JP2005254461A - Thermal head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal head which can improve the printing quality by increasing the continuity of adjacent printing dots while increasing the recording density. <P>SOLUTION: This thermal head is equipped with a plurality of heating resistors which are heated when power is fed. In the thermal head, the dimension in the resistor length direction of each heating resistor is specified to be larger at the central position in the resistor width direction than that at both end positions in the same direction (L>L'). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-performance thermal head mounted on a fusion thermal transfer printer.

  A thermal head for a melting heat transfer printer includes a plurality of heating resistors that generate heat when energized and an electrode layer that supplies electricity to the plurality of heating resistors, and melts ink by the heat of the heating resistors to print. Transfer to media. In this melting type, the print dot diameter can be varied by controlling the heat generation temperature of the heat generation resistor.

  In recent years, further higher recording density (about 600 dpi to 1200 dpi), smaller size, higher speed, and lower cost have been demanded. With this higher recording density, smaller size, higher speed, and lower cost, the number of heating resistors provided in the head can be increased without changing or reducing the size of the head, i.e., the number of printed dots. The planar size (heat generation area) of the heating resistors is small, and the inter-dot gap provided between the heating resistors is also becoming narrower.

JP 63-126767 A JP-A-4-255363 JP-A-4-255364 Japanese Utility Model Publication No. 4-47543

  However, if the inter-dot gap becomes too narrow, it is difficult to form the narrow inter-dot gap with high accuracy, causing variations in the resistance value of the heating resistor due to variations in the inter-dot gap, As a result, there is concern that the yield will be deteriorated. In consideration of the yield here, the inter-dot gap cannot be narrowed beyond a certain level, and the inter-dot gap becomes relatively large with respect to each heating resistor. In the heating resistor, when energized along the resistance length direction, the temperature rise in the central portion in the resistance width direction orthogonal to the energizing direction is larger than that in the peripheral portion. For this reason, as shown in FIG. 8, the printed dot shape is a circular shape that is closer to the center side than the peripheral edge of the heating resistor 105. It has been found that when the inter-dot gap α becomes relatively large with respect to each heating resistor 105, the adjacent print dots D become discontinuous, and the respective print dot shapes appear independently. Increasing the power supply to the heating resistor may increase the printing dot diameter to ensure continuity, but the power supply time to the heating resistor is limited during high-speed printing, and the supply power is low. Therefore, the discontinuity of printed dots is particularly remarkable.

  In the conventional thermal head having a recording density of 300 dpi or less, the planar size (resistance length l = 150 μm, resistance width w = 75 μm) of each heating resistor 105 can be sufficiently secured. Since the dot gap α (about 10 μm) is relatively small with respect to the heating resistor 105, the discontinuity of the printed dots is not a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain a thermal head capable of improving print quality by increasing the continuity of adjacent print dots while realizing high recording density.

  In the present invention, a large amount of current flowing along the resistance length direction of each heating resistor is shunted to both ends in the resistance width direction orthogonal to the energizing direction, so that the heat generation ratio in the vicinity of the gap between dots of each heating resistor can be reduced. This increases the focus of the printed dot shape extending in the resistance width direction, thereby improving the connection between the printed dots.

  That is, according to the present invention, in a thermal head provided with a plurality of heating resistors that generate heat upon energization, each heating resistor has a dimension in the resistance length direction parallel to the energizing direction of the heating resistor orthogonal to the energizing direction. It is characterized by being larger at the center than at both ends in the resistance width direction.

  Each heating resistor preferably has a protruding portion with the largest protruding amount at the central portion in the resistance width direction at at least one end portion in the resistance length direction. The protruding portion can be formed only at the central portion in the resistance width direction. When the protrusion is formed only at the center in the resistance width direction, it is practical to flatten both ends in the resistance width direction located on both sides of the protrusion.

  Specifically, the planar shape of the protruding portion can be a convex arc shape, a convex triangular shape, or a convex trapezoidal shape. In addition, when the protruding portion is formed only at the central portion in the resistance width direction, the planar shape of the protruding portion may be a convex rectangular shape.

  Electrodes are connected to both ends of each heating resistor in the resistance length direction, and it is preferable that the planar shape of each heating resistor is defined by these electrodes. Alternatively, an insulating barrier layer covering the surface of each heating resistor and electrodes connected to both ends in the resistance length direction of each heating resistor are provided, and the planar shape of each heating resistor is defined by the insulating barrier layer. It is preferable.

  According to the present invention, it is possible to obtain a thermal head capable of improving the printing quality by increasing the continuity of adjacent printing dots while realizing high recording density.

