Patent Application
20200391518
The present disclosure relates to thermal printheads.
JP-A-2007-269036 discloses an example of a conventional thermal printhead. The thermal printhead disclosed in this document includes a number of heating elements aligned in a primary scanning direction on a head substrate. Each of the heating elements is provided by forming, on a resistor layer, which is formed on the head substrate via a glaze layer, an upstream electrode layer and a downstream electrode layer so that the corresponding ends of the two electrode layers face each other with a portion of the resistor layer exposed between them. Flowing a current between the upstream electrode layer and the downstream electrode layer causes the exposed portion of the resistor layer (i.e., the heating element) to be heated by Joule effect.
The thermal printhead disclosed in the above document also includes a convex glaze part as a heat storage part extending in the primary scanning direction, and the heating elements are arranged on the top of the convex glaze part for realizing efficient heat transfer to a print medium and the resulting high-speed printing. Such a convex glaze part also allows a platen roller to reliably come into contact with each heating element, which is useful for improving the print quality.
The convex glaze part described above is typically formed by applying glass paste by screen printing and then baking the glass paste. However, with this method for forming a convex glaze part, the film thickness obtained by the printing process may vary among different products or different locations along the primary scanning direction. This has made it difficult to provide a uniform quality among different products or a uniform printing quality among different locations in a thermal printhead.
The present disclosure has been proposed in view of these circumstances. It is therefore an object of the present disclosure to provide a thermal printhead that allows a heat storage part to be formed below heating elements so as to provide a uniform heat storage performance.
To solve the above problems, the present disclosure takes the following technical measures.
According to a first aspect of the present disclosure, there is provided a thermal printhead comprising: a substrate having an obverse surface; a projection formed on the obverse surface and extending in a primary scanning direction; a plurality of heating elements arranged in the primary scanning direction on a top of the projection; a groove dented from the top of the projection and extending in the primary scanning direction; and a heat storage member filling at least an opening of the groove.
According to a second aspect of the present disclosure, there is provided a method for manufacturing a thermal printhead that comprises: a substrate having an obverse surface; a projection formed on the obverse surface and extending in a primary scanning direction; a plurality of heating elements arranged in the primary scanning direction on a top of the projection; a groove dented from the top of the projection and extending in the primary scanning direction; and a heat storage member filling at least an opening of the groove, wherein the projection includes a top surface and a pair of inclined outer surfaces spaced apart from each other via the top surface in a secondary scanning direction, the inclined outer surfaces being inclined with respect to the obverse surface, and the groove includes a pair of inclined inner surfaces each connected to the opening and inclined with respect to the obverse surface. In an embodiment, the method comprises: preparing a substrate material made of a single-crystal semiconductor material; and performing anisotropic etching to a predetermined region of an obverse surface of the substrate material to form the projection and the groove.
According to a third aspect of the present disclosure, there is provided a method for manufacturing a thermal printhead that comprises: a substrate having an obverse surface; a projection formed on the obverse surface and extending in a primary scanning direction; a plurality of heating elements arranged in the primary scanning direction on a top of the projection; a groove dented from the top of the projection and extending in the primary scanning direction; and a heat storage member filling at least an opening of the groove, wherein the projection includes a top surface, a pair of first inclined outer surfaces and a pair of second inclined outer surfaces, the second inclined outer surfaces being spaced apart from each other via the top surface in a secondary scanning direction, the first inclined outer surfaces being spaced apart from each other via the top surface and the second inclined outer surfaces in the secondary scanning direction, wherein an inclination angle of the first inclined outer surfaces with respect to the obverse surface is greater than an inclination angle of the second inclined outer surfaces with respect to the obverse surface, wherein the groove includes a pair of first inclined inner surfaces and a pair of second inclined inner surfaces, the first inclined inner surfaces being connected to the opening via the second inclined inner surfaces, the second inclined inner surfaces being connected directly to the opening, an inclination angle of the first inclined inner surfaces with respect to the obverse surface being greater than an inclination angle of the second inclined inner surfaces with respect to the obverse surface. In an embodiment, the method comprises: preparing a substrate material made of a single-crystal semiconductor material; performing anisotropic etching to a predetermined region of an obverse surface of the substrate material to form an intermediate projection and an intermediate groove, where the intermediate projection has surfaces to become the first inclined outer surfaces, and the intermediate groove has surfaces to become the first inclined inner surfaces; and performing anisotropic etching to the intermediate projection and the intermediate groove so as to obtain the projection with the first inclined outer surfaces, the second inclined outer surfaces and the top surface and also to obtain the groove with the first inclined inner surfaces and the second inclined inner surfaces.
