JP2008100508A - Reversible color developing multiple-core single membrane microcapsule particle and reversible thermo-sensitive recording medium using this microcapsule particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible color developing multi-core single membrane microcapsule particle which is excellent in color developing and color removing properties for a reversible thermo-sensitive recording medium and is effective in reduction of background coloring, and the reversible thermo-sensitive recording medium. <P>SOLUTION: The reversible color developing multi-core single membrane micro-capsules are characterized by encapsulating in a resin electron donor coloring compounds and electron acceptor compounds which can form a coloring condition or decoloring condition relatively due to at least a difference in heating temperature and/or in cooling speed after heating. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention uses a reversible thermosensitive coloring composition that utilizes a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound, and reversible coloring that enables color development and erasure by controlling thermal energy. More particularly, the present invention relates to a reversible thermosensitive recording medium using the microcapsule fine particles.

  2. Description of the Related Art Conventionally, thermal recording media using a color development reaction between an electron donating color developing compound (hereinafter also referred to as a color former or a leuco dye) and an electron accepting compound (hereinafter also referred to as a developer) are widely known. With the development 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. However, these conventional recording media that have been put to practical use are being reviewed for recycling and reduced usage due to environmental problems. However, since they are irreversible colors, once recorded images are erased. It cannot be used repeatedly, and the area of the recordable part is limited because new information is added to the part where no image is recorded. Therefore, the actual situation is that the amount of information to be recorded is reduced or the card is remade when the recording area runs out. Therefore, it has been desired to develop a reversible thermosensitive recording medium that can be rewritten any number of times, against the background of the dust problem and forest destruction problem that have been actively discussed in recent years.

  By the way, various reversible thermosensitive recording media have been proposed from these requirements. For example, polymer-type reversible thermosensitive recording media using physical changes such as transparency and cloudiness are disclosed (see Patent Documents 1 and 2). In addition, a dye-type reversible thermosensitive recording medium utilizing a chemical change has been newly proposed. Specifically, those using a combination of gallic acid and phloroglucinol as the developer (for example, see Patent Document 3), those using compounds such as phenolphthalein and thymolphthalein as the developer (for example, patents) Reference 4), a recording layer containing a homogeneous solution of color former, developer, and carboxylic acid ester (see, for example, Patent Documents 5, 6, and 7), and an ascorbic acid derivative used as the developer (See, for example, Patent Document 8).

The leuco dyes used in these reversible thermosensitive recording media have a problem that they are decomposed by irradiation with ultraviolet light and colored brown because they are particularly poor in stability to ultraviolet light.
Therefore, the present inventors previously proposed to provide a protective layer containing an ultraviolet-absorbing inorganic filler on the recording layer, thereby cutting the ultraviolet light to the recording layer, thereby improving the light resistance. It was possible to improve (Patent Document 9). However, the method for producing a reversible thermosensitive recording medium described in Patent Document 9 is a method in which a leuco dye, a developer, a resin, and the like are dispersed or dissolved in a solvent, applied and dried to form a recording layer, and then a protective layer and the like are laminated. At this time, there is a problem that a part of the leuco dye is dissolved in the solvent used for coating the protective layer and oozes out on the surface layer of the recording medium and is colored by light irradiation.

  Next, the present inventors have proposed to prevent diffusion due to dissolution of the dye from the recording layer to the protective layer by using a resin in a crosslinked state in the recording layer (Patent Document 10). However, although this method can prevent diffusion of the leuco dye into the protective layer, the adhesion between the recording layer and the protective layer is reduced, and the recording medium is bent when the recording medium is bent. Had.

Further, Patent Document 11 exemplifies a configuration in which an electron donating color developing compound and an electron accepting compound are microencapsulated as an example of the configuration of a reversible thermosensitive recording medium. To produce a capsule wall, and no specific examples are presented.
Furthermore, as a reversible two-color thermosensitive recording medium, one recording layer for mixing and holding two types of reversible thermochromic compositions in the first microcapsules and the second microcapsules was laminated. A reversible two-color thermosensitive recording medium having a structure is disclosed. (For example, see Patent Document 12)
However, this Patent Document 12 only exemplifies a resin for producing a microcapsule, and does not exemplify a specific production method or the like.

On the other hand, an electron donating color developing compound, an electron accepting compound, and a photothermal conversion material are encapsulated in a microcapsule, dispersed in a recording layer, and absorbs laser light to generate heat. (For example, see Patent Document 13)
However, these recording media have a problem that the whiteness of the background portion is low because the photothermal conversion material is colored. Further, there is a problem that the leuco dye undergoes a structural change and is discolored by repeatedly applying laser light. Furthermore, the recording device using laser light has problems such as difficulty in miniaturization and high cost compared to the recording device using a thermal head.

