Thermal head and printer

A thermal head has a heat storage layer bonded onto a surface of the substrate, a heating resistor provided on the heat storage layer, and a pair of electrode portions connected to the heating resistor. The heating resistor has a heating portion which does not overlap the pair of electrode portions. A hollow portion is provided in a region of at least one of the surface of the substrate and a surface of the heat storage layer, the region being opposed to the heating resistor. A center line of the hollow portion is shifted with respect to a center line of a heating portion of the heating resistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal head and a printer.

2. Description of the Related Art

There have been conventionally known a thermal head which is used in a thermal printer often mounted to a portable information equipment terminal typified by a compact hand-held terminal, and which is used to perform printing on a thermal recording medium based on printing data with the aid of selective driving of a plurality of heating elements (for example, see JP 06-166197 A).

In terms of an increase in efficiency of the thermal head, there is a method of forming a heat insulating layer below a heating portion of a heating resistor. By formation of the heat insulating layer below the heating portion, of an amount of heat generated in the heating resistor, an amount of upper-transferred heat which is transferred to an abrasion resistance layer formed above the heating portion becomes larger than an amount of lower-transferred heat which is transferred to a heat storage layer formed below the heating portion, and hence energy efficiency required during printing can be sufficiently obtained. In the thermal head described in JP 06-166197 A, a hollow portion is provided in a layer below the heating portion of the heating resistor, and this hollow portion functions as a hollow heat insulating layer. Thus, the amount of upper-transferred heat becomes larger than the amount of lower-transferred heat, and the energy efficiency is increased.

Further, in a printer in which a thermal head is installed, thermal paper is pressed, with a predetermined pressing force, against a head portion of a surface of the abrasion resistance layer formed above the heating portion. Therefore, the thermal head is required to have heat generation efficiency for improving printing quality as described above, and required to have strength for withstanding the pressing force of the platen roller.

However, in the hollow heat insulating layer of the thermal head described in Patent Document 1, a center position of the hollow portion substantially corresponds to a center position of the heat generating portion, the hollow heat insulating layer having a size with which the heat generating portion is contained in a region of the hollow portion. Therefore, when an external load is applied to the heat generating portion, deflection at a central portion of the heat storage layer becomes large. Particularly, there is a risk that deflection of the heat storage layer becomes excessive in the case of a sheet jam or the like, whereby the heat storage layer is broken. Further, there is a risk that, when a pressing force of the platen roller causes the heat storage layer to be deflected, a contact state between the thermal paper and the head portion is deteriorated so as to decrease a contact pressure, and it becomes difficult to be transfer heat to the thermal paper.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is therefore to provide a thermal head and a printer in which improvements in heat generation efficiency and strength against an external load are achieved.

In order to achieve the above-mentioned object, the present invention provides the following techniques.

The present invention provides a thermal head comprising: a substrate; a heat storage layer bonded onto a surface of the substrate; and a heating resistor provided on the heat storage layer, wherein: a concave portion is provided in a region, which is opposed to the heating resistor, of at least one of the surface of the substrate and a surface on a side of the substrate of the heat accumulating portion; and a center line of a hollow portion formed, by the concave portion, between the substrate and the heat storage layer is shifted with respect to a center line of the heating resistor.

According to the present invention, by causing the hollow portion to function as the hollow heat insulating layer, it is possible to inhibit the heat generated by the heating resistors from being transferred to the substrate through an intermediation of the heat storage layer. As a result, an amount of heat conducted above the heating resistors to be used for printing and the like is increased, whereby improvement in heat generation efficiency can be achieved.

A central axis of a platen roller pressing an object to be printed, such as thermal paper, against the heating resistors is caused to correspond substantially to the center line of the heating resistor, and hence the largest load is applied on the center line of the heating resistor. According to the present invention, the center line of the hollow portion is shifted with respect to the center line of the heating resistor, and hence the external load applied to the heat storage layer covering the hollow portion acts on a position shifted with respect to the center line of the hollow portion. That is, the external load acts on a position near any one of edges of the hollow portion, and hence the deflection amount of the heat storage layer supporting the heating resistors can be reduced in comparison with a case where the external load acts on the center line of the hollow portion. As a result, a strength against the external load can be improved.

