Thermal printing head and system including the same

Abstract: The present invention provides a thermal head including a substrate of alumina, a glaze layer formed on the substrate and patterning resistor and electrode layers on the glaze layer. The thermal head is of a whole glaze type in which a heating section is formed on the glaze layer at or adjacent to the edge portion thereof or of a partial glaze type in which a heating section is formed on the glaze layer at or adjacent to its partially cut edge portion. Thus, the thermal head can print more clearly.

Description: The present invention relates to a thermal printer head with an improved efficiency. Thermal heads are classified into partial-glaze type, double-partial-glaze type and through-edge type. As shown in Fig. 20, the partial-glaze type thermal head comprises a substrate 1, a partial glaze layer 2 formed on the substrate adjacent to its edge portion, having a width equal to about 300µ - 1200µ and an outwardly convex configuration, a resistive film layer 3 formed over the partial glaze layer 2, common and individual electrodes 5 and 6 formed on the resistive film layer 3 at the top positions of the glaze layer 2 opposite to each other to form a heating section 4 on the top of the glaze layer 2 and a protecting film 7 covering these layers as a whole. The double-partial-glaze type thermal head is similar to the partial-glaze type thermal head except that a portion of the glaze layer 2 placed at the heating section 4 is formed into an upwardly convex configuration by glaze etching or the like, as shown by 2a in Fig. 21. The through-edge type thermal head is one that has the glaze layer 2 and the heating section 4 formed so as to cover the edge of the substrate 1, as shown in Fig. 22. Fig. 23 shows a modification of the thermal head shown in Fig. 22, in which the edge portion of the substrate 1 is slantingly cut to provide a slope 1 B adjoining the top face 1 A of the substrate 1 and an edge face 1 C adjoining the slope 1 B and extending perpendicular to the top face 1 A . Glaze layers 2 A , 2 B and 2 C are formed over the respective faces 1 A , 1 B and 1 C . The heating section 4 is formed at the slope 1 B . In order to enable the printing of any rough sheet and to improve the efficiency of the thermal head, it is necessary to focus pressure onto the ink ribbon, transfer sheet and platen at the heating section. In the partial-glaze and double-partial-glaze type thermal heads, however, the engagement of the glaze layer 2 with the rubber platen 10 through the ink ribbon 8 and transfer sheet 9 at the heating section 4 will be widened and so not provide a sufficient concentration of pressure at the heating section 4, as seen from Fig. 24. Such a problem can be somewhat overcome by the through-edge type thermal head. At present, however, the through-edge type thermal head of Fig. 22 must include a substrate having a thickness equal to about 2 mm, so that the inherent advantages of the through-edge type thermal head will not be fully attained. Being common to the production of the conventional thermal heads, a substrate for each individual thermal head must be machined at its side edge before film formation and patterning are performed. Thus, a number of thermal heads cannot be produced from a single large-sized substrate. When it is desired to provide a thermal head in which the efficiency is improved by focusing pressure onto the heating section, the production becomes troublesome and expensive, leading to an increase in the cost for one thermal head. Both JP-A-62111764 and JP-A-1257064 disclose a thermal head comprising (a) a substrate having a substantially planar upper surface and an edge; (b) a glaze layer formed to cover said upper surface of said substrate adjacent said edge; (c) a resistive film formed on said glaze layer; (d) an electrode pattern formed on said resistive film; and (e) a heating section formed between said electrode pattern to perform printing in a thermal transfer manner when said electrode pattern is supplied with an electrical current. It is therefore an object of one embodiment of the present invention to provide a thermal head which can be inexpensively produced with an increased concentration of pressure at the heating section and thus with an improved printing efficiency. An object of another embodiment of the present invention is to provide a thermal head which is improved in efficiency and can be excellently separated from the ink ribbon. An object of another embodiment of the present invention is to provide a thermal head which is improved in efficiency and where the patterning process is simplified. An object of a further embodiment of the present invention is to provide a method of inexpensively producing a thermal head with an improved printing efficiency. The present invention provides a thermal head comprising (a) a substrate having a substantially planar upper surface and an edge; (b) a glaze layer formed to cover said upper surface of said substrate adjacent said edge; (c) a resistive film formed on said glaze layer; (d) an electrode pattern formed on said resistive film; and (e) a