Thermosensitive color developer dispersion and thermosensitive recording material

Abstract

A heat-sensitive color developer dispersion liquid, the dispersion liquid comprising a dispersant, a heat-sensitive color developer and a dispersion medium, the heat-sensitive color developer being 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone particles, and the dispersant being sodium salt of dioctyl sulfosuccinate dibutyrate.The heat-sensitive color developer dispersion liquid of the present application is obtained by wet milling the heat-sensitive color developer of 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone in the presence of the dispersant sodium salt of dioctyl sulfosuccinate dibutyrate, and has good stability and high color developing performance, and the heat-sensitive recording material prepared by using the dispersion liquid has low coating haze, high light transmittance, clear and stable color developing image.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat-sensitive color developer dispersion liquid and a heat-sensitive recording material, in particular to a heat-sensitive color developer dispersion liquid containing 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone and a heat-sensitive recording material prepared using the heat-sensitive color developer dispersion liquid. BACKGROUND

[0002] Traditional information recording mainly uses silver salt information recording material as the main carrier. The silver salt information recording material is a high-efficiency information recording material, which integrates information receiving, storage and reproduction, has high image resolution, and the device for realizing information recording is relatively simple. However, the silver salt information recording material uses noble metal silver as raw material, and the production process is complex. Moreover, a large amount of wastewater containing heavy metals is generated in the production and use process, polluting the environment, and the technical conditions required in the treatment and transmission are harsh, which cannot meet the requirements of social development.

[0003] With the continuous progress of science and technology, heat-sensitive recording materials gradually replace traditional information recording materials. Heat-sensitive recording materials mainly use electron-donating colorless dyes and electron-accepting compounds to form recording images through chemical reaction of the color developer. This heat-sensitive recording material has obvious advantages over traditional information recording materials, such as imaging using heat, relatively compact device structure, durable, easy to maintain and noiseless.

[0004] With the continuous expansion of the application field of heat-sensitive recording materials, various problems have occurred in the application process of heat-sensitive recording materials in the face of complex and variable use environment. For example, heat-sensitive recording materials prepared using 2,2-bis(4-hydroxyphenyl)propane, p-hydroxybenzyl benzoate, 4,4'-dihydroxy diphenyl sulfone, etc. as heat-sensitive color developer, when exposed to high temperature or high humidity environment, the image preservation becomes poor, and the image becomes blurred and unclear. In addition, in the harsh environment of high temperature and high humidity, the non-printing area will appear coloring, that is, the so-called haze and light transmittance change.

[0005] At present, the above problems are mainly overcome by developing hydroxydiphenyl sulfone derivatives as heat-sensitive color developer. Among them, the heat-sensitive recording material prepared using 4-hydroxy-4'-isopropoxydiphenyl sulfone as heat-sensitive color developer has the best improvement in image preservation. However, 4-hydroxy-4'-isopropoxydiphenyl sulfone is prone to produce hydrated crystals during storage when wet crushing, and the heat-sensitive recording material produced using the dispersion liquid containing such hydrated crystals has high haze and low light transmittance, thereby affecting the imaging performance of the heat-sensitive recording material. SUMMARY

[0006] The present application provides a thermal color developing agent dispersion liquid containing 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone and a thermal recording material prepared by using the thermal color developing agent dispersion liquid, the thermal color developing agent dispersion liquid has good stability and high color developing performance, and the thermal recording material prepared by using the dispersion liquid has low coating haze, high light transmittance, clear and stable color developing image.

[0007] The present application adopts the technical solution of:

[0008] A thermal color developing agent dispersion liquid, the dispersion liquid comprises a dispersant, a thermal color developing agent and a dispersion medium, the thermal color developing agent is 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone particles, and the dispersant is sodium salt of succinic acid dibutyric acid dioctyl ester sulfonic acid.

[0009] The thermal color developing agent dispersion liquid described above, the dispersant is 0.15-3.5 parts by mass relative to 100 parts by mass of the thermal color developing agent.

[0010] The thermal color developing agent dispersion liquid described above, the dispersant is 1-2 parts by mass relative to 100 parts by mass of the thermal color developing agent.

[0011] The thermal color developing agent dispersion liquid described above, the average particle size of the particles in the thermal color developing agent dispersion liquid is less than or equal to 1.0 μm.