The present invention provides a printer comprising: the above-mentioned thermal head of the present invention; and a pressure mechanism for feeding out an object to be printed while pressing the object to be printed against the heating resistor of the thermal head.

According to the present invention, because of high heat-generation efficiency of the thermal head, electrical power consumption at the time of printing onto a printed material can be reduced. Further, because of the small deflection amount of the heat storage layer with respect to the pressing force of the pressure mechanism, it is possible to reliably bring the heating resistors into contact with the object to be printed so as to transfer heat. Accordingly, it is possible to perform printing of excellent printing quality with a little electrical power.

In the above-mentioned aspect of the present invention, due to a relationship with a feeding direction of the object to be printed which is fed by the pressure mechanism, the center line of the hollow portion of the thermal head may be positioned forward in the feeding direction with respect to the center line of the heating resistor, and an end portion positioned rearward in the feeding direction of the hollow portion may be arranged in a region opposed to the heating resistor.

With the above-mentioned structure, the heat storage layer above the hollow portion, which supports the heating resistors, is more likely to be deflected, upon receiving the load applied by the pressure mechanism substantially to the center of the heating resistor, at a further forward position in the feeding direction with respect to the center line of the heating resistor. Therefore, a contact pressure between the object to be printed and the heating resistors becomes small, and hence trailing after turning off the electrical power of the printer can be inhibited. Note that, “trailing” refers to a phenomenon in which, due to remaining heat of the thermal head after turning off the electrical power of the printer, printing is performed on a portion following a region on which printing is to be performed though a printing instruction is not given in printing data.

Further, in the above-mentioned aspect of the present invention, due to a relationship with a feeding direction of the object to be printed by the pressure mechanism, the center line of the hollow portion of the thermal head may be positioned rearward in the feeding direction with respect to the center line of the heating resistor, and an end portion positioned forward in the feeding direction of the hollow portion may be arranged in a region opposed to the heating resistor.

By the foregoing construction, the heat storage layer above the hollow portion, which supports the heating resistors, is less likely to be deflected, upon receiving the load applied by the pressure mechanism substantially to the center of the heating resistor, at a further forward position in the feeding direction with respect to the center line of the heating resistor. For example, when the object to be printed is fed out by rotation of the pressure mechanism, such as the platen roller, the load applied to the heating resistors moves forward in the feeding direction with respect to the center. According to the present invention, it is possible to reduce the deflection of the heat storage layer with respect to the load applied to the heating resistors forward in the feeding direction.

According to the present invention, it is possible to provide an effect that improvements in heat generation efficiency and strength against the external load can be achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a thermal head1and a thermal printer (printer)10according to an embodiment of the present invention are described with reference to drawings.

The thermal printer10according to this embodiment includes: as illustrated inFIG. 1, a main body frame11; a platen roller13arranged horizontally; a thermal head1arranged oppositely to an outer peripheral surface of the platen roller13; a heat dissipation plate15(seeFIG. 3) supporting the thermal head1; a paper feeding mechanism17for feeding between the platen roller13and the thermal head1an object to be printed, such as thermal paper (paper medium)12; and a pressure mechanism19for pressing the thermal head1against the thermal paper12with a predetermined pressing force.

Against the platen roller13, the thermal head1and the thermal paper12are pressed by the operation of the pressure mechanism19. By this construction, load of the platen roller13is applied to the thermal head1through an intermediation of the thermal paper12.

The heat dissipation plate15is a plate-shaped member made of a resin, ceramics, glass, a metal such as aluminum, or the like, and serves for fixation and heat dissipation of the thermal head1.

The thermal head1has a plate shape as illustrated inFIG. 2. As illustrated inFIG. 3(which is a sectional view taken along the arrow A-A ofFIG. 2), the thermal head1includes: a rectangular supporting substrate (supporting plate)3fixed on the heat dissipation plate15; a heat storage layer5bonded onto the surface of the supporting substrate3; a plurality of heating resistors7provided on the heat storage layer5; electrode portions8A,8B connected to the heating resistors7; and a protective film9covering the heating resistors7and the electrode portions8A,8B so as to protect the same from abrasion and corrosion. The arrow Y inFIG. 2denotes a feeding direction of the thermal paper12by the paper feeding mechanism17.