Other features and advantages of the present disclosure will become more apparent from the detailed description given below with reference to the attached drawings.
Preferred embodiments of the present disclosure are described below with reference to the accompanying drawings.
The head substrate 1 is in the form of an elongated rectangle as viewed in plan, having a length along the primary scanning direction x and a width along the secondary scanning direction y. The size of the head substrate 1 may vary, but may be 50 to 150 mm in the primary scanning direction x, 2.0 to 5.0 mm in the secondary scanning direction y, and 725 μm in the thickness direction z, for example. Note that in the description given below, the side closer to the driver ICs 7 in the secondary scanning direction y is referred to as “upstream”, whereas the side farther from the driver ICs 7 in the secondary scanning direction y is referred to as “downstream”.
In the present embodiment, the head substrate 1 is made of a single-crystal semiconductor material. As a single-crystal semiconductor material, Si may be suitably used. The head substrate 1 has an obverse surface 11, which has a projection 13 formed integrally on its downstream side and extending in the primary scanning direction x. The projection 13 has a uniform cross section along the primary scanning direction x.
As shown in
The groove 14 in the top surface 130 of the projection 13 is filled with a heat storage member 15. The heat storage member 15 may be made of SiO2, for example. According to the manufacturing method described later, the heat storage member 15 is formed by applying SiO2 in a molten state into the groove 14 with a dispenser and then allowing it to solidify at room temperatures. In the present embodiment, the heat storage member 15 fills to the bottom of the groove 14 and gently rises to be exposed through the opening 140 of the groove 14.
The obverse surface 11 of the head substrate 1 and the projection 13 having the groove 14 filled with the heat store member 15 are covered with an insulating layer 19, a resistor layer 4, an electrode layer 3 and a protective layer 2, which are formed in the mentioned order.
The insulating layer 19 is formed over the obverse surface 11 and the projection 13 of the head substrate 1. Specifically, the insulating layer 19 is formed to cover the region where the resistor layer 4 and the electrode layer 3, which will be described later, are to be formed. The insulating layer 19 is made of an insulating material such as SiO2, SiN or TEOS (tetraethyl orthosilicate), for example. In the present embodiment, TEOS is suitably used. The thickness of the insulating layer 19 is not limited and may be 5 to 15 μm or preferably 5 to 10 μm.
The resistor layer 4 covers the insulating layer 19 and extends over the obverse surface 11 and the projection 13. The resistor layer 4 is made of TaN, for example. The thickness of the resistor layer 4 is not limited and may be 0.02 to 0.1 μm, or preferably, about 0.08 μm, for example. The resistor layer 4 provides a plurality of heating elements 41 at its exposed portions that are not covered with the electrode layer 3, which will be described later. Each of the heating elements 41, which are aligned in the primary scanning direction x, is formed in a portion or the entirety of the width H3 of the top surface 130 of the projection 13 in the secondary scanning direction y. The portions of the resistor layer 4 that provide the heating elements 41 are spaced apart from each other in the primary scanning direction x so that the heating elements 41 can be driven individually.
The electrode layer 3 includes a plurality of individual electrode layers 31 formed in the upstream area of the head substrate 1, and a common electrode layer 32 formed in the downstream area of the head substrate 1. Each of the individual electrode layers 31 is in the form of a strip extending generally in the secondary scanning direction y and has a downstream end located at an appropriate position on the projection 13. Each individual electrode layer 31 has an upstream end formed with an individual pad 311. The individual pads 311 are connected to the driver ICs 7 on the connecting substrate 5 with wires 61. The conmon electrode layer 32 has a plurality of teeth 324 and a common part 323 that connect the teeth 324 to each other. The common part 323 extends along the downstream edge of the head substrate 1 in the primary scanning direction x. The teeth 324 are in the form of strips branching from the conmon part 323 and extending in the secondary scanning direction y. Each of the teeth 324 has an upstream end located at an appropriate position on the projection 13 and faces the downstream end of a corresponding individual electrode layer 31 with a predetermined gap between them. As seen from
The resistor layer 4 and the electrode layer 3 are covered with the protective layer 2. The protective layer 2 is made of an insulating material such as SiO2, SiN, SiC, or AIN. The protective layer may have a thickness of 1.0 to 10 μm, for example.
