JP2002283602A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the lifetime of the heating elements in a thermal head and to lessen loss of thermal energy. SOLUTION: A heater 15 and a circuit board 16 are provided on the insulation layer 12 of a holding member 11 and an alumina substrate 20, on which a heating element array 18 is formed, is bonded onto the insulation layer 12 to cover the heater 15. A heater drive circuit and a heating element drive circuit are provided on the circuit board 16. A heat sink 21 incorporating a temperature sensor 22 is fixed to the lower surface of the holding member 11. The heater 15 is controlled by the heater drive circuit based on the temperature of the alumina substrate 20 measured by the temperature sensor 22 to heat the heating element array 18 through the alumina substrate 20 thus generating a specified bias thermal energy for each recording color. Each heating element in the heating element array 18 is driven by the heating element drive circuit to generate gradation thermal energy which is imparted to a recording sheet along with the bias thermal energy so that each pixel develops a color with an appropriate density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head, and more particularly, to a thermal head for extending the life of a heating element and reducing heat energy loss.

[0002]

2. Description of the Related Art In general, a thermal head has a substrate made of alumina or the like coated with glazed glass, a heating element and electrodes laminated thereon, and a wear-resistant protective film provided thereon. ing. Since the glazed glass has heat storage properties, when the heating element repeats heat generation,
The temperature of the thermal head gradually rises, and pixels having the same gradation level as those at the beginning of the thermal recording are recorded at a density higher than the appropriate density.

In order to improve such a defect, for example, a thermal head used for sublimation type or fusion type thermal transfer recording described in Japanese Patent Application Laid-Open No. 7-52430 has a higher thermal conductivity than alumina or stainless steel used for a normal substrate. Forms a substrate from a large material, and heats the substrate with a pair of auxiliary heating electrodes. By controlling energization to the auxiliary heating electrode so as to keep the heating temperature of the substrate constant, the temperature in the vicinity of the heating element can be kept constant. Are recorded at the same density.

[0004]

Since the thermal head described in the above publication is for thermal transfer, the thermal energy generated by each heating element is only the thermal energy for gradation expression corresponding to the gradation level of each pixel. It is. However, when thermal recording is performed on a color thermosensitive recording paper on which a plurality of thermosensitive coloring layers having different colors are formed, the heat energy required for coloring each thermosensitive coloring layer of the color thermosensitive recording paper greatly differs. Therefore, the deeper the heat-sensitive coloring layer, the higher the heat energy is required. For this reason, the load applied to the heating element of the thermal head increases, and the life of the heating element is shortened.

In general, a heat sink for heat dissipation is attached to the thermal head in order to prevent the holding member holding the substrate from storing heat. Although heat energy loss occurs due to the heat radiation effect of the heat sink, the thermal head used for sublimation-type thermal transfer recording as described above generates a small amount of heat. small. However, in a thermal head for recording color thermosensitive recording paper, since a large amount of heat is generated when a deep thermosensitive coloring layer is colored, a relatively large heat sink is attached, and heat energy loss is also large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal head that can prolong the life of a heating element and reduce heat energy loss.

[0007]

In order to achieve the above object, a thermal head according to the present invention is characterized in that a substrate on which a heating element array is formed is provided on one surface of a plate-like holding member. A heater for heating the substrate is provided between the member and the substrate. In addition, the holding member has heat conductivity, and a heat dissipation member is provided on the other surface side of the holding member, and the holding member or the heat dissipation member includes
A temperature sensor for measuring the temperature of the substrate is incorporated. Further, the number of the heaters is equal to or less than the number of the heating elements constituting the heating element array. The number of the temperature sensors is equal to or larger than the number of the heaters. Further, the heater is formed by printing.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 showing an example of a layer structure of a color thermosensitive recording paper (hereinafter simply referred to as a recording paper) 1, a recording paper 1 is provided on a support 2 and a cyan thermosensitive coloring layer 3, 365.
A magenta thermosensitive coloring layer 4 having photo-fixing property to ultraviolet rays of 4 nm, a yellow thermosensitive coloring layer 5 having a photo-fixing property to near ultraviolet rays of 420 nm, and a protective layer 6 are sequentially provided. These thermosensitive coloring layers 3 to 5 are provided in the order of thermal recording. For example, when thermal recording is performed in the order of magenta, yellow, and cyan, the yellow thermosensitive coloring layer 5 and the magenta thermosensitive coloring layer 4 are used. Is replaced.

