JPH06155906A - Reversible thermal recording method - Google Patents

Abstract

PURPOSE:To mainly prevent a sticking phenomenon, in a reversible thermal recording method using a reversible thermal recording medium, by using a thermal head as a means obtaining a developed color recording state and applying a lubricant to the thermal head immediately before the application of heat. CONSTITUTION:In reversible thermal recording, a reversible thermal recording medium equipped with a recording layer containing an electron-donating color forming compd. and an electron-acceptive compd. is used. A developed color state is generated by heating and melting and a color erased state is generated by heating at a temp. lower than the color forming recording temp. In this case, as a means obtaining the developed color recording state, a thermal head 1 is used and a lubricant is applied to the thermal head 1 immediately before the application of heat. That is, for example, the thermal head 1 is moved by a rotary shaft 3 immediately before (b) the application of heat and brought into contact with the lubricant coating roll 4 to which a lubricant 5 is pressed by a spring 6. At the time (a) of the application of heat, the thermal head 1 is returned to be brought into contact with a platen roll 2 through a recording medium 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent). The medium is widely known, and the output of electronic calculators, facsimiles, vending machines, printers of scientific measuring machines, C
Widely used in RT medical measurement printers. However, all of the conventional products are irreversible in color development, and it is not possible to alternately repeat color development and color erasing. On the other hand, according to the patent publication, a reversible color developing and erasing method is also proposed, and for example, a combination of gallic acid and phloroglucinol is used as a color developing agent. JP-A-61-237684, which uses a compound such as phenolphthalein or thymolphthalein as a color developer, and JP-A-61-237684, which contains a homogenous solution of a color developer, a color developer, and a carboxylic acid ester in a recording layer. 62-138556, JP-A-62-1385.
No. 68 and JP-A-62-140881, JP-A-HEI-2 using a salt of gallic acid and a higher aliphatic amine as a color developer.
JP-A-2-188293 and JP-A-2-188293 which use a salt of bis (hydroxyphenyl) acetic acid or butyric acid and a higher aliphatic amine as a color developer are disclosed.
However, various problems remain in the conventional reversible thermosensitive recording medium described above, and it is not yet satisfactory.

The applicant of the present invention previously used a compound such as an organic phosphoric acid having a long-chain aliphatic group, a carboxyl compound, a phenol compound or a hydroxyphosphonic acid as a color developer, which was used as a fluoran compound or the like as a color developing agent. By combining them, the coloring and decoloring can be easily performed only by heating, and the coloring and decoloring states can be maintained at room temperature, and the decoloring temperature is lower than the coloring temperature. In addition, a reversible thermochromic composition capable of repeatedly forming and erasing an image by changing temperature, and a reversible thermosensitive recording medium containing the same in a recording layer have been proposed (Japanese Patent Application No. 3- 355078). This reversible thermosensitive recording medium does not cause problems such as a decrease in color density and defective erasing even when it is repeatedly used a number of times, and can be used a number of times that is unthinkable from the prior art. However, when performing high-speed recording, it is necessary to supply a predetermined amount of heat energy in a short time, so the temperature of the thermal head inevitably rises, and the degree of surface wear when high-speed recording is repeated many times In order to fully utilize the advantages of the recording medium even under severe conditions such as high-speed recording, since it is incomparably larger than the case of recording several times at low speed,
It is necessary to install a protective layer to prevent the recording layer from being damaged by heat or abrasion.

The present applicant has conducted extensive studies on the protective layer of the reversible thermosensitive recording medium in order to enable it to be used many times even in a harsh environment, and a heat-resistant film having a melting point of 180 ° C. or higher is used as the protective layer. Method (Japanese Patent Application No. 4-6913)
9), a method in which a heat-resistant film is laminated on the recording layer with a thermosetting resin to form a protective layer (Japanese Patent Application No. 4-19915).
86), a method for forming a protective layer by crosslinking polyvinyl butyral with isocyanate (Japanese Patent Application No. 4-193306). The reversible thermosensitive recording medium having the above-mentioned protective layer filed by the present applicant has a large heat resistance and a tough protective layer, so that the possibility of deterioration of the recording medium due to heat or abrasion is greatly reduced. , The surface temperature of the thermal head is 40
Since the temperature is higher than 0 ° C., it is difficult to completely eliminate the development in which the resin on the surface of the recording medium is fused to the thermal head when heat is applied by the thermal head. When the above-mentioned fusion phenomenon called sticking occurs, it may cause a loud noise when the fused film is peeled from the thermal head, or cause the support to break due to difficulty in transport due to fusion and Also, the printing quality is remarkably deteriorated due to the resin residue or the like fused to the thermal head.

