Recording head including electrode supporting substrate having thin-walled contact end portion

Abstract: A recording head including at least one electrode (2, 3), and a substrate structure (1) for supporting each electrode. Each electrode and the substrate are held in contact with a recording medium or a planar intermediate member interposed between the recording medium and the recording head, so that an electric current is applied to the recording medium or the intermediate member. The substrate has a distal end portion (6) extending from a proximal portion for contact with the recording medium and the intermediate member. The distal end portion has a thickness (d) smaller than that of the proximal portion, as viewed in a direction perpendicular to a direction of extension of the end portion. The distal end portion is made of a material whose wear resistance is lower than that of the electrode.

Description: The present invention relates in general to a recording head for recording or printing images such as characters and graphical representations, by applying an electric current to a recording medium or a ribbon or film or other form of intermediate member interposed between the recording medium and the head. More particularly, the invention is concerned with the configuration of a distal end portion of such a recording head at which the head contacts the recording medium or intermediate member. There will be first described prior art recording heads, and problems encountered in these head. Various types of recording head for recording by application of an electric current to a recording medium or an intermediate member have been proposed up to the present. In particular, there is known a recording head having a laminar or multi-layer structure which includes a substrate or substrates, and an array of recording electrodes and an array of return circuit electrodes which are supported by or formed on the substrate or substrates. Examples of this type of recording head are disclosed in laid-open Publication Nos. 61-35972, 62-292461, 54-141140, 58-12790 and 61-230966 of unexamined Japanese Patent Applications. There is known another type of recording head, in which the array of recording electrodes is formed on one of opposite major surfaces of a substrate, as disclosed in laid-open Publication Nos. 58-104787, 61-37493, 63-30279, 63-87264, 63-160855, 60-78772 and 62-238767. As disclosed in the publications identified above, the recording head of the types indicated above is adapted such that an electric current is applied to an electrically resistive or conductive layer formed or coated on or carried by a suitable recording medium or a suitable planar intermediate support member in the form of a sheet, film or ribbon. The electrically resistive or conductive layer may be formed on a roller or other support member, or constitute an inner layer of the recording medium or support member. In a recording operation by using an intermediate ribbon or film having an electrically resistive layer and an ink layer, for example, an electric current applied to the resistive layer through the recording head causes Joule heat to be generated by the resistive layer, whereby selected local areas of the ink layer are heated, and the ink material in these heated local areas is fused, vaporized or diffused. As a result, the ink material is transferred to the appropriate local areas of the recording medium so as to form a black or colored image. If an electric current is applied directly to a recording medium, the appropriate local areas of the medium are suitably colored due to Joule heat generated by an electric current, or due to removal of the covering material from the medium surface due to an electrical discharge occurring thereon. The electrically resistive layer provided on the recording medium or intermediate support member may be an electrically conductive layer, an electrically conductive or resistive ink layer (which serves also as an ink-bearing layer), a heat-sensitive layer having an electrolyte, or any form of layer through which an electric current may flow. In a recording or printing operation by the recording head for use with the recording medium or intermediate support member as described above, the recording electrodes and the return circuit electrode or electrodes must be held in electrical contact with the electrically resistive layer of the recording medium or support member. To this end, the electrodes used in the known recording heads as disclosed in the publications indicated above are formed of a material which has a higher degree of wear resistance than the material of the substrate structure and an electrically insulating layer used for the heads. An example of such a known recording head is partly illustrated in Fig. 17, wherein a multi-layer structure is formed by two substrates 11, an array of recording electrode 12 formed on one of the substrates 11, an array of return circuit electrodes 13 formed on the other substrate, and an electrically insulating