JP2008073858A - Thermosensitive recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording medium, which utilizes a color developing reaction between an electron donative and colorable compound and an electron acceptive compound or the like, which keeps highly lustrous properties, no defects developable on the adhesion of a head scum, and sticking on print favorable and, in addition, which is superior in water resistance and solvent resistance and is a reflective one especially suitable for medical use application. <P>SOLUTION: In the thermosensitive recording medium, which is formed by providing a thermosensitive recording layer mainly made of a binder resin as a binding agent, a colorless or light-colored leuco dye and a developer thermally color-developing the leuco dye, and a topmost layer on a support, the topmost layer includes a core/shell type emulsion consisting of at least a shell made of water-soluble acrylic resin and a core part made of hydrophobic acrylic resin emulsion, a resinous component crosslinked by a crosslinker and, in addition, inorganic pigment having a volume average particle diameter of 0.005-0.5 μm and lubricant having a volume average particle diameter of 0.01-0.9 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording medium utilizing a color developing reaction between an electron donating color-forming compound and an electron-accepting compound, and in particular, diagnoses and refers to images such as X-rays, MRI and CT. For this purpose, it has the same high image quality, glossiness, high density, and high gradation as the silver salt film, and has excellent head matching and image preservation, and is particularly suitable as a medical image forming sheet. It is a thermal recording medium.

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. This recording system has advantages such as a compact and inexpensive recording machine and easy maintenance, such as a facsimile, an automatic ticket vending machine, a scientific measurement printer, a printer for barcode printing for POS, or It is used in a wide range of applications such as printers for CRT medical measuring instruments.
However, a major problem with this recording method is that 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) A number of inventions have been made, and various inventions have been made as inventions based on devices such as resins, lubricants, and fillers for the protective layer.

  In handling at medical sites, there is a high possibility of contact with water, alcohol and other solvents, and high barrier properties against water and alcohol on the surface of the recording medium are required. For these, barrier properties and high gloss are achieved by combining a crosslinking agent with a core / shell type emulsion having an electron beam or UV curable resin, a water-soluble resin, or a water-insoluble emulsion. Has been proposed.

However, in recent recording, high speed and high definition are required, and accordingly, there is a tendency to increase the applied power to one element of the thermal head.
In addition, since medical thermosensitive recording media are used for diagnosis and reference, the object of recording is mainly structural information or shape information such as the built-in human body or bones, and the recognized image is the original and original information. It is important that the shape information is accurately reflected, and it is expected that the image has excellent blackness, high gradation, and high glossiness, and is excellent in terms of shading and contrast.
Therefore, in medical applications, particularly in medical applications, medical recording media require higher gradation than conventional leuco thermal recording media, and therefore higher output recording is required. At that time, the release function and the slipperiness function at the time of heating the outermost surface of the recording medium and the thermal head become very important required functions.

  Taking these required qualities into consideration, the outermost surface layer of these thermal recording media is required to have a high mold release function for the lubricant. Generally, in order to give the thermal recording media gloss, Need to have high gloss. Therefore, in the outermost surface layer, a resin having a good film forming property is adopted, and fillers and lubricants that reduce gloss are reduced as much as possible. Furthermore, in order to achieve both glossiness, releasability, and lubricity, inventions have been made such that the outermost surface layer has a higher resin ratio, and more lubricants and fillers are added to the intermediate layer, the heat-sensitive recording layer, and the like. As described above, these had an effect on high output per image such as sticking against the increase in output of the thermal head in recent medical recording, but by continuous recording in consideration of actual use. For the various demands such as prevention of sticking of the head residue to the heating element, high gloss, water resistance, solvent resistance, etc., the inventions proposed so far do not satisfy all but require new improvements. It has become to.

Japanese Patent No. 3358007 Japanese Patent Publication No. 07-023025 JP 07-137442 A Japanese Patent Laid-Open No. 02-169292 JP 2003-320755 A Japanese Patent No. 3672289 Japanese Patent No. 3563867 Japanese Patent Laid-Open No. 04-219282 Japanese Patent Publication No. 03-072476 JP 2004-223994 A JP 2001-270247 A JP 2001-277732 A

  The present invention relates to a heat-sensitive recording medium utilizing a coloring reaction between an electron donating color-forming compound and an electron-accepting compound, and has no image defect due to head residue adhesion while maintaining high gloss. It is another object of the present invention to provide a reflective heat-sensitive recording medium which is excellent in sticking by printing and excellent in water resistance and solvent resistance, particularly suitable for medical use.

  As a result of intensive studies, the present inventors have found that in a thermal recording medium provided with a thermal recording layer and an uppermost layer in order to satisfy both high glossiness and good head matching that tend to be in a trade-off relationship at the same time. The uppermost layer contains a resin component obtained by crosslinking a core / shell type emulsion comprising at least a shell which is a water-soluble acrylic resin and a core part which is a hydrophobic acrylic resin emulsion with a crosslinking agent, and further contains volume average particles. Knowing that it is very effective to contain an inorganic pigment having a diameter of 0.005 to 0.5 μm and a lubricant having a volume average particle diameter of 0.01 to 0.9 μm, the present study was repeated. Invented.