JP 63-107584 A JP-A-4-78573 Japanese Patent Laid-Open No. 60-193691 Japanese Patent Laid-Open No. Sho 61-237684 JP-A-62-138556 JP-A-62-138568 JP-A-62-140881 Japanese Patent Laid-Open No. 63-173684 Japanese Patent Laid-Open No. 10-100541 JP-A-10-230680 JP-A-5-124360 JP-A-6-305247 JP 2005-205882 A

  The present invention relates to a reversible color-forming multi-core single-coated microcapsule microparticle that is effective in reducing the background coloring excellent in coloring and decoloring characteristics of a reversible thermosensitive recording medium, and a reversible thermosensitive recording medium using the microcapsule microparticle The purpose is to provide.

  As a result of analyzing the cause of the coloring of the background, the present inventors can reduce the coloring of the background by preventing the diffusion of the leuco dye into the protective layer, and in particular, microencapsulate the leuco dye and the developer. It was found that the diffusion of leuco dyes can be prevented. Furthermore, as a result of studying various types of encapsulation, the inventors have found that the use of multi-core single-coated microcapsules has excellent durability during repetition, and the present invention has been completed.

That is, the said subject is solved by following (1)-(5) of this invention.
(1) “At least an electron-donating color-forming compound and an electron-accepting compound that can form a relatively colored state and a decolored state due to a difference in heating temperature and / or cooling rate after heating, resin Reversible coloring multicore single-coated microcapsule microparticles characterized by being encapsulated in
(2) “Emulsifying a capsule particle forming liquid obtained by dispersing or dissolving an electron-donating color-forming compound and an electron-accepting compound together with an encapsulating resin using an organic solvent in water, and then distilling off the solvent. The reversible color-forming multicore single-coated microcapsule microparticles according to (1) above, which is produced by:
(3) “Reversible coloring multicore single-coated microcapsule microparticle according to (1) or (2) above, wherein the resin in the microcapsule is in a crosslinked state”;
(4) “At least a heat-sensitive recording layer including a reversible color-forming multicore single-coated microcapsule microparticle according to any one of (1) to (3) and a matrix resin is provided on a support. Reversible thermosensitive recording medium ";
(5) “The reversible thermosensitive recording medium according to (4) above, wherein the matrix resin is in a crosslinked state”.

  The reversible color-forming multicore single-coated microcapsule fine particles of the present invention are capable of reversible coloring / decoloring, and further, the reversible thermosensitive recording medium using the reversible color-forming multicore single-coated microcapsule fine particles. Is excellent in color developability and light resistance, and even when color development and erasure are repeated many times, it is possible to maintain a good state without cracking or peeling on the surface of the recording medium.

The present invention is described in detail below.
The reversible color-forming multicore single-coated microcapsule microparticles and the reversible thermosensitive recording medium of the present invention can form a relatively colored state and a decolored state depending on the heating temperature and / or the cooling rate after heating. . This basic coloring / decoloring phenomenon will be described.

FIG. 1 shows the relationship between the color density and temperature of this reversible thermosensitive recording medium. Introduction gradually heated the recording medium in the decolored state (A), leuco dye and the developer are mixed melt at temperatures T ₁ begins to melt, coloring occurs a molten color developed state (B). When rapidly cooled from the melt color state (B), the color state can be lowered to room temperature and a fixed color state (C) is obtained. Whether or not this color development state is obtained depends on the rate of temperature decrease from the molten state, and in slow cooling, the color disappears during the temperature decrease, and the same color disappearance state (A) or rapid color development state (C ) A relatively low concentration state is formed. On the other hand, rapidly cooled colored state (C) is again raised gradually and discoloring occurs at a lower temperature T ₂ than the coloring temperature (E from D), returns the beginning when the temperature decreases from here to the same decolored state (A). The actual color developing temperature and color erasing temperature vary depending on the combination of the developer and color former used, and can be selected according to the purpose. Further, the density of the melt coloring state and the coloring density when rapidly cooled are not necessarily the same and may be different.

  In the reversible thermosensitive recording medium of the present invention, the colored state (C) obtained by quenching from the molten state is a state in which the developer and the color former (leuco dye) are mixed in a state where they can be contacted with each other. This often forms a solid state. This state is a state where the developer and the color former are aggregated to maintain the color development, and it is considered that the color development is stabilized by the formation of this aggregated structure. On the other hand, the decolored state is a state in which both phases are separated. This state is a state in which molecules of at least one compound aggregate to form a domain or crystallize, and the color former and developer are separated and stabilized by aggregation or crystallization. It is done. In many cases, in the present invention, more complete color erasure occurs due to phase separation of the two and crystallization of the developer. In both the decoloring by slow cooling from the molten state and the decoloring by raising the temperature from the colored state shown in FIG. 1, the aggregation structure changes at this temperature, and phase separation and crystallization of the developer occur.

