Thermal printhead

Abstract

A thermal printhead is provided in which the structure of the common electrode strip portions (12) of the common electrode (10) is strengthened to enable it to withstand tension (60). A glaze layer is formed on the main face of a cover substrate (51), and the glaze layer has: a common electrode (10) having a common electrode connecting portion (11) and a plurality of common electrode strip portions (12); and a plurality of individual electrodes (20) having individual electrode strip portions (22). In an effective portion (30) of the electrodes formed by the common electrode strip portions (12) and the individual electrode strip portions (22) being alternately arranged at a prescribed interval in the main scanning direction, the gap formed by adjacent common electrode strip portions (12) and individual electrode strip portions (22) has a constant width in the main scanning direction, and the common electrode strip portions (12) have a portion in which the width in the main scanning direction in the range of the effective portion (30) of the electrodes from the base portion (12a) is greater than the width of the gap.

Description

Technical Field

[0001] This invention relates to thermal printheads, and more specifically, to thermal printheads with a reinforced comb-shaped common electrode structure. Background Technology

[0002] In the prior art, a thermal printhead is provided that heats up a resistive element formed on a substrate by passing an electric current through it, thereby enabling printing on printing media such as thermal recording paper. Figure 1 This is a diagram showing the structure of an example of an existing thermal printhead. Figure 1 The top view (a) shows the arrangement of electrodes in the thermal printhead that are formed on the main surface of the substrate 51 across the enamel layer 52 and extend in the main scanning direction to supply current to the resistive element 40. In the comb-shaped common electrode 10, the common electrode connecting portion 11 extends in the main scanning direction, and multiple common electrode strip portions 12 extend in the sub-scanning direction from base portions 12a protruding to one side of the common electrode connecting portion 11. The common electrode connecting portion 11 has a first layer 11a extending from the common electrode strip portions 12 and a second layer 11b covering a portion of the first layer 11a and reaching the enamel layer 52. Figure 1 In the figure, it represents a coordinate system in which the main scanning direction is set to the x-direction, the sub-scanning direction is set to the y-direction, and the height direction from the substrate 51 is set to the z-direction.

[0003] In the individual electrode 20, multiple individual electrode strips 22, whose base 22a is covered by multiple individual electrode connecting portions 21, extend in the sub-scanning direction such that they intersect between multiple common electrode strips 12. The common electrode strips 12 and individual electrode strips 22 are alternately arranged in the main scanning direction to form the effective portion 30 of the electrode. In the effective portion 30 of the electrode, the common electrode strips 12, the individual electrode strips 22, and the gaps between them are formed to have approximately the same width. In the effective portion 30 of the electrode, a resistor 40 is formed extending in the main scanning direction and connected to the intersecting common electrode strips 12 and individual electrode strips 22.

[0004] Figure 1 (b) and Figure 1 (c) in the middle is Figure 1 The cross-sectional view of section lines BB and CC in (a). Figure 1 (b) and Figure 1 As shown in (c), in the thermal printhead, the electrodes and resistors 40 are formed on the enamel layer 52 covering the main surface of the substrate 51. A first glass cover layer 53 and a second glass cover layer 54 are formed on the enamel layer 52 to cover the electrodes and resistors 40. The figure shows the printing medium 100, such as thermal recording paper, printed by the resistors 40, and its transport direction.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent document 1: Japanese Patent Application Publication No. 2012-228871. Summary of the Invention

[0008] The problem the invention aims to solve

[0009] However, as Figure 1 As shown in (c), the common electrode strip 12 formed on the glaze layer 52 is fixed to the glaze layer 52 by the second layer 11b of the common electrode connecting portion 11 and the resistor 40. Therefore, when the glass paste is melted to form the first glass cover layer 53 and the second glass cover layer 54, the common electrode strip 12 between them is subjected to tension 60 due to the expansion caused by the heating of the glaze layer 52. Sometimes the common electrode strip 12 cannot withstand the tension 60 and breaks.

[0010] The present invention is proposed in view of the above-mentioned actual situation, and its purpose is to provide a thermal printhead that strengthens the structure of the common electrode strip 12 of the common electrode 10 to withstand tension 60.

[0011] Technical means for solving problems

[0012] To address the aforementioned issues, the thermal printhead of this application includes: a substrate having a main surface; an enamel layer covering the main surface of the substrate; a common electrode formed on the enamel layer, comprising a common electrode connecting portion extending in the main scanning direction, and a plurality of common electrode strip portions extending from the common electrode connecting portion in a sub-scanning direction orthogonal to the main scanning direction; a plurality of independent electrodes formed on the enamel layer, each comprising a plurality of independent electrode strip portions extending in the sub-scanning direction between the plurality of common electrode strip portions; and a resistor formed on the effective portion of the electrodes in a manner extending in the main scanning direction, and intersecting with the plurality of common electrode strip portions and the plurality of independent electrode strip portions. The electrode has independent electrode strips connected, wherein the effective portion of the electrode is formed by alternating arrangement of multiple common electrode strips and multiple independent electrode strips at a predetermined interval in the main scanning direction; and a covering layer is formed on the enamel layer to cover the common electrode, multiple independent electrodes and resistors. In the effective portion of the electrode, the width of the gap formed by the multiple common electrode strips and multiple independent electrode strips in the main scanning direction is constant, and the multiple common electrode strips are included in the portion from the base connected to the common electrode to the effective portion of the electrode where the width in the main scanning direction is greater than the width of the gap in the main scanning direction.

