Thermal print heads and thermal printers

Abstract

To provide a thermal print head suited for improving abrasion resistance of a protective layer.SOLUTION: A thermal print head A1 comprises: a substrate 1 having a main surface 11 directed to a z1 side in a thickness direction z; a resistor layer 4 disposed on the main surface 11 and having a plurality of heating units 41 arranged in a main scanning direction; a wiring layer 3 disposed on the main surface 11 and conducted to the resistor layer 4; and at least a protective layer 5 that covers at least the resistor layer 4. The protective layer 5 (second layer 52) is formed by including a glass and additive particles. The additive particles include boron nitride particles.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses an example of a conventional thermal print head. The thermal print head disclosed in this document includes a substrate, a glaze layer, an electrode layer, a resistor layer, a protective layer, and a driving IC. The substrate is a plate-like member made of an insulating material, for example, a ceramic such as alumina (Al2O3). The glaze layer is formed on the surface of the substrate and is made of, for example, glass. The electrode layer is formed on the glaze layer and constitutes a current path for selectively flowing current to the resistor layer. The resistor layer has a plurality of heat generating portions arranged in the main scanning direction. The driving IC controls the current flowing through each heat generating portion. The protective layer covers at least the resistor layer.

[0003] In a thermal print head having such a configuration, while causing a plurality of heat generating portions to generate heat, the printing medium such as thermal paper is sent in the sub-scanning direction while being pressed against the protective layer, thereby printing on the printing medium. In the protective layer covering the resistor layer (plural heat generating portions), wear resistance is required due to repeated contact with the printing medium. In recent years, the printing speed has been increasing. Furthermore, with the diversification of printing media, a relatively hard printing medium may be used in some cases. Under such circumstances, improvement of the wear resistance of the protective layer is required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] This disclosure was conceived under the circumstances described above, and its primary objective is to provide a thermal printhead that can print properly on a printing medium by improving the abrasion resistance of the protective layer.

[0006] A thermal printhead provided by a first aspect of the present disclosure comprises a substrate having a main surface facing one side in the thickness direction; a resistor layer disposed on the main surface and having a plurality of heating elements arranged in the main scanning direction; a wiring layer disposed on the main surface and conductive to the resistor layer; and a protective layer covering at least the resistor layer, wherein the protective layer comprises glass and additive particles, the additive particles comprising boron nitride particles.

[0007] A thermal printer provided by a second aspect of this disclosure comprises a thermal print head relating to a first aspect of this disclosure and a platen positioned opposite the plurality of heating elements. [Effects of the Invention]

[0008] According to this disclosure, the abrasion resistance of the protective layer can be improved.

[0009] Other features and advantages of this disclosure will become more apparent from the detailed description below, with reference to the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a plan view showing a thermal print head according to the first embodiment of this disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is an enlarged plan view of a key part of a thermal print head according to the first embodiment of this disclosure. [Figure 4] Figure 4 is an enlarged cross-sectional view of a key part, which is a magnified portion of Figure 2. [Figure 5] Figure 5 is an enlarged cross-sectional view of a key part, which is a magnified view of a portion of Figure 4. [Figure 6]Figure 6 is an enlarged cross-sectional view of a key part of a thermal print head according to the second embodiment of this disclosure. [Figure 7] Figure 7 is an enlarged cross-sectional view of a key part, which is a magnified view of a portion of Figure 6. [Figure 8] Figure 8 is an enlarged cross-sectional view of a key part of a thermal print head according to the third embodiment of this disclosure. [Figure 9] Figure 9 is an enlarged cross-sectional view of a key part, which is a magnified portion of Figure 8. [Figure 10] Figure 10 is an enlarged cross-sectional view of a key part of a thermal print head according to the fourth embodiment of this disclosure. [Figure 11] Figure 11 is an enlarged cross-sectional view of a key part, which is a magnified view of a portion of Figure 10. [Figure 12] Figure 12 is an enlarged cross-sectional view of a key part of a thermal print head according to the fifth embodiment of this disclosure. [Figure 13] Figure 13 is an enlarged cross-sectional view of a key part, which is a magnified portion of Figure 12. [Figure 14] Figure 14 is an enlarged cross-sectional view of a key part of a thermal print head according to the sixth embodiment of this disclosure. [Figure 15] Figure 15 is an enlarged cross-sectional view of a key part, which is a magnified portion of Figure 14. [Modes for carrying out the invention]

[0011] Preferred embodiments of this disclosure will be described in detail below with reference to the drawings.

[0012] The terms "First," "Second," etc., used in this disclosure are merely labels and are not necessarily intended to assign a permutation to the objects.

[0013] In the present disclosure, unless otherwise specified, "a certain object A is formed on a certain object B" and "a certain object A is formed above a certain object B" include "a certain object A is directly formed on a certain object B" and "a certain object A is formed on a certain object B with another object intervening between the certain object A and the certain object B". Similarly, unless otherwise specified, "a certain object A is disposed on a certain object B" and "a certain object A is disposed above a certain object B" include "a certain object A is directly disposed on a certain object B" and "a certain object A is disposed on a certain object B with another object intervening between the certain object A and the certain object B". Similarly, unless otherwise specified, "a certain object A is located above a certain object B" includes "a certain object A is in contact with a certain object B and a certain object A is located above a certain object B" and "a certain object A is located above a certain object B with another object intervening between the certain object A and the certain object B". Further, unless otherwise specified, "a certain object A overlaps a certain object B when viewed in a certain direction" includes "a certain object A overlaps all of a certain object B" and "a certain object A overlaps a part of a certain object B". Also, in the present disclosure, "a certain surface A faces direction B (one side or the other side)" is not limited to the case where the angle of the surface A with respect to the direction B is 90°, and includes the case where the surface A is inclined with respect to the direction B.

