Thermal head and thermal printer equipped with the same

A thermal head includes: a substrate; a heat storage layer disposed on the substrate; a heat-generating section disposed on the heat storage layer; an electrode electrically connected to the heat-generating section; a protection layer which coats the heat-generating section and a part of the electrode; and a first coating layer which coats a part of the protection layer and is disposed downstream in a transportation direction of a recording medium, with respect to the heat-generating section, the first coating layer including a first protrusion protruding towards a recording medium side, an end on a heat-generating section side of the first coating layer being positioned between the first protrusion and the heat-generating section, and the end on the heat-generating section side of the first coating layer being positioned in a range of L/2 from the heat-generating section, in which L is a distance between the heat-generating section and the first protrusion.

FIELD OF INVENTION

The present invention relates to a thermal head and a thermal printer equipped with the same.

BACKGROUND

In the related art, various thermal heads have been proposed as a printing device such as a facsimile or a video printer. For example, a thermal head disclosed in Patent Literature 1 includes a substrate, a heat storage layer provided on the substrate, a heat-generating section provided on the heat storage layer, an electrode electrically connected to the heat-generating section, and a coating layer which coats a part of the electrode and is disposed downstream in a transportation direction of a recording medium, with respect to the heat-generating section.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

Meanwhile, in a conventional thermal head, a coating layer includes a protrusion. Accordingly, when printing is performed on a recording medium using this thermal head, the recording medium comes in contact with the protrusion, and thus print scratches or blurring may be generated on the recording medium.

Solution to Problem

A thermal head according to one embodiment of the invention includes: a substrate; a heat storage layer disposed on the substrate; a heat-generating section disposed on the heat storage layer; an electrode electrically connected to the heat-generating section; a protection layer which coats the heat-generating section and a part of the electrode; and a first coating layer which coats a part of the protection layer and is disposed downstream in a transportation direction of a recording medium, with respect to the heat-generating section. The first coating layer includes a first protrusion protruding towards a recording medium side, an end on a heat-generating section side of the first coating layer is positioned between the first protrusion and the heat-generating section, and the end on the heat-generating section side of the first coating layer is positioned in a range of L/2 from the heat-generating section, in which L is a distance between the heat-generating section and the first protrusion.

A thermal printer in accordance with one embodiment of the invention includes: the thermal head as described above; a conveyance mechanism which conveys a recording medium onto the heat-generating section; and a platen roller which presses the recording medium onto the heat-generating section.

Advantageous Effects of Invention

According to the invention, it is possible to reduce a possibility of print scratches or blurring being generated on the recording medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, a thermal head X1according to a first embodiment will be described with reference to the drawings. As shown inFIGS. 1 to 4, the thermal head X1according to the embodiment includes a radiator1, a head base body3which is disposed on the radiator1, and a flexible printed circuit5(hereinafter, referred to as a FPC5) which is connected to the head base body3.

The radiator1is made of a metal material such as copper or aluminum, for example, and includes a base portion1awhich has a rectangular shape and a protrusion1bwhich extends along one long side of the base portion1a, in a plan view. As shown inFIG. 2, the head base body3is bonded to an upper surface of the base portion1aexcluding the protrusion1b, with a double-sided tape or an adhesive (not shown). In addition, the FPC5is bonded to the upper portion of the protrusion1bwith a double-sided tape or an adhesive (not shown). The radiator1has a function of radiating some heat not contributing to printing, from heat generated in a heat-generating section9of the head base body3as will be described later.

As shown inFIGS. 1 to 4andFIGS. 6 to 8, the head base body3includes a substrate7which has a rectangular shape in a plan view, the plurality of heat-generating sections9which are arranged on the substrate7along a longitudinal direction of the substrate7, and a plurality of driving ICs11which are disposed on the substrate7in a line along an arrangement direction of the heat-generating sections9(hereinafter, referred to as an arrangement direction).

The substrate7is made of an electrically insulating material such as alumina ceramics, a semiconductor material such as single-crystal silicon, or the like.

As shown inFIGS. 2 to 4, a heat storage layer13is formed on the upper surface of the substrate7. The heat storage layer13includes a base layer13aand a swollen portion13b. The base layer13ais formed over the entire upper surface of the substrate7. The swollen portion13bis partially swollen from the base layer13aand extends along an arrangement direction of the plurality of heat-generating sections in a belt shape, and a sectional shape thereof is a substantial semi-elliptical shape. The swollen portion13bfunctions so as to successfully press a recording medium P to be printed against a protection layer25formed on the heat-generating section9.

The heat storage layer13can be made of glass having low thermal conductivity, for example, and temporarily stores some heat generated in the heat-generating section9. Accordingly, the heat storage layer functions so as to shorten the time necessary for increasing a temperature of the heat-generating section9and to increase thermal responsiveness of the thermal head X1. The glass for forming the heat storage layer13, for example, is formed by applying predetermined glass paste obtained by incorporating a suitable organic solvent to glass powder on the upper surface of the substrate7by conventionally well-known screen printing and by firing this at a high temperature.

As the glass for forming the heat storage layer13, a material containing SiO2, Al2O3, CaO, and BaO, a material containing SiO2, Al2O3, and PbO, a material containing SiO2, Al2O3, and BaO, or a material containing SiO2, B2O3, PbO, Al2O3, CaO, and MgO is used, for example.

