JP4868802B2 - Thermal recording medium, method for producing the same, and image forming method - Google Patents

Description

The present invention relates to a heat-sensitive recording medium utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound, a method for producing the heat- sensitive recording medium , and an image forming method . Gravure printing, offset printing And screen printing, screen printing plate printing plate-making film (image forming) sheet, overhead projector (hereinafter abbreviated as OHP) image forming film sheet, CAD image forming film sheet, etc. . In particular, it is intended to diagnose and refer to images such as X-rays, MRI, CT, etc. with reflection or transmission images by Saucusten, and can obtain the same high image quality, density and image storage stability as a silver salt film. The present invention relates to a heat-sensitive recording medium suitable as a medical image forming sheet.

  Conventionally, a heat-sensitive recording layer containing an electron donating color developing compound (hereinafter also referred to as a color former) and an electron accepting compound (hereinafter also referred to as a color developer) is formed on a support such as paper. Thermal recording media using a color development reaction between the two are widely known. A major problem with this recording method is that the heat is transferred directly from the thermal head and recording is performed by heating, so the surface layer of the recording medium that is in direct contact with the thermal head (generally called the over layer or protective layer) ), And a proposal for improving the head matching property has been made as an invention by devising a resin, a lubricant, a filler, etc. of the protective layer (see, for example, Patent Documents 1, 2, 3, and 4). .

  This heat-sensitive recording medium is used by customers as products such as facsimile recording paper, product labels or magnetic ticket paper, but in recent years a heat-sensitive recording medium produced using a translucent film as a support, so-called transparent Since the color image is projected onto the thermal recording medium, a wide range of applications using this property has been developed, and it has been expanded to be used for overhead projectors, the second original drawing of diazo, or for design drawings. It is also used as a plate-making film for plate making such as printing, offset printing and screen printing, and has been proposed to improve transparency and head matching (see, for example, Patent Documents 5, 6, 7 and 8).

  On the other hand, in general, a heat-sensitive recording medium for medical use has a very low translucency of the entire recording material or a reflection type in which an image is viewed by light reflection and a translucency of the entire recording material. There is a transmission type that uses light. The image characteristic level required for these is a very high level as compared with conventional applications. Furthermore, it is much higher than the latter transmission type and the former reflection type. This thermal recording medium can be used for making plate making for lithographic printing using a thermal recording medium on which an image is formed as a plate, in addition to medical treatment in which the formed image is examined by a backlight using the Schaukasten method. The heat-sensitive recording medium thus prepared can be used for OHP. Especially for medical applications that use a highly transparent and heat-sensitive recording medium that examines images with the backlight of the Schoukasten method, because it is for diagnosis, the target of recording is shape information such as the built-in human body or bones. It is important that images recognized by the backlight are excellent in terms of contrast and contrast, and that the original shape information is accurately displayed, and placed in a high-temperature and high-humidity environment. Is expected to retain the image for more than 10 years. Therefore, in heat-sensitive recording media, especially in medical applications, a much higher level of performance is required compared to conventional leuco-type heat-sensitive recording media. In addition, it has been proposed that a developer of the following general formula (1) is effective in order to achieve transparency, light resistance, and pure blackening, including a polyvinyl acetal resin (see, for example, Patent Document 9). ).

（式中、Ｒ１は炭素数４乃至１６の直鎖のアルキル基又はアルキルアミノ基を表わす。）
しかし、特に医療用途においては、記録速度の更なる高速化と共に非常に高精細な画像品質を要求されてきている。つまり、記録速度の高速化に伴い、短時間での高電力を印加する条件に対し、これまで以上に加熱によるヘッドカス付着や表面強度、さらには帯電によるゴミ付着等による画像欠陥が発生しやすい問題がおこっている。

(In the formula, R1 represents a linear alkyl group or alkylamino group having 4 to 16 carbon atoms.)
However, in medical applications in particular, there has been a demand for extremely high-definition image quality as the recording speed is further increased. In other words, as recording speed increases, image defects due to head debris adhesion and surface strength due to heating, and dust adhesion due to electrification are more likely to occur than in the past when high power is applied in a short time. Is happening.

  Further, the image after printing is also required to be stable for a long time and have little change even when exposed to light, heat, and humidity.

For these more severe requirements, the inventions proposed so far are not sufficient, and new improvements are required.
Japanese Patent No. 3563867 JP 2001-191643 A JP 2002-052830 A JP 2004-188706 A Japanese Patent Laid-Open No. 09-175028 JP 09-175023 A Japanese Patent Laid-Open No. 11-254831 JP 2000-218943 A JP 2004-276517 A

Therefore, the present invention has been made in view of the above, and in a thermal recording medium utilizing a color development reaction between an electron donating color-forming compound and an electron-accepting compound, head residue adhesion, scratches, and further Reflective and transmissive thermal recording media that are free of image defects due to dust adhering due to charging, etc., have no density reduction after printing, have good image stability, and are particularly suitable for medical use, and production of the thermal recording media It is an object of the present invention to provide a method and an image forming method using the thermal recording medium .

（式中、Ｒ ^１ は、炭素数が４乃至１６の直鎖のアルキル基又はアルキルアミノ基である。）
で示される化合物を含有し、前記保護層は、アクリルポリオール樹脂及び架橋剤を含有する組成物を架橋させることにより形成されており、前記アクリルポリオール樹脂は、酸価が０乃至３ＫＯＨｍｇ／ｇであり、水酸基価が１００乃至２００ＫＯＨｍｇ／ｇであり、
前記アクリルポリオール樹脂に対する前記架橋剤の重量比が０．２０乃至１．００であることを特徴とする。 The invention described in 請 Motomeko 1 comprises a support, heat-sensitive recording medium heat-sensitive recording layer and a protective layer are successively laminated, wherein the heat-sensitive recording layer contains a binder resin, a leuco dye and a color developer The developer has the general formula

(In the formula, R ¹ is a linear alkyl group having 4 to 16 carbon atoms or an alkylamino group.)
The protective layer is formed by crosslinking a composition containing an acrylic polyol resin and a crosslinking agent, and the acrylic polyol resin has an acid value of 0 to 3 KOHmg / g. The hydroxyl value is 100 to 200 KOHmg / g,
The weight ratio of the crosslinking agent to the acrylic polyol resin is 0.20 to 1.00 .

According to a second aspect of the invention, the thermosensitive recording medium according to claim 1, wherein the acrylic polyol resin has a glass transition point, characterized in that a 25 to 85 ° C..

According to a third aspect of the invention, the thermosensitive recording medium according to claim 1 or 2, wherein the acrylic polyol resin is characterized by a molecular weight of 20000 to 80000.

The invention according to claim 4 is the heat-sensitive recording medium according to any one of claims 1 to 3, wherein the protective layer contains a lubricant and a fatty acid amide having a melting point of 100 ° C. to 180 ° C. It shall be the feature.

The invention described in claim 5 is the heat-sensitive recording medium according to claim 4, wherein the protective layer shall be the wherein the total content of the lubricant and fatty acid amide is 1 to 20 wt%.

The invention described in claim 6 is the thermal recording medium according to any one of claims 1 to 5, wherein the protective layer has a thickness of you being 0.1 to 20 [mu] m.

The invention described in 請 Motomeko 7, heat-sensitive recording medium according to any one of claims 1 to 6, wherein the heat-sensitive recording layer contains the leuco dye three or more, the total weight of the leuco dye the ratio of the weight of the color developer for 0.5 to 2. It 5 is you characterized.

According to an eighth aspect of the present invention, in the thermal recording medium according to any one of the first to seventh aspects, the side of the support opposite to the side on which the thermal recording layer and the protective layer are formed. surface and the back layer is formed on the back layer, it characterized as having free antistatic agent.

The invention according to claim 9, in the heat-sensitive recording medium according to claim 8, wherein the back layer, you and the content of the antistatic agent is 5 to 90 wt%.

The invention according to claim 10, in the heat-sensitive recording medium according to claim 8 or 9, wherein the back layer, you further comprising including a filler.

The invention according to claim 11, in the heat-sensitive recording medium according to claim 10, wherein the filler shall be the wherein the average particle diameter of spherical particles of 6 to 25 [mu] m.

