JP7122448B2 - thermal print head - Google Patents

Description

The present invention relates to thermal printheads.

FIG. 18 shows an example of a conventional thermal printhead (see, for example, Patent Document 1). A thermal print head 101 shown in the figure has a glass layer 2 formed on a substrate 1 , and an electrode layer 3 and a resistor layer 4 formed on the glass layer 2 . Heat required for printing is generated by partially energizing the resistor layer 4 through the electrode layer 3 . The electrode layer 3 and resistor layer 4 are covered with a protective layer 5 . The protective layer 5 is made of glass, for example, and protects the electrode layer 3 and the resistor layer 4 .

In recent years, the printing speed has been increased. Moreover, with the diversification of printing paper, there are cases where printing paper containing a relatively hard substance is used. These are factors that promote damage to the protective layer 5 . The protective layer 5 is required to have abrasion resistance.

JP-A-7-186429

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal print head having a protective layer with excellent abrasion resistance.

A thermal printhead provided by the present invention comprises a substrate having a main surface which is one surface, a resistor layer formed on the main surface side of the substrate, and an electrode layer for energizing the resistor layer. and a protective layer covering at least part of the resistor layer, wherein the protective layer comprises a low-density layer containing carbon as a main component and a high-density layer containing carbon as a main component and having a higher density than the low-density layer. and a high-density layer, wherein the high-density layer is arranged outside the low-density layer.

In a preferred embodiment of the invention, the protective layer comprises at least two alternating layers of low density and layers of high density.

In a preferred embodiment of the present invention, the plurality of low density layers are thicker toward the outer side.

In a preferred embodiment of the present invention, the protective layer is disposed between the low-density layer and the high-density layer, contains carbon as a main component, and has a density equal to that of the low-density layer and the high-density layer. It further comprises a medium density layer that is in between.

In a preferred embodiment of the present invention, the protective layer comprises a plurality of medium density layers each having a different density, with the higher density layer facing outward.

In a preferred embodiment of the invention, said protective layer further comprises said high density layer inside said low density layer.

In a preferred embodiment of the invention at least one of said high density layers is electrically conductive.

In a preferred embodiment of the present invention, the protective layer further comprises an electrically conductive layer.

In a preferred embodiment of the present invention, in the boundary region between the low-density layer and the high-density layer, the density gradually increases from the low-density layer side toward the high-density layer side.

In a preferred embodiment of the invention, the low density layer and the high density layer are made of the same material.

In a preferred embodiment of the present invention, the low density layer and the high density layer are made of tetrahedral amorphous carbon.

In a preferred embodiment of the invention, the thickness of said high density layer is less than the thickness of said low density layer.

In a preferred embodiment of the present invention, the high density layer has a thickness of 5 to 50 [nm].

In a preferred embodiment of the present invention, the thickness of the low density layer is 200-2000 [nm].

In a preferred embodiment of the present invention, the thermal printhead further comprises a second protective layer arranged inside the protective layer, and the protective layer comprises a base layer in contact with the second protective layer. I have more.

In a preferred embodiment of the present invention, the electrode layer extends in the sub-scanning direction and is connected to a plurality of first strip-shaped portions arranged apart from each other in the main scanning direction, and to the plurality of first strip-shaped portions. and a plurality of individual electrodes each having a common electrode having a connecting portion extending in the main scanning direction and a second band-like portion extending in the sub-scanning direction, and are spaced apart from each other in the main scanning direction of the substrate. wherein the resistor layer is strip-shaped extending in the main scanning direction, and the first strip-shaped portion and the second strip-shaped portion alternately intersect the resistor layer in the main scanning direction. are arranged as

In a preferred embodiment of the present invention, grooves are formed in a direction perpendicular to the main scanning direction in a portion of the outer surface of the protective layer overlapping the resistor layer when viewed in the thickness direction of the substrate. .

In a preferred embodiment of the invention, the protective layer further comprises a metal layer made of metal or metal compound.

In a preferred embodiment of the present invention, the metal layer is made of metal nitride.

In a preferred embodiment of the invention, the metal layer is made of CrN.

In a preferred embodiment of the present invention, the metal layer is arranged on the outermost side of the protective layer.

According to the present invention, the protective layer includes a low-density layer and a high-density layer containing carbon as a main component. A high-density layer having a higher density is arranged outside the low-density layer. The high density layer has a higher hardness and a lower coefficient of friction than the low density layer. Therefore, the protective layer has excellent wear resistance.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