[0014] <First Embodiment> Figs. 1 to 5 show a thermal print head according to the first embodiment of the present disclosure. The thermal print head A1 of the present embodiment includes a substrate 1, a glaze layer 2, a wiring layer 3, a resistor layer 4, a protective layer 5, a plurality of wires 61, a drive IC 71, a protective resin 72, and a connector 73.

[0015] FIG. 1 is a plan view showing a thermal print head A1. FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG. 1. FIG. 3 is an enlarged plan view of a main part showing the thermal print head A1. FIG. 4 is an enlarged cross-sectional view of a main part obtained by enlarging a part of FIG. 2. FIG. 5 is an enlarged cross-sectional view of a main part obtained by further enlarging a part of FIG. 4. For ease of understanding, in FIGS. 1 and 3, the protective layer 5 is omitted. In FIG. 4, the connector 73 is omitted. In these figures, the thickness direction of the substrate 1 is referred to as the "thickness direction z". The upper side of FIGS. 2 and 4 is "one side in the thickness direction z" and is called the "z1 side in the thickness direction z". The lower side of FIGS. 2 and 4 is "the other side in the thickness direction z" and is called the "z2 side in the thickness direction z". Further, "plan view" means when viewed in the thickness direction z. Furthermore, the main scanning direction in the thermal print head A1 is referred to as the "main scanning direction x", and the sub-scanning direction in the thermal print head A1 is referred to as the "sub-scanning direction y". Regarding the sub-scanning direction y, the lower side of FIGS. 1 and 3 (the left side of FIGS. 2 and 4) is the upstream side where the print medium is sent and is called the "y1 side in the sub-scanning direction y". The upper side of FIGS. 1 and 3 (the right side of FIGS. 2 and 4) is the downstream side where the print medium is discharged and is called the "y2 side in the sub-scanning direction y".

[0016] The thermal print head A1 is incorporated into a thermal printer Pr (see FIG. 2) that prints on a print medium 82. The thermal printer Pr includes the thermal print head A1 and a platen roller 81. The platen roller 81 faces the thermal print head A1. The print medium 82 is sandwiched between the thermal print head A1 and the platen roller 81 and is conveyed in the sub-scanning direction y by the platen roller 81. Examples of such a print medium 82 include thermal paper for creating bar code labels and receipts. Instead of the platen roller 81, a platen made of flat rubber may be used. This platen includes a part having an arcuate shape in a cross-sectional view of a columnar rubber having a large radius of curvature. In the present disclosure, the term "platen" includes both the platen roller 81 and the flat platen.

[0017] The substrate 1 is made of a ceramic material such as Al2O3, and its thickness is approximately 0.5 to 1.5 mm. As shown in Figure 1, the substrate 1 is a long rectangle that extends along the main scanning direction x. The substrate 1 has a main surface 11. The main surface 11 faces the z1 side in the thickness direction z. The glaze layer 2, wiring layer 3, resistor layer 4, protective layer 5, drive IC 71, and protective resin 72 are each arranged on the main surface 11 of the substrate 1. The connector 73 is for connecting to external equipment and is provided, for example, at the y1 side end of the substrate 1 in the sub-scanning direction y.

[0018] The glaze layer 2 is placed on the substrate 1 and is made of a glass material such as amorphous glass. The softening point of this glass material is, for example, 800 to 850°C. The glaze layer 2 in this embodiment is formed to have a certain thickness and has a substantially flat glaze main surface 21 facing the z1 side in the thickness direction z. The thickness of the glaze layer 2 is, for example, 10 to 300 μm.

[0019] The thermal printhead A1 has a configuration known as a thick-film type and is manufactured using thick-film printing. The glaze layer 2 is formed by printing a glass paste thickly onto the substrate 1 and then firing it. The glaze layer 2 is formed using thick-film formation technology.

[0020] The wiring layer 3 is intended to form a path for current to flow through the resistive layer 4 and is located on the main glaze surface 21 of the glaze layer 2. The wiring layer 3 is formed to have a resistivity value smaller than that of the resistive layer 4. The wiring layer 3 is made of a conductor mainly composed of silver (Ag), for example. As an example of the thickness of the wiring layer 3, the thickness of the wiring layer 3 is, for example, about 0.5 to 30 μm.

[0021] As shown in Figures 3 to 5, the wiring layer 3 has a common electrode 31, a plurality of individual electrodes 32, a plurality of signal wiring sections 35, and a plurality of pad sections 36.

[0022] The common electrode 31 has a common portion 311 and a plurality of common electrode strip portions 312. Specifically, the common portion 311 is positioned at a distance from the resistive layer 4 on the y2 side of the sub-scanning direction y. The common portion 311 extends along the main scanning direction x, and its width dimension in the sub-scanning direction y is relatively large. Each of the plurality of common electrode strip portions 312 extends from the common portion 311 on the y1 side of the sub-scanning direction y and is arranged at equal pitches in the main scanning direction x.

