JP2006192799A - Reversible thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible thermal recording medium which makes the workability and chemical resistance of the medium compatible. <P>SOLUTION: In the reversible thermal recording medium, a thermal recording layer containing an electron-donating color-developable compound and an electron-accepting compound as main constituents and containing a reversible thermal composition which can form relatively colored and color-extinguished states according to a difference in a heating temperature and/or a cooling speed after heating is provided on a substrate, and a protective layer is provided on the thermal recording layer. The protective layer contains a polymerizable compound which is cured by radiation, and further contains a phosphine compound expressed by general formula (1). In the formula, R<SP>1</SP>-R<SP>3</SP>denote each a substituent selected from alkyl and alkoxy groups independently. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses a reversible thermosensitive coloring composition utilizing a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound, and can control the formation of a color image and erase it by controlling thermal energy. The present invention relates to a reversible thermosensitive recording medium and a method for forming and erasing the same.

  Conventionally, a heat-sensitive recording medium using a color development reaction between an electron donating color-forming compound (hereinafter also referred to as a color former) and an electron accepting compound (hereinafter also referred to as a developer) has been widely known. With the progress of OA, it is widely used as an output paper for facsimiles, word processors, scientific measuring instruments, etc., and recently as a magnetic thermal card such as prepaid cards and point cards. From the viewpoints of various durability, environmental problems, recycling, etc., in Patent Document 1, an organic phosphate compound, aliphatic carboxylic acid compound or phenol compound having a long-chain aliphatic hydrocarbon group is used as a developer. A reversible thermosensitive coloring composition capable of repeating color development and decoloring by combining with a leuco dye as a color former and a reversible thermosensitive recording medium using the same for a recording layer have been proposed. The use of a specific structure has been proposed for a phenol compound having an aromatic hydrocarbon group (see Patent Document 2).

  In order to prevent deterioration of this medium even if it is repeatedly used, it is general to use a material that is cured by radiation for the protective layer. Under such circumstances, with the expansion of the market, the forms and environments in which media are used are diversified, and the required specifications have increased. For example, since it is used as a card or sheet as described above, it is required to be easily cut into a card or sheet. This can be dealt with by lowering the hardness of the medium, particularly the hardness of the uppermost layer. On the other hand, since it is exposed to chemicals such as sweat, oil, plasticizers, and alcohol by carrying it everyday, there is a problem that these penetrate into the recording layer and the image disappears. For these, increasing the strength of the top layer Have responded. Since both the media processability and durability are in a trade-off relationship, as the required level increases, it has become impossible to ensure sufficient performance only by the balance of materials.

  As a means of improving the problem of such a recording medium, it can be easily imagined that the intensity of irradiated light is increased from the viewpoint of the process, but the organic compound in the coating layer deteriorates due to intense energy and the background turns yellow. have done. From the viewpoint of the material, a tertiary amine accelerator is applied in Patent Document 3 for the purpose of accelerating curing, but yellowing also occurred here due to deterioration of the amine. Many other studies have been made to improve the protective layer (see Patent Documents 4 and 5), but the purpose is to improve the light resistance of the recording layer and the head matching. There is no contribution to processability and chemical resistance, which are the problems in this case. There is a method to achieve by curing in a nitrogen atmosphere, but the cost is enormous due to the large amount of equipment and the amount of nitrogen consumed, and a method for improving performance without changing the conventional equipment has been demanded.

JP-A-5-124360 Japanese Patent Laid-Open No. 6-210954 JP-A-10-291370 Japanese Patent No. 3007946 JP 11-334220 A

  An object of the present invention is to provide a reversible thermosensitive recording medium that achieves both processability and chemical resistance of the medium.

  As a result of studies for solving these problems, the present inventors have applied a phosphine compound represented by the following general formula (1) to a protective layer containing a polymerizable monomer as a main component. It has been found that a medium that retains the workability and chemical resistance of the medium at a high level can be produced even when using.

（式中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれ独立して、置換基を有していてもよいアルキル基、アルコキシ基から選ばれるいずれかの置換基を表わす）
特にこの効果は下記一般式（２）の亜リン酸エステルを用いたときにさらに優れる。

(Wherein R ¹ , R ² and R ³ each independently represents any substituent selected from an alkyl group and an alkoxy group which may have a substituent)
In particular, this effect is further improved when a phosphite of the following general formula (2) is used.

（式中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれ独立して、置換基を有していてもよいアルキル基を表わす）

(Wherein R ¹ , R ² and R ³ each independently represents an alkyl group which may have a substituent)

  In the reversible thermosensitive recording medium of the present invention, it is preferable that the thermosensitive recording layer contains a curable resin, and additionally, an ultraviolet absorbing material and a curable resin are provided between the thermosensitive recording layer and the protective layer. The provision of the intermediate layer increases the practicality.

Furthermore, if the reversible thermosensitive recording medium of the present invention is provided with an information storage unit (magnetic recording layer, IC memory, optical memory, etc.) and irreversible visible information in advance, it becomes more practical.
The reversible thermosensitive recording medium of the present invention can form and erase images by heating with a thermal head, and at least one of a thermal head, a ceramic heater, a heat roll, a hot stamp, and a heat block. The image can be erased by heating with.

That is, the said subject is solved by following (1)-(11).
(1) “An electron-donating color-forming compound and an electron-accepting compound are contained as main components on the support, and the color developed and discolored relatively depending on the heating temperature and / or the cooling rate after heating. A thermosensitive recording layer containing a reversible thermosensitive composition capable of forming a state and a reversible thermosensitive recording medium comprising a protective layer on the thermosensitive recording layer, wherein the protective layer contains a polymerizable material that is cured by radiation. And a reversible thermosensitive recording medium further comprising a phosphine compound represented by the following general formula (1):

（式中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれ独立して、置換基を有していてもよいアルキル基、アルコキシ基から選ばれるいずれかの置換基を表わす）」、
（２）「前記ホスフィン化合物が下記一般式（２）で示される亜リン酸エステルであることを特徴とする前記第（１）項に記載の可逆性感熱記録媒体；

(Wherein R ¹ , R ² and R ³ each independently represents any substituent selected from an optionally substituted alkyl group and alkoxy group) ”,
(2) “The reversible thermosensitive recording medium according to item (1), wherein the phosphine compound is a phosphite ester represented by the following general formula (2);

