JP2005199704A - Reversible thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible thermal recording medium with a hollow particle-containing intermediate layer, by which a color-developed image is highly densified, void is reduced, the uniformity of the image is improved and the enlargement of an erasable energy region is contrived. <P>SOLUTION: In this reversible thermal recording medium, a recording layer comprised of a reversible thermal color developing composition utilizing the color-developing reaction between an electron donative colorable compound and an electron acceptive compound and a binder resin is provided on a support. As the electron acceptive compound, a specific phenolic compound is employed. Further, the hollow particle-containing intermediate layer is provided between the support and the recording layer. The hollow particles have a void ratio of at least 70% and the maximum particle diameter (D100) of the hollow particles is 5.0-10.0 μm and the ratio D100/D50 of the maximum particle diameter (D100) to the particle diameter (D50) at 50% frequency is 2.0-3.0. Furthermore, the width of an erasable energy region in the erasion with a thermal head is at least 0.1 mJ/dot. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention uses a reversible thermosensitive coloring composition utilizing a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound, and can control the formation of a color image and erase it by controlling thermal energy. More particularly, the present invention relates to a reversible thermosensitive recording medium having an intermediate layer (undercoat layer) between a support and a thermosensitive recording layer and having improved image density and erasing characteristics. .

  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 are disclosed (for example, 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 a developer (for example, see Patent Document 3), those using a compound such as phenolphthalein or thymolphthalein as a developer (for example, patents) Reference 4), a recording layer containing a homogeneous solution of a color former, a developer and a carboxylic acid ester (see, for example, Patent Documents 5 to 7), a developer using an ascorbic acid derivative as a developer (for example, And Patent Document 8), and those using a salt of bis (hydroxyphenyl) acetic acid or gallic acid and a higher aliphatic amine as a developer (for example, see Patent Documents 9 and 10).

  Furthermore, by using an organic phosphoric acid compound, aliphatic carboxylic acid compound or phenol compound having a long-chain aliphatic hydrocarbon group as a developer, and combining this with a leuco dye as a color former, coloring and decoloring can be achieved. A reversible thermosensitive coloring composition that can be easily performed under heating and cooling conditions, can stably maintain its coloring state and decoloring state at room temperature, and can repeat coloring and decoloring, and A reversible thermosensitive recording medium using this as a recording layer has been developed (for example, see Patent Documents 11 to 13).

However, these recording media are not always satisfactory in terms of color development sensitivity and image density, and improvements have been demanded. Several methods have already been disclosed as methods for improving the color density and color sensitivity, and one of them is a method of providing an intermediate layer having a heat insulating effect between the reversible recording layer and the support. is there.
For example, a method for setting an intermediate layer using hollow silica (for example, see Patent Document 14), a method for setting an intermediate layer using micro hollow particles of styrene-acryl (for example, see Patent Documents 15 and 16), hollow A method of installing an intermediate layer using a carboxyl group-containing copolymer latex (for example, see Patent Documents 17 and 18) is disclosed.
Furthermore, a method of disposing an intermediate layer using hollow particles of vinylidene chloride or porous alumino-silicate as a heat insulating layer is disclosed (for example, see Patent Document 19).
These methods are intended to increase the efficiency of heat applied by placing a layer made of hollow particles between the reversible thermosensitive recording layer and the support, so that the concentration can be increased accordingly. Effectiveness is recognized. However, the hollow particles used in these methods are limited in terms of the material and the production method, because they have either a low hollow rate or a large particle size. And a material satisfying both “small particle size” were not used. When particles having a low hollow ratio are used (for example, in the case of an intermediate layer using styrene-acrylic fine hollow particles having a hollow ratio of about 50% disclosed in Patent Documents 15 and 16), the heat insulation effect is slight. Only the effect could be exhibited, and the effect of increasing the concentration was never satisfactory. Further, when the particle size is large (for example, an intermediate layer using hollow particles of vinylidene chloride having a particle size of about 20 μm disclosed in Patent Document 19 and hollow silica having a particle size of about 40 μm disclosed in Patent Document 14). In the case of the used intermediate layer), the particle diameter of the hollow particles increases with respect to the thickness of the intermediate layer, and large irregularities are formed on the surface of the intermediate layer. As a result, when a reversible thermosensitive recording layer is laminated on it, a part with large particles on the surface of the intermediate layer is a part where the reversible thermosensitive recording layer is not formed, and white spots are likely to occur when a solid image is printed. It was never satisfactory for high concentration.

  Further, the erasing characteristics of the reversible thermosensitive recording medium have an erasing density that is practically possible with the erasing method using the heat roller, but the erasing density using the thermal head is insufficient. The phenomenon is remarkable, and improvement in this respect is strongly desired. Also, expanding the erasable energy range is important for enabling thermal head erasing, and this point has not yet reached a satisfactory level.

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 2003-11514 A JP-A-6-340174 JP-A-8-183254 JP 7-228050 A Japanese Patent Laid-Open No. 7-257036 Japanese Patent No. 3007899

  An object of the present invention is to improve the above-mentioned drawbacks of the prior art, increase the density of a color image, reduce white spots, improve image uniformity, and at the same time erase the density with an erasing method using a thermal head. Another object of the present invention is to provide a reversible thermosensitive recording medium having a hollow particle-containing intermediate layer that is excellent and further expands the erasable energy range.

  The present invention, as a result of intensive research on the hollow particles and binders used when providing an intermediate layer having heat insulation between the support and the reversible thermosensitive recording layer, the above-mentioned problems can be achieved by employing the following means. The present invention was found out to solve the problem. That is, it is inherently desirable to find that the appropriate binder is slightly different for each hollow particle used, and to consider the compatibility for achieving the purpose of the hollow particle having a specific particle size and hollowness and the binder resin. In the process of consideration, we came to note. Furthermore, as a result of conducting parallel studies on electron-accepting compounds and control agents used in the reversible thermosensitive recording layer, it has become possible to improve color development characteristics and erasing characteristics, leading to the present invention.

  That is, the above-described problem is solved by (1) “a reversible thermochromic composition utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound and a binder resin on the support. The recording layer forms a colored state by heating and cooling above the melting temperature of the composition, decolored by heating below the melting temperature, this decolored state is maintained by cooling, and A reversible thermosensitive recording medium in which this color development and decoloration state is repeated, wherein the electron-accepting compound has a long-chain aliphatic group having 10 or more carbon atoms as a partial structure and an active hydrogen-containing group capable of hydrogen bonding A compound is used, and an intermediate layer containing hollow particles is provided between the support and the recording layer. The hollow particles have a hollow ratio of 70% or more and a maximum particle diameter of the hollow particles ( D100) is 5.0 to 10.0 μm At the same time, the ratio D100 / D50 to the 50% frequency particle diameter (D50) is 2.0 to 3.0, and the width of the erasable energy region in erasing using a thermal head is 0.1 mJ / a reversible thermosensitive recording medium characterized in that it is a dot or more ", (2)" The material forming the hollow particles is a copolymer of acrylonitrile and / or methacrylonitrile "(1 The reversible thermosensitive recording medium according to the item), (3) “The material forming the hollow particles is a copolymer containing a monomer-derived structural unit represented by the following general formula (1): The reversible thermosensitive recording medium according to item (1) or (2);

（式中、Ｒは水素またはメチル基を表わす。）」、（４）「前記中間層の結着剤として疎水性エマルジョン樹脂、紫外線硬化樹脂、水溶性樹脂が用いられていることを特徴とする前記第（１）項乃至第（３）項のいずれかに記載の可逆性感熱記録媒体」、（５）「前記結着剤を中空粒子に対して１００〜２００重量％含有することを特徴とする前記第（１）項乃至第（４）項のいずれかに記載の可逆性感熱記録媒体」、（６）「前記電子受容性化合物が下記一般式（２）で表わされる化合物であることを特徴とする前記第（１）項乃至第（５）項のいずれかに記載の可逆性感熱記録媒体；

(In the formula, R represents hydrogen or a methyl group.), (4) “Hydrophobic emulsion resin, ultraviolet curable resin, water-soluble resin is used as the binder of the intermediate layer. The reversible thermosensitive recording medium according to any one of (1) to (3) above, (5) “100 to 200% by weight of the binder with respect to the hollow particles”. The reversible thermosensitive recording medium according to any one of items (1) to (4) ”, (6)“ The electron-accepting compound is a compound represented by the following general formula (2): The reversible thermosensitive recording medium according to any one of (1) to (5), characterized in that:

（式中、ｌは０〜２の自然数、ｍは０または１、ｎは１〜３の整数を示し、Ｘ，ＹはＮ原子またはＯ原子を含む２価の基を表わす。また、Ｒ_１は置換基を有していてもよい炭素数２以上の脂肪族炭化水素基を表わし、Ｒ_２は炭素数１以上の脂肪族炭化水素基を表わす。）」、（７）「前記可逆性感熱記録層中に消色促進剤を含有することを特徴とする前記第（１）項乃至第（６）項のいずれかに記載の可逆性感熱記録媒体」、（８）「前記可逆性感熱記録層上に該感熱記録層を保護するための保護層を有し、該保護層が架橋状態にある樹脂を含有することを特徴とする前記第（１）項乃至第（７）項のいずれかに記載の可逆性感熱記録媒体」によって解決される。
また、上記課題は、本発明の（９）「情報記憶部と可逆表示部を有し、該可逆表示部が少なくとも前記第（１）項乃至第（８）項のいずれかに記載の可逆性感熱記録媒体を構成する可逆性感熱記録層からなるものであることを特徴とする情報記録部を有する部材」、（１０）「前記情報記憶部を有する部材が、カード、ディスク、ディスクカートリッジ又はテープカセットのいずれかであることを特徴とする前記第（９）項に記載の情報記憶部を有する部材」、（１１）「前記第（１）項乃至第（８）項のいずれかに記載の可逆性感熱記録媒体を構成する支持体の可逆性感熱記録層を形成する面とは反対の面に、接着剤層又は粘着剤層を有することを特徴とする可逆性感熱記録ラベル」、（１２）「情報記憶部と可逆表示部を有し、前記情報記憶部を有する部材が、カード、ディスク、ディスクカートリッジ又はテープカセットのいずれかであり、前記可逆表示部が、前記第（１１）項に記載の可逆性感熱ラベルであることを特徴とする部材」によって解決される。
また、上記課題は、本発明の（１３）「前記第（１）項乃至第（８）項のいずれかに記載の可逆性感熱記録媒体、前記第（１２）項に記載の可逆性感熱記録ラベル、又は前記第（１０）項，（１１）項，（１２）項のいずれかに記載の情報記憶部を有する部材の可逆性感熱記録層を加熱することにより画像の形成及び／又は消去を行なうことを特徴とする画像処理方法」、（１４）「サーマルヘッドを用いて画像を形成することを特徴とする前記第（１３）項に記載の画像処理方法」、（１５）「サーマルヘッド又はセラミックヒータを用いて画像を消去することを特徴とする前記第（１３）項に記載の画像処理方法」によって解決される。
また、上記課題は、本発明の（１６）「前記第（１）項乃至第（８）項のいずれかに記載の可逆性感熱記録媒体、前記第（１２）項に記載の可逆性感熱記録ラベル又は前記第（１０）項，（１１）項，（１２）項のいずれかに記載の情報記憶部を有する部材を搭載し、画像の形成及び／又は消去を行なう手段を具備してなることを特徴とする画像処理装置」、（１７）「画像の形成手段がサーマルヘッドであることを特徴とする前記第（１６）項に記載の画像処理装置」、（１８）「画像の消去手段がサーマルヘッド又はセラミックヒータであることを特徴とする前記第（１６）項に記載の画像処理装置」によって解決される。

