Thermal printing head

Abstract

The invention provides a thermal print head. The thermal print head includes a substrate, a wiring layer, a heating resistor, and a protective layer. The wiring layer includes gold wiring portions, i.e., a plurality of strip-shaped portions, first independent wiring portions, and silver wiring portions, i.e., connection portions, detour portions, and second independent wiring portions. The protective layer includes a first layer constituting an outermost surface of the protective layer. The first layer includes glass and boron nitride particles dispersed in the glass. The first layer overlaps the heating resistor and is offset from the silver wiring portion in a plan view of the main surface of the substrate.

Description

Technical Field

[0001] This invention relates to thermal printheads. Background Technology

[0002] Japanese Patent Application Publication No. 2023-176504 discloses a thermal printhead comprising a substrate, a resistive layer disposed on the substrate, a wiring layer connected to the resistive layer, and a protective layer covering the resistive layer. The protective layer comprises glass and additive particles. The additive particles comprise boron nitride particles. Summary of the Invention

[0003] The purpose of this invention is to provide a thermal printhead that can prevent damage to the printing medium during printing.

[0004] The thermal printhead of the present invention comprises: a substrate having a main surface; a wiring layer disposed on the main surface; a heating resistor; and a protective layer covering the wiring layer and the heating resistor. The wiring layer includes gold wiring portions connected to the heating resistor and silver wiring portions connected to the gold wiring portions. The protective layer includes a first layer constituting the outermost surface of the protective layer. The first layer comprises glass and boron nitride particles dispersed in the glass. When viewed from above the main surface, the first layer overlaps with the heating resistor and is offset from the silver wiring portions.

[0005] The above and other objects, features, solutions and advantages of the present invention will become apparent from the following detailed description relating to the present invention, which shall be understood in conjunction with the accompanying drawings. Attached Figure Description

[0006] Figure 1 This is a schematic top view of the thermal printhead in the embodiment.

[0007] Figure 2 The edge of the thermal printhead in the implementation method Figure 1 A simplified enlarged sectional view of section line II-II shown.

[0008] Figure 3 This is a schematic partial enlarged top view of the thermal printhead in the embodiment.

[0009] Figure 4 This is a flowchart illustrating an example of a method for manufacturing a thermal printhead according to an embodiment.

[0010] Figure 5 This is a schematic cross-sectional view of a thermal printer including the thermal printhead of the embodiment.

[0011] Figure 6 This is a schematic top view of a comparative example thermal printhead.

[0012] Figure 7 The edge of the thermal printhead is a comparative example. Figure 6A simplified enlarged sectional view of section line VI-VI shown.

[0013] Figure 8 This is a magnified partial photograph of the outermost surface of the protective layer on the connecting part of the common wiring in the thermal printhead of the comparative example, showing the heating resistor and the common wiring in the thermal printhead.

[0014] Figure 9 This is a magnified photograph of the outermost surface of the protective layer on the first planarization layer in the thermal printhead of a comparative example.

[0015] Figure 10 This is a magnified photograph of the outermost surface of the protective layer on the connection portion of the common wiring in the thermal printhead of the embodiment.

[0016] Figure 11 This is a magnified photograph of the outermost surface of the protective layer on the first planarization layer in the thermal printhead of an embodiment.

[0017] In the diagram: 1, 1b—thermal printhead, 2—thermal printer, 10—substrate, 10a—main surface, 11—glaze, 12—heating glaze, 13—patch glaze, 15—planarization layer, 16—first planarization layer, 17—second planarization layer, 20—wiring layer, 21—common wiring, 22—strip section, 23—connector section, 24—detour section, 25—independent wiring, 26—first independent wiring section, 27—second independent wiring section, 30—heating resistor, 31—heating part, 33—protective layer, 34—first layer, 35—second layer, 40—driver IC, 43—sealing component, 45—protrusion, 46—paper pressure roller, 47—printing medium. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail based on the accompanying drawings. It should be noted that in the following drawings, the same or equivalent parts are labeled with the same reference numerals, and their descriptions are not repeated. At least a portion of the structures of the embodiments described below can be arbitrarily combined.