（式中、Ｒ^１、Ｒ^２、Ｒ^３はそれぞれ独立して、置換基を有していてもよいアルキル基を表わす）」、
（３）「前記重合性材料がウレタンアクリレートを主成分とすることを特徴とする前記第（１）項又は第（２）項に記載の可逆性感熱記録媒体」、
（４）「可逆性感熱記録部と情報記憶部を有することを特徴とする前記第（１）項乃至第（３）項のいずれかに記載の可逆性感熱記録媒体」、
（５）「前記情報記憶部が磁気記録層、磁気ストライプ、ＩＣメモリー、光メモリーの何れか少なくとも１種であり、媒体の１部に設けたことを特徴とする前記第（４）項に記載の可逆性感熱記録媒体」、
（６）「２種類以上のシートを貼り合わせた支持体が用いられることを特徴とする前記第（１）項乃至第（５）項のいずれかに記載の可逆性感熱記録媒体」、
（７）「前記第（１）項乃至第（６）項のいずれかに記載の可逆性感熱記録媒体の支持体の感熱記録面側の反対面側に接着剤層または粘着剤層を設けたことを特徴とする可逆性感熱記録ラベル」、
（８）「不可逆な可視情報が予め感熱記録面側表面及び／又は裏面の少なくとも１部に形成してあることを特徴とする前記第（１）項乃至第（６）項のいずれかに記載の可逆性感熱記録媒体又は前記第（７）項に記載の可逆性感熱記録ラベル」、
（９）「前記第（１）項乃至第（８）項のいずれかに記載の可逆性感熱記録媒体又は可逆性感熱記録ラベルを、加熱により画像形成及び／又は画像消去することを特徴とする画像形成・消去方法」、
（１０）「サーマルヘッドを用いて加熱して画像形成することを特徴とする前記第（９）項に記載の可逆性感熱記録媒体又は可逆性感熱記録ラベルの画像形成・消去方法」、
（１１）「サーマルヘッド、セラミックヒーター、ヒートロール、ホットスタンプ、ヒートブロックの少なくとも１種を用いて加熱して画像消去することを特徴とする前記第（９）項又は第（１０）項に記載の可逆性感熱記録媒体又は可逆性感熱記録ラベルの画像の消去方法」

(Wherein R ¹ , R ² and R ³ each independently represents an optionally substituted alkyl group) ”,
(3) “The reversible thermosensitive recording medium according to (1) or (2) above, wherein the polymerizable material contains urethane acrylate as a main component”,
(4) “Reversible thermosensitive recording medium according to any one of (1) to (3) above, comprising a reversible thermosensitive recording section and an information storage section”;
(5) The item (4) is characterized in that the information storage unit is at least one of a magnetic recording layer, a magnetic stripe, an IC memory, and an optical memory, and is provided in one part of the medium. Reversible thermosensitive recording medium ",
(6) “Reversible thermosensitive recording medium according to any one of (1) to (5) above, wherein a support on which two or more types of sheets are bonded together” is used,
(7) An adhesive layer or a pressure-sensitive adhesive layer is provided on the opposite side of the heat-sensitive recording surface side of the support of the reversible thermosensitive recording medium according to any one of items (1) to (6). Reversible thermosensitive recording label, "
(8) The irreversible visible information is formed in advance on at least a part of the surface on the thermal recording surface side and / or the back surface, according to any one of items (1) to (6), Reversible thermosensitive recording medium or reversible thermosensitive recording label according to item (7),
(9) “Forming and / or erasing an image by heating the reversible thermosensitive recording medium or the reversible thermosensitive recording label according to any one of (1) to (8)” Image forming / erasing method ",
(10) “Image formation / erasing method of reversible thermosensitive recording medium or reversible thermosensitive recording label according to item (9), wherein the image is formed by heating using a thermal head”;
(11) The item (9) or (10), wherein the image is erased by heating using at least one of a thermal head, a ceramic heater, a heat roll, a hot stamp, and a heat block. Method for Erasing Image of Reversible Thermosensitive Recording Medium or Reversible Thermosensitive Recording Label "

  The present invention can provide a reversible thermosensitive recording medium having both processability and chemical resistance.

The reversible thermosensitive recording medium of the present invention will be described in detail below.
In the present invention, the curable resin used for the recording layer includes, for example, a combination of a crosslinking agent and a resin having an active group that reacts with the crosslinking agent, and the resin can be crosslinked and cured by heat, ultraviolet rays, electron beams, or the like. is there. By including a curable resin in the recording layer, the heat resistance and coating strength of the recording layer are improved, and the repeated durability of the reversible thermosensitive recording medium is improved.

  Resins used for thermosetting have groups that react with crosslinking agents such as hydroxyl groups and carboxyl groups, such as phenoxy resins, polyvinyl butyral resins, cellulose acetate propionate, cellulose acetate butyrate, acrylic polyols, polyester polyols, polyurethane polyols, etc. There is a resin or a resin obtained by copolymerizing a monomer having a hydroxyl group or a carboxyl group with another monomer. Among them, acrylic polyol resin, polyester polyol resin, and polyurethane polyol resin are preferable, and it has been found that durability, coating film surface hardness, and crack resistance are improved when the hydroxyl value is 70 (KOHmg / g) or more. 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 constitution, for example, 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 resistance 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. Specifically, 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. As the addition amount of the crosslinking agent to the resin, the ratio of the functional group of the crosslinking agent to the number of active groups contained in the resin is preferably 0.01 to 2, and below this, the heat strength is insufficient. Addition of the above has an adverse effect on the coloring and decoloring properties. 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.
As the resin used for ultraviolet ray and electron beam curing, various known polymerizable monomers described in the section of the protective layer can be used.

  In addition to the curing system, various known copolymer resins can also be used, for example, vinyl chloride-based, acrylic-based, styrene-based resins, specifically vinyl chloride-vinyl acetate-vinyl alcohol copolymers, Examples include vinyl chloride-vinyl acetate-hydroxypropyl acrylate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, and the like.

The electron-donating color-forming compound used in the present invention is a leuco dye, and is applied alone or in combination of two or more. However, it is a colorless or light-colored dye precursor, and is not particularly limited. For example, triphenylmethanephthalide, triallylmethane, fluoran, phenothiocyan, thioferolane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilino A leuco compound such as a lactam, rhodamine lactam, quinazoline, diazaxanthene, or bislactone is preferably used.
Among these, fluorane-based and phthalide-based leuco dyes are particularly preferable in terms of color development / decoloration characteristics, color, storage stability, and the like, more preferably 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-Np-toluidino) amino-6-methyl-7-anilinofluorane, 3-di (n-butylamino) -6-methyl-7-anilinofluorane, 3-n-methyl Black-colored leuco dyes such as N-propylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7,8-benzofluorane, 3- (N-ethyl-N-isoamyl) -7 , 8-benzofluorane, 1,3-dimethyl-6-diethylaminofluorane, 1,3-dimethyl-6-di-n-butylaminofluorane, 3-diethylamino-7-methylfluorane , Red-coloring leuco dyes such as 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, crystal violet lactone, 3- (4-diethylamino-2-ethoxyphenyl)- Blue color development such as 3- (1-ethyl-2-methylindol-1-yl) -4-azaphthalide, 3- (4-diethylaminophenyl) -3- (1-ethyl-2-indol-3-yl) phthalide Leuco dyes, 10-diethylamino-2-ethylbenzo [1,4] thiazino [3,2-b] fluorane, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide, 3- [2,2-bis (1-ethyl-2-methyl-3-indolyl) vinyl] 3- (4-diethylamino-phenyl) phthalide, 3- [1,1-bis (4-diethylamino-phenyl) ethylene-2-yl] -6-dimethylamino phthalide leuco dye having absorption in the infrared region, such as de.
Among them, 2-anilino-3-methyl-6-disubstituted aminofluoranes such as 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-methyl-6-di (n-butylamino) fluorane Crystal violet lactone and 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-1-yl) -4-azaphthalide are preferable from the viewpoints of color tone and color-decoloring properties. . These may be used alone or mixed, and can be multicolored or full-colored by laminating layers that develop colors having different colors.

