Thermal head and thermal printer

Abstract

A thermal head (X1) has a substrate (7), electrodes (17, 19), and a resistive layer (15). The electrodes (17, 19) are located above the substrate (7) and extend along a first direction (D1) of the substrate (7) in plan view. The resistive layer (15) is located above the substrate (7) and above the electrodes (17, 19). The electrodes (17, 19) have first electrodes (17c) and second electrodes (19) that are side by side at given intervals in a second direction (D2) that intersects the first direction (D1). At least one of the first electrodes (17c) and the second electrodes (19) has a top surface (19a) that is located below the resistive layer (15), and a central portion of the second direction (D2) is more protruding than end portions of the second direction (D2).

Description

Technical Field

[0001] The disclosed implementations relate to thermal printheads and thermal printers. Background Technology

[0002] In the past, various thermal heads were proposed for printing equipment such as fax machines or image printers.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: JP Japanese Patent Application Publication No. 54-99443

[0006] Patent Document 2: JP 2019-119149 Summary of the Invention

[0007] One embodiment of the thermistor includes a substrate, electrodes, and a resistive layer. The electrodes are located above the substrate and extend along a first direction of the substrate. The resistive layer is located above the substrate and above the electrodes. The electrodes have a first electrode and a second electrode arranged side-by-side at a given interval in a second direction intersecting the first direction. At least one of the first electrode and the second electrode is located on an upper surface below the resistive layer, with the central portion of the second direction protruding more than its end portion.

[0008] Furthermore, one embodiment of the present invention includes a thermal printer comprising the thermal head, transport mechanism, and pressure roller described above. The transport mechanism transports the recording medium onto a heating element located above a substrate. The pressure roller presses the recording medium onto the heating element. Attached Figure Description

[0009] Figure 1 This is a schematic perspective view showing the thermal head involved in the implementation method.

[0010] Figure 2 It means Figure 1 The diagram shows a simplified cross-sectional view of the thermal head.

[0011] Figure 3 It means Figure 1 A schematic top view of the head base shown.

[0012] Figure 4 yes Figure 3 Sectional view of line IV-IV.

[0013] Figure 5 This is a cross-sectional view of the main parts of the thermal head involved in the reference method.

[0014] Figure 6These are cross-sectional views of the main parts of the thermal head involved in the first and second variations of the implementation.

[0015] Figure 7A yes Figure 6 The enlarged cross-sectional view of part P1 is shown.

[0016] Figure 7B yes Figure 6 The enlarged cross-sectional view of part P2 is shown.

[0017] Figure 8 This is a cross-sectional view of the main part of the thermal head involved in the third variation of the embodiment.

[0018] Figure 9 This is a cross-sectional view of the main part of the thermal head involved in the fourth variation of the embodiment.

[0019] Figure 10 This is a cross-sectional view of the main part of the thermal head involved in the fifth variation of the embodiment.

[0020] Figure 11 This is a cross-sectional view of the main part of the thermal head involved in the sixth variation of the embodiment.

[0021] Figure 12 This is a schematic diagram of the thermal printer involved in the implementation method.

[0022] Figure 13A It is a 3D view of the simulation model.

[0023] Figure 13B yes Figure 13A The top view of the simulation model shown.

[0024] Figure 14A Viewed from the long side Figure 13A The side view of the simulation model shown.

[0025] Figure 14B This is a side view of the simulation model of the thermal head involved in the implementation method, viewed from the short side.

[0026] Figure 14C This is a side view of the simulation model of the thermal head involved in the reference method, viewed from the short side.

[0027] Figure 15 It is a table summarizing the physical property values ​​used in the simulation.

[0028] Figure 16 It is a graph representing the simulation results.

[0029] Figure 17A This is a diagram showing the simulation results of the thermal head involved in the implementation method.

[0030] Figure 17B This is a graph showing the simulation results of the thermal head involved in the reference method. Detailed Implementation

[0031] The embodiments of the thermal head and thermal printer disclosed in this application are described below with reference to the accompanying drawings. However, the invention is not limited to the embodiments shown below.

[0032] In the existing construction of thermal printheads, there is still room for improvement, for example, in terms of enhancing print quality. In view of the above, this disclosure provides a thermal printhead and a thermal printer that can improve print quality.

[0033] <Implementation Method>

[0034] Figure 1 This is a schematic perspective view showing the thermal head involved in the embodiment. For example... Figure 1 As shown, the thermal head X1 according to the embodiment includes a heat sink 1, a head base 3, and an FPC (flexible printed wiring board) 5. The head base 3 is located on the heat sink 1. The FPC 5 is electrically connected to the head base 3. The head base 3 includes a substrate 7, a heat-generating part 9, multiple driver ICs 11, and a covering member 29.

[0035] The heat sink 1 is plate-shaped. Viewed from above, the heat sink 1 has a rectangular shape. The heat sink 1 has a heat dissipation function. Specifically, the heat sink 1 releases the heat generated in the heating part 9 of the head base 3 that is not contributed to the printing process to the outside of the thermal head X1. The head base 3 is bonded to the upper surface of the heat sink 1 using double-sided tape or adhesive (not shown). The heat sink 1 is made of metal materials such as copper, iron, or aluminum.

