JP3548571B2 - Thermal head - Google Patents

Description

  The present invention relates to a thermal head, and more particularly, to a thermal head having a protective layer having excellent wear resistance.

  Image recording devices of the thermal recording (thermal) type have the advantages that the device configuration is simple, advantageous for miniaturization, weight reduction, and price reduction, and that the recording sound is quiet and the power consumption is low. It is widely used for various recording applications such as printers and fax machines.

  The thermal head used in this thermal recording method, for example, if it is a line head, has a heating section in which a resistance heating element is formed in a line on an insulating substrate, and electrodes connected to each resistance heating element. I have. Then, the heating section is brought into contact with the recording paper via a recording medium such as a recording paper or an ink ribbon, and the recording information is sequentially input from the electrodes to each of the resistance heating elements as electric signals to perform recording in the main scanning direction. A two-dimensional recorded image is obtained by performing recording in the sub-scanning direction while running the paper.

  As such a thermal head, one having a structure as shown in FIG. 5 is conventionally known. 5A and 5B show an example of a line head. FIG. 5A is a plan view, and FIGS. 5B and 5C are cross-sectional views of AA main parts.

  In the thermal head 1 shown in FIGS. 5A, 5B, and 5C, reference numeral 2 denotes an insulating substrate made of glazed ceramic, and a glaze layer 2b is formed on the ceramic substrate 2a. On the insulating substrate 2, a resistance heating element 3 made of ruthenium oxide or the like and electrodes 4.4 made of gold (Au) or the like are formed by a combination of a film forming process of each layer and a photolithography process. . As described above, the electrodes 4.4 are formed in a fine pattern on the resistance heating element 3 and the electric power is selectively applied between the electrodes 4, 4 so that the resistance heating element 3 between the electrodes 4.4 is formed. Heat can be generated in the form of minute dots. A protective layer 5 is formed on them so as to cover the resistance heating element 3 and the electrode 4. As described above, the resistance heating element 3 and the electrodes 4 are formed by forming an electrode 4 on the resistance heating element 3 as shown in FIG. The resistance heating element 3 between the electrodes 4 may be heated in the form of minute dots by heating, or an electrode formed by opening the window by reversing the forming and stacking order as shown in FIG. The resistance heating element 3 may be formed on the layers 4 and 4 to generate heat in minute dots.

  The protective layer 5 in the thermal head 1 having the above-described structure is required to have high abrasion resistance against sliding with the recording paper in order to improve the durability, and to improve the adhesion and the sliding property with the recording paper. In order to obtain a good image quality by increasing the wear and to reduce the abrasion of the layer 5, a high smoothness of the surface, that is, a low surface roughness is required. Conventionally, as such a protective layer 5, a layer having a high hardness by a thin film manufacturing technique such as a sputtering method or a CVD method has been used, but these require a long time for layer formation due to a low film formation rate, and There is a problem that a large production cost is required because the film forming apparatus is expensive.

On the other hand, as the low-cost protective layer 5, a protective layer 5 made of glass formed by a thick film manufacturing technique such as printing and baking is often used. Some of the glass of the protective layer 5 have a low coefficient of thermal expansion to reduce the thermal stress applied to the resistance heating element, increase the abrasion resistance of the layer 5, and have good thermal conductivity. In order to achieve this, a filler such as alumina (Al ₂ O ₃ ) particles is contained.

  With respect to such a protective layer 5 made of glass, for example, Japanese Patent Application Laid-Open No. 63-216760 discloses a thick film type in which a heat resistance layer, an electrode, a heating resistor layer, and a protection layer are sequentially laminated on an insulating substrate. In the heat-sensitive recording head, the protective layer has a lower layer of the alumina filler-containing glass layer facing the heating resistor layer, and the content of the alumina filler formed on the outer surface side of the glass layer is zero or smaller than that in the glass layer. One including an upper layer of an amorphous glass layer has been proposed. As a result, the surface smoothness of the upper layer can be reduced to 0.2 μm or less, and even if the upper glass is worn, cracked or damaged, it will not be caught by the lower glass and will not spread downward, so it can be applied to the heating resistor. There is no influence, and therefore the reliability and the life of the thermal head can be improved.