That is, (1) “a thermosensitive recording layer and an uppermost layer comprising as a main component a binder resin as a binder on a support, a colorless or light leuco dye, and a color developer that heat-colors the leuco dye. A resin component obtained by crosslinking a core / shell type emulsion comprising at least a shell which is a water-soluble acrylic resin and a core portion which is a hydrophobic acrylic resin emulsion in a top layer with a crosslinking agent. A thermal recording medium comprising an inorganic pigment having a volume average particle size of 0.005 to 0.5 μm and a lubricant having a volume average particle size of 0.01 to 0.9 μm ”,
(2) “The core / shell type emulsion is a core / shell type emulsion composed of a shell containing an acrylamide resin and a core part containing an acrylic resin, and the crosslinking agent contains at least an aziridine compound. The heat-sensitive recording medium according to item (1), wherein:
(3) “Thermal recording medium according to (1) or (2) above, wherein at least one of the lubricants in the uppermost layer is fine particles of zinc stearate”,
(4) The above-mentioned items (1) to (1), wherein the inorganic pigment and the lubricant contained in the uppermost layer are a dispersion finely divided using at least a water-soluble resin and / or a nonionic surfactant. 3) thermal recording medium according to any one of items
(5) “Thermal recording medium according to item (4), wherein the nonionic surfactant is an ether type”,
(6) “The uppermost layer contains at least two kinds of particulate lubricants having different melting points at a melting point of 50 to 180 ° C., and the volume average particle diameter when these are mixed is 0.01 to 0.9 μm. The heat-sensitive recording medium according to any one of (1) to (5) above,
(7) The thermal recording medium according to any one of (1) to (6), wherein the softening point of the uppermost core / shell emulsion is 180 ° C. to 240 ° C. "
(8) The thermal recording medium according to any one of (1) to (7) above, wherein the uppermost layer contains at least 5 to 50 wt% of styrene-butadiene latex in the entire uppermost layer. "
(9) The above items (1) to (8), wherein the lower layer adjacent to the uppermost layer has a surface glossiness of 30 {GS (75 °)}% or more based on JIS-P-8142 ) Thermal recording medium according to any one of items
(10) “Thermal recording medium according to item (9), wherein an intermediate layer containing at least a water-soluble resin and / or a water-dispersible resin is provided between the uppermost layer and the thermosensitive recording layer”. ,
(11) containing a resin component obtained by cross-linking a core-shell emulsion composed of a shell and an acrylic resin, each of which is a water-soluble resin and / or a water-dispersible resin of the intermediate layer, with a cross-linking agent, The thermal recording medium according to item (10), wherein the crosslinking agent is an aziridine compound,
(12) The above-mentioned items (1) to (11), wherein the volume average particle diameter of leuco dye particles and developer particles contained in the heat-sensitive recording layer is 0.3 to 1.0 μm. The thermal recording medium according to any one of the items ",
(13) The above items (1) to (1), wherein the surface glossiness of the support on the heat-sensitive recording layer side based on JIS-P-8142 is 50 {GS (75 °)}% or more. The thermal recording medium according to any one of items 12),
(14) The thermal recording according to any one of (1) to (13), wherein a back layer is provided on a support opposite to the thermal recording layer of the thermal recording medium. Achieved by "medium".
Also, (15) “a recording method characterized in that the thermal recording medium described in any one of (1) to (14)” above is heated and colored by a printer equipped with a thermal head ”. ,
(16) "A recording method characterized in that the thermal recording medium according to any one of items (1) to (14) is used to develop a gradation image using a pulse control method",
(17) "A recording method characterized in that the thermal recording medium according to any one of (1) to (14) is characterized in that a gradation image is developed using a voltage control method". The

  As will be apparent from the following detailed and specific invention, according to the present invention, while maintaining high gloss, there is no image defect due to adhesion of the head residue, and sticking by printing is good, and water resistance and solvent resistance are excellent. In addition, the present invention has an extremely excellent effect that it is possible to provide a reflective heat-sensitive recording medium particularly suitable for medical use.

In recent recording, high speed and high definition have been demanded, and accordingly, the applied power tends to be increased for one element of the thermal head. Particularly in medical recording media, higher gradation is required, so higher output recording is required. At that time, the release function and the lubricity function when heating the outermost surface of the recording medium and the thermal head Becomes a very important requirement function.
In view of these required qualities, the outermost surface layer of these thermosensitive recording media is required to have a high mold release function for the lubricant.
However, in general, in order to give the glossiness of the heat-sensitive recording medium, it is necessary to make the outermost surface highly glossy. Therefore, in the outermost surface layer, a resin is used instead of film forming property, and the filler and the lubricant that reduce the gloss are reduced as much as possible. Furthermore, in order to achieve both glossiness, releasability and slipperiness, the outermost surface layer has an increased resin ratio, and inventions such as addition of a large amount of lubricants and fillers to the intermediate layer, the heat-sensitive recording layer and the like have been made. As described above, although there is an effect on the output per image such as sticking with respect to the higher output of the thermal head in the recent medical recording, the heating element by continuous recording in consideration of actual use It was not sufficient to prevent the sticking of the head residue to the head.

In the present invention, an inorganic pigment having a volume average particle diameter of 0.005 to 0.5 μm and a volume average particle diameter of 0.01 to 0.00 μm are provided on the outermost surface layer in order to satisfy sticking and head residue adhesion and high gloss. This is achieved by adding a 9 μm lubricant. Such a lubricant in the present invention includes, for example, an appropriate amount of an appropriate surfactant for ensuring wettability and an appropriate resin for preventing secondary aggregation in order to ensure liquid stability in miniaturization. This can be achieved by putting it in. In particular, in miniaturization, it is preferable to add more surfactant and water-soluble resin.

That is, high glossiness can be maintained without reducing the addition amount by refining these inorganic pigments and lubricant particles to a specific average particle size.
For inorganic pigments, if the average particle size is less than 0.005 μm, sufficient functions such as sufficient lubricity or releasability and oil absorption are not sufficient. On the other hand, if it exceeds 0.5 μm, there is a problem that the glossiness is lowered when the addition amount is increased. Regarding these inorganic pigments, it is preferable to add about 0.1 to 5 parts by weight, more preferably about 0.3 to 2 parts by weight with respect to 1 part of the resin used in the uppermost layer. Since these inorganic pigments have been refined to a volume average particle size of 0.005 to 0.5 μm, the gloss before heating can be maintained even if the amount added is increased.
However, when a recording medium containing a large amount of these inorganic pigments is heated and recorded with a thermal head, the color image becomes slightly whitish, and there may be a problem that the pure black image quality required for the medical image is impaired.

These problems can be solved by adding a lubricant that melts by heating. At the same time, it also exhibits the function of giving glossiness to the image surface.
As well as the above-mentioned effects, the lubricant has a function of preventing adhesion of debris by a releasing effect as well known, and a function of preventing sticking by imparting lubricity at the time of melting. It is.

As the lubricant used in the present invention, known lubricants can be used.
Specifically, various animal, vegetable, mineral or petroleum waxes such as higher fatty acids and their metal salts, higher fatty acid amides, higher fatty acid esters, montanic acid wax, polyethylene wax, paraffin wax, carnauba wax, rice wax, etc. And the like. These may be used alone or in combination of two or more.
Among these, metal salts of higher fatty acids have a high slip function release effect, and a high anti-sticking quality or an anti-scum effect. Furthermore, among these, zinc stearate is very effective, and it has been confirmed that good quality can be obtained.
Moreover, in the recording of medical images that particularly require gradation, it is necessary to cope with various thermal energies from the thermal head depending on the image to be recorded. By using a combination of two or more kinds of lubricant fine particles having different melting points, It is effective for these. In other words, by melting the lubricant for all images from low to high printing rates, it is possible to prevent head debris adhesion, sticking prevention, high image glossiness, and pure black images regardless of the printing rate. Can do.