[0013] Alternatively, the width of the gap in the main scanning direction within the effective portion of the electrode may be half the width of a predetermined interval between multiple shared electrode strips and multiple independent electrode strips alternately arranged in the main scanning direction. Alternatively, the multiple shared electrode strips and multiple independent electrode strips may each have a shape symmetrical about the extended sub-scanning direction. Alternatively, the multiple shared electrode strips and multiple independent electrode strips may each have a polygonal shape.

[0014] Alternatively, each of the multiple shared electrode strips may include a tapered portion within its range from the base to the effective portion of the electrode. Alternatively, the tapered portion may include a first tapered portion reaching the effective portion of the electrode and a second tapered portion connected to the first tapered portion within the effective portion of the electrode, the tapering angle of the second tapered portion being gentler than that of the first tapered portion. Alternatively, each of the multiple shared electrode strips may further include: a first fixed-width portion extending from the base to the first tapered portion; and a second fixed-width portion extending beyond the second tapered portion to the front end of the multiple shared electrode strips.

[0015] The tapered portion may extend to the front end of multiple common electrode strips within the effective portion of the electrode. It may also include a fixed-width portion extending from the base to the tapered portion.

[0016] Alternatively, the tapered portion may include a second tapered portion within the effective portion of the electrode, and multiple common electrode strips may each be located within the effective portion of the electrode, including an inverted tapered portion and a second tapered portion in the sub-scanning direction extending from the multiple common electrode strips. Alternatively, each of the multiple common electrode strips may further include a second fixed-width portion with a fixed width extending beyond the second tapered portion to the front end of the multiple common electrode strips. Alternatively, the tapered portion may further include a first tapered portion within its range from the base to the effective portion, and each of the multiple common electrode strips may further include: a first tapered portion extending to the effective portion of the electrode; and a first fixed-width portion extending to the first tapered portion.

[0017] Alternatively, the shared electrode connection may include: a first layer connected to multiple shared electrode strips; and a second layer covering a portion of the first layer and extending to the enamel layer. The first and second layers may also be formed of gold or silver, respectively.

[0018] Alternatively, each individual electrode may also include multiple individual electrode connecting portions, each of which covers the base of a multiple individual electrode strip and extends in a direction opposite to the multiple individual electrode strips. Alternatively, the multiple individual electrode strips and the multiple individual electrode connecting portions may be formed of gold or silver, respectively.

[0019] Invention Effects

[0020] According to the present invention, since the structure of the common electrode strip 12 of the common electrode is strengthened, it can withstand tension and will not break. Attached Figure Description

[0021] Figure 1 This is a diagram showing the structure of an example of an existing thermal printhead.

[0022] Figure 2 This is a diagram showing the thermal printhead of the first embodiment.

[0023] Figure 3 This is a top view showing the thermal printhead of the second embodiment.

[0024] Figure 4 This is a top view showing the thermal printhead of the third embodiment.

[0025] Explanation of reference numerals in the attached figures

[0026] 10 Common Electrode

[0027] 11 Common electrode connection part

[0028] 12 Common electrode strip

[0029] 20 independent electrodes

[0030] 21 Independent electrode connection part

[0031] 22 Independent electrode strip

[0032] 30 Effective part of the electrode

[0033] 40 Resistor

[0034] 51 substrate

[0035] 52 glaze layers

[0036] 100 Printing Media Detailed Implementation

[0037] Hereinafter, embodiments of the thermal printhead will be described in detail with reference to the accompanying drawings. In this embodiment, it is assumed that the resistive element and electrodes extend along the length direction of the main scanning direction. However, this embodiment relates to the reinforcement of the structure of the common electrode strip portion of the comb-shaped common electrode; therefore, the structure related to the arrangement of the electrodes including the common electrode strip portion will be described in detail. Additionally, other components such as a drive IC that supplies current to the heating element through the electrodes may be provided on the substrate, but these other structures known in the art are omitted for simplicity.

[0038] (First Embodiment)

[0039] Figure 2 This is a diagram showing the structure of the thermal printhead in the first embodiment. Figure 2 (a) in the diagram is a top view showing the configuration of the electrodes. Figure 2 (b) and Figure 2 (c) in the middle are respectively Figure 2 The cross-sectional view of the cutting lines BB and CC in (a).