Japanese Patent Application Laid-Open No. 2-292058 discloses that an underglaze layer is formed on an insulating substrate, and a heating resistor and an electrode for energizing the heating resistor are formed thereon. In a thick film type thermal head having a coat layer formed thereon, an overcoat layer is formed by using a first overcoat layer formed by using a thick film technique and a second overcoat layer formed by using a thin film technique on the layer. And an overcoat layer. The first overcoat layer is formed by printing and baking a glass paste, and a second overcoat layer made of sialon, Ta ₂ O ₅ , SiC or the like is formed on the surface thereof by a thin film technique such as sputtering or vacuum evaporation. Is done. According to this, a high hardness material is used for the second overcoat layer, and the surface thereof is smooth, so that the abrasion resistance can be improved without deteriorating the print quality.

Further, JP-A-61-229570 discloses a thermal substrate comprising a glaze substrate, a heating element portion and a conductive layer portion provided on the glaze substrate, and a wear-resistant glass layer formed thereon. In the head, it has been proposed that the wear-resistant glass layer be provided on the heating element portion and the conductive layer portion through an oxide thin film such as silicon oxide / alumina having a thickness of at least 300 mm. The oxide thin film is formed by the CVD method in the case of silicon oxide, and the sputtering method in the case of alumina. The wear-resistant glass is formed of lead borate glass (PbO-SiO ₂ -B ₂ O ₃ ) and a small amount of alumina. It is disclosed that printing and baking are performed with potassium (K ₂ O) added. As a result, the adhesion strength between the glass layer and the heating resistor portion can be increased, the heating resistor portion can be prevented from being oxidized during glass firing, and impurity ions in the glass diffuse to the heating resistor portion. As a result, there is no danger of changing the resistance value of the heat generating portion.
JP-A-63-216760 JP-A-2-29258 JP-A-61-229570 JP-A-3-104657

  However, when the present inventors examined these protective layers, it was found that there were the following problems even with the configurations described in the above publications.

  That is, when the protective layer has a two-layer structure as disclosed in JP-A-63-216760 and JP-A-2-292058, the surface smoothness of the protective layer can be improved, but the adhesion between the two layers can be improved. It is difficult to ensure sufficient durability against heat and thermal stress, and there is a problem in that the number of steps for forming the protective layer increases and the material and manufacturing cost increase.

  In view of the above circumstances, the present invention has been completed as a result of intensive studies by the present inventors, and an object of the present invention is to disperse fillers in glass in a thermal head having a protective layer made of filler-containing glass. An object of the present invention is to provide a high-reliability thermal head capable of obtaining good recorded image quality over a long period of time by improving abrasion resistance while improving smoothness and distribution to secure the smoothness of the protective layer surface.

  Still another object of the present invention is to provide a highly reliable and inexpensive thermal head by forming a low-cost protective layer having excellent abrasion resistance and stable characteristics.

  In the thermal head of the present invention, a resistance heating element and an electrode for supplying power to the resistance heating element are formed on an insulating substrate, and a protective layer made of glass containing filler is formed so as to cover the resistance heating element and the electrode. In the thermal head, the specific gravity of the glass forming the protective layer is made larger than the specific gravity of the filler, the average particle diameter of the filler is set to 0.5 μm or less, and the content of the filler is set to 5 wt% to 35 wt%. The amount of the filler projecting from the surface of the protective layer is reduced to less than half the particle diameter of the filler, and a smooth layer made of glass is interposed between the protective layer and the resistance heating element and the electrode.

  ADVANTAGE OF THE INVENTION According to the thermal head of this invention, the smoothness of the protective layer surface can be made favorable in the distribution state in which the filler is present more on the surface side in the paste glass at the time of printing and baking, and therefore, the recording paper and Abrasion resistance of the protective layer due to the sliding of, and good recording image quality can be obtained without deteriorating the surface roughness of the protective layer.

  In addition, since the protective layer is formed by a thick film forming technique such as printing and baking, the protective layer can be easily formed in a shorter time than a protective layer formed by a thin film forming technique. can do.

  Further, since a smooth layer made of glass is interposed between the resistance heating element and the electrode and the protective layer, it is possible to improve the surface smoothness of the protective layer and improve the adhesion of the recording paper during printing. it can.

  Hereinafter, the thermal head of the present invention will be described in detail. FIG. 1 shows the configuration of an embodiment of the thermal head of the present invention. FIG. 1 shows an example of a line head similar to FIG. 5, wherein FIG. 1 (a) is a plan view and FIG. 1 (b) is a cross-sectional view of a BB main part.

