Thermal head and thermal printer

Abstract

A thermal head according to the present disclosure comprises a substrate, a heat storage layer, an electrode, and a resistor layer. The heat storage layer is located on the substrate and extends along a first direction of the substrate. The electrode is located on the heat storage layer and extends along a second direction intersecting the first direction. The resistor layer is located on the heat storage layer and the electrode and extends along the first direction. The heat storage layer has a first protrusion protruding in the thickness direction of the substrate from the upper surface of the substrate. The resistor layer is located on the first protrusion and has a second protrusion protruding in the thickness direction from the upper surface of the electrode and the heat storage layer. When viewed in a cross-sectional view on a plane perpendicular to the first direction, the curvature of the second protrusion is greater than the curvature of the first protrusion.

Description

Thermal heads and thermal printers

[0001] The present disclosure relates to a thermal head and a thermal printer.

[0002] 2. Description of the Related Art Various thermal heads have been proposed as printing devices for facsimiles, video printers, and the like.

[0003] Japanese Unexamined Patent Publication No. 61-099443

[0004] A thermal head according to one aspect of the present disclosure includes a substrate, a heat storage layer, an electrode, and a resistor layer. The heat storage layer is located on the substrate and extends along a first direction of the substrate. The electrode is located on the heat storage layer and extends along a second direction intersecting the first direction. The resistor layer is located on the heat storage layer and the electrode and extends along the first direction. The heat storage layer has a first protrusion that protrudes from an upper surface of the substrate in a thickness direction of the substrate. The resistor layer is located on the first protrusion and has a second protrusion that protrudes from an upper surface of the heat storage layer and the electrode in a thickness direction. When viewed in cross section along a plane perpendicular to the first direction, the curvature of the second protrusion is greater than the curvature of the first protrusion.

[0005] FIG. 1 is a perspective view showing an outline of a thermal head according to an embodiment. FIG. 2 is a cross-sectional view showing an outline of the thermal head shown in FIG. 1. FIG. 3 is a plan view showing an outline of the head substrate shown in FIG. 1. FIG. 4 is a schematic enlarged view of region IV shown in FIG. 3. FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. FIG. 7 is a cross-sectional view showing another example of a thermal head according to an embodiment. FIG. 8 is a diagram showing an example of the outline of the outermost surface of a protective layer in a cross-sectional view taken along line V-V in FIG. 4. FIG. 9 is a schematic enlarged view of portion H shown in FIG. 8. FIG. 10 is a schematic view of a thermal printer according to an embodiment.

[0006] Below, a detailed description will be given of a thermal head and a thermal printer according to the present disclosure (hereinafter referred to as an "embodiment") with reference to the drawings. Note that the present disclosure is not limited to the embodiment. Furthermore, the embodiments can be appropriately combined as long as the processing content is not contradictory. Furthermore, the same components in the following embodiments are designated by the same reference numerals, and redundant description will be omitted.

[0007] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision or installation precision.

[0008] The structure of a conventional thermal head leaves room for improvement, for example, in terms of improving printing characteristics. The present disclosure has been made in view of the above, and provides a thermal head and a thermal printer that can improve printing characteristics.

[0009] Fig. 1 is a perspective view showing an outline of a thermal head X1 according to an embodiment. As shown in Fig. 1, the thermal head X1 according to an embodiment includes a heat sink 1, a head substrate 3, and an FPC (flexible printed circuit board) 5. Note that a connector may be used instead of the FPC 5. The head substrate 3 is located on the heat sink 1. The FPC 5 is electrically connected to the head substrate 3. The head substrate 3 includes a substrate 7, a heat generating portion 9, a plurality of driving ICs 11, and a covering member 29.

[0010] The heat sink 1 is plate-shaped. The heat sink 1 has a rectangular shape in a plan view. The heat sink 1 has a heat dissipation function. Specifically, the heat sink 1 dissipates heat generated in the heat generating portion 9 of the head substrate 3 that does not contribute to printing to the outside of the thermal head X1. The head substrate 3 is adhered to the top surface of the heat sink 1 with double-sided tape or adhesive (not shown). The heat sink 1 is made of a metal material such as copper, iron, or aluminum.

[0011] The head substrate 3 is plate-shaped. The head substrate 3 has a rectangular shape in a plan view. The head substrate 3 has each component that constitutes the thermal head X1 positioned on a substrate 7. The head substrate 3 prints on a recording medium P (see FIG. 10 ) in accordance with an electrical signal supplied from the outside.

[0012] The driving IC 11 is located on the substrate 7. The driving ICs 11 are arranged along the main scanning direction. The driving ICs 11 are electronic components that have the function of controlling the energization state of each heat generating portion 9. As an example, a switching member having a plurality of switching elements therein may be used as the driving IC 11.

[0013] The driving ICs 11 are covered with a covering member 29 made of a resin such as epoxy resin or silicone resin. The covering member 29 is positioned over the plurality of driving ICs 11. The covering member 29 is an example of a sealing material.

[0014] The FPC 5 has, for example, a pair of first and second ends in the short side direction. The first end of the FPC 5 is electrically connected to the head base 3. The second end of the FPC 5 is electrically connected to the connector 31. Note that the head base 3 and the connector 31 may be directly connected.

[0015] The FPC 5 is electrically connected to the head substrate 3 by a conductive bonding material 23 (see FIG. 2). As an example, the conductive bonding material 23 may be a solder material or an anisotropic conductive film (ACF) in which conductive particles are mixed into an electrically insulating resin.