  FIGS. 1 and 2 are a plan view (a state before forming a wear-resistant protective layer) and a cross-sectional view showing the thermal head according to the first embodiment of the present invention. This thermal head includes a first insulating layer 2, a heat storage layer 3, a second insulating layer 4, a plurality of heating resistors 5 that generate heat when energized, and a plurality of heating resistors 5 on a Si substrate 1 excellent in heat dissipation. Of the heating resistor 5 is provided with an electrode layer 7 that is electrically connected to both ends in the resistance length direction, and a wear-resistant protective layer 9 that protects the plurality of heating resistors 5 and the electrode layer 7 from contact with an ink ribbon or the like. Yes. This thermal head is for a melt thermal transfer type printer having a high recording density of 1200 dpi or more, and performs printing by melting ink by heat generated by each heating resistor 5 and transferring it to a printing medium. Although not shown, the thermal head is also provided with a drive IC, a printed circuit board, and the like for controlling energization to the plurality of heating resistors 5.

The Si substrate 1 is a p-type Si substrate doped with about 10 ¹⁷ to 10 ¹⁹ boron / cm ³ as an impurity. The specific resistance of the Si substrate 1 is at least 20 mΩ · cm or less, and it is easier to flow current than a Si substrate that does not contain impurities or has few impurities. Insulating films 12 and 13 are respectively formed on the side end face (peripheral end face in the thickness direction) 1b and the back face 1c of the Si substrate 1, and the electric insulation of the Si substrate 1 is provided via the insulating films 12 and 13. Sufficiently secured. The insulating films 12 and 13 are formed of, for example, a sputtered film made of an insulating material such as SiO ₂ , SiAlON, or SiON, or an anodic oxide film by thermal anodic oxidation or a thermal oxide film.

The heat storage layer 3 is made of an oxide compound containing Si, at least one selected from transition metals, and O _2, and has a high heat resistance of about 1000 ° C. The transition metal contained in the heat storage layer 3 is specifically selected from Ta, Ti, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, La, Ce, Hf, and W. 1 type or 2 types or more. In particular, Ta, Mo, and W are preferably used alone or in combination with other transition metals. The heat storage layer 3 has a convex portion having a uniform film thickness portion that causes a step between the Si substrate surface 1a and a tapered edge portion that gradually increases in thickness from the Si substrate surface 1a toward the uniform film thickness portion. As a part, it is formed in a part on the Si substrate surface 1a. Further, a first insulating layer 2 and a second insulating layer 4 made of, for example, SiO ₂ are formed on the upper and lower sides of the heat storage layer 3 as necessary, and above the tapered edge portion of the heat storage layer 3. A plurality of heating resistors 5 are arranged through the second insulating layer 4 so as to be arranged at a minute interval in the Y direction shown in the figure (a direction orthogonal to the paper surface of FIG. 2). The first insulating layer 2 and the fourth insulating layer 4 provide electrical insulation between the Si substrate surface 1a and the heat storage layer 3, and electrical insulation between the heat storage layer 3 and the plurality of heating resistors 5, respectively. It is secured.

  The plurality of heating resistors 5 are part of the resistance film 5 ′ formed on the second insulating layer 4 and generate heat when energized. An inter-dot gap α of about 3 μm is provided between the heating resistors 5. The inter-dot gap α is a space (groove) where the resistance film 5 ′, the insulating barrier layer 6, and the electrode layer 7 are not present and the second insulating layer 4 is exposed.

  The electrode layer 7 is formed on the resistance film 5 ′ over the entire surface, and is formed with an open portion 7c that exposes each heating resistor 5, and a plurality of heat generations are made through the open portion 7c. The resistor 5 is separated into a common electrode 7 a commonly connected to all of the resistors 5 and a plurality of individual electrodes 7 b connected independently to each of the plurality of heating resistors 5. An Al electrode for wiring is formed on each individual electrode 7b, and the width dimension of each individual electrode 7b is regulated by the inter-dot gap α existing between the adjacent individual electrodes 7b. The electrode layer 7 is made of a refractory metal material such as Cr, Ta, Mo, W, or Ti (Cr in this embodiment), and applies a large current with a very short period of about several hundred μs to generate a heating resistor. It is also possible to cope with high-speed printing operations in which 5 is turned on (energized) / off (not energized). The electrode layer 7 may be made of Al or Cu, and may be made of an alloy material containing the above refractory metal material or an alloy material containing Al or Cu.

