JP2020062825A - Thermal head and manufacturing method of thermal head - Google Patents

Abstract

To achieve a thermal head having excellent durability, in which a protective film covering a heat element is prevented from being peeled.SOLUTION: A thermal head includes: a heat element 16 arranged on a substrate 10; an electrode 13 that supplies power to the heat element 16; a first protective film 17 that has an insulation property, is arranged on the substrate 10, covers the heat element 16, and covers at least a part of the electrode 13; and a second protective film 19 arranged above the first protective film 17. An internal stress of the second protective film 19 is higher in a side close to the first protective film 17 than a side far from the first protective film 17.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermal head and a method for manufacturing a thermal head.

  The thermal head is used by being incorporated in a thermal printer as a printing device for producing label paper such as a barcode and recording paper such as a receipt. The thermal head includes a heating resistor for coloring the thermal paper and an electrode for energizing the heating resistor to generate heat. The heating resistor and the electrodes are made of a protective film made of glass or the like for protection when a label sheet such as a bar code or a recording sheet such as a receipt slides and for ensuring electrical insulation between a plurality of electrodes. Is covered with.

  At present, in the printing of barcodes, two-dimensional barcodes such as QR codes are generally used from the one-dimensional barcodes typified by the JAN code up to now. In printing receipts, not only letters and symbols that have been used up to now, but also image images are beginning to be used. As a result, the printing rate per unit area of recording paper such as label paper and receipt has increased. Further, in printing on label paper, there is also a method in which ink applied to a film ribbon is heated and transferred to the label paper. There are ribbons that are insensitive to heat, such as resin-based ribbons.

In this way, in order to increase the printing rate and transfer the amount of heat required for printing on media such as low sensitivity ribbon, the thermal head supplies more power to the heating resistor and generates more heat. I have to let you. The increase in the amount of heat generation affects the life of the thermal head as the recording paper slides.
As a protective film for protecting the heating resistor and the electrode, in order to increase the hardness of the surface of the protective film in contact with the recording medium, the film stress of the upper layer (surface side) of the protective film is lower than that of the lower layer (the heating resistor and the electrode side). It has also been proposed to set the stress higher than the film stress (see Patent Document 1).

JP, 2008-034407, A

  Patent Document 1 proposes to use a single-layer protective film as a protective film for protecting the heating resistor and the electrodes, and to change the film stress of the upper layer portion and the lower layer portion thereof. However, since the protective film is a single layer, the material usable as the protective film is limited to the insulating material. In Patent Document 1, an insulating silicon oxynitride film (SiON) is used as a material for the protective film. However, SiON has high hardness but low toughness, so that cracking or peeling is likely to occur, thus causing a problem of durability. Has not been completely resolved.

A thermal head according to the present invention includes a heating resistor arranged on a substrate, an electrode for supplying electric power to the heating resistor, arranged on the substrate to cover the heating resistor and at least the electrode. An insulative first protective film covering a part of the first protective film and a second protective film disposed above the first protective film are provided, and the internal stress of the second protective film is on a side far from the first protective film. In the above, it is higher than the side closer to the first protective film.
A method of manufacturing a thermal head according to the present invention includes forming a heating resistor on a substrate, forming electrodes for supplying electric power to the heating resistor, and disposing the heating resistor on the substrate. Forming an insulating first protective film that covers at least a part of the electrode while covering the electrode, and forming a second protective film disposed above the first protective film. The second protective film is formed by changing the film forming conditions so that the internal stress on the side far from the first protective film is higher than that on the side closer to the first protective film.

  According to the present invention, a thermal head having excellent durability can be realized.

It is a figure which shows the thermal head by 1st Embodiment of this invention, FIG.1 (a) is a figure which shows a top view, FIG.1 (b) is a figure which shows sectional drawing, FIG.1 (c) is a 2nd protection. The figure which shows the graph of the internal stress of the film | membrane 19. The figure which shows the thermal head of a modification. The figure which shows the thermal head by 2nd Embodiment of this invention.

(First embodiment)
FIG. 1 is a diagram showing a thermal head 50 according to a first embodiment of the present invention, FIG. 1 (a) is a top view of the thermal head 50, and FIG. 1 (b) is A- in FIG. 1 (a). It is sectional drawing which shows A cross section. Further, FIG. 1C is a graph showing the relationship between the position in the thickness direction of the second protective film 19 and the internal stress.
A glaze layer 12 made of glass or the like is partially or wholly disposed on the surface of a support substrate 11 made of ceramics such as alumina (Al2O3), and a comb-teeth-shaped common electrode 14 and a grid are provided on the glaze layer 12. The individual electrodes 15 are arranged.

