Thermal head and thermal printer equipped with the thermal head

A thermal head capable of decreasing the possibility of causing wrinkles in a recording medium is provided. A thermal head includes: a substrate; a heat generating portion disposed on the substrate; a driving IC disposed on the substrate and controlling actuation of the heat generating portion; a covering member covering the driving IC; and a projection portion disposed on the substrate and making contact with a recording medium. The substrate includes a first region and a second region in a plan view, the first region being defined by extending an area where the driving IC is disposed in a sub scanning direction and the second region being an area other than the first region. The projection portion is disposed on the second region closer to the heat generating portion than the area where the driving IC is disposed.

TECHNICAL FIELD

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

BACKGROUND ART

Various types of thermal heads have been proposed to date as printing devices for use in facsimiles, video printers, and so forth. For example, there is known a thermal head comprising: a substrate; a heat generating portion disposed on the substrate; a driving IC which controls actuation of the heat generating portion; and a covering member which covers the driving IC, the covering member serving also as an ink ribbon guide, in which a recording medium is conveyed while making contact with the covering member (refer to Patent Literature 1, for example). Moreover, when the substrate is seen in a plan view, this thermal head is composed of a first region defined by extending an area where the driving IC is disposed in a sub scanning direction, and a second region being an area other than the first region.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the thermal head as above described, however, the height of the second region free of the driving IC is lower than the height of the first region, thus causing poor contacting condition between a recording medium and the thermal head, which gives rise to the possibility of occurrence of wrinkles in the recording medium.

Solution to Problem

A thermal head in accordance with one embodiment of the invention comprises: a substrate; a heat generating portion disposed on the substrate; a driving IC disposed on the substrate and controlling actuation of the heat generating portion; a covering member covering the driving IC; and a projection portion disposed on the substrate and making contact with a recording medium under conveyance. Moreover, the substrate comprises a first region and a second region in a plan view, the first region being defined by extending an area where the driving IC is disposed in a sub scanning direction and the second region being an area other than the first region. In addition, the projection portion is disposed on the second region closer to the heat generating portion than the area where the driving IC is disposed.

A thermal printer in accordance with one embodiment of the invention comprises: the thermal head as described above; a conveyance mechanism conveying the recording medium onto the heat generating portion; and a platen roller pressing the recording medium onto the heat generating portion.

Advantageous Effects of Invention

According to the invention, the possibility of causing wrinkles in a recording medium can be decreased.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a thermal head X1will be described with reference toFIGS. 1 to 4. The thermal head X1comprises: a heatsink1; a head substrate3placed on the heatsink1; and a connector31connected to the head substrate3. InFIG. 1, the diagrammatic representation of the connector31is omitted, and, a region where the connector31is placed is indicated by alternate long and short dashed lines.

While the connector31will hereafter be described as a connecting member which makes external electrical connection, other members having flexibility such as a flexible printed wiring board, a glass epoxy substrate, or a polyimide substrate, can be used instead. In a case where external electrical connection is established by a flexible printed wiring board, a reinforcing plate made of resin such for example as a phenol resin, a polyimide resin, or a glass epoxy resin (not shown in the drawing) may be disposed between the flexible printed wiring board and the heatsink1.

The heatsink1has the form of a plate, and, in a plan view, the heatsink1is rectangular-shaped. The heatsink1is formed of a metal material such for example as copper, iron, or aluminum, and has the capability of dissipating, of heat generated by a heat generating portion9of the head substrate3, heat which is not responsible for printing. Moreover, the head substrate3is bonded to the upper surface of the heatsink1by means of double-faced tape, an adhesive, or otherwise (not shown).

In a plan view, the head substrate3has the form of a plate, and, constituent members of the thermal head X1are each disposed on a substrate7of the head substrate3. The head substrate3has the function of performing printing on a recording medium (not shown) in response to an electric signal issued from outside.

As shown inFIGS. 1 and 2, the connector31comprises: a plurality of connector pins8; and a housing10which accommodates the plurality of connector pins8. The plurality of connector pins8have one sides left exposed outside of the housing10, and have other sides stored within the housing10. The plurality of connector pins8have the function of ensuring electrical conduction between each of various electrodes of the head substrate3and an externally-disposed power supply, and are electrically independent of each other. The connector pins8are required to have electrical conductivity, and are therefore formed of a metal or an alloy.

The housing10has the function of accommodating the respective connector pins8in a state of being electrically independent of each other, and is therefore formed of an insulating member. The housing10effects supply of electricity to the head substrate3by means of attachment and detachment of an externally-disposed connector (not shown). The housing10is made of, for example, a thermosetting resin, an ultraviolet-curable resin, or a photo-curable resin.

Hereinafter, each of members constituting the head substrate3will be described.

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

A heat storage layer13is formed on the upper surface of the substrate7. The heat storage layer13comprises: an underlayer portion13a; and a protuberant portion13b. The underlayer portion13ais formed over the left half of the upper surface of the substrate7. The protuberant portion13bextends in the form of a strip along a main scanning direction of a plurality of heat generating portions9, and has a substantially semi-elliptical sectional profile. The underlayer portion13ais disposed near the heat generating portion9while being located below a protective layer25which will hereafter be described. The protuberant portion13bacts to press a recording medium which is subjected to printing against the protective layer25formed on the heat generating portion9in a satisfactory manner.

The heat storage layer13is formed of glass having a low heat conductivity, and accumulates part of heat generated by the heat generating portion9temporarily. Accordingly, the heat storage layer13is able to shorten the time required for a temperature rise in the heat generating portion9, and thus acts to improve the thermal response characteristics of the thermal head X1.