[0023] The multiple individual electrodes 32 are for partially conducting current to the resistive layer 4 and are in a position of opposite polarity to the common electrode 31. The individual electrodes 32 extend from the resistive layer 4 toward the drive IC 71. The multiple individual electrodes 32 are arranged in the main scanning direction x, and each has an individual electrode strip portion 33 and a connecting portion 34.

[0024] Each individual electrode strip portion 33 is a strip-shaped portion extending in the sub-scanning direction y, and is located between two adjacent common electrode strip portions 312 of the common electrode 31. The connecting portion 34 is a portion extending from the individual electrode strip portion 33 toward the drive IC 71, and most of it has portions aligned with the sub-scanning direction y and portions inclined with respect to the sub-scanning direction y. The connecting portions 34 are arranged at relatively narrow intervals in the main scanning direction x on the y1 side of the sub-scanning direction y. The distance between adjacent connecting portions 34 on the y1 side of the sub-scanning direction y is, for example, about 100 μm or less.

[0025] Multiple signal wiring sections 35 constitute a wiring pattern connected to the connector 73 and the drive IC 71. Although only one signal wiring section 35 is shown in Figure 4, multiple signal wiring sections 35 are arranged in the vicinity of the drive IC 71 in the main scanning direction x, and each extends in the sub-scanning direction y. The drive IC 71 used in the thermal print head A1 typically has a long rectangular planar shape (see Figure 1). The long side of the drive IC 71 is aligned with the main scanning direction x, which is the direction in which the resistive layer 4 extends.

[0026] As shown in Figures 3 and 4, the multiple pad portions 36 are connected to the drive IC 71 via multiple wires 61. Multiple pad portions 36 are arranged in both the main scanning direction x and the sub-scanning direction y. The multiple pad portions 36 are connected to the y1 end in the sub-scanning direction y of any of the multiple connecting portions 34 (individual electrodes 32), or to the y2 end in the sub-scanning direction y of any of the multiple signal wiring portions 35. Wires 61 for connection to the drive IC 71 are bonded to each of the multiple pad portions 36. In this embodiment, the multiple pad portions 36 connected to adjacent connecting portions 34 in the main scanning direction x are arranged alternately in the sub-scanning direction y. As a result, the multiple pad portions 36 connected to the multiple connecting portions 34 do not interfere with each other, even though they are wider than most of the connecting portions 34.

[0027] Furthermore, a portion of the wiring layer 3 may be made of a conductor mainly composed of gold (Au). Specifically, the portion of the wiring layer 3 mainly composed of Au includes, for example, the common portion 311 of the common electrode 31 and the multiple common electrode strip portions 312, and the individual electrode strip portions 33 of the multiple individual electrodes 32. Moreover, the entire wiring layer 3 may be made of a conductor mainly composed of Au.

[0028] The resistive layer 4 is made of a material with a higher resistivity than the material constituting the wiring layer 3, such as ruthenium oxide, and is formed in a strip shape extending in the main scanning direction x. As shown in Figure 3, the resistive layer 4 intersects with the multiple common electrode strips 312 of the common electrode 31 and the individual electrode strips 33 of the multiple individual electrodes 32. Furthermore, the resistive layer 4 is laminated on the side opposite to the substrate 1 with respect to the multiple common electrode strips 312 of the common electrode 31 and the individual electrode strips 33 of the multiple individual electrodes 32. The portion of the resistive layer 4 sandwiched between each common electrode strip 312 and each individual electrode strip 33 is designated as a heating portion 41 that generates heat when partially energized by the wiring layer 3. One printed dot is formed by the heat generated by two adjacent heating portions 41 flanking one individual electrode strip 33. The thickness of the resistive layer 4 is, for example, about 1 to 10 μm.

[0029] The protective layer 5 is for protecting at least the resistor layer 4 and mainly consists of glass, such as amorphous glass. In this embodiment, the protective layer 5 includes a first layer 51 and a second layer 52 that are laminated together.

[0030] The first layer 51 covers at least the resistor layer 4 (multiple heat-generating parts 41) and is in contact with the resistor layer 4. In this embodiment, the first layer 51 covers the entire resistor layer 4 and most of the wiring layer 3. Specifically, the first layer 51 is formed in a region extending from just before the y1 side edge of the substrate 1 in the sub-scanning direction y to the y2 side edge of the substrate 1 in the sub-scanning direction y. However, the first layer 51 exposes a region of the wiring layer 3 that includes multiple pad portions 36. As shown in Figure 4, the first layer 51 has multiple openings 519. Each opening 519 penetrates the first layer 51 in the thickness direction z. Each of the multiple openings 519 exposes a pad portion 36. In this way, the first layer 51 protects the wiring layer 3 and the resistor layer 4.

[0031] The first layer 51 is made of, for example, amorphous glass and may contain additives such as alumina particles. The softening point of the amorphous glass constituting the first layer 51 is, for example, about 780°C. The first layer 51 is formed by printing a glass paste thickly onto the glaze layer 2 so as to cover the resistor layer 4 and a part of the wiring layer 3, and then firing it. The thickness t1 of the first layer 51 is not particularly limited, but is, for example, about 6 to 8 μm.