[0036] The head substrate 3 is plate-shaped. Viewed from above, the head substrate 3 is rectangular. The components constituting the thermal head X1 are arranged on the head substrate 3 above the substrate 7. The head substrate 3 operates according to an externally supplied electrical signal on the recording medium P (reference). Figure 12 (to print the characters.)

[0037] The driver IC 11 is located on the substrate 7. Multiple driver ICs 11 are arranged along the main scanning direction. The driver IC 11 is an electronic component that controls the energizing state of each heating element 9. As an example, a switching component with multiple internal switching elements can be used as the driver IC 11.

[0038] The driver IC11 is covered by a coating member 29 made of resin such as epoxy resin or silicone resin. The coating member 29 is provided on multiple driver ICs 11. The coating member 29 is an example of a seal.

[0039] For example, FPC5 has a pair of first and second ends in the short side direction. The first end of FPC5 is electrically connected to the head base 3. The second end of FPC5 is electrically connected to the connector 31.

[0040] FPC5 uses conductive bonding material 23 (reference) Figure 2 It is electrically connected to the head substrate 3. As an example, an anisotropic conductive film (ACF) in which conductive particles are mixed into solder material or electrically insulating resin can be used as conductive bonding material 23.

[0041] The following is used Figures 1-3 To explain the components that make up the head base 3. Figure 2 It means Figure 1 The diagram shows a simplified cross-sectional view of the thermal head. Figure 3 It means Figure 1 A schematic top view of the head base shown.

[0042] The head substrate 3 also includes a substrate 7, a common electrode 17, an independent electrode 19, a third electrode 12, a fourth electrode 14, a terminal 2, a resistive layer 15, a protective layer 25, and a coating layer 27. Additionally, in Figure 1 In the text, protective layer 25 and coating layer 27 are omitted. Furthermore, Figure 3 The wiring of the head base 3 is simplified. Figure 3 In this text, the driver IC11, protective layer 25, and coating layer 27 are omitted. Furthermore, in... Figure 3 In this paper, the structure of the fourth electrode 14 is simplified.

[0043] The substrate 7 is rectangular in shape when viewed from above. The main surface (upper surface) 7e of the substrate 7 has a first long side 7a, a second long side 7b, a first short side 7c, and a second short side 7d. The substrate 7 is made of an electrically insulating material such as alumina ceramic or a semiconductor material such as single-crystal silicon.

[0044] Furthermore, the substrate 7 may have a heat storage layer 13. The heat storage layer 13 protrudes from the main surface 7e in the thickness direction of the substrate 7 and is a strip-shaped portion extending along the second direction D2 (main scanning direction). The heat storage layer 13 has the function of pressing the recording medium being printed against the protective layer 25 located on the heating part 9.

[0045] Additionally, the heat storage layer 13 may have a base. In this case, the base is a portion that is disposed over the entire area of ​​the main surface 7e side of the substrate 7.

[0046] The heat storage layer 13 contains, for example, glass. The heat storage layer 13 temporarily stores a portion of the heat generated in the heating element 9. Therefore, the heat storage layer 13 can shorten the time required for the temperature of the heating element 9 to rise. That is, the heat storage layer 13 has the function of improving the thermal response characteristics of the thermistor X1.

[0047] The heat storage layer 13 is fabricated, for example, by applying a given glass paste obtained by mixing glass powder with a suitable organic solvent using a method known in the past, such as screen printing, onto the main surface 7e side of the substrate 7 and then firing it. Alternatively, the substrate 7 may have only the base as the heat storage layer 13.

[0048] like Figure 3 As shown, the common electrode 17 is located on the main surface 7e of the substrate 7. The common electrode 17 is made of a conductive material. For example, any metal or alloy of aluminum, gold, silver, and copper can be used as the common electrode 17.

[0049] like Figure 3 As shown, the common electrode 17 has a first common electrode 17a, a plurality of second common electrodes 17b, a third common electrode 17c, and a plurality of terminals 2. The common electrode 17 is electrically connected to a common ground with the plurality of components of the heating unit 9.

[0050] The first common electrode 17a is located between the first long side 7a of the substrate 7 and the heating element 9. The first common electrode 17a extends in the main scanning direction. A plurality of second common electrodes 17b extend in the sub-scanning direction. One of the plurality of (here, two) second common electrodes 17b is located on the side of the first short side 7c of the substrate 7, and the other is located on the side of the second short side 7d. The second common electrode 17b connects the terminal 2 and the first common electrode 17a. The third common electrode 17c extends from the first common electrode 17a in a comb-like manner towards each element of the heating element 9, with a portion inserted on the opposite side of the heating element 9. The third common electrodes 17c are respectively provided at intervals from each other in the second direction D2 (main scanning direction). The third common electrode 17c is an example of the first electrode.

