JP2006334847A - Method for cooling thermal head and heatsink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variation in density due to difference in temperature in a main scanning direction of a thermal head. <P>SOLUTION: A heatsink 18 is constituted of divisional heatsink bodies 18a-18d. The divisional heatsink bodies 18a-18d are coupled by means of coupling plates 38a-38c. The divisional heatsink body 18a in the central part is fixed to be in intimate contact with the thermal head 16. The coupling plates 38a-38c are formed of bimetals each being bent in a temperature less than a deformation start temperature and is not bent in a temperature not less than the deformation start temperature. The deformation start temperature is set to be lower as the position goes from the coupling plate at the central part of the thermal head 16 to the coupling plate at the end part thereof. Along with the rising of the temperature of the thermal head 16 in the printing, the divisional heatsink bodies are sequentially brought into intimate contact with the thermal head 16 from the central part to the end part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal head cooling method and a heat sink attached to the thermal head.

  Using a thermal head equipped with a heating element array in which a plurality of heating elements are arranged in the main scanning direction, the thermal recording paper is conveyed in the sub-scanning direction while the heating element array is pressed against the thermal recording paper, A predetermined electric power is applied to the recording paper based on a printing signal from the printer main body, and the heating resistor is selectively Joule-heated by the heating element, and this heat is conducted to the thermal recording medium, and the thermal recording paper There is known a thermal printer that thermally records each image line by line. The heating element array is provided on one surface of the ceramic substrate, for example. Since the thermal head reaches a high temperature when the heat generating element array generates heat, a heat sink is generally attached as a heat radiating member to the other surface of the ceramic substrate.

  However, when a heat sink is attached, most of the heat generated by the heating element array is used to warm the heat sink at the initial stage of printer startup, etc., and the heat transmitted to the thermal recording paper out of the heat generated by the heating element array. The problem that the thermal efficiency which is the ratio of becomes low arises. If the thermal efficiency is low, the heating element array must generate extra heat, which is an obstacle to power saving of the printer.

  As a countermeasure, it is conceivable to reduce the heat sink performance by reducing the heat sink, and to increase the amount of heat directed to the thermal recording paper. However, if the heat dissipation performance of the heat sink is lowered, the temperature of the thermal head will continue to rise when printing is performed continuously. If the temperature of the thermal head continues to rise, the thermal head will eventually overheat and printing will have to be interrupted. The temperature rise of the thermal head is more remarkable during high-speed printing. Further, if the temperature of the thermal head is higher than the reference temperature, the thermally recorded image has no contrast, and there is a problem that the image quality is deteriorated.

  Against this background, a thermal head capable of changing the heat dissipation performance has been proposed. In the thermal head described in Patent Literature 1, a piezoelectric element is provided between the heat storage member (glaze layer) and the substrate, the thickness of the piezoelectric element is changed, and the volume of the gap is changed, thereby making the heat dissipation performance variable. ing. Thereby, when energizing the heat generating element, the heat dissipation performance is lowered to increase the thermal efficiency, and when the energization to the heat generating element is stopped, the heat dissipating performance is increased to quickly reduce the temperature.

Japanese Patent Laid-Open No. 9-123503

  By the way, since the heat dissipation performance in the main scanning direction of the thermal head increases as it goes from the center of the head to the head end, the temperature distribution of the thermal head during printing is high at the center of the head and decreases as it approaches the head end. There is a tendency. In particular, at the head end portion having high heat dissipation performance, heat for recording on the thermal recording paper is radiated by the heat sink, and desired heat cannot be applied to the thermal recording paper. The temperature difference due to the difference in the heat dissipation performance of the thermal head in the main scanning direction appears as an image density difference (density unevenness) between the head center and the head end, which deteriorates the image quality. Yes. Such density unevenness is also referred to as density loss at both ends because the density at the edge of the image is lower than that at the center. In particular, in the print in a state where the thermal head is cooled and the print in a state where the thermal head is sufficiently warmed by continuous printing, the above-described density loss at both ends due to the temperature difference of the thermal head during printing becomes significant. In the above-described Patent Document 1, no consideration is given to image density unevenness caused by the main scanning direction of the thermal head during printing and the temperature difference during printing.