[0032] The second layer 52 is formed on the first layer 51. The second layer 52 is located at the z1 side of the thickness direction z among the multiple layers (first layer 51 and second layer 52 in this embodiment) that constitute the protective layer 5. In a plan view (view in the thickness direction z), the second layer 52 overlaps the resistor layer 4 and is formed in an area that the printing medium 82 may come into contact with when the printing medium 82 is transported. The second layer 52 covers a part of the first layer 51. Specifically, in the sub-scanning direction y, the second layer 52 covers a part on each side of the resistor layer 4. The second layer 52 covers at least a part of the individual electrode strip portion 33 of each individual electrode 32 and the common electrode 31.

[0033] The second layer 52 is made of, for example, amorphous glass and contains one or more types of additive particles. The second layer 52 contains at least boron nitride (BN) particles as additive particles. In this embodiment, the second layer 52 contains boron nitride particles and alumina particles as additive particles. The second layer 52 may also be configured without alumina particles. In this embodiment, the softening point of the amorphous glass constituting the second layer 52 is, for example, about 700°C. Therefore, the softening point of the amorphous glass constituting the first layer 51 is higher than the softening point of the amorphous glass constituting the second layer 52. The glass material of the second layer 52 is made of, for example, lead-free glass that does not contain lead oxide. The boron nitride particles are, for example, grains made of cubic boron nitride (cBN) and preferably have a rounded shape. Cubic boron nitride has a hardness second only to diamond, with a Knoop hardness of about 4700 Hk. Furthermore, cubic boron nitride also exhibits excellent heat resistance. Alumina particles are grains made of alumina, and preferably have a rounded shape.

[0034] The thickness t2 of the second layer 52 is smaller than the thickness t1 of the first layer 51, for example, about 2 to 6 μm. The particle size of the boron nitride particles contained in the second layer 52 is less than or equal to the thickness t2 of the second layer 52, preferably about 0 to 4 μm.

[0035] In this embodiment, the blending ratio of additive particles (boron nitride particles and alumina particles in this embodiment) in the second layer 52 is, for example, 5 to 80% by weight. The blending ratio of boron nitride particles in the second layer 52 is preferably 10 to 30% by weight. The blending ratio of alumina particles in the second layer 52 is, for example, 0 to 70% by weight.

[0036] The second layer 52 is formed by printing a thick film of a material containing boron nitride particles and alumina particles mixed into a glass paste, and then firing it. The density of the amorphous glass constituting the second layer 52 and the density of the boron nitride particles are relatively similar. In the formed second layer 52, the boron nitride particles are generally uniformly dispersed. Unlike the second layer 52, the first layer 51 does not contain boron nitride particles.

[0037] The drive IC 71 performs the function of partially heating the resistive layer 4 by selectively energizing multiple individual electrodes 32. As shown in Figures 1 and 4, the drive IC 71 is positioned on the y1 side of the sub-scanning direction y with respect to the resistive layer 4 (multiple heating elements 41). In this embodiment, multiple drive ICs 71 are arranged on the glaze layer 2. Multiple pads are provided on the drive IC 71. As shown in Figure 4, the pads of the drive IC 71 and the multiple pad sections 36 are connected via multiple wires 61 bonded to each. The wires 61 are made of, for example, gold. As shown in Figures 2 and 4, the drive IC 71 is covered with a protective resin 72. The protective resin 72 is made of, for example, a black soft resin. The drive IC 71 and the connector 73 are connected by the multiple signal wiring sections 35. The drive IC 71 receives print signals, control signals, and voltages supplied to the multiple heating elements 41 transmitted from the outside via the connector 73. Multiple heating elements 41 are selectively heated by individually energizing them according to the printing signal and control signal.

[0038] Next, we will briefly explain an example of how to use the Thermal Printhead A1.

[0039] The thermal printhead A1 is used integrated into the thermal printer Pr. As shown in Figure 2, within the printer, each heating element 41 of the thermal printhead A1 faces the platen roller 81. When the printer is in use, the platen roller 81 rotates, feeding the printing medium 82, such as thermal paper, at a constant speed between the platen roller 81 and each heating element 41 along the sub-scanning direction y. The printing medium 82 is pressed by the platen roller 81 against the portion of the protective layer 5 that covers each heating element 41. Meanwhile, each individual electrode 32 shown in Figure 3 is selectively given a potential by the drive IC 71. This applies a voltage between the common electrode 31 and each of the individual electrodes 32. A current then selectively flows through the multiple heating elements 41, generating heat. The heat generated in each heating element 41 is then transferred to the printing medium 82 via the protective layer 5. Multiple dots are then printed on the line region extending linearly in the main scanning direction x on the printing medium 82. Furthermore, the heat generated in each heat-generating section 41 is also transferred to the glaze layer 2 and stored in the glaze layer 2.

[0040] Next, the operation of this embodiment will be described.

[0041] In the thermal print head A1, the protective layer 5 (second layer 52) that can come into contact with the printing medium 82 contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5 (second layer 52).

