JP2007296716A - Heat-sensitive recording medium, image forming device, and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording sheet or the like of which the maintenance is easy, which does not generate wastes such as a cartridge, and in addition, can facilitate the management of the recording sheet. <P>SOLUTION: At the time of an image formation, the recording sheet 10 is heated at a temperature T1, and also, a pressure P1 (>a normal pressure P0) is applied, and a low temperature color-developing layer 15 is color-developed. Then, the recording sheet 10 is heated at a temperature T3 (>T1) under the normal pressure P0, and a high temperature color-developing layer 11 is color-developed. In this case, since the pressure P1 has not been applied, the low temperature color-developing layer 15 does not develop a color. Also, since there is a heat barrier layer 9, an intermediate temperature color-developing layer 7 does not become a temperature T2 or higher, and does not develop a color. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal recording medium, an image forming apparatus for forming an image on the thermal recording medium, and a method thereof.

Currently available printers include an ink jet method, a thermal transfer method, and a laser method in which a copier is computerized. These all transfer ink, ink ribbon, toner, and the like to paper (sheet). Therefore, when printing is finished, ink, ink ribbon, and a dedicated cartridge containing them become waste. Also, in order to achieve photographic image quality, it is necessary to use special paper after all.
On the other hand, there are thermal printers used for facsimile and barcode printing as printers that require dedicated recording sheets but do not discard ink, ink ribbon, and dedicated cartridges. There are many technical difficulties to realize photographic image quality color printing by such a thermal method, and it has not been put into practical use.
The biggest technical barrier is that it is difficult to control each color layer of three colors and three colors by controlling them independently only by thermal control of the thermal head, and to control the density gradation by adding shades to each color to be colored. For this reason, it was not possible to achieve color image quality printing. Under such circumstances, the direct thermal recording system (TA system), which was released in 1996 based on the technical idea of Patent Document 1 of Fuji Photo Film Co., Ltd., is the only practical example.

In this TA method, a heat-sensitive coloring layer is laminated on a substrate in the order of cyan, magenta, and yellow, and a heat-resistant protective layer is disposed as the uppermost layer. The yellow and magenta color-developing layers use diazonium salt compounds and couplers as color-developing materials and can fix images with ultraviolet rays. In addition, since the cyan coloring layer does not need to be fixed, a dye precursor and an organic acid are used as coloring materials. The microcapsules in each layer have different thermal sensitivities and ultraviolet sensitivities. By giving different thermal energy and different wavelength ultraviolet rays in five steps, full color prints are made while repeating coloring and fixing.
Specifically, in the TA method, (1) a yellow image is formed with low thermal energy using yellow image information, (2) ultraviolet light having a wavelength of 419 nm is irradiated on the entire surface, (3) the yellow image is fixed, and (4 ) Form a magenta image with medium heat energy (At this time, the yellow coloring layer does not develop even when heated, so it is not affected), (4) Irradiate the entire surface with ultraviolet light having a wavelength of 365 nm, fix the magenta image, (5) A cyan image is formed with high thermal energy.

  In addition to the above TA method, Patent Document 2 proposes a system in which a color is produced by chemically reacting a diazo compound in a capsule and a coupler outside the capsule by combining three pressures and three temperatures. Yes.

JP 61-40192 A JP-A-11-170692

However, the TA method has a problem that it is difficult to store the recording sheet because the thermosensitive coloring layer is fixed with ultraviolet rays.
Further, the above-described system of Patent Document 2 has a problem that it is difficult to control the color by applying three levels of pressure to the recording sheet appropriately.
Furthermore, there is a demand for a thinner recording sheet and a simplified image forming process.

In order to solve the above-described problems of the prior art, the present invention facilitates maintenance of an image forming apparatus, can form an image on a heat-sensitive recording medium with simple control without generating waste such as cartridges, and the like. An object of the present invention is to provide a thermal recording medium, an image forming apparatus, and an image forming method capable of easily managing the recording medium.
Another object of the present invention is to provide a thermal recording medium, an image forming apparatus, and an image forming method capable of making the thermal recording medium thinner and simplifying the image forming process.

In order to solve the above-described problems of the prior art and achieve the above-described object, the thermal recording medium of the first aspect of the invention develops color under the condition that a predetermined pressure is applied at the first temperature. And a second coloring element that develops color at a second temperature higher than the first temperature regardless of the pressure.
According to the first aspect of the present invention, since pressure is required for color development of the first color development element, the first color development element does not color even when heated at the second temperature without fixing the first color development element. Therefore, the image forming process can be simplified, and the sheet can be thinned since no fixing agent is required.
According to a second aspect of the present invention, in the first aspect of the present invention, M further includes a third coloring element that develops color at a third temperature higher than the second temperature.
According to the second aspect of the invention, three colors can be developed, and an image can be formed by color.