(In the formula, l represents a natural number of 0 to 2, m represents 0 or 1, n represents an integer of 1 to 3, X and Y represent a divalent group containing an N atom or an O atom, and R _1. Represents an aliphatic hydrocarbon group having 2 or more carbon atoms which may have a substituent, and R ₂ represents an aliphatic hydrocarbon group having 1 or more carbon atoms.) ”, (7)“ Reversible thermosensitive The reversible thermosensitive recording medium according to any one of (1) to (6) above, wherein the recording layer contains a decoloring accelerator ”, (8)“ Reversible thermosensitive recording ” Any of (1) to (7) above, further comprising a protective layer for protecting the thermosensitive recording layer on the layer, wherein the protective layer contains a resin in a crosslinked state. The reversible thermosensitive recording medium described in “1.”
In addition, the above-mentioned problem is (9) “having an information storage unit and a reversible display unit” according to the present invention, and the reversible display unit is at least a reversible feeling according to any one of the items (1) to (8). A member having an information recording section characterized by comprising a reversible thermosensitive recording layer constituting a thermal recording medium ”, (10)“ the member having the information storage section is a card, a disk, a disk cartridge, or a tape The member having the information storage unit according to the item (9), which is any one of cassettes, and the component according to any one of the items (1) to (8), A reversible thermosensitive recording label comprising an adhesive layer or a pressure-sensitive adhesive layer on the surface opposite to the surface on which the reversible thermosensitive recording layer of the support constituting the reversible thermosensitive recording medium is formed ", (12 ) "The information storage unit and the reversible display unit, the information A member having a memory part is any one of a card, a disk, a disk cartridge, and a tape cassette, and the reversible display part is the reversible thermosensitive label according to item (11). Solved by.
Further, the above-mentioned problems are solved by (13) “reversible thermosensitive recording medium according to any one of (1) to (8)” and reversible thermosensitive recording according to (12). Image formation and / or erasure is performed by heating the label or the reversible thermosensitive recording layer of the member having the information storage section according to any one of the items (10), (11), and (12). An image processing method characterized in that it is performed ", (14)" an image processing method according to item (13) above, wherein an image is formed using a thermal head ", and (15)" a thermal head or This is solved by the image processing method according to item (13), wherein the image is erased using a ceramic heater.
Further, the above-mentioned problems are solved by (16) “reversible thermosensitive recording medium according to any one of (1) to (8)” and reversible thermosensitive recording according to (12). A device having a label or a member having the information storage section according to any one of (10), (11), and (12), and means for forming and / or erasing an image is provided. (17) “The image processing apparatus according to (16) above, wherein the image forming means is a thermal head”, (18) “The image erasing means is This is solved by the image processing apparatus according to item (16), which is a thermal head or a ceramic heater.

  The thermosensitive recording medium of the present invention is provided with a recording layer comprising a reversible thermochromic composition and a binder resin utilizing a color developing reaction between an electron donating color former and an electron accepting compound on a support, The recording layer forms a colored state by heating and cooling above the melting temperature of the composition and is decolored by heating below the melting temperature. The decolored state is maintained by cooling, and the colored and decolored state is maintained. A reversible thermosensitive recording medium, wherein the electron-accepting compound is a phenol compound having a long-chain aliphatic group and an active hydrogen-containing group capable of hydrogen bonding as a partial structure, and the support and the recording layer An intermediate layer containing hollow particles is provided between the hollow particles, the hollow ratio of the hollow particles is 70% or more, and the maximum particle diameter (D100) of the hollow particles is 5.0 to 10.0 μm. % Frequency particle size (D50) and By using hollow particles having a ratio D100 / D50 of 2.0 to 3.0, heat insulation is improved, image density can be improved, erasing density can be reduced, and the erasing energy region can be expanded. It is clear that the prevention of cracking and image definition have been achieved.

In the present invention, it is possible to remarkably improve the erasing characteristics when a thermal head is used as an erasing method. In that case, an important characteristic is expansion of an erasable energy region.
FIG. 6 shows the image density (= erasing density) with respect to the erasing energy in the thermal head erasing method. As can be seen from the figure, the erasing characteristic shows a change in which the image density is convex downward with respect to energy. This indicates that an erased state is formed in an energy region below the melting temperature of the recording layer, but a colored state is formed in an energy region above the melting temperature of the recording layer. Naturally, it is obvious that it is important as an erasing characteristic that the image density is as small as possible, but if the erasing image density is at the same level, the energy range for obtaining the erasing image density is wide. Is preferred. That is, when the reversible thermosensitive recording medium is actually used, the temperature of the reversible thermosensitive recording medium slightly changes even if the energy applied by the surrounding temperature environment is the same. Therefore, if the erasable energy width is small, the erasure image density changes greatly with respect to the change in temperature environment during use, and the erasure characteristic becomes unstable. On the other hand, when the erasable energy width is large, it is possible to obtain a stable erasing characteristic with a small erasing image density against a change in temperature environment during use. Therefore, in the thermal head erasing method, it is important to expand the erasable energy region.

  In the present invention, when erasing by the thermal head erasing method, a case where the erased image density is 0.3 or less is determined as an erased state. When the erased image density exceeds 0.3, it is possible to visually recognize the image before erasure, and since the erase level is insufficient, the erased image density of 0.3 or less is the erase level. Thus, an energy region having an image density of 0.3 or less at the time of erasing is an erasing energy width.

  In the present invention, the erasable energy width is preferably 0.1 mJ / dot or more. When the density is smaller than 0.1 mJ / dot, a phenomenon occurs in which the erased image density increases and the erasing characteristics deteriorate when the thermal head is erased in a low temperature environment or a high temperature environment. The erasable energy width is preferably large, but 0.5 mJ / dot or less is preferable in consideration of actual use.

In the present invention, for the expansion of the erasing energy region in the thermal head system, an intermediate layer containing hollow particles is installed, and the hollow particles have a hollow ratio of 70% or more, and the maximum particle diameter of the hollow particles (D100 ) Is 5.0 to 10.0 μm, and at the same time, it is possible to use hollow particles having a ratio D100 / D50 of 2.0 to 3.0 with a 50% frequency particle diameter (D50). discovered.
The 50% frequency particle size means the particle size when the cumulative percentage reaches 50% when the particle size distribution is expressed in cumulative percentage from the smallest.

  In the present invention, the maximum particle diameter of the hollow particles is preferably 5 to 10 μm. However, when the diameter is larger than 10 μm, when a heat-sensitive recording layer is provided on the intermediate layer using these, the large particle portion of the intermediate layer is heat-sensitive. A portion where the recording layer is not formed is formed, and white spots are likely to occur when a solid image is printed. On the other hand, when it is smaller than 5 μm, it becomes difficult to ensure a hollow ratio of 70% or more, and as a result, the sensitivity is lowered. Therefore, the maximum particle size of the hollow particles is preferably 5 to 10 μm. Further, considering only the increase in the color density, the effect can be obtained if the hollow ratio is 60% or more, but the reversible thermosensitive recording medium has an erasing process. In the erasing method using, the energy used for erasing is extremely small compared to the method using a heat roller, and therefore, the degree of effective utilization of applied energy needs to be increased. Therefore, in order to ensure the erasing density and the erasing energy range expansion in the erasing method using the thermal head, the hollow ratio of the hollow particles used in the intermediate layer is required to be 70% or more.

  In the present invention, the ratio D100 / D50 of the 50% frequency particle diameter (D50) and the maximum particle diameter (D100) of the hollow particles is preferably 2.0 to 3.0, but if larger than 3.0, the particle diameter This indicates that the distribution is in a broad state, the proportion of fine particles having a particle diameter of 1 μm or less increases, and the intermediate layer using these causes a phenomenon in which the distribution of hollow particles in the layer becomes non-uniform and sensitivity decreases. . On the other hand, when it is less than 2.0, it has a very sharp particle size distribution and is difficult to realize from the viewpoint of synthesis conditions. Therefore, the ratio D100 / D50 of the 50% frequency particle diameter (D50) and the maximum particle diameter (D100) of the hollow particles is preferably 2.0 to 3.0.

  In the present invention, the proportion of hollow particles of 2 μm or less is preferably 5 to 10%. However, when the proportion exceeds 10%, the proportion of fine particles having a particle diameter of 1 μm or less increases, and the intermediate layer using these particles is contained in the layer. The distribution of the hollow particles becomes non-uniform and the sensitivity is lowered. On the other hand, if it is less than 5%, it has a very sharp particle size distribution and is difficult to realize from the viewpoint of synthesis conditions. Therefore, the proportion of hollow particles of 2 μm or less is preferably 5 to 10%.