First, the reversible coloring multicore single-coated microcapsule fine particles of the present invention will be described.
The multi-core single-coated microcapsule microparticles of the present invention are made of, for example, fine particles having the structure shown in “New edition microcapsules—manufacturing method, properties, and applications (published by Sankyo Publishing Co., Ltd., Author: Kondo Tadashi, p. 38)”. It is encapsulated in a dispersed state, and is described as an example of known microencapsulation described in Patent Documents 11 to 13, and has a configuration different from that having a capsule wall on the particle surface belongs to.
The capsule wall of the microcapsule described in the above-mentioned patent document is obtained by providing a thin crosslinked film or a polymerized film on the capsule particle surface, and is a firm and thin capsule wall. When such a microcapsule having a thin and hard capsule wall is used for a reversible thermosensitive recording medium, the wall is broken by the heating and pressure of the thermal head during recording / erasing, and the color density during recording is reduced. Problems such as deterioration and unerased residue at the time of erasure occur.
On the other hand, since the microcapsule fine particles of the present invention do not have such a capsule wall, it is considered that the above problems do not occur.
As a recording medium using the multi-core single-film microcapsule of the present invention, a multi-film capsule (for example, described in Patent Document 13) having a capsule wall made of a wall material such as a conventionally known melamine-formalin resin is used. Compared to the case, it is excellent in durability when repeatedly used. The reason for this is not clear, but in the case of multiple film capsules, micro cracks occur between the resin inside the capsule and the wall surface of the capsule due to repeated thermal history, resulting in cracks on the surface of the recording medium. It may have occurred.

The reversible color-forming multicore single-coated microcapsule microparticles of the present invention can be prepared by a polymer dissolution suspension method or the like. As the method, a leuco dye and a developer are dispersed together with an encapsulating resin using an organic solvent or The capsule particle forming liquid obtained by dissolution is emulsified in water, and then the solvent is distilled off.
FIG. 2 is a schematic view of the reversible color-forming multicore single-coated microcapsule fine particles of the present invention. As shown in FIG. 2, both the electron donating color-forming compound and the electron accepting compound are dispersed in the encapsulating resin as a core substance.
In addition, the electron donating color-forming compound may be dissolved in the encapsulating resin.
The microcapsule fine particles used in the present invention are preferably 0.5 to 10 μm, more preferably 0.5 to 5 μm. If the thickness is less than 0.5 μm, there is a problem that the color density is lowered, and if it is larger than 10 μm, uniform coating becomes difficult when producing the recording medium, which causes uneven color density.
Furthermore, in the present invention, a reversible thermosensitive recording medium can be provided by coating and drying the reversible color-forming multicore single-coated microcapsule microparticles together with a matrix resin on a support to provide a reversible thermosensitive recording layer. .
FIG. 3 shows a schematic diagram of the reversible thermosensitive recording medium of the present invention. As shown in FIG. 3, a reversible thermosensitive recording medium in which a thermosensitive recording layer (4) in which microcapsule fine particles (2) are dispersed in a matrix resin (3) is laminated on a support substrate (1).

As the leuco dye used in the present invention, one or two or more kinds of compounds generally used in this type of reversible thermosensitive recording medium can be used. For example, phthalide compounds, azaphthalide compounds, fluorane compounds and the like are known. It is a dye precursor. Examples of these compounds are leuco dyes described in JP-A Nos. 5-124360, 6-210954, and 10-230680.
Of these, particularly preferred examples include 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di (n-butylamino) fluorane, 2-anilino-3-methyl-6. -(Nn-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N- Isobutyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-p-) Toluidino) fluoran, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- ( - ethyl-2-methylindole-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, and the like.

  In the present invention, a phenol compound having an aliphatic group having 8 or more carbon atoms represented by the following formula (1) is particularly preferably used as the developer.

（式中、Ｘ_１及びＸ_２は直接結合手または−ＮＨ−、−ＣＯ−、−Ｏ−、−ＳＯ_２−、−Ｓ−から選ばれる２価の基、或いはこれら２価の基を２個以上組み合わせた２価の基を示す。ただし、Ｘ_１及びＸ_２は同時に直接結合手であることはない。Ｒ_１は炭素数１〜２２の２価の炭化水素基を表わし、Ｒ_２は炭素数８〜３０の炭化水素基を表わす。また、ｐは０〜４の整数を表わし、ｐが２〜４のとき繰り返されるＲ_１およびＸ_２は同一でも、異なっていてもよい。また、ｐが０のとき、Ｘ_１は直接結合手ではない。さらに、ｑは１〜３の整数を表わす。）

(In the formula, X ₁ and X ₂ represent a direct bond or a divalent group selected from —NH—, —CO—, —O—, —SO ₂ —, and —S—, or 2 of these divalent groups. A divalent group in combination of two or more, wherein X ₁ and X ₂ are not directly a direct bond, R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents Represents a hydrocarbon group having 8 to 30 carbon atoms, p represents an integer of 0 to 4, and R ₁ and X ₂ repeated when p is 2 to 4 may be the same or different. when p is 0, _{X 1} is not a direct bond. further, q is an integer of 1-3.)

