A thermosensitive imaging material coating solution, a preparation method thereof, and a thermosensitive imaging material

Abstract

The present invention provides a thermosensitive imaging material coating liquid, a preparation method thereof, and a thermosensitive imaging material, belonging to the technical field of thermosensitive recording materials. A thermosensitive imaging material coating liquid, the raw materials for its preparation include: a thermosensitive dye dispersion liquid and a thermosensitive developer dispersion liquid, wherein: the thermosensitive dye dispersion liquid contains at least one colorless dye, and the colorless dye is a compound represented by formula (I): ; the thermosensitive developer dispersion liquid contains at least one phenol-free developer, and the phenol-free developer is a compound represented by formula (II):. The technical solution provided by the present invention is more environmentally friendly while improving the color density and storage thermal stability of the product.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermosensitive recording materials, and particularly relates to a thermosensitive imaging material coating solution, a preparation method thereof, and a thermosensitive imaging material. Background Art

[0002] At present, information recording and reproduction materials mainly include two categories: silver salt information recording materials and thermosensitive information recording materials. Among them, silver salt recording materials use precious metal silver as raw materials, with complex preparation processes and serious environmental pollution; the use technical conditions are harsh, the cost is high, and it is difficult to meet the requirements of social development. Thermosensitive information recording materials reproduce information using dry technology, do not require traditional development, can use ordinary paper or polyester film as a support, have simple processing technology, low price, and no noise during the recording process, showing development advantages.

[0003] In the thermosensitive recording material preparation technology, what is relatively mature and has a wide application range is: preparing a microcapsule solution with a colorless or light-colored basic dye precursor and a developer solution dissolved in an organic solvent, and then stirring and mixing the two solutions to obtain a thermosensitive color-developing layer coating solution. At the same time, based on the trend of coating waterborne

[0004] The existing patent document CN115534554A provides a developer for a thermosensitive printing medical film that can resist fogging and redness and a preparation method thereof. The developer uses β-cyclodextrin and developer D-8 as raw materials, and self-assembles D-8 in the cavity of β-cyclodextrin to form a D-8 inclusion complex of β-cyclodextrin. This invention utilizes the hydrophobic property of the cavity of β-cyclodextrin to self-assemble D-8 in the cavity of β-cyclodextrin, thereby avoiding the defects of migration and oxidation of D-8 at room temperature and improving the anti-fogging and anti-redness performance of thermosensitive medical films.

[0005] Again, CN111483250A provides a thermosensitive microcapsule color-developing material and a preparation method thereof, which specifically includes the following components: dye precursor microcapsules, a developer, a surfactant, and polyvinyl alcohol; the dye precursor microcapsules include a capsule wall and a core wrapped by the capsule wall, the capsule wall is polyurea or polyurethane, and the core includes a dye precursor and a solvent; the dye precursor includes S205, ODB-2, GN-2, and RED-3, and the solvent includes ethyl acetoacetate and ethyl acetate. Among them, a new type of dye precursor is used and cooperates with the developer to improve the color density, making the printed black effect pure and capable of being used as a medical recording material.

[0006] For another example, CN113774717A provides a thermosensitive dye microcapsule material, a preparation method thereof, and a thermosensitive coating. The material includes: microcapsules composed of a capsule wall and a capsule core, the capsule core includes a thermosensitive dye, the D50 range of the microcapsules is from 1 micron to 10 microns, and the thickness of the capsule wall is between 0.2 microns and 1 micron, and the uniform distribution degree makes the melting probability of the microcapsules within the ranges of 110°C to 120°C, 120°C to 130°C, and 130°C to 140°C differ by no more than 5%. The thermosensitive coating includes 2-10 parts by mass of a heat stabilizer, 1-3 parts by mass of a lubricant, 5-10 parts by mass of a dispersant, 2-20 parts by mass of a developer, and 20-80 parts by mass of the above-mentioned thermosensitive dye microcapsule material. The developer is selected from at least one of bisphenol A and p-hydroxybenzoic acid. This invention enables the thermosensitive dye microcapsule material to have a similar melting probability in each temperature region, which can help a thermal printer change the color gradation of the printed pattern as needed by changing the temperature.