[0019] Reference Figures 1 to 3 The thermal printhead 1 of the embodiment will be described. The thermal printhead 1 mainly includes a substrate 10, a glaze 11, a planarization layer 15, a wiring layer 20, a heating resistor 30, a protective layer 33, a driver IC 40, and a sealing component 43.

[0020] Reference Figure 1 and Figure 2The substrate 10 is, for example, a ceramic substrate such as an alumina substrate. The substrate 10 has a main surface 10a. When viewed from above the main surface 10a (hereinafter referred to as "top view"), the long side direction of the substrate 10 is the main scanning direction X, the short side direction is the sub-scanning direction Y, and the thickness direction of the substrate 10 is the thickness direction Z. The thickness direction Z is orthogonal to both the main scanning direction X and the sub-scanning direction Y. In the top view, the sub-scanning direction Y is a printing medium 47 such as thermal recording paper (see reference). Figure 5 The direction of transport.

[0021] Reference Figures 1 to 3 A glaze 11 is disposed on the main surface 10a of the substrate 10. The glaze 11 is formed, for example, from a glass material such as amorphous glass. The thermal conductivity of the glaze 11 may be lower than that of the substrate 10. The softening point of the glaze 11 is, for example, above 800 degrees Celsius and below 850 degrees Celsius. The glaze 11 is disposed on a portion of the main surface 10a of the substrate 10. That is, the glaze 11 is a so-called localized glaze. The glaze 11 includes a heated glaze 12 and a patch glaze 13.

[0022] Reference Figures 1 to 3 When viewed from above the main surface 10a, the heating glaze 12 extends in the main scanning direction X and has a strip-like shape. The heating glaze 12 is disposed between the heating resistor 30 and the substrate 10. The heating glaze 12 suppresses heat dissipation from the heating resistor 30 to the substrate 10. The heating glaze 12 is a heat storage layer. The heating glaze 12 protrudes from a portion of the main surface 10a. The heating glaze 12 is used to increase the height of the heating resistor 30 from the main surface 10a, thereby pressing the heating resistor 30 onto the printing medium 47 (see reference). Figure 5 It is set up for this purpose.

[0023] Reference Figure 1 and Figure 2 The patch glaze 13 is separately disposed upstream of the heating glaze 12 in the sub-scanning direction Y. When viewed from above the main surface 10a, the patch glaze 13 extends in the main scanning direction X and has a strip shape. The patch glaze 13 supports a portion of the wiring layer 20 and the driver IC 40.

[0024] Reference Figures 1 to 3 A planarization layer 15 is disposed on the main surface 10a of the substrate 10. The thickness of the planarization layer 15 is less than the thickness of the glaze 11. The planarization layer 15 can prevent the wiring layer 20 from being broken due to the roughness of the main surface 10a of the substrate 10 and the step between the main surface 10a and the glaze 11. The planarization layer 15 is formed of glass, for example. The planarization layer 15 includes a first planarization layer 16 and a second planarization layer 17. When viewed from above the main surface 10a, the first planarization layer 16 is disposed between the heated glaze 12 and the patch glaze 13. The second planarization layer 17 is disposed on the side opposite to the first planarization layer 16 in the sub-scanning direction Y relative to the heated glaze 12.

[0025] Reference Figures 1 to 3 A wiring layer 20 is disposed on the main surface 10a of the substrate 10. Specifically, the wiring layer 20 is disposed on the glaze 11 and the planarization layer 15. The wiring layer 20 forms a conductive path for supplying current to the heating resistor 30. The wiring layer 20 includes gold wiring portions (e.g., multiple strip portions 22 and a first independent wiring portion 26) connected to the heating resistor 30 and silver wiring portions (e.g., connecting portions 23, detour portions 24, and a second independent wiring portion 27) connected to the gold wiring portions. The wiring layer 20 includes a common wiring 21 and multiple independent wirings 25.

[0026] The common wiring 21 is disposed on the glaze 11 and the planarization layer 15. The common wiring 21 includes multiple strips 22, connecting portions 23, and detour portions 24.

