A thermally sensitive recording medium

Abstract: A thermally sensitive recording medium which comprises, in order on a substrate, a thermally sensitive recording layer and a glossing layer which has a surface glossiness based on JIS-P-8142 greater than 50% at an angle of incidence and angle of reflection of 75° and which comprises an inorganic pigment and a fixing composition which does not cause sticking at a temperature above 200°C. This recording medium has good printability and surface glossiness.

Description: The present invention relates to a thermally sensitive recording medium whose preservability, printability and glossiness are improved. A thermally sensitive recording medium having a thermally sensitive layer mainly composed of colorless or pale colored dye precursor which is an electron donating dye precursor (hereinafter shortened to a dye precursor) and a color developer which develops color by a chemical reaction with said dye precursor when heated, is disclosed in Japanese Patent Publication 45-14035 and is widely and practically used. For the recording means using said thermally sensitive recording medium, a thermal printer in which a thermal head is built is used. This recording method is superior to the conventional ordinary recording methods from the point of view of noiseless recording, no need of development and fixing procedures, maintenance free, relatively cheap and compact and provides a very clear image. Therefore, it is widely used in the field of facsimile and computer, various kinds of measuring equipment and labels. However, in the case of a conventional thermal recording medium, since only a thermally sensitive recording layer whose main components are dye precursor, color developer and fixing agent is coated on the surface of substrate, the resistance against light, water, heat, plasicizer and oil are not stable and the color change by aging at preservation is pointed out as a problem. Further, in a case of this type of thermal recording medium, the glossiness of image part and not image part is not considered. To solve the problem of the conventional thermally sensitive recording medium, the method of forming a protecting layer over the surface of the thermally sensitive recording layer has been suggested. For example, the method of using hydrophobic emulsion of a high polymer compound as disclosed in Japanese Patent Laid Open Publication 56-146794 or the method of forming an intermediate layer of water soluble high polymer compound or hydrophobic emulsion of high polymer compound and then forming a surface layer by oil type coating composed by hydrophobic high polymer compound over the above mentioned intermediate layer as disclosed in Japanese Patent Laid Open Publication 58-199189 are reported. In these methods, the preservative property of the image is improved, however, the glossiness of it is very low level. In general, UV varnish is coated over the surface of the thermally sensitive recording medium to provide the lustrous property. However, this method has several problems. That is, since the thermally sensitive recording medium by this method generates sticking during the printing procedure, it is not suited to a thermal head. Further, the fixing of ink on this thermally sensitive recording medium is not good and the printing property of it is not sufficient. In Japanese Patent Laid Open Publication 1-178486, a thermally sensitive recording medium having an intermediate layer composed of water soluble high polymer, pigment and cross-linking agent on the thermally sensitive recording layer, further having a glossing layer composed of lustrous hydrophobic high polymer compound and a slipping agent on said intermediate layer is described. However, since this glossing layer is coated using solvent, the working efficiency for coating is very bad and is not sufficient for practical use. Further, in Japanese Patent Laid Open Publication 2-169292, a thermally sensitive recording medium on which a protecting layer mainly composed of wax, resin, inorganic pigment smaller than 0.5 µm average diameter or composed mainly of resin and inorganic pigment smaller than 0.5 µm average diameter is disclosed. And, in Japanese Patent Laid Open Publication 2-175281, the lustrous thermally sensitive recording medium which has a protecting layer composed of silica whose average diameter is smaller than 0.05 µm and/or calcium carbonate and water soluble binder is disclosed. If these protecting layers are formed, and when printed by a thermal head, glossiness of the surface is deteriorated and sometimes a problem of sticking is generated. Further, in Japanese Patent Laid Open Publication 1-122483, the thermally sensitive recording medium which forms a protecting layer on the thermally sensitive recording layer mainly composed of a water soluble resin formed on a substrate, and whose surface glossiness based on JIS-P-8142 is bigger than 40(GS975°))% is described. However, when said thermally sensitive recording medium is printed using a thermal head, sometimes there is a problem that the glossiness is impaired. EP-A-0 431 594 provides a heat-sensitive recording material having a heat-sensitive color-forming layer formed on a substrate surface and comprising a substantially colorless dye precursor, a color-developing agent and binder. The recording material has an intermediate layer formed on the color-forming layer comprising a hydrophilic polymeric material and a pigment. A glossy surface layer is formed on the intermediate layer and comprises a hydrophobic polymeric material having a Tg of 60°C or more and a lubricant. EP-A-0 587 139 provides a heat-sensitive recording sheet having a heat-sensitive recording layer and a protective layer which includes a latex having a softening point of from 200 to 350°C. US 4,985,394 provides a thermosensitive recording material comprising a substrate, a thermosensitive coloring layer comprising a leuco dye and a color developer capable of inducing color formation in the leuco dye. The material also comprises a protective layer on the thermosensitive coloring layer which may comprise an inorganic pigment and a resin. The object of the present invention is to solve the above mentioned problems and to provide a thermally sensitive recording medium whose suitability for a thermal head and suitability for printing is improved. The inventors of this invention, have conducted an intensive study and have found that a thermally sensitive recording medium which has good image preserving ability and glossiness can be obtained by forming a glossing layer mainly composed of an inorganic pigment and a fixing composition having heatproof sticking tendency which does not cause sticking at higher temperatures on a thermally sensitive recording layer formed on the substrate, and have accomplished the present invention. The invention provides a thermally sensitive recording medium which comprises, in order on a substrate, a thermally sensitive recording layer and a glossing layer which has a surface glossiness based on JIS-P-8142 greater than 50% at an angle of incidence and angle of reflection of 75°, and which comprises an inorganic pigment and a fixing composition comprising a compound selected from fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol, together with a crosslinking agent, whereas the ratio of fixing composition to inorganic pigment of from 0.6 to 2.0 parts by weight to 1 part by weight, which does not cause sticking at a temperature of 200 °C, by the following method: (1) on paper of 60g/cm 2 density and 74 µm thickness, the fixing composition is coated in an amount of 20g/cm 2 , left for 5 minutes in an oven at 110 °C and the coated layer of the fixing composition is completely hardened; (2) the thus obtained coated paper is cut to 4 cm x 8 cm size and doubled up so as to bring coated surfaces into contact; to prepare a specimen of 4 cm x 4 cm size; (3) the specimen is placed on a hot plate heated to 200°C and a weight of 500 g (whose base diameter is 4 cm) is placed on the specimen for 5 seconds, the specimen is then cooled to room temperature, and checked whether the contacted coated surfaces can be separated easily or not. The invention further provides a thermally sensitive recording medium which comprises, in order on a substrate, a thermally sensitive recording layer and a glossing layer which has a surface glossiness based on JIS-P-8142 greater than 