JP2006142586A - Thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the matter of a long thermal head that stress due to thermal expansion of an internal layer is accumulated and a heat dissipation layer and an insulating substrate becomes susceptible to peeling and cracking. <P>SOLUTION: The thermal head comprises (a) an insulating substrate, (b) a heat dissipation layer composed of a metal film formed on the insulating substrate, (c) a thermal storage layer covering the heat dissipation layer, (d) a plurality of heating resistors formed on the thermal storage layer and arranged at a specified dot pitch in the main scanning direction, and (e) a wiring electrode group being connected electrically with each heating resistor. The heat dissipation layer is formed to be divided into a plurality of heat dissipators by slits formed at least at one position in the main scanning direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermal head in which heating resistors are arranged at a prescribed dot pitch in the main scanning direction.

Patent Document 1 is one of technical documents related to a thermal head. Patent Document 1 discloses a structure developed for the purpose of achieving both low power consumption and high-speed printing of a thermal head. That is, a thermal head having a structure in which a heat radiation layer, a heat storage layer, and a heating resistor are laminated on an insulating substrate is disclosed.
In this thermal head, a heat dissipation layer is disposed between the heat storage layer and the insulating substrate, and the residual heat after the printing is released from the heat storage layer to the insulating substrate, so that the applied pulse cycle is shortened. That is, the printing speed is improved.
Japanese Patent Laid-Open No. 5-50627

By the way, the linear thermal expansion coefficient of copper and aluminum forming the heat dissipation layer is an order of magnitude larger than the linear thermal expansion coefficient of the glass forming the insulating substrate and the polyimide resin forming the heat storage layer.
For this reason, when a long thermal head is manufactured with the same structure, distortion due to thermal expansion is accumulated, and there is a problem that peeling and cracking are likely to occur in the heat dissipation layer and the insulating substrate.

  Therefore, the inventor proposes a thermal head having the following structure. That is, a thermal head having a structure in which a heat radiation layer is divided into a plurality of heat radiators by a slit formed in at least one place in the main scanning direction is proposed.

By adopting the structure according to the invention, the individual heat dissipating bodies constituting the heat dissipating layer can be formed with a length that is a fraction of the thermal head length.
This makes it possible to realize a thermal head that can achieve both reduction in power consumption and high-speed printing even with a long thermal head. Of course, it is also effective for a short thermal head.

Embodiments of a thermal head that employs the technical technique according to the invention will be described below.
In addition, the well-known or well-known technique of the said technical field is applied to the part which is not illustrated or described in particular in this specification.
The embodiment described below is one embodiment of the present invention and is not limited thereto.

(A) Form example 1
(A) Thermal Head Structure FIG. 1 shows the head surface of the thermal head 1. In the thermal head 1, a plurality of heating elements (resistors) are arranged along the longitudinal direction. The longitudinal direction of the thermal head 1 corresponds to the main scanning direction. In actual printing, a print image is recorded on a recording medium by relatively moving the thermal head 1 and a recording medium (for example, printing paper) in a direction (sub-scanning direction) orthogonal to the main scanning direction.
In addition, in the reduced scale of FIG. 1, each heat generating body cannot be expressed. For this reason, in FIG. 1, a group of heating elements formed on the thermal head 1 is indicated by a thick line 3. Here, each heating element corresponds to each dot. Note that the individual heating elements are arranged at a dot density corresponding to the printing resolution in the main scanning direction.

FIG. 2 shows a partial cross-sectional structure of the thermal head 1. This partial cross-sectional structure corresponds to the cross-sectional structure of the AA portion in FIG. Therefore, the direction perpendicular to the paper surface is the main scanning direction.
The thermal head 1 has a structure in which a heat dissipation layer 13, a heat storage layer 15, a resistor film 17, and a wiring electrode 19 are sequentially laminated on an insulating substrate 11.
The insulating substrate 11 is made of glass, alumina ceramic or the like. Note that glass is less warped and can be easily increased in area. Therefore, a large number of head substrates can be taken out from one glass. Further, since glass is inexpensive, it is advantageous for reducing the manufacturing cost.

The heat dissipation layer 13 is made of copper, aluminum, or other metal material having high thermal conductivity. For the heat dissipation layer 13, a material having higher thermal conductivity than that of the base layer (insulating substrate 1) is used. Further, the heat radiation layer 13 is formed with a thickness necessary for efficiently releasing the heat stored in the heat storage layer 15.
Here, the length of the heat radiation layer 13 in the main scanning direction is at least equal to or longer than the thermal head length. Further, the length (width) L2 of the heat radiation layer 13 in the sub-scanning direction is formed wider than the width (resistor length) L1 of the heating element. Since L2> L1, the heat of the upper layer can be efficiently released to the lower layer.