heating section formed between said electrode pattern to perform printing in a thermal transfer manner when said electrode pattern is supplied with an electrical current; characterised in that said glaze layer has a top face opposed said upper surface of said substrate and a sloping face formed between said top face and said edge by cutting said glaze layer such that the thickness of said glaze layer decreases towards said edge; a corner portion being formed at the intersection between said top face and said sloping face; and said heating section being formed on said corner portion or said sloping face. In this thermal head, the heating section is formed so as to cover the sloping face or the corner portion of the glaze layer. Therefore, pressure will not be unnecessarily dispersed to the portions of the glaze layer and substrate that are out of the heating section. The pressure will be fully focused onto the heating section during operation. The glaze substrate is half-cut such that the substrate will be moved directly to the subsequent step such as film formation or patterning without full division. Thus, thermal heads can be mass-produced with a reduction in the cost for one thermal head. Since most of the heating section in the thermal head is formed on the slope portion or on the corner portion, the distance between the heating section and the side edge face of the substrate is smaller which improves the separation of the ink ribbon from the heating section. The present invention also provides a method of producing a thermal head according to claim 1, which comprises the steps of: (a) forming a glaze layer on a substantially planar substrate; (b) cutting at least said glaze layer to form at least one groove having a substantially trapezoidal cross-section, the formation of said groove being adapted to form said sloping face between a top face of said glaze layer and the bottom of the groove; (c) forming a resistive film layer over said top and sloping faces and patterning a heating section by forming a pattern of electrode conductors on said resistive film layer; (d) forming a protective film to cover said resistive film layer not covered by said electrode conductors, said electrode conductors and a heating section formed between said electrode conductors; and (e) cutting said substrate adjacent said glaze layer in said groove formed at the step (b) to provide a plurality of thermal heads. In accordance with a method of one embodiment of the present invention, a plurality of thermal heads each of which can focus pressure onto the heating section to improve the efficiency on printing can be produced simultaneously by forming non-through half-cut grooves used to divide the substrate into a plurality of thermal heads and film-forming and patterning a heating section onto each of the sloping faces or corner portions formed by these grooves. A rounded corner portion can be formed to eliminate any creation of burr and/or cutout. Thus, the film forming and patterning steps may be easily made against the smoothed face of the thermal head and so form the hearing section into a stable configuration. In accordance with the method of the present invention, the grooves used to provide a plurality of thermal heads may be formed on the substrate to extend downwardly through the glaze layer and to have a trapezoidal or substantially trapezoidal cross-section. The corner of the glaze layer so formed may be rounded by heat treatment. A resistive film layer and electrode conductor are then formed and patterned on the corner portions or sloping faces of the glaze layer to form a heating section. A protecting film is then formed over the resistive film layer, electrode conductor and heating section. Finally, the substrate is in the grooves cut to provide a plurality of thermal heads. Examples of the present invention will now be described with reference to the drawings, in which:- Fig. 1 is an enlarged cross-sectional view of the primary part of a first embodiment of a thermal head constructed in accordance with the present invention. Fig. 2 is an enlarged cross-sectional view of the primary part of a second embodiment of a thermal head constructed in accordance with the present invention. Fig. 3 is an enlarged cross-sectional view of the primary part of a third embodiment of a thermal head constructed in accordance with the present invention. Fig. 4 is a view illustrating one step of a method for producing the thermal head of the third embodiment of the present invention. Fig. 5 is a view illustrating one step of a method for producing the thermal head of the third embodiment of the present invention. Fig. 6 is a view illustrating one step of a method for producing the thermal head of the third embodiment of the present invention. Fig. 7 is a view illustrating one step of a method for producing the thermal head of the third embodiment of the present invention. Fig. 8 is an enlarged cross-sectional view of the primary part of a fourth embodiment of a thermal head constructed in accordance with the present invention. Fig. 9 is a view illustrating the patterns of electrode and resistive film in