  Further, the electron-accepting compound used in the present invention is not particularly limited as long as it can reversibly develop and decolorize by using heat as a factor, and has a structure having a color developing ability to develop a color former in the molecule, for example, A compound having at least one structure in which a phenolic hydroxyl group, a carboxylic acid group, a phosphoric acid group, and the like are connected to a structure that controls cohesion between molecules, for example, a long-chain hydrocarbon group. The linking moiety may be through a divalent or higher valent linking group containing a hetero atom, and the same linking group and / or aromatic group may be contained in the long-chain hydrocarbon group. In particular, it is preferable to use a phenol compound represented by the following general formula (3).

（式中、ｎは１〜３の整数を示し、ＹはＮ原子またはＯ原子を含む２価の基を表わす。また、Ｒ^４は置換基を有していてもよい炭素数２以上の脂肪族炭化水素基を表わし、Ｒ^５は炭素数１以上１４以下の脂肪族炭化水素基を表わす）

(In the formula, n represents an integer of 1 to 3, Y represents a divalent group containing an N atom or an O atom, and R ⁴ represents an aliphatic having 2 or more carbon atoms which may have a substituent. R ⁵ represents an aliphatic hydrocarbon group having 1 to 14 carbon atoms)

In the general formula (3), the aliphatic hydrocarbon group may be linear or branched, and may have an unsaturated bond. Examples of the substituent attached to the hydrocarbon group include a hydroxyl group, a halogen atom, and an alkoxy group. When the sum of the carbon atoms of R ⁴ and R ⁵ is 7 or less, the stability of color development and decoloring properties are lowered. Therefore, the number of carbon atoms is preferably 8 or more, and more preferably 11 or more. The X group is a divalent group containing an N atom or an O atom, particularly preferably an amide group and a urea group, and more preferably a urea group. R ⁴ represents an aliphatic hydrocarbon group having 2 or more carbon atoms, particularly preferably an aliphatic hydrocarbon group having 5 or more carbon atoms, and more preferably an aliphatic hydrocarbon group having 10 or more carbon atoms. The carbon number of R ⁵ is 1 or more and 14 or less, and particularly preferably the carbon number of R ⁵ is 8 or more and 14 or less. You may use 1 type or in mixture of 2 or more types.

  Further, by using together the developer having the above-described characteristics and a compound having at least one —NHCO— group or —OCONH— group in the molecule as a decoloring accelerator, the color disappearing in the process of forming a decoloring state. Intermolecular interaction is induced between the color accelerator and the developer, and the color development and decoloring characteristics are improved. Among these, compounds represented by the general formulas (4) to (10) are preferable.

（式中Ｒ^６、Ｒ^７、Ｒ^９は炭素数７以上２２以下の直鎖アルキル基、分枝アルキル基、不飽和アルキル基を表し、Ｒ^８は炭素数１〜１０の２価の官能基、Ｒ^１０は炭素数４〜１０の３価の官能基を表わす）

(Wherein R ⁶ , R ⁷ and R ⁹ represent a linear alkyl group having 7 to 22 carbon atoms, a branched alkyl group and an unsaturated alkyl group, and R ⁸ is a divalent functional group having 1 to 10 carbon atoms. , R ¹⁰ represents a trivalent functional group having 4 to ¹⁰ carbon atoms)

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

  The appropriate ratio of the color former to the color developer varies depending on the combination of the compounds used, but the developer is generally in the range of 0.1 to 20 with respect to the color developer 1 in molar ratio, preferably 0. In the range of 2-10. If the amount of the developer is less or more than this range, the density of the colored state is lowered, which causes a problem. Moreover, when adding a decoloring accelerator, the ratio is preferably 0.1 to 300% by weight, more preferably 3 to 100% by weight with respect to the developer. In addition, the color former and the developer can be used in a microcapsule. The ratio of the color developing component to the resin in the reversible thermosensitive recording layer is preferably 0.1 to 10 with respect to the color developing component 1, and if it is less than this, the heat intensity of the reversible thermosensitive recording layer is insufficient, and the ratio is higher. Is problematic because the color density is lowered.

  Examples of the support for the reversible thermosensitive recording medium of the present invention include paper, cellulose derivative films such as cellulose triacetate, polyolefin films such as polypropylene and polyethylene, polystyrene films or films obtained by bonding these, polyester, polycarbonate, synthetic paper, metal It is foil, glass or a composite thereof, and is preferably a polyester film such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or PET-G. Of these, polyethylene terephthalate and PET-G are preferable. In order to improve the adhesion of the coating layer, at least one surface can be subjected to surface modification by corona discharge treatment, oxidation reaction treatment (chromic acid or the like), etching treatment or the like. In order to obtain a sheet with high image clarity, polyethylene terephthalate and PET-G film having a haze of the support alone (haze defined by JIS K7105, haze) of 10% or less are particularly preferable. Moreover, the thing of the thickness as needed can also be used individually or by bonding. That is, a support having an arbitrary thickness from about several μm to about several mm is used. These supports may have a magnetic recording layer on the same surface and / or the opposite surface as the reversible thermosensitive recording layer.

For the formation of the recording layer, a coating liquid prepared by uniformly mixing and dispersing the mixture of the developer, color former, various additives, curing agent, crosslinked resin and coating solvent is used.
Solvents used for preparing the coating liquid include water, alcohol, ketone, amide, ether, glycols, glycol ethers, glycol ester acetates, esters, aromatic hydrocarbons, aliphatic hydrocarbons, halogenated carbonization. Examples thereof include hydrogens, sulfoxides, and pyrrolidones. Among these, water, methanol, ethanol, isopropanol, n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran, 1,4-dioxane, 3,4 -Dihydro-2H-pyran, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, methyl acetate, ethyl acetate, butyl acetate, toluene, xylene, hexane, heptane, cyclohexane, dimethyl sulfoxide, etc. are often used. Preferred are water, isopropanol, n-butanol, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, ethyl acetate, butyl acetate, toluene and xylene.
The coating liquid can be prepared using a known coating liquid dispersing apparatus such as a paint shaker, a ball mill, an attritor, a three-roll mill, a keddy mill, a sand mill, a dyno mill, or a colloid mill. In addition, these materials may be dispersed in a solvent using these coating liquid dispersing apparatuses, or may be dispersed and mixed in a solvent alone. Further, it may be dissolved by heating and precipitated by rapid cooling or cooling.
The thickness of the thermosensitive recording layer is preferably in the range of 1 to 20 μm, more preferably 3 to 15 μm.

