Thermal printhead and thermal printer

Abstract

To provide a thermal print head capable of suppressing a printing density level difference to secure good printing performance, and a thermal printer equipped with the same.SOLUTION: A thermal print head 100 comprises: a heat element 40 that generates heat when energized; a drive IC 7A that supplies power to a first part 40A which is a part of the heat element 40; a drive IC 7B that supplies power to a second part 40B which is the other part of the heat element 40; a ground electrode 10A that applies a ground potential to the drive IC 7A; a ground electrode 10B that applies a ground potential to the drive IC 7B; and a connection electrode 13 that electrically connects the ground electrode 10A and the ground electrode 10B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present embodiment relates to a thermal printhead and a thermal printer. [Background technology]

[0002] A thermal printhead, for example, includes a heating resistor having multiple heating elements arranged in the main scanning direction on a head substrate. A driving IC controls the multiple heating elements to selectively energize them, thereby selectively generating heat in any of the multiple heating elements. A thermal printhead includes multiple driving ICs, each of which is electrically connected to a ground electrode located in each area. For example, there is a thermal printhead in which two driving ICs are electrically connected to a first ground electrode located to the left of the center, and three driving ICs are electrically connected to a second ground electrode located to the right of the center. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-138335 Summary of the Invention [Problem to be solved by the invention]

[0004] The number of driver ICs directly connected to the first ground electrode is different from the number of driver ICs directly connected to the second ground electrode, and the amount of current flowing through the first ground electrode is different from the amount of current flowing through the second ground electrode. This results in different power losses in the first ground electrode and the second ground electrode, which causes different power consumption in each heat generating element. As a result, a "density step" like a seam occurs, where the print density differs dramatically near the boundary between areas with different ground electrodes. This density step can result in different colors on the left and right sides of a face, for example, when printing an image of a person photographed with a camera.

[0005] An object of one aspect of this embodiment is to provide a thermal printhead that suppresses density differences in print and ensures good printing performance, and a thermal printer equipped with the thermal printhead. [Means for solving the problem]

[0006] One aspect of this embodiment is a thermal printhead comprising: a heating resistor that generates heat when current is applied; a first driving IC that supplies power to a first portion that is a part of the heating resistor; a second driving IC that supplies power to a second portion that is another part of the heating resistor; a first ground electrode that applies a ground potential to the first driving IC; a second ground electrode that applies a ground potential to the second driving IC; and a connection electrode that electrically connects the first ground electrode and the second ground electrode.

[0007] Another aspect of this embodiment is a thermal printer including the thermal printhead described above. [Effects of the Invention]

[0008] According to this embodiment, it is possible to provide a thermal printhead that suppresses density differences in print and ensures good printing performance, and a thermal printer that includes this thermal printhead. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing a thermal printhead according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram of the circuit shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is an example of a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X. In FIG. [Figure 5] FIG. 5 is another example of a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X. In FIG. [Figure 6] FIG. 6 is another example of a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X. In FIG. [Figure 7] FIG. 7 is an enlarged plan view of region 20 in FIG. [Figure 8] FIG. 8 is an enlarged plan view of FIG. [Figure 9] FIG. 9 is a partial perspective view illustrating the thermal printhead according to this embodiment. [Figure 10] FIG. 10 is a partial cross-sectional view taken along line XX in the main scanning direction X of FIG. [Figure 11] FIG. 11 is a partial cross-sectional view taken along the line XI-XI in FIG. 9 in the sub-scanning direction Y. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, this embodiment will be described with reference to the drawings. In the drawings described below, identical or similar parts are designated by identical or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and planar dimensions of each component may differ from the actual relationship. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, it goes without saying that the drawings may include parts with different dimensional relationships and ratios.

[0011] Furthermore, the embodiments described below are merely examples of devices and methods for embodying the technical ideas, and do not specify the materials, shapes, structures, arrangements, etc. of the components. Various modifications can be made to the present embodiments within the scope of the claims.

[0012] A specific aspect of this embodiment is as follows.

[0013] <1> A thermal printhead comprising: a heating resistor that generates heat when current is applied; a first driving IC that supplies power to a first portion that is a part of the heating resistor; a second driving IC that supplies power to a second portion that is another part of the heating resistor; a first ground electrode that applies a ground potential to the first driving IC; a second ground electrode that applies a ground potential to the second driving IC; and a connection electrode that electrically connects the first ground electrode and the second ground electrode.

[0014] <2> the power supply electrode is disposed between the first ground electrode and the second ground electrode and is supplied with a power supply potential from an external source, and a portion of the connection electrode overlaps with the power supply electrode in a thickness direction of the power supply electrode. <1> 2. The thermal printhead according to claim 1 .

[0015] <3> the thermal printhead further includes a protective film disposed between the power electrode and the first ground electrode, between the power electrode and the second ground electrode in the main scanning direction of the thermal printhead, and between the power electrode and the connection electrode in the thickness direction of the power electrode; <2> 2. The thermal printhead according to claim 1 .