[0012] The thermal color developing agent dispersion liquid described above, the average particle size of the particles in the thermal color developing agent dispersion liquid is less than or equal to 0.8 μm.

[0013] The thermal color developing agent dispersion liquid described above, the average particle size of the particles in the thermal color developing agent dispersion liquid is 0.4-0.8 μm.

[0014] The thermal color developing agent dispersion liquid described above, the content of the thermal color developing agent is greater than 20 wt.%.

[0015] The thermal color developing agent dispersion liquid described above, the dispersion medium comprises 25 parts by mass of 10% polyvinyl alcohol aqueous solution and 50 parts by mass of deionized water, the polyvinyl alcohol in the polyvinyl alcohol aqueous solution has an alcoholysis degree of 88% and a polymerization degree of 1500-3000.

[0016] A thermal recording material, comprising a protective layer, an imaging layer, a support and a back layer arranged in sequence from top to bottom, the imaging layer is formed by drying a coating liquid comprising thermal dye microcapsules and the thermal color developing agent dispersion liquid on the support.

[0017] The thermal recording material described above, the haze of the imaging layer is less than 45, and the light transmittance of the imaging layer is greater than 60%.

[0018] The heat-sensitive color developing agent dispersion liquid of the present application is obtained by wet milling 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone heat-sensitive color developing agent in the presence of a dispersant sodium salt of dioctyl sulfosuccinate, and has good stability and high color developing performance compared with the existing 4-hydroxy-4'-isopropoxy diphenyl sulfone heat-sensitive color developing agent dispersion liquid, and avoids hydration crystallization of the heat-sensitive color developing agent during storage and use. The heat-sensitive recording material prepared by using the heat-sensitive color developing agent dispersion liquid of the present application has low coating haze, high light transmittance, clear and stable color developing image. DETAILED DESCRIPTION

[0019] The present application provides a 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone heat-sensitive color developing agent dispersion liquid, which is obtained by wet milling 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone heat-sensitive color developing agent under the protection of a dispersant. The dispersant used is sodium salt of dioctyl sulfosuccinate, which can be quickly and fully dissolved and ionized in water. As an anionic surfactant, the sodium salt of dioctyl sulfosuccinate can be quickly and effectively adsorbed on the surface of heat-sensitive color developing agent particles after ionization in water, forming a surface adsorption layer, and the stability of the dispersion system is improved due to the electrostatic repulsion between heat-sensitive color developing agent particles. In addition, after the heat-sensitive color developing agent particles adsorb the high molecular sodium salt of dioctyl sulfosuccinate dispersant on the surface, the particles will repel each other when they approach, making the heat-sensitive color developing agent particle dispersion system more stable and preventing agglomeration. This is the steric hindrance effect of the high molecular sodium salt of dioctyl sulfosuccinate dispersant, that is, the steric hindrance effect caused by the mutual approach of particles after adsorbing high molecular dispersants on the surface. This is because the high molecular sodium salt of dioctyl sulfosuccinate dispersant is adsorbed on the surface of the heat-sensitive color developing agent particles, forming a protective film that surrounds the surface of the heat-sensitive color developing agent particles, with hydrophilic groups extending into the liquid medium and a certain thickness. Therefore, when the particles approach each other, the adsorption force is greatly weakened, the repulsion force is increased, and the stability of the dispersion of heat-sensitive color developing agent particles is increased. Under the double effects, the dispersion stability and sanding efficiency of the heat-sensitive color developing agent particles are ensured.

[0020] The present application provides a heat-sensitive color developing agent dispersion liquid, which comprises a dispersant, a heat-sensitive color developing agent and a dispersion medium; the heat-sensitive color developing agent is 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone particles, the dispersant is sodium salt of dioctyl sulfosuccinate, and the dispersion medium is preferably polyvinyl alcohol aqueous solution and water. In the present application, the mass concentration of the polyvinyl alcohol aqueous solution is preferably 10%, and the polyvinyl alcohol in the polyvinyl alcohol aqueous solution has an alcoholysis degree of 88% and a polymerization degree of 1500-3000.