[0007] The above-mentioned prior arts all adopt an aqueous microencapsulated thermosensitive dye precursor and an aqueous developer system obtained by grinding. By microencapsulating the developer, it is possible to avoid the increase in the fog density of the recording material and the oxidation of the developer during storage and transportation, which cause the film to turn red, thereby affecting the image quality. The phenolic developer used in the above materials is not environmentally friendly; and the steps of the corresponding process are cumbersome and complex, and the quality stability is not easy to control. Summary of the Invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide a coating liquid for a thermosensitive imaging material, which is more environmentally friendly while improving the color density and storage thermal stability of the product.

[0009] To solve the above technical problem, the technical solution adopted by the present invention is:

[0010] A coating liquid for a thermosensitive imaging material, the preparation raw materials thereof include: a thermosensitive dye dispersion, a thermosensitive developer dispersion, an adhesive, and water, wherein:

[0011] The thermosensitive dye dispersion contains at least one colorless dye, and the colorless dye is a compound represented by formula (I).

[0012]

[0013] In the formula, R1 is an alkyl group with 1 to 8 carbon atoms, R2 is an alkyl group with 4 to 18 carbon atoms, R3 is a hydrogen atom, an alkyl group with 1 to 15 carbon atoms, or a halogen atom, and R4 is an unsubstituted or substituted aryl group with 6 to 20 carbon atoms. The substituent of R4 is an alkyl group with 1 to 5 carbon atoms, a halogenated alkyl group, or a halogen atom.

[0014] The thermosensitive developer dispersion contains at least one phenol-free developer, and the phenol-free developer is a compound represented by formula (II).

[0015]

[0016] In the formula, the R group is optionally connected to the ortho, meta or para position of the benzene ring; the R group is a hydrogen atom, a halogen atom or an alkyl group having 1 to 8 carbon atoms.

[0017] Preferably, the colorless dye represented by formula (I) is ODB-2 or crystal violet lactone;

[0018] The phenol-free developer represented by formula (II) is p-toluenesulfonyl hydrazide, p-fluorobenzenesulfonyl hydrazide or p-trifluoroalkylbenzenesulfonyl hydrazide.

[0019] Preferably, the thermosensitive dye dispersion is prepared by the following method: 20 to 30 parts by weight of an adhesive solution, 15 to 20 parts by weight of a colorless dye, and 40 to 70 parts by weight of deionized water are added to a reaction kettle and stirred, and then 0.5 to 2 parts by weight of a surfactant is added. Soak and stir slowly for 1 to 1.2 hours, and then transfer to a sand mill for circulating sanding until the average particle size ≤ 0.60 μm to obtain a thermosensitive dye dispersion.

[0020] Preferably, the thermosensitive developer dispersion is prepared by the following method: 20 to 30 parts by weight of an adhesive solution, 20 to 40 parts by weight of deionized water, and 20 to 30 parts by weight of a developer are added to a reaction kettle and stirred, and then 1 to 3 parts by weight of a surfactant is added. Soak and stir slowly for 1 to 1.2 hours, and then transfer to a sand mill for circulating sanding until the average particle size ≤ 0.40 μm to obtain a thermosensitive developer dispersion.

[0021] Preferably, the adhesive solution is an aqueous solution with a mass fraction of 8 to 12% made of at least one of polyvinyl alcohol, gelatin and cellulose derivatives.

[0022] Preferably, the surfactant is an aqueous solution with a mass fraction of 150 to 250 g / L made of at least one of sodium dodecylbenzenesulfonate, sodium dioctyl sulfosuccinate and polyethylene glycol.

[0023] Preferably, the thermosensitive imaging material coating liquid is made of the following raw materials in parts by weight:

[0024] Thermosensitive dye dispersion 25 - 40 parts,

[0025] Thermosensitive developer dispersion 35 - 50 parts,

[0026] Adhesive 8 - 12 parts,

[0027] Adjust the total amount to 100 parts with deionized water for the remainder, and the solid content is 18.0% - 24.0%.

[0028] Preferably, the binder is at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, gum arabic, gelatin, and polyvinylpyrrolidone; more preferably, it is a composition of polyvinyl alcohol and polyvinylpyrrolidone, and the dosage of polyvinyl alcohol is 2 - 4 times that of polyvinylpyrrolidone.

