JP4361848B2 - Reversible thermosensitive recording medium and image processing method - Google Patents

Description

  The present invention relates to a reversible thermosensitive recording medium and an image processing method.

  When a reversible thermosensitive recording medium is irradiated with light for a long period of time, a brownish color is produced, and a tendency that it does not disappear. This is considered to be because the molecular structure of the leuco dye is changed by light irradiation, and a colored product that is not reversible with respect to heat is generated. Therefore, in a reversible thermosensitive recording medium using a leuco dye, it is common to use an ultraviolet absorber so that ultraviolet rays do not reach the leuco dye directly.

For example, Patent Document 1 discloses a method in which an intermediate layer is provided between a recording layer and a protective layer and an ultraviolet absorber is added therein. However, the ultraviolet absorber used here is a low molecular weight ultraviolet absorber having a molecular weight in the range of about 200 to 400, and the main component of the ultraviolet absorber is lowered with time or by repeated erasing and printing. To the recording layer, causing problems such as changing the coloring / decoloring characteristics of the recording layer. In addition, the low molecular weight UV absorber may be deposited on the surface of the protective layer, causing a serious problem such as reducing the UV absorbing effect or adhering to the thermal head to disturb the printed image. In addition, the addition of an ultraviolet absorber reduces the film strength of the protective layer, and causes serious problems in practice such as occurrence of dents due to repeated erasing and printing.

  Patent Document 2 discloses a method of adding microcapsules encapsulating an ultraviolet absorbent that is liquid at room temperature into a protective layer. This is performed for the purpose of preventing bleeding out of the ultraviolet absorber. However, in this case, since the liquid phase is mixed in the protective layer, the film strength is lowered, and impact is generated by repeated erasing and printing. Also, if the microcapsules are damaged, the UV absorber diffuses inside or on the surface of the reversible thermosensitive recording medium, causing problems such as deterioration of color development / decoloration characteristics and contamination of card users and thermal heads. Will be generated. In addition, regarding the alcohol resistance in the solvent resistance test, if the alcohol is immersed for a long time, the image is discolored, resulting in a large practical problem.

In Patent Document 3, Patent Document 4, and the like, a method of adding a polymer having an ultraviolet absorbing structure to the protective layer is shown. However, these polymers are not cross-linked and have high heat resistance and durability required for the surface of the protective layer. Compared with cross-linked resins such as UV curable resins and thermosetting resins, these polymers are not in a cross-linked state. Is not enough. Even if the polymer is hardened with a resin in a cross-linked state, the layer becomes a sea-island structure and begins to collapse from the part of the polymer that is not cross-linked after many uses, and struck on the surface of the recording medium. End up. In this case as well, with respect to alcohol resistance in the solvent resistance test, if the alcohol is immersed for a long time, the image is discolored, causing a serious problem in practical use.

Patent Document 5 discloses a method of adding a specific inorganic pigment having an ultraviolet shielding effect to the intermediate layer or the protective layer. Inorganic pigments shield ultraviolet rays by their own ultraviolet absorbing ability and ultraviolet scattering ability due to controlled particle size. However, in order to exhibit an ultraviolet ray shielding effect with an inorganic pigment, it is necessary to add a large amount of very fine particles, and when the blending amount is increased, transparency is impaired. This is because if the transparency is impaired, the background is colored, the contrast is deteriorated, and the visibility is inferior. Further, the surface activity is remarkably increased by the microparticulation, which causes a catalytic action and leads to alteration of other compounding components. In addition, secondary aggregation is likely to occur, resulting in extremely poor dispersibility and pigment unevenness in the coating film, so that the surface of the recording medium is struck from a portion with little pigment after many uses. Had problems such as. In addition, with respect to alcohol resistance in the solvent resistance test, when the alcohol is immersed for a long time, the image is discolored, and it is very difficult to improve, which causes a large practical problem.

  On the other hand, regarding improvement of repeated durability, Patent Document 6 proposes improvement of repeated durability by adding particles having an average particle size of 1.1 times or more of the film thickness to the reversible thermosensitive recording layer, Patent Document 7 proposes an improvement in which the head matching property is improved and the decoloring property is maintained by providing a protective layer having a specific glossiness and surface roughness. Moreover, in patent document 8, durability is improved by including the pigment surface-treated with the silane coupling agent, the titanate coupling agent, or the aluminum coupling agent. However, even if these recording layers and protective layers are used, damage due to repeated printing and erasure increases, resulting in unerased residue, so that the number of repeated use is practically limited to a small number of times. have. Moreover, it is very difficult to improve the alcohol resistance in the solvent resistance test, which causes a large problem in practical use.

Further, Patent Document 9 proposes improvement of repeated durability, print density, and contrast by using a scaly filler in the recording layer or the under layer. However, in this case, the recording layer is penetrated by a protective layer. Therefore, it is difficult to prevent deterioration of the image in the solvent resistance test, which causes a serious problem in practical use.

  From the above, the present situation is that a reversible thermosensitive recording medium that sufficiently satisfies the qualities of repeated durability, light resistance and alcohol resistance cannot be provided.

JP 62-48585 JP JP 7-68937 JP JP 8-224960 JP JP 9-207437 JP JP 10-100541 JP JP 6-340171 JP JP 8-156410 A
JP 10-264521 A JP 5 193258 A

  An object of the present invention is to provide a reversible thermosensitive recording medium having an effect excellent in durability, light resistance and alcohol resistance by repeated printing, and an image processing method using the reversible thermosensitive recording medium.