The supporting substrate3is an insulative substrate such as a glass substrate and a silicon substrate. In a surface on the heat storage layer5side of the supporting substrate3, there is formed a rectangular concave portion2extending in a longitudinal direction.

The heat storage layer5is constituted by a thin plate glass having a thickness of approximately 10 to 50 μm. In the case where the supporting substrate3is a glass substrate, thermal fusion bonding is used for boning the heat storage layer5and the supporting substrate3together. Further, when the supporting substrate3is a silicon substrate, anodic bonding is used.

Between the supporting substrate3and the heat storage layer5, a hollow portion4is formed by covering the concave portion2of the supporting substrate3with the heat storage layer5(Hereinafter, hollow portion is referred to as “hollow heat insulating layer.”). The hollow heat insulating layer4functions as an insulating layer for inhibiting a heat inflow from the heat storage layer5to the supporting substrate3, and has a communicating structure opposed to all the heating resistors7. By causing the hollow portion to function as the heat insulating layer, it is possible to inhibit the heat generated by the heating resistors7from being transmitted through an intermediation of the heat storage layer5to the supporting substrate3. As a result, an amount of heat conducted above the heating resistors7to be used for printing and the like is increased, whereby improvement in heat generation efficiency is achieved.

The heating resistors7are each provided so as to straddle the hollow concave portion2in its width direction on an upper end surface of the heat storage layer5, and are arranged at predetermined intervals in the longitudinal direction of the hollow concave portion2. In other words, each of the heating resistors7is provided to be opposed to the hollow heat insulating layer4while sandwiching the heat storage layer5, and is arranged so as to be situated above the hollow heat insulating layer4.

The electrode portions8A,8B serve to heat the heating resistors7, and are constituted by a common electrode8A connected to one end of each of the heating resistors7in a direction orthogonal to the arrangement direction of the heating resistors7, and individual electrodes8B connected to the other end of each of the heating resistors7. The common electrode8A is integrally connected to all the heating resistors7.

When voltage is selectively applied to the individual electrodes8B, current flows through the heating resistors7connected to the selected individual electrodes8B and the common electrode8A opposed thereto, whereby the heating resistors7are heated. In this state, the thermal paper12is pressed by the operation of the pressure mechanism19against the surface portion (printing portion) of the protective film9covering the heating portions of the heating resistors7, whereby color is developed on the thermal paper12and printing is performed.

It is noted that of each of the heating resistors7, an actually heating portion is a portion of each of the heating resistors7on which the electrode portions8A,8B do not overlap, that is, a portion of each of the heating resistors7which is a region between the connecting surface of the common electrode8A and the connecting surface of each of the individual electrodes8B and is situated substantially directly above the hollow heat insulating layer4(Hereinafter, heating portion is referred to as “heating portion7A.”).

In the thermal head1according to this embodiment, when seen from the protective film9side, a region of the hollow heat insulating layer4is larger than a region of the opposed heat generating portion7A, and the heat generating portion7A is arranged within the region of the hollow heat insulating layer4. Further, the hollow heat insulating layer4is arranged, with a center line thereof being shifted with respect to a center line X of the heating resistor7, that is, with respect to the center line X of the heat generating portion7A.

Specifically, the center line of the hollow heat insulating layer4is positioned forward in the feeding direction Y of the thermal paper12with respect to the center line X of the heat generating portion7A. It is noted that the center line of the hollow heat insulating layer4and the center line X of the heat generating portion7A represent a line, as seen from the protective film9side, passing a center position of the surface of the heat generating portion7A or a center position of the surface of the hollow heat insulating layer4, and being parallel to a direction orthogonal to the feeding direction Y of the thermal paper12(longitudinal direction of the supporting substrate3).

In the following description, with reference to center line X of the heat generating portion7A, a distance from the center line X to an end portion positioned forward in the thermal paper feeding direction Y (hereinafter, referred to as “forward end portion”) of the heat generating portion7A is denoted by Lh1, and a distance from the center line X to an end portion positioned rearward in the thermal paper feeding direction Y (hereinafter, referred to as “rearward end portion”) of the heat generating portion7A is denoted by Lh2. In the heat generating portion7A, a relationship of Lh1=Lh2is established. Further, a distance from the center line X of the heat generating portion7A to an end portion positioned forward in the thermal paper feeding direction Y (hereinafter, referred to as “forward end portion”) of the hollow heat insulating layer4is denoted by Lc1, and a distance from the center line X to an end portion positioned rearward in the thermal paper feeding direction Y (hereinafter, referred to as “rearward end portion”) of the hollow heat insulating layer4is denoted by Lc2. In the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1>Lc2, Lc1>Lh2, and Lc2>Lh2are established.