An electrical resistance layer15is provided on the upper surface of the heat storage layer13. The electrical resistance layer15is interposed between the heat storage layer13, and a common electrode17, an individual electrode19, a ground electrode21, and an IC control electrode23which will be described later. As shown inFIG. 6, the electrical resistance layer15includes an area having the same shape as those of the individual electrode19, the common electrode17, the ground electrode21, and the IC control electrode23, in a plan view (hereinafter, referred to as an interposed area). In addition, the electrical resistance layer15includes a plurality of areas which are exposed from between the individual electrode19and the common electrode17(hereinafter, referred to as exposed areas).

Each exposed area of the electrical resistance layer15forms the heat-generating section9described above. As shown inFIGS. 2 and 7, the plurality of heat-generating sections9are arranged on the swollen portion13bof the heat storage layer13in a row. For convenience of description, the plurality of heat-generating sections9are simply shown inFIGS. 1,6and7, but the plurality of heat-generating sections are disposed at a density of 180 dpi (dot per inch) to 2400 dpi, for example.

The electrical resistance layer15is, for example, formed with a material having relatively high electrical resistance such as TaN-based, TaSiO-based, TaSiNO-based, TiSiO-based, TiSiCO-based, or NbSiO-based material. Accordingly, when a voltage is applied between the common electrode17and the individual electrode19and current is supplied to the heat-generating section9, the heat-generating section9generates heat by Joule heating.

As shown inFIGS. 1 to 4andFIGS. 5 to 8, the common electrode17, the individual electrode19, the ground electrode21, and the IC control electrode23are provided on the upper surface of the interposed area. The common electrode17, the individual electrode19, the ground electrode21, and the IC control electrode23are made of a material having conductivity, and are, for example, made of any one kind of metal among aluminum, gold, silver, and copper, or an alloy thereof.

As shown inFIG. 7, the common electrode17includes a main wiring portion17a, auxiliary wiring portions17b, and lead portions17c. The main wiring portion17aextends along one long side7aof the substrate7, and as shown inFIG. 4, a thick portion17dhaving a greater thickness than that of the other portions of the common electrode17is formed. Accordingly, it is possible to reduce wiring resistance of the common electrode17. The auxiliary wiring portions17bextend along one short side7cand the other short side7dof the substrate7, respectively, and each one end thereof is connected to the main wiring portion17a. Each of the lead portions17cextends towards each heat-generating section9from the main wiring portion17a.

As shown inFIG. 8, each of the other ends of the auxiliary wiring portion17bis connected to the FPC5, and each of tip portions of the lead portions17cis connected to the heat-generating section9. Accordingly, the FPC5and the heat-generating section9are electrically connected to each other.

As shown inFIGS. 2 and 8, the individual electrode19extends between each heat-generating section9and the driving IC11and electrically connects each heat-generating section9and the driving IC11to each other. The individual electrode19divides the plurality of heat-generating sections9into a plurality of groups, and electrically connects the heat-generating sections9of each group to the driving IC11provided corresponding to each group.

As shown inFIG. 7, the ground electrode21extends along the arrangement direction, in the vicinity of the other long side7bof the substrate7in a belt shape. As shown inFIGS. 3 and 8, the FPC5and the driving IC11are connected to the upper portion of the ground electrode21. In detail, as shown inFIG. 8, the FPC5is connected to end areas21E positioned in one end and the other end of the ground electrode21. In addition, the FPC5is connected to first intermediate areas21M of the ground electrode21positioned between adjacent driving ICs11.

Each driving IC11is connected to a second intermediate area21N between the end area21E and the first intermediate area21M of the ground electrode21. In addition, each driving IC11is connected to a third intermediate area21L between adjacent first intermediate areas21M. Accordingly, the driving ICs11and the FPC5are electrically connected to each other.

As shown inFIG. 8, each driving IC11is disposed so as to correspond to each group of the plurality of heat-generating sections9, and is connected to one end of the individual electrode19and the ground electrode21. The driving IC11is a component for controlling an electrical connection state of each heat-generating section9, and includes a plurality of switching elements therein, as will be described later. The internal electrical connection state changes, by switching of the switching elements. A first connection terminal11aconnected to the internal switching element (not shown) of each driving IC11is connected to the individual electrode19. In addition, a second connection terminal11bconnected to the switching element of each driving IC11is connected to the ground electrode21.

Although not shown, the plurality of first connection terminals11aconnected to the individual electrodes19and the plurality of second connection terminals11bconnected to the ground electrode21are provided so as to correspond to each individual electrode19. The plurality of first connection terminals11aare individually connected to each individual electrode19. In addition, the plurality of second connection terminals11bare connected to the ground electrode21in common.

The IC control electrode23is a component for controlling the driving IC11, and includes an IC power electrode23aand an IC signal electrode23b, as shown inFIGS. 6 and 7. Each IC power electrode23aincludes an end power electrode portion23aE and an intermediate power electrode portion23aM. The end power electrode portions23aE are disposed in both ends of the substrate7in the longitudinal direction and in the vicinity of the other long side7bof the substrate7. The intermediate power electrode portion23aM is disposed between adjacent driving ICs11, and electrically connects the adjacent driving ICs11to each other.

As shown inFIG. 8, one end of the end power electrode portion23aE is disposed in a disposition area of the driving IC11, and the other end thereof is disposed in the vicinity of the other long side7bof the substrate7, so as to surround the periphery of the ground electrode21. One end of the end power electrode portion23aE is connected to the driving IC11, and the other end thereof is connected to the FPC5. Accordingly, the driving ICs11and the FPC5are electrically connected to each other.