  As a means for solving one of the above-mentioned problems, a reversible thermosensitive recording medium having a protective layer, wherein the protective layer includes a scale-like filler containing at least silica as a main component. Can be provided. Thereby, a reversible thermosensitive recording medium having effects excellent in erasability, durability, light resistance and alcohol resistance by repeated printing can be provided. In addition, in this specification and a claim, having silica as a main component means that content of the silica in a scale-like filler exceeds 50 weight%.

  The present invention can further use a scale-like filler in which the ratio of the maximum length of the scale plate to the thickness of the scale plate is 10 or more. Thereby, a favorable color tone can be obtained.

The present invention can further use a scaly filler having a scale plate thickness of 0.01 μm or more and 0.5 μm or less. Thereby, it is possible to provide a reversible thermosensitive recording medium that is more excellent in alcohol resistance and less prone to image defects.
In the present invention, a scaly filler having a total surface area per unit weight of 20 m ² / g or more and 80 m ² / g or less can be used. Thereby, it is possible to provide a reversible thermosensitive recording medium that is more excellent in alcohol resistance and less prone to image defects.

  The present invention can further use a scaly filler having an average particle size of 4.0 μm or more and 6.0 μm or less. Thereby, it is possible to provide a reversible thermosensitive recording medium which is excellent in alcohol resistance and hardly causes image defects.

  The present invention can further use a protective layer containing an ultraviolet curable resin and / or a thermosetting resin. Thereby, a reversible thermosensitive recording medium having more excellent durability can be provided.

  The present invention can further use a protective layer containing a thermosetting resin crosslinked with isocyanate. Thereby, a reversible thermosensitive recording medium having more excellent durability can be provided.

  The present invention can further use a reversible thermosensitive recording medium having a surface dynamic friction coefficient of 0.3 or less. Thereby, image degradation due to mechanical damage can be eliminated.

  The present invention can further use a protective layer having an ultraviolet absorber.

  The present invention can further use a reversible thermosensitive recording medium having a surface roughness of 0.2 μm or less. Thereby, a favorable glossiness can be obtained.

  The present invention can further use a support obtained by bonding two or more types of sheets.

  The present invention can further use a reversible thermosensitive recording medium having visible information irreversible with respect to heat formed on the surface.

  The present invention can further use a reversible thermosensitive recording medium having a printable portion.

  The present invention can further provide a reversible thermosensitive recording medium provided with an adhesive layer or a pressure-sensitive adhesive layer.

  The present invention can further provide a reversible thermosensitive recording medium having an information storage unit.

  The present invention can further provide an image processing method for forming or erasing an image by heating the reversible thermosensitive recording medium according to any one of claims 1 to 13.

  According to the present invention, it is possible to provide a reversible thermosensitive recording medium having effects excellent in durability, light resistance and alcohol resistance by repeated printing, and an image processing method using the reversible thermosensitive recording medium.

  The present invention is a reversible thermosensitive recording medium having a protective layer, wherein the protective layer contains at least a scale-like filler made of silica. Thereby, the erasure residue by repeated printing and the durability and light resistance of the printed part are remarkably improved, and the alcohol resistance in the solvent resistance test is also excellent in image retention.

  The scaly filler has very thin scaly primary particles having a nano-size thickness. Usually, it has a peculiar structure like a secondary particle body having a laminated structure in which a plurality of scaly primary particles overlap each other. Unlike the amorphous and spherical fillers, the scale-like fillers are arranged in parallel to the layer. For example, when a solvent resistance test is performed, the permeation path into the recording layer becomes longer, which is effective for the solvent resistance test. Can be given.

  In addition, when a thermal recording label provided with a protective layer whose surface is roughened by a filler is thermocompression bonded onto a substrate sheet such as a card, the surface gloss is caused by the filler on the surface of the protective layer being pushed into the protective layer or the lower layer by thermocompression bonding. As a result, the effect of the filler is lost and the durability is repeatedly reduced, or when printing and erasing are repeated in a state where the surface gloss is further increased, the gloss of the printed and erased portion is reduced, There may be a problem that the difference in glossiness between the non-printed and non-erased parts is recognized as gloss unevenness, but the above-mentioned problem is also caused when the protective layer containing the scale-like filler of the present invention is used. can be solved. It is preferable that the surface roughness Ra of the reversible thermosensitive recording medium at this time is 0.20 μm or less because further glossiness can be obtained.

  About the scale-like filler which consists of inorganic pigments, what consists of silica is the most preferable. This is considered to be because when the scaly filler is made of silica, there are many silanol groups (—SiOH) at the terminals, and the involvement of the silanol groups improves the adhesion between the scales. . That is, by combining with a scaly shape and silica having a silanol group (-SiOH) at the end, a stronger adhesion than other inorganic pigments can be obtained, and the effect prevents the immersion of alcohol by a solvent resistance test with a protective layer. This is thought to be due to the effect of preventing penetration into the recording layer. Here, the solvent resistance test is stipulated in JIS X 6311 regarding cards, and specifically includes 6.3.11 chemical immersion resistance. Among them, in the alcohol test, it is very important to develop a protective layer that is not affected by alcohol resistance in use. The soaked alcohol easily penetrates into the protective layer due to the osmotic pressure, and has the function of easily separating the bond between the leuco dye and the developer, so that there is a problem that the image is decolored. Because.

  The ratio of the maximum length of the scale plate to the thickness of the scale plate of the scale-like filler is preferably 10 or more. This is because the alcohol resistance in the solvent resistance test is excellent, and when the ratio is less than 10, the thickness is increased, the transparency is lost, and it is difficult to obtain a good color tone.