For example, the heat storage layer13is formed by applying a predetermined glass paste, which is obtained by blending a suitable organic solvent in glass powder, onto the upper surface of the substrate7by means of heretofore known screen printing or otherwise, and subsequently firing the paste.

An electrical resistance layer15is disposed on the upper surface of the heat storage layer13, and, on the electrical resistance layer15are disposed a ground electrode4, a common electrode17, an individual electrode19, an IC-connector connection electrode21, and an IC-IC connection electrode26. The electrical resistance layer15is subjected to patterning so as to have the same shape as the ground electrode4, the common electrode17, the individual electrode19, the IC-connector connection electrode21, and the IC-IC connection electrode26, and has an exposed region serving as an exposed electrical-resistance layer15region lying between the common electrode17and the individual electrode19.

As shown inFIG. 1, there are arranged exposed regions of the electrical-resistance layer15in an array on the protuberant portion13bof the heat storage layer13, and, each of the exposed regions constitutes the heat generating portion9. The plurality of heat generating portions9, while being illustrated in simplified form inFIG. 1for convenience in explanation, are arranged at a density of 100 dpi to 2400 dpi (dot per inch), for example. The electrical resistance layer15is formed of a material having a relatively high electrical resistance such for example as a TaN-based material, a TaSiO-based material, a TaSiNO-based material, a TiSiO-based material, a TiSiCO-based material, or a NbSiO-based material. Thus, upon application of a voltage to the heat generating portion9, the heat generating portion9is caused to generate heat under Joule heating effect.

The ground electrode4, the common electrode17, the individual electrode19, the IC-connector connection electrode21, and the IC-IC connection electrode26are formed of a material having electrical conductivity, for example, one metal material selected from among aluminum, gold, silver, and copper, or an alloy of these metals.

The common electrode17comprises: a main wiring portion17a; a sub wiring portion17b; a lead portion17c; and a thick electrode portion17d. The main wiring portion17aextends along one long side of the substrate7. The sub wiring portion17bextends along each of one and the other short sides of the substrate7. The lead portion17cextends from the main wiring portion17atoward each of the heat generating portions9. The thick electrode portion17d, which is disposed on the main wiring portion17aand the sub wiring portion17b, is made thicker than the other portions of the common electrode17. The common electrode17provides electrical connection between the connector31and each of the heat generating portions9.

The thermal head X1is configured so that an electric current fed from the sub wiring portion17blocated at each end thereof in the direction of arrangement of the heat generating portions9(hereafter also referred to as “main scanning direction”) passes through the main wiring portion17a, flows through each of the lead portions17c, and is thereby supplied to each of the heat generating portions9. On the main wiring portion17a, as well as on the sub wiring portion17b, there is provided the thick electrode portion17dwhich acts to increase the current carrying capacity of the main wiring portion17aand the sub wiring portion17b. Exemplary of the thick electrode portion17dis an Ag paste.

A plurality of individual electrodes19provide electrical connection between each of the heat generating portions9and a driving IC11. Moreover, given that the heat generating portions9are bunched together in groups, the individual electrodes19allow the heat generating portions9in each group to make electrical connection with a corresponding one of the driving ICs11prepared for the heat generating portion groups, respectively.

A plurality of IC-connector connection electrodes21have one ends connected to the driving IC11and have other ends led out to an end face7aof the substrate7. The led-out ends are electrically connected to the connector31, thereby permitting electrical connection between the driving IC11and the connector31. The plurality of IC-connector connection electrodes21connected to each of the driving IC11are configured by a plurality of wiring lines having different functions.

The ground electrode4, which is placed between the IC-connector connection electrode21and the main wiring portion17aof the common electrode17, has a large area. The ground electrode4is grounded and maintained at a potential of 0 to 1 V.

A plurality of IC-IC connection electrodes26provide electrical connection between the driving ICs11arranged adjacent each other. The plurality of IC-IC connection electrodes26are disposed in correspondence to the IC-connector connection electrodes21, and transmit various signals to the adjacent driving ICs11. That is, an electric current is fed from the connector31to the driving IC11by way of the IC-connector connection electrodes21and the IC-IC connection electrodes26.

As shown inFIG. 1, the driving IC11is placed in correspondence to each of the groups including the plurality of heat generating portions9, and is connected to the individual electrode19, the IC-connector connection electrode21, and the ground electrode4. The driving IC11has the function of controlling the current-carrying state of each of the heat generating portions9. It is advisable to use a switching member having a plurality of built-in switching elements as the driving IC11.

As shown inFIG. 1, in a sub scanning direction S coincident with a conveying direction S in which a recording medium (not shown) is conveyed, in the thermal head X1, the substrate7comprises a first region R1and a second region R2in a plan view, the first region R1being defined by extending an area where the driving IC11is disposed in the sub scanning direction and the second region R2being an area other than the first region R1.

The first region R1has a width which is equal to the width of the driving IC11in the main scanning direction, and extends along the sub scanning direction S while maintaining the width. In other words, in a plan view, the first region R1is a region defined by virtual lines extending in the sub scanning direction S along side faces of the driving IC11that are perpendicular to the main scanning direction.