[0021] The addition time of the sodium salt of dibutyl dioctyl succinate sulfonate can be before, during or after the wet grinding of the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone thermal color developing agent, and the dispersant can be added in multiple times or once. Preferably, the dispersant is added once in the whole process during the wet grinding. The dispersant is 0.15-3.5 parts by mass, preferably 1-2 parts by mass, relative to 100 parts by mass of the thermal color developing agent. When the amount of the dispersant is less than 0.15 parts by mass, the dispersant cannot play a good protective role, and the particles are prone to agglomeration, which affects the use effect. When the amount of the dispersant is more than 3.5 parts by mass, the viscosity of the dispersion system increases rapidly, which leads to poor apparent quality after coating and increased cost.

[0022] The 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone thermal color developing agent dispersion is obtained by wet grinding. The grinding equipment used can be an ultrasonic disperser, a mechanical stirring disperser or a mill equipment. The mill equipment used includes a vertical sand mill, a horizontal sand mill and a rod pin sand mill. The rod pin sand mill is optimized in terms of sand grinding efficiency and stability. After wet grinding, the particle size of the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone thermal color developing agent is less than 1 μm, preferably 0.4-0.8 μm. When the particle size is less than 0.4 μm, great efforts are needed to prevent agglomeration between the particles, which is not cost-effective. When the particle size is greater than 1.0 μm, the image color density is low, which affects the use effect.

[0023] The present application also provides a thermal recording material, which comprises, from top to bottom, a protective layer, a thermal imaging layer, a support and a back layer. The imaging layer is formed by coating a coating liquid comprising thermal dye microcapsules and the thermal color developing agent dispersion described above on the support and drying. The thermal dye microcapsules used do not contain low-boiling organic solvents in the preparation process.

[0024] The heat-sensitive recording material provided by the present application comprises a protective layer, and the main components of the protective layer of the present application are various kinds of additives and adhesive. The adhesive used in the protective layer is water-soluble polymer resin, which can be completely alcoholized, intermediate alcoholized, partially alcoholized or modified polyvinyl alcohol. The various kinds of additives include cross-linking agent, lubricant, ultraviolet absorber, leveling agent, surfactant and antistatic agent, etc. The cross-linking agent should be able to form cross-linking reaction with the above-mentioned polyvinyl alcohol, such as: polyformaldehyde compound such as glyoxal, glutaraldehyde; water-soluble initial polycondensate of silane coupling agent, boric acid, borax, urea-formaldehyde, etc., layered silicate, nano-dioxide, nano-calcium carbonate, etc.; the lubricant has senior fatty acid or its metal salt, senior fatty acid amide, senior fatty acid ester, animal wax, plant wax, polyethylene wax, etc.; the leveling agent has silicone oil, polydimethylsiloxane, polyether polyester modified organosiloxane, alkyl modified organosiloxane, end group modified organosilicon, fluorine modified acrylic resin, etc.; the surfactant has alkali metal salt of sulfosuccinic acid, fluorine-containing surfactant, sulfonate, etc.; the ultraviolet absorber and the antistatic agent are not particularly limited herein. After mixing the required various kinds of additives and adhesive, the slope flow extrusion coating is used to finally form the protective layer.

[0025] The heat-sensitive recording material provided by the present application comprises a heat-sensitive imaging layer, which is obtained by coating the mixture of heat-sensitive dye microcapsule dispersion liquid, color developing agent dispersion liquid and auxiliary reagent uniformly. The color developing agent dispersion liquid is the color developing agent dispersion liquid described in the above technical solution. The heat-sensitive dye microcapsule dispersion liquid provided in the present application comprises capsule core, and the capsule core comprises leuco heat-sensitive dye, additive and solvent. In the present application, the leuco heat-sensitive dye preferably comprises fluoran type dye, triarylmethane type dye or spiro compound type dye; the fluoran type dye preferably comprises 2-anilino-3-methyl-6-diethylamino fluoran, 2-anilino-3-methyl-6-dibutylamino fluoran, 2-(2-4-xylidino)-3-methyl-6-diethylamino fluoran, 3-diethylamino-6-methyl-7-anilino fluoran, 3-dibutylamino-6-methyl-7-anilino fluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilino fluoran, 3-(N-ethyl-N-cyclopentylamino)-6-methyl-7-anilino fluoran, 3-dibutylamino-7-o-fluoroanilino fluoran or 3-diethylamino-7-(3,4-dichloroanilino) fluoran, and more preferably 2-anilino-3-methyl-6-diethylamino fluoran.