  On the Si substrate surface 1a, there is an exposed region 10 where the first insulating layer 2 and the heat storage layer 3 do not exist. On the exposed region 10, there is provided a contact portion 11 formed in contact with the end portion of the common electrode 7a adjacent to the exposed region 10 and making ohmic contact between the common electrode 7a and the Si substrate surface 1a. As described above, since the Si substrate 1 has a specific resistance of at least 20 mΩ · cm or less and a larger area and thickness than the common electrode 7 a, the Si substrate 1 is used as a part of the common electrode 7 a via the contact portion 11. It functions and greatly reduces the resistance value of the common electrode 7a. In the present embodiment, the contact portion 11 is formed integrally with the common electrode 7a. However, the contact portion 11 may be formed in contact with or covering the end of the common electrode 7a on the exposed region 10 side. . This contact portion 11 is made of any one of refractory metal materials such as Cr, Al, Ti, W, Mo, Nb, and Cu, or these, in order to improve the adhesion between both the Si substrate 1 and the common electrode 7a. It is preferably formed of a refractory metal material such as Cr, Al, Ti, W, Mo, or Nb or an alloy material mainly containing Cu. The contact portion 11 of this embodiment is made of Cr.

  The thermal head having the above configuration is characterized by the planar shape of the plurality of heating resistors 5. Hereinafter, the heating resistor 5 and the printed dot shape formed by the heat generated by the heating resistor 5 will be described in more detail with reference to FIGS. 1, 3, and 4.

  The heating resistor 5 has convex arcuate protrusions 5a having the largest protrusion amount at the center in the resistance width direction (Y direction in the figure) at both ends in the resistance length direction (X direction in the figure). The resistance length L (hereinafter simply referred to as “central resistance length”) L at the center position in the width direction is longer than the resistance length L ′ at the end position in the resistance width direction (hereinafter simply referred to as “end resistance length”) L ′. It has become. The planar shape (central resistance length L, end resistance length L ′, resistance width W) of the heating resistor 5 is defined by the electrode layer 7. Specifically, the central resistance length L of the heating resistor 5 can be about 56 μm, the end resistance length L ′ can be about 45 μm, and the resistance width W can be about 18 μm. For example, when compared with the conventional thermal head shown in FIG. 8, the inter-dot gap α of the present embodiment is relatively large with respect to the heating resistor 5. Here, when the heating resistor 5 is energized through the common electrode 7a and the individual electrode 7b, the heating resistor 5 can be regarded as an electrical resistance as shown in FIG. 3, and in the resistance length direction parallel to the energizing direction. The longer the dimension, the greater the electrical resistance value. Therefore, if the central resistance length L of the heating resistor 5 is larger than the end resistance length L ′, the electrical resistance value of the heating resistor 5 is larger at the central position in the same direction than the end position in the resistance width direction (see FIG. 3> r> r ′), current easily flows at both ends of the heating resistor 5 in the resistance width direction. That is, the amount of current flowing at both ends of the heating resistor 5 in the resistance width direction is larger than when the resistance length of the heating resistor 5 is constant, and the heat generation ratio at both ends of the heating resistor 5 in the resistance width direction is reduced. Can be increased. Therefore, as shown in FIG. 4, the print dot shape extends long in the alignment direction of the print dots D to form a substantially oval shape, and adjacent print dots D can be smoothly continuous. Thereby, even if the dot gap region α is relatively large with respect to the heating resistor 5 as the recording density is increased, the connection between the printing dots D can be improved, and high-quality printing can be realized.

  5 and 6 are a plan view (a state before forming the wear-resistant protective layer) and a sectional view showing the thermal head according to the second embodiment of the present invention. The second embodiment includes insulating barrier layers 6 that respectively cover the surfaces of the plurality of heating resistors 5, and the insulating barrier layer 6 allows the planar shape of each heating resistor 5 (central resistance length L, end resistance length L ′, It differs from the first embodiment in that it defines a resistance width W). The configuration is the same as that of the first embodiment except that the insulating barrier layer 6 is used in place of the electrode layer 7 to define the planar shape of each heating resistor 5. 5 and 6, the same reference numerals as those in FIGS. 1 and 2 are assigned to components having the same functions as those in the first embodiment.

The insulating barrier layer 6 is preferably formed of an insulating material having oxidation resistance and applicable to reactive ion etching (RIE). Specifically, SiO ₂ , Ta ₂ O ₅ , SiN, Si ₃ N ₄ , SiON, AlSiO, SiAlON or the like may be used. The insulating barrier layer 6 has a function of preventing surface oxidation of the plurality of heating resistors 5 and a function of protecting the plurality of heating resistors 5 from etching damage during the manufacturing process. The electrode layer 7 is formed over the resistance film 5 ′ and the insulating barrier layer 6, and then formed with an open portion 7 c that exposes the insulating barrier layer 6. Both end portions of the electrode layer 7 on the insulating barrier layer 6 side are overlaid on the insulating barrier layer 6.

