Thermal head

Abstract

To improve heat storage performance to high-speed driving and improve disconnection of a wiring pattern in a thermal head that is provided in a printer or the like.SOLUTION: The thermal head comprises: a substrate (12); a heat storage layer (14) formed on a main surface (13) of the substrate (12); a heat-generation resistive element layer (15) formed on the heat storage layer (14); an electrode layer (16) formed on the heat-generation resistive element layer (15) and supplies a current to the heat-generation resistive element layer (15); and a protective coating layer (17) formed to coat the heat-generation resistive element layer (15) and the electrode layer (16). The substrate (12) is formed of ceramics, and the main surface (13) has a flat surface part (13a) and an inclined surface part (13b) inclined downward from the flat surface (13a). The heat storage layer (14) has a first heat storage layer part (14a) on the flat surface part (13a) and a second heat storage layer part (14b) on the inclined surface part (13b). A vertical thickness (tc) of the second heat storage layer part (14b) is two times or more and six times or less of a thickness (tb) of the first heat storage layer part (14a).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] An embodiment of the present invention relates to a thermal head which is an image forming device. [Background technology]

[0002] Thermal heads are used as the main device that constitutes thermal recording devices in printers, plate-making machines, etc. This device is used, for example, as a key component in mini printers that are seen for outputting receipts, tickets on trains, and gas meter reading results, as well as in photo and image output devices such as Purikura.

[0003] Generally, in this type of thermal head, the heat generating parts of the heat generating resistor layer are arranged in parallel in a direction (main scanning direction) perpendicular to the direction (sub-scanning direction) in which a recording medium such as thermal paper is transported, and a plurality of driving ICs for driving the heat generating parts are arranged near the heat generating parts. The heat generating parts and the driving ICs are electrically connected by, for example, a circuit pattern provided on a wiring board. The driving ICs are used to supply electricity to the electrodes and the heat generating parts of the heat generating resistor layer, causing the heat generating parts to heat up and record on various media.

[0004] In recent years, it has been attracting particular attention in the thermal transfer printing (TTO) field, where date codes (such as expiration date / production lot) are printed on food packaging materials.

[0005] The thermal head is constructed by forming a glaze layer as a heat storage layer on a ceramic base such as alumina as a support substrate, on which a heating resistor layer and an electrode layer such as aluminum are laminated by a forming method such as sputtering or printing. Then, by photolithography, multiple pairs of heating resistor layers are formed in line with the heating parts and electrodes. Furthermore, a protective coating layer is formed on the necessary parts of the heating resistor layer and the electrode layer by a thin film forming method such as sputtering.

[0006] A technical challenge for the thermal head for thermal transfer applications is to print information at high speed and accurately. For this reason, in a thermal head that utilizes heat generated from a heating resistor layer, it is necessary to take into consideration the influence of a heat storage layer.

[0007] A feature of a thermal head is that it is a device that utilizes heat generated from the heat generating parts of the heating resistor layer, and is therefore heavily affected by the heat storage layer below the heating resistor layer. The role of the heat storage layer is to utilize the heat from the heat generating parts of the heating resistor layer and efficiently promote heating of the next printing point. However, conversely, if the heat does not decrease, the heat from the previous printing point will be carried over to the next printing point, causing trailing and bleeding during printing, so it is necessary to simultaneously satisfy the conflicting requirements of moderate heat storage and rapid heat reduction.

[0008] Therefore, various developments have been made for the structure of the heat storage layer depending on the application of the thermal head. The main glaze structures are a full glaze structure in which a glaze layer is placed on the entire main surface of the substrate, and a partial glaze structure in which a glaze layer is placed only directly below the heating resistor layer or in areas where flatness is required, and these structures are used depending on the application. Furthermore, there are also cases where a glaze layer is first placed on the entire surface, and then a glaze layer is placed only partially directly below the heating resistor layer.