In addition, the intermediate power electrode portion23aM extends along the ground electrode21, the one end thereof is disposed in the disposition area of one of the adjacent driving ICs11, and the other end thereof is disposed in the disposition area of the other one of the adjacent driving ICs11. One end of the intermediate power electrode portion23aM is connected to one of adjacent driving ICs11, the other end thereof is connected to the other one of the adjacent driving ICs11, and an intermediate portion thereof is connected to the FPC5(seeFIG. 3). Accordingly, the driving ICs11and the FPC5are electrically connected to each other.

The end power electrode portion23aE and the intermediate power electrode portion23aM are electrically connected to each other inside the driving IC11to which both electrode portions are connected. In addition, both adjacent intermediate power electrode portions23aM are electrically connected to each other inside the driving IC11to which both adjacent intermediate power electrode portions are connected.

As described above, by connecting the IC power electrode23ato each driving IC11, the IC power electrode23aelectrically connects each driving IC11and the FPC5to each other. Therefore, as will be described later, in the thermal head X1, it is possible to supply a current to each driving IC11from the FPC5through the end power electrode portions23aE and the intermediate power electrode portions23aM.

As shown inFIGS. 7 and 8, each IC signal electrode23bincludes an end signal electrode portion23bE and an intermediate signal electrode portion23bM. The end signal electrode portions23bE are disposed in both ends of the substrate7in the longitudinal direction and in the vicinity of the other long side7bof the substrate7. In addition, the intermediate signal electrode portion23bM is disposed between adjacent driving ICs11.

As shown inFIG. 8, in the same manner as the end power electrode portion23aE, one end of the end signal electrode portion23bE is disposed in the disposition area of the driving IC11, and the other end thereof is disposed in the vicinity of the right long side of the substrate7, so as to surround the periphery of the ground electrode21. One end of the end signal electrode portion23bE is connected to the driving IC11, and the other end thereof is connected to the FPC5.

One end of the intermediate signal electrode portion23bM is disposed in the disposition area of one of adjacent driving ICs11, and other end thereof is disposed in the disposition area of the other one of the adjacent driving ICs11so as to surround the periphery of the intermediate power electrode portion23aM. One end of the intermediate signal electrode portion23bM is connected to one of adjacent driving ICs11, and the other end thereof is connected to the other one of the adjacent driving ICs11.

The end signal electrode portion23bE and the intermediate signal electrode portion23bM are electrically connected to each other inside the driving IC11to which both electrode portions are connected. In addition, both adjacent intermediate signal electrode portions23bM are electrically connected to each other inside the driving IC to which both adjacent intermediate signal electrode portions are connected.

As described above, by connecting the IC signal electrode23bto each driving IC11, the IC signal electrode23belectrically connects each driving IC11and the FPC5to each other. Accordingly, as will be described later, a control signal which is transmitted to the driving IC11from the FPC5through the end signal electrode portion23bE is further transmitted to the adjacent driving ICs11through the intermediate signal electrode portion23bM.

The electrical resistance layer15, the common electrode17, the individual electrode19, the ground electrode21, and the IC control electrode23described above are, for example, formed by sequentially laminating each material layer configuring each component on the heat storage layer13, for example, by a conventionally well-known thin film formation technology such as a sputtering method, and processing the laminated body in a predetermined pattern by using a conventionally well-known photolithographic technology or etching technology. In addition, the thick portion17dcan be formed by forming common electrode17using the method described above and applying Ag paste thereon and firing the Ag paste using a thick film formation technology such as a screening printing method. A thickness of the common electrode17, the individual electrode19, the ground electrode21, and the IC control electrode23can be set to 0.4 μm to 2.0 μm, and a thickness of the thick portion17dof the common electrode17can be set to 5 μm to 40 μm.

As shown inFIGS. 2 to 4, the protection layer25which coats the heat-generating section9, a part of the common electrode17, and a part of the individual electrode19are formed on the heat storage layer13formed on the upper surface of the substrate7. In the example shown in the drawings, the protection layer25is formed along the arrangement direction, and is provided so as to coat an approximately left half area of the upper surface of the heat storage layer13in a plan view.

The protection layer25coats the heat-generating section9, a part of the common electrode17, and a part of the individual electrode19, and therefore it is possible to reduce a possibility of oxidation of each coated member due to a reaction with oxygen. In addition, it is possible to reduce a possibility of corrosion of the heat-generating section9, the common electrode17, and the individual electrode19caused by adhesion of moisture or dust contained in the atmosphere.

The protection layer25can be made of, for example, Si3N4, SiON, SiC, glass, SiCN, or the like. The protection layer25may contain another element such as Al or Y. In addition, the protection layer25may be formed as a single layer or may be formed by laminating a plurality of layers having different compositions.

As shown inFIGS. 1 to 4and6, a coating layer27which partially coats the common electrode17, the individual electrode19, the IC control electrode23, and the ground electrode21is provided on the heat storage layer13formed on the upper surface of the substrate7. In the example shown in the drawings, the coating layer27is provided so as to partially coat an approximately right half area of the upper surface of the heat storage layer13. The coating layer27is a component for protecting the common electrode17, the individual electrode19, the IC control electrode23and the ground electrode21, which are coated, from oxidation caused by contact with the atmosphere, or corrosion caused by adhesion of moisture or the like contained in the atmosphere. The coating layer27is formed so as to overlap the end of the protection layer25, in order to more reliably protect the common electrode17, the individual electrode19and the IC control electrode23. The coating layer27, for example, can be formed with a resin material such as an epoxy resin or a polyimide resin. In addition, the coating layer27can be formed by using a thick film formation technology such as a screen printing method, for example.

