JPS5921314B2 - Electric heating sheet for recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording current-generating sheet used in a heat-sensitive recording method by applying current from a recording electrode.

Various methods have been proposed for recording electrical signals as characters or figures on recording paper.

Among these methods, the thermal recording method has recently attracted particular attention as a recording method for facsimiles, computer printing devices, and the like. This is due to the advantages that the thermal recording method is a primary coloring method that does not require liquid or powder ink, that the printing section is easy to maintain, and that the thermal recording paper, which is a consumable material, is inexpensive. Since the heat-sensitive recording head used as a heat source for thermal recording has a slow thermal response speed, it also has the disadvantage of a slow recording speed. On the other hand, there is also a so-called energized thermosensitive recording method in which the recording paper is given heat-sensitive coloring properties and conductivity, and electricity is applied directly to the recording paper from the recording electrode, and the Joule heat generated in the recording paper itself is used as the heat source for recording.

Although this method was simple, it had the disadvantage of increasing the cost of recording paper. The present inventors have previously proposed a recording method that incorporates the advantages of both the thermal recording method and the electrically conductive thermosensitive recording method, which is used together with an electrode that supplies an electric signal for recording, and can cause localized heat generation by localized current application. The resistive layer is provided with a resistive layer and a conductive layer laminated in close contact with the resistive layer, and when the electrode is brought into contact with the resistive layer and electricity is supplied, the resistive layer between the electrode and the conductive layer is provided with the localized conductive layer. We proposed a thermal recording method that uses an energized recording sheet that generates heat.

As shown in FIG. 1, the structure of the current heating sheet 1 for recording includes a conductive layer 2 and a resistance layer 3 closely laminated to the conductive layer 2 and electrically and mechanically bonded. As the conductive layer 2, a metal foil having a thickness of 5 to 20 microns is used. As the resistance layer 3, a coating film of a conductive paint or a vapor deposited film of a semiconductor having a resistance value one order or more higher than that of the conductive layer 2 is used. The recording principle is as shown in FIG.
A pulse signal of 0 KHz and a pulse width of 100 to 250 microseconds is applied to the resistive layer 3 between the recording electrode 5 and the conductive layer 2.
A local current is applied to the area to cause local heat generation due to Joule heat. The heat generated in the resistive layer 3 passes through the conductive layer 2 and is transmitted to the coloring layer 8 of the thermal paper 7 that is in close contact with the energizing heat generating sheet 1 to form a recorded image 9. At this time, the current flows from the electrode 5 to the resistance layer 3.
, flows to the conductive layer 2, flows laterally through the conductive layer 2, and further flows from the conductive layer 2 through the resistance layer 3 to the return electrode 6, but the return electrode 6
Since the area of is sufficiently large, no heat generation occurs in the resistance layer 3 below the return electrode 6. At this time, the energized heating sheet 1 is heated to 300 to 400°C for several milliseconds, or the temperature is locally raised significantly due to discharge that may occur due to the movement of the electrode needle during recording. It may happen.

Therefore, the electrical heating sheet 1 is required to be made of a material that can withstand such temperature rise. On the other hand, since it is necessary to reduce the heat transfer resistance at the interface with the heat-sensitive paper 7 as much as possible in the energized heat-generating sheet 1, a load of about 11<9/d is applied to the recording electrode 5. Therefore, the electrical heating sheet 1 is also required to be flexible. The metal foil that is the material of the conductive layer 2 satisfies these conditions, but the conductive coating film or semiconductor vapor deposited film that is the material of the resistive layer 3 satisfies these conditions and is suitable for industrial production. An example of this is a conductive coating film using carbon black as a conductive agent. However, hydrophobic vinyl polymers such as vinyl acetate and vinyl acrylate are used as binders in conventional conductive paints, and when a coating film of these conductive paints is used for the resistive layer 3, 300 to 4 seconds
It cannot withstand a temperature rise of 00°C or a local temperature rise during discharge, resulting in thermal breakdown. Therefore, as the material for the resistive layer 3, it is impractical to use a conductive coating film using a binder that is resistant to electrical and thermal deterioration. From this point of view, the present inventors previously proposed the use of heat-resistant polyimide polymers as binders, but these polymers require the use of solvents that are harmful to the human body, such as toluene and xylene. A baking process at a high temperature of 160 to 200° C. is also required, which requires dedicated coating equipment and baking equipment, which poses a problem in terms of cost.

An object of the present invention is to provide an electrically heated sheet for recording that has excellent heat resistance, high recording quality, is easy to manufacture, and is inexpensive.

As a binder, a water-soluble polymer such as polyvinyl alcohol, which can use harmless water as a solvent and can form a coating film by using general-purpose drying equipment at 100 to 120°C, is used as a binder for the resistance layer 3. When we prototyped an electrified heating sheet for recording using this material and conducted a recording test, we found that it could withstand temperatures of 300 to 400°C for several milliseconds.
It has been found that a high quality electrically heated sheet 1 for recording can be obtained which is resistant to discharge occurring at an applied voltage of 15 to 20 volts and has excellent flexibility.