  Further, the thickness of the silica scale plate used in the present invention is preferably 0.01 μm or more and 0.5 μm or less. When the thickness of the silica scale plate is smaller than 0.01 μm, the interval is formed and the solvent easily penetrates, so that the alcohol resistance is weakened and the image is easily erased. When the thickness is larger than 0.5 μm, the image is printed. This is because defects are likely to occur.

The total surface area per unit weight of the scaly silica is preferably 20 m ² / g or more and 80 m ² / g or less. If the total surface area per unit weight is less than 20 m ² / g, the scale-like fillers are spaced, and the solvent easily penetrates, so that the alcohol resistance is weakened and image decoloration easily occurs. This is because if it is larger than 80 m ² / g, image defects are likely to occur during printing.

  It is preferable that the average particle diameter of the flaky filler is 4.0 μm or more and 6.0 μm or less. If it is smaller than 4.0 μm, image defects are liable to occur during printing, and if the average particle diameter is larger than 6.0 μm, the interval between the scaly fillers can be increased, and the solvent can easily permeate. This is because image erasure is likely to occur. In the present specification and claims, the average particle diameter of the scale-like filler is a value obtained by number-average of the maximum lengths of the plurality of scale-like fillers.

  The ratio of the resin and the flaky filler varies in an appropriate range depending on the combination of the compounds to be used, but is generally preferably 0.1% by weight or more and 200% by weight or less, more preferably 5% by weight or more and 150% by weight with respect to the resin. The following is preferable, and more preferably 10 wt% or more and 100 wt% or less. If the amount is less than 0.1% by weight, no effect can be obtained in reducing the image due to alcohol resistance. If the amount exceeds 200% by weight, the color density is lowered, which causes a problem.

  The protective layer preferably contains an ultraviolet curable resin and / or a thermosetting resin. This is because the cost can be reduced by using these resins.

  In order to improve the function of the protective layer resin, a plurality of monomers and oligomers can be mixed. UV curable resins include urethane acrylate, epoxy acrylate, polyester acrylate, polyether acrylate, vinyl, unsaturated polyester oligomers, various monofunctional and polyfunctional acrylates, methacrylates, vinyl esters, ethylene derivatives. And monomers such as allyl compounds. Particularly preferred are tetra- or higher functional polymerizable monomers and oligomers. Examples of multifunctional monomers and oligomers include trimethylolpropane triacrylate, pentaerythritol triacrylate, glycerin propyloxy addition triacrylate, trisacryloyloxyethyl phosphate, pentaerythritol tetraacrylate, trimethylolpropane propylene oxide 3 mol adduct Triacrylate, glyceryl propoxytriacrylate, dipentaerythritol polyacrylate, polyacrylate of dipentaerythritol caprolactone adduct, propionic acid / dipentaerythritol triacrylate, hydroxypivalaldehyde-modified dimethylolpropyne triacrylate, propionic acid・ Dipentaerythritol tetraacrylate, ditrimethylo Propane tetraacrylate, pentaacrylate of dipentaerythritol propionate, trimethylolpropane triacrylate added urethane prepolymer, dipentaerythritol hexaacrylate (DPHA), .epsilon.-caprolactone adducts of DPHA and the like

  In the case of curing using ultraviolet rays, a photopolymerization initiator and a photopolymerization accelerator can be used. Photopolymerization initiators can be broadly classified into radical reaction types and ion reaction types, and radical reaction types are further divided into photocleavage types and hydrogen abstraction types. Examples of photopolymerization initiators include isobutyl benzoin ether, isopropyl benzoin ether, benzoin ethyl ether benzoin methyl ether, 1-phenyl-1,2-propanedione-2- (o-ethoxycycarbonyl) oxime, 2,2- Dimethoxy-2-phenylacetophenone benzyl, hydroxycyclohexyl phenyl ketone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzophenone, chlorothioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, 2-methyl Examples thereof include thioxanthone and chlorine-substituted benzophenone, and are used alone or as a mixture of two or more thereof, but are not limited thereto. Further, as the photopolymerization accelerator, those having an effect of improving the curing rate with respect to hydrogen abstraction type photopolymerization initiators such as benzophenone series and thioxanthone series are preferable. For example, aromatic tertiary amines and fats are used. There are those based on the group amines. Specific examples include p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, and the like. These photopolymerization accelerators are used alone or in combination of two or more. The addition amount of these photopolymerization initiator and photopolymerization accelerator is preferably 0.1% by weight or more and 20% by weight or less, more preferably 1% by weight or more and 10% by weight or less, based on the total weight of the resin component of the protective layer. It is.

  Examples of thermosetting resins include phenoxy resins, polyvinyl butyral resins, cellulose acetate propionate, cellulose acetate butyrate, acrylic polyols, polyester polyols, polyurethane polyols, and the like having a group that reacts with a crosslinking agent such as a hydroxyl group or a carboxyl group. Alternatively, a resin obtained by copolymerizing a monomer having a hydroxyl group or a carboxyl group and another monomer can be used. Among them, acrylic polyol resin, polyester polyol resin, and polyurethane polyol resin are preferable. When the hydroxyl value is 70 (KOHmg / g) or more, durability, coating film surface hardness, and crack resistance can be improved. Especially preferably, it is 90 (KOHmg / g) or more. The magnitude of the hydroxyl value affects the crosslink density, and therefore affects the chemical resistance and physical properties of the coating film. Acrylic polyol resins have different characteristics depending on the structure, and hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA) as hydroxyl monomers. , 2-hydroxybutyl monoacrylate (2-HBA), 1,4-hydroxybutyl monoacrylate (1-HBA), etc. are used. 2-hydroxyethyl methacrylate is preferably used because of its good properties and durability.