layer 14 which separates the two arrays of electrodes 12, 13 and to which the electrode arrays 12, 13 are bonded by respective layers of a suitable adhesive 15, 15. In this arrangement, the end face of the substrate structure 11 occupies a considerably large portion of the entire contact face at the distal end of the head which is adapted to contact the surface of the electrically resistive layer of the recording medium or support member. In other words, the area of the contact end faces of the electrodes 12, 13 is comparatively small. This area ratio of the contact end face of the substrate structure 11 and electrodes 12, 13 does not provide for a desired electrical contact between the electrodes and the electrically resistive layer. When a recording operation requires a relatively large contacting force of the electrodes against the resistive layer, the known arrangement is not satisfactory for producing high-quality images. For improving the electrical contact between the electrodes and the resistive layer of an ink ribbon for example, a recording head having a generally pointed contact end portion is proposed as shown in Fig. 18. While this recording head assures improved electrical contact between the electrodes and the resistive layer during an initial period of use, the ratio of the contact end face area of the substrate structure 11 with respect to that of the electrodes 12, 13 increases as the pointed end of the head wears. Satisfactory contacting of the electrodes with the resistive layer may not be obtained if the worn-out contact end of the head is ground for re-shaping by a relatively easy method while the head remains installed on the relevant recording apparatus. An alternative known approach is to use the electrodes 12, 13 which have increased thicknesses, as indicated in Fig. 19. This arrangement, however, lowers the efficiency or ease of forming the electrodes in the desired patterns (in the form of mutually spaced apart stripes). Another type of recording head is illustrated in Fig. 20. This recording head has an array of recording electrodes 12 which is formed on one major surface of the substrate 11 and covered by an electrically insulating layer 7 made of a comparatively soft material. Although the contact of the electrodes 12 and insulating layer 7 with the resistive layer is better than the contact of the multi-layer heads indicated above, the contact end portion of the electrodes 12 comparatively rapidly wears since the head contacts the resistive layer at one edge thereof on the side of the electrode array 12. As the contact edge of the head is worn or ground for re-shaping, the area ratio of the contact end face of the substrate 11 with respect to the contact end face of the electrodes 12 increases, whereby the electrical contact of the electrodes is deteriorated during use of the head. JP-A-60-72733 discloses a recording head of a lamination structure. The thickness of the distal portion of the laminates is reduced in a direction perpendicular to the laminating direction, so as to form an end portion of a small contacting area. JP-A-62-99163 discloses a recording head having an electrode substrate with a hardness lower than that of the electrodes, so as to form a reliable contact between the electrodes and an ink film. It is therefore desirable to provide a recording head for recording by application of an electric current to a recording medium or an intermediate member interposed between the head and the medium, which recording head assures excellent electrical contact of the electrodes with the medium or intermediate member for a prolonged period of use while at the same time has a sufficient overall mechanical strength. According to the present invention, there is provided a recording head as set out in claim 1. The recording head of the present invention constructed as described above provides for excellent or satisfactory electrical contact between the electrode or electrodes and an electrically resistive layer or other layer of the recording medium or planar intermediate member for a prolonged period of use, while at the same time permitting the substrate structure to maintain a sufficient degree of mechanical strength. Thus, the present recording head assures a highly reliable recording operation for improved quality of recording images. In one form of the present invention, the recording head further comprises an electrically insulating layer, and there are a plurality of the electrodes comprising at least one recording electrode and at least one return circuit electrode. In this case, a substrate structure comprises two substrates which have mutually facing major surfaces on which the recording electrode or electrodes and the return circuit electrode or electrodes are formed, respectively. The recording electrode or electrodes and the return circuit electrode or electrodes are spaced apart from each other by the electrically insulating layer in the thickness direction of the distal end portions of the substrates. In