[0026] In the present application, auxiliary agents can be added according to actual needs, which preferably include sensitizer, ultraviolet absorber. In the present application, the main role of the sensitizer is to improve the image density and heat sensitivity of the recording material, and preferably includes bisethane, 2-benzyl naphthyl ether, 1,2-di-(3-phenoxy)ethane, 4-benzyl diphenyl, p-hydroxy benzoic acid benzyl ester and other sensitizers. The main role of the ultraviolet absorber is to improve the light stability of the heat-sensitive recording material, and preferably includes UV8515, UV384-2, UV-1577 and the like. The specific amount added is subject to the condition that it does not affect the present application.

[0027] In the present application, the boiling point of the solvent at standard atmospheric pressure is above 125℃; the solvent preferably includes one or more of tributyl phosphate, dicyclohexyl phthalate, butyl acetate, chlorobenzene, xylene, m-xylene, o-xylene, N,N-dimethylformamide, cyclohexanone, N,N-dimethylacetamide, ethylene glycol, N,N-dimethylaniline, 2-4-di-tert-amyl-phenol, dibutyl phthalate, ethylene glycol carbonate, acetamide, dimethylphenyl phosphate, trimethylphenyl phosphate, alkyl biphenyl and ethyl acetoacetate, and more preferably includes one or more of trimethylphenyl phosphate or ethyl acetoacetate or butyl acetate. The specific amount added is subject to the condition that it does not affect the present application.

[0028] The preparation method of the heat-sensitive dye microcapsule dispersion liquid adopts the interfacial polymerization reaction method known in the technical field.

[0029] In the present application, the auxiliary agent preferably includes a binder and a surfactant. The binder can be starch and its derivatives, carboxyl styrene butadiene latex, polyvinyl alcohol, etc., and preferably the carboxyl styrene butadiene latex with a solid content of 50±2%, pH=7.0~9.0, and viscosity (25℃) of ≤200mPa.s provided by Rixin Chemical Industry Co., Ltd. The surfactant is not particularly limited, as long as it does not have a wetting point during the coating process, and preferably a fluorine-containing surfactant.

[0030] The support used as the heat-sensitive recording material in the present application should have good thermal stability, no deformation and stretching when heated, low hygroscopicity, and high flatness, and it can be a transparent support such as a polyethylene film (PE), a polypropylene film (PP), a polyvinyl chloride film (PVC), a polyester film (PET), a polystyrene film (PS), a polyvinylidene chloride film (PVDC), etc. Color master batches can be added to it to form different colors, or it can be used directly without adding color master batches. The thickness of the selected support is not particularly limited, and the density is 0.16-0.24; preferably the thickness is 175 microns and the density is 0.19.

[0031] In the present application, the support also preferably comprises a primer layer on both surfaces of the support, the primer layer comprising a water-soluble environmentally friendly resin. The main function is to impart hydrophilicity to the surface of the support, ensuring that the other heat-sensitive imaging layer and the back layer can be coated smoothly.

[0032] The heat-sensitive recording material provided by the present application also comprises a back layer. In the present application, the main component of the back layer is one or both of a water-based polyurethane emulsion and a water-based acrylic resin. The main function of the back layer is to impart a certain roughness to the surface of the support. Therefore, a dispersion of polymethyl methacrylate can also be added to the back layer coating liquid to increase the roughness of the back layer.

[0033] The method for preparing the heat-sensitive recording material of the present application comprises the following steps:

[0034] coating a back layer on either surface of the support;

[0035] coating a heat-sensitive imaging layer and a protective layer on the other surface of the support in turn from bottom to top.

[0036] The present application does not have special requirements for the process of coating the back layer, and conventional technical means in the art can be used.

[0037] The present application can coat a heat-sensitive imaging layer and a protective layer on the other surface of the support in turn. The present application does not have special requirements for the process of coating the heat-sensitive imaging layer and the protective layer, and conventional technical means in the art can be used.

[0038] The technical solutions provided by the present application will be described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application. In the following examples, "parts" refer to "mass parts", and the average particle size is measured by a Malvern laser particle size analyzer.

[0039] Example 1

[0040] Preparation of heat-sensitive recording material

[0041] (I) Preparation of heat-sensitive dye microcapsule dispersion

[0042] 8 parts of ODB-2, 5 parts of GN-2, 2 parts of Y-1, 10 parts of ethyl acetoacetate, and 15 parts of polyurethane with isocyanate groups at the end (product model XD-1580N) were heated and dissolved at 95°C to obtain an oil phase.