[0016] Each member constituting the head substrate 3 will be described below with reference to Figures 1 to 4. Figure 2 is a cross-sectional view showing an outline of the thermal head X1 shown in Figure 1. Figure 3 is a plan view showing an outline of the head substrate 3 shown in Figure 1. Figure 4 is a schematic enlarged view of region IV shown in Figure 3.

[0017] The head substrate 3 further includes a substrate 7, a common electrode 17, a plurality of individual electrodes 19, a third electrode 12, a fourth electrode 14, a terminal 2, a resistor layer 15, a protective layer 25, and a covering layer 27. Note that the protective layer 25 and the covering layer 27 are omitted from Fig. 1. Fig. 3 also shows a simplified view of the wiring of the head substrate 3. The driving IC 11, the protective layer 25, and the covering layer 27 are omitted from Fig. 3. The configuration of the fourth electrode 14 is also simplified in Fig. 3.

[0018] The substrate 7 has a rectangular shape in a plan view. The substrate 7 has a first surface 7e, which is its upper surface and the surface with the largest area. The first surface 7e has a first long side 7a, which is one of the long sides, a second long side 7b, which is the other long side, a first short side 7c, and a second short side 7d. The substrate 7 is made of an electrically insulating material such as alumina ceramics, or a semiconductor material such as single crystal silicon.

[0019] The substrate 7 also has a heat storage layer 13. The heat storage layer 13 is located on a first surface 7e of the substrate 7. The heat storage layer 13 has a first protruding portion 13a that protrudes from the first surface 7e in the thickness direction of the substrate 7 and extends in a strip shape along a first direction D1 (main scanning direction). The first protruding portion 13a has the function of effectively pressing the recording medium P to be printed (see FIG. 10 ) against the protective layer 25 located on the heat generating portion 9.

[0020] The heat storage layer 13 may have a base portion (not shown). In this case, the base portion is a portion located over the entire area of ​​the first surface 7e side of the substrate 7.

[0021] The heat storage layer 13 contains, for example, a glass component. The heat storage layer 13 temporarily stores a portion of the heat generated by the heat generating unit 9. This allows the heat storage layer 13 to shorten the time required to increase the temperature of the heat generating unit 9. In other words, the heat storage layer 13 has the function of improving the thermal response characteristics of the thermal head X1.

[0022] The heat storage layer 13 is produced, for example, by applying a predetermined glass paste obtained by mixing glass powder with an appropriate organic solvent to the first surface 7e side of the substrate 7 using conventional screen printing or the like, and then firing it.

[0023] 3, the common electrode 17 is located on the first surface 7e of the substrate 7. The common electrode 17 is made of a conductive material. For example, the common electrode 17 may be made of any one of aluminum, gold, silver, and copper, or an alloy thereof.

[0024] The common electrode 17 has a first common electrode 17a, a plurality of second common electrodes 17b, a plurality of third common electrodes 17c, and a plurality of terminals 2. The common electrode 17 is electrically connected in common to the plurality of elements 9a of the heat generating portion 9.

[0025] The first common electrode 17a is located between the first long side 7a of the substrate 7 and the heat generating portion 9. The first common electrode 17a extends in the first direction D1 (main scanning direction). The multiple second common electrodes 17b extend in the second direction D2 (sub-scanning direction). One of the multiple (two in this example) second common electrodes 17b is located on the first short side 7c of the substrate 7. The other of the two second common electrodes 17b is located on the second short side 7d. The second common electrode 17b connects the terminal 2 to the first common electrode 17a. The multiple third common electrodes 17c extend in the second direction D2 (sub-scanning direction). The third common electrodes 17c extend in a comb-like shape from the first common electrode 17a toward each element 9a of the heat generating portion 9, with a portion of each third common electrode 17c inserted into the opposite side of the heat generating portion 9. At least a portion of the third common electrode 17c is located on the heat storage layer 13. The third common electrodes 17c are spaced apart from one another in the first direction D1 (main scanning direction). The third common electrodes 17c are an example of first electrodes.

[0026] The individual electrodes 19 are located on the first surface 7e of the substrate 7. At least a portion of each individual electrode 19 is located on the heat storage layer 13 (see FIG. 2). The individual electrodes 19 contain a metal component and are electrically conductive. The individual electrodes 19 are formed of metals such as aluminum, nickel, gold, silver, platinum, palladium, and copper, or alloys thereof. The individual electrodes 19 extend in the second direction D2 (sub-scanning direction). The individual electrodes 19 are located along the first direction D1 (main scanning direction). The individual electrodes 19 are located between two adjacent third common electrodes 17c. Therefore, in the thermal head X1, the third common electrodes 17c and the individual electrodes 19 are alternately arranged at a predetermined interval in the first direction D1 (main scanning direction). The individual electrodes 19 are connected to electrode pads 10 on the second long side 7b of the substrate 7. The individual electrodes 19 are an example of second electrodes.

[0027] The third electrodes 12 are connected to the electrode pads 10. The third electrodes 12 extend in the second direction D2 (sub-scanning direction). A driving IC 11 is mounted on the electrode pads 10.

[0028] The fourth electrode 14 extends in the first direction D1 (main scanning direction) and is located across the plurality of third electrodes 12. The fourth electrode 14 is connected to the outside via a terminal 2.