The melting point of these lubricants is preferably 50 ° C. to 180 ° C. If the melting point is less than 50 ° C., blocking when the recording medium is stored in a high temperature environment, or a low melting point lubricant on the surface of the thermal recording medium after thermal recording of the thermal head. However, there is a problem in that precipitates such as white powder are easily generated on the surface.
Also, those having a melting point exceeding 180 ° C. are difficult to melt due to the thermal recording of the thermal head, and there is a problem that the effect of releasability of the head residue is small.

In order to achieve the glossiness that is the object of the present invention, it is necessary to use a lubricant having a volume average particle size of 0.01 μm to 0.9 μm. If the thickness is less than 0.01 μm, sufficient functions for sufficient lubricity or releasability are not sufficient, and if it exceeds 1.0 μm, there is a problem that the glossiness is lowered when the addition amount is increased.
Regarding the average particle diameter of the lubricant, when two or more kinds of lubricant particles are added, the average particle diameter in a liquid obtained by mixing them is shown. For this reason, it is not suitable that a dispersion of several kinds of lubricant particles causes aggregation by mixing.
Moreover, even if it is a little larger than the scope of the invention with only one kind of lubricant, it is possible to make these average particle diameters range by lowering the ratio in the total amount of several kinds of lubricant particles.

  About these lubricants, it is good to add 0.05-1.0 weight part with respect to 1 part of resin used for the uppermost layer, More preferably, about 0.1-0.5 weight part is added. Since these lubricants have been refined to have a volume average particle size of 0.01 to 0.9 μm, the gloss before heating can be maintained even if the amount added is increased.

As a method for refining these lubricants to have a volume average particle diameter of 0.01 to 0.9 μm, various known methods such as an emulsification method and a pulverization method using various beads can be used.
When these lubricants are made fine with an aqueous medium, it is difficult to make them fine with a single lubricant, and it is preferable to make them fine with a known water-soluble resin or surfactant. In particular, metal salts of higher fatty acids, higher fatty acid amides, and the like have a poor affinity with water, and many of them are softer, so that the problem of stabilization of the liquid when miniaturized tends to occur.
For these problems, it is conceivable to add a surfactant as a dispersant or an emulsifier.
Among these surfactants, the use of anionic surfactants for dispersibility and liquid stabilization is conceivable. Particularly effective and generally used are sulfonic acid-based and carboxylic acid-based surfactants. Surfactants are excellent in terms of dispersibility and station stability, and are relatively frequently used in other fields for finer dispersions.
However, since these surfactants are reactive with the aziridine compound used as the cross-linking agent in the uppermost layer of the present invention, the cross-linking reaction proceeds in the liquid due to the reaction over time after the addition of the cross-linking agent. As a result, problems such as an increase in viscosity of the liquid and a decrease in gloss due to aggregation of the lubricant fine particle dispersion occur.
Further, it has been conventionally known that cationic surfactants cause problems of corrosiveness to the thermal head and fogging of the thermal recording material.
Therefore, it is preferable to use a water-soluble resin or a nonionic surfactant in the lubricant dispersion used in the present invention.

In these nonionic surfactants, various generally known surfactants can be used. These surfactants can generally be selected from the HLB value and the like in consideration of the compatibility between water and the dispersion.
Furthermore, ether type surfactants have a good effect on metal salts and amide compounds of higher fatty acids, which have been particularly difficult to refine, and phenyl ether type surfactants have a desired particle size. It was suitable for miniaturization.
Regarding these surfactants, one or two or more surfactants may be used in combination in consideration of wettability, dispersibility, foam suppression and antifoaming properties. In consideration of the dispersion stability of fine particles when miniaturized, a water-soluble resin or a combination thereof may be used. As these water-soluble resins, various known resins can be used.

  Furthermore, in addition to these lubricant fine particles, a known lubricant such as a silicone oil, a silicone resin, a fluororesin, a silane coupling agent, or a liquid lubricant or a lubricant can be used in the uppermost layer.

Various general inorganic pigments can be used as the pigment used in the uppermost layer of the present invention. Specific examples include inorganic pigments such as zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, wax, kaolin, aluminum hydroxide, calcined kaolin, and urea formalin resin, polyethylene powder, etc. Organic pigments such as can be used in combination.
The pigment used in the present invention is required to have an average particle size of 0.005 to 0.5 μm and requires surface gloss, so that the oil absorption is 100 cc / 100 g or less and the specific surface area is 100 m ^2. / G or more is preferable, and aluminum hydroxide, kaolin, calcium carbonate, etc. are easily miniaturized and have excellent surface gloss.

Furthermore, in the present invention, it is also possible to use organic pigments in addition to inorganic pigments, such as polystyrene resin, polyethylene resin, polypropylene resin, urea-formalin resin, silicone resin, polymethyl methacrylate acrylate resin, melamine-formaldehyde. Various generally known organic pigments such as resins, polyesters, and condensation polymers such as polycarbonate can be used, and these do not impair the gloss that is the object of the present invention. It is also possible to add particles having a volume ratio of less than 1.5 times to the resin for the above (the core / shell type emulsion + the volume after solidification of the other binder resin used if necessary).

The resin used in the protective layer of the present invention prevents sticking due to heat from the thermal head while maintaining high gloss. Alternatively, the adhesion of debris to the thermal head due to continuous printing with high energy is prevented. In addition, it has good film-forming properties from the viewpoint of water resistance and alcohol resistance when handling printed images, and also requires high heat resistance, release properties against high heat, and lubricity, and is insoluble in water and alcohol. It is necessary to have a function such as a property and a barrier function. Considering these facts, it was very effective to use a core-shell emulsion and an aziridine compound comprising at least a shell which is an acrylamide resin and a core portion which is an acrylic resin in the uppermost layer.
In other words, by using materials of core / shell structure with different materials and characteristics, it is possible to simultaneously satisfy the generally contradictory requirements of high film-forming properties, high heat resistance and flexibility, and water resistance and solvent resistance. did it.
The softening point of these core-shell emulsions is preferably about 160 ° C to 260 ° C.
When the softening point exceeds 260 ° C., the film itself tends to be hard, and there is a problem that the film is easily cracked or curled when bent during handling or bent in the conveyance path of the printer. This problem is particularly likely to occur in a low humidity environment.
When the softening point is less than 160 ° C., the surface tends to bend or become a head residue during heat recording with a thermal head, and a tailing phenomenon tends to occur in an image.

