THERMAL RECORDING MATERIAL

Abstract: A thermal recording sheet which is satisfactory in sensitivity in color development, background heat resistance, and background color, is free from powdering, and has excellent image retention. The sheet comprises supporting and formed thereon a thermal color development layer containing as main components a colorless or light-colored basic dye and an organic color developer, and is characterized in that the thermal color development layer contains at least one dihydroxydiphenyl sulfone compound represented by general formula (1) as the organic color developer, and further contains either at least one saturated fatty acid monoamide represented by general formula (2) in an amount of 1.5 to 5 parts per part of the organic color developer or a combination of at least one saturated fatty acid monoamide represented by general formula (2) and at least one diphenyl sulfone derivative represented by the general formula (3). In said formulas, R 1 and R 2 each represents C 1-8 alkyl, alkenyl, or halogeno; and a and b each is an integer of 0 to 3; R 3 represents C 11-21 alkyl; and R 4 to R 9 each represents hydrogen, alkyl, halogeno, nitro, alkoxy, cyano, or allyloxy.

Description: The present invention relates to a thermal recording material that has good color developing sensitivity, good resistance to heat and good ground color and does not generate powder, and further has an excellent image retention. DESCRIPTION OF THE PRIOR ART In general, a thermal recording material having a thermally sensitive color developing layer mainly composed of colorless or pale colored dye precursor and color developing agent that develops color by reacting with said dye prepursor when heated is disclosed in Japanese patent publication 45-14039 and is widely used in commercial scale. A thermal printer in which a thermal head is installed is used for the recording method of said thermal recording material. Since this kind of thermal recording method is superior to the conventional recording method from the view point of noiselessness of the recording process, does not need developing and fixing processes, is maintenance free, the equipment is relatively cheap and compact and the obtained image is very dear, therefore, this method is widely applied in the field of facsimile or computer, various kinds of measuring instrument and for a labeling machine along with the growth of an information industry. The recording devices attached to these instruments are becoming more diversified and more high-performance, and the required quality of the thermal recording material is becoming more severe. Along with the miniaturization of an instrument and requirement for higher recording speed, it becomes necessary to obtain a deep and clear color developing image. For the purpose of meeting the requirement, for example, in the Japanese Patent Laid open Publication 56-169087, a method of improving the color developing sensitivity by adding a thermo fusion substance to a thermally sensitive layer is disclosed, and in the Japanese Patent Laid Open Publication 56-144193, a method of improving the color developing sensitivity by using a new color developing agent which has high color developing ability is disclosed. However, these methods cannot be said to have a sufficient quality, because these methods have defects such as deterioration of ground color by heat, powder generation by aging and dropping of color density after being preserved for long time (reprinting ability). Further, the method to use dye and color developing agent together with an adequate sensitizer can be used. For example, in a case that the color developing agent is a phenol type compound represented by bisphenol A, p-benzylbiphenyl (Japanese Patent Laid Open Publication 60-82382), p-benzyloxybenzoicbenzyl (Japanese Patent Laid Open Publication 57-201691) or benzylnaphthylether (Japanese Patent Laid Open Publication 58-87094) can be used as an adequate sensitizer. When a sensitizer is used, the sensitizer is fused in the first place and the fused sensitizer dissolves dye and color developing agent and are mixed by molecular size level so as to cause the color developing reaction, therefore, the selection of the kind of sensitizer, dye and color developing agent is very important. Dihydroxydiphenylsulfone compound, which is used as an organic color developing agent is a well-known conventional compound, however, the color developing ability of it is too poor to meet the current requirement for high sensitivity. As a method of improving the color developing sensitivity, in Japanese Patent Laid Open Publication 4-69283, a method to add di(p-methylbenzyl)oxalate is disclosed and in Japanese Patent Laid Open Publication 8-67070, a method to add a solid solution composed of two types of oxalic acid ester derivatives is disdosed. By said methods, the color developing sensitivity can be improved more or less. However, from the viewpoints of powder generation and image preservation on aging, these methods cannot be said to be sufficient. As mentioned above, in a conventional thermal sensitive recording medium, it is difficult to meet the current requirement to improve color developing sensitivity. Further, it is also difficult to meet the other requirements for quality such as good heat resistance of ground color and excellent image preservative stability. DISCLOSURE OF THE INVENTION The object of this invention is to provide a thermal recording material which has good color developing sensitivity, strong heat resistance, excellent ground color and does not generate powder, and further has excellent image retention. The inventors of this invention have conducted an intensive study and Have found that in a thermal recording material which possesses a thermally sensitive color developing layer containing colorless or pale colored basic dye and an organic color developing agent as main components, the thermal recording material which comprises at least one organic color developing agent which is a dihydroxydiphenylsulfone type compound of formula (1) as a main component, at least one saturated fatty acid monoamide of formula (2) and at least one diphenyl sulfone derivative of formula (3) can solve the above mentioned problems, and accomplish the present invention. wherein R 1 and R 2 are each independently a C 1-8 alkyl group, a C 1-8 alkenyl group, or a halogen atom; and a and b are each from 0 to 3, R 3 -CONH 2 wherein R 3 is a C 11-21 alkyl group, wherein R 4 to R 9 are each independently a hydrogen atom, an alkyl group, a halogen atom, a nitro group, an alkoxy group, an alkoxy group, a