Invention according to claim 12, in the heat-sensitive recording medium according to claim 11, wherein the spherical particles contain polymethyl methacrylate, wherein the back layer, the content of the spherical particles 5 to 500 / it is a mm ^2.

The invention according to claim 13, in the heat-sensitive recording medium according to any one of claims 8 to 12, wherein the back layer, and wherein the glass transition point further comprises contains a 80 ° C. or more binder resins you.

The invention according to claim 14, in the heat-sensitive recording medium according to any one of claims 1 to 13, before Ki支 bearing member is a polyester film having a thickness of 50 to 250 [mu] m, equivalent thermosensitive recording medium, you wherein the haze value (JIS K7105) is 40% or less.

（式中、Ｒ ^１ は、炭素数が４乃至１６の直鎖のアルキル基又はアルキルアミノ基である。）
で示される化合物を含有し、前記アクリルポリオール樹脂は、酸価が０乃至３ＫＯＨｍｇ／ｇであり、水酸基価が１００乃至２００ＫＯＨｍｇ／ｇであり、前記アクリルポリオール樹脂に対する前記架橋剤の重量比が０．２０乃至１．００であることを特徴とする。 The invention according to claim 15, in the heat-sensitive recording medium according to any one of claims 1 to 14, which is attached see blue, that transparently concentration of 0.10 to 0.3 0 It shall be the feature.
According to a sixteenth aspect of the present invention, in the method for producing a thermal recording medium, a step of applying a coating liquid containing a binder resin, a leuco dye and a developer on a support to form a thermal recording layer; After applying a coating solution containing an acrylic polyol resin and a crosslinking agent on the heat-sensitive recording layer, the composition containing the acrylic polyol resin and the crosslinking agent is crosslinked to form a protective layer, Developer is a general formula

(In the formula, R ¹ is a linear alkyl group having 4 to 16 carbon atoms or an alkylamino group.)
The acrylic polyol resin has an acid value of 0 to 3 KOHmg / g, a hydroxyl value of 100 to 200 KOHmg / g, and a weight ratio of the crosslinking agent to the acrylic polyol resin of 0. 20 to 1.00.

The invention of claim 17 is the image forming method, using a pressurized heat means, to and forming an image by heating a thermosensitive recording medium according to any one of claims 1 to 15 The

By the present invention lever, f Ddokasu adhesion without also strongly film strength of the surface, further heat-sensitive recording medium having excellent image stability, image forming method using the manufacturing method and the thermosensitive recording medium of the thermosensitive recording medium Can be provided.

  Hereinafter, embodiments of the thermal recording medium of the present invention will be described.

  Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims of the present invention.

  The heat-sensitive recording medium of the present invention has a heat-sensitive recording layer mainly comprising a binder resin as a binder, a colorless or light-colored leuco dye, and a developer that heat-colors the leuco dye on the support. The protective layer is provided, and a specific resin is contained in the protective layer, and this is crosslinked with a crosslinking agent.

  As the resin used in the protective layer of the thermal recording medium of the present invention, it is very effective to crosslink an acrylic polyol resin in order to improve the hardness of the surface and to improve the destruction of the film due to the heat of the thermal head. is there.

  The hydroxyl value of these acrylic polyol resins is preferably from 100 to 200 (KOHmg / g). When the hydroxyl value is less than 100, the image storage stability tends to be poor, and the image density is particularly lowered due to moisture storage resistance. Moreover, there exists a problem that the intensity | strength of a coating film falls easily. In order to suppress the fogging of the background, the acid value is preferably 0 to 3 (KOHmg / g), and when the acid value exceeds 3, there is a problem that the background is easily fogged.

  Further, the Tg of the acrylic polyol resin is preferably 25 to 85 ° C., and if it is lower than 25 ° C., the strength of the film at the time of heating is not sufficient, and the surface tends to be sagged. When the temperature exceeds 85 ° C., there is a problem that the image density is easily lowered due to moisture resistance.

  Furthermore, the molecular weight of the acrylic polyol resin is preferably 20000 to 80000. If the molecular weight is less than 20000, the strength of the film during heating is insufficient, the surface of the film due to printing tends to drip, and it tends to cause head clogging, resulting in tailing in the printed image. The problem of doing.

  On the other hand, when the molecular weight exceeds 80,000, there is a problem that the viscosity as a material increases and it is difficult to handle.

  These acrylic polyol resins have different characteristics depending on the constitution. 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. Not a thing.

  Specific examples of the epoxy compound include ethylene glycol diglycidyl ether, butyl glycidyl ether, polyethylene glycol diglycidyl ether, and epoxy acrylate.

  The amount of these cross-linking agents added is preferably 20 to 120 parts by weight, preferably about 30 to 100 parts by weight, per 100 parts by weight of the acrylic polyol resin to be reacted. If it is less than 20 parts by weight, the crosslinking of the resin does not proceed sufficiently, and the physical strength and thermal strength of the resin film decrease, so that the image surface is easily damaged by contact with the thermal head during printing or heating. It tends to be in a state of being drunk.

  If the crosslinking agent exceeds 120 parts by weight, the amount of the crosslinking agent becomes excessive, so that the number of uncrosslinked products and self-crosslinked products due to moisture increases, which tends to cause head debris at the time of heat recording, and the tailing phenomenon tends to occur in the image.

  Further, in order to improve the head matching property, it is necessary to provide a sliding and releasing effect during heating, and a known lubricant can be used. Specific examples include higher fatty acids and their metal salts, higher fatty acid amides, higher fatty acid esters, animal, vegetable, mineral or petroleum-based waxes. These may be used alone or in combination of two or more.

  These fatty acid amides are preferably 1 to 30 wt% with respect to the protective layer. That is, when the content is less than 1 wt%, the surface resistance value and the slip function are not sufficient, and when the content exceeds 30 wt%, an image defect due to a head residue due to a melt is likely to occur.

The melting point of the fatty acid amide is preferably 100 ° C. to 180 ° C. If the melting point is less than 100 ° C., the fatty acid amide tends to bleed on the surface of the heat-sensitive recording medium after drying after coating the protective layer or after thermal recording of the thermal head. , A precipitate like white powder is likely to be generated on the surface. Further, there arises a problem that the moisture resistance of the image is easily reduced and the density is lowered.
Further, when the melting point exceeds 180 ° C., the precipitation of these white powders hardly occurs, but it is difficult to melt by the thermal recording of the thermal head, so that there is a problem that the effect of releasing the head residue is small.

  Furthermore, fatty acid bisamides are more preferable as products that suppress the generation of these white powders and have an excellent antistatic function.

  Next, in order to suppress the resistance of conveyance due to heating of the thermal head, electrification can be further suppressed by using these fatty acid amides together with a known lubricant.

  These solid lubricants and fatty acid amides are preferably used in combination, and both are preferably 1 to 20 wt% of the total protective layer. If it is less than 1 wt%, it is difficult to achieve sufficient lubricity and releasability, and if it exceeds 20 wt%, these lubricants have low film-forming properties, so that the strength of the protective layer tends to decrease and scratches are likely to occur. Will occur.

  Further, as a lubricant, general silicone oil, silicone resin, fluororesin, silane coupling agent, etc. can be used in combination.

  From the viewpoint of transparency, the protective layer in the present invention is ideally provided with a resin alone layer, but the protective layer made of resin alone is too smooth, and causes printing defects due to sticking and dust dragging. It is difficult to obtain sufficient performance. In particular, when a plastic film is used as a support, it tends to be smoother than when paper is used as a support, so that head matching tends to be reduced and dust tends to be dragged. In the case of a general thermoplastic resin, since the glass transition point is lower than that of heating by a thermal head, the protective layer of the resin alone may cause surface alteration, exposure of the recording layer, or the like. Such printing defects and defects are fatal as materials for outputting medical images.

  As a means for improving performance against sticking, dust dragging and the like, a protective layer generally contains a filler. However, in the case of a transparent thermosensitive recording medium, if the protective layer contains a filler as used in a conventional reflective recording material, the transparency often decreases. In order to maintain transparency by adding a filler, there are a method of finely roughening the surface with a small particle size filler and a method of partially roughening the surface by adding a small amount of a large particle size filler. In the present invention, the protective layer can be formed by combining the above two methods as necessary.