[0016] <4> the connection electrode is a conductive film; <1> ~ <3> 10. The thermal printhead according to claim 9,

[0017] <5> The connection electrode is a metal wiring. <1> ~ <3> 10. The thermal printhead according to claim 9,

[0018] <6> The connection electrode is a jumper resistor. <1> ~ <3> 10. The thermal printhead according to claim 9,

[0019] <7> the number of the first driving ICs directly connected to the first ground electrode is different from the number of the second driving ICs directly connected to the second ground electrode; <1> ~ <6> 10. The thermal printhead according to claim 9,

[0020] <8> The display device further includes a common electrode in contact with the heating resistor, a first individual electrode electrically connected to the common electrode via the first portion and electrically connected to the first driving IC, and a second individual electrode electrically connected to the common electrode via the second portion and electrically connected to the second driving IC. <1> ~ <7> 10. The thermal printhead according to claim 9,

[0021] <9> <1> ~ <8> A thermal printer comprising the thermal printhead according to any one of claims 1 to 4.

[0022] <Thermal print head> The thermal printhead according to this embodiment will be described with reference to the drawings.

[0023] FIG. 1 is a plan view showing a thermal printhead according to this embodiment. FIG. 2 is a schematic connection diagram of FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. The thermal printhead 100 of this embodiment mainly includes a heating resistor 40, multiple driving ICs 7A, multiple driving ICs 7B, ground electrodes 10A, 10B, and a connection electrode 13. The ground electrode 10A applies a ground potential to a portion of the heating resistor 40 (hereinafter also referred to as the first portion) via the multiple driving ICs 7A that supply power to the first portion. The ground electrode 10B applies a ground potential to a portion of the heating resistor 40 (hereinafter also referred to as the second portion) via the multiple driving ICs 7B that supply power to a portion of the heating resistor 40 different from the first portion (hereinafter also referred to as the second portion). The connection electrode 13 electrically connects the ground electrode 10A and the ground electrode 10B.

[0024] The configuration of the thermal printhead 100 will be described in more detail. The thermal printhead 100 includes an insulating substrate 15, a heat dissipation member 8, a plurality of wires 81 (described later), and a resin part 82. The thermal printhead 100 also includes a plurality of individual electrodes 31, a common electrode 32, a heating resistor 40, a plurality of driving ICs 7A, a plurality of driving ICs 7B, a ground electrode 10A, a ground electrode 10B, a connection electrode 13, and a protective layer 34.

[0025] A plurality of individual electrodes 31 are disposed on a substrate 15. A common electrode 32 faces the tip of each individual electrode 31 at a predetermined interval along the sub-scanning direction Y. A heating resistor 40 is disposed on the plurality of individual electrodes 31 and the common electrode 32. A plurality of driving ICs 7A are electrically connected to first portions of the heating resistors 40. A plurality of driving ICs 7B are electrically connected to second portions of the heating resistors 40. A ground electrode 10A is directly connected to the plurality of driving ICs 7A. A ground electrode 10B is directly connected to the plurality of driving ICs 7B. A connection electrode 13 electrically connects the ground electrode 10A and the ground electrode 10B. A protective layer 34 covers the individual electrodes 31, the common electrode 32, the heating resistors 40, and the like. The heating resistor 40 includes a plurality of heating resistor portions 41 that generate heat when a current flows through the individual electrodes 31 and the common electrode 32. The plurality of heat generating resistors 41 are formed independently between the individual electrodes 31 and the common electrode 32 .

[0026] The substrate 15 is mounted adjacent to the heat dissipation member 8 in the sub-scanning direction Y. The substrate 15 has a plurality of heat generating resistors (heat generating sections) 41 arranged in the main scanning direction X. The heat generating resistors 41 are driven to selectively generate heat by drive ICs 7A and 7B mounted on the substrate 15. The heat generating resistors 41 print on a print medium 92, such as thermal paper, pressed against the heat generating resistors 41 by a platen roller 91 in accordance with a print signal transmitted from the outside.

[0027] In this embodiment, the longitudinal direction in which the heating resistor 40 extends linearly is defined as the main scanning direction X, the direction perpendicular to the main scanning direction X and parallel to the upper surface of the substrate 15 is defined as the sub-scanning direction Y, and the direction corresponding to the thickness of the substrate 15, etc. is defined as the thickness direction Z. In other words, the thickness direction Z is a direction perpendicular to both the main scanning direction X and the sub-scanning direction Y. Furthermore, the direction in which the connection electrodes 13 are located relative to the substrate 15 is defined as the upward direction, and the direction in which the substrate 15 is located relative to the connection electrodes 13 is defined as the downward direction.