[0051] Individual electrodes 19 are located on the main surface 7e of the substrate 7. Individual electrodes 19 contain metallic components and are conductive. Individual electrodes 19 are formed, for example, of metals such as aluminum, nickel, gold, silver, platinum, palladium, copper, and their alloys. Multiple individual electrodes 19 are arranged along the main scanning direction. Individual electrodes 19 are located between two adjacent third common electrodes 17c. Therefore, the third common electrodes 17c and individual electrodes 19 of the thermistor X1 are alternately arranged in the main scanning direction. Individual electrodes 19 are connected to electrode pads 10 on the second long side 7b of the substrate 7. Individual electrodes 19 are an example of a second electrode.

[0052] The third electrode 12 is connected to the electrode pad 10. The third electrode 12 extends in the sub-scanning direction. The driver IC 11 is mounted on the electrode pad 10 as described above.

[0053] The fourth electrode 14 extends in the main scanning direction. The fourth electrode 14 is disposed around a plurality of third electrodes 12. The fourth electrode 14 is connected to the outside via a terminal 2.

[0054] Terminal 2 is located on the second long side 7b of substrate 7. Terminal 2 is connected to conductive bonding material 23 (see reference). Figure 2 It is connected to FPC5. Thus, the head base 3 is electrically connected to the outside.

[0055] The aforementioned independent electrode 19, third common electrode 17c, and third electrode 12 can, for example, use a conductive paste containing metal and glass components in an organic solvent as electrode materials. Furthermore, the independent electrode 19, third common electrode 17c, and third electrode 12 can be fabricated on the substrate 7 using methods such as screen printing, aniline printing, gravure printing, and offset gravure printing to form their respective material layers. Alternatively, the independent electrode 19, third common electrode 17c, and third electrode 12 can also be fabricated, for example, by sequentially stacking them using conventional thin-film forming techniques such as sputtering, and then processing the stacked body into a predetermined pattern using conventional photolithography.

[0056] Furthermore, the first common electrode 17a, the second common electrode 17b, the fourth electrode 14, and the terminal 2 described above can be fabricated on the substrate 7 using, for example, screen printing to form their respective material layers. The thickness of the first common electrode 17a, the second common electrode 17b, the fourth electrode 14, and the terminal 2 is, for example, about 5 to 20 μm. In this way, by forming thick electrodes, the wiring resistance of the head substrate 3 can be reduced. Additionally, the portion of the thick electrode... Figure 3 The dots are indicated in the image below, as are the dots in the following figures.

[0057] The resistive layer 15 spans the third common electrode 17c and the independent electrode 19, and is disposed in a separated state from the first long side 7a of the substrate 7. The portion of the resistive layer 15 located between the third common electrode 17c and the independent electrode 19 functions as elements of the heating element 9. The elements of the heating element 9... Figure 3 In a simplified description, for example, the elements can be arranged at a density of 100 dpi (dots per inch) or higher. Furthermore, the elements of the heating unit 9 can be arranged at a density of 200 to 2400 dpi.

[0058] The thickness of the resistive layer 15 is, for example, about 3 to 6 μm. The sheet resistance of the resistive layer 15 is, for example, about 500 to 8000 Ω / Ω. Furthermore, the coefficient of thermal expansion of the resistive layer 15 is, for example, about 5 to 10 ppm / ℃. Furthermore, the thermal conductivity of the resistive layer 15 is, for example, about 0.5 to 2 W / (m·K).

[0059] For example, on a substrate 7 patterned with various electrodes, a paste containing conductive and glass components can be formed into a long strip in the main scanning direction using screen printing or a dispensing device, thereby forming a resistive layer 15. The conductive component may, for example, contain ruthenium oxide. The glass component may, for example, contain lead borosilicate glass.

[0060] The protective layer 25 is located on the main surface 7e of the substrate 7 (reference). Figure 1 The heat storage layer 13 is covered by a protective layer 25. The protective layer 25 is provided along the main scanning direction of the substrate 7 so as to separate from the electrode pad 10 from the first long side 7a of the substrate 7.

[0061] The protective layer 25 is insulating. Therefore, the protective layer 25 protects the covered area from corrosion caused by the adhesion of moisture in the atmosphere, or from abrasion caused by contact with the recording medium used for printing. The protective layer 25 can be made of glass, for example. The protective layer 25 can be manufactured using thick-film forming techniques such as printing. The protective layer 25 can, for example, contain lead borosilicate glass. Furthermore, the protective layer 25 can, for example, further contain one or both of alumina and zirconium oxide.

[0062] Furthermore, the protective layer 25 can be fabricated using materials such as SiN, SiON, SiO2, SiC, C-SiC, TiN, TiAlN, TiC, TiCN, TiSiN, CrN, or DLC (diamond-like carbon). Such a protective layer 25 can be fabricated using thin film formation techniques such as sputtering.

[0063] Furthermore, the protective layer 25 may, for example, have a surface roughness Ra of less than 0.3 μm.

[0064] A coating layer 27 is located on the substrate 7, such that it partially covers the common electrode 17, the individual electrode 19, the third electrode 12, and the fourth electrode 14. The coating layer 27 protects the covered area from oxidation caused by contact with the atmosphere, or corrosion caused by the adhesion of moisture contained in the atmosphere. The coating layer 27 can be made of resin materials such as epoxy resin, polyimide resin, or silicone resin.

[0065] Next, use Figure 4 The main parts of the thermal head X1 involved in the implementation method will be described in detail. Figure 4 yes Figure 3 Sectional view of line IV-IV.