[0040] like Figure 2 (b) and Figure 2 As shown in the cross-sectional view (c) in the image, in the thermal printhead, the flat upper surface of a substrate 51 made of ceramic such as alumina (Al2O3) or aluminum nitride (AlN) is covered by a glaze layer 52 of a specified thickness made of amorphous glass. On the glaze layer 52, as... Figure 2 Electrodes are formed by configuring them as shown in (a). The electrodes extend along the main scanning direction of the thermal printhead and supply current to the resistor 40.

[0041] The electrode comprises a comb-shaped common electrode 10 extending in the main scanning direction and a plurality of independent electrodes 20 disposed opposite to the common electrode 10. The common electrode 10 comprises a common electrode connecting portion 11 extending along the main scanning direction and a plurality of common electrode strip-shaped portions 12 extending from the common electrode connecting portion 11 toward the plurality of independent electrodes 20 disposed opposite to the plurality of independent electrodes 20 along a sub-scanning direction orthogonal to the main scanning direction. Figure 2 In the diagram, the coordinate system is defined as follows: the main scanning direction is set to the x-direction, the sub-scanning direction is set to the y-direction, and the height direction from the main surface of substrate 51 is set to the z-direction. The coordinate systems are similarly represented below.

[0042] The common electrode connector 11 has: a first layer 11a having a predetermined width and extending in the main scanning direction, with a common electrode strip 12 protruding from one side therefrom; and a second layer 11b having a predetermined width and extending in the main scanning direction, such that one side is exposed and a portion of the first layer 11a is covered via the opposite side to the enamel layer 52. The common electrode 10 may also be made of gold or silver. Alternatively, the common electrode 10 may be entirely made of either gold or silver, or the first layer 11a and the common electrode strip 12 of the common electrode connector 11 may be made of gold, while the second layer 11b of the common electrode connector 11 may be made of silver.

[0043] The base 12a of the common electrode strip 12 protrudes from one side of the first layer 11a of the common electrode connector 11 and extends a predetermined length toward the opposing independent electrode 20 along the sub-scanning direction. The common electrode strip 12 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 12a connected to the common electrode connector 11, the common electrode strip 12 forms a first fixed-width portion 12b1 with a fixed width.

[0044] The independent electrode 20 has: a plurality of independent electrode strips 22 extending along the sub-scanning direction between a plurality of common electrode strips 12 toward the opposing common electrode 10; and a plurality of independent electrode connecting portions 21 covering the base 22a of the independent electrode strips 22. The portions of the independent electrode connecting portions 21 covering the base 22a of the independent electrode strips 22 are arranged at predetermined intervals in the main scanning direction with a predetermined gap between them and adjacent independent electrode connecting portions 21. The independent electrode connecting portions 21 extend in the direction opposite to the independent electrode strips 22 and are connected to a driver IC (not shown). The independent electrode 20 may also be made of gold or silver. The independent electrode 20 may be entirely made of either gold or silver, or the independent electrode connecting portions 21 may be made of silver and the independent electrode strips 22 may be made of gold.

[0045] The independent electrode strip 22 extends a predetermined length from the independent electrode connector 21 covering the base 22a toward the opposing common electrode 10 along the sub-scanning direction. The independent electrode strip 22 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 22a covered by the independent electrode connector 21, the independent electrode strip 22 forms a first fixed-width portion 22b1 with a fixed width.

[0046] A common electrode strip 12 and an independent electrode strip 22 are formed between the common electrode connecting portion 11 and the independent electrode connecting portion 21, forming an effective portion 30 of the electrode. The common electrode strip 12 and the independent electrode strip 22, extending in the sub-scanning direction, are alternately arranged at predetermined intervals along the main scanning direction. The effective portion 30 of the electrode is formed in the sub-scanning direction within a predetermined width range bounded by a straight line connecting the front ends of the common electrode strip 12 and a straight line connecting the front ends of the independent electrode strip 22. In the effective portion 30 of the electrode, adjacent common electrode connecting portions 11 and independent electrode connecting portions 21 face each other with a predetermined gap in the main scanning direction.

[0047] The common electrode strip 12 forms a first fixed-width portion 12b1 that extends beyond a predetermined length from the base 12a connected to the common electrode connecting portion 11, and gradually tapers towards the approximate center in the width direction of the effective portion 30 of the electrode. The first tapered portion 12c1 is formed in a third region 33 extending beyond the first fixed-width portion 12b1 to the effective portion 30 of the electrode, and a second tapered portion 12c2 is formed in a first region 31 extending beyond the third region 33 into the effective portion 30 of the electrode, reaching approximately the center in the width direction of the effective portion 30 of the electrode. The inclination of the second tapered portion 12c2 is gentler than that of the first tapered portion 12c1. Furthermore, a second fixed-width portion 12b2 of a fixed width is formed in a second region 32 extending beyond approximately the center in the width direction of the effective portion 30 of the electrode to the front end of the common electrode strip 12 on one side of the effective portion 30 of the electrode. The width of the second fixed-width portion 12b2 is narrower than the width of the first fixed-width portion 12b1.