[0043] 200 parts of polyvinyl alcohol with a concentration of 5% and 25 parts of 7# surfactant (China Lucky Group Co., Ltd.) were mixed uniformly to obtain an aqueous phase.

[0044] The above obtained oil phase was slowly added to the water phase stirred at 6000 r / min using a high speed shearing machine, and the high speed shearing stirring time was 10 min. The obtained oil-in-water dispersion was added to 150 parts of water and 5 parts of tetraethylenepentamine under stirring at 450 r / min, and reacted at 50°C for 2 h to obtain a thermosensitive dye microcapsule dispersion.

[0045] (II) Preparation of color developer dispersion

[0046] Preparation of color developer dispersion A

[0047] The following components were dispersed using an ESW-1.0 rod pin sand mill, and the volume average particle size of the obtained mixture was 0.72 μm, thereby preparing a color developer dispersion.

[0048] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 20 parts

[0049] 10% polyvinyl alcohol aqueous solution 25 parts

[0050] Deionized water 50 parts

[0051] Sodium salt of succinic acid dioctyl ester dibutyrate sulfonic acid 0.5 parts

[0052] (III) Preparation of thermosensitive imaging layer

[0053] The above prepared thermosensitive dye microcapsule dispersion and color developer dispersion A were mixed under stirring according to the amounts given in Table 1 below, and then the surfactant, adhesive and 10% polyvinyl alcohol aqueous solution were added to obtain a thermosensitive imaging layer coating liquid. The support containing the bottom layer was subjected to wave flow extrusion coating (coating amount 70 g / m 2 ) on the side containing the thermosensitive imaging layer, and dried to obtain a thermosensitive imaging layer.

[0054] Table 1 Material table of thermosensitive imaging layer coating liquid

[0055]

[0056] (IV) Preparation of protective layer

[0057] The above prepared thermosensitive dye microcapsule dispersion and color developer dispersion A were mixed under stirring according to the amounts given in Table 1 below, and then the surfactant, adhesive and 10% polyvinyl alcohol aqueous solution were added to obtain a thermosensitive imaging layer coating liquid. The support containing the bottom layer was subjected to wave flow extrusion coating (coating amount 70 g / m 2 ) on the side containing the thermosensitive imaging layer, and dried to obtain a thermosensitive imaging layer.

[0058] Table 2 Material table of protective layer coating liquid (Five) The main components of the back layer coating liquid, water-based polyurethane emulsion, water-based acrylic emulsion, polymethyl methacrylate dispersion and surface surfactant are sequentially added and mixed under stirring, and then the mixture is coated on the other side of the support containing the protective layer by slope flow extrusion and dried, to finally obtain a thermal recording material.

[0059] Example 2

[0060] A thermal recording material was prepared using color developer dispersion B, which was prepared as follows:

[0061] The following components were dispersed using an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the resulting mixture was 0.96 μm, thereby preparing the color developer dispersion.

[0062] 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone 25 parts

[0063] 10% aqueous polyvinyl alcohol solution 25 parts

[0064] Deionized water 50 parts

[0065] Sodium salt of dioctyl sulfosuccinate 0.04 parts

[0066] The remaining steps were the same as in the preparation of Example 1.

[0067] Example 3

[0068] A thermal recording material was prepared using color developer dispersion C, which was prepared as follows:

[0069] The following components were dispersed using an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the resulting mixture was 0.0.40 μm, thereby preparing the color developer dispersion.

[0070] 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone 25 parts

[0071] 10% aqueous polyvinyl alcohol solution 25 parts

[0072] Deionized water 50 parts

[0073] Sodium salt of dioctyl sulfosuccinate 0.08 parts

[0074] The remaining steps were the same as in the preparation of Example 1.

[0075] Example 4

[0076] A thermal recording material was prepared using color developer dispersion D, which was prepared as follows:

[0077] A color former dispersion liquid was prepared by dispersing the following components with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 0.64 μm.

[0078] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 25 parts

[0079] 10% aqueous polyvinyl alcohol solution 25 parts

[0080] Deionized water 50 parts

[0081] Sodium salt of dioctylphthalate sulfonate 0.2 part

[0082] The remaining steps were the same as in the preparation of Example 1.

[0083] Example 5

[0084] A color former dispersion liquid E was prepared by dispersing the following components with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 0.64 μm.