By incorporating an organic or inorganic filler and a lubricant into the protective layer, it is possible to considerably solve the problem of sticking caused by contact with a thermal head or the like. However, since the reversible thermosensitive recording medium proposed by the applicant can be used many times, when a filler and a lubricant are added to the protective layer to sufficiently solve the sticking problem, the thermal In order to replenish the filler and lubricant on the surface, which are continuously lost by being rubbed by the head, the filler and lubricant are constantly transferred from the inside of the protective layer to the surface, or even if the protective layer contains a large amount of filler and lubricant and disappears. You have to make sure there are no problems. In any case, a large amount of lubricant or filler must be contained in the protective layer, and addition of a large amount of filler or lubricant to the protective layer is accompanied by a decrease in transparency or thermal conductivity of the recording medium. This causes problems such as a decrease in color density due to a decrease in heating energy and inadequacy in a transparent recording medium. Furthermore, addition of a large amount of filler or lubricant to the protective layer causes a decrease in the strength of the protective layer, which is not preferable in terms of durability.

This sticking development also occurs in the case of thermal transfer recording and heat sensitive stencil printing, and in order to prevent this, a method of adding a heat fusion preventing agent such as silicone oil has been tried in addition to providing a heat resistant protective layer. ing. For example, it has been proposed to provide a layer in which silicone oil is added to ethyl cellulose resin in a thermal transfer recording medium (Japanese Patent Laid-Open No. 1-22).
21281). Further, a heat-sensitive transfer layer is provided on the upper surface of the film substrate, and oily phosphates are provided on the lower surface,
A thermal transfer recording material using this as a stick prevention layer has been proposed (JP-A-61-118291). However, even if such a sticking prevention method is effective for thermal transfer and the like in which heat is applied only once by the thermal head, the reversible heat-sensing method proposed by the present applicant is repeatedly used by applying heat many times. It does not show a sufficient sticking prevention effect on the recording medium.

[0007]

SUMMARY OF THE INVENTION According to the present invention, when heat is applied to a reversible thermosensitive recording medium by using a thermal head as a heat source, the sticking phenomenon is prevented from occurring without causing the above-mentioned inconvenience. The problem is that there is less noise and printing quality is good.
It is an object of the present invention to provide a reversible thermosensitive recording medium and a reversible thermosensitive recording method in which the life of a thermal head is also increased.

[0008]

The inventors of the present invention have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a recording layer containing a color former and a developer is provided, a color recording state is formed by heating and melting, and when the temperature is lower than the color recording temperature, an erased state in which recording disappears is formed. In a reversible thermosensitive recording medium,
A thermal head is used as a means for obtaining a color-developed state, and the thermal head or the recording medium immediately before heat is applied,
A reversible thermosensitive recording method is provided, which comprises applying a lubricant or a lubricant containing a filler.

The reversible thermosensitive recording medium used in the present invention instantly develops color upon heating, and the color development state thereof is stable even at room temperature, but the recording layer in the color development state is decolored by heating below the color development temperature, The decolored state is stable even at room temperature. The principle of coloring and erasing of the reversible thermosensitive recording medium used in the present invention, that is, the principle of image formation and image erasure will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density, the horizontal axis represents the temperature, and the solid line 1
Shows the image forming process by heating, and the broken line 3 shows the image erasing process by heating. A is the density in the completely erased state, B is the density in the saturated coloring state when heated to a temperature of T ₁ or higher, and C is T _{0 in the} saturated coloring state.
It is the density at the following temperatures, and D shows the density when the material is erased by heating at the temperature between T _{0 and} T ₁ . The reversible thermosensitive recording medium of the present invention is in a colorless state (A) at a temperature of T ₀ or lower.
It is in. To perform recording, heating with a thermal head or the like to a temperature of T ₁ or higher is performed, and color development (B) is performed to form a recorded image. Even if the recorded image is returned to the temperature of T ₀ or less according to the solid line 2, the state (C) is maintained as it is, and the recording memory property is not lost. Next, in order to erase the recorded image, the formed recorded image may be heated to a temperature between T _{0 and} T _{1, which} is lower than the coloring temperature, and the state becomes colorless (D). This state is maintained as it is even if the temperature is returned to T ₀ or lower (A). That is, the process of forming the recorded image reaches C by the path of the solid line ABC and the recording is held. During the process of erasing the recorded image, the erased state is maintained up to A by the path of the broken line CDA. The behavioral characteristics of formation and erasure of the recorded image are reversible and can be repeated many times.

FIG. 2 is an explanatory view showing an example of image formation and image erasure. S is a support and L is a reversible thermosensitive recording layer. The image forming steps (A) → (B) are achieved by recording and printing at a temperature of T ₁ or higher in FIG. 1 by an image forming heat source, for example, a thermal head H. Next, the image erasing step (B) → (A) is achieved by heating the image erasing heat source, for example, a heating roll R to a temperature between T _{0 and} T ₁ . In FIG. 2, P indicates a color image. The reversible thermosensitive recording medium of the present invention contains a color former and a developer as essential components. Then, the color development of the reversible thermosensitive recording medium of the present invention, a color former composition formed by the eutectic reaction of the developer and the color developer constituting the reversible thermosensitive recording layer by heating,
It is obtained by cooling to room temperature. Since this color-forming material composition has a decoloring temperature region on the lower temperature side than the melting temperature, it is generally preferable to perform rapid cooling in order to cool from the melt-colored state to room temperature while maintaining the color development. When gradually cooled, some color disappears when passing through the color-erasing temperature range, and the density often decreases.

