JP2007331357A - Thermal printer with forced cooling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize printing at fast speed, high printing quality, acceleration of tone printing, etc. by reducing thermal storage of a thermal head, and performing integrity absorbency. <P>SOLUTION: A forced cooling apparatus with a Peltier element provided outside of a printer is mounted a water-cooled head for a thermal head on a heat sink top face of the thermal head. Water is circulated to a heat absorbency side by the water-cooled head for the thermal head and tube, and the water in the thermal head whose temperature is elevated is cooled here. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a thermal printer, and particularly relates to countermeasures against troubles caused by heat accumulation of a thermal head accompanying heat generation.

The market scale and application range of thermal printers are expanding.
Advantages of thermal printers as commercial printers ・ Maintenance-free periodic inspection is not required, there are no replacement parts, and the life parts are limited to thermal heads (printing distances of 50 km and 100 km are very long)
・ On-demand printing is possible. There is no setup time, and there is no need for non-printable time during printing for self-cleaning, which is essential for inkjet printers.
・ Environmental resistance Printing in a poor environment such as printing in locations with vibrations or in dusty locations is possible only with a thermal printer.
Also, only thermal printers can perform printing according to demands such as chemical resistance, solvent resistance, gasoline resistance, and rubbing resistance.
・ Special printing such as gold, silver, foil, and hologram is possible. These printings are special printing that was possible only by conventional printing.
Printing with a thermal printer can be expected to be applied to the printing industry.
These mean the possibility of replacement for commercial printing.
In addition to the above advantages, the proposed technology can be applied to new fields.
・ In recent years, thermal printers are increasingly being applied to new fields.
There is a growing demand and need to print on-site (in the same place) as a professional printer. It was originally done by a professional printing shop, and it is essential to maintain a constant print quality even for several hours of continuous printing. However, with the current thermal printer technology, continuous printing is possible, but constant guarantee of print quality has not been considered.
As heat storage countermeasures for conventional thermal heads, heat history control (controlling applied energy from past printing history) and adjusting the energy applied from the temperature of the thermal head and the heat sink of the thermal head that stored heat dissipates heat into the air. It was. However, at present, as a limited heat storage measure, as described in the industrial application field, there are limitations such as the limitation of the printing speed of the color printer and the high speed of the date printer.
In the thermal printer system, printing is performed with heat generation, so the thermal storage of the thermal head is generated, although the amount of heat is large and small, and is the limit of printing. (Figure 6 shows the mechanism of heat storage)

-The application and application of thermal printers using this technology described in [Industrial application fields] is a problem and solution.
Printing is performed by the heat generated by the thermal printer, but the heat accumulates in the thermal head and causes various problems.
・ Degradation of print quality If printing is continuously performed, the thermal head (ceramic substrate, heat sink) accumulates heat, heat is generated more than expected, the print becomes too dark, and clear print cannot be performed.
This becomes a factor that the barcode cannot be read by the machine in barcode printing.
In addition, gradation printing is required in a color printer, but the thermal head stores heat, resulting in an amount of heat generation that is greater than expected, and gradation cannot be maintained.
The solution is to reduce or eliminate heat storage.
・ The higher the maximum printing speed, the more heat energy is required for printing.
For this purpose, the energy applied to the image receiving paper for printing needs to be a certain value or more regardless of whether it is high speed or low speed per unit area. Therefore, in the case of high-speed printing, applied energy is applied to generate high thermal energy. One third or more of the applied energy becomes heat storage and is stored in the ceramic and heat sink, which adversely affects printing deterioration and life.
・ Short life of thermal heads Short life is unavoidable The temperature of thermal heads is unavoidable, and if it rises, it will adversely affect the life of thermal heads.
This is because breakage due to oxidation of the heating element of the thermal head is promoted.
Oxidation promoting factors include temperature and ions. If the temperature rises, oxidation is promoted.
This is the solution. Reduce heat storage and improve the above three points.

