JP2017065021A - Thermal print head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal print head capable of printing high-quality images.SOLUTION: A thermal printer can pull a fixing range AF of a storage medium 5 from the surface of a heating resister substrate 12 of a thermal print head by forming a separate recession 12D on the downstream side of a heat element 23H in the heating resister substrate 12. Accordingly, the thermal printer can re-solidify thermosensitive components and molten materials without fixing the storage medium 5 to the surface of the heating resister substrate 12 when performing low heat print after subjecting the storage medium 5 to continuous heat print and thereby can print high-quality images while effectively suppressing generation of load fluctuation unevenness.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a thermal print head that is an image recording device.

  In the thermal print head, each heating resistor is heated in a heating portion in which a plurality of heating resistors are arranged along the main scanning direction, and pixels are formed on the recording medium by the heat. It is possible to print and print figures. This thermal print head is widely used in recording devices such as a barcode printer, a digital plate making machine, a photo printer, an imager, and a seal printer (see, for example, Patent Document 1).

  The thermal print head is preliminarily contained in the recording medium by causing each heating resistor to generate heat in the heat generating portion while pressing the recording medium against the platen roller and moving the recording medium in the sub-scanning direction by rotation of the platen roller. Each pixel is formed by melting a printing material such as a heat-sensitive component and solidifying the printing material on the recording medium.

Japanese Patent Laying-Open No. 2015-74131 (FIG. 1)

  By the way, in the thermal print head, the heating time for forming one pixel in the heating resistor is constant on the assumption that the moving speed of the recording medium by the platen roller is constant. Thus, the thermal print head can keep the length of each pixel in the moving direction of the medium (that is, the sub-scanning direction) constant.

  However, in a thermal printer equipped with a thermal print head, depending on the content of the image to be printed, the molten printing material moves to the downstream side of the heat generating part as the recording medium moves and adheres to the surface of the thermal print head when solidified. In some cases, the resistance between the recording medium and the thermal print head is temporarily increased or decreased.

  In such a case, in the thermal printer, the load acting on the recording medium fluctuates and the moving speed changes, thereby changing the length of each pixel in the sub-scanning direction, and improving the image quality of the printed image. There was a problem that it was greatly reduced.

  The present invention has been made in consideration of the above points, and intends to propose a thermal print head capable of printing a high-quality image.

  In order to solve this problem, in the thermal print head of the present invention, the recording medium is sandwiched between the peripheral side surface of the rotating platen roller and the heating resistor substrate and moves from the upstream side to the downstream side along the sub-scanning direction. A plurality of heating resistor substrates are arranged along the main scanning direction orthogonal to the sub-scanning direction, and the printing material is heated and melted by heat generation and then solidified on the recording medium. A heating resistor for printing pixels on the recording medium, and a separation recess formed on the downstream side of the heating resistor on the facing surface facing the platen roller, and separating the surface of the facing surface from the recording medium And so on.

  In the present invention, when the printing material heated and melted by the heating resistor is solidified on the downstream side of the heating resistor due to the progress of the recording medium, the recording medium is separated from the surface of the heating resistor substrate by the separation depression. Can be pulled apart. As a result, the present invention can prevent the recording medium from sticking to the heating resistor substrate, so that it is possible to prevent fluctuations in the moving speed due to fluctuations in the load of the recording medium and to avoid deterioration in image quality due to changes in the line pitch.

  According to the present invention, a thermal print head capable of printing a high-quality image can be realized.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a thermal printer. It is an approximate line sectional view showing composition of a heating resistor substrate. It is an approximate line sectional view showing the composition of the conventional heating resistor substrate. It is a basic diagram which shows the printing result by the conventional heating resistor board | substrate. It is a basic diagram which shows the relationship between the position of melting and solidification of heat-sensitive components in a recording medium. It is a basic diagram which shows the printing result at the time of changing the number of lines of a continuous heating printing. It is a basic diagram which shows the relationship between the position of a heating resistor, formation of a heating pixel, and a movement in case a continuous heating printing is made into 2 lines. It is a basic diagram which shows the relationship between the position of a heating resistor, and the formation and movement of a heating pixel when continuous heating printing is 4 lines. It is a basic diagram which shows the relationship between the position of a heating resistor, and formation and movement of a heating pixel when continuous heating printing is 8 lines. It is a basic diagram which shows the heating of the recording medium by the heat generating resistor board | substrate in embodiment. It is a basic diagram which shows the printing result by the heating resistor board | substrate in embodiment. It is a basic diagram which shows the structure of the heating resistor board | substrate by other embodiment.

  Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings. This embodiment is merely an example, and the present invention is not limited to this.

[1. Configuration of thermal print head]
As shown in the sectional view of FIG. 1, the thermal printer 1 according to the present embodiment has a configuration in which a recording medium 5 is sandwiched between a thermal print head 2 and a platen roller 3. The thermal printer 1 prints a desired image or character by causing the thermal printing head 2 to heat the printing material previously contained in the recording medium 5.

