JP2008168494A - Reversible thermosensitive recording medium - Google Patents

Abstract

A reversible thermosensitive recording medium excellent in high-speed erasability and compatible with high-speed rewriting is provided.
An electron donating color-forming compound and an electron-accepting compound are used on a support, and a relatively colored state and a decolored state are caused by a difference in heating temperature and / or cooling rate after heating. A reversible thermosensitive recording medium having a reversible thermosensitive recording layer which can be formed, wherein the reversible thermosensitive recording layer contains a zwitterionic resin.
[Selection] Figure 1

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.

  2. Description of the Related Art Conventionally, heat-sensitive recording media using a color developing 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 progress of OA, it is widely used as an output sheet 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 white turbidity have been disclosed (Patent Document 1: Japanese Patent Laid-Open No. 63-107584, Patent Document 2: Japanese Patent Laid-Open No. 4-78573). See the official gazette). In addition, a dye-type reversible thermosensitive recording medium utilizing a chemical change has been newly proposed. Specifically, a combination of gallic acid and phloroglucinol is used as a developer (see, for example, Patent Document 3: JP-A-60-193691), and phenolphthalein, thymolphthalein, etc. (For example, see Japanese Patent Application Laid-Open No. 61-237684), and a recording layer containing a homogeneous solution of a color former, a developer and a carboxylic acid ester (for example, Patent Document 5). : JP-A-62-138556, Patent Document 6: JP-A-62-138568, Patent Document 7: JP-A-62-140881), ascorbic acid derivative used as a developer ( For example, Patent Document 8: Japanese Patent Laid-Open No. 63-173684), and a bis (hydroxyphenyl) acetic acid or a salt of gallic acid and a higher aliphatic amine is used as a developer. Things (e.g., Patent Document 9: JP-A 2-188293 and JP-Patent Document 10: see Japanese Patent Laid-Open No. 2-188294) have been disclosed.

  Furthermore, the present inventors previously used an organic phosphate compound, aliphatic carboxylic acid compound or phenol compound having a long-chain aliphatic hydrocarbon group as a developer in Patent Document 11 (Japanese Patent Laid-Open No. 5-124360). By combining this with the leuco dye that is a color former, color development and decoloration can be easily performed under heating and cooling conditions, and the color development state and color erasure state can be stably maintained at room temperature. In addition, a reversible thermosensitive coloring composition capable of repeating coloring and decoloring and a reversible thermosensitive recording medium using the same for the recording layer have been proposed. Thereafter, it has been proposed to use a phenolic compound having a long-chain aliphatic hydrocarbon group having a specific structure (for example, Patent Document 12: Japanese Patent Laid-Open No. 6-210954, Patent Document 13: Japanese Patent 10-95175).

However, a recording medium using such a material has problems such as a slow erasing speed and a long time for rewriting, insufficient erasing, or low thermal stability of a color image. Therefore, the present inventors further use a phenol compound described in Patent Document 14 (Japanese Patent Laid-Open No. 10-67177) to provide a high contrast between color development and decoloration, enabling high-speed erasing, and color development in the image area. A recording medium with excellent stability was proposed. The recording medium using this phenol compound can be erased by a heating member such as a hot stamp, a heat roller, or a ceramic heater, and has excellent practicality.
Furthermore, in order to increase the repetition durability of the recording medium, the present inventors have proposed using a resin in a crosslinked state in Patent Document 15 (Japanese Patent Laid-Open No. 10-230680), which is the heat resistance of the recording medium. In addition, the mechanical strength was greatly improved, and the repeated durability of printing and erasing was improved. Further, Patent Document 16 (Japanese Patent Laid-Open No. 11-58963) also proposes that durability is improved by using a resin in a crosslinked state.
However, recently, a faster rewriting speed has been demanded, and these reversible thermosensitive recording media have a problem that the high-speed erasability is insufficient when erasing at high speed with a heat roller or a ceramic heater. .

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 JP-A-2-188293 JP-A-2-188294 JP-A-5-124360 Japanese Patent Laid-Open No. 6-210954 JP-A-10-95175 JP-A-10-67177 JP-A-10-230680 Japanese Patent Application Laid-Open No. 11-58963

  An object of the present invention is to provide a reversible thermosensitive recording medium excellent in high-speed erasability corresponding to high-speed rewriting.