The electrical resistance layer15, the common electrode17, the individual electrode19, the ground electrode4, the IC-connector connection electrode21, and the IC-IC connection electrode26thus far described are formed by, for example, stacking layers of their constituent materials on the heat storage layer13one after another by a heretofore known thin-film forming technique such as a sputtering method, and subsequently working the resultant layered body into predetermined patterns by a heretofore known technique such as a photo-etching method. Note that the common electrode17, the individual electrode19, the ground electrode4, the IC-connector connection electrode21, and the IC-IC connection electrode26can be formed at one time through the same process steps. Meanwhile, the thick electrode portion17dcan be formed by means of printing before or after the process of working the different electrodes into predetermined patterns.

As shown inFIGS. 1 and 2, the protective layer25which covers the heat generating portion9, part of the common electrode17, and part of the individual electrode19, is formed on the heat storage layer13formed on the upper surface of the substrate7. InFIG. 1, for convenience in explanation, a region where the protective layer25is formed is indicated by alternate long and short dashed lines, and its diagrammatic representation is omitted.

The protective layer25is intended to protect the covered areas of the heat generating portion9, the common electrode17, and the individual electrode19against corrosion caused by adhesion of, for example, atmospheric water content, or against wear caused by contact with a recording medium which is subjected to printing.

The protective layer25can be formed from SiN, SiO, SiON, SiC, SiCN, diamond-like carbon, or the like, and, the protective layer25may either be of a single layer or be composed of a stack of layers. Such a protective layer25can be produced by a thin-film forming technique such as the sputtering method, or a thick-film forming technique such as a screen printing method.

Moreover, as shown inFIGS. 1 and 2, a cover layer27which partly covers the ground electrode4, the common electrode17, the individual electrode19, and the IC-connector connection electrode21is disposed on the substrate7. InFIG. 1, for convenience in explanation, a region where the cover layer27is formed is indicated by alternate long and short dashed lines.

The cover layer27is intended to protect the covered areas of the ground electrode4, the common electrode17, the individual electrode19, the IC-IC connection electrode26, and the IC-connector connection electrode21against oxidation caused by contact with air, or corrosion caused by adhesion of atmospheric water content, for example.

In order to provide more secure protection for the common electrode17and the individual electrode19, as shown inFIG. 2, it is preferable that the cover layer27is so formed as to overlie an end part of the protective layer25. The cover layer27can be formed from a resin material such for example as an epoxy resin or a polyimide resin using a thick-film forming technique such as the screen printing method.

The cover layer27is formed with an opening (not shown) for leaving the individual electrode19, the IC-IC connection electrode26, and the IC-connector connection electrode21connected to the driving IC11exposed, so that the wiring lines can be connected to the driving IC11through the opening. Moreover, the driving IC11is, in a state of being connected to the individual electrode19, the IC-IC connection electrode26, and the IC-connector connection electrode21, covered with a covering member29formed of resin such for example as an epoxy resin or a silicone resin for the sake of protection of the driving IC11and also protection of the area of connection between the driving IC11and the wiring lines. In the present embodiment, the covering member29is disposed so as to straddle over a plurality of driving ICs11. The height of the cover layer27from the substrate7can be determined as appropriate in accordance with the form of the thermal head X1, and, a desirable range of the height is from 200 to 500 μm.

As shown inFIG. 2, at that side of the cover layer27located toward the end face7aof the main surface (not shown) of the substrate7, the ends drawn from the different electrodes are exposed from an exposed area where the different electrodes are left exposed (not shown) so as to be electrically connected to the connector31.

The connector31is disposed on the substrate7, and, the connector pin8is electrically connected to the led-out ends of the different electrodes by an electrically-conductive member23. In the thermal head X1, the connector31is disposed at each of the opposite ends and the midportion of the thermal head X1in the main scanning direction. Exemplary of the electrically-conductive member23are solder and an anisotropic conductive adhesive obtained by blending conductive particles in an electrically insulating resin. Note that a Ni-, Au-, or Pd-plating layer (not shown) may be disposed between the electrically-conductive member23and the led-out ends of the different electrodes.

The thermal head X1is provided with a protecting member12which protects, at least partly, the connector31. The protecting member12is disposed so as to cover the connector pin8, part of the upper surface of the housing10, and part of the cover layer27, as well as to cover the exposed area completely when seen in a plan view.

The protecting member12can be formed of a thermosetting resin, a thermosoftening resin, an ultraviolet-curable resin, or a visible light-curable resin, for example. Moreover, in a case where the different electrodes need to be electrically independent of each other, it is preferable that the protecting member12has an electrically insulating property.

Moreover, the protecting member12covers the connector pin8of the connector31which assures the electrical conduction, and, preferably, the protecting member12is disposed also on part of the upper surface of the housing10. By doing so, the connector pin8can be entirely covered with the protecting member12, thereby assuring the electrical conduction more positively.

Referring toFIGS. 3 and 4, a projection portion2will be described in detail.FIG. 3shows the vicinity of the projection portion2in an enlarged manner, andFIG. 4is a conceptual diagram illustrating a condition of contact between a recording medium P and the covering member29, as well as the projection portion2. A solid line drawn inFIGS. 4(a) and 4(b)indicates a position of conveyance of the recording medium P in the present embodiment, whereas a broken line drawn inFIG. 4(b)indicates a position of conveyance of the recording medium P in a case where the projection portion2is assumed to be absent.

As shown inFIG. 3, the projection portion2is disposed at a center of the substrate7in the main scanning direction so as to lie in the second region R2. Moreover, the projection portion2is disposed in a position spaced downstream from the driving IC11in the conveying direction S of the recording medium P. Furthermore, the projection portion2is disposed on the second region R2closer to the heat generating portion9than the area where the driving IC is disposed.