another form of the invention, there is at least one recording electrode, and one substrate which has opposite major surfaces. In this case, the recording electrode or electrodes is/are formed on one of the opposite major surfaces of the substrate. In a further form of the invention, there is a plurality of the electrodes comprising at least one recording electrode and at least one return circuit electrode, and a substrate structure comprises one substrate having opposite major surfaces on which the recording electrode or electrodes and the return circuit electrode or electrodes are formed, respectively. There may be an array of recording electrodes and an array of return circuit electrodes, which may be formed on two respective major surfaces of a substrate structure. These two major surfaces may be provided by one substrate or two respective substrates as indicated above. In this case, the return circuit electrodes may correspond to the recording electrodes. However, a single return circuit electrode may be provided commonly to the recording electrodes. Each substrate of the present recording head may have a shoulder surface formed adjacent to the distal end portion. The shoulder surface may take suitable configuration. For example, the shoulder surface is formed at right angles to the direction of extension of the distal end portion, or formed as a fillet surface which terminates in a surface of the distal end portion which is parallel to the direction of extension of the distal end portion. Alternatively, the shoulder may be an inclined surface which forms an obtuse angle with respect to a surface of the distal end portion which is parallel to the direction of extension of the distal end portion. The present recording head was developed on a basic concept that the wear resistance of the head at its distal end including the distal end portion of each substrate is desirably influenced by the wear resistance of the distal end portion of the electrode or electrodes. In other words, the present recording head is constructed so that the substrate structure has a mechanical strength or rigidity necessary to support the electrode or electrodes, while the distal end portion of the substrate structure has a sufficiently reduced thickness for improved electrical contact of the electrode or electrodes with the recording medium or intermediate support member. Further, the present recording head is constructed on a concept that the thickness of the distal end portion of the substrate structure is preferably constant in the direction of extension from the proximal portion, i.e., in the direction in which the distal end portion wears. Namely, it is desirable that the thickness of only the distal end portion at which the substrate structure contacts the recording medium (sheet of paper) or intermediate member (ink ribbon or film) is small and constant, so that the substrate structure has sufficient mechanical strength and permits easy installation of the recording head, and so that the recording medium or intermediate member may contact only the electrode or electrodes as much as possible. The present invention will be better understood by reading the following description of presently preferred embodiments of the invention, when considered in conjunction with the accompanying drawings, in which: Figs. 1-6, and Figs. 9, 10, 14 and 16 are explanatory elevational views in cross section of different forms of a recording head of the present invention, taken in a plane parallel to the direction of extension of the electrodes; Fig. 7 is an explanatory elevational view in cross section of the recording head of Fig. 4 whose distal end portion is worn out; Fig. 8 is a perspective view showing the distal end portion of another form of the recording head of the invention; Fig. 11 is a perspective view schematically illustrating the distal end portion of the recording head of Fig. 1; Fig. 12 is a perspective view schematically illustrating the distal end portion of the recording head of Fig. 4; Figs. 13 and 15 are perspective views schematically showing the recording heads of Figs. 14 and 16, respectively; Figs. 17 through 20 are explanatory elevational view in cross section of known recording heads, taken in a plane parallel to the direction of extension of the electrodes; and Fig. 21 is an elevational cross sectional view of the recording head of Fig. 20 whose distal end portion is worn out. Referring first to Figs. 1-3, there are shown three different forms of the recording head which have a laminar or multi-layer structure. Each of these recording heads of Figs. 1-3 includes a substrate structure 1, an array of recording electrodes 2, an array of return circuit electrodes 3, an electrically insulating layer 4, and two layers of an adhesive 5, 5. The substrate structure consists of two substrates 1, 1 each of which has opposite major surfaces. The array of recording electrodes 2 is formed on one of the opposite major surfaces of one of the two substrates 1, while the array of return