Specifically, R ₁ and R ₂ represent an optionally substituted hydrocarbon group, which may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and is composed of both of them. It may be a hydrocarbon group. 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, and an alkoxy group.
R ₁ has 1 to 22 carbon atoms, and if the carbon number exceeds 22, the color density is lowered, which is not preferable.
Further, R ₂ has 8 to 30 carbon atoms, and when the carbon number is 7 or less, the stability of color development and decoloring properties are lowered. Therefore, the carbon number is preferably 8 or more, and more preferably 11 or more. If the carbon number exceeds 30, the color density is lowered, which is not preferable.
X ₁ and X ₂ represent a direct bond or a divalent group containing a hetero atom shown in Table 1 below,

好ましくは、表１で表わされる基を少なくとも１個以上有する２価の基を表わす。
その具体例としては、下記のものが挙げられる。

Preferably, it represents a divalent group having at least one group represented by Table 1.
Specific examples thereof include the following.

  Specific examples of the phenol compound in the present invention are listed below, but the present invention is not limited thereto. Moreover, a phenol compound can also be used individually or in mixture.

（式中のｒ、ｓは前記のＲ_１およびＲ_２の炭素数を満足する整数を表わす）等が挙げられる。

(Wherein, r and s represent integers satisfying the carbon number of R ₁ and R ₂ described above).

  Besides these, for example, JP-A-5-124360, JP-A-6-210554, JP-A-10-95175, JP-A-9-290563, JP-A-11-188969, JP Developers described in No. 11-99749 can be used.

  Specific examples of the encapsulating resin used in the present invention include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, Examples include polycarbonate, polyacrylic acid esters, polymethacrylic acid esters, and the like.

  Among them, a resin in a crosslinked state is particularly preferably used, and specifically, a crosslinking agent such as acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, phenoxy resin, polyvinyl butyral resin, cellulose acetate propionate, cellulose acetate butyrate, and the like. A resin having a reactive group, or a resin obtained by copolymerization of a monomer having a group reactive with a crosslinking agent and another monomer may be used, but the present invention is not limited to these compounds.

  Further, in the present invention, a resin having a hydroxyl value of 70 (KOHmg / g) or more is preferably contained (initially used). Examples of the resin having a hydroxyl value of 70 (KOHmg / g) or more include acrylic polyol resins and polyester polyols. Resins, polyurethane polyol resins, and the like are used, and acrylic polyol resins are preferably used because they have particularly good color stability and good decoloring properties. The hydroxyl value is 70 (KOHmg / g) or more, particularly preferably 90 (KOHmg / g) or more. The magnitude of the hydroxyl value affects the crosslink density and thus affects the chemical resistance and physical properties of the coating film. The inventors of the present invention are particularly preferably used since the hydroxyl value is 70 (KOHmg / g) or more and the durability is improved.

  In addition, acrylic polyol resins have different characteristics depending on the structure. Hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate ( HPMA), 2-hydroxybutyl monoacrylate (2-HBA), 1,4-hydroxybutyl monoacrylate (1-HBA), etc. are used, but it is particularly preferable to use a monomer having a primary hydroxyl group. Since the crack resistance and durability are good, 2-hydroxyethyl methacrylate is preferably used.

  Examples of the crosslinking agent used in the present invention include conventionally known isocyanates, amines, phenols, epoxy compounds and the like. Among these, an isocyanate type crosslinking agent is preferably used. The isocyanate compound used here is selected from known modified monomers such as urethane modified products, allophanate modified products, isocyanurate modified products, burette modified products, carbodiimide modified products, and blocked isocyanates. In addition, as the isocyanate monomer forming the modified product, tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), naphthylene diisocyanate NDI), paraphenylene diisocyanate (PPDI) ), Tetramethylxylylene diisocyanate (TMXDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), lysine diisocyanate (LDI), isopropylidenebis (4-cyclohexylisocyanate) (IPC) Cyclohexyl diisocyanate (CHDI), tolidine diisocyanate (TODI), and the like. It is not limited to the compounds.

  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-diaza-bicyclo [2,2,2] octane, and metal compounds such as organic tin compounds.

  Further, in the present invention, in addition to the above developer and leuco dye, by using a coloring / decoloring control agent having a hydrogen bond group such as a linear hydrocarbon group, an amide group or a urea group, The storage stability of the color image is good and the erasability at the time of erasing is also improved, so that good erasability can be obtained.

  As a solvent for dispersing or dissolving these developers, leuco dyes, and resins, water-insoluble organic solvents are preferably used. For example, ketones such as methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, toluene, Aromatic hydrocarbons such as xylene, aliphatic hydrocarbons such as hexane, and ethers can be used alone or in combination.