[0029] Preferably, the preparation method of the thermosensitive imaging material coating liquid is carried out according to the following steps:

[0030] Prepare a thermosensitive dye dispersion: Add 20 - 30 parts by weight of a binder solution, 15 - 20 parts by weight of a colorless dye, and 40 - 70 parts by weight of deionized water to a reaction kettle and stir. Then add 0.5 - 2 parts by weight of a surfactant solution, soak and stir slowly for 1 - 1.2 hours, and then transfer to a sand mill for circulating sanding until the average particle size ≤ 0.60 microns to obtain a thermosensitive dye dispersion;

[0031] Prepare a thermosensitive developer dispersion: Add 20 - 30 parts by weight of a binder solution, 20 - 40 parts by weight of deionized water, and 20 - 30 parts by weight of a developer to a reaction kettle, stir, then add 1 - 3 parts by weight of a surfactant solution, soak and stir slowly for 1 - 1.2 hours, and then transfer to a sand mill for circulating sanding until the average particle size ≤ 0.40 microns to obtain a thermosensitive developer dispersion;

[0032] Uniformly mix the thermosensitive dye dispersion and the thermosensitive developer dispersion under stirring conditions, and add a binder and water to obtain a thermosensitive imaging material coating liquid.

[0033] The preparation method of the thermosensitive imaging material provided by the present invention, while omitting the microencapsulation step of the thermosensitive colorless dye, also does not have drawbacks such as the increase in fog density caused by the premature reaction of the colorless dye and the developer when using developer D - 8, and the film turning red due to the oxidation of developer D - 8. It not only optimizes the preparation process but also improves the image quality of the film.

[0034] The present invention also provides a thermosensitive imaging material, including a thermosensitive imaging layer formed by coating the thermosensitive imaging material coating liquid, and further including a carrier substrate and a protective film layer, and the thermosensitive imaging layer is located between the carrier substrate and the protective film layer.

[0035] The thermosensitive imaging recording material can adopt the coating methods of ordinary photosensitive materials, such as extrusion slope flow coating, dip coating, air knife coating, knife coating, roll coating, or gravure coating, etc.

[0036] The carrier substrate can be selected from PP, PVC, or PET.

[0037] In order to protect the surface of the thermosensitive imaging layer with good transparency, it is necessary to coat a transparent protective layer on the thermosensitive imaging layer, which has both excellent transparency and can significantly improve the adhesion to the thermosensitive recording head. Preferably, the weight part composition of the coating liquid of the protective film layer is as follows:

[0038]

[0039] The balance is adjusted to 100 parts with deionized water, and the solid content of the coating liquid is 9% - 15%.

[0040] The polyvinyl alcohol dispersion grinding liquid of zinc stearate is prepared by mixing and grinding zinc stearate with an aqueous solution of polyvinyl alcohol, and the mass fraction is 15 - 25%.

[0041] The mass fraction of the silica sol solution is 25 - 35%.

[0042] The mass fraction of the liquid paraffin dispersion is 10 - 20%.

[0043] The surfactant is an aqueous solution with a mass fraction of 4 - 6% made of at least one of sodium dodecylbenzenesulfonate, sodium dioctyl sulfosuccinate, and polyethylene glycol;

[0044] The mass fraction of the boric acid solution is 0.5 - 1.5%.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] Thermosensitive recording materials that have long been known for direct thermal printing applications have a thermosensitive reaction layer applied to a carrier substrate. Color formers and developers are usually present in the reaction layer, and they react with each other under the influence of heat, thus resulting in color development. Among them, inexpensive developers bisphenol A and bisphenol S have been widely used. Due to the presence of phenolic hydroxyl groups, such developers are prone to oxidation, have a high melting point, and poor sensitivity, and usually need to be used with a sensitizer to reduce the melting temperature. In addition, in the context of the public discussion on the toxicity potential of (bis)phenol-based chemical substances due to environmental load considerations, the interest in non-phenolic developers has increased sharply. The present invention breaks the cumbersome production steps of microencapsulating thermosensitive leuco dyes, uses a non-phenolic developer containing a benzenesulfonylhydrazide compound, which not only saves energy, optimizes the production process, but also makes a beneficial exploration of environmental friendliness.