  In the thermal head 6 of FIGS. 1A and 1B, reference numeral 7 denotes an insulating substrate made of glazed ceramic or the like. In this example, a glazed layer 7b is formed on a ceramic substrate 7a. On the insulating substrate 7, a resistance heating element 8 made of, for example, ruthenium oxide and electrodes 9.9 made of gold (Au) are formed by combining a film forming process of each layer and a photolithography process, as shown in FIG. It is formed with the same configuration as (b). In this manner, the electrodes 9.9 are formed in a fine pattern on the resistance heating elements 8 and the electric power is selectively applied between the electrodes 9.9, whereby the resistance heating elements 8 between the electrodes 9.9 are formed. Heat can be generated in the form of minute dots. The resistance heating element 8 and the electrodes 9 may be formed by reversing the order of formation as shown in FIG. 5C. The resistance heating elements 8 may be formed as independent heating elements depending on the pixel density, or may be formed as a continuous resistance heating element layer. On these, a protective layer 10 is formed so as to cover the resistance heating element 8 and the electrodes 9. The protective layer 10 is made of a glass 11 mainly composed of silicon oxide-lead oxide and alumina or the like. Of filler-containing glass in which the filler 12 is dispersed.

  Further, since the specific gravity of the glass 11 is made larger than the specific gravity of the filler 12, the distribution becomes such that the high-hardness filler 12 is largely contained in the upper half region in the thickness direction of the protective layer 10 as shown in FIG. , Especially near the surface. Thereby, the abrasion resistance of the protective layer 10 due to sliding with the recording paper is significantly improved.

  The filler 12 in the protective layer 10 is preferably distributed 70% or more in the upper half region of the protective layer 10 in the thickness direction. The shear stress generated by sliding contact or the like can be favorably reduced by the portion of the protective layer 10 in the lower half in the thickness direction where the filler 12 is small.

  The insulating substrate 7 of the thermal head 6 according to the present invention includes, in addition to the glazed ceramic in which the glaze layer 7b such as borosilicate glass is formed on the ceramic substrate 7a such as alumina or mullite / SiN as described above. And a plate glass made of borosilicate glass.

The resistance heating element 8 may be made of, for example, ruthenium oxide (RuO ₂ ), tantalum nitride (TaN), tantalum silicate (TaSiO), tungsten (W), chromium oxide (CrO ₂ ), titanium silicate (TiSiO), etc. It can be used and is formed by a thin film manufacturing technique such as various sputtering methods and CVD methods, or a thick film manufacturing technique such as drawing / firing. The thickness is appropriately set according to desired heat generation characteristics. The resistance heating element 8 may be formed as a uniform layer over the entire heating element region, or may be formed as an independent row of heating elements by a photolithography process or the like.

  In addition to the above-mentioned gold (Au), aluminum (Al), copper (Cu), or the like can be used for the electrodes 9.9, and thin film manufacturing techniques such as various sputtering methods and vacuum evaporation methods and photolithography steps can be used. A desired electrode wiring pattern is formed by a method such as a combination or a combination of a thick film manufacturing technique such as screen printing and firing and a photolithography step. The thickness is usually set to about 1 μm.

As the glass 11 forming the protective layer 10, a glass mainly composed of silicon oxide-lead oxide may be used. For example, lead borosilicate (SiO ₂ —PbO—B ₂ O ₃ ) -based glass or lead silicate (SiO ₂ -PbO) glass.

  These glasses 10 are formed by employing a conventionally known thick film manufacturing technique. Specifically, first, a glass powder having an average particle diameter of 1 μm or less and a softening temperature of 490 ° C. was kneaded with a vehicle to form a paste, which was screen-printed, and dried at a temperature of about 120 ° C. for about 30 minutes. Thereafter, it is preliminarily fired at a temperature of about 400 ° C. for about 60 minutes and finally fired at a temperature of about 500 ° C. If the average particle size of the glass powder is set to 1 μm or less as described above, the glass can be easily softened and easily flowed during firing, so that the surface of the glass can be made smoother. it can. Further, as described above, by temporarily firing the glass at a predetermined temperature lower than the softening temperature, even when relatively large foreign matter is mixed in the glass paste, the foreign matter is generated during the temporary firing. It can be blown off by blowing hot air, and it is possible to effectively prevent the formation of a film formation defect due to the entry of foreign matter into the protective layer 10. Further, in order to further effectively prevent foreign matter from entering the protective layer 10, after the above-described main baking, heating may be performed at a temperature of 525 to 530 ° C. for about 1 to 2 minutes. Foreign substances such as existing organic substances can be completely burned and released to the outside.