50% at an angle of incidence and angle of reflection of 75°, and which comprises an inorganic pigment and a fixing composition comprising a compound selected from hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, a copolymer of (meth)acrylic ester, acrylic ester and/or methacrylic ester, styrene and/or vinyl acetate, a copolymer of acrylic amide/acrylic ester/methacrylic acid, a copolymer of colloidal silica complex acrylic ester and a copolymer of colloidal silica complex styrene/acrylic ester, whereas the ratio of fixing composition to inorganic pigment of from 0.6 to 2.0 parts by weight to 1 part by weight, which does not cause sticking at a temperature of 200 °C, by the following method: (1) on paper of 60g/cm 2 density and 74 µm thickness, the fixing composition is coated in an amount of 20g/cm 2 , left for 5 minutes in an oven at 110 °C and the coated layer of the fixing composition is completely hardened; (2) the thus obtained coated paper is cut to 4 cm x 8 cm size and doubled up so as to bring coated surfaces into contact; to prepare a specimen of 4 cm x 4 cm size; (3) the specimen is placed on a hot plate heated to 200 °C and a weight of 500 g (whose base diameter is 4 cm) is placed on the specimen for 5 seconds, the specimen is then cooled to room temperature, and checked whether the contacted coated surfaces can be separated easily or not. In the present invention, as the example of an inorganic pigment used in the glossiness layer or in the intermediate layer, the compound which does not impair the properties of the thermal sensitive recording medium or the glossiness can be used. As specific examples, metal oxides such as silica, colloidal silica, titania, zirconia , alumina, antimony pentaoxide or zinc oxide, metal carbonates such as calcium carbonate or magnesium carbonate, aluminium hydroxide and barium sulfate can be mentioned, however, it is not intended to be limited to them. These compounds can be used in combination. Especially among these compounds, colloidal silica and barium sulfate are very useful to obtain an excellent lustrous surface because the primary particles of these compounds are stable and do not form flocks, further the refractive index of the particle is comparatively low. And, dispersions of colloidal silica and barium sulfate are very stable and it is hard to form a precipitation, further since fine particles of these compounds can be dispersed at comparatively high concentration, the coating amount can be adjusted to a higher level and has high work efficiency. Therefore, these compound are desirably used. In this invention, the property of the fixing composition which does not cause sticking at a temperature of 200 ° C is measured by the following method: (1) on paper of 60 g/m 2 density and 74 µm thickness, the fixing composition is coated by 20 g/m 2 , left for 5 minutes in an oven of 100 °C and the coated layer of fixing composition is completely hardened. (2) The obtained coated paper is cut to 4 cm x 8 cm size and doubled up so that the coated surface is contacted by the fixing composition. Thus the specimen of 4 cm x 4cm size is prepared. (3) The specimen is placed on a hot plate heated to 200°C and a weight of 500g (whose base diameter is 4cm) is placed on the specimen for 5 seconds. Then the specimen is cooled down to room temperature, and checked whether the contacted coated surfaces can be separated easily or not. In this invention, the fixing composition which does not cause sticking at a temperature of 200°C is prescribed as follows. Namely, the specimen whose contacted coated surfaces does not cause sticking, that is, the coated surface does not become sticky and can be separated easily, or causes partial sticking, but can be easily removed are ranked to the fixing composition which does not cause sticking at higher temperature than 200°C. In the conventional thermally sensitive recording medium which has lustrous properties the generation of the following problems is pointed out. Namely, at the printing procedure, the glossiness is spoiled, striped lines and cracks appear and the printed image becomes blurred. The ground of these problems is the destruction of a glossing layer (or a protecting layer) by instantaneous heating at 200-300°C of a thermal head. Namely, a binder component in the glossing layer become sticky by instantaneous heating and adhered to the thermal head, and since a recording paper is fed through the soiled thermal head, the glossing layer is partially removed. On the contrary, the thermally sensitive recording medium of this invention is an improved one whose heat resistance for destruction is improved by an use of fixing composition which does not cause sticking at a temperature of 200°C. That is, the glossing layer used in this invention does not generate sticking property even if exposed to high temperature, and the removing of glossing layer can be effectively prevented. As the fixing composition used in the glossing layer of this invention any composition which does not cause sticking at a temperature of 200°C and does not hurt the thermal sensitivity and lustrous property can be used. Concretely, various kinds of polyvinyl alcohol of 200∼2500 polymerization degree such as full saponified polyvinyl alcohol, partial saponified polyvinyl alcohol, denatured polyvinyl alcohol e.g. denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid or denatured polyvinyl alcohol by butylal, water soluble high polymer of cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose and acrylic ester resin such as (metha)acrylic ester copolymer, acrylic ester and/or methacrylic ester, copolymer of styrene and/or vinyl acetate, copolymer of acrylic amide/acrylic ester/methacrylic acid, copolymer of colloidal silica complex acrylic ester and copolymer of colloidal silica complex styrene/acrylic ester can be mentioned. However it is not intended to be limited to them. Among above mentioned water soluble high polymer substance, since a substance of high saponification has an excellent resistance to sticking by heat, is useful. Especially, the water soluble high polymer substance whose degree of saponification is bigger than 90% and degree of polymerization is bigger than 1000 is preferably used. As the concrete product of these, "PVA-117" (degree of saponification:98.5, degree of polymerization: 1700) of KURARAY Co., Ltd. can be mentioned. In this invention, the property of not causing a problem of sticking at a temperature higher than 200°C, is most important, and in comparison with the thermally sensitive recording medium containing the fixing composition which causes sticking at a temperature lower than 200°C, the improvement of the resistance to sticking by heat of the glossiness layer is remarkable. Even if the fixing composition does not display good resistance to sticking by heat at a temperature higher than 200°C when used alone, if it displays good resistance to sticking by heat by use together with an additive such as a cross-linking agent, it can be used as the fixing composition which does not cause sticking at a higher temperature than 200°C. That is, the fixing compound used in this invention is a compound which displays fixing ability by single use of the compound or in a composition containing additives. As the acrylic ester type resin, colloidal silica complex acrylic ester copolymer disclosed in Japanese Patent Laid Open Publication 7-26165, or (metha) acrylic ester copolymer containing a core shell structure disclosed in Japanese Patent Laid Open Publication 6-227124 are desirably used because these compounds display good heat resistance which does not generate sticking by single use at a higher temperature than 200°C. As the specific examples of commercialized products "ACRYSET SA-532" (product of NIHON SHOKUBAI Co., Ltd.) and "MOVINYL 8020" (product of CLARIANT POLYMER Co., Ltd.) can be mentioned. Meanwhile, for example, the glass transferring temperature (Tg), which is one of the indexes displaying heat resistance of a fixing agent, of the acrylic ester type copolymer (commercialized name of the product : MOVINYL 35, product of CLARIANT POLYMER Co., Ltd.), a kind of the acrylic ester type resin, is 25°C around, and is known to display comparatively good heat resistance. However, since said copolymer does not satisfy the important point of this invention which does not generate sticking at a temperature higher than 200°C, the