It is considered that in the color former composition, the molecules of the color former and the developer interact with each other to open the lactone ring of the color former to develop a color. The composition in the melted state and the rapidly cooled state contains, in addition to the chromophore molecule, the developer molecule and the chromophore molecule which are not directly involved in the formation of the chromophore. In the reversible thermosensitive recording medium of the present invention, the color-forming material composition at room temperature is in a solidified state due to the cohesive force between these molecules. Further, although the aggregate structure of the color former composition shows some regularity, it may be very regular or not very regular. This depends on the combination and amount ratio of the color developer and the color developer or the cooling conditions. The formation of such an aggregate structure is basically due to the alkyl chain structure part of the developer molecule forming the color former and the excess alkyl chain structure of the developer molecule not forming the color former. It is presumed that the cohesive force acting between the parts mainly acts. The formation of such an aggregated structure is related to the decoloring phenomenon of the color former composition.

The color former composition can be decolored by heating its color development state to a specific temperature range.
In this decoloring process, the aggregate structure of the color-developing state changes, and finally the developer molecules are separated and crystallized from the color-forming composition to form crystals of the developer alone, resulting in a stable decolorized state. Is confirmed by X-ray. As described above, in the reversible thermosensitive recording medium of the present invention, it is clear that the alkyl chain portion of the color developer plays a large role in the formation of the color-developed state and the decoloring process thereof. This is a characteristic of the color former composition formed on the thermosensitive recording medium. Therefore, the decoloring temperature can be controlled by the length of the alkyl chain portion of the color developing agent, and the longer the chain length, the more often the coloring and decoloring temperatures shift to the high temperature side. This is because the aggregation and motility of the developer molecules change depending on the length of the portion.

The reversible thermochromic composition formed in the recording layer of the recording medium used in the present invention is basically a composition obtained by combining the color developer and the color developer having an alkyl chain structure. And there are preferred color formers for each developer. The combination of the color-developing agent and the color-developing agent used in the reversible thermochromic composition is a color-developing state composition obtained by heating both of them to a melting temperature or higher, and decoloring that occurs when the composition is heated to a temperature lower than the melting temperature. It is appropriately selected depending on the ease of decolorization (erasability) and the characteristics such as the color tone of the coloring state. Among these, the decoloring property can be judged by the presence or absence of an exothermic peak appearing in the temperature rising process in the differential thermal analysis (DTA) or the differential scanning calorimetry (DSC) of the color-developed composition obtained by the combination. This exothermic peak is
It corresponds to the decoloring phenomenon that characterizes the composition, and serves as a criterion for selecting a combination having a good decoloring property. In the reversible thermosensitive recording medium used in the present invention, the third substance may be present in the reversible thermosensitive recording layer, and the reversible decoloring behavior can be maintained even if, for example, a polymer compound is present. it can.

In the reversible thermosensitive recording medium used in the present invention, the color developing agent used in combination with the color developing agent basically has a structure showing a color developing ability capable of developing the color developing agent in the molecule, and a molecule. It is a compound that also has an alkyl chain structure part that controls the cohesive force between the compounds, and is an organic phosphoric acid compound, an aliphatic carboxylic acid compound, or a phenol compound having an aliphatic group having 12 or more carbon atoms, or an aliphatic compound having 10 to 18 carbon atoms. Metal salt of mercaptoacetic acid having a group or carbon number of 5-8
It is an alkyl ester of caffeic acid having an alkyl group of. The aliphatic group includes a linear or branched alkyl group and alkenyl group, and may have a substituent such as halogen, an alkoxy group and an ester group. The reversible thermochromic composition constituting the recording medium used in the present invention is basically composed of a combination of the color developer and the color developer. The color former is a colorless or light-colored dye precursor exhibiting an electron donating property, and is not particularly limited, and conventionally known triphenylmethanephthalide compounds, fluoran compounds, phenothiazine compounds, leukoauramine compounds, indolinofta. Lido compounds and the like are used. Specific examples of the color developer and the color developing agent used in the present invention described above are described in detail in Japanese Patent Application Nos. 3-355078, 4-1911643 and 4-207604.

In the reversible thermosensitive recording medium used in the present invention, the ratio of the color former to the developer in the reversible thermosensitive recording layer needs to be appropriately selected depending on the physical properties of the compound used. The range is generally in a molar ratio of 1 to 20 for the color developer and 1 to 20 for the color developer, and preferably 2 to 10. If the amount of the developer is more than the above range, or the amount of the developer is more than the above range, the density of the color-developed state becomes low, which is a practical problem. Further, even in the above preferable range, the decoloring property changes depending on the ratio of the color developing agent and the color developing agent, and when the amount of the color developing agent is relatively large, the decoloring start temperature becomes low, and when the amount of the color developing agent is relatively small, Decolorization becomes sharp with respect to temperature. Therefore, this ratio must be appropriately selected according to the application and purpose. The reversible thermochromic composition is basically composed of the color developer and the color developer, but for the purpose of improving various properties such as decoloring property and storability,
Additives and the like having an effect of controlling crystallization of the color developer can be contained. The reversible thermosensitive recording medium used in the present invention is one in which a recording layer containing the above-mentioned reversible thermochromic composition is provided on a support, and the basic constitution of the recording medium is the lowermost support. And a recording layer and a protective layer are sequentially laminated thereon. The support used here is paper, synthetic paper, a plastic film or a composite thereof, a glass plate, and the like, as long as it can hold the recording layer.