circuit electrodes 3 is formed on one of opposite major surfaces of the other substrate 1 which faces the major surface of the above-indicated one substrate 1 on which the array of recording electrodes 2 is formed. The electrically insulating layer 4 separates the two arrays of electrodes 2, 3 in the direction of thickness thereof, and the adhesive layers 5, 5 are interposed between the electrode arrays 2, 3 and the insulating layer 4, so that the electrodes arrays 2, 3 are bonded to the insulating layer 4 by the interposed adhesive layers 5, 5. Referring next to Figs. 4-6, there are shown different form of the recording head in which the substrate structure consists of a single substrate 1 which supports an array of recording electrodes 2 formed on one of a major surface thereof. In these recording heads, the array of recording electrodes 2 is covered by a covering layer 7 made of a relatively soft electrically insulating material such as a synthetic resin, a ceramic material or a glass material. The synthetic resin may be epoxy resin or polyimide, and the ceramic material may be boron nitride or silica. The insulating material must be soft enough to avoid a substantial problem in terms of contact of the covering layer 7 with a recording medium or an intermediate member interposed between the recording head and the recording medium. In each of the recording heads shown in Figs. 1-6, each substrate 1 has a proximal portion (upper portion as viewed in the figures) which is located remote from the recording medium during operation of the head, and a thin-walled distal end portion 6 (lower portion as viewed in the figures) which extends from the proximal portion by a suitable length or distance (indicated at L in the figures) in the direction toward the recording medium. The distal end portion 6 has a thickness "d" which is smaller than that of the proximal portion, as viewed in the direction perpendicular to the direction of extension of the portion 6. This thin-walled distal end portion 6 is adapted so that the end face in which the electrodes 2, 3 (2) are exposed contacts the electrically resistive layer provided on the recording medium or ink ribbon (provided as the planar intermediate support member). The thin-walled distal end portion 6 is formed by providing the substrate 1 with a shoulder surface 1a, 1b, 1c, which is formed adjacent to the proximal end of the distal end portion 6, as shown in Figs. 1-6. As indicated at "A" in Fig. 1, the shoulder surface 1a, 1b, 1c terminates in the proximal end of the distal end portion 6. In the recording head of Fig. 1, each of the two substrate 1 of the substrate structure has the shoulder surface 1a which is perpendicular to the direction of extension of the distal end portion 6, i.e., parallel to the direction of thickness "d" of the distal end portion 6. In the recording head of Fig. 4, the single substrate 1 has the shoulder surface 1a similar to that of Fig. 1. The shoulder surface need not be at right angles to the direction of extension of the thin-walled end portion 6. In the recording head of Fig. 2, each of the two substrates 1 has the shoulder surface 1b which is a fillet having a suitable radius of arc and which terminates in the surface of the distal end portion 6 parallel to the direction of extension. In the recording head of Fig. 5, the shoulder surface 1b is provided for the single substrate 1. In the recording head of Fig. 3, each of the two substrates 1 has the inclined shoulder surface 1c which forms an obtuse angle with respect to the surface of the distal end portion 6 which is parallel to the direction of extension. In the recording head of Fig. 6, the single substrate 1 has the inclined shoulder surface 1c similar to that of Fig. 3. Fig. 7 shows the distal end portion 6 of the recording head of Fig. 4, which has a reduced length due to wear. Referring to Figs. 9 and 10, two further different forms of recording head are shown. In these recording heads, a single substrate 1 has opposite major surfaces on which the arrays of recording electrodes and return circuit electrodes 2, 3 are formed, respectively. In the recording head of Fig. 9, the inclined shoulder surface 1c is formed adjacent to the thin-walled distal end portion 6. In the recording head of Fig. 10, the two inclined shoulder surfaces 1c are formed adjacent to the thin-walled distal end portion 6 such that the distal ends of the two inclined shoulder surfaces 1c define the thickness "d" of the end portion 6. The thickness "d" of the thin-walled distal end portion 6 of the substrate 1, and the length "L" of the distal end portion 6 (which is shortened as the end portion 6 wears) are determined by the materials of the substrate structure 1, electrodes 2, 3, and by the required properties or characteristics to be exhibited by the distal end portion 6 during a recording operation, and are further determined by the desired force of electrical contact between the electrodes 2, 3 and the resistive layer of the recording medium or ink ribbon. Generally, the