[0047] The main process of the thermosensitive color development reaction of the present invention can be summarized as follows: in the presence of a developer, the lactone ring of the thermosensitive leuco dye opens, and the central carbon atom changes from SP 3 hybridization to SP 2Hybridization increases the molecular coplanarity, enhances the conjugation degree of the whole system, forms a large π bond, causing absorption red shift and showing color. Among them, in the chromogenic agent shown in formula (II), the R group is selected to be connected to the ortho, meta or para position of the benzene ring; the R group is a hydrogen atom, a halogen atom or an alkyl group with 1 to 8 carbon atoms; when the R group is -CH3, it is preferably p-toluenesulfonyl hydrazide; when the R group is a strong electron-withdrawing group, such as F, for example: p-fluorophenylsulfonyl hydrazide, p-trifluoroalkylphenylsulfonyl hydrazide, the existence of the electron-withdrawing effect makes the benzene ring more stable. As a reversible reaction, when the process of the chromogenic agent releasing H protons is more long-lasting and stable, it ensures that the reaction is more complete under specific conditions and the color development is stable without fading.

[0048] The chromogenic agent without phenol used in the present invention gets rid of the excessive environmental load pressure of traditional phenolic chromogenic agents such as D-8 and bisphenol A, and at the same time avoids adverse phenomena such as the film turning red due to the oxidation of phenolic chromogenic agents; meanwhile, it optimizes the cumbersome and complex production process in which traditional thermosensitive colorless dyes must be microencapsulated, simplifies the production process and improves the efficiency.

[0049] By using a novel thermosensitive chromogenic agent containing a benzenesulfonyl hydrazide compound, in the chromogenic reaction with each mole of ODB-2, the dosage of the novel chromogenic agent used is 80% of the dosage of the D-8 chromogenic agent to achieve the same chromogenic density, and the cost effect is obvious. The improved production process of the thermosensitive coating solution is significantly simplified, saving production time, improving production efficiency, and also enhancing the stability of the thermosensitive imaging film, making it more advantageous for development. Specific embodiments

[0050] To better understand the present invention, the content of the present invention will be further clearly described below in conjunction with embodiments, but the protection scope of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0051] Unless otherwise specified, all raw materials are commercially available products, and unless otherwise specified, they do not contain other components not explicitly indicated except for inevitable impurities.

[0052] Structural formula description of the compounds used in the present invention:

[0053] ODB-2:

[0054] Crystal violet lactone:

[0055] p-Toluenesulfonyl hydrazide:

[0056] p-Fluorobenzenesulfonyl hydrazide:

[0057] p-Trifluoroalkylbenzenesulfonyl hydrazide:

[0058] Example 1: Preparation of thermosensitive dye dispersion A1

[0059] 25 parts by weight of a 10% polyvinyl alcohol solution, 18 parts by weight of ODB-2, and 56 parts by weight of deionized water were added to a reaction kettle and stirred. Then, 1 part by weight of a 200 g / L sodium dodecylbenzenesulfonate solution was added, and the mixture was soaked and slowly stirred for 1 hour. Then, it was transferred to a sand mill and circulated and ground until the average particle size was 0.60 microns, obtaining a thermosensitive dye dispersion with a solid content of 20.5%.

[0060] Example 2: Preparation of thermosensitive dye dispersion A2

[0061] 20 parts by weight of an 8% polyvinyl alcohol solution, 15 parts by weight of ODB-2, and 63 parts by weight of deionized water were added to a reaction kettle and stirred. Then, 2 parts by weight of a 150 g / L sodium dioctyl sulfosuccinate solution was added, and the mixture was soaked and slowly stirred for 1 hour. Then, it was transferred to a sand mill and circulated and ground until the average particle size was 0.60 microns, obtaining a thermosensitive dye dispersion.