  When roughening the surface with a small particle size filler, considering the transparency and roughness, the particle size is preferably in the range of 0.05 to 0.5 μm. If it exceeds 0.5 μm, the transparency tends to be impaired. Moreover, when adding a small amount of a large particle size filler and roughening the surface partially, the range of 1-10 micrometers is preferable. When the thickness exceeds 10 μm, the convex portion on the surface becomes large, and heat transfer due to printing tends to be impaired, resulting in white spots. Moreover, even if a small amount of particles less than 1 μm are added, the effect of removing sticking and dust is reduced. Furthermore, when these large particle size fillers are added, an efficient effect can be obtained in a small amount by using a material having a uniform particle size as much as possible. The coefficient of friction on the surface of the protective layer is in the range of 0.07 to 0.14 when viewed from both the head matching (in the direction of increasing the slipperiness) and the drag prevention (in the direction of decreasing the slipperiness) of dust that is likely to occur in the plastic film. preferable.

Examples of fillers include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whiskers, talc, mica, glass flakes, calcium carbonate, plate calcium carbonate, aluminum hydroxide, plate aluminum hydroxide, silica, clay , calcined clay, kaolin, an inorganic filler such as hydrotalcite, and crosslinked polystyrene resin particles, urea - formalin copolymer particles, silicone resin particles, crosslinked polymethyl methacrylate methylation resins particles, guanamine - formaldehyde copolymer particles, An organic filler of melamine-formaldehyde copolymer particles is exemplified. In the present invention, crosslinked polymethacrylic acid methylation resins particles with an organic filler from the viewpoint of head wear, melamine - formaldehyde copolymer particles, calcium carbonate as an inorganic filler, kaolin, talc, aluminum hydroxide is preferable. However, the present invention is not limited to this, and a plurality of fillers may be used at the same time in order to impart various characteristics.

  There is no restriction | limiting in particular in the coating method of a protective layer, It can apply by a conventionally well-known method. The preferred protective layer thickness is 0.1 to 20 μm, more preferably 0.5 to 10 μm. If the protective layer thickness is too thin, the recording material's storability and the function as a protective layer such as head matching will be insufficient, and if it is too thick, the thermal sensitivity of the recording material will decrease, and it will be disadvantageous in terms of cost. is there.

  Next, the developer used in the present invention will be described. The developer used in the present invention is an electron-accepting compound, and various conventionally known electron-accepting developers can be used. Particularly preferred developers in the present invention are those represented by the following general formula (1). ) Is a salicylic acid derivative represented by:

（式中、Ｒ１は炭素数４乃至１６の直鎖のアルキル基又はアルキルアミノ基を表す。）
上記一般式（１）で表される化合物の具体例としては、４−（ｎ−ペンタノイルアミノ）サリチル酸、４−（ｎ−ヘキサノイルアミノ）サリチル酸、４−（ｎ−オクタノイルアミノ）サリチル酸、４−（ヘキサデカノイルアミノ）サリチル酸、４−（Ｎ’−ｎ−ブチルカルバモイルアミノ）サリチル酸、４−（Ｎ’−ｎ−ヘキシルカルバモイルアミノ）サリチル酸、４−（Ｎ’−ｎ−オクチルカルバモイルアミノ）サリチル酸、４−（Ｎ’−ヘキサデシルカルバモイルアミノ）サリチル酸等が挙げられる。

(In the formula, R1 represents a linear alkyl group having 4 to 16 carbon atoms or an alkylamino group.)
Specific examples of the compound represented by the general formula (1) include 4- (n-pentanoylamino) salicylic acid, 4- (n-hexanoylamino) salicylic acid, 4- (n-octanoylamino) salicylic acid, 4- (hexadecanoylamino) salicylic acid, 4- (N′-n-butylcarbamoylamino) salicylic acid, 4- (N′-n-hexylcarbamoylamino) salicylic acid, 4- (N′-n-octylcarbamoylamino) Examples include salicylic acid and 4- (N′-hexadecylcarbamoylamino) salicylic acid.

  In particular, when a compound represented by the following general formula (2) is used as a developer, a transmission type heat-sensitive recording material having little background fogging and excellent storage stability can be obtained.

（式中、Ｒ２は炭素数６乃至１２の直鎖アルキル基を表す。）
これらの化合物は単独、あるいは２種以上混合して用いることができる。また、さらなる効果向上を狙って、種々公知の顕色剤を混合することもできる。

(In the formula, R2 represents a linear alkyl group having 6 to 12 carbon atoms.)
These compounds can be used alone or in admixture of two or more. In addition, various known developers can be mixed in order to further improve the effect.

  The leuco dye used in the present invention is a compound exhibiting an electron donating property, and is applied alone or in combination of two or more. However, the leuco dye is a colorless or light-colored dye precursor, and is not particularly limited and is a conventionally known one. For example, triphenylmethanephthalide, triallylmethane, fluorane, phenothidian, thiofluorane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilinolactam, Preferred are leuco compounds such as rhodamine lactam, quinazoline, diazaxanthene and bislactone. Particularly preferred are fluoran and phthalide leuco dyes. Examples of such compounds include, but are not limited to, those shown below.

  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-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-iso-amyl-N-ethylamino) Fluorane, 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-Np-toluidino) fluorane, 2-anilino-3-methyl-6- (N-methyl-Np-toluidino) fluorane, 3-diethylamino-7, 8-benzofluorane, 1,3-dimethyl-6-diethylaminofluorane, 1,3-dimethyl-6-di-n-butylaminofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7 -Chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 10-diethylamino-2-ethylbenzo [1,4 Thiazino [3,2-b] fluorane, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4 -Azaphthalide, 3- [2,2-bis (1-ethyl-2-methyl-3-indolyl) vinyl] -3- (4-diethylaminophenyl) phthalide, 3- [1,1-bis (4-diethylaminophenyl) ) Ethylene-2-yl] -6-dimethylaminophthalide and the like.

  In particular, in the case of a transmissive thermosensitive recording medium for medical use, it is particularly preferable to use three or more leuco dyes together in order to obtain a single color tone.

  In the present invention, the weight of the developer in the heat-sensitive recording layer is preferably in the range of 0.5 to 2.5, particularly preferably in the range of 1.0 to 2.0 with respect to the total weight of the leuco dye. . When the weight of the developer is within this range, the halftone image storability is particularly improved with this developer. At this time, since the coloring efficiency increases, the maximum density can be obtained with a thin film. The advantages of thinning the gradation media are the film thickness control during coating, the reduction of residual moisture and residual solvent in the drying process, and the reduction in coating amount leads to cost reduction.

  In addition, when coating using an organic solvent, the dispersed component is only the developer, so the smaller the developer content, the more advantageous the light transmission of the coating layer, and the transmission type thermal recording. The medium has an effect of improving contrast and improving image recognition. When the developer represented by the general formula (1) is used, fastness is imparted to the color image by the leuco dye entering the developer network formed through hydrogen bonding. When the developer is present in excess of the above range, the network bond is strong, so that the leuco dye does not easily enter the developer. On the other hand, when the amount of the dye is excessive, the color development is considered to be weak because an appropriate network cannot be constructed.

  In order to obtain a single black image in the entire region from low density to high density, the leuco dye represented by the following general formula (3) is used in combination with the developer represented by the general formula (1). It is necessary as the first condition.