Next, the protective layer in the reversible thermosensitive recording medium of the present invention will be described.
The protective layer in the present invention is formed by curing at least a compound called a polymerizable monomer or oligomer with radiation light.
The polymerizable monomer or oligomer used in the present invention has at least one vinyl group in the molecule and causes a crosslinking reaction by ultraviolet rays, electron beams, or the like. Examples of the polymerizable monomer used in the present invention include urethane acrylate, epoxy acrylate, polyester acrylate, polyether acrylate, vinyl, unsaturated polyester oligomers, various monofunctional, polyfunctional acrylates, methacrylates, Examples thereof include monomers such as vinyl esters, ethylene derivatives, and 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 PO-added triacrylate, trisacryloyloxyethyl phosphate, pentaerythritol tetraacrylate, trimethylolpropane propylene oxide 3 mol adduct Triacrylate, glyceryl propoxytriacrylate, dipentaerythritol polyacrylate, polyacrylate of caprolactone adduct of dipentaerythritol, propionic acid / dipentaerythritol triacrylate, hydroxypivalaldehyde-modified dimethylolpropyne triacrylate, propionic acid / Dipentaerythritol tetraacrylate, ditrimethylol prop Tetraacrylate, pentaacrylate of dipentaerythritol propionate, trimethylolpropane triacrylate added urethane prepolymer, dipentaerythritol hexaacrylate (DPHA), include ε- caprolactone adducts of DPHA.

  Among these, it is preferable to use a polyfunctional monomer from the viewpoint of heat resistance and mechanical strength, and in particular, urethane acrylate as a main component, and a mixture of monofunctional acrylate, dipentaerythritol hexaacrylate and pentaerythritol tetraacrylate as a diluent. Is preferably used. It is preferable that urethane acrylate accounts for 10 to 90% in terms of the total resin content. If it is less than 10%, the performance of urethane acrylate is conversely, and if it exceeds 90%, the performance of the monomer on the combined side is not imparted. More preferably, it is 15 to 80%, especially 30 to 70%.

  Furthermore, the use of a polymerizable monomer having a silicone moiety such as polysiloxane improves surface lubricity and durability. The addition amount at this time is preferably 0.05 to 50% by weight with respect to the total weight of the resin component of the protective layer. If it is less than 0.05%, almost no effect is exhibited. Conversely, if it exceeds 50%, the film becomes too flexible and the durability is lost. Especially preferably, it is 0.1 to 30%.

In the protective layer of the present invention, an organic or inorganic filler can be used to improve the head matching property. Among them, it is particularly preferable to use metal oxide fine particles surface-treated with organosilane as a filler. As the metal oxide, general metal oxide fillers such as amorphous silica, alumina, zirconia, titanium dioxide, zinc oxide, talc, clay, mica and kaolin are used. preferable. Among them, those having a primary particle diameter of 100 nm or less are preferable, and 5 to 50 nm is particularly preferable. As a method for producing a filler having an average particle size of 100 nm or less, it can be prepared using a conventional technique such as a gas phase reaction method or a liquid phase reaction method. The particle size is measured by laser diffraction method or Coulter counter, so the aggregate particle size is measured, so the image is captured with an electron microscope such as a transmission electron microscope or a scanning electron microscope, and image analysis by a computer or manual histogram is performed. It is performed by a method of calculating the primary particle diameter by creation.
When the particle diameter is smaller than 100 nm, an appropriate viscosity is added to the protective layer liquid, and the liquid does not flow when applied, and a uniform film can be easily formed. In addition, although the cause is not clear, the liquid is less likely to aggregate and the particles are uniformly present in the layer. As a synergistic effect, there is an advantage that there are few coating defects.

  Various conventionally known silane coupling agents can be used. Various silicone oils such as trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane, hexamethyldisilazane, alkylsilane coupling agents, vinyltriethoxysilane, vinyltrichlorosilane, Vinylsilane compounds such as vinyltrimethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane , Γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane and other epoxy silane compounds, γ-aminopropyl Liethoxysilane, γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-phenylamino Aminosilane compounds such as propyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-isocyanatopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxy Examples include reactive silane compounds such as silane and ureidopropyltriethoxysilane. Among these, a vinyl silane compound, an epoxy silane compound, an amino silane compound, and a reactive silane compound are particularly preferable because the denseness and toughness of the layer are improved, and the reactive silane compound is most preferable.

In addition, other fillers may be added to the protective layer in order to provide functions such as roughening and printability. Examples of inorganic fillers include carbonates such as calcium carbonate and magnesium carbonate, phosphates such as calcium phosphate, anhydrous silicic acid, hydrous silicic acid, hydrous aluminum silicate, hydrous calcium silicate and the like; alumina, zinc oxide, Examples thereof include oxides such as iron oxide and calcium oxide; hydroxides such as aluminum hydroxide. Organic fillers include silicone resin, cellulose resin, epoxy resin, nylon resin, phenol resin, polyurethane resin, urea resin, melamine resin, polyester resin, polycarbonate resin, styrene, polystyrene, polystyrene / isoprene, styrene vinylbenzene Examples thereof include resins, acrylic resins such as vinylidene chloride acrylic, acrylic urethane, and ethylene acrylic, polyethylene resins, formaldehyde resins such as benzoguanamine formaldehyde, melamine formaldehyde, polymethyl methacrylate resins, and vinyl chloride resins.
When the filler is included, it is added in an amount of 1 to 80% by weight based on the total weight of the resin component of the protective layer, but is preferably 2 to 50% by weight, and more preferably 5 to 30% by weight.

  Examples of the method for curing the protective layer of the present invention include ultraviolet rays, electron beams, α-rays, β-rays, γ-rays, and X-rays. In practice, ultraviolet rays or electron beams are used. Alternatively, crosslinking and curing can be performed by using these in combination. In addition, sufficient strength of the coating can be obtained in a short time by electron beam cross-linking, but electron beam irradiation equipment is expensive, and it is necessary to replace with inert gas. Is more preferable. In the case of curing using ultraviolet rays, a photopolymerization initiator and a photopolymerization accelerator are used. The photopolymerization initiator used in the present invention can be broadly classified into a radical reaction type and an ion reaction type, and the radical reaction type is further classified into a photocleavage type and a hydrogen abstraction type. 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.