expected effect can not be obtained from said copolymer. As the cross-linking agent which can construct the fixing composition of this invention not causing the problem of sticking at a temperature higher than 200°C, a well-known cross-linking agent can be used as long as it does not deteriorate the thermal recording property and lustrous property. Concretely, dialdehyde type such as glyoxal or polyaldehyde, polyamine type such as polyethylamine, epoxy type, polyamide resin, melamine resin, diglycydil type dimethylolurea such as glycerin diglycidylether, further, ammonium persulfate, iron chloride and magnesium chloride can be mentioned, however, not limited to them. Compared with a three-dimensional bridged type glyoxal cross-linking agent, since a two-dimensional bridged type glyoxal does not deteriorate the glossiness, it is useful for the preparation of excellent lustrous surface. The reason why is not clear, however, it is considered that the light scattering is generated by micro scale when three-dimensionally bridged. The amount of cross-linking agent to be added can be adjusted voluntarily so as to be a fixing composition which does not cause sticking at a temperature higher than 200°C, and for instance from 0.05 to 0.3 parts can be added to 1 part of water soluble high polymer substance. In this invention, good image preservative property can be obtained beside the improvement of glossiness by preparing an intermediate layer mainly composed by inorganic pigment and fixing composition. The ground which image preservative property is improved is illustrated as follows. That is, by the presence of an intermediate layer, the barrier function, namely, the protecting ability to prevent the penetration of water, plasticizer, oil or solvent into a thermally sensitive recording layer is improved. As the fixing composition contained in the intermediate layer, any composition which generates barrier function and does not hurt the thermally sensitive recording property and lustrous property can be used. Concretely, various kinds of polyvinyl alcohol of 200 ∼ 2500 polymerization degree such as full saponified polyvinyl alcohol, partial saponified polyvinyl alcohol, denatured polyvinyl alcohol e.g. denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid or denatured polyvinyl alcohol by butylal, water soluble high polymer of cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose and acrylic ester type copolymer resin such as copolymer of (metha)acrylic ester, acrylic ester and/or methacrylic ester, styrene and/or vinyl acetate, copolymer of acrylicamide/acrylic ester/methacrylic acid, copolymer of colloidal silica complex acrylic ester and copolymer of colloidal silica complex srylene/acrylicester can be mentioned. However, it is not intended to be limited to them. Among the above mentioned water soluble high polymers, a high saponified one or one having a high polymerization degree may have a tendency to display high barrier function, and especially a water soluble polymer whose saponification degree is higher than 90% and polymerization degree is higher than 1000. In a case of the intermediate layer, among acrylic ester type resin it is slightly different from the case of glossing layer, aforementioned acrylic ester copolymer (commercialized name MOVINYL 735) is desirably used because it is in a good balance of heat resistance and barrier function. Further, when acrylic ester resin is contained in the intermediate layer, the glossiness is improved and is desirably used. The reason why is illustrated as because the micro smoothness is improved. Even if a water soluble high polymer can not provide a barrier function to an intermediate layer by itself, it is possible to improve a barrier function and to make it as a fixing composition which can be used in the intermediate layer of this invention by adding, a cross-linking agent. As the cross-linking agent which may be provided in the fixing composition contained in the intermediate layer of this invention, any kind of well known component which does not hurt the thermal sensitive recording property and the lustrous property can be used. As a specific example of the cross-linking agent, dialdehyde type such as glyoxal or polyaldehyde, polyamine type such as polyethyl amine, epoxy resin, polyamide resin, melamine resin and diglycidyl type dimethylol urea such as glycerin diglycidyl ether, further ammonium persulfate magnesium chloride can be mentioned. However, it is not intended to be limited to them. The amount of the cross-linking agent can be voluntary changed along with the desired property, and the desirable amount is from 0.05 to 0.35 parts to 1 part of the water soluble high polymer. Referring to the water soluble polymer such as polyvinyl alcohol used in the glossing layer or the intermediate layer of this invention, the coating viscosity (B type viscometer or high shear type viscometer) becomes high at the preparation of coating, therefore, have a strong point that the coating can be easily coated and high coating amount can be obtained. Therefore, the combined use of water soluble polymer such as polyvinyl alcohol with acrylic ester type resin as the fixing composition in the glossing layer or the intermediate layer can be said as the desirable embodiment. Referring to the lustrous property, since an excellent degree of glossiness can be obtained when the coating amount of glossing layer and intermediate layer is big, a small amount of polyvinyl alcohol can be added to provide a coating aptitude, even if another fixing composition is mainly used for the glossing layer or the intermediate layer. In this case, the amount of polyvinyl alcohol to be added is from 0.01 to 0.15 parts to 1 part of fixing composition. Further, it is effective to add a slipping agent in the glossing layer or the intermediate layer, for the purpose of improving the thermal head aptitude. As a slipping agent, the slipping agents which are generally used in the conventional thermally sensitive recording medium can be used. As specific examples, metallic salt of high fatty acid such as zinc stearate or calcium stearate and wax such as paraffin wax, polyethylene wax, carnauba wax, micro crystalline wax and acrylic type wax can be mentioned. Especially, when the thermal head aptitude is concerned, zinc stearate or calcium stearate are desirably used. Further, if the slipping agent is contained in the glossing layer or in the intermediate layer, the phenomenon that the degree of glossiness is improved is observed. The reason for this phenomenon is illustrated as follows. That is, the lustrous property is improved along with the improvement of the surface smoothness. The inorganic pigment or slipping agent contained in the glossing layer or the intermediate layer, the fixing composition contained in the glossing layer which does not cause sticking at the temperature higher than 200 °C and fixing composition contained in the intermediate layer realizes an excellent lustre when the average particle size is finer than 0.3µm. Since, this phenomenon is illustrated as that the scattering of visible ray is controlled by these components, when better glossiness is required, the content of particles bigger than 0.3µm must be little. Specifically, the effect can be acheived by adjusting the amount of 0.3µm or larger size particles of these compounds smaller than 0.03 parts to 1 part of that of particles smaller than 0.3µm. Thus a lustrous degree of over 70% can be obtained. Especially, in a case of the material which has higher refraction index, the average particle size affects degree of glossiness largely. So, it is effective to use finer average size to obtain good degree of glossiness. It is more desirable to use fine particles whose average particle size is finer than 0.2µm to obtain higher degree of glossiness. The particles of these material has an adequate distribution curve, and when the average particle size is finer than 0.2µm, the size of almost all particles is smaller than the wave length of the visible ray. The kinds and the amount of an inorganic pigment, a fixing composition which does not cause sticking, a slipping agent or other additives contained in the glossing layer of this invention are decided according to the required degree of glossiness and not to be limited. However, in general, the adequate amount of fixing composition which does not cause sticking at the temperature higher