cyano group or an allyloxy group. In general, it is desired that the velocity of dissolution and diffusion or solubility of the dye into the melted color developing agent give the important effects in the color developing sensitivity of thermal recording material. To improve said effects, a method of adding various kinds of material as a sensitizer is carried out. It is desired that the addition of sensitizer causes several effects such as decrease in melting point, decrease of activated energy, change of polarity, improvement of solubility between each materials, and the velocity for fusing, dissolving and diffusion and saturated solubility are improved. Thus the color developing sensitivity of the thermal recording material can be improved. In general, waxes containing saturated fatty acid monoamide are widely known as sensitizers. However, this invention has been accomplished by finding out that the thermal recording material whose color developing sensitivity is improved, has a strong heat resistance and does not generate powder, further has an excellent image retention can be obtained by providing dihydroxydiphenylsulfone compound as an organic color developing agent and including saturated fatty acid monoamide by the specific limit, preferably in an amount of from 1.5 to 5 parts to 1 part of the dihydroxydiphenylsulfone compound. Generally, if waxes or a sensitizer are used in a large amount to improve the color developing sensitivity, the color developing sensitivity can be improved. However, other problems such as deterioration of heat resistance of ground color or generation of powder occurs. Therefore, the amount of sensitizer is usually 1 part to 1 part of color developing agent. In the meanwhile, the inventors of this invention have found that the use of saturated fatty acid monoamide as a sensitizer can solve said problem. Namely, in this case, even if the amount of saturated fatty acid monoamide to dihydroxydiphenylsulfone compound is bigger than usual, the heat resistance or powder generation are not deteriorated, and high color developing sensitivity can be obtained. The reason why is not clear. However, it is related to the fact that by the use of saturated fatty acid monoamide the mutual solubility between dye, color developing agent and sensitizer becomes good and color developing sensitivity is improved, and since the remarkable decrease in melting point does not occur, the deterioration of heat resistance is very small. Further, since the saturated fatty acid monoamide is not a sublimated substance, the developed image formed by the reacted product by dye, color developing agent and sensitizer can be stably preserved. A diphenylsulfone derivative represented by formula (3) is also added as well as the dihydroxydiphenylsulfone compound as an organic color developing agent and the saturated fatty acid monoamide and a thermal recording material whose color developing sensitivity is further improved, whose ground color and heat resistance are maintained in the practical level, and has good image preservative property is obtained. The reason why is not clear. However, it is related to the fact that even if dihydroxydiphenylsulfone compound, saturated fatty acid monoamide and diphenylsulfone derivatives are contained together, remarkable decrease in melting point does not occur and the mutual solubility of each material is improved. Further, in this invention, when at least one kind of specific compound chosen from 4-benzyloxy-4'-(2,3-epoxy-2-methyl propoxy)diphenylsulfone, epoxy resin and diphenylsulfone bridgeable type compound is included it is recognized that the image preservative property of color developed part is improved. The reason why is not dear. However, it is related to the fact that said specific compound is bonded with an electro charge transferring complex which is formed by the reaction between dye and color developing agent and results in a more stable state. wherein X and Y are each independently a saturated or unsaturated linear or grafted C 1-12 hydrocarbon group which can possess an ether bond, or are or wherein R is a methylene group or an ethylene group, T is a hydrogen atom or a C 1-4 alkyl, and R 10 to R 15 are each independently a halogen atom, a C 1-6 alkyl group or a C 1-6 alkenyl group, and m, n, p, q, r, and t are each an integer of from 0 to 4, and d is an integer of from 0 to 10. The thermally sensitive recording medium of this invention, for example, can be produced by following method. That is, prepare the dispersion in which a dye and compounds represented by formula (1), formula (2) and formula (3) and optionally a stabilizer are dispersed with a binder, then a filler and other necessary additives are added. Thus the coating for a thermal sensitive color developing layer is prepared. The prepared coating is coated on a substrate and dried so as to form a thermally sensitive color developing layer. In this invention, a dihydroxydiphenylsulfone compound represented by formula (1) is provided as an organic color developing agent. Specific examples of formula (1) can be mentioned below. However, it is not intend to be limited to these compounds. 4,4'- dihydroxydiphenylsulfone (1-1) 2,4'- dihydroxydiphenylsulfone (1-2) bis-(3-allyl-4-hydroxyphenyl)sulfone (1-3) 3,3'-dimethyl-4,4'-dihydroxydiphenylsulfone (1-4) 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylsulfone (1-5) 2,2'-bis(4-chrolophenol)sulfone (1-6) 4-hydroxyphenyl-3'-isopropyl-4'-hydroxyphenylsulfone (1-7) bis-(3-ethyl-4-hydroxyphenyl)sulfone (1-8) 2,2'-bis(p-t-buthylphenol)sulfone (1-9) 2,2'-bis(p-t-penthylphenol)sulfone (1-10) 2,2'-bis(p-t-octylphenol)sulfone (1-11) of these compounds, compounds (1-1) to (1-3) are preferred, because of good sensitivity, strong heat resistance, and easy availability on the market. These color developing agents can be used alone or in combination. In this invention, a saturated fatty acid monoamide represented by formula (2) is provided. When this saturated fatty acid monoamide is used alone, the amount to be included is from 1.5 to 5 parts to 1 part of the organic color developing agent. With in these limits, a thermal recording material which has a high color developing sensitivity at the printing of a lower energy region can be. obtained, maintaining excellent quality level at a heat resistance and a color developing sensitivity without generating powder. Especially, when the amount to be included is within the limit of from 1.7 to 3.5 parts, a product having a more excellent quality can be obtained. Further, in this invention, diphenylsulfone derivatives represented by formula (3) are