  In the decoloring process of the reversible color erasing phenomenon of such a color former and developer composition, the present inventors have developed a color developer having a long-chain aliphatic group that forms a color development state. Considering that the influence of the matrix resin on the crystallization in the decoloring process is large, various studies were conducted. As a result, it has been found that the above problem can be solved by using an amphoteric ion resin in the reversible thermosensitive recording layer.

That is, the said subject is solved by the following (1)-(4) of this invention.
(1) “Using an electron-donating color-forming compound and an electron-accepting compound on a support, a relatively colored state and a decolored state depending on the difference in heating temperature and / or cooling rate after heating. A reversible thermosensitive recording medium having a reversible thermosensitive recording layer that can be formed, wherein the reversible thermosensitive recording layer contains a zwitterionic resin ”,
(2) “The reversible thermosensitive recording medium according to (1) above, wherein the zwitterionic resin has a Zwitter ion structure”,
(3) In the item (1), wherein the zwitterionic resin has a cation group and an anion group, the cation group is a quaternary ammonium salt, and the anion group is a carboxyl group. Reversible thermosensitive recording medium ",
(4) The reversible thermosensitive recording medium according to any one of (1) to (3), wherein a phenol compound is used as the electron accepting compound.

  The reversible thermosensitive recording medium of the present invention can provide a highly practical rewrite recording having a good color density and excellent high-speed erasability.

The present invention is described in detail below.
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 of this recording medium and the temperature. 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. 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 development 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 recording medium of the present invention, the color development state (C) obtained by quenching from the molten state is a state in which the developer and the color former are mixed in a state where they can contact each other and form a solid state. Often doing. 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.
In the recording medium of the present invention, a coloring composition comprising a leuco dye (coloring agent) and a developer is particles dispersed in a matrix resin on a support, and the coloring and decoloring described above are carried out in these particles. Is done reversibly. It is considered that the more stable the colored aggregate structure, the higher the stability of the image, and the faster the single crystallization of the developer in the decoloring process, the better the high-speed erasability can be obtained. This characteristic is largely attributable to the molecular structure of the developer, and the stability of the color development state varies depending on the color former to be combined.

Furthermore, the present inventors have found that the matrix resin that envelops the coloring composition has a great influence on the coloring and decoloring properties from the results of various studies.
In particular, the colored leuco dye is considered to be polarized and in a highly polar state. Therefore, a highly polar matrix resin can interact strongly with the colored leuco dye with respect to the colored leuco dye. The reason why the reversibility of the reversible thermosensitive recording medium of the present invention is good is not clear, but the zwitterionic resin such as a material having Zwitter ions strongly interacts with the colored leuco dye in the decoloring process. By acting, there is a possibility that separation of the leuco dye and the developer is promoted.

The material having a Zwitter ion described in the present invention is a structure in which both ions of a cation (positive charge) and an anion (negative charge) coexist through a covalent bond, or an N-oxide structure (N ⁺ without a covalent bond). -O ^-) negative charge has an electrically structure having a bipolar structure comes on negative atoms such as oxygen (O), such as and, means that one total charge of the molecule is zero In addition, a cation compound represented by a quaternary ammonium salt, an anion compound represented by a sulfonium salt, etc. In addition, a compound having a carboxyl group and an amino group such as an aminocarboxylic acid (specifically, a non-ionized covalent compound) (specifically, α, β, γ, δ-amino acids) are also very different.

  As the zwitterionic resin used in the present invention, those having a Zwitter ion structure are preferably used, and those having a betaine structure are particularly preferably used. Further, those having a cation group and an anion group in the same molecule are also preferably used, and a quaternary ammonium salt is preferably used as the cation group, and a carboxyl group is preferably used as the anion group. An example is shown below.

Examples of the Zwitter ion resin used in the present invention include Zwitter ions such as methacryloyloxyethylcarboxybetaine, acryloyloxyethylcarboxybetaine, methacryloyloxypropylcarboxybetaine, methacryloyloxybutylcarboxybetaine, methacryloyloxyhexylcarboxybetaine, and methacryloyloxyoctylcarboxybetaine. Copolymerization of monomer with (meth) acrylate monomer such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, or styrenic monomer Coalescence is preferably used.
The molecular weight is preferably about 100,000 to 5,000,000. 500,000 to 2,000,000 is particularly preferable. If the molecular weight is too large, mixing with other resins becomes poor and non-uniform, which is not preferable. On the other hand, if the molecular weight is small, there is a problem that strength is insufficient and repeated durability is lowered.