The recording layer may be in any form as long as the above-mentioned reversible thermochromic composition is present. Usually, the developer and the color former are sufficiently well dispersed in the binder resin to form the recording layer. And a reversible thermosensitive recording medium having a long life can be obtained by this method. The color-developing agent and the color-developing agent can be used as they are or by being encapsulated in microcapsules. Microencapsulation of the color developer and the color developer can be carried out by a known method such as a coacervation method, an interfacial polymerization method or an in situ polymerization method. The developer and the color former may be used alone or in combination of two or more. The recording layer may be formed by a known method in which a color former and a developer are uniformly dispersed or dissolved in water or an organic solvent together with a binder resin, and this is coated on a support and dried. The main role of the binder resin in the recording layer is to prevent the reversible thermochromic composition from aggregating due to repeated coloring and decoloring, and to keep the composition uniformly dispersed. Since the composition often agglomerates when heat is applied during color development, it is preferable to use a binder resin having high heat resistance. In the reversible thermosensitive recording medium used in the present invention, if necessary, for the purpose of improving coating properties or recording properties, various additives used in ordinary thermosensitive recording paper, such as a dispersant and a surfactant, A polymeric cationic conductive agent, a filler, a color image stabilizer, an antioxidant, a light stabilizer, a lubricant and the like can be added to the recording layer.

A protective layer is not essential for the reversible thermosensitive recording medium used in the present invention, but the protective layer prevents the surface from being deformed or discolored by heat and pressure when heat is applied. However, installation of a protective layer is extremely effective for many uses. In addition, the protective layer may have a role of improving chemical resistance, water resistance, abrasion resistance, head matching property, and the like. Therefore, it is preferable that the protective layer forming material has high heat resistance and high strength, and silicone rubber, silicone resin, polysiloxane graft polymer, ultraviolet curable resin, electron beam curable resin and the like are used. With the formation of such a protective layer with improved heat resistance, an organic solvent,
Resistance to contact with plasticizer, oil, sweat, water, etc. also increases,
It is possible to obtain a recording medium capable of repeating image formation and erasing without problems even in a bad environment. Further, by containing a light stabilizer in the protective layer, it is possible to obtain a recording medium in which the light resistance of the image and the background is remarkably improved,
Enables antistatic by adding a high molecular weight cationic conductive agent,
As a result, it is possible to prevent electric shock shock during development and handling when the recording medium is frictionally charged and stuck. Further, as described above, it is possible to considerably reduce the sticking development by adding an organic or inorganic filler and a lubricant to the protective layer, but to reduce the sticking to the extent that troubles can be sufficiently prevented. Is difficult for the above reasons.

The present invention addresses the above-mentioned problems caused in preventing sticking by adding a large amount of fillers and lubricants to the protective layer, and a clear and high-quality image can be obtained by a conventional thermal head, as well as repeated durability. The present invention provides a reversible thermosensitive recording method that has high properties and a low occurrence of sticking. Since the present invention applies a lubricant or a filler to the surface of the thermal head or the surface of the recording medium immediately before applying heat, it goes without saying that it is also effective for the recording medium having no protective layer. However, it is, of course, more preferable to use a recording medium provided with a protective layer, and further preferable results can be obtained by adding a filler or a lubricant to the protective layer within the range where the above-mentioned inconvenience does not occur. As with the recording layer formation method, the protective layer component may be formed by uniformly dispersing or dissolving the components of the protective layer in water or an organic solvent, and uniformly coating and drying this on the recording layer. The length is preferably about 0.5 to 10 μm.

The reversible thermosensitive recording medium used in the present invention may be provided with an undercoat layer. The undercoat layer is installed for the purpose of improving the heat insulation, improving the adhesion between the support and the recording layer, and improving the resistance of the support to the solvent when creating the recording layer.It is installed in consideration of the type of support. You can determine whether or not. One of the important roles of the undercoat layer is to improve the heat insulating property, and this is to make the applied heat energy useful for forming and erasing recording without waste.
By installing a heat insulating layer, coloring and decoloring can be performed sharply, and it is possible to support high-speed recording. The undercoat layer for the purpose of heat insulation may be formed by coating fine hollow particles made of an organic or inorganic material on a support, and specifically, a particle size of 10 to 50 μm formed of glass, ceramics, or plastic. It is sufficient that a small hollow body of a certain degree is well dispersed in a solvent together with a binder resin, and uniformly coated and dried on the support. When the support is a substance that easily absorbs liquid such as paper, it is sufficient to form an undercoat layer that is impermeable to liquid, and when a support soluble in a recording layer forming solvent is used. For the above, an undercoat layer insoluble in the solvent may be provided on the support. Instead of providing the heat insulating layer, a heat insulating support can be used to effectively utilize the applied heat energy.