[0029] The terminal 2 is located on the second long side 7b of the substrate 7. The terminal 2 is connected to the FPC 5 by a conductive bonding material 23 (see FIG. 2), thereby electrically connecting the head base 3 to the outside.

[0030] The individual electrodes 19, the third common electrode 17c, and the third electrode 12 can be made of, for example, a conductive paste containing a metal component and a glass component in an organic solvent. The individual electrodes 19, the third common electrode 17c, and the third electrode 12 can be formed by printing the material layers constituting each of them on the substrate 7 using, for example, screen printing, flexographic printing, gravure printing, or gravure offset printing. The thickness of the individual electrodes 19 and the third common electrode 17c is, for example, about 0.5 to 1.5 μm.

[0031] Furthermore, the material layers constituting the first common electrode 17a, second common electrode 17b, fourth electrode 14, and terminal 2 can be produced on the substrate 7 by, for example, screen printing. The thicknesses of the first common electrode 17a, second common electrode 17b, fourth electrode 14, and terminal 2 are, for example, approximately 5 to 20 μm. The first common electrode 17a, second common electrode 17b, fourth electrode 14, and terminal 2 are indicated by dots in FIG. 3, and the same applies to the following drawings.

[0032] The resistor layer 15 is positioned across the third common electrode 17c and the individual electrodes 19, spaced apart from the first long side 7a of the substrate 7. Portions of the resistor layer 15 located between the third common electrode 17c and the individual electrodes 19 function as the elements 9a of the heat generating unit 9 (see FIG. 4). In other words, the elements 9a of the heat generating unit 9 are located on the heat storage layer 13 and are arranged at predetermined intervals in the first direction D1. Although the elements 9a of the heat generating unit 9 are depicted in a simplified manner in FIG. 3, they may be positioned at a density of 100 dpi (dots per inch) or more. Furthermore, the elements 9a of the heat generating unit 9 may be positioned at a density of 200 to 2400 dpi.

[0033] The thickness of the resistor layer 15 is, for example, about 3 to 6 μm. The sheet resistance of the resistor layer 15 is, for example, about 100 to 10,000 Ω / □. The thermal expansion coefficient of the resistor layer 15 is, for example, about 5 to 10 ppm / °C. The thermal conductivity of the resistor layer 15 is, for example, about 0.5 to 2 W / (m·K).

[0034] The resistor layer 15 may be formed, for example, by applying a material paste containing a conductive component and a glass component in a long strip shape in the main scanning direction to the substrate 7 on which various electrodes have been patterned, using a screen printing method or a dispensing device. The conductive component may include, for example, ruthenium oxide. The glass component may include, for example, lead borosilicate glass.

[0035] The protective layer 25 is located on the heat storage layer 13 formed on the first surface 7e (see FIG. 1) of the substrate 7. The protective layer 25 covers the heat generating portion 9, the third common electrode 17c, and the individual electrodes 19. The protective layer 25 is located across the main scanning direction of the substrate 7 from the first long side 7a of the substrate 7 so as to be spaced apart from the electrode pads 10.

[0036] The protective layer 25 has insulating properties. This protects the covered area from corrosion due to adhesion of moisture contained in the atmosphere or abrasion due to contact with the recording medium P (see FIG. 10 ). The protective layer 25 can be made of, for example, glass. The protective layer 25 may contain, for example, lead borosilicate glass. The protective layer 25 may also further contain, for example, one or both of alumina and zirconia.

[0037] The protective layer 25 may have a surface roughness Ra of, for example, 0.3 μm or less. The detailed configuration of the protective layer 25 will be described later.

[0038] The covering layer 27 is located on the substrate 7 so as to partially cover the common electrode 17, the individual electrodes 19, the third electrode 12, and the fourth electrode 14. The covering layer 27 protects the covered area from oxidation due to contact with the atmosphere or corrosion due to adhesion of moisture contained in the atmosphere. The covering layer 27 can be made of a resin material such as an epoxy resin, a polyimide resin, or a silicone resin.

[0039] Next, the main parts of the thermal head X1 according to the embodiment will be described in detail with reference to Figures 5 and 6. Figure 5 is a cross-sectional view taken along line VV in Figure 4. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 4.

[0040] As shown in FIGS. 5 and 6, the thermal head X1 according to the embodiment includes a heat storage layer 13, a third common electrode 17c, individual electrodes 19, a resistor layer 15, and a protective layer 25.

[0041] The heat storage layer 13 is located on the substrate 7. The heat storage layer 13 has a first protrusion 13a protruding in the third direction D3 from the first surface 7e of the substrate 7. Specifically, as shown in FIG. 6 , the central portion of the first protrusion 13a in the second direction D2 protrudes further toward the third direction D3 than the end portions in the second direction D2. The third direction D3 is the thickness direction of the substrate 7 and is a direction intersecting the first direction D1 and the second direction D2. The central portion of the first protrusion 13a in the second direction D2 is, for example, the central region of three regions obtained by dividing the first protrusion 13a into three equal parts by the second direction D2.

[0042] The third common electrode 17c and the individual electrodes 19 are located on the heat storage layer 13. As shown in Fig. 5, the third common electrode 17c has a common protrusion 17d whose central portion in the first direction D1 protrudes further in the third direction D3 than the ends in the first direction D1. Similarly, the individual electrodes 19 have individual protrusions 19b whose central portion in the first direction D1 protrudes further in the third direction D3 than the ends in the first direction D1. The common protrusion 17d and the individual protrusions 19b are examples of third protrusions.