(Example of betaine structure)
Examples of the material having a betaine structure used in the present invention include those represented by the following general formula.

Ｒ_１：アルキレン（炭素数１〜１０）特に好ましくはエチレン基、
Ｒ_２，Ｒ_３：メチル基、エチル基、（イソ）プロピル基。特に好ましくはメチル基。ｎは自然数。
具体的には、下記式で表わされる材料（式中、ｎは自然数）が挙げられる。

R ₁ : alkylene (C1-10), particularly preferably an ethylene group,
R ₂ and R ₃ : methyl group, ethyl group, (iso) propyl group. Particularly preferred is a methyl group. n is a natural number.
Specifically, a material represented by the following formula (wherein n is a natural number) can be mentioned.

(Example of cationic group having quaternary ammonium salt)
Examples of the quaternary ammonium salt used in the present invention include those represented by the following general formula.

Ｒ_１：アルキレン（炭素数１〜１０）特に好ましくはエチレン基、
Ｒ_２，Ｒ_３：メチル基、エチル基、（イソ）プロピル基、フェニル基。特に好ましくはメチル基またはフェニル基。ｎは自然数。
具体的には、下記式で表わされる材料が挙げられる。

R ₁ : alkylene (C1-10), particularly preferably an ethylene group,
R ₂ , R ₃ : methyl group, ethyl group, (iso) propyl group, phenyl group. Particularly preferred is a methyl group or a phenyl group. n is a natural number.
Specific examples include materials represented by the following formula.

(Example of anion group having carboxyl group)
Examples of the anionic group having a carboxyl group used in the present invention include those represented by the following general formula.

Ｒ_１：結合手、アルキレン（炭素数１〜１０）。ｎは自然数。
具体的には、下記式で表わされる材料が挙げられる。

R ₁ : bond, alkylene (C 1-10). n is a natural number.
Specific examples include materials represented by the following formula.

（式中、ｎは自然数を表わす。）

(In the formula, n represents a natural number.)

In addition to the above, a conventionally known acrylic monomer or the like may be copolymerized.
Examples of copolymerizable monomers include hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, tetrahydro Furfuryl (meth) acrylate, styrene, styrene-butadiene, styrene-isobutylene, ethylene vinyl acetate, vinyl acetate, methacrylonitrile, vinyl alcohol, vinyl pyrrolidone, acrylonitrile, methacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate , Propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, ethylhexyl ( Acrylate), octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, lauryl tridecyl (meth) acrylate, tridecyl (meth) acrylate, cetylstearyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (Meth) acrylate, 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 , Penta contactor ethylene glycol (meth) acrylate, butylene di (meth) acrylate, pentaerythritol tetra (meth) acrylate Chromatography, tri trimethylolpropane tri (meth) acrylate, pentaerythritol decaethylene glycol di (meth) acrylate, phthalic acid diethylene glycol di (meth) acrylate include, but are not particularly limited.

  The amount of the ionic resin used in the present invention is preferably 1 to 200% by weight, more preferably 3 to 100% by weight based on the developer. When the addition amount is 1% by weight or less, no effect is observed. When the addition amount is 200% by weight or more, problems such as a decrease in color density occur.

  As the leuco dye used in the reversible thermosensitive recording layer, one or more compounds generally used for this type of reversible thermosensitive recording medium can be used. For example, phthalide compounds, azaphthalide compounds, fluorane compounds It is a known dye precursor. Examples of these compounds are leuco dyes described in JP-A-5-124360, JP-A-6-210594, JP-A-10-230680 and the like. 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.

Examples of the developer used in the recording layer include, as representative examples, developers described in JP-A-5-124360, JP-A-6-210554, JP-A-10-95175, and the like. It is. The developer used here is a structure having a color developing ability for developing a leuco dye in the molecule, such as a phenolic hydroxyl group, a carboxylic acid group, or a phosphate group, and a structure that controls the cohesion between molecules, such as a long It is a compound having one or more structures in which chain hydrocarbon groups are linked. The linking moiety may be via 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. Specific examples of such a reversible developer are disclosed in, for example, JP-A-9-290563, JP-A-11-188969, and JP-A-11-99749, in addition to the above-mentioned publications.
Among them, a phenol compound having an aliphatic hydrocarbon group having 8 or more carbon atoms is particularly preferably used from the viewpoint of color developability / decolorability, and examples thereof include compounds having a structure represented by the following formula (1). It is done.