[0042] In this embodiment, the protective layer 5 is composed of multiple layers, including a first layer 51 and a second layer 52. The first layer 51 is in contact with the resistor layer 4, while the second layer 52 is located at the top (the z1 side end in the thickness direction z) and overlaps the resistor layer 4 in a plan view. The second layer 52 contains boron nitride particles. On the other hand, the first layer 51, which is formed over a relatively wide area, does not contain boron nitride particles. With this configuration, the amount of boron nitride particles used can be suppressed while efficiently improving the wear resistance of the second layer 52, which can come into contact with the printing medium 82. Furthermore, according to the inventors' knowledge, when the wiring layer 3 contains Ag, it has been confirmed that when a glass layer containing boron nitride particles is directly formed on the wiring layer 3, a foaming phenomenon occurs near the Ag in the wiring layer 3. In this embodiment, the first layer 51, which is directly formed on the wiring layer 3, does not contain boron nitride particles. Therefore, when the wiring layer 3 contains Ag, the foaming phenomenon caused by Ag can be prevented.

[0043] The proportion of additive particles in the second layer 52 is 5 to 80% by weight. Furthermore, the proportion of boron nitride particles in the second layer 52 is 10 to 30% by weight. With this configuration, the boron nitride particles in the second layer 52 can be uniformly dispersed, and wear resistance can be improved. According to the inventors' findings, when printing is performed under the same conditions, although there is some variation depending on the print density, when the proportion of boron nitride particles in the second layer 52 is in the range of 10 to 30% by weight, the amount of abrasion in the second layer 52 is reduced, and improved wear resistance has been confirmed.

[0044] The thickness t1 of the first layer 51 is greater than the thickness t2 of the second layer 52. The thickness t2 of the second layer 52 is 2 to 6 μm. With this configuration, the thickness t2 of the second layer 52 can be kept relatively small, and the amount of boron nitride particles used can be effectively suppressed. In addition, the particle size of the boron nitride particles contained in the second layer 52 is less than or equal to the thickness t2 of the second layer 52, and is 0 to 4 μm. With this configuration, the boron nitride particles can be uniformly dispersed in the second layer 52, and the appearance of the outer shape of the boron nitride particles on the surface of the second layer 52 can be effectively suppressed. Therefore, the wear resistance of the protective layer 5 (second layer 52) can be improved, and the surface of the protective layer 5 (second layer 52) can be made moderately smooth.

[0045] According to the inventors' findings, when a glass paste containing boron nitride particles contains lead oxide, it has been confirmed that numerous bubbles are generated on the surface of the glass layer after firing. In this embodiment, the second layer 52 is made of lead-free glass that does not contain lead oxide. This effectively suppresses the generation of bubbles on the surface of the second layer 52 and maintains the smoothness of the surface of the protective layer 5 (second layer 52).

[0046] The softening point of the glass material constituting the first layer 51 is higher than that of the glass material constituting the second layer 52. With this configuration, when the temperature of the protective layer 5 rises, such as when using the thermal print head A1, the first layer 51 can maintain a relatively hard state even if the second layer 52 softens. This makes it possible to suppress the sedimentation of boron nitride particles contained in the second layer 52 from the second layer 52 to the first layer 51. Therefore, the foaming phenomenon that occurs when the wiring layer 3 contains Ag can be appropriately prevented.

[0047] <Second Embodiment> Figures 6 and 7 show a thermal print head according to a second embodiment of this disclosure. Figure 6 is an enlarged cross-sectional view of the main part of the thermal print head A2 of this embodiment, and is a cross-sectional view similar to that of Figure 4. Figure 7 is an enlarged cross-sectional view of the main part, which is a part of Figure 6. In the drawings from Figure 6 onward, elements that are the same as or similar to those of the thermal print head A1 of the above embodiment are denoted by the same reference numerals as in the above embodiment, and their descriptions are omitted as appropriate. Furthermore, the configurations of each part in each embodiment from Figure 6 onward can be appropriately combined with each other to the extent that no technical inconsistencies arise.

[0048] The thermal print head A2 of this embodiment differs from the thermal print head A1 of the above embodiment in the configuration of the glaze layer 2. In the thermal print head A2 shown in Figures 6 and 7, the glaze layer 2 has a heater glaze portion 22 and a glass layer 23. The heater glaze portion 22 has a cross-sectional shape perpendicular to the main scanning direction x, which bulges out on the z1 side in the thickness direction z, and is a long, band-shaped area in plan view in the main scanning direction x. The glass layer 23 is formed adjacent to the heater glaze portion 22, and has a flat glaze main surface 21 facing the z1 side in the thickness direction z. The glass layer 23 overlaps a part of the heater glaze portion 22. The resistor layer 4 (multiple heating elements 41) is arranged on the heater glaze portion 22 and overlaps with the heater glaze portion 22 in plan view (view in the thickness direction z). When forming the glaze layer 2 having such a heater glaze portion 22 and glass layer 23, the process of printing a thick film of glass paste onto the substrate 1 and then firing it is repeated multiple times.

[0049] In the thermal print head A2 of this embodiment, the protective layer 5 (second layer 52) that can come into contact with the printing medium (not shown) contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5 (second layer 52).