[0043] The width of the individual electrode 19 and the third common electrode 17c is, for example, about 10 to 50 μm, and may also be, for example, about 20 to 30 μm.

[0044] The resistor layer 15 is located on the third common electrode 17c and the individual electrodes 19, and on the heat storage layer 13 that does not have the third common electrode 17c or the individual electrodes 19. As a result, the third common electrode 17c and the individual electrodes 19 are sandwiched between the heat storage layer 13 and the resistor layer 15. As shown in FIGS. 5 and 6 , the resistor layer 15 has second protrusions 15a that protrude in the third direction D3 from the upper surfaces of the third common electrode 17c, the individual electrodes 19, and the heat storage layer 13. Specifically, as shown in FIG. 6 , the center of the second protrusion 15a in the second direction D2 protrudes further toward the third direction D3 than the end portions in the second direction D2. The second protrusions 15a are located above the centers in the second direction D2 of the first protrusions 13a of the heat storage layer 13.

[0045] 6 , when the thermal head X1 is viewed in cross section on a plane perpendicular to the first direction D1, the curvature of the second protrusion 15a is greater than the curvature of the first protrusion 13a of the heat storage layer 13. For example, the curvature of the second protrusion 15a may be 1.5 to 40 times the curvature of the first protrusion 13a. Specifically, the curvature of the central portion of the upper surface of the second protrusion 15a in the second direction D2 may be 1.5 to 40 times the curvature of the central portion of the upper surface of the first protrusion 13a in the second direction D2.

[0046] As described above, the thermal head X1 according to the embodiment has a two-step protrusion shape in which the second protrusion 15a of the resistor layer 15 is located above the first protrusion 13a of the heat storage layer 13. This configuration increases the pressure from the resistor layer 15 to the recording medium P (see FIG. 10 ) compared to a case without a two-step protrusion shape, improving heat transfer and improving the printing characteristics of the thermal head X1. Furthermore, in the thermal head X1 according to the embodiment, the curvature of the second protrusion 15a is greater than the curvature of the first protrusion 13a. Therefore, compared to a case in which the curvature of the second protrusion 15a and the curvature of the first protrusion 13a are the same, the pressure from the resistor layer 15 to the recording medium P is higher, improving the printing characteristics of the thermal head X1.

[0047] As described above, the third common electrode 17c has a common protrusion 17d in the center in the first direction D1 that protrudes further than the ends in the first direction D1. Similarly, the individual electrodes 19 have individual protrusions 19b in the center in the first direction D1 that protrude further in the third direction D3 than the ends in the first direction D1. In other words, the third common electrode 17c and the individual electrodes 19 are thicker at the centers in the first direction D1 than at the ends in the first direction D1.

[0048] With this configuration, the cross-sectional area and volume of each element 9a of the heat generating portion 9 are larger than when the thicknesses of the third common electrode 17c and the individual electrodes 19 are constant in the first direction D1. In the thermal head X1, where each element 9a of the heat generating portion 9 is large, heat is more easily transmitted to a farther portion of the resistor layer 15, allowing the temperature of the resistor layer 15 located above the third common electrode 17c and the individual electrodes 19 to be appropriately increased. As a result, the temperature difference between different portions on the top surface of the resistor layer 15 is reduced. This improves the connection between dots on the printed matter printed by the thermal head X1 and improves the print quality.

[0049] The curvatures of the first protrusion 13 a and the second protrusion 15 a can be measured using the following method. For example, in the manufacturing process, after forming the first protrusion 13 a (heat storage layer 13) and after forming the second protrusion 15 a (resistance layer 15), a surface profile is acquired using a contact-type surface profile measuring device or a non-contact-type laser microscope, etc. Then, the acquired profile can be used to calculate the curvatures of the first protrusion 13 a and the second protrusion 15 a, respectively. Alternatively, the following method may be used. First, a cross section of the first protrusion 13 a and the second protrusion 15 a cut along a plane perpendicular to the first direction D1 is imaged using a scanning electron microscope (SEM), etc. Then, the curvatures of the first protrusion 13 a and the second protrusion 15 a are calculated from the contours of the first protrusion 13 a and the second protrusion 15 a that appear in the image.

[0050] The dimension s1 (see FIG. 4 ) of the resistor layer 15 in the second direction D2 may be 0.9 to less than 1.45 times the distance d between the centers of the third common electrodes 17c located on both sides of a given individual electrode 19 in the first direction D1 (main scanning direction), and may be 1 / 10 to 1 / 3 of the dimension s2 of the heat storage layer 13 in the second direction D2. The dimension s1 of the resistor layer 15 in the second direction D2 is, for example, approximately 80 to 140 μm. The dimension s2 of the heat storage layer 13 in the second direction D2 is, for example, approximately 500 to 1200 μm.

[0051] The thickness t1 (see FIG. 6) of the second protrusion 15a of the resistor layer 15 may be from two to eight times the thicknesses t2, t3 (see FIG. 5) of the individual electrodes 19 and the third common electrode 17c, and from one-eighth to one-third of the thickness t6 of the first protrusion 13a of the heat storage layer 13. The thickness t1 of the second protrusion 15a of the resistor layer 15 is, for example, approximately 5 to 7 μm. The thickness t6 of the first protrusion 13a of the heat storage layer 13 is, for example, 15 to 35 μm.