  In the present invention, a cooling method for improving density unevenness due to a difference in heat dissipation performance in the main scanning direction of the thermal head and density unevenness due to a temperature difference of the thermal head during continuous printing, and a heat sink enabling such a cooling method. The purpose is to provide.

  In order to achieve the above object, according to the first aspect of the present invention, in the thermal head cooling method, the thermal head is cooled by attaching a heat sink to a thermal head in which a plurality of heating elements are arranged, and the heat sink is arranged in the arrangement of the heating elements. The divided heat sink body is divided into a plurality of divided heat sink bodies in the direction, and the divided heat sink bodies are connected by a connecting member made of bimetal, and the divided heat sink body in the center is fixed to the thermal head, and the temperature of the thermal head is fixed by the connecting member. As the height increases, the divided heat sink body is sequentially brought into contact with the thermal head from the center side to the end of the thermal head.

  According to a second aspect of the present invention, in a heat sink that is attached to a thermal head in which a plurality of heat generating elements are arranged and cools the thermal head, a divided heat sink body that is divided in the arrangement direction of the heat generating elements, and the heat generation of the thermal head A fixing member for fixing the divided heat sink body located at the center of the element arrangement direction to the thermal head and the plurality of divided heat sink bodies are connected, and one of the connected divided heat sink bodies is less than a certain temperature. And a connection member made of a bimetal that is separated from the thermal head and deforms when it reaches a certain temperature or more and contacts the thermal head. It is preferable that the divided heat sink is composed of five or more, and the deformation start temperature of the connecting member connecting the divided heat sink main bodies is set lower as the connecting member on the central side of the thermal head.

  The present invention provides a heat sink that is attached to a thermal head in which a plurality of heating elements are arranged and cools the thermal head, and is divided into heat sink elements arranged in the arrangement direction of the heating elements, and the arrangement direction of the heating elements of the thermal head A fixing member for fixing the divided heat sink body located at the center of the thermal head to the thermal head and a plurality of the divided heat sink bodies connected to each other. And a connecting member made of a bimetal that is deformed when it reaches a certain temperature or more and is brought into contact with the thermal head. By applying this heat sink, it becomes possible to minimize the temperature difference between the head center portion and the head end portion of the thermal head, which is the cause of density unevenness at both ends, and prints with good image quality can be performed. Also, since the temperature distribution is smoothed by the heat sink at all times, it is possible to minimize density unevenness between the print when the thermal head is not warm and the print when it is sufficiently warm during continuous printing. it can. Furthermore, the deformation start temperature of the connection member can be changed depending on the composition of the connection member, and the thermal head can be held at a desired temperature by appropriately selecting the deformation start temperature.

  As one of the countermeasures against the density unevenness at the time of printing as described above, when the thermal head is not sufficiently warmed at the time of cold start, a preheating time for heating the thermal head to a printable temperature is provided. Therefore, the density distribution (density profile) in the main scanning direction of the thermal head is obtained in advance for each number of printed sheets, and the applied power to each heating element is corrected based on this density distribution, and density unevenness in the main scanning direction is corrected. It is also possible to suppress the occurrence. However, in such a correction method, it is necessary to obtain a density profile in the main scanning direction for each number of prints, or to correct image data based on the density profile, and there is a problem that the control becomes complicated. In the present invention, such density profile correction is unnecessary.

  As shown in FIG. 1, the thermal printer 10 includes a paper feed roller 12, a transport roller 14, a thermal head 16, a heat sink 18, a platen roller 20, a light fixing device 22, a paper discharge roller 23, a cutter 24, and a discharge port 26. Is provided. The thermal printer 10 is loaded with a recording paper roll 28a in which a long color thermal recording paper 28 (hereinafter referred to as recording paper 28) is wound in a roll shape.