[0066] like Figure 4 As shown, the thermal head X1 according to the embodiment has a heat storage layer 13, a third common electrode 17c, an independent electrode 19, a resistive layer 15 and a protective layer 25.

[0067] The third common electrode 17c and the independent electrode 19 are located above the heat storage layer 13. The third common electrode 17c and the independent electrode 19 are separated by a gap d.

[0068] The resistive layer 15 is located above the third common electrode 17c and the independent electrode 19, and above the heat storage layer 13, which does not have the third common electrode 17c and the independent electrode 19. Thus, the third common electrode 17c and the independent electrode 19 are respectively sandwiched between the heat storage layer 13 and the resistive layer 15. Furthermore, the protective layer 25 is configured to cover the resistive layer 15.

[0069] Here, the cross-sectional shapes of the third common electrode 17c and the independent electrode 19 are described. The third common electrode 17c, located on the upper surface 17ca below the resistive layer 15, protrudes further towards the third direction D3 from the center of the second direction D2 than from the end of the second direction D2. The third direction D3 is the same as the first direction D1 (refer to...). Figure 3 And the direction in which the second direction D2 intersects. Similarly, the independent electrode 19 on the upper surface 19a below the resistive layer 15, the central part of the second direction D2 protrudes further toward the third direction D3 than the end of the second direction D2.

[0070] The width w of the independent electrode 19 and the third common electrode 17c is, for example, about 10 to 50 μm. Furthermore, the width w of the independent electrode 19 and the third common electrode 17c can be, for example, about 20 to 30 μm. Furthermore, the thickness t of the independent electrode 19 and the third common electrode 17c is, for example, about 0.5 to 5 μm. Furthermore, the thickness t of the independent electrode 19 and the third common electrode 17c can be, for example, about 1 to 2 μm. The width w of the independent electrode 19 and the third common electrode 17c can be the same or different. Furthermore, the thickness t of the independent electrode 19 and the third common electrode 17c can also be the same or different.

[0071] Thus, the central portions of the upper surfaces 17ca and 19a of the independent electrode 19 and the third common electrode 17c protrude toward the third direction D3. Therefore, the thermal head X1 according to the embodiment is flatter than the upper surfaces 17ca and 19a of the independent electrode 19 and the third common electrode 17c along the first direction D1 (refer to...). Figure 3 In the case of direction D2, the print quality is improved. (Using...) Figure 4 , Figure 5 Let me elaborate on this aspect further.

[0072] Figure 5 This is a cross-sectional view of the main parts of the thermal head involved in the reference method. For example... Figure 5As shown, the thermal head Y1 involved in the reference configuration, except that the cross-sections of the third common electrode 17c and the independent electrode 19 are rectangular, has the same... Figure 4 The thermal head X1 shown has the same structure.

[0073] Figure 4 The thermal head X1 shown and Figure 5 The thermal head Y1 shown heats up when a given voltage is applied between the third common electrode 17c and the independent electrode 19. Specifically, in Figure 4 In the thermistor X1 shown, the portion 9a of the resistive layer 15 with a generally trapezoidal cross-section sandwiched between the third common electrode 17c and the independent electrode 19 becomes the main heat-generating part.

[0074] On the other hand, Figure 5 In the thermistor Y1 shown, the portion 9b of the resistive layer 15 with a generally trapezoidal cross-section sandwiched between the third common electrode 17c and the independent electrode 19 becomes the main heat-generating part.

[0075] In thermal heads X1 and Y1, if the width w and thickness t of the third common electrode 17c and the independent electrode 19, and the spacing d between the third common electrode 17c and the independent electrode 19 are made consistent, then compared to part 9b, the cross-sectional area and volume of part 9a become larger. At this time, assuming it is between thermal heads X1 and Y1, Figure 4 The resistance values ​​between the third common electrode 17c and the independent electrode 19 are the same. In this case, if the same pulse voltage is applied to the thermal heads X1 and Y1, the thermal head X1, which has a larger heating area, transfers heat more easily to the resistive layer 15, which is farther away from the portion 9a, compared to the thermal head Y1. Therefore, it is possible to divide adjacent heating portions 9 (refer to...) Figures 1-3 The temperature of the resistive layer 15, located above the center of the upper surface 17ca and upper surface 19a in the second direction D2, rises moderately. As a result, the temperature difference between parts of the upper surface of the resistive layer 15 decreases. Consequently, the contact between dots in the printed material printed by the thermal print head X1 becomes better, and the print quality is improved.

[0076] As described above, the third common electrode 17c and the individual electrode 19 in the thermal head X1 can be fabricated on the substrate 7 using methods such as screen printing, aniline printing, gravure printing, and gravure offset printing to form their respective material layers. For example, a paste made by gravure printing with a desired groove shape is transferred onto a support serving as an intermediate support. Then, by appropriately adjusting the holding time and pressing intensity, the paste is transferred again onto the heat storage layer 13. Thus, a material layer with a desired shape can be positioned on the substrate 7. However, the method of fabricating the third common electrode 17c and the individual electrode 19 is not limited to the above; the third common electrode 17c and the individual electrode 19 can be arranged using any method.