[0048] The independent electrode strip 22 forms a first tapered portion 22c1 that gradually tapers in a fourth region 34, extending from a first fixed-width portion 22b1 (which is longer than a predetermined length) to the effective portion 30 of the electrode, covered by the independent electrode connecting portion 21. The independent electrode strip 22 forms a second fixed-width portion 22b2 of a fixed width in a second region 32, extending from beyond the fourth region 34 into the effective portion 30 of the electrode to approximately the center in the width direction of the effective portion 30 of the electrode. The width of the second fixed-width portion 22b2 is narrower than the width of the first fixed-width portion 22b1. In the second region 32, the shared electrode strip 12, the independent electrode strip 22, and the gap between them are formed to have approximately the same width. Furthermore, the independent electrode strip 22 forms a second tapered portion 22c2 that gradually tapers towards the tip in a first region 31, extending beyond approximately the center in the width direction of the effective portion 30 of the electrode to the tip of the independent electrode strip 22 on the other side of the effective portion 30 of the electrode. Here, the second tapered portion 22c2 of the independent electrode strip 22 and the second tapered portion 12c2 of the adjacent shared electrode strip 12 form parallel profiles that are opposite to each other.

[0049] A resistive element 40 extending in the main scanning direction and having a predetermined width is formed in the effective portion 30 of the electrode. The resistive element 40 is located approximately at the center in the width direction of the effective portion 30 of the electrode and is electrically connected to the intersecting common electrode strip 12 and individual electrode strip 22, respectively. The resistive element 40 may also be made of, for example, ruthenium oxide (RuO2) and glass.

[0050] A first glass cover layer 53 of a predetermined thickness, made of amorphous glass, is formed on the glaze layer 52 to cover and protect the electrodes and the resistor 40. A second glass cover layer 54 of a predetermined thickness, also made of amorphous glass, is formed on the first glass cover layer 53 to withstand friction between the second glass cover layer 54 and the printing medium 100, which is in partial contact with the resistor 40 and transported in the sub-scanning direction.

[0051] In this thermal printhead, the common electrode strip 12 of the common electrode 10 forms a first tapered portion 12c1 in a third region 33, extending beyond a predetermined length from the base 12a connected to the common electrode connection portion 11 to a first fixed-width portion 12b1, and a second tapered portion 12c2 in a first region 31. The inclination of the second tapered portion 12c2 is gentler than that of the first tapered portion 12c1. Therefore, the width of the common electrode strip 12 forming the second tapered portion 12c2 in the first region 31 is thicker in the effective portion 30 of the electrode than the gap, which has a width that is approximately constant in the main scanning direction. Furthermore, the width of the first tapered portion 12c1 of the common electrode strip 12 in the third region 33, extending from the base 12a to the first fixed-width portion 12b1 of the first tapered portion 12c1, is further wide than the width in the first region 31 of the effective portion 30 of the electrode. In this way, the width of the common electrode strip 12, from the base 12a connected to the common electrode connection portion 11 to the resistor 40, is ensured, thus strengthening the structure. Even if tension is generated in the sub-scanning direction in the common electrode strip 12, it is not easy to break because the tension is dispersed in the width direction.

[0052] In the process of forming the first glass cover layer 53 and the second glass cover layer 54 on the glaze layer 52, glass paste is melted to form amorphous glass cover parts, so the glaze layer 52 is also heated. Figure 2 As shown in (c), the common electrode strip 12 formed on the glaze layer 52 is fixed to the glaze layer 52 by the second layer 11b of the common electrode connecting portion 11 and the resistor 40, respectively. Therefore, when the glaze layer 52 expands due to heating, the common electrode strip 12 between them generates tension 60 in the sub-scanning direction. The common electrode strip 12 is formed with a thicker width in this range and its structure is strengthened, so it can withstand the tension 60 in the sub-scanning direction and is not easily broken.

[0053] When the common electrode strip 12 is made of silver, silver has lower ductility than gold, but as described above, the width of the common electrode strip 12 from the base 12a connected to the common electrode connection 11 to the resistor 40 is wider. Therefore, even when using silver, which has lower ductility than gold, it can withstand the tension 60 generated in the sub-scanning direction and will not easily break. In this case, by using cheaper silver instead of more expensive gold to make the common electrode strip 12, the cost of materials can be reduced.