In the present invention, the capsule forming liquid is prepared by dispersing or dissolving the above-described leuco dye, developer and the like together with the encapsulating resin in a solvent. As a dispersion method, a conventionally known method is used. For example, it can be dispersed with a paint shaker, a sand mill, or the like. The dispersed particle size, that is, the particle size of the core material contained in the capsule is preferably 5 μm or less, 0.5 μm or more, and more preferably 1 μm or less.
In addition, when using a crosslinking agent, it is preferable to introduce | transduce into a capsule formation liquid after completion | finish of dispersion | distribution.

  Furthermore, in the present invention, the capsule-forming solution prepared as described above is emulsified in water using a homogenizer or the like, and then the solvent is distilled off to prepare reversible color-forming multicore single-coated microcapsule microparticles. In the emulsification, a surfactant is preferably used.

  The surfactant used in the present invention is a nonionic, cationic or anionic surfactant, and preferably a nonionic or cationic surfactant. Specific examples are given below, but the present invention is not limited thereto. Moreover, surfactant can also be used individually or in mixture.

  Polyoxyethylene tridecyl ether, polyoxyalkylene branched decyl ether, polyoxyalkylene tridecyl ether, polyoxyethylene isodecyl ether, polyoxyethylene lauryl ether, polyoxyalkylene lauryl ether, polyoxyethylene alkyl ether, polyoxyethylene oleyl Cetyl ether, polyoxyethylene styrenated phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene polyoxypropylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene oleic acid ester, polyoxyethylene distearic acid ester , Polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, polyoxy Ethylene lauryl ether, polyoxyethylene lanolin alcohol ether, polyoxyethylene lanolin fatty acid ester, polyoxyethylene alkylamine ether, coconut oil fatty acid diethanolamide, coconut oil fatty acid diethanolamide, polyoxyethylene isotridecyl ether, polyoxyalkylene isotri Decyl ether, polyoxyalkylene branched decyl ether, polyoxyethylene isodecyl ether, lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, didecyldimethylammonium chloride, benzalkonium chloride solution, dimethylaminopropylamide stearate , Quaternary ammonium salts, etc.

  Furthermore, in the present invention, a reversible thermosensitive recording medium can be prepared by coating and drying reversible color-forming multicore single-coated microcapsule fine particles on a support together with a matrix resin to form a thermosensitive recording layer.

  The support used may be paper, resin film, PET film, synthetic paper, metal foil, glass, or a composite thereof, and the like, as long as it can hold the heat-sensitive recording layer. Moreover, the thing of the thickness as needed can be used individually or by bonding. That is, it is preferably 60 to 150 μm, and a support having an arbitrary thickness from about several μ to about several mm is used.

  Further, as the matrix resin used in the present invention, the same resin as the above microencapsulated resin can be used, and further water-soluble resins such as hydroxyethylcellulose, hydroxypropylcellulose, methoxycellulose, carboxymethylcellulose, methylcellulose, cellulose acetate, gelatin and the like. Can be used. Furthermore, these matrix resins can also be crosslinked with a crosslinking agent.

Further, according to the present invention, an intermediate layer can be provided between the recording layer and the protective layer in order to improve adhesion.
As the resin used for the intermediate layer, conventionally known thermoplastic resins and thermosetting resins are widely used, and examples thereof include polyester resins and polyurethane resins.
Furthermore, according to the present invention, a protective layer containing a resin in a crosslinked state can be provided on the reversible thermosensitive recording layer. As the resin used for the protective layer, a thermosetting resin, an ultraviolet curable resin, or an electron beam curable resin is used.
As the resin used in the protective layer, an ultraviolet absorbing polymer having an ultraviolet absorbing group in the molecular structure is preferably used.

  As the ultraviolet absorbing polymer, a monomer having an ultraviolet absorbing group and a polymer having a monomer having a crosslinkable functional group are preferably used. As the monomer having an ultraviolet absorbing group, (2 '-Hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-ω-butyl- A monomer having a benzotriazole skeleton such as 5′-methylphenyl) -5-chlorobenzotriazole is particularly preferably used.

  Examples of the monomer containing a functional group include 2-isopropenyl-2-oxazoline, 2-aziridinylethyl (meth) acrylate, methacrylic acid, glycidyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxyl Examples include propyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate, among which hydroxylethyl (meth) ) Acrylate, hydroxylpropyl (meth) acrylate and the like are particularly preferably used.