  In the second embodiment, since the central resistance length L of the heating resistor 5 is defined longer than the end resistance length L ′ by the insulating barrier layer 6, the resistance of the heating resistor 5 is the same as in the first embodiment. Current flows easily at both ends in the width direction, and the amount of heat generated at both ends increases, and as shown in FIG. 4, the printing dot shape extends in the alignment direction of the printing dots, so that adjacent printing dots are smoothed. Can be continuous. This makes it possible to achieve both high recording density and high quality printing. Further, by using the insulating barrier layer 6, even when the planar shape of the heating resistor 5 is defined in a complicated manner, it is possible to suppress variation in resistance value for each printing dot D.

In each of the embodiments described above, the heating resistor 5 includes the protruding arc-shaped protruding portion 5a, but the planar shape of the heating resistor 5 can be variously modified. FIG. 7 shows a modification of the planar shape of the heating resistor 5. FIG. 7A shows a heating resistor 15 having a protruding triangular protrusion 15a having the largest protrusion at the center in the resistance width direction, from the center position in the resistance width direction to both end positions in the same direction. The dimension in the resistance length direction gradually decreases. FIG. 7B shows the heating resistor 25 having a convex-shaped protrusion 25a having the largest protrusion at the center in the resistance width direction. In this aspect, the dimension in the resistance length direction at the central portion in the resistance width direction is substantially constant, and is larger than both end portions in the resistance width direction. FIG. 7C shows a convex arc-shaped protruding portion 35a formed only at the central portion in the resistance width direction at both ends in the resistance length direction, and both sides of the protruding portion 35a, that is, at both ends in the resistance width direction. A heating resistor 35 having a flat portion 35b is shown. FIG. 7D shows a protruding triangular protrusion 45a formed only at the center in the resistance width direction at both ends in the resistance length direction, and both sides of the protrusion 45a, that is, at both ends in the resistance width direction. A heating resistor 45 having a flat portion 45b is shown. FIG. 7E shows a convex trapezoidal protrusion 55a formed only at the center in the resistance width direction at both ends in the resistance length direction, and on both sides of the protrusion 55a, that is, at both ends in the resistance width direction. A heating resistor 55 having a flat portion 55b is shown. In any of the embodiments shown in FIGS. 7A to 7E, the heating resistor has a central resistance length L larger than the end resistance length L ′. The planar shape of the heating resistor is not limited to the example shown in the figure, and it is sufficient that the central resistance length L> the end resistance length L ′.

It is a top view which shows the thermal head by 1st Embodiment of this invention. It is sectional drawing which shows the thermal head. It is a schematic diagram which electrically explains the heating resistor of the thermal head. It is a schematic diagram explaining the relationship between the planar shape of the heating resistor of the thermal head and the printed dot shape. It is a top view which shows the thermal head by 2nd Embodiment of this invention. It is sectional drawing which shows the thermal head shown in FIG. It is a top view which shows another Example of the planar shape of the heating resistor by this invention. It is a schematic diagram explaining the relationship between the planar shape of the heating resistor of the conventional thermal head and the printed dot shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Si substrate 2 1st insulating layer 3 Thermal storage layer 5 'Resistance film 5 Heating resistor 5a Protruding part 6 Insulating barrier layer 7 Electrode layer 7a Common electrode 7b Individual electrode 7c Open part 10 Exposed area 11 Contact part D Print dot L Central resistance Length L 'End resistance length W Resistance width X Resistance length direction, heating resistor energization direction Y Resistance width direction α Inter-dot gap

Claims (7)

In thermal heads with multiple heating resistors that generate heat when energized,
Each of the heat generating resistors is characterized in that the dimension in the resistance length direction parallel to the energizing direction of the heat generating resistor is larger at the center than both ends in the resistance width direction orthogonal to the energizing direction. 2. The thermal head according to claim 1, wherein each of the heating resistors has a protruding portion having a largest protruding amount at a central portion in the resistance width direction at at least one end portion in the resistance length direction. The thermal head according to claim 2, wherein the protrusion is formed only at a central portion in the resistance width direction. 4. The thermal head according to claim 2, wherein a planar shape of the protruding portion is a convex arc shape, a convex triangular shape, or a convex trapezoidal shape. The thermal head according to claim 3, wherein a planar shape of the protruding portion is a convex rectangular shape. In the thermal head according to any one of claims 1 to 5, electrodes are connected to both ends of each heating resistor in the resistance length direction, and the planar shape of each heating resistor is formed by the electrodes. Specified thermal head. The thermal head according to any one of claims 1 to 5, wherein an insulating barrier layer that covers a surface of each heating resistor, electrodes connected to both ends of each heating resistor in a resistance length direction, and A thermal head in which a planar shape of each heating resistor is defined by the insulating barrier layer.

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