According to a third aspect of the present invention, in the second aspect of the invention, the first color developing layer enclosing the first color developing element, the second color developing layer enclosing the second color developing element, and the third color forming layer A third coloring layer containing a coloring element; and a thermal barrier layer, the second coloring layer, the thermal barrier layer, the third coloring layer, and the first coloring layer on a substrate. Are sequentially laminated.
In the invention of claim 3, by providing the thermal barrier layer, the third color forming layer can be arranged on the heating side with respect to the second color developing layer, and the energy efficiency at the time of image formation is good.

According to a fourth aspect of the present invention, in the second aspect of the invention, the first color forming layer enclosing the first color forming element, the second color forming layer including the second color forming element, and the third color forming layer And a third coloring layer containing a coloring element, and the second coloring layer, the first coloring layer, and the third coloring layer are sequentially laminated on a substrate. .
In the fourth aspect of the invention, since the first coloring layer is disposed between the second coloring layer and the third coloring layer, the first coloring layer functions as a thermal barrier when the third coloring layer is heated. In addition, color development of the second color development layer can be prevented.

  The invention according to claim 5 is the invention according to claims 1 to 4, wherein the coloring element is an element that emits a material contained in the coloring element outside the coloring element and reacts with a substance outside the coloring element to develop a color, Alternatively, a material outside the coloring element flows into the coloring element and reacts with a substance in the coloring element to develop a color in the coloring element.

According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: a thermal head that thermally records an image on a thermal recording medium; a pressurizing unit that applies pressure to the thermal recording medium; and the thermal head is heated at the first temperature. The process of controlling the pressurizing means to apply a predetermined pressure in a state where the pressure is applied, and the thermal head at the second temperature higher than the first temperature without the pressurizing means applying the pressure. And a control means for performing processing for controlling the recording medium to be heated.
According to a sixth aspect of the present invention, based on the control of the control means, the pressurizing means applies a predetermined pressure while the thermal head is heated at the first temperature. The thermal head heats the thermal recording medium at a second temperature higher than the first temperature in a state where the pressurizing means does not apply the pressure.

According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the sixth aspect of the present invention, wherein the thermal head and the pressurizing unit are integrally formed, and the pressure is applied by the heating surface of the thermal head that contacts the thermal recording medium. It is characterized by adding.
This makes it possible to form an image with one head and one pass with a small configuration.

  An image forming method according to an eighth aspect of the present invention includes a first step of applying a predetermined pressure to the thermal recording medium in a state heated at the first temperature, and the first pressure without applying the pressure to the thermal recording medium. A second step of heating the thermosensitive recording medium at a second temperature higher than the first temperature.

According to the present invention, maintenance of the image forming apparatus is easy, images can be formed on the thermal recording medium with simple control without generating waste such as cartridges, and the recording sheets can be easily managed. A thermal recording medium, an image forming apparatus, and an image forming method can be provided.
In addition, according to the present invention, it is possible to provide a thermal recording medium, an image forming apparatus, and an image forming method capable of reducing the thickness of the thermal recording medium and simplifying the image forming process.

Hereinafter, a recording sheet according to an embodiment of the present invention and a printer that forms an image on the recording sheet will be described.
<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described.
[Correspondence with Configuration of the Present Invention]
First, the correspondence between the components of the present embodiment and the components of the present invention will be described.
The low temperature coloring capsule 25 is an example of the first coloring element of the present invention, the medium temperature coloring capsule 21 is an example of the second coloring element, and the high temperature coloring capsule 23 is an example of the third coloring element.
The low temperature coloring layer 15 is an example of the first coloring layer of the present invention, the intermediate temperature coloring layer 7 is an example of the second coloring layer of the present invention, and the high temperature coloring layer 11 is the third coloring layer of the present invention. It is an example of a layer.
The thermal barrier layer 9 is an example of the thermal barrier layer of claim 3.
A thermal head 45 shown in FIG. 5 is an example of the thermal head and pressurizing means of the present invention. Moreover, the control part 51 shown in FIG. 5 is an example of the control means of this invention.