In the present invention, as the lubricant to be added to the protective layer or applied to the surface of the thermal head or the recording medium, zinc stearate, stearic acid amide, palmitic acid amide, lauric acid amide, ethylenebisstearylamide, methylenebis Waxes such as stearylamide, methylolstearylamide, paraffin wax, polyethylene wax, and carnauba wax; higher alcohols; higher fatty acids; higher fatty acid esters;
Silicone oil etc. are mentioned. Of these, particularly preferable are silicone oils which are liquid and easy to use and have excellent ability to spread on the surface of the recording medium, such as dimethylpolysiloxane, methylphenylpolysiloxane, methylvinylpolysiloxane and fluoroalkylpolysiloxane. In addition to the above silicone oils, various modified silicone oils are preferably used. Specific examples of the modified silicone oil include alcohol modification, polyether modification, α-methylstyrene modification, olefin modification,
It is a modified silicone oil such as amine-modified, epoxy-modified, mercapto-modified, carboxy-modified, higher fatty acid-modified, amide-modified and carnauba-modified.

In the present invention, the filler which is mixed with a lubricant and added to the protective layer or used for coating is polyethylene particles, polystyrene particles, urea-formaldehyde resin particles, fluororesin particles, various plastic micro hollows as organic fillers. The body etc. are mentioned. Further, as the inorganic filler, aluminum hydroxide, calcium carbonate, zinc oxide, titanium oxide, barium sulfate, silica gel, colloidal silica, alumina sol, activated clay, talc, clay, kaolin, diatomaceous earth, zirconium compound, glass particles, molybdenum disulfide. , Various inorganic micro hollow bodies and the like. These fillers have a particle size of 0.01 to 10 μm.
m, preferably 0.1 to 1.0 μm is used,
The amount of the filler added to the coating lubricant is 0.05 to 200% by weight, preferably 5 to 120% by weight. That is,
A larger amount of filler than the lubricant may be included. This composition ratio is determined by the recording medium used and the thermal head. In short, the composition ratio should be the optimum composition to prevent sticking and to prevent dust deposits on the thermal head. It may be used in any condition. The method of adding the filler to the lubricant is to add the filler to the lubricant melted at room temperature or by heating and stir it well to uniformly disperse it.If the lubricant is a solid, use it by cooling and solidifying. can do. When the lubricant is liquid at room temperature, it can be used as a liquid.

In the present invention, heat is applied by the thermal head to form an image, but the lubricant or the lubricant containing a filler is applied to the surface of the thermal head or the surface of the recording medium immediately before the application of heat to prevent sticking. It is characterized by that. Therefore, the coating amount of the lubricant on the surface of the thermal head is 5 × 10 ⁻³ to 1 × 10 ⁻⁴ g / cm for the solid lubricant.
² , preferably 1 × 10 ⁻³ to 1 × 10 ⁻⁴ g / cm ² , and 5 × 10 ⁻³ to 1 × 10 ⁻⁵ g / cm ^{2 for} a liquid lubricant, preferably 5 × 10 ⁻⁴ to 1 × 10. It should be ^-5 g / cm ² . The amount of lubricant used, including the filler weight when the filler is included,
When using a solid lubricant, 5 × 10 ⁻⁴ to 1 × 10 ⁻⁵ g / cm ² ,
It is preferably 1 × 10 ⁻⁴ to 1 × 10 ⁻⁵ g / cm ² ,
When using a liquid lubricant, 5 × 10 ⁻⁴ to 1 × 10 ⁻⁶ g / cm ² ,
Preferably, it should be 5 × 10 ⁻⁵ to 1 × 10 ⁻⁵ g / cm ² . The appropriate amount of lubricant applied to the surface of the recording medium is 5 to 0.1 g / m ² in the case of a solid lubricant, preferably 1 to 0.2 g / m ² .
m ² and for liquid lubricants 5 to 0.01 g / m ² , preferably 0.5 to 0.1 g / m ² . When a filler is included, the weight of the filler is 5 to 0.1 g / m ² , including the weight of the solid lubricant, and preferably 1 to ² when the liquid lubricant is used.
It may be set to 0.2 g / m ² . If the coating amount of the lubricant (hereinafter, including the lubricant containing the filler is referred to as a lubricant) is insufficient, the purpose is not achieved, and if the coating amount is excessive, the image density becomes unstable and dust and the like adhere to the applied lubricant. There is also the problem of damaging the thermal head. In the present invention, the lubricant may be applied to both the surface of the thermal head and the surface of the recording medium, but the application of the lubricant to both does not significantly increase the effect except in special cases. The image erasing in the present invention may be carried out by a method generally used for a reversible thermosensitive recording medium, including a heating roll, a sheet heating element, a constant temperature bath, warm air,
There is no particular limitation as long as a temperature condition for erasing such as a thermal head is given. It is also possible to form a recorded image with another thermal head set to the recording temperature while erasing the recorded image with the thermal head set to the erasing temperature.