[0028] Furthermore, in this specification, "electrically connected" includes a connection via "something that has some kind of electrical action." Here, "something that has some kind of electrical action" is not particularly limited as long as it enables the exchange of electrical signals between the connected objects. For example, "something that has some kind of electrical action" includes electrodes, wiring, switching elements, resistive elements, inductors, capacitive elements, and other elements with various functions.

[0029] 2, wiring for supplying a driving IC potential supplied from a terminal VDD to the plurality of driving ICs 7A and 7B, and wiring for supplying potentials supplied from other terminals (e.g., a strobe terminal (STB)) to the ground electrodes 10A and 10B (hereinafter, these wirings are collectively referred to as power electrodes 11) are densely packed near the center of the thermal printhead 100. Furthermore, wiring for supplying a ground potential supplied from a terminal GND to the ground electrodes 10A and 10B, wiring for supplying a common potential supplied from a terminal VH to the common electrode 32, and wiring 12 for supplying potentials supplied from other terminals (e.g., an input terminal (DI), an output terminal (DO), a clock terminal (CLK), a latch terminal (LAT), etc.) to the plurality of driving ICs 7A and 7B bypass one end of each of the ground electrodes 10A and 10B in the main scanning direction X and connect to the common electrode 32, the driving IC 7A, or the driving IC 7B. In this embodiment, the power supply electrode 11 includes wiring for supplying the driving IC potential supplied from the terminal VDD to the plurality of driving ICs 7A and 7B, but this is not limiting, and the wiring does not have to be included in the power supply electrode 11. Furthermore, although not shown, a thermistor used as a sensor for measuring the temperature of the heating resistor may be provided near the center of the thermal printhead 100.

[0030] A portion of the connection electrode 13 overlaps, but is spaced apart from, the power electrode 11 disposed between the ground electrode 10A and the ground electrode 10B in the thickness direction (Z direction) of the power electrode 11. As will be described later, a portion of the connection electrode 13 overlaps the power electrode 11 via a protective layer 34. With this configuration, power can be supplied from the power electrode 11 to the driving IC 7A and the driving IC 7B via the shortest path without detouring one end of each of the ground electrodes 10A and 10B in the main scanning direction X. This reduces the amount of voltage drop in the power electrode 11 (for example, the wiring for applying the driving IC potential supplied from the terminal VDD to the multiple driving ICs 7A and 7B), and suppresses malfunction of the driving ICs 7A and 7B.

[0031] In the thermal printhead 100, ground electrode 10A and ground electrode 10B are electrically connected to each other using connection electrode 13. For example, if the number of drive ICs 7A directly connected to ground electrode 10A is different from the number of drive ICs 7B directly connected to ground electrode 10B, or if the number of heat generating resistors 41 electrically connected to ground electrode 10A without connection electrode 13 is different from the number of heat generating resistors 41 electrically connected to ground electrode 10B without connection electrode 13, the amount of current flowing through ground electrode 10A and ground electrode 10B may differ. However, by electrically connecting ground electrode 10A and ground electrode 10B using connection electrode 13, the amount of current flowing through ground electrode 10A and ground electrode 10B can be equalized. This eliminates the difference between the power loss in ground electrode 10A and the power loss in ground electrode 10B, thereby equalizing the power consumed by each heat generating resistor 41. Therefore, it is possible to suppress concentration differences near the boundary between areas with different ground electrodes (in this embodiment, near the boundary between the area where the driving IC 7A, individual electrode 31, and common electrode 32 connected to the ground electrode 10A are arranged and the area where the driving IC 7B, individual electrode 31, and common electrode 32 connected to the ground electrode 10B are arranged).

[0032] The ground electrodes 10A and 10B are formed from a metal paste containing metal particles such as copper, silver, palladium, iridium, platinum, and gold. The ground electrodes 10A and 10B are obtained by applying the metal paste by screen printing or the like, followed by firing to form an electrode pattern.

[0033] The connection electrode 13 may be, for example, a conductive film, metal wiring, or a jumper resistor. Because the connection electrode 13 electrically connects the ground electrode 10A and the ground electrode 10B, it is preferable to shorten the connection electrode 13 itself to shorten the path through which the current flows and reduce resistance. This configuration can reduce power loss in the path through which the current flows.

[0034] The thermal printhead 100 of this embodiment is provided with two ground electrodes, but is not limited to this, and may be configured to have three or more ground electrodes that are electrically connected.

[0035] The configuration of the thermal printhead 100 near its center will now be described in more detail with reference to the drawings.

[0036] (First Configuration) In the first configuration, a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X is shown in FIG.