[0085] A color former dispersion liquid was prepared by dispersing the following components with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 0.80 μm.

[0086] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 30 parts

[0087] 10% aqueous polyvinyl alcohol solution 25 parts

[0088] Deionized water 50 parts

[0089] Sodium salt of dioctylphthalate sulfonate 0.1 part

[0090] The remaining steps were the same as in the preparation of Example 1.

[0091] Comparative Example 1

[0092] 1. Preparation of color former dispersion liquid F:

[0093] A color former dispersion liquid was prepared by dispersing the following components with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 0.80 μm.

[0094] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 30 parts

[0095] 10% aqueous polyvinyl alcohol solution 25 parts

[0096] Deionized water 50 parts

[0097] Sodium salt of dioctylphthalate sulfonate 1.5 parts

[0098] 2. Preparation of heat-sensitive recording material

[0099] The difference from Example 1 is that the color former dispersion liquid F is used to prepare the heat-sensitive recording material, and the remaining steps are the same.

[0100] Comparative Example 2

[0101] 1. Preparation of color former dispersion liquid G

[0102] The following components were dispersed with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 1.12 μm, thereby preparing a color former dispersion liquid.

[0103] 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone 25 parts

[0104] 10% polyvinyl alcohol aqueous solution 25 parts

[0105] Deionized water 50 parts

[0106] Sodium salt of dioctyl sulfosuccinate 0.02 parts

[0107] Since the amount of added sodium salt of dioctyl sulfosuccinate dispersant is small, it does not have a good dispersion stabilizing effect, and it is difficult to grind the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone to a volume average particle diameter of less than 1.0 μm.

[0108] 2. Preparation of heat-sensitive recording material

[0109] The difference from Example 1 is that the color former dispersion liquid G is used to prepare the heat-sensitive recording material, and the remaining steps are the same as in Example 1.

[0110] Comparative Example 3

[0111] 1. Preparation of color former dispersion liquid H

[0112] The following components were dispersed with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the mixture was 0.72 μm, thereby preparing a color former dispersion liquid.

[0113] 4-hydroxy-4'-isopropoxy diphenyl sulfone 20 parts

[0114] 10% polyvinyl alcohol aqueous solution 25 parts

[0115] Deionized water 50 parts

[0116] Sodium salt of dioctyl sulfosuccinate 0.5 parts

[0117] 2. Preparation of heat-sensitive recording material

[0118] The difference from Example 1 is that the color former dispersion liquid H is used to prepare the heat-sensitive recording material.

[0119] Comparative Example 4

[0120] 1. Preparation of Color Developer Dispersion I

[0121] The following components were dispersed with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the resulting mixture was 1.40 μm, thereby preparing the color developer dispersion.

[0122] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 25 parts

[0123] 10% aqueous polyvinyl alcohol solution 25 parts

[0124] Deionized water 50 parts

[0125] Sodium dioctyl sulfosuccinate 0 parts

[0126] Since the sodium dioctyl sulfosuccinate dispersant was not added, it was difficult to grind the 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone to a volume average particle diameter of 1.0 μm or less.

[0127] 2. Preparation of Heat-Sensitive Recording Material

[0128] The difference from Example 1 was that the color developer dispersion I was used to prepare the heat-sensitive recording material.

[0129] Comparative Example 5

[0130] 1. Preparation of Color Developer Dispersion J

[0131] The following components were dispersed with an ESW-1.0 rod pin sand mill, and the volume average particle diameter of the resulting mixture was 1.22 μm, thereby preparing the color developer dispersion.

[0132] 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone 25 parts

[0133] 10% aqueous polyvinyl alcohol solution 25 parts

[0134] Deionized water 50 parts

[0135] Sodium dodecyl sulfonate 0.2 parts

[0136] 2. Preparation of Heat-Sensitive Recording Material

[0137] The difference from Example 1 was that the color developer dispersion J was used to prepare the heat-sensitive recording material.

[0138] The thermal recording material obtained above was rated, and a 21-step density sheet was printed using a Konica DryMate 320 dry imager to establish the density values at different gray scales; the minimum density and the maximum density corresponding to the recording gray scale were recorded (i.e., the coating density was obtained by deducting the base density).

