Thermal head and thermal printer

A thermal head X1 according to the present disclosure includes a substrate, a heat generator, an electrode, and a protective layer. The heat generator is positioned on the substrate. The electrode is positioned on the substrate and connected to the heat generator. The protective layer covers the heat generator and part of the electrode. The protective layer contains titanium and nitrogen. The protective layer satisfies P2>P1 where P1 is the peak intensity of X-ray diffraction of the (111) plane, and P2 is the peak intensity of X-ray diffraction of the (200) plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is national stage application of International Application No. PCT/JP2018/011787, filed on Mar. 23, 2018, which designates the United States, incorporated herein by reference, and which claims the benefit of priority from Japanese Patent Application No. 2017-065424, filed on Mar. 29, 2017; and Japanese Patent Application No. 2017-208288, filed on Oct. 27, 2017, the entire contents of both of which are incorporated herein by reference.

FIELD

The present disclosure relates to a thermal head and a thermal printer.

BACKGROUND

Conventionally, various thermal heads have been developed as printing devices for facsimiles or video printers, for example. There has been developed a thermal head including a substrate, a heat generator, electrodes, and a protective layer, for example (refer to Patent Literature 1). The heat generator is positioned on the substrate. The electrodes are positioned on the substrate and connected to the heat generator. The protective layer covers the heat generator and part of the electrodes and contains titanium and nitrogen.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Utility Model Application Laid-open No. S62-3738

SUMMARY

A thermal head according to the present disclosure includes a substrate, a heat generator, an electrode, and a protective layer. The heat generator is positioned on the substrate. The electrode is positioned on the substrate and connected to the heat generator. The protective layer covers the heat generator and part of the electrode. The protective layer contains titanium and nitrogen. The protective layer satisfies P2>P1where P1is the peak intensity of X-ray diffraction of the (111) plane, and P2is the peak intensity of X-ray diffraction of the (200) plane.

A thermal printer according to the present disclosure includes the thermal head, a conveyance mechanism and a platen roller. The conveyance mechanism coveys a recording medium such that the recording medium passes over the heat generator, and the platen roller presses the recording medium against the heat generator.

DESCRIPTION OF EMBODIMENTS

To increase the abrasion resistance, the protective layer of the conventional thermal head contains titanium and nitrogen. The protective layers containing titanium and nitrogen are manufactured with high productivity because they have high hardness and can be formed into a thin layer. The protective layers have recently been required to have higher abrasion resistance.

A thermal head according to the present disclosure includes a protective layer having higher abrasion resistance and can run a longer running distance on a recording medium. The thermal head according to the present disclosure and a thermal printer provided with the thermal head are described below in greater detail.

First Embodiment

A thermal head X1is described below with reference toFIGS. 1 to 4.FIG. 1schematically illustrates the configuration of the thermal head X1. InFIG. 2, a protective layer25, a covering layer27, and a sealing member12are indicated by alternate long and short dash lines, and a covering member29is indicated by a dashed line.FIG. 3is a sectional view along line III-III ofFIG. 2.FIG. 4illustrates a part near the protective layer25of the thermal head X1in an enlarged manner.

The thermal head X1includes a head base3, a connector31, the sealing member12, a heat radiation plate1, and an adhesive member14. The connector31, the sealing member12, the heat radiation plate1, and the adhesive member14are not necessarily provided.

The heat radiation plate1radiates surplus heat of the head base3. The head base3is placed on the heat radiation plate1with the adhesive member14interposed therebetween. The head base3is supplied with a voltage from the outside, thereby printing an image on a recording medium P (refer toFIG. 5). The adhesive member14bonds the head base3to the heat radiation plate1. The connector31electrically connects the head base3to the outside. The connector31includes connector pins8and a housing10. The sealing member12joins the connector31and the head base3.

The heat radiation plate1has a rectangular parallelepiped shape. The heat radiation plate1is made of a metal material, such as copper, iron, or aluminum. The heat radiation plate1has a function of radiating heat not used for printing in the heat generated by heat generators9of the head base3.