In the present invention, the phosphine compound of the general formula (1) is used together with the photopolymerization initiator. Examples of the compound represented by the general formula (1) include trihexylphosphine, trioctylphosphine, tridecylphosphine, tridodecylphosphine, trioctadecylphosphine, tribenzylphosphine, tricyclohexylphosphine, and other aliphatic trisubstituted phosphines, dioctyltetradecyl. Examples include unequal three substituents such as phosphine, octylditetradecylphosphine and didodecylcyclohexylphosphine.
The phosphine compound is added in an amount of 0.1 to 20% by weight, preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the total weight of the resin component of the protective layer.

  Of these, a phosphite ester represented by the general formula (2) is preferable. Examples of the compound represented by the general formula (2) include trioctyl phosphite, tridodecyl phosphite, trioctadecyl phosphite, and tribenzyl phosphite.

Furthermore, for example, an aromatic tertiary amine or an aliphatic amine photopolymerization accelerator can be used in combination. Specifically, isoamyl p-dimethylaminobenzoate, ethyl p-dimethylaminobenzoate, 4,4′-bis (diethylamino) benzophenone, dimethylethanolamine, glycine, and aminoacrylate polymerizability which is a polymerizable compound Compound etc. are mentioned. These photopolymerization accelerators are used alone or in combination of two or more.
The amount of these photopolymerization initiator and photopolymerization accelerator added is preferably 0.1 to 20% by weight, more preferably 1 to 10% by weight, based on the total weight of the resin component of the protective layer.

The coefficient of dynamic friction on the surface of the reversible thermosensitive recording medium is preferably 0.3 or less in order to eliminate image deterioration due to mechanical damage even if printing and erasing are repeated. When 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, silicone grafted polymer, wax, mold release agent such as zinc stearate, and lubricant such as silicone oil can be added. The amount of these added is preferably 0.01 to 50% by weight, more preferably 0.1 to 40% by weight, 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.

  Moreover, you may contain an organic ultraviolet absorber in a protective layer, and the content has the preferable range of 0.5-10 weight% with respect to the resin component total weight of a 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 surface roughness Ra exceeds 0.2 μm, sufficient glossiness cannot be obtained, and gloss change may occur due to repeated use, and erasure marks are recognized. And there is a case where an illusion that the remaining erasure is increased.
The dynamic friction coefficient is measured using a ceramic ball with a HEIDON type tester. At that time, the load is 200 g, and the moving speed is 0.75 mm / s. The surface roughness Rz is measured based on the JIS B0601 method, and Ra represents the center line average roughness of the surface to be measured. The surface roughness Ra is measured using, for example, a surface roughness shape measuring device Surfcom 570A. The conditions at that time are 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. The radius is 5 μm.
The thickness of the protective layer is preferably in the range of 0.1 to 20 μm, more preferably 0.5 to 10 μm, and further preferably 1.5 to 6 μm.

The coating method for providing the recording layer and the protective layer is not particularly limited, and the substrate cut in a roll or continuously or into a sheet is conveyed, blade coating, wire bar coating, spray coating, air knife. Coating is performed by a known method such as coating, bead coating, curtain coating, gravure coating, kiss coating, reverse roll coating, dip coating, or die coating. The coated sheet is subsequently conveyed into a blower dryer and dried at 30 to 150 ° C. for 10 seconds to 10 minutes.
In particular, for defect-free coating, the coating solution is not only normal filter paper in advance or during feeding, but also a mesh such as stainless mesh, nylon mesh, natural or synthetic fiber filter such as cotton filter, fiber carbon filter, By passing through a membrane filter such as a membrane filter or applying ultrasonic waves for 1 minute to 200 hours, preferably 10 minutes to 80 hours, foreign substances can be removed, bubbles can be mixed, and dispersion can be prevented from agglomerating. Moreover, it is preferable to apply all layers consistently in a clean room of class 10,000 or less. For drying, it is preferable to heat an inert gas such as nitrogen or air that has passed through a filter and a dehumidifier, and spray this from the front surface, the back surface, or both. Among these, filtration by a cotton filter or a membrane filter or ultrasonic irradiation is particularly preferable. By appropriately selecting and using the apparatus as described above, the uniformity of the coating layer is improved, and the number of pinhole-shaped print defects per 1 m ² can be reduced to 100 or less.

  In the case of thermosetting, the recording layer and the protective layer are cured as necessary after coating and drying. By curing, in the case of thermal crosslinking, crosslinking can be promoted, and in other cases, the residual solvent can be reduced to stabilize the quality. A thermostatic bath or the like may be used for a relatively short time at a relatively high temperature, or a heat treatment may be performed at a relatively low temperature for a long time. The curing condition is preferably about 1 to 200 hours under a temperature condition of about 10 to 130 ° C. More preferably, heating is performed for about 2 minutes to 180 hours under a temperature condition of 15 to 100 ° C. In production, since productivity is emphasized, it is difficult to take time until the crosslinking is sufficiently completed. Therefore, it is preferable to heat at a temperature of 40 to 100 ° C. for about 2 minutes to 120 hours. The hot air may be directly applied to the application surface, or may be left in a thermostatic bath in a state of being cut into a roll shape or a sheet shape. If you do not want to lose the temperature, the vacuum drying method may be used. The physical properties can be controlled and the production process can be made more efficient by increasing or decreasing the temperature stepwise, or by dividing into multiple times such as after the upper layer coating or simply dividing the time.

Formation of the film by ultraviolet rays is performed by applying a photopolymerization reaction with an ultraviolet irradiation device after coating and drying. A conventionally known irradiation apparatus can be used for ultraviolet curing, and the light source includes a mercury lamp, a metal halide lamp, a gallium lamp, a mercury xenon lamp, a flash lamp, etc., and the photopolymerization initiator and the photopolymerization accelerator described above can be used. A light source having an emission spectrum corresponding to the ultraviolet absorption wavelength may be used. Further, as the irradiation conditions, the lamp output and the conveyance speed may be determined according to the irradiation energy necessary for crosslinking the resin. Further, by curing in a state where the oxygen concentration is 5% or less by nitrogen substitution, the polymerization probability is improved, and a denser film can be made.
When performing cross-linking curing with an electron beam, the electron beam irradiation device may be selected from a scanning type and a non-scanning type depending on the purpose such as irradiation area and irradiation dose, and the irradiation condition is to crosslink the resin. What is necessary is just to determine an electric current, irradiation width | variety, and a conveyance speed according to the dose required for this.

  In the present invention, for the purpose of improving the adhesion between the recording layer and the protective layer, preventing alteration of the recording layer due to the application of the protective layer, and preventing the additives in the protective layer from being transferred to the recording layer, an intermediate layer is provided between them. It is preferable to provide this, whereby the storage stability of the color image can be improved. Further, by using a curable resin for the intermediate layer, the heat resistance of the reversible thermosensitive recording medium is further improved, and better repeated durability can be obtained.