[0077] <Variation Example>

[0078] Next, the thermal head X1 involved in the first to sixth modifications of the embodiment will be described. Figure 6 These are cross-sectional views of the main parts of the thermal head involved in the first and second variations of the implementation.

[0079] like Figure 6 As shown, in the first modified example, the thickness t1 of the resistive layer 15 above the center portion in the width direction (second direction D2) of the thermistor X1 is smaller than the thickness t2 of the resistive layer 15 above the end portion in the second direction D2. By making the thickness t1 smaller than the thickness t2, the thickness of the resistive layer 15 above the heating portion 9 (see reference 9) is reduced. Figures 1-3 The heat conduction distance from the surface of the resistive layer 15 in region R1 (where heat generation is lower) to the surface of the resistive layer 15 in region R2 is shorter. As a result, the temperature difference between parts on the upper surface of the resistive layer 15 decreases. Consequently, the contact between dots in the printed material printed by the thermal printhead X1 becomes better, and the print quality is improved.

[0080] Furthermore, in the thermal head X1 involved in the second modification example, in Figure 6 The interfaces between parts P1 and P2 shown have different shapes. Figure 7A yes Figure 6 The enlarged cross-sectional view of part P1 is shown. Figure 7B yes Figure 6 The enlarged cross-sectional view of part P2 is shown.

[0081] like Figure 7A , Figure 7B As shown, the unevenness of the interface between the upper surface 17ca of the third common electrode 17c and the resistive layer 15 (refer to...) Figure 7A The unevenness of the interface 13a between the resistive layer 15 and the heat storage layer 13 can be compared (see reference). Figure 7BThe unevenness of the interface can be determined by measuring the difference in elevation between the highest and lowest points (the difference in elevation between the most prominent and the most recessed parts) within a 10 μm region along the interface at any location in a cross-sectional photograph, and setting this as the magnitude of the unevenness of the interface. The magnitude of the unevenness can be determined, for example, by visual inspection based on SEM (Scanning Electron Microscope) images. Furthermore, although the illustration is omitted, the unevenness of the interface between the upper surface 19a of the independent electrode 19 and the resistive layer 15 can be set to be the same as the unevenness of the interface between the upper surface 17ca and the resistive layer 15. That is, the unevenness of the interface between the upper surface 19a and the resistive layer 15 can be greater than the unevenness of the interface between the resistive layer 15 and the heat storage layer 13.

[0082] If the unevenness of the interface between the resistive layer 15 and the heat storage layer 13 is reduced, the deviation of the current path at the interface between the resistive layer 15 and the heat storage layer 13, for example, in region R2, becomes smaller. Furthermore, if the unevenness of the interface between the upper surface 17ca and the resistive layer 15 is increased, the interface resistance between the upper surface 17ca and the resistive layer 15, for example, in region R1, becomes smaller, thus reducing the deviation of the interface resistance. As a result, the deviation of the resistance values ​​between adjacent electrodes in the second direction D2 becomes smaller, and since the unevenness of the density between dots in the printed material printed by the thermal head X1 can be reduced, the print quality is improved.

[0083] Next, use Figure 8 To illustrate the thermal head X1 involved in the third variation. Figure 8 This is a cross-sectional view of the main part of the thermal head involved in the third variation of the embodiment.

[0084] like Figure 8 As shown, the thickness t3 of the protective layer 25 located above the third common electrode 17c (and the independent electrode 19) can be smaller than the thickness t4 of the protective layer 25 located above the resistive layer 15 located between the third common electrode 17c and the independent electrode 19.

[0085] By reducing the area located near the heating element 9 (reference) Figures 1-3 The thickness of the protective layer 25 in region R1, where heat generation is lower, results in a shorter heat conduction distance to the surface of the protective layer 25 compared to the distance to the surface of the protective layer 25 in region R2. Consequently, the temperature difference between parts on the upper surface of the protective layer 25 decreases. This leads to better dot adhesion in the printed material printed by the thermal printhead X1, improving print quality.

[0086] in addition, Figure 8The protective layer 25 shown can be fabricated using the following steps: For example, a pattern of a material layer without the protective layer 25 is formed above the resistive layer 15 located above the third common electrode 17c (and the individual electrode 19), for example, by screen printing. Then, through the softening and flow of the material layer caused by firing, it is possible to... Figure 8 The protective layer 25 shown is located above the resistive layer 15. Furthermore, there are no restrictions on the method of fabricating the protective layer 25; it can be fabricated using any method.

[0087] Next, use Figure 9 To illustrate the thermal head X1 involved in the fourth variation. Figure 9 This is a cross-sectional view of the main part of the thermal head involved in the fourth variation of the embodiment.

[0088] like Figure 9 As shown, the third common electrode 17c and the independent electrode 19 protrude more at the center of the upper surfaces 17ca and 19a in the second direction D2 than at the ends of the second direction D2. Furthermore, the third common electrode 17c and the independent electrode 19 may also protrude more towards the negative direction of the third direction D3 (the side of the heat storage layer 13) at the center of the lower surfaces 17cb and 19b located above the heat storage layer 13 than at the ends of the second direction D2.