The head base3has a rectangular shape in planar view and is provided with members constituting the thermal head X1on a substrate7. The head base3has a function of printing characters on the recording medium P based on electrical signals supplied from the outside.

The following describes the members constituting the head base3, the sealing member12, the adhesive member14, and the connector31with reference toFIGS. 1 to 3.

The head base3includes the substrate7, a heat storage layer13, an electrical resistant layer15, a common electrode17, individual electrodes19, first connection electrodes21, connection terminals2, a conductive member23, drive integrated circuits (ICs)11, the covering member29, the protective layer25, and the covering layer27. All these members are not necessarily provided. The head base3may include other members besides these members.

The substrate7is disposed on the heat radiation plate1and has a rectangular shape in planar view. The substrate7has a first surface7f, a second surface7g, and a side surface7e. The first surface7fhas a first long side7a, a second long side7b, a first short side7c, and a second short side7d. The members constituting the head base3are disposed on the first surface7f. The second surface7gis positioned opposite to the first surface7f. The second surface7gis positioned on the heat radiation plate1side and bonded to the heat radiation plate1with the adhesive member14interposed therebetween. The side surface7econnects the first surface7fand the second surface7gand is positioned on the second long side7b.

The substrate7is made of an electrical insulating material, such as alumina ceramic, or a semiconductor material, such as single crystal silicon.

The heat storage layer13is positioned on the first surface7fof the substrate7. The heat storage layer13rises upward from the first surface7f. In other words, the heat storage layer13protrudes in a direction away from the first surface7fof the substrate7.

The heat storage layer13is disposed side by side with the first long side7aof the substrate7and extends in a main scanning direction. The section of the heat storage layer has a substantially semi-elliptical shape. This shape enables the protective layer25formed on the heat generators9to reliably come into contact with the recording medium P on which an image is to be printed. The height of the heat storage layer13from the first surface7fof the substrate7may be 30 to 60 μm.

The heat storage layer13is made of glass having low thermal conductivity and temporarily accumulates part of the heat generated by the heat generators9. This structure can reduce the time required to raise the temperature of the heat generators9, thereby enhancing the thermal responsiveness of the thermal head X1.

The heat storage layer13is produced by: mixing an appropriate organic solvent with glass powder to obtain predetermined glass paste, applying the glass paste to the first surface7fof the substrate7by screen printing, and firing the glass paste, for example.

The electrical resistant layer15is positioned on the upper surface of the heat storage layer13. The common electrode17, the individual electrodes19, the first connection electrodes21, and second connection electrodes26are formed on the electrical resistant layer15. An exposure region in which the electrical resistant layer15is exposed is formed between the common electrode17and each of the individual electrodes19. As illustrated inFIG. 2, the exposure regions of the electrical resistant layer15are disposed in a row on the heat storage layer13and each serve as the heat generator9.

The electrical resistant layer15is not necessarily positioned between the various electrodes and the heat storage layer13. The electrical resistant layer15, for example, may be positioned only between the common electrode17and the individual electrodes19so as to electrically connect the common electrode17and the individual electrodes19.

While the heat generators9are schematically illustrated inFIG. 2for convenience of explanation, they are disposed at a density of 100 dot per inch (dpi) to 2400 dpi, for example. The electrical resistant layer15is made of a material having relatively high electrical resistance, such as a TaN-, TaSiO-, TaSiNO-, TiSiO-, TiSiCO-, or NbSiO-based material. When a voltage is applied to the heat generators9, the heat generators9generate heat by Joule heating.

The common electrode17includes main wiring portions17aand17d, sub-wiring portions17b, and leading portions17c. The common electrode17electrically connects the heat generators9to the connector31. The main wiring portion17aextends along the first long side7aof the substrate7. The sub-wiring portions17bextend along the first short side7cand the second short side7dof the substrate7. The leading portions17cextend individually toward the respective heat generators9from the main wiring portion17a. The main wiring portion17dextends along the second long side7bof the substrate7.