[0050] In this embodiment, the protective layer 5 is composed of multiple layers, including a first layer 51 and a second layer 52. The first layer 51 is in contact with the resistor layer 4, while the second layer 52 is located at the top (the z1 side end in the thickness direction z) and overlaps the resistor layer 4 in a plan view. The second layer 52 contains boron nitride particles. On the other hand, the first layer 51, which is formed over a relatively wide area, does not contain boron nitride particles. With this configuration, the amount of boron nitride particles used can be suppressed while efficiently improving the wear resistance of the second layer 52, which can come into contact with the printing medium (not shown). Furthermore, according to the inventors' knowledge, when the wiring layer 3 contains Ag, it has been confirmed that foaming occurs near the Ag in the wiring layer 3 when a glass layer containing boron nitride particles is directly formed on the wiring layer 3. In this embodiment, the first layer 51, which is directly formed on the wiring layer 3, does not contain boron nitride particles. Therefore, when the wiring layer 3 contains Ag, the foaming phenomenon caused by Ag can be prevented. In addition, it provides the same effects and advantages as the thermal print head A1 in the above embodiment.

[0051] <Third Embodiment> Figures 8 and 9 show a thermal printhead according to a third embodiment of this disclosure. Figure 8 is an enlarged cross-sectional view of a key part of the thermal printhead A3 of this embodiment, and is a cross-sectional view similar to that of Figure 4. Figure 9 is an enlarged cross-sectional view of a key part, which is a part of Figure 8. The thermal printhead A3 of this embodiment differs from the thermal printhead A1 of the above embodiment in the configuration of the protective layer 5.

[0052] In the thermal print head A3 shown in Figures 8 and 9, the protective layer 5 consists of a single layer. In this embodiment, the protective layer 5 corresponds to the first layer 51 in the thermal print head A1 and has a thickness similar to that of the first layer 51 in the thermal print head A1. On the other hand, in this embodiment, the protective layer 5 contains at least boron nitride (BN) particles as additive particles. In this embodiment, the protective layer 5 contains boron nitride particles and alumina particles as the additive particles. However, the protective layer 5 may also be configured without the alumina particles.

[0053] In the thermal printhead A3 of this embodiment, the protective layer 5 that can come into contact with the printing medium (not shown) contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5. In addition, within the same configuration range as the thermal printhead A1 of the above embodiment, the same effects and advantages as in the above embodiment are achieved.

[0054] <Fourth Embodiment> Figures 10 and 11 show a thermal printhead according to a fourth embodiment of the present disclosure. Figure 10 is an enlarged cross-sectional view of a key part of the thermal printhead A4 of this embodiment, and is a cross-sectional view similar to that of Figure 4. Figure 11 is an enlarged cross-sectional view of a key part, which is a part of Figure 10. The thermal printhead A4 of this embodiment differs from the thermal printhead A1 of the above embodiment in the configuration of the protective layer 5.

[0055] In the thermal printhead A4 shown in Figures 10 and 11, the protective layer 5 includes a first layer 51, a second layer 52, and a third layer 53. The protective layer 5 of this embodiment has an additional third layer 53 compared to the thermal printhead A1 of the above embodiment. The third layer 53 is interposed between the first layer 51 and the second layer 52 in the thickness direction z and is in contact with both the first layer 51 and the second layer 52. The specific configurations of the first layer 51 and the second layer 52 are the same as those of the thermal printhead A1 of the above embodiment. The third layer 53, like the first layer 51 and the second layer 52, is made of, for example, amorphous glass. The third layer 53 may contain additive particles. If the third layer 53 contains additive particles, the additive particles may be either boron nitride particles or alumina particles, or both boron nitride particles and alumina particles. The softening point of the glass material constituting the third layer 53 is preferably higher than that of the glass material constituting the second layer 52 and lower than that of the glass material constituting the first layer 51.

[0056] In the A4 thermal print head of this embodiment, the protective layer 5 (second layer 52) that can come into contact with the printing medium (not shown) contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5 (second layer 52).

[0057] In this embodiment, the protective layer 5 is composed of multiple layers, including a first layer 51 and a second layer 52. The first layer 51 is in contact with the resistor layer 4, while the second layer 52 is located at the top (the z1 side end in the thickness direction z) and overlaps the resistor layer 4 in a plan view. The second layer 52 contains boron nitride particles. On the other hand, the first layer 51, which is formed over a relatively wide area, does not contain boron nitride particles. With this configuration, the amount of boron nitride particles used can be suppressed while efficiently improving the wear resistance of the second layer 52, which can come into contact with the printing medium (not shown). Furthermore, according to the inventors' knowledge, when the wiring layer 3 contains Ag, it has been confirmed that foaming occurs near the Ag in the wiring layer 3 when a glass layer containing boron nitride particles is directly formed on the wiring layer 3. In this embodiment, the first layer 51, which is directly formed on the wiring layer 3, does not contain boron nitride particles. Therefore, when the wiring layer 3 contains Ag, the foaming phenomenon caused by Ag can be prevented. In addition, it provides the same effects and advantages as the thermal print head A1 in the above embodiment.

[0058] <Fifth Embodiment> Figures 12 and 13 show a thermal printhead according to a fifth embodiment of the present disclosure. Figure 12 is an enlarged cross-sectional view of the main part of the thermal printhead A5 of this embodiment, and is a cross-sectional view similar to that of Figure 4. Figure 13 is an enlarged cross-sectional view of the main part, which is a part enlarged portion of Figure 12. The thermal printhead A5 of this embodiment differs from the thermal printhead A1 of the above embodiment in the configuration of the protective layer 5.