This structure is possible because the heat radiation layer 13 is composed of a plurality of heat radiators 13A. That is, as compared with the case where the heat radiation layer 13 is formed of a single heat radiator, the length of each heat radiator 13A is remarkably shortened.
FIG. 3 shows a pattern example of the heat dissipation layer 13 formed on the insulating substrate 11. In the case of FIG. 3, the heat radiation layer 13 is formed by six heat radiators 13A divided by five slits 13B arranged at equal intervals in the main scanning direction.
In the case of this embodiment, the individual slits 13B are arranged between the heating elements. FIG. 4 shows the positional relationship between the slit 13B and the heating element (resistor). Note that the slits 13B are arranged within a range in which the individual radiators 13A can absorb stress.
The division pattern of the heat dissipation layer 13 is formed by photolithography.

The heat storage layer 15 is made of glass, polyimide resin, or the like. The heat storage layer 15 is used for accumulating Joule heat generated in the resistor film 17 located in the upper layer and increasing the amount of heat transmitted to the sheet or thermal paper coated with the solid ink.
The resistor film 17 is a conductive material that generates heat when current flows through the wiring electrodes 19 electrically connected to both ends thereof. For example, it is formed by TaSiO _2.
FIG. 5 shows a view of the heating element portion as viewed from above. A region sandwiched between the wiring electrodes 19 in the resistor film 17 corresponds to a heating element (resistor). In FIG. 5, the radiator 13 </ b> B located in the lower layer of the resistor is shaded. From FIG. 5, it can be seen that the length (width) L2 of the heat dissipating body 13B in the sub-scanning direction is wider than the length L1 of the heating element (resistor).

(B) Printing operation The internal operation during the printing operation will be briefly described.
First, during energization, energy necessary for drawing a corresponding dot is applied to each heating element (resistor). That is, a current necessary for drawing each dot is passed through the wiring electrode 19. Thereby, each heating element (resistor) generates heat according to each current value. The supply time of energy applied to each heating element (resistor) varies depending on the dots to be drawn.
The generated heat is accumulated in the heat storage layer 15 formed below the heating element (resistor). Therefore, the Joule heat of the heating element (resistor) can be efficiently transmitted to the sheet or thermal paper coated with the solid ink even with a small current. That is, low power consumption can be realized.

On the other hand, after the energization ends, the heat generation of the individual heating elements (resistors) stops. The timing at which energization ends is controlled for each heating element (resistor).
On the other hand, the heat stored in the heat storage layer 15 is retained even after the heat generation of the heating element (resistor) is stopped. For this reason, if the accumulated heat cannot be quickly released, recording by the heating element (resistor) is continued. That is, a tailing phenomenon occurs.
However, in the case of this thermal head 1, the heat stored in the heat storage layer 15 is quickly diffused to the insulating substrate 11 through the heat dissipation layer 13. At this time, since the width L2 of the heat dissipation layer 13 is wider than the width (resistor length) L1 of the heating element, the heat of the heat storage layer 15 is quickly diffused over a wide range.
As a result, the application cycle can be shortened and high-speed printing can be realized.

The heat radiation layer 13 has a linear thermal expansion coefficient that is one digit larger than that of the heat storage layer 15 and the insulating substrate 11. However, in the case of this embodiment, the length of each heat dissipating body 13A constituting the heat dissipating layer 13 in the main scanning direction is 1/6 of the thermal head length. That is, 1/6 of the conventional structure.
Accordingly, the stress in the main scanning direction acting on the individual radiators 13A is reduced to at least a fraction. As a result, the possibility of peeling or cracking due to thermal expansion is greatly reduced. That is, the reliability of the thermal head is improved and the product life is extended.

(C) Effect By adopting a configuration in which the heat radiating layer 13 is formed by a plurality of heat radiating bodies 13A, even in the case of a thermal head having the heat storage layer 15, it is possible to improve the cooling effect after energization and realize high-speed printing.
Moreover, by dividing the heat dissipation layer 13 into a plurality of heat dissipating bodies 13A, the stress of the bimetallic effect due to the difference in linear thermal expansion coefficient between the heat dissipation layer and the upper and lower layers can be relaxed, and long-term reliability can be ensured.
Further, by dividing the heat dissipation layer 13 into the plurality of heat dissipating bodies 13A, the influence of thermal expansion can be reduced, and the heat dissipating layer 13 can be embedded in a long thermal head.