  The hollow particles used in the present invention have a hollow ratio of 70% or more and at the same time the maximum particle diameter (D100) of the hollow particles is 5.0 to 10.0 μm and at the same time a particle diameter (D50) with a frequency of 50%. The ratio D100 / D50 is characterized by satisfying 2.0 to 3.0. Conventionally, it has not been known to use hollow particles that satisfy this condition for a reversible thermosensitive recording material. Conventionally, hollow particles used in reversible thermosensitive recording materials require a method of encapsulating a volatile substance in a thermoplastic polymer and volatilizing and foaming in order to achieve a hollowness of 60% or more. Had only hollow particles of 20 μm or more. On the other hand, in order to reduce the particle size, there was a type having a particle size of 1 μm or less by discharging water from particles enclosing water or the like using seed polymerization, but the hollow ratio was only 50% or less. . In the present invention, the hollow ratio is 70% or more and the maximum particle diameter (D100) of the hollow particles is 5.0 to 10.0 μm from the examination of the shell material, the polymerization method, and the volatile inclusion agent, and the particle diameter is 50% frequency. Hollow particles satisfying the ratio D100 / D50 of (D50) of 2.0 to 3.0 can be obtained, and their performance is sequentially determined through repeated trials for the first development in a reversible thermosensitive recording material. As a result of confirmation, a good reversible thermosensitive recording material could be realized.

  In the present invention, the Tg of the hollow particles is preferably 95 to 150 ° C, more preferably 95 ° C to 120 ° C. When Tg is lower than 95 ° C., an intermediate layer using these is fused with the thermosensitive coloring layer during printing with a thermal head, and as a result, sticking occurs and it becomes difficult to achieve good printing. On the other hand, when the temperature is higher than 150 ° C., the intermediate layer is in a rigid state at the time of printing with the thermal head and the flexibility is insufficient, so that a phenomenon that the adhesion with the head is lowered and the sensitivity is lowered is observed. The Tg is preferably 95 to 150 ° C.

  As described above, the hollow ratio of the intermediate layer of the heat-sensitive recording medium is 70% or more, the maximum particle size (D100) is 10.0 μm or less, preferably 5.0 to 10.0 μm, and the particle size with a frequency of 50%. The ratio D100 / D50 of (D50) to the maximum particle size (D100) is 3.0 or less, preferably 2.0 to 3.0, and the ratio of 2 μm or less is 10% or less, preferably 5 to 10%, By using hollow particles with a Tg of 95 ° C. or higher, preferably 95 to 150 ° C., heat insulation and head adhesion are improved, and the heat of the thermal head is efficiently transferred to the surface of the thermal recording medium, thereby achieving high sensitivity. In addition, the surface of the heat-sensitive recording medium is kept uniform to prevent the occurrence of printing whitening, and the uniformity of the printed image is improved.

The particle size values referred to in the present invention are all measured using a laser diffraction particle size distribution measuring device (Horiba Commissioned LA-900). The median diameter is a 50% frequency particle size, denoted as D50, and the maximum particle size is the maximum particle size of the distribution, denoted as D100. The hollowness of the plastic spherical hollow fine particles is a ratio of the outer diameter to the inner diameter of the hollow particles, and is expressed by the following formula.
Hollowness (%) = (inner diameter of hollow particles / outer diameter of hollow particles) × 100

  Tg used in the present invention is the glass transition temperature, and represents the Tg of the resin component of the hollow particles. This is one in which a solid is formed of the same resin as the resin component of the hollow particles, and Tg is measured for the solid by a usual method (DSC, DTA, TMA, etc.).

  In the present invention, since the hollow particles act as a heat insulating material and have elasticity, the thermal energy from the thermal head is efficiently used to improve the color development sensitivity. From the viewpoint of sensitivity, the hollow ratio is 70% or more, preferably 75 to 98%, and more preferably 85% to 95% hollow particles. When the hollow ratio is less than 70%, the above effect is small, and when the hollow ratio exceeds 98%, the film thickness becomes thin and the strength is poor.

  Various methods for producing hollow particles have been proposed. As a method for producing the hollow particles of the present invention, there is a method in which a volatile substance is included as a core material of a polymer, an outer layer is made of a thermoplastic polymer, and is volatilized and foamed. Usually used. Specific methods include those disclosed in WO / 43758, WO 99/46320, and JP 2000-24488. In this method, in order to increase the hollow ratio to 70% or more during heating and foaming, it is a requirement that the permeability of the shell material is low. Conventional polymers containing vinylidene chloride have low permeability but have environmental problems. Therefore, the present inventors have found that by using a crosslinked vinyl polymer instead of vinylidene chloride as a shell material for hollow particles having low permeability, the permeability can be lowered and the hollow ratio can be increased to 70% or more. It was.

  As the vinyl polymer used in the present invention, monomers having a carboxylic acid in the molecule such as acrylic ester, ethylene, propylene, vinyl acetate, styrene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, succinic acid, itaconic acid, Carboxylic acid metal salts such as magnesium acrylate, calcium acrylate, zinc acrylate, magnesium methacrylate, calcium methacrylate, zinc methacrylate, N-methylolacrylamide having a group reactive with carboxylic acid in the molecule, N-methylol methacrylamide, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2 Hydroxy-3-phenoxypropyl acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl methacrylate, magnesium monoacrylate, zinc monoacrylate, acrylamide, methacrylamide, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, methyl methacrylate, t-butyl methacrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, benzyl methacrylate, N-vinylpyrrolidone, styrene, N-phenylmaleimide, N-naphthylmaleimide, N -Cyclohexylmaleimide, methylmaleimide and the like.

  The hollow particles need to have a high hollow ratio and a thin shell. When the shell is thinned, the strength against pressure and the like is weakened and the shell is easily broken. On the other hand, if the shell is simply hardened to give strength, it tends to become brittle and is easily broken by bending. Therefore, a balance between hardness and flexibility is necessary for the shell material, and acrylonitrile and methacrylonitrile are listed as preferable shell materials having both hardness and flexibility. However, of course, the hollow particles having the above-mentioned particle size and hollow ratio are not arrogantly considered to be realized only by the specific shell material, polymerization method, and volatile inclusion agent. It cannot be denied that this is feasible.

The hollow particles used in the present invention can also form a crosslinked structure.
A material for forming a crosslinked structure, that is, a crosslinking agent, can be achieved by copolymerizing a bifunctional or higher monomer together with the vinyl monomer. Also suitable are vinyl monomers or divinylbenzene having two or more vinyl groups per molecule. The following are typical examples of this crosslinkable monomer.
Ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1.6-hexanediol di (meth) acrylate, trimethylolpropane Tri (meth) acrylate, glycerin di (meth) acrylate, triethylene glycol di (meth) acrylate, PEG # 200 di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, 1 , 3-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol Tetrale (meth) acrylate, pentaerythritol hexa (meth) acrylate 3-acryloyloxyglycerin monoacrylate, dimethylol tricyclodecane di (meth) acrylate, triallyl formal tri (meth) acrylate, polyethylene glycol dimethacrylate, triethylene glycol General crosslinking such as diacrylate, neopentyl glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2'-bis (4-acryloxydiethoxyphenyl) propane, trimethylolpropane trimethacrylate, diaryl phthalate, divinylbenzene, etc. Monomer can be used. As the crosslinkable monomer, a monomer that does not contain a halogen atom such as a chlorine atom is used, and in order to make the maximum particle size of the hollow particles 10 μm or less, the particle size distribution of the formed hollow particles is sharp. For this purpose, the copolymer containing the acrylic monomer represented by the formula (1) has a characteristic that the particle size distribution of the particles becomes sharp, and exhibits an excellent effect in this respect. . The terminal of the crossed bond of norbornane which is the left ring of the formula (1) is hydrogen, but may be a methyl group. The amount of the crosslinking agent used in the present invention is preferably about 0.1 to 10% in the monomer.

In producing actual microcapsules, conventional methods for producing foamable microcapsules are generally used. That is, a colloidal silica gel is used as the aqueous dispersant. A water-soluble polymer compound is used as an auxiliary dispersant.
As the water-soluble polymer, amphoteric or cationic water-soluble polymers such as diethanolamine adipic acid condensate, polyethyleneimine, and polyvinylpyrrolidone polymers are used.

In the present invention, an inorganic metal salt is used in order to use a large amount of a water-soluble monomer. As the water-soluble metal salt, a compound that dissolves in water in a neutral or acidic region such as sodium chloride, magnesium chloride, or sodium sulfate is used.
The amount used is a concentration from the saturation amount to the aqueous mixture to (saturation amount -5%). The said mixture is adjusted to pH 3-5 and made into an aqueous system.

  The oil phase is used by mixing it uniformly. The above-mentioned monomer mixture having a radical reactive unsaturated double bond, a solvent mixture having a boiling point suitable for synthesis, and a radical initiator mixture are used as the oil phase. As the solvent, an organic solvent having a boiling point equal to or lower than the temperature suitable for synthesis is used. Any solvent that does not dissolve in the outer wall polymer and has high foaming efficiency can be used. Hydrocarbon type solvents in the range of ° C are suitable for use. n-hexane, isohexane, n-heptane, n-octane, isooctane, n-decane, isodecane, and other petroleum fractionation components are used in a timely manner, but when a relatively low boiling point solvent is used, the foaming start temperature number decreases. There is a tendency.

As the radical initiator, two or more kinds are mixed and used. It is preferable to use two or more kinds of catalysts having a 10-hour half-life temperature difference of 20 ° C. or more in order to eliminate the remaining acrylonitrile monomer. The catalyst that can be used may be either a peroxide type or an azobis type, but those having a 10-hour half-life of 0 to 130 ° C, preferably 20 to 100 ° C are preferred.
Specifically, diisopropyl peroxycarbonate, dioctyl peroxydicarbonate, t-butyl peroxylaurate, lauroyl peroxide, dioctanoyl peroxide, benzoyl peroxide, azobisisobutyronitrile, azobis (2,4- Dimethylvaleronitrile), 1,1-azobis (cyclohexane-1-carbonitrile), dimethyl 2,2′-azobis (2-methylpropionate), etc. are used, and azobisisobutyronitrile and 1,1- The combined use of azobis (cyclohexane-1-carbonitrile) or the combined use of azobis (2,4-dimethylvaleronitrile) and 1,1-azobis (cyclohexane-1-carbonitrile) is more preferable.

