JP2008290408A - Thermal head, printing apparatus, and method for manufacturing thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a thermal head with a required quality even when a common electrode is formed by a screen printing technique. <P>SOLUTION: A material in an electrically conductive paste to be used for a common electrode layer has three peaks in its particle size distribution. The ratio of the particle diameters of three peaks is 10:2:1, and in addition, the peak with the maximum diameter is in a range of 1.5-4.0 μm. By using such the material as this having three peaks in the particle size distribution, the resistivity of the common electrode layer after calcination is decreased from 8.2 to 2.5 μΩcm, to be approximately 30% of the case where the peak of the particle size distribution counts one. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermal head, and more particularly to a thermal head mounted on various printer devices for business use and consumer use, a printing apparatus equipped with the thermal head, and a method of manufacturing the thermal head.

  There are thermal heads used for thermal recording of various printing apparatuses such as rewrite printers, card printers, video printers, barcode printers, label printers, facsimiles, and ticket vending machines. This type of thermal head prints on a medium or erases printed information by heating to a predetermined temperature. More specifically, the thermal head prints characters and pictures on media that reacts with the obtained thermal energy by selectively applying a potential to a single or multiple heating resistors that are linearly provided to generate heat. Or erase what is printed.

For example, as disclosed in Patent Document 1 (see FIG. 2), such a thermal head has a structure in which a heating resistor is laminated on a glaze layer (heat storage layer) formed on a substrate, and is further common. Thin film conductors that are electrodes and lead electrodes are laminated.
JP 11-129519 A

  By the way, as a method of forming an electrode layer such as a common electrode or a lead electrode, there are a method of patterning by photolithography after forming a conductor film as an electrode, and a method of printing and baking a conductive paste (screen printing method). . In general, a screen printing method is desired from the viewpoint of cost, but an altered layer or film peeling may occur due to the formation of an altered layer on the electrode layer and the surface on which the electrode layer is formed due to a high thermal load. As a result, the desired product quality may not be achieved. Further, when the firing temperature was lowered, the content of the low melting point glass was increased, the specific resistance was increased, the electrode layer was thickened, and the contact resistance with the base film and the upper film was increased. In addition, when the electrode layer has a large volumetric shrinkage during firing, the firing surface is greatly uneven, and the printed surface may be scratched during printing, or the formed electrode layer may be peeled off. There was also.

  This invention is made | formed in view of such a condition, Comprising: It aims at implement | achieving the thermal head which has an electrode layer of desired quality by a screen printing construction method.

The apparatus according to the present invention relates to a thermal head. This thermal head includes an electrode formed by a screen printing method using a conductive paste having a plurality of peaks in the particle size distribution of the main component metal.
The plurality of peaks may be three.
Further, the ratio of the particle diameters of the three peaks after firing may be 10: (2.55 ± 0.35) :( 1.75 ± 0.15).
The maximum diameter of the three peak particles may be in the range of 1.5 μm to 4.0 μm.
Moreover, the particle size after baking of the metal in the said electrically conductive paste may be 4.0 micrometers or less.
Further, the density of the electrode after the firing may be 87% or more of the bulk density of the metal used.
The apparatus according to the present invention relates to a printing apparatus. This printing apparatus includes the above-described thermal head.
The manufacturing method according to the present invention relates to a method for manufacturing a thermal head. This manufacturing method includes an electrode forming step of forming an electrode by a screen printing method using a conductive paste having a plurality of peaks in the particle size distribution of the main component metal.
Moreover, 600 degreeC or less may be sufficient as the baking process in the said screen printing construction method.
The thermal head according to the present invention is manufactured by the above manufacturing method.

  According to the present invention, a thermal head having an electrode layer of a desired quality can be realized by a screen printing method.

  FIG. 1 is a schematic diagram of a rewrite printer 10 according to the present embodiment. FIG. 1A is a plan view of the rewrite printer 10, and FIG. 1B is a diagram schematically showing an AA cross section. FIG. 2 is a functional block diagram relating to the main part of the rewrite printer 10. As shown in the figure, the rewrite printer 10 has a hexahedron-shaped casing 13, and a media transport path 12 through which the rewrite media M is transported in the forward and reverse directions (right and left in FIG. 1) is horizontal. Is formed.

  Here, one end (the left end in FIG. 1) of the media transport path 12 is opened to form a media insertion slot 11. Further, the other end (right end in FIG. 1) of the media transport path 12 is closed to form the deepest portion 12a. Further, in the casing 13, a printing thermal head 70 is attached downward with its heating resistor 72 facing the media conveyance path 12. Further, the erasing head 50 is attached to the back of the printing thermal head 70 (on the right side in FIG. 1) so that the heating resistor 52 faces the media transport path 12.