The individual electrodes19electrically connect the respective heat generators9to the drive IC11. The heat generators9are divided into a plurality of groups. The heat generators9in a group are electrically connected to the drive IC11disposed corresponding to the group by the respective individual electrodes19.

The first connection electrodes21electrically connect the drive ICs11to the connector31. The first connection electrodes21connected to the drive ICs11are a plurality of wires having different functions.

The second connection electrodes26electrically connect the drive ICs11disposed side by side. The second connection electrodes26are a plurality of wires having different functions.

The common electrode17, the individual electrodes19, the first connection electrodes21, and the second connection electrodes26are made of a conductive material, that is, a kind of metal out of aluminum, gold, silver, and copper, or an alloy of these metals, for example.

The connection terminals2are disposed on the second long side7bof the first surface7fso as to connect the common electrode17and the first connection electrodes21to an FPC5. The connection terminals2are disposed corresponding to the respective connector pins8of the connector31, which will be described later.

The conductive member23is provided on the connection terminals2. Examples of the conductive member23include, but are not limited to, solder, anisotropic conductive paste (ACP), etc. A Ni-, Au-, or Pd-plated layer may be disposed between the conductive member23and the connection terminals2.

The various electrodes constituting the head base3are formed by: sequentially laminating material layers made of metal, such as Al, Au, or Ni on the heat storage layer13by a thin-film formation technique, such as sputtering, and processing the obtained multilayered structure into a predetermined pattern by photo-etching, for example. The various electrodes constituting the head base3can be formed simultaneously by the same process.

As illustrated inFIG. 2, the drive ICs11are disposed corresponding to the respective groups of the heat generators9. The drive ICs11are connected to the individual electrodes19and the first connection electrodes21. The drive ICs11have a function of controlling the energized state of the heat generators9. The drive ICs11are provided as switching ICs.

The protective layer25covers the heat generators9, the common electrode17, and part of the individual electrodes19. The protective layer25protects the covered region against corrosion due to adhesion of water or the like included in the air or abrasion due to contact of the recording medium P on which an image is to be printed.

The covering layer27is disposed on the substrate7so as to partially cover the common electrode17, the individual electrodes19, the first connection electrodes21, and the second connection electrodes26. The covering layer27protects the covered region against oxidation due to contact with the air or corrosion due to adhesion of water or the like included in the air. The covering layer27is made of a resin material, such as epoxy resin, polyimide resin, or silicone resin.

The drive ICs11are sealed with the covering member29made of resin, such as epoxy resin or silicone resin, in such a manner as to be connected to the individual electrodes19, the first connection electrodes21, and the second connection electrodes26. The covering member29extends in the main scanning direction and integrally seals the drive ICs11.

The connector31includes the connector pins8and the housing10that accommodates the connecter pins8. The connector pins8each have a first end and a second end. The first end is exposed to the outside of the housing10. The second end is accommodated in the housing10and extracted to the outside. The first end of the connector pin8is electrically connected to the connection terminal2of the head base3. With this configuration, the connector31is electrically connected to the various electrodes of the head base3.

The sealing member12includes a first sealing member12aand a second sealing member12b. The first sealing member12ais positioned on the first surface7fof the substrate7. The first sealing member12aseals the connector pins8and the various electrodes. The second sealing member12bis positioned on the second surface7gof the substrate7. The second sealing member12bis disposed so as to seal the contact part of the connector pins8and the substrate7.

The sealing member12is disposed so as to prevent the connection terminals2and the first ends of the connector pins8from being exposed to the outside. The sealing member12is made of thermosetting epoxy resin, ultraviolet curing resin, or visual-light curing resin, for example. The first sealing member12aand the second sealing member12bmay be made of the same material. Alternatively, the first sealing member12aand the second sealing member12bmay be made of different materials.

The adhesive member14is disposed on the heat radiation plate1and bonds the second surface7gof the head base3to the heat radiation plate1. Examples of the adhesive member14include, but are not limited to, a double-sided adhesive tape, a resin adhesive, etc.