1 is a plan view showing a thermal print head according to a first embodiment of the invention; FIG. FIG. 2 is a plan view of a main part showing the thermal print head of FIG. 1; 3 is a cross-sectional view taken along line III-III of FIG. 2; FIG. 2 is an enlarged cross-sectional view of a main part showing the thermal print head of FIG. 1; FIG. FIG. 5 is a cross-sectional view taken along line VV of FIG. 4; FIG. 4 is an enlarged cross-sectional view of a main part showing a modification of the thermal print head according to the first embodiment; FIG. 5 is an enlarged cross-sectional view of main parts showing another modification of the thermal print head according to the first embodiment; FIG. 2 is a diagram showing an example of a film forming apparatus in the thermal print head of FIG. 1; It is an actual cross-sectional photograph of a protective layer. It is an actual cross-sectional photograph of a protective layer. It shows the test results of the accelerated wear resistance test, and is a photograph of the state of the surface before and after the test. It is a figure which shows the test result of an abrasion resistance accelerated test, and shows the cross-sectional profile before and behind a test. FIG. 7 is an enlarged cross-sectional view of a main part showing a thermal print head according to a second embodiment; FIG. 11 is an enlarged cross-sectional view of a main part showing a thermal print head according to a third embodiment; FIG. 11 is an enlarged cross-sectional view of a main part showing a thermal print head according to a fourth embodiment; FIG. 11 is an enlarged cross-sectional view of a main part showing a thermal print head according to a fifth embodiment; FIG. 11 is an enlarged cross-sectional view of a main part showing a thermal print head according to a sixth embodiment; FIG. 2 is an enlarged cross-sectional view of a main part showing an example of a conventional thermal printhead;

Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

1 to 5 show a thermal printhead 101 according to a first embodiment of the invention. FIG. 1 is a plan view showing the thermal print head 101. FIG. FIG. 2 is a plan view of the main part showing the thermal print head 101. As shown in FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. FIG. 4 is an enlarged cross-sectional view of the main part showing the thermal print head 101. As shown in FIG. 5 is a cross-sectional view taken along line VV of FIG. 4. FIG. In these figures, the longitudinal direction (main scanning direction) of the thermal print head 101 is defined as the x direction, the lateral direction (sub-scanning direction) is defined as the y direction, and the thickness direction is defined as the z direction. The same applies to the following figures. For convenience of understanding, the protective layer 5 is omitted in FIGS. 1 and 2. FIG.

The thermal printhead 101 includes a substrate 1, a glass layer 2, an electrode layer 3, a resistor layer 4, protective layers 5 and 6, and a drive IC71. The thermal print head 101 is incorporated in a printer that prints on thermal paper to create bar code sheets and receipts, for example.

The substrate 1 is made of ceramic such as Al ₂ O ₃ and has a thickness of about 0.6 to 1.0 [mm]. As shown in FIG. 1, the substrate 1 has a long rectangular shape extending in the x direction. The substrate 1 has a main surface 11 and a back surface 12 facing opposite to each other in the z-direction. A glass layer 2 , an electrode layer 3 , a resistor layer 4 and protective layers 5 and 6 are formed on the main surface 11 . A heat sink made of a metal such as Al may be provided on the rear surface 12 of the substrate 1 .

Glass layer 2 is formed on the entire main surface 11 of substrate 1 and is made of a glass material such as amorphous glass. The glass layer 2 is formed by printing a thick film of glass paste and then firing it. The glass layer 2 is provided to eliminate irregularities on the main surface 11 of the substrate 1 to facilitate lamination of the electrode layer 3 and to store heat generated in the resistor layer 4 . In order to make it easier to press the heat-generating portion 41, which is the portion of the resistor layer 4 that generates heat, with the thermal paper or the like that is the object to be printed, the portion of the glass layer 2 where the resistor layer 4 is formed has a yz plane It is also possible to form a partial grace whose cross-sectional shape is arc-shaped.

The electrode layer 3 constitutes a path for energizing the resistor layer 4 and is formed on the glass layer 2 on the main surface 11 of the substrate 1 . The electrode layer 3 is made of resinate Au to which rhodium, vanadium, bismuth, silicon or the like is added, for example. The electrode layer 3 is formed by printing a resinate Au paste as a thick film and then firing it. The electrode layer 3 may be formed by a thin film forming technique such as sputtering. Moreover, the electrode layer 3 may be configured by stacking a plurality of Au layers. Although the thickness of the electrode layer 3 is not particularly limited, it is, for example, about 0.6 to 1.2 [μm]. Electrode layer 3 may have a portion formed on a portion other than main surface 11 of substrate 1 . The electrode layer 3 has a common electrode 31 and a plurality of individual electrodes 35 .

The common electrode 31 includes a plurality of belt-shaped portions 32 , connecting portions 33 and detour portions 34 . As shown in FIGS. 2 and 3, the connecting portion 33 is arranged near the end of the substrate 1 on the downstream side in the y direction and has a strip shape extending in the x direction. In addition, in order to suppress heat generation due to the resistance of the connecting portion 33, the surface of the connecting portion 33 opposite to the substrate 1 is coated with a material (for example, Ag) having a lower resistivity than the connecting portion 33 (electrode layer 3). A strip-shaped auxiliary electrode layer extending in the x-direction may be formed. The belt-like portions 32 extend upstream in the y direction from the connecting portion 33 and are arranged in plurality at equal pitches in the x direction. The "strip-shaped part 32" corresponds to the "first strip-shaped part" of the present invention. The detour portion 34 extends in the y direction from one end of the connecting portion 33 in the x direction.

The individual electrode 35 is for partially energizing the resistor layer 4 , and has a reverse polarity with respect to the common electrode 31 . A plurality of individual electrodes 35 are arranged at equal pitches in the x-direction, each having a band-shaped portion 36 and a bonding portion 37 . The band-shaped portion 36 is a band-shaped portion extending in the y-direction and positioned between two adjacent band-shaped portions 32 . That is, the band-shaped portions 36 and the band-shaped portions 32 are alternately arranged in the x direction. The "strip-shaped part 36" corresponds to the "second strip-shaped part" of the present invention. The bonding portion 37 is provided at the y-direction upstream end portion of the strip portion 36 .