FIG. 2 showing the coloring characteristics of each of the thermosensitive coloring layers 3-5.
In each of the thermosensitive coloring layers 3 to 5, the deeper the layer, the greater the color developing heat energy is required to develop a color. As for the recording paper 1, the yellow thermosensitive coloring layer 3 has the lowest coloring thermal energy, and the cyan thermosensitive coloring layer No. 3 has the highest coloring heat energy.

When recording a yellow pixel, the recording paper 1 is supplied with heat energy obtained by adding gradation heat energy Egy to bias heat energy Eby for yellow. The bias thermal energy Eby is thermal energy immediately before the yellow thermosensitive coloring layer 3 develops a color, and the grayscale thermal energy Egy is determined according to the color density of the pixel to be recorded, that is, the grayscale level of the yellow image. The same applies to magenta and cyan, and the symbol Eb
m, Egm, Ebc, and Egc.

Referring to FIG. 3, which shows a thermal head for coloring and recording each of the thermosensitive coloring layers 3 to 5 of the recording paper 1, a thermal head 10 has an insulating layer 12 formed on an upper surface of a plate-like holding member 11 made of aluminum. Further, a thin film heater 15 for sequentially generating the bias thermal energy Eby, Ebm, Ebc and a circuit board 16 are provided thereon. Further, a heating element array 18 in which a large number of heating elements for generating the gradation thermal energies Egy, Egm, Egc are arranged in a line in a direction perpendicular to the drawing is formed on an alumina substrate 20. So as to cover the heater 15
It is adhered to the surface of the insulating layer 12.

The heater 15 is made of, for example, a ruthenium oxide (Ru ₂ O) -based paste, and a film and a pattern are formed by screen printing as is well known. In addition, for example, Ag-Pd, Au paste, or the like is used to form the conductive line 17 that connects the heater 15 and the circuit board 16.

A heater driving circuit for driving the heater 15 and a heating element driving circuit for driving the heating element array 18 are formed on the circuit board 16. A heat sink 21 is attached to the lower surface of the holding member 11. The heat sink 21 incorporates a temperature sensor 22 that measures the temperature of the alumina substrate 20 that changes due to the heat generated by the heater 15.

One heater 15 and one temperature sensor 22
The temperature control of the heater 15 is performed as a set. Heater 1
Increasing the number of pairs of 5 and the temperature sensor 22 enables accurate control of the temperature of the alumina substrate 20 and the size of the heat sink 21, but on the contrary, the thermal head 10 Increases cost. In the present embodiment, in consideration of this, as shown in FIG. 4, a set of the heater 15 and the temperature sensor 22 is connected to the heating element array 18.
Along the longitudinal direction.

As shown in FIG. 5, the heating element array 18 has a columnar partial glaze 24 formed on the upper surface of an alumina substrate 20 and a resistor 25 laminated thereon.
On the resistor 25, a pair of electrodes 26 and 27 are joined while being separated from each other. The heating element 28 for gradation expression is constituted by the portion of the resistor 25 between the electrodes 26 and 27. When a voltage is applied between the electrodes 26 and 27, the heating element 28
Generates heat. A large number of sets of electrodes 26 and 27 are provided in a line in a direction perpendicular to the drawing. Further, a wear-resistant layer 29 is provided on the resistor 25 and the electrodes 26 and 27.

In FIG. 6, which shows the color thermal printer 30, a long recording paper 1 is set in a paper feeding section by a roll 1a. The recording paper 1 is fed into a linear conveyance path 32 by a pair of feed rollers 31. The fed recording paper 1 is nipped by a pair of transport rollers 33 and sent to a recording position. At the recording position, a thermal head 10 and a platen roller 34 for pressing the recording paper 1 against the thermal head 10 facing the thermal head 10 are provided.

A conveyance roller pair 35 is provided near the platen roller 34, and downstream of the conveyance roller pair 35, a yellow light fixing device 37 for optically fixing the recording paper 1 on which heat has been recorded, a magenta light fixing device 38, A paper discharge roller pair 39 for discharging the recording paper 1 on which the thermal recording and the optical fixing have been completed toward an external tray (not shown) is provided.

The yellow light fixing device 37 is composed of a rod-shaped ultraviolet lamp 37a emitting near-ultraviolet light having an emission peak of approximately 420 nm and a reflector 37b. The magenta optical fixing device 38 has an emission peak of approximately 36.
An ultraviolet lamp 38a that emits 5 nm ultraviolet light and a reflector 38b are provided.