The IC-connector connection electrode21and the IC-IC connection electrode26are arranged around the projection portion2, and thus the projection portion2is placed so as to be surrounded by the IC-connector connection electrode21and the IC-IC connection electrode26.

As shown inFIG. 4, a convexity6is disposed below the projection portion2, and, the cover layer27is situated over the convexity6. The cover layer27covers not only the convexity6, but also the vicinity of the convexity6. Thus, the projection portion2is composed of the convexity6and the cover layer27. Note that the convexity6is disposed so as not to make contact with the IC-connector connection electrode21and the IC-IC connection electrode26. That is, the convexity6is electrically isolated from the IC-connector connection electrode21and the IC-IC connection electrode26.

The convexity6can be formed of a material similar to the material constituting the thick electrode portion17d. Moreover, the convexity6can be formed by means of printing. Therefore, by forming the convexity6concurrently with the formation of the thick electrode portion17d, it is possible to achieve shortening of takt time, and thereby increase the manufacturing efficiency. Note that the convexity6may also be formed by raising part of the substrate7.

It is preferable that the height of the convexity6from the substrate7falls in the range of 15 to 30 μm. The projection portion2has a rectangular shape when seen in a plan view, and its height h3from the substrate7preferably falls in the range of 40 to 70 μm. Moreover, the projection portion2is preferably given a surface roughness greater than the surface roughness of other area of the cover layer27than the projection portion2. This makes it possible to render the recording medium P less slippery, and thereby improve the condition of intimate contact between the projection portion and the recording medium under conveyance.

A height h1of the covering member29from the substrate7in the first region R1is greater than a height h2of the covering member29from the substrate7in the second region R2. This is ascribable to the presence or absence of the driving IC11located in a lower part of the covering member29. Note that the height h1, h2of the covering member29from the substrate7refers to the level of the vertex of the covering member29situated above the driving IC11, namely the height of that part of the covering member which is contacted by the recording medium P from the substrate7.

It is preferable that the height h1of the covering member29from the substrate7falls in the range of 300 to 500 μm. Moreover, the height h2of the covering member29from the substrate7preferably falls in the range of 200 to 400 μm. This makes it possible to support the conveyance of the recording medium P.

In measurement of height from the substrate7, for example, with use of a contact type or non-contact type surface roughness meter, a distance from a reference point can be measured. For example, the vertex of the protuberant portion13bof the heat storage layer13can be defined as the reference point. The surface roughness of the projection portion2and that of the cover layer27can be also measured by a similar method.

Among various members constituting the thermal head X1, and, particularly among the members disposed on the substrate7, the driving IC11has a noticeably large size. Therefore, the level of the surface of that part of the thermal head X1which is provided with the driving IC11and the level of the surface of that part of the thermal head X1which is free of the driving IC1differ greatly from each other.

Also in the case where the covering member29is so disposed as to straddle over the plurality of driving ICs11as shown inFIG. 1, the first region R1is greater in height than the second region R2. The recording medium P is conveyed while making contact with the covering member29, and, in the first region R1, the recording medium P is maintained at a predetermined level under the support of the covering member29.

However, in a conventional thermal head devoid of the projection portion2, since the height h1, h2of the covering member29from the substrate7varies depending on the presence or absence of the driving IC11located in a lower part thereof, it follows that the condition of conveyance of the recording medium P in the first region R1differs from that in the second region R2. That is, in the second region R2, as indicated by the chain-dotted line shown inFIG. 4(b), the recording medium P may sag down, which leads to a difference in recording medium P-to-covering member29distance between the first region R1and the second region R2. Therefore, the first region R1and the second region R2differ from each other in the condition of conveyance of the recording medium P. This gives rise to the possibility of causing wrinkles in the recording medium P which is being carried over the second region R2.

In contrast, in the thermal head X1, the projection portion2is disposed on the second region R2closer to the heat generating portion9than the area where the driving IC11is disposed, and, the projection portion2can make contact with the recording medium P. Thus, as indicated by the solid line inFIG. 4(b), the projection portion2is able to lift up the sagging recording medium P. This makes it possible to restrain the recording medium P against sagging motion, and thereby render the condition of conveyance of the recording medium P approximately uniform, wherefore the possibility of causing wrinkles in the recording medium P can be decreased.

Moreover, since the recording medium P makes contact with the covering member29and the projection portion2, the recording medium P is supported at two points. Therefore, even if the covering member29and the projection portion2are subjected to a stress when pressed by the recording medium P, the stress can be dispersed.

Moreover, in the process of performing sputtering of the protective layer25, there may be a case where a plurality of thermal heads X1are stacked while being displaced from each other by a predetermined distance so that their protective layers25can be formed at one time. In this case, the projection portion2acts to decrease the possibility of causing damage to the electrodes and so forth due to the overlapping arrangement of the thermal heads X1. More specifically, at the time of stacking the thermal heads X1one upon another, by placing each thermal head X1on the projection portion2, a space can be formed between the stacked thermal heads X1. This space helps protect the electrodes and so forth.

Moreover, the projection portion2is placed in a position spaced downstream from the driving IC11in the conveying direction S of the recording medium P. Accordingly, the recording medium P is brought into contact with the projection portion2after making contact with the covering member29located above the driving IC11. Thus, the recording medium P can be stably supported by the covering member29, and also, the recording medium P in a state of sagging down in a region between the driving IC11and the heat generating portion9can be upheld at a predetermined level by the projection portion2. As a result, the recording medium P can be conveyed smoothly to the heat generating portion9.