In the following description, with reference toFIGS. 4A-4D, a relationship is described between a load of the platen roller13acting on the thermal head1and a deflection of the heat storage layer5in the thermal printer10structured as described above.

The relationship between the load W of the platen roller13and the deflection v of the heat storage layer5is represented as follows:
v=(W/48EI)×K(3L2−4K2)  (Formula 1)

In (Formula 1), L represents a length of the hollow heat insulating layer4in the thermal paper feeding direction, K represents a distance from the forward end portion7aof the hollow heat insulating layer4, E represents a Young's modulus of a material of the heat storage layer5, and I represents a second moment of area (amount depending on a sectional shape) of the heat storage layer5.

Further, when (Formula 2) x=L/2 is established, a deflection amount of the heat storage layer5is a maximum. That is, the deflection amount is at a maximum when the external load is applied to the center of the heat storage layer5. It is noted that inFIGS. 4A-4D, the heating resistor7and the protective film9are omitted.

A central axis of the platen roller13is caused to correspond substantially to the center line X of the heating resistor7(center line7A of heat generating portion7A), and hence the largest external load is applied on the center line X of the heat generating portion7A. The center line of the hollow heat insulating layer4is shifted with respect to the center line X of the heat generating portion7A, and hence the external load applied to the heat storage layer5covering the hollow heat insulating layer4acts on a position shifted with respect to the center line of the hollow heat insulating layer4.

That is, the external load of the platen roller13acts on a position near an edge of the hollow heat insulating layer4, specifically, a rearward position in the thermal paper feeding direction Y of the hollow heat insulating layer4. Therefore, the deflection amount of the heat storage layer5supporting the heating resistors7can be reduced in comparison with a case where the external load acts on the center line of the hollow heat insulating layer4. As a result, strength against the external load of the heat storage layer5can be improved. Accordingly, even when a load applied to the heat storage layer is increased due to a sheet jam or the like, it is possible to prevent breakage of the heat storage layer.

As described above, in the thermal head1and the thermal printer10according to this embodiment, the heat generating portion7A is arranged within the region of the hollow heat insulating layer4, to thereby make the amount of heat conducted to an upper side of the heat generating portion7A larger than the amount of heat conducted to a lower side thereof. As a result, high heat-generation efficiency can be obtained. Further, the hollow heat insulating layer4is arranged with the center line thereof being shifted with respect to the center line X of the heat generating portion7A, thereby reducing the deflection amount of the heat storage layer5supporting the heating resistors7at an upper side of the hollow heat insulating layer4. As a result, the strength against the external load can be improved. By this construction, it is possible to achieve improvements in heat generation efficiency and strength against the external load.

Further, because of high heat-generation efficiency of the thermal head1, electrical power consumption at the time of printing onto the thermal paper12can be reduced. Further, because of the small deflection amount of the heat storage layer5with respect to the pressing force of the platen roller13, it is possible to reliably bring the heating resistors7into contact with the thermal paper12so as to transfer heat. Accordingly, it is possible to perform printing with excellent printing quality with reduced electrical power.

The embodiment described herein can be modified as follows.

For example, in this embodiment, the heat generating portion7A is arranged within the region of the hollow heat insulating layer4. However, as illustrated inFIGS. 5 and 6, in a thermal head101according to a first modification, the forward end portion4aof the hollow heat insulating layer4may be arranged outside the region of the heat generating portion7A, and the rearward end portion4bmay be arranged within the region of the heat generating portion7A. In this case, in the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1>Lc2, Lc1>Lh1, and Lc2<Lh2are established.