The reason why the instantaneous heat resistance was improved by using a water-soluble polymer as a binder is not clear, but the higher the indoor humidity, the higher the recording energy can be withstood, and the absorbed water molecules improve the instantaneous heat resistance. It seems that this contributes to the improvement of

By using a water-soluble polymer as a binder for the resistance layer 3, this invention improves instantaneous heat resistance while maintaining the flexibility of the coating film, and prevents the electrical heating sheet for recording from being thermally destroyed during use. It is characterized by its high recording density and the ability to obtain uniform, high-quality recording. Examples of water-soluble polymers include polyvinyl alcohol, polyvinyl methyl ether, polyacrylic acid, polymethacrylic acid, or copolymers thereof, casein, niwaka, gelatin, and methylcellulose.

The conductive layer 2 of the recording conductive sheet 1 has a thickness of about 5 to 2
0 micron metal foil, such as aluminum foil, tin foil, titanium foil, etc., can be used, but aluminum foil is preferable in terms of cost.
The thinner the conductive layer 2 is, the less thermal diffusion occurs and a high-quality recorded image can be obtained, but it is preferably about 10 microns in consideration of mechanical strength. Commercially available carbon black can be used as the conductive agent for the resistance layer 3, but grafted carbon with improved compatibility with resin is preferred. Hydrophilic polymers are used as the binder for the resistance layer 3, and among them, polyvinyl alcohol, which is a general-purpose polymer, has excellent film-forming properties and is most preferable in terms of cost. The thinner the resistance layer 3 is, the higher the thermal efficiency is, and a high recording density can be obtained even with the same recording energy. Therefore, due to the balance with mechanical strength, it is approximately 20 to 3
A film thickness of 0 microns is preferred. Examples of the present invention will be described below.

Example 1 Polyvinyl alcohol containing 35% by weight of carbon black was dissolved in an equal amount of water and dispersed in a ball mill for one day to prepare a liquid.

This liquid was applied onto the upper surface of an aluminum foil having a thickness of 10 microns by a wire bar method using an enameled wire of 0.2 mm diameter. It was dried at room temperature to form a coating film with a thickness of about 20 microns, and an electrically heated recording sheet 1 was obtained. Next, the energized heat generating sheet 1 was attached to a metal frame which also served as a return electrode 6 as shown in FIG. Using a recording electrode 5 made of a steel wire with a diameter of 1 mm and polished round, the voltage was 10 V, the frequency was 4 KHz, and the pulse width was 10.
The drum 10 was heated at 300 rpm while applying a pulse signal of 0 microseconds. p. When rotated at a speed of m, 4 pieces/Mm
A dot line with a resolution of . The obtained recorded image 9 was of good quality with a D density of 0.8 to 0.9 and a uniform density. Example 2 A liquid was prepared by dissolving methylcellulose containing 30% by weight of carbon black in an equal amount of water and dispersing it in a ball mill for a day and night.This liquid was milled thickly by the wire bar method using an enameled wire with a diameter of 0.3 mm. It was applied to the top surface of a 10 micron tin foil.

It was dried at room temperature to form a coating film with a thickness of about 30 microns, and an electrically heated recording sheet 1 was obtained. Next, a recording experiment was conducted in the same manner as in Example 1, and as a result, a good quality recorded image with a uniform density at a D density of 0.7 to 0.8 was obtained. Reference Example Prepare a liquid by dissolving vinyl acetate containing 35% by weight of carbon black in an equal amount of ethyl acetate and dispersing it in a ball mill for a day and night. It was applied to the top of a 10 micron thick aluminum foil.

It was air-dried indoors to form a coating film of about 20 microns, and an electrically heated sheet for recording was obtained. Next, a recording experiment was conducted in the same manner as in Example 1, and the results showed that when continuous pulse signals were applied, heat was accumulated in the energized heating sheet, and eventually thermal damage occurred and holes were formed in the sheet. , the recorded image of that part was missing. From the above, the recording current-generating sheet 1 using the hydrophilic polymer as the binder of the resistance layer according to the present invention can withstand temperatures of 300 to 400°C for several milliseconds and will not be thermally destroyed during use. It also has excellent flexibility and can reduce heat transfer resistance with thermal paper, making it possible to obtain clear recorded images with high D density.Moreover, it is easy to manufacture, safe, and low in manufacturing cost. Obviously it's cheap.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an energizing heat-generating sheet for recording related to the present invention, Fig. 2 is a diagram showing the recording principle of a recording method related to the present invention, and Fig. 3 is a test of the energizing heat-generating sheet for recording of the present invention. FIG. 2 is a schematic perspective view showing the device. 1... Electric heating sheet for recording, 2...
Conductive layer, 3... Resistance layer, 5... Electrode.

Claims (1)

[Scope of Claims] 1. A resistive layer that is used together with an electrode for supplying an electric signal for recording and that can generate local heat by local energization, and a conductive layer laminated in close contact with the resistive layer; In the current heating sheet for recording, which generates local heat generation in the resistance layer between the electrode and the conductive layer when the resistance layer is brought into contact with electricity and energized, the resistance layer contains 10% by weight.
An electrically conductive heating sheet for recording, characterized in that it comprises carbon black in an amount of 40% by weight and a water-soluble polymer in an amount of 90% by weight to 60% by weight. 2. The electric heating sheet for recording according to claim 1, wherein the water-soluble polymer is polyvinyl alcohol.