Moreover, since the projection portion2is located between the covering member29and the heat generating portion9, it follows that the recording medium P is brought into contact with the projection portion2after making contact with the covering member29. Accordingly, the recording medium P which is being carried toward the heat generating portion9can be upheld at a predetermined level, with consequent accomplishment of smooth conveyance of the recording medium P to the heat generating portion9. In addition, the projection portion2ensures more stable conveyance of the recording medium P to the heat generating portion9.

The height h3of the projection portion2from the substrate7is shorter than the height h1, h2of the covering member29from the substrate7. Thus, the recording medium P is supported by the taller covering member29, thereby achieving stable conveyance of the recording medium P. This is because the covering member29is greater in volume and strength than the projection portion2.

Moreover, in the conveying direction S, the height h3of the projection portion2located on the downstream side from the substrate7is shorter than the height h2of the driving IC11located on the upstream side in the second region R2from the substrate7. Accordingly, also in the second region R2, the recording medium P can be supported by the covering member29, and the projection portion2is able to convey the recording medium P smoothly to the heat generating portion9.

Moreover, it is preferable that the distance between the projection portion2and the heat generating portion9is 0.3 to 0.8 time the distance between the covering member29and the heat generating portion9, and that the height h3of the projection portion2from the substrate7is 0.05 to 0.3 time the height h1, h2of the covering member29from the substrate7.

By fulfilling the above prescribed ranges, it is possible to suppress an excessive increase in the area of contact between the recording medium P and the projection portion2, and thereby permit adequate contact of the recording medium P with the projection portion2. Accordingly, conveyance of the recording medium P can be effected satisfactorily. Moreover, it is more preferable that the distance between the projection portion2and the heat generating portion9is 0.4 to 0.6 time the distance between the covering member29and the heat generating portion9, and that the height h3of the projection portion2from the substrate7is 0.1 to 0.2 time the height h1, h2of the covering member29from the substrate7.

The distance between the covering member29and the heat generating portion9refers to a distance between the covering member29and the heat generating portion9arranged on a straight line extending along the sub scanning direction, and more specifically a distance between a side of the covering member29nearest the heat generating portion9and a virtual line extending along the main scanning direction while passing through the center of the heat generating portion9.

For example, the condition of contact of the covering member29and the projection portion2with the recording medium P can be checked by the following method. To begin with, a coating of paint is applied to the surfaces of the covering member29and the projection portion2, and then conveyance of the recording medium P is effected. Whether or not the covering member29and the projection portion2have made contact with the recording medium P can be checked by examining the presence or absence of the paint coating on the surfaces of the covering member29and the projection portion2.

The projection portion2is, as exemplified, composed of the convexity6and the cover layer27, but it is not so limited. For example, the projection portion2may be composed solely of the convexity6without providing the cover layer27over the convexity6. In another alternative, the projection portion2may be formed by laminating several cover layers27one after another. In this case, the projection portion2can be composed solely of the cover layer27.

Next, a thermal printer Z1will be described with reference toFIG. 5.FIG. 5is a view showing the general features of the thermal printer Z1, wherein the thermal head X1is illustrated as being larger than its actual size.

As shown inFIG. 5, the thermal printer Z1of the present embodiment comprises: the thermal head X1thus far described; a conveyance mechanism40; a platen roller50; a power-supply device60; and a control device70. The thermal head X1is attached to a mounting surface80aof a mounting member80disposed in a casing (not shown in the drawing) for the thermal printer Z1.

The conveyance mechanism40comprises: a driving section (not shown); and conveying rollers43,45,47, and49. The conveyance mechanism40is intended to convey the recording medium P such as thermal paper or ink-transferable image-receiving paper in a direction indicated by arrow S shown in the drawing so that the recording medium P can be conveyed onto the protective layer25situated on the plurality of heat generating portions9of the thermal head X1. The driving section has the function of driving the conveying rollers43,45,47, and49, and, for example, a motor may be used as the driving section. The conveying roller43,45,47,49can be constructed of, for example, a cylindrical shaft body43a,45a,47a,49aformed of metal such as stainless steel covered with an elastic member43b,45b,47b,49bformed of butadiene rubber or the like. Although not shown in the drawing, in a case where the recording medium P is ink-transferable image-receiving paper or the like, an ink film is interposed between the recording medium P and the heat generating portion9of the thermal head X1, and thus the recording medium P and the ink film are conveyed together.

The platen roller50has the function of pressing the recording medium P onto the protective layer25situated on the heat generating portion9of the thermal head X1. The platen roller50is disposed so as to extend along a direction perpendicular to the conveying direction S of the recording medium P, and is fixedly supported at its ends so that it is able to rotate while pressing the recording medium P onto the heat generating portion9. For example, the platen roller50can be constructed of a cylindrical shaft body50aformed of metal such as stainless steel covered with an elastic member50bformed of butadiene rubber or the like.

The power-supply device60has the function of supplying electric current for allowing the heat generating portion9of the thermal head X1to generate heat, as well as electric current for operating the driving IC11. The control device70has the function of feeding a control signal for controlling the operation of the driving IC11to the driving IC11in order for the heat generating portions9of the thermal head X1to generate heat in a selective manner.

In the thermal printer Z1, as shown inFIG. 5, the recording medium P is conveyed onto the heat generating portions9of the thermal head X1by the conveyance mechanism40while being pressed onto the heat generating portions9by the platen roller50, and, the heat generating portions9are 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 a case where the recording medium P is image-receiving paper or the like, printing is performed on the recording medium P by effecting thermal transfer of the ink of an ink film (not shown) which is being conveyed together with the recording medium P onto the recording medium P.