The present invention suppresses the heat storage of the thermal head in view of the above-mentioned conventional problems of the thermal printer.
According to the first aspect of the present invention, there is a limit to suppressing heat storage in the heat radiation of the heat sink of a normal thermal head (FIG. 1), and a forced cooling device is attached to the heat sink to suppress heat storage.
According to a second aspect of the present invention, a water cooling (oil cooling, vaporization / liquefaction device) device is attached to a heat sink as a forced cooling device and forcibly cooled. Since there is only a very narrow space around the thermal head of the thermal printer, the water cooled by the forced cooling device flows through the copper device attached with the heat sink, not the forced cooling device itself, and absorbs heat.
As shown in FIG.
The forced cooling device is installed outside the printer and has a forced cooler and water flow pump.
As shown in FIG.
The third aspect uses a Peltier element as the forced cooling device.
The Peltier element is optimal as a cooling device for this printer because it is inexpensive, has a high cooling capacity, is easy to handle, and can reduce the installation space.
Since the Peltier element generates heat simultaneously with heat absorption, a device that dissipates the heat generation is necessary. As a heat dissipation device, the Peltier element is cooled by a heat sink, fins, a fan as forced cooling, or the like.
It is very difficult to store these inside the printer, and it is installed outside the printer and the cooling water is used to cool the thermal head inside the printer.
The fourth aspect relates to the heat absorption force of the forced cooling device.
Even when the heat generation amount of the thermal head is maximum, it is possible to absorb the chant heat, and when the heat generation amount is small, the heat absorption force can be weakened so that the thermal head can be kept at a constant temperature. In order to keep the temperature of the thermal head constant, feedback control is performed.
Claim 5 is for efficient operation of cooling.
Originally, the heat sink of the thermal head is a device that dissipates heat into the surrounding air. How to dissipate it was a problem, but in this case, it absorbs heat inside the heat sink and is forced to cool outside the printer. It releases heat. That is, since the heat sink is at a lower temperature than the outside temperature, if the heat sink is opened, the temperature of the heat sink increases and the cooling effect decreases.
Further, since the heat sink is at a temperature lower than the external temperature, there is a risk that water droplets are generated on the surface of the heat sink, which also prevents the heat sink.
According to the sixth aspect of the present invention, a heater is provided on the surface of the heat shield in order to completely prevent the generation of water droplets on the surface of the heat sink described in the fifth aspect. Water droplets can be prevented by heating the surface of the heat shield to the external temperature.
Claim 7 is a measure for instantaneously increasing the temperature around the heating element due to the printing situation, that is, the printing rate.
Conventionally, correction is performed by adjusting the thermal history control and the temperature change of the heat sink (the energy to be printed is adjusted from now on).
For color printers such as photo printers that require even higher precision control (print density gradation control), more precise control is required.
Although the heat history control can predict the temperature of the heating element, it is different from the actual situation because the history of the surrounding heating elements cannot be taken into account. Further, the temperature of the thermal head is a measurement of the temperature (heat storage temperature) of a portion where the head is located, and an instantaneous temperature rise in the vicinity of each heating element cannot be detected.
This is because the heating elements arranged in a line (example 1, “1200 heating elements for a 300 dpi wide thermal head) and the temperature sensing thermistor must have a certain physical distance.
Therefore, in the temperature characteristics sensed by the thermistor and the temperature characteristics of the heating element,
・ Thermistor senses the temperature characteristics of the heating element with a slight delay. ・ Smoothness is smoothed to a certain extent until it reaches the thermistor, and the instantaneous temperature rise cannot be detected. It has also been reported that the temperature is detected and the printing conditions are predicted from that value. Also in this case, heat storage is unavoidable, and problems remain with high speed printing with high printing rate. Currently, the only solution is to forcibly cool the thermal head.
This is exactly what we propose.
Claims 8 and 9 directly forcibly cool the thermal head. (Fig. 4)
Attaching the Peltier element (instructions in FIG. 3) directly to the heat sink is the best in terms of efficiency, but the problem is the heat generation process.
The Peltier element cools and absorbs heat on one side, but must heat up and dissipate heat on one side. Since heat cannot be dissipated inside the printer or near the thermal head, it is necessary to transfer heat to the outside of the printer.
Heat pipes, water hoses, etc. are used.
Claim 10 is a measure of how quickly the temperature rise of the heating element of the thermal head is suppressed.
Conventionally, the ceramic and heat sink of the thermal head are attached with double-sided tape with low thermal resistance.
During this period, the thermal resistance value is suppressed, and the temperature of the heatsink is forced to cool, and the temperature of the heating element on the ceramic is stabilized.
Claim 11 is the same measure for improving the immediate effect of forced cooling as in claim 10.
Since the stable low temperature of the forced cooling part of the heat sink takes the heat of the heating element, the heat resistance of the heat sink is lowered. As shown in FIG.
Copper is the best metal available and is used. However, as a problem of copper, there is a lack of strength, and Claim 12 which maintains the strength by providing an iron plate or the like on the upper surface of the heat sink reduces heat storage itself.
Therefore, the applied energy of the thermal head can be suppressed by raising the temperature of the printing medium and ribbon. In addition, this effect is particularly effective when gradation printing is performed at a high speed by a color printer.
There are external temperatures, thermal head heat storage, print medium surface temperature, ribbon temperature, etc. that have an adverse effect on gradation printing. In the present invention, each of these can be managed to a certain value, and further print quality can be ensured.