  Examples of the thermal crosslinking crosslinking agent include isocyanates, amino resins, phenol resins, amines, and epoxy compounds. Of these, isocyanates are preferable, and polyisocyanate compounds having a plurality of isocyanate groups are particularly preferable. Specific examples include hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), xylylene diisocyanate (XDI), and trimethylols thereof. Examples thereof include adduct types such as propane, burette types, isocyanurate types, and blocked isocyanates. The addition amount of the crosslinking agent to the resin is preferably such that the ratio of the functional group of the crosslinking agent to the number of active groups contained in the resin is 0.01 or more and 2.00 or less, and if 0.01 or less, the heat strength is insufficient. In addition, addition of 2.00 or more adversely affects the color developing / decoloring characteristics. Furthermore, you may use the catalyst used for this kind of reaction as a crosslinking accelerator. Examples of the crosslinking accelerator include tertiary amines such as 1,4-diazabicyclo [2,2,2] octane, and metal compounds such as organotin compounds.

  In order to eliminate image deterioration due to mechanical damage even when printing and erasing are repeated, the surface dynamic friction coefficient is preferably 0.3 or less. This is because if the dynamic friction coefficient is larger than 0.3, the slipperiness of the medium surface is lowered and a conveyance failure occurs.

  In order to achieve this dynamic friction coefficient of 0.3 or less, silicone having a polymerizable group, a polymer grafted with silicone, a release agent such as wax or zinc stearate, or a lubricant such as silicone oil is added to the protective layer. I can do it. The amount added is preferably 0.01% by weight or more and 50% by weight or less, more preferably 0.1% by weight or more and 40% by weight or less, based on the total weight of the resin component of the protective layer. Even if the addition amount is small, the effect is exhibited, but if it exceeds 50% by weight, there may be a problem in adhesion to the lower layer.

  The dynamic friction coefficient was measured using a ceramic ball with a surface property measuring machine (HEIDON-14S) manufactured by Shinto Kagaku under conditions of a load of 200 g and a moving speed of 0.75 mm / s.

  Further, the protective layer may contain an organic ultraviolet absorber, and the content thereof is preferably in the range of 0.5% by weight to 10% by weight with respect to the total weight of the resin component of the protective layer. Furthermore, conventionally known surfactants, antioxidants, leveling agents, light stabilizers, antistatic agents and the like may be contained as additives.

  The surface roughness Ra of the medium surface is preferably 0.2 μm or less. If the thickness exceeds 0.2 μm, sufficient glossiness cannot be obtained, and repeated use may cause an illusion that gloss changes will occur or erase marks will be recognized, resulting in an increase in erase residue. It is. Ra is more preferably 0.1 μm or less. This is because glossiness increases and a high-class feeling is obtained.

  The surface roughness Ra indicates the centerline average roughness of the surface to be measured, and is measured based on the JISB0601 method. In the present invention, the surface roughness Ra is measured under the conditions of a cutoff value of 0.8 mm, a measurement length of 2.5 mm, a scanning speed of 0.3 mm / s, and a stylus curvature radius of 5 μm. Performed using 570A.

  The thickness of the protective layer is preferably in the range of 0.1 μm to 20 μm, more preferably 0.5 μm to 10 μm, and still more preferably 1.5 μm to 6 μm.

  The reversible thermosensitive recording layer contains at least a leuco dye and a developer, and shows a relatively colored state and a decolored state due to a difference in heating temperature and / or cooling rate after heating.

  As the developer, a phenol compound having an alkyl chain having 8 or more carbon atoms is preferably used.

  The heat-sensitive recording layer preferably contains a curable resin. This is because the repeated durability is improved.

  The reversible thermosensitive recording layer preferably contains a resin that is in a crosslinked state with an isocyanate compound.

  Additives for improving or controlling the coating characteristics and color developing / decoloring characteristics of the reversible thermosensitive recording layer can be used. These additives include, for example, surfactants, conductive agents, fillers, antioxidants, light stabilizers, color development stabilizers, and decolorization accelerators.

  In addition to the reversible thermosensitive recording layer and the protective layer, the reversible thermosensitive recording medium may be provided with an intermediate layer, a photothermal conversion layer, a back layer, or an under layer as necessary.

  By providing an intermediate layer between the reversible thermosensitive recording layer and the protective layer, the adhesion between the reversible thermosensitive recording layer and the protective layer is improved, the recording layer is prevented from being altered by the application of the protective layer, and the additive in the protective layer is recorded. It is possible to prevent the transition to the layer.

  The intermediate layer preferably contains an ultraviolet absorbing material and a curable resin. This is because the light resistance is improved.

  By providing the photothermal conversion layer, the laser beam can be absorbed and converted into heat, and laser recording on the reversible thermosensitive recording layer becomes possible.

  By providing the back layer, curling due to shrinkage of the reversible thermosensitive recording layer surface can be suppressed.

  By providing the under layer, the applied heat can be used effectively, so the color development sensitivity of the reversible thermosensitive recording medium is improved, the adhesion between the support and the thermosensitive recording layer can be improved, and the thermosensitive recording layer on the support is further improved. Infiltration of material can be prevented.

  A support on which two or more types of sheets are bonded can be used. As the base sheet, a sheet made of the following materials or a laminate thereof is used.