  The paper feed roller 12 rotates in contact with the outer periphery of the recording paper roll 28a and pulls out the recording paper 28 to the conveyance path. The conveyance roller 14 conveys the recording paper 28 in the paper feeding direction by rotating in the forward direction, and conveys the recording paper 28 in the printing direction by rotating in the reverse direction. The paper feed roller 12 and the transport roller 14 are driven by a motor, and the motor is controlled by a system controller.

  The thermal head 16 is provided downstream of the conveying roller 14 in the paper feeding direction. The thermal head 16 is displaced between a printing position where the thermal head 16 is pressed against the recording paper 28 on the platen roller 20 and a retracted position away from the platen roller 20. The thermal head 16 is driven by a head driver based on image data sent from the system controller. The platen roller 20 is provided at a position facing the thermal head 16 across the conveyance path. The platen roller 20 is driven to rotate as the recording paper 28 is conveyed.

  As is well known, the recording paper 28 is formed by sequentially providing a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer on a support. Each thermosensitive coloring layer is designed to develop color at a concentration corresponding to the thermal energy when a predetermined thermal energy is applied. The yellow thermosensitive coloring layer develops color with the smallest thermal energy, and the cyan thermosensitive coloring layer develops color with the greatest thermal energy. The yellow thermosensitive coloring layer loses the coloring ability of the uncolored portion when irradiated with yellow fixing light, which is blue-violet light having a wavelength of about 420 nm. Similarly, when the magenta thermosensitive coloring layer is irradiated with magenta fixing light, which is near-ultraviolet light having a wavelength of about 365 nm, the coloring ability of the uncolored portion is lost.

  The optical fixing device 22 is provided downstream of the thermal head 16 in the paper feeding direction. The optical fixing device 22 includes a yellow fixing lamp 30 that emits yellow fixing light, a magenta fixing lamp 32 that emits magenta fixing light, and a reflecting plate 34 that reflects light from these lamps 30 and 32. The optical fixing device 22 is driven by a light driver based on a signal from the system controller.

  The cutter 24 is provided downstream of the optical fixing unit 22 in the paper feeding direction. The cutter 24 cuts the recording paper 28 into a predetermined size. The paper discharge roller 23 and the discharge port 26 are provided on the downstream side of the cutter 24 in the paper feed direction. The paper discharge roller 23 conveys the cut recording paper 28 to the discharge port 26.

  Next, the thermal head 16 and the heat sink 18 will be described. As shown in FIG. 2, the thermal head 16 is configured by providing a heating element array 16b on one surface of an aluminum plate 16a. A printed circuit board 16c is attached to the surface on which the heat generating element array 16b is formed. The printed circuit board 16c is provided with a driver IC for driving each heat generating element. Each heating element is formed in a partial glaze layer protruding in a cylindrical shape, and a large number of heating elements are arranged in the main scanning direction to constitute a heating element array 16b. A heat sink 18 is attached to a surface of the thermal head 16 opposite to the heating element array 16b of a flat aluminum plate 16a that is long in the main scanning direction.

  As shown in FIGS. 3 and 4, the heat sink 18 is divided into seven parts in the main scanning direction, and is composed of seven divided heat sink bodies 18a, 18b, 18c, and 18d. The divided heat sink body 18a at the center is fixed to the aluminum plate 16a of the thermal head 16 by screws 35. Hereinafter, the divided heat sink body 18a attached to the central portion is referred to as a first divided heat sink body 18a, and those adjacent to the first divided heat sink body 18a are adjacent to the second divided heat sink body 18b and the second divided heat sink body 18b. The one adjacent to the third divided heat sink body 18c is referred to as a fourth divided heat sink body 18d. The length L1 in the main scanning direction of the first divided heat sink body 18a is approximately 65% with respect to the length L0 in the main scanning direction of the thermal head 16, and the lengths of the second to fourth divided heat sink bodies 18b to 18d are: The remaining approximately 35% is divided into six equal lengths L2. A large number of cooling fins 36 are formed side by side on the upper surfaces of the divided heat sink bodies 18a to 18d in order to increase the heat dissipation effect.