  The present invention uses hollow particles to improve sensitivity, which is one of the characteristics of the above particles, and uses a hydrophobic emulsion resin, an ultraviolet curable resin, a water-soluble resin, etc. as the binder, and the content thereof is changed to hollow particles. On the other hand, it has been found that the sensitivity can be greatly improved by setting the binder to 100 to 300% by weight, preferably 100 to 200% by weight. This is considered to be a result of further improving the smoothness of the surface of the intermediate layer by filling the voids of the hollow particles filled in the intermediate layer. When the binder is less than 100% by weight, the voids of the hollow particles remain. For this reason, the color density is lowered. On the other hand, when it exceeds 300% by weight, the proportion of the hollow particles in the intermediate layer is lowered, so that the heat insulating property of the intermediate layer is lowered and the sensitivity is lowered.

  Hydrophobic resins used in the intermediate layer include styrene / butadiene copolymer, latex of styrene / butadiene / acrylic ester copolymer, vinyl acetate, vinyl acetate / acrylic acid copolymer, styrene / acrylic ester copolymer, Examples thereof include emulsions such as acrylic ester resins and polyurethane resins. In addition, UV curable resins used for the intermediate layer include urethane acrylate water-soluble UV curable resins, epoxy acrylate water-soluble UV curable resins, alkoxy acrylate UV curable resins, polyurethane acrylate UV curable emulsions, acrylic monomers, urethane acrylics. Examples of such oligomers include ether-based urethane acrylate oligomers, ester-based urethane acrylate oligomers, and polyester acrylate oligomers. Further, the water-soluble resin used in the intermediate layer includes fully saponified polyvinyl alcohol, carboxyl modified polyvinyl alcohol, partially saponified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, silyl modified polyvinyl alcohol, acetoacetyl modified polyvinyl alcohol, diacetone modified polyvinyl. Examples include various modified polyvinyl alcohols such as alcohol.

  In the present invention, known water-soluble polymers can be used in combination as long as the quality such as sensitivity is not impaired. Known binders for water-soluble polymers and aqueous polymer emulsions include starch and derivatives thereof, cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic Examples thereof include acid ester copolymers, alkali salts of styrene / maleic anhydride, alkali salts of isobutylene / maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, casein, and the like. Water-soluble emulsions include styrene / butadiene copolymers, latexes of styrene / butadiene / acrylic ester copolymers, vinyl acetate, vinyl acetate / acrylic acid copolymers, styrene / acrylic ester copolymers, acrylic ester resins, and polyurethane resins. And the like.

In the present invention, it is possible to use an alkaline thickener in the intermediate layer in order to improve head matching. An alkaline thickener means a binder that thickens under alkaline conditions. A typical example of such an alkali thickening binder is an emulsion latex containing a styrene-butadiene copolymer as a main component. In the present invention, an alkali-thickening binder can be used alone, but in order to make the binder component stably exist as dispersed particles, for example, a carboxylated latex that is a copolymer of unsaturated carboxylic acid. Etc. are desirable. That is, when the pH of the carboxylated latex is increased, the highly carboxylated polymer on the particle surface is dissolved in water, so that the viscosity is increased, and thus the viscosity of the binder can be further improved. Since the undercoat layer according to the present invention has the above-described configuration, the dispersion stability of the plastic micro hollow particles is increased, so that a conventionally added thickener such as sodium montmorillonite or modified polyacrylic acid is added as in the past. There is no need to do. Further, since the alkali thickening binder firmly binds the hollow particles to each other in addition to the thickening action, matching with the thermal head is remarkably improved as compared with the case of using the thickening agent. The alkali thickening binder is desirably present in an amount of 1 to 80 parts, preferably 5 to 50 parts, per 100 parts of the hollow particles. The binder is preferably a styrene-butadiene copolymer, but is not limited to this, and any binder may be used as long as it thickens under alkaline conditions. In addition, a pH adjuster is required to keep the undercoat solution under alkali. As such, for example, NH ₃ water is used, but this is not limited unless it significantly inhibits color development. It is not what is done. In addition to the plastic micro-hollow particles and the alkali thickening binder, the undercoat layer may further contain auxiliary additive components commonly used in this type of heat-sensitive recording medium, such as fillers, heat-soluble substances, and surface active agents. An agent or the like can be used. In this case, specific examples of the filler and the heat-soluble material include various materials shown in relation to the reversible thermosensitive recording layer component in the following description.

  In the intermediate layer, together with the hollow particles and the binder, auxiliary additive components commonly used in this type of heat-sensitive recording medium, for example, fillers, heat-fusible components, surfactants, and the like are used as necessary. Can do. Moreover, in order to apply these intermediate layer components uniformly and at a higher speed, the viscosity of a 20% aqueous dispersion of hollow particles at a liquid temperature of 20 ° C. is 200 mPa.s. It is preferable that it is s or less. 200 mPa.s. When the viscosity exceeds s, the coating liquid prepared as described above has a high viscosity and uneven coating occurs. In addition, in order to smoothen the surface of the intermediate layer formed on the support as described above, the flat surface may be smoothed by calendering after forming the intermediate layer.

  In the present invention, the electron-accepting compound used for the reversible thermosensitive recording layer is preferably a compound represented by the general formula (2) from the viewpoint of color density and erasing properties.

（式中、ｌは０〜２の自然数、ｍは０または１、ｎは１〜３の整数を示し、Ｘ，ＹはＮ原子またはＯ原子を含む２価の基を表わす。また、Ｒ_１は置換基を有していてもよい炭素数２以上の脂肪族炭化水素基を表わし、Ｒ_２は炭素数１以上の脂肪族炭化水素基を表わす。）

(In the formula, l represents a natural number of 0 to 2, m represents 0 or 1, n represents an integer of 1 to 3, X and Y represent a divalent group containing an N atom or an O atom, and R _1. Represents an optionally substituted aliphatic hydrocarbon group having 2 or more carbon atoms, and R ₂ represents an aliphatic hydrocarbon group having 1 or more carbon atoms.)

In the general formula (2), the aliphatic hydrocarbon group may be linear or branched, and may have an unsaturated bond. Examples of the substituent attached to the hydrocarbon group include a hydroxyl group, a halogen atom, and an alkoxy group. When the sum of the carbons of R ₁ and R ₂ is 7 or less, the stability of color development and the decoloring property are lowered. Therefore, the number of carbons is preferably 8 or more, and more preferably 11 or more.
Preferable examples of R ₁ include the following.

これらの中でも−（ＣＨ_２）ｑ−が特に好ましい。
なお、式中のｑ、ｑ’、ｑ”、ｑ’”はそれぞれ前記Ｒ_１、Ｒ_２の炭素数を満足する整数を表わす。
また、Ｒ_２の好ましい例としては以下に示すものが挙げられる。

Among them - _(CH 2) q- are particularly preferred.
In the formula, q, q ′, q ″, and q ′ ″ each represent an integer that satisfies the carbon number of R ₁ and R ₂ .
Preferred examples of R ₂ include those shown below.

これらの中でも−（ＣＨ_２）ｑ−ＣＨ_３が特に好ましい。なお、式中のｑ、ｑ’、ｑ”、ｑ’”は前記と同じである。
Ｘ、ＹはＮ原子またはＯ原子を含む２価の基を示し、好ましくは

Among them _{- (CH 2) q-CH} 3 are particularly preferred. In the formula, q, q ′, q ″, and q ′ ″ are the same as described above.
X and Y represent a divalent group containing an N atom or an O atom, preferably

で表わされる基を少なくとも１個以上する２価の基を表わす。その例としては、以下示すものが挙げられる。

Represents a divalent group containing at least one group represented by the formula: The following are mentioned as the example.

これらのうち、特に好ましい基は次に示すものである。

Of these, particularly preferred groups are as follows.

更に、具体的なフェノール化合物としては、以下のものが挙げられる。ただし、本発明はこれらに限定されるものではない。

Furthermore, the following are mentioned as a specific phenol compound. However, the present invention is not limited to these.

（式中、ｒは２以上の整数、ｓは１以上の整数を表わす。）

(In the formula, r represents an integer of 2 or more, and s represents an integer of 1 or more.)

  In the present invention, the control agent used for the reversible thermosensitive recording layer is preferably a compound containing an amide group, a urethane group, a urea group, a ketone group, a diacyl hydrazide group or the like as a partial structure from the viewpoint of color density and erasing properties. Among these, compounds having an amide group, a secondary amide group, and a urethane group are particularly preferable, and specific examples include the following.

（式中、ｎ，ｎ’，ｎ”，ｎ’”，ｎ””は０〜２１の整数を示す。ただし全てが５以下であることはない。）

(In the formula, n, n ′, n ″, n ′ ″, n ″ ″ represent integers of 0 to 21. However, not all of them are 5 or less.)