As the cross-linking agent used in the present invention, an aziridine compound is the best, and since the cross-linking reaction is very fast, the function tends to be exerted immediately after drying the film. For this reason, it is possible to shorten and simplify the process, such as eliminating the need for a curing process for the crosslinking reaction.
The number of functional groups of the aziridine compound is preferably 2 or more, preferably 3 or more. By increasing the number of functional groups, the crosslinking density can be increased, and by having good barrier performance, water resistance and solvent resistance performance can be improved.
The amount of the crosslinking agent is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 part by weight with respect to 1 part by weight of the resin. If the crosslinking agent is less than 0.01 parts by weight, the crosslinking reaction is not sufficient, and the heat of the thermal head during heat recording causes the resin film to burn out or stick to the heating element of the thermal head. To do.
On the other hand, if the crosslinking agent exceeds 1 part by weight, the amount of the crosslinking agent becomes excessive, so that an uncrosslinked product or a self-crosslinked product due to moisture increases, which tends to cause head debris at the time of heat recording, and a tailing phenomenon tends to occur in an image.

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

In the present invention, it is preferable that gloss is achieved in the uppermost layer from the viewpoint of high gloss and that the adjacent lower layer is also highly glossy, and the adjacent lower layer has a surface glossiness of 30 based on JIS-P-8142. When it is {GS (75 °)}% or more, further excellent gloss can be achieved.
As a specific means, when it is a heat-sensitive recording layer as an adjacent lower layer, a colorless or light-colored leuco dye contained in the heat-sensitive recording layer, a color developer that heat-colors the leuco dye, and further a pigment or an additive, etc. These glossinesses can be achieved by setting the volume average particle size of the particles to 0.3 to 1.0 μm. Alternatively, it can also be achieved by setting the ratio of the resin binder contained in the heat-sensitive recording layer to 30 to 80 parts by weight of the heat-sensitive recording layer and imparting smoothness.

In addition, it is effective to provide an intermediate layer mainly composed of a resin between the heat-sensitive recording layer and the uppermost layer. By using a layer having a high resin ratio, very high glossiness can be achieved.
When these intermediate layers are provided, it is preferable that a water-soluble resin and / or a water-dispersible resin are mainly used in order to achieve high gloss. Furthermore, in order to provide a barrier function against water and solvent, it is desirable to use in combination with a crosslinking agent.
In order to provide further effects, it is desirable to contain an aziridine compound as a crosslinking agent and a core-shell type emulsion composed of a shell which is an acrylamide resin used in the uppermost layer and a core part which is an acrylic resin.

  There is no restriction | limiting in particular in the coating method of an intermediate | middle layer, It can apply by a conventionally well-known method. The preferred thickness is 0.1 to 20 μm, more preferably 0.5 to 10 μm. If the intermediate layer is too thin, the functions of water resistance and solvent resistance are insufficient for glossiness, and if it is too thick, the thermal sensitivity of the recording material is lowered and also disadvantageous in terms of cost.

(Developer)
As the developer used in the present invention, various electron-accepting materials that react with the leuco dye upon heating to develop the color are applied. Specific examples thereof include phenolic compounds as shown below. Substances, organic or inorganic acidic substances or esters and salts thereof may be mentioned.

  Gallic acid, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4,4′-isopropylidenediphenol, 1,1′-inopropylidenebis (2-chlorophenol), 4,4′-isopropylidenebis (2,6-dibromophenol), 4,4′-isopropylidenebis (2,6-dichlorophenol), 4,4′-isopropylidenebis (2-methylphenol), 4,4′-isopropylidenebis (2,6-dimethylphenol), 4,4-isopropylidenebis (2-tert-butylphenol), 4,4 '-Sec-butylidene diphenol, 4,4'-cyclohexylidenebisphenol, 4,4'-cyclo Silidenebis (2-methylphenol), 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 3,5-xylenol, thymol, methyl-4-hydroxybenzoate, 4- Hydroxyacetophenone, novolac type phenolic resin, 2,2′-thiobis (4,6-dichlorophenol), catechol, resorcin, hydroquinone, pyrogallol, phloroglysin, phloroglysin carboxylic acid, 4-tert-octylcatechol, 2,2 ′ -Methyl bis (4-chlorophenol), 2,2'-methyl bis (4-methyl-6-tert-butylphenol), 2,2, -dihydroxydiphenyl, ethyl p-hydroxybenzoate, p-hydroxybenzoate Pill, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-hydroxybenzoic acid-p-chlorobenzyl, p-hydroxybenzoic acid-o-chlorobenzyl, p-hydroxybenzoic acid-p-methylbenzyl, p -Hydroxybenzoic acid-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy-6-naphthoic acid, zinc 2-hydroxy-6-naphthoate, 4-hydroxydiphenylsulfone, 4 -Hydroxy-4'-chlorodiphenylsulfone, bis (4-hydroxyphenyl) sulfide, 2-hydroxy-p-toluic acid, zinc 3,5-di-tert-butylsalicylate, 3,5-di-tert-butylsalicylic acid Tin, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stear Acid, 4-hydroxyphthalic acid, boric acid, thiourea derivative, 4-hydroxythiophenol derivative, bis (4-hydroxyphenyl) acetic acid, bis (4-hydroxyphenyl) acetic acid ethyl, bis (4-hydroxyphenyl) acetic acid n-propyl, m-butyl bis (4-hydroxyphenyl) acetate, phenyl bis (4-hydroxyphenyl) acetate, benzyl bis (4-hydroxyphenyl) acetate, phenethyl bis (4-hydroxyphenyl) acetate, bis (3- Methyl-4-hydroxyphenyl) acetic acid, bis (3-methyl-4-hydroxyphenyl) acetic acid methyl, bis (3-methyl-4-hydroxyphenyl) acetic acid n-propyl, 1,7-bis (4-hydroxyphenylthio) ) 3,5-dioxaheptane, 1,5-bis (4-hydroxyphenylthio) ) 3-oxaheptane, dimethyl 4-hydroxyphthalate, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-ethoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy -4′-propoxydiphenylsulfone, 4-hydroxy-4′-butoxydiphenylsulfone, 4-hydroxy-4′-isobutoxydiphenylsulfone, 4-hydroxy-4-butoxydiphenylsulfone, 4-hydroxy-4′-tert- Butoxydiphenylsulfone, 4-hydroxy-4'-benzyloxydiphenylsulfone, 4-hydroxy-4'-phenoxydiphenylsulfone, 4-hydroxy-4 '-(m-methylbenzyloxy) diphenylsulfone, 4-hydroxy-4 - (p-methyl benzyloxycarbonyl) diphenyl sulfone, 4-hydroxy -4 '- (O-methyl benzyloxycarbonyl) diphenyl sulfone, 4-hydroxy -4' - (p-chloro-benzyloxycarbonyl) diphenyl sulfone.

  In the present invention, the weight of the developer in the heat-sensitive recording layer is preferably in the range of 0.5 to 5.0, particularly preferably in the range of 2.0 to 4.0 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 is increased, 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.