[0052] The thicknesses of the third common electrode 17c and the individual electrodes 19 will now be described with reference to FIGS. 5 and 7 . FIG. 7 is a cross-sectional view showing another example of the thermal head X1 according to the embodiment. The thickness t3 of the third common electrode 17c may be different from the thickness t2 of the individual electrodes 19. In the example of FIG. 5 , the thickness t2 of the individual electrodes 19 is thicker than the thickness t3 of the third common electrode 17c. Specifically, the central portion of the individual electrode 19 in the first direction D1 protrudes further in the third direction D3 than the central portion of the third common electrode 17c in the first direction D1. On the other hand, in the example of FIG. 7 , the thickness t4 of the third common electrode 17c is thicker than the thickness t5 of the individual electrodes 19. Specifically, the central portion of the third common electrode 17c in the first direction D1 protrudes further in the third direction D3 than the central portion of the individual electrodes 19 in the first direction D1.

[0053] In this way, the thickness t3 of the third common electrode 17c is different from the thickness t2 of the individual electrode 19. This improves the printing characteristics of the thermal head X1 according to this embodiment compared to when the thickness t3 of the third common electrode 17c is the same as the thickness t2 of the individual electrode 19. This point will be further explained using FIGS. 4, 5, and 7.

[0054] As shown in Fig. 4, the thermal head X1 prints one dot using a heat generating portion 9 corresponding to a predetermined individual electrode 19X and the third common electrodes 17cL and 17cR that are adjacent to the predetermined individual electrode 19X in the first direction D1 (main scanning direction). In other words, as shown by the two-dot chain line in Fig. 4, the printing area Tr of one dot in plan view extends from the third common electrode 17cL to the third common electrode 17cR in the first direction D1 (main scanning direction). In other words, the individual electrode 19X is close to the center of one dot, and the third common electrodes 17cL and 17cR are close to the outline of one dot.

[0055] When the thermal head X1 prints one dot on the recording medium P (see FIG. 10), for example, current flows from the third common electrodes 17cL, 17cR of the common electrode 17 to the individual electrode 19X, causing the elements 9aL, 9aR of the heat generating unit 9 to generate heat. As a result, printing is performed on the recording medium P by the heat of the two elements 9aL, 9aR aligned in the first direction D1 (main scanning direction). Furthermore, the region of the element 9a closer to the individual electrode 19 has a higher temperature when heated than the region closer to the third common electrode 17c.

[0056] 5, when the thickness t2 of the individual electrode 19 is thicker than the thickness t3 of the third common electrode 17c, the temperature of the resistor layer 15 located on the individual electrode 19 can be increased appropriately compared to when the thickness t2 of the individual electrode 19 and the thickness t3 of the third common electrode 17c are the same. Furthermore, when the thermal head X1 prints one dot on the recording medium P, the pressure applied to the recording medium P by the resistor layer 15 located on the individual electrode 19 increases. This makes the center of one dot clearer in the printed matter printed by the thermal head X1, improving the printing characteristics of the thermal head X1.

[0057] On the other hand, as shown in FIG. 7 , the thickness t4 of the third common electrode 17c may be thicker than the thickness t5 of the individual electrode 19. In this case, the temperature of the resistor layer 15 located above the third common electrode 17c can be increased more appropriately compared to when the thickness t5 of the individual electrode 19 and the thickness t4 of the third common electrode 17c are the same. Furthermore, when the thermal head X1 prints one dot on the recording medium P, the resistor layer 15 located above the third common electrode 17c exerts a higher pressure on the recording medium P. This results in a clearer outline of one dot on the printed matter printed by the thermal head X1, improving the printing characteristics of the thermal head X1. Furthermore, because the pressure on the recording medium P is lower from the region of the element 9a near the individual electrode 19, where the temperature during heating is relatively high, the heat-generating portion 9 is less susceptible to deterioration due to wear.

[0058] The difference in thickness between the individual electrodes 19 and the third common electrode 17c may be, for example, about 0.01 to 0.35 μm.

[0059] As shown in Fig. 6, the heat storage layer 13 is divided into two equal regions in the third direction D3, with the region closer to the substrate 7 designated as a first region R1 and the region farther from the substrate 7 designated as a second region R2. In this case, the curvature of the second region R2 may be greater than that of the first region R1. With this configuration, the pressure applied to the recording medium P from the resistor layer 15 located above the heat storage layer 13 is higher than when the curvatures of the first region R1 and the second region R2 are the same, thereby improving the printing characteristics of the thermal head X1. Furthermore, the curvature of the top surface of the heat storage layer 13 may increase from the end portions toward the center in the second direction D2.

[0060] As shown in FIG. 6 , the thickness of the protective layer 25 in the second direction D2 may be constant. In particular, the thickness of the portion of the protective layer 25 that overlaps with the heat storage layer 13 in a plan view of the thermal head X1 may be constant in the second direction D2. This configuration allows the two-step protrusion shape of the heat storage layer 13 and the resistor layer 15 to remain on the surface of the protective layer 25, compared to when the thickness of the protective layer 25 varies in the second direction D2. This increases the pressure from the resistor layer 15 to the recording medium P (see FIG. 10 ), improving heat transfer and improving the printing characteristics of the thermal head X1. Furthermore, this configuration allows heat and pressure to be transferred more uniformly from the resistor layer 15 to the recording medium P, compared to when the thickness of the protective layer 25 varies in the second direction D2.