In this specification, the support substrate 11 and the glaze layer 12 are collectively referred to as the substrate 10, and the common electrode 14 and the individual electrode 15 are also collectively referred to as the electrode 13.
The common electrode 14 and the individual electrode 15 are formed by, for example, thick-film printing a metal-containing paste and then firing the paste. Further, a conductive material such as silver is formed by thick film printing and baking so as to be laminated on the common electrode 14.
A heating resistor 16 is arranged on the substrate 10 so as to straddle the common electrode 14 and the individual electrode 15.
The center interval between the common electrode 14 and the individual electrode 15 arranged below the heating resistor 16 is, for example, about 40 to 70 μm.

  An insulating first protective film 17 is further arranged on the substrate 10 so as to cover the electrodes 13 and the heating resistors 16. An intermediate layer 18 is arranged on the first protective film 17, and a second protective film 19 made of a material different from that of the first protective film 17 is arranged on the intermediate layer 18. That is, the second protective film 19 is formed above the first protective film 17 (on the side away from the substrate 10).

  The first protective film 17 is, for example, an insulative protective film containing glass as a main component, and is formed by printing a thick film of glass paste and then firing the film. The thickness of the first protective film 17 is preferably about 3 to 10 μm. By the above-described method of sintering the glass paste, it is possible to inexpensively form the first protective film 17 having a relatively thick film. The first protective film 17 may be formed of a material other than glass, for example, silicon nitride, silicon carbide, or heat resistant silicone.

When the thermal head 50 is used, a potential difference is applied to one or more of the individual electrodes 15 and the common electrode 14 from a control circuit (not shown) via wiring (not shown). As a result, a current flows through the heating resistor 16 between the common electrode 14 and the individual electrode 15 to which a voltage is applied, and this portion locally generates heat, so that thermal printing on the thermal paper can be performed.
When the first protective film 17 is made of a glass-based material, its glass transition point is 500 to 600 ° C. Therefore, when the temperature of the first protective film 17 becomes about 500 to 600 ° C. or higher due to the heat generation of the heating resistor 16 during the operation of the thermal head 50, the thermal expansion of the first protective film 17 becomes remarkable.

  The first protective film 17 ensures the electrical insulation of the electrode 13 and the heating resistor 16. Therefore, a conductive material may be used for the intermediate layer 18 and the second protective film 19. As will be described later, the intermediate layer 18 is made of a material having a Young's modulus of less than 100 GPa.

The second protective film 19 contains, for example, any one of TiW, WC, SiC, SiN, and SiAlON as a main component, and has a substantially uniform composition inside the film. The internal stress is higher on the surface side of the second protective film 19 (the side farther from the first protective film 17) than on the lower layer side (the side closer to the first protective film 17).
FIG. 1C is a graph showing the relationship between the internal stress S of the second protective film 19 and the position T in the thickness direction. The internal stress Sa of the second protective film 19 increases as the position T in the thickness direction changes from the boundary surface Tb of the second protective film 19 with the intermediate layer 18 to the surface Tt of the second protective film 19. .

Generally, the internal stress of a film is higher when the density of the film is higher, and is lower when the density of the film is lower. Therefore, the internal stress of the film has a positive correlation with the density of the film.
As shown in FIG. 1C, the internal stress Sa of the second protective film 19 depends on the film forming conditions when the second protective film 19 is formed as compared with when the lower protective film 19 is formed. It can be formed by changing the time of film formation on the surface side.

  Specifically, for example, when the second protective film 19 is formed by sputtering, the total gas pressure of the sputtering is set to be high when forming the lower layer side, so that the film density can be lowered and the internal stress Sa can be lowered. it can. On the other hand, at the time of forming on the front surface side, the total gas pressure of sputtering is set low, so that the film density can be increased and the internal stress Sa can be increased. The change of the film formation conditions during the formation of the second protective film 19 may be stepwise or continuous. The characteristics shown in FIG. 1C can be obtained by continuously changing the film forming conditions.

  When the material of the second protective film 19 is a conductive material, DC sputtering with a high film forming rate can be used, and the film forming productivity is improved. Among the above-mentioned materials, TiW and WC have conductivity. Therefore, by using these materials, the film formation rate can be improved by sputtering.

The second protective film 19 can also be formed by a method other than sputtering. For example, it can be formed by plasma CVD, and in this case also, by changing the total gas flow rate of the process gas of plasma CVD during film formation, the film density on the lower layer side and the surface side of the second protective film 19 can be increased. Can also be changed.
Ar gas or the like can be used as a process gas for sputtering or plasma CVD.