The following describes the protective layer25in greater detail with reference toFIG. 4.

The protective layer25contains titanium (Ti) and nitrogen (N). Examples of the material of the protective layer include, but are not limited to, TiN, TiON, TiCrN, TiAlON, etc. If TiN is used for the protective layer25, the protective layer25can contain Ti of 40 to 60 at % and N of 40 to 60 at %, for example.

The thickness of the protective layer25can be set to 5 to 20 μm. By setting the thickness of the protective layer25to 5 μm or larger, the running distance of the thermal head X1on the recording medium P can be increased. By setting the thickness of the protective layer25to 20 μm or smaller, the heat of the heat generators9can be easily transmitted to the recording medium P, thereby improving the thermal efficiency of the thermal head X1.

When the peak intensity of X-ray diffraction of the (111) plane is P1(hereinafter, referred to as P1), and the peak intensity of X-ray diffraction of the (200) plane is P2(hereinafter, referred to as P2), the protective layer25has a relation of P2>P1. In other words, crystal grains constituting the protective layer25have the peak intensity of the (200) plane higher than that of the (111) plane and are oriented along the a-axis.

On the crystal planes of the crystal grains constituting the protective layer25, the number of (200) planes having smaller surface energy is larger than that of (111) planes. This structure makes the protective layer25finer, thereby increasing the abrasion resistance of the protective layer25.

The protective layer25has the (200) planes and the (111) planes, and the number of (200) planes is larger than that of (111) planes. With this structure, the (200) planes can make the protective layer25finer, and the (111) planes can reduce strain energy generated on the protective layer25. As a result, internal stress of the protective layer25is reduced, thereby making a crack less likely to be generated.

Alternatively, 1<P2/P1≤4.74 may be satisfied. With this structure, the thermal head X1can have a higher ratio of the (200) planes to the (111) planes. By causing the (200) planes to dominate, the protective layer25can be made finer. The (111) plane serves as a slip plane of the crystal. With the (111) planes, the protective layer25can have higher slipperiness, thereby making sticking less likely to occur in the thermal head X1.

In the protective layer25, the half width of the diffraction peak of the (200) plane measured by X-ray diffraction may be 0.5° to 1°. With this structure, the grain size of the crystals constituting the (200) plane increases, thereby reducing the contact area between the recording medium P and the protective layer25. As a result, dynamic frictional force received from the recording medium P can be reduced, thereby increasing the abrasion resistance of the protective layer25.

In the protective layer25, the half width of the diffraction peak of the (111) plane measured by X-ray diffraction may be 0.8° to 1.2°. With this structure, the grain size of the crystals constituting the (111) plane increases, thereby reducing the contact area between the recording medium P and the protective layer25. As a result, dynamic frictional force received from the recording medium P can be reduced, thereby increasing the abrasion resistance of the protective layer25.

The peak intensity of the crystal plane can be checked by the following method. First of all, the thermal head X1is cut in the thickness direction of the substrate7along a sub-scanning direction to form a cross section of the protective layer25. The peak intensity detected in a range of 2 θ: 20° to 80° in the diffraction pattern obtained by an X-ray diffraction analysis on the cross section is defined as the peak intensity of the crystal plane. The half width is measured using the diffraction pattern obtained by the X-ray diffraction analysis.

The hardness of the protective layer25may be 24 GPa or higher. With this structure, abrasion due to contact with the recording medium P is less likely to occur, thereby increasing the abrasion resistance of the thermal head X1. The hardness of the protective layer25may be 30 GPa or lower. This structure can reduce the possibility that the membrane stress of the protective layer25becomes so high as to generate a crack.

The Young's modulus of the protective layer25may be 320 GPa or higher. With this structure, the protective layer25is less likely to be damaged by a strain generated in the protective layer25due to contact with the recording medium P. The Young's modulus of the protective layer25may be 400 GPa or lower. This structure can reduce the possibility that the membrane stress of the protective layer25becomes so high as to generate a crack.