[0061] The protective layer 25 may have a plurality of laminated protective films 25a, 25b. At least one of the plurality of protective films 25a, 25b may be a thin protective film. The thin protective film is a protective film formed using a thin film formation technique such as a sputtering method. The thin protective film may be located on the surface of the protective layer 25. The thin protective film may be formed of SiO ２ , SiN, SiON, SiC, SiAlON, TiN, TiCN, TiCrN, TiAlN, and CrN.

[0062] In this way, the protective layer 25 has a plurality of protective films 25a, 25b, which improves the abrasion resistance and the durability of the thermal head X1 compared to when the protective layer 25 has one protective film.

[0063] A protective film other than a thin protective film may be formed using a thick film forming technique such as printing.

[0064] Although the protective layer 25 has two protective films 25 a and 25 b in this example, the number of protective films is not limited to this. For example, the protective layer 25 may have three or more protective films.

[0065] 6, the protective layer 25 covers the heat storage layer 13 and the resistor layer 15. In other words, the protective layer 25 covers the first protruding portion 13a and the second protruding portion 15a.

[0066] Fig. 8 is a diagram showing an example of the outline of the outermost surface of the protective layer 25 in a cross section taken along line VV in Fig. 4. Fig. 9 is a schematic enlarged view of a portion H shown in Fig. 8.

[0067] As shown in FIGS. 8 and 9 , the contour 100 of the outermost surface of the protective layer 25 when viewed in cross section on a plane perpendicular to the first direction D1 may have an inflection point 103. The inflection point 103 may be located in a section 110 from a first position 101 covering the end of the first protrusion 13 a (see FIG. 6 ) to a second position 102 covering the center of the second protrusion 15 a (see FIG. 6 ). The inflection point 103 is, for example, a point where, when the contour 100 is represented by y(x) in a two-dimensional coordinate system with the second direction D2 as the X axis and the third direction D3 as the Y axis, the value obtained by second-order differentiation of y(x) with respect to x becomes 0 and the sign of the second-order differentiation changes before and after the inflection point 103. In other words, the inflection point 103 is a point where the contour 100 changes from a concave shape to a convex shape or from a convex shape to a concave shape.

[0068] The contour 100 according to the embodiment has a concave shape before the inflection point 103, specifically, a curved portion from the first position 101 to the inflection point 103, and a convex shape after the inflection point 103, specifically, a curved portion from the inflection point 103 to the second position 102. Furthermore, the contour 100 according to the embodiment has a tangent with a gradient of 0 at the second position 102.

[0069] In this way, contour 100 may have an inflection point 103. This makes it less likely for the protective layer 25 and the recording medium P to stick together compared to when contour 100 does not have an inflection point 103, for example, when the slope of contour 100 monotonically decreases and becomes zero at second position 102. This is because a gap is generated between the recording medium P and protective layer 25 at the location of inflection point 103, thereby reducing the contact area between the recording medium P and protective layer 25.

[0070] The end of the first protrusion 13a refers to the end of the first protrusion 13a in the second direction D2, and the center of the second protrusion 15a refers to the center of the second protrusion 15a in the second direction D2. The center of the second protrusion 15a in the second direction D2 refers to, for example, the center of three regions obtained by dividing the second protrusion 15a into three equal parts in the second direction D2. The "end of the first protrusion 13a" may be read as the "end of the heat storage layer 13," and the "center of the second protrusion 15a" may be read as the "center of the resistor layer 15."

[0071] Next, a thermal printer Z1 having a thermal head X1 will be described with reference to Fig. 10. Fig. 10 is a schematic diagram of the thermal printer Z1 according to an embodiment.

[0072] The thermal printer Z1 according to the embodiment includes the thermal head X1, a transport mechanism 40, a platen roller 50, a power supply unit 60, and a control unit 70. The thermal head X1 is attached to a mounting surface 80a of a mounting member 80 disposed in a housing (not shown) of the thermal printer Z1. The thermal head X1 is attached to the mounting member 80 so as to be aligned in the main scanning direction, which is perpendicular to the transport direction S.

[0073] The transport mechanism 40 includes a drive unit (not shown) and transport rollers 43, 45, 47, and 49. The transport mechanism 40 transports a recording medium P, such as thermal paper or image receiving paper onto which ink is transferred, along the transport direction S indicated by the arrow, onto the protective layer 25 located above the heat generating elements 9 of the thermal head X1. The drive unit functions to drive the transport rollers 43, 45, 47, and 49. For example, a motor may be used as the drive unit. The transport rollers 43, 45, 47, and 49 may each have a cylindrical shaft 43a, 45a, 47a, or 49a made of a metal such as stainless steel, covered with an elastic member 43b, 45b, 47b, or 49b made of a material such as butadiene rubber. When the recording medium P is an image receiving paper onto which ink is transferred, an ink film (not shown) is transported between the recording medium P and the heat generating elements 9 of the thermal head X1 along with the recording medium P.

[0074] The platen roller 50 has the function of pressing the recording medium P onto the protective layer 25 located above the heat generating portion 9 of the thermal head X1. The platen roller 50 is disposed so as to extend in a direction perpendicular to the transport direction S, and both ends are supported and fixed so that it can rotate while pressing the recording medium P onto the heat generating portion 9. The platen roller 50 may be configured, for example, by covering a cylindrical shaft 50a made of a metal such as stainless steel with an elastic member 50b made of butadiene rubber or the like.