The intermediate layer is mainly made of a resin, and the resin used in the recording layer can be used as the resin used in the intermediate layer. Moreover, it is preferable to contain a ultraviolet absorber. Examples of the ultraviolet absorber used include benzotriazole-based, benzophenone-based, salicylic acid ester-based, cyanoacrylate-based, and cinnamic acid-based UV absorbers, preferably benzotriazole-based organic compounds.
Of these, those in which the hydroxyl group is protected by an adjacent bulky functional group are particularly preferred, and 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy) is particularly preferred. -3′-t-butyl-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2 ′ -Hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole is preferred. A skeleton having such an ultraviolet absorbing ability may be pendant to a copolymerized polymer such as an acrylic resin or a styrene resin. The content of these ultraviolet absorbers is preferably in the range of 0.5 to 10% by weight based on the total weight of the resin component in the intermediate layer.

Examples of the inorganic compound include metal compounds having an average particle size of 100 nm or less, such as zinc oxide, indium oxide, alumina, silica, zirconia, tin oxide, cerium oxide, iron oxide, antimony oxide, barium oxide, calcium oxide, Barium oxide, bismuth oxide, nickel oxide, magnesium oxide, chromium oxide, manganese oxide, tantalum oxide, niobium oxide, thorium oxide, hafnium oxide, molybdenum oxide, iron ferrite, nickel ferrite, cobalt ferrite, barium titanate, potassium titanate Metal oxides and their composite oxides, metal sulfides or sulfate compounds such as zinc sulfide, barium sulfate, titanium carbide, silicon carbide, molybdenum carbide, tungsten carbide, tantalum carbide Una metal carbide, aluminum nitride, silicon nitride, boron nitride, zirconium nitride, vanadium nitride, titanium nitride, niobium nitride, and metal nitrides such as gallium nitride.
Metal oxide ultrafine particles are preferable, and silica, alumina, zinc oxide, titanium oxide, and cerium oxide are more preferable among them. The surface can be treated with silicone, wax, organosilane, silica or the like. The content of these inorganic ultraviolet absorbers is preferably in the range of 1 to 95% in terms of volume fraction. These organic and inorganic ultraviolet absorbers may be contained in the recording layer.
The thickness of the intermediate layer is preferably in the range of 0.1 to 20 μm, more preferably 0.5 to 5 μm. As the solvent used in the intermediate layer coating liquid, the coating liquid dispersing device, the intermediate layer coating method, the intermediate layer drying / curing method, etc., known methods used in the recording layer and the protective layer may be used. it can.

In the present invention, in order to effectively use the applied heat, a heat-insulating undercoat layer can be provided between the support and the heat-sensitive recording layer. The undercoat layer can be formed by coating using a binder resin containing organic or inorganic fine hollow particles. An undercoat layer may be provided for the purpose of improving the adhesion between the support and the heat-sensitive recording layer and preventing penetration of the heat-sensitive recording layer material into the support.
For the undercoat layer, a resin similar to the resin for the heat-sensitive recording layer or the protective layer can be used. In addition, the heat-sensitive recording layer and the undercoat layer can contain inorganic fillers such as calcium carbonate, magnesium carbonate, titanium oxide, silicon oxide, aluminum hydroxide, kaolin, and talc and / or various organic fillers. In addition, a lubricant, a surfactant, a dispersant, and the like can be contained.

  In recent years, disc cartridges incorporating thick cards such as IC cards and optical cards, thin sheets such as non-contact IC tags, flexible disks, magneto-optical recording disks (MD), and disks that can rewrite storage information such as DVD-RAM. , CD-RW discs that do not use disc cartridges, CD-R discs, write-once discs, optical information recording media (CD-RW) using phase change storage materials, video tape cassettes, etc. From the surface opposite to the surface on which the heat-sensitive recording layer of the support constituting the reversible heat-sensitive recording medium is formed, an adhesive layer or a pressure-sensitive adhesive layer is provided to form a heat-sensitive recording label. You may affix on a 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.

  Commonly used materials can be used for the adhesive layer or the pressure-sensitive adhesive layer. For example, urea resin, melamine resin, phenol resin, epoxy resin, vinyl acetate resin, vinyl acetate-acrylic copolymer, ethylene-vinyl acetate copolymer, acrylic resin, polyvinyl ether resin, vinyl chloride-vinyl acetate Copolymer, polystyrene resin, polyester resin, polyurethane resin, polyamide resin, chlorinated polyolefin resin, polyvinyl butyral resin, acrylic ester copolymer, methacrylic ester copolymer, natural rubber , Cyanoacrylate resins, silicon resins, and the like, but are not limited thereto.

As the base sheet used in the present invention, a sheet made of the following materials or a laminate thereof is used.
Chlorine-containing polymer: 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, Polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, etc., polyester resin: polyethylene terephthalate resin (PET), polybutylene terephthalate resin (PBT), or acid components such as terephthalic acid or isophthalic acid Biodegradable plastic resins: polylactic acid resin, starch and modified poly, such as condensation ester resin (for example, PET-G: registered trademark of Eastman Chemical Co., Ltd.) with alcohol components such as ethylene glycol or cyclohexanedimethanol Natural polymer system consisting of Neil alcohol resin, 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. A laminated sheet, for example, a core sheet in which two white PET-G sheets with a thickness of 250 μm are laminated, and a laminated sheet of transparent PET-G with a thickness of 100 μm as an oversheet on the front and back surfaces of the core sheet, etc. .

As a method of attaching the base sheet and the thermosensitive recording label, as shown in FIG. 1 and FIG. 2, both are placed so as to face the mirror plate and sandwiched between the two mirror plates, and thermocompression bonding is performed. There is a way to do it. Thermocompression bonding, using known means, for example, a hot press, usually, 5~70kg / cm ^2, preferably to a pressure of 10 to 50 kg / cm ^2, 80 to 170 ° C., preferably in the range from 90 to 150 ° C. It is done in. The heating temperature at the time of thermocompression bonding is determined by selecting an optimum temperature range depending on the base sheet. Further, the heat-sensitive recording label and the base sheet can be heat-bonded after heat-bonding in advance. The thermal bonding may be performed by pressing a rubber roll or the like. Thereafter, the heat bonding is completed after the heat bonding. The thermal bonding is usually performed in a temperature range of 90 to 130 ° C. Such thermocompression bonding can be performed under the above-described conditions, for example, in a state of being held for less than 1 hour, preferably about 1 to 50 minutes. The holding time is merely an example, and is not particularly limited in the present invention.

  Here, for example, when a thermal recording label provided with a protective layer whose surface has been roughened with a filler is thermocompression bonded onto a substrate sheet such as a card, the filler on the surface of the protective layer is pushed into the protective layer or the lower layer by thermocompression bonding. If the surface gloss increases, as a result, the effect of the filler disappears and the durability decreases repeatedly, or if printing and erasing are repeated while the surface gloss is further increased, the gloss of the printed / erased portion decreases. Thus, there may be a new problem that a difference in glossiness from the non-printing / erasing part is recognized as gloss unevenness. However, the use of the protective layer of the present invention can also solve the above problem. If the surface roughness Ra of the reversible thermosensitive recording medium at this time is 0.15 μm or less, further glossiness is obtained, which is preferable.