_{C 11 H 23 CONHC 12 H 25} , C 15 H 31 CONHC 16 H 33, C 17 H 35 CONHC 18 H 37, C 17 H 35 CONHC 18 H 35, C 21 H 41 CONHC 18 H 37, C 15 H 31 CONHC ₁₈ H ₃₇ , C ₁₇ H ₃₅ CONHCH ₂ HNOCC ₁₇ H ₃₅ , C ₁₁ H ₂₃ CONHCH ₂ HNOCC ₁₁ H ₂₃ , C ₇ H ₁₅ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₅ , C ₉ H ₁₉ CONHC ₂ H ₄ HNOCC ₉ H ₁₉ , C ₁₁ H ₂₃ CONHC ₂ H ₄ HNOCC ₁₁ H ₂₃ , C ₁₇ H ₃₅ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₅ , (CH ₃ ) ₂ CHC ₁₄ H ₃₅ CONHC ₂ H ₄ HNOCC ₁₄ H ₃₅ (CH ₃ ) ₂ , C _{1 H 43 CONHC 2 H 4 HNOCC} 21 H 43, C 17 H 35 CONHC 6 H 12 HNOCC 17 H 35, C 21 H 43 CONHC 6 H 12 HNOCC 21 H 43, C 17 H 33 CONHCH 2 HNOCC 17 H 33, C ₁₇ H ₃₃ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₃ , C ₂₁ H ₄₁ CONHC ₂ H ₄ HNOCC ₂₁ H ₄₁ , C ₁₇ H ₃₃ CONHC ₆ H ₁₂ HNOCC ₁₇ H ₃₃ , C ₈ H ₁₇ NHCOC ₂ H ₄ CONHC ₁₈ H _{37 , C 10 H 21 NHCOC 2 H} 4 CONHC 10 H 21, C 12 H 25 NHCOC 2 H 4 CONHC 12 H 25, C 18 H 37 NHCOC 2 H 4 CONHC 18 H 37, C 21 H 43 NHOCC 2 H _{CONHC 21 H 43, C 18 H} 37 NHOCC 6 H 12 CONHC 18 H 37, C 18 H 35 NHCOC 4 H 8 CONHC 18 H 35, C 18 H 35 NHCOC 8 H 16 CONHC 18 H 35, C 12 H 25 OCONHC 18 H ₃₇ , C ₁₃ H ₂₇ OCONHC ₁₈ H ₃₇ , C ₁₆ H ₃₃ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ OCONHC ₁₈ H ₃₇ , C ₂₁ H ₄₃ OCONHC ₁₈ H ₃₇ , C ₁₂ H ₂₅ OCONHC ₁₆ H ₃₃ , C _{13 H 27 OCONHC 16 H 33, C} 16 H 33 OCONHC 16 H 33, C 18 H 37 OCONHC 16 H 33, C 21 H 43 OCONHC 16 H 33, C 12 H 25 OCONHC 14 H 29, C 13 _{27 OCONHC 14 H 29, C 16} H 33 OCONHC 14 H 29, C 18 H 37 OCONHC 14 H 29, C 22 H 45 OCONHC 14 H 29, C 12 H 25 OCONHC 12 H 37, C 13 H 27 OCONHC 12 H 37 C ₁₆ H ₃₃ OCONHC ₁₂ H ₃₇ , C ₁₈ H ₃₇ OCONHC ₁₂ H ₃₇ , C ₂₁ H ₄₃ OCONHC ₁₂ H ₃₇ , C ₂₂ H ₄₅ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ NHCOOC ₂ H ₄ OCONHC ₁₈ H ₃₇ , _{C 18 H 37 NHCOOC 3 H 6} OCONHC 18 H 37, C 18 H 37 NHCOOC 4 H 8 OCONHC 18 H 37, C 18 H 37 NHCOOC 6 H 12 OCONHC 18 H 37, C 18 H _{7 NHCOOC 8 H 16 OCONHC 18 H} 37, C 18 H 37 NHCOOC 2 H 4 OC 2 H 4 OCONHC 18 H 37, C 18 H 37 NHCOOC 3 H 6 OC 3 H 6 OCONHC 18 H 37, C 18 H 37 NHCOOC 12 H ₂₄ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ NHCOOC ₂ H ₄ OC ₂ H ₄ OC ₂ H ₄ OCONHC ₁₈ H ₃₇ , C ₁₆ H ₃₃ NHCOOC ₂ H ₄ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₃ H ₆ OCN ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₄ H ₈ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₆ H ₁₂ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₈ H ₁₆ OCONHC ₁₆ H _{33 , C 18 H 37 OCOHNC 6 H} 12 NHCOOC 18 H 37, C 16 H 33 OCOHNC 6 H 12 NHCOOC 16 H 33, C 14 H 29 OCOHNC 6 H 12 NHCOOC 14 H 29, C 12 H 25 OCOHNC 6 H 12 NHCOOC 12 H ₂₅ , C ₁₀ H ₂₁ OCOHNC ₆ H ₁₂ NHCOOC ₁₀ H ₂₁ , C ₈ H ₁₇ OCOHNC ₆ H ₁₂ NHCOOC ₈ H ₁₇ ,

Hereinafter, the reversible thermosensitive recording medium of the present invention will be described in more detail.
Examples of the binder resin used for forming the reversible thermosensitive recording layer include polyvinyl chloride, polyvinyl acetate, vinyl chloride vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, and aromatic polyester. , Polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, acrylic acid copolymer, maleic acid copolymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and starches.
The role of these binder resins is to keep the materials of the composition uniformly dispersed without being displaced by the application of heat for recording and erasing. Therefore, it is preferable to use a resin having high heat resistance as the binder resin. For example, the binder resin may be crosslinked with heat, ultraviolet light, electron beam, or the like.

  Specific examples of the crosslinked resin used in the present invention include acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, phenoxy resin, polyvinyl butyral resin, cellulose acetate propionate, and cellulose acetate butyrate. Examples thereof include a resin having a group that reacts with an agent, or a resin obtained by copolymerization of a monomer having a group that reacts with a crosslinking agent and another monomer, but the present invention is not limited to these compounds.

  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 urethane monomers, allophanate-modified, isocyanurate-modified, burette-modified, carbodiimide-modified, blocked isocyanate and the like. Examples of the isocyanate monomer forming the modified product include 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. Therefore, if the presence of a polymer structure in the solute cannot be confirmed, it can be said that the polymer is in a non-crosslinked state, and can be distinguished from a crosslinked polymer. Here, this can be expressed as a gel fraction.

  The gel fraction refers to the ratio of gel formation when a resin solute in a solvent loses its independent mobility due to interaction and assembles into an individualized state (gel). The resin preferably has a gel fraction of 30% or more, more preferably 50% or more, still more preferably 70% or more, and particularly preferably 80% or more. If the gel fraction is small, the durability will be reduced repeatedly. Therefore, in order to improve the gel fraction, a curable resin that is cured by heat, UV, EB or the like may be mixed in the resin, or the resin itself may be crosslinked. .

As a gel fraction measurement method, the membrane is peeled off from the support and the initial weight of the membrane is measured, and then the membrane is placed in a 400 mesh wire net and immersed in a solvent in which the resin before crosslinking is soluble for 24 hours. Then vacuum dry and measure the weight after drying.
The gel fraction calculation is performed according to the following formula.
Gel fraction (%) = [weight after drying (g) / initial weight (g)] × 100
When calculating the gel fraction by this calculation, the calculation is performed excluding the weight of organic low-molecular substance particles other than the resin component in the heat-sensitive layer. At this time, when the weight of the organic low molecular weight substance is not known in advance, the weight ratio is obtained from the area ratio per unit area and the specific gravity of the resin and the low molecular weight organic substance by cross-sectional observation such as TEM and SEM. The gel fraction value may be calculated by calculating the molecular substance weight.

  In the case of the above measurement, a reversible thermosensitive recording layer is provided on the support and another layer such as a protective layer is laminated thereon, or other layers are provided between the support and the thermosensitive layer. If there are other layers, as described above, first, the film thickness of the reversible thermosensitive recording layer and other layers is examined by observing the cross-section of the TEM, SEM, etc. And exposing the surface of the reversible thermosensitive recording layer, peeling the reversible thermosensitive recording layer, and measuring the gel fraction in the same manner as described above.

  In this method, when there is a protective layer made of an ultraviolet curable resin or the like in the upper layer of the reversible thermosensitive recording layer, the thickness of the protective layer is reduced and the reversible feeling is prevented in order to prevent this layer from being mixed as much as possible. The surface of the thermal recording layer must also be shaved slightly to prevent the influence on the gel fraction value.

Although the example of the leuco dye used by this invention is given to the following, this invention is not limited to these. In addition, leuco dyes can be used alone or in combination.
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-sec-butyl-N-methylamino) fluorane, 2 -Anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-iso-amyl-N-ethylamino) Luolan, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2- Anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-anilino-3-methyl-6- (N-methyl-p-toluidino) fluorane, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trichloromethylanilino) -3-methyl-6 (N-cyclohexyl-N-methylamino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluorane 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-ethylanilino) fluorane, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-propyl-p- Toluidino) fluoran, 2-anilino-6- (Nn-hexyl-N-ethylamino) fluorane, 2- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-chloroanilino) -6-dibutylamino Fluorane, 2- (m-trifluoromethylanilino) -6-diethylaminofluorane, 2,3-dimethyl-6-dimethylaminofluorane, 3-methyl-6- (N-ethyl-p-toluidino) fluorane 2-chloro-6-diethylaminofluorane, 2-bromo-6-diethylaminofluorane, 2-chloro-6-dipropylaminofluorane 3-chloro-6-cyclohexylaminofluorane, 3-bromo-6-cyclohexylaminofluorane, 2-chloro-6- (N-ethyl-N-isoamylamino) fluorane, 2-chloro-3-methyl-6 -Diethylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2- (o-chloroanilino) -3-chloro-6-cyclohexylaminofluorane, 2- (m-trifluoromethylanilino)- 3-chloro-6-diethylaminofluorane, 2- (2,3-dichloroanilino) -3-chloro-6-diethylaminofluorane, 1,2-benzo-6-diethylaminofluorane, 3-diethylamino-6- (M-trifluoromethylanilino) fluorane, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7- Azaphthalide, 3- (1-octyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindole-3- Yl) -3- (2-methyl-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl)- 7-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (4-diethylaminophenyl) -4-azaphthalide, 3- (1- Tyl-2-methylindol-3-yl) -3- (4-Nn-amyl-N-methylaminophenyl) -4-azaphthalide, 3- (1-methyl-2-methylindol-3-yl) -3- (2-hexyloxy-4-diethylaminophenyl) -4-azaphthalide, 3,3-bis (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3,3-bis (2-ethoxy-4) -Diethylaminophenyl) -7-azaphthalide.