[Recording sheet 10]
First, the recording sheet 10 used in this embodiment will be described.
FIG. 1 is a cross-sectional configuration diagram of a recording sheet 10 used in the present embodiment.
As shown in FIG. 1, the recording sheet 10 includes, for example, an intermediate temperature coloring layer 7, a thermal barrier layer 9, a high temperature coloring layer 11, a mixing prevention layer 13, a low temperature coloring layer 15 and a protective layer 19 in this order on a substrate 5. Laminated.

At the time of image formation of the recording sheet 10, the low temperature coloring layer 15 develops color on the condition that the recording sheet 10 is heated at the temperature T1 and the pressure P1 (> normal pressure P0) is applied.
Next, the recording sheet 10 is heated at the temperature T3 (> T1) at the normal pressure P0, and the high temperature coloring layer 11 develops color. At this time, since the pressure P1 is not applied to the recording sheet 10, the low temperature coloring layer 15 does not develop color. Further, since the thermal barrier layer 9 is present, the intermediate temperature coloring layer 7 does not rise above the temperature T2 and does not develop color.
Next, the recording sheet 10 is heated at a normal pressure P0 at a temperature T2 (T3>T2> T1), and the intermediate temperature coloring layer 7 is colored.

According to the recording sheet 10, since the color is not generated unless the low-temperature coloring layer 15 is at a pressure P1 higher than the normal pressure P0, the weather resistance is excellent.
Further, according to the recording sheet 10, since it is not necessary to fix the intermediate temperature coloring layer 7, the sheet can be thinned and the image forming process can be simplified.
Since the recording sheet 10 can develop three colors, a color image can be formed.

Hereinafter, each component of the recording sheet 10 will be described.
The substrate 5 is made of, for example, polyester or polyethylene terephthalate (PET). The base material 5 is white or transparent.

The intermediate temperature coloring layer 7 is configured by dispersing a medium temperature coloring capsule 21, a developer, and, if necessary, a basic substance or an acidic substance in a binder material. The medium temperature color developing capsule 21 encloses the color developing agent, and the glass transition point of the wall is a temperature T2 (for example, 160 ° C.) shown in FIG.
For example, when the intermediate temperature coloring layer 7 is in an intermediate temperature state that is equal to or higher than the temperature T2, the color developing agent contained in the intermediate temperature coloring capsule 21 and the visible color in the intermediate temperature coloring layer 7 even at the normal pressure P0 (even if the pressure P1 is not increased). Color develops by reacting with the colorant. That is, there is no pressure condition for color development of the intermediate temperature color development layer 7.

  The medium temperature coloring capsule 21 is a so-called microcapsule, and its wall is made of polyurea or polyurethane having a glass transition point of 150 to 280 ° C. The medium temperature coloring capsule 21 has a characteristic that the material permeability (permeability) increases before and after the glass transition point. Accordingly, as shown in FIG. 3A, when the temperature is lower than T2 (non-medium temperature), the color developer does not penetrate into the medium temperature color capsule 21 and the color developer in the medium temperature color capsule 21 does not develop color. On the other hand, as shown in FIG. 3B, when the temperature becomes T2 or higher (the above intermediate temperature state), the developer in the intermediate temperature coloring layer 7 penetrates into the intermediate temperature coloring capsule 21 regardless of the pressure, and The coloring agent and the coloring agent in the medium temperature coloring capsule 21 react with each other to form a dye and develop a color.

The wall of the microcapsule in the present embodiment such as the medium temperature coloring capsule 21 is formed of a synthetic resin such as a thermosetting resin or a thermoplastic resin. Specifically, a melamine-formaldehyde polymer, a urea-formaldehyde polymer, or the like is used as the wall of the medium temperature coloring capsule 21 or the like.
The average particle size of the microcapsules is, for example, about 3 to 4 μm, and the glass transition point is defined by the wall material. The microcapsule not only keeps the reacting substances in a multi-layered structure, but also disperses them in micron across the wall of the microcapsule so that it can coexist in a thin coating film of several microns at room temperature. While maintaining sufficient isolation, it has the function of giving sufficient material permeability instantaneously during heating.

In addition, the medium temperature coloring capsule 21 is configured such that when the medium temperature state is reached, the wall melts, the color developing agent in the capsule flows out of the capsule, and reacts with the developer outside the capsule to develop color. Also good.
In the present embodiment, the combination of the color former and the developer that reacts with the color developer includes, for example, a combination of a diazo compound (color developer) and a coupler (developer), or an electron-donating colorless dye (color developer). And an electron-accepting compound (developer). It is known that an arbitrary hue can be colored by a combination of a chemical structure of a diazo compound and a chemical structure of a coupler, or a combination of a chemical structure of an electron-donating colorless dye and a chemical structure of an electron-accepting compound.