The resistor layer 4 is made of, for example, ruthenium oxide, which has a higher resistivity than the material forming the electrode layer 3, and is formed on the glass layer 2 on the main surface 11 of the substrate 1 in a strip shape extending in the x direction. . The resistor layer 4 is formed by printing a thick film of a paste such as ruthenium oxide and then firing it. The resistor layer 4 may be formed by a thin film forming technique such as sputtering. Although the thickness of the resistor layer 4 is not particularly limited, it is, for example, about 6 [μm] in the case of thick film printing, and is, for example, about 0.05 to 0.2 [μm] in the case of sputtering. The resistor layer 4 is formed on the upper side of the plurality of strip portions 32 and the plurality of strip portions 36 so as to cross the plurality of strip portions 32 and the plurality of strip portions 36 respectively. A portion of the resistor layer 4 sandwiched between the strip portions 32 and the strip portions 36 serves as a heat generating portion 41 . The heat generating portion 41 is a portion that generates heat by being partially energized by the electrode layer 3, and this heat generation forms print dots.

The protective layers 5 and 6 are for protecting the resistor layer 4 and the electrode layer 3 . Protective layer 5 is made of, for example, amorphous glass. The softening point of this amorphous glass is, for example, about 700.degree. As shown in FIG. 3, the protective layer 5 extends from before the downstream edge of the substrate 1 (for example, 0.1 to 0.5 [mm] before the edge) to the bonding portion 37 of the individual electrode 35 in the y direction. It is formed in a front area and covers at least a plurality of heat-generating portions 41, and covers most of the electrode layer 3 in this embodiment. The protective layer 5 is formed by printing a thick film of glass paste and then baking it. The protective layer 5 is formed so that the height of the portion overlapping the resistor layer 4 from the main surface 11 of the substrate 1 when viewed in the thickness direction of the substrate 1 (viewed from the downstream side in the z direction) has a desired dimension. In addition, the surface is ground in order to enhance the adhesion with the protective layer 6 . As a result, a large number of grooves 5a parallel to the y-direction (perpendicular to the x-direction) are formed in the z-direction downstream side surface of the portion of the protective layer 5 overlapping the resistor layer 4 (see FIG. 5). Although the thickness of protective layer 5 is not particularly limited, it is, for example, about 6 to 8 [μm]. The protective layer 5 may be formed up to the downstream edge of the substrate 1 in the y direction. The "protective layer 5" corresponds to the "second protective layer" of the invention, and the "protective layer 6" corresponds to the "protective layer" of the invention.

As shown in FIGS. 4 and 5, the protective layer 6 is formed outside (downstream in the z-direction) of the protective layer 5 and includes an underlying layer 61, a low density layer 62 and a high density layer 63. As shown in FIG. In this embodiment, a base layer 61, a low density layer 62, a high density layer 63, a low density layer 62, and a high density layer 63 are laminated in order from the inside to the outside. Although the protective layer 6 is formed so as to cover the protective layer 5 in the present embodiment, it is not limited to this, and may cover at least the plurality of heat generating portions 41 when viewed from the downstream side in the z direction. The underlying layer 61 is provided to increase adhesion between the protective layer 5 and the low-density layer 62, and is, for example, silicon nitride made of a SiN-based material. Note that the underlying layer 61 may not be provided.

The low density layer 62 and the high density layer 63 are made of tetrahedral amorphous carbon (ta-C). Ta-C has a higher diamond content than diamond-like carbon (DLC) and is about 45 to 85% (DLC is about 25%). Further, while the density of DLC is about 2.2 [g/cm ³ ], the density of ta-C is 2.5 to
It is about 3.3 [g/cm ³ ]. Thus, ta-C is a carbon-based material with increased diamond content and increased density. Since ta-C has a high diamond content, it has a high hardness (approximately 35 to 80 [GPa]) and heat resistance temperature (approximately 600 to 800 ° C in a nitrogen atmosphere), and a coefficient of friction (approximately 0.08 to 0.1 ) is small.

The low-density layer 62 has a lower density of about 2.5 to 3.0 [g/cm ³ ] than the high-density layer 63, a sublimation temperature of about 350° C. (in a nitrogen atmosphere), and a Vickers hardness of 2000. It is about [Hv]. The thickness of the low density layer 62 is approximately 200 to 2000 [nm]. In this embodiment, the thickness of the low-density layer 62 is formed so that the outer side (downstream side in the z direction) becomes thicker. The thickness of each low-density layer 62 may be the same thickness, or may be thinner toward the outer side. However, it is desirable to make the outer one thicker. The high-density layer 63 has a higher density of about 3.1 to 3.3 [g/cm ³ ] than the low-density layer 62, a sublimation temperature of about 800° C. (in a nitrogen atmosphere), and a Vickers hardness of 8.
000 [Hv]. The thickness of the high density layer 63 is about 5 to 50 [nm]. A high density layer 63 is arranged on the outermost side of the protective layer 6 .