[0139] Image stability was defined as the difference in density before and after printing a 21-step gray scale using a Konica DryMate 320 dry imager under different temperature and humidity conditions, followed by summation, averaging, and then taking the arithmetic square root. The temperature conditions selected were (1) 25°C, 50% relative humidity, 1 h of storage, and then testing of the gray scale density; (2) 35°C, 60% relative humidity, 1 h of storage, and then testing of the gray scale density; and (3) 35°C, 70% relative humidity, 1 h of storage, and then testing of the gray scale density. The calculation formula is shown below: Image stability index = (D1-D2)2+ (D3-D2)2+ (D4-D2)2 / 4 Thermal imaging layer apparent smoothness of the coating was defined as the apparent quality of the thermal imaging layer coating liquid during coating and after drying, as observed by the naked eye.

[0140] The viscosity of the color developer dispersion was determined using an NDJ-8ST rotary viscometer.

[0141] The imaging layer (including the support) was determined using a WGT-S light transmittance / haze tester.

[0142] Table 3. Test data for examples and comparative examples

[0143] According to the evaluation results of Table 3, in Comparative Example 3, the 4-hydroxy-4'-isopropoxy diphenyl sulfone dispersion liquid crystallized and precipitated during use, resulting in a high haze and low light transmittance of the prepared thermal recording material. In Inventive Examples 1 to 5, the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone dispersion liquid was used, and the dispersant and color developer were added in the proportions defined in the present application. The thermal recording material prepared therefrom had better image stability (a lower value indicates less influence of temperature and humidity on the thermal recording material), lower minimum coating density, higher maximum coating density, lower haze (a higher value indicates a decrease in film gloss and transparency, especially imaging), and higher light transmittance (a higher value indicates better transparency of the thermal recording material). In Comparative Example 1, the amount of dispersant added exceeded the maximum value defined in the present application. Compared with Inventive Example 5, the thermal imaging layer of Comparative Example 1 had poor appearance (stripes), high haze, low light transmittance, and relatively poor image stability. This was because the excessive amount of dispersant caused the viscosity of the dispersion liquid system to rapidly increase, resulting in poor appearance after coating. In Comparative Example 2, the amount of dispersant added was less than the minimum value defined in the present application, and no dispersant was added in Comparative Example 4. Because of the small amount of or lack of sodium salt of dioctyl sodium sulfosuccinate dispersant, the dispersing stability was not good, making it difficult to grind the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone to an average particle size of less than 1.0 μm, and the particles were prone to agglomeration, affecting the use effect. In Comparative Example 5, another type of dispersant was used, which also did not have good dispersing stability, making it difficult to grind the 3,3'-diallyl-4,4'-dihydroxy diphenyl sulfone to an average particle size of less than 1.0 μm, and further resulting in high haze, low light transmittance, and small maximum coating density of the thermal imaging layer.

Claims

1. A thermal recording material, comprising, from top to bottom, a protective layer, an imaging layer, a support, and a backing layer, characterized in that: The imaging layer is formed by coating the support with a coating solution consisting of thermosensitive dye microcapsules and a thermosensitive colorimetric agent dispersion, followed by drying. The thermosensitive colorimetric agent dispersion comprises a dispersant, a thermosensitive colorimetric agent, and a dispersion medium. The thermosensitive colorimetric agent is 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone particles, and the dispersant is sodium dioctyl succinate dibutyrate sulfonate. The dispersion is obtained by wet pulverizing the 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone particles under the protection of the dispersant sodium dioctyl succinate dibutyrate sulfonate. The dispersant content is 0.15 to 3.5 parts by weight relative to 100 parts by weight of the thermosensitive colorimetric agent; The average particle size of the particles in the thermosensitive colorimetric reagent dispersion is 0.4~0.8μm; The dispersion medium comprises 25 parts by mass of a 10% aqueous solution of polyvinyl alcohol and 50 parts by mass of deionized water, wherein the degree of alcoholysis of the polyvinyl alcohol in the aqueous solution is 88% and the degree of polymerization is 1500~3000.

2. The thermal recording material according to claim 1, characterized in that: The dispersant is 1 to 2 parts by weight relative to 100 parts by weight of the thermosensitive colorimetric agent.

3. The thermal recording material according to claim 1, characterized in that: The content of the thermosensitive colorimetric agent is greater than 20 wt.%.

4. The thermal recording material according to any one of claims 1 to 3, characterized in that: The haze of the imaging layer is less than 45, and the transmittance of the imaging layer is greater than 60%.

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