式中、Ｘ_１はヘテロ原子を含む２価の基または直接結合手を示し、Ｘ_２はヘテロ原子を含む２価の基を示す。Ｒ_１は２価の炭化水素基を表わし、Ｒ_１は炭素数８から２２の炭化水素基を表わす。また、Ｒ_２は炭素数８以上の脂肪族炭化水素基を示す。
ｐは０から４の整数を表わし、ｐが２から４の時繰り返されるＲ_１およびＸ_２は同一でも、異なっていても良い。また、ｑは１から３を表わす。
Ｘ_１，Ｘ_２で示されるヘテロ原子を含む２価の基は−ＮＨ−、−ＣＯ−、−Ｏ−、−Ｓ−、−ＳＯ_２−、−ＣＳ−またはこれらの組み合わせによってできる基を表わす。
以下にＸ_１，Ｘ_２を例示する。

In the formula, X ₁ represents a divalent group containing a hetero atom or a direct bond, and X ₂ represents a divalent group containing a hetero atom. R ₁ represents a divalent hydrocarbon group, and R ₁ represents a hydrocarbon group having 8 to 22 carbon atoms. R ₂ represents an aliphatic hydrocarbon group having 8 or more carbon atoms.
p represents an integer of 0 to 4, and when p is 2 to 4, R ₁ and X _{2 that} are repeated may be the same or different. Q represents 1 to 3;
The divalent group containing a hetero atom represented by X ₁ or X _{2 represents} a group formed by —NH—, —CO—, —O—, —S—, —SO ₂ —, —CS— or a combination thereof. .
Examples of X ₁ and X ₂ are given below.

また、以下に本発明で用いられるフェノール顕色剤の好ましい例を挙げるが、本発明はこれらに限られるものではない。

Moreover, although the preferable example of the phenol developer used by this invention below is given, this invention is not limited to these.

  In the present invention, it is preferable to use a cross-linked resin in the reversible thermosensitive recording layer. Specifically, acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, phenoxy resin, polyvinyl butyral resin, cellulose acetate. Resin having a group that reacts with a cross-linking agent such as propionate and cellulose acetate butyrate, or a resin obtained by copolymerizing a monomer having a group that reacts with a cross-linking agent and other monomers, and the like. The material is not limited.

  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. Resin, polyurethane polyol resin, and the like are used, and polyester polyol resin and acrylic polyol resin are preferably used because of particularly good color stability and good decoloring property. 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 present inventors have found that durability, coating film surface hardness, and crack resistance are improved when the hydroxyl value is 70 (KOHmg / g) or more.

  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 curing agent used in the present invention include conventionally known isocyanates, amines, phenols, and epoxy compounds. Of these, isocyanate curing agents are 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. The isocyanate monomer that forms the modified product includes 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, the total amount of the curing agent may or may not undergo a crosslinking reaction.
That is, an unreacted curing agent may be present. Since this type of crosslinking reaction proceeds over time, the presence of an unreacted curing agent does not indicate that the crosslinking reaction has progressed at all, but an unreacted curing agent is detected. However, this does not mean that there is no resin in a crosslinked state. Further, as a method for distinguishing whether the polymer in the present invention is in a crosslinked state or in a non-crosslinked state, it can be distinguished by immersing the coating film in a highly soluble solvent. That is, since the polymer in the non-crosslinked state dissolves in the solvent and does not remain in the solute, the presence or absence of the polymer structure of the solute may be analyzed.

  Furthermore, according to the present invention, the recording layer contains a color development / decoloration control agent having a linear hydrocarbon group, a hydrogen bond group such as an amide group or a urea group, and the like together with the developer and the leuco dye. As a result, the storage stability of the color image is good, and the erasability at the time of erasing is also improved to obtain good erasability.

Further, 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, the same thermosetting resin, ultraviolet curable resin, and electron beam curable resin as those used for the recording layer are used.
As the resin used in the protective layer, an ultraviolet absorbing polymer having an ultraviolet absorbing group in the molecular structure is particularly 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.

The support for the reversible thermosensitive recording medium of the present invention is paper, resin film, PET film, synthetic paper, metal foil, glass or a composite thereof, and the like, as long as it can hold the thermosensitive 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 μm to about several mm is used.
Moreover, when providing the said under layer on these support bodies, generation | occurrence | production of a crack and generation | occurrence | production of a burr | flash are improved by providing through an contact bonding layer.
The adhesive layer can be formed by the same coating method as that for each of the above layers.