  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, phenothiocyan, 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 heat-sensitive 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.
Therefore, as a second condition necessary for the 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 and a near infrared coloring dye are used as the leuco dye. , One or more of each must be mixed and used.

（（式中、Ｒ２は水素原子、ハロゲン原子、炭素数１〜４のアルキル基又はアルコキシ基を、Ｒ３は炭素数１〜４のアルキル基を表す。）

(In the formula, R2 represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group, and R3 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). ) Fluoran.

  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 means a color tone that develops color when heated and shows 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 650 to 700 nm are filled to make the absorption in the visible region flat like silver salt.

  As a measure of blackening of the image, it can be roughly expressed by the minimum / maximum ratio of 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 lamps, such as daylight color and daytime white, can also 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 amount of the leuco dye represented by the general formula (3) is larger than the above range, it becomes difficult to blacken the image area, and when it is small, 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-isoamylamino) -3-methyl-1-phenyl-3′-one and the like.

In order to produce the heat-sensitive recording material of the present invention, when a leuco dye and a developer are bonded and supported on a support, various conventional binders can be appropriately used. Specific examples thereof include, for example, the following: Can be mentioned.
Polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic Acid terpolymers, styrene / maleic anhydride copolymer alkali salts, isobutylene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, as well as polyvinyl acetate , Polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer John and styrene / butadiene copolymer, styrene / butadiene / latex such as acrylic copolymer.
Moreover, these and surfactant, a crosslinking agent, and an adjuvant can be used together. By using together with the crosslinking agent that reacts with the binder, the adhesion to the support is excellent, and the water resistance and solvent resistance are improved.
Various conventional crosslinking agents can be used.

  Further, in the heat-sensitive recording layer of the present invention, together with the leuco dye and the developer, if necessary, auxiliary additive components commonly used in this type of heat-sensitive recording material, for example, a filler, a heat-fusible substance, A surfactant or the like can be used in combination. In this case, examples of the filler include inorganic fine powders such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, surface-treated calcium and silica, and the like. Organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, polystyrene resin and the like, and examples of heat-fusible substances include higher fatty acids or esters, amides or metal salts thereof. In addition, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, higher ketones, p-benzylbiphenyl, etc. And those having a melting point of about 50 to 200 ° C., such as heat fusible organic compounds.

  The method for applying the heat-sensitive recording layer is not particularly limited, and can be applied by a conventionally known method. The preferred thickness is 1-30 μm, more preferably 3-20 μm. If the thickness is too thin, the image density is not sufficient, and if it is too thick, the thermal sensitivity of the recording material is lowered, the background density is applied, and the cost is disadvantageous.

  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, and preferably synthetic paper mainly composed of polypropylene resin. However, it is not limited to these. Among these, in view of the contrast of image quality for use in reflection images, those having high opacity and whiteness are preferable. In consideration of surface gloss, reproducibility of printing, high definition, and the like, it is preferable that the support surface is smooth and has high gloss.

If the surface glossiness of the support is 50 {GS (75 °)}% or more based on JIS-P-8142 glossiness on the thermal recording layer side, not only the surface glossiness of the thermal recording medium is excellent, but also thermal Since it has excellent adhesion to the head, it also shows the effects of fineness during recording, missing images, and higher sensitivity.
In general, means for improving the quality of glossiness and high sensitivity by smoothing the heat-sensitive recording medium using a super calender or the like is used, but it is based on JIS-P-8142 as described above. By using a support having a surface glossiness of 50 {GS (75 °)}% or more, it is possible to provide an effect that these steps can be omitted and simplified.

In addition, in order to improve the adhesion of the coating layer of the thermal recording layer coating solution, at least one side of these supports is subjected to surface modification by corona discharge treatment, oxidation reaction treatment (chromic acid, etc.), etching treatment, etc. Can do.
For use in the medical field, a polypropylene-based synthetic paper of about 50 μm to 250 μm is easy to use because of ease of handling.

In the present invention, a back layer may be provided on the surface opposite to the recording layer and the protective layer.
The back layer can be provided with functions such as an antistatic function, an anti-curl function, and an adhesion prevention by overlapping.

With regard to the antistatic agent in the present invention, various antistatic agents are currently used in various applications. For the antistatic function, a surface resistance value of 10 ¹⁰ Ωcm or less is required.
The antistatic agents that can provide this level 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, such as materials doped with electron donors in organic polymers. Examples of organic polymers used in these polymers include polyacetylene. Aliphatic, aromatic such as polyparaphenylene, heterocyclic such as polypyrrole, conjugated polymers such as aromatic amines such as polyaniline, and cyclic π-conjugated groups in the side chain even if the main chain is not conjugated 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 a conductive function even under 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. Since many of these metal oxides are colored and impair transparency, it is preferable that the metal oxide be as small as possible as long as the requirements in the present invention are satisfied.

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 may be 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 adhering 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 Spherical organic fillers such as spherical inorganic fillers such as taruisite, polystyrene resins, polyethylene resins, polypropylene resins, urea-formalin resins, silicone resins, polymethylmethacrylate resins, melamine-formaldehyde resins, polyesters, polycarbonates, etc. Although a filler is mentioned, this invention is not limited to this.

  With respect to these fillers, those having an average particle diameter of 6 to 25 μm are particularly good in order to prevent adhesion, and spherical fillers are preferred because they can efficiently form convex portions on the surface. 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, Spherical inorganic fillers such as calcined clay and hydrotalicite, and condensation polymers such as polystyrene resin, polyethylene resin, polypropylene resin, urea-formalin resin, silicone resin, polymethyl methacrylate acrylate resin, melamine-formaldehyde resin, polyester, polycarbonate, etc. However, the present invention is not limited to this.

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

  The method for forming an image using the heat-sensitive recording medium of the present invention is performed by heating the heat-sensitive recording medium in an image-like manner by a heating means based on character and / or shape information. The heating means is not particularly limited depending on the purpose of use, such as a thermal pen, a thermal head, or laser heating, but the thermal recording medium of the present invention prints 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.

  In consideration of medical use, it is necessary to provide gradation to an image, and means for imparting gradation may be a pulse control system or a voltage control system.