As shown in
The connecting substrate 5 is arranged adjacent to and on the upstream side of the head substrate 1 in the secondary scanning direction y. The connecting substrate 5 may be e.g. a printed circuit board, on which the driver ICs 7 and the connector 59 are mounted. As viewed in plan, the connecting substrate 5 is in the form of a rectangle elongated in the primary scanning direction x.
The driver ICs 7 on the connecting substrate 5 energize the plurality of heating element 41 individually. The driver ICs 7 and the individual pads 311 of the individual electrode layers 31 are connected to each other with a plurality of wires 61. The driver ICs 7 are also connected to the wiring pattern on the connecting substrate 5 with wires 62. Printing signals transmitted from the outside through the connector 59 are inputted to the driver ICs 7. The heating elements 41 are individually energized in accordance with the printing signals to be selectively heated.
The driver ICs 7 and the wires 61 and 62 are covered with protective resin 78 that spreads over the head substrate 1 and the connecting substrate 5. The protective resin 78 may be a black insulating resin such as epoxy resin.
The heat sink 8 supports the head substrate 1 and the connecting substrate 5 and dissipates a portion of the heat generated by the heating elements 41 to the outside. The heat sink 8 may be made of a metal such as aluminum.
A method for manufacturing the thermal printhead A1 is described below with reference to
First, a substrate material 1A is prepared, as shown in
Next, with the obverse surface 11A covered with an appropriate masking layer, anisotropic etching using KOH, for example, is performed to form a projection 13 and a groove 14 each extending in the primary scanning direction x with a uniform cross section, as shown in
Next, the groove 14 is filled with a heat storage member 15, as shown in
Next, an insulating layer 19 is formed, as shown in
Next, a resistor film 4A is formed, as shown in
Next, a conductive film 3A is formed, as shown in
Next, as shown in
Next, a protective layer 2 is formed. Specifically, the protective layer 2 may be formed by depositing SiN and SiC by CVD on the insulating layer 19, the electrode layer 3 and the resistor layer 4. The protective layer 2 is then partially removed by e.g. etching to form the pad opening 21. Thereafter, attaching the head substrate 1 and the connecting substrate 5 to the heat sink 8, mounting the driver ICs 7 to the connecting substrate 5, bonding the wires 61 and 62, and forming the protective resin 78 are performed to provide the thermal printhead A1 shown in
The advantages of the thermal printhead A1 according to the first embodiment are described below.
Since the heating elements 41 are arranged near the top surface of the projection 13 formed on the head substrate 1, a print medium is reliably pressed against the heating elements 41 by the platen roller 91. Moreover, the projection 13 is formed by performing anisotropic etching to a single-crystal semiconductor material so that the projection 13 has a uniform cross section along the primary scanning direction x. Thus, the pressure exerted on the print medium when the print medium is pressed against the heating elements 41 is uniform along the primary scanning direction x. These hold true for the head substrates 1 of various production lots, which leads to improved printing quality.
The Si wafer, which is used as the material for the head substrate 1, has a relatively high thermal conductivity as compared with insulating materials such as Si02. Hence, if no measures are taken, heat generated by the heating elements 41 may unduly be conducted to the heat sink 8, which is not suitable for high-speed printing application. In the projection 13 of the thermal printhead A1, however, the heat storage member 15 arranged directly below the heating elements 41 reduces conduction of heat generated by the heating elements 41 to the heat sink 8, which contributes to ensuring high-speed printing. Moreover, the groove 14, in which the heat storage member 15 is arranged, is also formed by performing anisotropic etching to a single-crystal semiconductor material to have a uniform cross section along the primary scanning direction x. Thus, uniform heat storage performance by the heat storage member 15 is provided along the primary scanning direction x. This also leads to improved printing quality.
In the present embodiment, the projection 13 of the head substrate 1 has a top surface 130, a pair of second inclined outer surfaces 132 connected to the opposite edges of the top surface 130 in the secondary scanning direction y, and a pair of first inclined outer surfaces 131 connected to the respective outer edges of the second inclined outer surfaces 132 in the secondary scanning direction y and reaching the obverse surface 11. The paired first inclined outer surfaces 131 are flat surfaces inclined so as to become lower as proceeding away from the top surface 130 in the secondary scanning direction y, and their inclination angle α1 with respect to the obverse surface 11 may be 50 to 60 degrees, for example. The paired second inclined outer surfaces 132 are also flat surfaces inclined so as to become lower as proceeding away from the top surface 130 in the secondary scanning direction y, and their inclination angle α2 with respect to the obverse surface 11 may be 25 to 35 degrees, for example. In the present embodiment again, the projection 13 is formed to have a uniform cross section along the primary scanning direction x.