A thermal head X2in accordance with a second embodiment will be described with reference toFIG. 6.FIG. 6is a plan view showing an electrode pattern of the thermal head. The diagrammatic representations of the protective film, the cover layer, and the connector are omitted, and, the covering member29is indicated by alternate long and short dashed lines. InFIG. 6, except for a projection portion102, the other constituent components are similar to those of the foregoing embodiment, and thus the description thereof will be omitted. In what follows, similar reference characters are used to denote like members.

The projection portion102comprises a first projection portion102aand a second projection portion102b. The first projection portion102ais located at a center of the thermal head X2in the main scanning direction, and has the same configuration as that of the projection portion2of the thermal head X1. The second projection portion102bis located at each end of the thermal head X2in the main scanning direction. The second projection portion102bis formed integrally with a thick electrode portion117dprovided on a sub wiring portion17b.

In this construction, printing is performed on the recording medium P in a state of being pressed against the thermal head X2by the platen roller50(refer toFIG. 5). The platen roller50exhibits a greater pressing force at its ends than at other area in the main scanning direction, because the shaft body50aof the platen roller50is fixed at its ends in the main scanning direction. Therefore, chances of occurrence of wrinkles in the recording medium P are increased in the second region R2located at each end of the thermal head X2in the main scanning direction.

However, in the thermal head X2, The projection portion102comprises the first projection portion102aand the second projection portion102b. Since the second projection portion102bacts to support the recording medium P so as to restrain the recording medium P against sagging motion, it is possible to decrease the possibility of causing wrinkles in the recording medium P. Moreover, the second projection portion102balso acts to lessen the pressing force of the platen roller50, wherefore the pressing force distribution in the main scanning direction can be rendered approximately uniform.

The first projection portion102ais placed in a region formed on the substrate7by extending the region bearing an array of the heat generating portions9in the sub scanning direction S. On the other hand, the second projection portion102bis placed in a region other than the region formed on the substrate7by extending the region bearing an array of the heat generating portions9in the sub scanning direction S. Therefore, in the main scanning direction, the distance between the second projection portion102band the heat generating portion9is greater than the distance between the first projection portion102aand the heat generating portion9.

The thermal head X2is configured so that a distance Lb between the heat generating portion9and the second projection portion102bin the sub scanning direction is shorter than a distance La between the heat generating portion9and the first projection portion102ain the sub scanning direction. Accordingly, the second projection portion102bis located close to the heat generating portion9, and is therefore able to support the recording medium P which is being carried in the vicinity of the heat generating portion9. In this way, the recording medium P can be conveyed smoothly to the heat generating portion9.

It is preferable that the distance La between the heat generating portion9and the first projection portion102afalls in the range of 3 to 5 mm, and that the distance Lb between the heat generating portion9and the second projection portion102bfalls in the range of 2.5 to 4.5 mm. This makes it possible to support the recording medium P which is being conveyed in the vicinity of the heat generating portion9.

Moreover, the thermal head X2is configured so that a width Wb of the second projection portion102bis greater than a width Wa of the first projection portion102a. This makes it possible to increase the area of the second projection portion102bwhen seen in a plan view which is subjected to a great pressing force exerted by the platen roller50. Accordingly, the second projection portion102bis able to lessen the pressing force of the platen roller50, wherefore the possibility of causing wrinkles in the recording medium P can be decreased. Note that the width Wb of the second projection portion102bcoincides with the length of the second projection portion102bin the main scanning direction, and the width Wa of the first projection portion102acoincides with the length of the first projection portion102ain the main scanning direction.

It is preferable that the width Wa falls in the range of 0.5 to 1.5 μm, and that the width Wb falls in the range of 2 to 6 μm. This makes it possible to suppress variations in the condition of conveyance of the recording medium P in the main scanning direction, and thereby decrease the possibility of causing wrinkles in the recording medium P.

Moreover, the thermal head X2is configured so that the length of the second projection portion102bin the sub scanning direction is greater than the length of the first projection portion102ain the sub scanning direction. This makes it possible to increase the area of the second projection portion102bwhen seen in a plan view which is subjected to a great pressing force exerted by the platen roller50. Accordingly, the second projection portion102bis able to lessen the pressing force of the platen roller50, wherefore the possibility of causing wrinkles in the recording medium P can be decreased.

It is preferable that the length of the second projection portion102bfalls in the range of 1.5 to 2.5 μm, and that the length of the first projection portion102afalls in the range of 0.5 to 1.5 μm. This makes it possible to suppress variations in the condition of conveyance of the recording medium P in the main scanning direction, and thereby decrease the possibility of causing wrinkles in the recording medium P.

It is noted that the distance La between the heat generating portion9and the first projection portion102ain the sub scanning direction may be shorter than the distance Lb between the heat generating portion9and the second projection portion102bin the sub scanning direction. In fact, in the process of forming various electrode patterns, there may be a case where a region capable of placement of the first projection portion102ais smaller than a region capable of placement of the second projection portion102b.

In this case, the first projection portion102acannot be made larger than the second projection portion102b, wherefore the volume of an Ag paste forming the first projection portion102ais smaller than the volume of an Ag paste forming the second projection portion102b.

Accordingly, the first projection portion102ais less heat storable than the second projection portion102b, and can therefore be placed closer to the heat generating portion9. As a result, the first projection portion102ais able to convey the recording medium P smoothly to the heat generating portion9.