than 200°C is from 0.6 to 3.5 parts desirably from 0.75 to 3.5 parts to 1 part of inorganic pigment, and that of slipping agent is from 0.06 to 1 parts to 1 part of inorganic pigment. Especially, in a case to use paper as a substrate, it is desirable to use from 1.0 to 3.5 parts of fixing composition which does not cause sticking at the temperature higher than 200°C to 1 part of inorganic pigment. To the total amount of solid contained in the glossing layer, the desirable amount of inorganic pigment and fixing composition which does not cause sticking at the temperature higher than 200°C are respectively from 30 to 60%. Further, by increasing the coating amount to the glossing layer, higher degree of glossiness can be obtained, and ordinary adequate amount is from 1 to 10g/m 2 . When an intermediate layer is prepared between the thermally sensitive recording layer and the glossing layer, the kinds and the amount of an inorganic pigment, a fixing composition, a slipping agent or other additives contained in said intermediate layer are not limited. However, the desirable amount of inorganic pigment and fixing composition is respectively from 30 to 60% to the total amount of solid contained in said intermediate layer. Further, the amount of coating of the intermediate layer is decided according to the desired image preservative property and degree of glossiness. The ordinary adequate amount is from 1 to 4g/m 2 , and if the excellent image preservative property is required the effective coating amount is from 2 to 4g/m 2 . The thermally sensitive recording layer can be prepared by dispersing colorless or pale color dye precursor and organic color developer with binder, adding sensitizer, filler, UV absorbing agent, water proof agent or defoamer at need and coating and drying the obtained coating over the surface of a substrate. As a dye precursor used in this invention, all kinds of dye precursor which are well known in the field of pressure sensitive or thermally sensitive recording paper can be used and triphenylmethane type compound, fluorane type compound, fluorene type compound and divinyl type compound are desirably used. However, it is not intended to be limited to them. Specific examples are shown below. These dye precursors can be used alone or in combination. <Triphenylmethane type leuco dyes> 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide [another name is Crystal Violet Lactone] 3,3-bis(p-dimethylaminophenyl)phthalide [another name is Malachite Green Lactone] <Fluoran type leuco dyes> 3-diethylamino-6-methylfluoran 3-diethylamino-6-methyl-7-anilinofluoran 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran 3-diethylamino-6-methyl-7-chlorofluoran 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran 3-diethylamino-6-methyl-7-(o-chloroanilino)fluoran 3-diethylamino-6-methyl-7-(p-chloroanilino)fluoran 3-diethylamino-6-methyl-7-(o-fluoroanilino)fluoran 3-diethylamino-6-methyl-7-n-octylanilinofluoran 3-diethylamino-6-methyl-7-n-octylaminonofluoran 3-diethylamino-6-methyl-7-benzylanilinofluoran 3-diethylamino-6-methyl-7-dibenzylanilinofluoran 3-diethylamino-6-chloro-7-methylfluoran 3-diethylamino-6-chloro-7-anilinofluoran 3-diethylamino-6-chloro-7-p-methylanilinofluoran 3-diethylamino-6-ethoxyethyl-7-anilinofluoran 3-diethylamino-7-methylfluoran 3-dethylamino-7-chlorofluoran 3-diethylamino-7-(m-trifluoromethylanilino)fluoran 3-diethylamino-7-(o-chloroanilino)fluoran 3-diethylamino-7-(p-chloroanilino)fluoran 3-diethylamino-7-(o-fluoroanilino)fluoran 3-diethylamino-benzo[a]fluoran 3-diethylamino-benzo[c]fluoran 3-dibutylamino-6-methyl-fluoran 3-dibutylamino-6-methyl-7-anilinofluoran 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluoran 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluoran 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran 3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran 3-dibutylamino-6-methyl-chlorofluoran 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran 3-dibutylamino-6-chloro-7-anilinofluoran 3-dibutylamino-6-methyl-7-p-methylanilinofluoran 3-dibutylamino-7-(o-chloroanilino)fluoran 3-dibutylamino-7-(o-fluoroanilino)fluoran 3-di-n-pentylamino-6-methyl-7-anilinofluoran 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran 3-di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran 3-di-n-pentylamino-6-chloro-7-anilinofluoran 3-di-n-pentylamino-7-(p-chloroanilino)fluoran 3-pyrrolidino-6-methyl-7-anilinofluoran 3-piperidino-6-methyl-7-anilinofluoran 3-(N-methyl-N-n-propylamino)-6-methyl-7-anilinofluoran 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran 3-cyclohexylamino-6-chlorofluoran 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran 2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran 2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran 2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran 2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran 2-amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran 2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran 2-phenyl-6-methyl-p-(p-phenylaminophenyl)aminoanilinofluoran 2-benzoyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluoran <Fluorene type leuco dyes> 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide] 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide] <Divinyl type leuco dyes> 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide 3,3-bis-[1,1-bis(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-tetrabromophthalide 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylen-2-yl]-4,5,6,7-tetrachlorophthalide <Others> 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide 3,6-bis(diethylamino)fluoran-γ -(3'-nitro)anilinolactam 3,6-bis(diethylamino)fluoran-γ-(4'-nitro)anilinolactam 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrilethane 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,-β-naphthoyl ethane 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester. As an example of organic color developer used in this invention, bisphenol A, 4-hydroxybenzoic acid esters, 4-hydroxyphthalic acid diesters, phthalic acid monoesters, bis-(hydroxyphenyl)sulfides, 4-hydroxyphenylarylsulfones, 4-hydroxyphenylarylsulfonates, 1,3-di[2-(hydroxyphenyl)-2-propyl]-benzenes, 4-hydroxybenzoyloxybenzoic acid esters, derivatives of aminobenzenesulfonamide described in Japanese Patent Laid Open Publication 08-59603, diphenylsulfone cross-linkable type compound described in International Patent Laid Open publication WO97/16420 and bisphenolsulfones described in Japanese Patent Laid Open Publication 03-207688 and Japanese Patent Laid Open Publication 05-24366 can be mentioned. Typical examples of prior color developer are shown below, but are not intended to be limited to these compound. These compounds can be used alone or can be used in combination. Among these compounds, 2,4'-sulfonildiphenyl (another name is 2,4'-bisphenol S) and derivatives of aminobenzenesulfonamide have remarkably good heat resistance, and are suited for the use in which heat resistance is required. <bisphenol A type> 4,4'-isopropylidenediphenol (another name is bisphenol A), 4,4'-cyclohexylidenediphenol, p,p'-(1-methyl-n-hexylidene)diphenol, 1,7-di(hydroxyphenylthio)-3,5-dioxaheptane. <4-hydroxybenzoic acid ester type> 4-hydroxybenzyl benzoate, 4-hydroxyethyl benzoate, 4-hydroxypropyl benzoate, 4-hydroxyisopropyl benzoate, 4-hydroxybutyl benzoate, 4-hydroxyisobutyl benzoate, 4-hydroxymethylbenzyl benzoate. <4-hydroxyphthalic acid diester type> 4-hydroxydimethylphthalate, 4-hydroxydiisopropylphthalate, 4-hydroxydibenzylphthalate, 4-hydroxydihexylphthalate. <phthalic acid monoester type> monobenzyl phthalate, monocyclohexyl phthalate, monophenyl phthalate, monomethylphenyl phthalate, monoethylphenyl phthalate, monopropylbenzyl phthalate, monohalogenbenzyl phthalate, monoethoxybenzyl phthalate. <bis-(hydroxyphenyl)sulfide type> bis-(4-hydroxy-3-tert-butyl-6-methylphenyl)sulfide, bis-(4-hydroxy-2,5-dimethylphenyl)sulfide, bis-(4-hydroxy-2-methyl-5-ethylphenyl)sulfide, bis-(4-hydroxy-2-methyl-5-isopropylphenyl)sulfide, bis-(4-hydroxy-2,3-dimethylphenyl)sulfide, bis-(4-hydroxy-2,5-dimethylphenyl)sulfide, bis-(4-hydroxy-2,5-diisopropylphenyl)sulfide, bis-(4-hydroxy-2,3,6-trimethylphenyl)sulfide, bis-(2,4,5-trihydroxyphenyl)sulfide, bis-(4-hydroxy-2-cyclohexyl-5-methylphenyl)sulfide, bis-(2,3,4-trihydroxyphenyl)sulfide, bis-(4,5-dihydroxy-2-tert-butylphenyl)sulfide, bis-(4-hydroxy-2,5-diphenylphenyl)sulfide, bis-(4-hydroxy-2-tert-octyl-5-methylphenyl)sulfide. <4-hydroxyphenylarylsulfone