（式中、Ｒ４は水素原子、ハロゲン原子、炭素数１乃至４のアルキル基又はアルコキシ基を、Ｒ５は炭素数１乃至４のアルキル基を表す。）
前記一般式（３）の具体例としては、２−アニリノ−３−メチル−６−（Ｎ−エチル−ｐ−トリルアミノ）フルオラン、２−アニリノ−３−メチル−６−（Ｎ−メチル−ｐ−トリルアミノ）フルオランが挙げられる。この一般式（３）で表されるロイコ染料と、前記一般式（１）で表される顕色剤との反応によって得られる発色色調は、反射型感熱記録材料の場合であれば低濃度部が緑黒で高濃度部が黒に見えるが、透過型感熱記録材料とした場合には、低濃度部から高濃度部の全域で緑に見える。

(Wherein R4 represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group, and R5 represents an alkyl group having 1 to 4 carbon atoms.)
Specific examples of the general formula (3) include 2-anilino-3-methyl-6- (N-ethyl-p-tolylamino) fluorane, 2-anilino-3-methyl-6- (N-methyl-p- Tolylamino) fluorane. The color tone obtained by the reaction between the leuco dye represented by the general formula (3) and the developer represented by the general formula (1) is a low-concentration part in the case of a reflective thermosensitive recording material. Is black and the high density portion appears black, but in the case of a transmissive thermosensitive recording material, it appears green in the entire region from the low density portion to the high density portion.

  Therefore, as a second condition necessary for the transmission type heat-sensitive recording material, in addition to the leuco dye represented by the general formula (3), a red coloring dye and / or an orange coloring dye as a leuco dye, and a near infrared ray It is necessary to use a mixture of one or more coloring dyes. That is, as a total, it is necessary to mix at least 3 kinds of leuco dyes and, if necessary, 4 to 6 kinds. The red coloring dye, orange coloring dye or near-infrared coloring dye is one in which the color tone that develops color upon heating indicates the respective absorption wavelength region. The reason for adding a red coloring or orange coloring, near infrared coloring dye is that the colored body obtained using the leuco dye represented by the general formula (3) in the visible range has two absorption bands. This is because the valley portions seen in the vicinity of 450 to 600 nm and in the vicinity of 650 to 700 nm are filled, and the absorption in the visible region is made flat like silver salt.

  As a measure of blackening of the image, it can be roughly expressed by the ratio of the minimum / maximum absorbance in the 430 to 650 nm portion of the absorption spectrum. When this ratio is 0.65 or more, it is practically used at least on the Schaukasten. A typical black color can be satisfied. Moreover, if it is 0.75 or more, the influence by the kind of fluorescent lamp with which daylight color, daylight white, etc. are mounted | worn with shaukasten can be reduced, and it is preferable. As the mixing ratio of these dyes, it is preferable to increase the black color leuco dye having a large absorption from the viewpoints of high density, color tone adjustment, and storage stability, and the content of the leuco dye represented by the general formula (3) is all It is preferable that the red coloring or orange coloring dye and the near infrared coloring dye become 10 to 30% by weight in the range of 40 to 80% by weight of the leuco dye content.

  When the leuco dye represented by the general formula (3) is more than the above range, it is difficult to blacken the image area, and when it is less, it is difficult to ensure the maximum density.

  Examples of the red or orange dye used by mixing with the black coloring leuco dye represented by the general formula (3) in the present invention include the following. Rhodamine-B orthochloroanilinolactam, 3,6-bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,3-dimethyl-6-diethylaminofluorane, 1,3-dimethyl-6 -Dibutylaminofluorane, 2-chloro-3-methyl-6-diethylaminofluorane, 2-chloro-6-diethylaminofluorane, 3-chloro-6-N-cyclohexylaminofluorane, 6-diethylaminobenzo [α] Fluorane, 6- (N-ethyl-N-isopentylamino) benzo [α] fluorane, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, 3,3-bis ( 1-n-octyl-2-methylindol-3-yl) phthalide, spiro {chromeno [2,3C] pyrazole-4 (H -1' phthalan}-7-(N-ethyl--N- isoamyl amino) -3-methyl-1-phenyl-3'-one and the like.

  Among these, the orange coloring dye suitable for adjusting the absorption spectrum with respect to the use of the leuco dye represented by the general formula (3) used in the present invention is a compound represented by the following general formula (4). Is mentioned. This dye has a good absorption for filling a valley in the vicinity of 450 to 600 nm and is preferable. Specific examples of the compound represented by the general formula (4) include 1,3-dimethyl-6-diethylaminofluorane and 1,3-dimethyl-6-dibutylaminofluorane.

（式中、Ｒ６、Ｒ７は各々炭素数１乃至５のアルキル基、フェニル基、トリル基、シクロヘキシル基又はエトシキプロピル基から選ばれる一つを表す。）
また、近赤外発色染料の例としては、以下に示すものが挙げられる。６−ジエチルアミノ−２−エチルベンゾ［１，４］チアジノ［３，２−ｂ］フルオラン、３，３−ビス（４−ジエチルアミノ−２−エトキシフェニル）−４−アザフダリド、３−［２，２−ビス（１−エチル−２−メチル−３−インドリル）ビニル］−３−（４−ジエチルアミノフェニル）フタリド、３−｛１，１−ビス（４−ジエチルアミノフェニル）エチレン−２−イル｝−６−ジメチルアミノフタリド等。

(Wherein R6 and R7 each represents one selected from an alkyl group having 1 to 5 carbon atoms, a phenyl group, a tolyl group, a cyclohexyl group, or an ethoxypropyl group)
Examples of near-infrared coloring dyes include those shown below. 6-diethylamino-2-ethylbenzo [1,4] thiazino [3,2-b] fluorane, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azafudaride, 3- [2,2-bis (1-Ethyl-2-methyl-3-indolyl) vinyl] -3- (4-diethylaminophenyl) phthalide, 3- {1,1-bis (4-diethylaminophenyl) ethylene-2-yl} -6-dimethyl Aminophthalide etc.

  Among these, as described above, as a near-infrared coloring dye suitable for adjusting the absorption spectrum, 3,3-bis (4-diethylamino-2-ethoxyphenyl) represented by the following structural formula (5) is used. ) -4-Azafdalide. Since this dye has absorption at 650 to 700 nm, it is suitable for supplementing an insufficient absorption portion of the leuco dye represented by the general formula (3).

本発明においては、上記一般式（３）、（４）及び構造式（５）で表される各ロイコ染料を組み合わせることにより、極めて優れた銀塩ライクなフラットなスペクトルを形成することが可能となる。本発明において前記一般式（１）で表される顕色剤と、前記一般式（３）で表されるロイコ染料の代わりに、通常よく用いられる一般式（３）の６位のアミノ基がアルキル置換アミノ基のロイコ染料及び他色の染料とを組み合わせると、低濃度部でこのロイコ染料が優先的に発色するため、低濃度部を黒色にすることができない。このように一般式（１）で表される顕色剤を用いた場合に、一般式（３）で表される骨格のロイコ染料を用いた場合のみ、特異的に画像部の黒色化が達成できる。このようになる理由は定かではないが、染料と本発明で用いる特定のサリチル酸誘導体顕色剤との親和性に起因しているものと考えられる。

In the present invention, it is possible to form a very excellent silver salt-like flat spectrum by combining the leuco dyes represented by the general formulas (3), (4) and the structural formula (5). Become. In the present invention, instead of the developer represented by the general formula (1) and the leuco dye represented by the general formula (3), an amino group at the 6-position of the general formula (3) that is often used is When a leuco dye having an alkyl-substituted amino group and a dye of another color are combined, the leuco dye is preferentially colored at a low density portion, so that the low density portion cannot be made black. Thus, when the developer represented by the general formula (1) is used, the blackening of the image portion is specifically achieved only when the skeleton leuco dye represented by the general formula (3) is used. it can. The reason for this is not clear, but is thought to be due to the affinity between the dye and the specific salicylic acid derivative developer used in the present invention.

  In the present invention, a leuco dye having an amino group at the 6-position as described below having an alkyl-substituted amino group can be mixed in a small amount as long as it does not affect the color tone adjustment. For example, 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-methyl) Amino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-sec-butyl-N-ethylamino) Fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-iso-amyl-N-ethyl) Amino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane, etc.

  Further, conventionally known ones such as triphenylmethanephthalide, triallylmethane, fluorane, phenothiocyan, thiofluorane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, It is also possible to mix dyes such as rhodamine anilinolactam, rhodamine lactam, quinazoline, diazaxanthene and bislactone.