[0075] As described above, the power supply device 60 has a function of supplying a current for generating heat from the heat generating portion 9 of the thermal head X1 and a current for operating the driving IC 11. The control device 70 has a function of supplying a control signal to the driving IC 11 for controlling the operation of the driving IC 11 in order to selectively generate heat from the heat generating portion 9 of the thermal head X1.

[0076] The thermal printer Z1 presses the recording medium P onto the heat generating portion 9 of the thermal head X1 with the platen roller 50, transports the recording medium P onto the heat generating portion 9 with the transport mechanism 40, and selectively causes the heat generating portion 9 to heat with the power supply unit 60 and the control unit 70. In this way, the thermal printer Z1 performs a predetermined print on the recording medium P. Note that if the recording medium P is receiver paper or the like, printing on the recording medium P is performed by thermally transferring ink from an ink film (not shown) transported together with the recording medium P to the recording medium P.

[0077] As described above, the thermal head X1 according to the embodiment has a two-step protrusion shape in which the second protrusion 15a of the resistor layer 15 is located above the first protrusion 13a of the heat storage layer 13. This configuration increases the pressure from the resistor layer 15 to the recording medium P (see FIG. 10 ) compared to a case without a two-step protrusion shape, improving heat transfer and improving the printing characteristics of the thermal head X1. Furthermore, in the thermal head X1 according to the embodiment, the curvature of the second protrusion 15a is greater than that of the first protrusion 13a, so the pressure from the resistor layer 15 to the recording medium P is higher compared to a case in which the curvature of the second protrusion 15a and the curvature of the first protrusion 13a are the same. This improves the printing characteristics of the thermal head X1.

[0078] The present technology may also be configured as follows. (1) A thermal head (for example, thermal head X1) includes a substrate (for example, substrate 7), a heat storage layer (for example, heat storage layer 13), electrodes (for example, third common electrode 17c and individual electrodes 19), and a resistor layer (for example, resistor layer 15). The heat storage layer is located on the substrate and extends along a first direction of the substrate. The electrodes are located on the heat storage layer and extend along a second direction intersecting the first direction. The resistor layer is located on the heat storage layer and the electrodes and extends along the first direction. The heat storage layer has a first protrusion (for example, first protrusion 13a) protruding from an upper surface of the substrate in a thickness direction of the substrate. The resistor layer is located on the first protrusion and has a second protrusion (for example, second protrusion 15a) protruding in a thickness direction from an upper surface of the heat storage layer and the electrodes. When viewed in cross section on a plane perpendicular to the first direction, the curvature of the second protrusion is greater than the curvature of the first protrusion. (2) In the thermal head described in (1) above, the electrodes may include first electrodes (e.g., third common electrode 17c) and second electrodes (e.g., individual electrodes 19) alternately arranged at a predetermined interval in the first direction. In this case, the first electrodes and second electrodes may have third protrusions (e.g., common protrusion 17d and individual protrusion 19b) on the upper surface of the heat storage layer, whose central portions in the first direction protrude further than their ends in the first direction. (3) In the thermal head described in (1) or (2) above, the dimension of the resistor layer in the second direction may be 0.9 to 1.45 times the distance between the centers of the first electrodes located on both sides of a predetermined second electrode, and may be 1 / 10 to 1 / 3 of the dimension of the heat storage layer in the second direction. (4) In the thermal head described in any one of (1) to (3) above, the thickness of the second protrusion may be two to eight times the thickness of the third protrusion, and may be one-eighth to one-third the thickness of the first protrusion. (5) In the thermal head described in any one of (1) to (4) above, the curvature of the second protrusion may be 1.5 to 40 times the curvature of the first protrusion when viewed in cross section on a plane perpendicular to the first direction. (6) In the thermal head described in any one of (1) to (5) above, the electrodes may have first electrodes and second electrodes alternately arranged at a predetermined interval in the first direction.In this case, the thickness of the first electrode may be different from the thickness of the second electrode. (7) In the thermal head described in (6) above, the thickness of the second electrode may be thicker than the thickness of the first electrode. (8) In the thermal head described in (6) above, the thickness of the first electrode may be thicker than the thickness of the second electrode. (9) In the thermal head described in any one of (1) to (8) above, the heat storage layer is divided into two equal regions in the thickness direction, and the region closer to the substrate is defined as the first region, and the region farther from the substrate is defined as the second region. In this case, when viewed in cross section on a plane perpendicular to the first direction, the curvature of the second region may be greater than the curvature of the first region. (10) The thermal head described in any one of (1) to (9) above may further include a protective layer (e.g., protective layer 25) covering the electrodes and the heat storage layer. In this case, the thickness of the protective layer in the second direction may be constant. (11) In the thermal head described in (10) above, the protective layer may have a plurality of laminated protective films (for example, protective films 25a and 25b). In this case, at least one of the plurality of protective films may be a thin protective film. (12) In the thermal head described in (11) above, the thin protective film may be located on the surface of the protective layer. (13) In the thermal head described in (11) above, the thin protective film is made of SiO. ２, SiN, SiON, SiC, SiAlON, TiN, TiCN, TiCrN, TiAlN, and CrN. (14) The thermal head described in any one of (1) to (9) above may further include a protective layer covering the electrode and the resistor layer. In this case, when viewed in cross section along a plane perpendicular to the first direction, the contour of the outermost surface of the protective layer may have an inflection point between a position covering the end of the first protrusion and a position covering the center of the second protrusion. (15) The thermal head may include a substrate, a heat storage layer located on the substrate and extending along the first direction of the substrate, an electrode located on the heat storage layer and extending along a second direction intersecting the first direction, a resistor layer located on the heat storage layer and the electrode and extending along the first direction, and a protective layer covering the electrode and the heat storage layer. In this case, the thickness of the protective layer in the second direction may be constant. (16) In the thermal head described in (15) above, when viewed in cross section on a plane perpendicular to the first direction, the contour of the outermost surface of the protective layer may have an inflection point between a position covering an end of the heat storage layer and a position covering a center portion of the resistor layer. (17) A thermal printer (for example, a thermal printer Z1) may include the thermal head described in any one of (1) to (16) above, a transport mechanism (for example, a transport mechanism 40) that transports a recording medium onto a heat generating portion (for example, a heat generating portion 9) located on a substrate, and a platen roller (for example, a platen roller 50) that presses the recording medium onto the heat generating portion.