thickness "d" is desirably 700 µm or smaller, preferably within a range of 30-400 µm, and more preferably within a range of 30-100 µm. The length "L" of the distal end portion 6 is desirably held within a range of 50-4000 µm, preferably within a range of 100-1000 µm. The desirability of holding the thickness and length within the above-indicated ranges was confirmed by experiments in which the wear condition of specimen recording heads were observed. It is desirable that the material for the substrate structure 1 be an electrically insulating material which has a comparatively low resistance to wear and provides a mechanical strength sufficient to support the electrodes 2, 3, and which may be easily processed for shaping the distal end portion 6 with high precision. The electrically insulating material used for the substrate structure 1 preferably consists of a ceramic material having lower degrees of hardness and wear resistance than that of the electrodes 2, 3. For easy shaping of the distal end portion 6 and sufficient mechanical strength, it is particularly desirable to form the substrate structure 1 of a material selected from the group which consists of: highly machinable glass ceramic containing mica; boron nitride; highly machinable ceramic containing boron nitride; highly machinable ceramic containing aluminum nitride and boron nitride. In particular, the machinable glass ceramic containing mica is preferably used. The shaping of the substrate structure 1 for forming the thin distal end portion 6 may be formed before the electrodes (recording electrodes 2 and/or return circuit electrodes 3) are formed on the substrate structure. Where a substrate 1 has the electrodes 2 or 3 formed on one of the opposite major surfaces, the distal end portion 6 may be formed by a grinding, slicing or other suitable machining operation, after a laminar structure as illustrated in Figs. 17 and 20 are prepared. Where a substrate 1 has the recording and return circuit electrodes 2 and 3 formed on the respective opposite major surfaces thereof as illustrated in Figs. 9 and 10, it is usual that the substrate 1 is first subjected to the suitable shaping operation to form the distal end portion 6, and then the electrodes 2, 3 are formed on the shaped substrate 1. Referring to the perspective view of Fig. 8, the single substrate 1 has the recording electrode array 2 on one of its major surfaces, and the return circuit electrode array 3 on the other major surface. The distal end portion of this recording head of Fig. 8 which includes the distal end portion 6 of the substrate 1 is shown in Fig. 9, which is a cross sectional view taken in a plane which is parallel to the direction of extension of the electrodes 2, 3 and perpendicular to the plane of the substrate 1. The thickness "d" of the distal end portion 6 is 70 µm, and the length "L" of the same is 300 µm. It will be understood that the substrate 1 of the recording head of Figs. 8 and 9 also serves as a layer for electrically insulating the recording electrodes 2 and the return circuit electrodes 3 from each other. Thus, this embodiment of Figs. 8 and 9 eliminates the relatively exclusive electrically insulating layer 4 required in the embodiments of Figs. 1-3 described above and in an embodiment of Fig. 11. In the absence of the electrically insulating layer 4 which is relatively thin over its entire area and interposed between the two arrays of electrodes 2, 3, the recording head of Figs. 8 and 9 is desirable in terms of the ease of handling and mechanical strength. There is shown in Fig. 10 a recording head similar to the head of Figs. 8 and 9 in which the substrate 1 functions also as an electrically insulating layers for the electrodes 2, 3. In this embodiment of Fig. 10, the opposite major surfaces of the single substrate 1 should be shaped to provide the inclined shoulder surfaces 1c, 1c for forming the distal end portion 6. In this respect, the recording head of Figs. 8 and 9 is advantageous over the recording head of Fig. 10 having one inclined shoulder surface 1c, since the former head may be easily shaped with comparatively high dimensional accuracy. In the recording heads of Figs. 8-10, it may be preferable to reinforce the head structure for improving the thin distal end portion 6, by providing the substrate 1 or electrodes 2, 3 with a suitable covering layer for covering the surfaces of the substrate or electrodes. The covering layer may be formed of an electrically insulating material such as epoxy resin, polyimide and other synthetic resins, boron nitride, silica and other ceramic materials, or glass materials. The covering layer may be replaced by a thin film or sheet of a highly machinable glass ceramic material, highly machinable ceramic material, or metallic material, which is bonded to the substrate 1 or electrode arrays 2, 3. This film or sheet may be a metallic sheet coated with an electrically insulating material. If the recording heads of Figs. 8-10 in which the substrate 1 serves also as