the relationship between reaction force R11R2, contact pressure P+, Pz, and density unevenness, it was found that the difference in contact pressure P between the head substrate 2 and heat sink 4 has a closer relationship with the occurrence of density unevenness. It turns out that there is.

Considering from a heat transfer engineering point of view that the contact pressure between the head substrate 2 of the thermal head 1 and the heat dissipation plate 4 is different, such as PP due to... In the troughs and valleys, there is a difference in the amount of heat radiated from the thermal base plate 2, which is transmitted to the heat radiating plate 4. In other words, the head substrate 2
If the pressure increases even if the area of the contact surface of each part of the heat sink 4 is the same as that of 1. This is because each contact point on the contact surface deforms and the actual contact area increases, so the actual thermal conductivity increases. The difference in contact pressure between the heat dissipation plate 2 and the heat dissipation plate 4 can be replaced with the difference in the amount of heat dissipated at that portion.

From the above study results, since the contact pressure P with the heat sink 4 is small at the ridges of the undulations of the thermal head board 2, the amount of heat released to the heat sink 4 Q is small, and the head board 2 heats up accordingly. On the other hand, since the contact pressure P1 is large at the troughs of the waviness, heat is radiated more actively from the substrate 2 to the heat sink 4, and the heat radiation WQ is increased.
It can be seen that the contact area of the head substrate 2 is cooled more quickly and the transfer density is lower than that of other areas.

This phenomenon is a direct cause of density unevenness, and in order to suppress its occurrence, it is necessary to: It can be said that it is effective to do so.

Therefore, in the present invention, a means is provided for ensuring that heat transfer from the thermal head substrate to the heat sink is performed uniformly along the row direction of the heating resistor elements.

Hereinafter, specific embodiments of the thermal head according to the present invention will be described. FIG. 2 is a schematic perspective view of the first embodiment of the invention. As shown in FIG. 2, the thermal head 11 includes a head substrate 14 in which heating resistor elements 12 are arranged in rows on an insulating substrate 13 made of ceramic or the like, and a heat sink 16 is connected to the head substrate 14 through a rubber sheet 15 having good thermal conductivity. The rear end portion of the head substrate 14 is fixed to the heat dissipation mechanism 6 by the substrate holding portion 17 . The rubber sheets 15 (1, 7) are preferably made of, for example, heat dissipating silicone rubber used for dissipating heat from transistors, JC', etc. The rubber sheet 15 used in this example has a thermal conductivity of 1.68 [W/m-K
1, and this value is one order of magnitude larger than that of other resin materials.

Further, the thickness of the rubber sheet 15 used in this example was 20
0 μm, and the waviness of the head substrate 14 of 20” and 30 μrn is sufficiently absorbed within the range of elastic deformation of the rubber sheet 15.

FIG. 3, (B) is a sectional view schematically showing the state before and after inserting the rubber seal H5 between the head substrate 14 and the heat sink 16. As shown in the third diagram, when the rubber seam 5 is inserted, the contact pressure between the four head substrates 14 and the heat sink 16 is not uniform, and as described above, the head substrate 14 This results in uneven heat dissipation distribution.
f! IIJF unevenness occurs. In contrast, Figure 3...
), when a rubber seam 5 with good thermal conductivity is inserted between the head substrate 14 and the heat sink 16, the rubber sheet 15
(Bella)! The undulations of the substrate 14 are deformed and absorbed, and the spatula 1' base Fi contacts the entire back surface of the head substrate 14, so that heat transfer from the head substrate 14 to the heat dissipation plate 16 is performed relatively uniformly through the rubber sheet 15. Become. 7) When printing was performed using the thermal head with the rubber sheet 15 interposed in this way, the density of the parts corresponding to the peaks and troughs of the undulations was averaged, and density unevenness could not be discerned visually. It was confirmed that an effect of a certain degree can be obtained.

FIG. 4 shows a schematic cross section of the second embodiment.

In this embodiment, the shape of the heat sink 21 that contacts the head base 22 is determined by the undulation shape of the head base 22. , and the back surface of the head substrate 22 is connected to the heat dissipation plate 21.
It is constructed so that it comes in close contact with the camera. Heat sink 21
is created as follows. In other words, the head substrate 2
The shape of the heat sink 21 is measured in advance using a shape measuring machine or the like, and the contact surface of the heat dissipation plate 21 is patterned based on the measurement data to finish it in the same shape as the head substrate 22.