  In order to prevent the electrode 9.9 material from being deteriorated during the firing, it is necessary to set the firing temperature sufficiently lower than the melting point of the electrode 9.9 material. For example, when Al is used for the electrodes 9 and 9, the melting temperature of Al is 660 ° C., so that the firing temperature of the glass 11 must be at most 660 ° C. or less. Therefore, the temperature is preferably 600 ° C. or less. In order to reduce the firing temperature of the glass 11 to 600 ° C. or lower, the softening temperature of the glass is preferably 550 ° C. or lower. In addition, since the resistance heating element 8 generates heat to about 300 ° C. during thermal recording, the melting point of the glass 11 must be higher than that. Furthermore, glass with a sintering temperature of 450 ° C or less cannot secure sufficient heat resistance. Therefore, it is usually preferable to use the glass 11 having a firing temperature of 450 to 600 ° C.

  In addition, when a lead borosilicate glass is used among the above glass materials, the properties (thermal conductivity, abrasion resistance, etc.) of the glass 11 necessary for the protective layer 10 are greatly changed by changing the PbO content ratio in the components. Since the specific gravity can be changed without any change, and the firing temperature is 450 to 600 ° C., the Al electrode can be easily formed by printing and firing without altering the Al electrode.

  FIG. 2 is a diagram showing a change in specific gravity with respect to the PbO content ratio in the lead borosilicate glass. In FIG. 2, the horizontal axis represents the PbO content ratio (wt%) in the glass component, the vertical axis represents the specific gravity of the glass relative thereto, and the characteristic curve in the figure represents the change in the specific gravity with respect to the PbO content ratio. . As can be seen from the figure, the specific gravity of the glass can be increased as the PbO content ratio is increased. For example, when alumina having a specific gravity of 3.9 is used for the filler 12, if the PbO content ratio is 45 wt% or more, the specific gravity of the glass 11 can be increased. Can be set to 3.9 or higher. However, if the PbO content is 90 wt% or more, it will not be solidified even if fired, and cannot be used as the protective layer 10. Also, the firing temperature and softening point tend to decrease as the PbO content ratio increases, and the preferable firing temperature of 600 ° C. and softening point of 550 ° C. when Al is used for the electrodes 9.9 is that the PbO content ratio is It is when about 60 wt% or more. Therefore, the preferable PbO content ratio is 45 to 90 wt%, and it is more preferably set to 60 to 85 wt% in consideration of specific gravity and sinterability.

As the filler 12 dispersed in the glass 11 of the protective layer 10, diamond, quartz (SiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), or the like can be used in addition to the above alumina (Al ₂ O ₃ ). . For example, when using alumina as the filler 12, when its hardness and thermal conductivity are compared with those of lead borosilicate glass,
Vickers hardness of lead borosilicate glass: about 300 kg / mm ²
Vickers hardness of alumina: about 1,500 kg / mm ²
Thermal conductivity of lead borosilicate glass: about 2 × 10 ^-3 cal / cm · sec · ° C
Thermal conductivity of alumina: about 5 × 10 ^-3 cal / cm · sec · ° C
It is. Therefore, by including the alumina filler 12 in the glass 11, the hardness and the thermal conductivity are increased. The thermal expansion coefficient of lead borosilicate glass depends on the presence or absence of 15wt% alumina filler.
Thermal expansion coefficient of glass without alumina filler: about 60 × 10 ^-7 / ℃
Thermal expansion coefficient of alumina filler-containing glass: about 40 × 10 ^-7 / ° C
Thus, the thermal expansion coefficient of the glass 11 is reduced, the thermal stress due to the heat pulse from the resistance heating element 8 is reduced, and the pulse resistance can be improved.