[0009] In the case of a thermal head system in which the heating time of each heating resistor layer is controlled from the heating history, in order to minimize the effect of the heating history of the heating resistor layer and realize high-speed driving, an element of hot peeling, in which the medium such as paper is instantly peeled off after printing, is also required. Therefore, the shape of the path of the medium must also be taken into consideration. In response to these requirements, the thermal heads disclosed in Patent Documents 1, 2 and 3 have a shape in which the main surface of the base on which the heat storage layer is arranged has a partially inclined surface. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 4-83652 [Patent Document 2] JP 2015-157448 A [Patent Document 3] JP 2016-7837 A Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, even in a thermal head having a substrate with a partially inclined surface, the substrate surface on which the wiring pattern is disposed is required to be smooth in order to prevent breakage due to corrosion or the like of the wiring pattern, which determines the life of the thermal head.

[0012] Furthermore, in order to prevent the wiring pattern from being physically broken, it is necessary to eliminate the occurrence of edges on the base, and in order to cover the boundary (bend) where the flat portion transitions to the sloping portion, a continuous heat storage layer is required from the flat portion to the sloping portion.

[0013] Furthermore, regarding the effect of heat storage, the thickness of the heat storage layer on the sloped surface where the heating resistor layer is formed becomes an issue.

[0014] Regarding these requirements, as described above, the flat surface of the substrate requires a heat storage layer thickness that allows minimum smoothness to be obtained in order to form a wiring pattern. Also, the inclined surface requires a heat storage layer thickness required for the thermal head's function of retaining and storing heat under high-speed operation. In other words, the thicknesses of these layers need to be optimized.

[0015] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a highly reliable and high-quality thermal head by ensuring the smoothness of the flat surface of a ceramic base and optimizing the heat accumulation effect of the inclined surface. [Means for solving the problem]

[0016] In order to solve the above problem, the thermal head of the present invention is a thermal head comprising a base, a heat storage layer formed on a main surface of the base, a heating resistor layer formed on the heat storage layer, an electrode layer formed on the heating resistor layer and supplying current to the heating resistor layer, and a protective coating layer formed to cover at least the heating resistor layer and the electrode layer, wherein the base is formed of ceramic, the main surface of the base has a flat portion and a slope portion sloping downward from the flat portion, the heat storage layer is formed continuously from a first heat storage layer portion on the flat portion to a second heat storage layer portion on the slope portion, and the vertical thickness of the second heat storage layer portion is at least two times and at most six times the thickness of the first heat storage layer portion.

[0017] Another invention is a thermal head including a heat storage layer formed on a main surface of the base, a heating resistor layer formed on the heat storage layer, an electrode layer formed on the heating resistor layer and supplying a current to the heating resistor layer, and a protective coating layer formed to cover at least the heating resistor layer and the electrode layer, the base is made of ceramic, the main surface of the base has a flat surface portion and a slope portion sloping downward from the flat surface portion, the heat storage layer has a first heat storage layer portion on the flat surface portion and a second heat storage layer portion on the slope portion, and the first heat storage layer portion and the second heat storage layer portion are formed continuously from the flat surface portion to the slope portion. In this configuration, preferably, the boundary portion between the flat surface portion and the slope portion is subjected to a rounded R chamfering process.

[0018] Furthermore, in any of the above configurations, the inclination angle of the inclined surface portion with respect to the flat surface portion is preferably set to an angle in the range of 25 degrees to 45 degrees. Effect of the Invention

[0019] According to the present invention, the main surface of the thermal head base has a flat portion and an inclined portion, and the vertical thickness of the second heat storage layer portion formed on the inclined portion is set to be at least two times and at most six times the thickness of the first heat storage layer portion formed on the flat portion, thereby making it possible to improve heat storage properties for high-speed driving.

[0020] In addition, the first and second heat storage layers are formed continuously from the flat surface to the inclined surface, and the boundary is rounded, which reduces the occurrence of breaks in the wiring pattern at the boundary.