With this configuration, the back surface of the head substrate Fi, 22 is in close contact with the heat dissipation plate 21 over the entire contact surface, which eliminates uneven contact pressure distribution, and the heat dissipation distribution of the head substrate 22 is uniform even during printing pressure contact. Therefore, the occurrence of density unevenness can be effectively suppressed.

FIG. 5 is a diagram showing a schematic cross-sectional structure of a thermal head according to a third embodiment. In this embodiment, a gap is provided on the surface of the heat sink 31 facing the head substrate 32, and the gap is filled with paste-like resin 33 having good thermal conductivity. Due to its fluid nature, this paste-like resin 33 contacts the entire back surface of the head substrate 32 regardless of its undulation shape, and after being filled and hardened, it becomes rubber-like or solid, and is released from the head base 32. Heat is evenly transferred to the heat sink 31. As a result, it is possible to obtain the same effect as in the case of interposing the rubber seal [5] between the head base and the heat sink in the first embodiment C.

As described above, the present invention solves the density unevenness caused by the waviness of the head substrate without using convenient means such as conventional electrical correction or devising the head pressure contact mechanism. This problem is fundamentally solved with a simple structure. Therefore, especially in thermal heads with a wide recording width, the number of undulations on the substrate is large.
In some cases, the density unevenness is more noticeable, but by applying the present invention, it is possible to correct the film unevenness.
There is no need to make the pressure welding mechanism robust and complicated.
The present invention is particularly effective for such wide thermal heads.

Furthermore, as mentioned above, although the thermal dye sublimation recording method makes it easy to control the density gradation by controlling the heat of each dot, it has the disadvantage that density unevenness is likely to occur. By applying such a thermal head, it is possible to effectively suppress the occurrence of density unevenness even in images where density unevenness is easily noticeable, such as solid printing.

〔Effect of the invention〕

As described above based on the embodiments, the thermal head according to the present invention ensures that heat is uniformly transferred from the insulating substrate on which the heating resistor elements are formed to the heat sink along the column direction of the heating resistor elements. Since there is provided a means for changing the density of the printed image, it is possible to fundamentally prevent the occurrence of density unevenness in the printed image.

Furthermore, since there is no need to provide the platen roller with any means for correcting density unevenness, there is an advantage that peripheral devices can be installed at low cost with a simple structure.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining the principle of the thermal head according to the present invention, FIG. 2 is a schematic perspective view showing the first embodiment of the present invention, and FIG. Figure 1 - A sectional view schematically showing the state before and after insertion of the rubber sheet in the illustrated embodiment; Figure 4 is a sectional view schematically showing the second embodiment; A sectional view schematically showing an example,
FIG. 6 is a schematic diagram showing a thermal dye sublimation printer;
7 is a perspective view schematically showing a conventional thermal head, FIG. 8 is a sectional view of a thermal dye sublimation printer using the thermal head shown in FIG. 7, and FIG. 9 is a perspective view schematically showing a conventional thermal head. FIG. 2 is a diagram showing image receiving paper recorded by the printer shown in FIG. In the figure, 11 is a thermal head, 12 is a heating resistor element, 13 is an insulating substrate, 14 is a head substrate, 15 is a rubber sheet, 16 is a heat sink, 17 is a substrate holder, and 33 is a thermally conductive resin. Fig. 1 Fig. 3 (A) Fig. 2 17 plate @ arm part Fig. 4 / /22:・＼F :lE @ ＼21:il) plate Fig. 5 31: Heat dissipation plate 15゛Rubber sheet No. Figure 6 Figure 7 109 = Heat sink 103, fan roller Figure 8 Figure 9

Claims (1)

[Scope of Claims] 1. A thermal device constructed by forming a large number of heat-generating resistor elements in a row on an insulating substrate, and a heat sink is brought into contact with the surface of the insulating substrate opposite to the surface on which the heat-generating resistor elements are provided. 1. A thermal head comprising a uniform heat transfer means for uniformly transferring heat from the insulating substrate to the heat sink along the row direction of the heating resistor elements. 2. The thermal head according to claim 1, wherein the uniform heat transfer means is constituted by a thermally conductive member disposed between the insulating substrate and the heat sink in close contact with both. 3. The uniform heat transfer means is characterized in that the uniform heat transfer means is configured by forming the shape of the surface of the heat sink facing the insulating substrate so as to follow the undulating shape of the surface of the heat sink facing the heat sink. 1. The thermal head described in 1.