An opening portion (not shown) for exposing the end of the individual electrode19, and the ends of the second intermediate area21N and the third intermediate area21L of the ground electrode21and the IC control electrode23for connection of the driving IC11is formed on the coating layer27, and the wires are connected to the driving IC11through the opening portion. In addition, each driving IC11is coated and sealed with a coating member29made of a resin such as an epoxy resin or a silicone resin, in a state of being connected to the individual electrode19, the ground electrode21and the IC control electrode23, in order to protect the driving IC11itself and to protect connection portions of the driving IC11and the wires.

As shown inFIG. 8, the FPC5is connected to the common electrode17, the ground electrode21and the IC control electrode23. The FPC5is a well-known component in which a plurality of printed wires are wired inside an insulating resin layer, and each printed wire is electrically connected to an external power device or control device (not shown) through a connector31(seeFIGS. 1 and 8).

In detail, printed wires formed in the FPC5are connected to the end of the auxiliary wiring portions17bof the common electrode17, the end of the ground electrode21, and the end of the IC control electrode23, respectively by solder33(seeFIG. 3).

Hereinafter, the coating layer27will be described in detail with reference toFIGS. 4 and 5.FIGS. 4 and 5schematically show an aspect of transportation of the recording medium P when performing printing, and show a platen roller10with a dashed-two dotted line. Stress occurring in the thermal head X1is virtually shown with a dashed arrow. In addition, the drawings show an example of the thermal head X1in which a second protrusion4is provided on an end16of a first coating layer27a.FIG. 5shows a conventional thermal head X101.

The coating layer27includes the first coating layer27awhich is provided downstream in a transportation direction S of the recording medium P (hereinafter, referred to as a transportation direction S) with respect to the heat-generating section9, and a second coating layer27bwhich is provided upstream in the transportation direction S with respect to the heat-generating section9. The first coating layer27ais provided on the end on one long side7aside of the substrate7, from the upper portion of the heat storage layer13to the common electrode17. The second coating layer27bis provided so as to coat a part of the individual electrode19and a part of the IC control electrode23from the heat storage layer13.

The first coating layer27aincludes a first protrusion2which is provided on the thick portion17dof the common electrode17, and an end16which is disposed between the first protrusion2and the heat-generating section9. In addition, the first coating layer27aincludes the second protrusion4on the end16. The second protrusion4is positioned on the heat-generating section9side with respect to the first protrusion2. In addition, in the embodiment, the end16on the heat-generating section9side of the first coating layer27aindicates an area within 50 to 250 μm from the edge on the heat-generating section9side of the first coating layer27a. That is, the end on the heat-generating section9side of the first coating layer27ais an area corresponding to 20% of a length of the first coating layer27ain the transportation direction S from the edge on the heat-generating section9side of the first coating layer27ain a plan view. The second protrusion4is a part protruding towards the recording medium from the end16.

In the thermal head X1, the end16of the first coating layer27ais disposed between the first coating layer27aand the heat-generating section9. The end16of the first coating layer27ais positioned in a range of L/2 from the heat-generating section9, in which L is a distance between the heat-generating section9and the first protrusion2. A distance between the heat-generating section9and the first protrusion2is a distance from the edge on the first coating layer27aside of the heat-generating section9to an apex of the first protrusion2.

The thermal head X101shown inFIG. 5is a conventional thermal head in which the second protrusion4is not provided. In the thermal head X101, a platen roller110is controlled so as to press the recording medium P to a heat-generating section109with stress F109, and the printing is performed. However, as shown inFIG. 5, a void V in which a first coating layer127adoes not exist is generated between a first protrusion102and the heat-generating section109, and the platen roller110is deformed so that a part thereof infiltrates between the first protrusion102and the heat-generating section109. As a result, the stress F109 on the heat-generating section109decreases and stress F102 on the first protrusion102increases.

Accordingly, image quality of the printing of the thermal head X101may be decreased, and the image printed on the heat-generating section109may be strongly pressed against the first protrusion102to cause a print scratch generated by scratching a printed image or blurring due to blurring a printed image.

With respect to this, in the thermal head X1, the end16of the first coating layer27ais positioned in a range of L/2 from the heat-generating section9, in which L is the distance between the heat-generating section9and the first protrusion2, and therefore it is possible to reduce an amount of the platen roller10infiltrating between the first protrusion2and the heat-generating section9, and it is possible to reduce deformation of the platen roller10. Thus, it is possible to reduce a possibility of a decrease of stress F9 occurring on the protection layer25on the heat-generating section9, and to reduce a possibility of a decrease in image quality. In addition, since the contact of the platen roller with the first protrusion2is reduced, it is possible to reduce a possibility of print scratches or blurring generated in the printing of the thermal head X1.

In particular, when the thermal head X1includes the second protrusion4on the end16of the first coating layer27a, it is possible to further reduce a deformation amount of the platen roller10, and a possibility of generation of print scratches or blurring is easily reduced.

Stress F2 occurring on the first protrusion2, stress F4 occurring on the end16, and the stress F9 occurring on the protection layer25positioned on the heat-generating section9, occur in a direction perpendicular to contact surfaces of the recording medium P which come in contact with the first protrusion2, the end16, and the protection layer25positioned on the heat-generating section9. Forces F2′, F4′, and F9′ (not shown) occurring due to reaction against the stress F2, F4, and F9 occur in a reverse direction of the stress F2, F4, and F9, and these forces are referred to as forces occurring due to reaction F2′, F4′, and F9′, hereinafter.

As shown inFIG. 5, since the first protrusion102comes in contact with the recording medium P, pressure occurs on the first protrusion102. Accordingly, stress may occur inside the first protrusion102to damage the first protrusion102. In addition, since the first protrusion102comes in contact with the recording medium P, tensile stress occurs in the transportation direction, in addition to compressive stress occurring towards the first protrusion102, and thus the first protrusion102may be separated from the coating layer and the thermal head may be damaged.