[0021] Furthermore, by setting the downward inclination angle of the inclined surface portion relative to the flat surface portion to an angle of 25 degrees or more and 45 degrees or less, the hot peelability is improved, making it possible to improve the hot peelability of the thermal head. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic vertical cross-sectional view of a printing portion of a thermal head printer equipped with a thermal head according to an embodiment of the present invention. [Diagram 2] 3 is an enlarged view of the thermal head of FIG. 1 (an enlarged cross-sectional view taken along line II-II of FIG. 3). [Diagram 3] 3 is a partial plan view showing a part of the thermal head in FIG. 2 with a part cut away. [Figure 4] 3 is an enlarged vertical cross-sectional view of the vicinity of a heat generating portion of the thermal head of FIG. 2. [Diagram 5] 4 is an enlarged vertical cross-sectional view of the vicinity of the boundary between the inclined surface portion and the flat surface portion of the base body. FIG. [Figure 6] FIG. 2 is a cross-sectional view of the base body and the heat storage layer, with hatching omitted in order to clarify the measurement points of the dimensions of the base body and the heat storage layer. [Figure 7] Table 1 shows a list of 30 types of thermal head test samples with different manufacturing conditions. [Figure 8] Table 2 shows a list of the test specimens in Table 1 that were subjected to the high temperature and high humidity test, as well as the rate of corrosion. [Figure 9] Table 3 shows a list of the test specimens in Table 1 that were subjected to the running test and whether or not there was electrode breakage. [Figure 10] Table 4 shows a list of the test samples in Table 1 that were subjected to the patterning accuracy test, along with the results of the evaluation of the clarity of the line width. [Figure 11]Table 5 shows a list of the test samples in Table 1 that were subjected to the heat storage effect test, and the time it took for the heating resistor to drop from its peak temperature to 100°C. [Figure 12] 13 is a graph showing temperature changes at the time of input as a test method for verifying the heat storage effect in Table 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] [Embodiments of the present invention] 1 to 6 show an embodiment of the present invention, and the thermal head will be described based on these drawings.

[0024] FIG. 1 is a schematic vertical cross-sectional view of a printing portion of a thermal head printer 1 equipped with a thermal head 10, with the arrow Y indicating the paper transport direction of thermal paper (medium) 5. In FIG. 1, a platen roller 3 and a thermal head 10 are disposed substantially vertically facing each other near the paper outlet 1a of the thermal head printer 1. The platen roller 3 is cylindrical and rotates in the direction of arrow R about a rotation axis 3a extending in a direction perpendicular to the paper transport direction Y. The thermal head 10 has a number of heat generating parts G at its end downstream of the paper transport direction Y. The end downstream of the thermal head 10 in the paper transport direction Y is biased toward the platen roller 3 by a biasing means such as a spring (not shown). This causes the heat generating parts G to be pressed against the outer circumferential surface of the platen roller 3. Thermal paper 5 is supplied from a paper feeder (not shown) between the outer circumferential surface of the platen roller 3 and the heat generating parts G, and thermally printed by the heat of the heat generating parts G.

[0025] Fig. 2 is an enlarged vertical cross-sectional view of the thermal head 10. In Fig. 2, the thermal head 10 is configured to include a heat sink 11, a base 12 fixed onto the heat sink 11 with an adhesive, a heat storage layer 14 formed on a main surface 13 of the base 12, a heating resistor layer 15 covering the upper surface of the heat storage layer 14, an electrode layer 16 formed on the upper surface of the heating resistor layer 15, and a protective coating layer 17 formed so as to cover the upper surface of the electrode layer 16. The "main surface 13" of the base 12 refers to the surface (treatment surface) on which a laminate or the like is mounted.

[0026] The thermal head 10 is equipped with a circuit board 18 fixed to a step surface 11a formed on the upstream portion of the heat sink 11 in the paper transport direction Y, a drive IC 20 provided on the downstream portion of the circuit board 18 in the paper transport direction Y, a wiring pattern 21 formed on the circuit board 18, and a connector 23 provided at the upstream end of the circuit board 18 in the paper transport direction Y.

[0027] The driving IC 20 is electrically connected to an upstream end of the electrode layer 16 in the paper transport direction Y by a bonding wire 31, and is also electrically connected to the wiring pattern 21 by another bonding wire 32. The driving IC 20 and both bonding wires 31 and 32 are sealed with sealing resin 24 and protected from the outside.