In the present embodiment, the groove 14 formed in the top surface 130 of the projection 13 has a pair of second inclined inner surfaces 142 connected to the opposite edges of the opening 140 in the secondary scanning direction y, and a pair of first inclined inner surfaces 141 connected to the second inclined inner surfaces 142 on the side closer to the center of the top surface 130 in the secondary scanning direction y. The paired second inclined inner surfaces 142 are flat surfaces inclined so as to become lower as proceeding toward the center of the top surface 130 in the secondary scanning direction y, and their inclination angle β2 with respect to the obverse surface 11 maybe equal to that of the second inclined outer surfaces 132, which may be 25 to 35 degrees, for example. The paired first inclined inner surfaces 141 are also flat surfaces inclined so as to become lower as proceeding toward the center of the top surface 130 in the secondary scanning direction y, and their inclination angle β1 with respect to the obverse surface 11 may be equal to that of the first inclined outer surfaces 131, which may be 50 to 60 degrees, for example. In the present embodiment again, the groove 14 is formed to have a uniform cross section along the primary scanning direction x.
The groove 14 in the projection 13 is filled with a heat storage member 15, with a hollow portion 16 left at the bottom. The heat storage member 15 may be made of SiO2, for example. The heat storage member 15 gently rises to be exposed through the opening 140 of the groove 14.
Similarly to the first embodiment, the obverse surface 11 of the head substrate 1 and the projection 13 having the groove 14 filled with the heat store member 15 are covered with an insulating layer 19, a resistor layer 4, an electrode layer 3 and a protective layer 2, which are formed in the mentioned order.
The connecting substrate 5 arranged adjacent to the head substrate 1 and the heat sink 8 on which the head substrate 1 and the connecting substrate 5 are mounted have the same configuration as that in the first embodiment.
Next, a method for manufacturing the thermal printhead A2 according to the second embodiment is described with reference to
First, a substrate material 1A is prepared, as shown in
Next, with the obverse surface 11A covered with an appropriate masking layer, anisotropic etching using KOH, for example, is performed to form an intermediate projection 13A and an intermediate groove 14A each extending in the primary scanning direction x with a uniform cross section, as shown in
Then, anisotropic etching using e.g. TMAH is performed to form a pair of second inclined outer surfaces 132 to the intermediate projection 13A and a pair of second inclined inner surfaces 142 to the intermediate groove 14A, as shown in
Next, the groove 14 is filled with a heat storage member 15 so that a hollow portion 16 is left at the bottom. For this purpose, a resist material 16A is applied to the bottom of the groove 14, as shown in
Next, an insulating layer 19 is formed, as shown in
Next, a resistor film 4A is formed, as shown in
Next, a conductive film 3A is formed, as shown in
Next, as shown in
Next, a protective layer 2 is formed. Specifically, the protective layer 2 may be formed by depositing SiN and SiC by CVD on the insulating layer 19, the electrode layer 3 and the resistor layer 4. The protective layer 2 is then partially removed by e.g. etching to form the pad opening 21. Thereafter, attaching the head substrate 1 and the connecting substrate 5 to the heat sink 8, mounting the driver ICs 7 to the connecting substrate 5, bonding the wires 61 and 62, and forming the protective resin 78 are performed to provide the thermal printhead A2 shown in
The thermal printhead A2 according to the second embodiment have the same advantages as those described above as to the thermal printhead A1 according to the first embodiment.
Additionally, in the thermal printhead A2 of the present embodiment, each inclined outer side (or surface) of the projection 13 is made up of a first inclined outer surface 131 and a second inclined outer surface 132 that have different inclination angles. This configuration allows a print medium pressed against the projection 13 by the platen roller 91 to be transferred more smoothly in the secondary scanning direction y without being caught on the projection 13.
Moreover, in the thermal printhead A2 of the present embodiment, the hollow portion 16 below the heat storage member 15 in the groove 14 enhances heat storage directly below the heating elements 41. This saves electric power used for causing the heating elements 41 to generate heat and makes the thermal printhead suitable for high-speed printing application.
In the present embodiment, similarly to the second embodiment, the projection 13 on the head substrate 1 has a pair of second inclined outer surfaces 132 connected to the opposite edges of the top surface 130 in the secondary scanning direction y, and a pair of first inclined outer surfaces 131 connected to the respective outer edges of the second inclined outer surfaces 132 in the secondary scanning direction y and reaching the obverse surface 11. The groove 14 has only a pair of inclined inner surfaces 142. The inclination angle α1 of the paired first inclined outer surfaces 131 with respect to the obverse surface 11 may be 50 to 60 degrees. The inclination angle α2 of the paired second inclined outer surfaces 132 with respect to the obverse surface 11 and the inclination angle β2 of the paired inclined inner surfaces 142 with respect to the obverse surface 11 may be 25 to 35 degrees.