The diazo compound is, for example, tricresyl phosphate. The diazo compound is an electron donating dye precursor (dye precursor), and reacts with a coupler in a basic atmosphere to develop a color. The coupler is, for example, resorcil or phloroglucin, and forms a dye by coupling with a diazo compound in a basic atmosphere. The basic atmosphere is made of a hardly water-soluble or water-insoluble basic substance or a substance that generates alkali by heating (for example, an organic ammonium salt).
The electron-donating colorless dye is, for example, a leuco dye, and the electron-accepting compound is, for example, a phenolic acidic substance. In this combination, the leuco dye is adsorbed by the developer, which is an acidic substance, and oxidized to develop a color.

Moreover, as said coupler, 2-hydroxy-3 naphthoic acid anilide etc. are used, for example.
Moreover, as said electron-accepting compound, acidic substances, such as a phenol compound, an organic acid or its metal salt, and oxybenzoic acid ester, are used, for example.

  Further, in this embodiment, the case where the color former is encapsulated in the microcapsule is exemplified, but for example, the color former and the developer are dispersed and arranged in the binder, and the binder is melted by heating to cause the color former. The developer may react with the developer.

The thermal barrier layer 9 prevents the high temperature coloring capsule 21 and the medium temperature coloring capsule 23 from being mixed with each other, and prevents the intermediate temperature coloring layer 7 from being colored by the heat generated when the high temperature coloring layer 11 is colored.
The thermal barrier layer 9 is made of an arbitrary material including an inert material that undergoes a phase change during heating, for example, when the layer includes a thermal solvent. A typical material for the thermal barrier layer 9 is a polymer material such as poly (vinyl alcohol).

  The high-temperature coloring layer 11 is configured by dispersing a high-temperature coloring capsule 23, a developer, and, if necessary, a basic substance or an acidic substance in a binder material. The high-temperature coloring capsule 23 encloses the coloring agent, and the glass transition point of the wall is, for example, a high temperature of 300 to 350 ° C. When the high-temperature coloring layer 11 is in a high temperature state, for example, higher than the temperature T3 (eg, 330 ° C.) shown in FIG. 2, the developer in the high-temperature coloring layer 11 flows into the high-temperature coloring capsule 23 even at the normal pressure P0. Then, it reacts with the color former contained in the high-temperature color capsule 23 and develops color. The coloring principle of the high temperature coloring capsule 23 is the same as that of the medium temperature coloring capsule 21 described above except for the glass transition point.

  The mixing prevention layer 13 prevents the high temperature coloring capsule 23 and the low temperature coloring capsule 23 from being mixed.

The low temperature coloring layer 15 is constituted by dispersing a low temperature coloring capsule 25, a developer, and, if necessary, a basic substance or an acidic substance in a binder material. The low-temperature coloring capsule 25 encloses a coloring agent, and the glass transition point of the wall is, for example, a low temperature of 90 to 140 ° C.
For example, when the low temperature coloring capsule 25 is pressed at a pressure P1 or higher in a low temperature state equal to or higher than a temperature T1 (eg, 110 ° C.) shown in FIG. It flows into the interior and reacts with the color former contained in the low temperature color development capsule 25 to develop color.
Thus, in order for the low temperature coloring layer 15 to develop color, in addition to being in a low temperature state, it is necessary to apply a pressure equal to or higher than the pressure P1. The coloring condition of the low-temperature coloring layer 15 is determined by the capsule wall material that defines the glass transition point of the low-temperature coloring capsule 25 and the capsule diameter and wall thickness. In the low temperature coloring capsule 25, the pressure P1 required for coloring increases as the wall thickness / diameter value increases. Moreover, the temperature T1 required for color development becomes low as the glass transition point of the wall of the low temperature color development capsule 25 becomes low.
In the present embodiment, the low temperature color capsule 25 is based on temperature and pressure, and the medium temperature color capsule 21 and the high temperature color capsule 23 are only temperature based on the color development conditions.

  The protective layer 19 is a layer for protecting the low temperature coloring layer 15. The protective layer 19 has, for example, a heat resistance function.

In the present embodiment, the thickness of each of the medium temperature coloring layer 7, the high temperature coloring layer 11, and the low temperature coloring layer 15 is, for example, 1 to 4 μm. The thickness of the thermal barrier layer 9 is, for example, 5 to 25 μm.
For example, yellow is assigned to the medium temperature coloring layer 7, magenta is assigned to the low temperature coloring suppressing layer 15, and cyan is assigned to the high temperature coloring layer 7. However, this is an example, and the allocation pattern is arbitrary.