[0027] Multiple strip-shaped portions 22 are connected to the heating resistor 30. The multiple strip-shaped portions 22 are disposed on the heating glaze 12 and the second planarization layer 17. The multiple strip-shaped portions 22 extend along the sub-scanning direction Y. The multiple strip-shaped portions 22 are arranged at equal intervals in the main scanning direction X. The multiple strip-shaped portions 22 are gold (Au) wirings, formed from sintered gold particles.

[0028] Connector 23 is disposed on the second planarization layer 17. Connector 23 extends in the main scanning direction X. Connector 23 connects to a plurality of strips 22, linking the plurality of strips 22 together. Connector 23 is silver (Ag) wiring, formed by silver particle sintering.

[0029] The detour section 24 is disposed on the planarization layer 15, the heating glaze 12, and the patch glaze 13. The detour section 24 is connected to the connecting section 23. The detour section 24 extends from both ends of the main scanning direction X of the connecting section 23 upstream of the sub-scanning direction Y, bypassing multiple independent wirings 25. The detour section 24 is, for example, silver (Ag) wiring, formed by sintering silver particles. The connecting section 23 and the detour section 24 contain silver (Ag) instead of gold (Au) as the main component, thus reducing the cost of the thermal printhead 1.

[0030] Multiple independent wirings 25 are disposed on the glaze 11 and the first planarization layer 16. The multiple independent wirings 25 each include a first independent wiring portion 26 and a second independent wiring portion 27.

[0031] The first independent wiring portion 26 is connected to the heating resistor 30. The first independent wiring portion 26 is disposed on the heating glaze 12 and the first planarization layer 16. The first independent wiring portion 26 is gold (Au) wiring, formed by sintering gold particles.

[0032] The second independent wiring portion 27 is connected to the first independent wiring portion 26. The second independent wiring portion 27 is disposed on the heating glaze 12, the patch glaze 13, and the first planarization layer 16. The second independent wiring portion 27 is silver (Ag) wiring, formed by sintering silver particles.

[0033] Reference Figures 1 to 3 The heating resistor 30 is disposed on the heating glaze 12 (more specifically, the top of the heating glaze 12). The heating resistor 30 extends in the main scanning direction X and has a strip shape when viewed from above. The heating resistor 30 protrudes relative to the glaze 11 (more specifically, the heating glaze 12) to the side opposite to the substrate 10.

[0034] The heating resistor 30 is connected to the wiring layer 20. Specifically, the heating resistor 30 is connected to a plurality of strip portions 22 and a plurality of first independent wiring portions 26. In top view, the heating resistor 30 is arranged in a manner that intersects with the plurality of strip portions 22 and the first independent wiring portions 26. The heating resistor 30 is formed to span the plurality of strip portions 22 and the plurality of first independent wiring portions 26. (Refer to...) Figure 3 The portion of the heating resistor 30 sandwiched between the strip portion 22 and the first independent wiring portion 26 in the main scanning direction X is the heating portion 31. The heating portion 31 is heated by partial energization of the heating resistor 30. Heating of the heating portion 31 is reflected in the printing medium 47 (see reference). Figure 5 ) printed on it.

[0035] Reference Figure 1 and Figure 2 The protective layer 33 covers and protects the heating resistor 30. The protective layer 33 also covers and protects the wiring layer 20. The protective layer 33 includes a first layer 34. The first layer 34 forms the outermost surface of the protective layer 33. When printing using the thermal printhead 1, the outermost surface of the first layer 34 can contact the printing medium 47 (see reference 47). Figure 5 The protective layer 33 may also include a second layer 35. The protective layer 33 may also be a laminate of a first layer 34 and a second layer 35.

[0036] The second layer 35 is an insulating layer. The second layer 35 may contain, for example, a glass such as amorphous glass. The second layer 35 does not contain boron nitride particles. The second layer 35 may contain additives such as alumina particles. The softening point of the second layer 35 is higher than that of the first layer 34 but lower than that of the glaze 11. The softening point of the second layer 35 is, for example, approximately 780 degrees Celsius.