  The recording medium 5 is so-called thermal paper, and a thermal layer containing a thermal component that reacts with heat is provided on the surface. Although the heat-sensitive component as a printing material is initially colorless or white, it has a property of changing to another color (for example, black) by a chemical reaction when heat is applied. For this reason, the recording medium 5 is printed with images and characters by changing the properties of the portions to which heat is applied.

  For convenience of explanation, the direction toward the platen roller 3 is defined as the upward direction, and the direction toward the thermal print head 2 is defined as the downward direction. The traveling direction of the recording medium 5 is defined as the forward direction, and the opposite direction is defined as the backward direction. Further, the direction toward the front side of the page is defined as the left direction, and the direction toward the back of the page is defined as the right direction. Hereinafter, the left-right direction is also referred to as a main scanning direction, and the front-rear direction is also referred to as a sub-scanning direction. In addition to this, hereinafter, when focusing on the traveling direction of the recording medium 5, the rear side is also referred to as the upstream side, and the front side is also referred to as the downstream side.

  The thermal print head 2 is roughly composed of a heat radiating plate 11, a heating resistor substrate 12 and a circuit substrate 13. The heat radiating plate 11 as a whole is formed in a rectangular parallelepiped shape whose longitudinal direction is the left-right direction (main scanning direction), and has a sufficient thickness in the up-down direction, so that it does not easily deform with respect to external force, etc. It has sufficient rigidity.

  The heat radiating plate 11 is made of a metal having a high thermal conductivity such as aluminum (Al) or an aluminum alloy, for example. The heat generated in the heating resistor substrate 12 is mainly transmitted to the lower surface side and into the air. discharge. Incidentally, the upper surface of the heat radiating plate 11 is formed lower in the portion where the rear circuit board 13 is placed than in the portion where the front heating resistor substrate 12 is placed.

  The heating resistor substrate 12 is formed in a rectangular plate shape whose longitudinal direction is the left-right direction. As shown in FIG. 2, the heating resistor substrate 12 has a plurality of layers such as a glaze layer 22, a resistance film layer 23, a conductive layer 24, and a protective layer 25 sequentially stacked on a support substrate 21.

The support substrate 21 is made of ceramics such as alumina (Al ₂ O ₃ ), for example, and is formed in a thin plate shape that is elongated in the left-right direction. Further, the longitudinal length of the support substrate 21 is shorter than the longitudinal length of the heat sink 11. The glaze layer 22 is made of an insulating glass material, for example, a paste-like glass material is applied on the support substrate 21 and baked. Further, in the vicinity of the front end of the glaze layer 22, a protrusion 22 </ b> A that protrudes upward from the surroundings is formed. The protrusion 22A has a shape in which the outer shape (FIG. 2 and the like) when viewed from the left-right direction approximates a part of the circumference by firing the glass material.

The resistance film layer 23 is made of a cermet material such as Ta—SiO ₂ and has a relatively high electrical resistivity. The resistance film layer 23 is formed, for example, on the upper surface of the glaze layer 22 by sputtering, and is formed into a predetermined pattern by etching. Incidentally, the resistance film layer 23 is configured as a plurality of regions separated from each other in the left-right direction, that is, the main scanning direction.

  The conductive layer 24 is made of a material having high electrical conductivity such as aluminum (Al), for example, is formed on the upper surface of the resistance film layer 23 by sputtering, and constitutes a predetermined wiring pattern by etching. Incidentally, the wiring pattern of the conductive layer 24 is mainly formed with many portions along the front-rear direction, that is, the sub-scanning direction. In addition, a gap 24G that is electrically separated is formed in a part of the conductive layer 24 in the upper portion of the protrusion 22A.

  With such a configuration, when a current is supplied to the wiring pattern of the conductive layer 24, the heating resistor substrate 12 causes the current to flow through the resistance film layer 23 only in the gap 24G. be able to. Hereinafter, the portion of the resistance film layer 23 that generates heat when the current flows in this manner is also referred to as a heating resistor 23H, and the portion where the gap 24G is formed in the heating resistor substrate 12 is also referred to as a heating portion 12H.

  The protective layer 25 is made of, for example, SiON or the like and is formed by sputtering. The protective layer 25 is formed on the upper side of the conductive layer 24 so as to have a substantially uniform thickness, and protects the layers below the conductive layer 24. For this reason, the heating resistor substrate 12 is formed with a protrusion 12A that protrudes upward in accordance with the protrusion 22A. The protrusion 12A has a shape in which the outer shape when viewed from the left-right direction approximates a part of the circumference, like the protrusion 22A of the glaze layer 22. Further, the surface of the protective layer 25 is the uppermost surface of the heating resistor substrate 12 and is also a facing surface that faces the recording medium 5.

  Further, a portion of the upper surface side of the protective layer 25 is recessed on the downstream side (that is, the front side) of the heat generating resistor substrate 12 from the upstream side (rear side) of the heat generating portion 12H, so that it is depressed downward. A separation recess 12D is formed (details will be described later).