(B) Embodiment 2
(A) Structure of Thermal Head Here, another embodiment of the heat dissipation layer 13 will be described. In the case of Embodiment 1, the slit 13B was formed in parallel with the heating element (resistor). However, the temperature distribution of the heat storage layer 15 is disturbed at the slit 13B, and there is a possibility that heat radiation unevenness is perceived through the recording result.
Therefore, in this embodiment, the slit 13B is formed obliquely with respect to the main scanning direction so as to cross a plurality of heating elements (resistors). The structure is the same as that of Embodiment 1 except for the inclination of the slit 13B to be formed.

FIG. 6 shows a pattern example of the heat dissipation layer 13 formed on the insulating substrate 11. In the case of FIG. 6 as well, the heat dissipation layer 13 is formed of six heat dissipating bodies 13A divided by five slits 13B arranged at equal intervals in the main scanning direction.
FIG. 7 shows the positional relationship between the heating element (resistor) and the slit 13 </ b> B formed in the heat dissipation layer 13. In this case, the slit 13B is formed so as to cross two heating elements (resistors) diagonally. Including the electrode portion, the slit 13B is formed so as to cross the four resistor films 17 diagonally.

(B) Printing operation and effect In this case as well, the heat stored in the heat storage layer 15 is diffused to the insulating substrate 11 through the heat dissipation layer 13 after the end of energization. At this time, since the width L2 of the heat dissipation layer 13 is wider than the width (resistor length) L1 of the heating element, the heat of the heat storage layer 15 is quickly diffused over a wide range.
Also in this case, the temperature distribution of the heat storage layer 15 may be disturbed at the slit 13B. However, in this case, the influence of heat radiation unevenness is dispersed in at least two heat radiators (resistors). Therefore, it is possible to effectively avoid a phenomenon in which the gradation of the specific dot is conspicuous with respect to the gradation of the peripheral dots.

(C) Other Embodiments (a) In Embodiment 1 described above, the slit 13B is disposed so as to be positioned in the gap between the heating element (resistor) and the heating element. However, as shown in FIG. 8, the slit 13 </ b> B may be arranged so as to overlap with the arrangement position of the heating element (resistor). Incidentally, in the case of FIG. 8, the slit 13 </ b> B is disposed at a position that substantially bisects the heating element (resistor).
(B) In the above-described second embodiment, the slit 13B is formed obliquely so as to cross the two heating elements (resistors). However, the number of heating elements (resistors) traversed by the slit 13B is not limited to two, and may be three or more.

(C) In the above-described embodiment, the width L2 of the heat radiation layer 13 is formed wider than the width L1 of the heat storage layer 15, but it is preferable that L2 is about 1.5 to 2 of L1.
(D) In the above-described embodiment, the case where five slits are formed for one heat radiation layer 13 has been described. However, the number of slits may be one or more depending on the thermal head length, material, film thickness, and other structural conditions.
(E) In the above-described embodiment, the case where the slits 13B are arranged at equal intervals has been described. However, as long as stress can be absorbed by thermal expansion, it is not necessary to limit the arrangement interval of the slits 13B to an equal interval.
(F) Various modifications can be considered for the above-described embodiments within the scope of the gist of the invention. Various modifications and application examples created based on the description of the present specification are also conceivable.

It is a figure which shows the head surface of a thermal head. It is a fragmentary sectional view of a thermal head. It is a figure which shows the example of a pattern of the thermal radiation layer formed on the insulating substrate. It is a figure which shows the positional relationship of a slit and a heat generating body. It is the elements on larger scale of a heat generating body. It is a figure which shows the other example of a pattern of the thermal radiation layer formed on the insulating substrate. It is a figure which shows the other positional relationship of a slit and a heat generating body. It is a figure which shows the other positional relationship of a slit and a heat generating body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal head 11 Insulating board 13 Heat radiation layer 13A Heat radiator 13B Slit 15 Heat storage layer 17 Resistor film 19 Wiring electrode

Claims (5)

An insulating substrate, a heat dissipation layer made of a metal film formed on the insulating substrate, a heat storage layer covering the heat dissipation layer, and formed on the heat storage layer and arranged at a prescribed dot pitch in the main scanning direction In a thermal head having a plurality of heating resistors and a group of wiring electrodes electrically connected to each heating resistor,
The thermal head is divided into a plurality of radiators by a slit formed in at least one place in the main scanning direction. The thermal head according to claim 1,
A thermal head characterized in that a width L2 of the heat dissipation layer is formed wider than a resistor length L1 of each heating resistor. The thermal head according to claim 1,
The slit is disposed within a range in which each heat radiator can absorb stress due to linear thermal expansion. The thermal head according to claim 1,
The thermal head is characterized in that the slit is disposed between the heating resistor and the heating resistor. The thermal head according to claim 1,
The thermal head is characterized in that the slit is formed obliquely with respect to the main scanning direction so as to cross a plurality of heating resistors.

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