The rearward end portion7bof the heat generating portion7A is directly supported by the supporting substrate3, and the forward end portion7ais supported by the hollow heat insulating layer4. By this construction, the heat storage layer5above the hollow heat insulating layer4, which supports the heat generating portion7A, is more likely to be deflected, upon receiving the load applied by the platen roller13substantially to the center of the heating resistor7, at a further forward position in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A. Therefore, a contact pressure between the thermal paper12and the heating resistors7becomes small, and hence trailing in the thermal printer10after turning off the electrical power can be inhibited.

Further, in a thermal head201according to a second modification, as illustrated inFIG. 7, the center line of the hollow heat insulating layer4may be positioned rearward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A, and the heat generating portion7A may be arranged within the region of the hollow heat insulating layer4. In this case, in the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1<Lc2, Lc1>Lh1, and Lc2>Lh2are established.

During printing, the thermal paper12moves in the feeding direction Y by rotation of the platen roller13, whereby the load of the platen roller13in some cases moves forward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A. For example, there is a tendency that the external load is applied to a vicinity of a substantial center of the heat generating portion7A when a moving speed of the thermal paper12is low, and the large external load is applied forward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A when the moving speed of the thermal paper12is high. By reducing the region of the hollow heat insulating layer4, which supports the forward end portion7aside of the heat generating portion7A, it is possible to effectively reduce, regardless of the moving speed of the thermal paper12, the deflection amount of the heat storage layer5in a region in which the load of the platen roller13is applied, to thereby further improve the strength against the external load.

Further, in a thermal head301according to a third modification, as illustrated inFIG. 8, the center line of the hollow heat insulating layer4may be positioned rearward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A, the forward end portion4aof the hollow heat insulating layer4may arranged within the region of the heat generating portion7A, and the rearward end portion4bmay be arranged outside the region of the heat generating portion7A. In this case, in the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1<Lc2, Lc1<Lh1, and Lc2>Lh2are established.

The forward end portion7aof the heat generating portion7A is directly supported by the supporting substrate3, and the rearward end portion7ais supported by the hollow heat insulating layer4. By this construction, the heat storage layer5above the hollow heat insulating layer4, which supports the heat generating portion7A, is less likely to be deflected, upon receiving the load applied by the platen roller13substantially to the center of the heating resistor7, at a further forward position in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A. Therefore, as illustrated inFIG. 9, with respect to the load applied, when the rotation of the platen roller13feeds the thermal paper12forwardly in the thermal paper feeding direction Y with respect to the center of the heating resistor7, the deflection of the heat storage layer5can be reduced.

Further, in a thermal head401according to a fourth modification, as illustrated inFIGS. 10 and 11, the region of the hollow heat insulating layer4may be made smaller, when seen from the protective film9side, than the region of the heat generating portion7A. Further, the hollow heat insulating layer4may be arranged within the region of the heat generating portion7A, and the center line of the hollow heat insulating layer4may be arranged forward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A. In this case, in the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1>Lc2, Lc1<Lh1, and Lc2<Lh2are established.

By this construction, in comparison with a case of making larger the region of the hollow heat insulating layer4than the region of the heat generating portion7A, it is possible to improve the strength of the heat storage layer5against the external load from the platen roller13.

Further, in a thermal head501according to a fifth modification, as illustrated inFIG. 12, when seen from the protective film9side, the region of the hollow heat insulating layer4may be smaller than the region of the heat generating portion7A, the hollow heat insulating layer4may be arranged within the region of the heat generating portion7A, and the center line of the hollow heat insulating layer4may be positioned rearward in the thermal paper feeding direction Y with respect to the center line X of the heat generating portion7A. In this case, in the hollow heat insulating layer4and the heat generating portion7A, relationships of Lc1<Lc2, Lc1<Lh1, and Lc2<Lh2are established.

By the foregoing construction, in comparison with the case of making larger the region of the hollow heat insulating layer4than the region of the heat generating portion7A, it is possible to improve the strength of the heat storage layer5against the load applied forward with respect to the center of the heat generating portion7A.

As described above, while the embodiment of the present invention is described with reference to the drawings, the specific structure is not limited to the embodiment. The present invention also includes design modifications and the like without departing from the spirit of the present invention.

For example, in this embodiment, the concave portion2is formed on a surface on the heat storage layer5side of the supporting substrate3. However, the concave portion2may be formed in a region, which is opposed to the heating resistor7, of at least one of the surface of the supporting substrate3and the surface of the heat storage layer5on the supporting substrate3side.