The hardness and the Young's modulus are measured by the nanoindentation technique.

The arithmetic surface roughness Ra of the protective layer25may be 67.7 nm or lower. With this structure, the contact area between the protective layer25and the recording medium P can be reduced, thereby reducing the frictional force generated between the protective layer25and the recording medium P. As a result, the abrasion resistance of the protective layer25can be increased.

The arithmetic surface roughness Ra of the surface of the protective layer25may be 32.3 nm or lower. With this structure, the abrasion resistance of the protective layer25can be further increased.

The arithmetic surface roughness Ra is measured using an atomic force microscope (AFM).

The crystal grains constituting the protective layer25may include columnar grains that are long in the thickness direction of the substrate7. In other words, the crystal grains constituting the protective layer25are long in the thickness direction of the protective layer25. With this structure, the heat generated by the heat generators9can be transmitted efficiently in the thickness direction of the protective layer25. As a result, the recording medium P can be heated efficiently, thereby improving the thermal efficiency of the thermal head X1.

The structure of the crystals constituting the protective layer25can be observed by observing the cross section described above using a transmission electron microscope (TEM). By processing an image taken by the TEM, the length of the crystal grains in the thickness direction of the substrate7and the length thereof in a direction orthogonal to the thickness direction of the substrate7can be measured. The columnar grains that are long in the thickness direction of the substrate7include crystal grains inclining by an angle of 90°±20° with respect to the principal surface of the substrate7.

The average crystal gain size of the crystal grains constituting the protective layer25may be 205 nm to 605 nm. With this structure, crystal grains having a relatively large grain size are positioned on the surface of the protective layer25. As a result, the contact area between the grain boundary and the recording medium P per unit area decreases, thereby reducing the frictional force generated on the protective layer25. Consequently, the abrasion resistance of the protective layer25is increased.

The standard deviation of the average crystal gain size may be 16.7 nm to 60.8 nm. With this structure, the grain size of the crystal grains constituting the protective layer25varies widely. As a result, the protective layer25includes the crystal grains having a variety of grain sizes and can have higher abrasion resistance. In other words, the protective layer25can support the recording medium P with the crystal grains having different grain sizes, thereby efficiently dispersing the stress received from the recording medium P.

The average crystal grain size of the crystal grains can be checked by the following method, for example. First of all, the surface of the protective layer25is photographed using a scanning electron microscope (SEM). Subsequently, the crystal grains are marked on the photograph of the surface and subjected to an image analysis, thereby measuring grain size data on the crystal grains. In the present specification, the average crystal grain size means a median size (d50). The standard deviation of the average crystal gain size may be calculated based on the grain size data on the crystal grains.

The protective layer25may be formed by arc plasma ion plating or hollow cathode ion plating.

P1and P2may be controlled by the following method, for example. Let us assume a case where the protective layer25is formed by arc plasma ion plating, for example. In this case, the protective layer25that satisfies P2>P1may be formed by increasing the absolute value of a substrate bias voltage applied in deposition. Alternatively, the protective layer25that satisfies P2>P1may be formed by lowering the deposition pressure of a deposition device. Still alternatively, the protective layer25that satisfies P2>P1may be formed by raising the temperature of the substrate in deposition.

The following describes a thermal printer Z1including the thermal head X1with reference toFIG. 5.

The thermal printer Z1according to the present embodiment includes the thermal head X1, a conveyance mechanism40, a platen roller50, a power supply device60, and a control device70. The thermal head X1is attached to an attachment surface80aof an attachment member80disposed on a housing (not illustrated) of the thermal printer Z1. The thermal head X1is attached to the attachment member80in such a manner as to extend along the main scanning direction orthogonal to a conveyance direction S.