  The shape of the filler 12 may be granular, spherical, fibrous, or polygonal, but the average particle size of the filler 12 in the present invention is such that even when the filler 12 is largely present near the surface of the protective layer 10, 10 In order not to decrease the smoothness of the surface, the average particle size is preferably about 0.5 μm or less. This is because even when the filler 12 is present on the surface of the protective layer 10, more than half of the filler 12 particles themselves do not protrude from the surface, and the surface roughness Ra of the protective layer 10 is about two-half of the protruding amount. When the average particle diameter of the filler 12 is about 0.5 μm or less, the surface roughness Ra of the protective layer 10 can be reduced to about 0.1 μm or less to obtain good recording characteristics. The content of the filler 12 in the protective layer 10 is preferably set in the range of 5 to 35 wt%. If the content is less than 5 wt%, the effect of containing filler 12 such as improvement of abrasion resistance, thermal conductivity, and reduction of thermal expansion coefficient cannot be seen, and if it exceeds 35 wt%, the entire filler particles cannot be covered with glass, and protective layer 10 cannot be formed. Tends to be brittle.

  The protective layer 10 made of such a filler 12-containing glass 11 is formed so as to cover the resistance heating element 8 and the electrodes 9 and 9 in the vicinity thereof, but the thickness is sufficient to withstand sliding with the recording paper. Preferably, the thickness is set to about 3 to 14 μm, more preferably 7 to 10 μm, because of having high mechanical strength and transmitting heat from the resistance heating element 8 to the recording paper. When the thickness is less than about 3 μm, the mechanical strength is insufficient, and when the thickness is more than about 14 μm, good heat conduction is not achieved.

  Here, when the thickness of the protective layer 10 is smaller than about 7 μm, the difference between the thickness of the protective layer 10 on the resistance heating element 8 and the thickness of the protective layer 10 on the electrodes 9 and 9 becomes relatively large. The thermal stress due to the heat pulse from the resistance heating element 8 concentrates on a portion having a different thickness of the film 10, that is, a step portion, and the pulse resistance of the heating portion may be insufficient. Therefore, according to the present invention, this pulse resistance is enhanced, and at the same time, deterioration of the resistance heating element 8 and the electrodes 9, 9 during formation of the protective layer 10 due to oxidation or reaction with the glass 11 component of the protective layer 10 is prevented. In order to reduce the change in the resistance value of the resistance heating element 8, in the thermal head 6 having the above-described structure, the denaturation made of oxide or / and nitride is provided between the resistance heating element 8 and the electrodes 9. An intervening prevention layer is provided. FIG. 3 shows the configuration of one embodiment of such a thermal head of the present invention.

  FIG. 3 shows an example of a line head similar to that of FIG. 1, wherein FIG. 3 (a) is a plan view and FIG. 3 (b) is a cross-sectional view of a CC main part. In these drawings, the same parts as those in FIG. 1 are denoted by the same reference numerals.

  In the thermal head 13 shown in FIGS. 3A and 3B, a resistance heating element 8 and electrodes 9.9 are formed on an insulating substrate 7 in which a glaze layer 7b is formed on a ceramic substrate 7a. The order of the formation may be reversed as shown in FIG. On these, a protective layer 10 is formed so as to cover the resistance heating element 8 and the electrodes 9. The protective layer 10 is made of a filler-containing glass in which a filler 12 is dispersed in a glass 11. . Further, between the resistance heating element 8 and the electrodes 9 and the protective layer 10, an alteration preventing layer 14 made of oxide or / and nitride is interposed. In the thermal head 13, when the specific gravity of the glass 11 is larger than the specific gravity of the filler 12, the high-hardness filler 12 can be distributed more near the surface of the protective layer 10 as shown in FIG. .

An oxide or / and nitride is used for the alteration preventing layer 14 in the present invention. For example, silicon oxide (SiO ₂ ), alumina (Al ₂ O ₃ ), tantalum oxide (Ta ₂ O ₅ ) is used as the oxide. The nitride includes silicon nitride (SiN). The mixture of the oxide and the nitride includes sialon (SiAlON), and a mixture or a laminate of these may be used.

  The alteration prevention layer 14 made of such a material is formed by a thin film manufacturing technique such as a sputtering method or a CVD method, so that a layer having dense, high hardness, stable characteristics and excellent adhesion can be obtained. Can be Examples of the thin film preparation technique suitable for forming the alteration preventing layer 14 of the present invention include various sputtering methods such as RF sputtering, DC sputtering, reactive sputtering, RF magnetron sputtering, and DC magnetron sputtering, and plasma CVD.・ Various CVD methods such as thermal CVD method and optical CVD method, ion plating method, vacuum evaporation method, resistance heating evaporation method, electron beam evaporation method, laser beam evaporation method, active reaction evaporation method, etc. .