[0037] In this configuration, ground electrode 10A, ground electrode 10B, and power electrode 11 are disposed on substrate 15. Power electrode 11 is disposed between ground electrode 10A and ground electrode 10B and is spaced apart from ground electrode 10A and ground electrode 10B. Protective films 34A are disposed on substrate 15 between power electrode 11 and ground electrode 10A, between power electrode 11 and ground electrode 10B, and over ground electrode 10A, ground electrode 10B, and power electrode 11. Openings are formed in protective film 34A that reach ground electrode 10A and ground electrode 10B, and electrodes 12A and 12B are disposed to fill these openings. Conductive films 13A, which function as the above-mentioned connection electrodes 13, are disposed on electrodes 12A and 12B. In other words, ground electrode 10A is electrically connected to ground electrode 10B via electrode 12A, conductive film 13A, and electrode 12B. A portion of the conductive film 13A overlaps with the power electrode 11 in the thickness direction Z of the power electrode 11. A protective film 34B is disposed on the protective film 34A and the conductive film 13A. The protective films 34A and 34B are collectively referred to as a protective layer 34.

[0038] The electrodes 12A and 12B and the conductive film 13A are formed from a metal paste containing metal particles such as copper, silver, palladium, iridium, platinum, and gold. The electrodes 12A and 12B and the conductive film 13A are obtained by applying the above-mentioned metal paste by screen printing or the like, followed by firing to form an electrode pattern. The electrodes 12A and 12B and the conductive film 13A may be made of the same material as the ground electrodes 10A and 10B, or may be made of a different material. However, from the viewpoint of contact resistance, the electrodes 12A and 12B and the conductive film 13A are preferably made of the same material.

[0039] The protective films 34A and 34B can be made of an insulating material, such as amorphous glass, and are formed by applying a glass paste, which is a material paste, and then firing it.

[0040] In this configuration, a protective film 34A is provided to protect the power electrode 11, etc., and the conductive film 13A can be formed widely on the protective film 34A while avoiding contact with the power electrode 11, thereby significantly reducing resistance and further reducing power loss.

[0041] (Second Configuration) In the second configuration, a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X is shown in FIG.

[0042] In this configuration, a ground electrode 10A, a ground electrode 10B, and a power electrode 11 are disposed on a substrate 15. The power electrode 11 is disposed between the ground electrodes 10A and 10B and is spaced apart from the ground electrodes 10A and 10B. A protective layer 34 is disposed on the substrate 15 between the power electrode 11 and the ground electrode 10A, between the power electrode 11 and the ground electrode 10B, and on the ground electrodes 10A, 10B, and 11. The protective layer 34 has openings that reach the ground electrodes 10A and 10B, exposing portions of the ground electrodes 10A and 10B. A metal wiring 13B, which functions as the connection electrode 13 described above, is disposed so as to electrically connect the exposed portions of the ground electrodes 10A and 10B. In other words, the ground electrode 10A is electrically connected to the ground electrode 10B via the metal wiring 13B. A portion of the metal wiring 13B overlaps the power electrode 11 in the thickness direction Z of the power electrode 11.

[0043] The metal wiring 13B can be made of a conductor such as gold, silver, or copper. In this configuration, a single metal wiring 13B may be provided, or multiple metal wirings 13B may be provided. The power loss of the current flowing through a single metal wiring 13B depends on the type of metal and the thickness and length of the wiring, so from the perspective of power loss, it is preferable to provide multiple metal wirings 13B. On the other hand, if there are a large number of metal wirings 13B, the area occupied by the metal wirings 13B increases, which may increase the size of the entire thermal printhead or require the platen roller to be reduced in size. For this reason, it is preferable to select the number of metal wirings 13B appropriately, taking the above into consideration.

[0044] The metal wiring 13B is connected to the ground electrode 10A or the ground electrode 10B by direct bonding. The metal wiring 13B may be protected with epoxy resin or the like.

[0045] In this configuration, by adjusting the number of metal wirings 13B in the assembly process, a thermal printhead having the desired specifications can be easily manufactured.

[0046] (Third Configuration) In the third configuration, a partial cross-sectional view taken along line VV in FIG. 1 in the main scanning direction X is shown in FIG.

[0047] In this configuration, ground electrode 10A, ground electrode 10B, and power electrode 11 are disposed on substrate 15. Power electrode 11 is disposed between ground electrode 10A and ground electrode 10B and is spaced apart from ground electrode 10A and ground electrode 10B. A protective layer 34 is disposed on substrate 15 between power electrode 11 and ground electrode 10A, between power electrode 11 and ground electrode 10B, and on ground electrode 10A, ground electrode 10B, and power electrode 11. Openings are provided in protective layer 34 that reach ground electrode 10A and ground electrode 10B, and electrodes 12C and 12D are provided to fill these openings. Jumper resistors 13C, which function as the above-mentioned connection electrodes 13, are disposed on electrodes 12A and 12B. In other words, ground electrode 10A is electrically connected to ground electrode 10B via electrode 12C, jumper resistor 13C, and electrode 12D. A part of the jumper resistor 13C overlaps the power electrode 11 in the thickness direction Z of the power electrode 11.