[0028] FIG. 3 is a plan view of the thermal head 10 with some members (protective coating layer 17) cut away. In FIG. 3, the direction of the arrow X perpendicular to the paper transport direction Y coincides with the main scanning direction of the thermal head 10, and the paper transport direction Y coincides with the sub-scanning direction. In FIG. 3, the electrode layer 16 includes a large number of individual electrodes 16a connected to the driving IC 20 and earth, and folded electrodes 16b that are U-shaped in plan view and face each individual electrode 17a with a distance d between them. A pair of adjacent individual electrodes 16a face both ends of one folded electrode 16b with a distance d between them. Note that the reference characters (numbers) of the individual electrodes 16a and the folded electrodes 16b are only given to some of the individual electrode layers 16a and the folded electrode layers 16b due to space limitations in the figure.

[0029] Of a pair of adjacent individual electrodes 16a connected to one folded electrode 16b, one is electrically connected to the driving IC 20 and the other is, for example, grounded (earthed). The portions corresponding to the intervals d between the heating resistors 15 on the lower side of the electrode layer 16 are the aforementioned heating portions G. Thus, a large number of heating portions G are arranged at predetermined intervals in the main scanning direction X.

[0030] Fig. 4 is an enlarged vertical cross-sectional view of the downstream portion of the thermal head 10 in the paper transport direction Y. In Fig. 4, the heat sink 11 is made of a metal with high thermal conductivity such as aluminum. The base 12 is made of a ceramic such as alumina, and is bonded to the upper surface of the heat sink 11 with a heat-resistant adhesive.

[0031] The main surface 13 of the base 12 has a flat portion 13a and an inclined portion 13b formed at an end portion on the downstream side in the paper transport direction Y. The inclined portion 13b is inclined downward with respect to the flat portion 13a.

[0032] The heat storage layer 14 formed on the main surface 13 is a heat insulating layer (glaze layer) containing glass (SiO2) as a main component, and is formed, for example, by firing a paste-like glaze material containing glass powder.

[0033] The heat storage layer 14 has a first heat storage layer 14a formed on the flat surface portion 13a and a second heat storage layer 14b formed on the inclined surface portion 13b. The first heat storage layer 14a and the second heat storage layer 14b are formed continuously. In particular, on the boundary portion 13c between the flat surface portion 13a and the inclined surface portion 13b, the surface of the first heat storage layer 14a and the surface of the second heat storage layer 14b are formed smoothly and continuously without any steps.

[0034] The surface of the first heat storage layer 14a is formed substantially parallel to the surface of the flat portion 13a over substantially the entire width in the paper transport direction Y. On the other hand, the surface of the second heat storage layer 14b is formed in a convex or mountain shape with respect to the inclined portion 14b.

[0035] The heating resistor layer 15 formed on the heat storage layer 14 is a cermet film containing a heating resistor material such as TaSiO, TaSiNO, NbSiO, or TiSiCO, and is laminated on the upper surface of the heat storage layer 14 by sputtering.

[0036] The individual electrode 16a and the folded electrode 16b face each other with a distance d in between near the top of the second heat storage layer portion 14b, and as described above, the portion of the heating resistor layer 15 corresponding to the distance d constitutes the heating portion G. When a voltage is applied between the individual electrode 16a and the folded electrode 16b, a current flows through the heating portion G in the region corresponding to the distance d, generating heat.

[0037] Fig. 5 is an enlarged vertical cross-sectional view of the inclined surface portion 13b and its vicinity of the base body 12. In Fig. 5, the boundary portion 13c between the flat portion 13a and the inclined surface portion 13b is subjected to R-surface processing. That is, the boundary portion 13c is formed into an arc shape over the width W by grinding or polishing, thereby removing the edge. The downward inclination angle θ of the inclined surface portion 13b with respect to the flat portion 13a is set to an angle in the range of 25 degrees to 45 degrees.

[0038] 6 is a cross-sectional view of the base 12 and the heat storage layer 14, with hatching omitted, in order to clarify the measurement points of the dimensions of the base 12 and the heat storage layer 14. For use in the examples described later, the thickness of the base 12 is represented as ta, the thickness of the first heat storage layer portion 14a as tb, and the vertical thickness (approximately the maximum thickness) of the second heat storage layer portion 14b as tc.

[0039] In this embodiment, in order to improve the heat storage effect, the vertical thickness (approximate maximum thickness) tc of the second heat storage layer portion 14b is set in the range of 2 to 6 times the thickness tb of the first heat storage layer portion 14a.