  Furthermore, in order to increase the strength of the coating film and improve heat resistance, the following monomers may be copolymerized with a copolymer of a monomer containing an ultraviolet absorbing group and a monomer containing a functional group. For example, monomers such as styrene, styrene-butadiene, styrene-isobutylene, ethylene vinyl acetate, vinyl acetate, methacrylonitrile, vinyl alcohol, vinyl pyrrolidone, acrylonitrile, methacrylonitrile; acrylic acid, methyl (meth) acrylate, ethyl (meth ) Acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, ethylhexyl (meth) acrylate, octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) ) Acrylate, lauryl tridecyl (meth) acrylate, tridecyl (meth) acrylate, cetyl stearyl (meth) acrylate, stearyl (meth) acrylate (Meth) acrylic acid ester groups not containing functional groups such as cyclohexyl (meth) acrylate and benzyl (meth) acrylate; ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene Glycol di (meth) acrylate, decaethylene glycol di (meth) acrylate, pentacontahector ethylene glycol (meth) acrylate, butylene di (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, penta Decaethylene glycol di (meth) acrylate, phthalic acid diethylene glycol di (meth) acrylate, etc. have two or more polymerizable double bonds in one molecule Although it is mentioned from a monomer group etc., it is not particularly limited, among them, styrene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, Particularly preferred is t-butyl (meth) acrylate. Moreover, 2 or more types can also be used together as needed.

  From the above, specific preferred examples of the polymer having an ultraviolet absorption structure used in the present invention include 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole and 2-hydroxy methacrylate. Examples include a copolymer composed of ethyl and styrene, and a copolymer composed of 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2-hydroxypropyl methacrylate and methyl methacrylate. Is not to be done.

Furthermore, according to the present invention, the protective layer can contain inorganic fine particles having ultraviolet absorbing ability.
The inorganic pigment used in the present invention is arbitrary as long as it has an average particle size of 0.1 μm or less. Examples of such inorganic pigments include zinc oxide, indium oxide, alumina, silica, zirconium oxide, tin oxide, cerium oxide, iron oxide, antimony oxide, barium oxide, calcium 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, metal oxides such as potassium titanate and complex oxides thereof, zinc sulfide, Metal sulfides such as barium sulfate or sulfate compounds, titanium carbide, silicon carbide, molybdenum carbide, tungsten carbide, metal carbides such as tantalum carbide, aluminum nitride, silicon nitride, boron nitride, nitride Rukoniumu, vanadium nitride, titanium nitride, niobium nitride, and metal nitrides such as gallium nitride.
Among these, a pigment having an absorption edge in a wavelength region of 400 nm or less is particularly preferable.

  Such a pigment includes a pigment (A) having an absorption edge in the ultraviolet UV-A region, that is, an ultraviolet UV-A region having a wavelength of 320 to 400 nm, and an inorganic pigment having an absorption edge on the shorter wavelength side than the ultraviolet UV-A region ( B) can be classified into two groups. In the present invention, the inorganic pigment (A) or the inorganic pigment (B) can be used alone, but the effect of the present invention becomes more remarkable by using the inorganic pigment (A) and the inorganic pigment (B) in combination. When the inorganic pigment (A) or the inorganic pigment (B) is used alone, these pigments can be contained in either the intermediate layer or the protective layer. In the case where the inorganic pigment (A) and the inorganic pigment (B) are used in combination, these pigments can be simultaneously contained in the intermediate layer or the protective layer, but the inorganic pigment (A) and the inorganic pigment (B) are included in the intermediate layer. And can be contained separately in the protective layer. In this case, when the inorganic pigment (A) is contained in the intermediate layer and the inorganic pigment (B) is contained in the protective layer, the effect of the present invention is more remarkably exhibited.

Specific examples of the inorganic pigment (A) include zinc sulfide, titanium oxide, indium oxide, cerium oxide, tin oxide, molybdenum oxide, zinc oxide, and gallium nitride.
Specific examples of the inorganic pigment (B) include silica, alumina, silica-alumina, antimony oxide, magnesium oxide, zirconium oxide, barium oxide, calcium oxide, strontium oxide, silicon nitride, aluminum nitride, boron nitride, and barium sulfate. Can be mentioned.

  Further, in the present invention, inorganic / organic fillers, lubricants and the like used for this type of recording medium may be used in the protective layer.

  Next, the reversible color-forming multicore single-coated microcapsule microparticles of the present invention and the reversible thermosensitive recording medium using the same will be described with specific examples. However, the present invention is limited to the following examples. It is not something.

[Example 1]
Preparation of reversible coloring microcapsule fine particles (Preparation of reversible thermosensitive recording material dispersion)
Developer: 1.00 parts by weight of a phenol compound represented by the following chemical formula

メチルエチルケトン ５．２重量部
トルエン １５．３重量部
アクリルポリオール樹脂
（三菱レイヨン社製ＬＲ５０３ 固形分濃度５０％溶液） ８．５重量部
上記組成物をボールミルを用いて平均粒径約１μｍまで粉砕分散した。得られた分散液に、ロイコ染料２−アニリノ−３−メチル−６−ジエチルアミノフルオラン：０．２重量部、日本ポリウレタン社製 コロネートＨＬ（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）：２．９重量部を加え、よく攪拌し可逆性感熱記録材料分散液を調製した。

Methyl ethyl ketone 5.2 parts by weight Toluene 15.3 parts by weight Acrylic polyol resin (LR503, 50% solids concentration solution manufactured by Mitsubishi Rayon Co., Ltd.) 8.5 parts by weight The above composition was pulverized and dispersed to a mean particle size of about 1 μm using a ball mill. . To the obtained dispersion, leuco dye 2-anilino-3-methyl-6-diethylaminofluorane: 0.2 parts by weight, Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd.:2. 9 parts by weight was added and stirred well to prepare a reversible thermosensitive recording material dispersion.