provided together with the saturated fatty acid monoamide represented by general formula (2). The desirable amount of diphenylsulfone derivatives and saturated fatty acid is respectively from 0.25 to 1.7 parts to 1 part of dihydroxydiphenylsulfone. When the amount to be provided is within this limit, a thermal recording material which is excellent in color developing sensitivity, ground color, heat resistance and image preservative property at high humidity conditions can be obtained. Further, when the amount of each compound is within from 0.5 to 1.5 parts, the image preservative property at high humidity conditions can be further improved and a product of higher quality can be obtained. The preferred ratio of diphenylsulfone derivatives to saturated fatty acid monoamide is from 1:3 to 3:1, and within this ratio, qualities such as color developing sensitivity and heat resistance are desirably balanced. When the amount of diphenylsulfone derivatives represented by formula (3) is smaller than 4% to the total amount of solid part of the thermally sensitive coating, a thermally sensitve recording medium that does not generate powder by the printing of high energy can be obtained, maintaining the excellent quality level. Further, if the amount of saturated fatty acid monoamide is from 1.5 to 5 parts to 1 part of the organic color developing agent, the color developing sensitivity is further improved. In formula (2), R 3 indicates a hydrocarbon group and specifically a C 11-21 alkyl group can be mentioned. As specific examples of the compound of formula (2), compounds (2-1) to (2-4) can be mentioned, but it is not be intended to be limited to them. Especially, when compounds (2-2) and (2-3) are used in combination, good color developing sensitivity and heat resistance are obtained. Therefore, the mixture of (2-2) and (2-3) is desirably used. C 11 H 23 CONH 2 C 15 H 31 CONH 2 C 17 H 35 CONH 2 C 21 H 43 CONH 2 In formula (3), R 4 to R 9 can be substituted with a group that does not prevent the sensitizer effect, and as specific examples, hydrogen atom, alkyl group, halogen atom, nitro group, alkoxy group, cyano group and allyloxy group can be mentioned. Especially, hydrogen atom, C 1-6 alkyl group, C 1-6 alkoxy group, halogen atom and nitro group can be mentioned. Specific examples include compounds (3-1) to (3-46) as follows. However, it is not be intend to be limited to these compounds. Further, in this invention, 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy) diphenylsulfone, epoxy resin and diphenylsulfone bridgeable type compound of formula (4) can be included. If the amount of these compounds is too small compared to the dihydroxydiphenylsulfone compound of formula (1), the image stabilizing effect is insufficient, and if too much, the sensitivity and heat resistance are deteriorated. In this invention, it is desirable to use from 0.01 to 0.9 parts of these compounds to 1 part of dihydroxydiphenylsulfone compound. Especially, if the amount exceed 0.17 parts, the image preservative property to plasticizer can be improved. As the epoxy resin, bisphenol A type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin and a copolymer of glycidylmethacrylate and vinyl monomer can be mentioned. Among these compounds, a copolymer of glycidylmethacrylate and vinyl monomer can be desirably used because of the good effect as a stabilizer and excellent heat resistance. Further, a copolymer of glycidylmethacrylate and vinyl monomer whose average molecular weight is from 9000 to 11000, epoxy equivalent is from 300 to 600 and melting point is lower than 110°C is preferred. The diphenylsulfone bridgeable type compound of formula (4) is described in Japanese Patent Laid Open Publicat on 10-29969. In formula (4), specific examples of groups represented by X and Y are mentioned as follows. That is, a methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene group, decamethylene group, undecamethylene group, dodecamethylene group, methylmethylene group, dimethylmethylene group, methylethylene group, methyleneethylene group, ethylethylene group, 1,2-dimethylethylene group, 1-methyltrimethylene group, 1-methyltetramethylene group, 1,3-dimethyltrimethylene group, 1-ethyl-4-methyl-tetramethylene group, vinylene group, propenylene group, 2-butenylene group, ethynylene group, 2-butynylene group, 1-vinylethylene group, ethyleneoxyethylene group, tetramethyleneoxytetramethylene group, ethyleneoxyethyleneoxyethylene group, ethyleneoxymethyleneoxyethylene group, 1,3-dioxane-5, 5-bismethylene group, 1,2-xylyl group, 1,3-xylyl group, 1,4-xylyl group, 2-hydroxytrimethylene group, 2-hydroxy-2-methyltrimethylene group, 2-hydroxy-2-ethyltrimethylene group, 2-hydroxy-2-propyltrimethylene group, 2-hydroxy-2-isopropyltrimethylene group and 2-hydroxy-2-butyltrimethylene group can be mentioned. An alkyl or alkenyl group R 10 to R 15 is a C 1-6 alkyl group or a C 1-6 alkenyl group and as specific examples, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, n-hexyl group, isohexyl group, 1-metylpentyl group, 2-methylpentyl group, vinyl group, allyl group, isopropenyl group, 1-propenyl group, 2-butenyl group, 3-butenyl group, 1,3-butanedienyl group and 2-methyl-2-propenyl group can be mentioned. A halogen atom indicates chloride, bromine, fluorine or iodine. In this invention, referring to the diphenylsulfone bridgeable type compound of formula (4), several kinds of compounds whose substitution group and/or number of d are different can be used in combination. The mixing ratio is voluntary. As the mixing method, a mixing method by powder, a mixing method in aqueous dispersion and a method of reacting several kinds of diphenylsulfone bridgeable type compound simultaneously by controlling the reactive conditions can be mentioned. However, it is not intend to be limited to them. When several kinds of diphenylsulfone bridgeable type compound of formula (4) are used together, the desirable composition comprises more than 2 kinds of compound of formula (5) whose d values only are different. The method for preparation of these kinds of compound is not so difficult, that is, by changing reactive ratio of the starting materials, the compounds whose d values are different can be synthesized simultaneously. in the formula, X, Y, R 10 , m and d are same above. As specific examples of a compound of formula (4), the following compounds can be mentioned (4-1) 4,4'-bis[4-[4-(4-hydroxyphenylsulfonyl)phenoxy]-2-trans-butenyloxy]diphenyl sulfone (4-2) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-4-butyloxy]diphenylsulfone (4-3) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-3-propyloxy]diphenylsulfone (4-4) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-2-ethyloxy]diphenylsulfone (4-5) 4-[4-(4-hydroxyphenylsulfonyl)phenoxy-4-butyloxy]-4'-[4-(4-hydroxyphenyl sulfonyl) phenoxy-3-propyloxy]diphenylsulfone (4-6) 4-[4-(4-hydroxyphenylsulfonyl)phenoxy-4-butyloxy]-4'-[4-(4-hydroxyphenyl sulfonyl) phenoxy-2-ethyloxy]diphenylsulfone (4-7) 4-[4-(4-hydroxyphenylsulfonyl)phenoxy-3-propyloxy]-4'-[4-(4-hydroxyphenyl sulfonyl)phenoxy-2-ethyloxy]diphenylsulfone (4-8) 4-4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-5-pentyloxy]diphenylsulfone (4-9) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-6-hexyloxy]diphenylsulfone (4-10) 4-[4-[4-hydroxyphenylsulfonyl]phenoxy]-2-trans-butenyloxy]-4'-[4-(4-hydroxy phenylsulfonyl)phenoxy-4-butyloxy]diphenylsulfone (4-11) 4-[4-(4-hydroxyphenylsulfonyl)phenoxy-2-trans-butenyloxy]-4'-[4-(4-hydroxy phenylsulfonyl) phenoxy-3-propyloxy]diphenylsulfone (4-12) 4-[4-[4-(4-hydroxyphenylsulfonyl)phenoxy]-2-trans-butenyloxy]-4'-[4-(4-hydroxy phenylsulfonyl)phenoxy-2-ethyloxy]diphenylsulfone (4-13) 1,4-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenoxy-2-trans-butenyloxy]phenyl sulfonyl]phenoxy]-cis-2-butene (4-14) 1,4-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenoxy-2-trans-butenyloxy]phenyl sulfonyl]phenoxy]-trans-2-butene (4-15) 4,4'-bis[4-[4-(2-hydroxyphenylsulfonyl)phenoxy]butyloxy]diphenylsulfone (4-16) 4,4'-bis[4-[2-(4-hydroxyphenylsulfonyl)phenoxy]butyloxy]diphenylsulfone (4-17) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-2-ethylenoxyethoxy]diphenyl sulfone (4-18) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenyl-14-phenylenebismethyleneoxy] diphenylsulfone (4-19) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenyl-1,3-phenylenebismethyleneoxy] diphenylsulfone (4-20) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenyl-1,2-phenylenebismethyleneoxy] diphenylsulfone (4-21) 2,2'-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenoxy-2-ethyleneoxyethoxy]phenyl sulfonyl] phenoxy] diethyl ether (4-22) α,α'-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenyl-1,4-phenylenebismethylene oxy] phenylsulfonyl]phenoxy]-p-xylene (4-23) α,α'-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenyl-1,3-phenylenebismethylene oxy]phenylsulfonyl]phenoxy]-m-xylene (4-24) α,α'-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenyl-1,2-phenylenebismethylene oxy]phenylsulfonyl]phenoxy]-O-xylene (4-25) 2,4'-bis[2-(4-hydroxyphenylsulfonyl)phenoxy-2-ethyleneoxyethoxy]diphenyl sulfone (4-26) 2,4'-bis[4-(2-hydroxyphenylsulfonyl)phenoxy-2-ethyleneoxyethoxy]diphenyl sulfone (4-27) 4,4'-bis[3,5-dimethyl-4-(3,5-dimethyl-4-hydroxyphenylsulfonyl)phenoxy-2-ethyleneoxyethoxy]diphenylsulfone (4-28) 4,4'-bis[3-allyl-4-(3-allyl-4-hydroxyphenylsulfonyl)phenoxy-2-ethyleneoxy ethoxy]diphenyl sulfone (4-29) 4,4'-bis[3,5-dimethyl-4-(3,5-dimethyl-4-hydroxyphenylsulfonyl)phenyl-1,4-phenylenebismethyleneoxy]diphenylsulfone (4-30) 4,4'-bis[3,5-dimethyl-4-(3,5-dimethyl-4-hydroxyphenylsulfonyl)phenyl-1,3-phenylenebismethyleneoxy]diphenylsulfone (4-31) 4,4'-bis[3,5-dimethyl-4-(3,5-dimethyl-4-hydroxyphenylsulfonyl)phenyl-1,2-phenylenebismethyleneoxy]diphenylsulfone (4-32) 4,4'-bis[3-allyl-4-(3-allyl-4-hydroxyphenylsulfonyl)1,4-phenylenebis methyleneoxy]diphenylsulfone (4-33) 4,4'-bis[3-allyl-4-(3-allyl-4-hydroxyphenylsulfonyl)1,3-phenylenebismethylene oxy]diphenylsulfone (4-34) 4,4'-bis[3-allyl-4-(3-allyl-4-hydroxyphenylsulfonyl)1,2-phenylenebismethylene oxy]diphenylsulfone (4-35) 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy-2-hydroxypropyloxy]diphenyl sulfone (4-36) 1,3-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenoxy-2-hydroxypropyloxy]phenyl sulfonyl]phenoxy]-2-hydroxypropane. Further, among the compounds represented by formula (5), the compounds where d is O are disclosed in Japanese Patent Application 7-149713, PCT Laid Open Publication WO93/06074 and WO95/33714. Specifically 1,3-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-2-hydroxypropane, 1,1-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]methane, 1,2-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]ethane, 1,3-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]propane, 1,4-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]butane, 1,5-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]pentane, 1,6-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]hexane, α,α'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-p-xylene, α,α'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-m-xylene, α,α'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-o-xylene, 2,2'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]diethyl ether, 4,4'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]dibutyl ether, 1,2-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]ethylene and 1,4-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-2-butene can be mentioned. The compound represented by formula (4) can be obtained by the method described in International Patent Laid Open Publication WO97/16420 which reacts 4,4-dihydroxyphenylsulfone derivatives or 2,4'-dihydroxyphenylsulfone derivatives in the presence of a basic compound. The material of the invention may comprise one or more kinds of diphenylsulfone bridgeable type compound prepared by the above mentioned method, and the compounds obtained by following synthetic examples are desirably used. Synthetic Example 1 16.0g (0.4 mole) of sodium hydroxide is added to 21.2g of water and dissolved, then 50.0g (0.2mole) of 4,4-dihydroxydiphenylsulfone (BPS) is added. Then, 14.3g (0.10mole) of bis(2-chloroethyl)ether is added at 105°C, reacted for 5 hours at 110-115°C. After the reaction is over, 375ml of water is added to the reacted solution, stirred for 1 hour at 90°C. Then cooled down to the room temperature, neutralized by 20% sulfuric acid. The crystallized solid is filtrated, and 39.3g of white crystalline is obtained. The yield of bis(2-chloroethyl)ether is 88%. The obtained component is analyzed by high performance liquid chromatography and identified as follows. As the column, Mightysil RP-18 (product of Kanto Chemical Co., Ltd.) is used, and moving bed is CH 3 CN:H 2 O:1%H 3 PO 4 =700:300:5, and UV wave length is 260nm. d=0 : retention time 1.9 minutes : area % 32.9 d=1 : retention time 2.3 minutes : area % 21.7 d=2 : retention time 2.7 minute : area % 12.8 d=3 : retention time 3.4 minutes : area % 8.8 d=4 : retention time 4.2 minutes : area % 5.8 d=5 : retention time 5.4 minutes : area % 3.5 d=6 : retention time 7.0 minutes : area % 2.2 d=7 : retention time 9.0 minutes : area % 1.7 d=8 : retention time 11.8 minutes : area % 1.3 d=9 : retention time 15.4 minutes : area % 1.3 Synthetic Examples 2-4 The molar ratio of BPS and bis(2-chloroethyl)ether of Synthetic 1 is changed to 1.5:1, 2.5:1, 3.0:1, and following composition can be obtained. In a case of 1.5 : 1, d=0 is 20.8, d=1 is 33.0, d=2 is 14.2, d=3 is 7.9, d=4 is 3.9 In a case of 2.5:1, d=0 is 49.6, d=1 is 25.9, d=2 is 11.4, d=3 is 5.3, d=4.is 2.4 In a case of 3.0:1, d=0 is 56.9, d=1 is 24.9, d=2 is 9.6, d=3 is 3.7, d=4 is 1.3 Synthetic Example 5 In a mixed solution of 10.0g of 48% of aqueous solution of sodium hydroxide and 155g of N,N'-dimethylacetoamide, 30.0g (0.12 mole) of BPS is added. After the temperature is raised to 80°C and BPS is dissolved, 10.5g (0.06 mole) of α,α-dichloro-p-xylene dissolved in 15g of xylene, is dropped slowly. Then, the mixture is ripened for 2 hours at the same temperature. After ripening, the solution is poured into 900 ml of water and the crystallized solid is filtrated. The obtained crude crystalline is rinsed with methanol, filtrated and dried, and 19.7g of white crystalline solid is obtained. The product is analyzed by high performance liquid chromatography, and the main components are identified as follows. α,α'-bis[4-(4-hydroxyphenylsulfonyl)phenoxy]-p-xylene 59.1% 4,4'-bis[4-(4-hydroxyphenylsulfonyl)pheny-1,4-phenylenebismethyleneoxy]diphenylsulfone 23.1% α,α'-bis[4-[4-[4-(4-hydroxyphenylsulfonyl)phenyl-1,4-phenylenebismethyleneoxy]phenylsulfonyl]phenoxy]-p-xylene 11.1% As the leuco color developing type basic leuco dye used in this invention, any well known dye in the field of conventional pressure sensitive type or thermally sensitive type recording paper can be used, and triphenyl methane type compound, fluoran type compound, fluorene type compound or divinyl type compound are desirably used. However, it is not intended to be limited to them. Typical example of colorless or pale colored leuco dye (dye precursor) are mentioned below. Further, these dye precursor 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-(o-chloroanilino)fluoran 3-diethylamino-6-methyl-7-(p-chloroanilino)fluoran 3-diethylamino-6-methyl-7-(o-fluoroanilino)fluoran 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran 3-diethylamino-6-methyl-7-n-octylanilinofluoran 3-diethylamino-6-methyl-7-n-octylaminofluoran 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-diethylamino-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-trifluoromethylaniliono)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-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-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-benzyl-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[fluorehe-9,3'-phthalide] <Divinyl type leuco dyes> 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetra bromophthalide 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetra chlorophthalide 3,3-bis-[1,1-bis(4-pyrrolidinophenyl)ethyl en-2-yl]-4,5,6,7-tetrabromophthalide 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide <Others> 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-aza phthalide 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-aza phthalide 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 dimethylester. Among these compounds, especially, 3-di-n-pentylamino-6-methyl-7-anilinofluoran is desirably used because whiteness of ground color and heat resistance are good. In general, it is supposed that the coloring of the coating is caused as follows. Namely, a part of materials contained in the coating is dissolved in water, and it reacts with the dye. For example, 4,4-dihydroxy diphenylsulfone, which is a compound of formula (1) contains two -OH groups by which basic colorless dye is color developed, and is easily dissolved in water. In the meanwhile, since the degree of solubility in water of 3-di-n-pentylamino-6-methyl-7-anilinofluoran is lower than 1.349 × 10 -6 g/l, which is recognized as a very low level, it is possible to prevent the coloring of the coating by the combined use of 3-di-n-pentylamino-6-methyl-7-anilinofluoran with a compound of formula (1). In the present invention, the well known conventional sensitizers can be used. Specific examples include ethylenebisamide, montan acid wax, polyethylene wax, 1,2-di-(3-methylphenoxy)ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolylether, m-tarphenyl, 1,2-diphenoxyethane, dibenzyl4,4'-ethylenedioxy-bis-benzoate, dibenzoyloxymethane, 1,2-di(3-methylphenoxy)ethylene, 1,2-diphenoxyethylene, bis[2-(4-methoxy-phenoxy)]ethyl]ether, p-nitromethylbenzoate, dibenzyl oxalate, di(p-chloro benzyl) oxalate, di(p-methyl benzyl) oxalate, dibenzylterephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthylcarbonate, 1,4-diethoxy naphthalene, phenyl 1-hydroxy-2-naphthoate, o-xylene-bis-(phenylether), 4-(m-methylphenoxymethyl)biphenyl, o-toluenesulfoneamide and p-toluenesulfoneamide. However, it is not intended to be limited to them. These kinds of sensitizer can be used alone or in combination. As the binder to be used in the present invention, fully saponified polyvinyl alcohol of 200-1900 polymerization degree, partially saponified polyvinyl alcohol, denatured polyvinyl alcohol by carboxyl, denatured polyvinyl alcohol by amide, denatured polyvinyl alcohol by sulfonic acid denatured polyvinyl alcohol by butylal modified polyvinyl alcohol, derivatives of cellulose such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose, copolymer of styrene-maleic anhydride, copolymer of styrene-butadiene, polyvinyl chloride, polyvinyl acetal, polyacrylamide, 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 molecular compounds can be applied by being dissolved in 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. In this invention, as the image stabilizer showing oil resistance effect of recorded image, 4,4'-butylidene(6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulphonyldiphenol, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone and epoxy resin can be added in the limit not to prevent above mentioned desired effect. 