  Further, a pair of platen rollers 17 and 17 are disposed in front of the thermal head for printing 70 (left side in FIG. 1) so that the shafts are horizontally arranged in two upper and lower stages at a predetermined interval from each other. Each platen roller 17 is rotatably supported so as to face the media conveyance path 12.

  In addition, a pair of platen rollers 18 and 18 are disposed horizontally behind the erasing head 50 (on the right side in FIG. 1) so that the shafts are horizontally arranged in two upper and lower stages at predetermined intervals. Each platen roller 18 is rotatably supported so as to face the media conveyance path 12.

  When rewriting (rewriting) the data on the rewrite medium M using the rewrite printer 10, the data on the rewrite medium M is once erased entirely, and then new data is written. This process will be briefly described.

  First, when the rewrite medium M is inserted into the medium insertion slot 11, the main control unit 20 commands rewriting of data on the rewrite medium M.

  Then, the first sensor 21 detects that the rewrite medium M has been inserted into the medium insertion slot 11 and outputs a detection signal to that effect to the main control unit 20. In response to this, the main control unit 20 instructs the roller driving unit 23 to rotate the platen roller 17 forward. Then, the roller drive unit 23 drives the platen roller 17 to rotate in the forward direction.

  As a result, the rewrite medium M is conveyed in the forward direction (rightward in FIG. 1) through the medium conveyance path 12 and passes under the printing thermal head 70 and the erasing head 50 in order. Thereafter, the rewrite media M is guided by the platen roller 18 and reaches the deepest portion 12 a of the media transport path 12.

  Then, the second sensor 22 detects that the rewrite medium M has reached the deepest portion 12 a of the media transport path 12, and outputs a detection signal to that effect to the main control unit 20. In response to this, the main control unit 20 instructs the roller driving unit 23 to rotate the platen roller 17 in the reverse direction. Then, the roller drive unit 23 drives the platen roller 17 to rotate in the reverse direction. As a result, the rewrite medium M is conveyed in the reverse direction (leftward in FIG. 1) along the medium conveyance path 12, and sequentially passes below the erasing head 50 and the printing thermal head 70.

  Here, the main control unit 20 instructs the head control unit 25 to erase data on the rewrite medium M. Then, the head controller 25 drives the erasing head 50 to erase the entire data of the rewrite medium M. At this time, since the rewrite medium M is held at both ends or in the vicinity thereof by two sets of platen rollers 17 and 18 and is in tension, the data write operation of the rewrite medium M is performed by the heating resistor 52 of the erase head 50. This is appropriately done in the form of heat generation in the vicinity of the rewrite medium M.

  Subsequently, the head control unit 25 drives the printing thermal head 70 to newly record data of the rewrite medium M. At this time, since the rewrite medium M is held at both ends or in the vicinity thereof by the platen rollers 17 and 18 and is in tension, the rewrite medium M is rewritten by the heating resistor 72 of the thermal head 70 for printing by the rewrite medium M. It is performed reliably in the form of generating heat in the vicinity. Thereafter, the rewrite medium M is continuously conveyed in the reverse direction on the medium conveyance path 12 and discharged from the medium insertion port 11.

  Thereby, rewriting of the rewrite medium M by the rewrite printer 10 is completed. When only erasure of data on the rewrite medium M is instructed, the print thermal head 70 is not driven, and the data rewrite medium M from which the data has been erased is conveyed in the reverse direction on the medium conveyance path 12 to insert the medium. It is discharged from the mouth 11.

  Next, the thermal head will be described. Here, the sectional structure of the printing thermal head 70 will be described as an embodiment of the thermal head, but the erasing head 50 also has the same sectional structure. FIG. 3 is a diagram schematically showing a cross-sectional structure of the printing thermal head 70. The printing thermal head 70 includes a substrate 56, a stacked portion 74 stacked on the substrate 56, and a mount 55 to which the substrate 56 is attached. The mount 55 and the substrate 56 are fixed by a connection layer (not shown) interposed therebetween. The stacked portion 74 includes a heat storage layer 54, a heating resistor 72, two electrode layers including a common electrode portion 66 and a lead conductive layer 64b, and a protective layer 58 from the substrate 56 side.