In the first embodiment, since it is not necessary to consider the insulating property of the second protective film 19, it is possible to select an optimum material from the viewpoint of wear resistance and toughness. From the viewpoint of toughness, the material of the second protective film 19 is preferably TiW, WC, or SiN. Furthermore, by increasing the internal stress Sa on the surface side of the second protective film 19, the wear resistance of the second protective film 19 can be further improved. On the other hand, by lowering the internal stress Sa on the lower layer side of the second protective film 19, the adhesion with the intermediate layer 18 can be increased.
The second protective film 19 is made of a material whose melting point is higher than the softening point or melting point of the first protective film 17. The thickness of the second protective film 19 is preferably about 2 to 6 μm.

  The intermediate layer 18 made of a material having a Young's modulus of less than 100 GPa functions as a buffer layer for thermal stress caused by thermal expansion of the first protective film 17 when the thermal head 50 is used. That is, even when the first protective film 17 is non-uniformly thermally expanded and thereby a non-uniform deformation pressure is applied to the second protective film 19, the non-uniformity is caused by the deformation of the intermediate layer 18 having a low Young's modulus. Relax the deformation pressure. Thereby, peeling of the second protective film 19 can be suppressed, and a material having higher internal stress can be used as the material of the second protective film, which further improves the abrasion resistance of the second protective film 19. Can be improved.

On the other hand, when the intermediate layer 18 is made of a material having a Young's modulus of 100 GPa or more, it is difficult for the intermediate layer 18 to function as a buffer layer, so that the non-uniform deformation pressure from the first protective film 17 causes the second protective film 19 to have a non-uniform deformation pressure. The second protective film 19 is easily peeled off.
Suitable materials for the intermediate layer 18 having a Young's modulus of less than 100 GPa include metals such as aluminum, magnesium, gold, and silver. The intermediate layer 18 may be formed of an alloy having a Young's modulus of less than 100 GPa. In the present specification, metal includes alloys.

The intermediate layer 18 is preferably made of a material having a melting point (or softening point) of about 800 ° C. or higher in order to withstand the temperature during operation of the thermal head 50. Further, the linear expansion coefficient is preferably 20 × 10 ⁻⁶ [1 / K] or less so that the difference in linear expansion coefficient with the support substrate 11 made of alumina or the like does not become too large.
The thickness of the intermediate layer 18 is preferably about 0.1 to 1 μm. If the thickness of the intermediate layer 18 is thinner than this, the internal stress of the second protective film 19 cannot be relaxed sufficiently. On the other hand, if the thickness of the intermediate layer 18 is thicker than this, the heat of the heating resistor 16 may diffuse to the surroundings via the intermediate layer 18, which may cause deterioration of printing quality and increase the manufacturing cost. There is.
The intermediate layer 18 can be formed by thick film printing and firing.

When the material of the intermediate layer 18 is gold or a metal containing silver as a main component, both gold and silver have a linear expansion coefficient of 20 × 10 ⁻⁶ [1 / K] or less and are oxidized even at high temperature. Since it has excellent chemical stability such as difficulty, the durability of the thermal head can be further enhanced.
When the intermediate layer 18 functions sufficiently as a buffer layer for thermal stress, that is, when the Young's modulus is sufficiently small and the thickness is sufficient, the toughness is taken into consideration when selecting the material of the second protective film 19. You don't have to. Therefore, in this case, as the material of the second protective film 19, SiC or SiAlON, which is particularly excellent in wear resistance, can be used.

In the above-described first embodiment, the positional relationship between the electrode 13 and the heating resistor 16 is not limited to the case where the above-described heating resistor 16 is arranged above the electrode 13 (on the side far from the substrate 10), but the electrode 13 may be arranged. May be arranged above the heating resistor 16 (on the side far from the substrate 10).
Further, the first protective film 17 does not have to cover all the portions of the heating resistor 16 and the electrode 13. For example, the portions of the heating resistor 16 and the electrodes 13 that do not come into contact with the thermal paper or the like to be printed during the printing operation need not be covered with the first protective film 17.

The glaze layer 12 does not need to be arranged with a uniform thickness over the entire surface of the support substrate 11, and may be arranged only in the vicinity of the portion where the heating resistor 16 is arranged, for example. Alternatively, the thickness of the glaze layer 12 may be thick only in the vicinity of the portion where the heating resistor 16 is arranged and thin in other portions.
The glaze layer 12 may be omitted depending on the material of the support substrate 11.