[0062] Example 3: Preparation of thermosensitive dye dispersion A3

[0063] 30 parts by weight of a 12% polyvinyl alcohol solution, 20 parts by weight of crystal violet lactone, and 49.5 parts by weight of deionized water were added to a reaction kettle and stirred. Then, 0.5 part by weight of a 250 g / L sodium dodecylbenzenesulfonate solution was added, and the mixture was soaked and slowly stirred for 1 hour. Then, it was transferred to a sand mill and circulated and ground until the average particle size was 0.60 microns, obtaining a thermosensitive dye dispersion.

[0064] Example 4: Preparation of thermosensitive developer dispersion B1

[0065] 25 parts by weight of a 10% polyvinyl alcohol solution, 30 parts by weight of deionized water, and 25 parts by weight of p-toluenesulfonyl hydrazide were added to a reaction kettle and stirred. Then, 2 parts by weight of a 200 g / L sodium dodecylbenzenesulfonate solution was added, and the mixture was soaked and slowly stirred for 1 hour. Then, it was transferred to a sand mill and circulated and ground until the average particle size was 0.40 microns, obtaining a thermosensitive developer dispersion with a solid content of 33.7%.

[0066] Example 5: Preparation of thermosensitive developer dispersion B2

[0067] 20 parts by weight of a polyvinyl alcohol solution with a mass fraction of 8%, 20 parts by weight of deionized water, and 20 parts by weight of p-fluorobenzenesulfonyl hydrazide were added to a reaction kettle, stirred, and then 1 part by weight of a sodium dioctyl sulfosuccinate solution with a mass fraction of 150 g / L was added. After soaking and slow stirring for 1 hour, it was transferred to a sand mill and circulated and ground until the average particle size was 0.40 microns, obtaining a thermosensitive color developer dispersion with a solid content of 35%.

[0068] Example 6: Preparation of thermosensitive color developer dispersion B3

[0069] 30 parts by weight of a polyvinyl alcohol solution with a mass fraction of 12%, 40 parts by weight of deionized water, and 30 parts by weight of p-trifluoroalkylbenzenesulfonyl hydrazide were added to a reaction kettle, stirred, and then 3 parts by weight of a sodium dodecylbenzenesulfonate solution with a mass fraction of 250 g / L was added. After soaking and slow stirring for 1 hour, it was transferred to a sand mill and circulated and ground until the average particle size was 0.40 microns, obtaining a thermosensitive color developer dispersion with a solid content of 33%.

[0070] Example 7: Preparation of thermosensitive imaging material coating liquid E1

[0071] The thermosensitive dye dispersion A1 prepared in Example 1 and the thermosensitive color developer dispersion B1 prepared in Example 4 were uniformly mixed under stirring conditions, and polyvinyl alcohol, polyvinylpyrrolidone, and deionized water were added to obtain a thermosensitive imaging material coating liquid; specifically:

[0072] In the above thermosensitive imaging material coating liquid, the weight part ratios of the respective components are as follows:

[0073]

[0074] Example 8: Preparation of thermosensitive imaging material coating liquid E2

[0075] The thermosensitive dye dispersion A2 prepared in Example 2 and the thermosensitive color developer dispersion B2 prepared in Example 5 were uniformly mixed under stirring conditions, and polyvinyl alcohol, polyvinylpyrrolidone, and deionized water were added to obtain a thermosensitive imaging material coating liquid; specifically:

[0076] In the above thermosensitive imaging material coating liquid, the weight part ratios of the respective components are as follows:

[0077]

[0078]

[0079] Example 9: Preparation of thermosensitive imaging material coating liquid E3

[0080] The thermosensitive dye dispersion liquid A3 prepared in Example 3 and the thermosensitive developer dispersion liquid B3 prepared in Example 6 were uniformly mixed under stirring conditions, and polyvinyl alcohol, polyvinylpyrrolidone and deionized water were added to obtain a coating liquid for thermosensitive imaging material; specifically:

[0081] In the above coating liquid for thermosensitive imaging material, the weight parts of each component are as follows:

[0082]

[0083] Comparative Example 1: Preparation of thermosensitive dye dispersion liquid C