The substrate 56 is made of an insulating ceramic such as alumina. On the substrate 56, a heat storage layer 54 called a glaze layer having a desired thickness is formed by, for example, softening and baking glass. A heating resistor 72 having a desired thickness is formed on the heat storage layer 54. The heating resistor 72 is, for _example, a resistive body made of TaSiO 2, NbSiO ₂ like film or polysilicon so-called cermet-based material (Poly-Si) thin film, the heating resistor 72, the length of the printing thermal head 70 In a direction, the lines are discretely arranged at predetermined intervals. When the thermal head 50 is an erasing head, the heating resistor 52 is formed in a single dot band shape.

  On the heating resistor 72, two electrode layers, a common electrode portion 66 for supplying power and a lead conductive layer 64b, are formed. An intervening layer such as a refractory metal may be formed between the heating resistor 72 and the common electrode portion 66 or the lead conductive layer 64b. The common electrode portion 66 includes a common electrode layer 62 and a common conductive layer 64a.

  The common electrode portion 66 and the lead conductive layer 64b are made of metal such as silver (Ag), gold (Au), copper (Cu), nickel (Ni), tungsten (W), aluminum (Al), platinum (Pt), or An alloy containing these as a main component or a laminate of these metals and alloys.

Further, on the uppermost layer, a protective layer 58 made of, for example, SiO ₂ and having a desired thickness is formed so as to cover the common electrode portion 66, the lead conductive layer 64b, and the heating resistor 72.

  With respect to the thermal head having the above configuration, a process of forming the laminated portion 74 will be described with reference to FIG. Here, the laminated portion 74 of the printing thermal head 70 will be described.

  First, as shown in FIG. 4A, as the glaze layer forming step, the heat storage layer 54 is formed on the substrate 56 by softening and baking the glass as described above, for example. Subsequently, as a heating resistor forming step, the heating resistor 72 is formed on the heat storage layer 54 by using a thin film forming technique such as vacuum deposition, CVD (chemical vapor deposition), sputtering, or a photo etching technique. Or formed by a thick film forming technique (screen printing method) for printing and baking.

  Then, as shown in FIG. 4B, in the first electrode forming step, the above-described material is printed and baked in a desired region on the heating resistor 72 to form the common electrode layer 62. As the material of the common electrode layer 62, a conductive paste having three peaks in the distribution of the particle size (average of pulverized particle size) of the metal as the main component is used. These three peaks, the number of metal particles, the firing temperature, etc. will be described later.

  Subsequently, as shown in FIG. 4C, as a second electrode formation step, a conductive layer 64 having a desired thickness is formed on the entire surface of the common electrode layer 62 and the heating resistor 72. The conductive layer 64 may be formed by a thin film formation technique such as sputtering and a photoetching technique, or may be formed by a screen printing method.

  Further, as shown in FIG. 4D, as an electrode separation step, patterning is performed by photolithography to remove the conductive layer 64 in a desired region. By this step, the common electrode portion 66 (common electrode layer 62, common conductive layer 64a) and the lead conductive layer 64b are electrically separated.

  When the common electrode portion 66 and the lead conductive layer 64b are separated, a protective layer 58 is formed as the uppermost layer as a protective layer forming step.

  Next, a material (metal) in the conductive paste used for the common electrode portion 66 will be described. As described above, the metal in the conductive paste has three peaks in the particle size distribution. Specifically, the ratio of the particle sizes of the three peaks is 10: 2: 1. Furthermore, the largest particle size is included in the range of 1.5-4.0 micrometers among those peaks. The median diameter D50 was used as the particle diameter. The median diameter D50 is the particle diameter when the number or mass larger than a certain particle diameter represents 50% of the total powder in the particle size distribution of the powder (granule), that is, the oversize is 50%. Refers to particle size.

  FIG. 5 is a conceptual diagram showing the filling state of metal particles in the common electrode layer 62. FIG. 5 (a) shows the case where there is one peak in the particle size distribution, and FIG. The case of three peaks is shown. As shown in this figure, when there is one peak, there are many gaps between particles, and the particle filling rate is about 75%. On the other hand, when there are three peaks and the particle size ratio is 10: 2: 1 as described above, the gaps between the particles are filled, and the filling rate is about 87%. As a result, the density of the common electrode layer 62 increases and the specific resistance decreases. That is, the density of the common electrode layer 62 is 87% or more of the bulk density of the metal used. FIG. 6 shows the density of the bulk (bulk material A), the density after firing (printing material B), and the printing material B relative to the bulk material A for the metal used as the material of the common electrode layer 62 (common electrode portion 66) described above. The ratio (B / A;%) is shown. For example, in the case of silver (Ag), the printing material B is 87.6% of the bulk material A, and in the case of aluminum (Al), it is 88.9%. Moreover, since the contact point of particle | grains increases, a specific resistance can be made small also from this viewpoint. Moreover, if the number of contact points increases, the firing temperature can be lowered. For example, in the case of a conductive paste whose main component is silver (Ag), a firing temperature of 650 ° C. or higher is generally required, but by using such a conductive paste, from 550 ° C. to 600 ° C. Can be reduced.