[0059] In the thermal print head A5 shown in Figures 12 and 13, the formation region of the second layer 52 of the protective layer 5 differs from that of the thermal print head A1 in the above embodiment. In this embodiment, the second layer 52 overlaps with the resistor layer 4 in a plan view (viewed in the thickness direction z), but does not overlap with the common portion 311 in a plan view. Furthermore, in this embodiment, the softening point of the amorphous glass constituting the first layer 51 is below the softening point of the amorphous glass constituting the second layer 52.

[0060] In the thermal print head A5 of this embodiment, the protective layer 5 (second layer 52) that can come into contact with the printing medium (not shown) contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5 (second layer 52).

[0061] The softening point of the glass material constituting the first layer 51 is below the softening point of the glass material constituting the second layer 52. The common area 311 is formed over a relatively large area compared to the other elements of the wiring layer 3. The second layer 52 does not overlap the common area 311 in a plan view (viewed in the thickness direction z). With this configuration, when the temperature of the protective layer 5 rises, such as when using the thermal print head A1, even if the first layer 51 softens and the boron nitride particles contained in the second layer 52 settle from the second layer 52 to the first layer 51, foaming will not occur in the common area 311 when the wiring layer 3 contains Ag. Therefore, the foaming phenomenon caused by Ag when the wiring layer 3 contains Ag can be suppressed. In addition, within the range of a configuration similar to that of the thermal print head A1 in the above embodiment, the same effects and advantages as in the above embodiment are achieved.

[0062] <Sixth Embodiment> Figures 14 and 15 show a thermal printhead according to the sixth embodiment of this disclosure. Figure 14 is an enlarged cross-sectional view of the main part of the thermal printhead A6 of this embodiment, and is a cross-sectional view similar to that of Figure 4. Figure 15 is an enlarged cross-sectional view of the main part, which is a part enlarged portion of Figure 14. The thermal printhead A6 of this embodiment differs from the thermal printhead A1 of the above embodiment in the configuration of the protective layer 5.

[0063] In the thermal print head A6 shown in Figures 14 and 15, the protective layer 5 includes a first part 55 and a second part 56. The first part 55 is in contact with the resistor layer 4 and is formed around the resistor layer 4, covering the resistor layer 4 (multiple heat-generating parts 41). In a plan view (view in the thickness direction z), the first part 55 overlaps the resistor layer 4 and extends along the main scanning direction x. The first part 55 is made of the same material as the second layer 52 in the thermal print head A1 of the first embodiment. The first part 55 is made of amorphous glass, for example, and contains one or more types of additive particles. The first part 55 contains at least boron nitride particles as additive particles. In this embodiment, the first part 55 contains boron nitride particles and alumina particles as the additive particles. The first part 55 may also be configured not to contain alumina particles.

[0064] The second part 56 is formed in a region that does not overlap with the first part 55 in a plan view (viewed in the z-thickness direction), and is formed over a wider area than the first part 55. The second part 56 is made of the same material as the first layer 51 in the thermal print head A1 of the first embodiment described above. The second part 56 is made of amorphous glass, for example, and may contain additives such as alumina particles. Unlike the first part 55, the second part 56 does not contain boron nitride particles.

[0065] In the thermal print head A6 of this embodiment, the protective layer 5 (first part 55) that can come into contact with the printing medium (not shown) contains boron nitride particles as additive particles. With this configuration, boron nitride has high hardness, which can improve the wear resistance of the protective layer 5 (first part 55).

[0066] Part 1 55 overlaps the resistor layer 4 in a plan view, and boron nitride particles are contained in Part 1 55. On the other hand, Part 2 56, which is formed over a relatively wide area, does not contain boron nitride particles. With this configuration, the amount of boron nitride particles used can be suppressed while efficiently improving the wear resistance of Part 1 55, which can come into contact with the printing medium (not shown). Furthermore, within the same configuration as the thermal print head A1 of the above embodiment, the same effects and advantages as in the above embodiment are achieved.

[0067] The thermal printhead relating to this disclosure is not limited to the embodiments described above. The specific configuration of each part of the thermal printhead relating to this disclosure can be modified in various ways.

[0068] In the above embodiment, when the protective layer 5 is configured to include multiple layers laminated on the resistor layer 4, boron nitride particles are included only in the uppermost layer, which is located at the z1 end in the thickness direction z (the second layer 52 in the above embodiment). However, the disclosure is not limited thereto. When the protective layer 5 includes multiple layers laminated on the resistor layer 4, it is sufficient that boron nitride particles are included in any one of the multiple layers. For example, boron nitride particles may be included only in an intermediate layer located between the bottom layer (the layer in contact with the resistor layer 4) and the uppermost layer in the thickness direction z.