  The divided heat sink bodies 18a to 18d are connected by connection plates 38a, 38b, and 38c made of bimetal attached to both ends of the divided heat sink bodies in the main scanning direction. In the present embodiment, the first connection plate 38a is connected to the first and second divided heat sink bodies 18a, 18b, and the second connection plate 38b is connected to the second and third divided heat sink bodies 18b, 18c. The connection between the third and fourth divided heat sink bodies 18c, 18d is referred to as a third connection plate 38c. Each of the connection plates 38 a to 38 c is fixed to the divided heat sink body by screws 39.

  Each of the connection plates 38a to 38c is formed by laminating a plurality of types of metal plates having different thermal expansion coefficients. The connection plates 38a to 38c are substantially flat at a predetermined temperature. The split heat sinks 18b to 18d on the outer side in the scanning direction are lifted upward to form a gap with the aluminum plate 16a. Further, when the temperature is higher than a predetermined temperature, the aluminum plate 16a and the divided heat sinks 18b to 18d come into close contact with each other, so that the aluminum plate 16a tends to bend to the opposite side. Each of the connection plates 38a to 38c has its temperature at which deformation starts by changing the material, thickness, etc. of the metal plate used, and the deformation start temperature is set higher as the connection plate is located on the outer side. . In addition, an elastic heat conducting member 40 is provided in a region where the divided heat sinks 18b to 18d are in contact with the aluminum plate 16a due to the shape change of each connection plate 38a to 38c in order to improve adhesion and heat conduction efficiency. ing. As the heat conductive member 40, heat conductive grease, a heat conductive sheet, or the like is used.

  Since the deformation start temperature is set higher as the outer connection plate is formed in this way, as shown in FIG. 5A, when the temperature of the thermal head 16 is low, the connection plates 38a to 38c are moved upward. In this state, only the first divided heat sink body 18 a is in close contact with the thermal head 16.

  When energization of each heating element of the heating element array 16b is started and the temperature of the thermal head 16 gradually rises, as shown in FIG. 5B, the upper side of the first connection plate 38a is caused by the bimetal effect. And the second divided heat sink body 18b in close contact with the thermal head 16 in addition to the first divided heat sink body 18a. When the temperature of the thermal head 16 further increases, as shown in FIG. 5C, the second connection plate 38b also exhibits the same behavior, and the first to third divided heat sink bodies 18a to 18c are in close contact with the thermal head 16. To do. Similarly, when the temperature further rises, the first to fourth divided heat sink bodies 18a to 18d are also brought into close contact with the thermal head 16 as shown in FIG.

  When the temperature of both ends of the thermal head 16 is lower than that of the central portion due to heat dissipation, such as during a cold start, the divided heat sink body located at both ends separates from the thermal head 16 and heat dissipation by the heat sink 18 is performed. Therefore, the temperature drop at both ends of the thermal head 16 is small, and the temperature distribution in the main scanning direction of the thermal head 16 becomes almost uniform. When the temperature of the thermal head 16 rises due to the heating element array 16b, the temperature distribution in the main scanning direction of the thermal head 16 is always uniform, and is close to the center due to the bimetal effect of the connection plates 38a to 38c. The divided heat sink main body is in close contact with the thermal head 16 sequentially.

  Next, the operation of this embodiment will be described. When a print start command is input, the system controller rotates a feed motor (not shown) and feeds the recording paper 28 in the paper feeding direction. When the recording paper 28 for the recording area reaches the downstream side of the heating element array 16b of the thermal head 16, the feeding of the recording paper 28 in the paper feeding direction is stopped and the recording paper 28 is fed in the printing direction. In synchronization with the recording paper feed in the printing direction, each heating element of the heating element array 16b in the thermal head 16 is driven, and a yellow image is thermally recorded line by line in the recording area.

  When the recording of the yellow image in the recording area is completed, the recording paper 28 is sent in the paper feeding direction. At this time, the yellow fixing lamp 30 is turned on to irradiate the yellow image recording area with yellow fixing light, and yellow fixing is performed.