The density, sublimation temperature and Vickers hardness of the low density layer 62 and the high density layer 63 are not limited. Also, the low-density layer 62 and the high-density layer 63 are not limited to ta-C, and may be DLC. However, since DLC has a low sublimation temperature and is easily graphitized, at least the high-density layer 63 is desirably ta-C. Also, the thicknesses of the low-density layer 62 and the high-density layer 63 are not limited. Since the high density layer 63 has high internal stress, it is difficult to form it thickly. In this embodiment, the low-density layer 62 is formed thick, and two layers each of the low-density layer 62 and the high-density layer 63 are alternately laminated to form the protective layer 6 with a desired thickness. is doing. If the high density layer 63 is formed thicker, the low density layer 62 may be formed thinner.

In the present embodiment, two layers each of the low-density layer 62 and the high-density layer 63 are alternately stacked, but the number of layers is not limited. For example, one low-density layer 62 and one high-density layer 63 may be stacked as shown in FIG. 6, or four low-density layers 62 and four high-density layers 63 may be stacked as shown in FIG. You may laminate|stack one by one.

The low-density layer 62 and the high-density layer 63 are formed by the film forming apparatus 9 shown in FIG. The film forming apparatus 9 forms a film by an ion beam vapor deposition method. The film forming apparatus 9 first generates carbon plasma in the plasma generator 92 by arc discharge from the power source 91 . Plasma carbon ions 99 are extracted by an electromagnetic spatial filter 93 and a ta-C film is formed on a film-forming object W placed in a vacuum chamber 95 . In this embodiment, the substrate 1 on which the glass layer 2, the electrode layer 3, the resistor layer 4, the protective layer 5 and the base layer 61 are formed is placed in the vacuum chamber 95 as the film formation object W, and the base layer is formed. A low-density layer 62 and a high-density layer 63, which are ta-C films, are formed outside the film 61 . By changing the bias voltage applied to the film-forming object W, the film-forming processing apparatus 9 can change the energy level of the plasma carbon ions 99 and change the density of the ta-C film. In this embodiment, the bias voltage is switched between two voltages to alternately form the low-density layers 62 and the high-density layers 63 . Since the bias voltage is switched continuously, the density gradually increases from the low density layer 62 side to the high density layer 63 side in the boundary region between the low density layer 62 and the high density layer 63 . The method of forming the low-density layer 62 and the high-density layer 63 is not limited. Other methods may be used to form the low density layer 62 and high density layer 63 .

As shown in FIG. 5, a groove 5a is formed in the z-direction downstream side surface of the portion of the protective layer 5 overlapping the resistor layer 4, so that the outermost layer of the protective layer 6 stacked on the protective layer 5 is formed. A groove 6 a is formed in the outer surface of the high-density layer 63 (surface on the downstream side in the z direction). A large number of grooves 6a are formed in a portion overlapping the resistor layer 4 so as to be parallel to the y-direction, that is, perpendicular to the main scanning direction (x-direction). The groove 6a is shown in each photograph on the left side of FIGS. 11(a) and 11(b).

9 and 10 are actual cross-sectional photographs of the protective layer 6, taken by a transmission electron microscope (TEM) using energy dispersive X-ray spectrometry (EDX). It is what I did. The imaging was performed on the protective layer 6 (see FIG. 7) in which four low-density layers 62 and four high-density layers 63 were alternately laminated. FIG. 9(a) is an enlarged photograph of the region A surrounded by the thick line in FIG. FIG. 9(b) is a further enlarged photograph of the upper portion of FIG. 9(a), and FIG. 9(c) is a further enlarged photograph of the lower portion of FIG. 9(a). FIG. 10(a) is an enlarged photograph of a region B surrounded by a thick line in FIG. 9(b), and FIG. 10(b) is a photograph of a region C surrounded by a thick line in FIG. 9(b). This is an enlarged photo.

As shown in FIGS. 9 and 10, it can be confirmed that the low-density layers 62 and the high-density layers 63 are alternately laminated. The thickness of the low-density layer 62 was about 269-410 [nm], and the thickness of the high-density layer 63 was about 5-6 [nm]. As shown in FIG. 9, the low-density layer 62 arranged on the outer side (downstream side in the z direction) is thicker than that arranged on the inner side (upstream side in the z direction). Although the thicknesses of the outer two low-density layers 62 are reversed, they are within the margin of error. Further, as shown in FIG. 9C, the outer surface of the protective layer 5 has large irregularities, while the outer surface of the underlying layer 61 has smooth irregularities. This makes the outer surface of the protective layer 6 smooth. Further, as shown in FIG. 10, layers different from the low density layer 62 and the high density layer 63 are stacked in the boundary region between the low density layer 62 and the high density layer 63 . The layer is formed such that the density gradually increases from the low-density layer 62 side toward the high-density layer 63 side.