(Modification)
FIG. 2 is a diagram showing a cross-sectional view of a thermal head 50a of a modified example. The thermal head 50a of the modified example is obtained by omitting the intermediate layer 18 from the thermal head 50 of the first embodiment described above, and therefore, the same components are designated by the same reference numerals and the description thereof will be omitted.
However, if the intermediate layer 18 is simply omitted, as described above, the non-uniform deformation pressure from the first protective film 17 is directly transmitted to the second protective film 19, and the second protective film 19 is likely to peel off.

  Therefore, in the present modification, the surface roughness of the interface 20 between the first protective film 17 and the second protective film 19 is reduced, and even if the first protective film 17 thermally expands, the second protective film 19 is not affected. It is configured so that uniform deformation pressure is not transmitted. As an example, the first protective film 17 is a film made of a glass-based material, but the content of Al2O3, which is a filler component, is reduced, the firing temperature is raised, or the firing is divided into multiple times. This reduces the surface roughness of the interface 20. Alternatively, the surface roughness of the interface 20 can be reduced by performing a polishing treatment or the like for smoothing the surface of the first protective film 17 after forming the first protective film 17.

The surface roughness of the interface 20 is, for example, 0.12 μm as an arithmetic mean roughness Ra value measured by using a contact type surface roughness meter having a stylus having a tip radius of 2 μm and a cone taper angle of 60 °. The following is preferable.
Also in this modification, as in the above-described first embodiment, the internal stress of the second protective film 19 is higher on the surface side of the second protective film 19 than on the lower layer side. The material of the second protective film 19 is also the same as that of the first embodiment described above, but TiW, WC, and SiN, which have good toughness, are preferable.

(Second embodiment)
FIG. 3 is a diagram showing a cross-sectional view of the thermal head 50b of the second embodiment. 3A is a top view of the thermal head 50b, and FIG. 3B is a cross-sectional view showing a BB cross section in FIG. 3A.
Many parts of the thermal head 50b of the second embodiment are common to the thermal head 50 of the first embodiment described above. Therefore, the same parts as those of the thermal head 50 are designated by the same reference numerals and the description thereof will be omitted.

  The thermal head 50b of the second embodiment differs from the thermal head 50 of the first embodiment in the configuration of the heating resistor 16a. A plurality of heating resistors 16a are discretely formed so as to connect one of the comb teeth of the common electrode 14a and one of the grid-shaped individual electrodes 15a. When a voltage is applied between one of the grid-shaped individual electrodes 15a and the common electrode 14a via a wiring (not shown) from a control circuit (not shown), the electrodes are connected to one of the individual electrodes 15a. The heating resistor 16a generates heat.

Also in the thermal head 50b of the second embodiment, as in the above-described first embodiment, the internal stress of the second protective film 19 is higher on the surface side of the second protective film 19 than on the lower layer side. The material of the second protective film 19 is also the same as in the above-described first embodiment.
Further, the intermediate layer 18 is provided between the first protective film 17 and the second protective film 19, and exerts a non-uniform force on the second protective film 19 even if the first protective film 17 thermally expands. This can prevent the second protective film 19 from being worn or peeled off and enhance the durability of the second protective film 19.

  In the second embodiment as well, similar to the above-described first embodiment and the modification, the electrodes (common electrode 14a and individual electrode 15a) and the heating resistor 16a are arranged above and below in FIG. 3 (b). The arrangement may be reversed.

(Effects of Embodiments and Modifications)
(1) The thermal head of each of the above-described embodiments and modifications includes the heating resistors 16 and 16a arranged on the substrate 10, the electrodes 13 for supplying electric power to the heating resistors 16 and 16a, and the substrate 10. And an insulating first protective film 17 that covers at least a part of the electrode 13 while covering the heating resistors 16 and 16a, and a second protective film 19 that is disposed above the first protective film 17. The internal stress of the second protective film 19 is higher on the side farther from the first protective film 17 than on the side closer to the first protective film 17.
With this configuration, the material of the second protective film 19 can be selected with priority given to wear resistance or toughness without considering the insulation performance, and the surface of the second protective film 19 (printing paper) can be selected. The wear resistance in the vicinity of the frictional surface) can be further improved. This makes it possible to realize a thermal head with excellent durability.