  Further, after forming the above-mentioned alteration preventing layer 14 by employing the above-mentioned thin film forming technique, an extremely thin oxide film is formed on the surface of the alteration preventing layer 14 by heating at a temperature of 300 ° C. to 400 ° C. for about 120 minutes. In addition to increasing the affinity between the alteration preventing layer 14 and the protective layer 10, the alteration preventing layer 14 causes a rapid oxidation reaction with the oxygen contained in the protective layer 10 when the protective layer 10 is fired, and This can effectively prevent bubbles from being generated. This allows the protective layer 10 to be firmly adhered to the alteration preventing layer 14, and also allows the mechanical strength of the protective layer 10 to be improved.

The thickness of the alteration preventing layer 14 may be appropriately set according to the type of the alteration preventing layer 14, as shown in FIG. 4 showing the relationship between the thickness and the effect. Figure 4 shows the alteration prevention layer
FIG. 7 is a diagram showing the correspondence between the thickness and the alteration prevention effect for 14 types, in which the horizontal axis represents the thickness of the layer 14 and the vertical axis relatively represents the magnitude of the alteration prevention effect. In the figure, ● indicates the case of oxide, ○ indicates the case of nitride, and Δ indicates the case of a mixture of oxide and nitride, and the curves connecting them are the respective characteristic curves.

  As can be seen from FIG. 4, when an oxide is used for this layer 14, it is good to set it to be slightly thicker because it contains oxygen atoms, and to be 0.08 μm or more, preferably 0.15 μm or more, and optimally 0.20 μm or more. It is good to When a nitride is used, since it does not contain oxygen atoms, the effect of preventing oxidation is large. Therefore, the thickness is preferably 0.04 μm or more, preferably 0.08 μm or more, and most preferably 0.15 μm or more. In the case of using a mixture of an oxide and a nitride, the thickness may be 0.06 μm or more, preferably 0.10 μm or more, and more preferably 0.18 μm or more, which is an intermediate thickness. If the thickness is smaller than these, the pulse resistance tends to be insufficient.

  On the other hand, if the thickness of the layer 14 exceeds 2 μm, there is no problem in terms of characteristics or technology, but there is a problem that the manufacturing cost is increased. That is, when the alteration preventing layer 14 is formed by the thin film manufacturing technique, the film formation rate is relatively slow. Therefore, when the application to mass production is considered, spending one hour or more in the film formation time causes an increase in manufacturing cost. Is not preferred. Since the film forming speed of an oxide such as SiO2 by a thin film forming technique is about 0.011 μm / min, the thickness of this layer 14 is preferably about 0.66 μm or less, and the film forming rate of a nitride such as SiN is about 0.024 μm / min. Therefore, the thickness is preferably about 1.44 μm or less. In the case of a mixture of an oxide and a nitride, for example, sialon, the thickness is preferably about 1.11 μm or less. Then, within such a range, the thickness of the alteration preventing layer 14 is appropriately set according to required characteristics such as durability of the thermal head 13.

  Hereinafter, specific examples of the thermal head of the present invention will be described.

Example 1 A thermal head of the present invention having the structure shown in FIG. 1 was manufactured as follows. First, a resistive heating element 8 made of TaN having a thickness of about 0.05 μm is formed by sputtering on a glazed ceramic substrate 7 having a borosilicate glass glaze layer 7 b formed on the surface, and a thickness of about 1 μm is formed thereon by electron beam evaporation. Was formed, and electrodes 9 having a predetermined electrode wiring pattern were formed by a photolithography process.

On the other hand, the composition ratio as the glass 11 for forming the protective layer 10 is _{SiO 2: 15%, PbO:} 70%, B 2 O 3: 5%, ZnO: providing a 4% lead borosilicate glass powder, the filler 12 Alumina particles having an average particle size of 0.5 μm were prepared. The glass 11 had a specific gravity of 5.3 and a softening point of 490 ° C. 15% by weight of alumina particles were mixed with this glass powder, a vehicle was added, and the mixture was kneaded into a paste. This is printed on the resistance heating element 8 and the electrodes 9 and 9 by screen printing so as to cover them, and baked at 530 ° C. for 10 minutes to form a protective layer 10 made of a 7 μm thick filler-containing glass. A thermal head A of the present invention was manufactured.