the thermal head which is the fourth embodiment of the present invention. Fig. 10 is a view illustrating the patterns of electrode and resistive film in a modification of the fourth embodiment of the present invention. Fig. 11 is an enlarged cross-sectional view of the modification of the fourth embodiment of the present invention. Fig. 12 is a view illustrating one step of a method for producing the thermal head of the fourth embodiment of the present invention. Fig. 13 is a view illustrating one step of a method for producing the thermal head of the fourth embodiment of the present invention. Fig. 14 is a view illustrating one step of a method for producing the thermal head of the fourth embodiment of the present invention. Fig. 15 is a view illustrating one step of a method for producing the thermal head of the fourth embodiment of the present invention. Fig. 16 is a view illustrating an example of a printing system comprising a thermal head constructed in accordance with one embodiment of the present invention. Figs. 17 to 19 are views illustrating the details of the printing mechanism of a printing system which comprises a thermal head constructed in accordance with one embodiment of the present invention. Fig. 20 is an enlarged cross-sectional view of the primary part of a thermal head constructed in accordance with the prior art. Fig. 21 is an enlarged cross-sectional view of the primary part of a thermal head constructed in accordance with the prior art. Fig. 22 is an enlarged cross-sectional view of the primary part of a thermal head constructed in accordance with the prior art. Fig. 23 is an enlarged cross-sectional view of the primary part of a thermal head constructed in accordance with the prior art. Fig. 24 is a view illustrating the prior art thermal head during its operation. Fig. 1 shows a cross-sectional view of a first embodiment of a thermal head 300 constructed in accordance with the present invention. The thermal head 300 comprises a substrate 301, an under glaze layer 302 formed on the top face of the substrate 301, the under glaze layer including a top face 321, a slope face 324 formed in the under glaze layer 302 by slantingly cutting the edge portion thereof, and a corner portion 323 defined by an intersection between the top glaze face 321 and the slope face 324. A resistive film 303 is formed on the top glaze face 321 and slope face 324. In order to form a heating section 304, a common electrode 305 is disposed on the slope glaze face 324 while an individual electrode 306 is located on the top glaze face 321. The corner portion 323 of the thermal head 300 has an obtuse angle α. A protective film 307 is formed so as to cover all the layers and electrodes. Fig. 2 shows a cross-sectional view of the primary part of a second embodiment of a thermal head 400 constructed in accordance with the present invention. The thermal head 400 comprises a partial glaze layer 402 and a slope glaze face 424 formed by slantingly cutting the partial glaze layer 402 at its edge. The thermal head 400 also includes a corner portion 423 defined by an intersection between the top glaze face 421 and the slope glaze face 424 in the partial glaze layer 402. A heating section 404 is formed on the corner portion 423. Fig. 3 shows a cross-sectional view of the primary part of a third embodiment of a thermal head constructed in accordance with the present invention. The thermal head 600 of the third embodiment is substantially the same as that of the first embodiment. However, the third embodiment is different from the first embodiment in that while the thermal head of the first embodiment has a sharply formed corner 323, the thermal head of the third embodiment has a rounded corner portion 623. Components similar to those of the first embodiment are designated by similar reference numerals and will not be further described. The rounded corner portion 623 serve to eliminate any creation of burr and/or cutout and to promote the patterning. A method of producing a thermal head in accordance with the present invention will now be described in connection, with the thermal head 600 constructed in accordance with the third embodiment of the present invention. A half-cut groove 311 having a depth d equal to or larger than the thickness of the glaze layer 302 is first formed on the ceramic substrate 301 on the top face of which the glaze layer 302 has been formed, as shown in Fig. 4. In the first and third embodiments, this groove 311 is formed such that a corner portion 323 or 623 will be formed in the glaze layer 302 at each top edge of the groove 311 with an obtuse angle α. Thus, a slope face 324 is formed in the glaze layer 302 at each side wall of the groove 311. The depth d of the groove 311 may be equal to or smaller than the thickness of the glaze layer 302. This is true of the case when the glaze layer has a relatively large thickness or when the slope has a relatively large angle (obtuse angle). Being not illustrated, a plurality of such grooves 311 are actually formed on the substrate 301 having such a dimension that a plurality of thermal heads can be cut away therefrom. When the