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 or aluminum hydroxide can be mentioned. Further, a slipping agent such as waxes, an ultra violet ray absorbing agent such as benzophenone type or triasol type compound, a water proof agent such as glioxasal, a dispersing agent , a defoamer, an anti oxidation agent and fluoresene dye can be used. The amount of color developer and dye precursor, the kind and amount of other additives to be used in the thermal recording material 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 basic leuco dye and from 0.5 to 4 parts of filler to 1 part of color developing agent indicated by formula (1). The desirable amount of binder is from 5 to 25 % to the total amount of solid. The coating of the above mentioned component is coated over the surface of substrate such as paper, recycled paper, synthetic paper, film, plastic film, plastic foam film or non-woven cloth, and the desired thermal recording material can be obtained. A complex sheet composed of the above mentioned sheet can also be used. Further, to improve the preservative property, an overcoat layer can be prepared on the thermally sensitive color developing layer. Said organic color developer, basic leuco dye and other additives which are added as needed are ground to 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 as needed, thus the coating is prepared. The method of coating is not restricted, and can be coated by conventional well known methods, for example, an off machine coating machine with various coaters such as air knife coater, rod blade coater, bill blade coater or roll coater, or a coating machine can preferably used. EXAMPLE The thermal recording material of this invention will be illustrated more specifically by Examples. However, it is not intended to be limited to them. In the Examples and Comparative Examples, "parts" indicates weight part. [Preparation Example 1] According to the following recipe, dispersions of dye, color developing agent and sensitizer are separately ground in wet condition to average particle diameter of 0.5µm by a sand grinder. 〈dispersion of color developing agent〉 4,4-dihydroxydiphenylsulfone (1-1) 6.0 parts 10% aqueous solution of polyvinyl alcohol 18.8 parts water 11.2 parts 〈dispersion of dye〉 3-di-n-buthylamino-6-methyl-7-anilinofluoran (ODB2) 3.0 parts 10% aqueous solution of polyvinyl alcohol 6.9 parts water 3.9 parts 〈dispersion of fatty acid monoamide〉 (2-3) compound 12.0 parts 10% aqueous solution of polyvinyl alcohol 37.6 parts water 22.4 parts The compounds mentioned below are mixed and the coating for thermally sensitive layer is prepared. The obtained coating is coated over the surface of 50g/m 2 high grade paper and dried up so as to the coating amount is 6.0g/m 2 , and the obtained sheet is treated by a super calendar so as the Beck's smoothness become 200-600 sec. and the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 72.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts Preparation Examples 5 and 6 By the same process as Preparation Example 1, except changing ODB2 of the dye dispersion to 3-di-n-pentylamino-6-methyl-7-anilinofluoran (commercial name : Black305, product of Yamada Chemical Industries ; hereinafter shortened to B305) (Preparation Example 5), 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran (S205) (Preparation Example 6), the thermally sensitive recording media are obtained. [Preparation Example 10] According to the following recipe, dispersions of the following materials are prepared and are ground in wet conditions to an average particle diameter of 0.5µ m by a sand grinder. 〈dispersion of stabilizer〉 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone (commercial name : NTZ-95, product of Nihon Soda ; hereinafter shortened to NTZ) 1.0 parts 10% aqueous solution of polyvinyl alcohol 3.1 parts water 1.9 parts By the same process as Preparation Example 5, except adding dispersion of stabilizer, the thermal recording material of the following recipe is obtained. dispersion of color developing agent 36.0 parts dispersion of dye 13.8 parts dispersion of fatty acid monoamide 72.0 parts dispersion of stabilizer 6.0 parts 50% dispersion of kaolin clay 12.0 parts 30% dispersion of zinc stearate 6.7 parts [Example 15] According to the following recipe, dispersions of the following materials are prepared and are ground in wet conditions to an average particle diameter of 0.5µ m by a sand grinder. (dispersion of diphenylsulfone) (3-1) compound 9.0 parts 10% aqueous solution of polyvinyl alcohol 28.2 parts water 16.8 parts By the same process as Preparation Example 1 except changing the blending amount of the dispersion of fatty acid amide and adding dispersion of diphenylsulfone, the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 18.0 parts dispersion of diphenylsulfone ((3-1) compound) 54.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts [Example 16] By the same process as Example 15, except changing the blending amount of fatty acid amide dispersion and diphenylsulfone dispersion, the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 36.0 parts dispersion of diphenylsulfone((3-1) compound) 36.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts [Examples 17, 18] By the same process as Example 16, except changing ODB2 to B305 (Example 17) and to S205 (Example 18), the thermally sensitive recording media are obtained. [Example 19] By the same process as Example 15, except changing the blending amount of fatty acid amide dispersion and diphenylsulfone dispersion, the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 54.0 parts dispersion of diphenylsulfone((3-1) compound) 18.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts [Example 20] By the same process as Example 15, except changing the blending amount of fatty acid amide dispersion and diphenylsulfone dispersion, the thermal recording material of the following recipe is obtained. dispersion of color developing agent ((1-1) compound) (amount of solid is 7.88 parts) 36.0 parts dispersion of dye (ODB2) (amount of solid is 3.69 parts) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) (amount of solid is 15.76 parts) 72.0 parts dispersion of diphenylsulfone((3-1) compound) (amount of solid is 1.97 parts ; amount of solid diphenylsulfone is 1.5 parts) 9.0 parts 50% dispersion of kaolin clay (amount of solid is 13 parts) 26.0 parts 30% dispersion of zinc stearate (amount of solid is 2.01 parts) 6.7 parts [Example 21] By the same process as Example 17, except adding the dispersion of the stabilizer used in Preparation Example 10, the thermal recording material of following recipe is obtained. dispersion of color developing agent 36.0 parts dispersion of dye 13.8 parts dispersion of fatty acid monoamide 36.0 parts dispersion of diphenylsulfone 36.0 parts dispersion of stabilizer 6.0 parts 50% dispersion of kaolin clay 12.0 parts 30% dispersion of zinc stearate 6.7 parts [Examples 22, 23] By the same process as Example 21, except changing NTZ to NER (Example 22) and to the diphenylsulfone type bridgeable compound of Synthetic Example 1 (Example 23), the thermally sensitive recording media are obtained. [Comparative Example 1 ] By the same process as Example 1, except changing (1-1) compound of color developing agent dispersion to 4,4-isopropyridendiphenol (BPA), the thermal recording material is obtained. [Comparative Example 2] By the same process as Example 1, except changing the blending ratio of fatty acid monoamide dispersion as mentioned below, the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 36.