  Chlorine-containing polymers include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer. Examples of the polyester resin include a polyethylene terephthalate resin (PET), a polybutylene terephthalate resin (PBT), terephthalic acid, and the like. Condensed ester resins of acid components such as isophthalic acid and alcohol components such as ethylene glycol or cyclohexanedimethanol (for example, PETG: trademark of Eastman Chemical Co.) are listed. , Natural polymer resins comprising the starch and modified polyvinyl alcohol, microbial production resin consisting of β- hydroxybutyrate and β- hydroxyvaleric acid. Further examples include synthetic resin sheets or synthetic papers such as polyacetate, polystyrene (PS), epoxy resin, polyvinyl chloride (PVC) and polycarbonate (PC), polyamide resin, acrylic resin, and silicone resin. They may be combined or may be a laminate of these materials. As an example of such lamination, for example, a core sheet in which two white polyvinyl chloride resin sheets having a thickness of 250 μm are laminated, and a transparent polyvinyl chloride resin sheet having a thickness of 100 μm on the front and back surfaces of the core sheet are used as oversheets. For example, a laminated sheet, for example, a core sheet in which two white PETG sheets with a thickness of 250 μm are laminated, and a transparent PETG with a thickness of 100 μm laminated as an oversheet on the front and back surfaces of the core sheet, and the like.

  The reversible thermosensitive recording medium of the present invention may be used in combination with an irreversible thermosensitive recording layer. At this time, the color tone of each recording layer may be the same or different.

  Further, in the claims and the specification, the surface means the surface on the reversible thermosensitive recording layer side and is not limited to the protective layer, but can be printed on the surface of the printing layer, the surface of the OP layer, the surface of the laminate layer, etc. This means all or part of the surface that contacts the thermal head during erasing.

  In the reversible thermosensitive recording medium of the present invention, one having a printing portion can be used. Arbitrary pattern etc. by printing such as offset printing, gravure printing, or inkjet printer, thermal transfer printer, sublimation printer, etc. on part or the whole surface of the same surface and / or the opposite surface of the reversible thermosensitive recording layer A colored layer may be provided, and an OP varnish layer mainly composed of a curable resin may be provided on a part or the entire surface of the colored layer. When laminating, the above-described printing can be performed in advance on a support or a base sheet to be bonded. Arbitrary patterns include characters, patterns, patterns, photographs, information detected by infrared rays, and the like. Moreover, it can also color by adding dye and a pigment to either of each layer which comprises.

  Furthermore, a hologram can be provided for security. Character information and Braille information can be provided by embossing, or a relief image or an intaglio shape can be provided to provide design, and a design such as a person image, a company emblem, or a symbol mark can be provided.

  An adhesive layer or a pressure-sensitive adhesive layer can be provided on the opposite side of the support from the reversible thermosensitive recording layer side and used as a reversible thermosensitive recording label. At this time, it may be attached to a base sheet such as a card or another medium. Specifically, a thick card such as an IC card or an optical card, a thin sheet such as a non-contact IC tag, a flexible disk, a magneto-optical recording disk (MD), a disk that can rewrite storage information such as a DVD-RAM, and the like are incorporated. Adhering to disc cartridges, discs that do not use disc cartridges such as CD-RW, write-once discs such as CD-R, optical information recording media (CD-RW) using phase change storage materials, video tape cassettes, etc. This makes it possible to display information on each medium. At this time, there are an adhesive layer or a pressure-sensitive adhesive layer (non-peeling paper type) and an adhesive layer or pressure-sensitive adhesive layer with a release paper (peeling paper type). As a material constituting the material, a hot melt type material is usually used.

  The reversible thermosensitive recording label may be provided on the entire surface of the base sheet, or may be provided on a part thereof. Moreover, it may be provided on one side or both sides of the base sheet, and is appropriately selected. When a thermosensitive recording label is attached by thermocompression bonding, an adhesive layer or a pressure-sensitive adhesive layer is not necessarily required on the surface opposite to the surface on which the thermosensitive recording layer of the support constituting the reversible thermosensitive recording medium is formed.

  The information storage unit can be provided in the reversible thermosensitive recording medium. By providing both a thermoreversible recording unit and an information storage unit, information stored in the information storage unit can be displayed on the thermoreversible recording unit, so that information can be confirmed without a special device. , Improve convenience. Examples of the information storage unit used at that time include a magnetic recording layer, a magnetic stripe, an IC memory, and an optical memory.

  In addition, the reversible thermosensitive recording medium of the present invention can be processed into a shape according to its use, and processed into a card shape, a sheet shape, a roll shape, and the like. For cards processed into cards, application to prepaid cards, point cards, credit cards, etc. can be mentioned. Sheets processed into general document sizes such as A4 size can be printed by using a printing / erasing device. In addition to trial printing, it can be widely used for temporary output such as circulation documents and conference materials. Furthermore, what was processed into the roll shape can be used for a display board, a bulletin board, or an electronic blackboard by incorporating in a device having a printing / erasing section. Such a display device can be preferably used in a clean room or the like because it does not generate dust or dust.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “parts” and “%” are based on weight.