substrate is machined to form the half-cut grooves, burrs and/or cutouts may be formed on the corner portions 323 or 623 of the glaze layer 302. Further, the surface smoothness is lowered. Therefore, the substrate 301 is subjected to heat treatment at 800°C - 1000°C, this range of temperature being suitable for the conventional glaze materials, but may exceed 1000°C for a glass material having a higher softening point which will be developed in the future. Such a heat treatment rounds the corner portions 623 of the glaze layer 302 while improving the surface smoothness, as shown in Fig. 5. This facilitates the subsequent patterning operation. After the heat treatment, the resistive film layer 303, common electrode 305 and individual electrodes 306 are formed and patterned by the well-known photolithographic technique. The protecting film 307 is then formed to provide the before-division substrate as shown in Fig. 6. Finally, the substrate is divided along a line A-A in Fig. 6 into a plurality of individual thermal heads 600 which are shown in Fig. 7. Consequently, one can obtain thermal heads constructed in accordance with the third embodiment of the present invention. Since the glaze layer 302 is half-cut to provide the grooves and each of the corner portions 623 is formed with an obtuse angle, this method can produce a number of thermal heads simultaneously as in the conventional process of producing planar heads. If the film formation and patterning are carried out without any heat treatment after the burrs and/or cutouts have been removed in the step of Fig. 4, such a thermal head as constructed in accordance with the third embodiment of Fig. 1 can be provided. Although the method of the present invention has been described to provide a thermal head in which an under glaze layer 102 or 302 is formed on the top face of the substrate 301, it may be substantially similarly applied to produce a thermal head comprising a partial glaze 402 as shown in Fig. 2. Thus, the embodiments of the present invention described above provides a thermal head in which pressure can be fully concentrated onto the heating section since the heating section is formed on the corner portion in the glaze layer. Such a thermal head can perform an improved thermal transfer of ink onto a rough sheet. The increased concentration of pressure can improve the printing efficiency with lower energy and without excessive accumulation of heat and accomplish a high-speed printing operation. The distance of ribbon separation. which will be described later, can be decreased in accordance with the present invention. This also contributes to an improvement of the printing efficiency. Since the film formation and patterning are performed onto the substrate before division to form the heating sections on the corner portions by forming the non-through half-cut grooves and the rounded corner portions in the glaze layer, a plurality of inexpensive thermal heads each having an improved printing efficiency can be produced simultaneously. Fig. 8 shows a cross-sectional view of the primary part of a thermal head 700 constructed in accordance with the fourth embodiment of the present invention. The thermal head 700 comprises a substrate 701, an under glaze layer 702 formed on the top face of the substrate 701, a resistive film layer 703 formed on the glaze layer 702, common and individual electrodes 705 and 706 formed on the resistive film layer 703, and a protecting film 707 covering the resistive film layer 703 and electrodes 705, 706, all of these components defining a basic thermal head arrangement. This is not different from those of the first and third embodiments. The thermal head 700 of the fourth embodiment is characterized by the fact that it comprises a slope glaze face 724 formed by slantingly cutting a glaze layer 702 at its edge, a glaze corner portion 723 defined by an intersection between the top glaze face 721 and the slope glaze face 724, and a heating section 704 formed on the slope glaze face 724 rather than the glaze corner portion 723. More particularly, a resistive film layer 703 is formed from the top glaze face 721 to the slope glaze face 724. A common electrode 705 is formed on the slope glaze face 721 at a position adjacent to the edge thereof while each individual electrode 706 is formed from the top glaze face 721 to the glaze corner portion 723. The heating section 704 is positioned at a location adjacent to the edge of the glaze layer, rather than the glaze corner portion 723. Since the thermal head 700 of the fourth embodiment includes the heating section 704 formed on the slope glaze face 724 at a location adjacent to the edge of the glaze layer rather than the glaze corner portion 723, some degree of pressure can be concentrated onto the heating section 704 when the thermal head is pressed against a platen through a heat-sensitive sheet or ribbon. This means that the same pressure is applied to the heat-sensitive sheet or ribbon. Due to the fact that the heating section 704 is disposed on the substrate 701 adjacent to the edge thereof in addition to the application of pressure against the heat-sensitive