The conveyance mechanism40includes a driver (not illustrated) and conveyance rollers43,45,47, and49. The conveyance mechanism40conveys the recording medium P, such as thermal paper and receiver paper to which ink is transferred, in the arrow S direction illustrated inFIG. 5. The conveyance mechanism40conveys the recording medium P onto the protective layer25positioned on the heat generators9of the thermal head X1. The driver has a function of driving the conveyance rollers43,45,47, and49and is provided as a motor, for example. The conveyance rollers43,45,47, and49include columnar shafts43a,45a,47a, and49aand elastic members43b,45b,47b, and49bcovering the shafts43a,45a,47a, and49a, respectively. The shafts43a,45a,47a, and49aare made of metal, such as stainless steel, and the elastic members43b,45b,47b, and49bare made of butadiene rubber, for example. If the recording medium P is receiver paper to which ink is transferred, for example, the conveyance mechanism40conveys an ink film (not illustrated) together with the recording medium P between the recording medium P and the heat generators9of the thermal head X1.

The platen roller50has a function of pressing the recording medium P onto the protective layer25positioned on the heat generators9of the thermal head X1. The platen roller50is disposed extending along the direction orthogonal to the conveyance direction S. Both ends of the platen roller50are supported and fixed such that the platen roller50can rotate with the recording medium P pressed onto the heat generators9. The platen roller50includes a columnar shaft50aand an elastic member50bcovering the shaft50a. The shaft50ais made of metal, such as stainless steel, and the elastic member50bis made of butadiene rubber, for example.

The power supply device60has a function of supplying an electric current for causing the heat generators9of the thermal head X1to generate heat and an electric current for causing the drive ICs11to operate. The control device70has a function of supplying control signals for controlling operations of the drive ICs11to the drive ICs11so as to selectively cause the heat generators9of the thermal head X1to generate heat.

The thermal printer Z1prints a predetermined image on the recording medium P as follows: the platen roller50presses the recording medium P onto the heat generators9of the thermal head X1, the conveyance mechanism40conveys the recording medium P onto the heat generators9, and the power supply device60and the control device70selectively cause the heat generators9to generate heat. If the recording medium P is receiver paper, for example, the thermal printer Z1prints an image on the recording medium P by thermally transferring, to the recording medium P, the ink on the ink film (not illustrated) conveyed together with the recording medium P.

Second Embodiment

The following describes a thermal head X2according to a second embodiment with reference toFIG. 6. The thermal head X2is different from the thermal head X1in the structure of a protective layer225. The same members as those of the thermal head X1are denoted by like reference numerals, and explanation thereof is omitted.

The protective layer225includes a first layer225aand a second layer225b. The first layer225ais positioned on the substrate7. The second layer225bis positioned on the first layer225a. The first layer225aand the second layer225bcontain titanium (Ti) and nitrogen (N). Examples of the material of the first layer225aand the second layer225binclude, but are not limited to, TiN, TiON, TiCrN, TiAlON, etc. The first layer225aand the second layer225bmay be made of the same material. Alternatively, the first layer225aand the second layer225bmay be made of different materials.

In the first layer225a, the number of (200) planes is larger than that of (111) planes, and P2>P1is satisfied. This structure can make the first layer225afiner, thereby increasing the adhesion to the substrate7. Because the first layer225ais made finer, the adhesion between the substrate7and the second layer225bcan also be increased.

In the second layer225b, the number of (111) planes is larger than that of (200) planes, and P1>P2is satisfied. This structure causes the slip planes to dominate, thereby increasing the slipperiness of the second layer225b. As a result, the slip planes are positioned in the surface layer of the protective layer225, thereby increasing the abrasion resistance of the protective layer225.

P2/P1of the second layer225bmay be smaller than that of the first layer225a. With this structure, the slipperiness of the protective layer225can be increased. In other words, the slip planes are formed in the surface layer coming into contact with the recording medium P, thereby increasing the abrasion resistance of the protective layer225.

In the second layer225b, the number of (200) planes may be larger than that of (111) planes, and P2>P1may be satisfied. Also in this case, the finer layer is formed in the surface layer of the protective layer225coming into contact with the recording medium P, thereby increasing the abrasion resistance of the protective layer225.