  Various known resins can be used as the binder resin used in the present invention. For example, polyethylene, polyvinyl acetate, polyacrylamide, maleic acid copolymer, polyacrylic acid and its ester, polymethacrylic acid and its ester, Vinyl chloride / vinyl acetate copolymer, styrene copolymer, polyester, polyurethane, polyvinyl butyral, ethyl cellulose, polyvinyl acetal, polycarbonate, epoxy resin, polyamide, polyvinyl alcohol, starch, gelatin and the like can be used. These resins can be used alone or in combination of two or more. In particular, polyvinyl butyral and polyvinyl acetal have good storage stability.

  As the support used in the present invention, those used in conventional leuco-type heat-sensitive recording media can be applied. For example, plastic film, paper, plastic resin laminated paper, synthetic paper, and the like can be used. In the case of a transmissive thermosensitive recording medium, it is necessary to use a transparent support. Specific examples of the transparent support include cellulose derivatives such as cellulose triacetate, polyolefins such as polypropylene and polyethylene, polystyrene or a film obtained by bonding these, preferably polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like. However, the polyester is not limited to these. Among these, in order to obtain a highly transparent sheet, polyethylene terephthalate having a haze of 10% or less (haze defined by JISK7105) of the support alone is particularly preferable. Further, in order to improve the adhesion of the coating layer of the thermal recording layer coating solution, at least one surface can be surface-modified by corona discharge treatment, oxidation reaction treatment (chromic acid, etc.), etching treatment, or the like.

  For use in the medical field, a polyester film having a thickness of about 50 to 250 μm is easy to use because of ease of handling.

  This heat-sensitive recording medium can also be used by coloring it in blue for the purpose of antiglare effect or image recognizability improvement. As a method of bluing, a method of kneading a blue pigment on a support, a method of adding a blue dye or a blue pigment to any one or more of the coating layers, etc. are adopted. The range of 0.15 to 0.25 is a color tone of CIE-LAB color system a * = − 4 to −15, b * = − 5 to −15 (measurement conditions; d / 0, 10 degree field of view, A color in a range surrounded by a light source D65 measured by measuring absorbance every 10 nm is preferable. Blue pigments and blue dyes that can be used are not particularly limited, and various known materials can be used.

  In these heat-sensitive recording media, when an organic solvent is used as the coating liquid, the residual solvent as the recording medium is preferably 0.1 to 1.5%. If the residual solvent remains in an amount exceeding 1.5% after coating and drying, there arises a problem that the storability of the printed image is lowered.

  Because of these problems, when an organic solvent is used in the present invention, the residual solvent can be reduced by using a solvent having a low boiling point and easily evaporated.

  It is also effective to raise the temperature after drying so that the recording medium does not develop color. However, when the above two cannot be implemented from the viewpoint of solvent regulation and productivity, it is preferable to re-dry after all the layers of the heat-sensitive recording material have been applied and dried. As a re-drying method, a known drying method can be used.

  In the present invention, an antistatic layer may be provided on the surface opposite to the recording layer and the protective layer. By providing an antistatic layer on the back layer side of the protective layer in the present invention, an antistatic function is exhibited. Without these antistatic layers, a sufficient antistatic function is not exhibited, and the charge amount is The problem of sticking between films is high. These problems can be solved by providing an antistatic layer containing a commonly used conductive material on the opposite side of the recording layer and the protective layer.

As for the antistatic agent which is the subject of the present invention, various antistatic agents are currently used for various applications. For the antistatic function, a surface resistance value of about 10 ¹⁰ Ωcm or less is required.

  The antistatic agents that can provide such a degree of conductivity can be broadly classified into those using a surfactant, those using a conductive metal oxide, and those using a conductive polymer. First, those using the former surfactant account for most of the current antistatic agents. These surfactants can be classified into four types, anionic, cationic, nonionic and amphoteric. As antistatic agents, cationic or amphoteric surfactants are superior in terms of antistatic properties and durability. . These surfactant types are relatively inexpensive, have a wide variety of types, and have good performance, but many of them achieve conductivity by adsorbing moisture from the surfactant itself. It is easily affected by humidity, and the antistatic property under low humidity tends to decrease.

  In addition, conductive polymers are materials that have been developed in recent years, and examples thereof include materials in which an organic donor is doped with an electron donor. Organic polymers used for these include aliphatic groups such as polyacetylene, aromatic groups such as polyparaphenylene, heterocyclic rings such as polypyrrole, conjugated polymers such as aromatic amines such as polyaniline, and main chain Even if is not a conjugated system, a cyclic π-conjugated group or the like is included in the side chain, and these polymer materials are doped with an electron donor. Since these materials are not conductive due to moisture like conductive metal oxides and the like, they exhibit conductive functions even at low humidity. Moreover, although it varies depending on the polymer and the electron donor, the conductive function can be very high, and even a thin film can have a sufficient function for preventing charging.

On the other hand, those using conductive metal oxides are fewer and more expensive than the former surfactant type. However, since the metal oxide itself has electrical conductivity, the electrical conductivity is high, and excellent transparency can be maintained even with a low adhesion amount, so that high transparency can be maintained. In addition, the antistatic property is excellent even under low humidity without being affected by humidity. As the conductive metal oxide, for example, SnO ₂ , In ₂ O ₃ , ZnO, TiO ₂ , MgO, Al ₂ O ₃ , BaO, MoO _3, etc. are used alone or mixed with P, Sb, Sn, Zn, etc. Examples include, but are not limited to these. Many of these metal oxides are colored, and the transparency is impaired.

  Therefore, two or more kinds of antistatic agents such as a conductive metal oxide and a surfactant or a conductive polymer may be used in combination.

  The fine powder should be as fine as possible. The finer the powder, the better the transparency and antistatic effect. In the present invention, excellent transparency is realized by setting the average particle size of the antistatic agent to 0.2 μm or less.

  The antistatic agent is about 0.05 to 0.9 parts by weight, preferably 0.1 to 0.5 parts by weight, in 1 part by weight of the adhesion preventing layer. When the amount is less than 0.05 parts, a sufficient antistatic function is not waited. On the other hand, when the amount is more than 0.9 parts by weight, the function of bonding to the support may not be sufficient.

Further, in order to have an adhesion preventing effect in the present invention, it is effective to add a matting agent to the antistatic layer. Examples of fillers include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whiskers, talc, mica, glass bead flakes, calcium carbonate, platy carbon cal, aluminum hydroxide, silica, clay, kaolin, calcined clay, hydro Tarui site such spherical inorganic filler, polystyrene resin, polyethylene resin, polypropylene resin, urea - formalin resin, silicone resin, polymethacrylic acid methylation resins, melamine - formaldehyde resins, polyesters, spherical, such as condensation polymers such as polycarbonate Although an organic filler is mentioned, this invention is not limited to this.

Regarding these fillers, an average of 6 to 25 μm is particularly preferable in order to prevent adhesion, and a spherical filler is preferable because a convex portion can be efficiently formed on the surface. The term “spherical” as used herein means that the difference between the maximum value and the minimum value of the sphere diameter is within 20% of each average diameter. These spherical particles include phosphate fiber, potassium titanate, acicular magnesium hydroxide, whiskers, talc, mica, glass bead flakes, calcium carbonate, platy carbon, aluminum hydroxide, silica, clay, kaolin, talc, calcined clay, spherical, such as hydro Tarui sites inorganic filler, polystyrene resin, polyethylene resin, polypropylene resin, urea - formalin resin, silicone resin, polymethacrylic acid methylation resins, melamine - formaldehyde resins, polyesters, condensation polymers such as polycarbonate And the like, but the present invention is not limited to this.

Moreover Among these, easily general particle size control to obtain an easy and uniform particles, more polymethacrylic acid methylation resins is preferable as those having excellent transparency. Further, the number of particles in the adhesion prevention layer is not limited to the number of particles as long as it can prevent adhesion with the superimposed medium, and it is 5 to 500 particles / square millimeter, preferably about 10 to 100 particles / square millimeter. Adhesion can be prevented.

  At this time, if it is less than 5 pieces / square millimeter, the adhesion preventing function is not sufficient, and if it exceeds 500 pieces / square millimeter, the transparency is unnecessarily lowered.