(2) By providing the intermediate layer 18 having a Young's modulus of less than 100 GPa between the first protective film 17 and the second protective film 19, the intermediate layer 18 causes thermal expansion of the first protective film 17. Functions as a buffer layer for thermal stress. As a result, peeling of the second protective film 19 can be suppressed, and a thin film protective film material having a higher internal stress can be formed as the second protective film. The wear resistance can be further improved.
(3) By using glass as the main component of the first protective film 17, a relatively thick first protective film 17 can be formed at low cost by a method such as applying a glass paste and sintering.

(4) By using the tungsten alloy as the main component of the second protective film 19, it is possible to realize a thermal head having excellent abrasion resistance, high toughness, and excellent peeling resistance. Further, since the tungsten alloy is conductive, DC sputtering can be used during film formation by sputtering, so that productivity of film formation can be increased and production cost can be reduced.
(5) By using TiW as the main component of the second protective film 19, it is possible to realize a thermal head that is further excellent in abrasion resistance, toughness, and peeling resistance.
(6) Since the second protective film 19 is formed above the first protective film 17 whose main component is a glass material having a characteristic of being electrically insulating, the material of the second protective film 19 is conductive. A material having, for example, TiW can be used. As a result, it is possible to increase the resistance to static electricity applied to the second protective film 19 from a medium such as thermal paper in a printed state, and further, the second protective film 19 is a material having conductivity. Since it is also a good heat conductor, it is possible to improve the resistance to the energy applied to the thermal head 50.

(7) In the method of manufacturing the thermal head according to the embodiment, the heating resistor 16 is formed on the substrate 11, the electrode 13 for supplying electric power to the heating resistor 16 is formed, and the thermal head is arranged on the substrate 11. To form the insulating first protective film 17 that covers the heating resistor 16 and at least a part of the electrode 13, and to form the second protective film 19 disposed above the first protective film 17. The second protective film 19 is formed by changing the film forming conditions so that the internal stress on the side far from the first protective film 17 becomes higher than that on the side closer to the first protective film 17.
According to this configuration, since the stress distribution is applied in the thickness direction when the second protective film 19 is formed, the surface of the second protective film 19 (the surface where the printing paper rubs) does not require a complicated process. Wear resistance in the vicinity can be further improved. This makes it possible to manufacture a thermal head having excellent durability.

(8) In the method of manufacturing the thermal head, the second protective film 19 is formed by the sputtering method, and the gas pressure during sputtering when forming the film on the side far from the first protective film 17 is close to that of the first protective film 17. Lower than when forming the film on the side. With this configuration, the stress distribution can be given in the thickness direction of the second protective film 19 without increasing the manufacturing cost by simply changing the condition that the film density is controlled by controlling the gas pressure of the sputtering method.

  The present invention is not limited to the above contents. Other aspects that are conceivable within the scope of the technical idea of the present invention are also included within the scope of the present invention.

50, 50a, 50b: Thermal head, 10: Substrate, 11: Support substrate, 12: Glaze layer, 13: Electrode, 14, 14a: Common electrode, 15, 15a: Individual electrode, 16, 16a: Heating resistor, 17 : First protective film, 18: intermediate layer, 19: second protective film, 20: interface

Claims (7)

A heating resistor arranged on the substrate,
An electrode for supplying electric power to the heating resistor,
An insulating first protective film which is disposed on the substrate, covers the heating resistor, and covers at least a part of the electrode;
A second protective film disposed above the first protective film,
The thermal head in which the internal stress of the second protective film is higher on the side farther from the first protective film than on the side closer to the first protective film. The thermal head according to claim 1,
A thermal head having an intermediate layer having a Young's modulus of less than 100 GPa between the first protective film and the second protective film. The thermal head according to claim 1 or 2,
A thermal head in which the main component of the first protective film is glass. The thermal head according to any one of claims 1 to 3,
A thermal head in which the main component of the second protective film is a tungsten alloy. The thermal head according to claim 4,
The thermal head whose main component of said 2nd protective film is TiW. Forming a heating resistor on the substrate,
Forming an electrode for supplying electric power to the heating resistor,
Forming an insulating first protective film which is disposed on the substrate, covers the heating resistor, and covers at least a part of the electrode;
Forming a second protective film disposed above the first protective film,
The method of manufacturing a thermal head, wherein the second protective film is formed by changing film forming conditions so that the internal stress on the side far from the first protective film is higher than that on the side closer to the first protective film. The method of manufacturing a thermal head according to claim 6,
The second protective film is formed by a sputtering method,
A method of manufacturing a thermal head, wherein a gas pressure during sputtering when forming a film on a side far from the first protective film is lower than that when forming a film on a side closer to the first protective film.

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