[0040] [Examples of the present invention, comparative examples, and quality evaluation tests] (Production of test specimens) Table 1 in Fig. 7 shows a list of test samples of thermal head substrates prepared under various conditions for various quality evaluation tests. Specifically, the table shows 30 test samples No. 1 to No. 30 prepared by combining various combinations of the inclination angle θ of the inclined surface portion 13b of the thermal head 10, the thickness ta of the base body 12, the thickness tb of the first heat storage layer portion 14a on the flat surface portion 13a, the vertical thickness tc of the second heat storage layer portion 14b on the inclined surface portion 14b, and the presence or absence of R-chamfering of the boundary portion (bend portion) 13c. First, the method of preparing these 30 test samples will be described.

[0041] Referring to FIG. 6, the substrate 12 was made of a ceramic material, and the thickness ta of the substrate 12 was 2.0 mm.

[0042] In order to form the inclined surface portion 13b on the main surface 13 of the substrate 12, grooves were formed by bevel cutting with a blade having clearance angles of 25 degrees, 30 degrees, and 45 degrees. As a result, an inclined surface was formed in which the inclination angle of the blade cut portion was in the range of 25 degrees to 45 degrees. That is, the inclined surface portion 13b was formed with a downward inclination angle θ of 25 degrees, 30 degrees, and 45 degrees. At the same time, for comparison, test pieces with an inclination angle θ of 0 degrees (No. 9 and No. 10 in Table 1), test pieces with an inclination angle θ of 10 degrees (No. 7 and No. 8 in Table 1), and test pieces with an inclination angle θ of 60 degrees (No. 11 and No. 12) were also prepared. Note that the above-mentioned test pieces with an inclination angle θ of 0 degrees (No. 9 and No. 10 in Table 1) are test pieces that have substantially no inclined surface portion and the entire main surface 13 is a flat surface portion 13a.

[0043] The boundary (bend) 13c between the flat portion 13a and the inclined portion 13b was previously chamfered with a polishing device, taking into consideration the effect on the electrode pattern to be made later. At the same time, for comparison, test pieces (No. 4, No. 5, and No. 6 in Table 1) were made in which the boundary 13c was not chamfered with R. Incidentally, for test pieces No. 9 and No. 10, the boundary 13c was not bent, so R-chamfering was not possible.

[0044] Thereafter, a glaze that would become the first heat storage layer portion 14a and the second heat storage layer portion 14b was placed on the main surface 13 of the base body 12, and sintered to form the glaze.

[0045] As the first heat storage layer 14a of the flat surface 13a, in order to pursue only smoothness, a thickness tb of 5.0 μm and a thickness of 10.0 μm with two layers were prepared so as to fill in the unevenness of the ceramic surface. Again, for comparison, test pieces (No. 1, No. 2, No. 3) in which the first heat storage layer 14a was not formed on the flat surface 13a were also prepared.

[0046] Regarding the second heat storage layer 14b of the inclined surface portion 13b, in the test sample in which the first heat storage layer 14a having a thickness of 5.0 μm or 10.0 μm was arranged on the flat surface portion 13a as described above, the second heat storage layer 14b was formed continuously from the first heat storage layer 14a and formed in a mountain shape or a convex shape on the inclined surface portion 13b. In particular, the vertical thickness (approximate maximum thickness) tc with respect to the inclined surface portion 13b was formed in the range of 10.0 μm to 30.0 μm.

[0047] At this point, for test pieces No. 22, 23, and 24 in Table 1, the thickness tb of the first heat storage layer 14a on the flat surface 13a is 10.0 μm, while the vertical thickness tc of the second heat storage layer 14b on the inclined surface 13b is also 10.0 μm, so no convex portion can be formed. In other words, a heat storage layer 14 of uniform thickness (10.0 μm) is formed from the flat surface 13a to the inclined surface 13b. Therefore, since this is different from the aim of the main body, evaluation was postponed at this point.

[0048] Thermal heads were fabricated as follows using 30 types of prototype thermal head substrates No. 1 to No. 30 fabricated by the above-mentioned method.