  Furthermore, as the resin used for the back layer in the present invention, various known resins can be used, such as polyethylene, polyvinyl acetate, polyacrylamide, maleic acid copolymer, polyacrylic acid and its ester, polymethacrylic acid. Acids and esters thereof, vinyl chloride / vinyl acetate copolymer, styrene copolymer, polyester, polyurethane, polyvinyl butyral, ethyl cellulose, polyvinyl acetal, polycarbonate, epoxy resin, polyamide, polyvinyl alcohol, starch, gelatin and the like can be used. These resins can be used alone or in combination of two or more. It can be selected considering the affinity with the support or antistatic agent to be used.

  As the binder for these back layers, those having a Tg of 80 ° C. or more are preferable, which is very effective when the curling tends to occur on the thermal recording side.

  Immediately after the production of the transmission type heat-sensitive recording medium of the present invention, it is usually a long product, but the form as a product is the one that is rolled and hardened, and cut into a predetermined size and a predetermined number of sheets. Some are in a bag. Both are more preferably stored and distributed by wrapping in a normally light-shielding packaging material due to the nature of the product. A transmission type heat-sensitive recording medium which is opened at the time of use and taken out of the bag is mounted on the image forming apparatus.

  The method of forming an image using the transmission type thermal recording medium of the present invention is performed by heating the thermal recording medium in an image-like manner by a heating means based on character and / or shape information. What is used as the heating means is not particularly limited depending on the purpose of use, such as a thermal pen, a thermal head, or laser heating. However, the transmission type thermal recording medium of the present invention is a high-definition and high-gradation image such as a medical image. It is most preferable to use a thermal head from the viewpoint of the cost, output speed, and compactness of the apparatus.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples. In the following, parts and% are based on weight.

Comparative Example 1
The following composition was pulverized and dispersed with a ball mill until the volume average particle size became 0.5 μm or less to prepare a developer dispersion [A1 solution]. The particle size was measured with a laser diffraction particle size measuring device LA-700 manufactured by Horiba Ltd.

[A1 solution]
MEK 32.5 parts Toluene 32.5 parts 4- (N′-n-hexylureido) salicylic acid 15 parts 25% polyester solution (MEK / TOL = 1/1) 20 parts (Polyester skeleton: bisphenol A, ethylene glycol, Neopentyl glycol, terephthalic acid, isophthalic acid Tg = 75 ° C)
Next, the following composition was sufficiently stirred to prepare a recording layer coating liquid [A liquid] having a solid content of 18%.

[Liquid A ]
Developer dispersion liquid [ A 1 liquid] 32 parts The following leuco dye A (ETAC) 3 parts The following leuco dye B (Red 500) 0.2 part The following leuco dye C (Orange 100) 0.8 part 25% polyester solution (MEK / TOL = 1/1) 4 parts (Polyester skeleton: bisphenol A, ethylene glycol, neopentyl glycol, terephthalic acid, isophthalic acid Tg = 75 ° C.)
25% polyester polyol resin solution (MEK / TOL = 1/1) 12 parts (Unitika UE3320 hydroxyl value 60 Tg = 40 ° C.)
75% hexamethylene isocyanate ethyl acetate solution 2.7 parts (Nippon Polyurethane Coronate HL)
MEK 1 part TOL 15 parts [B1 liquid protective layer primary liquid]
MEK 48 parts Polyvinyl Acetal (Sekisui Chemical Co., Ltd. ESREC KS-1) 6 parts Calcium carbonate (Shiraishi Kogyo P-1) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part Volume average particle size 0 of the above composition in a ball mill The mixture was pulverized and dispersed to 5 μm or less to prepare a protective layer primary solution [B1 solution].

[B liquid protective layer liquid]
B1 solution 65 parts xylene diisocyanate (Takenate D120N 75%, Takeda Pharmaceutical Co., Ltd.) 3 parts The recording layer coating solution [A solution] prepared in this way is used on a synthetic paper with a thickness of 170 μm (FPG170 manufactured by Yupo Corporation) using a wire bar. Then, a dryer maintained at a temperature of 100 ° C. was passed through for 1 minute and dried to form a thermosensitive recording layer having a thickness of 15 μm.

  Further, the protective layer coating solution [B solution] prepared thereon was dried by passing it through a dryer maintained at a temperature of 70 ° C. for 1 minute to form a protective layer having a thickness of 4 μm.

  Thereafter, the coated product was further dried again at 75 ° C. for 1 h. A sample of Comparative Example 1 was obtained.

[Comparative Example 2]
[C1 liquid protective layer primary liquid]
MEK 40 parts Acrylic polyol Solid content 50% (MEK / butyl acetate) 14 parts (LR286 made by Mitsubishi Rayon Acid value 3.5, hydroxyl value 64 Tg81 ° C. molecular weight 23K)
Calcium carbonate (P-1 manufactured by Shiroishi Kogyo Co., Ltd.) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part The above composition was pulverized and dispersed with a ball mill until the volume average particle size was 0.5 μm or less, and the protective layer primary solution [C1 solution Was prepared.

[C liquid protective layer liquid]
C1 liquid 65 parts Xylene diisocyanate (Takeda Chemicals Takenate D120N 75%) 3 parts A heat-sensitive recording layer was formed in the same manner as in Comparative Example 1, and the protective layer coating liquid [C liquid] prepared thereon was heated to 70 ° C. A protective layer having a thickness of 4 μm was formed by passing through a dryer held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated product was further dried again at 75 ° C. for 1 h to obtain a sample of Comparative Example 2.

[Example 1]
[D1 liquid protective layer primary liquid]
MEK 40 parts Acrylic polyol A Solid content 50% (MEK / butyl acetate) 14 parts (acid value 0.5, hydroxyl value 133 Tg86 ° C. molecular weight 30K)
Calcium carbonate (P-1 manufactured by Shiroishi Kogyo Co., Ltd.) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part The above composition was pulverized and dispersed with a ball mill until the volume average particle size was 0.5 μm or less, and the protective layer primary solution [D1 solution Was prepared.

[D liquid protective layer liquid]
D1 solution 65 parts Xylene diisocyanate (Takenate D120N 75% manufactured by Takeda Pharmaceutical Co., Ltd.) 3 parts A heat-sensitive recording layer was formed in the same manner as in Comparative Example 1, and the protective layer coating solution [D solution] prepared thereon was heated to 70 ° C. The sample was dried by passing through a drier held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated product was further dried again at 75 ° C. for 1 h to obtain a sample of Example 1.

[Example 2]
[E1 liquid protective layer primary liquid]
MEK 40 parts Acrylic polyol B Solid content 50% (MEK / butyl acetate) 14 parts (acid value 0.5, hydroxyl value 133 Tg 50 ° C. molecular weight 10K)
Calcium carbonate (P-1 manufactured by Shiroishi Kogyo Co., Ltd.) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part The above composition was pulverized and dispersed with a ball mill until the volume average particle size was 0.5 μm or less, and the protective layer primary solution [E1 solution Was prepared.

[E liquid protective layer liquid]
E1 liquid 65 parts Xylene diisocyanate (Takeda Chemicals Takenate D120N 75%) 3 parts A heat-sensitive recording layer was formed in the same manner as in Comparative Example 1, and the protective layer coating liquid [E liquid] prepared thereon was heated to 70 ° C. The sample was dried by passing through a drier held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated product was further dried again at 75 ° C. for 1 h to obtain a sample of Example 2.

[ Reference Example 3]
[F1 solution protective layer primary solution]
MEK 40 parts Acrylic polyol C Solid content 50% (MEK / butyl acetate) 14 parts (acid value 0.5, hydroxyl value 133 Tg50 ° C. molecular weight 30K)
Calcium carbonate (P-1 manufactured by Shiroishi Kogyo Co., Ltd.) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part The above composition was pulverized and dispersed with a ball mill until the volume average particle size was 0.5 μm or less, and the protective layer primary solution [F1 solution Was prepared.

[F liquid protective layer liquid]
F1 liquid 21 parts Xylene diisocyanate (Takeda Pharmaceutical Takenate D120N 75%) 11 parts A heat-sensitive recording layer was formed in the same manner as in Comparative Example 1, and the protective layer coating liquid [F liquid] prepared thereon was heated to 70 ° C. A protective layer having a thickness of 4 μm was formed by passing through a drier held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated product was further dried again at 75 ° C. for 1 h to obtain a sample of Reference Example 3. At this time, the residual solvent of the sample of Reference Example 3 was 1.1%.