[0084] 18 parts by weight of ODB-2, 1.8 parts by weight of BON (2-naphthol benzyl ether), 1.8 parts by weight of dimethylnaphthalene (solvent), and 60 parts by weight of ethyl acetate (auxiliary solvent) were added to a dissolution tank, stirred, and slowly heated to a complete dissolution, then kept at a constant temperature. At the same time, the condensation device was turned on to distill out the excess ethyl acetate and condense it for recovery. Heating was stopped when the evaporation reached the specified marking line on the dissolution tank, and the temperature was slowly lowered to 55 °C. Then, 18 parts by weight of TDI (2,4-toluene diisocyanate) was added and stirred evenly to obtain an oil phase;

[0085] 20 parts by weight of an aqueous solution of polyvinyl alcohol with a mass fraction of 10%, 30 parts by weight of deionized water (40 ± 5 °C), and 5 parts by weight of sodium dioctyl sulfosuccinate (surfactant) were stirred evenly and added to the dispersion pot in two batches to prepare an aqueous phase;

[0086] The above oil phase was slowly added to the aqueous solution, and at the same time, high-speed shear stirring was used at a speed of 7800 revolutions per minute for 3 minutes to obtain an oil-in-water dispersion emulsion with an average particle size of 0.65 microns. The dispersed emulsion was transferred to a ripening pot, 1.8 parts by weight of tetraethylenepentamine was added thereto, and then the reaction was carried out at 55 ± 3 °C for 3.5 hours at a stirring speed of 600 revolutions per minute to obtain a thermosensitive dye (microcapsule) dispersion liquid with an average particle size of 0.65 microns and a solid content of 22%.

[0087] Comparative Example 2: Preparation of thermosensitive developer dispersion liquid D

[0088] 25 parts by weight of an aqueous solution of polyvinyl alcohol with a mass fraction of 10%, 30 parts by weight of deionized water, and 25 parts by weight of D-8 (4-hydroxy-4'-isopropoxydiphenyl sulfone) were added to a reaction kettle, stirred, and then 2 parts by weight of an aqueous solution of sodium dodecylbenzenesulfonate (200 g / L) was added and soaked and slowly stirred for 1 hour, and then transferred to a sand mill for circulating sand grinding until the average particle size of the particles was 0.40 microns to obtain a thermosensitive developer dispersion liquid with a solid content of 33.7%.

[0089] Comparative Example 3: Preparation of coating liquid E4 for thermosensitive imaging material

[0090] The thermosensitive dye dispersion liquid C prepared in Comparative Example 1 and the thermosensitive developer dispersion liquid D prepared in Comparative Example 2 were uniformly mixed under stirring conditions, and polyvinyl alcohol, polyvinylpyrrolidone and deionized water were added to obtain a coating liquid for thermosensitive imaging materials; specifically:

[0091] In the above coating liquid for thermosensitive imaging materials, the weight parts of each component are as follows:

[0092]

[0093] Comparative Example 4: Preparation of coating liquid E5 for thermosensitive imaging materials

[0094] The thermosensitive dye dispersion liquid A1 prepared in Example 1 and the thermosensitive developer dispersion liquid D prepared in Comparative Example 2 were uniformly mixed under stirring conditions, and polyvinyl alcohol, polyvinylpyrrolidone and deionized water were added to obtain a coating liquid for thermosensitive imaging materials; specifically:

[0095] In the above coating liquid for thermosensitive imaging materials, the weight parts of each component are as follows:

[0096]

[0097] The following are preparation examples of thermosensitive imaging materials.

[0098] A thermosensitive imaging material includes a thermosensitive imaging layer formed by coating the coating liquid for thermosensitive imaging materials, and also includes a carrier substrate and a protective film layer, and the thermosensitive imaging layer is located between the carrier substrate and the protective film layer.

[0099] Among them, the carrier substrate is selected as PET.

[0100] The weight part composition of the coating liquid for the protective film layer is shown in the following table:

[0101] Material Name Concentration / % Parts by Weight Zinc Stearate Polyvinyl Alcohol Dispersion 20％ 45 Silica Sol Solution 30％ 4 Liquid Paraffin Dispersion 15％ 5 Surfactant 5％ 2 Boric Acid Solution 1％ 3.5 Water / 40.5

[0102] In the table, the polyvinyl alcohol dispersion grinding liquid of zinc stearate is prepared by mixing and grinding zinc stearate with polyvinyl alcohol and water; the surfactant is selected as sodium dodecylbenzenesulfonate.