The pair of transport rollers 33 and 35 and the pair of discharge rollers 39 are driven by a transport motor 41 to transport the recording paper 1 in a feed direction α and a rewind direction β. The recording paper 1 is reciprocated in the transport path 32 by a pair of transport rollers 33 and 35 and a pair of paper discharge rollers 39, during which the thermal head 10 records yellow, magenta, and cyan images in a frame-sequential manner. The printed recording paper 1 is cut into a predetermined size by a cutter 42 provided between the paper feed roller pair 31 and the transport roller pair 33, and is discharged. Note that the recording paper 1 does not have to be a long recording paper, and a sheet-like recording paper cut in advance to a predetermined size may be used.

In FIG. 7, which shows the electrical configuration of the color thermal printer 30, a system controller 45 includes an image signal processing section 46, a transport motor driver 47, a lamp drive section 48, a heater drive circuit 50 of the circuit board 16, The element drive circuit 51 is connected. The print instruction is issued by the operation unit 52. Image signal processing unit 4
6 performs image processing such as color correction and gradation correction on the input image data, and sends the image data to the heating element drive circuit 51. The heating element driving circuit 51 drives the heating elements 28 by converting the image data subjected to the image processing into a driving voltage value corresponding to the gradation level of each pixel.

The heater drive circuit 50 drives the heater 15 at a voltage value set in advance for each color of an image to be printed, based on a signal from the system controller 45. Also,
The system controller 45 sends a signal from the temperature sensor 22 so that the temperature of the alumina substrate 20 does not exceed the target temperature (the temperature of the alumina substrate 20 when the temperature of the heating element array 18 becomes the bias thermal energy Eby, Ebm, Ebc). A temperature control signal is sent to the heater drive circuit 50 based on the measured value. Upon receiving this signal, the heater driving circuit 50
The temperature is adjusted by turning on / off the power supply to the heater 15. The target temperature is, for example, 35 ° C. for yellow image recording, 55 ° C. for magenta image recording, and 70 ° C. for cyan image recording.

The transport motor driver 47 includes the transport motor 4
1 is driven. When the leading edge detection sensor detects the leading edge of the recording paper 1, the system controller 45 operates a counter to measure the transport amount of the recording paper 1. The print size, recording start position, and recording end position of the recording paper 1 are set to predetermined values in advance, and the transport amount of the recording paper 1 is controlled based on the count value of the counter. Lamp drive unit 48
Turns on and off the fixing lamps 37a and 38a based on a signal from the system controller 45.

The operation of the above configuration will be described with reference to the flowchart shown in FIG. When a print instruction is given to the color thermal printer 30, the transport motor 41
Starts normal rotation, and the recording paper 1 nipped by the paper feed roller pair 31 is fed into the transport path. At this time, the leading end of the recording paper 1 is detected, and counting of the transport amount of the recording paper 1 is started. At the same time, the system controller 45
Sends a command signal to the heater drive circuit 50 to drive the heater 15 at a predetermined voltage value.

The heating temperature of the heater 15 depends on the alumina substrate 2
0 to the heating element array 18. The temperature of the alumina substrate 20 is measured by the temperature sensor 22 and input to the system controller 45. The system controller 45 determines that the value measured by the temperature sensor 22 is the target temperature 3
The heater 15 is controlled by the heater drive circuit 50 so that the temperature of the heater
On / off. When the value measured by the temperature sensor 22 is stabilized at the target temperature of 35 ° C., the heating element array 1
The thermal energy given by 8 to the recording paper 1 becomes a constant bias thermal energy Eby. At this time, since the heating element array 18 is not pressed against the recording paper 1,
The recording paper 1 has not yet been bias-heated.

When the recording sheet 1 is conveyed by the pair of conveying rollers 33 and passes through the thermal head 10 and the leading end of the recording sheet 1 is nipped by the pair of conveying rollers 35, the recording sheet 1 stops once. The thermal head 10 is moved by the shift mechanism, and the heating element array 18 is pressed against the recording paper 1. When the transport motor 41 rotates forward and the recording paper 1 is transported in the feeding direction, and the recording start position reaches the thermal head 10, first, the recording of the yellow image is started.