[Printer 40]
Next, a printer that forms an image on the recording sheet 10 shown in FIG. 1 will be described.
FIG. 5 is a configuration diagram of the printer 40 that records (prints) an image on the recording sheet 10 shown in FIG. 1.
As illustrated in FIG. 5, the printer 40 includes, for example, a sheet storage case 41, a sheet feeding roller 43, a thermal head 45, a platen roller 47, a sheet carry-out unit 50, and a control unit 51.
The sheet storage case 41 stores a plurality of recording sheets 10. The recording sheet 10 stored in the sheet storage case 41 is pressed toward the sheet feeding roller 43 by an urging means such as a spring 53.

  The sheet feeding roller 43 is positioned in contact with the uppermost recording sheet 10 of the sheet storage case 41. The sheet feeding roller 43 is rotationally driven by a motor (not shown) based on a control signal from the control unit 51. When the sheet feeding roller 43 rotates, the frictional force generated between the recording sheet 10 and the sheet feeding roller 43 by the urging force of the spring 53 interlocks with the rotation of the sheet feeding roller 43 and the uppermost stage of the sheet storage case 41. The recording sheet 10 is conveyed toward the thermal head 45. The controller 51 controls the position and feed amount of the recording sheet 10 by controlling the rotation amount of the motor (sheet feed roller 43) based on the control signal.

A thermal head 45 is provided on the downstream side of the sheet feeding roller 43 in the conveyance path of the recording sheet 10.
FIG. 6 is a diagram for explaining the thermal head 45.
The thermal head 45 heats and pressurizes the recording sheet 10 on the heating / pressurizing surface of the thermal head portion 545 that contacts the protective layer 19 of the recording sheet 10.
As shown in FIG. 6, the thermal head 45 is fixed to one end of a joint 520. The joint 520 rotates around the central axis 520a. The other end of the joint 520 is biased by a spring 541 in a direction in which the joint 520 is rotated counterclockwise about the rotation shaft 520a. The biasing force by the spring 541 acts as a force for pressing the recording sheet 10 or the like with the normal pressure P0 by the heating surface of the thermal head unit 545.

The joint 521 is installed so as to be rotatable about the rotation shaft 520 a, and the tip 521 a at one end is in contact with one side of the joint 520.
Further, the other end 521 b of the joint 521 is in contact with the outer periphery of the cam 530. Further, one end of the spring 540 is fixed to the joint 521. When the cam 530 rotates, the joint 521 rotates alternately around the rotation shaft 520a in the clockwise direction and the counterclockwise direction with a predetermined rotation angle width corresponding to the step on the outer periphery of the cam 530.
At this time, the tip 521a does not press the joint 520 at the position where the joint 521 is most rotated in the clockwise direction. That is, the biasing force of the spring 540 does not act on the thermal head portion 545. Accordingly, the normal pressure P0 is applied to the recording sheet 10 by the heating surface of the thermal head unit 545.

On the other hand, at the position where the joint 521 is most rotated counterclockwise, the tip 521a presses the joint 520, and the urging force of the spring 540 acts in a direction to press the thermal head 545 against the recording sheet 10. Thereby, the recording sheet 10 is pressurized with the pressure P1 (> P0) by the heating surface of the thermal head unit 545.
In the thermal head 45, the control unit 51 shown in FIG. 5 can control the pressure applied to the recording sheet 10 or the like via the heating surface of the thermal head unit 545 by controlling the rotation of the cam 530.

The thermal head unit 545 includes a heating element array in which a plurality of heating elements are arranged in a line in the main scanning direction. The thermal head unit 545 causes each heating element to generate heat in a pattern corresponding to an image to be formed with the heating element array in contact with the recording sheet 10. In the present embodiment, each heating element has at least four states of a non-heating state, a low temperature heating state, a medium temperature coloring state, and a high temperature heating state, and one of these four states is selected by the control unit 51.
The heat generation temperature of each heat generating element is controlled by the time during which a current flows through a resistor connected to the heat generating element. The control unit 51 controls the pulse width of the strobe signal that defines the time during which a current flows to each heating element of the thermal head unit 545 according to the heating time.
Note that the thermal head unit 545 may be capable of adjusting a plurality of heat generation temperatures in accordance with the gradation of the image data in each of the low temperature coloring state, the medium temperature coloring state, and the high temperature coloring state.