(Preparation of aqueous surfactant solution)
Neugen TDS-500F manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 3.3 parts by weight Neugen EA207D manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 6.0 parts by weight 77.1 parts by weight of ion-exchanged water Stir with a stirrer until the surfactant is dissolved.

(Preparation of microcapsule fine particles)
The above reversible thermosensitive recording material dispersion was put into an aqueous surfactant solution stirred with a homogenizer at a rotational speed of 5000 rpm, and emulsified so as to have an average particle diameter of 5 μm. The obtained emulsion was depressurized with an evaporator, and methyl ethyl ketone and toluene were distilled off to obtain a dispersion of microcapsule fine particles. Then, it heated on 60 degreeC conditions for 12 hours, and bridge | crosslinked resin.
Next, the microcapsules are washed with water, and washing with water is repeated until the residual surfactant concentration in the washing liquid becomes 0.1% or less.
After washing with water, the obtained microcapsule fine particles were filtered and dried to obtain reversible color-forming multicore single-coated microcapsule fine particles. The average particle size of the microcapsule fine particles was 3 μm.

When the microcapsules produced as described above were sandwiched between two slide glasses, heated on a hot plate at 180 ° C. and then put into ice water, the color developed into dark black. Next, when the particles were reheated on a hot plate at 120 ° C., they became almost white and were decolored.
When the above operation was repeated, the microcapsule fine particles could be repeatedly colored and decolored.

[Example 2]
Production of reversible thermosensitive recording medium using reversible color-forming microcapsule fine particles [Preparation of thermosensitive recording layer]
Reversible coloring multicore single-coated microcapsule fine particles prepared in Example 1 1.5 parts by weight 10% Itaconic acid-modified polyvinyl alcohol aqueous solution 1.5 parts by weight Water 5 parts by weight 25% polyamide epichlorohydrin resin 0.2 parts by weight or more The liquid of the composition was sufficiently stirred with a magnetic stirrer to prepare a thermosensitive recording layer forming liquid. This heat-sensitive recording layer forming solution was applied to a 100 μm PET film (polyethylene terephthalate) with a wire bar and dried to apply a heat-sensitive recording layer having a thickness of about 15 μm.

(Preparation of intermediate layer)
Zinc oxide fine particles (Sumitomo Osaka Cement Co., Ltd. ZS-303 solid content concentration 30%) 4 parts by weight Acrylic polyol resin (Mitsubishi Rayon LR503 solid content concentration 50% solution) 2 parts by weight Nippon Polyurethane Co., Ltd. Coronate HL
(Adduct type hexamethylene diisocyanate
75% ethyl acetate solution) 0.5 parts by weight Methyl ethyl ketone 5 parts by weight The above composition was dissolved and stirred well to prepare an intermediate layer forming solution. The obtained intermediate layer forming liquid was applied onto the thermosensitive recording layer using a wire bar and dried to provide an intermediate layer having a thickness of 1.5 μm.

(Creation of protective layer)
Urethane acrylate UV curable resin (C7-157 solid content concentration: 75% by Dainippon Ink & Co., Ltd.) 15 parts by weight Silicone macromonomer (AK-5 solid content concentration by Toagosei Co., Ltd .: 40%) 0.5 parts by weight Isopropyl Alcohol 85 weight part The said composition was melt | dissolved and stirred well and the protective layer coating liquid was prepared. A protective layer coating solution having the above composition,
The intermediate layer is coated with a wire bar, dried at 80 ° C. for 1 minute, and then cured by passing through a UV lamp with an irradiation energy of 80 W / cm at a conveyance speed of 9 m / min, and a protective layer having a thickness of 3 μm. And then heated at 60 ° C. for 2 days to produce a reversible thermosensitive recording medium.

[Comparative Example 1]
Reversible in the same manner as in Example 2 except that the microcapsule particles prepared as follows were used in place of the reversible color-forming microcapsule fine particles of the present invention used in the thermosensitive recording layer forming liquid of Example 2. A heat-sensitive recording medium was produced.