  Moreover, since the filling rate is large, the shrinkage rate of the common electrode layer 62 in the firing process is small. In general, when the shrinkage rate is large, the formed common electrode layer 62 tends to be peeled off. Therefore, the common electrode layer 62 is hardly peeled off by reducing the shrinkage rate. In addition, if the shrinkage is large, the unevenness of the fired surface is increased, and the unevenness of the common conductive layer 64a and the protective layer 58 formed thereon is also increased. As a result, the printed surface may be damaged during printing. . However, by reducing the shrinkage rate, it is possible to reduce such irregularities and prevent the printed surface from being damaged during printing.

  An experiment was conducted to confirm the effect of the thermal head with the above configuration, and the results are shown below. Silver (Ag) was used as the metal of the conductive paste. Further, the particle diameter is a median diameter (D50), and there are three types: paste A: 2.0 μm, paste B: 0.4 μm, and paste C: 0.2 μm. Sample 1 was made of only paste A. For sample 2, a material in which paste A and paste B were mixed at a ratio of 1: 4 was used. For sample 3, a material in which paste A, paste B, and paste C were mixed at a ratio of 1: 4: 2 was used.

FIG. 7 is a diagram showing the results of measuring the density of the common electrode layer 62 after firing for the materials of Samples 1 to 3 described above. The case of sample 1 is 9.1 g / cm ³ , the case of sample 2 is 9.6 g / cm ³ , and sample 3 is 10.1 g / cm ³ . Sample 3 has increased to about 110% of sample 1.

  FIG. 8 is a diagram showing the results of measuring the shrinkage rate of the common electrode layer 62 during firing for the materials of Samples 1 to 3 described above. Sample 1 has a shrinkage of 46.5%, sample 2 has a shrinkage of 24.6%, and sample 3 has a shrinkage of 19.9%. That is, the shrinkage rate of sample 2 is reduced to about 53% as compared with sample 1, and further, that of sample 3 is reduced to about 43%.

  FIG. 9 is a diagram showing the results of measuring the specific resistance of the fired common electrode layer 62 for the materials of Samples 1 to 3 described above. The sample 1 is 8.2 μΩ · cm, the sample 2 is 2.9 μΩ · cm, and the sample 3 is 2.5 μΩ · cm. That is, the specific resistance of sample 2 is reduced to about 35% as compared with sample 1, and further, that of sample 3 is reduced to about 30%.

  Although not shown, the firing temperature of the common electrode layer 62 could be set to 650 ° C. for the sample 1, 570 ° C. for the sample 2, and 550 ° C. for the sample 3. That is, when a conductive paste having a plurality of peaks in the particle size distribution as in the sample 3 is used, energy input to the formation of the common electrode layer 62 can be suppressed.

  Moreover, FIG. 10 is a figure which shows the result of having measured the specific resistance using the material which made the particle size distribution of the metal (silver Ag) in an electrically conductive paste have two peaks. Here, the specific resistance was measured while the ratio value of the large particle size (A particle size) was fixed to “10” and the small particle size (B particle size) was changed from 0.5 to 5. As shown in the figure, the specific resistance is approximately 3 mΩ · cm when the B particle size is 1.5, 2.0, or 2.5. Therefore, when using a conductive paste having two peaks in particle size, the ratio of A particle size to B particle size is preferably 10: (2 ± 0.5) and should be 10: 2. More preferred.

  FIG. 11 is a diagram showing the results of measuring the specific resistance using a material having three peaks in the particle size distribution of the metal (silver Ag) in the conductive paste. Here, the ratio value of the largest particle size (A particle size) is “10”, the ratio value of the intermediate particle size (B particle size) is “2”, and the smallest particle size (C particle size) The specific resistance was measured by changing the ratio value from 0.25 to 4. As shown in the figure, the lowest measurement result is shown when the value of the C particle size ratio is 1, and when the value is 0.75 to 1.5, the specific resistance is 3 mΩ · cm or less.