As the color former used in the present invention, a conventionally known leuco dye can be used alone or in combination, in addition to the above-mentioned fluorane compound and azaphthalide compound. The color former is shown below.
2- (p-acetylanilino) -6- (Nn-amyl-Nn-butylamino) fluorane, 2-benzylamino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-benzylamino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-benzylamino-6- (N-methyl-p-toluidino) fluorane, 2-benzylamino-6- (N- Ethyl-p-toluidino) fluoran, 2- (di-p-methylbenzylamino) -6- (N-ethyl-p-toluidino) fluoran, 2- (α-phenylethylamino) -6- (N-ethyl- p-toluidino) fluorane, 2-methylamino-6- (N-methylanilino) fluorane, 2-methylamino-6- (N-ethylanilino) fluorane, 2-methylamino-6 (N-propylanilino) fluorane, 2-ethylamino-6- (N-methyl-p-toluidino) fluorane, 2-methylamino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2 -Ethylamino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-dimethylamino-6- (N-methylanilino) fluorane, 2-dimethylamino-6- (N-ethylanilino) fluorane, -Diethylamino-6- (N-methyl-p-toluidino) fluorane, 2-diethylamino-6- (N-ethyl-p-toluidino) fluorane, 2-dipropylamino-6- (N-methylanilino) fluorane, 2- Dipropylamino-6- (N-ethylanilino) fluorane, 2-amino-6- (N-methylanilino) fluorane, 2-amino-6- (N-ethylanilino) fluorane, 2-amino-6- (N-propylanilino) fluorane, 2-amino-6- (N-methyl-p-toluidino) fluorane, 2-amino-6 -(N-ethyl-p-toluidino) fluorane, 2-amino-6- (N-propyl-p-toluidino) fluorane, 2-amino-6- (N-methyl-p-ethylanilino) fluorane, 2-amino- 6- (N-ethyl-p-ethylanilino) fluorane, 2-amino-6- (N-propyl-p-ethylanilino) fluorane, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluorane 2-amino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N-propyl-2,4-dimethylanilino) fluoro 2-amino-6- (N-methyl-p-chloroanilino) fluorane, 2-amino-6- (N-ethyl-p-chloroanilino) fluorane, 2-amino-6- (N-propyl-p-chloroanilino) ) Fluorane, 1,2-benzo-6- (N-ethyl-N-isoamylamino) fluorane, 1,2-benzo-6-dibutylaminofluorane, 1,2-benzo-6- (N-methyl-N) -Cyclohexylamino) fluorane, 1,2-benzo-6- (N-ethyl-N-toluidino) fluorane, and others.

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

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

For the formation of the recording layer, a coating liquid prepared by uniformly mixing and dispersing the mixture of the developer, color former, various additives, curing agent, crosslinked resin and coating solvent is used.
Specific examples of the solvent used for preparing the coating liquid include water; alcohols such as methanol, ethanol, isopropanol, n-butanol, and methyl isocarbinol; acetone, 2-butanone, ethyl amyl ketone, diacetone alcohol, isophorone, and cyclohexanone. Ketones such as N; N-dimethylformamide, amides such as N, N-dimethylacetamide; ethers such as diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, and 3,4-dihydro-2H-pyran Glycol ethers such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, ethylene glycol dimethyl ether; 2-methoxyethyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl Glycol ether acetates such as acetate; Esters such as methyl acetate, ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylene carbonate; Aromatic hydrocarbons such as benzene, toluene, and xylene; Hexane, heptane, iso-octane Aliphatic hydrocarbons such as cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, dichloropropane, chlorobenzene; sulfoxides such as dimethyl sulfoxide; N-methyl-2-pyrrolidone, N-octyl Examples include pyrrolidones such as -2-pyrrolidone.

  The coating liquid can be prepared using a known coating liquid dispersing apparatus such as a paint shaker, a ball mill, an attritor, a three-roll mill, a keddy mill, a sand mill, a dyno mill, or a colloid mill. Moreover, each material may be disperse | distributed in a solvent using the said coating-liquid dispersion | distribution apparatus, and each may be disperse | distributed and mixed together in a solvent individually. Further, it may be dissolved by heating and precipitated by rapid cooling or cooling.

  The coating method for providing the recording layer is not particularly limited. Blade coating, wire bar coating, spray coating, air knife coating, bead coating, curtain coating, gravure coating, kiss coating, reverse roll coating Known methods such as coating, dip coating and die coating can be used.

  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, as long as it can hold the recording layer. Moreover, the thing of the thickness as needed can be used individually or by bonding. That is, a support having an arbitrary thickness from about several μm to about several mm is used. These supports may have a magnetic recording layer on the same surface and / or the opposite surface to the reversible thermosensitive recording layer. The reversible thermosensitive recording medium of the present invention may be attached to another medium via an adhesive layer or the like. Alternatively, a back coat layer is provided on one side of a support such as a PET film, the release layer used for the thermal transfer ribbon on the opposite side of the back coat layer, the thermal recording layer of the present invention on the release layer, and paper on the surface, A resin layer that can be transferred to a resin film, a PET film, or the like may be provided and transferred using a thermal transfer printer. The reversible thermosensitive recording medium of the present invention may be processed into a sheet shape or a card shape, and the shape can be processed into an arbitrary shape, and printing on the surface of the medium can be performed. In the reversible thermosensitive recording medium of the present invention, an irreversible thermosensitive recording layer may be used in combination, and at this time, the color tone of each recording layer may be the same or different.

As a method for drying / curing the recording layer, after coating and drying, a curing treatment is performed as necessary. A high temperature bath or the like may be used for a relatively short time at a relatively high temperature, or a heat treatment may be performed at a relatively low temperature for a long time. As specific conditions for the crosslinking reaction, it is preferable to heat from about 1 minute to 150 hours under a temperature condition of about 30 ° C. to 130 ° C. from the viewpoint of reactivity. More preferably, heating is performed for about 2 minutes to 120 hours under a temperature condition of 40 ° C to 100 ° C. In addition, since productivity is emphasized in production, it is difficult to take time until the crosslinking is sufficiently completed. Therefore, a crosslinking step may be provided separately from the drying step. As a condition for the crosslinking step, it is preferable to heat at a temperature of 40 ° C. to 100 ° C. for about 2 minutes to 120 hours.
The film thickness of the reversible thermosensitive recording layer is preferably in the range of 1 to 20 μm, more preferably 3 to 15 μm.

  Improvement of adhesion between reversible thermosensitive recording layer and protective layer, prevention of alteration of recording layer by application of protective layer, additive contained in protective layer migrates to recording layer, or additive contained in recording layer is protective layer An intermediate layer may be provided between the two for the purpose of preventing the transition. The thickness of the intermediate layer is preferably in the range of 0.1 to 20 μm, more preferably 0.3 to 10 μm. As the solvent used in the intermediate layer coating solution, the dispersion device of the coating solution, the binder, the coating method, the drying / curing method, etc., known methods used in the recording layer can be used.

  In the formation of the protective layer, the thickness of the protective layer is preferably in the range of 0.1 to 20 μm, more preferably 0.3 to 10 μm. The solvent used for the coating liquid of the protective layer, the dispersion apparatus of the coating liquid, the binder, the coating method, the drying / curing method, and the like can be known methods used for the recording layer.

  Other fillers that do not have ultraviolet absorbing performance or ultraviolet shielding performance may be added to the reversible thermosensitive recording layer, intermediate layer, and protective layer, and the filler can be divided into inorganic fillers and organic fillers. Inorganic fillers include calcium carbonate, magnesium carbonate, anhydrous silicic acid, hydrous silicic acid, hydrous aluminum silicate, hydrous calcium silicate, alumina, iron oxide, calcium oxide, magnesium oxide, chromium oxide, manganese oxide, silica, talc, Mica, etc. Organic fillers include silicone resins, cellulose resins, epoxy resins, nylon resins, phenolic resins, polyurethane resins, urea resins, melamine resins, polyester resins, polycarbonate resins, styrenes such as styrene, polystyrene, polystyrene / isoprene, and styrene vinylbenzene. Examples thereof include resins, acrylic resins such as vinylidene chloride acrylic, acrylic urethane, and ethylene acrylic, polyethylene resins, formaldehyde resins such as benzoguanamine formaldehyde, melamine formaldehyde, polymethyl methacrylate resins, and vinyl chloride resins. In the present invention, the filler can be used alone, but two or more kinds may be included. In the case of a plurality, there are no particular limitations on how to combine the inorganic filler and the organic filler. Examples of the shape include a spherical shape, a granular shape, a plate shape, and a needle shape. Content of the filler in a protective layer is 5-50 volume% by a volume fraction.

  A lubricant may be added to the reversible thermosensitive recording layer, intermediate layer, and protective layer. Specific examples of the lubricant include synthetic waxes such as ester wax, paraffin wax, and polyethylene wax: vegetable waxes such as hardened castor oil: Animal waxes such as beef tallow oil: Higher alcohols such as stearyl alcohol and behenyl alcohol: Higher fatty acids such as margaric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid: higher fatty acids such as sorbitan fatty acid ester Fatty acid esters: amides such as stearic acid amide, oleic acid amide, lauric acid amide, ethylene bis stearic acid amide, methylene bis stearic acid amide, and methylol stearic acid amide. The content of the lubricant in the layer is 0.1 to 95%, more preferably 1 to 75% in terms of volume fraction.

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. The basic coloring / decoloring phenomenon of the composition comprising the color former and developer used in the present invention 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), a molten colored state occurs coloration at temperatures T ₁ begins to melt (B). When rapidly cooled from the melt color state (B), the color state can be lowered to room temperature and a solid 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 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.

  The reversible thermosensitive recording label of the present invention is one in which an adhesive layer or a pressure-sensitive adhesive layer is provided on the surface opposite to the surface of the support constituting the reversible thermosensitive recording medium described above. This reversible thermosensitive recording label includes an adhesive layer or a pressure-sensitive adhesive layer (non-peeling paper type), and a release paper attached under the adhesive layer or pressure-sensitive adhesive layer (peeling paper type). As a material constituting the adhesive layer, a hot melt type material is usually used.

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

Next, a description will be given of a member that includes an information storage unit and a reversible display unit and includes a heat-sensitive layer constituting the above-described reversible thermosensitive recording medium as the reversible display unit.
The members having the information storage unit and the reversible display unit can be roughly classified into the following three items.
(1) A member having an information recording part is used as a support for a reversible thermosensitive recording medium, and a thermosensitive layer is directly formed.
(2) A member having an information recording unit and having a support surface of a reversible thermosensitive recording medium separately formed and having a thermosensitive layer on the support.
(3) The reversible thermosensitive recording label is bonded to a member having an information recording portion via an adhesive layer or an adhesive layer.
In these cases (1), (2), and (3), it is necessary to set each function of the information storage unit and the reversible display unit so that the setting position of the information storage unit is Further, it can be provided on the surface of the support opposite to the surface on which the heat-sensitive layer is provided in the thermoreversible recording medium, or between the support and the heat-sensitive layer, or on a part of the heat-sensitive layer.