Similarly to the first embodiment, the obverse surface 11 of the head substrate 1 and the projection 13 having the groove 14 filled with the heat store member 15 are covered with an insulating layer 19, a resistor layer 4, an electrode layer 3 and a protective layer 2, which are formed in the mentioned order.
The connecting substrate 5 arranged adjacent to the head substrate 1 and the heat sink 8 on which the head substrate 1 and the connecting substrate 5 are mounted have the same configuration as that in the first or the second embodiment.
Next, a method for manufacturing the thermal printhead A3 according to the third embodiment is described with reference to
First, a substrate material 1A is prepared, as shown in
Next, with the obverse surface 11A covered with an appropriate masking layer, anisotropic etching using KOH, for example, is performed to form an intermediate projection 13A extending in the primary scanning direction x with a uniform cross section and an intermediate groove 14A extending in the primary scanning direction x along the center of the top surface 130A of the intermediate projection 13A in the secondary scanning direction y. The intermediate projection 13A has a top surface 130A and a pair of inclined outer surfaces 131A flanking the top surface 130A in the secondary scanning direction y. Portions of the paired inclined outer surfaces 131A that are close to the obverse surface 11A are to become the paired first inclined outer surfaces 131. The top surface 130A is a flat surface provided by a remaining portion of the obverse surface 11A of the substrate material 1A and is a (100) surface. The paired inclined outer surfaces 131A are flat surfaces connected to the top surface 130A in the secondary scanning direction y and inclined so as to become lower as proceeding away from the top surface 130A in the secondary scanning direction y. The inclination angle of the paired inclined inner surfaces 141A, which forms the intermediate groove 14A, with respect to the obverse surface 11A is equal to the inclination angle of the paired inclined outer surfaces 131A with respect to the obverse surface 11A and may be 50 to 60 degrees.
Next, as shown in
Next, as shown in
Next, an insulating layer 19 is formed, as shown in
Next, a resistor film 4A is formed, as shown in
Next, a conductive film 3A is formed, as shown in
Next, as shown in
Next, a protective layer 2 is formed. Specifically, the protective layer 2 may be formed by depositing SiN and SiC by CVD on the insulating layer 19, the electrode layer 3 and the resistor layer 4. The protective layer 2 is then partially removed by e.g. etching to form the pad opening 21. Thereafter, attaching the head substrate 1 and the connecting substrate 5 to the heat sink 8, mounting the driver ICs 7 to the connecting substrate 5, bonding the wires 61 and 62, and forming the protective resin 78 are performed to provide the thermal printhead A3 shown in
The thermal printhead A3 according to the third embodiment have the same advantages as those described above as to the thermal printhead A1 according to the first embodiment.
Additionally, in the thermal printhead A3 of the present embodiment, the projection 13 has a first inclined outer surface 131 and a second inclined outer surface 132 that have different inclination angles. This configuration allows a print medium pressed against the projection 13 by the platen roller 91 to be transferred more smoothly in the secondary scanning direction y without being caught on the projection 13.
The scope of the present disclosure is not limited to the foregoing embodiments, and all modifications within the scope of the subject matter set forth in the claims are included in the scope of the present disclosure.
For example, the hollow portion 16 at the bottom of the groove 14, which is described as to the thermal printhead A2 of the second embodiment, may be provided in the thermal printhead A1 of the first embodiment or the thermal printhead A3 of the third embodiment.
The thermal printhead A2 of the second embodiment may not include the hollow portion 16 at the bottom of the groove 14.
Moreover, in the configuration of the thermal printhead A2 or A3 of the second or the third embodiment, the projection 13 may further include a third inclined outer surface (not shown), having an inclination angle with respect to the obverse surface 11 smaller than that of the second inclined outer surfaces 132, between each of the second inclined outer surfaces 132 and the top surface 130. Such an arrangement, which provides a gentler profile of the projection 13, is also within the scope of the present disclosure.
Moreover, the plurality of heating elements 41, which comprise exposed portions of the resistor layer aligned in the primary scanning direction, may have any configuration as long as they are able to be selectively energized for heating.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-108396 | Jun 2019 | JP | national |