[0079] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0080] X1 Thermal head Z1 Thermal printer 1 Heat sink 3 Head base 7 Substrate 9 Heat generating portion 10 Electrode pad 11 Driving IC 15 Resistive layer 17 Common electrode 17c Third common electrode 19 Individual electrode 25 Protective layer 27 Covering layer 29 Covering member 40 Transport mechanism 50 Platen roller

Claims

1. A thermal head comprising: a substrate; a heat storage layer located on the substrate and extending along a first direction of the substrate; an electrode located on the heat storage layer and extending along a second direction intersecting the first direction; and a resistor layer located on the heat storage layer and the electrode and extending along the first direction, wherein the heat storage layer has a first protrusion protruding from an upper surface of the substrate in a thickness direction of the substrate, and the resistor layer is located on the first protrusion and has a second protrusion protruding from an upper surface of the heat storage layer and the electrode in the thickness direction, and when viewed in cross section on a plane perpendicular to the first direction, the curvature of the second protrusion is greater than the curvature of the first protrusion.

2. A thermal head as described in claim 1, wherein the electrodes include first electrodes and second electrodes arranged alternately at a predetermined interval in the first direction, and the first electrodes and the second electrodes have third protrusions on the upper surface of the heat storage layer, the central portions of the first electrodes protruding in the first direction more than the ends in the first direction.

3. A thermal head as described in claim 2, wherein the dimension of the resistor layer in the second direction is 0.9 times or more and less than 1.45 times the distance between the centers of the first electrodes located on both sides of a predetermined second electrode, and is 1 / 10 or more and 1 / 3 or less of the dimension of the heat storage layer in the second direction.

4. A thermal head as described in claim 2 or 3, wherein the thickness of the second protrusion is between two and eight times the thickness of the third protrusion, and between 1 / 8 and 1 / 3 the thickness of the first protrusion.

5. A thermal head described in any one of claims 1 to 4, wherein, when viewed in cross section on a plane perpendicular to the first direction, the curvature of the second protrusion is 1.5 to 40 times the curvature of the first protrusion.

6. A thermal head according to any one of claims 1 to 5, wherein the electrodes have first electrodes and second electrodes arranged alternately at a predetermined interval in the first direction, and the thickness of the first electrodes is different from the thickness of the second electrodes.

7. A thermal head according to claim 6, wherein the thickness of the second electrode is greater than the thickness of the first electrode.

8. A thermal head according to claim 6, wherein the thickness of the first electrode is greater than the thickness of the second electrode.

9. A thermal head according to any one of claims 1 to 8, wherein when the heat storage layer is divided into two equal regions in the thickness direction, the region closer to the substrate is defined as a first region and the region farther from the substrate is defined as a second region, the curvature of the second region is greater than the curvature of the first region when viewed in cross section on a plane perpendicular to the first direction.

10. A thermal head according to any one of claims 1 to 9, further comprising a protective layer covering the electrodes and the heat storage layer, the thickness of the protective layer being constant in the second direction.

11. A thermal head according to claim 10, wherein the protective layer has a plurality of laminated protective films, and at least one of the plurality of protective films is a thin protective film.

12. The thermal head according to claim 11, wherein the thin protective film is located on the surface of the protective layer.

13. The thin protective film is made of SiO ２ 13. The thermal head according to claim 11, further comprising any one of SiN, SiON, SiC, SiAlON, TiN, TiCN, TiCrN, TiAlN, and CrN.

14. A thermal head as described in any one of claims 1 to 9, further comprising a protective layer covering the electrodes and the resistor layer, wherein when viewed in cross section on a plane perpendicular to the first direction, the contour of the outermost surface of the protective layer has an inflection point between a position covering the end of the first protrusion and a position covering the center of the second protrusion.

15. A thermal head comprising: a substrate; a heat storage layer located on the substrate and extending along a first direction of the substrate; electrodes located on the heat storage layer and extending along a second direction intersecting the first direction; a resistor layer located on the heat storage layer and the electrodes and extending along the first direction; and a protective layer covering the electrodes and the heat storage layer, wherein the thickness of the protective layer in the second direction is constant.

16. A thermal head as described in claim 15, wherein, when viewed in cross section on a plane perpendicular to the first direction, the contour of the outermost surface of the protective layer has an inflection point between the position covering the end of the heat storage layer and the position covering the center of the resistor layer.

17. A thermal printer comprising: a thermal head according to any one of claims 1 to 16; a transport mechanism for transporting a recording medium onto a heat generating portion located on the substrate; and a platen roller for pressing the recording medium onto the heat generating portion.

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