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts [Comparative Example 3] By the same process as Example 1, except changing the blending ratio of fatty acid monoamide dispersion as mentioned below, the thermal recording material is obtained. dispersion of color developing agent ((1-1) compound) 36.0 parts dispersion of dye (ODB2) 13.8 parts dispersion of fatty acid monoamide ((2-3) compound) 216.0 parts 50% dispersion of kaolin clay 26.0 parts 30% dispersion of zinc stearate 6.7 parts [Comparative Example 4] By the same process as Example 1, except changing the fatty acid monoamide dispersion as follows, the thermal recording material is obtained. 〈dispersion of p-benzylbiphenyl〉 p-benzylbiphenyl 12.0 parts 10% aqueous solution of polyvinyl alcohol 37.6 parts water 22.4 parts [Comparative Example 5] By the same process as Example 1, except blending the following dispersion instead of the fatty acid monoamide dispersion, the thermal recording material is obtained. 〈dispersion of diphenylsulfone〉 (3-1) compound 6.0 parts 10% aqueous solution of polyvinyl alcohol 18.8 parts water 11.2 parts [Comparative Example 6] By the same process as Example 1, except blending the following dispersion instead of fatty acid monoamide dispersion, the thermal recording material is obtained. 〈dispersion of polyethylene wax〉 polyethylene wax 12.0 parts 10% aqueous solution of polyvinyl alcohol 37.6 parts water 22.4 parts [Comparative Example 7] By the same process as Example 1, except blending the following dispersion instead of fatty acid monoamide dispersion, the thermal recording material is obtained. 〈dispersion of oxalic acid di(p-methylbenzyl)〉 oxalic acid di(p-methylbenzyl) 12.0 parts 10% aqueous solution of polyvinyl alcohol 37.6 parts water 22.4 parts [Comparative Example 8] By the same process as Comparative Example 5, except adding the following stabilizer dispersion, the thermal recording material is obtained. 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone (commercial name : NTZ-95, product of Nihon Soda) 1.0 parts 10% aqueous solution of polyvinyl alcohol 3.1 parts water 1.9 parts [color developing sensitivity] Thermal recording is carried out on the prepared thermally sensitive recording media using TH-PMD, which is a product of Ohkura Denki Co., by 0.22mJ/dot impressive energy. Further, a printing test is carried out by UBI printer (product of UBI Co.,) by 24mj/mm 2 impressive energy. Image density after printing and after quality test are measured by means of a Macbeth densitometer (umber filter used) [degree of whiteness of ground color] Degree of whiteness of the uncolored developed portion of the specimen is measured by Hunter Whiteness tester (product of Toyo Seiki Seisakusho, blue filter). A larger value indicates a good result. [heat resistance test] A specimen which has not been color developed is left in an atmosphere of 60°C for 24 hrs, and measured by a Hunter Whiteness tester (product of Toyo Seiki Seisakusho, blue filter). [image remaining ratio after humidity resistance test] A specimen of a printed image using UBI printer (product of UBI Co.,) by 24mJ/mm 2 impressive energy is treated in an atmosphere of 40 °C, 90%condition for 24 hrs, and measured by a Macbeth densitometer. The image remaining ratio is calculated from the Macbeth density before and after treatment, using the following numerical formula. Image remaining ratio(%) = [(Macbeth density after treatment) / (Macbeth density before treatment)] × 100 [image remaining ratio after plasticizer resistance test] A single sheet of polyvinylchloride wrap (HIGHWRAP KMA : Mitsui Toatsu Chemicals Co., Ltd.) was wound round with 1 ply on a paper tube, stuck thereon a thermal recording medium recorded by TH-PMD, which is a product of Ohkura Denki Co., by 0.22mJ/dot impressive energy, further wound round with 3 plys of the polyvinylchloride wrap, allowed to stand at 20°C for 24 hours, and measured by a Macbeth densitometer. The image remaining ratio is calculated from the Macbeth density before and after treatment, using the above mentioned numerical formula. [image remaining ratio after heat resistance test] A specimen of a printed image using TH-PMD, which is a product of Ohkura Denki Co., by 0.22mJ/dot impressive energy is left in an atmosphere of 60°C for 24hrs. The image remaining ratio is calculated from the Macbeth density before and after treatment, using the above mentioned numerical formula. [powder generation] A specimen of a printed image using TH-PMD, which is a product of Ohkura Denki Co., by 0.22mJ/dot impressive energy is left for 1 month, and powder generation at the image part by lower energy is inspected by the naked eye of an inspector. A specimen printed by UBI printer (product of UBI Co.,) by 24mJ/mm 2 impressive energy is left for 24 hrs, and powder generation at the image part by higher energy is inspected by the naked eye of an inspector. ○ no powder generation Δ slight powder generation × powder generated The test results are summarized in Tables 1 to 4. In Tables 1 and 2, FMA : indicates saturated fatty acid monoamide, DPS : indicates diphenylsulfone derivatives, The number in parenthesis indicates the blending parts to 1part of color developing agent. Example color developing agent FMA DPS dye stabilizer Prep. 1 1-1 2-3(2) ODB2 Prep. 5 1-1 2-3(2) B305 Prep. 6 1-1 2-3(2) S205 Prep. 10 1-1 2-3(2) B305 NTZ(0.17) 15 1-1 2-3(0.5) 3-1(1.5) ODB2 16 1-1 2-3(1) 3-1(1) ODB2 17 1-1 2-3(1) 3-1(1) B305 18 1-1 2-3(1) 3-1(1) S205 19 1-1 2-3(1.5) 3-1(0.5) ODB2 20 1-1 2-3(2) 3-1(0.25) ODB2 21 1-1 2-3(1) 3-1(1) B305 NTZ(0.17) 22 1-1 2-3(1) 3-1(1) B305 NER(0.17) 23 1-1 2-3(1) 3-1(1) B305 Synthetic Ex.1 (0.17) Comparative Example color developing agent FMA DPS dye stabilizer 1 BPA 2-3 (2) ODB2 2 1-1 2-3 (1) ODB2 3 1-1 2-3 (6) ODB2 4 1-1 PBB (2) ODB2 5 1-1 3-1 (1) ODB2 6 1-1 polyethylene wax(2) ODB2 7 1-1 oxalic acid di(p-methylbenzyl)(2) ODB2 8 1-1 3-1 (1) ODB2 NTZ (0.17) Example sensitivity degree of whiteness ground color heat resistance 60°C Image remaining ratio after resistance test to powder generation 0.22mJ/dot 24 mJ/mm 2 humidity plasticizer heat 0.22mJ/dot 24 mJ/mm 2 15 0.62 1.39 80% 76% 84% 5% 46% ○ Δ 16 0.64 1.4 80% 76% 81% 5% 46% ○ Δ 17 0.64 1.4 82% 82% 81% 5% 46% ○ Δ 18 0.75 1.4 76% 73% 89% 5% 47% ○ Δ 19 0.64 1.4 80% 76% 