The yellow image data is sent to the image signal processing unit 4
6. After image processing such as color correction and gradation correction is performed by 6,
It is sent to the heating element drive circuit 51. Heating element drive circuit 5
1 drives each heating element 28 by converting the yellow image data into a driving voltage value corresponding to the gradation level of each pixel. Each heating element 28 is driven so as to give the recording paper 1 gradation thermal energy Egy for expressing the gradation of each pixel of the yellow image, and the heating element array 18 is biased by the heat generated by the heater 15. Since Eby is applied to the recording paper 1, the bias heat energy E is applied to the recording paper 1.
The coloring heat energy Ey obtained by adding the by-by and the gradation heat energy Egy is given. Thus, a yellow image is recorded on the yellow thermosensitive coloring layer 5 line by line.

When the recording of the yellow image is started, the fixing lamp 37a of the yellow optical fixing device 37 is turned on. When the recording paper 1 reaches the light fixing device 37 for yellow,
The recording paper 1 is irradiated with ultraviolet rays, and the yellow thermosensitive coloring layer 5 is optically fixed. When the optical fixing is completed, the thermal head 10 is moved by the shift mechanism, and the heating element array 1 is moved.
After the sheet 8 is retracted from the position where the sheet 8 is pressed against the recording sheet 1, the conveying motor 41 rotates in the reverse direction to convey the recording sheet 1 in the rewinding direction. Further, the fixing lamp 37a is turned off.

While the recording paper 1 is being rewound, the drive voltage value of the heater 15 is switched from yellow to magenta, and the target temperature of the alumina substrate 20 is changed from 35.degree.
° C. When the recording start position of the recording paper 1 reaches the thermal head 10, the transport motor 41 temporarily stops, the heating element array 18 is pressed against the recording paper 1, the transport motor 41 is switched to the normal rotation, and the magenta image data is changed. Is the heating element driving circuit 5 through the image signal processing unit 46.
Sent to 1. The heating element drive circuit 51 drives each heating element 28 by converting magenta image data into a drive voltage value corresponding to the gradation level of each pixel.

Each heating element 28 applies gradation heat energy Egm representing the gradation of each pixel of the magenta image to the recording paper 1, and the heating element array 18 biases the heating element array 18 via the alumina substrate 20 by the heat generated by the heater 15. The thermal energy Ebm is given to the recording paper 1. Accordingly, the recording paper 1 has the bias heat energy Ebm and the gradation heat energy Ebm.
gm and the total heat energy Em is given, and a magenta image is recorded on the magenta thermosensitive coloring layer 4 line by line.

Simultaneously with the start of recording of the magenta image, the fixing lamp 38a of the magenta optical fixing device 38 is turned on, and the recording paper 1 on which the magenta image is recorded is moved to the magenta optical fixing device 38.
Is reached, the recording paper 1 is irradiated with ultraviolet rays from the fixing lamp 38a, and the magenta thermosensitive coloring layer 4 is optically fixed.
When the light fixing of the magenta thermosensitive coloring layer 4 is completed, the heating element array 18 is retracted from the position where the heating element array 18 is pressed against the recording paper 1, and
The transport motor 41 rotates in the reverse direction, and the recording paper 1 is rewound again.

While the recording paper 1 is being rewound, the drive voltage value of the heater 15 is switched from magenta to cyan, and the target temperature of the alumina substrate 20 is from 55 ° C. to 70 ° C.
Is changed to When the recording start position of the recording paper 1 reaches the thermal head 10, the transport motor 41 stops temporarily, the heating element array 18 is pressed against the recording paper 1, the transport motor 41 is switched to the normal rotation, and the cyan image data is changed. Is sent to the heating element drive circuit 51 via the image signal processing section 46. The heating element drive circuit 51 drives each heating element 28 by converting the cyan image data into a drive voltage value corresponding to the gradation level of each pixel.

Each heating element 28 applies gradation heat energy Egc representing the gradation of each pixel of the cyan image to the recording paper 1 and generates heat from the heater 15 to the alumina substrate 2.
The heating element array 18 gives the bias heat energy Ebc to the recording paper 1 via the line 0. Therefore, the recording paper 1 has the bias heat energy Ebc and the gradation heat energy Ebc.
gc is added to the heat energy Ec, and a cyan image is recorded on the cyan thermosensitive coloring layer 3 line by line. When the recording of the cyan image is completed, the recording paper 1 is further conveyed in the feeding direction, cut into sheets by the cutter 42, and discharged to a tray provided outside the color thermal printer 30.