[0054] In the effective portion 30 of the electrode, adjacent common electrode strips 12 and independent electrode strips 22 are positioned opposite each other with a predetermined gap in the main scanning direction. Therefore, in the resistor 40 formed in the effective portion 30 of the electrode extending in the main scanning direction, a predetermined gap can be ensured between the adjacent common electrode strips 12 and independent electrode strips 22, providing a substantially constant resistance value between them. Since the predetermined gap in the main scanning direction between adjacent common electrode strips 12 and independent electrode strips 22 in the effective portion 30 of the electrode is substantially constant regardless of its position in the sub-scanning direction, even if the position of the resistor 40 changes slightly in the sub-scanning direction, a substantially constant resistance value is provided from the resistor 40 to the adjacent common electrode strips 12 and independent electrode strips 22, and the resistor generates a predetermined amount of heat when energized.

[0055] (Second Implementation)

[0056] Figure 3 This is a top view showing the electrode arrangement of the thermal printhead according to the second embodiment. The thermal printhead of the second embodiment has the same structure as that of the first embodiment, except for the electrode arrangement. The electrode arrangement of the second embodiment will be described below.

[0057] Electrodes are formed on a flat main surface of a substrate 51 (not shown), and consist of a comb-shaped common electrode 10 extending in the main scanning direction and a plurality of individual electrodes 20 disposed opposite to the common electrode 10. The common electrode 10 consists of a common electrode connecting portion 11 extending along the main scanning direction and a plurality of common electrode strip portions 12 extending from the common electrode connecting portion 11 toward the plurality of individual electrodes 20 disposed opposite to the plurality of individual electrodes 20 along a sub-scanning direction orthogonal to the main scanning direction.

[0058] The common electrode connector 11 has: a first layer 11a having a predetermined width and extending in the main scanning direction, with a common electrode strip 12 protruding from one side therefrom; and a second layer 11b having a predetermined width and extending in the main scanning direction, such that one side is exposed and a portion of the first layer 11a is covered via the opposite side to the enamel layer 52. The common electrode 10 may also be made of gold or silver. Alternatively, the common electrode 10 may be entirely made of either gold or silver, or the first layer 11a and the common electrode strip 12 of the common electrode connector 11 may be made of gold, while the second layer 11b of the common electrode connector 11 may be made of silver.

[0059] The base 12a of the common electrode strip 12 protrudes from one side of the first layer 11a of the common electrode connector 11 and extends a predetermined length toward the opposing independent electrode 20 along the sub-scanning direction. The common electrode strip 12 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 12a connected to the common electrode connector 11, the common electrode strip 12 forms a fixed-width portion 12b.

[0060] The independent electrode 20 has multiple independent electrode strips 22 extending towards the opposing common electrode 10 between multiple common electrode strips 12 along the sub-scanning direction, and multiple independent electrode connecting portions 21 covering the base 22a of the independent electrode strips 22. The portions of the independent electrode connecting portions 21 covering the base 22a of the independent electrode strips 22 are arranged at predetermined intervals in the main scan direction with a predetermined gap between them and adjacent independent electrode connecting portions 21. The independent electrode connecting portions 21 extend in the direction opposite to the independent electrode strips 22 and are connected to a driver IC (not shown). The independent electrode 20 may also be made of gold or silver. The independent electrode 20 may be entirely made of either gold or silver, or the independent electrode connecting portions 21 may be made of silver and the independent electrode strips 22 may be made of gold.

[0061] The independent electrode strip 22 extends a predetermined length from the independent electrode connector 21 covering the base 22a toward the opposing common electrode 10 along the sub-scanning direction. The independent electrode strip 22 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 22a covered by the independent electrode connector 21, the independent electrode strip 22 forms a fixed-width portion 22b.

[0062] A common electrode strip 12 and an independent electrode strip 22 are formed between the common electrode connecting portion 11 and the independent electrode connecting portion 21, forming an effective portion 30 of electrodes that extends in the sub-scanning direction and are alternately arranged at predetermined intervals along the main scanning direction. The effective portion 30 of the electrodes in the sub-scanning direction is formed within a predetermined width range bounded by a straight line connecting the front ends of the common electrode strip 12 and a straight line connecting the front ends of the independent electrode strip 22. In the effective portion 30 of the electrodes, adjacent common electrode connecting portions 11 and independent electrode connecting portions 21 face each other with a predetermined gap in the main scanning direction. This gap is approximately half the length of the interval between the alternately arranged common electrode strips 12 and independent electrode strips 22 in the main scanning direction.

[0063] The common electrode strip 12 has a tapered portion 12c that gradually tapers at the front end in the fifth region 35, extending from the base 12a connected to the common electrode connection portion 11 to the front end of the common electrode strip 12, which is a fixed width portion 12b that exceeds a predetermined length, to the side that becomes the effective portion 30 of the electrode.