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, all 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 0.8 μm or less to prepare a developer dispersion.
(1) Preparation of heat-sensitive recording layer coating solution [A solution] Preparation of dye dispersion-2-Alinino-3-methyl-6-dibutylaminofluorane 20 parts-Polyvinyl alcohol 10% aqueous solution 20 parts-Water 60 parts [ Liquid B] Developer dispersion, 4-hydroxy 4'-isopropoxydiphenyl sulfone 12 parts, silica 4 parts, stearamide 4 parts, 10% aqueous solution of polyvinyl alcohol 20 parts, water 60 parts [C liquid] recording layer Liquid / A liquid 12.5 parts / B liquid 62.5 parts / Polyvinyl alcohol 10% aqueous solution 25 parts Each of the above-mentioned blends is magnetic ball milled so that the average particle size is 1.5 μm or less. [Liquid A] and [Liquid B] were prepared. Next, 12.5 parts of [Liquid A], 62.5 parts of [Liquid B], and 25 parts of modified polyvinyl alcohol (Kuraray K Polymer KL-318, solid content 10%) were mixed and stirred to produce a thermosensitive recording layer solution. [C liquid] was adjusted.
The recording layer coating solution [C solution] was coated on a synthetic paper with a thickness of 170 μm (Nanya PX170 surface gloss 60%) using a wire bar, and dried by passing it through a dryer maintained at a temperature of 70 ° C. for 3 minutes. Thus, a thermosensitive recording layer A (surface glossiness of 25%) having a thickness of 8.5 g / m ² was formed.
[Liquid] Top layer liquid (H liquid)
-Core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts-D liquid stearic acid amide dispersion (volume average particle system 0.7 μm) 6 parts-F liquid calcium carbonate dispersion volume average particle system 0. 2 parts) 30 parts, 63 parts of water, polyamide epichlorohydrin compound (manufactured by Seiko PMC, paper strength agent WS-525, solid content 25%) 8 parts

[Comparative Example 2]
The following composition was pulverized and dispersed with a ball mill until the volume average particle size became 0.8 μm or less to prepare a developer dispersion.
(1) Preparation of heat-sensitive recording layer coating solution [A solution] Preparation of dye dispersion-2-Alinino-3-methyl-6-dibutylaminofluorane 20 parts-Polyvinyl alcohol 10% aqueous solution 20 parts-Water 60 parts [ Liquid B] Developer dispersion, 4-hydroxy 4'-isopropoxydiphenyl sulfone 12 parts, silica 4 parts, stearamide 4 parts, 10% aqueous solution of polyvinyl alcohol 20 parts, water 60 parts [C liquid] recording layer Liquid / A liquid 12.5 parts / B liquid 62.5 parts / Polyvinyl alcohol 10% aqueous solution 25 parts Each of the above-mentioned blends is magnetic ball milled so that the average particle size is 1.5 μm or less. [Liquid A] and [Liquid B] were prepared. Next, 12.5 parts of [Liquid A], 62.5 parts of [Liquid B], and 25 parts of modified polyvinyl alcohol (Kuraray K Polymer KL-318, solid content 10%) were mixed and stirred to produce a thermosensitive recording layer solution. [C liquid] was adjusted.
The recording layer coating solution [C solution] was coated on a synthetic paper with a thickness of 170 μm (Nanya PX170 surface gloss 60%) using a wire bar, and dried by passing it through a dryer maintained at a temperature of 70 ° C. for 3 minutes. Thus, a thermosensitive recording layer A (surface glossiness of 25%) having a thickness of 8.5 g / m ² was formed.

(2) Adjustment of uppermost layer coating liquid [D liquid] Adjustment of lubricant dispersion
20 parts of stearic acid amide 20 parts of polyvinyl alcohol 20 parts 60 parts of water [E liquid] filler dispersion 20 parts of calcium carbonate (Brt15) 20 parts of 10% aqueous solution of polyvinyl alcohol 60 parts of water [liquid F ] Upper layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 40 parts D liquid stearic acid amide dispersion (volume average particle system 1.2 μm) 2 parts E liquid calcium carbonate dispersion volume average Particle system 0.2 μm) 12 parts, water 56 parts, aziridine compound (Chemite PZ-33 manufactured by Nippon Shokubai Co., Ltd.) 2 parts Each of the above blends was pulverized with a magnetic ball mill, and the volume average particle system 1.2 [mu] m [Liquid D] and a volume average particle system 0.2 [mu] m [Liquid E] were prepared, mixed and stirred to prepare the uppermost layer F liquid. Furthermore, it was coated on the recording layer A using a wire bar and dried by passing through a dryer maintained at a temperature of 70 ° C. for 3 minutes to form a top layer of 3 g / m ² , thereby preparing a comparative example 2 sample. .
The particle size was measured with a laser diffraction particle size measuring device LA-920 manufactured by Horiba.

[Example 1]
The recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 except that the uppermost layer liquid dispersion D was used as the uppermost layer liquid I liquid. Example 1 sample was prepared.
[Liquid I] Uppermost layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts / H liquid stearic acid amide dispersion (volume average particle system 0.7 μm) 6 parts / F liquid calcium carbonate dispersion Liquid volume average particle system 0.2 μm) 30 parts, 63 parts of water, polyamide epichlorohydrin compound (manufactured by Seiko PMC, paper strength agent WS-525, solid content 25%) 8 parts

[Comparative Example 3]
[Liquid G] Top layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts D liquid stearic acid amide dispersion (volume average particle system 1.2 μm) 6 parts F liquid calcium carbonate dispersion Liquid volume average particle system 0.2 μm) 30 parts, water 63 parts, aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 2 parts Recording layer, The uppermost layer was formed, and a comparative example 3 sample was prepared.

[Example 2]
The recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 except that the uppermost layer liquid dispersion D was used as the uppermost layer liquid II liquid. Example 2 A sample was prepared.
[Liquid II] Uppermost layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts / H liquid stearic acid amide dispersion (volume average particle system 0.7 μm) 6 parts / F liquid calcium carbonate dispersion Liquid volume average particle system 0.2 μm) 30 parts, water 63 parts, aziridine compound (Chemite PZ-33 made by Nippon Shokubai) 2 parts

[Comparative Example 4]
[Liquid J] Top layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts / Zinc stearate emulsion liquid (volume average particle size 0.9 μm Chukyo Yushi F-930 solid content 40%) 3 parts / F liquid calcium carbonate dispersion volume average particle system 0.2 μm) 30 parts / water 66 parts / aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 2 parts In the same manner as in Example 1, the recording layer and the uppermost layer were formed, and a sample of Comparative Example 4 was prepared.

[Example 3]
[Liquid K] Top layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 30 parts / Zinc stearate emulsion liquid (volume average particle size 0.2 μm Chukyo Yushi K-994 solid content 20%) 7 parts F liquid calcium carbonate dispersion volume average particle system 0.2 μm) 30 parts water 66 parts aziridine compound (Chemite PZ-33 made by Nippon Shokubai) 2 parts Stearic acid with volume average particle diameter 0.2 μm Example 3 A recording layer and an uppermost layer were formed in the same manner as in Comparative Example 1 except that the solution was a zinc emulsion (Kyotsu K-994 20% solution, metal salt of dispersant anionic alkylbenzene sulfonic acid). A sample was created.