  FIG. 12 is a table showing the measurement results of the particle size distribution of the fired metal (silver Ag). FIG. 12A shows the measurement results for the material having three peaks, and FIG. 12B shows the measurement results for the material having two peaks. As the measurement conditions, the firing temperature is three conditions of 500 ° C., 550 ° C., and 600 ° C. And the value of the largest particle size (particle size A) is set to “10”, and the ratio of particle size A: particle size B: particle size C is obtained. In addition, the particle size distribution before firing is 10: 2: 1 in the measurement of FIG. 12A and 10: 2 in the measurement of FIG. In addition, the number in the parenthesis in the table | surface has shown the magnitude | size on the basis of the particle size before baking. As a particle size measurement method, the particle size distribution before firing was measured by a light scattering particle size measurement method, and the particle size distribution after firing was measured by calculating the particle size from a two-dimensional image of a sectional view.

  As shown in the measurement results, when a material having three peaks with a particle size ratio before firing of 10: 2: 1 is used, the particle size ratio after firing is 10: (2.55 ± 0.35). : (1.75 ± 0.15). When a material having two peaks with a particle size ratio before firing of 10: 2 is used, the particle size ratio after firing is 10: (2.35 ± 0.17). Furthermore, in any material, the ratio of the particle diameters B and C having a smaller particle diameter increases as the firing temperature increases. That is, the smaller the particle size, the easier it is to aggregate, and the particle size tends to increase by firing.

  As described above, according to the present embodiment, a thermal head having a desired quality can be realized as described above even when the electrode layer is formed using the screen printing method. Moreover, the input energy at the time of electrode formation using a screen printing method can be reduced.

  The present invention can be widely used for a thermal head mounted on various types of printers for business use and consumer use, and a printing apparatus equipped with the thermal head.

1 is a schematic diagram of a rewrite printer according to an embodiment of the present invention. 1 is a block diagram showing a main configuration of a rewrite printer according to an embodiment of the present invention. It is the figure which showed typically the cross-section of the thermal head for printing. It is a figure which shows the manufacturing process of the thermal head for printing. It is the conceptual diagram which showed the filling state of the metal particle in an electrode layer. About the metal used as the material of the common electrode layer (common electrode portion), the density of the bulk (bulk material A), the density after firing (printing material B), and the ratio of the printing material B to the bulk material A (B / A;%) ). It is a figure which shows the result of having measured the density of the electrode layer after baking about the material of samples 1-3. It is a figure which shows the result of having measured the shrinkage rate of the electrode layer at the time of baking about the material of samples 1-3. It is a figure which shows the result of having measured the specific resistance of the electrode layer after baking about the material of the above-mentioned samples 1-3. It is a figure which shows the result of having measured the specific resistance using the material which made the particle size distribution of the metal (silver Ag) in an electrically conductive paste have two peaks. It is a figure which shows the result of having measured the specific resistance using the material which made the particle size distribution of the metal (silver Ag) in an electrically conductive paste have three peaks. It is a figure which shows the table | surface of the result of having measured the ratio of the particle size distribution of the metal (silver Ag) in the electrode layer before and behind baking.

Explanation of symbols

10 ... Rewrite printer (printing device)
50 ... Erase head (thermal head)
52 ... Heating resistor 54 ... Heat storage layer (glaze layer)
56 ... Substrate 58 ... Protective layer 62 ... Common electrode layer 64 ... Conductive layer 64a ... Common conductive layer 64b ... Lead conductive layer 66 ... Common electrode part 70 ... Printing Thermal head (thermal head)
72 ... Heating resistor

Claims (10)

  A thermal head comprising an electrode formed by a screen printing method using a conductive paste having a plurality of peaks in a particle size distribution of a main component metal.   The thermal head according to claim 1, wherein the plurality of peaks are three.   The thermal head according to claim 2, wherein a ratio of the particle diameters of the three peaks after firing is 10: (2.55 ± 0.35) :( 1.75 ± 0.15).   4. The thermal head according to claim 1, wherein the maximum diameter of the three peaks is in a range of 1.5 μm to 4.0 μm.   The thermal head according to any one of claims 1 to 4, wherein a particle diameter of the metal in the conductive paste after firing is 4.0 µm or less.   The thermal head according to any one of claims 1 to 5, wherein the density of the electrode after the firing is 87% or more of a bulk density of a metal to be used.   A printing apparatus comprising the thermal head according to claim 1.   A method of manufacturing a thermal head, comprising an electrode forming step of forming an electrode by a screen printing method using a conductive paste having a plurality of peaks in a particle size distribution of a main component metal.   The method for manufacturing a thermal head according to claim 8, wherein the firing step in the screen printing method is 600 ° C. or less.   A thermal head manufactured by the manufacturing method according to claim 8.

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