[0037] The second layer 35 is formed on and covers the heating resistor 30. The second layer 35 is formed on and covers the common wiring 21 and the plurality of individual wirings 25. Specifically, the second layer 35 is formed on and covers the plurality of strip portions 22, connecting portions 23, detour portions 24, the plurality of first individual wiring portions 26, and the plurality of second individual wiring portions 27. When viewed from above on the main surface 10a of the substrate 10, the second layer 35 overlaps with the plurality of strip portions 22, connecting portions 23, detour portions 24, the plurality of first individual wiring portions 26, and the plurality of second individual wiring portions 27. The second layer 35 is disposed between the heating resistor 30 and the first layer 34.

[0038] The second layer 35 can be a laminate of an insulating layer and a conductive layer. The insulating layer covers the heating resistor 30 and is disposed between the heating resistor 30 and the conductive layer. The conductive layer is formed on the insulating layer. The conductive layer contains glass and conductive particles dispersed in the glass. The conductive particles are, for example, ruthenium oxide (RuO2) particles. When the second layer 35 includes a conductive layer, it is possible to prevent the second layer 35 from becoming charged due to static electricity generated by the contact between the printing medium 47 and the first layer 34. It is possible to prevent the deterioration of the heating resistor 30 and electrical damage to the driver IC 40 caused by the charging of the second layer 35.

[0039] The first layer 34 is, for example, an insulating layer. The first layer 34 comprises a glass such as amorphous glass and boron nitride particles dispersed within the glass. The first layer 34 may also contain alumina particles dispersed within the glass. The glass is, for example, lead-free glass (i.e., glass that does not contain lead oxide). The proportion of boron nitride particles in the first layer 34 is, for example, 5% by weight or more and 70% by weight or less. The particle size of the boron nitride particles is less than or equal to the thickness of the first layer 34. The particle size of the boron nitride particles is, for example, 4 μm or less. The proportion of alumina particles in the first layer 34 is, for example, 70% by weight or less. The softening point of the first layer 34 is, for example, approximately 700 degrees Celsius.

[0040] The first layer 34 may also contain conductive particles such as ruthenium oxide (RuO2), making it a conductive layer. When the first layer 34 is conductive, it prevents the first layer 34 from becoming charged due to static electricity generated from contact between the printing medium 47 and the first layer 34. This prevents deterioration of the heating resistor 30 and electrical damage to the driver IC 40 caused by the first layer 34 becoming charged.

[0041] The first layer 34 is formed on the second layer 35. When viewed from above the main surface 10a, the outer edge of the first layer 34 is surrounded by the outer edge of the second layer 35. The thickness of the first layer 34 is less than the thickness of the second layer 35. When viewed from above the main surface 10a, the first layer 34 overlaps with the heating resistor 30 and is offset from the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the plurality of second independent wiring portions 27). That is, when viewed from above the main surface 10a, the first layer 34 as a whole does not overlap with the silver wiring portions. When viewed from above the main surface 10a, the first layer 34 may also overlap with the gold wiring portions (e.g., the plurality of strip portions 22 and the plurality of first independent wiring portions 26).

[0042] Reference Figure 1 as well as Figure 2 The driver IC 40 selectively energizes multiple independent wirings 25. The driver IC 40 is configured on a surface mount 13. The driver IC 40 is electrically connected to multiple second independent wiring portions 27.

[0043] Reference Figure 1 as well as Figure 2 The sealing component 43 seals the drive IC 40. The sealing component 43 is electrically insulating. The sealing component 43 is formed, for example, of an insulating resin material such as epoxy resin.

[0044] Reference Figures 1 to 3 The thermal printhead 1 includes a protrusion 45 formed on the main surface 10a. The protrusion 45 includes a heating glaze 12, a wiring layer 20 (more specifically, a plurality of strips 22 and a plurality of first independent wiring portions 26), a heating resistor 30, and a protective layer 33.

[0045] Reference Figure 4 An example of a method for manufacturing the thermal printhead 1 according to this embodiment will be described.

[0046] A glaze 11 is formed on the main surface 10a of the substrate 10 (step S1). For example, a glass paste is printed onto the main surface 10a of the substrate 10. The glass paste is then fired. In this way, the glaze 11 is formed. The glaze 11 includes, for example, a heated glaze 12 and a patch glaze 13.