76% 5% 45% ○ Δ 20 0.65 1.38 80% 76% 72% 5% 50% ○ ○ 21 0.61 1.37 82% 80% 91% 26% 91% ○ Δ 22 0.61 1.38 82% 80% 90% 19% 90% ○ Δ 23 0.61 1.36 82% 81% 84% 48% 83% ○ Δ Comp. Example sensitivity degree of whiteness ground color heat resistance 60°C Image remaining ratio after resistance test to powder generation 0.22mJ/dot 24 mJ/mm 2 humidity plasticizer heat 22mJ/dot 24mJ/mm 2 1 0.59 1.4 69% 60% 93% 5% 50% ○ ○ 2 0.40 1.41 80% 76% 72% 5% 43% ○ ○ 3 0.44 1.03 80% 75% 65% 5% 41% ○ ○ 4 0.83 1.36 69% 60% 74% 5% 44% Δ Δ 5 0.34 1.39 80% 76% 88% 5% 43% × × 6 0.15 1.07 80% 76% 71% 5% 40% ○ ○ 7 0.34 1.28 80% 76% 62% 5% 46% ○ ○ 8 0.31 1.35 80% 74% 98% 26% 88% × × As is clearly understood from the above mentioned results, Examples 15 to 23, which comprise the compounds of formulae (1), (2) and (3) in a thermally sensitive layer are excellent in qualities such as color developing sensitivity, degree of whiteness of ground color, heat resistance, image remaining ratio and powder generation. Examples 15 to 19, 21 to 23 which contain from 0.5 to 1.5 parts of saturated fatty acid monoamide and diphenylsulfone derivatives to 1 part of color developing agent are especially excellent in color developing sensitivity, and also have good heat resistance and image preservability. Example 20 whose content of diphenylsulfone is smaller than 4% in the solid part of the thermally sensitive coating is excellent in controlling powder generation, further has good color developing sensitivity, heat resistance and image remaining ratio. Further, Examples 17 and 21 to 23 which use B305 as dye are superior to other Examples which use other kinds of dye in whiteness of ground color and in heat resistance. In Examples 21 to 23 which contain a stabilizer, the image preserve ability is preferably improved. Especially, when the amount of stabilizer is bigger than 0.17 parts to 1 part of color developing agent, the improvement of image preservability to a plasticizer is remarkable. In the meanwhile, Comparative Examples 1 to 7 which do not meet the important point of this invention, products that have good quality cannot be obtained. Comparative Example 1, which does not use the color developing agent regulated in this invention has a problem in heat resistance. Comparative Examples 2 and 3 whose containing amount of saturated fatty acid monoamide are out of the limit prescribed in this invention have a problem in color developing sensitivity. Comparative Examples 4 to 7 which use different types of sensitizer from this invention have problems in all qualities. Comparative Example 8, which uses different type of sensitizer from this invention together with a stabilizer, indicates a good image remaining ratio, but is inferior in other qualities. Possibility to be used in an industrial scale Since the thermal recording material of this invention is excellent in color density, ground color, heat resistance, image remaining ratio and preventing ability of powder generation, can be used as a facsimile paper, printing paper, register paper and thermally sensitive paper, and can provide a high quality and reliable thermal recording material.

Claims: A thermal recording material which comprises a substrate having thereon a thermally sensitive color developing layer comprising colorless or pale colored basic dye, at least one organic color developing agent which is a dihydroxydiphenylsulfone type compound of formula (1) as a main component, at least one saturated fatty acid monoamide of formula (2) and at least one diphenylsulfone derivative of formula (3), wherein R 1 and R 2 are each independently a C 1-8 alkyl group, a C 1-8 alkenyl group, or a halogen atom and a and b are each from 0 to 3, R 3 -CONH 2 wherein R 3 is a C 11-21 alkyl group, wherein R 4 to R 9 are each independently a hydrogen atom, an alkyl group, a halogen atom, a nitro group, an alkoxy group, a cyano group or an allyloxy group. A thermal recording material according to claim 1, wherein the colorless or pale colored basic dye is 3-di-n-pentylamino-6-methyl-7-anilinofluorane. A thermal recording material according to claims 1 or 2, which further comprises at least one compound chosen from 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone, epoxy resin and a diphenyl sulfone bridgeable type compound of formula (4), wherein, X and Y are independently a saturated or unsaturated linear or grafted C 1-12 hydrocarbon group, optionally having an ether bond, or wherein R is a methylene group or an ethylene group, T is a hydrogen atom or a C 1-4 alkyl group, and R 10 to R 15 are each independently a halogen atom, a C 1-6 alkyl group, or an alkenyl group, m, n, p, q, r and t are each from 0 to 4, and d is from 0 to 10. A thermal recording material according to any preceding claim, wherein the compound of formula (1) is chosen from: 4,4'dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, bis-(3-allyl-4-hydroxyphenyl)sulfone, 3,3'-dimethyl-4,4'-dihydroxydiphenylsulfone, 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylsulfone, 2,2'-bis(4-chrolophenol)sulfone, 4-hydroxyphenyl-3'-isopropyl-4'-hydroxyphenylsulfone, bis-(3-ethyl-4-hydroxyphenyl)sulfone, 2,2'-bis(p-t-butylphenol)sulfone, 2,2'-bis(p-t-pentylphenol)sulfone, and 2,2'-bis(p-t-octylphenol)sulfone A thermal recording material according to any preceding claim, wherein the saturated fatty acid monoamide of formula (2) is present in an amount of from 1.5 to 5 parts by weight to 1 part by weight of the compound of formula (1). A thermal recording material according to any preceding claim, wherein the diphenysulphone derivative of formula (3) and the saturated fatty acid monoamide of formula (4) are present in weight ratio of from 1:3 to 3:1. A thermal recording material according to any of claims 3 to 6, wherein the compound chosen from 4 benzyloxy-4'-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, epoxy resin and a compound of formula (4) is present in an amount of from 0.01 to 0.9 parts by weight to 1 part by weight of the compound of formula (1).

Inventors: HAMADA KAORU, KIMURA YOSHIHIDE, MIDORIKAWA YOSHIMI, SEKINE TOMONORI, SUMIKAWA NAOMI, TSUZUKI YUJI, HAMADA, KAORU, KIMURA, YOSHIHIDE, MIDORIKAWA, YOSHIMI, SEKINE, TOMONORI, SUMIKAWA, NAOMI, TSUZUKI, YUJI, HAMADA, Kaoru, Res. Lab. Prod. Development, KIMURA, Yoshihide, Res. Lab. Prod. Development, MIDORIKAWA, Yoshimi, Res. Lab. Prod. Development, SEKINE, Tomonori, Res. Lab. Prod. Development, SUMIKAWA, Naomi, Res. Lab. Prod. Development, TSUZUKI, Yuji, Res. Lab. Prod. Development
Applicants: JUJO PAPER CO LTD, NIPPON PAPER INDUSTRIES CO., LTD.
Application year: 2000
Main classification: B41M5
IPC codes: B41M5