sheet or ribbon, the separation of ribbon, which will be described later, can be improved to provide clear printed letters. Fig. 9 is a top plan view of the thermal head 700 constructed in accordance with the fourth embodiment of the present invention, illustrating a pattern in which the resistive film layer 703, common electrode 705 and individual electrode 706 are disposed on the thermal head 700. As will be apparent from Fig. 9, the common electrode 705 includes a common electrode portion 705a and a common return electrode portion 705b. These electrode portions 705a and 705b co-operate with the individual electrode 706 to generate heat at the resistive film layer 703. In Fig. 8, the distance from the edge P of the heating section 704 to the edge Q of the thermal head is a distance of separation required to separate a printed sheet from an ink ribbon. As can be seen from Fig. 9, the edge P of the heating section is on the boundary between the resistive film layer 703 and the common return electrode 705b while the edge Q of the thermal head is on the edge of the protecting film 707. When an ink ribbon is used as a heat transfer means, it will be pulled by a thermally printed sheet through the distance between the edges P and Q. Thus, this distance is called a distance of ribbon separation. As the distance of ribbon separation is increased, the printing is performed less clearly. In the present heat transfer system, an ink ribbon has been currently utilized which contains an ink having an increased viscosity for enabling the ink ribbon to print on rough paper. This increases the distance of ribbon separation. If the viscosity of the ink in the ink ribbon is reduced to cause the ink to flow fully into the rough surface of the printing sheet, the ink will blot on the paper. By causing the ink to have some viscosity, the ink can be applied from the ink ribbon to the printing paper with a given pattern of letter under the pressure from the thermal head, as in the transfer paper. More particularly, a desired pattern of letter is thermally formed on the ink ribbon and then applied to the paper under the pressure from the thermal head. The thermal transfer of the ink onto the rough paper can be accomplished by causing the ink to have some viscosity and then to separate from the rough paper on heating. Thus, the transfer and separation of the ink will be carried out simultaneously on heating. As the time interval between the transfer and the separation is decreased, the printing can be made more clearly. If such a time interval increases, it becomes difficult for the pattern of the letter to transfer and separate properly from the ink ribbon. This degrades the transfer of ink onto the paper. Furthermore, if time passes away after heating, the ink to be transferred will be cooled and hardened so that the ink or the formed pattern of letter will not be transferred to the paper. It is therefore required that the distance between the edges P and Q, that is, the distance of ribbon separation is as small as possible. Referring to Fig. 11, there is shown a modification of the fourth embodiment in which the common return electrode 705b is omitted while retaining the common electrode 705a. Further, an edge portion 726 is formed to align the edge P of the heating section 704 with the edge Q of the thermal head 700 at the edge portion 726. Thus, the distance of ribbon separation becomes substantially zero. As a result, the ink ribbon can be separated more properly to improve the printing. The thermal head of Fig. 11 can be produced in accordance with the following process. As shown in Fig. 12, a half-cut groove 711 having a depth d equal to or larger than the thickness of the glaze layer 702 is first formed on the ceramic substrate 701 on the top face of which the glaze layer 702 has been formed. This groove 711 is formed into an inverse trapezoidal configuration such that a corner portion 323 will be formed in the glaze layer 702 at each top edge of the groove 711 with an obtuse angle α. Thus, a slope face 724 is formed in the glaze layer 702 at each side wall of the groove 711. The depth d of the groove 711 may be equal to or smaller than the thickness of the glaze layer 702. This is true of the case when the glaze layer has a relatively large thickness or when the slope has a relatively large angle (obtuse angle). Being not illustrated, a plurality of such grooves 711 are actually formed on the substrate 701 having such a dimension that a plurality of thermal heads can be cut away therefrom. When the substrate is machined to form the half-cut grooves, burrs and/or cutouts may be formed on the corner portions 723 of the glaze layer 702. Further, the surface smoothness is lowered. Therefore, the substrate 701 is subjected to heat treatment at 800°C - 1000°C. Such a heat treatment rounds the corner portions 723 of the glaze layer 702 while improving the surface smoothness, as shown in Fig. 13. This facilitates the subsequent patterning operation. After the heat treatment, the resistive film layer 703, common electrode 705 and individual electrodes 706 are formed and patterned by the well-known