(Preparation of microcapsule particles)
The reversible thermosensitive recording material dispersion obtained in the same manner as in Example 1 and the following surfactant aqueous solution were emulsified with a homogenizer and emulsified and dispersed so that the average particle diameter was 5 μm.
[Surfactant aqueous solution]
Neugen TDS-500F manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 3.3 parts by weight Neugen EA207D manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 6.0 parts by weight Polyvinylbenzenesulfonic acid (partially soda salt) 5.0 parts by weight Ion-exchanged water 77. 1 part by weight of the obtained emulsion was depressurized with an evaporator to distill off methyl ethyl ketone and toluene. Subsequently, 100 weight part of melamine-formalin aqueous solution was mixed, 20% acetic acid aqueous solution was dripped, and it adjusted to pH6.
Thereafter, the liquid temperature was raised to 65 ° C., the polymerization reaction was carried out for 30 minutes, and then dried to obtain melamine-formalin wall microcapsules.

[Comparative Example 2]
A reversible thermosensitive recording medium was produced in the same manner as in Example 2 except that (Production of thermosensitive recording layer) in Example 2 was performed as follows.
Developer: 1.00 parts by weight of the following chemical formula (2)

メチルエチルケトン １９．８重量部
アクリルポリオール樹脂
（三菱レイヨン社製ＬＲ５０３ 固形分濃度５０％溶液） ２．８重量部
上記組成物をボールミルを用いて平均粒径約１μｍまで粉砕分散した。得られた分散液に、ロイコ染料２−アニリノ−３−メチル−６−ジエチルアミノフルオラン：０．４重量部、日本ポリウレタン社製 コロネートＨＬ（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）：０．９重量部を加え、よく攪拌し可逆性感熱記録層形成液を調製した。
得られた可逆性感熱記録形成液を１００μｍＰＥＴフィルム（ポリエチレンテレフタレート）にワイヤーバーにて塗布、乾燥し、膜厚約１５μｍの感熱記録層を塗工した。

Methyl ethyl ketone 19.8 parts by weight Acrylic polyol resin (LR503 manufactured by Mitsubishi Rayon Co., Ltd., 50% solid concentration solution) 2.8 parts by weight The above composition was pulverized and dispersed to an average particle size of about 1 μm using a ball mill. To the obtained dispersion, leuco dye 2-anilino-3-methyl-6-diethylaminofluorane: 0.4 parts by weight, Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. 9 parts by weight was added and stirred well to prepare a reversible thermosensitive recording layer forming liquid.
The obtained reversible thermosensitive recording liquid was applied to a 100 μm PET film (polyethylene terephthalate) with a wire bar and dried to apply a thermosensitive recording layer having a film thickness of about 15 μm.

The following tests were conducted on the reversible thermosensitive recording medium produced as described above.
<Evaluation test>
Color development density test Using a thermal printing apparatus manufactured by BCOM, printing was performed at a voltage of 21 V and a pulse width of 2 msec, and the obtained image and background density were measured with a Macbeth densitometer RD-914.
-Erase density test The color image obtained in the color density test was erased with a thermal tilt tester manufactured by Toyo Seiki Co., Ltd. at 140 ° C for 1 second, and the density and background density of the image area after erasing were Measurement was performed in the same manner as in the color density test. Next, the unerased density was calculated from the following formula.
Unerased density = (Density of image area after erasure)-(Background density)
Durability test The above color density test and erase density test were repeated 30 times, and the state of the recording medium surface was visually evaluated.
* 1) Rank 3: No cracking or peeling at the surface of the recording medium.
Rank 2: The surface of the recording medium is slightly cracked and peeled off.
Rank 1: The surface of the recording medium is markedly cracked and peeled off.
-Light resistance test The background density after storing the produced recording medium at 5000 lux for 100 hours was measured in the same manner.

It is a figure which shows the color development and decoloring characteristic of the reversible thermosensitive coloring composition of this invention. It is a figure which shows the schematic of the reversible coloring multi-core single membrane | film | coat microcapsule particle of this invention. It is a figure which shows the schematic of the reversible thermosensitive recording medium using the reversible coloring multi-core single membrane | film | coat microcapsule particle of this invention.

Claims (5)

  At least an electron-donating color-forming compound and an electron-accepting compound capable of forming a relatively colored state and a decolored state depending on the heating temperature and / or the cooling rate after heating are encapsulated with a resin. Reversible coloring multicore single-coated microcapsule microparticles characterized by   It was prepared by emulsifying a capsule particle forming liquid obtained by dispersing or dissolving an electron-donating color-forming compound and an electron-accepting compound together with an encapsulating resin using an organic solvent in water and then distilling off the solvent. The reversible color-forming multicore single-coated microcapsule fine particles according to claim 1.   The reversible color-developing multicore single-coated microcapsule microparticle according to claim 1 or 2, wherein the resin in the microcapsule is in a crosslinked state.   A reversible thermosensitive recording medium comprising a thermosensitive recording layer comprising at least a reversible color-forming multicore single-coated microcapsule fine particle according to any one of claims 1 to 3 and a matrix resin on a support.   The reversible thermosensitive recording medium according to claim 4, wherein the matrix resin is in a crosslinked state.

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