[0069] This disclosure includes the following annotations:

[0070] [Note 1] A substrate having a main surface facing one side in the thickness direction, A resistor layer having a plurality of heating elements arranged on the main surface and aligned in the main scanning direction, A wiring layer disposed on the main surface and conductive to the resistor layer, A protective layer covering at least the resistor layer, The protective layer is composed of glass and additive particles, The aforementioned additive particles include boron nitride particles in a thermal print head. [Note 2] The protective layer includes a plurality of layers laminated on the resistor layer, The thermal print head according to claim 1, wherein at least one of the plurality of layers comprises the boron nitride particles. [Note 3] The protective layer is composed of the plurality of layers, including the first layer and the second layer. The first layer is in contact with the resistor layer, The second layer is located at one end of the plurality of layers in the thickness direction and overlaps the resistor layer when viewed in the thickness direction. The second layer is a thermal print head as described in Appendix 2, comprising the boron nitride particles. [Note 4] The thermal print head described in Appendix 3, wherein the first layer does not contain the boron nitride particles. [Note 5] The thermal print head as described in Appendix 4, wherein the blending ratio of the additive particles in the second layer is 5 to 80% by weight. [Note 6] The thermal print head as described in Appendix 5, wherein the proportion of boron nitride particles in the second layer is 10 to 30% by weight. [Note 7] The protective layer contains alumina particles as the additive particles, The thermal print head according to Appendix 5 or 6, wherein the blending ratio of the alumina particles in the second layer is 0 to 70% by weight. [Note 8] The thermal print head according to any one of appendices 4 to 7, wherein the thickness of the second layer is 2 to 6 μm. [Note 9] The thermal print head as described in Appendix 8, wherein the particle size of the boron nitride particles is less than or equal to the thickness of the second layer. [Note 10] The thermal print head described in Appendix 9, wherein the particle size of the boron nitride particles is 0 to 4 μm. [Note 11] The protective layer consists of the first layer and the second layer, The thermal print head described in Appendix 8, wherein the thickness of the first layer is greater than the thickness of the second layer. [Note 12] The thermal print head according to any one of appendices 4 to 11, wherein the second layer is made of lead-free glass that does not contain lead oxide. [Note 13] A thermal print head according to any one of appendices 4 to 12, wherein the softening point of the first layer is higher than the softening point of the second layer. [Note 14] The softening point of the first layer is below the softening point of the second layer. The wiring layer is arranged at a distance from the resistor layer in the sub-scanning direction and has a common portion extending in the main scanning direction. The second layer is a thermal print head as described in any of appendices 4 to 12, which does not overlap the common portion when viewed in the thickness direction. [Note 15] The main surface further comprises a glaze layer disposed on the main surface, The resistive layer is disposed on the glaze layer, and the thermal print head is as described in any one of appendices 1 to 13. [Note 16] A thermal print head as described in any of Appendix 1 to 14, A thermal printer comprising a platen arranged opposite to the plurality of heating elements.

[0071] A1, A2, A3, A4, A5, A6: Thermal print heads Pr: Thermal printer 1: Circuit board 11: Main surface 2: Glaze layer 21: Glazed main surface 22: Heater Glaze Section 23: Glass layer 3: Wiring layer 31: Common electrode 311:Common section 312: Common electrode strip 32: Individual electrode 33: Individual electrode strip portion 34:Connection part 35: Signal wiring section 36: Pad section 4:Resistor layer 41: Heat-generating part 5:Protective layer 51: 1st layer 519 :Aperture 52: 2nd layer 53:Third layer 55: Part 1 56: Part 2 61: Wire 71: Driver IC 72: Protective resin 73: Connector 81: Platen Roller 82:Print media

Claims

1. A substrate having a main surface facing one side in the thickness direction, A resistor layer having a plurality of heating elements arranged on the main surface and aligned in the main scanning direction, A wiring layer disposed on the main surface and conductive to the resistor layer, A protective layer covering at least the resistor layer, The protective layer is composed of glass and additive particles, The aforementioned additive particles include boron nitride particles. The protective layer includes a plurality of layers laminated on the resistor layer, At least one of the aforementioned plurality of layers contains the boron nitride particles, The protective layer is composed of the plurality of layers, including the first layer and the second layer. The first layer is in contact with the resistor layer, The second layer is located at one end of the plurality of layers in the thickness direction and overlaps the resistor layer when viewed in the thickness direction. The second layer contains the boron nitride particles, The first layer does not contain the boron nitride particles, The proportion of the additive particles in the second layer is 5 to 80% by weight. A thermal print head in which the proportion of boron nitride particles in the second layer is 10 to 30% by weight.

2. The protective layer contains alumina particles as the additive particles, The thermal print head according to claim 1, wherein the blending ratio of the alumina particles in the second layer is 0 to 70% by weight.

3. The thermal print head according to claim 1, wherein the thickness of the second layer is 2 to 6 μm.

4. The thermal print head according to claim 3, wherein the particle size of the boron nitride particles is less than or equal to the thickness of the second layer.

5. The protective layer consists of the first layer and the second layer, The thermal print head according to claim 3, wherein the thickness of the first layer is greater than the thickness of the second layer.

6. The thermal print head according to claim 1, wherein the second layer is made of lead-free glass that does not contain lead oxide.

7. The thermal print head according to claim 1, wherein the softening point of the first layer is higher than the softening point of the second layer.

8. The softening point of the first layer is below the softening point of the second layer. The wiring layer is arranged at a distance from the resistor layer in the sub-scanning direction and has a common portion extending in the main scanning direction. The thermal print head according to claim 1, wherein the second layer does not overlap the common portion when viewed in the thickness direction.

9. The main surface further comprises a glaze layer disposed on the main surface, The thermal print head according to claim 1, wherein the resistive layer is disposed on top of the glaze layer.

10. A thermal print head according to any one of claims 1 to 9, A thermal printer comprising a platen arranged opposite to the plurality of heating elements.

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