Next, the method of applying the lubricant will be described with reference to the drawings. FIG. 3 shows a coating method using a rotatable thermal head and a lubricant coating roll. The thermal head 1 is moved by a rotating shaft 3 from a recording position to a position where it contacts the lubricant coating roll 4. The lubricant coating roll 4 may be fixed or movable, and when it is movable, it is moved to a position where it contacts the thermal head, and in any case, it contacts the recording medium of the thermal head. A shape capable of contacting all the surfaces and supplying the lubricant to all the contact surfaces is required. 3, (a) shows the time when heat is applied to the recording medium 7, and (b) shows the time when the lubricant is applied to the thermal head. Further, in FIG. 3, 2 is a platen roll. The lubricant application is performed by rotating the lubricant application roll 4 in contact with the thermal head 1 for a certain period of time, and by this operation, an appropriate amount of the lubricant attached to the surface of the lubricant application roll 4 is supplied to the surface of the thermal head 1. To be done. A liquid lubricant 5 in which a solid lubricant or a sponge is impregnated is pressed against the lubricant application roll 4 by a spring 6, and is supplied to the application roll 4 little by little.

FIG. 4 shows the case of using the non-rotatable fixed type thermal head 1. In this case, the platen roll 2 is used.
Is moved from the position facing the thermal head, and the coating roll 4 is installed at the position occupied by the platen roll 2 when heat is applied to the recording medium 7. Here, the lubricant is applied to the surface of the thermal head 1 in the same manner as in FIG. To supply. Figure 4 (a)
Shows the time when heat is applied to the recording medium 7, and (b) shows the time when the lubricant is supplied to the thermal head. The method of supplying the lubricant to the coating roll 4 is the same as in the case of FIG. FIG. 5 shows a system in which a lubricant sheet 8 obtained by applying a lubricant to a sheet similar to a recording medium is used, and the lubricant is applied to the thermal head 1 by periodically passing through the sheet. In FIG. 5, (a) is when heat is applied to the recording medium and (b) is when lubricant is supplied to the thermal head. FIG. 6 shows a system in which a solid or liquid lubricant is applied to the recording medium, and the lubricant supply system is exactly the same as in FIGS. In this case, the coating roll 4 has a length equivalent to the width direction of the recording medium 7, and is designed to apply a substantially equal amount of lubricant in the width direction of the recording medium. However, it is desirable to minimize the amount of lubricant applied to the recording medium.
The coating may be applied intermittently in the advancing direction of the recording medium, and such a sloppy coating method is one method for minimum application.

FIG. 7 shows a system different from that of FIG. 6 in which a liquid lubricant is applied to a recording medium. The feature of this case is that the liquid lubricant in the lubricant tank 9 is supplied to the coating roll 4 through the porous impregnated sheet 10. That is the point. In this method, the impregnation sheet 1
0 serves as a liquid lubricant transport pipe, one end of which is immersed in the liquid lubricant in the lubricant tank 9, and the other end of which is in contact with the coating roll 4 at a constant pressure. Further, in this system, in order to make the amount of lubricant supplied to the recording medium constant, a rotatable metal roll is provided between the coating roll 4 and the impregnation sheet 10, and when the surface of the coating roll 4 lacks the lubricant, Since the friction between the metal roll and the coating roll is large, the metal roll rotates with the rotation of the coating roll, so that the lubricant is supplied to the coating roll. Roll does not rotate, therefore coating roll 4
It is also possible to stop the supply of lubricant to the.
Further, in this method, the coating roll 4 is rotatable, and when the lubricant is insufficient, the lubricant is supplied because the coating roll rotates due to the frictional force between the coating roll and the recording medium. It is also possible to adopt a system in which the rotation of the coating roll is stopped due to insufficient frictional force between the recording medium and the coating roll, so that the lubricant supply is stopped.
The difference between the method of FIG. 6 and the method of FIG. 7 is only the lubricant supply method, and in other respects the method of FIG. 6 and the method of FIG. 7 are exactly the same. Further, the lubricant supply system of FIG. 7 can be applied to the case of applying the lubricant to the thermal head.

FIG. 8 shows an example of a recording method to which the reversible thermosensitive recording method of the present invention is applied, which is preferably applied to a display device or the like using the endless belt-shaped recording medium 7. FIG. 8 shows a method of applying a lubricant to the recording medium, but the method is not limited to this method when the endless belt-shaped recording medium is used, and the lubricant is applied to the thermal head by using the endless belt-shaped recording medium. It is needless to say that a method of supplying the liquid lubricant to the lubricant coating roll 4 can be used, or a method of supplying the liquid lubricant to the lubricant coating roll 4 as shown in FIG. In FIG. 8, 11 is a decoloring heating plate, 12 is a decoloring heating roll, and the method of FIG. 8 is an overwrite type heat applying and erasing device. As described in detail above, there are many application examples of the lubricant coating method to the thermal head and the recording medium, and the method of the present invention as shown in FIG. 8, but the present invention is not limited to these, and the thermal head surface and Any lubricant application method may be adopted as long as it is a method that improves the lubricity when the surface of the recording medium comes into contact with it and has no adverse side effect on the thermal head or the recording medium.