  The circuit board 13 (FIG. 1) is, for example, a so-called glass epoxy board, and is a single-layer or multilayer wiring board. The circuit board 13 is formed in a rectangular plate shape that is thin in the vertical direction, and the length in the left-right direction is substantially the same as that of the heating resistor board 12. A predetermined wiring pattern is formed on the circuit board 13 with a conductive material such as copper (Cu). On this wiring pattern, electrodes for attaching bonding wires and terminals of electronic components are formed. This wiring pattern is protected by an insulating protective material except for electrode portions.

  A plurality of driver ICs (Integrated Circuits) 14 are attached to the front side of the upper surface of the circuit board 13 so as to be aligned in the left-right direction. A number of terminals for electrical connection are provided on the upper surface of the driver IC 14. The driver IC 14 is electrically connected by bonding wires 15 between these terminals and terminals formed on the upper surface of the heating resistor substrate 12 and between these terminals and terminals formed on the upper surface of the circuit board 13. Connected. Further, the driver IC 14 and the bonding wire 15 are sealed with a resin 16 made of an epoxy resin material.

  Incidentally, the circuit board 13 is provided with a connector (not shown), and a cable (not shown) provided in the main body of the thermal printer 1 is connected to this connector so that a power source, a control signal, etc. Is supplied.

  With this configuration, when the power and control signals are supplied from a cable (not shown) via a connector, the thermal print head 2 supplies the power to the driver ICs 14 with a wiring pattern on the circuit board 13. The driver IC 14 is connected to the ground line and functions as a switch based on the control signal.

  The heating resistor substrate 12 generates heat by flowing the supplied current forward through the resistance film layer 23 in the gap 24G by the circuit pattern formed by the conductive layer 24. As a result, the heat generating resistor substrate 12 can cause the heat generating portion 12H to generate heat only at a location based on the control signal in the main scanning direction.

  The platen roller 3 includes a central shaft 31 and a cylindrical portion 32. The central axis 31 is formed in an elongated cylindrical shape whose center is along the left-right direction (that is, the main scanning direction). The cylindrical portion 32 has a cylindrical shape with the center extending in the left-right direction, and the central shaft 31 is inserted through the central portion. The cylindrical portion 32 is made of a material having a predetermined elasticity and a relatively large frictional force. Therefore, the cylindrical portion 32 is elastically deformed when an external force is applied, and a reaction force against the external force is applied.

  The platen roller 3 is urged with a central shaft 31 toward the protruding portion 12A of the heating resistor substrate 12 by an urging member (not shown). For this reason, the platen roller 3 can press the recording medium 5 against the protrusion 12 </ b> A of the heating resistor substrate 12. At this time, the platen roller 3 is elastically deformed, thereby deforming the recording medium 5 into a shape along the surface of the protrusion 12A and pressing it stably.

  Further, the platen roller 3 rotates counterclockwise in the drawing when a driving force is transmitted from a motor (not shown). At this time, when the platen roller 3 is in contact with the recording medium 5 in the vicinity of the lower end of the outer peripheral surface thereof as shown in FIG. 1, the friction force is applied to the recording medium 5 to cause the recording medium 5 to move. It can be moved forward.

  With this configuration, when performing printing, the thermal printer 1 rotates the platen roller 3 so that the recording medium 5 is pressed against the protruding portion 12A of the heating resistor substrate 12 in the thermal print head 2 along the sub-scanning direction. And move forward. At the same time, the thermal printer 1 appropriately changes the control signal supplied to the circuit board 13 and changes the heat generation pattern of each heat generating resistor 23H in the heat generating portion 12H as the recording medium 5 advances. As a result, the thermal printer 1 can heat the recording medium 5 only for desired pixels line by line, and by repeating this for a plurality of lines, an image, a character, or the like consisting of a set of these pixels is displayed on the recording medium 5. It can be formed, i.e. printed.

  For convenience of explanation, the formation of pixels by causing the heat generating portion 12H to generate heat and heat sensitive components contained in the recording medium 5 will be referred to as heating printing, and the pixels formed at this time will be referred to as heating pixels. This heating pixel is, for example, a black pixel. On the contrary, the fact that the heat generating portion 12H does not generate heat and the recording medium 5 is not heat sensitive is called non-heated printing, and the pixel formed at this time is called non-heated pixel. This non-heated pixel is, for example, a white pixel.

[2. Effect and fluctuation of load on recording medium]
Next, a case where a load acts on the recording medium 5 and a case where this load varies will be described. Here, before describing the heating resistor substrate 12 according to the present embodiment, a case of a conventional heating resistor substrate will be described as a comparison object.

  As shown in FIG. 3 corresponding to FIG. 2, the conventional heating resistor substrate 112 has a protective layer 125 instead of the protective layer 25 as compared with the heating resistor substrate 12 according to the present embodiment. The heating resistor substrate 12 is not formed with a separation recess 12D on the downstream side (that is, the front side) of the heating portion 12H. That is, the protective layer 125 is formed substantially symmetrically in the front-rear direction in the vicinity of the protruding portion 112A with the heat generating portion 12H interposed therebetween.