The crystal planes of the first layer225aand the second layer225bare measured by nanobeam electron diffraction.

The protective layer225may be formed by the following method, for example.

Let us assume a case where the protective layer225is formed by arc plasma ion plating, for example. In this case, the absolute value of a substrate bias voltage is set to 200 to 400 V to form the first layer225athat satisfies P2>P1. Subsequently, the absolute value of the substrate bias voltage is increased to 500 V to form the second layer225b. With this method, the protective layer225including the first layer225aand the second layer225bmay be formed.

The protective layer225may be formed by making the deposition pressure in deposition of the first layer225ahigher than that in deposition of the second layer225b. Alternatively, the protective layer225may be formed by making the temperature of the substrate in deposition of the first layer225ahigher than that in deposition of the second layer225b.

The thermal head according to the present disclosure is not limited to embodiments, and various changes may be made without departing from the spirit of the disclosure. While a thin-film head including the heat generators9having a small width produced by forming a thin film of the electrical resistant layer15has been described as an example, the thermal head according to the present disclosure is not limited thereto. The thermal head may be a thick-film head including the heat generators9having a large width produced by patterning the various electrodes and then forming a thick film of the electrical resistant layer15.

While a flat-surface head including the heat generators9on the first surface7fof the substrate7has been described as an example, the thermal head according to the present disclosure may be an end-surface head including the heat generators9on the end surface of the substrate7.

The heat generators9may be formed by forming the common electrode17and the individual electrodes19on the heat storage layer13and forming the electrical resistant layer15only in the region between the common electrode17and the individual electrodes19.

The sealing member12may be made of the same material as that of the covering member29that covers the drive ICs11. In this case, the covering member29and the sealing member12may be formed simultaneously by printing the sealing member12on the region where it is to be formed when printing the covering member29.

While the connector31is directly connected to the substrate7, a flexible printed circuits (FPC) may be connected to the substrate7.

First Example

To examine the relation between the crystal planes of the crystal grains constituting the protective layer and the abrasion resistance of the protective layer, the following experiment was carried out.

A plurality of substrates were prepared as samples provided with the various electrode wires, such as the common electrode17, the individual electrodes19, the first connection electrodes21, and the second connection electrodes26. The protective layer25having a thickness of 5 μm was deposited using an arc plasma ion plating device. In deposition of the protective layer25, the substrate bias voltages indicated in Table 1 were applied.

Thermal heads were produced by mounting the drive ICs11on the substrate7provided with the protective layer25and applying and curing the covering member29. Three thermal heads were produced for each of sample No. 1 to 4. The produced thermal heads were each assembled in the housing together with the platen roller50to produce thermal printers. The following running test was carried out.

The abrasion resistance of the protective layer25was checked using one thermal head out of the three heads. The running test was carried out using thermal paper as the recording medium under the following conditions: conveyance speed of 300 mm/s, character printing period of 0.7 ms/Line, applied voltage of 0.3 W/dot, and pressing pressure of 10 kgF/head. If dot omission occurred in printing, it was determined that the protective layer25was damaged, and the distance of running until the dot omission was recorded as the running distance.

It was checked whether sticking occurred using the other two thermal heads. The thermal printers provided with the thermal heads of sample No. 1 to 4 printed characters by 1000 mm using thermal paper as the recording medium at conveyance speed of 300 mm/s with all the heat generating elements turned on. The thermal paper on which the characters were printed was checked. A sample neither of the two thermal heads of which had no character missing was represented by very good in Table 1. A sample one of the two thermal heads of which had character missing was represented by good in Table 1.

It was found out that the running distances of the thermal printers provided with the thermal heads of sample No. 1 to 4 exceeded 110 km and that the abrasion resistance of the protective layer25was increased. It was also found out that the sticking was evaluated as very good or good and that the slipperiness of the protective layer25was increased.

In the thermal heads of sample No. 3 and 4 satisfying 3.59>P2/P1, sticking was evaluated as very good, that is, no sticking occurred.