As described above, since bias heating is performed by the heater 15 and each heating element 28 only needs to perform gradation heating, the load applied to each heating element 28 is reduced.
The life of each heating element 28 is extended. Also, bias heating,
Since each control of the gradation heating is performed by the heater driving circuit 50 and the heating element driving circuit 51, each circuit configuration is simplified. In addition, the response of the heating element 28 is improved, and the tailing phenomenon and the sharpness at the time of rising are greatly improved even when recording a black character requiring the most power.

Since the heater 15 and the temperature sensor 22 can perform stable bias heating from the start of printing to the end of printing, the printing density at the start of printing does not become lower than the original image. Thus, thermal recording with a density faithful to the original image can be performed. Further, even in continuous printing, there is no difference in density between the first print and the last print. Further, since the temperature of the alumina substrate 20 can be kept constant by the heater 15 and the temperature sensor 22, the size of the heat sink 21 can be reduced, and the amount of driving power can be reduced by about half compared to when a thermal head provided with a large heat sink is driven. Can be dropped to the extent.

In the embodiment described above, the number of heaters is two. However, the present invention is not limited to this, and may be one or three or more in a range smaller than the number of heating elements. The two heaters may be heated by the heater. In the above embodiment, the number of temperature sensors is equal to the number of heaters. However, the present invention is not limited to this.
Two heaters may be provided with two temperature sensors. In this case, the temperature distribution of the heater can be detected. Although the heater is formed on the holding member side, it may be formed on the alumina substrate side. Also, the temperature sensor was provided on the heat sink,
It may be provided on the holding member.

[0036]

As described above, according to the thermal head of the present invention, the heater for heating the substrate is provided between the holding member for holding the substrate of the heating element array and the substrate. Bias heating can be performed individually, the load on the heating element can be reduced, and the life of the heating element can be extended. Further, the control of the thermal head can be simplified, and the control circuit can be simplified. Further, since a heat radiating member is provided on the other surface side of the holding member and a temperature sensor is incorporated in the heat radiating member or the holding member, the temperature of the heating element array can be quickly controlled. Therefore, the size of the heat radiating member can be reduced, and the amount of heat absorbed by the heat radiating member can be reduced, so that the loss of heat energy can be reduced and the thermal head can be downsized. Also, if the number of heaters is the same as the number of heating elements, more accurate and quick bias heating can be performed, or if the number of heaters is smaller than the number of heating elements, the thermal head can be reduced in cost. it can. Further, since the same number or more temperature sensors are provided as the number of heaters, the heater can be controlled quickly and accurately. Also, since the heater was formed by printing,
The heater can be formed thinly and easily, which can contribute to making the thermal head thinner and improving the suitability for manufacturing.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a layer structure of a color thermosensitive recording paper.

FIG. 2 is a graph showing the color development characteristics of a color thermosensitive recording paper.

FIG. 3 is an explanatory diagram illustrating an example of a configuration of a thermal head.

FIG. 4 is an explanatory view showing a heater formed on an insulating layer of a holding member.

FIG. 5 is a cross-sectional view illustrating a configuration of a heating element array.

FIG. 6 is a schematic diagram showing a color thermal printer.

FIG. 7 is a block diagram showing an electrical configuration of the color thermal printer.

FIG. 8 is a flowchart showing a print sequence of the color thermal printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal head 11 Holding member 15 Heater 18 Heating element array 20 Alumina substrate 21 Heat sink 22 Temperature sensor 30 Color thermal printer

Claims (5)

[Claims] 1. A thermal head in which a substrate on which a heating element array is formed is provided on one surface side of a plate-shaped holding member, wherein a heater for heating the substrate is provided between the holding member and the substrate. Thermal head. 2. The holding member has thermal conductivity, a heat radiation member is provided on the other surface of the holding member, and a temperature sensor for measuring the temperature of the substrate is provided on the holding member or the heat radiation member. The thermal head according to claim 1, wherein the thermal head is incorporated. 3. The thermal head according to claim 1, wherein the number of the heaters is equal to or less than the number of the heating elements constituting the heating element array. 4. The temperature sensor according to claim 2, wherein the number of the temperature sensors is equal to or greater than the number of the heaters.
Or the thermal head according to 3. 5. The thermal head according to claim 1, wherein the heater is formed by printing.