The driving IC 71 selectively energizes the plurality of individual electrodes 35 to arbitrarily generate heat in any one of the plurality of heat generating portions 41 . As shown in FIGS. 1 and 3, a plurality of drive ICs 71 are arranged on the glass layer 2 in this embodiment. In this embodiment, part of the electrode layer 3 and the support glass layer 27 are interposed between the drive IC 71 and the glass layer 2 (see FIG. 3). As shown in FIG. 2, a plurality of pads 72 are formed on the driving IC 71 . The plurality of pads 72 are connected via a plurality of wires 73 to the bonding portions 37 of the plurality of individual electrodes 35 or pads that are part of the electrode layer 3 formed on the glass layer 2 . As shown in FIG. 1, the driving IC 71 is covered with a sealing resin 82. As shown in FIG. The sealing resin 82 is made of, for example, a black insulating soft resin. 2 and 3, the sealing resin 82 is omitted for convenience of understanding.

Further, as shown in FIG. 1, the board 1 is provided with a connector 83 . The connector 83 is connected to a printer-side connector when the thermal print head 101 is installed in a printer, for example.

Next, the action of the thermal print head 101 will be described.

According to this embodiment, the protective layer 6 is formed outside the protective layer 5 (on the downstream side in the z direction). The protective layer 6 comprises a low density layer 62 and a high density layer 63 . The low density layer 62 and the high density layer 63 are made of tetrahedral amorphous carbon (ta-C). ta-C has a high hardness and a small coefficient of friction. Therefore, the protective layer 6 of the thermal print head 101 is hard to be damaged and has excellent abrasion resistance. A high-density layer 63 having a higher density than the low-density layer 62 and having superior wear resistance is arranged outside the low-density layer 62 . Therefore, the protective layer 6 of the thermal print head 101 has better abrasion resistance.

11 and 12 are diagrams showing test results of an accelerated wear resistance test of the thermal print head 101. FIG. In this test, (a) two low-density layers 62 and two high-density layers 63 were alternately laminated (see FIG. 4), (b) one low-density layer 62 and one high-density layer 63 were laminated. (see FIG. 6), and (c) when SiC is laminated instead of the protective layer 6, an accelerated wear resistance test was performed. In each case, wrapping paper #8000 was run for 2.0 [km] to confirm the amount of wear.

In FIG. 11, the left side is a photograph of the surface state before the test, and the right side is a photograph of the surface state after the test (after running 2.0 [km]). In both cases (a) where two layers were alternately laminated and (b) where one layer was laminated, the surface was worn away after the test and the grooves 6a were no longer visible. In addition, when (c) SiC was laminated, the surface was similarly abraded after the test, and the grooves were no longer visible.

FIG. 12 shows cross-sectional profiles before and after the test, where D is the cross-sectional profile before the test and E is the cross-sectional profile after the test. The paper feeding direction is from left to right in each figure. (a) When two layers were alternately laminated, the maximum wear was 0.74 [μm]. Although not shown, the maximum wear was 0.39 [μm] at the time of running 1.0 [km]. (b) Abrasion of 0.51 [μm] at maximum when layered one by one. Although not shown, the maximum wear was 0.31 [μm] at the time of running 1.0 [km]. (c) When SiC was laminated, the maximum wear was 2.88 [μm]. Although not shown, the maximum wear was 1.34 [μm] at the time of running 1.0 [km]. The amount of wear after the test was about 1/4 of the case of (c) in the case of (a), and less than 1/5 of the case of (c) in the case of (b).

As described above, both (a) the case of alternately laminating two layers and (b) the case of laminating one layer at a time, the amount of wear is overwhelmingly smaller than the case of (c) laminating SiC. The difference between the case (a) and the case (b) is within the range of error, and it is considered that the amount of wear has nothing to do with the number of laminations. From this test result, it is clear that the wear resistance of the protective layer 6 is significantly superior to that of the protective layer laminated with SiC.

Moreover, according to the present embodiment, since the protective layer 6 includes the low-density layer 62 that can be formed thicker than the high-density layer 63, it can be formed thick. Furthermore, since two layers each of the low-density layer 62 and the high-density layer 63 are alternately laminated, the thickness of the protective layer 6 can be increased. The thickness of the protective layer 6 of the thermal print head 101 can be adjusted to a desired thickness by adjusting the thickness and number of layers of the low-density layer 62 as in the modified examples shown in FIGS. .

The low density layer 62 and the high density layer 63 are both formed by ta-C and differ only in density. Therefore, the formation of the low density layer 62 and the high density layer 63 can be performed in the same process. 8, the low-density layer 62 and the high-density layer 63 can be formed by switching only by switching the bias voltage applied to the film-forming object W. FIG. Therefore, there is no need to switch materials or processes in the middle. Therefore, the process of forming the protective layer 6 can be completed in a short time.

Further, according to the present embodiment, a portion of the outer surface of the outermost high-density layer 63 of the protective layer 6 (the surface on the downstream side in the z direction), which overlaps with the resistor layer 4, is provided with a line perpendicular to the main scanning direction (x direction). 11(a) and 11(b), a large number of grooves 6a are formed. This can prevent the thermal recording paper from sticking to the outer surface of the protective layer 6 due to friction.

Further, according to the present embodiment, in the boundary region between the low-density layer 62 and the high-density layer 63, the density gradually increases from the low-density layer 62 side toward the high-density layer 63 side. Since the hardness gradually increases in the boundary region, the internal stress also gradually increases. Therefore, the difference in internal stress between the low-density layer 62 and the high-density layer 63 is alleviated, and strain due to the internal stress difference can be reduced.