Second Example

A plurality of substrates were prepared as samples provided with the various electrode wires, such as the common electrode17, the individual electrodes19, the first connection electrodes21, and the second connection electrodes26. In deposition of the protective layer225, the first layer225aand the second layer225bwere deposited using an arc plasma ion plating device by applying the substrate bias voltages indicated in Table 2. The thickness of the first layer225awas 2.5 μm. The thickness of the second layer225bwas 2.5 μm.

The same running test as that in the first example was carried out to check the abrasion resistance of the protective layer225. To check the adhesion of the protective layer225, a sample in which the protective layer225had no peeling after the running test was represented by very good in Table 2. A sample in which the protective layer225had peeling was represented by good in Table 2.

It was found out that the running distances of the thermal printers provided with the thermal heads of sample No. 5 to 8 exceeded 100 km and that the abrasion resistance of the protective layer225was increased. It was also found out that the adhesion of the thermal heads was evaluated as very good or good and that the adhesion of the protective layer225was increased.

In the thermal head of sample No. 7, the first layer225asatisfied P2>P1, and the second layer225bsatisfied P1>P2. It was found out that the running distance of the thermal head of sample No. 7 was 200 km or longer and that the abrasion resistance of the protective layer225was increased. It was also found out that the adhesion was evaluated as very good and that the adhesion of the protective layer225was increased.

In the thermal head of sample No. 7, P2/P1of the second layer225bwas smaller than that of the first layer225a. It was found out that the slipperiness of the protective layer225was increased and that the running distance was 200 km or longer.

It was found out that the adhesion of the thermal head of sample No. 8 was evaluated as very good and that the adhesion of the protective layer225was increased.

Third Example

A plurality of substrates were prepared as samples provided with the various electrode wires, such as the common electrode17, the individual electrodes19, the first connection electrodes21, and the second connection electrodes26. In deposition of the protective layer225, the first layer225awas deposited using an arc plasma ion plating device by applying a substrate bias voltage of 600 V. The second layer225bwas deposited by applying the substrate bias voltages indicated in Table 3. The thickness of the first layer225awas 2.5 μm. The thickness of the second layer225bwas 2.5 μm.

The same running test as that in the first example was carried out to check the abrasion resistance of the protective layer225. In addition, it was checked whether sticking occurred.

To check the adhesion, a scratch test was carried out using a scratch tester CSR-1000 manufactured by RHESCA including a diamond indenter having a radius R of 0.2 mm and an angle of 120°.

The substrate7was cut in the thickness direction of the substrate7to form a cross section of the protective layer25, and the peak intensity of X-rays was measured. The X-ray intensity ratio in Table 3 indicates the X-ray intensity ratio of the entire protective layer225.

It was found out that the running distance of the thermal printers provided with the thermal heads of sample No. 9 to 12 exceeded 150 km and that the abrasion resistance of the protective layer225was increased. In addition, it was found out that the sticking of all the thermal heads was evaluated as very good.

As the result of the scratch test, it was found out that the adhesion strength of the thermal heads of sample No. 9 to 12 was 2.5 kgf or higher and that the adhesion of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 satisfying P2/P1≤3.42, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 having a half width of the diffraction peak of the (200) plane of 0.5° to 0.7°, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 having a half width of the diffraction peak of the (111) plane of 0.8° to 1.2°, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 having hardness of the protective layer225of 24 GPa or higher, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 having a Young's modulus of the protective layer225of 320 GPa or higher, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In the thermal heads of sample No. 9 to 12 having arithmetic surface roughness Ra of the protective layer225of 67.7 nm or lower, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.

In particular, in the thermal heads of sample No. 10 to 12 having arithmetic surface roughness Ra of the protective layer225of 32.3 nm or lower, the results of the running test exceeded 170 km.

In the thermal heads of sample No. 9 to 12 having an average crystal grain size of the crystal grains constituting the protective layer225of 405 nm to 550 nm, it was found out that the results of the running test exceeded 150 km and that the abrasion resistance of the protective layer225was increased.