The member used as the member having the information recording unit is not particularly limited, but generally there is a card, a disk, a disk cartridge, or a tape cassette.
The following can be mentioned as these examples.
Thick cards such as IC cards and optical cards, flexible disks, disk cartridges with built-in disks that can rewrite storage information such as magneto-optical recording disks (MD) and DVD-RAM, disks that do not use disk cartridges such as CD-RW A member having both the reversible display unit and the information storage unit, such as a write-once disc such as a CD-R, an optical information recording medium (CD-RW) using a phase change storage material, a video tape cassette, etc. In the case of, by displaying a part of the information stored in the information storage unit on the reversible thermosensitive recording layer, the cardholder etc. can confirm the information by just looking at the card without a special device Therefore, the convenience is greatly improved as compared with a card to which the reversible thermosensitive recording medium is not applied.

  The information storage unit is not particularly limited as long as it can store necessary information. For example, magnetic recording, contact IC, non-contact IC, or optical memory is useful. The magnetic recording layer is formed by coating the support using a commonly used metal compound such as iron oxide or barium ferrite and a resin such as vinyl chloride, urethane or nylon, or without using a resin. It forms by methods, such as vapor deposition and sputtering, using the said metal compound. Further, the reversible thermosensitive recording layer in the reversible thermosensitive recording medium used for display can also be used as a storage unit in a manner such as a barcode or a two-dimensional code.

As an example of using the reversible thermosensitive recording label of (3) above, if the reversible thermosensitive recording layer is difficult to apply as a support, such as a vinyl chloride card with a magnetic stripe, the entire surface or An adhesive layer or a pressure-sensitive adhesive layer can be provided in part. By doing so, the convenience of this medium can be improved, such as being able to display a part of the information stored in the magnetism.
The reversible thermosensitive recording label provided with the adhesive layer or the pressure-sensitive adhesive layer is applicable not only to the above-described magnetic PVC card but also to a thick card such as an IC card or an optical card.

Further, the reversible thermosensitive recording label can be used in place of a display label on a disk cartridge having a built-in disk capable of rewriting storage information such as a flexible disk, MD, and DVDRAM.
FIG. 2 shows an example in which a reversible thermosensitive recording label is pasted on an MD disk cartridge. Further, in the case of a disc that does not use a disc cartridge such as a CD-RW, a reversible thermosensitive recording label can be directly attached to the disc, or a reversible thermosensitive recording layer can be provided directly on the disc. By doing so, it is possible to apply to applications such as automatically changing display contents in accordance with changes in the stored contents.

FIG. 3 shows an example in which a reversible thermosensitive recording label is pasted on a CD-RW.
The reversible thermosensitive recording label of the present invention can also be displayed by rewriting a part of the stored information added to the CD-R by sticking the reversible thermosensitive recording label on a write-once disc such as a CD-R.
Further, as shown in FIG. 4, it may be used as a display label of a video tape cassette.

As a method of providing a thermoreversible recording function on a thick card, a disc cartridge, and a disc, in addition to the method of applying the reversible thermosensitive recording label, a method of directly applying a reversible thermosensitive recording layer on them, There is a method of forming a reversible thermosensitive recording layer on the support and transferring the thermosensitive recording layer onto a thick card, a disc cartridge, or a disc.
When transferring, an adhesive layer such as a hot melt type or an adhesive layer may be provided on the reversible thermosensitive recording layer.
When attaching a reversible thermosensitive recording label or providing a reversible thermosensitive recording layer on a rigid object such as a thick card, disk, disk cartridge, tape cassette, etc., improve the contact with the thermal head. In order to form an image uniformly, it is preferable to provide a cushioning layer or sheet between the rigid substrate and the label or the reversible thermosensitive recording layer.

  According to the present invention, there is further provided an image processing method and the reversible thermosensitive method, wherein the reversible thermosensitive recording medium, the member having the information storage unit or the label is used to form and / or erase an image by heating. An image processing apparatus having a recording medium, a member having the information storage unit or the label and forming and / or erasing an image by heating is provided.

  For image formation, an image recording means such as a thermal head, a laser or the like that can partially heat the medium on the image is used. 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. For that purpose, not only the surface smoothness but also the uniform dispersion of each material used in each layer is indispensable, and this is achieved by the present invention.
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.

FIG. 5 shows an example of the image processing apparatus of the present invention. FIG. 5 shows a schematic example of an apparatus for erasing an image with a ceramic heater and forming an image with a thermal head according to the present invention.
In the image processing apparatus of FIG. 5, first, information stored in the magnetic recording layer of the recording medium is read with a magnetic head, then the image recorded on the reversible thermosensitive recording layer is heated and erased with a ceramic heater, Based on the information read by the magnetic head, new processed information is recorded on the reverse heat-sensitive layer by the thermal head. Thereafter, the information on the magnetic recording layer is also rewritten with new information.

That is, in the image processing apparatus of FIG. 5, the thermoreversible recording medium having the magnetic recording layer provided on the opposite side of the thermosensitive layer is transported along the transport path shown by the reciprocating arrow, or along the transport path. Then it is transported in the reverse direction.
The thermoreversible recording medium is magnetically recorded or erased on the magnetic recording layer between the magnetic head (34) and the transport roller (40), and heat-treated for image erasure between the ceramic heater (38) and the transport roller (40). Then, an image is formed between the thermal head (53) and the conveying roller (47), and then carried out of the apparatus. However, the rewriting of the magnetic recording may be before or after the image erasure by the ceramic heater. If desired, after passing between the ceramic heater (38) and the transport roller (40), or after passing between the thermal head (53) and the transport roller (47), the transport path is transported in the opposite direction, and the ceramic heater ( The heat treatment according to 38) and the printing process again with the thermal head (53) can be performed.

Next, the present invention will be described in more detail with reference to examples. All parts and% shown below are based on weight.
<Preparation of hollow particles a>
Dissolve 55 g of sodium chloride in 160 g of ion-exchanged water, add 1.0 g of adipic acid-diethanolamine condensate and 25 g of colloidal silica 20% aqueous solution, adjust the pH from 3.8 to 4.2 with sulfuric acid, and uniformly Mix to make the aqueous phase. 45 g of acrylonitrile, 16 g of methacrylonitrile, 5 g of N-methylolacrylamide, 23 g of isobornyl methacrylate, 0.1 g of ethylene glycol dimethacrylate, 0.3 g of azobisisobutyronitrile, 1,1-azobis (cyclohexane-1-carbonitrile (V-40) 0.1 g and isobutane 15 g are mixed, stirred and dissolved to form an oil phase, which is mixed with an aqueous phase and an oil phase, and stirred with a homomixer at 4000 rpm for 1 minute. This was transferred to a separable flask and purged with nitrogen, and then reacted with stirring at 70 ° C. for 6 hours and then at 90 ° C. After the reaction, the mixture was cooled and filtered to obtain capsule particles. The foam was heated to form hollow particles, which were Tg, hollow rate, particle size D100, D100 / D of the hollow particles. 0 of the value shown in Table 1.
In the method for adjusting the hollow particles a, the hollow resin resin particles b were prepared in the same manner as the hollow particles a except that the number of revolutions of the homomixer was changed to 3500 rpm. Next, the hollow resin resin particle c was prepared by the same method as the hollow particle a except that N-methylolacrylamide was removed in the method for preparing the hollow particle a. Next, in the method for preparing the hollow particles a, hollow resin resin particles d were prepared in the same manner as the hollow particles a except that isooctane was used instead of isobutane. Next, in the method for preparing the hollow particles a, hollow particles e were prepared in the same manner as the hollow particles a except that the amount of isobornyl methacrylate was changed to 20 g. Next, in the method for preparing the hollow particles a, hollow particles f were prepared in the same manner as for the hollow particles a except that the amount of isobornyl methacrylate was changed to 15 g and the amount of acrylonitrile was changed to 55 g. Next, in the method for preparing the hollow particles a, hollow particles g were prepared in the same manner as the hollow particles a except that vinylidene chloride was used instead of isobornyl methacrylate. Table 1 shows the ratio D100 / D50 of the Tg of hollow particles b to g, the hollow ratio, the maximum particle size (D100), and the 50% frequency particle size (D50).

Example 1
<Preparation of intermediate layer>
Aqueous dispersion of hollow particles (hollow particles a in Table 1) (solid content concentration 30%) 30 parts Polyurethane resin emulsion (solid content concentration 35%, Superflex 150, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 28 parts (Solid content concentration 16%) 9 parts Water 50 parts The above mixture was stirred and dispersed to prepare an intermediate layer coating solution. The intermediate layer coating solution having the above composition is coated on a white PET film with a magnetic layer having a thickness of about 250 μm (manufactured by Dainippon Ink) using a wire bar, dried at 115 ° C. for 1 minute, and having a thickness of about 6.0 μm. An intermediate layer was provided.
<Preparation of reversible thermosensitive recording layer>
2-anilino-3-methyl-6-diethylaminofluorane 2 parts Developer with the following structure 8 parts

下記構造の制御剤 ２部

2 parts of control agent with the following structure

アクリルポリオール樹脂の１５％ＴＨＦ溶液 １５０部
（水酸基価：７０、酸価：１．０未満、分子量：３５０００、
ガラス転移温度：５２℃、
水酸基モノマー：２−ヒドロキシエチルメタクリレート）
コロネートＨＬ １０部
上記組成物をボールミルを用いて平均粒径０．１〜３μｍまでなるように粉砕分散した。得られた分散液で可逆性感熱記録層塗布液を調製した。
上記組成の該記録層塗布液を、前記中間層の上にワイヤーバーを用い塗布し、１１５℃１分で乾燥した後、６０℃３６時間加熱して、膜厚約１１．０μｍの可逆性感熱記録層を設けた。
＜保護層の作製＞
ウレタンアクリレート系紫外線硬化性樹脂
（大日本インキ社製Ｃ７−１５７） １５部
酢酸エチル ８５部
上記組成を良く攪拌し保護層液を調製した。この塗液を、上記記録層の上にワイヤーバーを用いて塗工し９０℃で１分間乾燥させたのち、照射エネルギー８０Ｗ／ｃｍの紫外線ランプ下９ｍ／分の搬送速度で通して硬化して膜厚約３μｍの保護層を設けて本発明の可逆性感熱記録媒体を作製した。

150 parts of 15% THF solution of acrylic polyol resin (hydroxyl value: 70, acid value: less than 1.0, molecular weight: 35000,
Glass transition temperature: 52 ° C.
Hydroxyl monomer: 2-hydroxyethyl methacrylate)
Coronate HL 10 parts The above composition was pulverized and dispersed using a ball mill to an average particle size of 0.1 to 3 µm. A reversible thermosensitive recording layer coating solution was prepared from the obtained dispersion.
The recording layer coating solution having the above composition is coated on the intermediate layer using a wire bar, dried at 115 ° C. for 1 minute, and then heated at 60 ° C. for 36 hours to have a reversible thermosensitive film thickness of about 11.0 μm. A recording layer was provided.
<Preparation of protective layer>
Urethane acrylate UV curable resin (C7-157 manufactured by Dainippon Ink & Co.) 15 parts Ethyl acetate 85 parts The above composition was well stirred to prepare a protective layer solution. This coating solution is applied onto the recording layer using a wire bar, dried at 90 ° 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. A protective layer having a thickness of about 3 μm was provided to produce a reversible thermosensitive recording medium of the present invention.