[0027]

EXAMPLES Next, the present invention will be explained more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, this Example and Comparative Example,
Lubricants of various compositions were applied to the surface of the thermal head or the recording medium, and the effect was examined. The apparatus used for this purpose and the evaluation method are as follows. (I) Device for applying to the surface of the thermal head (Ia) Lubricant applying device Using the applying device of the system shown in FIG.
m, 11 mm diameter SUS-304 stainless steel roll surface coated with 4 mm thick urethane rubber was used as a lubricant-coated roll, and the lubricant had a length of 250 mm and a width of 10 m.
A solid lubricant having a rectangular cross-sectional area of m and a thickness of 10 to 15 mm was used. This lubricant is pressed against a lubricant applying roll with a load of about 300 g, and at the time of applying the lubricant shown in FIG.
It was pressed with a load of 0 g. These pressing pressures were appropriately changed depending on the hardness of the lubricant, and were adjusted so that an appropriate amount of lubricant adhered to the surface of the thermal head. The number of rotations of the lubricant coating roll is 1 for each lubricant coating on the thermal head surface.
Although the number of rotations is set appropriately between 5 and 5, this number of rotations is adjusted to an appropriate value by the amount of lubricant attached to the surface of the thermal head. (Ib) Thermal head applied energy: 0.418
Joule / dot (Ic) platen roll A roll having a surface of a SUS-304 stainless steel roll having the same shape as the lubricant application device was coated with 4 mm thick silicon rubber was used, and the platen roll pressure was 4 kg / 250 mm length. (I-d) Decoloring roll A roll having a length of 250 mm and a diameter of 30 mm, which is hollow and made of aluminum having a thickness of 5 mm, is coated with a silicone rubber having a thickness of 0.1 mm. The roll surface temperature was controlled at 70 ° C. by blinking the halogen lamp. The recording medium on which printing color was developed was put between two such decoloring rolls, and the rolls were passed through the rolls for 1 second to decolor.

(II) Apparatus for coating the surface of the recording medium (II-a) Lubricant applying apparatus Liquid lubricant is supplied to the lubricant applying roll by the lubricant supplying method shown in FIG. 7, and the endless belt shape shown in FIG. A liquid lubricant was applied to the recording medium. The lubricant coating roll is the same as above. Further, the moving speed of the endless belt is 30 mm / sec, and the rotation speed of the lubricant application roll and the contact pressure between the roll and the endless belt-shaped recording medium are 1.0 g / m ² of the lubricant application amount on the surface of the recording medium. It was adjusted to the extent. (II-b) Thermal head surface shown in (I) except that an endless belt-shaped recording medium such as a thermal head, a platen roll, and a color erasing roll is used and a liquid lubricant is applied to the surface of the recording medium by the method of FIG. An experiment was conducted using the same standard product as when the lubricant was applied. That is, as the erasing / coloring member such as the thermal head, the platen roll and the erasing roll, the same products as in the case of the above (I) were used.

(III) Evaluation method By the method described in (I) or (II), printing with a thermal head and erasing with a erasing roll are repeated on a reversible thermosensitive recording medium to apply heat depending on the sticking property. It was evaluated according to the magnitude of the noise at the time. Further, the thermal head after the heat application and the heat erasing were repeated 50 times was visually observed and evaluated for the amount of thermal head residue attached. Further, the color image on the recording medium obtained by the 50th application of heat was visually observed to examine the degree of scratches on the surface of the recording medium and the presence or absence of white streaks appearing in the image. The white streak appearing in the image shows the image missing due to the adhesion of the head dust. The results of these evaluations are summarized in Tables 4 to 7. In these tables, ⊚ indicates that very favorable results were obtained, and ∘ indicates that favorable results were obtained.
Slightly dissatisfied results were obtained, and x indicates unfavorable results.

The recording media used in the experiments of Examples and Comparative Examples are shown below. [Recording Layer] The following composition was pulverized and dispersed by a ball mill to an average particle size of hexadecylphosphonic acid of 1 to 4 μm to prepare a coating solution, which was then coated on a polyester film having a thickness of 100 μm with a wire bar and dried. , Film thickness after drying 6
A reversible thermosensitive recording medium having a recording layer of μm was prepared. 2- (o-chloroanilino) -6-dibutylamino 14 parts by weight Fluoran hexadecylphosphonic acid 42 parts by weight Vinyl chloride monovinyl acetate copolymer (42 parts by weight manufactured by Union Carbide VYHH) Methyl ethyl ketone 210 parts by weight Toluene 210 parts by weight [ Protective Layer] The following composition was sufficiently dispersed by a ball mill to prepare a protective layer-forming coating liquid, which was applied onto the recording layer of the recording medium with a wire bar so that the film thickness after drying was 4 μm. After the solvent was evaporated and dried, UV rays were irradiated to cure the solvent, and a protective layer was provided on the recording medium. 75 wt% of urethane acrylate UV curable resin 100 parts by weight Butyl acetate solution (Dainippon Ink and Chemicals; Unidick C7-157) Aluminum hydroxide (particle size 0.5 μm; Showa Denko 5 parts by weight Heidilite H34M) Silicone oil (Shin-Etsu Silicone: KF96; 1 part by weight Viscosity: 100 centipoise) Butyl acetate 50 parts by weight

Among the lubricants used in the examples, solid ones are shown in Table 1, and liquid ones are shown in Table 2. Table 3 shows the fillers used in the examples.