type> 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4-hydroxy-4'-n-butyloxydiphenylsulfone. <4-hydroxyphenylarylsulfonate type> 4-hydroxyphenylbenzenesulfonate, 4-hydroxyphenyl-p-tolylsulfonate, 4-hydroxyphenylmethylenesulfonate, 4-hydroxyphenyl-p-chlorobenzenesulfonate, 4-hydroxyphenyl-p-tert-butylbenzenesulfonate, 4-hydroxyphenyl-p-isopropoxybenzenesulfonate, 4-hydroxyphenyl-1'-naphthalenesulfonate, 4-hydroxyphenyl-2'-naphthalenesulfonate. <1,3-di[2-(hydroxyphenyl)-2-propyl]benzene type> 1,3-di[2-(4-hydroxyphenyl)-2-propyl]benzene, 1,3-di[2-(4-hydroxy-3-alkylphenyl)-2-propyl]benzene, 1,3-di[2-(2,4-dihydroxyphenyl)-2-propyl]benzene, 1,3-di[2-(2-hydroxy-5-methylphenyl)-2-propyl]benzene, <resorcinol type> 1,3-dihydroxy-6(α,α-dimethylbenzyl)-benzene. <4-hydroxybenzoyloxybenzoic acid ester type> 4-hydroxybenzoyloxybenzyl benzoate, 4-hydroxybenzoyloxymethyl benzoate, 4-hydroxybenzoyloxyethyl benzoate, 4-hydroxybenzoyloxypropyl benzoate, 4-hydroxybenzoyloxybutyl benzoate, 4-hydroxybenzoyloxyisopropyl benzoate, 4-hydroxybenzoyloxy-tert-butyl benzoate, 4-hydroxybenzoyloxyhexyl benzoate, 4-hydroxybenzoyloxyoctyl benzoate, 4-hydroxybenzoyloxynonyl benzoate, 4-hydroxybenzoyloxycyclohexyl benzoate, 4-hydroxybenzoyloxy β-phenethyl benzoate, 4-hydroxybenzoyloxyphenyl benzoate, 4-hydroxybenzoyloxy α-naphthyl benzoate, 4-hydroxybenzoyloxy β-naphthyl benzoate, 4-hydroxybenzoyloxy-sec-butyl benzoate <bisphenolsulfone type (I)> bis-(3-1-butyl-4-hydroxy-6-methylphenyl)sulfone, bis-(3-ethyl-4-hydroxyphenyl)sulfone, bis-(3-propyl-4-hydroxyphenyl)sulfone, bis-(3-methyl-4-hydroxyphenyl)sulfone, bis-(2-isopropyl-4-hydroxyphenyl)sulfone, bis-(2-ethyl-4-hydroxyphenyl)sulfone, bis-(3-chloro-4-hydroxyphenyl)sulfone, bis-(2,3-dimethyl-4-hydroxyphenyl)sulfone, bis-(2,5-dimethyl-4-hydroxyphenyl)sulfone, bis-(3-methoxy-4-hydroxyphenyl)sulfone, 4-hydroxyphenyl-2'-ethyl-4'-hydroxyphenylsulfone, 4-hydroxyphenyl-2'-isopropyl-4'-hydroxyphenylsulfone, 4-hydroxyphenyl-3'-isopropyl-4'-hydroxyphenylsulfone, 4-hydroxyphenyl-3'-sec-butyl-4'-hydroxyphenylsulfone, 3-chloro-4-hydroxyphenyl-3'-isopropyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-butylphenyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-aminophenyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-isopropylphenyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-octylphenyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-butylphenyl-3'-chloro-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-butylphenyl-3'-methyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-butylphenyl-3'-isopropyl-4'-hydroxyphenylsulfone, 2-hydroxy-5-t-butylphenyl-2'-methyl-4'-hydroxyphenylsulfone. <bisphenolsulfone type (II)> 4,4'-sulfonyldiphenol, 2,4'-sulfonyldiphenol, 3,3'-dichloro-4,4'-sulfonyldiphenol, 3,3'-dibromo-4,4'-sulfonyldiphenol, 3,3',5,5'-tetrabromo-4,4'-sulfonyldiphenol, 3,3'-diamino-4,4'-sulfonyldiphenol. <others> p-tert-butylphenol, 2,4-dihydroxybenzophenone, novolac type phenolic resin, 4-hydroxyacetophenone, p-phenylphenol, benzyl-4-hydroxyphenylacetate, p-benzylphenol. 4,4'-bis(p-tolylsulfonylaminocarbonilamino)diphenylmethane, 4,4'-bis(phenylaminothiocarbonylamino)diphenylsufido. Further, metallic chelate type color developing components composed by higher fatty acid metal double salt and polyhydric hydroxy.aromatic compound disclosed in Japanese Patent Laid Open Publication 10-258577 or others can be used as the image forming material. And, these chelate type color developing components can be used alone or can be used together with afore mentioned leuco dye and organic color developer. In this invention, a conventional well known sensitizer can be used in the limitation in which the desired effect of this invention is not prevented. As an example of the sensitizer, stearic acid amide, palmitic acid amide, methoxycarbonyl-N-benzamidestearate, N-benzoyl stearic acid amide, N-eicosenoic acid amide, ethylene-bis-stearic acid amide, behenic acid amide, methylene-bis-stearic acid amide, methylolamide, N-methylolsteric acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, p-benzyloxybenzylbenzoate, 1-hydroxy-2-phenylnaphthoate, dibenzyloxalate di-p-methylbenzyloxalate, di-p-chlorobenzyloxalate, 2-naphthylbenzylether, m-terphenyl, p-benzylbiphenyl, 4-biphenyl-p-tolylether di(p-methoxyphenoxyethyl)ether 1,2-di(3-methylphenoxy)ethane 1,2-di(4-methylphenoxy)ethane 1,2-di(4-methoxyphenoxy)ethane 1,2-di(4-chlorophenoxy)ethane 1,2-diphenoxyethane 1-(4-methoxyphenoxy)-2-(2-methylphenoxy)ethane p-methyltiophenylbenzylether 1,4-di(phenyltio)buthane p-acetotoluidide p-acetophenetidide, N-acetoacetyl-p-toluidine, di-(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane 1,2-bis(phenoxymethyl)benzene p-toluenesulfonamide, o-toluenesulfonamide, di-p-tolylcarbonate and phenyl- α-naphtylcarbonate can be mentioned. However it is not intended to be limited to these compounds. These sensitizers can be used alone or by mixing more than two kinds of them. As the binder used in the present invention, various kinds of polyvinyl alcohol of 200∼2500 polymerization degree such as full saponified polyvinyl alcohol, partial saponified polyvinyl alcohol, denatured polyvinyl alcohol e.g. denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid or denatured polyvinyl alcohol by butylal, derivatives of cellulose such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose, copolymer of styrene-maleic unhydride, copolymer of styrene-butadiene, polyvinyl chloride, polyvinyl acetal, polyacrylicamide, polyacrylic acid ester, polyvinylbutylal, polystyrene or copolymer of them,polyamide resin, silicon resin, petroleum resin, terpene resin, ketone resin and cumarone resin can be illustrated. These macro molecule compounds can be applied by being dissolved into solvents such as water, alcohol, ketone, ester or hydrocarbon or by being dispersed in water or other medium under an emulsion state or a paste state and these forms of application can be used in combination according to the quality requirement. As a filler which can be used in this invention, an inorganic or an organic filler such as silica, calcium carbonate, kaoline, calcined kaoline, diatomaceous earth, talc, titanium oxide, zinc oxide, aluminum hydroxide, polystyrene resin, urea-formaldehyde resin, copolymer of styrene-methacrylic acid, copolymer of styrene-butadiene and hollow plastic pigment can be mentioned. Further, a parting agent such as metallic salt of fatty acid, a slipping agent such as wax, benzophenon. or triazole-based ultraviolet absorbers, water proof agent such as glyoxal, dispersing agent, defoamers anti-oxidation agent and fluorescent dye can be used as an additive. As a substrate, paper, synthetic paper, plastic film, plastic foam film, nonwoven fabric, recycled paper metallic foil and a complex of these material can be used. The amount of color developer and dye precursor, the kind and amount of other additives to be used to the thermally sensitive recording medium of this invention are decided according to the required quality and recording feature, and not restricted. However, in general, it is preferable to use from 0.1 to 2 parts of dye precursor, from 0.5 to 4 parts of filler and from 0.05 to 2 parts of stabilizer and sensitizer to 1 part of color developer and from 5 to 25 % of binder to the total amount of solid. These color developer, dye and other additives which are added as required are ground to the fine particles smaller than several microns diameter by means of a pulverizer such as a ball mill, an attriter or a sand grinder, or by means of an adequate emulsifying apparatus, then binder and other additives are added at need, thus the coating is prepared. As a method to coat the coating, a hand coating, a size press coating method, a roll coating method, an air knife coating method, a blend coating method, a flow coating method, a comma direct method, a gravure direct method, a gravure reverse method and a reverse·roll coating method can be mentioned. Further, the method to dry up after sputtering, spraying or dipping can also be used. In the thermally sensitive recording medium of this invention, an undercoating layer composed mainly of filler and binder can be formed between thermally sensitive recording layer and substrate for the purpose of improving the quality of the image. As the binder, the