アクリルポリオール樹脂５０％溶液（三菱レーヨン社製：ＦＲ４７５４） ６１部
上記組成物をペイントシェーカーにて粒径１．０μｍまで粉砕分散した。得られた分散液にアダクト型ヘキサメチレンジイソシアネート７５％酢酸エチル溶液（日本ポリウレタン社製：コロネートＨＬ）２０部を加え、よく撹拌し感熱記録層塗布液を調製した。上記組成の感熱記録層塗布液を、厚さ２５０μｍの白色ＰＥＴフィルム上にワイヤーバーを用いて塗布し、１００℃で乾燥した後、６０℃で２４時間加熱して、膜厚約１１μｍの感熱記録層を設けた。
（中間層の作製）
ポリエステルポリオール樹脂
（武田薬品工業社製：タケラックＵ−２１） １部
酸化亜鉛
（住友大阪セメント社製：ＺｎＯ−３０５） １部
コロネートＨＬ ２部
メチルエチルケトン ９部
上記組成物を良く攪拌して調製した中間層塗布液をワイヤーバーで塗布し、９０℃１分で乾燥した後、７０℃２時間加熱して、膜厚約２．０μｍの中間層を設けた。
（保護層の作製）
鱗片状シリカ
（洞海化学工業社製：サンラブリーＣ：粒径５．７μｍ、厚み０．１μｍ、表面積の総和２０ｍ^２／ｇ、厚みと最大長さ比率８０） ２部
トリス（アクリロキシエチル）イソシアヌレート（日立化成社製：ＦＡ−７３１Ａ） ８部
光重合開始剤
（日本チバガイギー社製：イルガキュア９０７） ０．４部
イソプロピルアルコール ９部
トルエン ９部
上記組成物をペイントシェーカーにて３０分間振盪して保護層塗布液を調整した。この保護層塗布液を前記感熱記録層塗布済みフィルム上にワイヤーバーにて塗布、加熱乾燥した後、照射エネルギー８０Ｗ／ｃｍの紫外線ランプ下を１０ｍ／分の搬送速度で通して硬化させた後、６０℃で２４時間加熱して膜厚約４μｍの保護層を設け、可逆性感熱記録媒体を作製した。 [Example 1]
<Preparation of thermosensitive recording layer>
3-diethylamino-6-methyl-7-anilinofluorane 4.5 parts Developer with the following structure

Acrylic polyol resin 50% solution (Mitsubishi Rayon Co., Ltd .: FR4754) 61 parts The above composition was pulverized and dispersed with a paint shaker to a particle size of 1.0 μm. 20 parts of an adduct type hexamethylene diisocyanate 75% ethyl acetate solution (manufactured by Nippon Polyurethane Co., Ltd .: Coronate HL) was added to the resulting dispersion and stirred well to prepare a thermal recording layer coating solution. The thermosensitive recording layer coating solution having the above composition is applied onto a white PET film having a thickness of 250 μm using a wire bar, dried at 100 ° C., and then heated at 60 ° C. for 24 hours to form a thermosensitive recording having a thickness of about 11 μm. A layer was provided.
(Preparation of intermediate layer)
Polyester polyol resin (Takeda Pharmaceutical Co., Ltd .: Takelac U-21) 1 part Zinc oxide (Sumitomo Osaka Cement Co., Ltd .: ZnO-305) 1 part Coronate HL 2 parts Methyl ethyl ketone 9 parts Intermediate prepared by thoroughly stirring the above composition The layer coating solution was applied with a wire bar, dried at 90 ° C. for 1 minute, and then heated at 70 ° C. for 2 hours to provide an intermediate layer having a thickness of about 2.0 μm.
(Preparation of protective layer)
Scale-like silica (manufactured by Dokai Chemical Industries, Ltd .: Sun Lovely C: particle size 5.7 μm, thickness 0.1 μm, total surface area 20 m ² / g, thickness to maximum length ratio 80) 2 parts Tris (acryloxyethyl) Isocyanurate (manufactured by Hitachi Chemical Co., Ltd .: FA-731A) 8 parts Photopolymerization initiator (manufactured by Ciba Geigy Japan Inc .: Irgacure 907) 0.4 parts Isopropyl alcohol 9 parts Toluene 9 parts The above composition was shaken for 30 minutes in a paint shaker. The protective layer coating solution was prepared. After applying this protective layer coating solution on the heat-sensitive recording layer-coated film with a wire bar, heating and drying, and passing through a UV lamp with an irradiation energy of 80 W / cm at a conveying speed of 10 m / min and curing, A protective layer having a thickness of about 4 μm was provided by heating at 60 ° C. for 24 hours, and a reversible thermosensitive recording medium was produced.

[Example 2]
Scale-like silica (manufactured by Dokai Chemical Industries, Ltd .: Sun Lovely C: particle size 5.7 μm, thickness 0.1 μm, total surface area 20 m ² / g, thickness to maximum length ratio 80) 2 parts Tris (acryloxyethyl) Isocyanurate (Hitachi Chemical Co., Ltd .: FA-731A) 4 parts Dipentaerythritol hexaacrylate (Nippon Kayaku Co., Ltd .: DPHA) 2 parts Urethane acrylate oligomer (Negami Kogyo Co., Ltd .: Art Resin UN-3320HS) 2 parts Photopolymerization started Agent (Nippon Ciba Geigy Co., Ltd .: Irgacure 907) 0.4 parts Isopropyl alcohol 9 parts Toluene 9 parts The above composition was stirred well to prepare a protective layer coating solution. Using this protective layer coating solution, a protective layer was provided on the heat-sensitive recording layer and intermediate layer coated film of Example 1 in the same manner as in Example 1 to produce a reversible thermosensitive recording medium.

[Example 3]
Scale-like silica (manufactured by Dokai Chemical Industries, Ltd .: Sun Lovely C: particle size 5.7 μm, thickness 0.1 μm, total surface area 20 m ² / g, thickness and maximum length ratio 80) 20 parts Tris (acryloxyethyl) Isocyanurate (Hitachi Chemical Co., Ltd .: FA-731A) 0.5 parts Dipentaerythritol hexaacrylate (Nippon Kayaku Co., Ltd .: DPHA) 3.5 parts Urethane acrylate oligomer (Negami Kogyo Co., Ltd .: Art Resin UN-3320HS) 4 Part Photopolymerization initiator (Nippon Ciba Geigy Co., Ltd .: Irgacure 907) 0.4 part Isopropyl alcohol 9 parts Toluene 9 parts The above composition was stirred well to prepare a protective layer coating solution. Using this protective layer coating solution, a protective layer was provided on the heat-sensitive recording layer and intermediate layer coated film of Example 1 in the same manner as in Example 1 to produce a reversible thermosensitive recording medium.