[0048] Each of the electrodes 12C and 12D functions as a terminal of the jumper resistor 13C. The electrodes 12C and 12D are formed from a metal paste containing metal particles such as copper, silver, palladium, iridium, platinum, and gold. The electrodes 12C and 12D are obtained by applying the metal paste by screen printing or the like, followed by firing to form an electrode pattern. The electrodes 12C and 12D may be made of the same material as the ground electrode 10A and the ground electrode 10B, or may be made of a different material. However, from the viewpoint of contact resistance, the electrodes 12C and 12D are preferably made of the same material.

[0049] The jumper resistor 13C is a micro-sized chip resistor that can withstand a certain amount of current and has a very low resistance value that is very close to 0 Ω (for example, 50 mΩ or less). The jumper resistor 13C is easy to mount and remove, and it is easy to change it to a normal resistor in a later design change or to change the product specifications.

[0050] To electrically connect jumper resistor 13C to ground electrode 10A or ground electrode 10B, first, solder paste (cream solder) is applied between ground electrode 10A and electrode 12C and between ground electrode 10B and electrode 12D, respectively, and then the solder paste is melted by heat treatment in a reflow furnace under an inert gas atmosphere such as nitrogen. This allows the jumper resistor 13C to be electrically connected to ground electrode 10A and ground electrode 10B using the melted solder.

[0051] Furthermore, the electrodes 12C, 12D, and jumper resistor 13C may be protected with epoxy resin or the like.

[0052] In this configuration, by arranging the jumper resistor 13C in the assembly process, a thermal printhead having the desired specifications can be easily manufactured.

[0053] The substrate 15 has a planar shape of an elongated rectangle with its longitudinal direction in the main scanning direction X and its transverse direction in the sub-scanning direction Y. The size of the substrate 15 is not limited, but as an example, the dimension in the main scanning direction X is, for example, 50 to 150 mm, the dimension in the sub-scanning direction Y is, for example, 2.0 to 5.0 mm, and the dimension in the thickness direction Z is, for example, 725 μm.

[0054] The substrate 15 is made of ceramic or a single crystal semiconductor. As the ceramic, for example, alumina can be used. As the single crystal semiconductor, for example, silicon can be used.

[0055] The connection substrate 5 may be, for example, a printed wiring board. The connection substrate 5 has a structure in which a base layer and a wiring layer (not shown) are laminated together. The base layer may be made of, for example, glass epoxy resin. The wiring layer may be made of, for example, metal particles such as copper, silver, palladium, iridium, platinum, and gold.

[0056] The heat dissipation member 8 has a function of dissipating heat from the substrate 15. The substrate 15 and the connection substrate 5 are attached to the heat dissipation member 8. The heat dissipation member 8 can be made of a metal such as aluminum.

[0057] The wires 81 may be made of a conductor such as gold. There are multiple wires 81, some of which are bonded to connect the driving IC 7A or 7B to each individual electrode. Some of the other wires 81 are bonded to connect the driving IC 7A or 7B to the connector 59 via the wiring layer of the connection board 5.

[0058] The resin section 82 may be made of, for example, black resin. For example, epoxy resin, silicone resin, or the like may be used as the resin section 82. The resin section 82 covers the driving IC 7A, driving IC 7B, and the plurality of wires 81, etc., and protects the driving IC 7A, driving IC 7B, and the plurality of wires 81. The connector 59 is fixed to the connection board 5. Wiring is connected to the connector 59 to supply power to the thermal printhead from outside the thermal printhead and to control the driving IC 7A and driving IC 7B.

[0059] The protective layer 34 covers the substrate 15. Specifically, the protective layer 34 is disposed between the power electrode 11 and the ground electrode 10A and between the power electrode 11 and the ground electrode 10B in the main scanning direction X, and between the power electrode 11 and the connection electrode 13 in the thickness direction Z of the power electrode 11. The protective layer 34 can be made of an insulating material, such as amorphous glass. The protective layer 34 is formed by applying a glass paste, which is a material paste, and then firing it. The thickness of the protective layer 34 is not particularly limited and is, for example, 5 to 15 μm, and preferably 5 to 10 μm.

[0060] The heating resistor 40 generates heat due to the current flowing between the individual electrode 31 and the common electrode 32. This heat generation forms print dots. The heating resistor 40 is made of a material having a higher resistivity than the material constituting the individual electrode 31 and the common electrode 32, such as tantalum nitride or silicon oxide containing tantalum. Ruthenium oxide may also be used as the material for the heating resistor 40. In this embodiment, the thickness of the heating resistor 40 is, for example, about 0.05 to 0.2 μm.

[0061] The individual electrodes 31 and the common electrode 32 form a path for passing electricity through the heating resistor 40. The individual electrodes 31 and the common electrode 32 are made of a conductor. Examples of the conductor include metal particles such as copper, silver, palladium, iridium, platinum, and gold. From the viewpoint of metal properties and ionization tendency, copper, silver, platinum, and gold are preferred, and from the viewpoint of metal properties, ionization tendency, and cost reduction, silver is more preferred. In this embodiment, the thickness of the individual electrodes 31 and the common electrode 32 is, for example, about 0.2 to 0.8 μm.