  When a specific print content is printed on the recording medium 5 by the conventional thermal print head on which the conventional heating resistor substrate 112 is mounted, the image quality may be deteriorated. This specific print content refers to continuous heating printing for a plurality of lines (hereinafter referred to as continuous heating printing), and then continuous non-heating printing for a plurality of lines, or the ratio of heating pixels. Is a low print (hereinafter collectively referred to as low heat print).

  For example, FIG. 4 shows a hatched portion obtained when a hatched line having a line width of 1 pixel is repeatedly printed at predetermined intervals after continuous heating printing using the conventional heating resistor substrate 112. The print result P1 is shown. This print result P1 is printed along the direction of the arrow J1, and after the continuous heating printing is completed at the boundary line LB1, printing with diagonal lines is started.

  Here, attention is focused on the oblique line Q1 obtained by connecting the pixels formed in the printing result P1. The oblique line Q1 meanders with respect to a straight auxiliary line LS1 representing an ideal oblique line. Specifically, the oblique line Q1 approximates the auxiliary line LS2 in the range up to the first sixth line, and the inclination with respect to the boundary line LB1 is smaller than the auxiliary line LS1. This means that in this range, the period of each pixel in the sub-scanning direction of the print result P1 (hereinafter referred to as the line pitch) is narrowed (clogged).

  The oblique line Q1 approximates the auxiliary line LS3 in the range from the seventh line to the tenth line, and the inclination with respect to the boundary line LB1 is larger than that of the auxiliary line LS1. This means that the line pitch of the printing result P1 is widened in this range. Further, the oblique line Q1 meanders with respect to the auxiliary line LS1 with a relatively small amplitude even after the 11th line. That is, the print result P1 gradually converges while the line pitch is repeatedly enlarged and reduced.

  Such a change in line pitch is considered to be caused by a change in the traveling speed of the recording medium 5 in the sub-scanning direction. Originally, the recording medium 5 travels at a constant traveling speed by a constant force applied from the platen roller 3 (FIG. 1). For this reason, some load acts on the recording medium 5 after the end of continuous heating printing, or friction is generated between the heating resistor substrate 112 and the load or frictional force fluctuates. Guessed. In the following, such repeated variation of the line pitch is referred to as occurrence of load variation unevenness.

  As schematically shown in FIG. 5A, the heating resistor substrate 112 heats the heating resistor 23H (that is, the heating portion 12H) and transfers the generated heat to the recording medium 5 when performing heat printing. . In response to this, the recording medium 5 makes the predetermined area 5A abut against the heat generating portion 12H to make it heat sensitive.

  At this time, after the heat-sensitive component contained in the heat-sensitive layer is once melted by heat, the region 5A is cooled while moving forward as the platen roller 3 (FIG. 1) rotates, and gradually solidifies (that is, re-solidifies). To go. Eventually, the region 5A is completely solidified, so that pixels (that is, heat-sensitive pixels) are formed on the recording medium 5.

  Here, in the recording medium 5, since the formed pixels are colored by chemical change, when the heat-sensitive component is once melted in the region 5A, some dissolved matter is generated, and this region 5A is cooled while moving forward. Thus, when reaching the downstream side of the heat generating part 12H, it is possible that the melted material is re-solidified together with the heat-sensitive component. At this time, it is presumed that the load (frictional force) is increasing in the region 5A of the recording medium 5 as the heat-sensitive component and the dissolved material are re-solidified so as to adhere to the surface of the heating resistor substrate 112 in contact therewith. .

  Further, when the non-heated printing is continuously performed after the continuous heating printing is performed as described above, the heating resistor substrate 112 stops the heat generation of the heat generating portion 12H when the continuous heating printing is finished. At this time, the recording medium 5 has the longest elapsed time from the completion of the heating among the plurality of adjacent regions continuously melted, and the distance from the vicinity of the heat generating portion 12H where the residual heat remains is the longest. It will resolidify sequentially from the farthest, most downstream area.

  Further, the recording medium 5 has a traveling path in the vicinity of the protrusion 112A due to the rotational speed and deformation degree of the platen roller 3 (FIG. 1) and the arrangement of guide rollers (not shown) for guiding the recording medium 5. Determined. Specifically, the recording medium 5 is pressed (i.e., nipped) against the surface of the protrusion 112A by the platen roller 3 (FIG. 1) in the nip range AN in FIG. Since the region 5A of the recording medium 5 is separated from the surface of the protrusion 112A when it deviates from the nip range AN, the force to be fixed due to re-solidification of the heat-sensitive component and the melt, that is, the load (frictional force) is also generated. No longer occurs.