the insulating layers for the electrodes 2, 3 considerably suffer from accumulation of heat at the thin distal end portion 6, it is possible and desirable to provide a suitable reinforcing film or sheet which is formed principally of a highly thermally conductive material such as a metallic material, boron nitride and aluminum nitride, so that this film or sheet serves as a heat-dissipating layer as indicated at 8 in Figs. 13-16. In these figures, reference numeral 5 designates an adhesive, while reference numeral 7 designates an electrically insulating layer. The recording and return circuit electrodes 2, 3 are formed of an electrically conductive material which has a higher degree of wear resistance than the substrate structure 1 for supporting the electrodes, or than the electrically insulating layer 4. Preferably, a major content of the electrically conductive material for the electrodes 2, 3 is selected from the group which includes: metals such as chromium, titanium, tantalum and zirconium; alloys containing these metals; and compounds of the metals. These materials are advantageously used owing to their comparatively high wear resistance and comparatively low rate of consumption due to an electrical effect during use of the head. Particularly, chromium, and an alloy or a compound containing chromium are preferably used as a major component of the electrically conductive material for the electrodes. More preferably, the electrodes are formed principally of an alloy or compound containing chromium and nitrogen. The thickness of the recording and return circuit electrodes 2, 3 is preferably at least 1 µm. The electrodes 2, 3 may be plated with nickel, tin, copper, gold or other suitable metal, as required. Referring next to Fig. 11, there is schematically shown in perspective a laminar structure of the recording head of Fig. 1. It will be understood that the cross sectional view of Fig. 1 is taken in a plane which is parallel to the direction of extension of the electrodes 2, 3 and perpendicular to the plane of the substrates 1. In this specific embodiment of Figs. 1 and 11, the two substrates 1 of the substrate structure are formed of a highly machinable glass ceramic material containing mica, and the electrode arrays 2, 3 are formed by first applying by sputtering respective chromium layers on the appropriate major surfaces of the respective substrates 1, and photoetching the chromium layers in predetermined patterns such that a plurality of chromium strips for each of the two electrode arrays 2, 3 extend parallel to each other and are spaced apart from each other in the direction perpendicular to the direction of extension of the chromium strips. Then, the formed spaced-apart chromium strips are heat-treated in an atmosphere which contains a nitrogen gas and a hydrogen gas. The formed array of the recording electrodes 2 consists of 480 chromium strips which are arranged at a spacing pitch of 170 µm, and each of the chromium strips has a width of 100 µm and a thickness of 6 µm. The two substrates 1, 1 having the electrode arrays 2, 3 are bonded together by the adhesive layers 5, with the electrically insulating layer 4 interposed between the two electrode arrays 2, 3 (two substrates 1, 1). The insulating layer 4 consists of an integrated or foliated mica sheet having a thickness of 100 µm. The thin distal end portion 6 (Fig. 1) of each substrate 1 has a thickness "d" of 100 µm, and a length "L" of 2000 µm. A recording head different in structure from that of Fig. 11 is schematically illustrated in Fig. 12, and in the cross sectional view of Fig. 4. As shown in these Figs. 4 and 12, this recording head uses one substrate 1 consisting of a highly machinable glass ceramic sheet. On one of the opposite major surfaces of this substrate 1, there is formed the array of the recording electrodes 2 in the same manner as described with respect to the embodiment of Figs. 1 and 11. The distal end portion 6 (Fig. 4) has a thickness "d" of 100 µm, and a length "L" of 500 µm. The different forms of the recording head which have been described above were tested as incorporated in a recording apparatus, such that the electrodes 2, or the electrodes 2 and 3 were held in sliding contact with an electrically resistive layer of an ink ribbon, during repetitive printing cycles. The quality of the images printed by the individual recording heads were evaluated. The test revealed satisfactory results obtained from all the tested specimens, i.e., sufficiently high density and clearness or crispness of the printed images, and excellent state of contacting of the electrodes 2, 3 with the resistive layer of the ink ribbon. Fig. 7 shows the recording head of Fig. 4 whose distal end portion 6 has been worn out. As indicated in Fig. 7, the ratio of the contact area of the substrate 1 with respect to that of the electrode 2 remains unchanged even after the wearing of the distal end portion 6. Namely, the distal end portion 6 maintains the initial contacting state for a long period of use.