[0049] Heat generating resistor layers 15 were formed in the same batch by sputtering, and then electrode layers 16 serving as wiring were laminated.

[0050] In this example, individual electrodes 16a and folded electrodes 16b are formed as a wiring pattern by photolithography as the electrode layer 16. It is also possible to form a single wiring pattern in which a common electrode is arranged in place of the folded electrodes 16b.

[0051] After forming the wiring pattern of the electrode layer 16, a protective covering layer 17 was formed to protect the electrode layer 16, thus completing the thermal head substrate.

[0052] Following this, as shown in FIG. 2, the heat sink 11 and the circuit board 18 were joined together, the driving IC 20 was disposed, and electrical connections were made with bonding wires 31 and 32, etc., to complete the thermal head.

[0053] The thermal heads manufactured were all unified as 12 dpm (dots / mm) 6 inch long thermal heads.

[0054] (Example 1: High temperature and high humidity test) Table 2 shows the corrosion occurrence rate of the electrode layer 16 as a result of the high temperature and high humidity test performed on 18 test pieces selected from the 30 test pieces in Table 1. The 18 test pieces selected are No. 1 to No. 3, No. 13 to No. 21, and No. 25 to No. 30. That is, three levels of test pieces No. 1 to No. 3 that do not have the first heat storage layer 14a on the flat portion 13a, and 15 levels of test pieces No. 13 to No. 21 and No. 25 to No. 30 that have the first heat storage layer 14a on the flat portion 13a and examine the thickness ratio tc / tb of the first heat storage layer 14a and the second heat storage layer 14b were tested for each level, with 5 pieces as the base number.

[0055] The test conditions were that the sample was placed in a high-temperature, high-humidity furnace at 90° C. and 80% RH (relative humidity) for 500 hours, and the extent to which the electrode layer 16 was corroded by moisture was confirmed.

[0056] (Test Results of Example 1) The test results are examined with a focus on whether the first heat storage layer 14a is formed on the flat surface 13a. Corrosion occurred in all of the test pieces No. 1 to No. 3, which do not have the first heat storage layer 14a formed on the flat surface 13a. The occurrence rate of corrosion was 2 out of 5 pieces (2 / 5P) in No. 1, 1 out of 5 pieces (1 / 5P) in No. 2, and 3 out of 5 pieces (3 / 5P) in No. 3. The cause of corrosion was that the thin heating resistor layer 15 and electrode layer 16 were formed directly on the flat surface 13a of the main surface 13 of the ceramic base 12 without the first heat storage layer 14a in between. In other words, it is presumed that the uneven shape of the flat portion 13a of the main surface 13 of the base 12 was directly picked up by the heating resistor layer 15 and the electrode layer 16, which deteriorated the step coverage of the protective coating layer 17 formed subsequently, causing corrosion of the electrode layer 16.

[0057] On the other hand, when the first heat storage layer 14a was provided on the planar portion 13a, as in Nos. 13 to 21 and Nos. 25 to 30, if the thickness tb of the first heat storage layer 14a was 5.0 μm or more (5.0 μm and 10.0 μm in this case), no corrosion occurred within the test time of 500 hours.

[0058] (Example 2: Running test with and without R surface processing) Table 3 shows the test results of 18 test pieces selected from the 30 test pieces in Table 1 for the running test of the thermal paper 5, and indicates the presence or absence of breakage of the electrode layer 16. The 18 test pieces selected are test pieces No. 4 to No. 6, No. 13 to No. 21, and No. 25 to No. 30. That is, three test pieces No. 4 to No. 6 that do not have R surface processing on the boundary 13c between the flat portion 13a and the inclined portion 13b, and 15 test pieces No. 13 to No. 21 and No. 25 to No. 30 that have R surface processing on the boundary 13c were subjected to the running test, and the presence or absence of electrode breakage was compared.

[0059] The test method was to attach a thermal head having each of the selected test samples to a normal printer and continuously print up to 100 color patterns. During this time, the presence or absence of an open state in the print was checked to confirm the disconnection of the electrode layer 16 at the boundary 13c.

[0060] (Test Results of Example 2) In the test samples No. 4 to No. 6 in which the borders 13c were not chamfered, an open state of the color pattern, that is, a break in the electrode layer 14, was confirmed on the 32nd, 41st, and 72nd sheets.