[Example 4]
A recording layer, an intermediate layer, and the same as in Example 2 except that tris (acryloxyethyl) isocyanurate in Example 2 was replaced with neopentyl glycol modified trimethylolpropane diacrylate (Nippon Kayaku Co., Ltd .: R-604). A protective layer was provided to produce a reversible thermosensitive recording medium.

[Example 5]
A recording layer, an intermediate layer and a protective layer were provided in the same manner as in Example 2 except that tris (acryloxyethyl) isocyanurate in Example 2 was replaced with tetrahydrofurfuryl acrylate (manufactured by Sartomer: SR-285). A thermal recording medium was produced.

[Example 6]
Scale-like silica (manufactured by Dokai Chemical Industries, Ltd .: Sun Lovely C: particle size 5.7 μm, thickness 0.1 μm, total surface area 20 m ² / g, thickness and maximum length ratio 80) 2 parts dipentaerythritol hexaacrylate ( Nippon Kayaku Co., Ltd .: DPHA) 8 parts Urethane acrylate oligomer (Negami Kogyo Co., Ltd .: Art Resin UN-3320HS) 8 parts Photopolymerization initiator (Nippon Ciba Geigy Co., Ltd .: Irgacure 907) 0.4 parts Isopropyl alcohol 9 parts Toluene 9 Part The above composition was well stirred to prepare a protective layer coating solution. Using this protective layer coating solution, a protective layer was provided on the heat-sensitive recording layer and intermediate layer coated film of Example 1 in the same manner as in Example 1 to produce a reversible thermosensitive recording medium.

[Example 7]
The protective layer coating solution of Example 2 was irradiated with ultrasonic waves for 10 minutes with an ultrasonic cleaning machine VS-100 (frequency 50 KHz) manufactured by AS ONE, and then a protective layer was provided in the same manner as in Example 2 to provide a reversible thermosensitive recording medium. Was made.

[Example 8]
(Preparation of protective layer coating solution)
Scale-like silica (manufactured by Dokai Chemical Industries, Ltd .: Sun Lovely C: particle size 5.7 μm, thickness 0.1 μm, total surface area 20 m ² / g, thickness to maximum length ratio 80) 4 parts Tris (acryloxyethyl) Isocyanurate (Hitachi Chemical Co., Ltd .: FA-731A) 6 parts Dipentaerythritol hexaacrylate (Nippon Kayaku Co., Ltd .: DPHA) 3 parts Urethane acrylate oligomer (Negami Kogyo Co., Ltd .: Art Resin UN-3320HS) 2 parts UV curable Silicone resin 30% solution (Toray Dow Corning: AY42-146-U10) 1 part Photopolymerization initiator (Nippon Ciba Geigy: Irgacure 907) 0.4 part Isopropyl alcohol 9 parts Toluene 9 parts Stir the above composition well Thus, a protective layer coating solution was prepared. Using this protective layer coating solution, a protective layer was provided on the heat-sensitive recording layer and intermediate layer coated film of Example 1 in the same manner as in Example 1 to produce a reversible thermosensitive recording medium.

[Example 9]
A reversible thermosensitive recording medium was produced in the same manner as in Example 2 except that no intermediate layer was provided. Although the recording layer-coated film was milky white, it was colored light reddish brown when UV crosslinking was performed after coating the protective layer.

[Comparative Example 1]
A recording layer, an intermediate layer and a protective layer were provided in the same manner as in Example 7 except that the scaly silica in Example 6 was replaced with amorphous silica (P-526: particle size 1.4 μm, manufactured by Fuji Silysia Co.). A heat-sensitive recording medium was produced.

[Comparative Example 2]
A recording layer, an intermediate layer, and a protective layer were provided in the same manner as in Example 2 except that the scaly silica in Example 2 was replaced with organosilane spherical silica (manufactured by Asahi Glass Co., Ltd .: Sunsphere) to prepare a reversible thermosensitive recording medium. .

[Comparative Example 3]
A recording layer, an intermediate layer, and a protective layer were provided in the same manner as in Example 7 except that the scaly silica in Example 6 was replaced with fine powder silica (manufactured by Fuji Silysia Co., Ltd .: Silo Hovic 100), and a reversible thermosensitive recording medium. Was made.

[Comparative Example 4]
A recording layer, an intermediate layer, and a protective layer were provided in the same manner as in Example 7 except that the scaly silica in Example 6 was omitted to prepare a reversible thermosensitive recording medium.

[Comparative Example 5]
A recording layer, an intermediate layer, and a protective layer are provided in the same manner as in Example 2 except that the scaly silica in Example 2 is changed to scaly talc (manufactured by Miyoshi Kasei Co., Ltd .: PT-46) to produce a reversible thermosensitive recording medium. did.

  Table 1 shows the evaluation results of the repeated durability of the reversible thermosensitive recording medium produced as described above.

  The repeated test was conducted manually in consideration of actual use. That is, every time printing is performed, the entire surface of the recording surface is touched with the belly of the finger, and erasure printing is performed again after 3 minutes.