Figures 13-17 show another embodiment of the invention. In these figures, the same or similar elements as in the above embodiment are denoted by the same reference numerals as in the above embodiment.

FIG. 13 is an enlarged cross-sectional view of a main part showing a thermal print head according to a second embodiment of the invention. The thermal print head 102 shown in FIG. 13 differs from the thermal print head 101 (see FIGS. 1 to 5) according to the first embodiment in the structure of the protective layer 6. As shown in FIG. The protective layer 6 according to the second embodiment includes one low-density layer 62 and one high-density layer 63, and between the low-density layer 62 and the high-density layer 63, the first medium-density layer 64 and the A second medium density layer 65 is provided. The first medium-density layer 64 is arranged inside (on the low-density layer 62 side) the second medium-density layer 65 . Therefore, the protective layer 6 is laminated in the order of the low density layer 62, the first medium density layer 64, the second medium density layer 65, and the high density layer 63 from the inside to the outside.

The first medium density layer 64 and the second medium density layer 65 are formed by ta-C, like the low density layer 62 and the high density layer 63 . The densities of the first medium density layer 64 and the second medium density layer 65 are higher than the density of the low density layer 62 and lower than the density of the high density layer 63 . Also, the density of the first intermediate density layer 64 is lower than the density of the second intermediate density layer 65 . That is, the protective layer 6 is laminated so that the density increases from the inside toward the outside. Also, the properties of the first medium density layer 64 and the second medium density layer 65 exhibit properties between those of the low density layer 62 and the high density layer 63 . Also, the thicknesses of the first intermediate density layer 64 and the second intermediate density layer 65 are thicker than the low density layer 62 and thinner than the density of the high density layer 63 . Also, the thickness of the first medium density layer 64 is thicker than the second medium density layer 65 . That is, the protective layer 6 is laminated such that the thickness of each layer decreases from the inside to the outside.

Also in this embodiment, the low density layer 62, the high density layer 63, the first medium density layer 64, and the second medium density layer 65 are all formed by ta-C, and the high density layer 63 is the low density layer 62, Since it is formed outside the first medium-density layer 64 and the second medium-density layer 65, the same effects as in the first embodiment can be obtained. Further, according to this embodiment, between the low density layer 62 and the high density layer 63 are disposed a first medium density layer 64 and a second medium density layer 65 of hardness therebetween. Therefore, the difference in internal stress between adjacent layers is alleviated, and strain due to the internal stress difference can be reduced.

In addition, in the present embodiment, the case where the two first intermediate density layers 64 and the second intermediate density layers 65 are provided between the low density layer 62 and the high density layer 63 has been described, but the present invention is not limited to this. . The number of layers arranged between the low-density layer 62 and the high-density layer 63 may be one, or three or more.

FIG. 14 is an enlarged cross-sectional view of a main part showing a thermal print head according to a third embodiment of the invention. The thermal print head 103 shown in FIG. 14 differs from the thermal print head 101 (see FIGS. 1 to 5) according to the first embodiment in the structure of the protective layer 6. As shown in FIG. The protective layer 6 according to the third embodiment further includes a high density layer 63 between the low density layer 62 and the underlying layer 61 .

Also in this embodiment, since the high density layer 63 is formed outside the low density layer 62, the same effect as in the first embodiment can be obtained.

FIG. 15 is an enlarged cross-sectional view of a main part showing a thermal print head according to a fourth embodiment of the invention. The thermal print head 104 shown in FIG. 15 differs from the thermal print head 101 (see FIGS. 1 to 5) according to the first embodiment in the structure of the protective layer 6. As shown in FIG. The protective layer 6 according to the fourth embodiment has a conductive high-density layer 63 ′ instead of the high-density layer 63 on the outermost side.

The conductive high-density layer 63' is obtained by adding conductivity to the high-density layer 63, and is formed by doping Ni, Ti, Al, N, or the like, for example, during film formation. The conductive high-density layer 63' is electrically connected to the common electrode 31, for example.

Also in this embodiment, since the conductive high-density layer 63' having the same characteristics as the high-density layer 63 is formed outside the low-density layer 62, the same effects as in the first embodiment can be obtained. . Furthermore, in this embodiment, since the conductive high-density layer 63' has conductivity, static electricity generated by friction between the outer surface of the protective layer 6 and the thermal recording paper can be released efficiently. As a result, it is possible to prevent the thermal recording paper from sticking to the outer surface of the protective layer 6 due to static electricity, and the adhesion of paper dust (fine dust resulting from part of the thermal recording paper being peeled off).

In addition, in the present embodiment, the case where the outermost layer of the protective layer 6 is the conductive high-density layer 63' has been described, but the present invention is not limited to this. Other high density layers 63 may be conductive high density layers 63'. For example, in the thermal print head 101 shown in FIG. 4, the high density layer 63 sandwiched between the two low density layers 62 may be the conductive high density layer 63'. Also, in the thermal print head 103 shown in FIG. 14, the innermost high density layer 63 may be a conductive high density layer 63'. Also, one of the low-density layers 62 may be made conductive. In addition to the low-density layer 62 and the high-density layer 63, a conductive layer having conductivity may be added. Even in these cases, the same effects as in the fourth embodiment can be obtained.