With respect to this, in the thermal head X1, the second protrusion4is included between the first protrusion2and the heat-generating section9, and thus the recording medium P comes in contact with both the first protrusion2and the second protrusion4. Accordingly, the recording medium P comes in contact with at least two portions which are the first protrusion2and the second protrusion4of the coating layer27, and therefore it is possible to reduce the stress F2 occurring on the first protrusion2. That is, it is possible to disperse the stress F2 occurring on the first protrusion2by the force occurring due to reaction F4′ (not shown) occurring on the second protrusion4. Therefore, it is possible to reduce a possibility of the damage of the coating layer27.

After the recording medium P comes in contact with the first protrusion2, the recording medium is separated from the first coating layer27a, and the first protrusion2has a function of guiding the recording medium P. In the thermal head X1, it is possible to apply the forces occurring due to reaction F2′ and F4′ to the recording medium P from the thermal head X1in at least two portions which are the first protrusion2and the second protrusion4, and it is possible to further separate the recording medium P from the thermal head X1, compared to a case of guiding the recording medium P only by the first protrusion2.

In the second protrusion4, since the stress F4 is applied to the recording medium P so as to release the stress F2 occurring on the first protrusion2, it is possible to reduce the stress F2 occurring on the first protrusion2. Therefore, it is possible to reduce a possibility that an image printed above the heat-generating section9is strongly pressed against the first protrusion2, and it is possible to reduce a possibility of generation of print scratches or blurring. In addition, since the recording medium P receives the force occurring due to reaction F4′ from the second protrusion4, it is possible to efficiently release the recording medium P from the first coating layer27aon the downstream side of the second protrusion4in the transportation direction S.

In the thermal head X1, the first protrusion2is provided on the thick portion17d. Accordingly, the thick portion17dis formed on the common electrode17to perform the print formation of the first coating layer27a, and thus to form the first protrusion2, and therefore it is possible to simply provide the first protrusion2.

In addition, it is preferable that a surface roughness of the first protrusion2is larger than a surface roughness of the end16. Since the surface roughness of the first protrusion2is larger than the surface roughness of the end16, it is possible to increase contact points of the recording medium P and the first protrusion2on the first protrusion2where great stress F2 occurs, and it is possible to disperse the stress F2 occurring on the first protrusion2. In order to have a surface roughness of the first protrusion2which is larger than the surface roughness of the end16, the resin to be the first coating layer27ais applied onto the protection layer25, and dried and cured, for example. After that, the surface of the first coating layer27aon the end16may be filed to process the surface coarsely. In addition, the surface of the first coating layer27aon the end16may be chemically processed.

As shown inFIG. 4, in the thermal head X1, a height Ha of the first protrusion2from the substrate7is configured to be greater than a height Hb of the second protrusion4from the substrate7. Accordingly, great stress F4 may occur from the recording medium P, on the second protrusion4positioned on the heat-generating section9side with respect to the first protrusion2, but by setting the height Hb of the second protrusion4to be smaller than the height Ha of the first protrusion2, it is possible to reduce excessive stress F4 occurring on the second protrusion4. The height Ha of the first protrusion2from the substrate7can be set to be 35 to 45 μm, and the height Hb of the second protrusion4from the substrate7can be set to be 20 to 30 μm. It is preferable that the height Hb of the second protrusion4from the substrate7is 0.4 to 0.8 times the height Ha of the first protrusion2from the substrate7. The height Ha of the first protrusion2from the substrate7and the height Hb of the second protrusion4from the substrate7may be suitably set in accordance with the size of the thermal head X1and the recording medium P. The height Hb of the second protrusion4from the substrate7is a height of the end16from the substrate7.

The end16on the first coating layer27ais disposed on the swollen portion13bof the heat storage layer13, in a plan view. Accordingly, it is possible to set a protrusion height of the second protrusion4and a protrusion height of the swollen portion13bto the height Ha of the second protrusion4from the substrate7. In addition, it is possible to easily increase the height Ha of the second protrusion4from the substrate7.

In the thermal head X1, a length Wa between the first coating layer27aand the heat-generating section9is configured to be smaller than a length Wb between the second coating layer27band the heat-generating section9. The distance between the first coating layer27aand the heat-generating section9indicates a distance from the edge of the heat-generating section9to the first coating layer27ain a plan view. The distance between the second coating layer27band the heat-generating section9indicates a distance from the edge of the heat-generating section9to the second coating layer27bin a plan view.

As described above, since the length Wa between the first coating layer27adisposed downstream in the transportation direction S and the heat-generating section9is smaller than the length Wb between the second coating layer27bdisposed upstream in the transportation direction S and the heat-generating section9, it is possible to increase the force occurring due to reaction F2′ from the first protrusion2provided on the first coating layer27adisposed downstream in the transportation direction S and the force occurring due to reaction F4′ from the second protrusion4, and it is possible to efficiently release the recording medium P from the first coating layer27a. At that time, the first protrusion2and the second protrusion4function as guiding sections.

In the thermal head X1, a height Hc of the protection layer25positioned on the heat-generating section9from the substrate7is greater than the height Hb of the second protrusion4from the substrate7and is smaller than the height Ha of the first protrusion2from the substrate7. Accordingly, it is possible to allow the first protrusion2distant from the heat-generating section9to function as a guiding section of the recording medium P, and it is possible to allow the second protrusion4disposed on the heat-generating section9side with respect to the first protrusion2to function as a stress release section. As a result, it is possible to efficiently transport the recording medium P and to release the stress F2 occurring on the first protrusion2.