For example, when a laminate such as a transparent polyvinyl chloride sheet / white polyvinyl chloride sheet / white polyvinyl chloride sheet / transparent polyvinyl chloride sheet is used as the base sheet, the heating temperature during the thermocompression bonding is as follows: About 130-150 degreeC is preferable, and the heating temperature at the time of using a laminated body like transparent PET-G / white PET-G / white PET-G / transparent PET-G is about 100-130 degreeC, Also good.
Such thermocompression bonding may be performed by other means, but the pressure and temperature conditions at that time are the same as described above.

  In the reversible thermosensitive recording medium of the present invention, the thermosensitive recording label may be provided on the entire surface of the base sheet, may be provided on a part thereof, or provided on one or both sides of the base sheet. It is often selected as appropriate. 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 reversible thermosensitive recording medium of the present invention provides both a thermoreversible recording unit and an information storage unit, and displays information stored in the information storage unit on the thermoreversible recording unit. Information can be confirmed even without it, improving convenience. A magnetic recording layer, an IC recording unit, or the like is preferably used as the storage unit used at that time.

  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.

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, on the same side and / or the opposite side of the heat-sensitive recording layer of the reversible thermosensitive recording medium of the present invention, a part or the whole of the surface is arbitrarily selected by printing such as offset printing, gravure printing, ink jet printer, thermal transfer printer, sublimation printer, etc. A colored layer having the above-described pattern or the like 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. In the case of laminating, the above-described printing can be performed in advance on the support and the base sheet to be bonded. Examples of the arbitrary pattern include characters, patterns, patterns, photographs, information detected by infrared rays, and the like. It is also possible to add a dye or pigment to any one of the simply configured layers for coloring.
Furthermore, a hologram can be provided for security. For embossing, character images, Braille information, or reliefs and intaglio shapes can be added to provide design such as a person image, a company emblem, a symbol mark, etc.

In order to form a color image using the reversible thermosensitive recording medium of the present invention, the color image may be rapidly cooled after being heated above the color development temperature. Specifically, for example, when the thermal recording layer is heated for a short time with a thermal head or laser light, the heat-sensitive recording layer is locally heated, so that the heat is immediately diffused and rapid cooling occurs, and the color development state can be fixed.
On the other hand, in order to erase the color, it may be heated and cooled for a relatively long time using an appropriate heat source, or may be temporarily heated to a temperature slightly lower than the coloring temperature. When heated for a long time, the temperature of a wide range of the recording medium rises, and the subsequent cooling becomes slow. As a heating method in this case, a hot roller, a hot stamp, hot air, or the like may be used, or heating may be performed for a long time using a thermal head.
Further, in order to heat the thermosensitive recording layer to the decoloring temperature range, for example, the applied energy may be lowered slightly from the time of recording by adjusting the voltage applied to the thermal head and the pulse width. If this method is used, recording / erasing can be performed only by the thermal head, and so-called overwriting becomes possible. Of course, the image can be erased by heating to a decoloring temperature range with a heat roller or a heat stamp.
In addition, the surface of the reversible thermosensitive recording medium of the present invention is the surface of the thermosensitive recording layer side and is not limited to the protective layer, but is a thermal head for erasing printing such as the printing layer surface, OP layer surface, and laminate layer surface. Means all or part of the surface that contacts

Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “parts” and “%” are based on weight.
Example 1
(Preparation of thermal recording layer)
3-diethylamino-6-methyl-7-anilinofluorane 4.5 parts 15 parts developer with the following structure

アクリルポリオール樹脂５０％溶液 ６１部
（三菱レーヨン社製：ＦＲ４７５４）

61 parts of acrylic polyol resin 50% solution (Made by Mitsubishi Rayon Co., Ltd .: FR4754)

  The composition was pulverized and dispersed to a particle size of 1.0 μm with a paint shaker. 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 heat-sensitive 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 heat-sensitive recording having a thickness of about 11 μm. A layer was provided.

(Preparation of intermediate layer)
Polyester polyol resin 1 part (Takeda Pharmaceutical Co., Ltd .: Takelac U-21)
1 part of zinc oxide (Sumitomo Osaka Cement Co., Ltd .: ZnO-305)
Coronate HL 2 parts Methyl ethyl ketone 9 parts The intermediate layer coating solution prepared by thoroughly stirring the above composition was applied with a wire bar, dried at 90 ° C for 1 minute, and then heated at 70 ° C for 2 hours to obtain a film thickness of about 2. A 0 μm intermediate layer was provided.

(Preparation of protective layer)
Organosilane-treated silica 2 parts (Fuji Silysia Co., Ltd .: Silo Hovic 100: particle size 1.4 μm)
4 parts of polyester acrylate (manufactured by Daicel UCB: Ebecryl 830)
4 parts of polyester acrylate (Daicel UC: Ebecryl 1810)
2 parts of polyester acrylate (Nippon Kayaku Co., Ltd .: KAYARAD DPCA-120)
Trioctylphosphine 0.1 part Photopolymerization initiator 0.4 part (Ciba Geigy Japan, Inc .: Irgacure 907)
Isopropyl alcohol 9 parts Toluene 9 parts The composition was shaken with a paint shaker for 30 minutes to prepare a protective layer coating solution. After applying this protective layer coating solution on the heat-sensitive recording layer-coated film with a wire bar, heating and drying, and then 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 film thickness of about 4 μm was provided by heating at 60 ° C. for 24 hours to produce a reversible thermosensitive recording medium.

Example 2
Each layer was provided in the same manner as in Example 1 except that trioctylphosphine in Example 1 was changed to dihexyloctadecylphosphine to prepare a reversible thermosensitive recording medium.

Example 3
Each layer was provided in the same manner as in Example 1 except that trioctylphosphine in Example 1 was changed to dimethoxyoctadecylphosphine, thereby producing a reversible thermosensitive recording medium.

Example 4
Each layer was provided in the same manner as in Example 1 except that trioctylphosphine in Example 1 was changed to isobutyldioctadecylphosphine to prepare a reversible thermosensitive recording medium.

Example 5
Each layer was provided in the same manner as in Example 1 except that the trioctylphosphine in Example 1 was changed to trioctyl phosphite to prepare a reversible thermosensitive recording medium.

Example 6
(Preparation of protective layer)
Organosilane-treated silica 2 parts (Fuji Silysia Co., Ltd .: Silo Hovic 100: particle size 1.4 μm)
2 parts of polyester acrylate (manufactured by Nippon Kayaku Co., Ltd .: KAYARAD DPHA)
5 parts of urethane acrylate (Negami Kogyo Co., Ltd .: Art Resin UN-3320HA)
3 parts of urethane acrylate (Daicel UC: Ebecryl 8803)
Trioctyl phosphite 0.1 part Photopolymerization initiator 0.4 part (Nippon Ciba Geigy Co., Ltd .: Irgacure 907)
9 parts isopropyl alcohol 9 parts toluene

  The composition was shaken with a paint shaker for 30 minutes 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.