  When the temperature change of the region 5A in the recording medium 5 is graphed, it can be expressed as a curve QT in FIG. In FIG. 5B, the resolidification temperature T1 is a temperature at which the heat-sensitive component or the like resolidifies. Incidentally, in FIG. 5B, the change in the amount of the portion of the recording medium 5 in which the heat-sensitive component is melted to become liquid by heating is also displayed by a curve QV.

  In FIG. 5B, the position where the curve QT reaches the resolidification temperature T1 on the downstream side of the heat generating portion 12H is a position where the heat-sensitive component and the melted material in the recording medium 5 resolidify and start fixing. (Hereinafter, this will be referred to as a sticking start position S1). In FIG. 5B, when the region 5A of the recording medium 5 reaches the downstream end point in the nip range AN, it is separated from the heating resistor substrate 112, so that the fixing is finished. Hereinafter, the position where the fixing between the recording medium 5 and the heating resistor substrate 112 is also referred to as a fixing end position S2. Further, for convenience of description, the center position in the front-rear direction of the heating resistor 23H is also referred to as a heating center position S0.

  That is, it is considered that the recording medium 5 and the heating resistor substrate 112 are fixed due to re-solidification in the range from the fixing start position S1 to the fixing end position S2. Hereinafter, this range is referred to as a fixing range AF. The length in the front-rear direction in the fixing range AF is related to the size of the area where the fixing occurs, and is generated between the size of the load acting on the recording medium 5 or between the recording medium 5 and the heating resistor substrate 112. It is also related to the magnitude of frictional force.

  For example, when the fixing range AF is relatively long, the recording medium 5 increases the acting load and the traveling speed decreases, as in the range up to the first sixth line in the print result P1 (FIG. 4), It is estimated that the line pitch is reduced. On the other hand, in the recording medium 5, when the fixing range AF becomes relatively short, the acting load decreases and the traveling speed is restored (that is, increases toward the original traveling speed), and the printing result P1 (FIG. 4). It is estimated that the line pitch is expanded as in the seventh to tenth lines.

  Therefore, the occurrence of load fluctuation unevenness is that a fixing range AF where a part of the recording medium 5 is fixed to the surface of the heating resistor substrate 112 occurs and the length in the sub-scanning direction varies. It is thought to be the cause.

[3. Identification of fixing range]
Next, after performing continuous heating printing on the recording medium 5 using the heating resistor substrate 112 under a plurality of conditions, in order to conduct a detailed investigation on the fixing range AF that causes the occurrence of load variation unevenness. Low heat printing was performed. In this low-heat printing, as with the printing result P1 (FIG. 4), it is possible to record fluctuations in the line pitch in the printing result by repeatedly printing diagonal lines with a line width of one pixel at predetermined intervals. .

  Specifically, whether or not the fixing range AF is formed by changing the number of lines for continuous heating printing to 2 lines, 4 lines, 8 lines, and 16 lines and visually observing the print results obtained in each line. The fixing start position S1 and the fixing end position S2 were confirmed. Incidentally, the resolution of the heating resistor substrate 112 is 1200 [dpi: dot per inch], and accordingly, the period of one line in the sub-scanning direction is 21.1 [μm].

  6 (A), (B), (C) and (D) show the printing results P2 obtained when the number of lines for continuous heating printing is 2 lines, 4 lines, 8 lines and 16 lines, respectively. P3, P4 and P5 are represented. The auxiliary line LS1 represents an ideal oblique line as in the case of FIG.

  From the printing result P2, when the continuous heating print is 2 lines, it is considered that the fixing range AF is not formed because the line pitch hardly fluctuates. Here, the relationship between the position of the heating resistor 23H and the formation and movement of the heating pixel when the continuous heating printing is two lines can be summarized as shown in FIG.

  In FIG. 7, the horizontal direction represents a position along the sub-scanning direction, and each line is divided by a broken line. The nip upstream range AN1 and the nip downstream range AN2 respectively represent a range on the upstream side and a downstream side of the heat generation center position S0 in the nip range AN, and are about 140 [μm] and about 134 [μm], respectively. It is. Incidentally, the length LH in the front-rear direction (sub-scanning direction) of the heating resistor 23H is about 13 [μm] shorter than the cycle of one line.

  In FIG. 7, the vertical direction represents the passage of time, and heating printing was performed at times K1 and K2 to form black pixels (heating pixels), and non-heating printing was performed at times W1 to W10 following this. This shows that white pixels (non-heated pixels) are formed.

  On the other hand, from the printing results P3 to P5 (FIG. 7), when the continuous heating printing is 4 lines or more, the line pitch does not change from the first to the second line after the end of the continuous heating printing. The line pitch fluctuates in FIG.

  Among these, from the printing result P3, when the continuous heating printing is 4 lines, the line pitch is narrowed in the second to third lines after the end of the continuous heating printing, and it is considered that the fixing range AF is formed at this time. It is done. Further, from the printing results P4 and P5, when the continuous heating printing is 8 lines or more, the line pitch is narrowed in the second to sixth lines after the end of the continuous heating printing, and the fixing range AF is formed at this time. it is conceivable that.