・ It is possible to reduce and completely absorb the thermal storage of the thermal head, and realize high-speed printing, high printing quality, high-speed gradation printing, and the like.

FIG. 8 shows a schematic diagram of the thermal printer.
The most common type of thermal transfer printer in this case is a system in which a plastic film coated with ink is heated and the ink is melted and transferred.
・ Thermal head and print control ・ Thermal ribbon and drive system ・ It consists of printing paper, transport system and printer controller.
The temperature of the head rises in accordance with the amount of current passed through the thermal head. The thermal ribbon pigment is melted by the heat, and transferred to the printing paper. Thus, the printing operation is performed.
At this time, as shown in FIG. 6, a part of the heat is stored in the thermal head.

Example 1

This will be described with reference to the water-cooled forced cooling device plan of FIG. The thermal printer used in this case is a 600 dpi, 2 "/ S thermal printer. A thermal head water cooling head is installed on the top of the heat sink of the thermal head. Water is circulated between the head water cooling head and the tube, and the water whose temperature has risen in the thermal head is cooled here.
・ Peltier element uses 12Vx8A, 60W suction type.
The Peltier element can be selected from the required heat absorption amount.
(57W type, 80W type, etc)
-A copper heat sink and fan are attached to the heat generating side of the Peltier element.
・ Thermistor for temperature detection was used for feedback control of the temperature of the thermal head.
The installation location was as close to the heating element as possible. In this case, a hole was dug in the heat sink. (Back of I heating element) As a control method, if the temperature of the thermal head detected by the thermistor is higher than the specified temperature, the Peltier element is operated. If the temperature is lower than the specified temperature, the Peltier element is not operated. did.
(Pulse method is generally applied to Peltier device)
・ Used a pump for circulating water. ・ Conducted thermal cooling control and thermal head temperature change control simultaneously with the above water cooling forced cooling.
The thermal history control is to control the energy to be printed from the past printing progress of each heating element that has been conventionally performed, and a certain effect is shown in FIG.
The effect of this apparatus was tremendous as shown in FIG.
When this forced cooling device is not used, the temperature rise rises in a straight line to a certain value due to the thermal storage of the thermal head. This is because the temperature detected by the thermistor of the thermal head has a time difference from the temperature of the heating element, and thermal control is not effective.
Furthermore, thermal printers can only guarantee thermal control at a printing rate of 30% or less. At higher printing rates, control becomes impossible, the temperature rises, and finally Printing stops at the thermal head breakage protection temperature (thermistor temperature is about 75 degrees). In this embodiment, the print head evaluation is 90% or more (FIG. 8), and the thermal head temperature falls within a certain range due to the effect of the forced heat control device (the thermal head is 30 degrees or less at a normal temperature of 27 degrees). Thermal control is effective and continuous printing is possible.
(Continuous printing was possible with one roll of ribbon (300m to 600m))
During implementation, water droplets were generated on the thermal head. As a countermeasure, a 2 mm thick heat-resistant tape was applied around the thermal head, particularly the heat sink. Water drops have been greatly reduced.
This correspondence also has an effect of suppressing the temperature rise of the cooled thermal head.
Reduction of cooling time for forced cooling, reduction of electric energy for cooling (decrease in applied power of Peltier element) Further, as in claim 6, a surface heater was attached to the surface of the heat-resistant tape.
The temperature was set at ambient temperature. No water droplets were generated from the heat sink.
A preheating mechanism according to claim 12 is provided immediately before the thermal head.
As the preheater, a ceramic heating element provided in a straight line was used.
(Use erasing head for rewritable printer)
The temperature was set to 80 degrees and the ribbon and the image receiving paper were preheated.
The fact that the surface temperature of the ribbon and the image receiving paper is actually reflected depends on the characteristics of the ribbon and the paper. In actual use, it is necessary to set the preheat temperature in consideration of the characteristics of the surface of the ribbon and the paper.
In this example, the same print density was obtained even when the applied energy to the thermal head was reduced.
This is also due to the effect of external temperature, especially the temperature of the image receiving paper, and the print sensitivity changes greatly (printing is poor at low temperatures).
Example 2

As shown in FIG. 4, a forced cooling device (Peltier element) was directly mounted on the thermal head.
A mechanism for forcibly cooling the thermal head directly according to the temperature change of the thermal head is a very efficient system. The problem is whether to remove the heat generated by the Peltier element out of the printer. In Example 2, a copper water flow device was provided on the heat generating side of the Peltier element, and a silicon rubber hose was connected to the water flow device, which was connected to a cooling mechanism outside.