[Table 1]

[0032]

[Table 2]

[Table 3] ━┛

Examples 1 to 12 and Comparative Example 1 5 × 1 solid lubricant without filler was applied to the surface of the thermal head.
The experiments of Examples 1 to 12 were carried out by a method of applying about 0 ⁻⁴ g / cm ^2, and compared with the experiment (Comparative Example 1) in which the lubricant was not applied to the thermal head, the results of Table 4 were obtained.

[Table 4]

Examples 13 to 18 Experiments of Examples 13 to 18 were carried out by applying a liquid lubricant containing no filler of about 1.0 g / m ^{2 to} the surface of the recording medium, and the results shown in Table 5 were obtained.

[Table 5]

Examples 19 to 24 A solid lubricant containing a filler was applied to the surface of the thermal head in an amount of 6 × 1.
The experiments of Examples 19 to 24 were conducted by a method of applying about 0 ⁻⁴ g / cm ² , and the results shown in Table 6 were obtained.

[Table 6]

Examples 25 to 29 A liquid lubricant containing a filler was applied to the surface of a recording medium at 1.0 g / m ^2.
The experiments of Examples 25 to 29 were carried out by the method of applying the coating to some extent, and the results shown in Table 7 were obtained.

[Table 7]

[0037]

According to the reversible thermosensitive recording method of the present invention,
Immediately before applying heat to the reversible heat-sensitive recording medium to form a color image, a lubricant containing a lubricant or a filler is applied to the surface of the recording medium or the surface of the thermal head to be used to prevent sticking. It is possible to prevent insufficient density of a color image due to a decrease in thermal conductivity that occurs when a lubricant or a filler is added to the toner, and to prevent sticking sufficiently without causing insufficient transparency when preparing a transparent recording medium. Therefore, noise during recording is significantly reduced, and images with stable image density and high resolution and good print quality can be continuously obtained for a long period of time. Further, the frequency of cleaning the thermal head is greatly reduced, and the life of the thermal head and the recording medium is increased.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between color density and temperature of a reversible thermosensitive recording medium of the present invention, and is an explanatory view of the principle of color development and color erasing. The solid line (A → B → C) indicates the image forming process, and the broken line (C
→ D → A) shows an image erasing process.

FIG. 2 is an explanatory diagram of an image forming process and an image erasing process.

3A and 3B are explanatory views showing an example of a lubricant applying method to a thermal head, wherein FIG. 3A shows a time when heat is applied to a recording medium by the thermal head, and FIG. 3B shows a time when lubricant is applied to the thermal head. ing.

4A and 4B are explanatory views showing another method of applying a lubricant to a thermal head, wherein FIG. 4A shows the time when heat is applied to the recording medium by the thermal head, and FIG. 4B shows the time when the lubricant is applied to the thermal head. ing.

5A and 5B are explanatory views showing another method of applying a lubricant to a thermal head, wherein FIG. 5A is a time when heat is applied to a recording medium by the thermal head, and FIG. 5B is a lubricant application to the thermal head. Showing the time.

FIG. 6 is an explanatory diagram showing an example of a method of applying a lubricant to a recording medium.

FIG. 7 is an explanatory diagram showing another example of applying a liquid lubricant to a recording medium.

FIG. 8 is an explanatory diagram in the case of applying a lubricant to a recording medium, applying heat with a thermal head, and erasing an image at the same time.

[Explanation of symbols]

S Support 1 Thermal head L Reversible thermosensitive recording layer 2 Platen roll P Color development image 3 Rotation axis H Thermal head 4 Lubricant application roll R Heating roll 5 Lubricant 6 Spring 7 Recording medium 8 Lubricant sheet 9 Lubricant tank 10 Impregnation sheet 11 Decoloring Heating plate 12 Decolorizing heating roll

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B41M 5/36 9305-2C B41J 3/20 109 J 8305-2H B41M 5/26 102

Claims (2)

[Claims] 1. A color-erasing state in which a recording layer containing an electron-donating color-forming compound and an electron-accepting compound is provided, and a color-recorded state is formed by heating and melting, and the recording disappears when heated below the color-recording temperature. In a reversible thermosensitive recording medium for forming a reversible thermosensitive recording medium, a thermal head is used as a means for obtaining a color recording state, and a lubricant or a lubricant containing a filler is applied to the thermal head immediately before heat is applied. Method. 2. A color-erasing state in which a recording layer containing an electron-donating color-forming compound and an electron-accepting compound is provided, and a color-recorded state is formed by heating and melting, and when the temperature is lower than the color-recording temperature, the recording disappears. In the reversible thermosensitive recording medium for forming a reversible thermosensitive recording medium, a thermal head is used as a means for obtaining a color recording state, and a lubricant or a lubricant containing a filler is applied to the recording medium immediately before heat is applied. Method.