[0064] In the sixth region 36, extending from the fixed-width portion 22b, which exceeds a predetermined length from the base 22a covered by the independent electrode connecting portion 21, to the front end of the independent electrode strip 22 on the other side of the effective portion 30 of the electrode, a tapered portion 22c that gradually tapers towards the front end is formed. Here, the tapered portion 22c of the independent electrode strip 22 and the tapered portion 12c of the adjacent shared electrode strip 12 form parallel profiles that are opposite to each other.

[0065] A resistive element 40 extending in the main scanning direction and having a predetermined width is formed in the effective portion 30 of the electrode. The resistive element 40 is located approximately at the center in the width direction of the effective portion 30 of the electrode and is electrically connected to the intersecting common electrode strip 12 and individual electrode strip 22, respectively. The resistive element 40 may also be made of, for example, ruthenium oxide (RuO2) and glass.

[0066] In this thermal printhead, the common electrode strip 12 of the common electrode 10 forms a tapered portion 12c in a fifth region 35 extending beyond a predetermined length of a fixed-width portion 12b from the base 12a connected to the common electrode connection portion 11. The width of the portion of the common electrode strip 12 extending from the base 12a connected to the common electrode connection portion 11 to the resistor 40 is ensured, thus strengthening the structure. Therefore, even if tension in the sub-scanning direction is generated in this portion of the common electrode strip 12, the tension is dispersed in the width direction, preventing easy breakage.

[0067] When the common electrode strip 12 is made of silver, although silver has lower ductility than gold, as described above, the width of the portion of the common electrode strip 12 from the base 12a connected to the common electrode connection 11 to the resistor 40 is increased, thus strengthening the structure. Therefore, even when using silver, which has lower ductility than gold, it can withstand the tension generated in the sub-scanning direction and will not easily break. In this case, by using cheaper silver instead of more expensive gold to form the common electrode strip 12, the cost of materials can be reduced.

[0068] In the effective portion 30 of the electrode, adjacent common electrode strips 12 and independent electrode strips 22 are positioned opposite each other with a predetermined gap in the main scanning direction. Therefore, in the resistor 40 formed in the effective portion 30 of the electrode extending in the main scanning direction, a predetermined gap can be ensured between the adjacent common electrode strips 12 and independent electrode strips 22, providing a substantially constant resistance value between them. Since the predetermined gap in the main scanning direction between adjacent common electrode strips 12 and independent electrode strips 22 in the effective portion 30 of the electrode is substantially constant regardless of its position in the sub-scanning direction, even if the position of the resistor 40 changes slightly in the sub-scanning direction, a substantially constant resistance value is provided from the resistor 40 to the adjacent common electrode strips 12 and independent electrode strips 22, and the resistor generates a predetermined amount of heat when energized.

[0069] (Third Implementation)

[0070] Figure 4 This is a top view showing the electrode arrangement of the thermal printhead according to the third embodiment. The thermal printhead of the third embodiment has the same structure as that of the first embodiment, except for the electrode arrangement. The electrode arrangement of the third embodiment will be described below.

[0071] Electrodes are formed on a flat main surface of a substrate 51 (not shown), and consist of a comb-shaped common electrode 10 extending in the main scanning direction and a plurality of individual electrodes 20 disposed opposite to the common electrode 10. The common electrode 10 consists of a common electrode connecting portion 11 extending along the main scanning direction and a plurality of common electrode strip portions 12 extending from the common electrode connecting portion 11 toward the plurality of individual electrodes 20 disposed opposite to the plurality of individual electrodes 20 along a sub-scanning direction orthogonal to the main scanning direction.

[0072] The common electrode connector 11 has: a first layer 11a having a predetermined width and extending in the main scanning direction, with a common electrode strip 12 protruding from one side therefrom; and a second layer 11b having a predetermined width and extending in the main scanning direction, such that one side is exposed and a portion of the first layer 11a is covered via the opposite side to the enamel layer 52. The common electrode 10 may also be made of gold or silver. Alternatively, the common electrode 10 may be entirely made of either gold or silver, or the first layer 11a and the common electrode strip 12 of the common electrode connector 11 may be made of gold, while the second layer 11b of the common electrode connector 11 may be made of silver.

[0073] The base 12a of the common electrode strip 12 protrudes from one side of the first layer 11a of the common electrode connector 11 and extends a predetermined length toward the opposing independent electrode 20 along the sub-scanning direction. The common electrode strip 12 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 12a connected to the common electrode connector 11, the common electrode strip 12 forms a first fixed-width portion 12b1 with a fixed width.