  Here, in the case where the continuous heating printing is 4 lines and 8 lines, the relationship between the position of the heating resistor 23H and the formation and movement of the heating pixel is summarized as shown in FIGS. 8 and 9 corresponding to FIG. Can be represented.

  In FIG. 8, unlike FIG. 7, four times of heating printing are repeatedly performed at times K <b> 1 to K <b> 4, and black pixels (heating pixels) are continuously formed. Incidentally, in FIG. 8, the “clogged” column on the right side indicates that the line pitch is clogged at the times W2 and W3.

  FIG. 9 shows that heating pixels are repeatedly printed eight times at times K1 to K8 to continuously form black pixels (heating pixels). In FIG. 9, in the “clogged” column on the right side, the line pitch is clogged at times W2 to W6.

  The timing at which clogging of the line pitch starts from time W2 in FIG. 8 and FIG. 9 is about 42 [μm] when the last heated pixel moves to the downstream side by two lines, that is, from the heat generation center position S0. Presumed when moving downstream. The timing at which the line pitch clogging ends from time W6 in FIG. 9 is when the last heated pixel has moved to the downstream side by six lines, that is, about 127 [μm] downstream from the heat generation center position S0. Inferred when moving. The position on the downstream side of about 127 [μm] from the heat generation center position S0 substantially coincides with the end points on the downstream side in the nip range AN and the nip downstream range AN2.

  To summarize the above investigation results, in the conventional heating resistor substrate 112, when low heating printing is performed after continuous heating printing, the heating pixel that has been subjected to the last heating printing is the fixing range AF, that is, the fixing start position S1 and the fixing end. When the position is between the positions S2, the line pitch is clogged. When the resolution of the heating resistor substrate 112 is 1200 [dpi], the fixing start position S1 and the fixing end position S2 are about 42 [μm, which corresponds to about two lines and about six lines from the heat generation center position S0. ] Downstream side and about 127 [μm] downstream side.

  Therefore, in the heating resistor substrate 112, if the contact between the surface of the heating resistor substrate 112 and the recording medium 5 can be avoided between the fixing range AF, that is, between the fixing start position S1 and the fixing end position S2. It is considered that clogging of the line pitch can be suppressed.

[4. Avoiding load fluctuation unevenness]
Therefore, in the thermal printer 1 according to the present embodiment, the separation recess 12D is formed on the downstream side of the heat generating portion 12H (that is, the heat generating resistor 23H) in the heat generating resistor substrate 12 (FIG. 2) of the thermal print head 2.

  The separation recess 12D is located on the downstream side of the heating resistor 23H, in the range from the recess upstream position D1 to the recess downstream position D2, in the vicinity of the upper surface of the protective layer 25 from the case of the conventional heating resistor substrate 112 (FIG. 3). Is also formed by recessing downward.

  The depression upstream position D1 is about 40 [μm] downstream from the heat generation center position S0 and slightly upstream from the fixing start position S1 (about 42 [μm] downstream from the heat generation center position S0). The depression downstream position D2 is about 130 [μm] downstream from the heat generation center position S0 and slightly downstream from the fixing end position S2 (about 127 [μm] downstream from the heat generation center position S0). .

  That is, the separation recess 12D is set to a position that is slightly wider than the fixing range AF between the fixing start position S1 and the fixing end position S2 and that reliably includes the fixing range AF. The separation recess 12D is recessed downward by about 3 [μm] as compared with the case of the conventional heating resistor substrate 112 (indicated by a broken line in the drawing).

  In the heating resistor substrate 12, in the manufacturing process, for example, the glaze layer 22 is formed on the support substrate 21, and the resistance film layer 23 is further formed thereon. Subsequently, after the conductive layer 24 is formed on the heat generating resistor substrate 12 by a photolithography process or the like to form the electrode and the heat generating resistor 23H, the protective layer 25 having a single layer or a multilayer is formed on the conductive layer 24.

  Finally, the heating resistor substrate 12 is selectively etched in the vicinity of the surface of the protective layer 25 by a photolithography process or the like, thereby forming the separation recess 12D. That is, the heating resistor substrate 12 is additionally formed with the separation recess 12D after the protective layer 25 is formed by the same manufacturing process as the conventional heating resistor substrate 112 (FIG. 3).

  As shown in FIG. 10, when the recording medium 5 is pressed by the platen roller 3, the heating resistor substrate 12 is fixed to the portion of the recording medium 5 in the fixing range AF by the separation recess 12 </ b> D. 12 surfaces can be pulled apart. As a result, when the low-temperature printing is performed after the continuous heating printing is performed on the heating resistor substrate 12, the heat-sensitive component and the melted material melted in the recording medium 5 are transferred from the recording medium 5 to the heating resistor substrate 12. It can be re-solidified without sticking to the surface.