In the printer 40, since a plurality of heating temperatures and pressurization can be realized with one head, an image can be formed on the recording sheet 10 in one pass. That is, an image can be formed by passing the recording sheet 10 in contact with the head once. This is useful for reducing the manufacturing cost because the thermal head is expensive, and can meet the demand for miniaturization.
That is, when a single line-type thermal head is realized, in the conventional TA system, the recording sheet is passed through the thermal head two and a half times, so that the image forming time is long. In addition, the TA method also requires a UV lamp and two types of filter switching means, which increases the size of the printer. The printer 40 can solve such a problem.

  The platen roller 47 is provided with a thermal head portion 545 of the thermal head 45 on the opposite side across the conveyance path of the recording sheet 10. The platen roller 47 rotates in accordance with the conveyance of the recording sheet 10, and stabilizes the contact state between the recording sheet 10 and the heating element of the thermal head unit 545.

  The sheet unloading unit 50 unloads the recording sheet 10 that has finished coloring.

  The control unit 51 is an electronic circuit such as a microcomputer, for example, and comprehensively controls the operation of the printer 40.

Hereinafter, an operation example of the printer 40 will be described with reference to FIGS.
FIG. 8 is a flowchart for explaining an operation example of the printer 40 shown in FIG. 5 and the like for forming an image on the recording sheet 10 shown in FIG.
Each step shown in FIG. 8 is comprehensively controlled by the control unit 51.

Step ST0:
A plurality of recording sheets 10 are stored in a sheet storage case 41 of the printer shown in FIG. The recording sheet 10 stored in the sheet storage case 41 is pushed toward the paper feed roller 43 by the urging force of the spring 53, and a frictional force is generated between the uppermost recording sheet 10 and the paper feed roller 43. .

Step ST1:
Based on the control from the control unit 51, the sheet feeding roller 43 rotates and the recording sheet 10 accommodated in the uppermost stage of the sheet accommodation case 41 is conveyed toward the thermal head 45.

Step ST2:
Based on the control from the control unit 51, the cam 530 shown in FIG. 6 rotates, and the joint 521 reaches the most counterclockwise position. As a result, the pressure P <b> 1 is applied to the recording sheet 10 by the thermal head unit 545.
In this state, based on the control from the control unit 51, each heating element of the thermal head unit 545 generates low temperature heat with a pixel pattern corresponding to the low temperature coloring component of the image formed on the recording sheet 10. As a result, the low-temperature coloring layer 15 of the recording sheet 10 has a pixel pattern of a low-temperature coloring component corresponding to image information and is heated at a low temperature at the temperature T1 shown in FIG. The developer and the developer around it react to develop color (low temperature development).

Step ST3:
Subsequent to step ST2, the cam 530 rotates based on the control from the control unit 51, and the pressure applied to the recording sheet 10 becomes the normal pressure P0.
Further, the thermal head 45 causes each heating element of the thermal head unit 545 to generate heat at a high temperature for a short time with a pixel pattern corresponding to the high-temperature coloring component of the image formed on the recording sheet 10. As a result, the high-temperature coloring layer 11 of the recording sheet 10 has a pixel pattern of a high-temperature coloring component corresponding to image information and is heated at a high temperature for a short time at the temperature T3 shown in FIG. The color former and the developer around it react to develop color (high temperature color development).
In the present embodiment, the high-temperature coloring layer 11 develops a color on the condition that it has been heated at a temperature T3 or higher for a short time or longer.
At this time, since the pressure P1 is not applied to the recording sheet 10, the low temperature coloring layer 15 does not develop color. Further, since the thermal barrier layer 9 is present, the intermediate temperature coloring layer 7 does not develop color.

Step ST4:
Subsequent to step ST3, in a state where the pressure applied to the recording sheet 10 is set to the normal pressure P0, the thermal head 45 has each pixel pattern of the thermal head unit 545 with a pixel pattern corresponding to the medium temperature coloring component formed on the recording sheet 10. The heating element is heated to a medium temperature for a medium time. As a result, the medium temperature coloring layer 7 of the recording sheet 10 is heated in the medium temperature coloring capsule 21 at the position where the medium temperature heating is performed at the temperature T2 shown in FIG. The color former and the developer around it react to develop color (medium temperature color development). In the present embodiment, the medium time is a concept longer than the short time. Further, the medium temperature coloring layer 7 develops color under the condition that it is heated at a temperature T2 or higher for a medium time or longer.

  As shown in FIG. 7A, the operations in steps ST2 to ST4 can be continuously performed by controlling the temperature and time with one head in the thermal head 45 of the printer having the configuration shown in FIG.