[Comparative Example 3]
[G1 solution protective layer primary solution]
MEK 47 parts Acrylic polyol C Solid content 50% (MEK / butyl acetate) 7 parts (acid value 0.5, hydroxyl value 133 Tg 50 ° C. molecular weight 30K)
Calcium carbonate (P-1 manufactured by Shiroishi Kogyo Co., Ltd.) 9 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part The above composition was pulverized and dispersed with a ball mill until the volume average particle size was 0.5 μm or less, and the protective layer primary solution [G1 solution Was prepared.

[G liquid protective layer liquid]
Solution G1 65 parts Xylene diisocyanate (Takenate D120N 75%, Takeda Pharmaceutical Co., Ltd.) 5 parts A heat-sensitive recording layer was formed in the same manner as in Comparative Example 1, and the protective layer coating solution [G solution] prepared thereon was heated to 70 ° C. Then, a protective layer having a thickness of 4 μm was formed by passing through a dryer held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated material was further dried again at 75 ° C. for 1 h to obtain a sample of Comparative Example 3.

(Comparative Example 4)
After forming a heat-sensitive recording layer and a protective layer in the same manner as in Reference Example 3, a sample of Comparative Example 4 was obtained.

  At this time, the residual solvent of the sample of Comparative Example 4 was 4.8%.

Example 4
[H1 solution protective layer primary solution]
MEK 40 parts Acrylic polyol D Solid content 50% (MEK) 14 parts (acid value 0.1, hydroxyl value 133 Tg50 ° C. molecular weight 30K)
Calcium carbonate (P-1 manufactured by Shiraishi Kogyo Co., Ltd.) 5 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part Ethylene bisbehenamide (Nippon Kasei Sripacks B melting point 142 ° C.) 4 parts The protective layer primary solution [H1 solution] was prepared by pulverizing and dispersing to 5 μm or less.

[H liquid protective layer liquid]
Liquid H1 65 parts Xylene diisocyanate (Takenate D110N 75%, manufactured by Takeda Pharmaceutical Co., Ltd.) 3 parts A heat-sensitive recording layer was formed in the same manner as Comparative Example 1, and the protective layer coating liquid [H liquid] prepared thereon was heated to 70 ° C. The sample was dried by passing it through a dryer held for 1 minute to form a protective layer having a thickness of 4 μm, and the coated product was further dried again at 75 ° C. for 1 h to obtain a sample of Example 4.

(Example 5)
[I-1 liquid protective layer primary solution]
MEK 40 parts Acrylic polyol D Solid content 50% (MEK) 14 parts (acid value 0.1, hydroxyl value 133 Tg50 ° C. molecular weight 30K)
Calcium carbonate (P-1 manufactured by Shiraishi Kogyo Co., Ltd.) 8 parts Zinc stearate (manufactured by Sakai Chemical Co., Ltd.) 1 part Ethylene bisbehenamide (Nippon Kasei Sripacks B melting point 142 ° C.) 1 part The protective layer primary solution [I-1 solution] was prepared by pulverizing and dispersing to 5 μm or less.

[Liquid I protective layer]
Liquid I-1 65 parts Xylene diisocyanate (Takenate D110N 75%, manufactured by Takeda Pharmaceutical Co., Ltd.) 3 parts A heat-sensitive recording layer was formed in the same manner as Comparative Example 1, and the protective layer coating liquid [Liquid I] prepared thereon was 70 ° C. After a dryer maintained at a temperature of 1 mm was dried for 1 minute to form a protective layer having a thickness of 4 μm, the coated material was further dried again at 75 ° C. for 1 h to obtain a sample of Example 4.

(Comparative Example 5)
[J1 liquid]
MEK 32.5 parts Toluene 32.5 parts Stearylphosphonic acid 15 parts 25% polyester solution (MEK / TOL = 1/1) 20 parts (Polyester skeleton: bisphenol A, ethylene glycol, neopentyl glycol, terephthalic acid, isophthalic acid Acid Tg = 75 ° C)
Next, the following composition was sufficiently stirred to prepare a recording layer coating liquid [ J liquid] having a solid content of 18%.

[J liquid]
Developer dispersion liquid [J1 liquid] 32 parts The following leuco dye D (ODB) 3 parts The following leuco dye B (Red 500) 0.2 part The following leuco dye C (Orange 100) 0.8 part 25% polyester solution ( MEK / TOL = 1/1) 4 parts (Polyester skeleton: bisphenol A, ethylene glycol, neopentyl glycol, terephthalic acid, isophthalic acid Tg = 75 ° C.)
25% polyester polyol resin solution (MEK / TOL = 1/1) 12 parts (Unitika UE3320 hydroxyl value 60 Tg = 40 ° C.)
75% hexamethylene isocyanate ethyl acetate solution 2.7 parts (Nippon Polyurethane Coronate HL)
MEK 1 part TOL 15 parts The thus prepared recording layer coating liquid [J liquid] is coated on a synthetic paper having a thickness of 170 μm (FPG170 manufactured by YUPO Corporation) using a wire bar and kept at a temperature of 70 ° C. The dried dryer was passed through for 1 minute to form a heat-sensitive recording layer having a thickness of 15 μm.

  Further, the protective layer coating solution [I solution] was further dried thereon by passing it through a dryer maintained at a temperature of 70 ° C. for 1 minute in the same manner as in Example 5 to form a protective layer having a thickness of 4 μm. The coated material was further dried again at 75 ° C. for 1 h to obtain a sample of Comparative Example 5.

(Example 6)
[K liquid back layer liquid]
α-Ethyl (trimethylammonium) alkanoyl ester (SAT-5, manufactured by Nippon Pure Chemical) 39 parts Methanol 60 parts After forming a heat-sensitive recording layer and a protective layer in the same manner as in the examples, the coated product was further dried at 75 ° C. After re-drying 1h, the K liquid was applied to the opposite surface using a wire bar and dried to obtain a sample of Example 6 having a back layer of 4 μm.

(Example 7)
[L liquid, back layer liquid]
α-ethyl (trimethylammonium) alkanoyl ester (SAT-5, manufactured by Nippon Pure Chemical Industries) 39 parts Methanol 60 parts Crosslinked PMMA particles (MX1000 average particle size 10 μm, manufactured by Soken Chemical Co., Ltd.) 1 part After the formation, the coated material was further dried again at 75 ° C. for 1 h, and then the liquid L was coated on the opposite surface using a wire bar and dried to obtain a 4 μm back layer of Example 7 A sample was obtained.

(Example 8)
[M liquid back layer liquid]
α-ethyl (trimethylammonium) alkanoyl ester (SAT-5, manufactured by Nippon Pure Chemical) 15 parts Acrylic resin (BR-77, manufactured by Mitsubishi Rayon) 24 parts MEK 42 parts Methanol 18 parts Crosslinked PMMA particles (Made by Soken Chemical Co., Ltd. MX1000 average particle size 10 μm) ) 1 part After forming a heat-sensitive recording layer and a protective layer in the same manner as in the examples, the coated material was further dried for 1 h at 75 ° C. using a wire bar on the opposite side. Was applied and dried to obtain a sample of Example 8 having a back layer of 4 μm.

Example 9
A support was prepared in the same manner as in Example 8 except that a transparent polyester film having a thickness of 175 μm (haze value: 3%) was obtained, and a sample of Example 9 was obtained. At this time, the haze was 24%.

(Example 10)
A sample of Example 10 was obtained in the same manner as in Example 9 except that 0.04 part of a blue dye (manufactured by Bayer, MACROLEX BLUE3R GRAN) was added to the recording layer coating liquid (A liquid).