  Regarding the evaluation method of repeated durability, the reversible thermosensitive recording media obtained in the above examples and comparative examples are punched into a credit card and printed in an erase print mode with a card printer R-28000 (manufactured by Panasonic Communications). Went. The erasure printing is a method in which an image is rewritten by inserting and reciprocating the card once and inserting the card again. The erasing is performed by a ceramic heater (erase bar), and the printing is continuously performed by a thermal head. As conditions, the printing energy was set to about 0.42 mJ / dot, and the erasing energy of the ceramic heater was set to the center value of a region where there was no disappearance due to lack of energy and there was no fogging due to over energy. The density of the printed part was measured by the black density of a Macbeth densitometer RD914.

  The remaining erasure is the difference between the density of the non-printed part before printing and the density of the part obtained by erasing and printing the part where the solid character (■) is erased and printed 100 times. The degree of melting and elution of the recording layer components by heat and platen pressure is evaluated. If the density difference is 0.03, it cannot be recognized.

  The background stain is the difference between the density of the non-printed part before printing and the density of the part that did not receive any thermal history during the repeated printing test. The ease of oil stains on the medium is evaluated. As with the remaining erase, it cannot be recognized if the density difference is 0.03.

  The crack is evaluated by changing the appearance of the portion where solid characters are printed 100 times. ○ indicates no change in appearance, Δ indicates a slight print crack (less than 1 mm in length), and × indicates a state in which a crack having a length of 1 mm or more is present in the solid print portion.

  A dent is a pattern that prints a solid pattern for 100 times and leaves it erased for an even number of times, and evaluates the difference in appearance between adjacent parts that have no temperature history other than the ceramic heater. is doing. ○ indicates no dent, Δ indicates a dent, and X indicates peeling.

Light resistance is the Macbeth densitometer when the printed part after the first repetition using the card printer R28000 is left for 100 hours under 5500 lux irradiation and then the entire printed part is erased by the card printer R28000. It is measured by RD914, and the light resistance is expressed by the difference in the change. The change in the unerased density after light irradiation can be defined as follows.
Unerased density change after light irradiation = erased density after light resistance test-background density after light resistance test

  Solvent resistance is determined by immersing in a 60% aqueous ethanol solution at room temperature for 24 hours and then naturally drying at room temperature for 24 hours to measure the concentration value. A density value of 0.6 or more was given as ◯, 0.4 or more and less than 0.6 as Δ, and less than 0.4 as x.

  Each of the reversible thermosensitive recording media according to the present invention using the scaly filler mainly composed of silica in the protective layers of Examples 1 to 9 was excellent in durability by repeated printing, light resistance and alcohol resistance. Showed the effect.

  In Comparative Example 1, an amorphous silica was used instead of the scaly filler mainly composed of silica. However, durability, light resistance, and alcohol resistance due to repeated printing were all inferior. It was.

  In Comparative Example 2, a configuration using organosilane spherical silica was used instead of the scaly filler mainly composed of silica, but the durability, light resistance and alcohol resistance due to repeated printing were all inferior results. became.

  In Comparative Example 3, instead of the scaly filler containing silica as a main component, a configuration using synthetic silica with a particle size adjusted to a micron size was used. However, durability by repeated printing, light resistance, and alcohol resistance are In either case, the results were inferior.

  In Comparative Example 4, the scale-like filler mainly composed of silica was removed, but the durability, light resistance, and alcohol resistance due to repeated printing were all inferior.

  In Comparative Example 5, instead of the flaky filler containing silica as a main component, a configuration using a flaky filler containing talc as a main component was adopted, but durability, light resistance, and alcohol resistance due to repeated printing were any. However, the results were inferior.

Claims (16)

  A reversible thermosensitive recording medium having a protective layer, wherein the protective layer contains at least a scaly filler mainly composed of silica.   The reversible thermosensitive recording medium according to claim 1, wherein the ratio of the maximum length of the scale plate to the thickness of the scale plate of the scale-like filler is 10 or more.   The reversible thermosensitive recording medium according to claim 1 or 2, wherein a thickness of the scale plate of the scale-like filler is 0.01 µm or more and 0.5 µm or less. The reversible thermosensitive recording medium according to any one of claims 1 to 3, wherein a total surface area per unit weight of the scaly filler is 20 m ² / g or more and 80 m ² / g or less.   The reversible thermosensitive recording medium according to any one of claims 1 to 4, wherein an average particle diameter of the scale-like filler is 4.0 µm or more and 6.0 µm or less.   The reversible thermosensitive recording medium according to any one of claims 1 to 5, wherein the protective layer contains an ultraviolet curable resin and / or a thermosetting resin.   The reversible thermosensitive recording medium according to claim 6, wherein the thermosetting resin is crosslinked with isocyanate.   The reversible thermosensitive recording medium according to any one of claims 1 to 7, wherein a surface dynamic friction coefficient is 0.3 or less.   The reversible thermosensitive recording medium according to any one of claims 1 to 8, wherein the protective layer contains an ultraviolet absorber.   The reversible thermosensitive recording medium according to any one of claims 1 to 9, wherein the surface roughness is 0.2 µm or less.   The reversible thermosensitive recording medium according to any one of claims 1 to 10, further comprising a support on which two or more types of sheets are bonded.   12. The reversible thermosensitive recording medium according to claim 1, wherein visible information irreversible with respect to heat is formed on the surface.   The reversible thermosensitive recording medium according to any one of claims 1 to 12, further comprising a printable portion.   The reversible thermosensitive recording medium according to any one of claims 1 to 13, further comprising an adhesive layer or an adhesive layer.   The reversible thermosensitive recording medium according to any one of claims 1 to 14, further comprising an information storage unit.   An image processing method for forming or erasing an image by heating the reversible thermosensitive recording medium according to any one of claims 1 to 15.