Step ST5:
Based on the control from the control unit 51, the platen roller 47 rotates, and the recording sheet 10 is conveyed toward the sheet carrying-out unit 50 on the right side in FIG. 5 as shown in FIG. 7B.

As described above, by using the recording sheet 10, the printer 40 can form an image on the recording sheet 10 with simple control without generating waste such as a cartridge. Therefore, maintenance of the printer 40 is facilitated.
Further, the low-temperature coloring layer 15 of the recording sheet 10 is colored on the condition that it is heated at the temperature T1 and the pressure P1 (> normal pressure P0) is applied. Therefore, the low temperature coloring layer 15 is excellent in weather resistance. Further, since the low-temperature coloring layer 15 does not need to be fixed, it is not necessary to provide a fixing layer in the recording sheet 10 and the sheet can be made thin. Further, since the fixing step of the low temperature coloring layer 15 is not required at the time of image formation, the image formation can be performed in a short time with a simple printer configuration. In other words, according to the recording sheet 10, one of the three layers is colored by pressure and the two layers are colored by controlling time and heat, so control is easier than controlling all three layers by heat and time. It is.

  Further, according to the printer 40 of the present embodiment, by using the thermal head 45 shown in FIGS. 5 and 6, images can be continuously formed by controlling the temperature, pressure and time with one head.

Second Embodiment
In the printer 40 described with reference to FIGS. 5 and 6 of the first embodiment described above, the contact surface of the thermal head unit 545 to the recording sheet 10 is exemplified as the heating surface and the pressing surface. Then, a heating mechanism and a pressurizing mechanism are provided separately.
FIG. 9 is a partial configuration diagram of the printer according to the present embodiment.
As shown in FIG. 9, the printer includes a platen roller 202 that rotates about a rotation shaft 204.
The platen roller 202 rotates around the rotation shaft 204 while being in contact with the surface of the substrate 5 of the recording sheet 10.
The pressing unit 206 moves the platen roller 202 in the direction of the arrow in FIG. 9 to switch the pressing state of the recording surface of the recording sheet 10. Specifically, in the case of the first embodiment, the pressurizing unit 206 pressurizes the recording sheet 10 in either of the normal pressure P0 and the pressure P1 shown in FIG.

A plurality of heating elements 210 are arranged in a line on the opposite side of the recording sheet 10 with respect to the platen roller 202.
In the printer shown in FIG. 9, for example, the recording sheet 10 is conveyed so that the protective layer 19 side of the recording sheet 10 is in contact with the heating element 210 and the base material 5 is in contact with the platen roller 202.
In the printer shown in FIG. 9, control is performed so that the pressure P1 is applied to the recording sheet 10 by the pressure unit 206 in step ST2 shown in FIG. 8, and the normal pressure P0 is applied to the recording sheet 10 in steps ST3 and ST4.
Further, the heating element 210 generates low temperature heat in step ST2 shown in FIG. 8, generates high temperature in step ST3, and generates intermediate temperature in step ST4.
A color image can also be formed on the recording sheet 10 by the printer shown in FIG.

<Third Embodiment>
In the first embodiment described above, the case where the low-temperature coloring layer 15 is disposed on the protective layer 19 side as shown in FIG. 1 is exemplified. However, in the recording sheet 110 of this embodiment, as shown in FIG. 5, the intermediate temperature coloring layer 7, the low temperature coloring layer 15, and the high temperature coloring layer 11 are laminated in this order.
Here, the base material 5, the intermediate temperature coloring layer 7, the low temperature coloring layer 15, and the high temperature coloring layer 11 are the same as those described in the first embodiment.
According to the recording sheet 110 shown in FIG. 10, since the low temperature coloring layer 15 functions as a thermal barrier during the high temperature coloring of the high temperature coloring layer 11, there is no need to separately provide the thermal barrier layer required in the first embodiment. . Therefore, the recording sheet 110 can be thinned.

<Modification>
In the first embodiment described above, as shown in FIG. 8, after the low temperature coloring layer 15 is colored at low temperature, the high temperature coloring layer 11 is colored at high temperature, and then the intermediate temperature coloring layer 7 is colored at medium temperature. Prior to 11, the medium temperature coloring layer 7 may be colored.
Further, the coloring process for the low temperature coloring layer 15 may be performed after the coloring process for the high temperature coloring layer 11 or the medium temperature coloring layer 7.