Example 2
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the hollow particles b were used in place of the hollow particles a in Example 1.

Example 3
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the hollow particles c were used in place of the hollow particles a in Example 1.

Example 4
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1 except that the hollow particles d were used in place of the hollow particles a in Example 1.

Example 5
Reversible in the same manner as in Example 1 except that an acrylic resin emulsion (solid content concentration 35%, Johnson's John Krill 538) was used instead of the polyurethane resin emulsion (Daiichi Kogyo Seiyaku, Superflex 150) in Example 1. A heat-sensitive recording medium was produced.

Example 6
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the intermediate layer was formed by the following method in Example 1.
<Preparation 2 of intermediate layer>
Aqueous dispersion of hollow particles (hollow particles a in Table 1) (solid content concentration 30%) 30 parts Urethane acrylate UV curable resin emulsion (solid content concentration 35% / Arakawa Chemical Industries Beam Set EM-90) 28 parts Darocur 1173 0.5 parts Complete saponified polyvinyl alcohol aqueous solution (solid content concentration 16%) 9 parts Water 50 parts The above mixture was stirred and dispersed to prepare an intermediate layer coating solution. The intermediate layer coating solution having the above composition is coated on a white PET film with a magnetic layer having a thickness of about 250 μm (manufactured by Dainippon Ink) using a wire bar, dried at 90 ° C. for 1 minute, and irradiated energy of 80 W / cm. Was cured by passing at a conveyance speed of 9 m / min under an ultraviolet lamp, and an intermediate layer having a thickness of about 6 μm was provided.

Example 7
In Example 6, a urethane acrylate-based ultraviolet curable resin emulsion (solid content concentration 35% / DICEL CB DW7825) was used instead of the urethane acrylate-based ultraviolet curable resin emulsion (Arakawa Chemical Industries Beam Set EM-90). Produced a reversible thermosensitive recording medium in the same manner as in Example 7.

Example 8
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the hollow particles e were used in place of the hollow particles a in Example 1.

Example 9
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1 except that the hollow particles f were used in place of the hollow particles a in Example 1.

Comparative Example 1
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1 except that the hollow particles g were used in place of the hollow particles a in Example 1.

Comparative Example 2
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that Fuji Balloon S35 (particle diameter 40 μm) manufactured by Fuji Silysia Chemical Co., Ltd. was used instead of the hollow particles a in Example 1.

Comparative Example 3
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1 except that Micropearl F-30 (particle diameter 20 μm) manufactured by Matsumoto Yushi Seiyaku Co., Ltd. was used instead of the hollow particles a in Example 1.

Comparative Example 4
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1, except that Ropeke HP-91 (hollow rate: 50%, particle size: 1 μm) manufactured by Rohm & Haas was used in place of the hollow particles a.

Comparative Example 5
A reversible thermosensitive recording medium was produced in the same manner as in Example 1 except that the intermediate layer was not provided in Example 1.

(Evaluation methods)
(1) Image Density, Erase Density, Erase Energy Region Using the reversible thermosensitive recording medium produced using a thermal printing simulator manufactured by Yashiro Seisakusho using an EUX-ET8A9AS1 end face type thermal head (resistance value 1152 ohm) manufactured by Matsushita Electronic Components Co., Ltd. Printing and erasing were performed under the following conditions, and the density was measured using a Macbeth densitometer RD-914.
Evaluation conditions: pulse width 2 ms, line period 2.86 ms, printing speed 43.10 mm / s, sub-scanning density 8 dots / mm
Image density: The maximum density when printing is performed by changing the voltage in the range of applied energy of 0.25 mJ / dot to 0.62 mJ / dot.
-Erase density: When a solid image is formed with the applied energy that obtains the maximum density at the above image density, and the applied energy is erased by changing the voltage in the range of 0.15 mJ / dot to 0.52 mJ / dot. Minimum erase density is used.
Erase energy region: An energy width in which the erase density is less than 0.3 in the erase density evaluation is used.
(2) White spots; white spots were determined by visual observation of the color image of the image density evaluation.
○: No whiteout ×: Whiteout (3) Fineness: A print image in which the image density is 0.6 in the image density evaluation print sample is visually confirmed with a microscope for the fineness of 1-dot printing. The finer the better the one-dot shape (square) is (see Table 2).

以上の評価結果を表３に示す。

The above evaluation results are shown in Table 3.

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 example which stuck the reversible thermosensitive recording label on the disk cartridge of MD. It is a figure which shows the example which stuck the reversible thermosensitive recording label on CD-RW. It is a figure which shows the example used as a display label of a videotape cassette. It is a figure which shows the example of the image processing apparatus of this invention. It is the figure which showed the mode of the image density (= erase density) with respect to the erase energy in the thermal head erase system of this invention.

Explanation of symbols

34 Magnetic head 38 Ceramic heater 40 Transport roller 47 Transport roller 53 Thermal head

Claims (18)

On a support, there is a recording layer comprising a reversible thermochromic composition utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound and a binder resin, and the recording layer has the composition Reversible thermosensitive recording in which a colored state is formed by heating and cooling above the melting temperature of the product, decolored by heating below the melting temperature, this decoloring state is maintained by cooling, and this coloring and decoloring state is repeated As the electron-accepting compound, a phenol compound having a long-chain aliphatic group having 10 or more carbon atoms as a partial structure and an active hydrogen-containing group capable of hydrogen bonding is used as the medium, and the support and the recording layer An intermediate layer containing hollow particles is provided between the hollow particles, and the hollow particles have a hollow ratio of 70% or more and the maximum particle diameter (D100) of the hollow particles is 5.0 to 10.0 μm. At the same time, 50% frequency particle size (D50 The ratio D100 / D50 is 2.0 to 3.0, and the width of the erasable energy region in erasing using a thermal head is 0.1 mJ / dot or more, which is reversible thermosensitive recoding media. The reversible thermosensitive recording medium according to claim 1, wherein the material forming the hollow particles is a copolymer of acrylonitrile and / or methacrylonitrile. The reversible thermosensitive recording medium according to claim 1 or 2, wherein the material forming the hollow particles is a copolymer containing a structural unit derived from a monomer represented by the following general formula (1).

(In the formula, R represents hydrogen or a methyl group.) The reversible thermosensitive recording medium according to any one of claims 1 to 3, wherein a hydrophobic emulsion resin, an ultraviolet curable resin, or a water-soluble resin is used as a binder for the intermediate layer. The reversible thermosensitive recording medium according to any one of claims 1 to 4, wherein the binder is contained in an amount of 100 to 200% by weight based on the hollow particles. The reversible thermosensitive recording medium according to any one of claims 1 to 5, wherein the electron-accepting compound is a compound represented by the following general formula (2).

(In the formula, l represents a natural number of 0 to 2, m represents 0 or 1, n represents an integer of 1 to 3, X and Y represent a divalent group containing an N atom or an O atom, and R _1. Represents an optionally substituted aliphatic hydrocarbon group having 2 or more carbon atoms, and R ₂ represents an aliphatic hydrocarbon group having 1 or more carbon atoms.) The reversible thermosensitive recording medium according to any one of claims 1 to 6, wherein the reversible thermosensitive recording layer contains a decolorization accelerator. The protective layer for protecting the thermosensitive recording layer is provided on the reversible thermosensitive recording layer, and the protective layer contains a resin in a crosslinked state. Reversible thermosensitive recording medium. An information storage unit and a reversible display unit, wherein the reversible display unit comprises at least a reversible thermosensitive recording layer constituting the reversible thermosensitive recording medium according to any one of claims 1 to 8. A member having an information recording unit. The member having an information storage unit according to claim 9, wherein the member having the information storage unit is any one of a card, a disk, a disk cartridge, and a tape cassette. 9. An adhesive layer or a pressure-sensitive adhesive layer is provided on a surface opposite to a surface on which a reversible thermosensitive recording layer of the support constituting the reversible thermosensitive recording medium according to claim 1 is formed. A reversible thermosensitive recording label. The reversible thermosensitive device according to claim 11, further comprising: an information storage unit and a reversible display unit, wherein the member having the information storage unit is a card, a disk, a disk cartridge, or a tape cassette. A member characterized by being a label. A reversible thermosensitive recording medium according to any one of claims 1 to 8, a reversible thermosensitive recording label according to claim 12, or a member having an information storage section according to any one of claims 10, 11 and 12. An image processing method comprising forming and / or erasing an image by heating a reversible thermosensitive recording layer. The image processing method according to claim 13, wherein an image is formed using a thermal head. The image processing method according to claim 13, wherein the image is erased using a thermal head or a ceramic heater. A reversible thermosensitive recording medium according to any one of claims 1 to 8, a reversible thermosensitive recording label according to claim 12, or a member having the information storage section according to any one of claims 10, 11 and 12. And an image processing apparatus comprising means for forming and / or erasing an image. The image processing apparatus according to claim 16, wherein the image forming unit is a thermal head. The image processing apparatus according to claim 16, wherein the image erasing means is a thermal head or a ceramic heater.

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