[0062] The individual electrodes 31 and the common electrode 32 can be formed using a metal paste containing the above-mentioned metal particles. The solvent contained in the metal paste has the function of uniformly dispersing the metal particles, and examples thereof include, but are not limited to, one or a mixture of two or more of ester-based solvents, ketone-based solvents, glycol ether-based solvents, aliphatic solvents, alicyclic solvents, aromatic solvents, alcohol-based solvents, and water.

[0063] Examples of ester-based solvents include ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and dimethyl carbonate. Examples of ketone-based solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone benzene, diisobutyl ketone, diacetone alcohol, isophorone, and cyclohexanenone. Examples of glycol ether-based solvents include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, and ethylene glycol monobutyl ether, as well as acetate esters of these monoethers, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, as well as acetate esters of these monoethers.

[0064] Examples of aliphatic solvents include n-heptane, n-hexane, cyclohexane, methylcyclohexane, and ethylcyclohexane. Examples of alicyclic solvents include methylcyclohexane, ethylcyclohexane, and cyclohexane. Examples of aromatic solvents include toluene, xylene, and tetralin. Examples of alcohol solvents (excluding the above-mentioned glycol ether solvents) include ethanol, propanol, and butanol.

[0065] The metal paste may contain, as necessary, a dispersant, a surface treatment agent, a friction resistance improver, an infrared absorber, an ultraviolet absorber, a fragrance, an antioxidant, an organic pigment, an inorganic pigment, an antifoaming agent, a silane coupling agent, a titanate coupling agent, a plasticizer, a flame retardant, a moisturizing agent, an ion scavenger, and the like.

[0066] The individual electrodes 31 and the common electrode 32 will now be described in detail with reference to FIGS. 7 and 8. FIG. 7 is an enlarged plan view of region 20 in FIG. 1. FIG. 8 is an enlarged plan view of FIG. 7. As shown in FIGS. 7 and 8, each individual electrode 31 has a strip shape extending generally in the sub-scanning direction Y, with its lower end extending to the position of region 30. The individual electrodes 31 are not electrically connected to one another. Therefore, when a printer incorporating the thermal printhead is used, different potentials can be applied to each individual electrode 31. An individual pad portion 311 is formed at the upper end of each individual electrode 31.

[0067] The common electrode 32 has an electrical polarity opposite to that of the individual electrodes 31 when a printer incorporating the thermal printhead is used. The common electrode 32 has a plurality of comb-tooth portions 324 and a common portion 323 connecting these comb-tooth portions 324. The common portion 323 is formed along the edge of the substrate 15 in the main scanning direction X, and each comb-tooth portion 324 has a strip shape that branches off from the common portion 323 and extends in the sub-scanning direction Y, with its upper tip facing the tip of each individual electrode 31 at a predetermined interval. This configuration allows the pitch of the heating resistor portions 41 to be narrowed, enabling high-resolution printing.

[0068] The individual electrodes 31, the common electrode 32, the heating resistor 40, etc. are covered with a protective layer 34. An insulating material such as silicon nitride or silicon oxide can be used for the protective layer 34. The thickness of the protective layer 34 is, for example, about 3 to 8 μm.

[0069] The driving ICs 7A and 7B are mounted on the substrate 15 and are provided to individually energize the heating resistor sections 41. The driving ICs 7A and 7B are directly connected to the individual pad sections 311 of the individual electrodes 31 by wires (not shown). The driving ICs 7A and 7B receive print signals sent from the outside, and the heating resistor sections 41 are individually energized in accordance with the print signals, thereby selectively generating heat.

[0070] Furthermore, an example of a thermal printhead including the above-mentioned components will be described with reference to the drawings.

[0071] FIG. 9 is a partial perspective view showing a thermal printhead. FIG. 10 is a partial cross-sectional view taken along line XX in FIG. 9 in the main scanning direction X. FIG. 11 is a partial cross-sectional view taken along line XI-XI in FIG. 9 in the sub-scanning direction Y. FIGS. 9 to 11 show a portion of a thermal printhead (corresponding to one thermal printhead), and in this embodiment, this one thermal printhead is referred to as a piece-shaped thermal printhead 100a. The piece-shaped thermal printhead 100a includes a substrate 15, a heat storage layer 33 on the substrate 15, a plurality of individual electrodes 31 on the heat storage layer 33, a common electrode 32 on the heat storage layer 33, heating resistors 40 on the heat storage layer 33, the plurality of individual electrodes 31, and the common electrode 32, and a protective layer 34 covering the heat storage layer 33, the individual electrodes 31, the common electrode 32, and the heating resistors 40. The heating resistor 40 includes a plurality of heating resistance portions 41 that generate heat due to a current flowing through the individual electrodes 31 and the common electrode 32. The plurality of heating resistance portions 41 are formed independently between the individual electrodes 31 and the common electrode 32. The plurality of heating resistance portions 41 are omitted from Fig. 9. The plurality of heating resistance portions 41 are arranged linearly on the heat storage layer 33.