[0047] A planarization layer 15 is formed on the area exposed from the glaze 11 in the main surface 10a of the substrate 10 (step S2). For example, glass paste is printed on the area exposed from the glaze 11 in the main surface 10a. The glass paste is then fired. In this way, the planarization layer 15 is formed. The planarization layer 15 includes, for example, a first planarization layer 16 and a second planarization layer 17.

[0048] Forming the wiring layer 20 (step S3). For example, a conductive paste containing gold (Au) particles is printed onto the heating glaze 12 and the planarization layer 15. The conductive paste is patterned by photolithography and then fired. This forms the gold wiring portions of the wiring layer 20 (e.g., the plurality of strip portions 22 of the common wiring 21 and the first independent wiring portions 26 of the plurality of independent wirings 25). A conductive paste containing silver (Ag) particles is printed onto the planarization layer 15, the heating glaze 12, and the patch glaze 13. The conductive paste is patterned by photolithography and then fired. This forms the silver wiring portions of the wiring layer 20 (e.g., the connection portions 23 and the detour portions 24 of the common wiring 21, and the second independent wiring portions 27 of the plurality of independent wirings 25).

[0049] The heating resistor 30 is formed (step S4). For example, a resistor paste is applied to the heating glaze 12, the plurality of strip portions 22, and the plurality of first independent wiring portions 26. The resistor paste may contain, for example, a conductive material such as ruthenium oxide, tantalum nitride, tantalum or silver vanadium, and glass. Then, the resistor paste is fired. In this way, the heating resistor 30 is formed.

[0050] A protective layer 33 is formed (step S5). Specifically, a glass paste without boron nitride particles is printed onto the glaze 11, the planarization layer 15, the wiring layer 20, and the heating resistor 30. This glass paste may contain alumina particles. The glass paste is then fired. This forms a second layer 35. Next, a glass paste containing boron nitride particles is printed onto the second layer 35. This glass paste may contain alumina particles. The glass paste is then fired. This forms a first layer 34.

[0051] The laminate of substrate 10, glaze 11, planarization layer 15, wiring layer 20, heating resistor 30, and protective layer 33 is divided (step S6). For example, a cutting groove is formed on substrate 10 by laser scribing. The laminate is cut along the cutting groove. In this way, the laminate is monolithized.

[0052] The driver IC40 is mounted on the surface mount glaze 13 (step S7). For example, the driver IC40 is fixed to the surface mount glaze 13 using a bonding component (not shown) such as resin adhesive or solder. The driver IC40 is electrically connected to a plurality of second independent wiring portions 27.

[0053] The driver IC 40 is sealed using the sealing component 43 (step S8). For example, a sealing resin material is poured onto the driver IC 40. The sealing resin material is then cured to form the sealing component 43. Thus, the thermal printhead 1 is obtained.

[0054] Reference Figure 5 The operation of the thermal printhead 1 in this embodiment will be explained.

[0055] The thermal printer 2 includes a thermal printhead 1 and a pressure roller 46 according to this embodiment. A protrusion 45 faces the pressure roller 46. The pressure roller 46 rotates to feed a printing medium 47 toward the thermal printhead 1. The printing medium 47 is transported from the downstream side of the sub-scanning direction Y to the upstream side of the sub-scanning direction Y. The printing medium 47 is supplied between the protrusion 45 and the pressure roller 46.

[0056] The driver IC40 connects multiple heat-generating components 31 via multiple independent wirings 25 (see reference). Figure 2 An electric current is applied individually. The heating element 31 among the plurality of heating elements 31 to which the electric current is applied selectively heats up. The heat generated by the heating element 31 is transferred to the printing medium 47. Thus, the thermal printhead 1 prints on the printing medium 47.

[0057] Comparing Figure 6 and Figure 7 The operation of the thermal printhead 1b of this embodiment will be explained while showing the comparative example thermal printhead 1b. The comparative example thermal printhead 1b is constructed in the same way as the thermal printhead 1 of this embodiment, but the first layer 34 is formed wider on the second layer 35, which is different from the thermal printhead 1 of this embodiment. Specifically, in the comparative example thermal printhead 1b, when viewed from above on the main surface 10a of the substrate 10, the first layer 34 also overlaps with the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the plurality of second independent wiring portions 27).