[Example 4]
[Liquid L] Preparation of lubricant dispersion
・ 10 parts of zinc stearate ・ 10 parts of 10% aqueous solution of polyvinyl alcohol ・ 2 parts of acetylenic diol surfactant (nonionic) ・ 78 parts of water [M liquid] Top layer liquid ・ Core / shell resin (Barrier Star made by Mitsui Chemicals) B1000 20% liquid) 30 parts / L liquid zinc stearate dispersion (volume average particle system 0.6 μm, solid content 20%) 12 parts / F liquid calcium carbonate dispersion volume average particle system 0.2 μm) 30 parts / water 59 Part ・ Aziridine compound (Chemite PZ-33 manufactured by Nippon Shokubai Co., Ltd.) 2 parts Each compound consisting of the above ingredients was pulverized with a magnetic ball mill to prepare [Liquid L] having a volume average particle size of 0.7 μm. The recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 except that the uppermost layer M solution was prepared by mixing and stirring to prepare a sample of Example 4.

[Example 5]
[N liquid] Preparation of lubricant dispersion
・ Zinc stearate ・ 10 parts ・ 10 parts of polyvinyl alcohol 10 parts ・ Phenyl ether type surfactant (Daiichi Kogyo Seiyaku Neugen EA-87) 2 parts ・ Water 78 parts [O liquid] Top layer liquid ・ Core / Shell resin (barrier star B1000 20% liquid manufactured by Mitsui Chemicals) 30 parts · N liquid zinc stearate dispersion (volume average particle system 0.5 µm solid content 20%) 12 parts · F liquid calcium carbonate dispersion volume average particle system 0 .2 μm) 30 parts / water 59 parts / aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 2 parts Each of the above blends was ground in a magnetic ball mill and the volume average particle size 0.5 μm. [N solution] was prepared, mixed and stirred, and the recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 except that the uppermost layer O solution was prepared.

[Example 6]
[Liquid P] Top layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B1000 20% liquid) 20 parts / F liquid calcium carbonate dispersion volume average particle system 0.2 μm) 20 parts / zinc stearate emulsion dispersion 1 Part (Chukyo Yushi F-930 solid content 40%)
・ Carnauba wax emulsion dispersion 2 parts (Sekyo 524 Sesol 524 solid content 40%)
・ Polyethylene wax emulsion 4 parts (L-787 solid content 30% made by Chukyo Yushi)
・ 59 parts of water ・ Aziridine compound (Chemite PZ-33 manufactured by Nippon Shokubai) 1 part 1 part of zinc stearate emulsion dispersion (F-930), 2 parts of carnauba wax emulsion dispersion (Sesol 524) and polyethylene wax emulsion (L- 787) 4 parts were mixed, and the volume average particle diameter measured by a laser diffraction particle diameter measuring apparatus LA-920 manufactured by HORIBA, Ltd. was 0.3 μm.
Except for the uppermost layer P solution, the recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1, and a sample of Example 6 was prepared.

[Example 7]
[Liquid Q] Top layer liquid / core / shell resin (Mitsui Chemicals Barrier Star B2000 20% liquid) 20 parts / F liquid calcium carbonate dispersion volume average particle system 0.2 μm) 20 parts / zinc stearate emulsion dispersion 1 Part (Chukyo Yushi F-930 solid content 40%)
・ Carnauba wax emulsion dispersion 2 parts (Sekyo 524 Sesol 524 solid content 40%)
・ Polyethylene wax emulsion 4 parts (L-787 solid content of Chukyo Yushi) 30%
-59 parts of water-Aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 1 part Except that the uppermost layer liquid was changed to the Q liquid, the recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 It was created.

[Example 8]
[R liquid] Top layer liquid, styrene-butadiene latex emulsion (PA-9159, 47.5%, manufactured by A & D) 2 parts, core / shell resin (Mitsui Chemicals Barrier Star B2000 20% liquid), 20 parts, F liquid carbonic acid Calcium dispersion volume average particle system 0.2 μm) 20 parts, zinc stearate emulsion dispersion 1 part (F-930, solid content 40% by Chukyo Yushi)
・ Carnauba wax emulsion dispersion 2 parts (Sekyo 524 Sesol 524 solid content 40%)
・ Polyethylene wax emulsion 4 parts (L-787 solid content 30% made by Chukyo Yushi)
・ 59 parts of water ・ Aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 1 part Except for the uppermost layer R solution, the recording layer and the uppermost layer were formed in the same manner as in Comparative Example 1 to prepare Example 8 samples. did.

[Example 9]
[S liquid] Recording layer liquid / A liquid 10 parts / B liquid 50 parts / Polyvinyl alcohol 10% aqueous solution 40 parts The recording layer coating liquid [S liquid] is placed on a 170 μm-thick synthetic paper (PX170 made by Nanya) with a wire bar. And dried by passing through a drier maintained at a temperature of 70 ° C. for 3 minutes to form a thermosensitive recording layer B (surface glossiness 35%) having a thickness of 10 g / m ² . Except for the above, the uppermost layer was formed in the same manner as in Example 7 to prepare Example 9.

[Example 10]
[T solution] Intermediate layer solution 1
・ Water 12 parts ・ Polyvinyl alcohol 10% aqueous solution 100 parts ・ Polyamide epichlorohydrin (paper strength agent WS-525 25%) 8 parts Intermediate layer T solution was coated on the thermal recording layer A using a wire bar, A dryer maintained at a temperature of 70 ° C. was passed through for 3 minutes to form a film having a thickness of 3 g / m ² , and an uppermost layer R solution was formed thereon to prepare a sample of Example 10.

[Example 11]
[U liquid] Intermediate liquid 2
・ 70 parts of water ・ Core / shell resin (Mitsui Chemicals Barrier Star B2000 20% solution) 120 parts ・ Aziridine compound (Chemite PZ-33 made by Nippon Shokubai Co., Ltd.) 5 parts A coating was applied using a bar, and a dryer maintained at a temperature of 70 ° C. was passed through for 3 minutes to dry to form a film having a thickness of 3 g / m ^2. Further, the uppermost layer R solution was formed thereon, Example 11 A sample was created.

[Comparative Example 5]
A sample of Comparative Example 5 was prepared in the same manner as in Example 11 except that FPG200 (PP film manufactured by YUPO 200 μm, surface glossiness 11%) was used as the support.