[0072] A heat storage layer 33 (also referred to as a glaze layer) having the function of storing heat is laminated on the substrate 15. The heat storage layer 33 stores heat generated from the heating resistor portion 41 described below. The heat storage layer 33 can be made of an insulating material, such as silicon oxide or silicon nitride, which are the main components of glass. The dimension of the heat storage layer 33 in the thickness direction Z is not particularly limited and is, for example, 5 to 100 μm, and preferably 10 to 30 μm.

[0073] An individual electrode 31 and a common electrode 32 formed from a metal paste are provided on the heat storage layer 33. The individual electrode 31 and the common electrode 32 are obtained by applying the above-mentioned metal paste by screen printing or the like, and then firing the paste to form an electrode pattern.

[0074] The individual thermal printheads 100a can be manufactured by singulating the substrate 15, on which the heat storage layer 33, individual electrodes 31, common electrode 32, heating resistors 40, etc. are mounted. A dicer, for example, can be used to singulate the substrate 15. Alternatively, the substrate 15 can be singulated using a laser or the like. For example, a solid-state laser such as a fiber laser can be used as the laser.

[0075] The thermal printhead 100 can be manufactured by mounting the driver ICs 7A and 7B on individual substrates (also referred to as individual substrates) and thermally curing the underfill resin filled between the individual substrates and the driver ICs 7A or 7B to form the underfill material. For mounting, solder bumps are provided between the individual substrates and the driver ICs 7A or 7B, and a heat treatment is performed in a reflow furnace under an inert gas atmosphere such as nitrogen to melt the solder bumps, thereby electrically connecting the individual substrates and the driver ICs using solder.

[0076] According to this embodiment, it is possible to obtain a thermal printhead that suppresses density differences in printing and ensures good printing performance.

[0077] <Thermal printer> As described above, as shown in FIG. 3, the thermal printhead 100 includes a substrate 15 (heat storage layer 33 and the like on the substrate 15 are not shown), a heat dissipation member 8, a plurality of drive ICs 7A (not shown), a plurality of drive ICs 7B, a plurality of wires 81, and a resin portion 82. The substrate 15 is mounted adjacent to the heat dissipation member 8 in the sub-scanning direction Y. A plurality of heat-generating resistor portions 41 are formed on the substrate 15 and arranged in the main scanning direction X. The heat-generating resistor portions 41 are driven to selectively generate heat by the drive ICs 7A and 7B mounted on the substrate 15. The heat-generating resistor portions 41 print on a print medium 92, such as thermal paper, pressed against the heat-generating resistor portion 41 by a platen roller 91 in accordance with a print signal transmitted from an external device.

[0078] A thermal printer prints on a print medium transported in the sub-scanning direction Y. Typically, the print medium is transported from the connector 59 side toward the heating resistor 41 side. Examples of print media include thermal paper for creating barcode sheets and receipts.

[0079] The thermal printer includes, for example, a thermal printhead 100, a platen roller 91, a main power supply circuit, a measurement circuit, and a control unit. The platen roller 91 faces the thermal printhead 100.

[0080] The main power supply circuit supplies power to the multiple heating resistors 41 in the thermal printhead 100. The measurement circuit measures the resistance value of each of the multiple heating resistors 41. The measurement circuit measures the resistance value of each of the multiple heating resistors 41, for example, when no printing is being performed on the print medium. This makes it possible to determine the lifespan of the heating resistors 41 and whether or not there are any faulty heating resistors 41. The control unit controls the drive state of the main power supply circuit and the measurement circuit. The control unit controls the power supply state of each of the multiple heating resistors 41. The measurement circuit may be omitted.

[0081] The thermal printhead 100 may include a connector for communicating with external devices. Through the connector, the thermal printhead 100 may be electrically connected to a main power supply circuit and a measurement circuit. Through the connector, the thermal printhead 100 may be electrically connected to a controller.

[0082] The driving ICs 7A and 7B receive signals from the control unit. Based on the signals received from the control unit, the driving ICs 7A and 7B control the energization state of each of the plurality of heating resistors 41. Specifically, the driving ICs 7A and 7B selectively energize the plurality of individual electrodes to selectively cause any of the plurality of heating resistors 41 to generate heat.

[0083] The thermal printhead may be configured without wires 81 by flip-chip mounting, or without heat dissipation member 8.

[0084] Next, how to use the thermal printer will be described.

[0085] When printing on a print medium, a first electric potential, which is an input signal, is applied from the main power supply circuit to an external connection terminal such as a connector. In this case, the plurality of heating resistor elements 41 are selectively energized and generate heat. The heat is transferred to the print medium, thereby printing on the print medium. As described above, when the first electric potential is applied from the main power supply circuit to the connection terminal, a current path to each of the plurality of heating resistor elements 41 is secured.