Image formation using the reversible thermosensitive recording medium of the present invention uses an image recording means such as a thermal head or a laser that can partially heat the medium on the image. For erasing the image, an image erasing means such as a hot stamp, a ceramic heater, a heat roller, hot air, a thermal head, or a laser is used.
Among these, a ceramic heater is preferably used. By using a ceramic heater, the apparatus can be miniaturized, a stable erased state can be obtained, and an image with good contrast can be obtained.
The set temperature of the ceramic heater is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and even more preferably 115 ° C. or higher.
Further, by using a thermal head as the image erasing means, it is possible to further reduce the size of the entire apparatus, to reduce power consumption, and to realize a battery-driven handy type apparatus. If a single thermal head is used for both forming and erasing, the size can be further reduced.
When forming and erasing with a single thermal head, once the previous image has been erased, a new image may be formed again. The energy is changed for each image, and the previous image is erased at one time. It is also possible to use an overwrite method that forms the film.
In the overwrite method, the time required for forming and erasing is reduced, and the recording speed is increased. In the case of using a card having a reversible thermosensitive recording layer and an information storage unit, the above device includes means for reading and rewriting the memory of the information storage unit.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the text, “part” or “%” is based on weight unless otherwise specified.

(Example 1)
[Creation of thermal recording layer]
N- (4-hydroxyphenyl) -N'-octadecylurea 4 parts Acrylic polyol resin 9 parts (LR503, solid content concentration 50% solution manufactured by Mitsubishi Rayon Co., Ltd.)
N-methacryloyloxyethyl N, N-dimethylammonium-α-N-methyl carboxybetaine, methacrylic acid alkyl ester copolymer 1 part (RAM Organic Resin 2000, Osaka Organic Chemical Industry Co., Ltd.)
70 parts of methyl ethyl ketone

The composition was pulverized and dispersed to a mean particle size of about 1 μm using a ball mill. To the obtained dispersion, 1.5 parts of 2-anilino-3-methyl-6-dibutylaminofluorane and 2 parts of Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. are added and stirred well. A thermal recording layer coating solution was prepared.
The thermal recording layer coating solution having the above composition was applied to white PET having a thickness of 188 μm using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to form a recording layer having a thickness of about 11.0 μm. Was established.

[Create protection layer]
40% solution of UV-absorbing polymer (UV-G300 manufactured by Nippon Shokubai Co., Ltd.) 10 parts Isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., Coronate HX) 1.4 parts Silicone-based acrylic resin (GS-1015 manufactured by Toagosei Co., Ltd.) 0 .5 parts Methyl ethyl ketone 10 parts The above composition was well stirred to prepare a protective layer coating solution.
A protective layer coating solution having the above composition is applied onto the recording layer using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to provide a protective layer having a thickness of about 3.5 μm. The reversible thermosensitive recording medium of the invention was produced.

(Example 2)
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the following thermosensitive recording layer coating solution was used.
[Creation of thermal recording layer]
N- (4-hydroxyphenyl) -N'-octadecyl urea 4 parts Acrylic polyol resin 9 parts (LR503, Mitsubishi Rayon Co., Ltd., solid content concentration 50% solution)
Acrylamide, acrylic acid, methacrylic acid N, N-dimethylaminoethyl copolymer
1 part (Diafricks KA005, made by Diamond Nitrix)
(Molecular weight: 4,000,000)
70 parts of methyl ethyl ketone The above composition was pulverized and dispersed to a mean particle size of about 1 μm using a ball mill. To the obtained dispersion, 1.5 parts of 2-anilino-3-methyl-6-dibutylaminofluorane and 2 parts of Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. are added and stirred well. A thermal recording layer coating solution was prepared.

(Example 3)
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the following thermosensitive recording layer coating solution was used.
[Creation of thermal recording layer]
N- (4-hydroxyphenyl) -N'-octadecylurea 4 parts Acrylic polyol resin 9 parts (LR503, solid content concentration 50% solution manufactured by Mitsubishi Rayon Co., Ltd.)
Acrylamide, acrylic acid, 2- (acryloyloxy) ethyltrimethylammonium chloride, 2- (methacryloyloxy) ethyltriethylammonium chloride copolymer 1 part (Diafricks KA804E,
(Molecular weight: 700,000,000)
70 parts of methyl ethyl ketone The above composition was pulverized and dispersed to a mean particle size of about 1 μm using a ball mill. To the obtained dispersion, 1.5 parts of 2-anilino-3-methyl-6-dibutylaminofluorane and 2 parts of Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. are added and stirred well. A thermal recording layer coating solution was prepared.