FIG. 16 is an enlarged cross-sectional view of a main part showing a thermal print head according to a fifth embodiment of the invention. A thermal print head 105 shown in FIG. 16 differs from the thermal print head 101 (see FIGS. 1 to 5) according to the first embodiment in the structure of the protective layer 6 . The protective layer 6 according to the fifth embodiment has a metal layer 66 further outside the outermost high-density layer 63 .

The metal layer 66 is made of CrN, for example, and is formed outside the outermost high-density layer 63 . Metal layer 66 is formed by a thin film forming technique such as sputtering. Although the thickness of the metal layer 66 is not particularly limited, it is, for example, about 0.2 to 1.0 [μm]. In this embodiment, the metal layer 66 is formed to cover the entire surface of the outermost high-density layer 63 . Note that the metal layer 66 may be electrically connected to the common electrode 31, for example.

Also in this embodiment, since the protective layer 6 includes the low density layer 62 and the high density layer 63, and the high density layer 63 is formed outside the low density layer 62, the same effect as in the first embodiment can be obtained. be able to. Furthermore, in this embodiment, a metal layer 66 is formed further outside the outermost high-density layer 63 . Since the metal layer 66 has high releasability, it is possible to suppress adhesion of paper shavings of the thermal recording paper to the outer surface of the protective layer 6 . Furthermore, when the metal layer 66 is electrically connected to the common electrode 31, static electricity generated by friction between the outer surface of the protective layer 6 and the thermal recording paper can be released efficiently. As a result, it is possible to prevent paper dust from adhering to the outer surface of the protective layer 6 due to static electricity.

Although the metal layer 66 is formed to cover the entire surface of the outermost high-density layer 63 in this embodiment, the present invention is not limited to this. Since paper dust tends to adhere to a region of the protective layer 6 that is protruded in the z direction by the resistor layer 4, the metal layer 66 should be formed at least in that region. For example, it may not be formed on the projecting portion. Even if the metal layer 66 formed on the protruding portion is scraped off by friction with the thermal recording paper and the high-density layer 63 is exposed, the metal layer 66 in the region immediately downstream of the protruding portion remains. Therefore, the effect of suppressing adhesion of paper waste is not reduced.

Moreover, although the case where the metal layer 66 is made of CrN has been described in the present embodiment, the material of the metal layer 66 is not limited. For example, metal compounds such as TiN, TiC, TiCaN, ZnN, etc. with high releasability may be used. According to experiments conducted by the inventors, when the metal layer 66 was made of a metal nitride, the adhesion of paper dust could be further suppressed, and when the metal layer 66 was made of CrN, the adhesion of paper dust could be suppressed most effectively. It is desirable to

A mixed layer in which ta-C and CrN are mixed may be laminated in the boundary region between the outermost high-density layer 63 and the metal layer 66 . When CrN is sputtered in the step of forming the metal layer 66, CrN may be mixed in the outer region of the outermost high-density layer 63, forming a mixed layer in the boundary region. The present invention also includes the case where the mixed layers formed in this manner are laminated.

FIG. 17 is an enlarged cross-sectional view of essential parts showing a thermal print head according to a sixth embodiment of the present invention. A thermal print head 106 shown in FIG. 17 differs from the thermal print head 105 (see FIG. 16) according to the fifth embodiment in the structure of the protective layer 6 . The protective layer 6 according to the sixth embodiment has a metal layer 66 between the outer low density layer 62 and the inner high density layer 63 in addition to the outer side of the outermost high density layer 63. . That is, the protective layer 6 of the thermal print head 106 is laminated in the order of the low-density layer 62, the high-density layer 63, the metal layer 66, the low-density layer 62, the high-density layer 63, and the metal layer 66 from the inside to the outside. It is

The metal layer 66 formed between the low density layer 62 and the high density layer 63 is similar to the metal layer 66 formed outside the outermost high density layer 63 . That is, it is made of CrN, for example, formed by a thin film forming technique such as sputtering, and has a thickness of, for example, about 0.2 to 1.0 [μm]. In the protective layer 6, a low-density layer 62 and a high-density layer 63 are formed by ion beam vapor deposition using the film forming apparatus 9 shown in FIG. 8, and a metal layer 66 is formed by a thin film forming technique such as sputtering. is formed by repeating twice. The metal layer 66 formed between the low density layer 62 and the high density layer 63 may be electrically connected to the common electrode 31, for example.

Also in this embodiment, since the protective layer 6 includes the low density layer 62 and the high density layer 63, and the high density layer 63 is formed outside the low density layer 62, the same effect as in the first embodiment can be obtained. be able to. Furthermore, in the present embodiment, since the metal layer 66 is formed further outside the outermost high-density layer 63, it is possible to suppress adhesion of paper scraps of the thermal recording paper to the outer surface of the protective layer 6. can be done. Furthermore, since the metal layer 66 is formed between the low density layer 62 and the high density layer 63, the thickness of the protective layer 6 can be increased. In addition, since the metal layer 66 has the high-density layer 63 and the low-density layer 62 excellent in wear resistance formed on the outside, it is hard to wear. When the metal layer 66 is electrically connected to the common electrode 31, static electricity generated by friction between the outer surface of the protective layer 6 and the thermal recording paper can be released efficiently. As a result, it is possible to prevent paper dust from adhering to the outer surface of the protective layer 6 due to static electricity. In this case, the outer metal layer 66 exerts releasability and the inner metal layer 66 exerts the function of suppressing static electricity charging, thereby further suppressing adhesion of paper waste.