[0061] On the other hand, in the test pieces No. 13 to No. 21 and No. 25 to No. 30 in which the boundary 13c was subjected to R surface processing, no open state of the color pattern, i.e., no break in the electrode layer 16, was observed up to 100 sheets, demonstrating the effect of preventing electrode breakage by the R surface processing at the boundary 13c.

[0062] (Example 3: Patterning accuracy test according to the inclination angle of the inclined surface portion 13b) Table 4 is a table in which the change in patterning accuracy due to the inclination angle θ of the inclined portion 13b was verified and judged for all 30 test pieces in Table 1. The patterning was performed using photoetching. The test results were judged to be good if the error was within ±10 μm for a line width of 85 μm created at 12 dpm (dots per mm). The line width was measured using a microscope capable of micrometry. The inclination angles θ of the inclined portion 13b were 0 degrees, 10 degrees, 25 degrees, 30 degrees, 45 degrees, and 60 degrees.

[0063] (Test Results from Example 3) Although it depends on the accuracy of the exposure device that controls the patterning, the aspect ratio (height / width) of the inclined surface portion 13b and the flat surface portion 13a increases with an increase in the inclination angle θ, but it was possible to obtain the targeted line width when the inclination angle θ was up to 45 degrees. However, as in the case of test samples No. 11 and No. 12, when the inclination angle θ was 60 degrees or more, the aspect ratio was affected and the targeted accuracy could not be obtained. In other words, the line width became too large.

[0064] (Example 4: Tests on heat accumulation effect and peeling under heat) Table 5 shows 19 test pieces extracted from the 30 test pieces in Table 1 for testing the heat storage effect and peeling under heat. The test results show the time it takes for the heating resistor layer 15 to drop from its peak temperature to 100°C.

[0065] As mentioned above, for Nos. 22, 23, and 24 in Table 1, the thickness tb of the first heat storage layer 14a of the flat portion 13a and the thickness tc of the second heat storage layer 14b of the inclined portion 13b are the same, so no convex or mountain-like shape can be formed on the inclined portion 13b, and so they were not included in the extracted test samples.In addition, in each test of Examples 1 to 3, test samples Nos. 1 to 3 (NG moisture resistance), test samples Nos. 4 to 6 (electrode break at the boundary portion), and test samples Nos. 11 and 12 (poor patterning accuracy) did not meet the evaluation criteria, and were not included in the extracted test samples. That is, for test pieces No. 7 to No. 10, No. 13 to No. 21, and No. 25 to No. 30, the thickness tc of the second heat storage layer portion 14b, the thickness tb of the first heat storage layer portion 14a, the ratio thereof tc / tb, and the inclination angle θ of the inclined portion 13b were taken into consideration in order to verify the heat storage effect and peeling under heat.

[0066] The test method was to measure the heat generation temperature when maximum power was applied using the specifications of a commercially available inclined printer, and measure the time it took for the temperature to drop from the peak temperature (approximately 360°C) to 100°C. This was quantified as the heat accumulation effect, and the hot peeling time of 3.0 ms required for high-speed operation was used as the judgment criterion (see graph in Figure 12).

[0067] (Test Results of Example 4) In the test pieces No. 8 and No. 9, in which the inclination angle θ of the inclined portion 13b was 0 degrees, i.e., test pieces that had no inclined portion at all, the drop times were 4.5 ms and 4.8 ms, which were significantly longer than the standard hot peel time of 3.0 ms. In the test pieces No. 7 and No. 8, in which the inclination angle θ of the inclined portion 13b was 10 degrees, the drop times were 3.8 ms and 3.7 ms, which were also longer than the standard hot peel time of 3.0 ms.

[0068] Therefore, it was verified that, in terms of hot peelability, when the inclination angle θ of the inclined portion 13b relative to the flat portion 13a is in the range of 25 degrees or more and 45 degrees or less, and the ratio tc / tb of the thickness tc of the second heat storage layer portion 14b to the thickness tb of the first heat storage layer portion 14a is in the range of 2 or more and 6 or less, the film has good hot peelability.