  The distribution state of the filler 12 in the protective layer 10 of the thermal head A was examined by examining the cross section of the protective layer 10 with an electron microscope. As a result, many fillers 12 were distributed on the surface of the protective layer 10 and the resistance heating element 8 and the electrode It was confirmed that the distribution was small on the 9.9 side. When the surface roughness Ra of the protective layer 10 was measured with a stylus surface roughness meter, it was 0.1 μm and had good smoothness.

Further, when an image recording test was performed by an image recording tester using this head A to evaluate the image quality, the print density was 1.1 or more, there was no print blur or print bleeding, and a sufficient print density was secured. Was also a good result. Further, when the wear resistance of the protective layer 10 was evaluated using a long-term actual printing running life tester, it was confirmed that the protective layer 10 had excellent wear resistance with a wear amount of 2 μm after traveling 30 km. In addition, 3 × 10 ⁷ pulses were applied to the resistive heating element 8 by printing 30 km. However, no missing dots were found and it was confirmed that the resistive heating element 8 had sufficient heat resistance.

  [Example 2] A thermal head of a comparative example was manufactured as follows, in which the specific gravity of the glass 11 was made smaller than the specific gravity of the filler 12 in the same structure as in [Example 1].

First, electrodes 9.9 and a resistance heating element 8 were formed on a glazed ceramic substrate 7 in the same manner as in [Example 1]. Then, the protective layer 10 the composition ratio as the glass 11 for forming the can _{SiO 2: 40%, PbO:} 20%, B 2 O 3: 15%, ZnO: providing a 15% lead borosilicate glass powder, a filler As an example 12, an alumina powder having an average particle size of 0.5 μm and a specific gravity of 3.9 was prepared. The specific gravity of this glass 11 was about 3.2, and the softening point was about 690 ° C.

  15 wt% of the above alumina filler was mixed with the above glass powder, a vehicle was added, and the mixture was kneaded into a paste. This is printed on the resistance heating element 8 and the electrodes 9 and 9 so as to cover them by screen printing, and baked at 740 ° C. for 10 minutes to form a protective layer 10 made of a filler-containing glass having a thickness of 7 μm. The thermal head C of the comparative example was produced.

  When the distribution state of the filler 12 in the protective layer 10 of the thermal head C was examined in the same manner as in [Example 1], the filler 12 was more distributed near the resistance heating element 8 and the electrodes 9. It was confirmed that.

  In addition, when the image quality was evaluated in the same manner as in [Example 1], the print density was 1.1 at the initial stage, and the print density was good without print blurring or print bleeding. The amount was severely abraded at 4 μm. In addition, a large number of running scratches were formed on the surface of the heat generating portion, and cracks occurred in the protective layer 10. Further, among the 1,728 resistance heating elements per head, the resistance values of the eight resistance heating elements drifted by 15% or more, which caused dot missing in printing.

  Example 3 In this example, a thermal head of the present invention having the structure shown in FIG. 3 was manufactured as follows. First, a resistive heating element 8 made of TaSiO having a thickness of about 0.05 μm is formed on a glazed ceramic substrate 7 having a lead borosilicate glass glaze layer 7b formed on the surface thereof by RF sputtering, and an Al layer having a thickness of about 1 μm is formed thereon. A layer was formed, and a resistive heating element 8 and electrodes 9 and 9 wiring patterns were formed by a photolithography process. Next, an alteration preventing layer 14 made of sialon (SiAlON) having a thickness of 0.3 μm was formed on the resistance heating element 8 and the electrodes 9 by RF sputtering.

On the other hand, the composition ratio as the glass 11 for forming the protective layer 10 is _{SiO 2: 15%, PbO:} 70%, B 2 O 3: 5%, ZnO: providing a 4% boric acid lead glass powder, a filler 12 Alumina particles having an average particle size of 0.5 μm were prepared. The glass 11 had a specific gravity of about 5.3 and a softening point of about 490 ° C. 15 wt% of alumina particles were mixed with this glass powder, and a vehicle was added to form a paste. This is printed on the resistance heating element 8, the electrodes 9.9, and the alteration preventing layer 14 by screen printing so as to cover them, and baked at 530 ° C. for 10 minutes to form a protective layer 10 made of a 7 μm thick filler-containing glass. Thus, the thermal head D of the present invention was manufactured.

  Also, a thermal head E of the present invention was manufactured in the same manner as above except that a 0.2 μm thick silicon nitride (SiN) was formed as the alteration preventing layer 14.