[0058] When printing using the comparative example thermal printhead 1b, on the printing medium 47 (reference) Figure 5 Scratches appeared on it. The reason is that, for example... Figure 8 and Figure 9 As shown, during printing, a small protrusion is formed in the area on the outermost surface of the first layer 34 that the printing medium 47 can contact, which overlaps with the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the plurality of second independent wiring portions 27) when viewed from above the main surface 10a of the substrate 10. Figure 8 and Figure 9 The black dots shown are tiny protrusions. These tiny protrusions are formed by bubbles generated in the portion of the first layer 34 that overlaps with the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second independent wiring portion 27) when viewed from above the main surface 10a of the substrate 10. The bubbles cause a portion of the outermost surface of the first layer 34 to bulge. The bubbles are generated by the diffusion of silver atoms from the silver wiring portions into the first layer 34 of the protective layer 33. Since the first layer 34 contains boron nitride particles, it is believed that the bubbles are difficult to detach from the first layer 34, thus the bubbles remain in the first layer 34.

[0059] In contrast, when printing using the thermal printhead 1 of this embodiment, on the printing medium 47 (refer to...) Figure 5 No scratches were found on it. The reason is that, for example... Figure 10 and Figure 11 As shown, during printing, the outermost surface of the first layer 34 that the printing medium 47 can contact hardly forms any micro-protrusions. Figure 10 and Figure 11 No such observation was made in China. Figure 8 and Figure 9 The black dots shown indicate that no micro-protrusions are formed in the thermal printhead 1 of this embodiment. In this embodiment, when viewed from above on the main surface 10a of the substrate 10, the first layer 34 of the protective layer 33 containing boron nitride particles deviates from the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second independent wiring portion 27). Therefore, it is possible to prevent silver atoms from the silver wiring portions from diffusing into the first layer 34. It is possible to prevent the formation of bubbles in the first layer 34, thereby preventing the formation of micro-protrusions on the outermost surface of the first layer 34.

[0060] The effects of the thermal printhead 1 in this embodiment will be explained.

[0061] The thermal printhead 1 of this embodiment includes: a substrate 10 having a main surface 10a; a wiring layer 20 disposed on the main surface 10a; a heating resistor 30; and a protective layer 33 covering the wiring layer 20 and the heating resistor 30. The wiring layer 20 includes gold wiring portions (e.g., a plurality of strip portions 22 and a first independent wiring portion 26) connected to the heating resistor 30 and silver wiring portions (e.g., connecting portions 23, detour portions 24, and second independent wiring portions 27) connected to the gold wiring portions. The protective layer 33 includes a first layer 34 constituting the outermost surface of the protective layer 33. The first layer 34 contains glass and boron nitride particles dispersed in the glass. When viewed from above the main surface 10a, the first layer 34 overlaps with the heating resistor 30 and is offset from the silver wiring portions.

[0062] Therefore, air bubbles can be prevented from forming in the first layer 34. Tiny protrusions can be prevented from forming on the outermost surface of the first layer 34. Damage to the printing medium 47 by the first layer 34 during printing can be prevented. Furthermore, since the outermost surface of the protective layer 33 is composed of the first layer 34 containing boron nitride particles, the wear resistance of the protective layer 33 is improved. Moreover, the wiring layer 20 includes silver wiring portions (e.g., connectors 23, detours 24, and second independent wiring portions 27), thus reducing the cost of the thermal printhead 1.

[0063] In the thermal printhead 1 of this embodiment, when viewed from above the main surface 10a, the first layer 34 overlaps with the gold wiring portion (e.g., a plurality of strip portions 22 and a first independent wiring portion 26).

[0064] Therefore, the gold wiring portions (e.g., multiple strips 22 and the first independent wiring portion 26) can be protected by the first layer 34. The reliability of the thermal printhead 1 is improved.