Claims: A recording head operable to apply an electric current, comprising at least one electrode (2,3) and a further layer (1) against the electrode, the electrode (2,3) and the further layer (1) in use being held in contact with one of a recording medium and a planar intermediate member interposed between a recording medium and the recording head, so that electric current is applied to the recording medium or the planar intermediate member, wherein the further layer (1) has a proximal portion, and a distal end portion (6) extending from the proximal portion by a predetermined distance (L) in a first direction towards the recording medium for contact with the recording medium or the planar intermediate member, and the distal end portion has a thickness (d) smaller than that of the proximal portion in a second direction perpendicular to said first direction; characterised in that the further layer (1) is a supporting substrate for the electrode (2,3) and the electrode (2,3) lies against a face of the substrate (1) which is transverse to said second direction and the distal end portion (6) of the substrate (1) is made of a material whose wear resistance is lower than that of the electrode (2,3). A recording head according to claim 1, further comprising an electrically insulating layer (4), and wherein there are a plurality of said electrodes comprising at least one recording electrode (2) and at least one return circuit electrode (3), and there are two said substrates (1) which have mutually facing major surfaces on which the recording electrode (2) and the return circuit electrode (3) are formed, respectively, the recording electrode and the return circuit electrodes being spaced apart from each other by the electrically insulating layer (4) in said second direction. A recording head according to claim 1, wherein the electrode is a recording electrode (2), and there is one substrate (1) which has opposite major surfaces, the recording electrode being formed on one of the opposite major surfaces of the one substrate. A recording head according to claim 1, wherein there are a plurality of the electrodes (2,3) comprising at least one recording electrode (2) and at least one return circuit electrode (3), and there is one substrate (1) having opposite major surfaces on which the recording electrode and the return circuit electrode are formed, respectively. A recording head according to any one of claims 1, 2 and 4, wherein there are a plurality of the electrodes comprising an array of recording electrodes (2) and an array of return circuit electrodes (3), and the substrate or substrates (1) have at least two major surfaces on which the arrays of recording electrodes and return circuit electrodes are formed, respectively. A recording head according to any one of claims 1-5, wherein the or each substrate (1) has a shoulder surface (1a, 1b, 1c) formed adjacent to the distal end portion (6). A recording head according to claim 6, wherein the shoulder surface (1a) is perpendicular to said first direction. A recording head according to claim 6, wherein the shoulder surface (1b) is a fillet surface (1b) which terminates in a surface of the distal end portion (6) which is parallel to the said first direction. A recording head according to claim 6, wherein the shoulder surface (1c) is an inclined surface which forms an obtuse angle with respect to a surface of the distal end portion (6) which is parallel to said first direction. A recording head according to any one of claims 1-5, wherein said substrate (1) has at least one shoulder surface (1a, 1b, 1c) formed adjacent to said distal end portion (6). A recording head according to claim 10, wherein there are two said substrates (1) each having a said shoulder surface (1a, 1b, 1c) formed adjacent to said distal end portion of the corresponding one of said two substrates. A recording head according to claim 10, wherein there is one said substrate (1), and said shoulder surface (1a, 1b, 1c) is formed adjacent to said distal end portion of said one substrate. A recording head according to claim 10, wherein there is one said substrate (1) having two said shoulder surfaces (1c) each formed adjacent to said distal end of said one substrate. A recording head according to any one of claims 1-13, wherein the thickness (d) of said distal end portion (6) is 700 µm or smaller. A recording head according to claim 14, wherein the thickness (d) of said distal end portion (6) is within a range of 30-400 µm. A recording head according to any one of claims 1-15, wherein said predetermined distance (L) is within a range of 50-4000 µm. A recording head according to claim 16, wherein said predetermined distance (L) is within a range of 100-1000 µm. A recording head according to any one of claims 1-17, wherein the or each said substrate (1) is made of a highly machinable ceramic material. A recording head according to any one of claims 1-18, wherein the or each said electrode is made of an electrically conductive material whose major component consists of a metal which is at least one of chromium, titanium, tantalum and zirconium, or a compound thereof. A recording head according to any one of claims 1-19, further comprising an insulating layer (7) which covers said electrode (2,3). A recording head according to any one of claims 1-20, further comprising a heat-dissipating layer (8) which covers at least a portion of said electrode (2).

Inventors: HIROTA TOSHIKAZU NGK INSULATOR, OKADA SHIGEKI NGK INSULATORS L, SHIMOGAWA NATSUMI, TAKEUCHI YUKIHISA, HIROTA, TOSHIKAZU NGK INSULATORS, LTD., OKADA, SHIGEKI NGK INSULATORS, LTD., SHIMOGAWA, NATSUMI, TAKEUCHI, YUKIHISA
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1989
Main classification: B41J2
IPC codes: B41J2