[0074] The independent electrode 20 has multiple independent electrode strips 22 extending along the sub-scanning direction between multiple common electrode strips 12 and opposite to the common electrode 10, and multiple independent electrode connecting portions 21 covering the base 12a of the independent electrode strips 22. The portions of the independent electrode connecting portions 21 covering the base 22a of the independent electrode strips 22 are arranged at predetermined intervals in the main scanning direction with a predetermined gap between them and adjacent independent electrode connecting portions 21. The independent electrode connecting portions 21 extend in the direction opposite to the independent electrode strips 22 and are connected to a driver IC (not shown). The independent electrode 20 may also be made of gold or silver. The independent electrode 20 may be entirely made of either gold or silver, or the independent electrode connecting portions 21 may be made of silver and the independent electrode strips 22 may be made of gold.

[0075] The independent electrode strip 22 extends a predetermined length from the independent electrode connector 21 covering the base 22a toward the opposing common electrode 10 along the sub-scanning direction. The independent electrode strip 22 has a polygonal shape that is symmetrical about the sub-scanning direction and is arranged at predetermined intervals in the main scanning direction. Within a predetermined length from the base 22a covered by the independent electrode connector 21, the independent electrode strip 22 forms a first fixed-width portion 22b1 with a fixed width.

[0076] A common electrode strip 12 and an independent electrode strip 22 are formed between the common electrode connecting portion 11 and the independent electrode connecting portion 21. Effective portions 30 of the electrodes, extending in the sub-scanning direction, are alternately arranged at predetermined intervals along the main scanning direction. The effective portions 30 of the electrodes are formed in the sub-scanning direction within a predetermined width range bounded by a straight line connecting the front ends of the common electrode strip 12 and a straight line connecting the front ends of the independent electrode strip 22. In the effective portions 30 of the electrodes, adjacent common electrode connecting portions 11 and independent electrode connecting portions 21 are opposite each other with a predetermined gap in the main scanning direction.

[0077] The common electrode strip 12 has a first tapered portion 12c1 that gradually tapers in a third region 33 extending from the base 12a connected to the common electrode connection 11 beyond a predetermined length to the effective portion 30 of the electrode. The common electrode strip 12 also has an inverted tapered portion 12d that gradually thickens at the tip in a first region 31 extending from the third region 33 into the effective portion 30 of the electrode to approximately the center in the width direction of the effective portion 30. Furthermore, in a second region 32 extending beyond approximately the center in the width direction of the effective portion 30 of the electrode to the tip of the common electrode strip 12 on one side of the effective portion 30 of the electrode, a second tapered portion 12c2 that gradually tapers in length beyond approximately the center in the width direction is formed, followed by a second fixed-width portion 12b2 of a fixed width.

[0078] The independent electrode strip 22 forms a first tapered portion 22c1 that gradually tapers in a fourth region 34, extending from a first fixed-width portion 22b1 (which exceeds a predetermined length from the base 22a covered by the independent electrode connecting portion 21) to the effective portion 30 of the electrode. In a second region 32, extending from beyond the fourth region 34 into the effective portion 30 of the electrode to approximately the center of the effective portion 30, the independent electrode strip 22 forms a second fixed-width portion 22b2 with a fixed width for a predetermined length, and then this second fixed-width portion 22b2 forms a second tapered portion 22c2 that gradually tapers. Here, the second tapered portion 22c2 of the independent electrode strip 22 and the second tapered portion 12c2 of the adjacent shared electrode strip 12 form parallel profiles that are opposite each other. Furthermore, in the first region 31 extending from approximately the center of the effective portion 30 of the electrode to the tip of the independent electrode strip 22 on the other side of the effective portion 30 of the electrode, an inverted conical portion 22d that gradually thickens at the tip is formed. Here, the inverted conical portion 22d of the independent electrode strip 22 and the inverted conical portion 12d of the adjacent shared electrode strip 12 form parallel profiles that are opposite to each other.

[0079] A resistive element 40 extending in the main scanning direction and having a predetermined width is formed in the effective portion 30 of the electrode. The resistive element 40 is located approximately at the center in the width direction of the effective portion 30 of the electrode and is electrically connected to the intersecting common electrode strip 12 and individual electrode strip 22, respectively. The resistive element 40 may also be made of, for example, ruthenium oxide (RuO2) and glass.

[0080] In this thermal printhead, the common electrode strip 12 of the common electrode 10 forms a first tapered portion 12c1 in a third region 33, which is a first fixed-width portion 12b1 extending beyond a predetermined length from the base 12a connected to the common electrode connection portion 11, and an inverted tapered portion 12d in the first region 31. Therefore, the common electrode strip 12 with the inverted tapered portion 12d formed in the first region 31 has a width in the effective portion 30 of the electrode that is larger than the gap with a width approximately constant in the main scanning direction. Similarly, the first tapered portion 12c1 in the third region 33 and the first fixed-width portion 12b1 extending from the base 12a to the first tapered portion 12c1 also have a width in the effective portion 30 of the electrode that is larger than the gap with a width approximately constant in the main scanning direction. In this way, the portion of the common electrode strip 12 from the base 12a connected to the common electrode connection portion 11 to the resistor 40 ensures a sufficient width, thus strengthening the structure. Therefore, even if tension is generated in the sub-scanning direction in the common electrode strip 12 in this part, the tension will be dispersed in the width direction, so it will not easily break.