[Example 12]
[V liquid] Back layer, water 45 parts, 10% aqueous solution of polyvinyl alcohol 40 parts, silica (Mizusawa Chemical P527) 1 part, antistatic agent (Chemitat KM-7005) 10 parts, polyamide epichlorohydrin (paper strength agent WS- 525 25%) 4 parts Example 10 Sample was prepared as a 4 g / m ² back layer by coating V solution on the opposite side of Example 10 sample and drying.

(Evaluation methods)
In addition, for the heat-sensitive recording materials of Examples and Comparative Examples produced as described above,
1. 1. Surface glossiness 2. Head casks Sticking
4). 4. Cracks 5. Water resistance 6. Solvent resistance 7. Pot life of liquid The transportability of the film was evaluated.

1. Glossiness Measured with Nippon Denshoku Industries glossiness meter Model 1001DP 75 °.
The higher the value, the higher the glossiness.
2. Head casks
With a variable energy horizon (manufactured by CODONICS) equipped with a gradation head with a resolution of 300 dpi, a pattern with a printing rate of 100% in the width direction and a printing rate of 0% in the other half is created. Halftones with a printing rate of 40-80% are printed before and after the test, and the effect on the image is judged visually.
○: No change in front and rear halftone images.
(Triangle | delta): The density of the printing rate 100% part looks dark after continuous printing.
X: After continuous printing, an image with a printing rate of 100% becomes light and scratched.
3. Sticking With a variable energy horizon (manufactured by CODONICS) equipped with a gradation head with a resolution of 300 dpi, printing with a pattern that prints gradation in the flow direction, and visually determining the effect on the image.
○: No stick is generated.
Δ: A stick line can be seen, but the print length is not a problem.
X: The stick line is clearly visible and the image length is short.
4). Cracks Samples were cut to a width of 50 mm and a length of 100 mm and stored in an environment of 10 ° C. and 30% Rh for 3 hours or more. Then, the thermal layer was wound around a Φ20 mm roll and returned to the surface. Evaluation.
○: Cracks do not occur.
Δ: Cracks occur in several places.
X: Cracks occur on the entire wound surface.
5. Water resistance After dropping 1 drop of water on the surface of the sample with a dropper and wiping with gauze after 1 min, the wiping trace is visually evaluated.
〇: There is no trace at all.
Δ: Some traces are visible.
X: The film is completely peeled off.
6. Alcohol resistance One drop of 70% IPA liquid water was dropped on the surface of the sample with a dropper, and after wiping with gauze after 1 min, the wiping trace was visually evaluated.
〇: There is no trace at all.
Δ: Some color marks are visible.
X: Completely colored.
XX: The film is completely peeled. Pot life of coating liquid The liquid property of the uppermost layer was compared between the initial state after addition of the crosslinking agent and the liquid property after 5 hours.
○: No change.
Δ: Slightly thickened.
X: The liquid hardly moves.
8. Film transportability Cut the sample into A4 size, stack two sheets, and evaluate the double feed after printing one test pattern on horizon (Codonics).
○: Transport without problems.
Δ: The lower one is moving partway through the printing.
X: Two sheets are completely fed and printed. Or a conveyance error occurs on the way.
The evaluation results are shown in Table 1.

Claims (17)

In a heat-sensitive recording medium comprising a binder resin as a binder, a colorless or light leuco dye, and a heat-sensitive recording layer mainly composed of a developer that heat-colors the leuco dye and an uppermost layer on the support, The uppermost layer contains a resin component obtained by crosslinking a core / shell emulsion composed of at least a shell which is a water-soluble acrylic resin and a core portion which is a hydrophobic acrylic resin emulsion with a crosslinking agent, and further has a volume average particle diameter. A heat-sensitive recording medium, comprising an inorganic pigment having a volume average particle diameter of 0.01 to 0.9 μm and an inorganic pigment having a diameter of 0.005 to 0.5 μm. The core / shell type emulsion is a core / shell type emulsion composed of a shell containing an acrylamide resin and a core part containing an acrylic resin, and the crosslinking agent contains at least an aziridine compound. The heat-sensitive recording medium according to claim 1. 3. The heat-sensitive recording medium according to claim 1, wherein at least one of the top layer lubricants is zinc stearate fine particles. 4. The thermal recording according to claim 1, wherein the inorganic pigment and the lubricant contained in the uppermost layer are a dispersion finely divided using at least a water-soluble resin and / or a nonionic surfactant. Medium. The thermal recording medium according to claim 4, wherein the nonionic surfactant is an ether type. The uppermost layer contains at least two kinds of particulate lubricants having different melting points at a melting point of 50 to 180 ° C., and a volume average particle diameter when they are mixed is 0.01 to 0.9 μm. The heat-sensitive recording medium according to claim 1. The thermosensitive recording medium according to any one of claims 1 to 6, wherein the softening point of the uppermost core / shell emulsion is 180 ° C to 240 ° C. The thermosensitive recording medium according to any one of claims 1 to 7, wherein the uppermost layer contains at least 5 to 50 wt% of styrene-butadiene latex in the entire uppermost layer. 9. The thermal recording medium according to claim 1, wherein the lower layer adjacent to the uppermost layer has a surface glossiness of 30 {GS (75 °)}% or more based on JIS-P-8142. . The thermal recording medium according to claim 9, wherein an intermediate layer containing at least a water-soluble resin and / or a water-dispersible resin is provided between the uppermost layer and the thermal recording layer. A water-soluble resin and / or a water-dispersible resin in the intermediate layer contains a resin component obtained by cross-linking a core-shell type emulsion made of a shell and an acrylic resin made of an acrylamide resin with a cross-linking agent, and the cross-linking agent is aziridine The thermosensitive recording medium according to claim 10, which is a compound. The heat-sensitive recording medium according to any one of claims 1 to 11, wherein the volume-average particle diameter of the leuco dye particles and developer particles contained in the heat-sensitive recording layer is 0.3 to 1.0 µm. The heat-sensitive recording according to any one of claims 1 to 12, wherein the surface glossiness on the heat-sensitive recording layer side of the support is 50 {GS (75 °)} or more based on JIS-P-8142. Medium. 14. The thermosensitive recording medium according to claim 1, wherein a back layer is provided on a support opposite to the thermosensitive recording layer of the thermosensitive recording medium. 15. A recording method, wherein the heat-sensitive recording medium according to claim 1 is heated and colored by a printer equipped with a thermal head. 15. A recording method, wherein a gradation image is developed on the heat-sensitive recording medium according to claim 1 using a pulse control method. 15. A recording method comprising: forming a gradation image on the heat-sensitive recording medium according to claim 1 by using a voltage control method.