filler and other additives contained in the undercoating layer, the materials which are indicated as the compound composing the thermally sensitive recording layer can be used according to the required quality. Among these compounds, calcined kaolin, fine hollow spherical particle with shell disclosed in Japanese Patent Publication 3-54074 or cup shape hollow polymer particle disclosed in Japanese Patent Laid Open Publication 10-258577 can be desirably used, because these fillers used to the undercoating layer of the conventional thermally sensitive recording medium have a good function as a heat insulating material. Further, the resistance to water or to chemicals of the recorded image or ground part against the water or chemicals which bleed out from the back surface of the substrate can be improved by using a well known cross-linking agent such as glyoxal. In the thermally sensitive recording medium of this invention, a back coating layer can be formed under the back surface of the substrate to prevent the bleeding out of water or chemicals from the back surface of the substrate. In this case, it is desirable to use the above mentioned binder and cross-linking agent such as glyoxal. The thermally sensitive recording medium of this invention can be applied to various kinds of field. Especially, because of the above mentioned excellent glossiness and image preservative property, it is applied to a thermally sensitive label sheet or a thermally sensitive recording type magnetic ticket paper. In the case of a thermally sensitive label, a thermally sensitive recording layer, a glossing layer and an intermediate layer as required are formed on one side of the substrate, and a removing paper (liner) is provided on the another side of the substrate through an adhering layer or a sticking agent layer. And in a magnetic ticket paper, a magnetic recording layer mainly composed of a strong magnetic substance and a fixing agent is formed instead of a removing paper. The thermally sensitive recording medium of this invention can obtain an excellent lustre without a calendar treatment. If a higher degree of glossiness (angle of incidence and angle of reflect is 75 degree) is required, it is effective to make the surface smoothness higher than 3000 second by Beck Smoothness by a calendar treatment. Thus, by improving surface smoothness of the thermally sensitive recording medium, since the scattering of ray at the surface is controlled, it is effective to obtain higher degree of glossiness. Especially, if degree of glossiness higher than 80% is required, it is desirable to make the smoothness higher than 5000 second. EXAMPLES AND COMPARATIVE EXAMPLES The present invention will be illustrated more specifically by Examples, however, it is not intended to be limited by them. In the Examples and Comparative Examples, "parts" and "%" indicates weight parts and wt%. Example 1 <preparation of thermally sensitive recording medium> Dispersion of color developer (A solution), dispersion of colorless dye precursor (B solution) and dispersion of sensitizer (C solution) of following blending ratio are separately ground in wet condition to average particles diameter of 1µm by a sand grinder. A solution (dispersion of color developer) 2,4'-sulfonyldiphenyl [2,4'-bisphenolS] 6.0 parts 10% aqueous solution of polyvinyl alcohol 18.8 parts water 11.2 parts B solution (dispersion of dye precursor) 3-dibutylamino-6-methyl-7-anilinofluoran [ODB-2] 2.0 parts 10% aqueous solution of polyvinyl alcohol 4.6 parts water 2.6 parts C solution (dispersion of sensitizer) 1,2-bis(phenoxymethyl)benzene 3.0 parts 10% aqueous solution of polyvinyl alcohol 9.4 parts water 5.6 parts The dispersions are mixed by following ratio and the coating is prepared. A solution (dispersion of color developer) 36.0 parts B solution (dispersion of colorless dye precursor [OBD-2]) 9.2 parts C solution (dispersion of sensitizer) 18.0 parts kaolin clay (50% dispersion) 12.0 parts <preparation of coating for glossing layer> At the preparation of the coating for glossing layer of Example 1, colloidal silica (average particle size : 0.07-0.1 µm, 40% dispersion, commercialized name : SNOWTEX ZL, product of Nissan Chemical Industries Co., Ltd.) as an inorganic pigment, copolymer of colloidal silica complex acrylicester (average particle size : 0.04 µm, 43% dispersion, commercialized name : MOVINYL 8020, product of Clariant Polymer Co., Ltd., hereinafter shortened to Resin A) as a fixing agent which does not cause sticking at the temperature higher than 200°C and zinc stearate (average particle size : 0.17µm, 20% dispersion, commercialized name : HYDRIN F-115, product of Chukyo Yushi Co., Ltd., hereinafter shortened to Slipping agent A) as a slipping agent are used. These compounds are mixed by the mixing ratio shown as below, stirred and formed a coating solution (D solution). D solution (dispersion of coating for glossing layer) colloidal silica (40%) 5.0 parts resin A (43%) 8.14 parts slipping agent A (20%) 1.5 parts <preparation of a thermally sensitive recording layer> The prepared coating for thermally sensitive recording layer is coated over the one side surface of 50g/m 2 substrate paper as to the coating amount be 6.0g/m 2 , dried up and the thermally sensitive recording layer is prepared. Then the coating for glossing layer is coated over the surface of thermally sensitive recording layer as to the coating amount be 3.0g/m 2 . After dried up, treated by a super calendar and the thermally sensitive medium of 5000 sec. smoothness is obtained. Example 2, 3 In Examples 2 and 3, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, barium sulfate (average particle size : 0.03µm, 20% dispersion, commercialized name : Barium Sulfate BF-20P, product of Sakai Chemical Industries Co., Ltd., Example 2), titanium oxide (average particle size : 0.015µm, 20% dispersion, commercialized name : Titanium Oxide MT-100S, product of Teika Co., Ltd., Example 3) are used. The mixing ratio of every compounds at the preparation of D solution are mentioned below. Example 2 barium sulfate (20%) 10 parts Example 3 titanium oxide (20%) 10 parts Example 4 In Example 4, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, copolymer of (metha) acrylicester (average particle size : 0.37µm, 25% dispersion, commercialized name : ACRYSET SA-532, product of NIHON SHOKUBAI Co., Ltd., hereinafter shortened to Resin B) is used as a fixing agent which does not cause sticking at the temperature higher than 200°C. The mixing ratio of every compounds at the preparation of D solution are mentioned below. Resin B (25%) 14 parts Example 5-8 In Examples 5-8, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, copolymer of (metha) acrylicester (average particle size : 0.25 µm, 20% dispersion, commercialized name : ACRYSET SA-558, product of NIHON SHOKUBAI Co., Ltd., hereinafter shortened to Resin C, Example 5), polyvinylalcohol (degree of saponification : 98.5%, degree of polymerization : 1700, 10% aqueous solution, commercialized name : PVA-117, product of Kuraray Co., Ltd., hereinafter shortened to Resin D, Example 6), polyvinylalcohol (degree of saponification : 98.5%, degree of polymerization : 500, 10% aqueous solution, commercialized name : PVA-105, product of Kuraray Co., Ltd., hereinafter shortened to Resin E, Example 7), polyvinylalcohol (degree of saponification : 79.5%, degree of polymerization : 2000, 10% aqueous solution, commercialized name : PVA-420, product of Kuraray Co., Ltd., hereinafter shortened to Resin F, Example 8) and glyoxal (40% aqueous solution) are used as a fixing agent which does not cause sticking at the temperature higher than 200°C. The mixing ratio of every compounds at the preparation of D solution are mentioned below. Example 5 Resin C(20%) 17.5 parts glyoxal (40%) 0.875 parts Example 6 Resin D (10%) 35 parts glyoxal (40%) 0.875 parts Example 7 Resin E (10%) 35 parts glyoxal (40%) 0.875 parts Example 8 Resin F (20%) 35 parts glyoxal (40%) 0.875 parts Example 9 In Example 9, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, as an inorganic pigment, aluminium hydroxide of 1µm average particle size (40% dispersion) and colloidal silica (average particle size : 0.07-0.1µm, 40% dispersion, commercialized name : SNOWTEX ZL, product of NISSAN Chemical Industries Co., Ltd.) is used together with. The mixing ratio of every compounds at the preparation of D solution are mentioned below, and