photolithographic technique. The protecting film 707 is then formed to provide the before-division substrate as shown in Fig. 14. Finally, the substrate is divided along a line A-A in Fig. 14 into a plurality of individual thermal heads 700 which are shown in Fig. 15. Consequently, one can obtain thermal heads constructed in accordance with the fourth embodiment of the present invention and also thermal heads 700a constructed in accordance with the modification of the fourth embodiment as shown in Fig. 11. Since the glaze layer 702 is half-cut to provide the grooves and each of the corner portions 723 is formed with an obtuse angle, this method can produce a number of thermal heads simultaneously as in the conventional process of producing planar heads. In the first to fourth embodiments, the size of the heating section is equal to about 100µ - about 200µ, with the pitch thereof being equal to about 60µ. Fig. 16 shows the arrangement of a printing system 40 including a thermal head which is constructed in accordance with one embodiment of the present invention. The printing system 40 comprises an inlet port 44 for inserting a document 42 into the system, a feed roller 46 for transporting the document to the thermal head, an image sensor 48 for reading the document, a printing section 50 for printing a recording sheet 54 and a recording platen roller 52 located adjacent to the printing section 50. The printing system 40 is actuated by electric energy. As documents 42 are inserted into the printing system 40 through the inlet port 44, they are separated from each other by separator means 43 and transported to the image sensor 48 one at a time. The pattern on the surface of the document 42 is converted into electric signals at the image sensor 48. Based on these electric signals, the recording sheet 54 will be printed at the printing section 50. In order to accommodate the printing on rough paper, the printing system uses an ink ribbon 62. Although the printing system has been described as a copying machine or facsimile including a reading-out mechanism, the thermal head of the present invention may be used in a printer having no reading-out mechanism. Figs. 17 to 19 shows the details of the printing section 50 shown in Fig. 16. Referring first to Fig. 17, the recording sheet 54 will run on the rubber platen 60 of the platen roller 52. A thermal head 64 constructed in accordance with any one of the first to fourth embodiments will be pressed against the recording sheet through an ink ribbon 62. The thermal head 64 is diagrammatically illustrated in Fig. 17. Since the thermal head of the present invention is pressed against the rubber platen 60 adjacent to the corner portion of the thermal head in which a pressing force is increased. Thus, the rubber platen is recessed by the pressing force from the thermal head, at which position the printing will be carried out. By moving a heating section 68 into the recessed portion of the rubber platen 60, the pattern of a letter is thermally formed while applying the pattern of the letter onto the recording sheet under pressure. A distance L between the heating section 68 and the edge portion 70 of the thermal head is the distance of ribbon separation. If this distance of ribbon separation L is too large, the ink ribbon 62 would be placed in contact with the recording sheet 54 for an elongated time period after the thermal transfer has been completed. This will have cooled the ink ribbon 62 until the recording sheet 54 is separated from the ink ribbon 62 at the point of separation 72. The pattern of the letter transferred from the ink ribbon 62 to the recording sheet 54 will be returned to the ink ribbon 62. An angle  included between the ink ribbon 62 and the thermal head is called an angle of separation. If this angle of separation is too large, the recording sheet 54 will be placed in contact with the ink ribbon 62 for a prolonged time period after the heat transfer as in case when the distance of ribbon separation L is too large. This leads to the same defect in printing as described above. If the thermal head constructed in according to the present invention is used, however, the distance of ribbon separation L can be reduced or nullified and the angle of ribbon separation  can also be decreased, as described. Thus, the thermal head of the present invention can produce good, clear printing. Figs. 18 is an enlarged view of the primary part of Fig. 16, in which the rubber platen 60 is replaced by the platen roller 52 and the thermal head 64 is held stationary with the recording sheet being transported by roller means. However, the thermal head of the present invention may be applied to a serial printer system in which the thermal head 64 is movable on a flat platen 79 with a ribbon cassette 77 being utilized. The thermal ahead of the present invention is economically advantageous in that a number of inexpensive thermal heads can be mass produced. By incorporating a thermal head into a printing system, the latter can be modified into a printing system which is improved in cost and performance to perform the printing economically and clearly.