  When the yellow fixing is completed, the recording paper 28 is sent in the printing direction, and when the leading edge of the recording area reaches the heating element array 16b, a magenta image is thermally recorded. After the thermal recording of the magenta image is completed, the recording paper 28 is fed in the paper feeding direction. During this feeding, the magenta fixing lamp 32 is turned on, the magenta fixing light is irradiated to the magenta image recording area, and the magenta fixing is performed. Done.

  After the magenta fixing is completed, the recording paper 28 is sent in the printing direction, and the cyan image is recorded in the same manner. When the cyan image recording is completed, the recording paper 28 is fed in the paper feeding direction. During this feeding, the magenta fixing lamp 32 is turned on to bleach the uncolored area in the recording area. In this way, when the yellow, magenta, and cyan images are sequentially recorded on the recording area to form a full-color image, the recording paper 28 is cut by the cutter 24 at the boundary between the recording area and the unrecorded area. Cut and get a full color image print. This print is discharged from the discharge port 26 to the outside by the discharge roller 23.

  At the time of thermal recording by the thermal head 16, the thermal head 16 is not sufficiently warmed immediately after the start of printing. Therefore, as shown in FIG. 5A, only the first divided heat sink main body 18a at the center is attached to the thermal head 16. The second to fourth divided heat sink main bodies 18b to 18d on both sides are in close contact with the thermal head 16, and a gap is formed. Therefore, since the heat sink 18 is not in contact with both ends of the thermal head 16, overcooling at both ends of the thermal head 16 is avoided, and the temperature distribution of the thermal head 16 in the main scanning direction becomes substantially uniform.

  As the number of continuous prints progresses, the thermal head 16 gradually accumulates heat. As the temperature rises, not only the first divided heat sink body 18a but also the second divided adjacent to the first divided heat sink body 18a due to the bimetal effect of the first connection plate 38a. The heat sink body 18b is also in contact with the thermal head 16. As described above, by adding the heat radiation effect by the second divided heat sink body 18b, the temperature distribution of the thermal head 16 in the main scanning direction becomes substantially uniform. Similarly, even if the temperature of the thermal head 16 further rises, the outer third and fourth divided heat sink bodies 18c and 18d are brought into close contact with the thermal head 16 in accordance with this, and the temperature of the thermal head 16 in the main scanning direction. Distribution is almost uniform. Thus, according to the heat storage state of the thermal head 16, the second to fourth divided heat sink bodies 18b to 18d sequentially contact the thermal head 16 by the connection plates 38a to 38c, and the temperature distribution of the thermal head 16 in the main scanning direction. Therefore, there is no occurrence of density loss at both ends where the density is low only at both ends in the main scanning direction of the recording area as in the prior art. In addition, since density profiles in the main scanning direction are obtained in advance and image data is corrected accordingly, it is not necessary to perform density missing correction at both ends, and control is simplified. In addition, although density control in the main scanning direction is added to the density correction in the main scanning direction by the first to fourth divided heat sink bodies 18a to 18d in the present embodiment, the control becomes complicated, but density unevenness is further suppressed. Can do.

  The number of divisions of the divided heat sink main body and the deformation start temperature of the connection plates 38 a to 38 c in the above embodiment are appropriately determined according to the usage state of the thermal head 16. If more accurate density unevenness correction is to be performed, the number of divisions may be increased. If density unevenness correction is to be made inconspicuous and the configuration is to be simplified, the number of divisions may be decreased.

  In the above embodiment, the length L1 of the first divided heat sink body 18a at the center in the main scanning direction is set to about 65% with respect to the length L0 of the thermal head 16 in the main scanning direction, and the remaining is about 35%. Are divided equally by the second to fourth divided heat sink bodies 18b to 18d, but the length of each divided heat sink body in the main scanning direction may be appropriately changed according to the mounting position. For example, the one close to the central part may be long and gradually shortened toward the end. In addition, although the number of divisions of the heat sink 18 is seven in the above embodiment, the number is not limited to this and may be three or more. The length L1 of the first divided heat sink body in the main scanning direction is preferably 40 to 80%, more preferably 50 to 70%, with respect to the length L0 of the thermal head 16 in the main scanning direction. Note that the deformation start temperatures of the connection plates 38a to 38c are not limited to those in the above embodiment, and may be changed as appropriate.