[0089] Furthermore, in the third common electrode 17c, the amount of protrusion of the central portion relative to the end in the second direction D2 is such that the lower surface 17cb is smaller than the upper surface 17ca. Similarly, in the independent electrode 19, the amount of protrusion of the central portion relative to the end in the second direction D2 is such that the lower surface 19b is smaller than the upper surface 19a.

[0090] exist Figure 9 In the thermal head X1 shown, if a given voltage is applied between the third common electrode 17c and the independent electrode 19, the portion 9c of the resistive layer 15 sandwiched between the third common electrode 17c and the independent electrode 19 becomes the main heat-generating area. By making the protrusions on the lower surfaces 17cb and 19b smaller than those on the upper surfaces 17ca and 19a, the heat generation on the heat storage layer 13 side of the lower portion 9c located on the side opposite to the upper surface of the resistive layer 15 can be reduced. Furthermore, the temperature on the upper surface side of the resistive layer 15 can be appropriately increased. As a result, the dot contact in the printed material printed by the thermal head X1 becomes better, and the print quality is improved.

[0091] Here, the ratio (lower surface protrusion) of the lower surfaces 17cb and 19b to the upper surfaces 17ca and 19a (upper surface protrusion) can be set to, for example, 0.75 or less. The lower surface protrusion can also be 0. However, the value of the lower surface protrusion / upper surface protrusion is not limited to the range described above.

[0092] Next, use Figure 10 To illustrate the thermal head X1 involved in the fifth variation. Figure 10 This is a cross-sectional view of the main part of the thermal head involved in the fifth variation of the embodiment.

[0093] like Figure 10 As shown, the end 17ce of the third common electrode 17c in the second direction D2 protrudes further in the second direction D2 than the end 17cc of the lower surface 17cb of the third common electrode 17c in the second direction D2. Furthermore, the end 17cf of the third common electrode 17c located on the side opposite to end 17ce protrudes further in the opposite direction D2 than the end 17cd of the lower surface 17cb located on the side opposite to end 17cc.

[0094] Similarly, the end 19e of the independent electrode 19 in the second direction D2 protrudes further in the second direction D2 than the end 19c of the lower surface 19b of the independent electrode 19 in the second direction. Furthermore, the end 19f of the independent electrode 19 located on the side opposite to the end 19e protrudes further in the side opposite to the second direction D2 than the end 19d of the lower surface 19b located on the side opposite to the end 19c.

[0095] That is, at least one of the third common electrode 17c and the independent electrode 19 protrudes towards the other of the third common electrode 17c and the independent electrode 19 from the portion closer to the upper surfaces 17ca and 19a than the lower surfaces 17cb and 19b. Additionally, in Figure 10 In the example shown, the third common electrode 17c and the other of the independent electrodes 19 also protrude toward one of the third common electrode 17c and the independent electrode 19 from the portion closer to the upper surfaces 17ca and 19a than the lower surfaces 17cb and 19b, but this may not be the case.

[0096] Thus, the ends 17ce and 19e of the third common electrode 17c and the independent electrode 19 that protrude most towards the second direction D2 can be located at positions that move away from the lower surfaces 17cb and 19b towards the third direction D3, respectively. In this case, the concentration point of the electric field generated between the third common electrode 17c and the independent electrode 19 by energizing is close to the central portion of the resistive layer 15 in the thickness direction (third direction D3). As a result, since the proportion of the portion of the electric field generated between the third common electrode 17c and the independent electrode 19 located inside the resistive layer 15 increases, the heating efficiency of the resistive layer 15 is improved.

[0097] In the above-described embodiments and variations of the thermal head X1, the protective layer 25 located above the resistive layer 15 is described as a single layer, but it is not limited thereto. Figure 11 This is a cross-sectional view of the main part of the thermal head involved in the sixth variation of the embodiment.

[0098] Figure 11 The thermal head X1 shown differs from the thermal head X1 in the embodiment in that it has a first protective layer 25a and a second protective layer 25b instead of the protective layer 25.

[0099] The first protective layer 25a is located above the resistive layer 15. The first protective layer 25a can be made of glass, for example. The first protective layer 25a can, for example, contain lead borosilicate glass. In addition, the first protective layer 25a can further contain one or both of alumina and zirconium oxide.

[0100] The first protective layer 25a is insulating. Therefore, the first protective layer 25a protects against corrosion caused by the adhesion of moisture and other substances contained in the atmosphere.

[0101] The second protective layer 25b is located above the first protective layer 25a. The second protective layer 25b can be made of materials such as SiN, SiON, SiO2, SiC, C-SiC, TiN, TiAlN, TiC, TiCN, TiSiN, CrN, or DLC.

[0102] The second protective layer 25b is insulating. Thus, the second protective layer 25b is protected from corrosion caused by the adhesion of moisture in the atmosphere, or from abrasion caused by contact with the recording medium on which the printing is performed.

[0103] Next, refer to Figure 12 To illustrate the Z1 thermal printer with thermal printhead X1. Figure 12 This is a schematic diagram of the thermal printer involved in the implementation method.