  Actually, when the heating resistor substrate 12 is used and the low heating printing is performed after the continuous heating printing is performed on the recording medium 5, the printing result P6 shown in FIG. 11 corresponding to FIGS. 4 and 6 is obtained. It was. In this print result P6, when compared with the auxiliary line LS1, a slight oblique wave, that is, a change in the line pitch is recognized, but the degree of the wave and the fluctuation range of the line pitch are smaller than those in FIG. It can be seen that it is much smaller.

  Thus, the heating resistor substrate 12 can remarkably reduce the amount of load fluctuation unevenness even when low heating printing is performed after continuous heating printing, and the line pitch is kept substantially constant. A high-quality image can be printed as it is.

  According to the above configuration, the thermal printer 1 forms the fixing area AF of the recording medium 5 by forming the separation depression 12D on the downstream side of the heating resistor 23H in the heating resistor substrate 12 of the thermal print head 2. The heating resistor substrate 12 can be separated from the surface. Therefore, when the thermal printer 1 performs low-heat printing after performing continuous heating printing on the recording medium 5, the thermal printer 1 does not fix the recording medium 5 on the surface of the heating resistor substrate 12 and Since the melt can be re-solidified, a high-quality image can be printed while effectively suppressing the occurrence of load variation unevenness.

[5. Other Embodiments]
In the above-described embodiment, the sticking start position S1 and the sticking end position S2 are each about 42 [μm] downstream from the heat generation center position S0 based on the investigation results (FIGS. 6 to 9) regarding the sticking range AF. And about 127 [μm] downstream is described. However, the present invention is not limited to this, and the sticking range AF is investigated using the heating resistor substrate and the recording medium actually used, and the sticking start position S1 and the sticking end position S2 are determined based on the obtained investigation results. Each may be set. In this case, factors affecting the sticking start position S1 and the sticking end position S2 include the radius of the protrusion on the heating resistor substrate, the heat generation distribution characteristics and resolution, the radius and rigidity of the platen roller 3, and the like. The torque to be applied, the type and temperature characteristics of the recording medium 5 (re-solidification temperature, etc.), the moving speed, etc. are assumed.

  For example, when the resolution is changed from 1200 [dpi] to 600 [dpi], which is half that of the thermal printer 1, the period of each line is doubled to about 82 [μm], so that fixing starts from the heat generation center position S0. It is conceivable that the distance to the position S1 is also doubled to about 80 [μm]. Similarly, when the resolution is set to 1/4 [300 dpi], it is conceivable that the distance from the heat generation center position S0 to the fixing start position S1 is about 160 [μm], which is four times as large.

  Moreover, in embodiment mentioned above, the case where the position of the hollow upstream position D1 in the separation hollow 12D was arrange | positioned upstream from the adhering start position S1 was described (FIG. 2). However, the present invention is not limited to this. For example, the depression upstream position D1 may be set at various positions with respect to the fixing start position S1, such as the same position as the fixing start position S1. In this case, the depression upstream position D1 can be set on the downstream side of the fixing start position S1, but it is assumed that the effect is reduced as compared with the embodiment.

  Furthermore, in the above-described embodiment, the case where the position of the depression downstream position D2 in the separation depression 12D is arranged on the downstream side of the fixing end position S2 has been described (FIG. 2). However, the present invention is not limited to this. For example, the depression downstream position D2 may be set at various positions with respect to the fixing end position S2, such as the same position as the fixing end position S2. In this case, the depression downstream position D2 can be set on the upstream side of the fixing end position S2, but it is also assumed that the effect is reduced more than the embodiment, so it is desirable to set it as downstream as possible. . Or you may make the hollow downstream position D2 correspond with the front end of the heating resistor board | substrate 12. FIG.

  Furthermore, in the above-described embodiment, a case where the depth, that is, the depth of the separation recess 12D in the heating resistor substrate 12 when compared with the conventional heating resistor substrate 112 is uniformly set to 3 [μm]. Stated. However, the present invention is not limited to this. For example, the depth of the separation recess may be other values such as 5 [μm] or 8 [μm], or may be different for each part. In short, it is only necessary that the surface of the heating resistor substrate is separated from the fixing range AF of the recording medium 5 and the fixing due to contact can be avoided.

  Further, in the above-described embodiment, the case where the separation recess 12D is formed in the heating resistor substrate 12 by the manufacturing process of selectively etching the protective layer 25 by a photolithography process or the like has been described. However, the present invention is not limited to this, and the separation recess may be formed in the heating resistor substrate by other various manufacturing processes.

  For example, as shown in FIG. 12A corresponding to FIG. 2, the heating resistor substrate 212 is formed after the conductive layer 24 is formed by the same manufacturing process as the heating resistor substrate 12, and then the protective layer 25. The first protective layer 225 is thinner and more uniformly formed, and a range corresponding to the separation recess 212D is selectively etched from the first protective layer 225. Subsequently, in the heating resistor substrate 212, the second protective layer 226 is uniformly formed, so that the separation recess 212D is formed.