Evaluation Method In addition, a gray scale was printed on the heat-sensitive recording materials of Examples and Comparative Examples produced as described above with a variable energy printer Sony video printer UP-D70XR equipped with a gradation head with a resolution of 300 dpi. 1. 1. background density, 2. Change in storage resistance to moisture 3. Light-resistant storage stability; 4. Head matching (tailing), 5. 5. Head matching property (surface scratch), 6. Charged sticking, 7. Double feeding of film, Carl, 9. 10. Transportability The glare when mounted on the shaukasten was evaluated.

1. The background density was measured with a densitometer TD-904 manufactured by GretagMacbeth.
○: 0.1 or less △: 0.1 to 0.12
X: 0.13 or more The density of the image with the density immediately after printing with moisture-resistant storage was measured, and the amount of density change after storing the film at 40 ° C. and 90% Rh24h was evaluated. Judgment was carried out from the portion of the largest change in each gradation.
The concentration was measured using a densitometer TD-904 manufactured by GretagMacbeth.
The density change from the initial image was measured with a densitometer and evaluated.
○: Concentration change rate is ± 10% or less △: Concentration change rate is ± 10-30% or less ×: Concentration change rate exceeds ± 30% The density of the image was measured with the density just after light-fast storage printing, and the film was stored under a fluorescent lamp of 5000 lux for 100 hours, and the film was visually evaluated for the yellowing of the background and the color change of the coloring portion.
○: Almost no change is known.
Δ: Color change is observed.
X: Discoloration can be confirmed clearly.

4). Head matching (image tailing)
The presence / absence of occurrence of an abnormal image of image tailing due to head fusion when 10 test patterns are continuously printed is determined according to the following criteria.
A: There is no fusion to the head after printing 10 sheets, and no abnormal image occurs.
A: After 10 sheets are printed, fusion to the head is observed, but no abnormal image occurs.
Δ: After 10 sheets are printed, fusion to the head is observed, and an abnormal image is slightly generated.
X: Fusion to the head is observed after printing 10 sheets, and an abnormal image is generated.

5. Head matching (surface scratches)
Evaluation of defects on scratches on printed images. O: There are almost no scratches on the surface.
Δ: Some scratches are observed on the surface.
X: Many scratches are seen on the surface.

6). Three test patterns with electrostatic sticking were continuously printed, and the sticking condition of the stock film after printing was evaluated.
○: There is no sticking.
Δ: Slightly close feeling but no sticking.
X: All three sticks.

7). Three sheets of the transportability test pattern were continuously printed, and the overlapped films were in close contact with each other during the print transport, and double feed was evaluated.
○: All three sheets are transported normally and there is no double feed.
Δ: One of the three sheets was double-fed.
X: Two or more of the three sheets were double-fed.

8). The curl after printing a curl test pattern of a printed image was evaluated on a flat surface.
The curl value is the average value of the four corners.
○: ± 3mm or less
Δ: ± 3 mm to 10 mm
×: ± 10 mm or more The permeability of the image when mounted on a 8000-10000 Lux Schaukasten was sensory evaluated and judged according to the following criteria.
◯: Permeated and no hindrance.
Δ: Slightly cloudy X: Not transmitted at all The glare when mounted on a shaucusten of 8000 to 10000 Lux was sensory evaluated and judged according to the following criteria.
〇: It does not feel glare so much and there is no obstacle to observation.
Δ: A slight glare is felt, but observation is possible.
X: A feeling of glare is quite felt and observation is impossible.

(Residual solvent amount)
A sample consisting of 10 cm × 10 cm was placed in a pressure-resistant sealed container, and the organic solvent gasified after treatment at 130 ° C. for 15 minutes was quantified by gas chromatography.

(Haze)
A transparent thermosensitive recording medium of 50 mm × 50 mm is used as a test piece, and haze (haze) is measured with a direct reading haze meter manufactured by Toyo Seiki. The lower the haze value, the better the transparency.
◎: Haze 25% or less ○: Haze 25-30%
Δ: Haze 30-35%
X: Table 1 shows the evaluation results higher than haze 35%.

この表１から分かるように、本発明によって、ヘッドカス付着や、キズ、さらには帯電によるゴミ付着等による画像の欠陥がなく、また印画後の濃度低下がない、画像安定性が良好な、特に医療用途に好適な反射型、透過型の感熱記録媒体が提供される。

As can be seen from Table 1, according to the present invention, there is no image defect due to head debris, scratches, or dust adhesion due to electrification, there is no decrease in density after printing, and image stability is good. A reflective and transmissive thermal recording medium suitable for the application is provided.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Claims (17)

In a thermal recording medium in which a thermal recording layer and a protective layer are sequentially laminated on a support,
The heat-sensitive recording layer contains a binder resin, a leuco dye and a developer,
The developer is a general formula

(In the formula, R ¹ is a linear alkyl group having 4 to 16 carbon atoms or an alkylamino group.)
Containing a compound represented by
The protective layer is formed by crosslinking a composition containing an acrylic polyol resin and a crosslinking agent ,
The acrylic polyol resin has an acid value of 0 to 3 KOHmg / g, a hydroxyl value of 100 to 200 KOHmg / g,
A heat-sensitive recording medium, wherein the weight ratio of the crosslinking agent to the acrylic polyol resin is 0.20 to 1.00 . The heat-sensitive recording medium according to claim 1 , wherein the acrylic polyol resin has a glass transition point of 25 to 85 ° C. The heat-sensitive recording medium according to claim 1 or 2, wherein the acrylic polyol resin has a molecular weight of 20,000 to 80,000. The protective layer, a thermosensitive recording medium according to any one of claims 1 to 3 lubricant and melting point, characterized in that it contains the fatty acid amide is 100 ° C. to 180 ° C.. The heat-sensitive recording medium according to claim 4, wherein the protective layer has a total content of the lubricant and the fatty acid amide of 1 to 20% by weight. The protective layer, a thermosensitive recording medium according to any one of claims 1 to 5 thickness and wherein the range of 0.1 to 20 [mu] m. The heat-sensitive recording layer contains the leuco dye three or more,
The ratio of the weight of the developer to the total weight of the leuco dye is 0.5 to 2. The thermosensitive recording medium according to any one of claims 1 to 6, characterized in that 5 a. A back layer is formed on the surface of the support opposite to the side on which the thermosensitive recording layer and the protective layer are formed ;
The back layer, the thermosensitive recording medium according to any one of claims 1 to 7, characterized in that it has free antistatic agent. The thermal recording medium according to claim 8 , wherein the back layer has a content of the antistatic agent of 5 to 90% by weight . The back layer, the thermosensitive recording medium according to claim 8 or 9, further comprising including a filler. The heat-sensitive recording medium according to claim 10 , wherein the filler is a spherical particle having an average particle diameter of 6 to 25 µm. The spherical particles may contain polymethyl methacrylate,
The back layer, the thermosensitive recording medium according to claim 11, wherein the content of the spherical particles is 5 to 500 / mm ^2. The back layer, the thermosensitive recording medium according to any one of claims 8 to 12, characterized in that the glass transition point is more and containing not 80 ° C. or more binder resins. Before Ki支 bearing member is a polyester film having a thickness of 50 to 250 [mu] m,
Those heat-sensitive recording medium has a haze value (JIS K7105) is sensitive thermal recording medium according to any one of claims 1 to 13, characterized in that 40% or less. It is blue seen with, sensitive heat recording medium according to any one of claims 1 to 14 transparently concentration is characterized in that 0.10 to 0.3 0.   Forming a heat-sensitive recording layer by applying a coating liquid containing a binder resin, a leuco dye and a developer on a support; and
  After applying a coating solution containing an acrylic polyol resin and a crosslinking agent on the heat-sensitive recording layer, the composition containing the acrylic polyol resin and the crosslinking agent is crosslinked to form a protective layer,
  The developer is a general formula

(Wherein R ¹ Is a linear alkyl group or alkylamino group having 4 to 16 carbon atoms. )
Containing a compound represented by
  The acrylic polyol resin has an acid value of 0 to 3 KOHmg / g, a hydroxyl value of 100 to 200 KOHmg / g,
  A method for producing a thermal recording medium, wherein the weight ratio of the crosslinking agent to the acrylic polyol resin is 0.20 to 1.00. Using a pressurized thermal means, an image forming method and forming an image by heating the thermosensitive recording medium according to any one of claims 1 to 15.