[0104] The thermal printer Z1 according to the embodiment includes the aforementioned thermal head X1, transport mechanism 40, pressure roller 50, power supply 60, and control device 70. The thermal head X1 is mounted on the mounting surface 80a of the mounting member 80 disposed in the housing (not shown) of the thermal printer Z1. Furthermore, the thermal head X1 is mounted on the mounting member 80 along the main scanning direction, which is orthogonal to the transport direction S.

[0105] 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 transfer ink image receiving paper, along the transport direction S indicated by the arrow onto a protective layer 25 located on a plurality of heating elements 9 of the thermal head X1. The drive unit functions to drive the transport rollers 43, 45, 47, and 49. For example, an electric motor can be used as the drive unit. The transport rollers 43, 45, 47, and 49 can, for example, be structures in which cylindrical shafts 43a, 45a, 47a, and 49a made of metal such as stainless steel are covered with elastic members 43b, 45b, 47b, and 49b made of materials such as butadiene rubber. Furthermore, when the recording medium P is image receiving paper or the like with transfer ink, the ink film (not shown) and the recording medium P are transported together between the recording medium P and the heating elements 9 of the thermal head X1.

[0106] The pressure roller 50 has the function of pressing the recording medium P onto the protective layer 25 located on the heating part 9 of the thermal head X1. The pressure roller 50 is configured to extend in a direction orthogonal 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 heating part 9. The pressure roller 50 can be constructed, for example, by covering a cylindrical shaft 50a containing a metal such as stainless steel with an elastic member 50b containing butadiene rubber or the like.

[0107] The power supply unit 60, as described above, provides current for heating the heating element 9 of the thermal head X1 and current for operating the drive IC 11. The control unit 70, as described above, supplies a control signal to the drive IC 11 to selectively heat the heating element 9 of the thermal head X1, thereby controlling the operation of the drive IC 11.

[0108] The thermal printer Z1 presses the recording medium P onto the heating element 9 of the thermal printhead X1 via the pressure roller 50, and transports the recording medium P onto the heating element 9 via the transport mechanism 40. Simultaneously, the heating element 9 is selectively heated via the power supply unit 60 and the control unit 70. Thus, the thermal printer Z1 performs a given print on the recording medium P. Alternatively, when the recording medium P is image receiving paper or the like, printing is performed on the recording medium P by thermally transferring ink from an ink film (not shown) transported along with the recording medium P onto the recording medium P.

[0109] <Experimental Example>

[0110] Next, the simulation performed to confirm the effectiveness of the present invention will be described. First, using... Figures 13A to 14C The construction of the simulation model will be explained below. Furthermore, regarding the simulation model, two models are created: a simulation model X2 of the thermal head according to the implementation method and a simulation model Y2 of the thermal head according to the reference method. The common structures in these two models will be described using the same accompanying drawings.

[0111] Figure 13A It is a 3D view of the simulation model. Figure 13B yes Figure 13A The top view of the simulation model shown. Figure 14A Viewed from the long side Figure 13A The side view of the simulation model shown. Figure 14B This is a side view of the simulation model X2 from the shorter side. Figure 14C This is a side view of the simulation model Y2 from the shorter side.

[0112] Simulation models X2 and Y2 include: a heat storage layer 13; electrodes 20A to 20C located above the heat storage layer 13; and a resistive layer 15 covering the heat storage layer 13 and a portion of electrodes 20A to 20C. Alternatively, electrodes 20A to 20C may sometimes be referred to simply as electrode 20. Electrode 20A, electrode 20C, and electrode 20B are respectively considered as the first electrode and the other as the second electrode.

[0113] The heat storage layer 13 is rectangular with a long side S1 = 300 μm, a short side S2 = 151 μm, and a height of 25 μm. Electrodes 20A to 20C extend along the long side S1 of the heat storage layer 13. Electrodes 20A to 20C are arranged side-by-side at equal intervals along the short side S2. Electrodes 20A to 20C each have a width of 26 μm and a thickness of 1 μm. The maximum height of the resistive layer 15 from the heat storage layer 13 is 6 μm. The resistive layer 15 covers the central portion of the heat storage layer 13 and each of the electrodes 20A to 20C along their respective length directions. The maximum width of the resistive layer 15 is 130 μm.

[0114] like Figure 14B As shown, the upper surface 20a of electrode 20 in simulation model X2 has a curved shape with a central protrusion in the width direction. That is, in simulation model X2, on the upper surface 20a of electrode 20, the central portion in the short side S2 direction protrudes more than the end portion in the short side S2 direction. In contrast, as... Figure 14C As shown, the cross-section of electrode 20 in simulation model Y2 is rectangular, which differs from simulation model X2 in this respect.

[0115] Figure 15 This is a table summarizing the physical property values ​​used in the simulation. Figure 15 The values ​​of thermal conductivity, specific heat, density, and resistivity of electrode 20, resistive layer 15, and heat storage layer 13 are shown. Additionally, the resistivity values ​​of the resistive layer differ slightly in simulation models Y2 and X2. This is because the resistance value between the first and second electrodes (correctly...) Figure 13B The resistance values ​​of parts P11 and P13 and the resistance values ​​between parts P12 are adjusted to be equal in the simulation models Y2 and X2.