Moreover, in the thermal head X2, the width Wa of the first projection portion2may be shorter than the width Wb of the second projection portion2. In this case, the second projection portion2is able to lessen the pressing force of the platen roller50effectively, wherefore the possibility of causing wrinkles in the recording medium P can be decreased.

A thermal head X3in accordance with a third embodiment will be described with reference toFIG. 7.

When the thermal head X3is seen in a plan view, a projection portion202has a triangular shape. Moreover, in a plan view, two oblique sides thereof define inclined parts214. The projection portion202is placed, with its base located on the upstream side in the conveying direction S. That is, the projection portion202is so shaped that its area when seen in a plan view becomes narrower gradually toward the downstream side in the conveying direction S. In other words, the projection portion202is so shaped that the area of contact with the recording medium P becomes narrower gradually in the same direction.

Thus, the projection portion202is so shaped that the area of contact with the recording medium P becomes narrower gradually toward the downstream side in the conveying direction S. This makes it possible to lessen a frictional force developed between the recording medium P and the projection portion202, and thereby achieve smooth conveyance of the recording medium.

In particular, since the projection portion202has a triangular shape, and the two oblique sides thereof define the inclined parts214, it is possible to achieve a gradual decrease in the area of contact between the recording medium P and the projection portion202. Accordingly, the frictional force developed between the recording medium P and the projection portion202can be reduced gradually without causing a sharp decrease in the area of contact between the recording medium P and the projection portion202. This helps decrease the possibility of occurrence of a sticking phenomenon.

It is sufficient that, when the substrate7is seen in a plan view, the inclined part214is inclined with respect to the sub scanning direction S, and, the angle which the inclined part214forms with the conveying direction S preferably falls in the range of 40 to 140°. Moreover, by configuring the projection portion202to have a triangular shape when seen in a plan view, it is possible to make efficient use of a space between the IC-IC connection electrodes26, and thereby achieve downsizing of the thermal head X3.

Referring toFIG. 7(b), a modified example of the thermal head X3will be described. When the thermal head X3is seen in a plan view, a projection portion302has a C-shape which is obtained by cutting a small trapezoid from a large trapezoid. The projection portion302comprises three sides, namely two oblique sides314and one side315. A space surrounded by the two oblique sides314and the one side315is free of the projection portion302.

The one side315is disposed along the main scanning direction, and, the inclined part314is located at each end of the one side315. The angle which one of the inclined parts314forms with the one side315and the angle which the other one of the inclined parts314forms with the one side315are equal to each other. Accordingly, the configuration of the projection portion302is line-symmetrical about a centerline of the projection portion302in the main scanning direction.

The projection portion302is configured to support the recording medium P in a manner such that the sagging recording medium P can be upheld gradually from each end in the main scanning direction by the projection portion302. Accordingly, as conveyance of the recording medium P proceeds, a central part of the recording medium P in the main scanning direction in a state of sagging down most deeply can be gradually lifted up by the projection portion302. This makes it possible to smooth wrinkles while decreasing the possibility of occurrence of a large stress in the recording medium P without rapid elimination of wrinkles.

It is possible to dispose the IC-IC connection electrode26in the projection portion302-free space surrounded by the two oblique sides314and the one side315. That is, by providing the IC-IC connection electrode26in the space surrounded by the two oblique sides314and the one side315, it is possible to increase the area of the IC-IC connection electrode26, and thereby decrease interconnection resistance.

A thermal head X4in accordance with a fourth embodiment will be described with reference toFIG. 8.

The thermal head X4includes a third projection portion402a, a fourth projection portion402b, and a fifth projection portion402c. Moreover, the projection portion402is disposed on each of the IC-IC connection electrodes26that are electrically independent of each other.

In the projection portion402, the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care arranged sequentially in the order named from the upstream side in the conveying direction S. In a plan view, the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care rectangular-shaped and have substantially the same size.

In the projection portion402, the recording medium P is brought into contact with the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402cone after another in the order named. It is therefore possible to smooth wrinkles gradually from the third projection portion402atoward the fifth projection portion402c. Moreover, the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care each disposed on the IC-IC connection electrode26, wherefore the current carrying capacity of the IC-IC connection electrode26can be increased.

Moreover, the recording medium P is brought into contact with the projection portion402several times, wherefore a stress developed between the recording medium P and the projection portion402can be dispersed. Furthermore, since the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care disposed on their respective different IC-IC connection electrodes26, it follows that the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care thermally independent of each other.

Accordingly, it is possible to increase the quantity of heat absorbed into the projection portion402from the recording medium P when the recording medium P is brought into contact with the projection portion402. That is, in the case where the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care disposed on their respective different IC-IC connection electrodes26, as compared with a case where the recording medium is brought into contact with the projection portion402in a single-piece form, improved heat dissipation capability can be attained.

While the thermal head X3is, as exemplified, configured so that the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402care disposed on their respective different IC-IC connection electrodes26, alternatively, the third projection portion402a, the fourth projection portion402b, and the fifth projection portion402cmay be disposed on a single IC-IC connection electrode26. Also in this case, the current carrying capacity of the IC-IC connection electrode26can be increased.

Referring toFIG. 8(b), a modified example of the thermal head X4will be described. A projection portion502comprises a third projection portion502a, a fourth projection portion502b, and a fifth projection portion502cthat are arranged sequentially in the order named from the upstream side in the conveying direction S. In a plan view, the third projection portion502a, the fourth projection portion502b, and the fifth projection portion502care arranged in order of decreasing area.