[0103] The obtained coating liquids were coated by a slope flow extrusion coating method with coating amounts of 95 and 50 g / m for the thermosensitive imaging layer and the protective film layer respectively 2 and fully dried to obtain sample films; the thermosensitive imaging layers were respectively coated with the coating liquids E1, E2, E3, E4 and E5 for thermosensitive imaging materials, and the finally obtained sample films were sequentially marked as sample 1, sample 2, sample 3, sample 4 and sample 5.

[0104] The following performance tests were carried out on samples 1-5.

[0105] (1) Maximum black density test: Measure their density values respectively, and compare the maximum black density of the sample film before and after printing.

[0106] For the black density test of the film, a transmission densitometer is used. For the color development of the sample film at different temperatures, the company's existing adjustable constant temperature heating device is used, and the heating temperature is 80 - 220 °C (the minimum scale value is 10 °C).

[0107] (2) Thermal stability test of the raw thermosensitive film during storage: Store it at different temperatures for 1 d, 7 d, and 14 d respectively, and evaluate the thermal stability of the sample during storage by observation. Among them:

[0108] The evaluation criteria for the thermal stability performance during storage are as follows:

[0109] A: The surface of the coating is bright, without turning red or dull, and there is no change in the appearance before and after storage.

[0110] B: The surface of the coating is bright, without turning red or dull. After storage, the appearance turns slightly red or dull, and color difference appears.

[0111] C: There are local dullness, black shadows, and redness on the surface of the coating, and the appearance phenomenon after storage is significantly aggravated.

[0112] (3) The test results are shown in the following table:

[0113]

[0114] The above data show that the present invention gets rid of the excessive environmental load pressure of traditional phenolic developers such as D-8 and bisphenol A, and at the same time avoids adverse phenomena such as the film turning red caused by the oxidation of phenolic developers; it optimizes the cumbersome and complex production process in which traditional thermosensitive colorless dyes must be microencapsulated, simplifies the production process. At the same time, compared with the traditional D-8 developer, the new developer shows significant progressiveness in that it has excellent color development performance with less dosage, can reduce costs and increase efficiency.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A thermosensitive imaging material coating solution, characterized in that: The raw materials for its preparation include: a heat-sensitive dye dispersion liquid and a heat-sensitive color developer dispersion liquid, wherein: The heat-sensitive dye dispersion liquid contains at least one colorless dye, and the colorless dye is a compound represented by the formula (I): （I）， In the formula, R1 is an alkyl group with 1 to 8 carbon atoms, R2 is an alkyl group with 4 to 18 carbon atoms, R3 is a hydrogen atom, an alkyl group with 1 to 15 carbon atoms, or a halogen atom, and R4 is an unsubstituted or substituted aryl group with 6 to 20 carbon atoms. The substituent of R4 is an alkyl group with 1 to 5 carbon atoms, a halogenated alkyl group, or a halogen atom; The heat-sensitive color developer dispersion liquid contains at least one phenol-free color developer, and the phenol-free color developer is a compound represented by the formula (II): （Ⅱ）， In the formula, the R group is connected to the para position of the benzene ring; the R group is a methyl group, a fluorine atom, or a trifluoroalkyl group.

2. A coating liquid for a heat-sensitive imaging material according to claim 1, wherein: The colorless dye represented by the formula (I) is ODB-2 or crystal violet lactone; The phenol-free color developer represented by the formula (II) is p-toluenesulfonyl hydrazide, p-fluorobenzenesulfonyl hydrazide, or p-trifluoroalkylbenzenesulfonyl hydrazide.

3. The coating liquid for a thermosensitive imaging material according to claim 1, wherein: The heat-sensitive dye dispersion liquid is prepared by the following method: Add 20 to 30 parts by weight of an adhesive solution, 15 to 20 parts by weight of a colorless dye, and 40 to 70 parts by weight of deionized water to a reaction kettle and stir. Then add 0.5 to 2 parts by weight of a surfactant, soak and stir slowly for 1 to 1.2 hours, and then transfer to a sand mill for circulating sand grinding until the average particle size ≤ 0.60 μm to obtain the heat-sensitive dye dispersion liquid.