For the first protrusion2and the second protrusion4, the first coating layer27acan be formed of the resin described above having great viscosity. After forming the first coating layer27ato have an even thickness, a material for forming the first coating layer27ais further applied in the positions for forming the first protrusion2and the second protrusion4, and accordingly, the first protrusion2and the second protrusion4can be provided.

The example in which one second protrusion4is provided on the first coating layer27ais shown, but the embodiment is not limited thereto. Two or more second protrusions4may be provided. In this case, the plurality of second protrusions4function as stress release sections. Even in a case of providing the first protrusion2and the second protrusion4on the second coating layer27b, the first protrusion2and the second protrusion4may be formed with the same method.

As the recording medium P, thermal paper or image receiving paper to be printed by using heat can be exemplified. In the specification, in a case of performing the printing on the medium through an ink ribbon which sublimates when receiving heat, the ink ribbon and the medium are collectively referred to as the recording medium P.

Next, one embodiment of a thermal printer of the invention will be described with reference toFIG. 9.FIG. 9shows an enlarged view of the thermal head X1for easy understanding. As shown inFIG. 9, a thermal printer Z of the embodiment includes the thermal head X1described above, a transportation mechanism40, a platen roller50, a power device60, and a control device70. The thermal head X1is attached to an attachment surface80aof an attachment member80provided in a housing (not shown) of the thermal printer Z. The thermal head X1is attached to the attachment member80so that the arrangement direction of the heat-generating section9is a direction orthogonal to the transportation direction S of the recording medium P which will be described later. As described above, the first coating layer27ais provided downstream in the transportation directions of the recording medium P.

The transportation mechanism40, which is intended to transport the recording medium P such as thermal paper or image receiving paper to which ink is transferred, onto the plurality of heat-generating sections9of the thermal head X1in an arrow S direction ofFIG. 9, includes transportation rollers43,45,47, and49. The transportation rollers43,45,47, and49, for example, can be configured by coating cylindrical shafts43a,45a,47a, and49amade of metal such as stainless steel with elastic members43b,45b,47b, and49bmade of butadiene rubber. Although not shown, in a case where the recording medium P is the image receiving paper to which ink is transferred, the recording medium P and the ink film are transported between the recording medium P and the heat-generating section9of the thermal head X1.

The platen roller50, which is intended to press the recording medium P onto the heat-generating section9of the thermal head X1, is disposed so as to extend along a direction perpendicular to the transportation direction S, and is supported, at its ends, so that it is able to rotate while pressing the recording medium P onto the heat-generating section9. For example, the platen roller50can be constructed of a cylindrical shaft body50amade of metal such as stainless steel covered with an elastic member50bmade of butadiene rubber or the like.

The power-supply device60is intended to supply electric current for causing the heat-generating sections9of the thermal head X1to generate heat as above described, and also electric current for operating the driving IC11. The control device70is intended to supply control signals for controlling the operation of the driving IC11to the driving IC11in order to cause the heat-generating sections9of the thermal head X1to generate heat in a selective manner as above described.

In the thermal printer Z of the present embodiment, as shown inFIG. 9, the recording medium P is conveyed, while being pressed onto the heat-generating sections9of the thermal head X1by the platen roller50, onto the heat-generating sections9by the conveyance mechanism40, and simultaneously the heat-generating sections9are caused to generate heat in a selective manner by the power-supply device60and the control device70, whereby predetermined printing can be performed on the recording medium P. In the case of using image-receiving paper or the like as the recording medium P, printing can be performed on the recording medium P by thermally transferring the ink of an ink film (not shown) being conveyed together with the recording medium P to the recording medium P.

Second Embodiment

A thermal head X2will be described with reference toFIG. 10.FIG. 10shows the recording medium P with a dotted line. In the thermal head X2, the end16of the first coating layer27ais formed by an inclined portion12, an upper surface of which is an inclined side. In addition, a dashed-dotted line is drawn downwards to show the first protrusion2clearly. The thermal head X2is different from the thermal head X1in a point that the inclined portion12is provided, and the other points are same. The same reference numerals refer to the same members as those of the thermal head X1, and those are assumed to be the same members.

In the thermal head X2, the upper surface of the inclined portion12is an inclined surface which is inclined from the first protrusion2towards the second protrusion4provided on the heat-generating section9side. The inclined portion12is inclined downwards gradually to the second protrusion4. Accordingly, the first protrusion2and the second protrusion4gradually connect to each other, and a recess in which the platen roller (not shown) infiltrates is not formed between the first protrusion2and the second protrusion4. Therefore, it is possible to reduce a possibility of generation of print scratches or blurring generated due to the platen roller infiltrating therein. In addition, since the recess is not formed between the first protrusion2and the second protrusion4, it is possible to reduce dirt or dust attached to the recording medium P attaching between the first protrusion2and the second protrusion4.

Further, since the inclined surface which is the upper surface of the inclined portion12also comes in contact with the recording medium P, it is possible to release the stress F2 occurring on the first protrusion2and the stress F4 occurring on the second protrusion4, and it is possible to reduce a possibility of damage to the first protrusion2and the second protrusion4.

The inclined portion12can be formed by forming the first protrusion2and the second protrusion4, and then applying and curing the same material as the coating layer27. The inclined portion12may be provided at the same time as the first protrusion2and the second protrusion4.