the average particle size of inorganic pigment is 0.39µm. aluminium hydroxide (40%) 1.67 parts colloidal silica (40%) 3.33 parts Example 10 In Example 10, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, zinc stearate of 5.5µm average particle size (30% dispersion, commercialized name : HYDRIN Z-7-30, product of Chukyo Yushi Co. ,Ltd., hereinafter shortened to Slipping agent B) is used as a slipping agent. Slipping agent B (30%) 1 part Example 11 In Example 11, the thermally sensitive recording medium is prepared by same procedure to Example 1. An intermediate layer is formed between thermally sensitive recording layer and glossing layer, and as an inorganic pigment colloidal silica (average particle size : 0.07-0.1µm, 40% dispersion, commercialized name : SNOWTEX ZL, product of NISSAN Chemical Industries Co., Ltd.), as a fixing agent polyvinylalcohol (degree of saponification : 98.5%, degree of polymerization : 1700, 10% aqueous solution, commercialized name : PVA-117, product of Kuraray Co., Ltd., hereinafter shortened to Resin D, Example 6) and melamine resin (60% aqueous solution, commercialized name : SUMIREZ RESIN 613sp, product of Sumitomo Chemical Industries Co., Ltd.) and as a slipping agent zinc stearate (average particle size : 0.17µm, 20% dispersion, commercialized name : HYDRIN F-115, product of Chukyo Yushi Co., Ltd., hereinafter shortened to Slipping agent A) are used. These compounds are mixed by the ratio mentioned below and stirred. Thus the coating solution (E solution) is prepared. E solution (dispersion of coating for intermediate layer) colloidal silica A (40%) 5 parts resin D (10%) 30.0 parts melamine resin (60%) 1.67 parts slipping agent A (20%) 1.25 parts The thermally sensitive layer is prepared by same procedure to Example 1, then said coating for intermediate layer is coated as to the coating amount be 2g/m2 layer, further, the coating for glossing layer is coated as to the coating amount be 3.0g/m2 . After dried up, treated by a super calendar and the thermally sensitive medium of 5000 sec. smoothness is obtained. Example 12, 13 In Example 12 and 13, the thermally sensitive recording medium is prepared by same procedure to Example 11. At the formation of intermediate layer, copolymer of acrylicester (average particle size : 0.08 µm, 43% dispersion, commercialized name : MOVINYL 735, product of Clariant Polymer Co., Ltd., hereinafter shortened to Resin G, Example 12) and colloidal silica complex copolymer of acrylicester (average particle size : 0.08 µm, 43% dispersion, commercialized name : MOVINYL 8020, product of Clariant Polymer Co., Ltd., hereinafter shortened to Resin A, Example 13) are used as a fixing agent. The mixing ratio of E solution preparation are mentioned below. Example 12 Resin G (43%) 6.98 parts Example 13 Resin A (43% 6.98 parts Example 14 In Example 14, the thermally sensitive recording medium is prepared by same procedure to Example 11. At the formation of intermediate layer, copolymer of acrylicester (average particle size : 0.08µm, 43% dispersion, commercialized name : MOVINYL 735, product of Clariant Polymer Co., Ltd., hereinafter shortened to Resin G) and polyvinylalcohol (degree of saponification : 98.5%, degree of polymerization : 1700, 10% aqueous solution, commercialized name : PVA-117, product of Kuraray Co., Ltd., hereinafter shortened to Resin D) are used as a fixing agent. The mixing ratio of E solution preparation are mentioned below. Resin G (43%) 5.81 parts Resin D (10%) 10 parts Example 15 In Example 15, the thermally sensitive recording medium is prepared by same procedure to Example 11. At the formation of intermediate layer, aluminium hydroxide of 1µm average diameter (40% dispersion) is used as an inorganic pigment. The mixing ratio of E solution preparation are mentioned below. aluminium hydroxide (40%) 5 parts Example 16 In Example 16, the thermally sensitive recording medium is prepared by same procedure to Example 11. At the formation of intermediate layer, zinc stearate of 5.5µm average diameter (30% dispersion, commercialized name : HYDRIN Z-7-30, product of Chukyo Yushi Co., Ltd., Slipping agent B) is used as a slipping agent. The mixing ratio of E solution preparation are mentioned below. slipping agent B (30%) 0.83 parts Comparative Example 1 In Comparative Example 1, the thermally sensitive recording medium is prepared by same procedure to Example 6. At the formation of glossing layer, an inorganic pigment is not added. Comparative Example 2 In Comparative Example 2, the thermally sensitive recording medium is prepared by same procedure to Example 6. At the formation of glossing layer, polyvinyl alcohol (degree of saponification : 90% around, degree of polymerization : 300, 10% aqueous solution, commercialized name : GL-03, product of Nihon Gosei Chemical Co., Ltd., hereinafter shortened to Resin II) and glyoxal (40% solution) is used as a fixing agent. The mixing ratio of D solution preparation are mentioned below. Resin H (10%) 0.35 parts glyoxal (40%) 0.875 parts Comparative Example 3 In Comparative Example 3, the thermally sensitive recording medium is prepared by same procedure to Example 6. At the formation of glossing layer, glyoxal is not added. Comparative Example 4 In Comparative Example 4, the thermally sensitive recording medium is prepared by same procedure to Example 1. At the formation of glossing layer, copolymer of acrylicester (average particle size : 0.08 µm, 43% dispersion, commercialized name : MOVINYL 735, product of Clariant Polymer Co., Ltd., Resin G) is used as a fixing agent. The mixing ratio of D solution preparation are mentioned below. Resin G (43%) 8.14 parts <Heat resistance test for sticking of a fixing composition> Whether the fixing compositions used in a glossing layer cause sticking at the temperature higher than 200°C are detected by following method. (1) Resin A-H used in above mentioned Examples and Comparative Examples, or the compound to which cross-linking agent is added are the fixing compositions (refer to Table 1 ). On the paper of 60g/m 2 density and 74 µm thickness, the fixing composition is coated by 20 g/m 2 , left, for 5 minutes in an oven of 110°C and the coated layer of fixing composition is completely hardened. (2) The obtained coated paper is cut to 4cm × 8cm size and doubled up so as to the coated surface by fixing composition is contacted. Thus the specimen of 4cm x 4cm size is prepared. (3) The specimen is placed on a hot plated heated to 200°C and a weight of 500g (whose base diameter is 4cm) is placed on the specimen for 5 seconds. Then the specimen is cooled down to the room temperature, and checked whether the contacted coated surfaces can be removed easily or not, and indicated by following standard (refer to Table 1). o ○ no sticking is observed ○ almost no sticking and easily removed Δ partially sticking and can be removed × can not be removed <Evaluation of thermal recording property> Thermal recording was carried out on the prepared thermally sensitive recording media using TH-PMD (thermally sensitive printer in which thermal head is installed, product of Kyocera Co., Ltd.) by 0.41mj/dot impressive energy. Recording density of the recorded portion is measured by means of a Macbeth densitometer (RD-914, amber filter used) (refer to Table 2 and Table 3). <Evaluation of degree of glossiness> A digital glossiness meter (Product of Murakami Color Technique Laboratory Co., Ltd., Model GM-26D For 75° ) is used. The degree of glossiness (an angle of incidence and an angle of reflect is 75 degree) of not recorded part is measured (refer to Table 2 and Table 3). <Evaluation for plasticizer resistance > A single sheet of polyvinylchloride wrap( HIGHWRAP KMA : Mitsui Toatsu Chemicals Co., Ltd.) was wound round with 1 plie on a paper tube, stuck thereon a thermal recording medium recorded by the above printer, further wound round with 3 plies of the polyvinylchloride wrap, allowed to stand at 40°C for 24 hours, and measured for the Macbeth densitometer of the recorded part (refer to Table 2 and Table 3). <Thermal head aptitude> A checker mark is printed, using an automatic measuring label issurance system IP-21100ZX of Ishida Co., Ltd., setting printing density to 9, and whether the glossing layer is destroyed by heat (surface looses glossiness by heat, or removed) is observed and indicated by following standard (refer to Table 2 and Table 3). ○ not destroyed by heat × destroyed