Comparative Example 1
Each layer was provided in the same manner as in Example 1 except that trioctylphosphine in Example 1 was removed, thereby producing a reversible thermosensitive recording medium.

Comparative Example 2
(Preparation of protective layer)
Organosilane-treated silica 2 parts (Fuji Silysia Co., Ltd .: Silo Hovic 100: particle size 1.4 μm)
10 parts of polyester acrylate (Nippon Kayaku Co., Ltd .: KAYARAD DPHA)
Photopolymerization initiator 0.5 part (Nippon Ciba Geigy Co., Ltd .: Irgacure 907)
9 parts isopropyl alcohol 9 parts toluene

  The composition was shaken with a paint shaker for 30 minutes 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.

Comparative Example 3
(Preparation of protective layer)
Organosilane-treated silica 2 parts (Fuji Silysia Co., Ltd .: Silo Hovic 100: particle size 1.4 μm)
Urethane acrylate 10 parts (Negami Kogyo Co., Ltd .: Art Resin UN-3320HA)
Photopolymerization initiator 0.5 part (Nippon Ciba Geigy Co., Ltd .: Irgacure 907)
9 parts isopropyl alcohol 9 parts toluene

  The composition was shaken with a paint shaker for 30 minutes 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.

Comparative Example 4
Each layer was provided in the same manner as in Example 1 except that trioctylphosphine in Example 1 was changed to ethyl p-dimethylaminobenzoate to prepare a reversible thermosensitive recording medium.

Comparative Example 5
(Preparation of protective layer)
2 parts of silica treated with organosilane
4 parts of polyester acrylate (manufactured by Daicel UCB: Ebecryl 830)
3 parts of polyester acrylate (Daicel UC: Ebecryl 1810)
2 parts of polyester acrylate (Nippon Kayaku Co., Ltd .: KAYARAD DPCA-120)
Amino acrylate 1 part (Daicel UCB: Ebecryl 7100)
Photopolymerization initiator 0.5 part (Nippon Ciba Geigy Co., Ltd .: Irgacure 907)
9 parts isopropyl alcohol 9 parts toluene

  The composition was shaken with a paint shaker for 30 minutes 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.

Table 1 shows the evaluation results of the reversible thermosensitive recording medium produced as described above.
Sheet workability is evaluated by cutting each sample with the paper cutter made by Plus, with the recording surface facing up, and observing the state of the cutting residue generated at that time and cracks entering the end surface with an optical microscope. It was. Evaluation of chemical resistance was performed by punching out the reversible thermosensitive recording media obtained in the above Examples and Comparative Examples into a credit card, and printing in an erase printing mode with a card printer R-28000 (manufactured by Panasonic Communications). The image density was measured before dipping in a 60% aqueous ethanol solution and immediately after pulling up after 24 hours, and the retention with respect to the density before dipping was calculated and evaluated. The print density was measured by the black density of a Macbeth densitometer RD914.

・裁断カス
×：糸状、あるいは粉状の切りカスが出る
△：裁断端面が毛羽立っている
○：カスが出ない
・端面ヒビ
×：明らかに塗布層が破壊され、剥離している
△：亀甲状にヒビが激しく走っている
○：ヒビはわずかに入っている
◎：ヒビがほとんど見えない
・耐薬品性
浸漬後に十分乾燥すると画像濃度が上がり、７０％以上あると浸漬前の９５％以上にまで復活する。

・ Cutting waste ×: Threaded or powdered cutting residue is generated △: Cutting end surface is fluffy ○: Waste is not generated ・ End surface crack ×: The coating layer is clearly broken and peeled △: Tortoise shape ○: Cracks are slightly visible ◎: Cracks are barely visible ・ Chemical resistance When fully dried after immersion, the image density increases, and when it is 70% or more, it reaches 95% or more before immersion. To be resurrected.

It is a figure which shows an example of the thermocompression bonding process of the reversible thermosensitive recording label and base sheet in this invention. It is a figure which shows the other example of the thermocompression bonding process of the reversible thermosensitive recording label and base sheet in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot plate 2 Mirror surface plate 3 Reversible thermosensitive recording label 4 Base sheet 5 Reversible thermosensitive recording medium 6 Core sheet 7 Oversheet

Claims (11)

It contains an electron-donating color-forming compound and an electron-accepting compound as main components on the support, and forms a relatively colored state and a decolored state depending on the heating temperature and / or the cooling rate after heating. A heat-sensitive recording layer containing a reversible heat-sensitive composition to be obtained and a reversible heat-sensitive recording medium comprising a protective layer provided on the heat-sensitive recording layer, wherein the protective layer contains a polymerizable material that is cured by radiation, and A reversible thermosensitive recording medium comprising a phosphine compound represented by formula (1).

(Wherein R ¹ , R ² and R ³ each independently represents any substituent selected from an alkyl group and an alkoxy group which may have a substituent) The reversible thermosensitive recording medium according to claim 1, wherein the phosphine compound is a phosphite ester represented by the following general formula (2).

(Wherein R ¹ , R ² and R ³ each independently represents an alkyl group which may have a substituent) The reversible thermosensitive recording medium according to claim 1, wherein the polymerizable material contains urethane acrylate as a main component. The reversible thermosensitive recording medium according to any one of claims 1 to 3, further comprising a reversible thermosensitive recording section and an information storage section. The reversible thermosensitive recording medium according to claim 4, wherein the information storage unit is at least one of a magnetic recording layer, a magnetic stripe, an IC memory, and an optical memory, and is provided in one part of the medium. 6. The reversible thermosensitive recording medium according to claim 1, wherein a support on which two or more kinds of sheets are bonded together is used. A reversible thermosensitive recording label comprising an adhesive layer or a pressure-sensitive adhesive layer provided on the opposite side of the support of the reversible thermosensitive recording medium according to any one of claims 1 to 6. The reversible thermosensitive recording medium according to any one of claims 1 to 6, wherein the irreversible visible information is previously formed on at least a part of the surface and / or the back surface of the thermosensitive recording surface. The reversible thermosensitive recording label as described. An image forming and erasing method comprising heating the reversible thermosensitive recording medium or the reversible thermosensitive recording label according to any one of claims 1 to 8 and / or erasing the image by heating. 10. The image forming / erasing method for a reversible thermosensitive recording medium or reversible thermosensitive recording label according to claim 9, wherein the image is formed by heating using a thermal head. The reversible thermosensitive recording medium or reversible thermosensitive recording according to claim 9 or 10, wherein the image is erased by heating using at least one of a thermal head, a ceramic heater, a heat roll, a hot stamp, and a heat block. How to erase the image on the label.

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