Speeding up printers Applications such as photographic printers and color printers for EDP.
The use of silver halide photography as a color printer is indispensable, and the thermal printer method is most appropriate when business use is closely examined. (Maintenance-free and safety)
The marketability and marketability in this field are astronomical.
The current problem is the printing speed, and the 1 head system does not reach 1 "/ S.
By using this technology, the speed can be increased more than twice.
(2) Printing with a printing rate of 95% or more can be continuously performed.
Normal printing has a printing rate of 50% or less (how much area is printed on one image receiving paper). If the printing rate higher than that is continuously performed, the thermal head accumulates heat and the printing quality deteriorates. This technology solves that.
(3) When printing with a thermal printer on a material with poor paste (Japanese paper, cloth, etc.), it is possible to print gold foil, silver foil, hologram, etc. that are difficult to transfer.
In addition, it is possible to print an RFID inlay antenna that is expected to be used in the future.
In this case, it is necessary to increase the energy applied to the thermal head. However, the life of the thermal head is remarkably shortened. This technology is a countermeasure.
(4) Capable of super-high-speed printing Although 10 ″ / S is the maximum speed in the market, this technology can increase the speed by 2 to 3 times.
High speed printing is required by date on the product package.
The food-related market is big

Fig. 1 Structure of thermal head Fig. 2 Forced water cooling system Fig. 3 What is a Peltier element? Fig. 4 Direct forced cooling of the thermal head Fig. 5 Effect of heat history 6 Effect of heat storage measures 7 Control flow diagram 8 Schematic diagram of thermal printer

Claims (12)

A thermal printer that moves with a print medium sandwiched between a thermal head and a platen roller, and that prints on the print medium, and includes a forced cooling device in the thermal head to suppress heat storage of the thermal head associated with printing. Thermal printer The forced cooling device according to claim 1 has a cooling device, a pump, and a temperature control device outside the printer, and a device for circulating water, oil, vaporized / liquefied substances cooled by the cooling device, and a thermal head temperature sensor attached to the thermal head. thing. A forced cooling device using a Peltier element for cooling the cooling water, oil, and vaporized / liquefied substance according to claim 2. The thermal printer according to claim 1, further comprising a cooling device in which the amount of suction heat of the forced cooling device provided in the thermal head is larger than the maximum amount of heat generated during printing of the thermal head, and a device for detecting the temperature of the thermal head. Printer that can control the temperature of the machine at the right time 2. The thermal printer according to claim 1, wherein the thermal head temperature is not affected by the ambient temperature, and the thermal head is covered with a heat insulating material. Regarding the heat shield product of claim 5 above, a heater is provided on the surface of the heat shield material in order to make the appearance surface of the heat shield product about room temperature in order to prevent generation of frost and water droplets. In the thermal printer according to claim 1, in order to suppress the temperature change of each heating element portion of the thermal head, the thermal history control of each heating element and a thermal device including a device for reflecting the temperature change of the thermal head in the applied energy in the future. printer The forced cooling device for the thermal printer according to claim 1, wherein a thermal head uses a device that uses a Beltier element. The thermal printer according to claim 8, wherein the cooling device is housed in a narrow space around the thermal head of the thermal printer, so that the heat generated on the heat generating side of the Peltier element is absorbed and transferred to the outside of the printer. In the thermal head forced cooling system according to the first aspect, the temperature of each heating element slightly changes depending on the printing state of the heating element of the thermal head. In order to quickly drop the temperature to the temperature of the thermal head, it is necessary to keep the temperature resistance value from the heating element of the thermal head to the heat sink low. For this purpose, a ceramic plate having a heating element and a heat sink are joined using a silver paste or the like having a low thermal resistance value. In claim 1, in order to remove heat storage of the thermal head by forced cooling system as quickly as possible, the heat sink of the thermal head is made of a copper material having the lowest thermal resistance, and has a strength reinforcing material (iron, etc.). Thermal printer In order to more efficiently take measures against heat storage in claim 1 above, in the case of printing media (image receiving paper) and transfer printing, the ribbon is preheated immediately before printing (the temperature of the printing surface of the image receiving paper is increased) to generate heat. Thermal printer that can keep energy low