The arrangement of the inner metal layer 66 is not limited to that described above. For example, the metal layer 66 may be formed between the outer high density layer 63 and the outer low density layer 62 or between the inner high density layer 63 and the inner low density layer 62 . Alternatively, the metal layer 66 may be provided only between the low-density layer 62 and the high-density layer 63 without providing the metal layer 66 outside the outermost high-density layer 63 . That is, the protective layer 6 may be formed by laminating the low-density layer 62, the high-density layer 63, the metal layer 66, the low-density layer 62, and the high-density layer 63 in this order from the inside to the outside. Even in this case, when the metal layer 66 is electrically connected to the common electrode 31, the static electricity can be efficiently released, so that the adhesion of paper dust to the outer surface of the protective layer 6 can be suppressed.

In the first to sixth embodiments, the protective layer 6 according to the present invention is applied to a so-called thick-film type thermal print head, but the present invention is not limited to this. The protective layer 6 according to the present invention can also be used for a so-called thin film type thermal print head. Moreover, regardless of the shape of the substrate 1 and the glass layer 2, it can be used for any type of thermal printhead.

The thermal printhead according to the invention is not limited to the embodiments described above. The specific configuration of each part of the thermal print head according to the present invention can be changed in various ways.

101 to 106: Thermal print head 1: Substrate 11: Main surface 12: Back surface 2: Glass layer 27: Supporting glass layer 3: Electrode layer 31: Common electrode 32: Strip (first strip)
33: connecting portion 34: detour portion 35: individual electrode 36: strip-shaped portion (first strip-shaped portion)
37: Bonding portion 4: Resistor layer 41: Heat generating portion 5: Protective layer (second protective layer)
5a: Groove 6: Protective layer 61: Base layer 62: Low density layer 63: High density layer 63': Conductive high density layer 64: First medium density layer 65: Second medium density layer 66: Metal layer 6a: Groove 71: drive IC
72 : Pad 73 : Wire 82 : Sealing resin 83 : Connector 9 : Film-forming processing device 91 : Power supply 92 : Plasma generator 93 : Electromagnetic spatial filter 95 : Vacuum chamber 99 : Plasma carbon ion W : Film-forming object

Claims (12)

a substrate having a main surface that is one surface;
a resistor layer formed on the main surface side of the substrate;
an electrode layer for energizing the resistor layer;
a protective layer covering at least a portion of the resistor layer;
and
The protective layer includes a low-density layer containing carbon as a main component and a high-density layer containing carbon as a main component and having a higher density than the low-density layer,
The high density layer includes a first high density layer and a second high density layer located outside the first high density layer,
The low-density layer is located between a first low-density layer located closer to the substrate than the first high-density layer and the first high-density layer and the second high-density layer, a second low density layer thicker than the first low density layer ;
Both the low-density layer and the high-density layer are made of tetrahedral amorphous carbon having a density of 2.5 g/cm ³ or more,
thermal print head. In the boundary region between the low-density layer and the high-density layer, the density gradually increases from the low-density layer side toward the high-density layer side.
A thermal printhead according to claim 1 . the thickness of the high density layer is less than the thickness of the low density layer;
3. A thermal printhead according to claim 1 or 2 . The thickness of the high-density layer is 5 to 50 [nm],
4. A thermal printhead according to any one of claims 1 to 3 . The thickness of the low density layer is 200 to 2000 [nm],
A thermal printhead according to any one of claims 1 to 4 . further comprising a second protective layer disposed inside the protective layer,
The protective layer further comprises an underlying layer in contact with the second protective layer,
A thermal printhead according to any one of claims 1 to 5 . The electrode layer is
a plurality of first strips extending in the sub-scanning direction and spaced apart from each other in the main scanning direction; and a common electrode having a connecting portion connected to the plurality of first strips and extending in the main scanning direction. ,
a plurality of individual electrodes each having a second band-shaped portion extending in the sub-scanning direction and arranged apart from each other in the main scanning direction of the substrate;
and
The resistor layer is
It has a strip shape extending in the main scanning direction,
The first strip-shaped portion and the second strip-shaped portion are alternately arranged in the main scanning direction so as to intersect the resistor layer,
A thermal printhead according to any one of claims 1 to 6 . Grooves are formed in a direction orthogonal to the main scanning direction in a portion of the outer surface of the protective layer that overlaps with the resistor layer when viewed in the thickness direction of the substrate.
A thermal printhead according to claim 7 . The protective layer further comprises a metal layer made of a metal or metal compound,
A thermal printhead according to any one of claims 1 to 8 . The metal layer is formed of a metal nitride,
A thermal printhead according to claim 9 . wherein the metal layer is made of CrN;
A thermal printhead according to claim 10 . wherein the metal layer is arranged on the outermost side of the protective layer;
A thermal printhead according to any one of claims 9 to 11 .

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