by heat <Evaluation of printing aptitude> RI printer (RI-III type) of AKIRA Co., Ltd. is used as the printer and UV hardening type ink Tack 12, product of Dainippon Ink Chemical Industries Co., Ltd. is used as an ink, and evaluation of printing aptitude (surface intensity, transferring of ink etc.) is measured and indicated by following standard (refer to Table 2 and Table 3). ○ good Δ surface intensity is good, ink transferring is not good × not good glossing layer fixing composition resin cross-linking agent heat resistance for sticking resin A - o ○ resin B - ○ resin C glyoxal (0.1) ○ resin D - × resin D glyoxal (0.1) ○ resin E glyoxal (0.1) ○ resin F glyoxal (0.1) Δ resin G - × resin H glyoxal (0.1) × Example Co. Ex. intermediate layer glossing layer inorganic pigment fixing composition inorganic pigment fixing composition 1 - - colloidal Si Resin A 2 - - BaSO 4 Resin A 3 - - TiO 2 Resin A 4 - - colloidal Si Resin B 5 - - colloidal Si Resin C/glyoxal 6 - - colloidal Si Resin D/glyoxal 7 - - colloidal Si Resin E/glyoxal 8 - - colloidal Si Resin F/glyoxal 9 - - colloidal Si/ Al(OH) 3 Resin A 10 - - colloidal Si Resin A 11 colloidal Si Resin D/Me.resin colloidal Si Resin A 12 colloidal Si Resin G colloidal Si Resin A 13 colloidal Si Resin A colloidal Si Resin A 14 colloidal Si Resin G/Resin D colloidal Si Resin A 15 Al(OH) 3 Resin D/Me.resin colloidal Si Resin A 16 colloidal Si Resin D/Me.resin colloidal Si Resin A Co. Ex. 1 - - - Resin D/glyoxal Co.Ex.2 - - colloidal Si Resin H/glyoxal Co.Ex.3 - - colloidal Si Resin D Co.Ex.4 - - colloidal Si Resin G Remarks "colloidal Si "indicates colloidal silica, "Me.resin" indicates Melamine resin "Co.Ex." indicates Comparative Example Example Co. Ex. degree of glossine ss recording density resistance to plasticizer head aptitude printing aptitude 1 81% 1.50 0.32 ○ ○ 2 80% 1.50 0.31 ○ ○ 3 80% 1.52 0.31 ○ ○ 4 77% 1.41 0.38 ○ ○ 5 76% 1.40 0.37 ○ ○ 6 81% 1.47 0.50 ○ ○ 7 79% 1.44 0.40 ○ ○ 8 80% 1.44 0.42 ○ ○ 9 53% 1.30 0.15 ○ ○ 10 64% 1.35 0.20 ○ ○ 11 84% 1.54 1.05 ○ ○ 12 85% 1.55 0.89 ○ ○ 13 85% 1.54 0.45 ○ ○ 14 84% 1.53 0.98 ○ ○ 15 75% 1.36 0.80 ○ ○ 16 77% 1.40 0.75 ○ ○ Co.EX.1 81% 1.54 0.55 ○ Δ Co.EX.2 80% 1.41 0.30 × ○ Co.Ex.3 80% 1.44 0.27 × ○ Co.Ex.4 77% 1.40 0.39 × ○ As clearly understood from above mentioned results, Examples 1-10 which have a glossing layer of this invention, display good results at degree of lustrous, recording density, head aptitude and printing aptitude. Further, the Examples 11-16 which has an intermediate layer display good resistance to a plasticizer. On the contrary, Comparative Example 1 which does not contain inorganic pigment in a glossing layer is not good in the printing aptitude. In comparative Examples 2-4 which use a fixing composition not having heat resistance for sticking prescribed in this invention, since the glossing layer is destroyed by heat at the printing process, is not suited to the practical use. Meanwhile, in the Examples of this invention, Examples which use materials whose average particle size is smaller than 0.3µm are superior in degree of glossiness to Examples 9, 10, 15 and 16 which use inorganic pigment whose average diameter is bigger than 0.3µm. Therefore, if more excellent degree of glossiness is required, it is effective to use the materials whose average particle size is smaller than 0.3µm. The thermally sensitive recording medium of this invention is the medium which has a glossing layer mainly containing fixing composition which does not cause sticking at the temperature higher than 200°C, which has a good lustrous property and has a thermal head aptitude and a printing aptitude. By above mentioned structural characteristics, the thermally sensitive recording medium of this invention becomes to have high lustrous property and high image density and evaluated as a high quality medium. It is not necessary to coat a varnish layer using organic solvent on it and so is very economical. Furthermore, by forming an intermediate layer between thermally sensitive recording layer and a glossing layer, degree of glossiness is improved more, and resistance to plasticizer is improved more, and the useful thermally sensitive recording medium can be obtained.

Claims: A thermally sensitive recording medium which comprises, in order on a substrate, a thermally sensitive recording layer and a glossing layer which has a surface glossiness based on JIS-P-8142 greater than 50% at an angle of incidence and angle of reflection of 75 °, and which comprises an inorganic pigment and a fixing composition comprising a compound selected from fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol, together with a crosslinking agent, wherein the ratio of fixing composition to inorgamic pigment is from 0.6 to 2.0 parts by weight to 1 part by weight, which does not cause sticking at a temperature of 200 °C, by the following method: (1) on paper of 60g/cm 2 density and 74 µm thickness, the fixing composition is coated in an amount of 20g/cm 2 , left for 5 minutes in an oven at 110 °C and the coated layer of the fixing composition is completely hardened; (2) the thus obtained coated paper is cut to 4 cm x 8 cm size and doubled up so as to bring coated surfaces into contact; to prepare a specimen of 4 cm x 4 cm size; (3) the specimen is placed on a hot plate heated to 200 °C and a weight of 500 g (whose base diameter is 4 cm) is placed on the specimen for 5 seconds, the specimen is then cooled to room temperature, and checked whether the contacted coated surfaces can be separated easily or not. A thermally sensitive recording medium which comprises, in order on a substrate, a thermally sensitive recording layer and a glossing layer which has a surface glossiness based on JIS-P-8142 greater than 50% at an angle of incidence and angle of reflection of 75 °, and which comprises an inorganic pigment and a fixing composition comprising a compound selected from hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, a copolymer of (meth)acrylic ester, acrylic ester and/or methacrylic ester, styrene and/or vinyl acetate, a copolymer of acrylic amide/acrylic ester/methacrylic acid, a copolymer of colloidal silica complex acrylic ester and a copolymer of colloidal silica complex styrene/acrylic ester, wherein the ratio of fixing composition to inorganic pigment is from 0.6 to 2.0 parts by weight to 1 part by weight, which does not cause sticking at a temperature of 200 °C, by the following method: (1) on paper of 60g/cm 2 density and 74 µm thickness, the fixing composition is coated in an amount of 20g/cm 2 , left for 5 minutes in an oven at 110 °C and the coated layer of the fixing composition is completely hardened; (2) the thus obtained coated paper is cut to 4 cm x 8 cm size and doubled up so as to bring coated surfaces into contact; to prepare a specimen of 4 cm x 4 cm size; (3) the specimen is placed on a hot plate heated to 200 °C and a weight of 500 g (whose base diameter is 4 cm) is placed on the specimen for 5 seconds, the specimen is then cooled to room temperature, and checked whether the contacted coated surfaces can be separated easily or not. A thermally sensitive recording medium according to claim 1 or 2, which further comprises an intermediate layer between the thermally sensitive recording layer and the glossing layer which intermediate layer comprises an inorganic pigment and a fixing composition. A recording medium according to claim 1 or 3 wherein the fixing composition comprises a partially saponified polyvinyl alcohol with a degree of saponification of from 79.5 to 98.5%. A recording medium according to any one of the preceding claims wherein the glossing layer comprises from 30 to 60 wt% of the inorganic pigment and from 30 to 60 wt% of the fixing composition based on the total weight of solid of the glossing layer, and the ratio of the fixing composition to the inorganic pigment in the glossing layer is from 0.6 to 2.0 parts by weight to 1 part by weight. A recording medium according to any of claims 2 to 5, wherein, the fixing composition comprises a crosslinking agent.

Inventors: FUKUCHI TADAKAZU, HAMADA KAORU, IMAI DAISUKE, KIMURA YOSHIHIDE, OGAWA HIDENORI, SATO REIKO, TSUZUKI YUJI, FUKUCHI, TADAKAZU, HAMADA, KAORU, IMAI, DAISUKE, KIMURA, YOSHIHIDE, OGAWA, HIDENORI, SATO, REIKO, TSUZUKI, YUJI
Applicants: JUJO PAPER CO LTD, NIPPON PAPER INDUSTRIES CO., LTD.
Application year: 1999
Main classification: B41M5
IPC codes: B41M5