[0065] In the thermal printhead 1 of this embodiment, the boron nitride particles in the first layer 34 are mixed at a ratio of 5% by weight or more and 70% by weight or less.

[0066] Because the boron nitride particles in the first layer 34 have a concentration of 5% by weight or more, the wear resistance of the protective layer 33 is improved. Because the boron nitride particles in the first layer 34 have a concentration of 70% by weight or less, the boron nitride particles can be more uniformly dispersed in the first layer 34. This further improves the wear resistance of the protective layer 33.

[0067] In the thermal printhead 1 of this embodiment, the particle size of the boron nitride particles is less than or equal to the thickness of the first layer 34.

[0068] Therefore, it is possible to prevent the appearance of boron nitride particles on the outermost surface of the protective layer 33. The outermost surface of the protective layer 33 becomes smooth. It is possible to prevent the first layer 34 from damaging the printing medium 47 during printing.

[0069] In the thermal printhead 1 of this embodiment, the boron nitride particles have a particle size of 4 μm or less.

[0070] Therefore, in the first layer 34, boron nitride particles can be more uniformly dispersed. The wear resistance of the protective layer 33 is improved.

[0071] In the thermal printhead 1 of this embodiment, the glass is lead-free glass.

[0072] Therefore, it is possible to prevent air bubbles from forming in the first layer 34. It is possible to prevent the formation of tiny protrusions on the outermost surface of the first layer 34. It is possible to prevent the first layer 34 from damaging the printing medium 47 during printing.

[0073] In the thermal printhead 1 of this embodiment, the protective layer 33 contains alumina particles dispersed in glass. The proportion of alumina particles in the first layer 34 is 70% by weight or less.

[0074] Therefore, in the first layer 34, boron nitride particles and aluminum oxide particles can be more evenly dispersed. The wear resistance of the protective layer 33 is improved.

[0075] In the thermal printhead 1 of this embodiment, the protective layer 33 further includes a second layer 35. The second layer 35 does not contain boron nitride particles and is disposed between the heating resistor 30 and the first layer 34. When viewed from above the main surface 10a, the second layer 35 overlaps with the silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second independent wiring portion 27).

[0076] Therefore, it is possible to prevent the formation of minute protrusions on the outermost surface of the first layer 34. It is also possible to prevent the first layer 34 from damaging the printing medium 47 during printing. The silver wiring portions (e.g., the connecting portion 23, the detour portion 24, and the second independent wiring portion 27) can be protected by the second layer 35. This prevents the silver wiring portions from being oxidized. The reliability of the thermal printhead 1 is improved.

[0077] In the thermal printhead 1 of this embodiment, the thickness of the first layer 34 is less than the thickness of the second layer 35.

[0078] Therefore, the amount of boron nitride particles used in the first layer 34 can be reduced. The cost of the thermal printhead 1 is reduced.

[0079] In the thermal printhead 1 of this embodiment, the softening point of the second layer 35 is higher than that of the first layer 34.

[0080] Therefore, even when the temperature of the protective layer 33 rises and the first layer 34 softens due to the use of a thermal printhead 1, the second layer 35 remains cured. This prevents boron nitride particles contained in the first layer 34 from settling into the second layer 35. It also prevents the formation of air bubbles in the protective layer 33, thus preventing the formation of tiny protrusions on the outermost surface of the protective layer 33. Furthermore, it prevents the first layer 34 from damaging the printing medium 47 during printing.

[0081] Hereinafter, various aspects of the present invention will be summarized as appendices.

[0082] (Postscript 1)

[0083] A thermal printhead comprising:

[0084] A substrate having a main surface;

[0085] The wiring layer is configured on the aforementioned main surface;

[0086] Heating resistor; and

[0087] A protective layer that covers the aforementioned wiring layer and the aforementioned heating resistor.

[0088] The aforementioned wiring layer includes a gold wiring portion connected to the aforementioned heating resistor and a silver wiring portion connected to the aforementioned gold wiring portion.

[0089] The aforementioned protective layer includes a first layer constituting the outermost surface of the aforementioned protective layer.

[0090] The first layer described above comprises glass and boron nitride particles dispersed within the glass.