[0086] When printing on a print medium is not being performed, the resistance value of each heating resistor 41 is measured. During this measurement, no potential is applied to the connection terminal from the main power supply circuit. During measurement of the resistance value of each heating resistor 41, a second potential is applied to the connection terminal from the measurement circuit. In this case, the multiple heating resistors 41 are energized in sequence (for example, sequentially from the heating resistor 41 located at the end in the main scanning direction X). The measurement circuit measures the resistance value of each heating resistor 41 based on the value of the current flowing through the heating resistor 41 and the second potential. As described above, when the second potential is applied to the connection terminal from the measurement circuit, the current paths to each of the multiple heating resistors 41 other than the one whose resistance is being measured are essentially cut off. This allows the measurement circuit to more accurately measure the resistance value of each heating resistor 41, making it possible to determine the lifespan of the heating resistor 41 and whether or not there is a faulty heating resistor 41.

[0087] To address the density discontinuity, a configuration can be adopted in which all driver ICs are electrically connected to a single ground electrode. This configuration can uniformly distribute the power consumed by each heat-generating element and reduce density discontinuities. However, because the power supply electrode, which receives the external power supply potential and supplies power to the driver IC, is located outside the ground electrode, wiring must be routed to the left and right edges to avoid the ground electrode, and then routed back to the center to connect to the driver IC. The longer the wiring path from the power electrode to the driver IC, the greater the voltage drop at the power electrode, which could lead to driver IC malfunction. Using thicker wiring or providing two power electrodes is effective in preventing driver IC malfunction. However, designing the same size requires a smaller platen roller, which limits printing performance.

[0088] According to this embodiment, the above-mentioned problems can be solved, and a thermal printer can be obtained that suppresses density differences in printing and ensures good printing performance.

[0089] (Other embodiments) As described above, one embodiment has been described, but the descriptions and drawings that form part of the disclosure are illustrative and should not be understood as limiting. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. Thus, the present embodiment includes various embodiments not described herein. [Explanation of symbols]

[0090] 7A, 7B driver IC 8 Heat dissipation material 10A, 10B ground electrode 11 Power electrode 12 Wiring 13 Connecting electrode 13A conductive film 13B Metal wiring 13C jumper resistor 15 PCB 20, 30 areas 31 Individual electrodes 32 Common electrode 33 Heat storage layer 34 Protective layer 34A, 34B Protective film 40 Heating resistor 41 Heating resistor 81 Wire 82 Resin part 91 Platen roller 92 Print media 100 Thermal Printhead 100a individual thermal printhead 311 Individual pad section 323 Common section 324 Comb teeth

Claims

1. a heating resistor that generates heat when energized; a first driving IC that supplies power to a first portion that is a part of the heating resistor; a second driving IC that supplies power to a second portion that is another part of the heating resistor; a first ground electrode for applying a ground potential to the first driving IC; a second ground electrode for applying a ground potential to the second driving IC; a connection electrode electrically connecting the first ground electrode and the second ground electrode; a power supply electrode disposed between the first ground electrode and the second ground electrode and supplied with a power supply potential from an external source; a portion of the connection electrode overlaps with the power electrode in a thickness direction of the power electrode; Thermal print head.

2. 2. The thermal printhead according to claim 1, further comprising a protective film disposed between the power supply electrode and the first ground electrode, and between the power supply electrode and the second ground electrode in the main scanning direction of the thermal printhead, and between the power supply electrode and the connection electrode in the thickness direction of the power supply electrode.

3. 3. The thermal printhead according to claim 1, wherein the connection electrodes are conductive films.

4. A heating resistor that generates heat when current is applied; a first driving IC that supplies power to a first portion that is a part of the heating resistor; a second driving IC that supplies power to a second portion that is another part of the heating resistor; a first ground electrode for applying a ground potential to the first driving IC; a second ground electrode for applying a ground potential to the second driving IC; a connection electrode electrically connecting the first ground electrode and the second ground electrode, the connection electrode is a conductive film; Thermal print head.

5. 5. The thermal printhead according to claim 1, wherein the connection electrodes are metal wiring.

6. 5. The thermal printhead according to claim 1, wherein the connection electrodes are jumper resistors.

7. A thermal printhead described in any one of claims 1 to 6, wherein the number of the first driving ICs directly connected to the first ground electrode is different from the number of the second driving ICs directly connected to the second ground electrode.

8. a common electrode in contact with the heating resistor; a first individual electrode electrically connected to the common electrode via the first portion and electrically connected to the first driving IC; A thermal printhead according to any one of claims 1 to 7, further comprising a second individual electrode electrically connected to the common electrode via the second portion and electrically connected to the second driving IC.

9. A thermal printer comprising the thermal printhead according to any one of claims 1 to 8.

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