  In the above embodiment, the connection plates 38a to 38c are provided on the surface side of the heat sink 18 that contacts the thermal head 16. However, the present invention is not limited to this, and the same effect can be obtained even if provided on the opposite surface.

  In the above embodiment, the heat sink 18 of the thermal head 16 of the thermal printer 10 is described. However, the present invention is not limited to this, and the present invention can be applied as a heat sink of a printer head of another printer.

  In the above embodiment, the cooling method for the thermal head has been described. However, the method can be applied as a cooling method for a general cooling member and a heating element. By applying this method, the temperature distribution of the contact surface between the heating element and the cooling member can be reduced. Smoothing and holding are possible, and the influence of the temperature distribution of the heating element can be minimized.

  In the above embodiment, the method for smoothing the temperature distribution in the uniaxial direction only in the main scanning direction is described. However, the present invention is not limited to this, and the temperature distribution in the direction of two or more axes can be smoothed using the same principle. is there.

It is a schematic block diagram of the thermal printer which mounted the heat sink of this invention. It is a perspective view which shows the outline of the thermal head which mounted the heat sink. FIG. 7 is a side view of the heat sink when the thermal head is sufficiently warmed and the first to fourth divided heat sink bodies are in close contact with the thermal head when viewed from the sub-scanning direction. It is the side view to which the IV section of FIG. 3 was expanded. (A) is a side view when the thermal head and the heat sink immediately after a cold start are viewed from the sub-scanning direction. (B) is a side view showing a state in which the temperature of the thermal head rises from the state of (A) and the first and second divided heat sink bodies are in close contact with the thermal head due to the bimetal effect. (C) is a side view showing a state in which the temperature of the thermal head rises from the state of (B) and the first to third divided heat sink bodies are in close contact with the thermal head due to the bimetal effect.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Thermal printer 12 Paper feed roller 14 Conveyance roller 16 Thermal head 16a Aluminum board 16b Heat generating element array 16c Printed circuit board 18 Heat sink 18a-18d Division | segmentation heat sink body 20 Platen roller 22 Optical fixing device 23 Paper discharge roller 24 Cutter 26 Output port 28 Color heat sensitivity Recording paper 30 Yellow fixing lamp 32 Magenta fixing lamp 34 Reflector plate 35, 39 Screw 36 Cooling fins 38a to 38c Connection plate 40 Heat conducting member

Claims (3)

In the thermal head cooling method in which a heat sink is attached to a thermal head in which a plurality of heating elements are arranged to cool the thermal head.
The heat sink is divided into a plurality of divided heat sink bodies in the arrangement direction of the heating elements,
While connecting these divided heat sink bodies with a connecting member made of bimetal, fix the divided heat sink body in the center to the thermal head,
A method of cooling a thermal head, wherein the divided heat sink body is brought into contact with the thermal head sequentially from the center side to the end of the thermal head as the temperature of the thermal head increases by the connecting member. In a heat sink that is attached to a thermal head in which a plurality of heating elements are arranged and cools the thermal head,
A divided heat sink body divided in the arrangement direction of the heating elements;
A fixing member for fixing the divided heat sink body located at the center of the thermal head in the arrangement direction of the heating elements to the thermal head;
A connecting member made of a bimetal that connects the plurality of divided heat sink bodies and separates the connected one of the divided heat sink bodies from the thermal head when the temperature is lower than a certain temperature, and deforms and contacts the thermal head when the temperature exceeds a certain temperature. And a heat sink. 3. The divided heat sink body is composed of five or more pieces, and the deformation start temperature of the connecting member connecting the divided heat sink bodies is set lower as the connecting member on the center side of the thermal head. The heat sink described.

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