[0116] In the simulation model X2 and Y2 described above, a voltage pulse (100μs) is applied to make... Figure 13B Parts P11 and P13 are set to 20V, while part P12 is set to 0V, to simulate the heat generation and temperature of each part. The results are then displayed in... Figure 16 , Figure 17A , Figure 17B As shown.

[0117] Figure 17A , Figure 17B This is a graph showing the heat output of each part. Figure 17A , Figure 17B In the diagram, the parts that generate more heat are shown in a darker color. According to... Figure 17A , Figure 17B As can be seen, in simulation model X2, compared with simulation model Y2, the part with more heat generation extends towards the center in the width direction of electrodes 20A to 20C. In addition, since the parts further outward than electrodes 20A and 20C are not considered in this simulation, the area near electrode 20B in the center is the closest to the actual state.

[0118] Figure 16 This is a graph showing the temperature in the upper surface of the resistive layer 15, indicating that... Figure 13B The temperature of the portion indicated by MP. According to Figure 16 It can be seen that, in simulation model X2, compared with simulation model Y2, the temperature of the part of the upper surface of resistive layer 15 located above electrode 20B is higher.

[0119] The simulations above confirm that the present invention is effective in improving the printing quality of thermal printheads.

[0120] The embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments. Various modifications can be made as long as they do not depart from its spirit. For example, the two or more third common electrodes 17c and independent electrodes 19 involved in the embodiments and their variations can be suitably combined. In addition, only one of the third common electrode 17c and independent electrode 19 may be set as the third common electrode 17c or independent electrode 19 involved in the embodiments and their variations.

[0121] Furthermore, the thermal head X1 can be, for example, a planar head located above the main surface 7e of the substrate 7, including the heating element 9, the heat storage layer 13, the common electrode 17, and the independent electrode 19. However, it is not limited to this; the heating element 9, the heat storage layer 13, the common electrode 17, and the independent electrode 19 may also be located on a surface other than the main surface 7e of the substrate 7.

[0122] Furthermore, the illustration used a so-called thick-film head that forms the resistive layer 15 by printing, but it is not limited to a thick-film head. A so-called thin-film head that forms the resistive layer 15 by sputtering can also be used.

[0123] Alternatively, the connector 31 can be directly electrically connected to the head base 3 without the FPC5. In this case, the connector pin (not shown) of the connector 31 and the electrode pad 10 can be electrically connected.

[0124] Furthermore, a thermal head X1 with a coating layer 27 is illustrated, but the coating layer 27 is not necessarily required. In this case, the protective layer 25 (or the first protective layer 25a and the second protective layer 25b) can be extended to the area where the coating layer 27 is provided.

[0125] Further effects. Variations can be readily derived by those skilled in the art. Therefore, the broader scope of this disclosure is not limited to the specific, detailed, and representative embodiments shown and described above. Thus, various modifications can be made without departing from the spirit or scope of the invention as defined by the appended claims and their equivalents.

[0126] Symbol Explanation

[0127] X1 thermal head

[0128] Z1 Thermal Printer

[0129] 1 Heat sink

[0130] 3-head base

[0131] 7 substrate

[0132] 9. Heating section

[0133] 10 electrode pads

[0134] 11 Driver IC

[0135] 15 Resistor Layer

[0136] 17c Third Common Electrode

[0137] 19 Independent Electrodes

[0138] 25 Protective Layer

[0139] 27. Covering layer

[0140] 29. Covered components.

Claims

1. A thermal head, comprising: substrate; An electrode, located above the substrate, extends along a first direction of the substrate; and A resistive layer is located above the substrate and above the electrodes. The electrode has a first electrode and a second electrode arranged side by side at a given interval in a second direction intersecting the first direction. At least one of the first electrode and the second electrode is located on the upper surface below the resistive layer, wherein the central portion in the second direction protrudes further toward the third direction than the end portion in the second direction, wherein the third direction is a direction that intersects the first direction and the second direction. The portion of at least one of the first electrode and the second electrode that is closer to the upper surface than the lower surface protrudes toward the other of the first electrode and the second electrode.

2. The thermal head according to claim 1, wherein, In at least one of the first electrode and the second electrode, the thickness of the resistive layer located above the central portion in the second direction is smaller than the thickness of the resistive layer located above the end portion in the second direction.

3. The thermal head according to claim 1 or 2, wherein, The surface roughness of the interface between the upper surface of at least one of the first electrode and the second electrode and the resistive layer is greater than the surface roughness of the interface between the resistive layer and the substrate.

4. The thermal head according to claim 1 or 2, wherein, The thermistor includes a protective layer located above the resistive layer. The thickness of the protective layer located above the first electrode and the second electrode is smaller than the thickness of the protective layer disposed above the resistive layer located between the first electrode and the second electrode.

5. The thermal head according to claim 1 or 2, wherein, The substrate has a heat storage layer on at least a portion of its upper surface. The electrode and the resistive layer are located above the heat storage layer.

6. A thermal printer, comprising: The thermal head according to any one of claims 1 to 5; A transport mechanism transports the recording medium to a heating element located above the substrate; and The pressure roller presses the recording medium onto the heating element.

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