Claims: A thermal head comprising a) a substrate (301, 401, 701) having a substantially planar upper surface and an edge; b) a glaze layer (302, 402, 702) formed to cover said upper surface of said substrate (301, 401, 701) adjacent said edge; c) a resistive film (303, 403, 703) formed on said glaze layer (302, 402, 702); d) an electrode pattern (305, 306, 405, 406, 705, 706) formed on said resistive film; and e) a heating section (304, 404, 704) formed between said electrode pattern (305, 306, 405, 406, 705, 706) to perform printing in a thermal transfer manner when said electrode pattern (305, 306, 405, 406, 705, 706) is supplied with an electrical current; characterised in that said glaze layer (302, 402, 702) has a top face (321, 421, 721) opposed said upper surface of said substrate (301, 401, 701) and a sloping face (324, 424, 724) formed between said top face (321, 421, 721) and said edge by cutting said glaze layer (302, 402, 702) such that the thickness of said glaze layer (302, 402, 702) decreases towards said edge; a corner portion (323, 423, 623, 723) being formed at the intersection between said top face (321, 421, 721) and said sloping face (324, 424, 724); and said heating section (304, 404, 704) being formed on said corner portion (323, 423, 623, 723) or said sloping face (324, 424, 724). A thermal head as claimed in Claim 1 characterised in that said glaze layer (302, 402, 702) is a substantially planar layer covering the whole of said upper surface of said substrate (301, 401, 701). A thermal head as claimed in Claim 1 characterised in that said glaze layer (302, 402, 702) only partially covers said upper surface of said substrate (301, 401, 701), said resistive film (303, 403, 703) is formed on said upper surface of said substrate (301, 401, 701) not covered by said glaze layer (302, 402, 702). A thermal head as claimed in any preceding claim characterised in that said glaze layer (302, 402, 702) is thermally treated to round said corner portion (323, 423, 623, 773). A thermal head as claimed in any preceding claim characterised in that said heating section (304, 404, 704) is formed by a protective layer (307, 407, 707) formed on said resistive film (303, 403, 703) between said electrode pattern (305, 306, 405, 406, 705, 706). A method of producing a thermal head as claimed in Claim 1, comprising the steps of: a) forming a glaze layer (302) on a substantially planar substrate (301, b) cutting at least said glaze layer to form at least one groove (311) having a substantially trapezoidal cross-section, the formation of said groove (311) being adapted to form said sloping face (324) between a top face (321) of said glaze layer (302) and the bottom of the groove (311); c) forming a resistive film layer (303) over said top and sloping faces (321, 324) and patterning a heating section by forming a pattern of electrode conductors (305, 306) on said resistive film layer (303); d) forming a protective film (307) to cover said resistive film layer (303) not covered by said electrode conductors (305, 306), said electrode conductors and a heating section (304) formed between said electrode conductors (305, 306); and e) cutting said substrate (301) adjacent said glaze layer (302) in said groove (311) formed at the step b) to provide a plurality of thermal heads. A method of producing a thermal head as claimed in Claim 6 characterised by the step of heat treating said glaze layer (302) to round the intersection between said top face (321) and said sloping face (324). A print system comprising the thermal head as defined in any one of Claims 1 to 5.

Inventors: ONISHI HIROAKI, TANIGUCHI HIDEO, ONISHI, HIROAKI, TANIGUCHI, HIDEO
Applicants: ROHM CO LTD, ROHM CO., LTD.
Application year: 1992
Main classification: B41J2
IPC codes: B41J2