Thus, the thermal head is configured so that the area of contact between the recording medium P and the projection portion502becomes smaller gradually from the upstream side in the conveying direction S. In this construction, the third projection portion502awhere the recording medium P is most strongly pressed against the projection portion502, has the largest area of contact with the recording medium, and, the fourth projection portion502band the fifth projection portion502cact to disperse a pressing force which diminishes gradually as the recording medium moves forward in the conveying direction S. As a result, the contacting area is adjusted in conformity with the pressing force exerted on the recording medium P, wherefore the recording medium P can be fed smoothly to the heat generating portion9.

Moreover, in this construction, the fifth projection portion502chas the smallest area of contact with the recording medium P, wherefore the frictional force developed between the fifth projection portion502cand the recording medium P can be kept small. Accordingly, the recording medium P can be separated from the fifth projection portion502csmoothly.

A thermal head X5implemented as the fifth embodiment will be described with reference toFIGS. 9 and 10.

The thermal head X5differs from the thermal heads X1to X4in that a ground electrode604is disposed along the end face7aof the substrate7so as to be surrounded by the end face7aof the substrate7, an IC-connector connection electrode521, the individual electrode19, and the IC-IC connection electrode26.

A convexity606is disposed on the ground electrode604. A ground electrode604disposed below the convexity606is electrically connected to the ground electrode604extending along the end face7aof the substrate7via a coupling electrode614. The convexity606has a trapezoidal shape when seen in a plan view, and is made of the earlier described Ag paste. Therefore, the convexity606has electrical conductivity, and is maintained at a ground potential.

The convexity606is disposed so as to protrude from the cover layer27, and the upper surface of the convexity606is left exposed from the cover layer27. That is, the projection portion602is configured to have the exposed convexity606. The recording medium P under conveyance is brought into contact with the upper surface of the convexity606left exposed from the cover layer27.

Thus, even if static electricity is generated in the recording medium P, it is possible to eliminate the static electricity through the projection portion602maintained at a ground potential that is contacted by the recording medium P. This makes it possible to decrease the possibility of causing electrostatic damage to the heat generating portion9or the recording medium P.

Moreover, it is advisable to apply a plating layer formed of Au, Ni, Pd, or the like onto the convexity606for suppressing corrosion of the convexity606. This helps enhance the corrosion resistance of the convexity606.

Furthermore, an electrically-conductive protective film (not shown) may be provided on the convexity606. In this case, the convexity606and the electrically-conductive protective film constitute the projection portion602.

While several embodiments of the invention have been described heretofore, it should be understood that the application of the invention is not limited to the embodiments thus far described, and that many modifications and variations of the invention are possible within the scope of the invention. For example, the thermal printer Z1employing the thermal head X1according to the first embodiment has been shown herein, but this does not suggest any limitation, and thus the thermal heads X2to X5may be adopted for use in the thermal printer Z1. Moreover, the thermal heads X1to X5according to several embodiments may be used in combination.

Moreover, the process of printing an Ag paste has been described as a way to form the thick electrode portion17dand the convexity2following the formation of various electrodes, but this does not suggest any limitation. For example, it is possible to print an Ag paste in a predetermined position prior to the formation of the electrical resistance layer15, and subsequently form the electrical resistance layer15and various electrodes.

Moreover, in the thermal head X1, the protuberant portion13bis formed in the heat storage layer13, and the electrical resistance layer15is formed on the protuberant portion13b, but this does not suggest any limitation. For example, the heat generating portion9of the electrical resistance layer15may be placed on the underlayer portion13bof the heat storage layer13without forming the protuberant portion13bin the heat storage layer13. In another alternative, the heat storage layer13may be formed over the entire area of the upper surface of the substrate7. Also in this case, the protecting member12finds its way through the second exposed part16to the surface of the heat storage layer13, wherefore the strength of adhesion between the substrate7and the protecting member12can be enhanced.

The protecting member12and the covering member29which covers the driving IC11may be formed of the same material. In this case, the covering member29and the protecting member12can be formed together at one time by performing printing also on the protecting member12-forming region during the printing process for forming the covering member29. Moreover, while the covering member29is, as exemplified, disposed so as to straddle over a plurality of driving ICs11, the covering member29may be provided for each of the driving ICs on an individual basis. In this case, the difference in height between the first region R1and the second region R2becomes more noticeable, wherefore it is possible to utilize the invention efficiently.

Moreover, while the flat-type head in which the heat generating portion9is disposed on the main surface of the substrate7has been shown by way of exemplification, the invention is applicable to an edge-type head in which the heat generating portion9is disposed on the end face of the substrate7. Furthermore, the invention may adopt a turned-back pattern in which adjacent heat generating portions9are connected to each other by a turned-back electrode (not shown).

Moreover, the driving IC11is, as exemplified, flip-chip mounted on the substrate7, but this does not suggest any limitation. For example, the driving IC11may be disposed on the substrate7so as to be electrically connected to various electrodes by means of wire bonding. Moreover, the head substrate3may be electrically connected to an external substrate without providing the connector31, and thus, also in a case where an external substrate having the driving IC11disposed on an upper surface thereof is abutted on the head substrate3so that the head substrate3and the external substrate can be juxtaposed, and then the driving IC11is electrically connected to various electrodes by means of wire bonding, it is possible to utilize the invention efficiently.

REFERENCE SIGNS LIST

X1-X5: Thermal head

Z1: Thermal printer

R1: First region

R2: Second region

3: Head substrate

9: Heat generating portion

11: Driving IC

13: Heat storage layer

15: Electrical resistance layer

27: Cover layer

29: Covering member