  The distribution state of the filler 12 in the protective layer 10 and the surface roughness Ra of the protective layer 10 of the thermal heads D and E were examined in the same manner as in [Example 1]. And a small distribution near the resistance heating element 8 and the electrodes 9.9 was confirmed, and the surface roughness Ra was 0.1 μm, indicating good smoothness.

  Further, the deterioration of the resistance heating element 8 and the electrodes 9.9 due to the baking of the protective layer 10 was determined by measuring the resistance value between the common electrode and the individual electrode of the electrodes 9.9, and the resistance before and after the protective layer 10 was formed. The results were as shown in Table 1 when evaluated by the rate of change and appearance observation. Table 1 also shows, as a comparative example, the results of a thermal head F manufactured in the same manner except that the deterioration preventing layer 14 was not formed.

  As can be seen from the results shown in Table 1, the thermal heads D and E of the present invention having the alteration preventing layer 14 had small resistance change rates of 3.2% and 2.5%, respectively. It was a good result without being seen. On the other hand, in the head F of the comparative example in which the alteration preventing layer 14 was not formed, the rate of change of the resistance value was as large as 200 to 300%, and blackening was observed in the electrodes. . From these results, it was confirmed that in the thermal heads D and E of the present invention, the alteration of the resistance heating element 8 and the electrodes 9, 9 was suppressed by the alteration preventing layer 14.

  Next, image quality evaluation and abrasion resistance evaluation were performed using these heads D and E in the same manner as in [Example 1]. As a result, the print density was 1.1 or more, and there was no print blur or bleeding. The conductivity was also good. In addition, the abrasion resistance was good, with the amount of wear being 2 μm after running for 30 km.

In addition, 3 × 10 ⁷ pulses were applied to the heating element 8 by performing actual printing at 30 km. However, it was confirmed that there was no missing dot and the heat resistance was sufficient.

  Although the above embodiment has been described with reference to a line head as an example, the present invention is not limited to this, and it can be applied to a serial head to obtain the same operation and effect. Needless to say.

  In the thermal head of the above-described embodiment, when the resistance heating elements and the electrodes are formed by a thick film manufacturing technique such as screen printing, a smooth layer made of glass or the like may be interposed between these and the protective layer. In this case, in addition to the effects similar to those of the above-described embodiment, the surface smoothness of the protective layer can be increased to improve the adhesion of the recording paper during printing. The formation of such a smooth layer is performed using a glass paste having a shrinkage ratio (for example, 88%) larger than the glass paste (shrinkage ratio: 56%) forming the protective layer. The method is performed by, for example, applying the film on the thick film portion and drying it, and then simultaneously firing the glass of the protective layer when firing.

  Further, in the above embodiment, the filler in the protective layer is concentrated near the surface of the protective layer, but instead, the filler in the protective layer is gradually increased from the resistance heating element side to the surface side. May be distributed.

(A) is a plan view showing a configuration of an embodiment of the thermal head of the present invention, and (b) is a cross-sectional view of a BB main part thereof. FIG. 3 is a diagram showing a change in specific gravity with respect to a PbO content ratio in a lead borosilicate glass. (A) is a plan view showing a configuration of another embodiment of the thermal head of the present invention, and (b) is a cross-sectional view of the CC main part thereof. FIG. 4 is a diagram showing the relationship between the thickness of a deterioration preventing layer and its effect in the thermal head of the present invention. (A) is a plan view showing a configuration of a conventional thermal head, and (b) and (c) are cross-sectional views of AA main parts thereof.

Explanation of reference numerals

1, 6, 13: Thermal head 2, 7, ... Insulating substrate 3, 8, ... Resistance heating element 4, 9, ... Electrode 5, 10, ... Protection layer
11 ... Glass
12 ・ ・ ・ ・ ・ ・ ・ Filler
14 ・ ・ ・ ・ ・ ・ Change prevention layer

Claims (1)

A thermal head in which a resistance heating element and an electrode for supplying power to the resistance heating element are formed on an insulating substrate and a protective layer made of filler-containing glass is formed to cover the resistance heating element and the electrode,
The specific gravity of the glass forming the protective layer is made larger than the specific gravity of the filler, the average particle size of the filler is 0.5 μm or less, and the content of the filler is set to 5 wt% to 35 wt%. A thermal head characterized in that the amount of the protruding filler is reduced to less than half the particle size of the filler, and a smooth layer made of glass is interposed between the protective layer and the resistance heating element and the electrode.

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