[0091] When viewed from above, the first layer overlaps with the heating resistor and deviates from the silver wiring portion.

[0092] (Postscript 2)

[0093] According to the thermal printhead described in Appendix 1, wherein...

[0094] When viewed from above, the first layer overlaps with the gold wiring portion.

[0095] (Note 3)

[0096] According to the thermal printhead described in Appendix 1 or 2, wherein,

[0097] The ratio of the boron nitride particles in the first layer is 5% by weight or more and 70% by weight or less.

[0098] (Postscript 4)

[0099] The thermal printhead according to any one of Annexes 1 to 3, wherein,

[0100] The particle size of the aforementioned boron nitride particles is less than or equal to the thickness of the first layer.

[0101] (Note 5)

[0102] According to the thermal printhead described in Appendix 4, wherein...

[0103] The aforementioned boron nitride particles have a particle size of less than 4 μm.

[0104] (Note 6)

[0105] According to any one of Appendices 1 to 5, the thermal printhead, wherein...

[0106] The glass mentioned above is lead-free glass.

[0107] (Note 7)

[0108] According to any one of Appendices 1 to 6, the thermal printhead, wherein...

[0109] The first layer described above contains alumina particles dispersed in the glass.

[0110] The proportion of the alumina particles in the first layer is less than 70% by weight.

[0111] (Note 8)

[0112] According to any one of Appendices 1 to 7, the thermal printhead, wherein...

[0113] The aforementioned protective layer also includes a second layer.

[0114] The second layer does not contain the boron nitride particles and is disposed between the heating resistor and the first layer.

[0115] When viewed from above, the second layer overlaps with the silver wiring portion.

[0116] (Note 9)

[0117] According to the thermal printhead described in Appendix 8, wherein...

[0118] The thickness of the first layer is less than the thickness of the second layer.

[0119] (Postscript 10)

[0120] According to the thermal printhead described in Appendix 8 or 9, wherein...

[0121] The softening point of the second layer is higher than that of the first layer.

[0122] The embodiments disclosed herein should be considered illustrative rather than restrictive in all respects. The scope of the invention is defined not by the foregoing description but by the scope of the technical solutions, and is intended to include all modifications within the meaning and scope equivalent to the scope of the technical solutions.

Claims

1. A thermal printhead, characterized by, Possessing: a substrate having a main surface; a wiring layer disposed on the main surface; a heat generating resistor; and a protective layer covering the wiring layer and the heat generating resistor, the wiring layer includes a gold wiring portion connected to the heat generating resistor and a silver wiring portion connected to the gold wiring portion, the protective layer includes a first layer constituting a surface of the protective layer, the first layer contains glass and boron nitride particles dispersed in the glass, when the main surface is viewed in plan, the first layer overlaps the heat generating resistor and is offset from the silver wiring portion.

2. The thermal printhead according to claim 1, wherein when the main surface is viewed in plan, the first layer overlaps the gold wiring portion.

3. The thermal printhead according to claim 1 or 2, wherein a blending ratio of the boron nitride particles in the first layer is 5% by weight or more and 70% by weight or less.

4. The thermal printhead according to any one of claims 1 to 3, wherein a particle diameter of the boron nitride particles is below a thickness of the first layer.

5. The thermal printhead according to claim 4, wherein the particle diameter of the boron nitride particles is 4 μm or less.

6. The thermal printhead according to any one of claims 1 to 5, wherein the glass is a lead-free glass.

7. The thermal printhead according to any one of claims 1 to 6, wherein the first layer contains alumina particles dispersed in the glass, a blending ratio of the alumina particles in the first layer is 70% by weight or less.

8. The thermal printhead according to any one of claims 1 to 7, wherein the protective layer further includes a second layer, the second layer does not contain the boron nitride particles and is disposed between the heat generating resistor and the first layer, when the main surface is viewed in plan, the second layer overlaps the silver wiring portion.

9. The thermal printhead according to claim 8, wherein a thickness of the first layer is smaller than a thickness of the second layer.

10. The thermal printhead according to claim 8 or 9, wherein a softening point of the second layer is higher than a softening point of the first layer.

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