[0069] (Summary of Examples) From the verification results of Examples 1 to 4, the following became clear.

[0070] From the viewpoint of moisture resistance, it is necessary to interpose the first heat storage layer 14a on the flat surface 13a. Furthermore, the results of the running test showed that the boundary (bend) 13c between the flat surface 13a and the inclined surface 13b needs to be rounded with a chamfered R-shape, and the first heat storage layer 14a and the second heat storage layer 14b need to be continuous so as to cover the boundary 13c.

[0071] Furthermore, for the base 12 having the inclined portion 13b, it was verified that a precise wiring pattern (electrode layer 16) can be formed with high accuracy when the inclination angle θ of the inclined portion 13b with respect to the flat portion 13a is in the range of 25 degrees or more and 45 degrees or less, and that taking into account the influence of heat storage, it is appropriate that the thickness tc of the second heat storage layer portion 14b of the inclined portion 13b is 2 times or more and 6 times or less the thickness tb of the first heat storage layer portion 14a of the flat portion 13a.

[0072] As described above, according to the embodiment of the present application, the main surface 13 of the base 12 of the thermal head 10 is shaped to have a flat portion 13a and an inclined portion 13b, and the vertical thickness tc of the second heat storage layer portion 14b formed on the inclined portion 13b is set to be between two and six times the thickness tb of the first heat storage layer portion 14a formed on the flat portion 13a, thereby improving the heat storage properties during high-speed operation.

[0073] In addition, the first heat storage layer portion 14a and the second heat storage layer portion 14b are formed continuously from the flat portion 13a to the inclined portion 13b, and the boundary portion (bend portion) 13c between the flat portion 13a and the inclined portion 13b is subjected to rounded R-chamfering, so that when forming the wiring pattern of the electrode layer 16, pattern breakage from the flat portion 13a to the inclined portion 13b can be improved.

[0074] Furthermore, the hot peelability could be improved by forming the downward inclination angle θ of the inclined surface portion 13b with respect to the flat surface portion 13a to be in the range of 25 degrees to 45 degrees.

[0075] [Other embodiments] (1) Instead of providing the electrode layer with an individual electrode and a folded electrode, a structure having an individual electrode and a common electrode may be used as already described.

[0076] Although several embodiments of the present invention have been described, the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0077] 1 Thermal head printer 5 Thermal Paper 10 Thermal head 12 Base 13 Main surface 13a Flat part 13b Slope section 13c Boundary part (bending part) 14 Heat storage layer 14a first heat storage layer 14b Second heat storage layer 15 Heating resistor layer 16 Electrode layer 16a Individual electrode 16b Folded electrode 17 Protective coating layer 20 Driver IC G Heating part ta: thickness of the substrate 13 tb Thickness of the first heat storage layer 14a tc Thickness of the second heat storage layer portion 14b θ Tilt angle

Claims

1. A substrate; A heat storage layer formed on a main surface of the base body; a heating resistor layer formed on the heat storage layer; an electrode layer formed on the heating resistor layer and supplying a current to the heating resistor layer; a protective covering layer formed to cover at least the heating resistor layer and the electrode layer, A thermal head, wherein the main surface of the base has a flat portion and an inclined portion sloping downward from the flat portion.

2. 2. The thermal head according to claim 1, wherein said heat storage layer has a first heat storage layer portion on said flat surface portion and a second heat storage layer portion on said inclined surface portion.

3. 3. The thermal head according to claim 2, wherein the second heat storage layer has a vertical thickness that is at least two times but not more than six times the thickness of the first heat storage layer.

4. The substrate is made of a ceramic, 4. The thermal head according to claim 2, wherein the first heat storage layer and the second heat storage layer are formed continuously from the flat surface portion to the inclined surface portion.

5. 3. The thermal head according to claim 1, wherein a boundary between the flat surface portion and the inclined surface portion is subjected to a rounded R-chamfering process.

6. 3. The thermal head according to claim 1, wherein an inclination angle of the downward inclination of the inclined surface portion with respect to the flat surface portion is set to be equal to or greater than 25 degrees and equal to or less than 45 degrees.

7. 3. The thermal head according to claim 1, wherein the substrate is made of ceramic.

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