The example in which the inclined portion12which is inclined downwards from the first protrusion2to the second protrusion4is provided on the end16of the first coating layer27ais shown, but there is no limitation thereto. For example, the inclined portion12having a concave-convex form on the inclined surface may be provided so as to fill the portion between the first protrusion2and the second protrusion4. The inclined portion may be provided to have other embodiments, as long as it reduces the stress applied to the first protrusion2from the recording medium.

Third Embodiment

A thermal head X3according to a third embodiment will be described with reference toFIGS. 11 and 12. In the thermal head X3, an end8on the heat storage layer13side of the first coating layer27aand the end8on the heat storage layer13side of the second coating layer27bare shaped in a wave form in a plan view. That is, the end8on the heat storage layer13side of the first coating layer27aand the end8on the heat storage layer13side of the second coating layer27bare shaped in a concave-convex form in a plan view. The other configurations are the same as those of the thermal head X1, and therefore the description thereof will be omitted.

On the end on the heat storage layer13side, the first coating layer27aand the second coating layer27bconfiguring the thermal head X3have different distances from the heat-generating section9in the arrangement direction of the substrate7. In detail, an end8aof the first coating layer27ais disposed on the heat storage layer13side with respect to an end8bof the first coating layer27a. As shown inFIG. 12, the end8aof the first coating layer27ais disposed on the heat-generating section9side with respect to the end8bof the first coating layer27a. Accordingly, the length Wa between the end8aand the protection layer25on the heat-generating section9is configured to be different from the length Wb between the end8band the protection layer25on the heat-generating section9.

In a case of performing printing on a hard recording medium such as a card, the printing on the recording medium is performed by interposing the ink ribbon between the recording medium and the thermal head. Herein, when speeding-up of the driving of the thermal head is realized according to high-speed printing, in a case where a release property of the ink ribbon from the thermal head is degraded or in a case where static electricity is generated on the recording medium, blurring may occur on the printed image.

With respect to this, in the thermal head X3, the end8on the heat storage layer13side of the first coating layer27aand the end8on the heat storage layer13side of the second coating layer27bare shaped in a concave-convex form in a plan view. Accordingly, it is possible to easily release the ink ribbon R from the first coating layer27aand the second coating layer27bat the time of printing. In detail, when the ink ribbon R is transported onto the first coating layer27a, in the end8bof the first coating layer27awhich is the concavity, as shown inFIG. 12(b), the ink ribbon R is in a state of partially floating above the end8bof the first coating layer27awhich is the concavity. Therefore, even when the ink ribbon R is adhered to the first coating layer27aby static electricity, it is possible to easily release the ink ribbon R from the first coating layer27a.

As shown inFIG. 12(b), only the first protrusion2of the first coating layer27acomes in contact with the ink ribbon R, and the second protrusion4which is the end8bof the first coating layer27adoes not come in contact with the ink ribbon R, but as shown inFIG. 12(a), since the first protrusion2of the first coating layer27aand the second protrusion4which is the end8aof the first coating layer27acome in contact with the ink ribbon, it is possible to reduce a possibility of damage to the first protrusion2.

Since the shape of the end8on the heat storage layer13side of the first coating layer27aand the shape of the end8on the heat storage layer13side of the second coating layer27bare shaped in a wave form in a plan view, the ink ribbon R disposed in the same position in the transportation direction S is in a state of partially floating above the first coating layer27aand the second coating layer27b, as described above. Accordingly, it is possible to easily release the ink ribbon R from the first coating layer27aand the second coating layer27b. In addition, in a plan view, the wave form indicates that the distance between the end8of the coating layer27and the heat-generating section9is not a constant value and the end8of the coating layer27is formed to have a continuous curve.

In a case where the end8of the coating layer27is shaped in the wave form, when a distance between the end8of the coating layer27and the center of the heat-generating section9is set as an average distance W, the end8of the coating layer27is preferably positioned in a range of ±0.15 mm from the average distance W. Accordingly, it is possible to efficiently perform the release of the thermal head X3from the ink ribbon R. The wave form thereof is formed by suitably adjusting a printing step when forming the coating layer27or viscosity of a resin for forming the coating layer27.

As an example where the end8of the coating layer27is shaped in a concave-convex form in a plan view, the example where the end8of the coating layer27is shaped in the wave form is shown, but there is no limitation thereto. For example, the concave-convex form of the end8of the coating layer27may be shaped in a stepwise manner, to define a stepwise form.

In addition, the example in which the end of the first coating layer27aand the end of the second coating layer27bare shaped in the concave-convex form in a plan view, is shown, but there is no limitation thereto. Either the end of the first coating layer27aor the end of the second coating layer27bmay be shaped in the concave-convex form in a plan view. In addition, either the end of the first coating layer27aor the end of the second coating layer27bmay be shaped in the wave form in a plan view.

Fourth Embodiment

A thermal head X4according to a fourth embodiment will be described with reference toFIGS. 13 and 14. In the thermal head X4, the end8of the first coating layer27ais shaped in a concave-convex form when seen from the transportation direction S of the recording medium. The other points are the same as those in the thermal head X1, and therefore the description thereof will be omitted.

As shown inFIG. 13(b), in the thermal head X4, the concave-convex form is provided on the upper surface of the end8of the first coating layer27a. That is, the thickness of the first coating layer27ais configured to be different in the arrangement direction. In detail, the thickness of the end8aof the first coating layer27ais configured to be greater than the thickness of the end8bof the first coating layer27a. Since the arrangement direction is a main scanning direction, in the thermal head X4, the end8of the first coating layer27ais configured to be shaped in the concave-convex form in the main scanning direction.