[0081] When the common electrode strip 12 is made of silver, although silver has lower ductility than gold, as described above, the width of the portion of the common electrode strip 12 from the base 12a connected to the common electrode connection 11 to the resistor 40 is increased, thus strengthening the structure. Therefore, even when using silver, which has lower ductility than gold, it can withstand the tension generated in the sub-scanning direction and will not easily break. In this case, by using cheaper silver instead of more expensive gold to form the common electrode strip 12, the cost of materials can be reduced.

[0082] In the effective portion 30 of the electrode, adjacent common electrode strips 12 and independent electrode strips 22 are positioned opposite each other with a predetermined gap in the main scanning direction. Therefore, in the resistor 40 formed in the effective portion 30 of the electrode extending in the main scanning direction, a predetermined gap can be ensured between the adjacent common electrode strips 12 and independent electrode strips 22, providing a substantially constant resistance value between them. Since the predetermined gap in the main scanning direction between adjacent common electrode strips 12 and independent electrode strips 22 in the effective portion 30 of the electrode is substantially constant regardless of its position in the sub-scanning direction, even if the position of the resistor 40 changes slightly in the sub-scanning direction, a substantially constant resistance value is provided from the resistor 40 to the adjacent common electrode strips 12 and independent electrode strips 22, and the resistor generates a predetermined amount of heat when energized.

[0083] Industrial availability

[0084] This invention can be used in the manufacture of thermal printheads.

Claims

1. A thermal printhead, characterized in that, include: A substrate with a main surface; A glaze layer covering the main surface of the substrate; A common electrode is formed on the glaze layer and includes a common electrode connection portion extending in the main scanning direction and a plurality of common electrode strip portions extending from the common electrode connection portion in a sub-scanning direction orthogonal to the main scanning direction. Multiple independent electrodes are formed on the glaze layer, and multiple independent electrode strips extending in the sub-scanning direction are respectively included between the multiple shared electrode strips; A resistor is formed in the effective portion of an electrode in a manner extending in the main scanning direction and connected to the plurality of intersecting common electrode strips and the plurality of independent electrode strips, wherein the effective portion of the electrode is formed by the plurality of common electrode strips and the plurality of independent electrode strips being alternately arranged at a predetermined interval in the main scanning direction; and A covering layer is formed on the glaze layer in a manner that covers the common electrode, the plurality of individual electrodes, and the resistive element. In the effective portion of the electrode, the width of the gap formed by adjacent common electrode strips and individual electrode strips in the main scanning direction is constant. The common electrode strips include portions from the base connected to the common electrode connection portion to the effective portion of the electrode where the width in the main scanning direction is greater than the width of the gap in the main scanning direction. The plurality of shared electrode strips each include a tapered portion in the range from the base to the effective portion of the electrode. The tapered portion includes a first tapered portion that reaches the effective portion of the electrode and a second tapered portion that connects to the first tapered portion in the effective portion of the electrode, wherein the inclination of the tapered portion of the second tapered portion is gentler than that of the first tapered portion.

2. The thermal printhead as described in claim 1, characterized in that: The width of the gap in the main scanning direction of the effective portion of the electrode is half the length of a predetermined interval in which the plurality of shared electrode strips and the plurality of independent electrode strips are alternately arranged in the main scanning direction.

3. The thermal printhead as described in claim 1, characterized in that: The plurality of shared electrode strips and the plurality of independent electrode strips each have a shape symmetrical about the extended sub-scanning direction.

4. The thermal printhead as described in claim 1, characterized in that: The plurality of shared electrode strips and the plurality of independent electrode strips each have a polygonal shape.

5. The thermal printhead as described in claim 1, characterized in that: The plurality of common electrode strips further include: a first fixed-width portion extending from the base to the first tapered portion; and a second fixed-width portion extending beyond the second tapered portion to the front end of the plurality of common electrode strips.

6. The thermal printhead as described in claim 1, characterized in that: The common electrode connection portion includes: a first layer connected to the plurality of common electrode strip portions; and a second layer covering a portion of the first layer and reaching the glaze layer.

7. The thermal printhead as described in claim 6, characterized in that: The first layer and the second layer are respectively formed of gold or silver.

8. The thermal printhead as described in any one of claims 1 to 7, characterized in that: The independent electrode also includes a plurality of independent electrode connecting portions, which respectively cover the base of the plurality of independent electrode strip portions and extend in the opposite direction to the plurality of independent electrode strip portions.

9. The thermal printhead as described in claim 8, characterized in that: The plurality of independent electrode strips and the plurality of independent electrode connecting portions are respectively formed of gold or silver.

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