  Further, as shown in FIG. 12B corresponding to FIG. 2 and FIG. 12A, the heating resistor substrate 312 is formed with a depression corresponding to the separation depression 312D in advance with respect to the glaze layer 322 instead of the glaze layer 22. Has been. In the heating resistor substrate 312, the same manufacturing process as that of the heating resistor substrate 12 is sequentially performed on the glaze layer 322, whereby the resistance film layer 323, the conductive layer 324, and the protective layer 325 are sequentially formed. Thus, a desired separation recess 312D is formed.

  Further, in the above-described embodiment, the case where the recording medium 5 is so-called thermal paper has been described. However, the present invention is not limited to this, and the printing material contained in the recording medium may have various properties changed by heating. In short, it is only necessary to be able to perform heat printing on a heated portion of the recording medium. The recording medium is not limited to a medium having a property as a so-called heat-sensitive medium in which pixels are formed at a heated location. For example, ink (printing material) of an ink ribbon is melted by heating and transferred to the recording medium. A method may be used. Alternatively, for example, the recording medium may be a printing plate for offset printing, and a heat-sensitive layer containing a heat-sensitive component that reacts with heat may be provided on the surface. In this case, the heat-sensitive component as the printing material may be, for example, one that is initially hydrophilic but has a property of changing to lipophilicity when heat is applied. This recording medium can function as a printing plate by printing images and characters by changing the properties of the location where heat is applied.

  Furthermore, in the above-described embodiment, the case where the protruding portion 12A is formed on the heating resistor substrate 12 and the heating portion 12H is provided on the protruding portion 12A has been described. However, the present invention is not limited to this, and for example, the heating resistor substrate may be formed in various shapes such as a flat plate shape, and a heating portion may be provided in any part thereof.

  Further, the present invention is not limited to the above-described embodiment and other embodiments. That is, the scope of the present invention extends to embodiments in which some or all of the above-described embodiments and other embodiments described above are arbitrarily combined, and embodiments in which some are extracted. is there.

  Further, in the above-described embodiment, the case where the thermal print head 2 having the heating resistor substrate 12 constituted by the heating resistor 23H as the heating resistor and the separation recess 12D as the separation recess is described has been described. . However, the present invention is not limited to this, and a thermal print head having a heating resistor substrate having a heating resistor having various configurations and a separation recess may be configured.

  The present invention can be used in, for example, a thermal printer that prints characters and images by heat-sensitive a recording medium made of a printing plate for offset printing.

DESCRIPTION OF SYMBOLS 1 ... Thermal printer, 2 ... Thermal print head, 3 ... Platen roller, 5 ... Recording medium, 5A ... Area, 11 ... Heat sink, 12, 112 ... Heating resistor board, 12A, 112A ... ... Projection, 12D ... Separate depression, 12H ... Heat, 13 ... Circuit substrate, 21 ... Support substrate, 22 ... Glaise layer, 23 ... Resistive film layer, 23H ... Heat resistor, 24 ... conductive layer, 24G ... gap, 25, 125 ... protective layer, AF ... fixed range, AN ... nip range, AN1 ... nip upstream range, AN2 ... nip downstream range, D1 ... depression upstream position , D2: downstream position of the depression, S0: heat generation center position, S1: fixing start position, S2: fixing end position, T1: resolidification temperature.

Claims (4)

A thermal print head for printing on a recording medium sandwiched between a peripheral side surface of a rotating platen roller and a heating resistor substrate and moving from the upstream side to the downstream side along the sub-scanning direction,
The heating resistor substrate is:
A plurality of heating resistors arranged in the main scanning direction perpendicular to the sub-scanning direction, each of which heats and melts the printing material by heat generation, and then solidifies it on the recording medium to fix it, thereby printing pixels on the recording medium. Body,
A thermal print head, comprising: a separation recess formed on a downstream side of the heating resistor on a facing surface facing the platen roller, and separating a surface of the facing surface from the recording medium. The most upstream depression upstream position in the separation depression,
The printing material is recorded on the recording material by not heating the heating resistor after the predetermined number of heating lines have been continuously printed for a predetermined number of lines to heat the predetermined heating resistor to fix the printing material on the recording medium. When performing low heating printing with a high ratio of non-heated printing not fixed on the medium, the printing material melted by the heating printing on the recording medium resolidifies while abutting against the opposing surface of the heating resistor substrate. 2. The thermal print head according to claim 1, wherein the thermal print head is located upstream of a fixing start position where the fixing starts. The most downstream depression downstream position in the separation depression,
After performing the heat printing at least the number of the colored lines and then performing the low heat printing, the printing material melted by the heat printing on the recording medium comes into contact with the opposing surface of the heating resistor substrate. The thermal print head according to claim 2, wherein the thermal print head is located downstream of a fixing end position where the fixing ends when re-solidifying. The heating resistor substrate is:
A ridge that further protrudes in a convex shape toward the platen roller with a part of the facing surface along the main scanning direction;
The thermal print head according to claim 1, wherein the heating resistor is provided on the protrusion.

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