4. The coating liquid for a thermosensitive imaging material according to claim 3, characterized in that: The adhesive solution is an aqueous solution with a mass fraction of 8 to 12% made of at least one of polyvinyl alcohol, gelatin, and cellulose derivatives; The surfactant is an aqueous solution with a mass fraction of 150 to 250 g / L made of at least one of sodium dodecylbenzenesulfonate, sodium dioctyl sulfosuccinate, and polyethylene glycol.

5. The coating liquid for a thermosensitive imaging material according to claim 1, wherein: The heat-sensitive color developer dispersion liquid is prepared by the following method: Add 20 to 30 parts by weight of an adhesive solution, 20 to 40 parts by weight of deionized water, and 20 to 30 parts by weight of a color developer to a reaction kettle, stir, then add 1 to 3 parts by weight of a surfactant, soak and stir slowly for 1 to 1.2 hours, and then transfer to a sand mill for circulating sand grinding until the average particle size ≤ 0.40 μm to obtain the heat-sensitive color developer dispersion liquid.

6. The coating solution for a heat-sensitive imaging material according to claim 5, wherein: The adhesive solution is an aqueous solution with a mass fraction of 8 to 12% made of at least one of polyvinyl alcohol, gelatin, and cellulose derivatives; The surfactant is an aqueous solution with a mass fraction of 150 to 250 g / L made of at least one of sodium dodecylbenzenesulfonate, sodium dioctyl sulfosuccinate, and polyethylene glycol.

7. The coating liquid for a thermosensitive imaging material according to claim 1, characterized in that: The coating liquid for the heat-sensitive imaging material is made of the following raw materials in parts by weight: The balance is adjusted to 100 parts with deionized water, and the solid content is 18.0% to 24.0%; The adhesive is at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, gum arabic, gelatin, and polyvinylpyrrolidone.

8. The coating liquid for a heat-sensitive imaging material according to claim 7, wherein: The adhesive is a composition of polyvinyl alcohol and polyvinylpyrrolidone, and the dosage of polyvinyl alcohol is 2 to 4 times that of polyvinylpyrrolidone.

9. The preparation method of a thermosensitive imaging material coating solution according to any one of claims 1-8, characterized in that: Proceed according to the following steps: Preparation of thermosensitive dye dispersion: 20 - 30 parts by weight of binder solution, 15 - 20 parts by weight of colorless dye, and 40 - 70 parts by weight of deionized water are added to a reaction kettle and stirred. Then, 0.5 - 2 parts by weight of surfactant solution is added, and the mixture is soaked and stirred slowly for 1 - 1.2 hours. Then, it is transferred to a sand mill for circulating sand grinding until the average particle size ≤ 0.60 μm, obtaining the thermosensitive dye dispersion; Preparation of thermosensitive developer dispersion: 20 - 30 parts by weight of binder solution, 20 - 40 parts by weight of deionized water, and 20 - 30 parts by weight of developer are added to a reaction kettle and stirred. Then, 1 - 3 parts by weight of surfactant solution is added, and the mixture is soaked and stirred slowly for 1 - 1.2 hours. Then, it is transferred to a sand mill for circulating sand grinding until the average particle size ≤ 0.40 μm, obtaining the thermosensitive developer dispersion; The thermosensitive dye dispersion and the thermosensitive developer dispersion are uniformly mixed under stirring conditions, and binder and water are added to obtain a coating liquid for thermosensitive imaging material.

10. A thermosensitive imaging material, characterized in that: It includes a thermosensitive imaging layer formed by coating the coating liquid for thermosensitive imaging material according to any one of claims 1 - 8 or the coating liquid for thermosensitive imaging material obtained by the preparation method according to claim 9.

11. A thermosensitive imaging material according to claim 10, characterized in that: It further includes a carrier substrate and a protective film layer, and the thermosensitive imaging layer is located between the carrier substrate and the protective film layer.

12. A thermosensitive imaging material according to claim 11, characterized in that: The weight - part composition of the coating liquid for the protective film layer is as follows: The total amount is adjusted to 100 parts with deionized water for the balance, and the solid content of the coating liquid is 9% - 15%.

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