(Comparative Example 1)
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the following thermosensitive recording layer coating solution was used.
[Creation of thermal recording layer]
N- (4-hydroxyphenyl) -N'-octadecylurea 4 parts Acrylic polyol resin 9 parts (LR503, solid content concentration 50% solution manufactured by Mitsubishi Rayon Co., Ltd.)
70 parts of methyl ethyl ketone The above composition was pulverized and dispersed to a mean particle size of about 1 μm using a ball mill. To the obtained dispersion, 1.5 parts of 2-anilino-3-methyl-6-dibutylaminofluorane and 2 parts of Coronate HL (adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. are added and stirred well. A thermal recording layer coating solution was prepared.

The reversible thermosensitive recording medium produced as described above was tested as follows.
An image was printed under the conditions of a pulse width of 2.0 msec and a voltage of 18 V using a printing simulator manufactured by BCOM, and the color density of the printed portion and the background density of the non-printed portion were measured using a Macbeth densitometer RD914. Next, the obtained color image was erased at a heating temperature of 130 ° C. and a linear speed of 40 mm / s using an erasing tester having a heat roller having a diameter of 2 cm. Table 1 shows the density of the coloring portion (image portion) and the background portion, and the concentration of the original coloring portion (original image portion) after the decoloring operation as a result of the erasing test.

Example 4
The same procedure as in Example 1 was conducted except that N- (4-carboxymethylphenyl) -N′-octadecylurea was used instead of N- (4-hydroxyphenyl) -N′-octadecylurea used in Example 1. A reversible thermosensitive recording medium was prepared.

(Example 5)
The same procedure as in Example 2 was conducted except that N- (4-carboxymethylphenyl) -N′-octadecyl urea was used instead of N- (4-hydroxyphenyl) -N′-octadecyl urea used in Example 2. A reversible thermosensitive recording medium was prepared.

(Example 6)
The same procedure as in Example 3 was conducted except that N- (4-carboxymethylphenyl) -N′-octadecyl urea was used instead of N- (4-hydroxyphenyl) -N′-octadecyl urea used in Example 3. A reversible thermosensitive recording medium was prepared.

(Comparative Example 2)
The same procedure as in Comparative Example 1 was performed except that N- (4-carboxymethylphenyl) -N′-octadecyl urea was used instead of N- (4-hydroxyphenyl) -N′-octadecyl urea used in Comparative Example 1. A reversible thermosensitive recording medium was prepared.

About the reversible thermosensitive recording medium produced as mentioned above, the test was implemented as follows similarly to Examples 1-3 and the comparative example 1. FIG.
An image was printed under the conditions of a pulse width of 2.0 msec and a voltage of 18 V using a printing simulator manufactured by BCOM, and the color density of the printed portion and the background density of the non-printed portion were measured using a Macbeth densitometer RD914. Next, the obtained color image was erased at a heating speed of 130 ° C. and a linear speed of 30 mm / s using an erasing tester having a heat roller having a diameter of 2 cm. Table 2 shows the density of the coloring portion (image portion) and the background portion, and the density of the original coloring portion (original image portion) after the erasing operation as a result of the erasing test.

It is a figure which shows the color development and decoloring characteristic of the reversible thermosensitive coloring composition of this invention.

Claims (4)

Reversible that can form a relatively colored state and a decolored state on the support using an electron-donating color-forming compound and an electron-accepting compound, depending on the heating temperature and / or the cooling rate after heating. A reversible thermosensitive recording medium comprising a reversible thermosensitive recording layer, wherein the reversible thermosensitive recording layer contains a zwitterionic resin. The reversible thermosensitive recording medium according to claim 1, wherein the zwitterionic resin has a Zwitter ion structure. The reversible thermosensitive recording medium according to claim 1, wherein the zwitterionic resin has a cation group and an anion group, the cation group is a quaternary ammonium salt, and the anion group is a carboxyl group. . The reversible thermosensitive recording medium according to any one of claims 1 to 3, wherein a phenol compound is used as the electron-accepting compound.

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