As described above, since the surface of the end8of the first coating layer27ais shaped in the concave-convex form in the main scanning direction, as shown inFIG. 14, the second protrusion4on the end8aof the first coating layer27ahaving a greater thickness comes in contact with the ink ribbon R, but the end8bof the first coating layer27ahaving a smaller thickness does not come in contact with the ink ribbon R. Accordingly, a part where the ink ribbon R does not come in contact with the end8of the first coating layer27ais generated, and therefore it is possible to easily release the ink ribbon R from the first coating layer27a.

The concave-convex form provided on the surface of the end of the first coating layer27acan be formed by polishing. Alternatively, the concave-convex form can be formed by forming a concave-convex shape using a resin in advance and bonding it to the surface of the end. In addition, a difference in height of the concave-convex form may be 5 to 20 μm.

The example where the concave-convex form is provided on the end8of the first coating layer27ain the arrangement direction is shown, but the concave-convex form may be provided only on the second coating layer27bin the arrangement direction. Even in this case, a part where the ink ribbon R does not come in contact with a part of the end8of the second coating layer27bin the main scanning direction can be formed, and therefore it is possible to effectively improve the release property of the ink ribbon R from the thermal head X4.

Fifth Embodiment

A thermal head X5will be described with reference toFIG. 15. In the thermal head X5, the second coating layer27bis disposed downstream in the transportation direction with respect to the heat-generating section9. An end18of the second coating layer27bis a third protrusion14. The other configurations are the same as those in the thermal head X1.

The second coating layer27bincludes the third protrusion14on the end on the heat-generating section9side. In the thermal head X5, the third protrusion14is disposed upstream of the heat-generating section9. Accordingly, the recording medium P comes in contact with the third protrusion14and then comes in contact with the protection layer25disposed on the heat-generating section9. Therefore, the recording medium P is guided to the protection layer25disposed on the heat-generating section9by the third protrusion14, and it is possible to efficiently transport the recording medium to the protection layer25disposed on the heat-generating section9. Particularly, in a case of a soft recording medium P such as thermal paper, since the recording medium is guided by the third protrusion14, it is possible to reduce a possibility of a paper jam in the thermal head X5.

That is, it is possible to reduce a possibility of the platen roller10infiltrating between the protection layer25on the heat-generating section9and the second protrusion4, and it is possible to reduce a possibility of deformation of the platen roller10. Accordingly, also on the second protrusion4side, it is possible to reduce a possibility of a decrease of the stress F9 occurring on the protection layer25on the heat-generating section9, caused by a force occurring due to reaction F4′ which occurs from the second protrusion4. Therefore, it is possible to reduce a possibility of generation of print scratches in the thermal head X5.

In addition, in the thermal head X5, a height Hd of the third protrusion14from the substrate7is configured to be smaller than a height Hb of the second protrusion4from the substrate7. Accordingly, it is possible to have the greater stress F4 occurring by the second protrusion4, compared to the stress F14 occurring by the third protrusion14. As a result, it is possible to efficiently guide the recording medium to the protection layer25disposed on the heat-generating section9by the third protrusion14on the upstream side of the transportation direction S, it is possible to have the greater force occurring due to reaction F4′ which occurs from the second protrusion4, on the downstream side of the transportation direction S, and it is possible to efficiently release the recording medium P from the protection layer25.

A relationship among the height Ha of the first protrusion2from the substrate7, the height Hb of the second protrusion4from the substrate7, the height Hd of the third protrusion14from the substrate7, and the height Hc of the protection layer25positioned on the heat-generating section9from the substrate7, preferably satisfies a relationship of Ha>Hc>Hb>Hd. Accordingly, it is possible to optimize stress F2, F4, F9 and F14 occurring on the recording medium P, and forces occurring due to reaction F2′, F4′, F9′ and F14′.

Hereinabove, one embodiment of the invention has been described, but the invention is not limited to the embodiments described above, and various modifications is possible without departing from the scope of the invention. The example where the thermal head X1is used in the thermal printer Z is shown, but any of the thermal heads X2to X5may be used. In addition, the thermal heads X1to X5according to the plurality of embodiments may be used in combination.

For example, the example of a flat head where the swollen portion13bof the heat storage layer13is provided on the main surface of the substrate7and the heat-generating section9is formed on the main surface of the substrate7is shown, but there is no limitation thereto. For example, the invention may be applied to an edge head including the heat storage layer13provided on an edge of the substrate and the heat-generating section9provided on the heat storage layer13. Even in this case, it is possible to obtain the same effects as in the invention. In the thermal head provided with the heat-generating section9on the edge, the plan view means an edge view. That is, in the specification, the plan view means the plan view of the heat-generating section9.

In addition, in the thermal head X1of the embodiments, for example, the heat storage layer13includes the swollen portion, which is partially swollen on the substrate7, formed by providing, on the base layer13a, the swollen portion13bwhich is partially swollen from the base layer13a, but the configuration of the heat storage layer13is not limited thereto. For example, the heat storage layer13may be configured only with the swollen portion13bwithout providing the base portion13a.

In addition, the example where the FPC5is used as the external substrate is shown, but there is no limitation thereto. Instead of the FPC5, a glass epoxy substrate which is a hard rigid substrate may be used or the connector31may be directly mounted on the substrate7. In addition, the example of a thin-film head in which the heat-generating section9is formed by a thin film formation technology, is shown, but there is no limitation thereto. A thick-film head in which the heat-generating section9is formed by a thick film formation technology may be used.

REFERENCE SIGNS LIST

Z1: Thermal printer

P: Recording medium

3: Head base body

8,16: End of first coating layer

13: Heat storage layer

15: Electrical resistance layer

25: Protection layer

27a: First coating layer

27b: Second coating layer