The present invention is not limited to the embodiment described above.
That is, those skilled in the art may make various modifications, combinations, subcombinations, and alternatives regarding the components of the above-described embodiments within the technical scope of the present invention or an equivalent scope thereof.
For example, in the above-described embodiment, the case where recording is performed by coloring the recording sheet in three colors is exemplified, but recording may be performed by causing the recording sheet to develop colors in four or more colors. For example, black may be added to three colors of yellow, cyan, and magenta to develop a recording sheet with four colors, or light cyan and light magenta may be added to develop a recording sheet with five colors.

  In the above-described embodiment, the recording sheet is exemplified as the heat-sensitive recording medium of the present invention, but the shape of the heat-sensitive recording medium of the present invention may be other than the sheet shape.

  The present invention is applicable to a system for recording on a thermal recording medium.

FIG. 1 is a configuration diagram of a recording sheet according to the first embodiment of the present invention. FIG. 2 is a diagram for explaining the characteristics of the high-temperature coloring capsule, the low-temperature coloring capsule, and the medium-temperature coloring capsule in the recording sheet shown in FIG. FIG. 3 is a diagram for explaining the coloring principle of the medium temperature coloring capsule and the high temperature coloring capsule shown in FIG. FIG. 4 is a diagram for explaining the coloring principle of the low-temperature coloring capsule shown in FIG. FIG. 5 is a diagram for explaining the printer according to the first embodiment of the present invention. FIG. 6 is a diagram for explaining the thermal head of the printer shown in FIG. FIG. 7 is a continuation diagram of FIG. 5 for explaining the image forming operation of the printer according to the first embodiment of the present invention. FIG. 8 is a flowchart for explaining the image forming operation of the printer according to the first embodiment of the present invention. FIG. 9 is a partial configuration diagram of the printer according to the second embodiment of the present invention. FIG. 10 is a configuration diagram of a recording sheet according to the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,110 ... Recording sheet, 5 ... Base material, 7 ... Medium temperature coloring layer, 9 ... Thermal barrier layer, 11 ... High temperature coloring layer, 13 ... Anti-mixing layer, 15 ... Low temperature coloring layer, 19 ... Protective layer, 21 ... Medium temperature Coloring capsule, 23 ... High temperature coloring capsule, 25 ... Low temperature coloring capsule, 41 ... Sheet storage case, 43 ... Sheet feeding roller, 45 ... Thermal head, 47 ... Platen roller, 204 ... Platen roller, 206 ... Pressure unit, 210 ... Heating element

Claims (8)

A first coloring element that develops color on condition that a predetermined pressure is applied at the first temperature;
A heat-sensitive recording medium comprising: a second coloring element that develops color at a second temperature higher than the first temperature regardless of the pressure. The thermosensitive recording medium according to claim 1, further comprising a third coloring element that develops color at a third temperature higher than the second temperature. A first color development layer containing the first color development element;
A second coloring layer containing the second coloring element;
A third coloring layer containing the third coloring element;
A thermal barrier layer,
The thermal recording medium according to claim 2, wherein the second coloring layer, the thermal barrier layer, the third coloring layer, and the first coloring layer are sequentially laminated on a base material. A first color development layer containing the first color development element;
A second coloring layer containing the second coloring element;
A third coloring layer containing the third coloring element;
Have
The heat-sensitive recording medium according to claim 2, wherein the second coloring layer, the first coloring layer, and the third coloring layer are sequentially laminated on a substrate. The coloring element is an element that emits a material contained in the coloring element outside the coloring element and reacts with a substance outside the coloring element, or a material outside the coloring element in the coloring element. The thermal recording medium according to any one of claims 1 to 4, wherein the thermal recording medium is an element that flows into the coloring element and reacts with a substance in the coloring element to develop a color. A thermal head for thermally recording an image on a thermal recording medium;
Pressurizing means for applying pressure to the thermal recording medium;
A process of controlling the pressurizing unit to apply a predetermined pressure while the thermal head is heated at the first temperature; and the thermal head is configured to apply the first pressure while the pressurizing unit does not apply the pressure. And a control unit that performs a process of controlling the heat-sensitive recording medium to be heated at a second temperature that is higher than the temperature of the image forming apparatus. The image forming apparatus according to claim 6, wherein the thermal head and the pressure unit are integrally configured, and the pressure is applied by a heating surface of the thermal head that contacts the thermal recording medium. A first step of applying a predetermined pressure to the thermosensitive recording medium while being heated at a first temperature;
And a second step of heating the thermosensitive recording medium at a second temperature higher than the first temperature without applying the pressure to the thermosensitive recording medium.